Advances in Vehicle Design

Advances in Vehicle Design

To Ruth

Advances in Vehicle Design

by

John Fenton

ProfessionalEngineeringPublishing

Professional Engineering Publishing LimitedLondon and Bury St Edmunds, UK

First published 1999

This publication is copyright under the Berne Convention and the InternationalCopyright Convention. All rights reserved. Apart from any fair dealing for thepurpose of private study, research, criticism, or review, as permitted under theCopyright Designs and Patents Act 1988, no part may be reproduced, stored ina retrieval system, or transmitted in any form or by any means, electronic,electrical, chemical, mechanical, photocopying, recording or otherwise, withoutthe prior permission of the copyright owners. Unlicensed multiple copying of thispublication is illegal. Inquiries should be addressed to: The Publishing Editor,Mechanical Engineering Publications Limited, Northgate Avenue, Bury StEdmunds, Suffolk, IP32 6B W, UK.

© John Fenton

ISBN 1 86058 181 1

A CIP catalogue record for this book is available from the British Library.

The publishers are not responsible for any statement made in this publication.Data, discussion, and conclusions developed by the Author are for informationonly and are not intended for use without independent substantiating investi-gation on the part of the potential users. Opinions expressed are those of theAuthor and are not necessarily those of the Institution of Mechanical

Engineers or its publishers.

Printed and bound in Great Britain by St Edmundsbury Press Limted,Suffolk, UK

CONTENTS

vii Preface

Chapter 1: Materials and construction advances2 Steel durability and structural efficiency3 Vigorous development of light alloys4 Hybrid metal/plastic systems7 Recycled PET, and prime PBT, for sun-roof parts10 Material property charts and performance indices13 Design for self-pierce riveting

Chapter 2: Structure and safety20 Structure analysis for interior noise24 Preparing for statutory pedestrian protection27 Design for the disabled31 Adaptive restraint technologies

Chapter 3: Powertrain/chassis systems36 Powertrains: the next stage?45 Constant-pressure cycle: the future for diesels?47 Valve arrangements for enhanced engine efficiency52 Trends in transmission design58 The mechanics of roll-over62 Suspension and steering linkage analysis

Chapter 4: Electrical and electronic systems70 Automotive electronics maturity76 Navigation system advances79 Digital circuits for computation81 Proprietary control system advances84 Hybrid drive prospects90 Automation of handling tests

Chapter 5: Vehicle development96 Mercedes A-class102 Ford Focus108 Land Rover Freelander112 Project Thrust SSC

Chapter 6: Systems development: powertrain/chassis118 Engine developments122 Engine induction systems124 Refinement and reduced emissions128 Drive and steer systems133 Suspension development139 Braking systems

Chapter 7: System developments: body structure/systems144 Structural systems144 Controlled collapse145 Body shell integrity147 Chassis/body shell elements151 Car body systems151 Occupant restraint155 Doors, windows and panels159 Trim and fittings161 Aerodynamics and weight saving163 CV systems163 CV chassis-cab configuration164 Cab/body fittings168 Advanced bus/ambulance design

173 References175 Index

Preface

This lite'rature survey is aimed at providing the vehicle design engineer with anupdate in vehicle and body systems. The author has scanned the considerableoutput of technical presentations during 1997- 9 to extract and distil developingtechnologies of particular import to the working designer. The easily digestiblepresentation, with unusually high dependence on diagrammatic presentation,continues the popular style used for the original handbooks that were compiledby the author, and published by Professional Engineering Publishing. These arelisted on the Related Titles page overleaf. Advances in Vehicle Design serves bothas an update to the earlier volumes and as a stand-alone volume. The referencedleads provided in the text are intended to help designers and engineers fromwhatever background discipline. Widespread availability of computing power todesigners and engineers has created the possibility of considerably shortening thelead-times between design conception and prototype manufacture. Much of thematerial covered here will assist in establishing predictive techniques.

Advances in Vehicle Design is an update of vehicle and body systems designin that it provides readers with an insight into analytical methods given in a widevariety of published sources such as; technical journals, conference papers, andproceedings of engineering institutions, for which a comprehensive list of refer-ences is provided. The analyses are therefore not necessarily fully developed orrigorously evaluated. Recourse to the original references is necessary particularlyin order to understand the limiting assumptions on which the analyses are based.

Much of the analytical work is centred around impending legislation and, wherethis is quoted in the text, it is for illustration only and it is, of course, important toexamine the latest statutes in the locality concerned. The list of references givenat the end of the volume is a key element of the publication, providing wherepossible a link to the original publication source. Where the original publication isnot available in bookshops, many of the sources can be found in libraries such asthose of the Institution of Mechanical Engineers, London, or the Motor IndustryResearch Association, in Nuneaton, UK,as well as the BritishLibrary.Othersimilarrespositories of techincal information should be able to provide a selection oforiginal source material. Where the source is a company announcement oftechniques and systems, names, but not addresses, of the companies/consultan-cies are given. Most operate internationally and have different national locations,best found by enquiry in the country concerned. For the patent reviews in chapterssix and seven, full specifications can be purchased from The Patent Office, CardiffRoad, Newport, NP91RH, UK.

JOHNFENTON

Related Titles

Title Editor/Author ISBN/ISSN

Multi-Body Dynamics HRahnejatGasoline Engine Analysis J FentonHandbook of Automotive Body Construction J Fentonand Design AnalysisCranes - Design, Practice and Maintenance J VerschoofHandbook of Automotive Body Systems Design J FentonHandbook of Automotive Powertrain and J FentonChassis DesignVehicle Handling Dynamics J EllisHandbook of Vehicle Design Analysis J FentonAutomotive Braking: - Recent Developments D BartonBrakes and Friction Materials G A HarperAutomotive Engineer Monthly Magazine W KimberleyJournal of Automotive Engineering (IMechE Proceedings Part D)

1 80058 122 60 85298 634 31 86058 073 4

1 86058 130 71 86058 067 X1 86058 075 0

0 85298 885 00 85298 963 61 86058 131 518605812770307/64900954/4070

For full details of all Professional Engineering Publications please contact:

Sales DepartmentProfessional Engineering PublishingNothgate AvenueBury St EdmundsIP326BWUKTelephone: +44 (0)1284 763 277Fax: +44(0)1284718693E-mail: [email protected]

Chapter 1:

Materials and construction advances

The considerable comeback made by the steel industry inrestating its case for structural superiority over the light alloys,and the ever moving goalposts of developing aluminium andpolymer composites, open this chapter. The re-emergence ofhybrid metal/plastic structures is also discussed as well as thecreation of reinforced plastics with recycled-polymer matrices.The move to material property charts which lead to thecreation of performance indices is next examined and thechapter concludes with the efforts to make self-pierce rivetinga viable alternative to conventional welded joints in bodyconstruction.

VEHICLE DESIGN

Steel durability

and structural efficiencyAccording to researchers at Lotus Engineering1, mar-ket expectations for durability of vehicle body panelsis typically seven years or 100 000 miles, with anexpectation of 10 years corrosion-free life. BritishSteel engineers2 have shown the main influences ondurability with the corrosion triangle of Fig 1. Inproduct design the traditional approach has been toremove moisture traps, allow better penetration ofpaint and evolve design with greater resistance tostone chipping. There had also been gradual adoptionof one-side zinc-coated steel panels, offering protec-tion on the inside and good paintability on the out-side. More recently there had been a move from hotdip galvanized to electrozinc panels, spurred byJapanese manufacturers; these offer a range ofductilities, increased weldability and the ability toalloy the coating to provide various coating thick-nesses and corrosion resistance levels. Now double-sided coated steels are favoured with differentialcoating weights: typical thicknesses are now 45-60g/m2. Future quality improvements are promised bydevelopment work in surface treatment andformability. Permanent organic based topcoats orphosphate coatings are providing improved perform-ance in both weldability and corrosion prevention.Another new initiative is a drive by the OEMs toreplace electroplated products by 'galvanneal' onesfor outside parts, in the interests of productioneconomy. These have the ability to provide goodpaintability.

In a joint venture between British Steel StripProducts and Rover Group, trial parts were preparedfor the Rover 600, including front fender, front doorskin, rear door skin and bonnet. In 1997 all newmodels were produced with two-sided galvannealfull-finished panels. In the longer term, the authorssee the development of non-bake hardening, higherstrength steel substrates with enhanced formabilityfor use with galvanneal coatings, and the introduc-tion of extra high strength transformation inducedplasticity (TRIP) steels as substrates for zinc typecoating which will offer yield strength approaching1500 MPa, alongside high ductility. Prepainted bodyfinished sheet steel, which obviate the electropheriticprimer coat are also expected, as is a possible newcoating process based on vapour deposition of zinc in

a vacuum.Car body weight reduction of 25%, without

cost penalty, plus a 20% reduction in part count, hasbeen the result of the final phase of the USLABproject for light-weighting steel automotive struc-tures carried out by an international consortium ofsteel companies supervised by Porsche EngineeringServices. The objective of a feasible design, usingcommercially available materials and manufactur-ing processes, has also been met. An 80% gain intorsional rigidity, and 52% in bending, has also beenrecorded and estimated body-shell cost of $947 com-pares with $980 for a year 2000 comparison figure for

Environment(including micro environment)

Autobody

Materials ofConstruction

Design

Fig 1: Triangle of factors affecting corrosion

Fig 2: ULSAB body shell

Fig 3: Monoside panel

Fig 4 : Side roof rail

MATERIALS AND CONSTRUCTION

a conventionally constructed body to a similar speci-fication. The 203 kg body shell (Fig 2), of 2.7 metreswheelbase, has a torsional rigidity of 20,800 Nm/degand a first torsional vibration mode of 60 Hz, usingthe well-documented construction techniques.

A supercomputer analysis of crashworthinesshas shown that frontal NCAP and rear moving-barrier levels have been achieved at 17% higher thanthe required speed. The body has also satisfied 55kph/50% offset AMS, European side impact and roofcrush requirements. The 35 mph frontal NCAP showeda peak deceleration of 31 g, considered satisfactory inthat stiffer body sides are required to meet 50% AMSoffset requirements. The offset AMS frontal impactdeceleration showed a peak at 35g, considered a goodresult in relation to the severity of the test. Thesimulation was carried out at 1350 kg kerb weight,plus 113 kg luggage and 149 kg for two occupants. Atthe final count, high strength steel was used for 90%of the structure, ranging from 210 to 550 MPa yield,in gauges from 0.65 to 2 mm. Around 45% of thestructure involved laser-welded tailored blanks, in-cluding the monoside panels, Fig 3, which ranged ingauge from 0.7 to 1.7 mm and was made up of steelelements having yield strengths from 210 to 350MPa. Fig 4 shows the hydroformed side roof rail.

To the casual observer the elements of thecomplete body shell 'look' more structurally effi-cient but they still seem a far cry from a fullyoptimized shape for the steel 'backbone', as much ofthe material seems to be still used in relatively lowstress areas where its function is as a 'cover' ratherthan a fully working structural element. Perhaps thenext stage in weight reduction should be in designinga highly efficient steel monocoque, then mouldingover plastic elements for the non-structural coveringand closure shaping details, using the hybrid metal/plastics techniques discussed later in this chapter.

Vigorous

development of light alloysPhase 2 of Audi's aluminium alloy body constructionprogramme was unveiled at a recent Motor Show inthe form of the A12 concept car, Fig 5. The 3.76 metrelong times 1.56 metre high car weighs just 750 kg in1.2 litre engined form, some 250 kg less than aconventional steel body vehicle, it was argued. Thenumber of cast nodes has been reduced comparedwith the Phase-one aluminium alloy structure of theAudi A8. Most of the nodes are now produced bybutt-welding the extruded sections. High level seat-ing is provided over a sandwich-construction floor.Use of internal high pressure reshaping techniqueshas reduced the number of shaping and cutting opera-tions required

The 1997 International Magnesium Associa-tion Design Award for applications went to the die-cast instrument panel support beam, Fig 6, on the GMG-van. It is a one-piece design weighing, at 12.2 kg,5.9 kg less than the welded steel tubular structure itreplaced. Proponents of magnesium alloy are point-ing out that as die-castings in the material solidifyfrom the outside in, they enjoy a dense chilled skintogether with a relatively course-grained interior.Skin thickness is said to be relatively constant regard-less of total wall thickness so that reductions insection size can often be made when the material isused as a substitute. The AZ91D (9% aluminium, 1%zinc) alloy is now finding application in removablerear seats for minivans. In the seat systems shown inFig 7, Delphi Automotive have achieved 60% weightreduction over conventional construction by adopt-ing a cast magnesium cushion frame and an extruded

Fig 5 A12 conceptcar and structure

VEHICLE DESIGN

aluminium back frame. Other magnesium grades arebeing used in combination with engineering plasticsfor composite instrument panels. VW have alsodemonstrated a Polo door in pressure die-cast magne-sium with a carbon fibre reinforced outer panel,which offers over 40% weight reduction over con-ventional steel construction.

Hybrid metal/plastic systemsMetal/plastic composites have been promoted againby Bayer in a recent presentation to body engineers3.A compelling argument is made for using simplifiedthin-wall structures in high strength metals which arestabilized by plastic composites which can also cutdown on welding operations when combined as an in-mould assembly. The complexity of CV-cab and carbodies has often ruled against the effective use oflightweight metal systems on their own.

In the latest version of the technique, the pro-cesses of inserting, where metal parts such as bushesare included in a polymer moulding, and/or outsertingwhere various functions in plastic are moulded on toa metal baseplate, are taken a stage further. Cross-sectional distortion of thin-walled metal beams canbe prevented by relatively small forces applied in thenew process by the presence of moulded plasticsupports in the form of x-pattern ribbing.

The deformation behaviour of various sectionprofiles under bending and torsion is shown in Fig 8a and b. Interconnecting points between plastic andmetal are preformed in the metal part before it entersthe plastics mould. Either corrosion-protected steelor aluminium alloy is the normal choice of metal withglass-fibre reinforced, impact modified, polyamide-6 (Bayer's Durethan BKV) being the plastic choice.Bayer say it is not always desirable to have the metal'preform' in one piece, separate sections being joinedby moulding resin around the prefabricated inter-

Fig 9: Front end structure in hybrid metal/plastic

Fig 10: Metal/plastic hybrid door structure

Fig 6 : Instrument panel beam

Fig 7: Mg and Al used in seat frame


locking points or by means of clinching integratedinto the mould. It is said that for recycling purposes,it takes only a few seconds to break a metal/plasticcomposite, using a hammer mill, and that the resinelement has properties akin to the virgin material, onreuse.

Sample applications include instrument panelsupports. In the cross-car beam co-developed byGM's Delphi a 40% reduction in weight was obtainedagainst the replaced assembly, along with a 10%

reduction in component and investment cost, for thesame performance capability. Car front-ends withintegrated bumper systems are further good candi-dates, Fig 9. A research project has also been carriedout on car side doors having sufficient structuralintegrity to transmit impact forces from A- to B-postin the closed position. Fig 10 shows a sample door,requiring no further framework to support wingmirror, lock or other door 'furniture'. Seat frameswith integral belt-anchorages have also been made

0 2Fig 8a: Deformation behaviour

40

10 12 14Deformation

18 20

Nm

30

25

20

15

10

5

00 2

Fig 8b: Behaviour in twist6 8 10 12

Twisting18

VEHICLE DESIGN

for the Mercedes-Benz Viano minibus in the process.The first volume car to incorporate the technology isthe Audi A6. The front-end design was developed inassociation with the French ECIA company. The partis injection moulded in one piece and incorporatesengine mountings, together with support for radiatorand headlights.

Bayer have also been active in a joint-ventureglazing project with GE Plastics. A $40 milliondevelopment programme is under way on abrasion-resistant, coated polycarbonate vehicle windows asan alternative to glass systems. An abrasion-resist-ance equal to that of glass is targeted and high-volume production of windows is foreseen. Some40% weight saving is forecast against equivalentglass systems and greater design freedom plus higherimpact resistance is also claimed. Better resistance toforced entry, and reduced injuries in side-impact androll-over accidents, have also been mooted.

Structural designin polymer compositesWork reported from Delphi Interior and Lighting4 hasshown the possibility of constructing instrumentpanel crossbeam and display panel assemblies ininjection-moulded plastics. The structural crossbeamprovides both structural integrity, to the assembly,and an air passage for the primary air vents; itattaches to the A-pillars at each of its ends andoperates as a simply supported beam. In one conceptby the company, Fig 11, the beam supports thedisplay panel but is not integral with it. In the secondconcept, Fig 12, the panel and beam form an integralstructure. The advantage of this second concept is theallowance of further integration of components intothe single total assembly.

Both concepts were built for retrofitting into acurrent production vehicle so that proper in-serviceevaluation could be obtained. In the CAD analysis

Fig 13: Audi A6 sun-roof

Fig 14: Sun-roof with Venetian blind

DEFROSTER DUCT

Fig 11: Plastic structural beam


the initial objective was to develop a design for theplastic structures that would provide static stiffnessequivalent to that of the baseline steel structure. Thefirst natural frequency of the beam was also matchedto the steel baseline. Both objectives were met with-out resort to wall thicknesses that would have com-promised conventional injection-mould cycle times.

The next requirement was to meet FMVSSimpact energy absorption levels resulting from inputloads to the knee bolsters supported by the system ina 30 mph crash. It was found that materials with strainrates as low as 2% could absorb this energy withoutoverload to the occupant's femur. Finally the struc-ture had to meet these performance levels underspecified temperature and vibrational environments,necessitating an evaluation of creep and fatiguecapability. Temperature range of-30 to +190 F andfatigue criteria were based on subjection to serviceloads measured under real road conditions.

Retention of properties USCAR/EWCAP Class 3Temperature/Humidity Testing

Standard Crastin- Standard Crastin. Competitive15%GRPBT HR5015F 30%GRPBT HR5030F HR PBT

(30% Glass)Tensile strength, MpaInitialAfter 40 cycles*Retention, %

Elongation, %InitialAfter 40 cycles"Retention, %

1095752

3.01.550

7475101

3.52.983

1459062

2.81,350

99104105

3.32.879

11410693

3.32.267

" Each cycle consists of 6 hr. at 900C/95% Rh followed by 2 Hr. at 125'C with humidity vented

Recycled PET, and prime PBT,

for sun-roof partsFollowing the recent interest shown in Chrysler'splan for using low-cost, glass-reinforced polyethyleneterephthalate (PET) for its China car body construc-tion, comes an announcement from DuPont that it issupplying recycled PET for corner mouldings of theWebasto sun-roof of the Audi A6, Fig 13. Themouldings hold the sliding roof frame's aluminiumrails together and incorporate guides for the cablethat moves the roof and channels off rain-water. Thematerial has withstood 30,000 open-close cycles intrials of the sun-roof. In another sun-roof application,DuPont's polybutylene terephthalate (PBT) resin byWestmont Technik of Dusseldorf is used in a newdesign of sliding roof incorporating a built-in Venetianblind, Fig 14. The PBT slats of the blind can beadjusted to deflect cooling air into the vehicle in hotweather. The company has also introduced a PBTgrade, Crastin 5000, for electrical connectors andparts. This has improved hydrolysis resistance forhigh temperature and high humidity operation. Thefirst variants produced, for connectors, have 30%glass reinforcement and properties are seen in thetable, left.

Further details have also been released on theChrysler China car which is now called the Compos-ite Concept Vehicle. Its shell structure is made up offour major elements, Fig 15, to fit over a steel chassis.Target cost of the PET-based GRP is less than £2 perkg, compared with £6.50 - £8.50 for SMC and SRIM.

DEFROSTER DUCT

JOINED SURFACES

S4WDEFOGGER

STRUCTURAL I.P. DUCTFig 12: Plastic structural instrument panel

VEHICLE DESIGN

When the four shell elements are bonded to-gether enough torsional stiffness is available withoutthe need for further reinforcement. Ashland Pliogripfast-cure adhesive is used and cycle time for makingthe four main mouldings is three minutes, sevenminutes faster than for equivalent sized SRIM mould-ings. The low cycle time has been achieved by asequence of gate openings and gas injections into themould to help guide the process, which was devisedusing computer-aided mould-flow techniques. An8500 tonne machine injects the PET resins into the145 tonne moulds, which each measure a massive 4.5X 2.5 X 2 metres.

Structural-colouredfibre has body trim potentialNissan has announced the development of what isclaimed to be the world's first structural-colouredfibre, in a joint venture with Teijin Limited andTanaka Kikinzoku KK, Fig 16. The colour of thefibre is produced by its structure and does not involvethe use of dyes. The principles of this technology arebased on research into biometrics, an engineeringpractice that looks at prominent functions of livingthings and applies them in practical applications.One of the findings of this research is the principlebehind the iridescence of the wings of Morpho butter-flies native to South America. Research has beenconducted to apply this knowledge to the productionof coloured fibres for interior and exterior trim mate-rials, including seat fabric. The structural-coloured

fibre has been developed by applying the theory ofmultilayered thin-film interference to a cross sectionof the fibre. This is the principle behind the iridescentscales of Morpho butterfly wings. The fibre displaysa high metallic sheen and a clear colour shade underexposure to different types of light, including natural,fluorescent and incandescent. The colour propertiesand tint also vary depending on the light source usedand the viewing angle. As the fibre does not use anydyes, the production of the fibre reduces environ-mental pollution due to waste dye solutions. It alsoprevents any worries about skin rashes or otherallergic reactions to dyes.

Fig 15: Composite Concept Vehicle shell

2.0

Fig 16: a: right,Reflective spectra ofsome samples; b,opposite, thetechnology explained

1.0

Structural-colored filament

0.4 0.5 0.6Wavelength (um)


10 VEHICLE DESIGN

Material property charts and

performance indicesA rigorous method for evaluating the choice ofmaterials for new designs has been made by a re-searcher5 of the Cambridge University EngineeringDesign Centre which avoids the 'hunch' or 'guessti-mating' approach so common in making these deci-sions.

The author points out that it is seldom that theperformance of a component depends on just oneproperty of its constituent material. So by plottingone property against another (stiffness and density,say, for lightweight components), and mapping outthe fields of materials in each material class, rapidassessment of material suitability is possible.

Fig 17 shows how, on a log scale plot of elasticmodulus and density, the data for a particular class ofmaterials clusters together in envelopes. The slopinglines show how other derived properties, based on thetwo basic ones, can also be plotted on the graph. Theelongated envelopes refer to material classes in whichthere is structure-sensitivity, in that properties can bealtered significantly by such techniques as micro-alloying and heat treatment. While the modulus of asolid is a relatively well defined quantity, the authorexplains, strength is not and the envelopes take updifferent shapes, Fig 18. The shapes alter again whenfracture toughness and other properties are plottedagainst density and the author provides explanationsfor these in the book, based on the behaviour of thematerial's molecular structure.

In general the charts show the range of anygiven property accessible to the designer and identifythe material class associated with segments of thatrange.

Logical design involves asking such questionsas 'what does the component do; what is to bemaximised and minimised; what non-negotiable con-ditions must be met and what negotiable and desir-able conditions ...', defining function, objective andconstraints. Property limits can be derived from thesetogether with indices that will optimize materialselection. Performance indices are groupings of thematerial properties which can maximize some per-formance aspect of the component, ratio of modulusto density being the classic one of specific stiffness,which would be a key consideration in the design ofa light, stiff tie-rod. Many such indices exist each

characterizing a particular combination of function,objective and constraint, as in the beam case, Fig 19.

In this 'index and chart' material selectionprocedure, the index isolates the combination ofmaterial properties and shape information thatmaximiszes performance prior to using the chart forselecting the appropriate material as described above.Fig 20 shows how the index derived by isolating thekey parameters from the equations describes theobjective function after the constraints have elimi-nated the free variables.

Design of a mechanical component, Ashbyasserts, is specified by three groups of variables: thefunctional requirements F (need to carry loads, trans-mit heat, etc.), geometric specifications G and somecombination of properties p so that maximized per-formance

P=f(F,G,p)

When these three groups are separable such that

P = f 1 ( F ) , f 2 ( G ) , f 3 ( p ) ,

as they usually are, the optimum choice of materialcan then become independent of many of the designdetails and a merit index can be much more simplydefined. Thus the steps in Fig 20 involve identifyingprimary function, writing down the equation for theobjective (could be the energy stored per unit volumein a spring example) then identifying the constraintsthat limit the optimization by this last process interms of a specific value of stiffness, say. The freevariables can then be eliminated in leading to theindex value (the objective function).

In the case of a beam, for a simply supportedlength L, under transverse load F, there might be aconstraint on the stiffness 5" such that it must notdeflect more than 8 at mid-span. Here

S = F/s>/= CEI/L3

where E is modulus and / section second moment ofarea, C being a constant depending on load distribu-tion. For a square section beam, width b, I is A2/12where A is section area ,which can be reduced in orderto lessen weight, but only until the stiffness constraintis met. Eliminating A in the objective function givesthe mass

MATERIALS AND CONSTRUCTION 11

m >/= (C12S)1/2(l5/2)(p/E1/2)

and the best materials for a light, stiff beam are thosewith large values of the material index

M = El/2/p

where p is density.Because section shape is critical to bending

stiffness a shape factor is defined as

0 = 4phiI/A2

which is dimensionless and can take values as high as100 for very efficient sections.

Cross-substitution of these equations can becarried out to eliminate the free variables and a Fig 79. identifying the primary function

0 = 2

Fig 17: Specific stiffness property chart Density (p), Mg/m3

12 VEHICLE DESIGN

modified performance index would include a shape-

Fig 20

Function

Tie

BeamV

A A

Shaft

Column

Mechanical,thermal,

electrical...

• Establishing material

factor term.The author also

for panels. with in-

Objective

Minimum cost

Maximumenergy storage

Minimumenvironmental

impact

material performance index

buckling failure, anbook, as well as those

so includes performplane compressionlong the many casese for vibration limi

Constraints

Stiffness specified —

Strength specified

Fatigue limit

Geometry

Index

Fig 18: Specific strength property chart Density(p), Mg/m3

MATERIALS AND CONSTRUCTION 13

Design for self-pierce riveting

More widespread use of aluminium alloys, and light-weight coated steels, in automotive body construc-tion is leading to alternatives to the old certainty ofspot-welding. Textron's Fastriv system is proving areliable substitute, a leak-proof system with fullyautomated installation equipment, and claimed greaterdynamic strength than spot-welding.

The Fastriv self-piercing fastening system, Fig21, can join two or three metal sheets with combinedthickness from 1.5 to 8.5 mm. In the placing sequenceof Fig 22, a tubular rivet is driven by a hydraulicallyoperated press tool into the materials to be joined;first the rivet pierces the top sheets then it flaresradially into the lower sheet against the die, withoutbreaking through, and forms a mechanical interlock,the assembly process being complete within 1-2seconds.

A single Fastriv joint is said to be close to theshear strength of an equivalent spot-weld and strongerin peal strength, without the disadvantage of a heat-affected zone; the suppliers say at least 30% of spot-welding applications could be displaced by its use.There must, however, be access for tooling on bothsides of the sheets and sheet thickness/hardness mustfall within a given range.

Optimized Fastriv joint performance is ob-tained when the sheet material with the higher elon-gation is placed on the die side, when joining sheetsof dissimilar material. For joining sheets of dissimi-lar thickness, the thinner sheet should be placed onthe punch side and a large-head rivet should be used.Since joint elements of self-pierce fastening are notsymmetrical on both sides, joint arrangements needspecial attention and suggestions are given in Fig 23.

Suggested automotive application areas areshown in Fig 24, the company recommending com-bination with adhesive bonding for load-bearingcarrier beams. Steel panels can be joined to alu-minium ones, where necessary, and the pre-paintedpanels can also be successfully joined by the process.A number of finishes are available on the rivets toensure against corrosion. The standard finish used iselectroplated bright zinc but Almac mechanicallyapplied coating has higher corrosion resistance thanzinc. Kalgard has an organic binder containing alu-minium; Deltaseal has an organic microlayer top-coat with PTFE; finally, Dacromet has an organic

binder containing both zinc and other protectivesolids.

Similar to that for spot-welding, installationequipment can be floor-mounted or portable, suspen-sion-mounted, and have manual or robotic manipula-tion. Fasteners can be either tape-fed from reels orblow-fed from a vibrating bowl, through plastictubing. Fig 25 shows proportions of the rivetingmodule, from which an idea of joint access can beobtained. Various rivet head forms are available aswell as the standard oval head, including flat counter-

Fig 21: Fastriv configuration

Fig 22: Installationsequence

Fig23: Suggested rivetorientations

14 VEHICLE DESIGN

sunk and a 'tinman' head which is a flat head whichstands proud for occasions when a visual feature isrequired to be made. Head diameters can range from5.38 to 9.78 mm for rivet diameters from 3.10 to 4.78mm. For the 5 mm (nominal) rivet size, fatigueperformance is as shown in Fig 26.

100

1

1,000 10,000 100,000 1,000,000Life Reversals

Sourc: Rover Group LtdFig 24: Automotive body applications (below)Fig 25: Riveting module sizes (right)Fig 26: Fatigue performance (above)

ID*

Riveting module

NOTE:- LARGER THROAT DEPTHSOR CUSTOMISED C FRAME SHAPESCAN BE DESIGNED TO SUIT

C-frame

STANDARD RIVETING MODULE CONFIGURATIONSTANDARD DAYLIGHTSIZES "D"(mm)

254055

RIVETING MODULE LENGTH"L'(mm)302317332

APPROXIMATEWEIGHT (KG)6-25

6.56.75

STANDARD "C" FRAME SIZES (FOR 4Omm DAYLIGHT)

THROAT DEPTHTSO100150200

ARM DEPTH"G'"(mm)SO71

81as

FRAME DEPTH"G"(mm)120

190280360

APPROXIMATEWEIGHT(KG)5.5

8.51520

NOTE:- FOR OTHER RIVETING MODULE SIZES PROPORTIONS WILL CHANGE.

Chapter 2:

Structure and safety

Vehicle structural design innovation continues to be drivenby the impetus for improved passenger protection and light-weighting for lower fuel consumption and reduced CO2

emission. With the perfection of controlled collapse front-ends the next stage in development is an analysis of footwelldeformation so that controlled-collapse can be extended tothat region. For further integrity of the occupant survival shellattention is also being paid to pillar/rail joint stiffness inreducing the likelihood of body shell collapse. Techniques ofstructural analysis are also being used for the prediction ofnoise level within the body shell. Attention is also finallyturning from the protection of the vehicle occupant to that ofthe pedestrian road-user and realistic pedestrian models arenow being produced for authentic laboratory crash analysis.In vehicle packaging, generally, is beginning to focus on theageing and infirm section of the population and occupantrestraint systems are being designed to be adaptive in theirperformance.

16 VEHICLE DESIGN

Understanding footwelldeformation in vehicle impact

Recently published work by researchers at the USAutomobile Safety Laboratory, and its collabora-tors1, is suggesting a way of better understanding thecollapse mechanism for a passenger-car footwellduring frontal and front/side impacts. Hitherto, theauthors maintain, the study of structural intrusion inthis region has been based on toe-board mountedaccelerometers set up to measure in the direction ofthe vehicles longitudinal axis. Since the instrumentitself can easily be disoriented from its measurementaxis, during the intrusion process, reliable dynamicdeformation data has been difficult to forecast. Inparticular, a three-dimensional characterization ofthe collapse and buckling of the thin metal structuresis difficult to obtain, except perhaps using X-ray

speed-photography techniques for a qualitative ap-praisal. Obtaining orthogonal frames of reference isconsidered difficult with any conventional cine-phototechnique.

Post-crash measurements can only provide in-trusion data for the last instant of impact and noelastic effects occurring during or after the crash canbe evaluated — nor can a progressive sequence oftoe-pan translations and rotations be obtained. Hencethe stimulus for these researchers to use a sled systemfor obtaining a toe-pan deformation pulse, akin tothat obtained by sleds for vehicle deceleration as awhole. To design an intrusion system using a labora-tory sled, work commences with obtaining a simpletranslational intrusion profile parallel to the ground,Fig 1. The intrusion simulator has been designed toallow rotational components and asymmetrical load-

Fig 1: Post-crash profile oftoe-pan intrusion

Fig 2: Hydraulicdecelerator:projected view ofprogrammed rowof holes

Pre-CrashNCAPOffset rigidBarrierRepresentativeIntrusion SimulatorFinal ToepanPosition

10 20 30 40 50 60cm (From arbitrary reference location)

7.62cm

STRUCTURE AND SAFETY 17

CylinderRod

Toepan/Footplates

BuckSupport

Guide Rail

Fig 3: Intrusion simulation mechanism

Fig 4: Sled deceleration vs toe-pan acceleration ina sled frame

20 40 60 80 100 120 140 160

Fig 5: Left distal tibia load for intrusion and no-intrusion sled tests

ing effects, at a later stage.The toe-pan produces a typical 20 kN force

applied to both legs, about twice that of the axialtibial breaking strength. The panel is generally capa-ble of 25 cm maximum displacement during a crashevent and it has been found by accident-studies that85.6% of below-knee injuries are sustained with lessthan 14 cm intrusion. The sled therefore moves thetoe-panel in a progammed displacement time profile,with these maxima, by integrating the actuation ofthe panel components with the function of the sled'shydraulic decelerator. The sled and test buck aretypically accelerated to a predetermined velocityand decelerated according tot he crash pulse. Thedecelerator is configured as a cylinder with an arrayof discrete orifices over its length, Fig 2 suggesting aflat-pattern view. At the start of an impact, hydraulicpressure is transmitted to both sides of the slavecylinder, holding the toe-pan stationary with respectto the buck. When the decelerator piston passes thecontrol-side output port, pressure on that side dropsand the toe-pan moves under the force of the hydrau-lic drive lines remaining in front of the sled piston. Aconstant force internal stop in the cylinders at themaximum mechanical stroke is used to determinemaximum toe-pan travel according cylinder posi-tion. The intrusion pulse is controlled by variation oforifice sizes on the drive and control sides. Fig 3shows the physical set-up, the simulator consisting ofa toe-pan carriage with separate footrests for eachfoot. Toe-pan carriage travel is 25 cms and thehydraulic cylinder diameter is 6.4 cms. The rearmounting position is adjustable to limit toe-pantravel in increments of 2.5 cm. Controllable toe-panintrusion parameters, during the impact event, in-clude initiation, by location of a control line withinthe hydraulic decelerator; stroke, controlled by cyl-inder mount location and cylinder stop; and accelera-tion profile, depending on a combination of passiveorifices in the drive lines forming an hydraulic accu-mulator so that dynamic effects of the sled pulse canbe used to tailor the toe-pan pulse.

The researchers demonstrated the use of theintrusion simulator with sled tests carried out withzero to 7.9 cm intrusion, using the ALEX dummydeveloped by NHTSA. The test buck was configuredas a mid-size car and based on a crash pulse measuredby damped accelerometers. Sled velocity at initia-tion of the crash pulse was fixed at 58.2 km/hand full

18 VEHICLE DESIGN

intrusion stroke is selected to be at 71 ms into the sledimpact. In Fig 4 of a representative sled decel pulseand toe-pan intrusion pulse, intrusion decel relativeto the test sled is approximately sinusoidal, with 80g peak, or 100 g relative to the ground. Net effect ofsled and toe-pan decels is movement of the toe-paninto the occupant compartment, providing a poten-tially realistic translation intrusion pulse most rel-evant for lower extremity injury. Left tibia axialcompressions are shown in Fig 5 for both representa-tive and no intrusion cases, the significant effect oftoe-pan intrusion being demonstrated after about 70ms. The second peak of the intrusion means tribialaxial compression is more than doubled from the no-intrusion run.

roof rail roof railspring element

spring stiffnessreference coordinate

1 mm y - equivalentJoint beam

B pillar

triad

Pillar to rail joint stiffnessLow frequency vibration characteristics of a vehiclebody structure are considerably influenced by thecompliance of joints between the main pillars andrails, according to researchers at Kookmin Univer-sity2. While these effects have been examined at thedesign stage by using torsional spring elements tosimulate the joint stiffnesses, apart from the inaccu-racy of the assumption it has been difficult to analysethe whole structure using the NASTRAN optimiza-tion routine because these mass-less spring elementscannot be represented. Because the rotational stiff-ness of the joint structure has a major influence, theauthors have proposed a new modelling technique forthe joint sub-structure involving an equivalent beamelement. Fig 6 shows the traditional and proposedmodelling techniques applied to a B-pillar to roofjoint. The joint stiffness is computed using familiarfinite element methods, Fig 7. Unit moments areapplied at the tip of the pillar, with both ends of theroof-rail fixed. FE static analysis gives the deformedrotation angle from which rotational stiffness can bederived.

Fig 6: Traditional andproposed modellingtechnique

Fig 9: Joint stiffness results

9

£

C0

0

l,1

0 0 0

•

-


In the subsequent MSC/NASTRAN optimiza-tion run, if the section moments of inertia are chosenas design variables, their optimal values can beobtained to meet the vehicle's frequency require-ments. The table in Fig 8 shows a design changeguideline to obtain optimum joint stiffness in thisrespect. The joint stiffnesses in the X and Y planes,plus the rotational stiffness about the Z-axis of thesection centroid can be obtained. When these resultsare plotted out as a bar-graph as in Fig 9, the authorsexplain that it is relatively simple to which stiffnessesneed increasing and which could perhaps be reduced.The example in the figure implies that the Y-direc-

tion rotational stiffness of the B-pillar joint needs tobe increased while the other directional stiffnessesmay be decreased. Detail study then showed thethickness and shape of the reinforcement panel neededto be altered in this case, establishing thickness andnodal co-ordinates of the panel as design parameters.

The reinforcement may be optimally posi-tioned anywhere between the inner and outer panelsof the joint, to satisfy the stiffness requirements, andby setting the objective function of the optimizationrun for minimizing mass, the constraints can beevaluated for achieving the required rotationalstiffnesses, Fig 10.

unit: %

Fig 7: FE model of joint

A-pillar to roof

B-pillar to roof

C-pillar to roof

FBHP to A-pillar

FBHP to rocker

B-pillar to rocker

C-pillar to QLP

IY

+25.6

+30.0

+16.9

-63.6

-0.2

+20.6

-63.8

Iz

-34.9

+7.0

-66.9

-20.8

+8.9

-1.1

+0.1

J

+39.9

+7.0

-46.0

-16.1

-3.1

-53.4

-0.6

Fig 8: Design change guideline

(a) initial (b) optimal

Stiffness

designvariables

thickness

shape

+7.48

+ 34.15

+ 7.18

+33.33

refer to Fig. 8

Fig 10: Joint configuration

20 VEHICLE DESIGN

Structure analysis for interior noiseA researcher at Rover3 insists that refinement at hiscompany is now designed-in at the concept phase ofnew products. In a recent paper he differentiatedbetween component and system modelling for NVHand pointed out the difficulties of examining highfrequency behaviour, above 70 Hz. At these fre-quency levels, the author explains that vehicle prob-lems are dominated by flexible modes of the compo-nents direct-connected to the body and care is neededin interrogating information from the standpoints ofnon-linearities arising, for example, in rubber an-chorages and structural complexity where crude beammodels are typically 25-30% inaccurate.

Suppliers are now requested to carry out de-tailed modelling for analysis purposes with predic-tions of natural frequency for something like asubframe being to 10 % inaccuracy. Fig 11 comparesa beam-element model with an accurate suppliermodel for a subframe and Fig 12 shows the drivingpoint modal response of these two models. While itcan be seen that the mass is predicted well in bothmodel cases (amplitude at low frequency beforeresonance is proportional to the mass of the compo-nent), the bem element model only recognises twomain resonances and misses the smaller ones be-tween 300 and 350 Hz because these modes are outof the plane of excitation they are poorly excited.

Above 300 Hz, the author argues, FE model-ling is unsuitable because the non-linear behaviour of

most systems gives poor levels of prediction andexperimental test methods have to be used. Cur-rently, statistical energy analysis (SEA) techniquesare being evaluated in conjunction with ISVR and anumber of trim suppliers that eventually will allowaccurate prediction of vehicle interior noise from 300Hz upwards. Rigid lumped-mass representations ofbodies are giving way to models which allow theeffect of flexible modes. However, usually structuralmodels for crashworthiness analysis are unsuitable asthey do not incorporate closures and trim. Since theBMW acquisition of Rover the ability to add trimitems to the models has been developed. Large trimareas such as head-linings are modelled as non-structural masses, additional damping effect beingadded to the elements representing the adjacentpanel. For other items such as facia panels, which addstiffness to the structure, tuned spring/damper ele-ments are added to the structural model.

The author suggests that a current 90,000 ele-ment model for a vehicle body will increase in termsof number of elements by 50% every time that a newmodel is introduced. He thinks model solution timewill remain constant as machine speed is increasingat similar rate. Another development is studyingeffects of modifications to body structures by meansof super-element whole-vehicle models which com-bine body and powertrain, Fig 13. The company alsoemploys SYSNOISE software for acoustic model-ling activities, specifically for problems with engineintake and exhaust systems. Vehicle interior acousticmodelling, Fig 14, has been used for some time toassess panel sensitivity and work is underway tocouple the acoustic models to the full-vehicle mod-els.

A case study in assessing the refinement ben-

Fig 11: Beam model vs superelementFrequency Hz

Fig 12: Correlation of FE models


Fig 13: "Whole vehicle" model

Fig 14: Acoustic model of vehicle cabin

Interior Noise LHF outer ear

Interior Noise LHR outer ear

Fig 15.Frequency Hz

Road noise characteristics

Frequency Hz

Fig 16: FE model prediction

efits of a compliantly mounted front subframe wasgiven by the author. Fig 15 shows typical interiornoise measurement for a vehicle driven at constant 50kph along a surface of 20 mm cold-rolled chippings.At 25-45 Hz global modes of the vehicle bodystructure are evident; from 75-130 Hz excitation ofthe 1st and 2nd longitudinal cavity modes of thevehicle occurs and main noise source is tyre treadblocks impacting and releasing from the road sur-face; at 220-260 Hz strong excitation is generated atthe wheel hub by an acoustic resonance of the airwithin the tyre, seen as two modes describing wavestravelling forwards and backwards within the tyre.

The proposed subframe involved a front sus-pension system with body mounted MacPhersonstrut with an L-shaped lower arm mounted to thesubframe at two locations; steering rack and anti-rollbar are similarly subframe mounted. The lower tie forthe engine mounting is also attached to the subframebut the upper tie-bar is body-mounted. There is alsoa primary vibration route via the drive-shafts to thewheel hubs and back through the suspension system,the primary one for structure-borne high frequencygear noise.

When in-service recorded load inputs wereapplied to the model, results for the left hand frontsubframe mount are shown in Fig 16 as a level offorce going into the body (not interior noise). Below100 Hz there are additional resonances attributable torigid body modes of the subframe on its mounts.Beyond 100 Hz there is marked improvement for thecompliantly mounted set-up.

22 VEHICLE DESIGN

According to a researcher of Ove Arup andPartners, in his paper to the recent FMechE VehicleNoise and Vibration conference4, NVH refinementrivals crashworthiness as the major contemporaryautomotive design target. The author described anindirect boundary element method used to predict thenoise sensitivity of a vehicle body. A modal model ofthe vehicle body is coupled to a boundary elementmodel of the interior cavity, with unit forces, in thethree transational degrees of freedom, applied at theengine mounts and damper towers. The method thendepends on noise transfer functions being predictedbetween these force input locations and the occu-pants ear positions.

In normal finite element modelling, the authorexplains, predicting the body acoustic sensitivitystarts with generating a finite element mesh, whichmight even simulate glazing, closures and trim (itcould contain 200,000 elements for extracting some800 modes); normal modes in the frequency rangebelow 200 Hz are then extracted to obtain vectorialdata, along the modal damping ratios, for making themodal model.

The airspace cavity is modelled using 10-20modes, depending on cabin space geometry. A modaldamping model is used which effectively 'smears'the damping over the entire model rather than justrepresenting local area absorptions such as seatsurfaces. Wavelengths of these acoustic waves aremuch greater than those of the body structure in thisunder 200 Hz range so elements up to 50-100 mm inlength can be used for the model compared withelement lengths for the structural model of 10-20mm.

The two models are next coupled together andthe loads applied to solve for airspace pressure. Asthe design progresses the models can be modified toaccount for the greater complexity brought about beyadded features. At the early crude modelling stagefocus is on the low-frequency noise sensitivity. Themain drawback with FEM, however, is the timerequired for mesh generation.

With boundary element modelling (BEM), issuitable for acoustics applications where there areexterior or interior fields. The indirect BEM is pro-posed by the author in this case because the interiornoise problem has several domains, cabin, seats andboot airspace. While BEM uses the same structuralmodal model as the FEM method described above,

but cabin and boot airspaces are modelled using 2-Delements.

A typical structural model is in Fig 17 and aboundary element model in Fig 18. The latter can becreated in a proprietary pre-processor and can berapidly created from the structural mesh. A fieldpoint mesh, Fig 19, has also to be generated sooccupant ear sound pressure level (SPL) functionscan be calculated and the pressure field visualised. Asurface impedance model is used to simulate seat andother trim absorption. The indirect BEM modelworks in the inverse of impedance, the admittance(velocity normal to the element divided by pressure).

The coupled indirect BEM requires a so-calledsurrogate structural model (SSM) and an acousticmodel. The structural modal model is transferred onto the SSM and the search algorithm maps a vectorcomponent of each of the structural nodes on to thenodes of the BEM model. The modal model isconsiderably reduced by this process as the numberof structural nodes is much greater than those of theBEM. For the example in the figures, a 2000 elementacoustic model is involved; there are 531 structuralmodes, 91 frequencies and 24 load cases so consider-able computer power is involved.

Results of the example analysis illustrated here,solved by supercomputer, gives the NTFs displayed

Fig 18: Cabin acoustic model

Fig 19: Cabin field point mesh


on a magnitude/phase plot, Fig 20, and cabin/bootairspace sound pressure distribution as in Fig 21.Where NTFs are above target, as at 144 Hz a noise

SEDAN ACOUSTIC MODEL

Fig 17: Vehicle body FEM

boom occurs. Panel contribution and modal partici-pation analysis is used to determine the controllingNTF factors at this frequency.

Fig 20 left: Vehicle body NTF, phase pressure top and NTFmagnification (dB/N) pressure bottomFig 21 above: Interior pressure distribution

24 VEHICLE DESIGN

Preparing for statutory

pedestrian protection

The next stage in structural design for safety, oftrying to design-in protection for pedestrians subjectto vehicle impacts, is being addressed with vigour bythe UK Transport Research Laboratory5 whose firstpriority is developing pedestrian impactor physical-models, to be a base for the development of standard-ised testing.

Since the historic work of Ralph Nader in the1960s, culminating in his best-selling book 'Unsafeat any speed', little has been done for that mostvulnerable of roadway cas ualties, the pedestrian.Even if motorists can be persuaded to respect thespeed limits in intensively pedestrianised areas, orhave his/her speed more forcibly reduced by traffic-calming measures, much can be done to vehiclefront-end structures to increase the chance of pedes-trian survival under impact.

According to TRL researchers a recent surveyhas shown more than one third of road deaths were ofunprotected road users such as pedestrians and pedalcycles, some 60% of whom are struck by car front-ends. The laboratory produced an experimental safetycar in 1985, with front-end modified using conven-tional materials, which demonstrated a considerableimprovement in reduced injury level in 40 kph im-pacts, but this was largely ignored by UK legislators,despite DoT funding, in terms of ruling in measuresto reduce the death/serious-injury toll of up to 100,000per year.

Key impact areas, in order of occurrence afterfirst strike, are lower-limb to bumper, femur/pelvis tobonnet leading-edge, and head to bonnet-top. There-fore, in response an EC directive, arising from re-search by the TNO-chaired Working Group, impactorsnow being developed represent knee-joint shear forceand bending moment; femur bending moment andpelvis loads; child and adult head accelerations. Eachimpactor is propelled into the car and output fromassociated instrumentation establishes whether en-ergy absorbing characteristics of the car are accept-able. TRL's responsibility is development of theupper leg-form to bonnet leading-edge test methodand the laboratory now supply both leg-form andupper legform impactors to the car industry. Theyovercome the unreliability of testing using conven-tional dummies.

Initial impact with pedestrians is confirmed tobe mostly side-on, in road-crossing situations; thebumper contacts typically below the knee and accel-erates the lower leg against the inertia of the body

The knee bending angle (b) can be found from the following formula:

b = C + arcsin ( - x sin C )

The shear displacement (d) can be found from the following formula:

d = e x sin D

Fig 22a: TRL knee joint at maximum bendingdisplacement, above, and maximum sheardisplacement, below, showing trigonometriccalculations for actual displacements


Fig 22b: TRL bending ligament

Fig 22c: TRL leg-form impactor

above and below the contact point, reaction forcescausing bending and shearing with reactions betweenfoot and road, hip-joint and upper body mass, addingto these forces. Resulting injuries are bending andlocal crushing of leg bones and/or knee ligamentinjury through bending and shearing.

The legform impactor thus consists of 'femur'and 'tibia' sections joined by a mechanical knee, withsideways loaded joint stiffness, the elements of theimpactor having physical properties akin to a 50thpercentile male. Studies with cadavers, and compu-ter-simulations, have shown that leg inertia forceshave major influence but foot-road reaction andupper body inertia only minor influence on these legforces. The impactor is not 'fooled' by palliativeefforts to soften only the bumper area which mightreduce lower leg injury at the expense of knee jointdamage. The TRL 'knee' comprises an elastic springto produce shear stiffness and disposable deformableligaments for the bending stiffness. The elastic springis in the form of a parallelogram, a pair of bendingligaments joining the knee ends of each leg element;this particular configuration provides necessary shearstiffness whilst being unaffected by the bendingmoments required to deform the bending ligaments.Individual potentiometers separately determine bend-ing and shear displacements, their angular outputsbeing converted trigonometrically, Fig 22.

The design of the upper legform impactor isgeared to the realisation that while first contact ismade between lower leg and bumper, next phase isfor the pedestrian's legs to be swept away frombeneath with contact then occurring between bonnetleading edge and upper leg, the first contact havingbeen found to have an effect on the second one bymodifying upper leg angle and impact velocity to anextent dependent on vehicle shape. Principally theupper leg impact causes bending of the femur andcorresponding forces in the hip joint, the mass seenby the car bonnet being a combination of that of theupper leg and the inertia of body parts above andbelow it, its effective value again dependent on bodyshape. To determine the effect of shape, testing awide range of body configurations has led to therecording of data in the form of look-up graphs for theuse in the eventual assessment procedures.

Fig 23 shows the current upper legform impactorwhich comprises vertical front member representingthe adult femur, supported top and bottom by load

26 VEHICLE DESIGN

transducers on a vertical rear member, in turn mountedon the end of the guidance system through a torque-limiting joint. The front member has strain gauges tomeasure bending and is covered with a 50 mm foamlayer to simulate flesh. Since the test procedure hasbeen designed to make the impactor aim at a linedefined by the car's shape, highest bending momentdoes not necessarily occur at the midpoint, if the carspeak structural stiffness occurs above or below it, someasurement is made at midpoint and 50 mm aboveand below. Provision is made to attach weights to theimpactor so its mass can be adjusted to the effectivemass of the upper leg on impact appropriate to eachcar shape, described by the look-up graphs. Thetorque-limiting joint is specified to protect the guid-ance system from damage on cars with poor impactprotection, its minimum torque setting providing arigid joint on cars meeting the desired protectioncriteria.

To meet the knee shear and lower leg accelera-tion acceptance criteria the car front must be able toabsorb energy whilst to meet knee-bending criteriathe car must make a well distributed contact along thelength of the legform. While the second criterionmight imply a requirement for a vertical front-end, infact the TRL authors say that local deformationeffectively "converts a streamlined shape into a moreupright one". While the design of bumpers to meetmandatory low-speed impact legislation do providesome advantage to pedestrian protection, the re-searchers say it is those which have a substantialdistance between the plastic bumper skins and thestrong underlying structure that best meet the re-quirements of the legform test. Ideally a locallydeformable lightweight outer bumper skin should besupported by an integrally stiff energy absorbingfoam reacting against the strong underlying struc-ture, the crush depth being at least 40 mm. A deepbumper/spoiler making a low contact with the pedes-trian's leg at the same time as the bumper wouldreduce bending cross the knee.

In terms of upper legform impact, for a car withbonnet leading edge height of about 700 mm thedepth of crush required would be 110 mm for atypical 100 mm bumper lead. At 900 mm bonnetleading edge height the crush depth requirementincreases to 210 mm under the specified impactloading. The limit on bending moment also meansthat the contact force on the impactor must not be

concentrated at one point, requiring generously con-toured front ends. Usually the existing heavy outerbonnet reinforcing frame should be weakened andmoved slightly backwards so as to allow easierdeformation of the leading edge. The bonnet lockshould also be move back and deformable clearplastic headlamp front-faces should be employed anda revised mounting system allow the lamps beneathto collapse inwards into space that is normally avail-able rather than rigidly mounting them to a bulkhead.

In terms of the head injury criteria, a limit onacceleration is the key requirement with both childand adult head-forms having a minimum stoppingdistance of 70 mm which reduces according to theamount from which the bonnet inclines from thenormal-to-surface impact situation. Some currentbonnet skins are acceptable provided underlyinglocalised reinforcements could be replaced by moreevenly spread systems. Proper clearance is also re-quired from suspension towers and engine surfaces,the authors point out.

Holes for Studdingto Attoch Skin

Lood Transducer

Fig 23: TRLupper-leg-formimpactor

Flesh, Skin, Spoceraand Studdingnot Shownin this View


Design for the disabledAccording to researchers of the Royal College ofArt6, a hard look at the realities of environmentalstress, the ageing of populations and the crisis wel-fare systems are encountering, suggests that a new-concept "Mobility for all" vehicle may be a viablealternative to car ownership. At the same time, thisshift from 'A Car for All' to 'Mobility for All' is quitein keeping with contemporary thinking about theshift from product to service and from the material to

Fig 25: The "urban rickshaw"

the virtual. Environmentalists talk of reducing theglobal impact of human activity by a factor of be-tween five and 50 over the next 50 years, and a goodpoint to start is transportation. The authors have beenthinking about what this might mean and offer thefollowing case studies of staff and student work as aninsight into how this new mix of services and vehicletypologies might evolve.

They argue that for the generation now movinginto retirement, personal transport is synonymouswith freedom, dignity and security. This suggeststhat mobility, in the future, will mean having agreater range of transport solutions at our disposal —a more integrated transport policy that blurs thetraditional boundaries between public and privateservices and vehicles. Patterns of car ownership willchange as more vehicles are banished from town andcity centres, increasingly pedestrianised to ease con-gestion, improve security and provide a better qualityof life for all those who work, live and pursue leisureactivities there. While reservations about public trans-port — mixing with other people, lack of comfort andsecurity, etc — can be greatly improved by interiorlayout, better seating, lighting to aid security andprivacy, and higher grade interior materials andaccessories to promote a feeling of ambient luxury.

The increasing pressures to reduce materialsand energy consumption in vehicle manufacture, anduse, will lead to vehicles that last longer, can beadaptable throughout their working life and recycledor re-manufactured at the end of it. In simple termscars will last longer and be more adaptable. Forexample, the traditional family car may encompassthe needs of a growing family for its younger users,and act as a social space — and extension of the house— as they grow older. In America, older people aretaking to the highways in their retirement to explorethe vastness of their native country which they havebeen unable to enjoy during their working lives.Future trends indicate that vehicles and transportsystems will have to respond to an increased empha-sis on freedom, versatility, variety of use and socialinteraction, and do so by exploiting technical ad-vances. Over the past twenty years personal securityhas become a prerequisite of everyday life: theft,vandalism and personal attacks are more prevalentand directed not specifically at the elderly or vulner-able. Consequently, security in and out of the vehiclehas become a priority across the age ranges.

28 VEHICLE DESIGN

Where restrictions in the range of movementsare encountered, ergonomics remains an area ofsignificant interest to drivers of all ages, in particularas expectations of comfort, fatigue reduction andpersonalisation of the driving environment have risensubstantially. This leads to a great deal of interest inincreased flexibility, adaptability and user-friendli-ness in the mainstream of vehicle design.

The problem is that the major car manufactur-ers of the world continue to realise new designsaround the slow and calculated evolution of a genericproduct. Experience tells them that if they get thingswrong the costs can be enormous, like the profits ifthey get things right. So, advances in new directionsare difficult to accommodate. Where age-friendlydesign can succeed is in offering a new direction forresearch and innovation, the results of which can beintroduced to mainstream product ranges and tar-geted at the age sectors which are at present expand-ing and will continue to do so in future. Designedcorrectly, such improvements can appeal to a widermarket sector by diminishing age differences andoffering real benefits to younger purchasers—a 'carfor all' that the marketing people can understand!

The 50+ private carVehicles targeted at particular user groups e.g. 'la-dies' or 'oldies' cars, can be seen as patronising andbe rejected by both target group and other potentialpurchasers, whereas off-road and MPV's have dem-onstrated the benefits of a large cabin area, easy entryand exit, high roofs and large door apertures whichappeal to a majority of consumers and that can beparticularly helpful for older people. The seat heightallows the user to sit 'on' rather than 'in' the car,aiding parking, improving visibility, and making iteasier to turn in the driving seat.

Although few older people are wealthy, a sig-nificant proportion are 'comfortably' provided forand some have considerable disposable income. Twoexamples from Royal College of Art students JimDas and Geoff Gardiner, address this market sectorby exploring a 'classic' solution in terms of styling,taking care to integrate many of the age-friendlyelements identified above to appeal to drivers of allages. Features include sliding doors, level floor,spacious cabin, increased roof height, lowered bootaccess etc., and the interior components are designedto be adaptable: e.g. the seats can be upgraded to give

extra support or to pivot for ease of entry. The driveris assisted with automatic gear change and powersteering, and is offered joystick type controls in onedesign, which give the driver more space and makethe car usable for people who would presently requirean adapted vehicle.

Instrumentation is by 'head up display', pro-jected on the windscreen to aid driver concentration.Information is 'hierarchically driven', and only whatis important is presented at any time so as not tooverload the driver.

The format of a large coupe, Fig 24, reflects thelifestyle of a prosperous semi-retired couple, and thedesigns portrays qualities of sophistication and value.The cars features high shoulder lines to give a feelingof security and the front and rear sections have softreactive surfaces that aid protection and reduce repaircosts. The car would be manufactured from light-weight steels and re-cyclable plastics.

Taxis and people moversThe London Cab has been recently re-designed tooffer more interior space and be wheelchair friendly.The London Cab is not only an icon of the capital, italso offers one of the most flexible transport systems

Fig 26:Short-haultaxi

Fig 27: Driverless taxi


available. Ideally it should form the core of anintegrated transport system within the capital, bridg-ing the gap between people's homes and other trans-port services like the bus and underground. Theproblem is that it is relatively expensive and not easyto order for short trips, which means that for manyolder people it is not a viable travel option. A numberof alternative scenarios have been investigated at theRoyal College of Art, all of which seek to keep faresat an affordable level by reducing the capital andrunning costs of the taxi, use information technologyto offer transport on 'demand' — with passengersbooking by telephone or teletext — and extending itsuser profile to include disabled and older users.

The urban rickshawOn London's congested streets a black cab is unlikelyto travel more than 60 miles in a day, making analternative power source (electricity, hydrogen, LPG)feasible. This would reduce space requirements anddesign limitations by eliminating engine and gear-box. Sotoris Kavros drew the inspiration for hislightweight taxi, Fig 25, from the Tuk-Tuk rickshawof Indonesia, reworking the idea around an alterna-tive power source. The two passengers sit behind thedriver, and the Urban Rickshaw has been designed tobe as narrow as possible, to aid travelling through citystreets and parking, while offering good headroomand easy access through doors that fold back along-side the vehicle. The exterior is styled to look 'taxi-like' with soft bumpers to prevent pedestrian injury.

The greatly reduced capital cost of this vehiclecompared with a new Metro cab costing £28,000,could cut fares in half and still offer the driver a goodliving.

Short-haul taxiIn designing this taxi, Fig 26, Peri Salvaag envisageda future where large parts of the city are closed to cars.The function of this vehicle is move people fromplace to place within the city centre and link touristand leisure attractions with public transport. The taxiruns on electricity, with the batteries forming thefloor pan of the vehicle. It would be used for shortjourneys, typically lasting less than 20 minutes atrelatively slow speeds, and would be able to enterpedestrianised areas. Safety is therefore an importantfeature, along with accessibility. The passengerswould order the cab electronically — in the foyer ofa museum say — and be advised about when toexpect it to arrive. The driver is there to providesecurity and assistance, and payment would be bycredit card.

Short trips do not require the same level ofpassenger comfort as longer ones do and the vehicleexploits every inch of its tiny footprint with aninterior design that features a centrally mounteddriving seat with either two passengers perchingbehind on small half seats (bum rests), or a wheel-chair passenger who would enter through a door andramp at the rear. The exterior is designed to lookstrong, stable and dignified.

Driverless taxiThe most radical proposal for a city taxi that has beeninvestigated is for a driverless vehicle that wouldwork within pedestrian zones. The taxi, Fig 27,follows a guidance system in the road surface and isin constant communication with a control station thatlocates vehicles as demanded, manages their jour-

Fig 28: Kyoto tram(left and next page)

30 VEHICLE DESIGN

neys in the most efficient way and parks them inparking zones when not in use. During peak periods,the vehicles cruise the streets until 'called' by apassenger, just as in the case of the short-haul cababove. The individual vehicle then picks up thepassenger, and the user also advises the drop-offpoint so that the control station can plan its nextjourney.

The cab is shared by up to four passengers toreduce costs and optimise use. It has large glass areasto give the passengers better visibility and a sense ofsecurity, while gull-wing doors aid entry and protectthe interior from the weather. As there is no driver,the interior is designed so that passengers face oneanother around a central unit on which informationabout the city and route is projected.

Shopping ferryThis is a ferry service to be offered by a supermarketwith the vehicle being commissioned or leased by thesupermarket from the manufacturers. Out-of-towndevelopments mean that more people rely on cars, tothe detriment of older and disabled people. Back-ground research for this vehicle demonstrated thatmost supermarket journeys are weekly and less thanone trolley-load of goods per person is purchased.Regular transport to and from appropriate points, orfollowing a route around housing areas could reduceroad traffic and build customer loyalty.

In Mike Leadbetter's scenario, the bus wouldbe owned and run by the supermarket and would becalled or booked by the customer, who would becollected from a point near their home. The size of the

bus is optimised to work within conventional citystreets and carries ten passengers and their shoppingto keep the journey and waiting times down. Luggageprovision is under each seat, wheelchair access beingby ramped entry aided by external wheels whichallow the bus to kneel, and the bus is driven by hubmotors in the wheel rims, saving valuable space. Thedriver will provide security and assistance as re-quired.

Kyoto tramKyoto is an historic city and the challenge here wasto design a tram which suits a very wide user profile,including older and disabled people, mothers withchildren, and tourists, as well as commuters. Theinternal layout is spacious with groups of seats re-placing conventional benches, providing flexibleseating options for single passengers, couples andpeople with small children as well as extending theclear floor area to aid wheelchair access.

To further aid access the tram has a low floorand large doors that open flush with the sides of thevehicle and the interior has built-in grab handles.

The tram, Fig 26, features large glazed areasthat offer visibility to seated passengers and those inwheelchairs, as well as to standing passengers. Infor-mation is presented graphically to the passengers onthe internal window surfaces with LCD technology,while the exterior of the tram has a low ride height toappear non-threatening and a soft, smooth front tominimise accidental injury. At night lighting effectssimilar to those used on aircraft would enhance theambience, security, and safety of the vehicle.


Adaptive restraint technologiesAirbag systems is considered by Delphi Automotive7

to be the fastest growing sector of the automotivecomponents market.

The limitations of current technology centrearound the fact that most airbag systems today deploywith constant force, regardless of occupant position,weight, size or seatbelt usage. Although the majorityof airbag deployments occur in impacts with signifi-cantly lower speeds than are used for regulatorytesting, current system designs make no distinction inthe level of protection for restrained or unrestrainedoccupants, crash severity or the type or position ofoccupant involved in the crash. The next generationof airbag system will take these factors into account,monitoring occupants' characteristics and the crashseverity then tailoring airbag inflation to the situa-tion, Fig 27.

Fundamental sensing and control elements forsuch systems include: characterisation of vehiclecrash severity; detection and recognition of occupantsize and location; sensing restraint system compo-nent configuration — seat belt usage, seat positionand presence of a child seat; also adapting restraintsto achieve maximum protection while minimisingrisk of injury. A Delphi team is developing sensorsand restraints for Generation I ART systems targetedfor late 1998 and Generation II systems targeted for2001, Fig 28.

Crash severity sensingCurrent airbag systems utilise a Single Point Sensingand Diagnostics Module (SDM), in the passenger

Fig 27: ASI passenger-side low-mount air-bag

compartment, to detect a crash through vehicle de-celeration. Using a complex algorithm, the SDMdetermines the appropriate conditions and timing fordeploying the airbag. Airbags are triggered at thelowest vehicle speed that might produce injury yetare designed to provide maximum restraint in theworst crash scenarios. Typically, airbags are de-ployed above 14-22 km/h Equivalent Barrier Speed(EBS) and require only 50-75 ms to deploy. AdaptiveRestraints require an estimate of the potential occu-pant injury severity to make the best restraint activa-tion decision. Although they are not necessarily thesame, crash severity can be related to occupant injuryseverity potential. Total change in vehicle velocityduring the crash, for example, can be used to estimatethe maximum occupant injury potential. This infor-mation is needed early in a crash, to determineseverity and appropriate deployment.

Due to the filtering effect of the vehicle struc-ture during a crash event, the total delta velocity maynot always be established early enough with a singlepoint sensor. To support the crash severity algorithmin the SDM, an accelerometer-based sensor locatedin the crush-zone of the,car could be used. Thisinformation would be sent to the SDM and used forsituations where multi-level deployments are avail-able. Delphi is also exploring Anticipatory CrashSensing (ACS), which senses the speed at which thevehicle approaches exterior objects, to provide ear-lier crash severity estimates and significantly im-prove deployment decisions. A rollover sensing mod-ule is also being studied which can predict impendingrollover and pitchover so as to trigger rollover safetydevices, including seat belt reelers, inflatable cur-tains and side-airbags. Algorithm simulations sug-gest that it can predict rollover as much as 300milliseconds in advance of those events, critical forthe occurrence of occupant injury.

Occupant sensingThe company is also developing technologies tomeasure occupant mass and position in order toenable airbag suppression for occupants below aspecified seated weight. This technology could alsobe used to classify occupants into weight categories,thus improving the adaptation of restraint force forvarious impact situations. Transponders or 'tags' arealso available for use with rearward facing child

32 VEHICLE DESIGN

seats. They can thus be detected by a seat-basedsensor and used to disable the airbag. Occupantsensing systems can work together with the SDM tocontrol airbag deployment.

Delphi's Occupant Position and RecognitionSystem (OPRS) recognises the passenger position aswell as monitoring a specified zone around the airbagfor occupant presence. The system determines whethera passenger is in the immediate proximity of theairbag at the time of a possible deployment andinitiates appropriate action. Now under developmentit will initially detect empty seats, rearward facinginfant seats and dangerously close occupants (pas-senger airbag only). Several sensing technologies areunder consideration, including infrared, ultrasonic,thermal and capacitive. However it is likely that thefinal system will require a combination of these.

System integrationA complete system approach ensures that the limita-tions of current airbag systems will be remedied inthe most efficient way. For example, the time atwhich the crash sensors have to make deploymentdecisions in order to properly protect the occupant isclosely related to the characteristics of the airbag.

This is also true for the desired classification ofoccupant weight and height based on the restraintsystem properties. Thus, sensors and airbags devel-oped together will utilise the full capacity of both,whereas a 'system' formed by individually devel-oped components may be less efficient and morecomplex.

Collecting, processing and utilising the occu-pant and crash situation data required for fully devel-oped adaptive restraint systems is a challenge to bemet by developing a Safety Bus and DistributedRestraint System Architecture, based on the 'plug-and-play' concept used in the personal computerindustry. The new system allows the addition ordeletion of sensors and deployment loops (actuators)without redesigning the system.

The Safety Bus concept uses two wires; eachnode derives its electrical power directly from thebus. The 'arbitration' bus architecture allows anydevice to initiate a transmission when the bus is in anidle state. The design accommodates two transmis-sion rates: high speed (500 kHz) for rapid systemparameter updates and low speed (10 kHz) for diag-nostic/sensor information — seat occupancy, weightand seat belt status. Message throughput on the

Fig 28:Adaptiverestrainttechnologies


company's bus is eight times faster than existingCAN-bus protocols, it is claimed.

A complete system approach also ensures thatmany of the limitations of the current airbags will beeffectively remedied. For example, the time at whichthe crash sensors make deployment decisions inorder to properly protect the occupant is closelyrelated to the airbag's characteristics. The desiredclassification of occupant weight and height based onthe restraint system properties would work in asimilar way. The company offers a complete line ofhighly integrated driver, passenger and side impactairbag systems and is an experienced manufacturerand integrator of steering wheels, dashboards, doormodules, door trim and airbags leading to fullyintegrated modular cockpits. Products such as theSnap-In, Recessed and Invisa-ModTM Integral Steer-ing Wheel and Driver Airbag Module consolidatecomponent function in this way.

Attention to Leg InjuriesA conventional airbag system supplements the safetybelt in that it offers additional protection to vulner-able areas such as the head, the neck and the spine.However, lower body injuries have been put in focusrecently because the introduction and use of safetybelts and airbags have greatly reduced the severity ofmost upper body injuries and also because many leginjuries have been found to have long-term conse-quences. Traditionally, a 'kneebolster' is used: apadded structure that faces the occupant's knees andapplies restraint force to the occupant's lower bodythrough the femurs. In order to work properly, theknee-bolster must be positioned fairly close to the

Fig 29: Pyrotechnic actuated venting

occupant, but that also means it takes up valuablespace and reduces the leg room for the driver andpassenger.

Hence, deployable knee-bolsters are now made.This makes it possible to move the dashboard for-ward in the vehicle, as the knee-bolster automaticallypositions itself in proper proximity to the occupantsknees if a crash occurs. Recent development workhas also shown that a properly designed, deployableknee-bolster has the potential to reduce lower leginjuries, keeping the legs in a more favourable posi-tion during a crash.

The company offers an unique, low-mountairbag for application on the passenger side. It incor-porates a deployable knee-bolster, which is filledimmediately when the bag deploys. An intricatechamber system then makes the gas fill differentparts of the airbag at different times, thus eliminatingthe need for aggressive, immediate inflation of thewhole system . The arrangement allows more free-dom in the design of the passenger area, not onlybecause it eliminates the need for a knee bolster, butalso because it wraps around and covers the instru-ment panel completely, helping to protect the passen-ger from potentially harmful surfaces.

Controlling restraint deploymentThe ability to control airbag deployment force is acritical aspect of any adaptive restraint system. Del-phi's Pyrotechnic Actuated Venting (PAV) airbagmodule utilises a slide mechanism to direct inflatorenergy into the airbag, Fig 29. When combined withdeveloping sensor technology, PAV will provide fullor 'lower-power' performance based on sensor inputon occupant and crash characteristics. The system —available for both driver and passenger applications— combines the advantages of variable inflationwith the cost-effectiveness of a single output inflator.

Multiple inflators and pyrotechnically control-led venting help maximise occupant protection andminimise injury risk by adapting airbag inflationspeed and stiffness to the occupant characteristicsand crash situation. A new generation of algorithmsfor these technologies is being computer simulatedand sled testing to evaluate the cost/benefit ratio.Airbag restraining stiffness can remain 'HIGH', as isthe case with all current airbag systems, or can bemodified to 'NONE' or 'LOW', based on various

34 VEHICLE DESIGN

sensor inputs. Note that the 'HIGH' level airbagrestraining force is only needed when the occupant isan unbelted adult and the crash severity is moderateto high.

While fully adaptive restraint systems are notyet available, Delphi already produces a uniqueairbag design to protect out-of-position passenger-side occupants from injury during airbag deploy-ment. The patented Bias Deployment Flap airbagincorporates a box-shaped guide element, a 'flap' ofmaterial that diverts the deployment direction of theairbag away from an occupant located too close to thedeployment surface. Through the Aegis joint ven-ture, they are able to offer the D-60 driver airbag withpyrotechnic, non-azide inflator. The use of non-azidepropellant means that it creates virtually no residueor toxic gas.

The Hybrid Inflator System, which was co-developed with OEA, provides a smoke-free gas toinflate the cushion; deployment is aided by a smallpyrotechnic charge. Cushion inflation is preciselycontrolled for specified occupant energy manage-ment and a future adaptive inflation technology willprovide dual-stage inflation of the airbag.

Safety seating developmentsOther innovative restraint systems by the companyinclude the Pro-tech self-aligning head restraint whichhas been specified for the latest Saab 9-5. It isdesigned to reduce whiplash injuries during lowspeed rear impacts, by lifting and moving forwardand upward into the optimum position for occupanthead and neck protection. The system is also avail-

able as part of the so-called Catcher's Mitt Seatingfrom the company to be introduced this year, Fig 30,where it combines with a high-retention seat and theABTS integrated seating and seat belt system inwhich the belt is attached to and moves with the seat.The seat absorbs energy during rear impact by allow-ing the pelvis and lower back to penetrate the seatsquab in a controlled way, safely pocketing theoccupant during the course of the impact. The Pro-tech head-restraint is activated by the energy of theimpact, rearward motion of the occupant actuating apressure plate and system of levers to move therestraint. ABTS involves the use of a high-strengthseat structure and floor attachment to absorb beltanchorage loads. It particularly suits open car loca-tions where no B-pillar anchorage is available, alsoremovable seat situations or those where a largeamount of adjustment is provided. A low-mass ver-sion is available weighing 25 kg. Bosch has an-nounced that its Smart Airbag System is being imple-mented in three stages, the end of 1997 seeing start ofproduction of the SMINC smart inflation concept tocontrol the sequence of inflation according to theparticular crash situation. Currently being introducedis the Automotive Occupancy Sensoring (AOS) sys-tem seen in Fig 31 which offers adult and child seatoccupancy and out-of-position detection devices. Ina latter phase a pre-crash sensor will be able to detectthe relative crash speed before a collision, triggeringindividual protection mechanisms before impact.

Fig 30: Catcher's Mitt seating Fig 31: AOS system

Chapter 3:

Powertrain/chassis systems

The challenge of natural gas engines increases as emissionslegislation toughens for petrol and diesel engines. However,the further development of the small HSDI diesel, and thedirect injection gasoline engine, is showing, thus far, that theyare up to the challenge. The future could also lie in revisedcombustion cycles such as the constant-pressure one; there isconsiderable scope too in revised valve arrangements onotherwise conventional 1C engines. In transmission design,clutch-to-clutch automatics vie with electronically controlledCVT, while in chassis systems, the mechanics of roll-overhas come under the spotlight again, in vehicle handlinganalysis, as has the computer-simulation of suspension linkagemotions.

36 VEHICLE DESIGN

Power-trains: the next stage?Careful comparative studies are revealing some strongemissions advantages for natural gas engines, butLNG may be preferred to CNG for CVs. For lighterduty vehicles, lean burn natural gas competes withadvanced diesel and gasoline concepts but the ulti-mate solution may be IC-engines operating in arestrictive speed band in conjunction with continu-ously variable transmission.

Important work on rating particulate emissionsin terms of environmental damage has been carriedout by MIRA's Powertrain & Emissions Technologyteam. Using the test set-up seen in Fig 1, a feel for therelative merits of gasoline, diesel and CNG enginesis obtained in this respect. The research team underSimon Greenwood have shown that particulate nu-clei start to grow as they leave the combustionchamber and pass down the exhaust tracts, as tem-peratures drop below 300C. Soot particles are foundto agglomerate into chains with hydrocarbons andnitrates/sulphates condensing on to them. Some 90%of the particle size distribution is below one micronas measured by the Scanning Mobility Particle Sizer(SMPS)

Greenwood explains that particle sizing testsused a 20 cm diameter particulate dilution tunnel,with an exhaust dilution of about 20:1. The exhaustsources were various motor vehicles on a 50 kWemissions chassis dynamometer. The SMPS probewas a steel tube facing the aerosol flow connected tothe SMPS inlet. Vehicle and tunnel were precondi-tioned by driving at 50 km/h and constant speedswere chosen as being representative of the constantmodal conditions within the European emissions

drive cycle. These speeds ranged from idling to 120km/h. Two diesel vehicles were tested for this work.The vehicles had a normally aspirated IDI engine anda medium sized turbocharged IDI diesel with cata-lyst, Fig 2. All three gasoline-fuelled vehicles pro-duce few particulates at idle and low power condi-tions. Particulates that were formed did not show anyidentifiable distribution. At higher power conditionsthere were large particulate populations, Fig 3.

Of the fuels tested, 'Vehicle Petrol 1' producedthe fewest particulates. A significant increase inparticulate numbers started as low as 30 km/h and 1.0kW. The peak position developed at around 34 nm.'Petrol 2' produced distributions that were narrowerand only developed above 80 km/h and 7.1 kW. Thepeak first formed at 25 nm, corresponding to theNucleation Mode, before abruptly shifting to 70 nmat high powers. This shift occurred as the particulatesstarted to aggregate and received condensate fromexcess fuel. 'Petrol 3' showed similar behaviour butat a higher particulate concentration, the higherpower peak diameter being 40 nm rather than 70 nm.

The two CNG-fuelled vehicles produce fewparticulates at idle and low load, Fig 4. Howeverunlike the gasoline vehicles/fuels described above,the particulates that are formed at low powers tend toform an identifiable and typically bi-modal nature.The first peak is at 60 nm, the second at 120 nmdiameter. At higher powers a smaller diameter peakappeared and grew sharply to produce a very large butnarrow particulate size distribution, with totalparticulate numbers similar to those seen in dieseland gasoline vehicles. In these tests, this vehicle peakoccurred at 20-30 nm.

The diesel vehicles produced similarly shapeddistributions but with the normally aspirated engineproducing rather more particulates. The differencemay be the result of the catalyst on the turbochargedcar. The diesels were the only vehicles to producesignificant quantities of particulate matter at idle.The measured loaded peak positions were in therange 70-90 nm for the normally aspirated diesel and50 -60 nm for the turbo diesel. The particulates at idlewere smaller at 32 and 46 nm respectively. Theparticulate diameters pass through a maximum in themedium power range before decreasing again. This isthe result of the two competing processes. At idle,there are fewer particulates produced as there is lessfuel delivered to the engine, meaning that the number

POWERTRAIN/CHASSIS SYSTEMS 37

MIRA PARTICULATE SIZEANALYSIS EXPERIMENT

Fig 1: Particle sizeanalysis test set-up

of particulate cores is lower than under load. Withfewer cores available, the particulate chains cannotgrow as long as under load. In addition, the concen-tration of excess hydrocarbons is low so less conden-sation occurs. As the fuelling increases, the meanchain length and condensation rate increase. How-ever, at high powers, although the number ofparticulates is very large, the exhaust throughput isalso rapid. This means that whilst agglomerationdoes occur, it has less time to proceed to completion.

In general the gasoline vehicles produced muchlower particulate concentrations than the diesel atlow and medium powers. At higher loads a peakforms in the range 20 to 30 nm, half that seen in thediesel experiments. The initial peak is formed at

around 50 km/h and 3 kW for two of the threevehicles. The growth in the distribution is rapid atroad loads over 10 kW. In two of the gasolinevehicles, this growth is paralleled with a shift tohigher diameter, 40 nm and 70 nm respectively,clearly showing the bi-modal nature of the particulatesize distributions as the shift is the change betweenthe Nucleation mode and an Accumulation mode. Ithas been suggested that the engine oil also has a rolein this behaviour, Greenwood points out. Theparticulate numbers at high power are similar to thoseseen in the diesel experiments.

Generally, the natural gas vehicles producedfew particulates at low load. However there was aclear bi-modal distribution at this load. This indicates

Fig 3: Gasoline particulate sizedistribution

38 VEHICLE DESIGN

that there is a mechanism working to produce theseparticulates unlike in the gasoline vehicles. At highloads, the number of particulates increased verysharply. The high load distributions are very narrowand have peak values an order of magnitude higherthan for diesel and gasoline although at a smallerdiameter. This allows the total number of particulatesunder the distributions to be quite significant even incomparison to the diesel and gasoline vehicles.

Greenwood concludes that all three fuel cat-egories produce significant numbers of particulatesat high engine loading but at low loads it is the dieselwhich is the significantly heavier polluter andparticulate size, too, is significantly higher.

Truck and bus emissionsIn a seminar held by Millbrook Proving Ground, theresults of tests on truck emissions were reportedwhich were based on what the GM facility calls 'real-world' emissions testing. This is an important dis-tinction because current heavy-duty vehicle legisla-tion is based on engine-dynamometer rather thanwhole-vehicle testing. Using Millbrook's VTEC fa-cility complete vehicles are evaluated for emissionsunder simulated operating conditions approachingfield service.

The Proving Ground's Andrew Eastlake dem-onstrated the importance of using equipment such asVTEC since on choosing a catalyst formulation for aLondon bus, to give best results on the legislativedynamometer tests, this actually showed a conver-sion efficiency of only 40% under the 'real-life'conditions of the VTEC tests. By examining tran-

Fig 5: Road traffic NOx emissions, AD 2000 estimate

Fig 6: Brake specific HC (top) CO(middle) and NOx (bottom) emissions

Fig 4: CNG particulate sizedistribution


sient- operation emission data Eastlake found con-siderable cooling-off of the catalyst over long peri-ods, typified by long periods of idle experienced, say,in Oxford Street. On re-selecting a catalyst formula-tion to give best results on VTEC tests, 90-95%conversion levels were obtained.

The crucial importance of truck and bus testingwas also demonstrated by the projected emissionslevels for different vehicle categories, shown at the

Fig 7: BOC DS LNG-powered ERF

Fig 8: Gas storage requirement for equivalentrange, CNG (top) against LNG (bottom).

Fig 9: Torque characteristics: diesel vs gas

seminar by the pie chart of Fig 5, referring particu-larly to NOx emission in the year 2000. This isdespite the far lower vehicle volumes in this categorythan those of passenger cars. In the case of buses,however, the engine emissions for passengers carriedare much lower than those applying to passengercars. With the European 13 Mode test for heavy-dutyvehicle engines, testing is carried out at a series ofsteady speeds and loads, emissions being measured ateach point. There is no measurement of transientacceleration effects nor cold-start emission effects.Because one type of engine is used in a variety ofdifferent heavy-duty vehicle types, the engine manu-facturer only needs to design and calibrate one engineiteration. Once this is homologated it can be sold tomany different vehicle builders who are likely tooptimize the installed engine for fuel economy anddriveability rather than reduced emission levels. It istherefore proposed to adopt a new transient cycle testfor Europe in AD 2000. However, it is still likely tobe based on engine, rather than vehicle, testing.

CNG's advantage over gasolineResearch at the University of British Columbia1,carried out over a wide range of air/fuel ratios, hasshown while generally power output is reduced bysome 12% with CNG (compared with gasoline) dueto the displacement of air by the gas, emission levelswere substantially reduced. While both fuels exhib-ited nearly equal thermal efficiency, importantlynatural gas showed increased efficiency at very leanmixture running, due to an extension of the lean limitof combustion over gasoline. The authors argue thatby using a lean-burn strategy, with a carefullyoptimized SI CNG-engine, this might result in bothlight- and heavy-duty engines meeting current andproposed emissions regulations without the need fora catalytic converter.

Tests were carried out in the university' s Alter-native Fuels Laboratory in a Ricardo Hydra engine atthree speeds and for one full-load plus two part-loadconditions. Emissions results are shown in Fig 6 as afunction of relative air/fuel ratio (RAFR) for gasoline(G) and natural gas (NG). At wide open throttle, HCemissions are some 50% lower with CNG while COwas 100% lower for all operating ranges. NOx levelshave similar peak values, for both fuels, under full-load conditions but the advantage increases for CNGunder part-load conditions.

40 VEHICLE DESIGN

Liquified natural gas (LNG)The 12.2 litre Perkins Eagle LNG engine has demon-strated the effectiveness of natural gas in a realoperating environment, used in ten ERF tractor unitsoperating for BOC Distribution Services, Fig 7. The320 bhp engine is developed from the Perkins 2000Series of gas engines and Eagle TX range of diesels.The so-called TxSi unit is air-to-air charge cooled,fitted with a wastegated turbocharger and two-wayoxidation catalyst. LNG has a fuel density overdouble that of CNG, allowing more energy to bestored in a smaller volume, Fig 8. LNG also hasconsistently high methane content, which allowsreliable running in high compression ratio enginesand gives more consistent emission control, sayVarity-Perkins.

The IMPCO electronic air and fuel manage-ment system is a key feature of the engine. It simul-taneously measures the mass of both air and gas, in adirect manner and with very fast response, so that theunit returns very low emission levels even undertransient operating conditions. It meets AD 2000legal requirements and, because LNG contains virtu-ally no sulphur, long catalyst life is predicted. Noiseemission is also very considerably less and at idle thelevel is down by 7 dBA against diesel. As seen in thetorque characteristic of Fig 9, the engine can lugcomfortably down almost to low idle speed.

Exploiting the low CO2

emission of small HSDI dieselsRicardo engineers2 have shown the possibilities ofusing diesel propulsion for sub-B class cars whichwill emit less than 90 g/km CO2 exhaust emission.Potential fuel consumption less than 3 litre/100 km isalso mooted for a 1.2 litre 4-cylinder engine with 70mm bore. Such a car would have weight of 750-800kg and power rating of 45-55 kW. Fuel injection andmaximum cylinder pressures (140-150 bar) are bothconsiderably higher than existing HSDI diesels andcommon rail fuel distribution, with 17 mm dia injec-tor, is suggested.

According to the authors, the current industry'standard' 17 mm diameter fuel injectors are moresuitable for truck engines than small passenger carswhen packaging for diameter and length. Experiencehas proved that an injector mounted vertically andcentral in the bore between a 4-valve pattern typi-cally provides the best overall performance for HSDI

engines. However, with a relatively large injectorand small bore, the space available for valves wasnaturally at a premium. The critical section wasbetween the fuel injector and inlet valve centres, Fig10. The maximum size of inlet valves was limited onone side by the clearance to the cylinder bore and onthe other side by the requirement to achieve a coolantpath between the inlet port and the injector, alsobetween the valve springs and injector. The use of aseparate injector sleeve, in preference to a cast boss,has allowed for the maximum possible inlet valvesize whilst maintaining cooling and casting integrity.Together the inlet valves shown gave a total flow areaof around 15% of the bore area which was shown bysimulation to allow performance targets to be reached.

Fig 11 shows three possible porting arrange-ments: (a) shows two directed inlet ports and atandem exhaust port. This achieved a swirl ratio of2.5 Rs and was also unrestrictive, leading to highvolumetric efficiency — but had the disadvantagethat narrow water jacket sections under the portswould result in weak sand cores and potential castingproblems. The small bore of 70 mm meant that it wasnot possible to separate, with coolant, the long inletport wall from the exhaust port of the next cylinder,

Fig 10: Injector/inlet-valve positions


introducing the possibility of inlet charge heating, (b)shows two helical ports, one long and one short. Thisarrangement had similar performance but the addedadvantage that if inlet port deactivation was consid-ered, a better range and control of swirl was possible,(c) shows side by side helical inlet ports, found to berestrictive and also limited to a maximum swirl ratioof 2.1. Their structure does not improve cylinderhead stiffness, unlike the tandem arrangements.

The packaging of the fuel injectors consideredwas dependent on their type, Fig 12. Two types ofcommon rail injector were investigated: internal andexternal solenoid designs. Both B and C had externalsolenoid designs where the solenoid is attached to theinjector either in-line or at 90 deg to the body. Withthis type the solenoid envelope requires a space ofapproximately 30 X 70 mm; A, however, has an

a) Directed ports b) Long and short helical ports c) Side by side helical ports

Fig 11: Alternative porting

Injector A Injector B

Injector CFig 12: Alternative injector installations

integral solenoid which fits completely inside the 17mm body of the injector. The figure shows that aninjector with an integral solenoid offered improvedpackaging into the 300 cc/cylinder engine. Thisinjector allowed for more freedom of valve-traindesign and achieved the smallest overall packagesize in the cylinder head area. Another advantage wasthat, due to its relatively short length and top fuelfeed, it was possible to design a novel fuel rail whichwould also function as an injector clamp on a multi-cylinder engine.

The main constraints on the valve-train werethat the four valves had to be close to vertical and theinjector had to package in the centre of the bore. Fig13 shows the alternative valve-train layouts that wereconsidered most feasible. DOHC direct-attack wasthe simplest and potentially least expensive valve-train, but required a 9 deg valve included angle toallow for the central injector. This meant that deadvolume in the head increased, which dropped the 'Kfactor' below the minimum desirable level of 70%. ADOHC valve-train was feasible, however, when us-ing finger followers which allowed positioning of thecamshafts away from the centre of the engine andprovided adequate clearance to the fuel injector.Although this design would be more expensive andless stiff than the direct-attack design the verticalvalve inclinations allowed the least possible deadvolumes and hence the lowest predicted engine emis-sions. Both alternative SOHC valve-train layoutsused bridge pieces to connect the inlet and exhaustvalve pairs.

The SOHC-rocker design had a low camshaftand hence potentially the smallest overall packageheight when also considering the camshaft pulley.However, this design would be more expensive thanthe SOHC-finger design because of the extra rockershaft machining required. OHV-pushrod/rocker wasconsidered feasible for a low cost design but theperformance of the engine would probably be limitedby the high inertia and low stiffness of the valve-traincomponents, making it impossible to produce theaccelerations required to achieve the desired valveperformances. Electro-hydraulic operation of thevalves was investigated briefly, and potentially thefreedom to have variable control over valve timing,lift, and duration would naturally allow for betteroptimization of the gas exchange process includinginternal EGR.

42 VEHICLE DESIGN

The main structure could be conventional,using separate cylinder block and head, or amonoblock, Fig 14. Aluminium was considered agood compromise between cost and performance, apossible engine structure being shown left, the alu-minium head and block being through bolted fromunderneath, which allows extra packaging space forvalve-train and fuel equipment in the cylinder head.The pistons are shown running in the parent borealuminium which would be surface treated to achieveacceptable wear resistance. A monoblock enginestructure is shown right. The head and block areintegral, and the structure is completed by a boltedbedplate. The more uniform loading and cooling ofthe upper cylinder would reduce bore distortion andhence reduce oil consumption and oil sourced emis-sions. Satisfactory manufacture of a monoblockpresents some difficulties. Firstly, the cylinder borecannot be through-honed due to the closure of thecylinder by the gas face, which means honing wouldstop short of the gas face. A piston with a deep topland would then be required, penalizing emissionsdue to the increased crevice volume. This honingproblem could be solved by inserting a fully honeddry liner into the bore, the only penalty being a smallincrease in engine length and weight; also machiningthe valve seat insert bores into the gas face has to bedone through the bore. However, using a dry linermeans that extra clearance is available before the

liner is inserted. With this arrangement it was possi-ble to achieve acceptable tool clearance with valvesizes large enough to achieve the required perform-ance. In order to achieve good fuel consumption,parasitic losses to engine ancillaries must be mini-mized. Mechanical drives to these components meansthey are driven at speeds in a fixed ratio to enginespeed rather than at their most efficient operatingconditions. An alternative to a conventional alterna-tor is to use a flywheel starter/generator which couldbe used to crank the engine at high speed for startingand then generate the required electrical output oncethe engine is running. High speed cranking wouldhelp to reduce start- up emissions and electrical driveinput could improve idle stability and reduce emis-sions during critical phases of the drive cycle. Thissystem would be more commercially feasible if theHSDI engine were used in a hybrid diesel and electricvehicle. With vehicle demands for greater electricaloutputs the demands on alternators has increased.Alternator manufacturers are developing water cooledalternators which have higher outputs and are lessnoisy than their air cooled predecessors, the authorspoint out.

A novel approach to packaging the ancillariesfor a 1.2 litre HSDI engine is shown in Figure 15. Theair conditioning compressor is mounted at the frontof the engine with its clutch being driven directlyfrom the crankshaft. A belt from the crankshaft

SOHC - Rocker SOHC - Finger OHV - Pushrod/Rocker

Fig 13: Alternativevalve-train layouts DOHC-Direct Attack DOHC - Finger


pulley would drive a water cooled alternator, alsofront-mounted. Electrical power steering would beused. This arrangement reduces the width of theengine and in a transverse installation would meaneither increased frontal crash protection or the possi-bility to reduce bonnet length. Two types of transmis-

Timing belt housingWater cooled

alternator

Fig 15: Ancillary packagi

Transmissionintegral with engine

Fig 16: Integrated engine/transmission

sion configuration were considered, conventionaltransaxle and an integrated engine and transmissionstructure. A transverse mounted engine with frontwheel drive was assumed in both cases. A conven-tional bolt-on transaxle transmission provides theopportunity to easily adopt a range of transmissionsfor the vehicle. These would probably include manual,automatic, CVT and AWD. It is also known currenttechnology. An integrated engine and transmission isshown in Fig 16. This arrangement has the transmis-sion components housed in the cylinder block withthe final drive on the split line between the block andthe bedplate. This powertrain would be stiffer andhence quieter than a conventional design, and wouldalso be lighter. Overall powertrain length is reduced,which allows the engine to be mounted more cen-trally and for the drive shafts to have equal lengths,reducing torque steer and part-count. The disadvan-tage of this arrangement is that it would be moredifficult to have vehicles with a range of transmis-sions when compared to a conventional bolt-ontransaxle transmission.

Direct injection gasolineRicardo engineers are also taking direct-injectiongasoline engines closer to production realizationwith work on the optimization of the combustionsystem3. In-cylinder gas sampling has been used toobtain local air-fuel ratio measurements in the devel-opment of a suitable piston bowl design. The meas-urements are used to validate CFD codes valuable tothe design process. Stable combustion at 50a-60:1 A/F ratios has enabled unthrottled operation down to

Fig 14: Through-bolt (left) and monoblock (right) configurations

44 VEHICLE DESIGN

zero load.Relatively low cost electronically controlled

common-rail fuel injection systems are spurring arenewed interest in stratified-charge combustion, saythe authors, using the technique of early injection atfull load and late injection at part-load. Reducedcold-start enrichment and improved fuelling controlin transient operation are also in sight, with theeventual goal of achieving the theoretically possiblefuel economy of a diesel coupled with specific powerof a gasoline engine. Success will depend on effortsnow being made to control NOx emissions in the leanexhaust.

The optimum-shaped piston bowl of the com-bustion chamber is one which can produce an ignit-able mixture at the spark-plug at a crank angle forphased combustion to occur, producing best trade-offbetween thermodynamic efficiency and HC/NOxemissions over a wide speed/load range. Ricardohave modelled the process in the four steps of Fig 17:(a) applying Bernoulli's theorem to the fluid flow inthe injector nozzle to calculate spray characteristics;(b) comparing spray penetration with piston positionto predict time when impingement on the piston isreached; (c) fuel flow along the piston until it de-taches as a vapour cloud; (d) assistance by air motionin bringing the vapour to the plug in time for ignition;Fig 18 shows a dynamic visualization of the flow-field using CFD.

Fig 19 shows an example result of the totalcalculation over the four steps, its use being in thequick screening of combustion chamber design op-tions. Here, four different start-of-ignition timingshave been used in calculating the fuel spray trajecto-ries prior to piston impingement. After flow along thepiston and departure as a spray-cloud, it is assumedthe tumble motion, measured at BDC by CFD, iscompressed into the bowl as the piston rises and anangular momentum calculation is used to estimate airvelocity at the edge of the piston bowl and hence thetransportation time for the cloud to reach the plug. In-cylinder sampling tests were carried out using flat-piston crown, square and spherical bowl shapes,start-of-injection being varied between 310 and 330deg and injection duration held at 20 deg, equivalentto a load of 2.5 bar BMEP. Resulting A/F ratio at theplug is seen in Fig 20.

Fig 17: Fuel stratification and transport mechanism

Fig 18: Dynamic visualization of in-cylinder flow field

20

TDC

-30 -25 -20 -15 -10 -5Sample Valve Timing At Maximum Lift (deg. ATDC)

Fig 19: Fuel spray transport calculation result


-35 -30 -25 -20 -15 -10 -5 0 SSample Valve Timing At Maximum Lift (deg. ATDC)

10 15 20

Fig 20: Effect of injection timing on A/F ratio atthe plug

Piston

Piston rod

Hydrauliccylinder

Connectingbolt

Hydraulicoil

Fig 21: Hydraulically-sprung connecting rod

Fig 22: Ideal cycle for Deocp engine

Constant-pressure

cycle: the future for diesels?

Researchers at Newcastle University and the DalianMaritime University in China4 have hinted that thelimitations on diesel development, imposed by se-vere exhaust pollution control regulations, may besolved by unlocking the cycle efficiency of theconstant-volume cycle.

A variable engine cylinder volume controlledby cylinder pressure has been achieved in a dieselengine modified by a hydraulic cylinder, Fig 21,inserted into the connecting rod. The diesel enginewith oil-cushioned piston gives the unit its name ofDeocp. It is characterized by high cycle efficiency,improved low-load performance and good startingability. The theoretical combustion cycle for theengine is seen in Fig 22 (points 123451) overlaid onthe conventional cycle (12'3451).

The effective stiffness K (with correspondingconstant pressure Pk) of the hydraulic cylinder can bealtered to change the characteristics of the engine, thetable of Fig 23 indicating that engine compressionratio £ and efficiency n increase as the engine load p1decreases. A solid connecting rod is given by k= 2.26X 109 and here it is seen that efficiency does notchange with load.

In tests of a physical engine, account had to betaken of the fact that piston movement on the Deocpis not exactly dependent on crank angle, owing to thehydraulic spring, hence the measurement techniqueshown in Fig 24 was used by the authors. Tests werecarried out at 100, 90, 75, 50 and 25% full load.Results in Fig 25 (the PV diagram) show the 9%increase in thermal efficiency at 25% full load andthe 1.6% gain at full load.

The authors attribute the gain in thermal effi-ciency to the piston of the Deocp reaching its highestposition, at the end of the exhaust stroke, because ofits inertial force. Improved scavenging results fromsmall clearance volume, and high static compressionratio, especially at low loads. Swirl is also created atthis point by the rapid increase in cylinder pressure.

The authors have calculated that the combus-tion process finishes about 7 degrees of crank angleearlier than that of a comparable conventional diesel.In examination of the indicator diagram, in crank-angle form (Fig 26), it can be deduced that thecylinder pressure of the conventional engine (CE) is

46 VEHICLE DESIGN

higher than the Deocp at the beginning of the com-pression stroke because the CE has a relatively largeamount of remnant waste gas. After about 55 degreesof crank angle BTDC the Deocp's compression pres-sure increases faster because of its high compressionratio. During the expansion stroke, as cylinder pres-sure falls, the compression energy stored inside thehydraulic spring is released to the engine cylinder

and the expansion line of the Deocp is resultinglyhigher. The diagram also shows significant compres-sion of the hydraulic spring occurs at about 4 degreesBTDC, where combustion starts, with maximumcompression taking place 10 degrees ATDC.

SFC results are shown in Fig 27 and the de-tailed test results in Fig 28.

K (N/m) (bar) (bar) p2

1.49 X 107 49.05

2.26 X 10 9 39.24

2.4551.9621.4710.981

2.4551.9621.4710.981

12.5213.2214.171 5.46

1 1 .6711.6711.6711.67

1.2351.2281.2181.197

1.0101.0081 .0061 .004

.569

.608

.653

.719

.732

.8952.1162 548

60.2761.2062.3763.86

61.5761.5761.6461.70

Fig 23: Ideal cycle efficiency

Static TDCDEOCP pislon displacement at 100% loadSpring low end displacement

Engine Load100%OCDE

100%CE

25%OCDE

25% CE

-100 -80 -60 -40 -20 0 20 40 60Crank shaft angle (°CA)

100 120 140

Fig 26: Cylinder pressure vs crank-angle

Displacement

2

I5

I

Pushing rod

Displacemeitransducer

Spring

DMC-101

Fig 24: Piston displacement measurement

80

70

60

50

40

30

20

10

0

Engine Load100% DEOCP

100%'CE

25% DEOCP

25% CE

10 20 30 40 56 60

Cylinder volume (x10"5m3)

Fig 25: Cylinder pressure vs volume

70

Diesel engine with an oil cushioned piston Comparison engine

Load (%)

p\ (bar)n (r/min)Ni (kW)

g, (g/kW h)p3 (bar)

Ne(kW)ne (%)ge (g/kW h)

t1 (°C)tc (°C)

10011.721.76

10106.2939.17

215.2279.5945.075.2332.59258.6716.5

250

90

1.65965

5.0135.82

235.3876.7546294.6833.64250.6017.0

242

7513.281.47

9054.5937.39

225.4769.5347.253.86

31.42268.2817.5244

5014.951.23

7993.3436.26

232.5058.6647.462.6228.47296.0917.5

236

2515.931.05

6361.9732.91

256.2150.4747.631.13

21.83386.3018200

10013.291.76

10106.2038.56

218.6380.1445.385.4233.70

250.1511.5

250

9013.291.65

9655.6140.19

209.7970.8842.754.9635.55

237.1311.5

242

7513.291.47

9074.6337.46

225.0563.9943.484.0632.91

256.1311.5

249

5013.291.23

7943.1435.28

238.9451.4341.612.7330.70274.6411.5

242

2513.291.05

6301.5930.19

279.2341.3739.051.33

25.18334.7811.0

224

Remark e0 = 18.47, K = 1.68 X K)7 N/m,

Fig 28: Full test-results= 38 bar


Valve arrangements for

enhanced engine efficiency

Three recent contributions to the literature of enginedesign and development show how major changes inengine efficiency can be effected by different valvecontrol systems and configurations

Intake valve disablementAccording to Rover researchers5 the technique ofdisabling airflow through one inlet valve (RoverAsymmetric Combustion Enhancement, RACE) is away of generating stronger axial and barrel swirl toimprove engine combustion efficiency. In conjunc-tion with EGR it improved efficiency from 3 to 7%and with lean burn from 7 to 11%. Because highlevels of EGR or excess air normally lead to poorignitability, slower combustion, instable combustionand unburnt HC emissions, a method has to be foundof increasing the tolerance of charge dilution. Devel-

300

280

260

240

220

200550 660 750 850 960 1050

Engine speed (rpm)

Fig 27: Specific fuel consumption

Air+fuel( +EGR)

Fig 29: High activity, Port blankedhomogeneous charge concept

opment work was therefore carried out on a 10.5:1compression ratio 4-valve per cylinder engine, fittedwith air-assist fuel injection.

Previous work had shown that increasing barrelswirl alone was not enough to achieve charge dilutiontolerance and hence the decision to increase bothaxial and barrel swirl with an arrangement as seen inFig 29 used for high activity, homogeneous chargecontrol. Prior to disabling the second inlet valve, aninducer in the form of a port mask was fabricated togive barrel swirl ratio of 2.4 with both ports flowing.Flow testing of the cylinder head the gave the resultsof Fig 30.

Air/fuel ratio loops at a 2000 rpm/2-bar BMEPtest condition were obtained for the RACE engine,with and without the inducer, and compared with thebase engine as shown in Fig 31. A very good lean burnlimit and large fuel economy benefit resulted, withthe low-swirl engine working slightly better than thehigh swirl one. Generally, high activity of the RACEengine speeds up the early burn and stabilises leancombustion. Lean burn NOx limit emissions werealso lower than the base engine although emissionswere higher at stoichiometric due to the faster burnof the RACE system. Higher EGR tolerance andgreater fuel consumption better than the base enginewere also achieved.

Hot-wire anemometry measurements were usedto show that high levels of turbulence were presentwhile maintaining low bulk velocities in the combus-tion chamber, believed by the authors to be the key toigniting a dilute mixture.

Exhaust valveremoved forprevious project

Central sparkplug

Fig 30: Results of flow tests

Base headBase head with port blanked ("RACE, lowswirl")Port blanked + 2.4 inducer ("RACE, highswirl")

Barrel swirlratio

1.22.2

3.2

Axial swirl ratio

0.02.6

4.5

48 VEHICLE DESIGN

Late intake valve closingResearchers at Sheffield Hallam University6 haveshown fuel savings as much as 7% can be obtained bythe elimination of most of the pumping work energyloss inherent in late intake valve closing (LIVC) loadcontrol. They have also shown that, combined with avariable compression ratio device, LIVC can achieveup to 20% savings and a two-state LIVC controlmechanism is under evaluation.

Energy loss in pumping gas past the throttle, tothe point where no useful output is generated at idle,is considered by the authors to be an importantcontributor to engine inefficiency. The LIVC con-cept achieves engine power modulation without theneed for a throttle valve, trapped charge mass beingreduced by keeping the valve open during a portionof the compression stroke, allowing excess inducedcharge to be returned to the intake manifold. Fig 32compares the throttled and LIVC engines by their PVdiagrams, shaded areas depicting pumping losses.While conventional variable valve-timing mecha-nisms can alter valve phasing by some 30%, theauthors consider that for pure LIVC operation altera-tions in excess of 100% are necessary.

Earlier workers reportedly noted a slight loss inindicated thermal efficiency with LIVC, mostlycaused by a reduction in effective compression ratio.Some workers used a secondary camshaft above therockers, on a push-rod engine, to achieve LIVC of upto 90 degrees of crank angle. Other workers report-edly tackled the loss of thermal efficiency by adopt-ing the Otto-Atkinson combustion cycle, restoringthe compression ratio at light loads by a variable

compression device for reducing clearance volume.The Sheffield Hallam approach of allowing a

two-state LIVC control involves a relatively simplemechanism compared with that used by earlier work-ers, some of the load control being carried out with aconventional throttle. Seen in Fig 33, the arrange-ment consists of an intake camshaft with a profile tocause late closing of the intake valve at all timeswhile for full-load operation a reed valve in the intakemanifold prevents the charge being rejected from thecylinder. At low loads the reed valve is bypassed toallow the charge to return to the manifold. Theauthors point out that the reed valve must be posi-tioned as close as possible to the inlet valve whileleaving sufficient space for the bypass. Future devel-opment is seen as incorporating the system within anOtto-Atkinson cycle engine

Conventional throttling

Pumping loss

Late intake valve closing

TDC

Fig 32: Part load modulation by late intake valve closing

102 -

100

Fig 31: Effect of AFR on fuel

92

9020 22

AFR24 26 28


Six valve Eight valve

(b)

Single valve Three valve Five valve

(0Fig 34: Generic areas for (a) single, andFig 35:(b) even number and (c) oddnumber of valves

Multiple valve arrangementsWith the trend to increasing efficiency by the use ofmulti-valve combustion chambers, researchers atQueen Mary and Westfield College, London Univer-sity7, have developed a simple method of makingpreliminary assessments of such schemes, based oncalculation of valve effective flow areas for cham-bers with eight or less valves. Seven valve heads areseen as an upper limit, with 5-7 valve systemsmeriting investigation in view of 4-valve heads beingshown to have a 37% increase in valve area over thetraditional 2-valve systems.

Effective area is calculated from the steadyflow equations applied to a constant pressure modelfor obtaining steady mass flowrate. The authorsquote expressions for effective area in both chokedand unchoked modes of flow. They obtain a non-dimensional effective area by dividing the abovevalues by the generic area of the valve seat as pd2/4.The resulting values are compared in Fig 34/35 fordifferent poppet valves as a function of valve lift.

Maximum ideal area, generic area, of a singlevalve (Fig 34) is given by the authors as

[R/(l + cosec a)]2p

and for TV valves the half angle a is p/N and thegeneric area ratio

4n.(r/R)2

Fig 33: Reed valve location

50 VEHICLE DESIGN

where j = i or e, the ratio of valve and cylinder radiiand area ratios being shown in the table of Fig 36; thegeneric flow area ratio of the different valve arrange-ments is seen in Fig 37. These two figures describethe authors' key ideas, the last figure having curvesintended only to show curves, just the points havingphysical meaning.

The analysis above is based on inlet and ex-haust valves of identical head diameter and Fig 38 hasbeen provided to show an extension of the analysisfor unequal size heads. This three valve case has thesame exhaust area as that for the two valve head whilethe inlet valves have a 58% combined larger area.The method could be used to optimize valve areas,possibly, the authors suggest, by slightly increasingexhaust while reducing inlet valve head sizes, to givesignificant overall gain.

A special case for 5-valve heads is made (1)with two inlet valves the same size as in the four-valve head, giving 37% increase in area over the two-valve case and (2) with three exhaust valves the samesize as those for the six-valve case, giving a 33% areaincrease. These points are shown in Fig 39. Fig 38: Ideal 3-valve scheme

Ref 4 Cylinder diameter 8.255 cmRef 4 Cylinder diameter 10.16cmRef 3Ref 6

0.2

Valve l i f t l/d

0.3 0.4Fig 39: Poppet valveeffective areacomparison

POWERTRAIN/CHASSIS SYSTEMS

O Inlet' valves

A Exhaust valves

• Inlet and exhaust valves,number of

51

2.4-

2.2-

2.0-

1.8-

1.6-

1.4-

Fig 37: Generic area ratio tototal number of valves for vanmulti-valve schemes

Curve for N - 1 valvesused for inlet

Seven valve

V - 2 inletvalves

Cases considered

Total number Half angleof valves subtended Radius ratio

used by onevalve a K

1 180° Practical valuesay 0.5

2 90° 1/2 = 0.53 60° 0.46414 450 1

1 + 25 36° 0.3702

6 30° i = 0.3333

7 25.7143° 0.30268 22.5° 0.2768

7 — 1/3 = 0.3333Special

case

Number ofinlet

valvesne

1232

43543476544

Number ofexhaustvalves

nc

1

1112

12123312343

Area ratiofor number

of inletvalves

—

11.72312.05921.3728

2.19271.64452.22221.77781.33331.46562.14481.83841.53201.22561.7778

Area ratiofor numberof exhaust

valves

1

10.86160.68641.3728

0.54821.09630.44440.88881.33331.09920.30640.61280.91921.22561.3333

Fig 36: Poppet valve half angles, radius ratios, area ratios and number of valves considered

52 VEHICLE DESIGN

Trends in transmission design

The design of the 4-speed all-clutch-to-clutch elec-tronically-controlled automatic transmission devel-oped by Honda for the 1998 Accord was describedrecently by company engineers8. Newly developedtechnology guarantees improved shift quality andfail-safe at high speed without dependency on one-way clutches as in the more conventional system itreplaced. Already, by 1996, the company had devel-oped an all-clutch-to-clutch 3-shaft design of shortoverall length. Old and new gear train schematics areshown in Fig 40.

In the conventional system seven engagingelements involve five multiple disk clutches, a 1-2one-way clutch and a servomechanism. Thecountershaft-mounted one-way clutch transmits driv-ing torque when accelerating in 1 st gear but it overrunswithout torque transmission when decelerating inthis gear or when driving in other gears. In 1 st gear theholding clutch engages to apply engine braking fordeceleration. The one-way clutch thus performs dualfunctions of improving up-shift quality from 1st to2nd and preventing 1st gear drive when a high speedmalfunction occurs.

In the new system there are five engagingelements comprising four clutches and a servomecha-nism. The 1st clutch transmits torque, while acceler-ating in 1st, to the 1st range and applies enginebraking for deceleration. Cross-section of the newtransmission is shown in Fig 41 and its specification

1 st Gear Holding

aa

a11

1-2 One-way

I

1

1 Servo

a

a_

Main Shaft

Counter Shaft

Secondary Shaft

in the table of Fig 42. The elimination of the two partsmeant that two separate approaches to maintainingthe performance criteria had to be taken.

When the conventional transmission shifts upfrom 1st to 2nd, engine torque output first is transmit-ted to the main shaft via the torque converter, then onto the idle gear, secondary shaft, 1st clutch, 1st gear,one-way clutch, countershaft and finally to the driveshaft. The computer starts to engage the 2nd clutchwhen 1st to 2nd gear requirement is indicated, andwhen 2nd-gear torque has increased to equal mainshafttorque, the transmission changes to the inertia phaseand 2nd gear takes over all power transmission. Atthis point the one-way clutch overruns so that 1st geardoes not contribute to power transmission and theshift quality is governed by the drive shaft torque asthe product of mainshaft torque Tm and ratios i of 2ndand final drive F gears.

When shifting up from 1st to 2nd gear with thenew transmission, operation is the same as for theconventional one up to the point when the computerstarts to engage the 2nd clutch. Then, when secondgear torque has increased to the sum of mainshaft andIst-gear torques, the transmission changes to theinertia phase. As the transmission does not have aone-way clutch, the 1st gear contributes to powertransmission and the drive shaft torque is given by:

T m i2 if -T (i1 -i2) if

The minimum drive shaft torque value, when3rd 4th

Reverse Main Shaft

Fig 40: Gear train schematics for conventional (left) and new Honda (right) automatic transmissions


Fig 41: Honda automatic transmission

the clutch-to-clutch transmission changes from thetorque phase to the inertia phase, is reduced by T](il

- i2) ip. At this time the driver senses that the torquehas dropped and the shift quality has deteriorated.Therefore, in order to prevent this deterioration inshift quality, it was necessary to establish a methodfor accurately controlling the 1st and 2nd clutchhydraulics at highly precise timing so that T1 = Owhen Tm = T2 Dealing with the occurrence of highspeed malfunction in the conventional transmissioninvolved a fuel cut operating as engine speededabove its set limit and overunning of the one-way

2nd clutch clutch. With the new transmission a centrifugal hy-draulic cancellation device eliminated centrifugalpressure build-up by the rotating 1st and 2nd clutches;the control system is reworked and two linear sole-noid added which switch clutch hydraulics at theappropriate timings. There is also a new shift-logichydraulic circuit employing a fail-safe system, in-volving three non-linear switching solenoids, to pre-vent downshifting into 1st with an engine overspeed.

CVT for 2-litre engined vehicleNissan engineers9 have succeeded in commercializ-ing continuously variable transmission for the upper-middle class of car, and improving accelerative per-formance from rest over existing CVT systems by theincorporation of a torque converter which has alsoresulted in better creep capability. The electronic

Engine

TorqueConverter

ModelVersion

Type

SizeGear Train Type

Gear Ratio

1st2nd3rd4th

ReverseReduction Ratio

Used Oil TypeTotal Amount

Repair Weight (wet)Overall Length

F23A2.31 SOHC VTEC

PGM-FI3-element. 2-phasewith Lock-up Clutch

232mmConstant-mesh Type with

Three Parallel Shafts2.5281.4270.9310.6201.8634.466

Honda ATF6.21

83.5kg390mm

Fig 43: Nissan CVT for 2-litre carsFig 42: Honda transmission specification

54 VEHICLE DESIGN

control system has achieved improved fuel economyby attaining fine-tuned driveability and lock-up op-eration at low speeds; also a manual shift mode hasbeen successfully incorporated.

A cross-section through the new unit is seen inFig 43 indicating the principal elements of (a) torqueconverter, (b) forward/reverse actuator, (c) ratio-change mechanism, (d) electro-hydraulic circuitsand e. reduction gears. Specification and configura-tion are in Figs 44 and 45. The structural layout issimilar to a conventional automatic transmission,only the change-speed mechanism being adapted tobelt and pulley layout of a CVT. Overall length,including torque converter, is thus much the same asa conventional automatic gearbox for a 2-litre car.

Less booming noise than that of a conventionalautomatic's geartrain is inherent in the new unit,however, because inertia of the belt and pulleys islarger. The lock-up clutch has been given facingmaterial with twice the durability of that on a conven-tional automatic to give lock-up speed of around 20kph compared with the normal 50 kph, providing themain fuel economy benefit. The ratio-change mecha-nism uses a newly developed 30 mm wide VanDoorne belt, with nine layer steel band and 400friction elements. The additional width over thenormal 24 mm gives the unit its higher torque capac-ity. Fig 46 shows the enhanced performance over asystem used for a 1.3 litre Nissan car.

The variable-ratio pulleys are arranged suchthat a tandem piston design on the primary pulleygives two-stage operation to generate the necessary

force required in overdrive operation. On the second-ary pulley, because of its particular high speed opera-tion, a cancelling chamber is incorporated into thehydraulic cylinder; it prevents any loss in perform-ance due to centrifugal effects on the hydraulic fluid.

High-torque manual transmissionEngineers at New Venture Gear10 described the de-velopment of the company's NVT-750 gearbox, de-

Control system

Shift device

Fig 45: Nissan CVT configuration

Applicable engine

Ratio change range

Basicconstruction Launch element

Forward/reverseactuation mechanismRatio changemechanismOil pump type

Final gear ratio

Fluid type used

Displacement. 2.0LMax power: 1 90ps/7000rpm

2.326 - 0.434

Torque converter withlow-speed lock-up clutchPlanetary gearset+ wet multiplate clutch30-mm-wide steel belt

pulleysHypotrochoid gear pump

5.473Nissan Genuine ATF(special-purpose CVT fluid)

Nissan belt-drive CVTBelt working radius at Low ratio(Primary pulley)

Pulley force at Low ratio(Primary pulley)

Friction coefficient betweenelements and pulleysu

Pulley angle

Fx R

F x R ratio

1.3-L class

27.1 mm

28.9 kN

009

11°

783.2 kNmm

1

<

<

=

=

<

<

2.0-L class

33.9 mm

37.6 kN

009

11°

1274.6 kNmm

1.63

Fig 46: Torque capacity potential of belt-drive CVTs

Fig 44: Nissan CVT specification


Fig 47: New Venture Gear NVT-750 gearbox

Fig 48: Net form clutch teeth

Fig 49: 3/4 shift system

signed as a high torque density transaxle suitable forheavy duty FWD operation. The development objec-tives were the achievement of greater durability thanthe 650 unit while achieving world-class gear noisereduction targets. The 5-speed unit has torque capac-ity of 290 Nm, synchronization on all forward gears,13.08 maximum reduction and a 200 mm distancebetween input and output, Fig 47.

Greater gear durability was obtained chieflywith a 15-20% increase in face-width but this wasobtained without any change in the length of thegearbox over the previous model. This was achievedby developing net-forming clutch teeth tucked insidethe gear width and reducing shaper cut tool clearanceby going from one to two-piece welded construction,Fig 48. Gears were designed with total overlaps lessthan three times the sum of helical and profile; some10-15% compressive stress reduction resulted.

The bearing installation was redesigned so as toincrease effective shaft rigidity, the input shaft nowbeing supported on a roller-ball combination de-signed to negate the effect of differential thermalexpansion between aluminium alloy and steel with-out loss of support. The front intermediate shafttaper-roller bearing is now fitted with a high tempera-ture polymer cage which allows more rollers to beincluded within a given space envelope, despite thenarrower width constraint placed by the increasedgear face-width.The taper bearing cup is first pressedinto the case, during assembly, the bearing thenseated in the cup and, finally, the whole intermediateshaft assembly pressed into the taper bearing conebore without brinelling the rollers. Easy gauging ofthe bearings is thus permitted with a simplifiedassembly process.

The dual-cone synchonizers have organic fric-tion material, the 3/4th and 5th synchonizers beingarranged with a common blocking ring, giving aclaimed 400% increase in energy absorption over theconventional brass ring set-up. The reverse idler isengaged between the input shaft and an external spurgear on the 3/4 synchronizer sleeve, torque transmit-ted resulting in lateral motion of the sleeve duringdrive and coast reverse engagements. This motion islimited to 1-1.52 mm by using the 3/4 fork as a thrustsurface, Fig 49; clutch teeth are located away fromthe sleeve by 1.27 mm to compensate for the remain-ing motion left in the sleeve, preventing prematureengagement with the blocker ring.

56 VEHICLE DESIGN

Fig 50: Base (above) and high level (below) strategies

Control strategies for CVTA timely study of the control criteria for continuouslyvariable transmission has been made by researchersat Ricardo-FFD11 who have provided a most lucidexplanation of engine/transmission matching. Theyremind us that too little overlap in the torque curvesfor different ratios of a stepped transmission results ingaps in the shift sequence with engine speed, andhence power, having to drop too far between shifts —thus breaking the gear-change rhythm. Connectingthe peak power points in a group of typical 2-D graphsof this sort would show a 100% efficient transmissioncharacteristic working with an engine held at full-power continuously. When plotted in 3-D form,physical 3-D steps can be seen between the torquecurves and these become a smooth surface with CVT.The surface has depth in the sense that part-throttleperformance characteristics also exist and navigatingthrough the resulting solid volume is the job of a CVTcontrol system.

The FFD PDSL simulator allows control sys-tems to be tried out on a sophisticated computermodel of the powertrain. Control strategies analo-gous to those in-built into human responses formanual gearbox control can be tested, for example.Fig 50 compares PDSL interpretation of a basestrategy 'if in doubt move up the ratio range' with ahigher level one of 'kick-down' for possible overtak-ing, say. Similar strategies are also provided by the

g

cars and

delivery vehicles, as extrem e exam-

Fig 51: Proposed CVT enginetorque curve matching to widerange CVT

authors to demorstrate the operating rquirements ofracing cars and delivary vehicles as extrems exa


Fig 53: Drive strategy for influencing factors

Fig 54: Adaptation ranges of drive strategy

pies, the first wanting to hold maximum powerthrough the accelerating sequence while the secondis wanting a narrowing of the performance corridor topreclude cargo-damage. FFD believe a CVT strategyshould be broadened from merely providing an infi-nite number of ratio selections to sophisticated en-gine/transmission interaction in a way that the driversees no limiting characteristics of the transmission.The opportunity to map the control domain existsrather than moving from one rigid strategy to another,giving the driver hints and feedbacks as to the rightway to use the transmission. Matching conventionalengines to conventional transmissions requires, inthe case of heavy haulage, for example, engine torqueback-up for reducing the need to change gear. How-ever, this flexibility in power delivery is paid forbecause the engine is compromised between twoduties, providing maximum power at maximum speedand maximum torque at usually a much slower speed.With a wide-range CVT there is no need for suchflexibility and engine operating speed range canpotentially be considerably narrowed down. Thisscenario has been modelled in PDSL, Fig 51.

In the case of the German maker ZF's CFT20CVT, flow of signals between driver, engine andtransmission is seen in Fig 52. Fuzzy logic control isinvolved and the ECU is adaptable to different driverstrategies. Achieving optimum drive characteristicswas done by arranging for automatic specification ofthe engine operating point, accounting for the specialfeatures of each driveline. With the extensive rangeof possible system modes available an adaptive strat-egy is necessary and this led to the use of fuzzy logicin specifying the operating point, Fig 53 showing thesystem structure. The operating point is generallyfixed by the need to optimize fuel economy and isonly adapted to higher engine speeds (more power)by driver demand or operational task such as gradientnegotiation. Converting performance demand intoincrease in operating point involves the evaluation ofmany parameters; for example, a distinction beingmade between setting off in an urban environmentand overtaking out-of-town. Performance level evalu-ation takes the form of an adaptation factor infinitelyvariable between minimum fuel consumption andmaximum road performance. A large adaptation areais also covered by the range of engine characteristics,plus accounting for all driveability requirements,Fig 54.

58 VEHICLE DESIGN

The mechanics of roll-overAs economy vehicles for urban operation becomeshorter, and therefore taller so that volume capacityand visibility are not compromised, the problem ofroll-over intensifies. The appearance of new softwarefrom American Technical Publishers for allowingcalculation in the fundamentals of vehicle dynamicsgives an opportunity to better predict likely vehicleperformance in this respect at the design stage.

According to Gillespie12, who originated thesoftware, the initial simplified quasi-static behaviourof the vehicle in cornering can be studied with theelementary model of Fig 55. The vehicle is assumedto be in a steady- state turn without any roll accelera-tion and the tyre forces shown represent the sum offront and rears. Super-elevated (banked) highwayshelp to resist the overturning effect and the symbol jfor the road-banking angle is used in calculation aspositive when tilted towards the cornering vehicle.Lateral acceleration in gravities can thus be ex-pressed as:

{(t/2) + (p/h- (Fz/Mg)t}/h

and the limiting value when load on the inner wheelbecomes zero is:

fh}/h

thus on level roads only the CG height and track arenecessary for a first estimate of resistance to roll-over. Though this term gives conservative values forpropensity to roll-over it is useful for comparisonpurposes and the author gives the table of Fig 56 toillustrate this. Since the peak tyre-to-ground frictionco-efficient is quoted as 0.8, the table suggests thatthe lighter vehicles are safe from roll-over as theywould slide out of the curve, which of course has beendisproved in practice.

In fact, by neglecting the compliances of thetyres and suspensions, roll-over threshold is overes-timated as the lateral offset of the CG is unaccountedfor. Thus by considering the more refined model ofFig 57, incorporating the hypothetical roll-centre,lateral acceleration, related to roll rate R0, becomes:

over threshold, usually around 0.95 the author ex-plains, but quite a lot higher for a low-slung sportscar. Solid axles, with high roll-centres, reduce theeffect of lateral CG shift compared with many inde-pendent suspension systems with roll-centres at nearground level. Lateral deflection of the tyres adds afurther 5% reduction of the threshold, it is explained.

However, for an accurate assessment completemodelling of the vehicle suspension is required ac-counting for such factors as lateral shift of roll-centreand lateral movement of the line-of-action of tyrevertical force, due to cornering forces and deflectionsarising from changes in the overturning momentunder combined cornering and cambering effects.Such modelling would result in quasi-static rollresponse, indicated by Fig 58. This shows the linear-ity of the response breaks when one of the inner

\

Fig 55: Forces inducing roll-over

the curly bracketed term showing the factoring roll-Fig 56: Roll reactions on suspended vehicle


Vehicle TypeSports car

Compact car

Luxury car

Pickup truck

Passenger van

Medium truck

Heavy truck

CG Height

18-20 inches

20-23

20-24

30-35

30-40

45-55

60-85

Tread

50-60 inches

50-60

60-65

65-70

65-70

65-75

70-72

Rollover Threshold

l.2-1.7g

1.1-1.5

1.2-1.6

0.9-1.1

0.8-1.1

0.6-0.8

0.4-0.6

Fig 57: Threshold comparisons

Fig 58: Equilibrium lateral acceleration

TimeFig 59: Roll response to step input

1.0Frequency (Hz)

Fig 60: Threshold as a function of sinusoidal steer

wheels lifts off. The plot suggests that highest roll-over threshold will be achieved by maintaining sprungmass roll rate at the highest level by using high rollstiffness suspension and designing so that simultane-ous lift-off of front and rear inner wheels occurs at thecornering limit.

Transient roll-overTo examine vehicle response to rapid changes inlateral acceleration a transient model is required. Thesimplest one would be that of Fig 57 but with a rollmoment-of-inertia term added. This is useful forresponses to step inputs such as changes in roadsurface friction or release of brakes after wheel-lock,the response of the system being similar to a singledegree of freedom system, Fig 59. The fact that roll-angle can overshoot, depending on the degree of rolldamping, the author explains, means that wheel lift-off may occur at lower levels of lateral accelerationinput in transient manoeuvres, hence a lower roll-over threshold.

In the case of sinusoidal lateral accelerationinput, as approximated by the slalom 'moose' test,roll-over threshold response is shown in Fig 60 as afunction of frequency for different classes of vehicle,the values approaching the steady-state corneringcase at zero frequency. Heavy trucks are seen as beingparticularly sensitive to this effect since their rollresonant frequency is often less than 1 Hz and lane-change or certain roundabout manoeuvres of around0.5 Hz could result in roll-over. Cars having lowerCG positions usually have roll resonances at about1.5 Hz.

The most complete and accurate picture isprovided by models which simulate both yaw and rollresponse. Using such a model to examine sinusoidalsteer inputs reveals the important additional effect offront and rear tyre force phasing lag caused by the reartyre not building up side force until a slip angle buildsup. Fig 61 illustrates the effect. Here the front to rearlateral force build up lag is 0.2 seconds for the 1 Hzsteer input case. The lateral acceleration for thewhole vehicle is diminished from 0.8 to 0.5 g and tothe driver there is a perception of lack of responsive-ness in transient manoeuvres. Four wheel steer carseliminate this lag and improve responsiveness; how-ever, the author points out, it could contribute to roll-over propensity.

In tractor-trailer vehicle combinations the phase

60 VEHICLE DESIGN

lag is particularly pronounced and the response in Fig62 is typical. Here a 2 second sinusoidal steer inputexcites both a rearward amplification of the yawresponse and roll-resonance of the full trailer, suchthat it experiences much larger lateral accelerationthan the tractor, creating a dangerous whip-lasheffect. The effect is prevented by using a tractor-trailer coupling which transfers roll-couples fromtractor to trailer.

Software exampleGillespie used the quasi-static model to demonstratethe effect of highway super-elevation on vehicleoccupants. The objective here is to find what anglewould make the occupants experience 0.1 g lateralacceleration in a 40 mph steady-state turn of 500 ftradius in a vehicle of 60 inches track, 20 inches CGheight and weighing 2200 pounds.

Fig 63 shows the data input spread sheet withthese values entered. On solving, the sheet generatesthe first three views of Fig 64, the third of which is avector diagram showing the relationship between thevectors ac and g (relative to horizontal and vertical)and ay and az (relative to the vertical axis). The pointcommon to the upper left corners of both rectanglesrepresents the CG location while the line from the CGto G is centrifugal acceleration ay and the verticalline from CG to the other G is gravity acceleration g.On the other rectangle the line slanting right andupwards from CG to point V is lateral accelerationexperienced by the occupants ay and the one slantingright downwards to the other V is the vertical accel-eration they experience.

Neutral speed is that at which the occupantsexperience no lateral acceleration relative to thevehicle and the program allows back-solving for thiscase by changing 0 from an output to an inputvariable, changing the input instruction for ay andblanking the V input field. This produces the sheet ofFig 65 and the fourth view of Fig 64, a vector diagramin which G = global axes (ac and g); V = vehicle axes(ay and az).

The neutral speed for this curve is 29 mph andthe equilibrium lateral acceleration plots are thesame for this solution because the radius, super-elevation, track and CG height are unchanged. How-ever, the vector plot is different because centrifugalacceleration ac is smaller and the lateral accelerationay is now zero.

St Input

4050060202200

.1

Name

VRacthW9MayazFziFzophi

Vrollacrollayrollazroll

Output

.21394745

12200

1.01772961046.16921192.83596.4644744

120.56351.94365351.81870841.2124722

Unit

mphftg'sininIb9'sIbm

g'sg'sIbIbdeg

mph9'sg's9's

CommentFundamentals of VehicleDynamicsby Thomas D. Gillespie

Chapter 9: RolloverQuasi-Static Rollover of RigidVehicleEq. 9-1 , p. 31 1 , and Fig. 9.2, p.313

VelocityRadius of turnLateral acceleration (horizontal)Track width (tread)Height of CGWeight of vehicle = M*gAcceleration of gravity (default: 1g)Mass of vehicleAcceleration along vehicle y-axisAcceleration along vehicle z-axisNormal force on inside tireNormal force on outside tireRoad cross-slope angleRollover thresholds:VelocityLateral acceleration (horizontal)Acceleration along vehicle y-axisAcceleration along vehicle z-axis

Fig 63: First input spreadsheet

st: Input

500

60202200

0

6.4644744

Name

VRacthWgM

ayazFziFzophi

Vrollacrollayrollazroll

Output

29.109577.11330756

12200

1 .00639881107.03871 107.0387

120.56351 .94365351.81870841.2124722

Unit

mphftg'sinInIb9'sIbm

g'sg'sIbIbdeg

mphg'sg'sg's

CommentFundamentals of VehicleDynamicsby Thomas D. Gillespie

Chapter 9: RolloverQuasi-Static Rollover of RigidVehicleEq. 9-1, p. 31 Land Fig. 9.2,p. 313VelocityRadius of turnLateral acceleration(horizontal)Track width (tread)Height of CGWeight of vehicle = M'qAcceleration of gravity(default: 1 g)Mass of vehicle

Acceleration along vehicle y-axisAcceleration along vehicle z-axisNormal force on inside tireNormal force on outside tireRoad cross-slope angleRollover thresholds:VelocityLateral acceleration

(horizontal)Acceleration along vehicle

y-axisAcceleration along vehicle

z-axis

Fig 65: Second input spreadsheets

62 VEHICLE DESIGN

Suspension and steering

linkage analysisFor light vehicles, advances in modelling techniquesare making the analysis of handling behaviour amuch more realistic process than was possible withclassical quasi-static techniques. The same is true ofanalysing suspension behaviour with respect to roaddamage by heavy vehicles.

The change from active suspension systems inFormula One race-cars brought about by the 1994revised regulations focused a new interest in theperfection of passive systems. According to BresciaUniversity researchers13, double-wishbone configu-ration, with either tie-bar or compression-strut brakeforce reaction, remains the favourite means of con-trolling wheel-to-chassis relative movements impor-tant for maintaining roll-centre location and stabilityof the tyre-ground contact patch.

Continuing conflict existed, the authors main-tained, between low roll-centre to reduce lateral

scrub at full-bump spring deflection, as well as largeweight transfer and roll angles in cornering, against,with high roll-centre, reduced weight transfer butincreased lateral scrub and the jacking effect. Keyobjective in design was to restrict the movement ofthe roll axis to a minimum to ensure constant levelsof weight transfer in different operating conditions.Fl practice is to adopt long parallel wishbone arms inorder to minimize camber sensitivity to change insuspension ride height.

Fig 66: 16-node suspension model

Piano XZ Piano YZ

Fig 67: Orthogonal projection of Fig 66


The authors have developed MMGB designsoftware for race-car suspension, in conjunction withDallara Snc, for a complete 3-D analysis. Fig 66shows a prototype configuration involving a 16-nodekinematic system, the wheel, hub-carrier and springrocker lever being assumed to be infinitely stiff. Thewishbones are each represented by two pin-endedmembers connected at the outer node. The spring-damper unit is modelled as a variable length beamwhile the spring-reaction and steering arms are con-sidered to be rigid. The program permits the linkageto be seen in orthogonal projection as seen in Fig 67.Data input files handle spring rate and road loads andthe program is based on algorithms for kinematicsolution and force equilibrium.

The kinematic module computes geometry van-

's <^ 6040

V. 20

ation during wheel travel and full bump reboundsituations can be examined with the chassis effec-tively held still. Main suspension property outputsare seen in the graphs of Fig 68. A graphic animationis also available to simulate the motion of the suspen-sion for observation by the designer. The force mod-ule computes link loads, rocker-pivot loads and springforce for given wheel displacement and externalloading. There is also a compliance module whicheffectively measures the interaction between the firsttwo modules but taking into account link elasticity.

Additional modules have been developed sincethe program was first launched. These allow studyof wheel rate and sprung mass frequency variation asthe vehicle progresses along its track, arising fromrising-rate or preload effects, also the effect of reduc-

c

A

-40

40

20

0

-40

.

Fig 68: Main suspension geometry outputs from analysis

Fig 69: Chassisroll of 4 degrees

64 VEHICLE DESIGN

ing fuel weight and aerodynamic downforce inputs.Anti-dive and anti-squat configurations can also beexamined. A roll-centre module can examine not justvertical but also lateral motions of the roll-axis. Thevery considerable lateral movement for a nominallyground-level roll-centre suspension design is seen inFig 69 for a chassis roll of 4 degrees.

The authors also referred to the work on sus-pension compliance of John Ellis whose book onvehicle handling dynamics was published in the sameyear14. Ellis recommends a vectorial approach tosuspension analysis which is not dependent on loca-tion of roll-centre and which can be applied at anyvehicle attitude. For two-dimensional analysis, inFig 70, the origin O is fixed in the vehicle body planeand an outboard point O is at the wheel-groundcontact. His analysis considers the velocities of thesepoints in relation to the body and wheel velocities,relating them by the rigid link which effectivelyexists between the inboard and outboard points.

Referring to the co-ordinates of these points,shown in the figure, velocity of the inboard point is

That of the outboard point is composed of the wheelvelocity V and a component p due to rate of camberrotation of the wheel in

the two velocities acting at the opposite ends of linkAD. Since the relative velocities of these points alongthe line of AD is zero, the scalar products of thesevelocities with the unit vector of the link must equaleach other, Ellis explains. By representing the link asunit vector

ad = mj + nk

where m and n define the spatial position of the linkdefined by co-ordinate geometry. Velocities of bodyand wheel/road interface then become related by theexpression:

(-pza)m + (W + pyjn = (V - pzd)m -p'yd n

Fig 70: Two-dimensional analysis

By repeating this procedure for each link con-Fig 71: Compliance representation


necting body and wheel, a set of equations is obtainedwhich can be solved simultaneously by matrix meth-ods to give useful design relationships such as the rateof contact patch lateral velocity with bounce velocityof the suspension; tyre scrub due to roll; and camberchange due to bounce and roll.

Ellis also carries out a three-dimensional sus-pension analysis using these techniques and finds theinterrelationship with the steering system, as well asmodelling the effects of tyre stiffness. Complianceeffects are examined for the flexible mountings of thesuspension. He defines the change in suspensioncharacteristics due to external forces as the compli-ance and describes its quantification using the two-dimensional representation of Fig 71.

Forces on the inboard bearings are found bystatic equilibrium equations, the stub axle OCDbeing under the action of normal and lateral forces atthe road/tyre interface, which can be expressed alge-braically for this purpose. The line of action of theforce within the suspension link AD intersects theforce vector at a. The vector O 3 is known, so also are

Fig 72: Roll effects

the directions of the force vectors for joints D and C.The lower suspension link is under the action ofspring force along FE and the forces at B and C.Directions of the reaction C and the spring force areknown and intersect at b, so the direction of thereaction at b can be obtained and the vector diagramdrawn. By inputting the stiffness of the joints 1 and4, the deflections of these joints can be obtained andnew positions of the inboard nodes of the suspensionlinkage obtained and the change in handling behav-iour calculated. A similar analysis for a 3D suspen-sion model is given in the book.

He uses the steady state roll angle of thesuspension, derived from energy and work equations,and expressed in terms of the suspension derivatives,to examine roll attitudes and load transfer. The roll ofthe body causes potential energy to be stored in thesprings and work is done by the tyres in developinglateral forces to keep the vehicle in a corner; anddeveloping lateral motion as a result of the roll. Asthe vehicle moves on its curved path, the lateralinertial force acting at the centre of mass gives rise toan overturning moment, transferring normal loadfrom inner to outer wheels. Because redistribution ofnormal forces causes the lateral forces generated bythe tyres to change in a non-linear way, the balanceof the vehicle may change, Ellis explains.

Roll-induced steering is possible at both frontand rear axles, the relative roll stiffness of the suspen-sions affecting the proportion of the load transfercarried by each axle. Added to this are the effects ofsteering of the road wheels under roll-displacement,components of the lateral velocity at each contactpatch due to tyre scrub also the camber of the wheelswith roll displacement. Fig 72 (top) shows a 2-dimensional suspension for the case in which roll isthe only motion and it is seen that the kinematicdesign of the suspension will constrain the motion ofthe road wheels in response to the roll of the vehicle.The kinetic energy of the system due to roll is

2T = Ip2 + (m'V'2 + I'p'2)

but as V ' = dy'/do.p and p = df/do.p, suspensionderivatives referring to the centres of mass of thesuspensions, then for the whole vehicle, Fig 72b, theeffective inertia in roll is

66 VEHICLE DESIGN

Current review of road-friendlinessCebon joined with colleagues from Warwick andNottingham Universities to give an up-to-date as-sessment of road-friendliness research15 with particu-lar reference to the common case of the articulatedHGV. Recent thinking is that the dynamic compo-nent of tyre forces is the main factor in contributingto road damage. Not only is this significant comparedwith mean (static) tyre force but it is believed thatdifferent vehicles generate similar spatial patterns ofdynamic loading. At a given speed, the tyre forcetime histories generated by a particular vehicle arerepeated closely on successive runs over a givenstretch of road, the phenomenon of spatialrepeatability. This means that certain points alongthe road will be subjected to the peak dynamic tyreforces generated by many vehicles, thus significantlyincreasing the damage incurred at those points, theauthors explain. Assessment procedures should there-fore follow the criteria shown in the table of Fig 73.

As well as the dynamic loading effect on roaddamage discussed above, a road stress factor has alsobeen used based on the so-called fourth power law:

where P(t) is tyre force; E[] an expectation operator;P the static tyre force; and s the co-efficient of

stat —

variation of dynamic tyre force (the die). However, itmust be noted that the stress factor does not accountfor the spatial distribution of tyre forces and is nomore than a 'plausible rule-of-thumb'.

The need to have road damage criteria thatrelate to specific points along the road has involvedsumming the measured dynamic forces of each axleraised to a power n, applied to each location along aroad, or sensor in a road measuring mat. This isknown as a weighted aggregate force model, the nthpower aggregate force Ank measured at location kbeing given by

Z. ,(Pnjk) for k = 1,2,3,..., N

the power of n being chosen to represent the type ofroad damage being considered (4 for fatigue damageand 1 for rutting). The dlc and aggregate forcemethods have been compared in tests on a trunk road,Fig 74 showing the dlc averaged over all suspensionsin each class of axle group for all trailer axle groups

'Road-friendliness' assessment tests should:

1 account for the effects of tyre and axle arrangements and static loadsharing as well as dynamic loading performance;

2 use testing equipment which is not dependent on the arrangement ofaxles and tyres, and therefore does not bias vehicle design towardsparticular configurations;

3 be based on assessment criteria which reflect the potential of thevehicle to inflict fatigue and rutting damage to representativepavement structures;

4 be conducted for representative conditions of speed, road roughnessand road constaiction;

5 account correctly for whcelbase filtering;6 account for the effects of all axles of the vehicle on the pavement;7 resolve/sample correctly both high- and low-frequency dynamic

tyre forces;8 utilize statistically significant samples of tyre force-time histories;9 account for the effects of spatial repeatability of dynamic pavement

loads;10 account for the dynamic interaction between the suspensions of

tractors and trailers.

Fig 73: Assessment procedure criteria

13 14 15 16 17 18 19

Fig 74: Dlc results (2a and 3a refer to 2/3-axleair suspension and 2a/3a to 2/3-axle steelsuspension respectively)

Fig 75: Fourth power results, error bars showingstandard deviation


for which suspension type was identified. Fig 75shows the fourth power results for the same traileraxle groups, normalized using the static weight of theaxle group to enable different vehicles to be com-pared directly. The two criteria rank the suspensionclasses in different orders; this is due to spatialcorrelation between the tyre forces in an axle groupwhich is not handled properly by the dlc.

Generally it has been observed that dynamicwheel loads increase with increasing road speed androad roughness; that walking beam and pivoted springtandem bogie suspensions generate the highest loads,leaf spring suspensions generate less, and air andtorsion bar suspensions generate the smallest levelsof dynamic loads. An important feature of dynamicloading is that all suspensions and tyres on a vehicleare involved in the sprung mass modes of vibrationand so effect of tractor-trailer interaction is impor-tant. A trailer performing well with one tractor mayperform badly with another. A practical assessmenttest is therefore likely to require a standard tractor fortesting with every trailer and a standard trailer fortesting with all tractors.

This page intentionally left blank

Chapter 4:

Electrical and electronic systems

The maturity of automotive electronics is seen in the desire tosee the controller as seamlessly integrated with the vehiclesystem. This is evident in new developments in engine knocksensing, suspension, steering and drivetrain control. Vehiclesystem development is also being driven by telematic trafficmanagement systems and the goal of vehicle headway controlis not far away. Engineers from different disciplines are seek-ing knowledge of the digital systems used in electronic cir-cuits and applying the knowledge to driver-vehicle man-ma-chine control systems for creating information links with thesurrounding road infrastructure and the driver becoming apredictable control link within refined electronic steering sys-tems. The greater sophistication in hybrid, electric and IC en-gine, drive for vehicles is seen in the more accurate matchingof performance to the actual drive cycles which such vehiclesare likely to experience. The use of map-controlled drive man-agement is emerging and some of the latest control techniquesare seen in the first production hybrid, the Toyota Prius. Fu-ture possible hybrid development is considered by some to bewith the use of supercapacitors to work in conjunction withenergy storage systems based on batteries. Electronic controlis even seen to be advancing into vehicle test engineering withthe appearance of automated handling systems for track use.

70 VEHICLE DESIGN

Automotive electronics maturityThe seamless electro-mechanical vehicle is the cur-rent aim of automotive electronics engineers whoseek to bring an end to inefficiencies caused bygrafting on electric controls to systems originallydesigned for mechanical operation. This approach isseen here applied to engine, suspension, steering anddrivetrain control. Meanwhile the principal growtharea, telematics, is beginning to see firm proposalsfor OE navigation systems for less expensive vehi-cles in the adaptive cruise control and headwaysensor described here alongside a proposal for aguidance system to allow vehicles to follow roadwaywhite lines. Major proprietary system releases revealthe latest in engine management and rival systems forbusiness driver communication with his/her office.

According to Chrysler Advanced Technolo-gies specialist Dr Chris Bodoni-Bird1, the emergingtechnology of mechatronics is set to bring about theseamless electro-mechanical vehicle which can learnfrom Nature in its development. The theme is reduc-tion in mass by using seamless electro-mechanicalintegration by either exploiting intelligence and/ordeveloping multi-functional componentry. This willalso suit the increasing demand for new featureswithin a fixed space envelope. Biometics is the studythat sees how man-made systems can emulate Na-ture. In the key field of sensors and actuators perhapsman can learn from the sensing capabilities of certainbird species, for magnetism and light polarization,and electric eels and rattlesnakes for electricity andheat, he suggests. Exhaustive historical analysis ofpatents has shown that systems tend to evolve frommechanical through chemical and electro-mechani-cal to electro-magnetic (optical), and vehicle sensordevelopment is said to reflect this. Because elec-tronic systems also have the capability for integra-tion, sensors can be shared between vehicle func-tions, as seen in Fig 1. Because, however, mechanicalsystems are often cheaper and difficult to replace,institutionally and technically, the compromise dis-cipline of mechatronics is seen by the author as set forgrowth.

A way of providing an on-board control systemwithout the addition of hardware is described byresearchers at NGK Spark Plug2 who show how ionformation around the spark-plug can be used as anengine control technique. While the ion densityrepresents the condition status of combustion, analy-

sis of the condition is made possible by measuringvoltage/current between plug-gap and ignition due tothe magnitude of ion formation. In so doing the needis removed for sensors of EGR or knock and a plug-gasket type pressure sensor.

While it is expensive to provide an ion detectorfor each cylinder, here the authors propose a tech-nique in which the spark plug electrodes are used fordetection. But to avoid damage being caused by hightension voltages a point on the ion response curve,Fig 2, must be used after high-tension discharge.However, some increase in circuit complexity isinvolved, Fig 3. To measure ion density a coil is usedto generate several 100 V pulses consecutively withthe spark ignitions, the electrical circuitry providing

Heightsensors

Lateralacceleration

Longitudinalacceleration

Verticalacceleration

Yawsensor

Vehiclespeed

-

-

SuspensionECU

steer ECU

L

EngineECU

ECU

Heightcontrol

Steeringsensor

Stop lampswitch

Shiftposition

Fig 1: Systems integration effect on sensors

Fig 2: Ion current response

ELECTRICAL/ELECTRONIC SYSTEMS 71

the means to measure voltage decay with time, whichis proportional to ion density, Fig 4. The ECU analy-ses combustion by examining the pressure-wavepattern (magnitude and pulse-width) using ion-den-sity and decay-period data. Input ignition signals,firing pulses, misfiring signals and the decay curve(and periods) are seen in the lower part of Fig 3.Amount of fuel injected is controlled so as to reducethe difference between fluctuation rate of the decayperiod and its standard fluctuation rate. Knock canalso be detected because ignition and ion densitywaves are synchronized during detonation. But thedecay period measurement technique alone cannotbe used. The ion density voltage pulsation must bemeasured continuously. A capacitor is used to accu-mulate current generated by ion density voltagepulsation, and current flowing through an associatedresistor in series with it, in order to sense the onset ofknock.

Smart materialsfor suspension controlConventional mechanical suspension systems arepotentially convertible to active control with the useof electronically monitored smart materials, in theopinion of researchers3 at TRW Inc. Effective controlof the motions of sprung and unsprung masses of aspring-suspended vehicle can only be achieved byinterconnecting hardware responding and adaptingto changing disturbances. Optimum performance isobtained, it is argued, when system energy can bedecreased and increased as necessary. Achievingvariable spring rate with conventional active suspen-sion systems requires high amounts of energy, withserious drain on the vehicle's capability.

By using smart materials, controllable by anexternal energy field, performance can be made tochange in a predictable and repeatable manner. Amongthe smart solids, piezo-electrics exhibit a control-lable energy transformation between electrical and

08

0.2

0

-

•

30

5

Fig 3: Secondary voltage ionised current method Fig 4: Determining flame resistance around plug gap

72 VEHICLE DESIGN

mechanical modes, hence their use in noise andvibration control, the authors explain. Smart liquidsinclude those of Nature such as elastically deform-able red blood cells suspended in plasma which maybe reshaped with reduced diameters for easier flowthrough small blood vessels.

In suspension applications, rheological fluidsare attractive and their behaviour is represented in asimple way by Fig 5: constituent particles which arerandomly distributed in a zero-energy field, becomealigned with the field under excitation. Considerablechanges in shear force between the plates occursduring excitation by the field, hence viscosity iscontrollable. Both electro- and magneto-field ex-cited types have been studied for many years.

So-called electro-rheological magnetic (ERM)fluids can develop very high levels, above 50 psi, offluid shear stress while operating on vehicle batteryvoltage levels or moderate currents. This fluid alsohas the ability to set up shear forces independent ofvelocity, so no fluid flow is required. With such afluid, a variable suspension damping characteristic ispossible while reverting from current, space-wastingtypes to the more compact rotary configurations ofearlier years. A typical parallel lower control armsuspension is shown in Fig 6. The electronic controlallows an algorithm to process information for thecontrol of the ERM fluid shear forces, hence thetorque which the RACD can generate. Its cross-section in Fig 7 shows that energy is absorbed purelyin shear mode between sprung and unsprung masses.

In controlling the fluid, the output signal fromthe ECU is transformed from an analogue voltageinto a frequency, in the V/F converter, and used in apulse-width-modulated power driver causing a cur-rent level to flow to a set of electro-magnets. Fig 8shows a schematic of the ECU, the left side depicting

Fig 5: Particle orientation in rheological fluid

Fig 6: Parallel lower arm configuration

Fig 8: Electronic control unit


the inputs from the sensors which are converted forprocessing by the DSP and then reconverted to ana-logue for transformation to the appropriate pulse-width-modified signal. The ECU can tune the vehi-cle through software without any hardware change.This could involve mere days of work compared withthe months currently involved in tuning the dampersfor a new vehicle platform.

ROTARY POSITIONSENSOR

HOUSING

- BLADE

SEAL

HOUSI NIG

SHAFT

F L U I D CHAMBER

ELECTROMAGNETASSEMBLY

Fig 7: Cross section ofRACD damper unit

The multi-degree of freedom matrix equationto control the dampers according to both vehicle androad dynamics is represented by the algorithm of Fig9. For the future, more complex algorithms andintegrated electronics are forecast by the authors.Microprocessor instructions could be executed at therate of millions per second, transforms between timeand frequency domains becoming possible and hencemore complex control strategies permitted.

Electronic controlof electric steeringFollowing Honda's successful pioneering of electricsteering on the NSX car, company engineers4 havereported a new-generation system for future applica-tion of intelligent steering, Fig 10. Its lighter andmore compact construction allows its substitution forhydraulic PAS on a wide range of light vehicles.

The torque sensor, Fig 11, on the steeringcolumn relates steering input torque from the driver

Fig 9: ERM/RACD control algorithm

74 VEHICLE DESIGN

with axial displacement and senses change of induct-ance in its field coil. The steering servo motor drivingthe rack has current feedback control and as well asthe input from the column torque sensor also has avehicle input related to instantaneous road speed; aPWM drive with power MOSFET is involved.

The seamless design of the torque sensor, inte-grated into input shaft, allows driver input and roadkick-back to be evaluated. On the input shaft, steer-ing wheel turning speed is derived from differentialvalue of the torque as well as the direct value. On theoutput shaft, motor assist-torque data, and the reac-tion torque from the road, is obtained as a micro-vibration trace. Information on the inertia of the rotoris also obtained from the output shaft and the detri-mental increment of inertia is cancelled out electri-cally to prevent its transmission to the steering wheel.

In the ECU for the new generation system, themicroprocessor performance has been raised from 8bit 12 MHz to 16 bit 16 Mhz. ASICs are nowemployed to customize the input and output circuits,

with a resultant 35% reduction in part-count. Be-cause the steering motor requires some 10 amperesfor control, MOSFET switching and metal stripconductors are exploited with specially developedconnectors. Motor and control-unit are now adjacentto one another so as to minimize cable losses.

Input shaft Torsion barInformation from input shaft side• Input steering torque• Rotating speed at start of steering handle

Fig 11: Torque sensor Torques sensed by torque sensorDr

iving c

ircuit

Fig 10: Honda intelligent steering system


Drivetrain controlThe farther future in mechatronics is seen by re-searchers at Vairex Corporation5 as the electricdrivetrain. Full drive-by-wire will eliminate me-chanical connections and replace them by electri-cally powered components and electronic controls,with the eventual reality of each wheel being capableof instantaneously, accurately and independently

absorbing or developing torque between tyre androad with positive or negative value on any surface —with a dramatic improvement in traction, braking andhandling performance. A particular advantage wouldbe the introduction of electro-magnetic braking of atype that is more efficient than regenerative systemsbeing pioneered on electric and hybrid propulsionvehicles. With regen braking, maximum braking

Conventional Drivetrain Electric Drivetrain

Fig 12:Conventional(left) andelectric(right)drivetrainscompared

2)

3)

1)150kw IC Engine

Automatic Transmission

Logic Module

4) Transfer Case

5) Driveshafts

6) Differentials

7) CV Joints

8) Disc Brake Assemblies

9) ABS/SC Hydraulic Module

10) Brake Hydraulic Pump/Accumulator

1 1 ) Power Steering Rack

13) 40 L Fuel Tank

B) 75 kW Alternator

C) Power Module

D) Logic Module

E) 35 to 50 kW Wheel Motors

F) Steering Rack

G) 20 L Fuel Tank

H) Battery/Ccpacitor Module

76 VEHICLE DESIGN

force is limited by the rate at which the energy storagesystem can absorb and dispense power; without theuse of ultracapacitors, therefore, only supplementarybraking is possible electro-magnetically. Also brak-ing effectiveness is reduced to the degree that to thedegree that zero braking force is reached slightlybefore the vehicle reaches zero speed. If reversepower rather than a load is applied to the generator,braking force down to zero speed can be generatedand held there. The braking requirements of anaverage saloon car, say the authors, would requirewheel motors, on each of the four wheels, withindividual capacity of 35-50 kW. Fig 12 shows theauthor's electric drivetrain proposal alongside a con-ventional drivetrain. This would suit a 1750 kgvehicle, having all-wheel-drive, electronic torquesplit, traction control, automatic transmission, ABSbraking and stability control. For safety, a conven-tional friction park-brake would probably be re-quired.

Navigation system advancesThe 1998 SAE Congress in Detroit was the occasionfor the reporting of important telematics develop-ments bringing closer the prospects of intelligenttransportation systems on public highways.

Researchers from Hitachi6 described an adap-tive cruise control (ACC) system using a wheeltorque management technique and involving a longi-

tudinal control method. An electronically controlledthrottle valve, electrically controlled brake and auto-matic transmission work co-operatively to providesmoother acceleration, better shift performance andbetter fuel economy in ACC mode (at a desiredheadway distance detected by a micro-wave radarsensor), while, in manual driving, wheel torque isproportional to throttle pedal displacement.

The management system seen in the lower partof Fig 13 selects signals from throttle-control, trans-mission and brake to send commands which dependupon the requested wheel torque. Conventional cruisecontrol is obtained by adding a speed controller to thewheel torque manager, and on top of this, headwaycontrol computes a command speed and sends it tothe speed controller which calculates the requiredwheel torque. Block diagrams for the speed andheadway controllers are shown in Fig 14.

Fig 13: Constituents of ACC

20Fig 14: Speed controller (top) Time [sec]and headway controller Fig 15: Experimental results of ACC


Tests carried out with the system installed in avehicle showed the ACC performance as in Fig 15.From ACC start-up at t = 0, the preceding vehicleincreases its speed v at time t1 then decreases itsspeed at time t3 by braking and at time t4 its speed iskept constant. The wheel torque shows its peak at thebeginning of acceleration and keeps it a constant asspeed increases; in the deceleration phase, at about-2.5 m/s2, the torque becomes negative under electri-cal braking.

Headway sensor designThe development of a suitable radar sensor for ACChas been described by engineers at Bosch7 which isdue for European introduction in the current modelyear in its initial form as a high-cost option on top-of-the-range vehicles. For more general application aless expensive version is under development, the firststage of which is an integrated sensor and control unitdescribed in the paper. This would be incorporated ina typical ACC system depicted in Fig 16.

The main functional advantage of integrationis improved communication between sensor andcontroller and that not only the prime target preced-ing vehicle is considered but up to 8 objects in thepath of the vehicle (valuable when a vehicle ahead ofthe preceding vehicle brakes suddenly). Basic speci-fication of the sensor is as follows:

RangeRelative speedAngleResolution cellMeasurement rate

2-120m-60m/s ... +60m/s

...+/-5°0.6m, 1.7m/s

10 Hz

Freeways and inter-state highways with a mini-mum curve radius of about 500 m require a lateraldetection angle as shown. A monostatic three beamfrequency modulation continuous wave (FMCW)-type radar is employed, working at 76-77 GHz, allthree beams sending and receiving simultaneously.Characteristic data for the radar are:

Frequency allocationTotal average output powerBandwidthNumber of beamsBeam width (measured at the-6dB point of the radar-diagram)Overlap of two beams(,,Squint Angle")Total angular range

76 - 77.0 GHz1mW

220 MHz3

4°

2°

+/-5°

A block diagram for the integrated system isseen in Fig 17.

Road guidance for drowsy driversTo provide vehicles with a guidance means based onwhite road-line recognition, a system based on laneregion extraction and line edge detection has beendescribed by Matsushita engineers. The proposedmethod uses both low and high spatial frequencyimage data, respectively, to detect these two at-tributes of the white lines. The company has shownthat detection from 5 to 40 metres in front of thevehicle is accurately performed at a detection rate ofover 99.4%. As well as protecting drivers who be-come drowsy the system also is used to distinguish

Fig 16: ACC systemcomponents

78 VEHICLE DESIGN

present lane from adjacent lanes in automatic cruisecontrol. The two separate modes of image detectiondescribed above are intended to overcome the prob-lems of intermittent white line fading and the prob-lem of the detection camera vibrating in sympathywith the vehicle. Fig 18 distinguishes between thetwo modes. Lane region extraction uses a knowl-edge-based brightness rule to distinguish the insidelane area and/or a low spatial frequency image inorder to smooth the brightness of the lane region. Thesystem checks there is a smooth transition betweenthe dark area in front of the vehicle and the bright areafurther away. Edge data are determined using eachthreshold in each scan direction between 50 lines and200 lines, the following contour points being re-moved: those which are more than 20 dots away fromthe end-of-lane region (extracted from the low-fre-quency image); all non-continuous points and thosewhich do not fit within the road width. Resultant

white lines are calculated using a spline of 3 degrees,the detection process illustrated being implementedon a network of transputers. Camera-angle errorcompensation is based on distance between the linesbeing constant, contour points of lines in the imagebeing transferred to points on the world co-ordinatemapped image seen in Fig 19.

Detected white lines

Parallel white lines

Lateral distance

Fig 19: Mapped image

Fig 17: Block diagram ofACC-SCU

Fig 18:White lines detection process


Digital circuits for computationLogic gates (switching circuits) are known as build-ing blocks for electronic circuits used in computercontrol. A recent work8 on engineering mathematicsprovides an unusually accessible description of thebuilding of such circuits, in the author's chapters onBoolean Algebra and Digital Systems.

The Boolean variable, he explains, involvesthe realization of the two logical states, 0 and 1,analogous to the open and closed positions of amechanical switch but in digital electronics repre-sented by low and high voltages in 'positive' logic.The logic gates, Fig 20, provide Boolean functionsanalogous to multiplication, division, inversion andtheir different combinations.

Further combination of the basic gates may beused to form functional logic circuits such as that inFig 2la which might be used for a vehicle warningbuzzer so that it sounds when the key is in the ignition(A) and a door open (B) or when the headlamps areon (C) and a door open (A). Here there are two ANDgates and an OR gate. The first two give the outputA.B + C. A which is the input to the OR gate which hasoutput A.(B + C).

Fig 21b: 7408 and 7402 integrated circuits

Fig 21a: Warning buzzer circuit

Fig 20: Logic circuits, a. AND; b. OR; c. NOT; d. XOR; e. NAND; f. NOR

80 VEHICLE DESIGN

In multiple combinations they come as rela-tively inexpensive integrated circuits, Fig 21b illus-trating the 7408 and 7402 circuits. The first has fourtwo-input AND gates supplied as a 14 pin package,with power supply connected to pins 7 and 14,supplying the operating voltage for all the four ANDgates. A notch is cut between 1 and 14 to show atwhich end of the package pin 1 starts. In the 7402package there are four two-input NOR gates. The useof 7408 as a clock enable circuit is shown in the viewin Fig 21c, where signals are passed on to a receivingdevice only when a switch is set to an enable position.The clock emits a sequence of 0 and 1 signals(pulses), Fig 22. The AND gate will give an outputwhen both input signals are 1.

Computer control usually involves implemen-tation of arithmetic operations for which the binarynumbering system is used having binary digits (bits)0 and 1. Fig 23a shows a half-adder circuit giving thesum equal to 1 when either first or second inputnumbers, but not both numbers, is 1, obtained with anXOR gate. The carry-out bit is to be 1 when first andsecond numbers are both 1, obtained with an AND

gate. A full adder circuit is seen in Fig 23b; the sumoutput arriving from the three inputs, first, secondand carry-in number. This provides a 1 output whenthere is an odd number of 1 inputs, obtained by twoXOR gates. The carry-out output is 1 when any twoof the inputs are 1, obtained with three AND gates andan OR gate.

The half and full adder circuits can be com-bined to realize multi-bit adder circuits. Thus, for a 4-bit adder, Fig 24 is an appropriate circuit, in which thefull and half adders are represented as blocks forsimplicity. By connecting the carry-out from one 4-bit adder to the carry-in for another one, an 8-bitadder circuit can be obtained (used for adding posi-tive numbers together), Bolton explains.

Second number

Fig 21c: Clock enable circuit using 7406 1C Fig 23a: Half-adder

Fig 23b: Full adder Fig 24: 4-bit adder


Fig 25: Personal Productivity info-technologies

Fig 26: TEC mobility system

Proprietary control

system advancesThe Delphi Personal Productivity vehicle is a com-bination of information technologies, Fig 25, for per-mitting business drivers to remain in constant com-munication with their offices. First demonstrated ina Saab car it has involved co-operation between thesuppliers and Microsoft/Mecel. By means of Win-dows CE, installed in an on-board computer, the sys-tem links with office-based Windows PCs. A speechinterface called Auto PC allows hands-free commu-nication for the driver with voice commands beingused to send E-mail messages, for example. The fa-cility also uses speech synthesis to convert incomingmessages for the driver. There is, too, the option ofusing steering-wheel mounted controls instead ofaudio communication. The Delco Mobile Media Linkemployed is a high-speed fibre-optic serial data linkcapable of transmitting data at 98 MB/sec. It alsohas sufficient band width to allow reception of up to50 channels of stereo audio and 15 channels of TV-quality compressed video. A cellular modem connec-tion allows information like traffic updates to be in-put from an internet provider.

Following the introduction of the Magneti-Marelli Route Planner in-car navigation system, thenext generation TEC mobility system under develop-ment, Fig 26, will allow the driver to access Pentiumcomputer power through ConnectCar-PC via a voice

Fig27:MotronicMED 7enginemanagementsystem

82 VEHICLE DESIGN

recognition interface. As well as helping the driver tonavigate, he/she will be able to place and receivetelephone calls and even browse the internet or sendan E-mail.

The Bosch Motronic MED 7 engine manage-ment system, Fig 27, is designed for direct-injectiongasoline engines and calls on a wide variety of sensorinputs before computing engine torque response tothrottle-pedal displacement. Some 15-20% fuel sav-ings are claimed for DI engines using the systemcompared with conventional state-of-the-art gaso-line engines.

Delphi's E-STEER electronic steering incor-porates a steering gear assist mechanism, Fig 28, andelectronic controller to provide responsive steeringassist, in several configurations, Fig 29. Sensorsmeasure two primary inputs—vehicle speed anddriver torque (or effort) on the steering shaft at theassist unit. These two primary inputs, along withother system variables and inputs, are continuouslyfed into an electronic control module, which analysesthe data and determines the direction and the amountof steering assist required. The controller then gen-erates a command to the variable-speed, 12-voltelectric motor. Using intricate control algorithms,the controller's command varies the torque of theelectric motor, which drives a gear mechanism toprovide the required assist. A permanent magnetbrushless motor is used, which allows the smallestpackage size, the smallest mass, and the lowest rotorinertia (for more responsiveness). The motor is alsoquieter, more reliable, and more powerful than manytypes of electric motors; it uses the vehicle's battery

as its power source. This can be especially importantto drivers who experience an engine stall whileturning a sharp corner or rounding a steep mountaincurve.

Traditional hydraulic systems can be sluggishuntil fluids warm up, especially in very cold climates.The Delphi system provides cold-weather rapid start.With its engine independence and fluid-free design,the system is less sensitive to cold temperatures even

Fig 28: Assist mechanism

Fig 29: Different configurations

Fig 30a: Vehicle fuel consumption rating — comparison between manual steering and E-Steer;


at -40C The system also eliminates the large energyloss typically involved in those first few minutes ofwarm-up. When a major European manufacturerconducted a fuel economy test, it found virtually nodifference in fuel usage between this EPS and manualsteering, Fig 30a.

This EPS is an 'on-demand' system, runningin a monitoring mode until assist is needed. Typicallyusing less than 0.5 amp at idle and with the averageusage between 1 to 2 amp, the system has extremelylow parasitic energy losses for maximum efficiency.In addition to reducing engine drain, the system mayalso reduce overall mass. The system also providesimproved stability for greater passenger comfort,control, and safety. There is smoother transition fromone effort level to another—without compromisingpower steering assist between parking manoeuvresand highway driving .

System design with more options Speed-sensi-tive variable effort steering is an increasingly popularoption, but the need for a controller makes it a costlyaddition to conventional hydraulic systems. Delphi'sE-Steer can calculate the required assist level, basedon vehicle speed and driver torque input, using itsexisting software and controller, Fig 30b. This makesspeed-sensitive variable effort steering (and otheroptions) available for very little added cost.

A further benefit of electric power steering isthat assist can be provided in both directions, so it isno longer necessary to compromise suspension de-sign in order to achieve the required returnabilitycharacteristics. The system's optional Assisted Re-turn feature allows the returnability to be optimizedindependently, so that when the driver turns and thenreleases the wheel, E-Steer returns it safely to centre.The company has also developed a unique Steer

Damping option that helps to provide a smoother feeland reduce the effects of issues such as free control.A conventional hydraulic steering system wouldrequire time-consuming and expensive mechanicalmodifications, but with E-Steer this can be achievedwith software.

Fast system tuning The operating characteris-tics of any steering assist system must be carefullytuned to match the vehicle design objectives. Withconventional hydraulic systems, tuning requires theremoval of the steering gear and the manufacture andfitment of modified valves and torsion bars. Thisprocess limits testing to two or three configurationsper day, with the whole process typically taking fromone to six months. E-Steer allows very fast tuningwithout mechanical intervention, allowing the de-sired feel and performance to be achieved in a smallfraction of the time previously required. All that isrequired is a laptop computer with Delphi's propri-etary tuning package.

Reliability In addition to engine independ-ence, there are specific reliability features built intothe system. During development, company engi-neers set up testing situations to simulate possiblefaults in the system. With this knowledge, they builtin several reliability features. The system continu-ously runs detailed self-checks and diagnostics, en-suring that all areas of the system are functioningproperly. Redundancy (back-up or 'repeat' systemelements) has been engineered into the system toprovide reliability.

Packaging flexibility With no pumps, hoses, orbelts on the engine, this simplified packaging pro-vides maximum design and engineering flexibility.The system controller can be incorporated with thecolumn, the rack, the pinion, or in a stand-alone

Fig 30b: Performance parameters: left: steer damping; centre: tuning capability; right: variable effort

84 VEHICLE DESIGN

location. The controller can be in the engine or thepassenger compartment. The system frees up the partof the engine where a belt and pulley to drive thepump would otherwise be placed. This makes roomfor other features like pollution control or an air-conditioning compressor. And there are no morehoses snaking through the engine compartment. Thesystem can help reduce the number of parts the carmanufacturer has to track, order, and store. Forexample, two models in the same platform, a 4-doorsedan and a 2-door coupe, can use the same physicalsteering system. With the advanced tuning technol-ogy of the system, one could custom tune a luxuryfeel for the sedan and a sporty feel for the coupeinstantly.

For the future Delphi Steering anticipates thedevelopment of several options for future electricpower steering systems. Potential combinations in-clude selectable steering to go with a selectablechassis where the driver could push a button for asportier feel, for example. Hand-held diagnostic toolscould be used at the dealership, allowing consumersto request changes to the feel of their steering. As acost-reduction strategy, the system could be veryuseful in advanced systems integration. With up-level integration, algorithms/software for other sys-tems could be combined—like security, collisionavoidance, steer by wire, or automated highwaysystems.

Hybrid drive prospectsA neat description of the problems of hybrid drivevehicles has come out of the results of the three-yearHYZEM research programme undertaken by Euro-pean manufacturers. According to Rover partici-pants9, controlled comparisons of different hybriddrive configurations, using verified simulation tools,are able to highlight the profitable fields of develop-ment needed to arrive at a fully competitive hybriddrive vehicle and demonstrate, in quantitative terms,

c

3.

\6

432

V

Fig 31: Characterizing a hybrid powertrain

Fig 32: Use of vehicle per dayFig 34: Synthetic urban drive cycle

Fig 33: Daily distancesand trip lengths


the trade-off between emissions, electrical energyand fuel consumption. Only two standard test pointsare required to describe the almost linear relation-ship: fuel consumption at point of no overall changein battery state-of-charge (SOC) and point of electri-cal consumption over the same cycle in pure electricmode. A linear characteristic representing an ideal

Fig 35: BMW parallel hybrid drive

lossless battery can also be added to the graph, toshow the potential for battery development, Fig 31.

Confirmation was also given to such empiricalassessments that parallel hybrids give particularlygood fuel economy because of the inherent effi-ciency of transferring energy direct to the wheels asagainst the series hybrids' relatively inefficient en-ergy conversion from mechanical to electrical drive.The need for a battery which can cope with muchmore frequent charge-discharge cycles than one for apure electric-drive vehicle was also confirmed. Al-though electric energy capability requirement is lessstringent, a need to reduce weight is paramount inovercoming the problem of the redundant drive inhybrid designs.

A useful analyis of over 10,000 car journeysthroughout Europe was undertaken for a better un-derstanding of 'mission profile' for the driving cyclesinvolved. Cars were found to be used typically be-tween 1 and 8 times per day, Fig 32, and total dailydistances travelled were mostly less than 55 km.Some 13% of trips, Fig 3, were less than 500 metres,showing that we are in danger of becoming likeAmericans who drive even to visit their next doorneighbours! Even more useful velocity and accelera-tion profiles were obtained, by data recoding at 1 Hzfrequency, so that valuable synthetic drive cycleswere obtained such as the urban driving one shownin Fig 34.

Combustion engine1.8-ltr. 4-cylElectric motor/alternator

Transmission ratios

Final driveNi/MH battery

Ni/Cd battery

Weight, unladen kg (Ib)Performance weightkg (Ib)

518i Hybrid162 Nm (119 Ib-ft).83kW(113 bhp)Siemens asynchronous200V. max 280A, 95 Nm(70 Ib-ft)(l65Nm/122 Ib-ft max).18 kW (26 kW max)5.09/2.8/1,76/1 24/1.0

3.25DAUG-HoppeckeCell type: X40. 180 1 2Vcells,'40Ah/1.06kg, totalenergy content 9 kWh.maintenance-freeDimensions: 803/465/418 mm3DAUG-Hoppecke. celltype:X35, 1681.2Vcells/35Ah/1.15kgEnergy content 7 kWh,maintenance-freeDimensions: 859/400/4101940(4278)

2139(4716)

518i standard162 Nm (119 Ib-ft)83 kW (113 bhp)

5.1/2.77/1.72.'1.22/1.0

1418(3127)

1618(3568)

Fig 38: Ragone diagram for the two battery systems Fig 37: Vehicle specification

86 VEHICLE DESIGN

BMW researchers10 have shown the possibilityof challenging the fuel consumption levels of con-ventional cars with parallel hybrid levels, by usingmap-controlled drive management. The 2-shaft sys-tem used by the company, Fig 35, uses a rod-shapedasynchronous motor, by Siemens, fitted parallel tothe crankshaft beneath the intake manifold of the 4-cylinder engine, driving the tooth-belt drive systemas seen in Fig 36; overall specification comparedwith the 518i production car from which it is derivedis shown in Fig 37. The vehicle still has top speed of180 kph (100 kph in electric mode) and a range of 500km; relative performance of the battery options isshown by Fig 38. Electric servo pumps for steeringand braking systems are specified for the hybridvehicle and a cooling system for the electric motor isincorporated. The motor is energized by the batteryvia a 13.8 V/ 50 A DC/DC converter. The keyelectronic control unit links with the main systems ofthe vehicle as seen in Fig 39.

To implement the driving modes of eitherhybrid, electric or 1C engine the operating stategy isbroken down into tasks processed parallel to oneanother by the CPU, to control and monitor engine,motor, battery and electric clutch. The mode taskdetermines which traction condition is appropriate,balancing the inputs from the power sources; theperformance/output task controls power flow withinthe total system; the battery task controls batterycharging. According to accelerator/braking pedal

Digital MotorElectronics

Fig 39: Vehicle management

Generator rpin

Carrier

The three vertical lines in the diagram show theshaft in the planetary

Fig 41: Power interaction diagram

Fig 40:Optimizedre-chargestrategy


inputs, the monitoring unit transfers the power targetrequired by the driver to the CPU where optimaloperating point for both drive units is calculated in acontinuous, iterative process. Fig 40 gives an exam-ple of three iterations for charge efficiency, alsodetermined by the CPU, based on current chargelevel of the battery.

Production control-systemIn the Toyota Prius production hybrid-drive car,described in a separate article in this issue, for thepower-split device which is a key part of the system,company engineers" have provided the diagram ofFig 41 to show how the engine, generator and motoroperate under different conditions. At A level withvehicle at rest, engine, generator and motor are alsoat rest; on engine start-up the generator produces

Battery

Brake

3

Engine speed

*

7

Generatorcontrol

Motorcontrol

electricity acting as a starter to start the engine as wellas operating the motor causing the vehicle to moveoff as at B. For normal driving the engine suppliesenough power and there is no need for generation ofelectricity, C. As the vehicle accelerates from thecruise condition, generator output increases and themotor sends extra power to the drive shaft for assist-ing acceleration, D. The system can change enginespeed by controlling generator speed; some of theengine output goes to the motor via the generator asextra acceleration power and there is no need for aconventional transmission.

The control system schematic for the vehicle isin Fig 42, the THS (Toyota Hybrid System) calcu-lates desired and existing operating conditions andcontrols the vehicle systems accordingly, in realtime. The ECU keeps the engine operating in apredetermined high torque to maximize fuel economy.The corresponding schematic for the ECU is in Fig43. It is made up of 5 separate ECUs for the majorvehicle systems. The hybrid ECU controls overalldrive force by calculating engine output, motor torqueand generator drive torque, based on accelerator andshift position. Request values sent out are received byother ECUs; the motor one controls the generatorinverters to output a 3-phase DC current for desiredtorque; the engine ECU controls the electronicthrottle in accordance with requested output; thebraking ECU co-ordinates braking effort of motor-regeneration and mechanical brakes; the battery ECUcontrols charge rate.

Fig 42: THS control system

Fig 44: EDLC model (a), above, and cell (b), below

VEHICLE DESIGN

Energy storage initiativesAccording to researchers at NEC Corp12, the super-capacitor will be an important contributor to theenergy efficient hybrid vehicle, the absence of chemi-cal reaction allowing a durable means of obtaininghigh energy charge/discharge cycles. Tests haveshown for multi-stop vehicle operations a 25-30%fuel saving was obtained in a compact hybrid vehiclefitted with regenerative braking.

While energy density of existing, non-automo-tive, supercapacitors is only about 10% of that oflead-acid batteries, the authors explain, it is stillpossible to compensate for some of the weak pointsof conventional batteries. For effective power assistin hybrids, supercapacitors need working voltage ofover 100 V, alongside low equivalent series resist-ance and high energy density. The authors haveproduced 120V units operating at 24 kW fabricatedfrom newly developed activated carbon/carbon com-posites. Electric double layer capacitors (EDLCs)depend on the layering between electrode surfaceand electrolyte, Fig 44(a) shows an EDLC model.Because energy is stored in physical adsorption/desorption of ions, without chemical reaction, goodlife is obtained. The active carbon electrodes usuallyhave specific surface area over 1000 m2/g and dou-ble-layer capacitance is some 20-30 uF/cm2 (acti-vated carbon has capacitance over 200-300 F/g). TheEDLC has two double-layers in series, so it is possi-ble to obtain 50-70F using a gram of activatedcarbon. Working voltage is about 1.2V and storableenergy is thus 50 J/g or 14 Wh/kg.

Fig 44(b) shows a cell cross-section, the con-ductive rubber having 0.2 S/cm conductivity andthickness of 20 microns. The sulphuric acid electro-lyte has conductivity of 0.7 S/cm. Fig 45(a) shows the

Fig 45: High-power EDLC schematic (above)andspecification (below)

0.1 1.0 10 100 1000

Energy density / Wh-kg-1

Fig 46b: Power density, y-axis in W/kg, vs energydensity for high-power EDLC

Fig 46a: Constant power discharge characteristics Fig 47: ELCAPA configuration


high-power EDLC suitable for a hybrid vehicle andthe table in Fig 45(b), its specification. Plate size is68 X 48X1 mm3 and the weight 2.5 g, a pair having300 F capacity. Fig 46(a) shows constant powerdischarge characteristics and Fig 46(b) compares theEDLC's energy density with that of other batteries.

Fuji Industries's ELCAPA hybrid vehicle, Fig47, uses two EDLCs (of 40 F total capacity) inparallel with lead-acid batteries. The stored energycan accelerate the vehicle to 50 kph in a few secondsand energy is recharged during regenerative braking.When high energy batteries are used alongside thesupercapacitors, the authors predict that full com-petitive road performance will be obtainable.

A high energy battery receiving considerableattention is the lithium ion cell unit, the developmentof which has been described by Nissan and Sonyengineers13 who point out that because of the high cellvoltage, relatively few cells are required and betterbattery management is thus obtained. Accurate de-tection of battery state-of-charge is possible based onvoltage measurement. In the battery system devel-oped, Fig 48, cell controllers and a battery controllerwork together to calculate battery power, and re-maining capacity, and convey the results to thevehicle control unit. Charging current bypass circuitsare also controlled on a cell to cell basis. Maximizinglifetime performance of an EV battery is seen by theauthors to be as important as energy density level.Each module of the battery system has a thermistor todetect temperature and signal the controllers to acti-vate cooling fans as necessary.

Nissan are reported to be launching the UltraEV in 1999 with lithium-ion batteries; the car is said

to return a 120 mile range per charge. For the fartherfuture lithium-polymer batteries are reported to becapable of giving 300 mile ranges.

There is also less strength in the argumentsagainst EVs with news of cheaper solar cells. Rapidthermal processing (RTP) techniques are said to behalving the time normally taken to produce siliconsolar cells, while retaining an 18% energy conversionefficiency from sunlight. Researchers at GeorgiaInstitute of Technology have demonstrated RTPprocessing involving a 3 minute thermal diffusion, asagainst the current commercial process taking threehours. An EC study has also shown that mass-produc-tion of solar cells could bring substantial benefits andthat a £350 million plant investment could produceenough panels to produce 500 MW annually and cutthe generating cost from 64p/kWh to 13p.

A move towards fuel cells for electrical powergeneration is also gaining ground. Ballard Genera-tion Systems has announced the start-up of a PEMfuel cell, natural gas fuelled, with 250 kW capacityand using Johnson Matthey electrodes and platinumcatalysts. Compared with on-board fuel cells, thelarger stationary generating ones can better exploitthe high operating efficiency in relation to the rela-tively high capital cost. The US Dept of Energyargues that over one year 1MW of electricity gener-ated by fuel cells will avoid 45 tonnes of sulphurdioxide and 19 tonnes of nitric oxides being emitted.

Ballard are also in joint agreement with Daim-ler-Benz on in-vehicle fuel cells and an A-classMercedes-Benz, thus powered, is scheduled for around2004. Mass production to bring down the cost of fuelcells is the objective.

remaining capacitybattery power limit

Fig 48: Overall system configuration

signal line T: temp, sensorpower line V: voltage sensorK A: current sensor

90 VEHICLE DESIGN

Automation of handling testsRecent publicity surrounding deaths of road usersdue to accidents caused by OEM's road-test drivers,and the need to reproduce laboratory conditions ofrepeatability into track testing, will hasten the ac-ceptance of the ABD steering robot, announced byAnthony Best Dynamics. Essentially the device com-prises a motorized assembly (which replaces thesteering wheel) whose stator is linked to a pair of loadcells measuring torque reaction; these are, in turn,coupled to an adjustable arm clamped on to a pillarmember between the vehicle floor and suction capson the windscreen.

The computer-controlled steering robot pro-vides steering inputs to vehicles during track testing.Historically, this type of testing has been carried outmanually, but it has been difficult to ensure thataccurate and repeatable inputs are generated. Thesystem developed by ABD overcomes these prob-lems, making it easy to obtain meaningful compari-sons between different vehicles and vehicle configu-rations. The robot, whichcan be used in cars, vans andHGVs, is capable of performing the range of testsdescribed in the international standard ISO7401 aswell as many special tests, and has a specificationborn out of detailed discussions with a number ofpotential customers who all had considerable experi-ence in this type of testing. The computer and controltechnology employed is a spin off from ABD'ssuccessful Suspension Parameter Measurement Ma-chine (SPMM) installed in both the UK and the US.The SPMM is a cost-effective four wheel-stationmachine which can measure the suspension, kin-ematic and compliance characteristics of a widerange of vehicles. The new steering robot uses tech-nology transferred from the SPMM to apply steeringinputs to vehicles so that their transient responsecharacteristics can be studied, providing accurateand repeatable inputs even in low frequency sinusoi-dal tests.

General objectivesAt the heart of the robot is a direct drive DC torquemotor with incremental encoder feedback. This pro-vides the motive force in a small package which fitswithin the diameter of a standard car steering wheel.The steering robot therefore only requires a DCelectrical supply, which is normally taken from the

vehicle's own electrical system.The steering robot gives very precise, smooth

control of the steering without the need for gears orclutch, in a high performance package with mini-mum weight and inertia. The direct drive design alsoenables the driver to steer the vehicle easily when theunit is de-energized, as there is very little torquerequired to back-drive the motor. This enables theunit to be used to learn driver inputs, which can thenbe replayed by the motor, as well as providing a verysimple and inherently safe construction.

The stationary side of the motor is connected tothe vehicle body via a special universal torque reac-tion mechanism utilizing a built-in torque trans-ducer, which is installed in the passenger side of thevehicle between the windscreen and the floor, Fig 49.The system is designed to be installed easily, toprovide no access restrictions for the driver, to causeminimal loss of field of view and to be very rigid. Thetorque reaction system accommodates steering col-umn run out without generating side forces or degrad-ing the torque measurement. The motor assembly isnormally fitted to the steering column in place of thevehicle's standard steering wheel, as this provides avery compact installation with minimum inertia.However, an adaptor plate can be supplied to enableattachment to the rim of the standard steering wheelfor situations where it is difficult to reproduce thesplines on the steering column or where only a smallamount of installation time is available.

The steering robot is controlled by a portableindustrial PC running a Windows NT based softwarepackage. The software enables a database of vehiclesand tests to be built up with great flexibility in the testspecifications. A range of sinusoidal tests are pro-vided as standard; single period, continuous andswept sine, as well as step and pulse inputs. Alterna-tively, test profiles can be played out from pointsstored on a disk file which have been generatedelsewhere (special tests or random inputs for exam-ple) or learnt from driver inputs. During operation,tests are selected and initiated using a touch screen,which also provides status information as the testprogresses. Whilst the robot is operating the driverholds a joystick which gives him the ability to adjustthe steering drift of the vehicle and to attenuate theplayout amplitude. The robot is automatically de-energized if the joystick is released to enable thedriver to regain manual control of the steering.


Fig 49 : Steering robot installed

Fig 51: Computer test screen

The computer system also has the ability tocapture and store run-time data from the robot's owntransducers as well as up to twelve user-definedanalogue inputs and three encoder inputs. The systemalso provides digital outputs to trigger external datacapture, and analogue outputs of motor torque, angleand velocity.

The new test systems ABD has developed area response to an increased thrust in the industry toreduce time from concept to production of a newvehicle, with increased use of computer analysis andprediction techniques. Initial design parameters maybe based on experience but, increasingly, use is beingmade of measurements on previous models and oncompetitor 'target' vehicles. Steering and suspen-sions are refined with the aid of models for whichmeasured data is essential; also managers need toensure that development work is carried out only onvehicles that are known to be built to specification.All this can be achieved only by making the relevantmeasurements.

A particular specificationThe following specification describes a robotic ma-chine for applying low frequency inputs to a vehi-cle's steering system to enable repeatable measure-ments to be made whilst testing on a track. Fig 50shows a schematic diagram of the robot. On the rightof the figure is the servo-motor and angular positionencoder which mounts directly to the vehicle's steer-ing column. The torque reaction frame also functionsas a stand for a flat, touch-screen, display (notshown). This is the user interface for the computersystem, which is housed in a separate case locatedelsewhere in the vehicle (and not shown in thefigure). A second, stacking case houses the motoramplifier and signal conditioning for the torquemeasuring system. Manual steering of the vehicle isstill possible because the servo-motor is a direct-drive type and will back-drive easily when the poweris removed. The motor has a steering wheel mountedaround it to enable the vehicle to be driven normally.The motor is servo-controlled using position feed-back from an encoder. This task is undertaken by adedicated motion controller. The user interface, com-munication with the motion controller, and other nontime-critical functions are handled by a Pentium-based industrial computer.

A telescopic pole between the vehicle floor andwindscreen functions as the torque reaction frame forthe motor. The two sections of the pole form apneumatic actuator which is extended during fittingby using a low pressure air supply. Once firmly inposition, a cross bar may be adjusted to allow theforce links to be fitted to the drive unit at the correctangle. The two force links use charge devices tomeasure their axial loads. The steer torque is calcu-lated from these loads by the computer. The torquereaction frame also acts as a mount for a removablecontrol box which houses the colour, TFT, displaywith a touch screen. This provides the principalcontrol interface during testing on the track. Anothercontrol box, mounted to the driver's window withsuction pads, holds a two-axis joystick incorporatinga button for activating closed-loop control of themotor. The spring centred left-right plane of thejoystick adjusts the DC steering position, enablingthe driver to cancel any drift of the vehicle during atest, while the forwards-backwards plane adjusts theattenuation of the test amplitude. The forwards-backwards plane has a built in friction brake to

92 VEHICLE DESIGN

prevent accidental movement when altering the steer-ing position. A third control box on a flying leadcontains an emergency stop button, to cut all powerto the motor, and a button which can be used toinitiate tests (as an alternative to using the touchscreen). This box can be placed in any convenientposition within the driver's reach. The computersystem, motor amplifier and signal conditioning hard-ware are housed in two separate rugged cases. Theseare designed to stack one on top of the other and havestrong handles to enable them to be strapped securelywithin the vehicle. Interconnection cables betweenthe boxes are arranged on one side of the boxes andare protected by hinged covers. The connections tothe control devices, motor, transducers and powersupply are all on the opposite side. The connectorsare protected when not in use by removable lids. Thecontrol cases can be mounted at any convenientposition, typically a front or rear seat. The mainpower supply is provided via a large DC to DCconverter. This is typically located in the foot-well ofthe vehicle.

The steer angle, and torque, are measured andrecorded by the steering robot and output on +10Vanalogue (DAC) channels for sampling by otherequipment. In addition, velocity or acceleration canbe output on a third DAC channel. A further 12analogue input (ADC) channels and 3 encoder chan-nels are available for monitoring any other signalsduring a test. The scale factors (EU/V) and offsets forall these channels are adjustable to maximize thedynamic range. The software features a databasewhich records all the vehicles that have been tested,and catalogues the tests performed and the results.Fig 51 shows a typical screen for selecting the testvehicle. The results files contain the steer angle,velocity and acceleration, the torque values, and thespare analogue and encoder channels all sampled at100 Hz. The files are available in ASCII format witha header describing the test and each channel of data.A facility to copy files to a network, or other drive, isincluded to facilitate transferring the results to otherpost-processing software. A number of standard tests,

Fig 50: :reaction


or 'templates', are available to make setting up testsfor new vehicles easier. It is possible to add extratemplates if required.

During a test, the steer angle and test timeremaining are displayed digitally on the touch screenin large text. The steer torque is also displayed but inthe form of an analogue bar graph. In addition up tofour of the spare channels can also be displayed, onedigitally (primarily intended for a speed display ifavailable), and three as bar graphs (for lateral accel-eration). A target limit can also be set for each sparechannel. Reaching the target level during the testcauses the colour of the display to change to give aclear visual indication to the driver. The bar graphsalso have a peak hold facility to show the maximumlevels achieved in each direction during the test.

Performance modesThe software performs the following types of steer-ing test: in the continuous sine test, for a fixefrequency sine output, the user can select the fre-

quency, amplitude and test time. The playout isautomatically ramped at start and finish to helpmaintain a straight vehicle heading. In the sine sweeptest, the user can select the test time, start and finishfrequencies and a start and finish amplitude. A facil-ity to generate a sweep with constant peak velocity isalso available. In this mode the software calculatesthe instantaneous amplitude necessary to maintainthe peak velocity constant throughout the test. Thesweep is logarithmic in frequency. There is also asingle period sine test for lane change testing. Theamplitude, frequency and direction can be specified.Pulse tests, in addition, allow step or ramped inputsto be applied as a half cycle (move to an angle, dwell,move back to zero). The overall time, step angle andramp rate can be specified. In User data test mode thesoftware outputs data contained in a file. The soft-ware will check the file to make sure that the robot iscapable of generating the speed required. The datawill have previously been saved to the file by usingthe 'learn mode', or may be generated externally andimported from an ASCII file. The software also hasa learn mode to record steering movements input bya driver and save the results in a file. The file can thenbe played out as a test

94 VEHICLE DESIGN

Installation and operationA hole through the motor assembly makes attach-ment to the steering column easy, Fig 52. Installationof the torque reaction system is very simple andrequires no tools other than a low pressure air supply.The computer system can be installed at any suitableplace in the vehicle within 2 metres of the driver, andthe display and joystick are easily attached.

The database would normally be set-up for anew vehicle and any tests defined whilst the vehicleis in the running-shop. A normal PC keyboard (andmouse) would be used at this stage. Simple modifica-tions can be made to the test setups later while on theroad, by using the touch screen. Once at the test site,the driver would set the correct direction and veloc-ity, and would press and hold the joystick button toengage the motor. The robot will then be in control ofthe steering. Any drift of the vehicle may be can-celled by the driver by moving the joystick in the left-right plane. Pressing the touch screen button (orremote button) will start the first test in the sequence,and cause a digital output to change state to signal toexternal data capture systems. The playout will begin

after a preset delay (defined in the test setup). Asecond digital output will signal the start of theplayout. During the test, the joystick up-down planecontrols attenuation of the test amplitude. Releasingthe joystick button at any time will disengage themotor and allow manual steering. Pressing the touchscreen during a test will stop the test and reset thesteering to straight ahead. Tests may be modified andrepeated via the touch screen or by using the key-board.

During the test the display will show:1) The steering wheel angle (large text)2) Direction of first turn in the test3) Warning that the robot is not following the testprofile to a user-set tolerance4) Percentage test amplitude (100% clearly indi-cated)5) Test time remaining 6) Test and robot status7) Bar graph displays of ADC and encoder channels

The data from a series of tests would be savedto disk for post processing later, but results can beviewed graphically on the touch screen immediatelya test is complete.

Chapter 5:

Vehicle development

Among the recent vehicle introductions, four stand out asmarking a major innovative input to vehicle development.The Mercedes A-class is a significant advance in small carpackaging as well as breaking new ground in secondary safety.Ford's Focus brings the company's 21st century hard-edgestyling to its most mainstream model and also marks acompleted market repositioning of a class of vehicle startingas the Mark 1 Escort to a vehicle refined enough to competein the neo-luxury sector. The Land Rover Freelander bringsthe price of comfortable 4-wheel drive vehicles down torealistic levels and is a breakthrough in body option versatility.Project Thrust SSC presents the ultimate in competitionvehicles and gives a taste of the technologies required at thelimits of vehicle-to-ground adhesion.

96 VEHICLE DESIGN

Mercedes A-classThe world's pioneering motor manufacturer, andpossibly still the most prestigious, had a momentousyear in 1998, and seemed to emerge as the seniorpartner in Daimler-Chrysler. Its earlier attempts tobreak into compact car making have also now bornefruit in the re-launched moose-proof A-class, Fig 1,which has become possibly the class-leader in citycars. The revised suspension system is said to makethe A-class the safest car in its class. The modifiedrear suspension, Fig 2, now has the special tie rod,shown, incorporated and all models benefit fromESP, the company's Electronic StabilityProgramme.Chassis was also slightly lowered, anti-roll torqueincreased, rear track extended slightly, dampers/tyres replaced, suspension stiffened and greaterundersteer built into the handling dynamics.

Secondary safety systemsThe sandwich floor concept allows the engine anddrive assembly of the A-class to be shunted backunderneath the body in the event of a frontal impactrather than penetrating the passenger compartment.This ingenious layout, Fig 3, means that the newMercedes model virtually achieves the high safetystandard of the E-class. Even in the event of a sideimpact the 'sandwich' concept of the double layerfloor, Fig 4, provides clear advantages, because theoccupants sit about 20 centimetres higher than inother cars, with the result that the impact occursbelow the occupant cell. The A-class complies notonly with the future EU frontal impact crash teststandard but also with strict safety regulations on sideimpacts in the USA and the European Union. In termsof safety a car measuring only 3.57 metres long witha kerb weight of only about 1000 kg has a number ofbasic disadvantages to overcome — especially if it isbuilt on conventional lines. The low vehicle mass,short front-end structure and limited space availablefor crumple zones are fundamental handicaps thatuntil now have left little room in this vehicle class forfurther progress in vehicle safety. This situation hasbeen revolutionized with the A-class.

The main aim in the safety development of thecar was to make maximum use of the short frontcrumple zone in a head-on collision and to clear allcomponents that obstructed the crumpling processout of the way. Because of the rigid structure ofengine and gearbox, they play practically no part in

Fig 1: Mercedes A-class

Fig 2: Revised rear suspension

Fig 3: Slant-mounted power unit

VEHICLE DEVELOPMENT 97

the deformation, and in conventional compact carsthey can be pushed back in a single block that canintrude into the interior and injure the occupants.

Here the innovative arrangement of engine andgearbox reduces the risk of their forming a singleblock and therefore makes an essential contributionto occupant safety. In the A-class, the engine andgearbox are positioned at an angle partly in front ofthe occupant cell and partly underneath it, so that inthe event of frontal impact they can slide downwardsrather than straight back. This is possible due largely

Fig 4: Double-level floor

Fig 5: Vehicle chassis-frame construction

Fig 6: Deformation zones

to three unusual features: the unique inclined con-struction of the engine and gearbox, the shape andinstallation of which are specifically designed toaccord with the crash principle of the A-class; thedevelopment of a frame-type integral support toaccommodate the engine and gearbox (Fig 5), whichin a crash can disengage at two of its eight fixingpoints thereby allowing the engine and gearbox toslide downwards; thirdly the design of the stable frontfloor panel (pedal floor) as a surface along which theengine and gearbox can slide in the event of a crash.

This maximum possible deformation lengthavailable at the front end of the Mercedes A-class isdue solely to the fact that the rigid engine and gearboxare displaced under the passenger cell in a serioushead-on collision. Without this capacity for evasionand the ability of the engine and gearbox to 'duck' outof the deformation area, the front end of the A-classwould have to be about 25 cm longer in order to givethe occupants the same degree of protection. The factthat the short crumple zone also does not subject theoccupants to severe stresses as a result of the higherdeceleration values is due to the retaining systemsspecially matched to the front end structure.

Other advantages of the new body concept arethe straight side members. They absorb high defor-mation forces right from the start of body deforma-tion and thereby permit much more favourable decel-eration characteristics than in cars of conventionaldesign. As a result, the occupants share in the decel-eration of the vehicle earlier and over a longer period,which reduces the stresses to which passengers aresubjected. The triggering threshold of seat belttensioners and airbags on the driver and front passen-ger side can also be more precisely defined thanks tothe longitudinal rigidity of the body structure. Thefront end structure has deformation zones, Fig 6, onthree levels. The impact energy in the front area of theA-class is widely distributed over three planes: theframe-type integral support, which serves to accom-modate the front axle, engine and gearbox; the straightside members leading to the aluminium and steelfront module; the second upper side member plane ona level with the headlamps.

Since most frontal impacts are offset crasheswith unilateral stressing of the front end structure,there are strong transverse connections between theimpact zones designed to ensure that the deformationareas on the opposite side, remote from the impact,

98 VEHICLE DESIGN

are also involved. This produces an homogeneousfront end structure which will prove effective in alltypes of frontal collision. The front wheels also havea role to play in energy absorption. They form anadditional load path and in an impact are braced atthe stable nodal points of A-pillar and sill. This effectis particularly important in the frequent front endcrashes with overlap on one side — the so-calledoffset collisions.

M-B engineers have matched the strength ofthe occupant cell to the high front end deformationforce. The raised flat floor, which is welded frombelow to a grid-like support structure, gives theoccupant cell a high degree of stability so that it isessentially not deformed either in a frontal impact orin an offset crash with 40 or 50 percent overlap.Airbags and belt tensioners and a polystyrene insertin the footwell, which form part of the standardequipment on all Mercedes cars, complete the list ofmeasures to protect the occupants.

From the outset the 'Big versus Small' aspectwas a prime consideration in the safety developmentof the A-class. In a head-on collision involving twocars of differing mass a suitable distribution of thedeformation load between the two vehicles must beachieved so that there is no danger particular to theoccupants of the smaller car. For some time nowMercedes-Benz has been developing its cars accord-ing to this principle and claims to be the first to testcars through crash tests against a deformable barrier.This test method, which will not be specified for allnew cars in the European Union until October 1998,

permits an especially realistic simulation of typicalaccidents involving oncoming traffic, and specifies ahead-on collision at 56 km/h and 40 percent overlapagainst a deformable barrier. The A-class passes thistest even at an impact speed of 65 km/h, correspond-ing to a significantly high stress loading.

Compatibility means that in a collision involv-ing two vehicles they should activate one another'scrumple zones and be capable of transmitting thedeformation load uniformly to both bodies. For thisto happen it is necessary for the front end deformationresistance of large and small cars to approximate toone another. As an example, in the E-class the frontend structure of this Mercedes model is constructedso that in a crash the impact energy for the othervehicle is reduced — intelligent safety engineeringmeans mutual protection. In a smaller car, however,the design principle is just the opposite. Because ofthe lower mass and the shorter front end the Mercedesengineers designed the A-class with an especiallyrigid front end so that in an accident with another,larger oncoming vehicle it can activate the othervehicle's deformation zones. In addition to matchingthe levels of force, the uniform distribution of impactforces over the entire height and width of the frontend plays a particularly important role. On the A-class this purpose is served by the second impactplane with its stable transverse connections to thelower support structure. Even in a frontal collisionwith a larger car, the occupants of the smaller one arenot at a major disadvantage in this case.

The strengths of the sandwich concept of the

Fig 7:Body-in-white


car are not confined to front-end crashes. They alsoapply to side and rear impact collisions: in the side-on crash the other car hits the A-class at the preciselevel where the body of the A-class is at its strongest,at the level of the load-bearing structure for the floor.The occupants are seated above this impact level andare therefore optimally protected. The load bearingstructure of straight cross members, Fig 7, and sidemembers is better able to contain and reduce theimpact energy than in a car of conventional bodydesign in which the impact mostly occurs above thefloor structure.

The short crumple zones at the front of the A-class make it necessary to activate the belt tensionerimmediately after the crash. As a result, the occu-pants not only take part earlier and longer in thedeceleration of the vehicle, but they also have alonger distance for their crash-induced forward move-ment. The earlier the safety belt builds up its restrain-ing force, the longer the distance available to the beltand belt tensioner in which to arrest the forwardmovement of the occupants. In this way, the forcesunleashed on the occupants are low, despite themassive deceleration of the occupant cell. This alsoserves to compensate for the design disadvantages ofshort deformation zones in small and compact cars.The innovative restraint system in the A-class in-cludes full-size airbags for driver and front passen-ger. The airbags fitted as standard have a volume of64 and 130 litres. They are operated by a newpropellant technology which offers certain advan-tages when recycling: the gas generator for the driv-er's airbag is filled with an acid-free solid propellant,and the passenger airbag contains an environmen-tally safe liquid gas mixture of helium and argon.

The car has inertia-reel seat belts with belttensioners on the front seats: newly developed com-pact belt tensioners compensate for seat belt slackand ensure that in a crash the occupants are evenbetter tied to the passenger cell by snugly fittingbelts. The belt strap is tensioned by small steel ballsin the seat belt retractors which, when the belttensioner is activated, are set in motion and rotatecounter to the belt strap shaft. In this way they firststop the belt strap and then coil it back up at highspeed. This drive system has two outstanding advan-tages: high tensioning capacity and compact con-struction of the seat belt retractor.

The inertial reel seat belts for the front seat

occupants are height-adjustable in three stages. Theseat belt retractors of the front seat belts incorporatetorsion bars which in a crash are slowly deformedfrom a certain force upwards, thereby reducing thelocking action of the inertial reel seat belts. Thisreduces the risk of injury to the occupants whomoreover, thanks to the force limiter, can sink verygently into the airbags. Belt force limiters and airbagsare thus designed to function as part of a precisely co-ordinated system. The side airbags in the front doorsform part of the standard specifications of the A-class.A newly developed gas generator with liquid gasfilling is also used for these. M-B also fits belttensioners as standard on the outer seats of the rearseat unit. These ensure that in a crash rear seatpassengers also benefit in good time from the decel-eration of the body structure. The height adjustmentof the inertial reel seat belts functions automaticallyon the rear seats. As on the C- and E-class cars, childseats which fold out of the rear seats at the touch of abutton are available as an option.

Primary safety systemFor the first-launched vehicle, the front axle has amodified McPherson suspension system with coilsprings, twin-tube shock absorbers and torsion barstabiliszer, Fig 8. The suspension components aremounted together with the rack-and-pinion steeringgear, engine and gearbox on a frame-type integralsupport that is bolted to the body at eight points.Unlike the original McPherson suspension, the anti-roll bar of the A-class does not take part in wheellocation but is linked to the suspension strut viaplastic suspension: the results include better elasto-kinematics and increased rolling comfort.

Ride comfort is also enhanced by the low-friction suspension struts and damper guide units, theTeflon coating of the front bearing of the torsion barand the various noise-damping measures. All wheellocation, suspension and damping components havebeen weight-optimized, such that engineers haveachieved an exceptionally good balance betweenload-bearing ability and intrinsic weight: the effectsof this balance only become evident in the sum of thecar's many detailed solutions.

Another conceptual advantage that is felt in thehandling of the car is the position of the steering gearin front of the centre of the wheel: this layout is only

100 VEHICLE DESIGN

possible because of the sandwich double-layer floorconcept, with the engine and gearbox located partlyunderneath the floor panel. Steering response isimproved by this geometry.

A compact servo pump for the steering of theA-class, for the first time in a Mercedes is notmechanically driven but is powered by an electricmotor with electronic control. Pump capacity can beadjusted precisely to suit demand and the instantane-ous traffic situation. For example, when driving onthe straight, the electric motor runs at reduced speedand consumes less energy. The three-spoke steeringwheel of the car is a new development and is designedin particular to satisfy the needs of lightweight con-struction. The 370 millimetre diameter steering wheelis an aluminium pressure-casting, with a rim ofpolyurethane foam coated in plastic or leather, de-pending on the equipment level and customer option.The steering wheel material crumples in a controlledway in the event of high-force collision impact.

The company opted for trailing arm suspensionwith coil springs, torsion bar stabilizer and single-tube gas-pressure shock absorbers. The main advan-tage is that trailing arm suspension can be designedwith all its components underneath the load floor, sothat it does not encroach on the interior space. The

shock absorbers and springs are located in an other-wise unused space in front of the wheel centre. Withthis geometry, the suspension components supportthe straight side members in a crash, thereby alsoimproving occupant safety.

The dynamic qualities of the rear suspensionare particularly due to special tie-bolts that controlthe elastic deformation of the side members andcombine with them to form a rectangular linkagestructure, Fig 9. Changes in the angle of the side

Fig 8: Front suspension

Fig 9:Suspensionsupports


member and wheel about the vertical axis are com-pensated with up to 75 percent efficiency. The sus-pension components, side members, coil springs andshock absorbers are mounted on a suspension subframein a single compact block that is fixed to the body-work on four sound-proofed rubber bearings, partlywith hydraulic damping. The rear suspension unit ismounted with the aid of four vertical assembly bolts.None of the suspension components projects up-wards above the level of the floor.

The technology and layout of the brakes, Fig10, correspond to the particular features of the A-class drive system and vehicle concept. Engineersopted for floating-calliper disc brakes at the front anddrum brakes at the rear, because this combinationprovides optimal braking safety, stability and endur-ance for a front-wheel drive car, say M-B. A brakebooster and the anti-lock braking system provideadded safety. The drum brakes on the rear wheels arecharacterized by a lightweight construction: the sup-porting body for the wheel brake cylinder and brakeshoes, the anchor plate and brake cylinder are madeof aluminium. In order to satisfy the high safetyrequirements, the hubs are made of steel and thebrake cylinders of grey cast iron. An automatic

adjusting system compensates for brake pad anddrum wear. The parking brake in the A-class isoperated manually, using a lever between the frontseats. The control cables are maintenance-free, sincethey have automatic length adjustment.

ESP keeps the A-class directionally stable andreduces the risk of skidding when cornering byselectively applying the front and rear brakes. Whiledriving, the ESP computer compares the actual be-haviour of the vehicle with the calculated set points.If the car is deviating from the safe 'ideal line', thesystem responds at high speed with a specially devel-oped logic, bringing the car back to the right track intwo ways, firstly by the precisely dosed braking ofone or more wheels and/or by controlling enginetorque. By these methods, ESP corrects both drivingerrors and skidding movements caused by slippery orwet surfaces, loose chippings or other difficult roadconditions that normally give the driver very littlechance to keep the car in line by steering and brakingaction. The A-class is the first and only car in the sub-compact and compact car class to have such aninnovative driving safety system. The ElectronicStability Programme also includes the compnay'selectronic Brake Assist System.

Fig 10: Brakingsystem

102 VEHICLE DESIGN

Ford FocusFord's Focus, Fig 11, brings the company's 21stcentury hard-edge styling to its most mainstreammodel and also marks a completed market reposi-tioning of a class of vehicle starting as the Mark 1Escort to a vehicle refined enough to compete in theneo-luxury sector. The refinement of individual sys-tems to achieve the transformation is described be-low.

Friction within the front suspension struts isreduced by off-set coil springs that eliminate bendingforces acting upon the strut, Fig 12. Zero off-setgeometry — via new A-arms supported by stiff, frontA-arm bushes — provides precise lateral wheelcontrol for enhanced precision and on-centre steeringdefinition. Large, rear A-arm bushes permit longitu-dinal compliance for reduced impact harshness andimproved ride performance. Negative scrub radius(-12 mm) enhances braking stability, particularly onsurfaces in which available grip varies between theleft- and right-hand tyres. Low steering friction lev-els minimize resistance and stickiness for improvedfeel, response and driver confidence. . Body-roll iscontrolled by anti-roll bars, which are 20 mm diam-eter front and rear. Large, pre-loaded bushes provideimmediate linear control. Steering input inducesimmediate directional change (turn-in) with verylittle body roll. Ultra-stiff cross member, attacheddirectly to floorpan, increases the precision of geo-metric wheel control and further stiffens the body.Friction within the steering system has been reduced20 per cent and damping friction reduced, Fig 14.

Adoption of a fully independent, Control Blademulti-link rear suspension system, though similar tothe system used on the Ford Mondeo estate, is rede-signed for Focus. Here the Control Blade makesextensive use of stampings for key components,which reduces cost, unsprung weight—by 3.5 kg perwheel — and assembly time, while offering evengreater geometric precision, Fig 13. It has ride com-fort, steering precision, handling, braking and stabil-ity advantages, as well as NVH and package gainsover the common twist-beam axle. There is greaterlongitudinal compliance without compromising lat-eral stiffness, which boosts steering precision, feel,handling and driver confidence. Intrinsic stability isprovided by passive rear-wheel steer. The widerdistribution and de-coupling of five separate loadpaths, compared with two for the twist beam design,

Fig 11: Ford Focus

helps to reduce transmission of noise, vibration andharshness levels to the passenger compartment. Thecontrol blade, spring link and toe link are all pressed-steel components. The camber link is the only cast-ing. Compliant bush provides recession, which al-lows rear wheels to move both upwards and rear-wards to absorb road bumps.

An all new, highly rigid yet lightweight plat-form architecture (826 kNm/rad; 1070 kg for the 3-door — stiffest and lightest in class) provides bestpossible base for enhanced ride, handling, steeringand active/passive safety. The combination isachieved through laser-welding, optimized panelgauges, extensive swaging, local reinforcement ofcritical points and optimized spot-weld distribution.Cross-member and powertrain pick-up points are asmuch as 150% stiffer than surrounding areas. Thelightest model weighs just 1070 kg; both lighter anda full 15 per cent stiffer than all recent class entrants.

The rear side rails, for example, are tradition-ally made from four separate parts. For Focus, theseparts have been replaced by a single laser-weldedblank, in which the gauge reduces progressively inthree stages from front to rear. The result is a structurethat is stiffer, with more rigid mounting points for thesuspension, has improved crash performance andsaves more than 1 kg per rail in weight. Similarly, thegauge of steel in the B-pillar is 2.25 mm thick at thetop but tapers to just 1.1 mm at the base, providing astiff upper section for a controlled and superiorperformance in the event of a side-impact crash.

Zero offset geometry gives total separation ofload paths, with lateral forces being fed through thestiff forward A-arm bush (1) while longitudinal forcesare controlled by the more compliant rear A-armbush (2) shown in Fig 13. Large-diameter coil springsare offset, to feed suspension loads directly to them,eliminating bending forces on the struts for reducedfriction and superior responses, Fig 14.


Fig 12: Large diameter coil springs are offset sothat suspension loads are fed to them withoutbending forces applied to the struts

Fig 13: Zero-offset geometry allows lateral forcesto be fed through bush (1) while longitudinal onesare controlled by bush (2)

Fig 14: Low friction seals ensurequick response of dampers

Stability is enhanced by maintaining optimumbraking performance to the rear wheels in all condi-tions, whether the vehicle is heavily laden or carryingonly the driver. On non-ABS-equipped vehicles, thisis provided by a pressure cut-off proportioning valve.For the 1.8- and 2.0-litre petrol and diesel estate, aload-sensitive pressure limiting valve is used.

When ABS is specified, brake proportioning isachieved using the electronic brake-force distribu-tion (EBD) system. It uses the ABS sensors to moni-tor the speed of front and rear wheels and adjusts thepressure distribution to help the rear wheels retaintraction. EBD is self-compensating for all load con-ditions and imperceptible to most drivers. It is de-signed to reduce stopping distances and improvesvehicle stability in conditions that fall short of trig-gering the ABS. ABS also forms the basis of the car'sTraction Control System (TCS) and Electronic Sta-bility Programme (ESP). TCS is a development ofFord's dual-mode system with low-speed brake in-tervention coupled to a cut in engine power, above 31mph, delivered via the EEC-V engine managementmodule.

ESP acts whether or not the driver operates thebrakes. In tests, it maintains vehicle stability at muchhigher speeds than would be possible without it —thereby placing less demand upon driver skill andreducing stress in extreme conditions. ESP usessoftware to control engine power and brake indi-vidual wheels to restore stability when the driver hasexceeded or is beginning to exceed the car's dynamiccapabilities. Driver's intentions — direction of travel,measured via a steering angle sensor — are comparedagainst vehicle behaviour. Vehicle behaviour is moni-tored constantly by three additional sensors for yawrate (rotation), lateral acceleration (centrifugal force)and wheel speed, with the latter sensors being inte-gral to the ABS. Yaw control is achieved via thevehicle's ABS, with braking being directed to indi-vidual wheels through the ESP modulator. ESP usesinformation from three sensors and the four ABSwheel-speed sensors to determine the cornering be-haviour. It interactively compares the data in a dy-namic handling map stored in a special on-boardcomputer. Additional ESP sensors monitor steeringangle, lateral acceleration and yaw moment, whichdenotes the vehicle's tendency to turn about itsvertical axis. As soon as any tendency for the vehicleto move off the chosen line is detected, engine power

104 VEHICLE DESIGN

is reduced, and individual brakes are applied momen-tarily to bring the car back on course.

Powertrain With the Zetec SE low-frictionengine, Ford used high-compression ratios, knocksensing and low idle speeds to deliver a 25 per centreal-world fuel economy improvement over pastengines. The existing 1.4-litre Zetec SE unit, nowfully re-calibrated for Focus to serve as a fuel-efficient 75 PS power unit, is supplemented by an all-new all-alloy 100 PS 1.6-litre Zetec SE engine. Allengines require servicing only every 10,000 miles,with spark plug renewal every 40,000 miles andvalve clearance attention only every 100,000 mileson petrol versions. All also feature a new torque rollaxis (TRA) mounting system, which helps reducepowertrain shake on rough roads, results in a smootheridle quality and greatly reduces the degree of noiseand vibration transmitted from the drivetrain into thebody shell, Fig 18. Internally, the Zetec engines fea-ture an alloy ladder frame between the base of theblock and the crankcase, Fig 19,which boosts rigidityof the powertrain assembly by 30 per cent. The alloyblock Zetec SE has a similar stiffening memberadded as a bearing beam within the crankcase skirt.These devices — together with new lightweightpistons and con rods — reduce second-order shakingforces by 20 per cent. Newly designed cam coversand low-noise ancillary drive systems generate sig-nificant improvements in running refinement andreduce perceived engine noise by 50 per cent.

Cables transmit fore/aft and left/right gear le-ver movements to the selector mechanism, eliminat-ing a potential path for NVH to the interior, Fig 20.Cable shift also is smoother than a rod-operatedsystem. Hydraulic clutch requires lighter pedal effortwith less travel for a smoother take up. An updatedversion of the Ford B5 five-speed manual transmis-sion has external ribs along the transmission andclutch housing to increase drivetrain stiffness forreduced noise and vibration. Internally, first andsecond gears are equipped with double-conesynchronizers for smoother downshifts. Selection ofreverse is also slicker. Durability is enhanced by theincorporation of strengthened final drive bearingsand a new synthetic oil lubricant, which also easesgear selection when cold. New sealed-for-life bear-ings and fluid seals protect from dirt particle ingressfor extended transmission life.

Now available on Focus is a four-speed auto-

Ford FocusFig 16: Current single-piece Control Blade

Fig 18: Powertrain mass is supported by twomounts in line with the virtual axis of rotation, aseparate arm resisting torque


matic transmission which features an overdrive-topand lock-up torque converter. It has been designedspecifically for use in front-wheel drive applicationsand is unusually light and compact. It is controlled byan electronic synchronous shift control (ESSC) mod-ule linked to the EEC-V engine management system.A centrally mounted quadrant selection lever has sixpositions (P,R,N,D,2,1), while overdrive can beswitched by a separate, thumb-operated push-buttonat the side of the lever. The ESSC works in conjunc-tion with the EEC-V using information read from 18different engine and transmission sources to calcu-late the best possible shifting strategy for the drivingand operating conditions. Fuel economy and per-formance are close to those of the equivalent manualtransmission models, while the system's shift qualityand speed of response set new standards for this classof vehicle.

Fig 19: Cast alloybearing beamreinforces the ZetecSE bottom end

Fig 20: Cable shift actuation ischosen to reduce noise paths

Body structure and systems Focus meets morethan 100 different real-world crash tests, modes andevents, well beyond existing or currently proposedlegislation, including all mandatory European andUS destructive tests. At the front, beyond the bumpersupport beam, the car's cross member is made fromultra-high-strength steel, so it is robust and stable andwill not tear upon impact, Fig 21. Resistance totearing helps spread crash energy into the car's lowerside rails, which is particularly effective in offsetimpacts. Additional to the progressive collapse of thelower side rails, which absorbs most of the energyahead of the passenger safety cell, a secondary loadpath channels the remaining energy over the roof andaround the doors to ensure safe evacuation of passen-gers.

At the rear, the objective is to minimize intru-sion of the passenger compartment in a rear impact,while also ensuring that the doors remain operableand the integrity of the fuel system is maintained.This is achieved via the progressive collapse of therear side rails, supported by the wheel housings.Stamped and laser-welded, the side rails are made upof three different metal gauges — changing in thick-ness from 1.6 mm to 2.6 mm (in the area of the fueltank) and 2.4 mm — to provide progressive control-led collapse. The compound structure avoids over-gauging near the rear bumper and eliminates the needto add reinforcement further back. Vehicle weight isthus reduced, by 1 kg per side, and the number of partsand welding operations are reduced, improving as-sembly tolerances and providing robust control of thecollapse performance. For side-impact protection,the entire side structure, which includes door beamsand anti-burst door latches, is designed to absorbenergy and reduce intrusion, especially above thedoor bars. To achieve this, the B-pillar is made froma laser-welded, high-strength steel blank, with agauge thickness that reduces from 2.25 mm at the topto 1.1 mm at its base. Additional inner reinforcement,designed to increase rigidity, makes it highly resist-ant to 'kinking', so it can more effectively channelcrash energy into both the rocker and roof rail, andsupport the side airbag during deployment.

All elements of the Focus restraint systemwork in harmony so that the whole structure isintegrated and fine-tuned to provide maximum pro-tection. This starts with the locking of the inertia seatbelt reels which occurs approximately 6 milliseconds

106 VEHICLE DESIGN

after impact. (All timings depend upon the nature ofthe impact, whether it be straight, angled, offset,against a solid object or another vehicle). Approxi-mately 4 milliseconds later, before the head and chestbegin to move forward, the airbag sensors trigger thefront airbags and the small pyrotechnic charges in thepre-tensioners, which eliminate any slack in the seatbelt and negate the effects of bulky or layered cloth-ing. The front airbags take approximately 35 milli-seconds to fully inflate, which is completed justbefore the occupant meets the bag, approximately 50milliseconds after impact. To reduce chest loadingand minimize injury, Focus is equipped with load-limiting devices within the inertia reel assemblies.These pay-out belt webbing after a predeterminedload is exceeded. This process is progressive andoccurs between 45 and 70 milliseconds after impact,ensuring that the cross belt pressure against theoccupant's chest remains fairly constant.

The load-limiting device consists of a torsionbar within the traditional inertia reel, and the typicalpay-out is 150 mm. The system is calibrated to helpensure that front seat occupants do not meet theairbag until the optimum point, which is just as it isbeginning to deflate. The progressive pay-out alsoensures that the upper torso is less likely to twist, anaction that can compromise the efficiency of the frontairbag. Seatbelt pre-tensioners are designed to pullthe buckles down and take up any slack, optimizingtheir position on the torso and maximizing the re-straint provided by the belt webbing.

Focus' new head-and-chest combination sideairbags provide greatly enhanced head and chestprotection in side impacts. In addition to acting as abarrier between the occupant and the side of thevehicle, the tall, 15.5-litre side airbag — stored in theseat back's outer side bolster — is designed tocushion the head, minimiszing lateral head injuries.

The car is equipped with the latest version ofFord's Safeguard Passive Anti-Theft System (PATS).Safeguard is a Thatcham-approved high-securityengine immobiliszer operated via a miniature trans-ponder within the key head. It transmits a uniquecoded signal, with several trillion possible codes, toa transceiver situated around the steering lock. Oncethe key is identified as correct, the engine is mobi-lized. Without it, the engine will not start and iseffectively dead. PATS offers several advantagesover competitive systems. The system arms itself,

Fig 22: Seats are designed to attenuate vibrationin the 10-50 Hz frequency range


eliminating human error through forgetfulness. Theinterception of the key code by a thief is virtuallyimpossible because the transponder only has thepower to pass the code by radio to the transceiverwhen it is within the electrical field of the transceiver.PATS also incorporates a special erasing procedureand smart 'learning' mode to maintain security afterresale and eliminate the requirement for a master key.In addition, a new, key-operated hood-release mecha-nism makes a potential theft even more difficult. Byeliminating access to the engine compartment via thetraditional cabin lever and cable, to ensuree that awould-be thief could gain access to the engine oralarm siren only with the car's ignition key.

Fig 21: High specific-stiffness body shell

Fig 23: Large diameter rear A-arm bushes givelongitudinal compliance without compromisinglateral stiffness

The car's shrouded lock mechanisms and wir-ing present the first obstacle to forced entry, render-ing break-in many times more difficult. A furtherobstacle is posed by a double-locking door system,which is linked to the car's central locking andoptional remote-control facility. Once the doublelocks have been set, only the key or remote button canrelease the locks. A further deterrent is presented bya tamper-proof perimeter and interior scanning alarm.Once armed, it detects the opening of any doors,tailgate or hood, as well as any movement within thepassenger compartment. The remote-control lockingsystem has a 10-metre range and uses a miniaturetransmitter working on a rolling frequency system toeliminate possible interception by an electronic scan-ner.

The body structure and seating were tuned toreduce resonant peaks and move natural vibrationfrequencies outside the operating range, Fig 22. Deepswaging of body panels, especially the floorpan, helpto maintain stiffness while permitting down-gaugingfor weight reduction. Where this was not possible,around the bulkhead for example, dual-function dead-ening pads were developed, with a viscous layer todampen sound and a mass layer to absorb it. As wellas tuned suspension mounts, Fig 23, torque roll axisengine mounts also are used to reduce powertrainnoise, improve idle quality and reduce powertrainshake on rough roads. Such a mounting systemseparates the powertrain mass from its torque reac-tions by using two rubber-to-metal bonded mountslocated at either end of the assembly, in line with theaxis of rotational inertia, plus a dedicated torquereaction link. The front mount incorporates a hydrau-lic chamber so the modulus of the rubber can beoptimized to reduce NVH transmission at high en-gine revs, without reducing idling smoothness.

Two direct acoustic paths from the drivetrain tothe interior have been eliminated with the adoption ofa hydraulic clutch mechanism and cable-operatedgearshift. A unique flexible exhaust joint, situatedbehind the engine manifold, limits the transmissionof drivetrain vibrations along the length of the ex-haust system. It also has specially tuned exhausthangers positioned at the natural vibrational nodes toprovide further isolation. 'Helmholtz' resonators areused to filter or select individual frequencies so thatan appropriately purposeful, yet subdued sound isobtained.

108 VEHICLE DESIGN

Land Rover FreelanderWith prices pitched at under £16 000 the Freelander,Fig 24, has finally brought Land Rover within graspof the profitable small sports-utility-vehicle marketand first results are showing the vehicle to be per-forming well financially. Trade sources have pro-jected higher residual values than the Honda CRVand Toyota RAV4. It is the first of the company'svehicles with a unitary construction body shell andtransverse power unit and a well-planned enginecompartment gives good service access, Fig 25.

StructureThe integrated underframe comprises high-strengthsteel box-section longitudinals, with eightcrossmembers, all welded through to the floor pan.Box-sectioned outriggers from the crossmembersconnect the side sills through to the centre tunnelmember. Front and rear suspension sub-frames arebolted rigidly to the shell to enhance its torsionalrigidity. The upper shell involves monoside pressings;there is a deep rear-heelboard serving as a furthercrossmember; there is a strong integral fascia panel,too; all these combining to enhance the stiffness ofthe superstructure. For the three-door variant thetorsional figure is 13,500 Nm per degree and rises to17,500 on the Station Wagon.

Within each lower A-post there are five dia-phragm pressings to stabilize the box-beam and

provide additional crush resistance under impact.Front-ends of the underframe longitudinals crushprogressively on impact, after initial deflection ofbumper armature and crush cans, a tapered box-section in the top of each engine bay side-panel also

Fig 24: Land Rover Freelander

Fig 25: Under-bonnet access


absorbing impact. In more severe crashes, bending ofthe curved portions of the main longitudinals takesplace. The suspension towers are braced back to thestrong A-pillar area via box-sectioned members ei-ther side of the bulkhead. The rear bush mountingsfor the lower front suspension arras are designed tobreak free of the subframe, under severe impact, tominimize intrusions into the front footwells. Fromthe bulkhead backwards the floor structure has a'branching' layout to help spread impact forces aswidely as possible, with a curved 'horn' box-membersweeping back from the longitudinal to the centraltunnel area, the box-sectioned side sills also beingbrought into play.

Body systemsA spoiler-type electrically operated glass sun-roofhas been engineered to tilt open at the rear and slidebackwards above the roof panel, to maximize rearheadroom, two-stage slides permitting 70% clearaperture opening against the usual 50%. At the front

of the vehicle's roof there is a twin-panel targastructure, with detachable T-bar. Panels can be indi-vidually tilted open at the trailing edge, or taken out— at which point wind deflectors spring into posi-tion. Detached panels stow in a bag on the back of therear seat squab. The complete targa unit is con-structed as a cassette, having a one-piece SMC mould-ing which is bonded to the bodyshell with a poly-urethane seal. Together with a number of the interiormouldings this is made by a gas injection mouldingtechnique to increase specific strength and stiffness.

Roof modules for the 3-door vehicle come ineither softback or hardback forms, both of whichinvolve the same tail-door electrically operated drop-glass as the station wagon, Fig 26. Roofs are thusinterchangeable for those customers wishing to in-vest in the alternative. On the softback variant, Fig27, the vinyl roof folds upwards and furls within anintegral tonneau at roof level so rear vision is unim-paired. PVC sidescreens are zipped in place and canbe individually removed to leave the rear roof as a

Fig 26: Station-wagon variant

110 VEHICLE DESIGN

canopy with strong air through-flow. Key body di-mensions are tabulated in Fig 27.

A green-tinted laminated windscreen is bondedin place and all other window glass is PilkingtonOptikool solar-control glazing, cutting solar trans-mission by 50%. Front wing panels are in an engi-neering polymer chosen for its damage resistance and1.5 kg per wing weight saving. They are jointlypainted with the main shell and have to withstand 180C stoving temperature. Headlamp lens too are poly-mer-mouldings, a silicon-coated polycarbonate be-ing used to allow a complex optical pattern whichmaximizes beam control. The front bumper andgrille surround is a large polypropylene mouldingmounted on an aluminium armature while that at therear is mounted on a compression moulded glass-matreinforced polypropylene member. Also inpolypropylene are wheelarch mouldings, wheelarchliners, lower sill flange finishers, tail-door loweredge finishers and mudflaps.

Interesting interior detail is the facia-mountedrocker switch construction, Fig 29. The switch con-tact metal is integrated during the injection mouldingand a common base moulding and contact plate areused. Switch warning lights are LEDs rather thanbulbs. Another detail is in the driver seating, whichhas an adjustable lumbar support that does not stiffenthe squab springing when adjusted outwards.

The side-hinged tail-door carrying the sparewheel also involves a specialized construction tech-nique, for mounting the wheel without bridging innerand outer skins over the space required for the drop-glass. A large die-cast aluminium drum-mouldingcarries the wheel and spreads the mounting bolt loadsover a very wide area. A neat support arm for thehigh-level stop-lamp is integrated into the drum. Agas-spring strut beneath the door has 'keeps' at halfand fully open positions and facilitates operation byusers of all sizes. The drop-glass has a grooved sealat its top edge and electrical interlocks are providedalongside a short-drop/lift control system to releasethe glass from the groove when the door is opened andclosed.

Vehicle mechanical systemsA key quality of the vehicle is the provision of goodoff-road performance while maintaining on-road han-dling comparable with the best of conventional car

practice. Rover Cars experience was drawn upon forthe independent suspension system involvingMcPherson struts on all four wheel stations whichprovide vertical travels of 7 in front and 8 in rear.There are high levels of fore-aft compliance, aroundtwice the normal 5 mm. Steer fight is avoided bycarefully designed suspension bush configuration,aided by a steering rack with centre take-off, givingvery long track rods. An anti-kickback valve in thepower steering hydraulics eases the shocks of cross-country driving, Fig 30. While disc brakes are used atthe front, the rear wheels rely on drum brakes toprovide park-brake performance appropriate to theextremes of cross-country operation. The ABS has aspecial control system which builds in electronictraction control (ETC) and hill-descent control (HDC).

Fig 27: Key dimensions


Fig 28: Softback variant

ETC adds a further degree of limited slip control, tothat provided between front and rear axles by theviscous coupling, but across each axle. HDC pre-vents tobogganing on sharp downhill brake applica-tions by a hands/feet-off approach in which engineoverrun at idle is detected and brakes gently appliedto maintain maximum descent speed of 4.4 mph.

The powertrain involves either the K- or L-series engines, the K being specially tuned to providepower peak 250 rpm further down the speed range.The engine is also the first to use a returnless petrolinjection supply system, with more sophisticatedelectronic control over the in-tank fuel pump. The L-series diesel has water-cooled EGR to reduce NOxemissions.

Fig 29: Interior features

Fig 30: Steering system

112 VEHICLE DESIGN

Project Thrust SSCG. T. Bowsher, Chief Designer (Mechanical) ThrustSSC Project, was responsible for spaceframe/struc-ture/wheels/brakes/suspension/steering systems/en-gine mounts/ throttle systems. Seen in Fig 31 with theDunlop-made wheel and brake, he described theengineering to a contemporary specialist journal1.

He explained that Thrust SSC, although en-tirely new in concept, with twin jet engines and rearwheel steering , incorporates technology developedin Thrust 2, which regained the world land speedrecord in 1973. A major feature of the rolling gear isthe adoption of solid aluminium alloy wheels and apower hydraulic braking system which uses two discbrake callipers acting on each specifically designedhigh speed carbon disc. The Thrust 2 experience gavevaluable information on the safe 'footprint' size fortransferring vehicle weight to a desert surface. It alsomade it possible to predict how wheel brakes mighteffectively be used to stop the vehicle. This is be-cause the same rolling interface applies (aluminiumalloy wheels and the low adhesion, friable surface ofBlack Rock desert where the very high speed runswere carried out). The shape and ground clearance ofthe new car dictated a wheel diameter of 34 inches(0.86 m). At the anticipated peak design speed of8400 rpm this means that the radial acceleration at thewheel periphery is 34,000 g — effectively making 1gm of material weigh 34 kg.

Dunlop undertook the manufacture of allwheels for the jet car, both the high speed solid alloysets (with spares) and the low speed wheels whichutilized the main undercarriage tyres of the Lightning

Fig 31: Chief Designer G.T. Bowsher with Dunlopwheel and brake

fighter. This proved a major contribution at an earlystage, and at a time when credibility for the projectwas of great importance. To produce the high speedwheels solid L.77 forged aluminium blanks suppliedby HDA Forging were machined to provide a rollingtread width of 10 inches (0.25 metre) for the frontwheels and 6 inches (0.152 metre) for the rear,steering, wheels. This is in line with the weightdistribution of the vehicle's 10 ton static weight.

A straight web design for both front and rearwheels became essential in order to minimize stress,but for the front wheels, with the wider tread profileand larger peripheral mass, it also became necessaryto omit the traditional central hole and have a solidcentred wheel; only then could the high speed stressesbe kept within the limitations of the L.77 material. Interms of the wheel installation this did not matter, asthe decision, already taken, to steer Thrust SSC by the

Figs 31/32: Front and rear wheels after final machining


rear wheels and not the front meant that the centralhole was not essential: its principal use would havebeen as a location for machining. As the rear wheelswere to be steered a central bearing/stub axle holewas a necessity, but this could still be accommodatedwithin the material's stress limits because of thenarrower tread width and lower peripheral mass.Three dimensional computational finite element stressanalysis techniques were used in the design of thewheels, minimizing errors before a commitment tocostly machining. Of interest, the rear wheels areslightly higher stressed than the fronts at any givenspeed, indicating the effect of the central hole.

The finalized wheel shapes are given in Fig 31for the front wheels and Fig 32 for the rear wheels. Fig33 shows the three dimensional stress contours of afront wheel at 8000 rpm., the darkest shade indicatingthe highest stresses (note those in the bolt holes) andthe lightest the lowest stresses, with the other shadesgiving intermediate values. All wheels should offerminimal resistance to rolling and yet have a highlateral resistance in order to provide good vehiclecontrol. Three circumferential grooves on the radiusedprofile of each front wheel tread provided for this,allowing a progressive take up of wheel load and fordesert surface deformation to give the required lat-eral stability. Twin keels were a feature of each rearwheel, with the tread shape again profiled to give a

progressive take up of load, these were intended topenetrate the desert surface and allow the generationof lateral steering forces, when steering took place, inaddition to providing good lateral stability to the rearof the jet car. The wide spacing of the keels improvedthe damping capacity at the desert surface interfaceand helped prevent wheel 'shimmy', a feature of thefirst set of rear wheels, which exhibited only a singlecentral keel of low damping capacity.

Although a parachute was the primary meansof stopping the jet car from high speed, Fig 34,wheelbrakes were essential to cover the lower speed range(200 mph to rest), when the parachute loses much ofits effectiveness. In an emergency (if the parachutefailed), the wheel brakes would need to stop thevehicle from over 300 mph.

In most respects, the wheel brakes for ThrustSSC were laid down as a design fourteen years beforefollowing the conclusion of the Thrust 2 project: thebest features of that design were retained whilst otherfeatures were design-developed as a natural followon and improvement. It was simply a question ofwaiting for a new vehicle. Each wheel brake com-prises a wheel driven disc/rotor and a pair (oneleading and one trailing) of brake callipers whichhydraulically clamp the disc between suitable fric-tion stators (brake pads). The brake callipers react thefriction drag loads developed between the brake pads

Fig 34: The jet car was stopped from full speed with parachute-assist

114 VEHICLE DESIGN

and disc and pass them into the vehicle's structure,whilst the brake disc absorbs the vehicles kineticenergy in the form of heat. The twin callipers equal-ize the brake loads in the system, particularly thosereacting through the wheel bearings, and much im-prove the heat distribution in the brake disc.

A critical element in the brake design, theauthor explains, is the drive junction between thewheel and brake disc. That of Thrust SSC took theform of its predecessor's brake in having drive slotsof a particular shape machined into the inner periph-ery of the disc, and engaging these with drive lugsmachined into the wheel carriers. The slots, of almost'keyhole' shape, allowed the disc to expand dueeither to high temperature or high rotational speed bysliding radially on the drive lugs whilst retaining itsconcentricity with the wheel, the precision of the slot/lug fit ensuring this. The shape of the 'keyhole' driveslot minimizes disc stresses, either thermal or rota-tional, whilst allowing a failure mode which retainedthe integrity of the disc as a major safety feature.

A degree of lateral compliance between thehydraulically actuated brake pads and disc is essen-tial, partly to provide for evenness in the lateral forceclamp, but also to allow the brake pads to move clearof the disc when not in use. In the Thrust SSC'spredecessor's brake this compliance came by later-ally springing the brake disc into a fixed position, andapplying a pair of twin opposed piston callipers: theopposed pistons would move the brake pads into andout of contact with the brake disc, whilst the lattercould still expand and contract radially as required.The webs of the Thrust 2 wheels had been crankedaround the brake callipers, an arrangement com-

pletely unacceptable for the straight webbed wheelsof Thrust SSC. For the new vehicles brake callipers,the body is fixed, and the disc allowed to moveaxially on the slot/lugs in order to provide the neces-sary lateral compliance in connection with singlesided hydraulic pistons. Now, the hydraulic pistonswould move the outboard brake pad into contact withthe disc, then move the disc laterally into contact withthe fixed inboard pad in order to provide the brakeclamp. This arrangement minimized the space re-quired for the fixed arm/fist element of the calliper,and fitted in well with the straight webs of the newwheels. In a laterally moving disc it is essential thatall lateral forces are equal and equally disposed aboutthe brake disc's axial centreline, this ensures that thedisc does not jam in the drive lugs when actuated. The

Fig 35: Calliper and disk assembly

Fig 33: Results of FE stress analysison front wheel at 8000 rpm


two callipers (one leading and one trailing), of theSSC brake arrangement provide for this, but eachcalliper has two pistons the pistons: are thereforediagonally connected on separate hydraulic lines, sothat should an hydraulic line failure occur, the brakedisc will still be evenly loaded in both the axial androtational planes. The arrangement of the SSC brakeis illustrated in Figs 35 and 36. Brake design wascommon throughout the jet car, with two brakesapplied to each front wheel, and one for each rearwheel: brake effort therefore matched the dynamicweight distribution of the vehicle when deceleratingon a low adhesion desert.

As both the wheels and brake discs were in-tended to operate at much higher speeds than in theformer jet car, the compacted graphite iron of theoriginal discs could not be used again. Several alter-natives were considered, one being to minimize highspeed stresses by reducing the mass density of thedisc material. Of three possibilities in this area, onewas the use of carbon/carbon fibre, used so effec-tively in aviation and race car brakes. It was with thisin mind that Dunlop were approached in order toassess both the suitability of carbon as a disc material,

Fig 36a:Front brake

and their interest in supplying such discs.In order to use this material, the brake pads

would need to be from the same material, eventhough its thermal properties would ensure very hightemperatures throughout the pad depth when com-pared with conventional materials. In view of theanticipated high brake pad temperatures two changeswere made to the brake calliper design: the fixedcalliper bridge/fist, originally specified in light alloy,became re-specified in steel, and the automotivestyle hydraulic pistons were changed to the DunlopAviation standard screw-in units, which were alreadyfitted with a high temperature heat insulator. Inaddition, the brake discs were slightly reduced inoutside diameter in order to use an available carbondisc blank, and the quantity of disc drive slots in-creased to sixteen.

All rotary components from the wheel/brakeassembly needed proof testing before being passedfor use on the jet car. Quite apart from any theoreticalanalysis of wheel/disc shapes, spin testing to at least9000 rpm would ensure the use of the equipment at upto the 8400 rpm design speed. Spin testing took placeat Pystock/Farnborough, under the good offices ofthe DRA, following balancing by Schenck, and allcomponents passed without problem, particular em-phasis on the post run inspections being directed tothe relatively highly stressed wheel bolt holes. Be-cause of the relatively large inertia of the wheelscompared with the available motor power of thespinning machine, a spin test from rest to 9000 rpmand back to rest took 35/45 minutes, with a full 5minute stress soak in the critical region of 8500-9000rpm. An additional test, for one brake disc only, wasto spin test to destruction: this occurred at 10,500r.p.m.. For physical reasons, it was not possible tospin test a wheel to destruction.

In operation the brakes, because of large inter-face friction variation with generated temperature,required a learning curve in order to get the best outof them. This done, the brakes have been trouble freefor the whole of the project, and pad/disc wear hasbeen small enough for only one complete set of brakeparts to be used for all 66 runs completed. Althoughsmall, a disc/pad damage differential became pro-gressively noticeable between the front and rearbrakes as the run numbers increased, with the rearstaking the greater punishment, the likely cause wasthe heavily dust laden air, disturbed from the desert

116 VEHICLE DESIGN

dust by the front wheels, passing with a scrubbingaction between the rear pads and discs. Generally,brake temperatures peaked in the region of 450/500C, but in a parachute failed situation temperatures of800 C were reached, these temperatures were easilycoped with. The high speed wheels were never oper-ated to their true operational limits, and thereforenever achieved the maximum stresses anticipatedfrom both rotational speed and wheel loading. Treaddamage from stone impacts during the second Jorda-nian test series became a potential problem as speedrose to the mid-500's: these damaged areaswould bestress raisers on an increasingly stressed surface ateven higher speeds.

Wheel interaction with the desert surface be-came a dominant feature of the Black Rock operationas speeds rose above 600 mph, and good vehiclecontrol became even more critical as the variations indesert hardness and surface texture over a 13 mile runlength played their hand, particularly as an interme-diate rainy period had changed the desert character-istics. In general, speeds up to 500 mph allowed thedesert to imprint the shapes of the wheel treads, butthrough 600+ mph the desert beneath the wheelsbecame very broken in their passing, possibly due tothe formation of 'impact' shock waves. In the regionof 650-750 mph the desert both beneath and eitherside of the car broke up considerably, probably due tothe formation of large vehicle generated shock waves,those which were not airborne being dissipated by thedesert itself. Beneath the wheels, to a depth whichvaried from 0.75 inch to 4 inches, the desert becamepulverized into a fine dust: it was almost as if at highspeed the jet car ran on a 'fluidized bed' rather thana solid desert, though sensors still indicated thedynamic variations in wheel load. In terms of desertfirmness, miles 7-13 were best whilst miles 0-6 weresofter with the measured mile being a combination ofboth: it was quite possible to feel the difference indesert drag over this length when driving a conven-tional vehicle.

Intermediate rain before the final supersonicruns changed these characteristics, with reducinghardness, and with a particular detrimental effect onmiles 4-6, where the surface became particularlyfriable. A total of 66 runs completed the programmefor the Thrust SSC jet car, from the first tentative 40mph on the Farnborough runway to the final pairwhich created the world's first Supersonic Land

Speed Record at 763.035 mph, (Mach 1.0175), andtaking an intermediate LSR of 717.144 mph on theway. All runs were officially timed by the UnitedStates Auto Club under FIA rules. In the configura-tion used, with the Spey 202 engines the jet car wouldgo no faster, as it could not penetrate the rapidlyincreasing supersonic drag. An engine change to themore powerful Spey 205 engines might have helpedan increase in speed to 800 mph, but the true super-sonic objective had been reached, and it was decidedto leave that mark to those who follow.

Fig 36b: Rear brake

Chapter 6:

Systems development: powertrain/chassis

A decade of patents specifications and company productreleases provides an insight into automotive productdevelopment up to the period of new designs covered in thefirst five chapters. In the area of powertrain and chassis systemsthe trends to reducing both power losses and environmentalpollution are clear in the examples which follow.

118 VEHICLE DESIGN

Engine developments

Performance 'on spec'Cosworth Engineering's MBA high performanceengine, first built as a technology demonstrator, is ahigh power-density unit which develops near maxi-mum torque over a very wide speed range andincorporates many race-learnt techniques.

Having a dry weight of only 120 kg (overalldimensions 536 mm high X 20 wide X 490 long), thepeak power of the MBA at 162 kW at 7000 rpm iscommendable and the maximum torque of 256 Nm isdeveloped at 4500; good in-gear acceleration can beobtained from 4000 rpm, in fact. Being producedindependently of any client programme, consider-able detail is now available on its design and con-struction. The aluminium alloy unit is configured asa 2.5 litre, 24 valve, 90 degree V-6 and is notable forsuch innovations as inlet port throttling and anunusual head and block structure. The block itselfweighs only 26 kg with its 87 mm bore and 70 mmstroke layout. This 1.24 B/S ratio allows the fitmentof large diameter valves for high specific perform-ance but a lower ratio would be used for moreemission-conscious variants. The block has a contra-rotating balance-shaft built into it which, running atengine speed, balances the primary couple inherentwith this cylinder configuration.

This shaft also has a centrifugal oil-separa-tor incorporated with it, Fig 1, as part of the advancecrankshaft ventilation system. Oil is jetted to theunderside of the pistons for cooling at high enginespeeds. The head has pent-roof combustion cham-bers, giving 11:1 compression ratio, but the head-to-block joint is unique and involves angled head bolts.

To induction System

Camshafts are pre-assembled into separate housingswhich simplify the main head casting. Valves are 35mm diameter for the inlet and 30 for the exhaust andhave an included valve angle of 40 degrees. Thebarrel apertures which form the port-throttles are alsoincorporated into the head.

Cylinder block side walls are held in tensionby the angled head bolts while the cylinder wall is incompression by reaction to the bolt load. Solid firerings seal each bore while O-rings seal the water andoil galleries. Cross-bolting of the main-bearing caps,Fig 2, helps to contain costs by eliminating the needfor tight-tolerance machining. Mating horizontalsurfaces on the block and iron caps are first machinedflat then the bolt holes are drilled and tapped. Afterbolting down the caps, dowel holes are drilled in thetwo vertical clearance slots between each cap and theblock. Cross-drilled dowel pins, and then bolts, arethen fitted prior to line boring the assembly. A two-

Fig 1: Vertical section through block showingbalance shaft axis above that of crankshaft

CrawBolt

Fig 2: Cross-bolting of main-bearing caps

POWERTRAIN/CHASSIS DEVELOPMENT 119

stage camshaft drive is featured with helical gear onthe cam nose driving two primary gears which inde-pendently chain-drive one pair of camshafts. Thetwo-stage reduction thus allows smaller camshaftsprockets than usual, which reduces the overall sizeof the engine. Chain life is also extended with thisslower moving layout, made quiet by individualcases moulded in special grade of nylon, Fig 3.

The crankshaft has offset pins to provideeven firing, main and big ends being 50 and 42 mmrespectively. Connecting rods weigh only 0.49 kgand are 128 mm between centres; piston weight, too,is kept down to 0.4 kg. The induction system com-prises a variable-geometry plenum which helps tospread WOT torque over a wide speed band. Twochambers into the plenum individually feed one bankof cylinders; they are linked together by two pipeswith switchable valves controlled by the enginemanagement system.

In a conventional plenum-throttled enginethere is pressure differential at part throttle betweeninlet and exhaust ports. Conventionally there issimultaneous opening of inlet and exhaust valvestowards the end of the exhaust stroke which allows

residual exhaust gas to flow back into the inlet port,the resulting charge reduction lowering NOx emis-sion. An external EGR system would accentuate thisprocess with external pipes. The MBA has a patentedinternal EGR system which circulates exhaust gasesrich in HC; this claims to reduce both NOx and HCemissions. A high performance engine usually re-quires long cam durations and a large valve overlapperiod and the resulting exhaust dilution is greaterthan on a conventional unit. On the MBA the result-ing rough running that this would cause is obviatedby port-throttling which limits the reverse flows. Thedepression created in the inlet port, during induction,recovers after the inlet valve closes, according tospeed and load conditions. As the inlet reopens thereis little pressure differential between inlet and ex-haust ports. The independent throttle mechanism,Fig 4, on the MBA involves a port-throttle upstreamof the inlet valves, the tracts being fed into a commonplenum. Thus, at a given speed and load, degree ofexhaust gas dilution is a function of inlet port depres-sion. Internal EGR is therefore controlled by therelationship between the two throttles, Fig 5.

Cylinder-head section

Head to block joint

Barrel-port throttle

Fig 5: Cylinder head details (above left and right) Fi8 4: Plenum and port throttles

120 VEHICLE DESIGN

Advanced car and truck enginesLotus Engineering's Jewel Project, Fig 6, seeks tomeet some of the challenges of future engine require-ments. It involves a monobloc design to improve heatflow from the head to the main water jacket, thecylinder head having hardened surfaces interfacingwith the aluminium alloy monobloc. Resulting re-duced temperatures for pistons and liners permit asafe raising of the compression ratio for greaterengine efficiency.

A hollow crankshaft saves weight and lowersinertial forces — also helped by the use of metalmatrix composite conn-rods. Corrosion of such partsas water pump and thermostat housings is avoided bythe use of GRP composites; fuel rails, too, are injec-tion-moulded for both lighter weight and better ther-mal properties for resisting fuel vaporization. Camcovers and outer walls of the coolant jacket are alsoof composite construction. A rubber joint isolates themonobloc casting from manifold and sump to reducenoise transmission.

Scania has become the first truck manufacturerto undertake series production of a turbo-compounddiesel engine, Fig 7, with an efficiency of 46%, over10% higher than the best gasoline engine figure.Exhaust energy is recovered in two stages; the firstturbocharger (1) drives a compressor to force moreair into the cylinders while the second is a powerturbine (2) supplying additional power to the fly-wheel (4) through a hydraulic coupling and gear train(3). Power and torque are about 5% higher at 400 bhpand 1750 Nm. There is also a 6 gm/kWh saving inspecific fuel consumption.

At the left of the figure the power turbine isseen downstream of the turbocharger turbine, thelatter being small in relation to mass flow at high

Fig 6: Lotus JewelProject engine

engine speed — where, pressure ratio across thepower turbine being high, it still provides enoughoutput to drive the compressor. At low speed whenpressure ratio across it is reduced, the compressor'spressure ratio is maintained — partly because of thesmall turbine housing. Increased charge pressure atlow speed thus makes it possible to inject more fueland increase torque without air/fuel ratio becomingtoo low. Power turbine is connected to the crankshaftvia a two stage spur gear set and hydraulic coupling.Mass inertia of the power turbine, converted tocrankshaft speed, is about half that of a normalflywheel (gearratio 1:30); the 'soft' coupling reducesthe peak torque amplitudes. The set-up is believed byScania engineers to be a more satisfactory route thana variable-geometry turbocharger, some of whichcontain more than 100 moving parts and are liable toreliability problems. However, it is pointed out thatgreatest advantage comes with engines operatingunder heavy and sustained loads.


Improved engine temperaturemanagement and differentialexpansion controlDuring the cooling cycle of an engine, after combus-tion, there can be an unduly long retention of heat bysome of the components. This heat can flow back intothe incoming air-fuel charge with resultant loss inengine efficiency. The design in Fig 8 thus aims tomake combustion chamber and charge inductionsurfaces store and release heat selectively, to limit thepiston surface temperature and control thermal ex-pansion. The use of sprayed insulant coatings on theinside walls of engine combustion chambers is pro-posed here to manage the heat release from thecombustion process. A low thermal expansion/highconductivity insert is also cast into the piston crownto inhibit differential expansion. An abradeable coat-ing is also sprayed on the piston walls, above the topring, in order to reduce clearance and thereforeenhance heat transfer. Under crown oil-spray coolingis employed, too, together with a dual wall construc-tion for inlet and exhaust manifolds, the net effect ofwhich is to reduce the onset of knock and thereforeallow the use of higher compression ratios to provideenhanced efficiency.

The problem of differential thermal expansionof engine cylinder head and block, in different mate-rials, is said to be overcome in the design of Fig 9. Analuminium alloy head is secured to a cast-iron cylin-der block by extra-long bolts which engage withthreaded bosses deep down in the block. Above thethreaded portions the bolts pass through oil galleriesand are warmed sufficiently to cause the correctlinear expansion to compensate for that of the cylin-der head, between its support faces.

Improved turbochargerwaste-gate control and move toconstant-pressure cycleA simple and reliable turbocharger pressure-control-ler, for providing enhanced operation of the waste-gate valve, is provided in the design of Fig 10 whichpermits standard exhaust bypass operation. The flowcontrol element is positioned within the exhaustbypass conduit and the waste-gate actuator is respon-sive to bypass air pressure for actuating the controlelement. An air pressure control device has an intake

port connected with the intake-air outlet and an outletport providing bypass air pressure to the flow controlactuator. When airflow paths between intake andoutlet ports provides for continuous flow at least oneother inhibits through airflow.

Provision of a sprung element in the connect-ing rod of a piston engine is achieved by a series ofbelleville washers in the design of Fig 11. Theyconstrain a piston within a piston, the inner one ofwhich moves on a steel liner in the aluminium body

Fig 8: Patented temperaturemanagement system by FordMotor Co (GB2293863A)

Fig 9: Differentialexpansion control by RoverGroup (GB2312020A)

Fig 10: Turbocharger waste-gate control byCummins Engine (GB2311556A)

122 VEHICLE DESIGN

of the outer piston. A retainer ring at the base of theliner restricts the movement of the inner piston.Because, after ignition, the first element of the 'stroke'is compression of the springs and thus an increase inclearance volume, there is a drop in cylinder pres-sure, and temperature, in the combustion chamber.As the energy stored in the springs is released afterTDC, although ignition occurs before TDC, engineefficiency is increased because there is no longer anynegative torque occurring before TDC, changing thetheoretical air cycle of the engine to a constant-pressure one.

Engine induction systemsLow-cost supercharging andelectromagnetic valve actuationAn inexpensive vehicle engine supercharger, havingan integral by-pass mechanism, is proposed in thedesign of Fig 12. Of the rotary, positive-displacementtype, it incorporates a duct within its casing tocommunicate with the suction and discharge ports ateach end, for supplying naturally aspirated air to theengine. Rotors also compress the air entering fromthe inlet port on the right to supply the discharge port,to the engine, on the left. The by-pass passage iscontrolled by a valve and actuator on the extremeright of the mechanism. On the extreme left is theelectromagnetic clutch which drives the superchargerbut drive is broken when the by-pass valve senses apredetermined maximum boost pressure and opensthe bypass port.

Long valve opening time, and so adequatecylinder filling at high engine speeds, is among theadvantages claimed for this electromagnetically ac-tuated poppet valve, Fig 13. The armature of the'solenoid' has switching magnets which hold thevalve in open and closed positions. Compressionsprings are positioned between magnets and valve toavoid free-play in both the opening and closingmodes.

Better fuel-spray atomization,integrated air/fuel induction system,fuel injection rethought and storingswirl energyThe design in Fig 14 exploits the advantage that

Fig 11: Constant-pressure cycle pistonmodification by GF Galvin (GB2318151A)

Fig 12: Low-cost supercharging by Tochigi FugiSangyo (GB2301149A)

Fig 13: Electromagnetic vahactuation by Daimler-Benz(GB2312244A)

Fig 14: Better fuel spray atomisation by Ford(GB2312923A)


suddenly vaporized, or flashed, fuel effectively breaksup the spray from a fuel injection nozzle, when the

Fig 15: Air-intakesilencing by Ford (GB2318153A)

Fig 16: Fuel injection rethought by Robert Bosch(GB2295204A)

Fig 17: Storing swirl energy by Ford(GB2299373A)

fuel is subjected to a rapid pressure drop as it dis-charges into the inlet port or combustion chamber.The proposed engine incorporates a heat-exchangerfor pre-heating the fuel, upstream of the injectors.Temperature is maintained at a constant level justbelow the fuel's boiling point and the heating fluidmay be coolant water or exhaust gas. Heating can beassisted by an electrical coil and insulated reservoir.

Efficient engine air-intake silencing with mini-mum space usage around the engine is achieved in thedesign of Fig 15. The intake air-box and manifoldducts are integrated in one unit, the air-box volumesurrounding the intake ducts. An air-plenum andthrottle valve is also integrated into the assemblytogether with the fuel rail delivering to the injectors.

A fundamental problem has existed with directfuel injection into engine combustion chambers. Thisis in the conflict between providing a fuel-rich mix-ture for ignition at the sparking plug yet providing anarrow enough spray cone to avoid wetting thecylinder walls with fuel which would fail to vaporizeand result in unwanted hydrocarbon emissions in theexhaust. In the design of Fig 16, a poppet valve typeinjector provides a narrow conical spray but has asubsidiary conical arc sprayed towards the sparkingplug. This is achieved by a recess in the annular wallof the injector downstream of the valve seat.

In an engine designed so that two intake portbranches supply each inlet valve, the first branchbeing connected to a common plenum of an airsupply manifold while the second is connected to acommon plenum of a second manifold, this secondmanifold acts as a stratified charge storage arrange-ment as covered by an earlier patent by Ford. Now thecompany have extended this concept to lean burnengines so as to improve charge preparation andcombustion quality, Fig 17. Air drawn from the firstbranch into the second swirls while in storage andretains kinetic energy for the next intake stroke.When the intake valve of the left hand cylinder isclosed air is drawn through the lower throttle butter-fly into the dotted line drawn duct under the action ofthe intake depression caused by the adjacent right-hand cylinder as its valve opens, there being a tangen-tial swirl connection into the second plenum, down-stream of which fuel is injected and upstream ofwhich the plenum duct is shaped to retain swirlenergy. The upper of the two butterfly valves may beopened at high engine loads.

124 VEHICLE DESIGN

Refinement and reduced

emissions

More on the Sarich 2-stroke and aRover K-series developmentThe promise of greater fuel economy using two ratherthan four stroke engines has been given a new interestby the Australian Sarich engine which has caught theattention of the volume builders. Sarich has donemuch to advance the cause of two-strokes by allayingfears of poor emissions performance by devising theacclaimed system of injecting fuel-air mixture intothe cylinder. The metering and injection system isshown in Fig 18. Fuel is metered through chamber (a)via port (b) and compressed gas is introduced via anair-port (c) to displace the fuel and deliver it to theengine. Crucial phasing of the valves is controlled toensure fuel inlet and outlet (d) valves are closedbefore the air one opens and that any residual gas isexpelled before the next charge. Gas inlet to thechamber is controlled by valve (e) opening at a higherpressure than it requires to close the outlets.

A stretched version of the Rover K-series en-gine features variable valve timing in Fig 19. So-called 'damp-liner' technology has been used involv-ing bore walls just 3 mm thick and a water coolingjacket of just 0.65 mm. An extra long crank throwthen brings swept volume to 1.8 litres. The VVTmechanism continually varies the inlet cam period to

optimize power. An eccentric disc controlled by theEMS alters the phasing of camshaft to crankshaft soas to lengthen the inlet valve opening period above400 rpm. A maximum power of 143 bhp at 7000 rpmpropels the 2359 Ib vehicle (MGF) at its maximumspeed of 130 mph.

Fig 18: Improved Sarich 2-stroke, in PatentGB2210413A

Fig 19: VVT for K-series


Variable valve timing made easy,enhanced fatigue life for valve gearand variable geometry engine intakeBy using a lateral displacement device for the chaindrive to an engine valve operating mechanism, aphase change can be obtained between the driver anddriven sprockets in a system announced by SachsIndustries, Fig 20. Engine oil pressure is used toeffect the displacement via a chain tensioner device.A check valve, shown in the sectional view of thetensioner, controls the operating pressure and a sole-noid valve connected to the pressure cylinder causesthe device to change from chain tensioning to dis-placement mode. The solenoid is switched by theengine management system and in the arrangement

Fig 21: Enhanced fatigue lifefor valve gear by Mercedes-Benz (GB2297805A)

shown at A around 30 degrees of crankshaft angledisplacement is involved in the phase-change. In the3 or 4 position arrangement at B, both camshafts canbe controlled and, by using a proportional solenoidvalve, a possible future application may be continu-ously variable cam-phasing.

A valve drive system has been suggested whichcombines long fatigue life with maximum stiffness ofall its constituent elements. In Fig 21 an 1C enginecamshaft is supported by a housing comprising pil-lars and beams which do not require complex ma-chining of the cylinder head. A short bearing intervalensures avoidance of camshaft bending vibration andthe beams joining the bearing support pillars are onlyinterrupted by cut-outs for the extra short rockers andthus form an unusually secure mounting for therocker shafts.

Obtaining induction ram effect at more thanone 'resonant' speed is the object of the design in Fig22. The carburettor or fuel-injection choke tube isconnected to a plenum chamber in a barrel rotatableby a motor geared to engine speed. The effectivelengths of the intake and outlets vary with barrelposition by their formation, in part, by grooves in thebarrel wall.

Fig 20: Sachs variable valve timing

Fig 22: Variable geometry intake by Tickford, inPatent GB2205609A

126 VEHICLE DESIGN

Economical flywheel to crankshaftconnection and secondary engineforce balancer for motorcycleA more cost-effective connection between engineflywheel and crankshaft is possible, without loss inreliability, with the design in Fig 23. It uses a collar,held by an expansion screw, in a concentric openingin the crankshaft. Dog teeth on shaft and flywheelform the connection, the joint being made firm bytensioning of an axial spring acting on an expansionscrew where the two parts mate. The flywheel has acollar which extends into the crankshaft opening, thecentre of the collar having a hole through which theexpansion screw operates.

Normally there is difficulty incorporating a fullLanchester-type harmonic balancer into a motorcycle engine because of the high rotational speeds

involved. In the design of Fig 24 , a compromise isreached in which a large, crankshaft-mounted, gear-wheel drives two smaller co-planar gears in oppositedirections, one by a further countershaft gear.

Low emission CVsInitiatives taken by MAN for diesel engine pollutionreduction include the air-injection system shown inFig 25 for dealing with visible smoke on initial take-off and subsequent acceleration before the turbo-charger achieves full compression. Normally fuel isnot completely burnt under these conditions as theengine is not supplied with enough air — so an airreservoir is introduced which is fed from the com-pressor. The injection system comprises a pressurepipe with solenoid valve and non-return valve in thecharge-air line at the inlet to the air distribution pipe.By means of an electronic controller, throttle pedaldepression opens the solenoid valve to inject air for

Fig 23: Economical Fig 24: Balancerflywheel to crankshaft system by Triumphconnection by Fichtel & Motorcycles in PatentSachs (GB2301166A) GB2186914A

Fig 25: MAN diesel pollution control


a 0.7 second period. Closure of the non-return valveprotects flow from the turbocharger while the ECUreleases a matching quantity of fuel for injection. Thesystem is used on the company's NL202 and NG272low-floor buses. The company has also developed itsparticulate filter technology in which both duplexand full-flow arrangements are used to overcome theproblems of filter clogging with deposits which can-

Fig 26: Filtering diesel particulates by Mercedes-Benz

Fig 27: Speeding engine warm-up, by Ford,covered in Patent GB2199368A

Fig 28: Quicker catalyst light-up time by RoverGroup (GB2316338A)

not be burnt off in conventional layouts becauseexhaust gas temperature from low-consumption en-gines is too low. In addition, oxidiszing catalyticconverters are being developed for exhaust gas post-treatment.

An exhaust filtering system for dieselparticulates is now offered on Mercedes bus chassis.The so-called ceramic candle type filter featurescatalytic regeneration. The system, Fig 26, complieswith emission limits for urban buses which came intoforce in the US during 1991. The company is reportedto have rejected the philosophy of developing cata-lytic control systems originally engineered for spark-ignition engines, on the grounds that diesel emissioncontrol needs solutions with less flow resistance,proneness to blockage and better thermal and me-chanical resistance in the harsher CV environment.

Speeding engine warm-up, quickerlight-up time for denox converterand use of scotch-yoke crankExhaust ducting cast in the cylinder head is used inthis design proposal, Fig 27. The ducts allow alter-nate paths for the engine exhaust according to posi-tion of two-way valves. As well as warming up theinlet manifold during initial running of the engine,exhaust gases also warm up the engine coolant andlubrication systems.

Faster catalyst warm-up time from engine start-up is the objective of the design of Fig 28 whichinvolves providing excess fuel and air to enter theconverter for part of the combustion cycle. A fuellingdevice controls the exhaust gas entering the catalyticconverter such that a combustible mixture is intro-duced to enable the converter to more quickly reachlight-off temperature or regain it if very cold operat-ing conditions cause the catalyst to 'go out'.

The Collins CMC scotch-yoke engine, Fig 29,has attracted considerable interest. Exhibited re-cently by consultants Emdair who are R&D contrac-tors to the Australian builders, the engine has in-verted-tee cylinder formation in the 2-litre two-stroke version shown here. Compact size is thanksmainly to the scotch yoke mechanism joining thepistons to the crankshaft. It has been calculated thata vehicle designed to exploit the lower package sizeof the engine would achieve a 10% fuel saving overa conventional design.

128 VEHICLE DESIGN

Drive and steer systems

Transport of the future — guidedlanes or electric/flywheel hybrid carpropulsion?Tribus, Fig 30, has been described as being to thetrolleybus what light-rapid-transit is to trams. But italso applies to both goods and passenger vehicles —to urban and inter-urban traffic. A segmented barpantograph collector overcomes the traditional limi-tations of trolley booms. This results in a multi-lanehigh speed equivalent to a trolleybus which couldhave attractions both for commuting and dense traf-fic motorway driving. The overhead wiring structureis vastly simplified from traditional trolleybus lay-outs and the ability to 'jump' from lane to lane, andthrough junctions, is made possible by reserve energyprovided by on-vehicle fly wheels and/or hybrid elec-tric/petrol drive systems. On the three lane motorwayinstallation shown, only the two inside lanes wouldtypically be electrified. Inset is shown how two ormore elements of the segmented pantograph bar arealways in contact with overhead feed cables. Theoriginators are Lawrence Designs, 40 Lower BroadStreet, Ludlow, SY8 1PH.

The US company American Flywheel Systemsis claiming ranges for electric cars of 300-600 milesagainst the 50-100 miles which is representative ofexisting battery-electric technology. The AFS 'me-chanical battery', Fig 31, stores kinetic energy invacuum-enclosed rotors running at high speeds onmagnetic bearings. The charge current causes therotors to accelerate up to speed and energy is drawnfrom the spinning windings by the unit acting as agenerator. The technology is made possible by newmaterials for the fibre windings and the magneticbearings. The vacuum housing is shown at (a), fibrewindings at (b) and stationary shaft at (c); counter-

rotating rim wheels are at (d), spoke tubes containingthe magnets at (e) and magnetic bearings at (f) — (g)and (h) being the pick-up coils and end-bell respec-tively.

Fig 29: Collins scotch-yoke engine

AFig 31: Flywheel battery

First two lanesonly electrified

Fig 30: Guided lane system


Fig 32: Sure-fire gear engagement by Mercedes-Benz (GB2308165A)

C

Fig 33: Multi input/output gearbox byJCB Transmissions(GB2304834A)

Fig 34: Rapid-actuation diff-lock byTochigi Fuji Sangyo(GB2305224A)

Ensuring sure-fire gear engagementand multi input/output gearboxInertial effects which might impair proper gear-selection in a change-speed linkage, between shift-lever and selector forks, are negated in the design ofFig 32. An extrusion lever with an inertial mass at itsend is linked by a ball-jointed pull-rod to the gear-change lever on the selector shaft. The geometry ofthe linkage is such that pivot arm of the ball-joint, onthe extension-arm, to the selector shaft is larger thanthat between the ball-joint and the arm's own pivot-point. Also the pivot arm between the ball-joint andselector shaft axis on the change-gear lever is largerthan that between the hinge-point which connects tothe shift-lever, and that lever's pivot-point, on theselector shaft axis.

An additional transmission path, providingfurther gear ratio, is the objective of the design of Fig33. The first input A has the conventional outputwhile a second input B has a mechanism C associatedwith it, and a common gearwheel D, which allowsincorporation of part of the change-speed train of themain gearbox to be used with the secondary transmis-sion path which has output to a transfer drive at thebase of the assembly.

Rapid actuation diff-lock, improvedracing clutch and automatic driveselectionThe differential housing in Fig 34 is turned by thefinal drive gear and contains a pair of auxiliary drivegears, engaging their respective pinions. These rotatein bearing apertures within the housing. A lockablepart A is coupled to a differential part, turnable in onedirection with respect to the housing. A lockingelement B also turns with the housing and a couplingmechanism C is located between locked and freeelements to block rotation of the differential, oper-ated by the adjustable member D. A cam mechanismE increases the coupling force.

Avoiding undue wear in the slipping of highperformance car clutches is the objective of thedesign in Fig 35. The main, driver-disengageable,clutch is supplemented by a smaller, belleville-spring-loaded, clutch between the drive plate and the splinedgearbox input shaft. The second clutch is arranged toslip at a higher torque than that of the main clutch,

130 VEHICLE DESIGN

which is of a multi-plate carbon-carbon type. Be-cause the high torques which cause slipping of thesecondary clutch are only applied for brief periods,little heat is generated.

Power transmission to the front or rear axle ofa vehicle can be made a function of the speeddifference between the front and rear wheels but, thusfar, the necessary mechanisms have been unwieldy.In the design of Fig 36, a compact drive splittingmechanism is devised offering considerable freedomof location on the underside of the vehicle. A trochoidalgear pump is mounted between a shaft and co-axiallyrotating cylinder, each connected respectively tofront and rear axle prop-shafts. A piston slides in thecylinder in response to pressure generated by thepump to actuate a clutch which locks front and reardrive together.

Easy-change CV-UJ assembly,Better performing plunge joint andbetter CV-joint packagingEase of replacement of constant-velocity universaljoint assemblies is considerably improved by makingthe hub and joint housing members as separate units,Fig 37. The hub comprises a flange portion, to whichthe road-wheel is bolted, and an integral body sup-ported by hub-bearings for which the body forms theouter race. Hub and joint housing each have interfac-ing conical surfaces as well as an interconnectingsplined joint. A spigot on the joint housing has aprojection on it which is deformed on assembly so asto lock on to the conical surface of the hub.

Attempts have been made to reduce the plungeresistance of tripode universal joints under highinstalled angles by the use of both inner and outerrollers mounted to the tripode trunnions, each having

Fig 35: Improved racing clutch by AutomotiveProducts (GB2294300A)

Fig 37: Easy-change CV-UJ

assembly by GKN Automotive

(GB2303428A)

Fig 38: Better performing plunge joint by NTNCorporation (GB2299393A)

Fig 36: Automatic drive selection byDaihatsu, covered in PatentGB2207208A


spherical outer surfaces and cylindrical inner ones.Although induced thrust is lower than in earlier typesfurther reduction is limited by the tendency of theouter rollers to follow the inner rollers because offriction between them with increase in both contactstresses and rolling resistance. In the arrangement of

Fig 39: Better CV-joint packaging by Lohr andBromkamp (GB2295365)

Fig 40: Balanced torque triaxle drive

Fig 41: Sophisticated auto-steer for trailer by GWMitchell (GB2315471A)

Fig 38, the inner surfaces of the outer rollers are suchas to direct a load component parallel to the axis ofeach trunnion.

By offsetting the centre of the CV joint out-wards of the centre plane of the front wheel bearing,several advantages have been achieved in this inven-tion, Fig 39. A longer drive shaft, resulting, meansless angularity on bump and rebound. Since the innertracks of the wheel bearing lie axially adjacent to theouter running grooves in the outer member of the CVjoint, bearing performance is unaffected by torquetransmitted and the overall bearing diameter can bereduced. Finally the CV joint can be assembled fromthe outside into the hub member, which doubles asouter race of the CV joint and inner race of the wheelbearing.

Balanced torque triaxle drive,sophisticated auto-steer for trailerIn order to overcome the problems of uneven torquesplitting between the three axles of a triaxle drive, thedesign in Fig 40 by GKN Axles proposes the use ofa spur gear epicyclic differential unit at the point oftorque input to the bogie. This is designed to splittorque unevenly, passing some 67% of the inputtorque down a through shaft inside another tubularshaft which conveys the remaining 33% to the firstaxle inter-wheel differential unit. The initial 67% canthen be split evenly between second and third axlesin the normal manner.

Automatic steering of the leading and trailingaxles of a three axle trailer bogie is possible, in thedesign of Fig 41, in response to the relative move-ment of the main chassis with the bogie suspensionsub-frame, a change in direction of the steering beingeffected with just one movement of the steeringmounting plate. The movement of the steering mount-ing plate, relative to the main chassis between itsoutermost positions, is such that the line of action ofthe joining-ends of the primary link crosses the axisabout which the main chassis rotates. The leadingand trailing axles are pivotable with respect to thetriaxle subframe, a linkage mechanism coupling eachof the steerable wheels to the steering mounting plateon the main chassis. The mounting plate rotatesbetween two positions which govern the direction ofsteer-angle.

132 VEHICLE DESIGN

Wheeled tanks challenge tracklayersand more efficient engine-coolantairflowA challenge to tracklaying armoured fighting vehi-cles was made by Timoney Technology of Ireland ina presentation to Autotech, Fig 42. Arguing againstthe assertion that wheeled vehicles are more vulner-able than tracked ones in a combat situation, theauthors argued that an 8 X 8 off-roader could oftenkeep going with one wheel station out of action. Anotable feature is overall height of just 1.3 metres tothe turret ring, some 500 mm lower than othervehicles of this category. Axles are fitted with in-board hydraulic disc brakes and have differentiallock facility. Patented wheel hubs have a one-piecestub-axle casting with lugs to carry the wishboneball-joint bearings. The planetary gear system is also

inboard of the stub axle and the ring gear is attachedto and rotates with the hub housing — importantlypermitting a small diameter rotary air seal for thecentralized tyre inflation system. Suspension is of thedouble-arm type with two springs mounted on thelower wishbone, resulting in low overall profile andminimum hull intrusion. Suspension movement of400 mm is supplemented by high deflection of thelarge tyres. Maximum speed for the 24-31 tonnecombat weight vehicle is over 100 km/h.

Reduction in back-flow of air drawn through avehicle engine coolant radiator, by the fan, is theobjective of the design in Fig 43. The cowl whichextends backwards from the radiator, to the fan,incorporates a C-shaped scoop facing the clearancearound the fan. Back-flow is thus inhibited by turningit back on itself to create eddies within the fan-bladetip vortex region.

Fig 42: Wheeled tanks challenge tracklayers

Fig 43: More efficient engine-coolant airflow byRover Group (GB2311562A)


Suspension development

Transverse spring compositesuspension and optimizingunsprung mass with wheel travelA transverse single leaf spring made from polymercomposites forms the lower control arms for thewheels and hubs in the suspension system design ofFig 44. Where the spring attaches to the centralmounting it is in the form of an inverted dihedral andremains clamped as such even after the normal loadof the vehicle has deflected the outer arms of thespring into an upwardly inclined attitude.

In the suspension configuration for drivenwheels of Fig 45, part of the mass of the transmissionunit is supported as sprung mass by the body. At thesame time, vertical movement of the transmission isallowed so that the wheels can also travel verticallyover an increased distance before the universal jointsreach their angular limits. The suspension arm foreach driven wheel is connected to both sprung andunsprung parts of the vehicle while drive to thewheels is through articulating shafts. During motionof the suspension, vertical motion of either of thewheels will be transmitted through the respectivearm to produce a smaller vertical movement of thetransmission unit.

Advanced suspension linkageActive rear axle kinematics is the name given byBMW for its rear suspension design on the 850icoupe, Fig 46. As well as providing anti-squat andanti-dive, wheel-camber is adapted to reduce tyrestrain at high speed and roll-steer is built-in whichachieves load reversal reactions. As well as fourwheel control links, a fifth joins two of the others tomodify their relative motions. Two lower and oneupper transverse link form the 'wishbones' while atrailing link provides fore-aft location. This link hasa secondary connection via an intermediate link tothe upper transverse link. Coil-spring and damper are

Fig 44: Transverse spring compositesuspension by BV Booker in the USA,covered in Patent GB2202498A

Fig 45 :Optimizingunsprung masswith wheeltravel by RoverGroup(GB2302066A)

mounted adjacently on the rear wishbone. The wheel-carrier pivot is above and ahead of the wheel-axis, toachieve anti-dive/squat. The intermediate (fifth) linkis a strut which transfers braking torque on the wheelcarrier, through the upper 'wishbone' to the trailinglink. Because the strut lower pivot has less velocitythan the wheel-carrier pivot on the trailing arm,during vertical travel of the wheel, this velocity isalso seen at the upper wishbone. This causes thewheel carrier to rotate more slowly than the trailinglink about the wheel-axis, and twisting of the wheelcarrier on braking is suppressed without losing thehorizontal compliance in the anchorage bushes of thediff-carrier at the root of the transverse links. The linkalso compensates for horizontal forces on the wheeleither side of the vehicle so no swivelling of thewhole suspension, with the diff-carrier, takes place.The elasto-kinetic function arises from the interac-tion of the anchorage bushes with the linkage geom-etry. In braking, for example, the two links formingthe lower wishbone are subject to differential tensionand compression. At the same time the anchoragebush of the trailing arm yields. Transverse linkmotions are such as to ensure that resulting motion ofthe wheel carrier is purely horizontal, without caus-ing steer effects as the wheels move vertically. Withthe short wheelbase of the coupe compared with thesaloon, and the comparatively high driving torques,smooth behaviour under load reversal conditions hasto be ensured. This is helped again by the design ofthe trailing arm anchorage. At high lateralaccelerations, wishbone links are distinctly skew tothe body of the tilting vehicle. With load reversalcaused by sudden removal of driving torque, the diff-carrier swivels due to the resilience of its mounts.Simultaneously it puts the pivot point of the upperwishbone link within it, horizontally, and the front/rear lower wishbone links are displaced by (fv) and(fh) respectively. Tilt of the wishbone also causeslateral displacements of the pivot points (rv) and (rh),causing understeer in both wheels. This effect is only

134 VEHICLE DESIGN

Fig 46: BMW 850isuspension

achieved because the suspension of the trailing linkis independent of that of the diff-carrier from whichthe transverse links pivot.


Improved suspension geometrycontrol, avoiding suspensioncompliance conflict/steer fight inbraking/accelerating and smootheraction for suspension strutThe desire to change from rigid beam axle to inde-pendent suspension on vehicle categories such as4X4 sports/utility vehicles may be restricted by con-cerns for loss of accurate suspension geometry, par-ticularly when an off-centre differential is required toclear an engine sump and unequal length drive-shaftsare involved. In Fig 47 a compact form of IPS isproposed. Tubular members which surround the drive-shafts are pivotally connected to the hub carrier unitsand chassis-mounted differential casing in a 'wish-bone' arrangement. The wishbone length is maxi-mized, by the position of the pivots, to give bettergeometric compromise.

A torsion bar front suspension system for avehicle which is simple in construction, and yet does

Fig 47: Improved suspensiongeometry control by GKNAutomotive (GB2295988)

not result in bending of the torsion bar when thevehicle is subjected to lateral loading, has beenachieved in the design of Fig 48. By ensuring thetorsion bar axis is at a small angle to the axis of thelower suspension arm fulcrum and laterally dis-placed from it, appropriate values of La, Lb, Lc, Sand 0 can be chosen so that sufficient suspensioncompliance is available in the fulcrum bushes with-out any bending moment being applied to the torsionbar. The spring plate connecting the bar to the arm isslender enough to be flexible in the fore-aft direction.

Reduction of the steer effect in braking isclaimed for this suspension configuration, Fig 49, forthe steered wheels of vehicles. Compliant bushes, Band B', normally permit the suspension arm to rotateabout an axis Am as the road wheel rises and falls butthis can change to either A or A under appropriateloading. During braking or acceleration the angle 6and the compliance of the bushes allows the suspen-sion arm to turn in the horizontal plane and compen-sate for steering displacement of the road-wheel hub.

Reduction in ride harshness is achieved in thisindependent wheel suspension linkage configura-tion, Fig 50. The centre portion of the spring-damperstrut is used as an anchorage for the anti-roll bar, alink from which is angled to the axis of the suspensionstrut in such a way that transverse reaction loads fromthe ground-level cornering forces are balanced byloads induced in the anti-roll bar so that sidewaysdeflection of the damper tube-and-rod is minimized.

Fig 48: Avoidingsuspensioncompliance conflictby YorozuCorporation(GB2294668A)

Fig 49: Avoiding steer fight inbraking/accelerating by RoverGroup (GB2311499A)

Fig 50: Smoother action forsuspension strut by Rover Group(GB2306411A)

136 VEHICLE DESIGN

Fluid-actuated anti-roll control, non-stick front forks and freer movingbogie suspensionLower weight and greater compactness is said to arisefrom the use of this fluid-actuated anti-roll system,Fig 51, which claims to achieve a high degree oflateral stabilization. Hydraulic actuators act on theupper ends of telescopic suspension struts; the actua-tor pistons are hydraulically linked in a way thatmotion in one is mirrored in the other. Excessive loadon one suspension unit is thus transferred to theopposite side unit varying according to vertical sus-pension travel.

Overcoming the problem of high friction in sealsystems used on the front forks of motor cycles is thesubject of the design in Fig 52. The usual telescopicfork arrangement gives way to a twin-wishbone sus-pension arrangement. Universal joints at the outerends of the wishbones allow steering motions as wellas vertical suspension travel. A pivoting triangularframework is also used to transfer steering torquefrom the handlebars to the forks which support thefront wheel.

Less chance of bearing seizure at opposite endsof the walking beams of a tandem bogie suspensionresults from this design, Fig 53. Forked axle bracketsconnect to the beam ends via exposed bolts withbushes and convenient stroke mechanism — whichalso lowers the vehicle to the ground on electric jacks.Steering involves the use of a highly flexible steeringwheel including a fork or ball used to give the user astable support. A voice command system is used fora number of the secondary controls.

V

Fig 52: Nonstick front forks by NH Hossack(GB2207645A)

Fig 53: Freer moving bogie suspension by the USBoler Company in Patent GB2192596A

Fig 51: Fluid-actuated anti-roll control by AMGMotorenbau & Entwicklung (G B2315716A)


Fig 54: Easy prestressing for swivel pin bearingsby Claas KGAA (GB2316050A)

Fig 55a: Uncomplicatecsteering-castor adjustnnby Daimler-Benz(GB2315469A)

Fig 55b: Steering column immobiliser byMarshall Wolverhampton (GB2303108A)

Fig 56: Tiller steering by Kazunaga Morimoto inGB2293143A

Easy prestressing for swivel pinbearings, uncomplicatedsteering-castor adjustment and asteering column immobilizerAn unusual arrangement of steering swivel pins onthis steer-drive axle for industrial vehicles, Fig 54,allows prestressing of the taper roller bearings to becarried out without difficulty. Outwardly facing swivelpins are used in a design which is said to be lessexpensive than normal arrangements of comparableperformance. Forked ends of the axle body, contain-ing the pins, engage with forked ends of the hubcarrier. Each swivel is in the form of a circular pinprovided with central collar and constrained at oneend in a bore of the axle body fork. One of thecorresponding bores in the hub carrier fork has aninternal thread into which a cover is screwed with aninner collar bearing against the outer race of the taperroller bearing.

The problem of providing degrees of castoradjustment without weakening the integrity of wheellocation, or involving heavy expense, is alleviated inthe design of Fig 55. A steering ball joint incorporatesa wide flange which overlaps the transverse link towhich it is connected and there is a connecting dowelwhich pivots one part with the other. The parts areclamped together through cleverly profiled holes forthe securing bolts. These allow three different angu-lar positions between the joint and the link so as toprovide stepped adjustment of castor with secure fitwhen the clamping bolts are tightened. A compara-tively modest torque can be used to lock a steeringwheel/column against rotation by using a high ratiogear pair between the column and the clutched lock-ing device, Fig 55b. A member which has coded inputresponse to a key or other immobiliszer controls theaction of the clutch, which is based on teeth cut intothe shaft of the pinion of the gear pair.

Back to tiller steering and an anti-dive motor cycle suspension?As the concern for driver safety increases, the veryconcept of a circular steering wheel attached to arigid column will be questioned. This is the view ofan invention, Fig 56, which replaces the wheel witha laterally moving handle shaped to optimize protec-tion of the thorax region, on impact. The handle isconnected to a rack-and-pinion by deformable arms,

138 VEHICLE DESIGN

and an hydraulic valve, which transfer the side-to-side steering motion into swivelling of the roadwheels.

Two fore-and-aft suspension arms form a four-bar linkage which gives anti-dive suspension geom-etry to the front wheel of a motor cycle when braking.In the arrangement of Fig 57, geometry is such as toallow positioning of a steering arm which articulateswithout steer fight on vertical travel of the suspen-sion.

Control strategy for 4-wheel steer,self-steering in forward and reverseand a necked hub memberLotus have released more information about theactive rear steer system they have under development— which they say is an extension to their activesuspension work using closed loop control strategies.This allows steering to respond to both driver inputsand external disturbances. Vehicles thus equippedwould therefore respond to crosswinds or split brak-ing in a controlled manner. There is also less sensitiv-ity to vehicle load and tyre performance — unlikeopen-loop and predictive-type strategies which canonly be optimized for specific operating conditions.The system, Fig 58, is said to operate at normalpower-steering system pressures and work is underway on production-intent actuators and controllers.

To overcome the limitations of existing self-steering axles, this design by an Italian inventor, Fig59, comprises a tubular member which slides over theaxle while road wheels pivot directly on the frame ofthe vehicle. Two tie-rods positioned on either side ofthe axle have their ends linked eccentrically to thewheel hubs. Thus, while reversing or moving for-ward, actuators are caused to restore the tie rods andtherefore the wheels to their neutral position.

Improved heat insulation for the tyre and greaterspace for the brake actuator cam arise in this hubdesign, Fig 60. The tapered hub section and neckingbetween the bearings produce the desired configura-tion.

Fig 59: Self-steeringsystem by SansaviniBertozzi, covered inPatent GB2202811A

Fig 57: Anti-dive suspensionby Elf France, in PatentGB2201642A

Fig 58: Lotus 4-wheel steer controlFig 60: Necked hub by Trailor inPatent GB2192959A


Fig 61: First electronic booster

E-Booster Modified Basic Unit LSC 80 (10")Master Cylinder 22.2CV/CVFunction I Automatic BrakingFunction II Automatic Booster Operation

Input Rod ForceInput Rod SpeedKneepoint 80 barResponse Time 200msRelease Time 180 ms

Function III Variable Ratio - PedaloperatedInput Rod Force 1400 NInput Rod Speed 0 - IOO mm/sKneepoint 125 barResponse Time 170 msRelease Time 180ms

Fig 62: Initial booster + proportional valvespecification

Fig 63: Variable ratio characteristic (full-linebase ratio; dashed line medium ratio; chain linehigh ratio)

Braking systems

Electronic brake actuation systemLucas Varity have determined that the typical driveris usually inhibited against applying optimum pres-sure to effect an emergency stop. The company aretherefore advocating the use of an electronic actua-tion system (EAS) based on the electronic boosterseen in Fig 61 that has been replacing the fast-vacuum booster, fitted to many cars, and which waslimited to providing assistance only at a fixed ratioand often reacted too slowly in emergency.

A proportional control valve has been devel-oped such that the output stroke is proportional to theinput control current signalled through the brakepedal. A control loop is partially closed via an ECUwhich measures output/input force ratio and com-pares it with a vehicle-specific algorithm. An initialspecification was as shown in the table of Fig 62 andinvolved electronic booster control superimposed ona mechanical booster. Performance curves for aseries of possible ratios are in Fig 63.

A parallel development of the long-stroke (LS)booster meant that the benefits of electronic controlcould be applied to heavier cars and replace tandembooster arrangements which tend to be restricted toeither high-performance cars or heavier van deriva-tives. The company is concentrating on the develop-ment of the LSC 115 T tandem power unit, Fig 64,which has an integrated electronically proportioningsolenoid control valve. Shown enlarged in Fig 65,this valve is seen to be an electrical analogue of theproven servo control valve, but with input/outputratios compared electronically rather than by rubberreaction disk.

The company believe the full potential of suchsystems can only be realized when legal insistence onmechanical back-up is dropped and 100% reliabilityof the electronics can be guaranteed. Money savedcould be used to incorporate other electronic fea-tures, Fig 66, such as ABS and engine management.The ECU would be able to compare actual vehicledeceleration with the theoretical value based on agiven booster output force, and thus forewarn ofbrake-fade. The ECU could also relate engine torqueto achieved acceleration for assessing loading on thevehicle so that the system is informed of prevailingroad gradient. In integrating ABS, the booster wouldprovide the energy source and the combined system

140 VEHICLE DESIGN

ECUs could help to create the next stage of automaticbraking, in controlled traffic conditions, involvingintelligent cruise control. Functions such as tractioncontrol, hill-hold and variable pressure boost forABS could be incorporated.

The first stage of the project will be seen onsome Mercedes cars early in 1996 as 'brake assist-ant'. For this application the vacuum chamber of aconventional vacuum booster is equipped with theMercedes position sensor. This tells the ECU that thebooster piston has travelled a given distance in lessthan a pre-defined time and switches on the solenoidvalve. Atmospheric air then enters the booster work-ing chamber to amplify driver effort with maximumavailable servo power. Without this device fulldecelerative advantage with ABS is lost. In an activestability control feature, the ECU helps to controlside-slipping out of a corner by selectively applyingbraking force to one of the outside wheels, generatingbraking force from the booster and modulating it bythe ABS. In stage two, hill-hold will be added suchthat brake pressure will automatically be appliedwhen a vehicle stops on a hill and automaticallyreleased when it pulls away. This will involve theproportional solenoid valve and the booster generat-ing the necessary braking pressure by metering the airintake into its working chamber. Such metering isalso essential for automatic braking and adaptivecruise control, ACC. Current cruise control, it isargued, can suffer a lack of sufficient engine decel-eration on steep gradients such that the vehicle gainsspeed; EAS can supply precisely metered brakingpressure to prevent this. Beyond this, EAS can gen-erate pressure for ACC so that a vehicle is kept at asafe distance from the one ahead, without having torely on engine-braking which might prove inad-

equate. For stage three the problem of varying brakepressure requirement with degree of vehicle payloadis tackled. Here, not only is brake booster pressuremetered but also the pressure level boosted propor-tionally to the pedal force (measured by a sensor onthe piston rod) applied, so that constant decelerationis obtained with a constant pedal force irrespective ofpayload.

Fig 64: LSC 115 T with integral solenoid valve

Fig 65: Enlargea view of valve

Fig 66: Features of EAS 3 with (right) interaction of ABS, EAS and EMS


Fig 67: Brake apportioning for solo or coupledmode by Daimler-Benz from Patent GB2146720A

Fig 68: Electromagneticbraking by Siemens(GB2312260A)

Fig 69: Auto-adjusting electro-brake by Mercedes-Benz (GB2315527A)

Fig 72: Brake boosterby Delphi France(GB2312718A)

Fig 70: Fail-safe electricbrake actuator by DelphiAutomotive(GB2305478A)

Fig 71: Fcat-safe brake actuator by Mercedes-Benz(GB2307529A)

Brake apportioning for solo orcoupled mode, electromagneticbraking, auto-adjusting electro-brake and fail-safe electric brakeactuatorsA car braking master-cylinder is 'tandem-like' inconfiguration and the pressures in front/rear wheelbrake chambers apportioned according to vehicleload. This effect is altered according to whether ornot a trailer is coupled, in the design of Fig 67, bymeans of a 3/2 way solenoid valve.

A means of applying braking selectively toindividual wheels is provided in the design of Fig 68.The brake actuator is rigidly mounted on the disc-brake calliper and uses electromagnetic operation.The actuator comprises an electric motor, the arma-ture spindle of which is threaded so as to producetranslatory motion/force against the pad pack-platefor rotary motion of the armature.

An electrical brake actuation system is coveredin the design of Fig 69 which has the advantage thatbraking fluid does not have to be relied upon tobalance out brake-pad wear. The electromagneticactuator comprises a spindle axially driven by anelectric motor via a threaded roller drive with theaxial force boosted by a lever mechanism in transfer-ring it to a pressure plate acting on a brake piston. Amechanical correcting device is incorporated forpad-wear balance.

An indication of the applied braking force issupplied to the driver in this electric, or electro-hydraulic, brake actuator which is backed-up byhydraulic brake application upon detection of fail-ure. A sensor behind the brake pedal detects anyelectrical faults and triggers the adjacent hydraulicsystem into actuation, while providing a reactionforce at the pedal. The hydraulic unit has a throughbore, to the master cylinder, containing two pistonswhich can slide relative to one another, Fig 70.

Only a relatively small movement of the brakepedal is necessary in the design of Fig 71, in the eventof hydraulic pressure failure, before mechanical cou-pling of piston rod and piston takes place within themaster cylinder. Mechanical coupling is achievedbetween two co-axially sliding members when thelength of the piston stroke exceeds a threshold value.A locking catch, at A, is spring-loaded in the openposition normally but is closed by the action of a camwhen the stroke exceeds the threshold.

142 VEHICLE DESIGN

Easy-assemble brake booster,compact integration of clutch servoactuator parts and set-speed down-hill brakingIn the Fig 72 design a booster housing having frontand rear walls is held together by through tie-boltswhich also form the mountings to a vehicle bulkheadand a means of securing the brake master cylinder tothe housing. At the master-cylinder side of the booster,the outer wall of the housing is assembled against asplined collar which also gives the booster a measureof controlled collapse on impact.

A compact clutch actuator, which can be easilyinstalled, is the essence of the design of Fig 73.Pressurized fluid is used to actuate the clutch and thedevice incorporates a pump and drive, to the left ofthe diagram, feeding a pressure reservoir within thefluid container, to the right of the diagram. There isa valve, shown centre, between it and a servo cylin-der. Between reservoir and container there is a presetpassage-constriction formed, by their integration, torestrict and control fluid flow.

Problems of automatic down-hill 'active' brak-ing have been identified as due to uneven axleloadings due to the shift of vehicle centre-of-gravityon the incline. This causes wheel-locking in thelightly laden axle and consequent undue use of theABS. In the design of Fig 74 the braking effortdistribution is such that only the highly laden axle isbraked in normal cases. Only when deviation fromthe set speed or slip at the braked wheels exceeds acertain value will the brakes be applied on the lightlyladen axle.

Easy height-adjust for trailercoupling and auto-adjusting towbarExisting adjustable-height trailer couplings are un-wieldy to adjust because of the heavy knuckle forgings,incorporating the hirth gears, being awkward to re-move and replace for resetting the engagement of thegears. In Fig 75 a parallelogram linkage is formed outof the front and rear supports of the coupling. Thehirth gears are at the lower end of the front support anda gas spring damps the movement of the mechanismduring adjustment. The geometry is such that up tohalf of the total towing force is taken up by the rearmember.

Loss of payload carrying area on a drawbartrailer truck combination arises from the need to have

an inordinately long drawbar so that prime-moverand trailer do not foul one another on sharp corneringmanoeuvres at low speed. In the design of Fig 76, thedrawbar is made to increase in length on acute angledcorners and in normal driving can be set much closerthan is usually the case, to the advantage of availableload space within a maximum overall length ofcombination. A tractor to trailer angular measuringdevice on the tow bar has an arm that engages a stopdisplaced from the axis of the towing hook. Thissignals a control unit which extends a hydrauliccylinder in the telescopic drawbar.

Fig 73:Clutchactuator byFichtel &Sachs(GB23014WA)

Fig 74: Set-speed braking by Wabco GmbH(GB2317930A)

Fig 75: Height-adjust coupling by BradleyDoubledock (GB2318107A)

Fig 76: Auto-adjust towbar by Fruehauf Corporation

Chapter 7:

System developments: body structure/systems

A decade of patents specifications and company releasesprovides an insight into automotive product development upto the period of new designs covered in the first five chapters.In the area of body structures and systems, the trends toreducing vehicle weight and increasing occupant safety areclear in the examples which follow.

144 VEHICLE DESIGN

Structuralsystems

Controlled collapseSafety and weight reduction continue to be the maindrivers of structural developments. Better control offrontal collapse is receiving particular attention.Avoidance of bending collapse of the front longitu-dinal members of a vehicle body in impact is theobjective of the design in Fig 1. Because such mem-bers usually involve a curved section to provideclearance with mechanical systems it is difficult toprevent the onset of bending collapse, under endload, prior to the desired controlled longitudinalcollapse of the box sections. While vertical beads areformed into the vertical walls of the box-members toinduce longitudinal buckling, the claimants havefound that inclining these at an angle is successful incancelling the bending moment induced by the frontend-load. Asymmetric side beads have also beenused in vehicle body front-end longitudinals to con-trol crush characteristics in frontal impact. The beadsact as fold initiators but are not fully effective as thecomers of the members take greater load than thesides. In Fig 2, asymmetric corner divots are intro-duced as triggers and the arrangement particularlysuits larger and heavier vehicles which have thickgauge longitudinals. Because the divots help to re-duce the bending moment of inertia at the crosssections where the beads are, this proposed designrelies only on specially configured corner divots —with long and short axes arranged to pair with oneanother as seen here. Two-stage energy absorption isanother approach, avoiding premature firing of theoccupant-protection airbags . This is the object of thebumper configuration in Fig 3. Two-stage impactenergy absorption is obtained by a soft outer bumper,supported on relatively weak collapse-tubes, de-forming under minor impact without firing the airbag.Heavier impact causes the more rigid inner bumper tocollapse on its support tubes, with sufficientdecelerative force to fire the airbag. Structurallyefficient longitudinals are also needed behind thefront-end. An improved structural efficiency for theplatform underbody of an integral-bodied vehicleresults from the use of a novel design of side-rail inFig 4. The side-rail is a built-up beam having channelsection flanges and a form of corrugated web inbetween. Preferably a pair of rails are sandwichedbetween upper and lower floor panels with the wholestructure supporting a pillar-arch and cowl.

Fig 1: Patented front-end by Fuji Jukogyo(GB2318552A)

Fig 2: Patentedcontrolled collapsesystem by Ford(GB2295358)

Fig 3: Two-stageenergy absorptionby Rover Group(GB2308100A)

BODY STRUCTURE DEVELOPMENT 145

Fig 4: Patented longitudinal design by AmericanMotors (GB 2187686A)

Fig 5: Patented body shell construction by Honda(GB2305639A )

Figs 6/7: Patented side impact protection structure(and section) by Fuji Jukogyo (GB2306922A)

Fig 8: A novelwindscreen pillarpatented by Toyota(GB2293798A)

Body shell integrityIn giving structural integrity to the whole body shellframe a number of new approaches have been tried.In this body-shell made from rings, a light alloyintegral framework for a car body is made possible.In the design of Fig 5, which affords minimummaterial wastage in the form of off-cuts. Almost theentire shell framework is made from extruded stripformed into polygonal looped rings. The rings areinterconnected over the lengths of their side to obtaingood structural integrity.

There is much effort to concentrated on im-proving structural integrity in side-impact. Prevent-ing intrusion into the passenger survival space of thesill and rear quarter panel, during side impact, is theobject of the design in Fig 6/7. At the intersection ofsill and rear quarter panel, shown in the cross-sectionview, an additional longitudinal crash tube is intro-duced and the joint is braced across the vehicle by aU-sectioned transverse member which forms a box-tube when welded to the floor panel.

Combining rigidity with energy-absorbency isa further requirement of the structural engineer whenhe considers the vehicle interior. The construction ofvehicle body pillars and rails is generally such as toprovide the highest possible strength and rigidity fora given weight of material and cost of fabrication.This conflicts with the requirement for a degree ofenergy absorption when these structural members areexposed to the vehicle occupants. So a better compro-mise is achieved by using the elements shown in thistypical section, of a windscreen pillar, Fig 8. Theconventional pillar section has an extra membersandwiched between its outer and inner 'panels' sothat panel thicknesses can be reduced accordingly.Then the inner panel has an extra, U-shaped sectionspot-welded to its walls so as to provide an additionalenergy-absorbent panel of yet thinner gauge. Theusual deformable plastic garnish panel then separatesthe absorber from direct contact with the occupant inan impact situation. Also shown in the sectional vieware the door pillar and weatherseals which define theshape of the basic windscreen pillar section.

Exploiting wall forces to grip occupants isanother interesting approach. An unusually highdegree of occupant protection in side impacts isafforded by the seat and airbag layout of Fig 9. Theupper portions of the seat backrests are extendedoutwards to almost touch one another and the adja-

146 VEHICLE DESIGN

cent areas of door trim. Platforms thus formed con-tain airbags which fire forwards but exert side pres-sure on the occupants by reacting against the door orsidewall trim.

Extra protection from B-pillar impact can alsobe designed in. Means to permit the vehicle occupantto swing laterally in a pendulum effect, with pivot atthe upper side rail, is proposed in the design of Fig 10.A yieldable portion of the B-pillar to sill joint col-lapses, with an adjacent section of the floor-pan,under side impact. The patent also covers proposalsfor controlled collapse of the B-pillar based on sepa-rate deformable portions.

Taking the injury out of side impact is alsopossible with the arrangement seen in Fig 11. Nor-mally the B-pillar bends under side-impact at thediscontinuity between the upper, window, and thelower, door, portions of the pillar, at occupant chestlevel. Here the centre-pillar has a designed-in strengthdiscontinuity portion at seat level. In order to ensurethis failure mode takes place, top and bottom anchor-age supports for the pillar also must be reinforced.This is achieved by using a box-sectioned pillarrooted to box-sectioned transverse members at roof,X, and floor level, Y, which make up a ring framearound the vehicle and include reinforcement of thefloor centre tunnel, Z.

An associated proposal, Fig 12/13, to that inFig 6/7 comes from Toyota and covers the provisionof an energy absorber within the trim of the door tofurther increase side-impact protection. Conventionalcushioning devices added to the trim protrude intothe passenger survival space. Here the cushions areprovided within the thickness of the door and itsassociated trim case and configured to optimize theenergy absorbency and allow the occupant to take theimpact at hip level.

Chassis/body shell elementsSlotted construction for chassis frames is an interest-ing way of reducing the weight of vehicle structuralelements. The possibility to make a lightweightvehicle chassis frame in aluminium alloy, withoutthe need to form a complex one-piece taperedsidemember, is clear in the design of Fig 14. Rela-tively short lengths of constant section extrudedsidemember portions are joined together by stronglight interconnection members of hollow ribbed con-struction which can have such items as spring hanger

Fig 9: Technique of occupant protection in side-impact by Mercedes-Benz (GB2309440A)

Fig 10: Design forprotection from the B-pillar by Fuji JukogyoKK (GB2311259A)

Fig 11: An improved survival space under side-impact arises from this arrangement proposed byFuji Jukogyo in Patent GB2292716.

Fig 14: Patented sidemember construction byDana in GB2313577A


7

Fig 12/13: Associated proposal in GB2292913A,

Fig 15: Technique for maintaining shear strength,patented in GB2203393A

Fig 16: Oddments box doubling as structuralmember in patent by Daimler-Benz (GB2312190A)

brackets integrated with them.Protecting chassis sidemember shear strength

is a particular problem which occurs on skeletalsemi-trailers, for container transporting, because ofthe comparatively shallow depth of the main longitu-dinal beams. This means that transverse, bolster,crossmembers of rectangular section cannot easily beinserted through them and welded in position. Thecut-outs which pierce the sidemember webs can betoo large to allow any residual shear strength in thesidemembers. In this arrangement by Crane Fruehauf,Fig 15, a pair of plates and connecting tube areinserted inside the crossmember so that the platescorrespond to the cutouts in the sidemember. Afterwelding up they replace the lost web area in thesidemember.

Even a dual purpose oddments-compartmentcan be used to enhance occupant protection in im-pact. The proposal for a centre-console locker in Fig16 includes provision for a measure of side-impactsupport and the possibility of having its contentswarmed by heater ducting. The box structure has twocross bulkheads, two side ones, stiffened by foldedflanges, and a floor bulkhead. The sides also form theouter walls of fore/aft running heater ducts.

Stiffening up a convertible body is often neces-sary when the roof panel is removed from a car bodyshell. Increasing the torsional and bending rigidity ofthe rear-end of an open convertible car structure is theobject of the design in Fig 17. A vertical structuralwall forms the front-end of the hood stowage com-partment at the very rear of the vehicle. At its outer

Fig 17: Patented method of strengtheningconvertible body, by Porsche (GB2308104A)

148 VEHICLE DESIGN

edges, and in a cruciform across its leading side, railstructures react loads imposed on the body structureby the rear part of the chassis, the upper crossmemberdirecting the loads to the flux point K. The forcesreach this bulkhead via cranked box-section mem-bers, and a tapered pillar of substantial section, whichconnect to the sills and main chassis.

A suspension-location structure can be used tosupplement body shell structural rigidity. This ap-plies to Porsche in the chassis construction of the 911Carrera. Of particular interest is the rear suspensionarrangement which involves a sophisticated sub-frame structure, Fig 18, which is elastically mountedto the body. The LSA lightweight strut axle com-prises a five-link wheel location system, the linksbeing arranged in two planes, two forming the upper'wishbone' and three, including a tie-rod, formingthe lower one. As the wishbones are effectively eacha pair of tension/compression members, these arelargely relieved of twisting or bending moments.Combined with its brakes and drive-shafts the wholeis a pre-assembled module. Each suspension strut ispivot-mounted at either end, to wheel-carrier andsub-frame respectively. The suspension 'struts' aredie-cast by the Acural process and are of C-section,with webs reinforced by diagonal ribs. These are inaluminium alloy AlSITMg with 240 N/mm2 yieldstrength. The sub-frame members are of similarconstruction but use a H- rather than C-section. Totalweight of the assembly is 17 kg.

Many of the smaller body-builders consider theway ahead in structural efficiency lies with compos-ite bodies. Three dimensional weaving of glass-fibrepreforms by the technique announced recently byCambridge Consultants is likely to open up newopportunities for composite structures. Bycomputeriszing the complex instructions to a Jac-quard loom, which works by passing longitudinalfibres through loops in vertical wires, moved verti-cally as the shuttle carrying the thread moves be-tween them, automated construction of the preform ispossible. A box beam having longitudinally orientedfibres in the flanges and at 45 degrees on the webs canreadily be programmed. Vehicle seats, bumpers andside beams are seen as other applications as thetechnique allows curved forms and flanged edges tobe achieved without difficulty. The main limitationof the process is the 50-55% fibre content limit inGRP needed for the resin to penetrate between the

fibres in resin transfer moulding. A resin injectiontechnology such as RTM or network injection mould-ing is seen as a key part of the automating process, forwhich production rates of between 10,000 and 100,000per year are seen as optimal by CCL. Fig 19 showsstraight, curved and tapered parts which it is possibleto construct, making the truck chassis frame to be apotential application as well as body side panels. It iseven possible to envisage economical integral con-struction of monocoque van bodies provided a large-enough loom could be found to handle the size of thepreform.

Structural/suspension innovations have alsoreached production in a Lotus model. Torsionalstiffness of 6600 Ibs ft / degree has been achieved forthe open body structure of the Elan, with a steel and

Fig 18: For she suspension sub-frame

Fig 19: Pans made from the CCL process


polymer composites combination structure, Fig 20.Body panels are produced by the VARI process. Aconstant curing temperature and newly modifiedresin systems have since improved the productioncure time. Also a new preform system is used toproduce the panels which enables sharper corners tobe achieved. Body shape gives 0.34 drag coefficientand front/rear lift coefficients of 0.30 and 0.065respectively. The chassis structure has departed fromthe traditional Lotus pure backbone with the integra-tion of the composite platform which is a single-piece3 mm thick moulding, including inner sill, toeboard,heelboard, 'A' and 'B' posts. The resin is anisopthalicpolyester reinforced by continuous filament glassfibre with additional reinforcement at the matingpoints with the backbone outriggers. The latter aremade from 18 gauge steel which is E-coated and waxinjected. Body panels are joined by elastomericpolyurethane adhesives. There is also a steel subframereinforcing 'A' and 'B' posts, sills and rear suspen-sion anchorages. The relatively large number ofseparate 2 mm thick skin panels makes for quite easyfuture facelifting, according to the company. Bump-ers are of RRIM and doors, unusually, swing in an arc

inside rather than outside the front A-panel.A patented 'interactive wishbone' suspension

assembly is mounted on a separate raft of heat-treatedaluminium alloy. The raft allows very stiff fulcrumbushes to be employed but without passing roadnoise; it also permits abnormally low caster angle andaccurately controls suspension geometry under allconditions. Torque steer effects are also reducedwhile allowing longitudinal wheel compliance with-out changes in handling. There is not the normalexcessive loss of caster during braking, caused bydeflection of the fulcrum bushes, and braking stabil-ity has actually been enhanced by offsetting the hubspindle rearwards relative to the steering axis. Track-ing stability is also optimized by commonizing cam-ber change geometry, with bump travel, on both frontand rear suspensions. Roll centre heights (30 mm,

Fig 20: Lotus Elan structure

150 VEHICLE DESIGN

front, 60 mm, rear) remain virtually constant fornormal roll angles and steering geometry of 60 percent Ackermann has been chosen.

Many believe the achievement of optimumstructural rigidity in car bodies will require the use ofa punt-type structure with sandwich floor panels. Asandwich structure for a roadster chassis is seen in Fig21/22. Mazda engineers1 released details of thissandwich panel sports-car project in SAE papers, inwhich the admirably simple 'punt' structure is de-scribed. This approach is felt to be justified in open-top cars which otherwise demand costly and weightyunderstructure modifications when derived fromstandard saloons. Structural efficiency was measuredby calculating the strain-energy involvement of eachpanel by finite-element techniques. Aluminium alloyface and honeycomb core are used to obtain bodybending rigidity of 1.0 X 103 kNm and torsionalrigidity of 0.7 kNm/rad from the 100 kg.structurewhose natural frequency in bending and torsion wasabove 40 Hz. The latter figure is well above 'shake'prone adapted saloon open-tops. Main floor panel is100 mm thick and attaches to the structural side sillsas shown inset.

Car body systems

Occupant restraintOccupant protection has also been considerably af-fected by developments in vehicle seating and sur-roundings.

Preventing submarining or similar motion of achild in its safety seat is proposed in this Volkswagenpatent, Fig 23. The shell of the seat is a carrier bodyfor airbags which inhibit motion of the child during

vehicle impact. Inflation pressure is also controlledso as not to over stress the child during this event. Afurther airbag is mounted in a play-table which is anintegral part of the seat. A weight sensor and infra-redsensor determine the mass and size of the child and apreferred arrangement also includes inflatable shoul-der and lap belts to increase the restraint effect. Theairbag and gas generator assemblies are preferably ofthe plug-in type, the base of the sockets being elec-trically wired to the main harness of the vehicle, asshown.

Fig 23: Child safety seat by VW in GB2290505A

Fig 24: Patented pre-tensioner by Allied-Signal (GB2304027A)

Fig 21/22: Mazda punt structure

1


Fig 25: Safe install pretensioner by Allied SignalSpA GB2315983A

Fig 26: Energy-absorbing anchorage by TokaiRika Denki Seisakusho (GB2307168A)

Fig 27: Side airbag within seat back by AlliedSignal (GB2305638A)

Pretensioners for seat belts are another safetysystem receiving attention. In Fig 24, a relativelyeasily assembled and installed seat belt pretensionermechanism has a strong piston locking element which,while allowing free movement of the piston in thewebbing tensioning direction, locks the piston in theweb-loosening direction. The cylinder is internallythreaded at one end for setting the pretension and atthe other has a toothed profile into which the lockingelement engages as well as two O-ring seals spacedat one tooth pitch.

The hazard of handling seat-belt pretensioners,while armed is overcome in the design of Fig 25,which also makes it difficult for unauthorized dealersto fit pre-used units and provides a visual indicationto safety inspectors when this happens. The action offitting the unit to the vehicle causes the lever of thearming bracket to be actuated and the bracket incor-porates a flange for limiting access to the fixingscrews. The arming bracket is secured to the retractorframe by a twin headed arming screw, the headsbeing separated by a weak portion of the stem. Ontightening, the stem shears to detach the outer headand leaves the inner one protected by an envelopingsealing ring.

Energy-absorbing belt anchorages are anotherapproach to lessening impact injury. In Fig 26, anupper seat-belt anchorage is provided which incorpo-rates an additional measure of energy absorption.The body of the anchorage which supports the web-bing has a specially shaped support-pin passingthrough it, and the adjacent body centre-pillar, whichengages an exterior reinforcement plate in a specialway. The energy absorber is positioned around thecircumference of the outer end of the pin and isarranged to expand outwards under crash loading onthe interior belt mounting.

Out-of-view side-impact airbags protect pas-sengers from impacts in other directions. In thedesign of Fig 27, no obtruding into cabin space, ordetraction from the interior styling, results from amodular side-impact protection airbag which fitswithin the seat back. A specially constructed ex-truded seat-back support housing has a fold over part,behind which the bag (plus inflator) is stowed, whichallows the bag to deploy forwards, between theoccupant and the door.

In another ingenious design the frontal airbagmodule is the horn push, Fig 28. Provision of tactile

152 VEHICLE DESIGN

indication of when sufficient pressure has been ap-plied to sound the horn is inherent in this steeringwheel configuration which also prevents unwantedapplication of the airbag. The airbag module ismovable with respect to the rim of the wheel and ismounted on three resilient elements which are alsoelectrical contacts of the horn switch. The force/deflection characteristics of these elements are suchthat the resistive force rises to a maximum duringinitial movement and then falls to a minimum andrises once more to a second maximum with continuedmovement.

Side protection is also possible with an openwindow in the design of Fig 29. Protection of vehicleoccupants during side impact, when a side-window iseither broken or open, is the objective. A strap thatthreads through the deflated airbag is anchored tostructural pillars either side of the window. When thebag inflates, the strap is tensioned by the dispositionof inflating cells around the strap such that theoccupant is constrained inside the window opening.

One school of thought believes that occupantprotection is best served by having seat belts an-chored into the seat, particularly in open roadsters.Seats on the M-B 300 SL, Fig 30, have ten wayelectric adjustment with memory pre-set and a struc-ture which includes anchorage for the shoulder beltinertia reel. It was designed with the aid of thematerial supplier, Norsk Hydro. Possibility to adjustthe seat-belt harness to almost any occupant size is animportant contributor to safety in an open car whichotherwise has to rely on safety-reel anchorage by thehalf-height C-pillar. Since the crash loads on the seatfrom the safety harness are very considerable theintegrity of the structure and its slide mechanism iscrucial and required a 5800 element FE analysis inthe SL design

A particularly compact seat-belt pretensionerhas been patented by an Asian manufacturer. Avoid-ance of a long cylinder and rack to effect pre-tensioning of a seat-belt retractor is one of the objec-tives of the compact design in Fig 31. The retractoruses gas pressure to move the rack and rotate thepinion gear. A clutch mechanism transmits motionbetween the member attached to the pinion gear anda belt take-up spindle, the clutch mechanism beingdriven through step-up epicyclic gearing.

More effective seat-belt locking is claimed foranother ingenious design. In particular, a faster, more

Fig 28: Airbag module as horn push by Autoliv(GB2309123A)

Fig 29: Protection from side-window shattering byAutoliv Development (GB2312877A)

Fig 30: Seat of Mercedes 300 SL


Fig 31: Compact pretensioner by NSK(GB2292304A)

Fig 33: Adjustment mechanism by Dunlop Cox,GB2293972A

effective, release of the clamping wedge and spoolassembly of a seat-belt retractor is achieved, in thedesign of Fig 32, when the loading on the belt dropsbelow the spring bias force. The spool assembly ismounted so that linear movement with respect to thewedge housing pushes one or more clamping wedgesvertically to lock the seat belt. Ideally, the spool iscoupled to the wedges by coil springs and it issupported in a slider which is also the spool-assemblyframe. The slider moves linearly with the spool toactivate the wedges.

An improved manual height/tilt adjuster for aseat has solved a long-standing problem. Seat adjust-ment mechanisms using double pinned discs to en-gage notched racks have previously been impracticalbecause of the difficulty of turning a coaxialhandwheel through 180 degrees. For the design in Fig33, a 3-pinned disc allows a more manageable anglefor hand-turning and incorporation of such an actua-tor in the mechanism shown, and when fitted eitherend of a vehicle seat slide, allows a convenient wayto provide front and rear height adjustment.

A simplified headrest adjuster is also a wel-come advance. In many small cars the headrest haslittle use, apart from the protection afforded againstwhiplash injury, as different sized drivers cannotadjust the fore-aft position even to make contact withthe rest. In the design of Fig 34, lighter weightconstruction and improved comfort follow from alocking mechanism design for a seat head supportwhich allows an adjustable position for the rest. Keyto the mechanism is an actuating lever within theretaining yoke of the headrest. At its top end is arelease button and at the bottom end the lockingelement.

Fig 32: Improvedbelt locking by Allied-Signal (GB2300797A)

Fig 34: Simplified head rest adjuster byVolkswagen (GB2302706A)

154 VEHICLE DESIGN

Controlling headrest position is also improvedby a mechanism for helping to prevent whiplashinjury. The design in Fig 35 incorporates an antici-patory crash sensor which signals when an externalobject at the rear of the vehicle has greater than athreshold closing speed. Another sensor determineshead location with respect to the headrest. A proces-sor works out the correct headrest repositioning tominimize injury and actuates the mechanism accord-ingly.

A simpler seat slide control that would seem tofavour powered drive is seen in Fig 36. Substantialsimplification of a seat slide and adjuster mechanismfollows from the adoption of a system based on beltsand pulleys rather than a serrated rack and pawl. Fourseat-mounted pulleys are involved plus a simplebrake mechanism, at the leading edge of the seat,which clamps the belt in any position and thereforeprovides finer adjustment than is possible with atoothed channel.

A quieter belt-retractor for a seat belt is seen inthe interesting design of Fig 37. It enables theratcheting noise to be eliminated, of the pawl drag-ging over the locking teeth of a seat belt retractormechanism, on rewind. A spool with a ratchet is usedfor carrying belt webbing while a rewinder is used forrotating the spool. An upturned cup-shaped memberacts as a sensor for detecting acceleration of thevehicle over a given threshold, causing a lever tomove upwards and move a pivotally mounted pawl tolock the spool. A blocking arm, frictionally coupledto the spool, disables the pawl when the spool isrewinding, its movement being limited by arcuatelyspaced abutments.

Doors, windows and panelsAn interlocked split-tailgate is a way of overcomingdifficulties that have arisen with two-piece tailgateson cross-country vehicles and estate cars — of inde-pendent securing of the upper (window) portion andthe lower (flap) portion when long protruding loadsare required to be carried. In the design of Fig 38, agas strut is used to automatically open the windowportion when the latch is released. However, if thewindow is open when the flap is open, it cannot beclosed unless the flap is closed first, whether the flapis hinged horizontally or vertically. The flap can alsobe independently locked to the body via the D-pillar.In the closed position the window rests against a seal

Fig 35: Controlling headrest position byAutomotive Technologies (GB2301906A)

Fig 36: Patented design for a power-slide byRover Group (GB2306880A)

Fig 37: Quieter belt-retractor by Allied-Signal(GB2303044A)

Fig 39: Door seal byDraftex (GB230994A)

Fig 40: Easy-assembledoor strip by Draftex(GB2293191A)


(a) which extends around to the roof, via the sidepillars. In its lower part the window rests against seal(b) on the flap and the window is locked to the flapwith a mechanism that prevents the flap being openedwhile the window is closed. The window raisinglinkage ensures no damage can be done to it when theflap is opened and closed. Reference to the insetenlargement of the window hinge linkage shows thewindow to have a horizontally hinged tilting lever(c), with a roller attached to it, which has a secondlever (d) pivoted to it, the angular motion of which is

Fig 38: Opel split-tailgate proposal covered byPatent GB 2290060A

Fig 41: Winder mechanism by Nifco Inc(GB2313873A)

limited by a stop (e). If the unlocking mechanism isactuated when the window is closed, the windowmoves from the closed position into the partiallyopen position (f). Further automatic opening of thewindow can then only occur after a manual pushbecause the 'power' lever arm is then too short.Closing of the window under manual pressure isarranged so that the window pivots a given distanceuntil the roller rests again on its track. Under furtherpressure, the tilting lever pivots about axis (g) and theroller moves on its track until the shackle catchesbehind the latch at the bottom of the window.

Improvements in door sealing are the subject ofmany patent applications. In the design shown in Fig39 the upper rail of the door frame is made with alipped channel section whose open-end faces in-wards to receive the specially designed weatherstripsection. The lip of the channel holds the weatherstripin place after its integral locking contour has snappedinto position. The door periphery is then sealed, onclosure, in two places by direct compression of aninbuilt 'balloon' and by shear deformation of theouter edge of the seal.

Weatherstripping without tools is possible withthe design in Fig 40. The ability to assemble andremove a door weatherstrip without special toolingfollows from the metal reinforced elastomeric stripfitting over flange A in the usual way but beinglocked into position by a snap-over section of theresilient strip B which can be withdrawn with modestforce.

A successful yet inexpensive window winderfor curved glass taxed designers for many years.Unless a complex compensating mechanism is intro-duced into a window regulator used for curved win-dows, there is a tendency for a wrenching force on theglass-holding clamp. This is because the clamp risesin a linear path while the glass rises in a curved one.In the design of Fig 41, the glass clamp is rotatablymounted to the raising linkage so no unwanted torqueis induced.

A long-life window-winder drive is promisedby the design of Fig 42. Deterioration in operation ofwindow regulators can occur in conventional chaindriven systems due to stretch of the associated wirerope — and the inability of the spring-tensioner tocompensate for the stretch. Here an integrally formedchain has interior teeth and a flat outer side with awire rope wrapped between inner and outer sides. An

156 VEHICLE DESIGN

electric drive is used with the endless chain, whichengages driver and driven gears enclosed by a chainprotector. The chain-runs lie in flexible tubes.

Easy access for door hardware assembly is theobject of the design in Fig 43. A further improvementin modular door construction comes in this design inwhich hardware mechanisms such as door latch/lockand window regulator are built into a central frame-work. It also forms the structural integrity of the doorand supports items such as rear-view wing mirrorsand hinges. Inner and outer non-structural skin andtrim panels are snap fitted to the central frameworkafter it has been fully assembled with the necessaryhardware, without access hindrance.

An extending door handle to ease operation isseen in the design of Fig 44. The problem encoun-tered by relatively small stature people, in drivingtwo-door cars, of being able to reach the door handleto close the door from its fully-open position, isaddressed by this design. A strap-type door handle ismade extensible by means of a linkage between thedoor and its frame-surround. As the door is pivotedopen, one end of the resiliently flexible handle ismoved towards the other end causing it to bowoutwards and be easier to grasp by the vehicle occu-pant.

The current sophistication in door latching andlocking systems is exemplified by the Bosch inte-grated door latch, lock and auto-closing system. Thecompany have revealed details of their electronicallycontrolled automatic door closing and security sys-tem in a recent paper2. Only one actuator motor isinvolved and the functions of the device are inte-grated into one system. In an effort to minimize thenumber of mechanical parts, for closing and locking,only motor, gearbox, driving/stop plates, guide mecha-nism and ratchet are required; door slider and lockslider are located on one bracket. Door position isseen by the displacement of the drop latch, monitoredby two proximity switches, while that of the drivingplate is seen by two Hall-effect sensors. Shown at Fig45 (a) are the door in open and the first ratchetpositions; the auto-closing system is inoperative whenthe closing pin is introduced in the first ratchetposition as this actuates the controller via a proximityswitch. The ratchet then holds the drop latch andprevents the door from springing open. The drivingplate is connected to the gearbox output which turnsthe drop-latch into the closed position via a sprung

Fig 42: Long-life winder by Chin-Yun Huang(GB2313407A)

Fig 43: Easy access to door hardware by Honda(GB2315513A )

Fig 44: Extending handle by Prince Corporation(GB2318385A)


Fig 46: Rack and pinion mechanism by RoverGroup, covered in Patent GB2291109A

stop-plate. The drive plate then completes one revolu-tion and the door can then be mechanically opened bythe exterior/interior handles. A console switch signalsthe actuator, via the CAN bus, to enter the centrallocking mode. The driving plate is then motored to thedoor-locked position (b). The driving pin on the stopplate prevents the drop latch from being handle-opened from the outside — but interior handles willturn the stop plate against its spring with the slider.Turning the locking key signals the actuator to enterthe anti-theft mode in which the driving plate takes upthe position monitored by the sensor; both inner andouter handles are then disconnected as in (c).

Another way of foiling the thief is with avehicle locking system which overcomes the gravelimitation of many existing systems, that once thethief has prised the lock from the body the latchescan be operated by the pull rods linking them to thelock. In this arrangement, Fig 46 , the lock actuatoris a key-driven rack and pinion, the rack of which isconnected to a Bowden cable that links withthe latch. The lock, rack and pinion, and the end ofthe Bowden cable are all located in a casing such thatthe locking function cannot be operated without thekey to the lock, even if the lock is prised out of thedoor.

Fig 45: Integrated latch/lock system by Bosch

158 VEHICLE DESIGN

A way of minimizing operating forces on acentral-locking system is the design of Fig 47 inwhich the electric motor only needs to be sizedaccording to the operating forces of the locking leversystem. Manual operation can also be carried outonly against the resistance of these forces, in theevent of motor power failure. Thus a rotary latch,pawl and release lever have an operating lever whichcomprises at least one operating lever plus a lockinglever system. This involves an interior locking lever,central locking drive and locking element connectedto it. The drive is a reversible motor with power takeoff having an eccentric control pin. The pin is con-trolled in a way that it rotates in either direction tomove the central locking element into 'locked' or'unlocked' position. This element has a forked re-ceiver with control surfaces on its sides which causethe interior locking lever to be rigidly connected to it.Part of the control pin arc of rotation is outside theforked receiver and the central locking element hasa stop face on both sides, for the control pin. Controlmovements of the pin are restricted by its striking oneof these faces and the motor being switched off as thishappens.

A particularly compact power door latch isobtained from the design in Fig 48. Existing pow-ered-closing devices for vehicle doors cover a largeprojected area of the door. This is because the cancel-ling lever normally projects beyond the output mem-ber. In this design a compact layout is achieved by thecancelling lever overlapping the output member, aswell as the member connecting the output member tothe intermediate lever being shorter. The outputmember is rotated by a motor, moving the latch froma half-latched to a full-latched position. The cancel-ling cam surface is brought into contact with theconnecting member to disconnect the output mem-ber, and the intermediate lever, when the openinghandle is turned.

Another body mechanism which receivesconsiderable design attention is that for convertiblehoods. A compact folding-roof arrangement for boot-stowage is covered in the design of Fig 49, whichmaximiszes the space within the stowage cavity. Topivot the boot-lid frame upwards a hydraulic jack isextended and a slot in the lower end of the jack slidesdown over a fixed pivot. This initial motion of the slotcauses the foot of the jack to pull on a cable, to unlockthe boot lid. Further jack-extension raises the boot

Fig 47: Reduced locking force system by KiekertAG (GB2292768A)

Fig 48: Compact door latch by Mitsui KKK Kaisha(GB2313408A)

Fig 49: Boot-stowage of folding roof by Mercedes-Benz, covered in Patent GB2300671A


lid; jacks are positioned at each side of the boot,behind the wheel arches. Leaf springs are positionedat the side of the slots to stabilize the pivot positions.

Trim and fittings

Fig 50: Mirror system by MurakamiKaimeido, covered by PatentGB2299560A

Fig 51: Sliding door drive by Mitsui(GB2305228A)

Fig 52: Reliable bonnet latch by BloxwichEngineering (GB2312921A)

A mirror system without rain-blur is seen in thedesign of Fig 50. Substitutes for conventional rear-view mirrors have been proposed which avoid theconsiderable protrusion of the mirror from the sidewallof the vehicle. However, a drawback of such systemsis the blurred image obtained in wet weather when theimage is distorted by rain droplets. In this patenteddesign, a housing on the vehicle side has a concavemirror inside it to reflect light collected by a circularconcave lens at the rear of the housing. The lens iscoated with a water repellent and is mounted inbearings so that it can be spun by gear teeth, on itsperiphery, driven by a motor pinion.

An improved sliding-door drive which doesnot require exclusive use of power is suggested in Fig51. A clutch mechanism, for transmitting power frommotor to movable member, has racks fixed to station-ary members and engages with gears to drive themovable member. The clutch unit is supported on aswinging member, spring-biassed to a central neutralposition. Gear A is engaged with the output gear B,and the stationary rack, while gear C is frictionallycoupled to gear A. On energizing the motor theassembly swings away from the neutral position toengage with the movable-door drive gear.

A more positive and reliable bonnet releasemechanism is proposed in the design of Fig 52. Thisimproves on the conventional type comprising aheaded striker pin mounted on the bonnet and adapted,as the bonnet is closed, to pass through an opening ina catch plate attached to the grille surround andbecome engaged by a catch lever. Here a latch forretaining a striker pin does so by the action of alatching member in the latch on the head portion ofthe pin. The latch has a resilient member, which ischordal to the bore, to retain the striker pin in thelatch. A release ring rotates about the axis of the boreand has an abutment which engages with the resilientmember to spring it from the bore and release thestrike pin.

Cushioning a bonnet top impact is the object ofthe design in Fig 53 for a pedestrian protectiondevice. In the cases of frontal impact with the vehicle,uses an external airbag triggered by a decelerationsensor. Protection is given particularly against vio-lent head impact from the whiplash effect of the bodyfolding after leg impact from a low bonnet. Theairbag is stored in a protective cover which ruptures

160 VEHICLE DESIGN

on inflation of the bag, the cover being contained ina nudge-bar extension of the normal bumper bar,which is itself covered with soft material to minimiseleg injury.

Protection of the occupants is the object of thiscontrolled-collapse trim system in Fig 54. Providinga crash impact waveform with a number of progres-sive deceleration peaks is an objective of a trimfinisher for fitting to the interior of the windscreenpillar. Earlier attempts to do this have usually re-sulted in undue bulk of the trim member with conse-quent intrusion into the passenger space and/or ob-struction of the front doorway. Here the generallychannel-section plastic trim member has reinforcingribs at right angles to its surface and arranged withdifferent clearance dimensions from the screen pil-lar. Fastening of the trim to the pillar is via integralbosses parallel to the ribs which engage with a sprungplate with lugs engaging spring-clip fasteners fittedin holes in the pillar.

A simplified level-sensing system for lampadjustment is seen in Fig 55. Undue complexity, anda large number of individual parts, in existing vehiclelevel-detection devices have resulted in costly solu-tions for automatic on-vehicle headlamp adjustmentand suspension levelling. In this proposal a sensor isused having just two angularly moveable parts, re-spectively coupled to the vehicle body and suspen-sion. The 'fixed' part is attached to a body-structuremember in a way that allows the sensor to be coaxialwith the fulcrum of a wheel suspension control arm,an attaching leaf-spring from which holds the 'mov-ing' part of the sensor. The rubber bush of thesuspension control arm compensates for any motionof the arm at right angles to the axis of rotation of thesensor moving-part.

A system of fibre-optic light division for head-lamps is seen in the design of Fig 56. This headlampdesign uses fibre-optics so that only one high inten-sity discharge bulb is required for both main- anddipped-beam operation. Light conducted from theupper (main beam) source, by the optical fibre at therear of the lamp, serves as a source for the lower,dipped-beam unit, a shutter mechanism controllingthe amount of light passed. The arrangement is alsosaid to improve colour distribution between eachsource, give better balance of luminous intensity andthus better forward vision.

Body system innovation in the fuel tank region

Fig 53: Pedestrian protection device patented byConcept Mouldings Ltd (GB2316371A)

Fig 54: Controlled-collapse trim by Nissan(GB2318551A)

Fig 55: Simplified level-sensing by Mercedes-Benz(GB2292614A)


includes the fuel delivery system of Fig 57. Simpli-fied assembly and test can take place of this fueldistributor system, which is an add-on unit to a fueltank, rather than fabricated within it. The carriercasing, which is mounted to the fuel tank, has a non-return valve, bottom right, and an ingenious jet-pumparrangement, for filling. The jet-pump, left side ofcarrier, involves excess fuel flowing back through aduct from the engine.

An improved fuel tank, overall, is covered inthe patented design of Fig 58. Prevention of overfill-ing on refuelling, and avoidance of any bad effects ofvapour formation on vehicle acceleration, are theobjectives of this fuel tank design. Two separateullage spaces are formed by means of an invertedcanister suspended from the roof of the tank, which

Fig 56: Fibre-optic light division system by FujiJukogyo (GB2315538A)

Fig 57: Fuel deliverysystem by Mercedes-Benz (GB2304821A)

Fig 58: Improved fueltank layout by FordGB2306952A

Fig 59: Exhaustfixing by CalsonicCorp (GB2313581A)

forms a vapour reservoir. An acceleration-sensitivevalve controls the opening between the two ullagespaces which are also interconnected by a small bleedvalve.

An exhaust clamp without bolts is an interest-ing piece of underbody innovation, Fig 59. Problemsof looseness in an exhaust pipe assembly, followingthe fixing clamp nuts becoming untightened in serv-ice, are overcome in this relatively easy-to-assembledesign. The ubiquitous bolted exhaust pipe clamp isreplaced by a spring-clip-shaped member which at-taches to a support arm by notched engagement withits flattened end. The rod is hung from a flexiblemount in the usual way.

Aerodynamics

and weight savingAttention to underbody panel shape is also importantin extracting the last mph of speed. Dr Dominey ofDurham University3 points out that the stability ofregulations has led to a convergence of design whichmeans that competitive circuit performance nowdepends on fine tuning of aerodynamic design. Asground clearance beneath the front wing is reducedflow can no longer tolerate the pressure gradient andthe aerofoil stalls in the limiting condition. Thelimited permitted span of the aerofoils makes itnecessary to control the associated tip effects. Theend-plate solution aimed at maintaining approximatetwo-dimensional flow increases loading at the wingtips but does not eliminate strong tip vortices — forwhich semi-tubular guides along the lower edges ofthe end-plates has been one of the ways of containingthem. To overcome the compromising effect of thefront wing on engine cooling performance, the use offlapped aerofoils has been introduced — with chordand camber at the outer end of the flap greater than atthe chassis end. Combining this with taller andnarrower engine air-intakes ensures that only thewake from the inner section of the wing impinges onthe intake. With rear-wing aerofoils the requirementfor high downforce to be generated from alreadydisturbed airflow has necessitated the use of highlycambered multi-element configurations which areinefficient in terms of drag. The trailing edge of thewing is governed by regulations while leading edgeposition is chosen as a compromise between a highone better exploiting airflow and a low one allowing

162 VEHICLE DESIGN

a larger aerofoil to be used. The undertray of the caris the other important factor, Fig 60, air flowingbeneath the car leading to a high-pressure stagnationpoint on the upper surface and a separation bubblebelow the entry lip. Addition of a diffuser creates afurther zone of low pressure and its design is crucialto obtaining marginal advantage.

How the influence of a vehicle underbodyaffects aerodynamic drag was also discussed byRover engineer J.P. Howell4. He showed, Fig 6la, at(a) the contributions made by different elements ofthe body on the overall aerodynamic drag of a salooncar. By fairing the complete underbody of an 800saloon it was found possible to improve drag byfactors of 0.39 and 0.46 for a notchback and hatch-back configuration respectively. So as to gauge theeffect of progressively adding fairing panels (b),wind-tunnel tests were made with successive in-crease in the numbered panels to obtain the results in(c). The extremities of the floor gave the largest gainsbut there is evidence of interactions between differ-

Fig 60: Aerodynamic under-layer

ent sections of the floor. Also obtained were interest-ing results due to the progressive alteration of rear-end shape between the limits of notch- and hatch- (3)and of adding on and progressively increasing thedepth of a front spoiler (6).

An innovative body construction material islow density structural RIM. An LD-SRIM system hasbeen trailed as a RRIM replacement for production ofautomotive interior trim panels via the Strappaziniprocess. Trials at United Technologies Automotiveconfirm that Id's MDI-based polyurethane LD-SRIM system has exhibited advantages over thecommercial RRIM system. The Strappazini processis a patented method of moulding in place multiplecovers with well finished joints and seams. Theprocess is useful in moulding complex automotiveinterior trim components, including interior doorpanels. 'RIMline' SL-87339, a system containing aninternal mould release (IMR), was tested in a Cor-vette RRIM door panel tool at UTA. In a closedmould, with only slight variations in mould tempera-tures and throughput of the current production equip-ment, the 'RIMline' system was poured directly ontoa glass mat using the Strappazini process. Multiplereleases were demonstrated with Id's new IMRtechnology. During initial evaluation, 15 releaseswere achieved. Based on previous production expe-rience, it is expected that in a plant environment atleast 30 to 40 additional releases between externalmould release applications can be achieved. In com-parison, the current RRIM system is not availablewith IMR technology.

The LD-SRIM part, Fig 61b, weighed 20 per-cent less than the same door part moulded from theRRIM material. This was accomplished without op-timization of part thickness or density. An additional20 to 25 percent weight reduction can be achieved byreducing part thickness due to the superior strengthproperties of low density SRIM composite. RRIMrequires substantially thicker sections to meet stiff-ness and thermal stability requirements as well asadequate impact resistance.

Fig 62: GM Corvette doors: front in RRIM rearview in LD-SRIM

Fig 61: Drag factors involved


CV systems

CV chassis-cab configurationAdvanced-concept trucks are the trendsetters in truckdesign; DAF's future concept vehicle (FCV), Fig 62,is a fully driveable working unit whose features allhave prospects, individually, for eventual productionfitment. The chassis-frame is a fabricated rectangularsection aluminium alloy box beam; the box girder

design gives high torsional rigidity necessary tomount the independent suspension assemblies. Out-board of it are also hung fuel tanks and air reservoirs,while inside houses the major elements of thedrivetrain. The apertures in the box tube are foraccess to various parts of the drive train, the frontrectangular one giving engine access. A flat-bottomsump is fitted to the engine which is installed as lowas possible within the box-tube, forward of the frontwheels centre-line.

While engine, semiautomatic transmission andprop-shaft are otherwise conventional, the rear wheeldrive is novel, in the form of a 'double drive differ-ential system,. A torque apportioning device trans-mits two-thirds of it through a straight-through shaftto the second axle, the other third passing, via anannular gear drive, to the input pinion of the leadaxle. Being a hypoid gear, its pinion offset allows thethrough-shaft to pass beneath the cross-shaft of thefront differential. A short propshaft then connects thedrive to the second axle. Independent suspension isfitted to both front and second 'axles', the latter bothdriving and steering. Special low-profile air-springsare employed which bear on saddles on the stub-axles. Lower links of the wishbone suspension, whoseroll-centre is at ground level, are cranked downwardsto clear the inboard disc brakes. In the second axle,drive extends outwards to the wheel hubs via a ring-type kingpin housing. Suspension travel is 80 mm tobump and 160 mm to rebound stops. For the thirdaxle, twinned wheels on special two-flange hubs aresupported by stub axles on a rectangular frame. Its

Fig 62a: DAF concepttruck, with suspension anddrive detail above

164 VEHICLE DESIGN

Fig 62b: Concept truck suspension and drive detail

slender, deep sidemembers have brackets extendingoutwards, beyond the inner road-wheels, to give aswide a spring-base as possible.

Concept has become production in the case ofthe important breakthrough which has been made byDennis Specialist Vehicles. It involves a dedicatedspace-frame chassis for the new Rapier fire-appli-ance vehicle, Fig 63. Dramatic improvement in rideand handling is claimed over the conventional lad-der-frame and leaf-spring layout — with the avail-ability of a more rigid frame to mount a suspension ofgreater sophistication. Over a tonne of weight hasbeen pared from the conventional structure and a lowdeck height has also been achieved — with a particu-larly low-slung engine. The latter has permitted thecab to be mounted 250 mm lower than usual, remov-ing the need for entry steps. The entire crew cab tiltsin one piece and the lightweight body is made incorrugated aluminium alloy sheet over an extrudedsection frame — incorporating water tanks madefrom plastic. Substantial coil springs suspend bothfront and rear wheels and, at the rear, wheels areindependently suspended by a double wishbone sys-tem. Body roll, under 0.6 g lateral acceleration, hasbeen reduced to 3.1 degrees compared with 8.5degrees for a comparable conventional vehicle.

Cab/body fittingsRecent patent specifications reveal a number of thedetailed improvements which have been made totruck systems. An example is the suspended cab-tiltpivot design in Fig 64. Here a truck cab suspensionwhich is sympathetic to the cab-tilt system, withoutcausing discomfort to the occupants, is proposed.The cab itself hinges on the uppermost pivot of the

Fig 63: Dennis Rapier space-frame chassis

Fig 64: Soft-mounted cab tilt by ERF, in PatentGB2188884A


Fig 65: Return-load tanker by ClaytonCommercials (GB2298830 A)

Fig 66: Variable cube body by York Trailers inPatent GB2198091A

Fig 67: Air-bag system van-cube system by JRCramp, covered in Parent GB2299311A

mechanism shown while beneath it a second pivotforms the scissor linkage of the suspension mecha-nism — based on a rubber 'doughnut' compressionspring and hydraulic damper.

A return-load tanker is the subject of the inter-esting patented design in Fig 65. The classic diffi-culty is tackled here in the operation of tankers andbulkers, not being able to fill the tanks with a returnload, which might contaminate the principal productcarried. According to the claimants, existing effortsto build dual purpose vehicles, carrying both drygoods and flow products on flat-topped tankers, haveinvolved overweight structures. Here the lower por-tion of the vehicle, for flow products, comprisestypically two large cylindrical vessels which formsubstantial structural members of the vehicle. Cra-dles around the vessels support the upper floor forcarrying dry goods as well as proving a mounting forthe running gear of the vehicle.

A number of attempts have been made toproduce 'variable cube' bodies. A means of, literally,raising the roof of this van body is proposed by thedesign in Fig 66. An air-inflatable bag is positionedbetween the body wall and a lever which compressesthe bag. Inflation of the bag moves the lever and pullscables to operate the roof-raising device. Shown inthis example mounted to the step of a step-frametrailer, cables from the pulleys shown pass beneaththe chassis to operate jacks in the body corner posts.Another proposal also concerns raising the roof withairbags. Previous efforts have made been made to liftthe roof of curtain-sided vehicle by an amount corre-sponding to the depth of the projecting border whichcovers the curtain tracks, to allow easier loading oftall cargo items. Because such efforts have thus farinvolved cumbersome mechanisms, the design of Fig67 is aimed to simplify the approach by the use of air-bags. A scissor linkage is associated with the air-bag,positioned at the top front/rear corners of the vehiclebody. The compressed air supply would normally bereservoir tanks fed by the vehicle's air-compressorand air-lines would run through the roof supportuprights.

Improved cargo retention is the object of thedesign in Fig 68. Problems of complexity, and asso-ciated proneness to wear, of existing cargo retentiondevices for goods vehicles can be reduced by theadoption of this mechanism in the design shown.Channels on each side of the deck anchor bracing

166 VEHICLE DESIGN

beams, by means of a socket beneath each channel.The beams are either stowed within the channels ortilted upwards to brace the load. The beam is releasedfrom the load-retention position by raising it towardsthe vertical and then displacing it axially, from whereit is pivoted to the stowed position. The interior of thebeam encloses a restraining strap which is withdrawnto secure the cargo, the strap retracting into the beamautomatically when not in use.

The object of the Fig 69 design is to provide aneasy-access curtainsider. Means to avoid complexslider mechanisms for the body-side support pillarsof a curtainsider are provided in the arrangementshown. In order to move the pillars to ease side-access of bulky loads, the pillars are mounted on ahinged linkage.

Hinged corner-posts for a curtainsider are cov-ered by the design of Fig 70. The need to providefront-corner posts, of curtain sided CV bodies, whichare faired in plan view to achieve aerodynamicefficiency, results in a dead space behind the sectionprofile when loading the container body by fork truckfrom the side. In order to avoid a secondary loadingoperation, to enable pallets to fill the dead space,hinged post sections are suggested. When the flapsare in their closed position the side-curtain is wrappedaround them and secured in socket catches prior totensioning.

Considerably reduced effort to open and closethe side-curtains of a curtainsider truck-body isclaimed in the interesting roller arrangement of Fig71. The roller track section is profiled to allow tiltingof the rollers as they roll along the track. The rollerscomprise ball bearings with convex sectioned tyresof hard plastic over their outer races. This set-upovercomes the problem with conventional systems of

Fig 68: Improved cargo retention system suggestedby Boalloy Industries, covered in PatentGB2301067A

Fig 69: Easy-access curtainsider by CartwrightFreight Systems (GB 2185715A)

Fig 71: Improved curtam-sider by Montraconcovered by Patent GB2291095A

Fig 70: M &G Tankers & Trailers have suggestedhinged post sections, in Patent proposal,GB2293144A


Fig 72: Simplified curtainsider support post inPatent GB2209712A by John J Cameron

Fig 73: Compact sliding door gear by BedwasBodyworks, in Patent GB2203184A

Fig 74: Tail-liftin door by TiddStrongbox,covered inPatentGB2207112A

Fig 75: Upper-deck levelling achieved by the UKLift Company, covered in Patent GB2299791A

binding of the rollers when the curtain is displacedsideways by the operator during pulling. Each hangerbracket is supported by two or more rollers.

A simplified support post for curtainsider CVbodies is proposed in the design of Fig 71. Thecumbersome toggle linkage provided at the lowerend of the column is dispensed with. The upper endslides on the cant rail, as normal practice, but thelower end locks to the side-rave, by means of a simplespigot linkage shown here.

A compact sliding door gear system is offeredin the design of Fig 73. The difficulty is overcomehere of accommodating two ISO pallets lengthwiseacross the platform of a goods vehicle — within themaximum legal vehicle width and the clearanceenvelope of the door gear. This design uses a 'master'plug-and-slide door suspended from a carriage andswing-arm assembly.

Tail-lift in a door is the result of the ingeniousdesign of Fig 74. A tail-lift platform which doubles asa part-closure to prevent cold air fallout from refrig-erated vehicles is raised and lowered by carriages inthe rear doors of the body in this design. The bodycomprises a number of refrigerated compartmentsand a separate folding canopy can temporarily closethe upper ones.

Levelling a lifting deck is the object of the Fig75 design. Existing mechanisms used to raise thedecks of goods vehicle bodies, to achieve two-tierstowage of the payload, suffer from the moving deckbecoming unlevel as it is raised on jacks. In thisdesign movement of the deck is synchronized by theinteraction of two toothed racks mounted on the bodyand toothed wheels mounted on the moving deck.Connection of the wheels by shaft or endless chainensures the level movement of the deck regardless ofram motions.

Folding catwalk rail is covered by the design ofFig 76. Added safety for road tanker operators isprovided by this pivoting catwalk rail. When accessto the top of the tanker is not required the rail lays flatacross the catwalk to prevent ingress by unwantedintruders. When legitimate access is required hy-draulic rams raise the rail to an upright position whileinterlocks ensure the vehicle's brakes stay on, in thisposition.

Perhaps the ultimate in cab access is offered bythe Fig 77 design. Overcoming the ingress and exitrestrictions for driver and operators of crew-cabbed

168 VEHICLE DESIGN

commercial vehicles is the objective, particularlysuited to vehicles with front overhead loaders. Thedriver's seat and controls are centrally mountedwhile those for the crew are mounted above andbehind, on either side of the cab and over the wheelhousings. Doors of 1.9 metres in height open in-wardly to prevent pavement obstruction. The floor isinclined upwards at the front and level at the back andprovides cross cab access ahead of the engine com-partment.

Advanced

bus/ambulance designRethinking the ambulance configuration is behindthe design of Fig 78. Emergency transport of accidentvictims in heavy traffic was the impetus behind aninteresting vehicle to handle urban emergencies dis-cussed at a recent Autotech congress. Authors DaSilva and Miranda of Lisbon Technical Universityexplained that the key design factor was provision ofan efficient life condition support for the patient in avehicle with exceptional traffic mobility. That in-volved a highly compact layout yet a comfortableposture and space for medical assistance to the pa-tient in transit. The short journeys inherent in theduties of the vehicle make it an attractive propositionfor electric traction and in the proposed design thepatient would be positioned above the battery con-tainer. Twin rear wheels would be mounted on anoscillating axle, the 'banking' of which would be

controlled by the driver, or 'rider' in a semi motor-cycle situation, sitting behind the single steeringfront wheel of the vehicle. Retractable outriggerwheels would also be used to provide corneringstability in less dense traffic conditions. Translucentpanelling around the patient compartment wouldreduce the claustrophobic effect as would carefulcolour selection for the interior.

A joint venture between MAN and Voith hasresulted in the NL 202 DE low floor concept city bus,Fig 79, designed to carry 98 passengers at a maxi-mum speed of 70 km/h. No steps are involved at anyof the entrances, which lead directly to a completelylevel deck height of between 317 to 340 mm. Therear-mounted horizontally positioned diesel engineallows fitment of a bench seat at the rear of the bus;it drives a generator with only electrical connection

Fig 76:Pivoting cat-walk railproposed bySafewalkRailings inPatent GB2203390A

Fig 77: Short-haul ambulanceFig 77: Easy-access cab by Britannia Trucks(GB2297951A)


Fig 79a: NL 202 DEconcept MAN buswith propulsionsystem detail below

to the Voith transverse-flux wheel motors, whichdrive the wheels through two-stage hub-reductiongear sets. The diesel is rated at 127 kW and thegenerator at 135 kW; the controller is of the IGBTconverter type and also developed by Voith. It pro-vides a differential action to the wheel motors oncornering. Permanent magnet synchronous wheel-motors are rated at 57 kW and have a maximum speedof 2500 rev/min; see Table 1 in Fig 79a. The bus is 12metres long and has water-cooling for its generator,converters and wheel motors. As well as providingvirtually jerk-free acceleration, the drive system isseen by MAN as providing the possibility of four-wheel drive on future articulated buses to improvetraction and stability in slippery road conditions. Theterm 'transverse flux motor' refers to the means usedto guide the magnetic flux in the stator; this is new toinverter-supplied PM types and involves a novelcollector configuration. Double-sided magnetic forcegeneration is also new and involves a patented doubleair gap construction having high idling inductancesand force densities up to 120 kNm/m2, with relativelylow losses.

A new control process permits operation of themotor in a field-weakening type mode, in spite ofPM excitation. The generator is almost identical inconcept but involves no field weakening. Each hasconcentric construction of permanent magnets, ro-tor/stator soft-iron elements and stator winding; seeFig 79a. Armature elements are U-shaped cut strip-wound core sections, embedded in the ring-shapedsupporting structures of inner and outer stators. Eachcore surrounds the windings and forms a stator polewith its cut surfaces facing the rotor. The latter ispot-shaped and positioned between poles of the outerand inner stators. In the stator pole region it com-prises magnet and soft iron element while in the wind-ing region a ring of GRP serves as the connecting

TFM wheel motor TFM generatorPower

Rated speedApprox. max. speedMax. fundamental frequency of statorRated torqueApprox. max. torqueApprox. torque conversionPower/weight ratio

57 kW735 rev./min.2,500 rev/min.1 ,350 Hz740 Nm

1 ,050 Nm

1:31.8kg/kW

135 kW

1 ,750 rev./min.2,400 rev./min.

-740 Nm740 Nm

0.9 kg/kW

VEHICLE DESIGN

Fig 81: Aero-style luggage rack designed byIkarus covered by Patent GB2209140A

element. The inverters supply the motors with sinu-soidal currents and voltages until the nominal oper-ating point is reached; operating frequency is 10 kHz.In field-weakening mode the induced voltage exceedsintermediate circuit voltage and only square wavevoltages are supplied to the motor. Power output thenremains constant and the operating frequency equalsthe fundamental motor frequency. A large speed ra-tio, 1.5:1, is thus possible.

An electric city-bus designed for low drag isseen in the Centre concept midibus from CapocoDesign, Fig 80. It is intended to show the practicalityof 'available now' electric drive technology for citycentre operation. The 7.3 metre long vehicle wouldoperate at up to 40 kph and have a range of 40 miles.Energy consumption is reduced by the vehicle's dragcoefficient of just 0.31 and low rolling-resistancetyres of modest section profile. A lightweight struc-ture comprises mechanically fastened aluminium

\) EGR electromagnetic control valve2) Electronic control unit3) Accelerator position reinforcement4) Brake pedal switch5) Clutch pedal switch6) EGR valve7) Thermostarter8) Thermostarter feed valve9) Instrumented injector10) Water temperature sensor11) Engine speed sensor12) Vehicle speed sensor13) Water in fuel sensor14) Water flow and temperature sensor15) Engine stalling solenoid16) Engine advance adjustment17) Fuel flow and temperature adjustment18) Injection pump.

Fig 79 b: Performance characteristic andpower-unit environmental control system


alloy extrusions covered by a single-piece roof mould-ing. In full standee form up to 56 passengers can becarried and deck height is just 290 mm. Shown alsoin Fig 80 is the economical packaging of batteriesand drive motor, with near vertical drive axis. Widthof the vehicle is 2380 mm and height 2550 m, on a4050 mm wheelbase.

An aero-style bus saloon assembly followsfrom modular elements used in this patented roofliner and luggage rack assembly, Fig 81, for touringcoaches. The arrangement involves zed-shaped brack-ets screwed to the roof frame which secure headlin-ing, ventilating ducts and luggage shelves. The shelfelements incorporate a profiled channel, for housinglight fittings, which is closed by a snap-fit translucentcover.

Fig 80: Capoco Centra electric bus

This page intentionally left blank

173

References

Chapter 11 Sears, K., Automotive engineering: strategic over-view, Steel Times, Vol. 2. No.l, 19972 Matthews and Davies, Precoated steels develop-ment for the automotive industry, Proc. I.Mech.E.,Vol. 211., Part D, 19973 Rink and Pugh, The perfect couple — metal/plastichybrids making effective use of composites, IBCAMConference, 19974 Merrifield, R., Instrument panel structural conceptswhich integrate functions utilizing injection mouldedplastic components, Paper C524/120/97, AutotechCongress, 19975 Ashby, M., Material Property Charts, Perform-ances Indices, Section 4, Material Selection andDesign,20th edition , ASM International, 1997

Chapter 21 Bass et al, A system for simulating structuralintrusion, Proc. I.Mech.E., Vol. 211., Part D, 19972 Yim and Lee, Design optimization of the pillar jointstructures using equivalent beam modelling tech-nique, SAE Paper 971544, part of P-3083 Hardy, M., Automotive modelling and NVH semi-nar, Proc.I.Mech.E., 19974 Hargreaves, J., I .Mech.E .Vehicle noise and vibra-tion conference, 19985 Lawrence and Hardy, Development and use ofpedestrian impactors to reduce the injury potential ofcars, paper C524/049/97, Autotech 19976 Coleman and Harrow, Car design for all, IMechEseminar , 19977 Delphi Automotive, Adaptive restraint technolo-gies, Vehicle Engineer, December 1998

Chapter 31 Evans and Blaszczyk, A comparative study of theperformance and exhaust emissions of a spark igni-tion engine fuelled by natural gas and gasoline,Proc.I.Mech.E., Vol. 211, Part D, 19972 Perkins and Penny, Design options and perform-ance characteristics for 0.25-0.3 litre/cylinder HSDIdiesel engines, Euro 4challenge: future technologyand systems, IMechE Seminar, 19973 Sadler et al., Optimization of the combustionsystem for a direct-injection gasoline engine using a

high speed in-cylinder sampling valve, Euro 4chal-lenge: future technology and systems, I.Mech.E.Seminar, 19974 Zhou and Qian, Development of a modified dieselengine cycle, Proc. I.Mech.E., Vol 212, Part D, 19985 Cains et al., High dilution combustion throughaxial and barrel swirl, I.Mech.E. Seminar Publica-tion: Automotive Engines and Powertrains, 19976 Bassett et al., A simple two-state late intake valveclosing mechanism, Proc IMechE, Vol 211, Part D,19977 Woods and Brown, Flow area of multiple poppetvalves, Proc IMechE, Vol 210, Part D, 19968 Ohashi et al, Honda's 4 speed all clutch to clutchautomatic transmission, SAE Paper 9808199 Abo et al., Development of a metal belt-drive CVTincorporating a torque converter for use with 2-litreclass engines, SAE Paper 98082310 Ahluwalia et al, The new high torque NVT-750manual transaxle, SAE Paper 98082811 Turner and Kelly, A transmission for all seasons,Advanced vehicle transmission and powertrain con-ference, I.Mech.E., 199712 1998 SAE software based on book: Gillespie, G,Fundamentals of vehicle design, SAE, 199213 Gadola and Cambiaghi, MMGB: a computer-based approach to racing car suspension design, ATA,Vol. 47., no. 6/7., 199414 Ellis, J, Vehicle handling dynamics, MechanicalEngineering Publications, 199415 Potter et al, Assessing 'road-friendliness': areview, Proc. I.Mech.E., Vol. 211., Part D, 1997

Chapter 4la. Bodoni-Bird, C, What can seamless electro-mechanical vehicles learn from Nature?, 96C001,1b. Miyata et al, Engine control by ion densityanalysis, 96C003Ic. Pinkos and Shtarkman, Electronically controlledsmart materials in active suspension systems, 96C0041d. Hatanaka and Noro, New approach for intelligentsteering system development, 96C007le. Milburn, S, Integration of advanced functionsinto electric drivetrains, 96C050...from the bound volume of proceedings of the 1996Convergence Transportation Electronics Associationconference2a Kuragaki et al, An adaptive cruise control usingwheel torque management technique, 980606

174 VEHICLE DESIGN

2b Olbrich et al., Light radar sensor and control unitfor adaptive cruise control, 980607...from the bound volume of proceedings of the ITSAdvanced controls and vehicle navigation systemsseminar at the 1998 SAE Congress3 Bolton, W., Essential mathematics for engineer-ing, Heinemann4 Jones et al., HYZEM — a joint approach towardsunderstanding hybrid vehicle introduction intoEurope, Proceedings of the IMechE Combustionengines and hybrid vehicles conference, 19985 Friedmann et al., Development and application ofmap-controlled drive management for a BMW parallelhybrid vehicle, SAE Special Publication SP1331,19986 Nagasaka et al., Development of the hybrid/batteryECU for the Toyota Hybrid System, SAE SpecialPublication SP1331, 19987 Saito et al., Super capacitor for energy recyclinghybrid vehicle, Convergence 96 proceedings8 Origuchi et al., Development of a lithium-ionbattery system for EVs, SAE paper 970238

Chapter 51 Bowsher , G, Braking and traction at supersonicspeeds, Special Vehicle Engineer, January 1998

Chapter 71 SAE papers 870147/82 I.Mech.E .Autotech paper C427/40/1083 Proc. I.MechE., Vol 206, Aerodynamics of GrandPrix cars4 I.Mech.E .Autotech Paper C427/6/032

INDEX 175

Index

Access to door hardware 156Acoustic model of vehicle cabin 21Adaptive restraint technologies 31Advanced car and truck engines 120Advanced suspension linkage 133Aero-style luggage rack 170Aerodynamics 161Aged 50+ coupe 27Airbag module as horn-push 152A12 concept car 3Alternative injector installations 41Alternative valvetrain layouts 42Anti-dive motor cycle suspension 137Ashland Pliogrip fast-cure adhesive 8ASI passenger-side low-mount airbag 31Auto-adjust towbar 142Auto-steer for trailer 131Automatic cruise control, ACC 78Automatic drive selection 129Automation of handling tests 90Automotive electronics maturity 70

B

Bayer Durethan BKV polymer composite 4BMW for its rear suspension, 850i coupe 133BMW parallel hybrid drive 85Body shell integrity 145Body structure and systems, Ford Focus 105Body systems of Freelander 109Body-in-white of M-B A-class 98Bonnet latch 159Boot-stowage of roof 158Bosch Motronic MED 7 management system 81Brake apportioning for solo or coupled mode 141Braking system of M-B A-class 101Braking systems 139Bus and ambulance design 168

Cabin acoustic model 22Calliper and disk assembly, Thrust SSC 114Cambridge Consultants composite structures 148Capoco Centre electric bus 170Car body systems 151Cargo retention system 166

Chassis systems 133Chassis/body shell elements 147Child safety seat 151Chrysler China car 7Clock enable circuit 80CNG's advantage over gasoline 39Collins CMC scotch-yoke engine 127Compact door latch 158Compact sliding door gear 167Compliance representation 64Constant-pres sure cycle 121Constant pressure cycle piston modification 122Constant-pressure cycle: the future for diesels? 45Control Blade rear suspension 104Control strategies for CVT 56Control strategy for 4-wheel steer 138Controlled -collapse trim 151, 160Controlled collapse 144Controlling restraint deployment 33Conventional and electric drivetrain 75Cosworth Engineering's MBA engine 118Crash severity sensing 31Cross-bolting of main-bearing caps 118CV chassis-cab configuration 163CV systems 163CV-joint packaging 131CVT engine torque curve matching 56CVT for 2-litre engined vehicles 53

D

DAF concept truck 163Dallara MMGB suspension design software 63Delphi E-STEER electronic steering 82Dennis Rapier space-frame chassis 164Design for the disabled 27Diesel engine with oil-cushioned piston 45Digital circuits for computation 79Direct injection gasoline 43Door seals 155Doors, windows and panels 155Double-level floor of Mercedes A-class 97Drive and steer systems 128Drive strategy for influencing factors 57Driverless taxi 29Drivetrain control 75

EEasy-access cab 168Easy-access curtainsider 166

176 VEHICLE DESIGN

Easy-assemble brake booster 142Easy-change CV-UJ assembly 130Electric double-layer capacitors (EDLCs) 88Electro-rheological magnetic (ERM) fluids 72Electromagnetic braking 141Electromagnetic valve actuation 122Electronic brake actuation system 139Electronic control of electric steering 73Electronic Stability Programme on Focus 103Emissions of small HSDI diesels 40Energy storage initiatives 88Engine developments 118Engine force balancer for motorcycle 126Engine refinement 124Engine temperature management 121Engine-coolant airflow 132Equilibrium lateral acceleration 59European 13 Mode test 39Exhaust fixing 161

Fail-safe brake actuator 141Fatigue life of valve gear 125Fatigue performance of Fastriv system 14Fibre-optic light division system 161Filtering diesel particulates 127Fluid-actuated anti-roll control 136Flywheel battery 128Flywheel to crankshaft connection 126FMVSS impact energy absorption levels 7Footwell deformation in vehicle impact 16Ford Focus 102Freer moving bogie suspension 136Front and rear wheels, Thrust SSC 112Front brake, Thrust SSC 115Fuel delivery system 161Fuel injection rethought 122Fuel stratification 44Fuji Industies ELCAPA hybrid vehicle 89

G

Gas storage requirement 39Gear train schematics 52

H

Handling software example 60Head rest adjuster 154Headway sensor design 77

Height-adjust for trailer coupling 142High activity, homogeneous charge concept 47High-torque manual transmission 54Honda automatic transmission 53Honda intelligent steering system 74Hybrid drive prospects 84Hydraulically sprung connecting rod 45

Ideal cycle efficiency 46Intake valve disablement 47Integrated air/fuel induction system 122Integrated engine/transmission 43Integrated latch/lock system by Bosch 157Integration of clutch servo actuator parts 142Interior noise analysis 20Interior sound pressure distribution 23Intrusion simulation mechanism 17Ion current response 70

K

Kyoto tram 30

L

Land Rover Freelander 108Late intake valve closing 48Lateral acceleration of tractor/trailer 61LD-SRIM composite panel construction 162Leg injuries 33Light-alloys development 3Liquified natural gas (LNG) 40LNG-powered ERF truck 39Logic circuits 79Lotus Elan structure 149Lotus Engineering Jewel Project engine 120Low-cost supercharging 122

M

Magnesium Association Design Award 3MAN diesel pollution control 126MAN and Voith NL 202 DE low floor city bus 168Material property charts/performance indices 10Mazda punt structure 150Mechanical systems on Freelander 110Mechanics of roll-over 58Mercedes A-class 96Metal/plastic systems 4Millbrook VTEC facility 38Mobility for all 27

INDEX 177

MSC/NASTRAN 19Multi input/output gearbox 129Multi-node suspension model 62Multiple valve arrangements 49

N

Navigation system advances 76Necked hub member 138New Venture Gear NVT-750 gearbox 55Nissan CVT configuration 54Nissan CVT for 2-litre cars 53Non-stick front forks 136

o

Occupant protection in side impact 146Occupant restraint 151Occupant sensing 31Optimized re-charge strategy 86Optimizing unsprung mass with wheel travel 133

Parallel hybrid drive mechanism 85Part-load control by late intake valve closing 48Particle orientation in Theological fluid 72Particle size analysis 37Particulate size distribution 37Passive Anti-Theft System (PATS) 107Pedestrian protection device 160Pedestrian protection in impact 24PEM fuel cell, natural gas fuelled 89Personal Productivity info-technologies 81Pillar to rail joint stiffness 18Plastic structural beam 6Plenum and port throttles 119Plunge joint 130Poppet valve effective area comparison 50Poppet valve half-angles/radius-ratios 51Porshe suspension sub-frame 148Power interaction diagram for hybrid drive 86Powertrain on Ford Focus 104Powertrains: the next stage? 36Primary safety system of M-B A-class 99Production hybrid-drive control system 87Proprietary control system advances 81Pyrotechnic actuated venting 33

QQuicker catalyst light-up 127

R

RACD damper unit 73Racing clutch 129Rapid-actuation diff-lock 129Rear brake, Thrust SSC 116Recycled PET, and prime PBT, for sun-roof parts 7Reduced-emission systems 124Refinement of individual systems, Ford Focus 102Return-load tanker 165Road guidance for drowsy drivers 77Road traffic NOx emissions 38Road-friendliness, a current review 66Roll effects 65Roll reactions on suspended vehicle 58Roll response to step input 59Rover Asymmetric Combustion Enhancement 47

Sachs variable valve timing 125Sarich 2-stroke 124Scania turbo-compound diesel 120Seamless electro-mechanical vehicle 70Seat adjustment mechanism 153Seat of Mercedes 300 SL 153Seat-belt pretensioners 151Secondary safety systems 96Self-pierce riveting 13Self-steering in forward and reverse 138Set-speed down-hill braking 142Shopping ferry 30Short-haul taxi 28Side airbag within seat back 152Side impact protection structure 145Sidemember construction novelty 147Sill and quarter panel joint 146Simplified level sensing 160Sliding door drive 159Smart materials for suspension control 71Soft-mounted cab tilt 164Specific stiffness property chart 11Specific strength property chart 12Speeding engine warm-up 127Split tailgate 155Steel durability and structural efficiency 2Steer fight in braking 135Steering assist mechanism 82Steering column immobilizer 137Steering robot 91

178 VEHICLE DESIGN

Steering system on Freelander 111Steering-castor adjustment 137Storing swirl energy 122Strengthening a convertible body 148Structural-coloured fibre has body trim potentialStructural design in polymer composites 6Structural systems 144Structure of Freelander 108Supercapacitors for hybrid drive 88Super-element in FEA 20Sure-fire gear engagement 129Suspension and steering linkage analysis 62Suspension compliance conflict 135Suspension compliance work of John Ellis 64Suspension development 133Suspension geometry control 135Suspension supports of M-B A-class 100Swivel pin bearing pre-stressing 137Synthetic urban drive cycle 84Systems integration effect on sensors 70

Valve arrangements for engine efficiency 47Variable cube body 165Variable geometry engine intake 125Variable valve timing 125Vehicle body FEM 23Visualization of in-cylinder flow 44VVT for Rover K-series 124

wWheeled battle-tank 132Winder mechanism 156

Zero-offset geometry 103ZFCFT20CVT 57

Tail-lift in door 167Taxis and people movers 28TEC mobility system 81Textron Fastriv system 13Through-bolt and monoblock configurations 43Thrust SSC land-speed jet car 112Tiller steering 137Torque reaction system for steering robot 92Torque roll axis engine mounts on Focus 107Toyota Hybrid System 87Transient roll-over 59Transmission design trends 52Transverse spring composite suspension 133Tribus guided vehicle system 128Trim and fittings 159TRL knee joint model 24TRL leg-form impactor 25Truck and bus emissions 38Tuned suspension mounts on Focus 107Turbocharger waste-gate control 121Two-dimensional suspension analysis 64Two-stage energy absorption 144

uULSAB body shell 2Urban rickshaw 27

Documents

Advances in Vehicle Design