Upload
alex-oses
View
219
Download
2
Embed Size (px)
Citation preview
Modern Vehicle Systems
Design (ENG 3170)
A. Sorniotti Senior Lecturer in Advanced Vehicle Engineering (16AA03)
Email: [email protected], Ext: 9688
S. Fallah Lecturer in Vehicle and Mechatronic Systems (11AA03)
Email: [email protected], Ext: 6528
Modern Vehicle Systems Design – Dr. A. Sorniotti
The Vehicle Engineering Group •Coordinator of the FP7 E-VECTOORC project;
•Principal investigator in the FP7 projects iCOMPOSE, PLUS-
MOBY and FREE-MOBY, WP leader in AUTOSUPERCAP;
•Optimisation and testing of novel transmission systems;
•Development of novel automotive controllers
www.e-vectoorc.eu
Examples of results
• Three driving modes (sport, normal, eco) selectable by the driver;
Torque-vectoring controller
• Vehicle response ‘designed’ through the controller
Skid pad test
results
• Three driving modes (sport, normal, eco) selectable by the driver;
Torque-vectoring controller
• Vehicle response ‘designed’ through the controller
• Reduced delay
Step steer results
• Increased yaw damping;
Examples of results
Examples of results Drivetrain modelling
and testing
Outline
Modern Vehicle Systems Design – Dr. A. Sorniotti
•Part 1: basic theory of vehicle dynamics;
•Part 2: hybrid electric and fully electric vehicles
Final Mark
•40% coursework due on Tuesday week 11 (report dealing with
the set of design calculations that will be assigned in week 6);
•60% final exam (2 hour duration, including exercises, multiple-
choice questions, open questions)
Main References
•Milliken WF and DL, Race Car Vehicle Dynamics, SAE
International, 1995, ISBN 1-56091-526-9;
•Reimpell J, Stoll H and Betzler H, The Automotive Chassis,
Butterworth-Heinemann, 2001, ISBN 0 7506 5054;
•Limpert, R., Brake Design and Safety, 1999, SAE
International;
•Ehsani M, Gao Y, Gay SE, Emadi, A, Modern Electric, Hybrid
Electric and Fuel Cell Vehicles, CRC, 2010, ISBN
1420053981;
•Chan CC, Chau KT, Modern Electric Vehicle Technology,
Oxford University Press, 2001, ISBN 978-0-19-850416-0;
•Lecture Notes
Modern Vehicle Systems Design – Dr. A. Sorniotti
Modern Vehicle Systems Design – Dr. A. Sorniotti
Part 1 - Topics
•Revision of basic concepts relating to tyre behaviour;
•Derivation of analytical formulas for the calculation of the load
transfer in traction/braking and discussion of the criteria for
braking system design;
•Derivation of the analytical formulas for the calculation of the
load transfers in cornering conditions;
•Fundamentals of braking system design;
•Discussion of vehicle pitch dynamics
Modern Vehicle Systems Design – Dr. A. Sorniotti
Part 1 – General Philosophy
•Many of the concepts to be presented in this module have
already been discussed in the level 2 vehicle dynamics
module;
•This module aims at the analytical and quantitative description
of these concepts;
•Real engineers must be able to carry out design calculations;
•By the end of the module it is expected to be able to carry out
load transfer calculations, basic suspension analysis and
design, simulation of vehicle longitudinal dynamics
Modern Vehicle Systems Design – Dr. A. Sorniotti
Revision – Tyre Behaviour
Longitudinal force
𝑆𝑙𝑖𝑝 𝑅𝑎𝑡𝑖𝑜 =𝜔
𝜔0− 1
• Various possible definitions according
to different textbooks;
• According to this definition the slip ratio is positive in traction and
negative in braking;
• As a consequence, it is:
−1 < 𝑆𝑙𝑖𝑝 𝑅𝑎𝑡𝑖𝑜 < ∞
Wheel locked during braking
Wheel spinning in conditions of
vehicle standstill
Revision – Tyre Behaviour
Modern Vehicle Systems Design – Dr. A. Sorniotti
Longitudinal force
𝐹𝑧
• The location of this
peak depends on the
tyre and surface
characteristics;
• The presence of this
peak justifies the
difficulty of tyre slip
control during anti-
lock braking and
traction control
𝜇𝑥,𝑀𝐴𝑋 =𝐹𝑥,𝑀𝐴𝑋
𝐹𝑧
Modern Vehicle Systems Design – Dr. A. Sorniotti
Revision – Tyre Behaviour
Longitudinal force
• The variability of these
characteristics is very
significant;
• For example, some sources
report an increase of the
longitudinal force vs. slip
ratio on snow
𝜇𝑥 =𝐹𝑥
𝐹𝑧
Modern Vehicle Systems Design – Dr. A. Sorniotti
Revision – Tyre Behaviour
𝑥
𝑦
𝑉
Slip Angle
Lateral Force
Aligning Moment
Lateral force
Key concepts
• Tyre reference system;
• Slip angle;
• Lateral force;
• Aligning moment
𝛼
Modern Vehicle Systems Design – Dr. A. Sorniotti
Revision – Tyre Behaviour
Lateral force
Key concepts
• Cornering stiffness C;
• Non-linear behaviour;
• Friction coefficient
𝜇𝑦,𝑀𝐴𝑋 =𝐹𝑦,𝑀𝐴𝑋
𝐹𝑧
Revision – Tyre Behaviour
Lateral force
Modern Vehicle Systems Design – Dr. A. Sorniotti
Notice that in this case
the tyre has an
asymptotic behaviour
(frequent case) as a
function of slip angle
Modern Vehicle Systems Design – Dr. A. Sorniotti
Revision – Tyre Behaviour
𝜇𝑦 =𝐹𝑦
𝐹𝑧
Lateral force
Please pay attention!
𝐹𝑧
𝐹𝑧
Revision – Tyre Behaviour
Modern Vehicle Systems Design – Dr. A. Sorniotti
Interaction between longitudinal and lateral force
These trends justify the regulations about brake distribution and the
adoption of anti-lock braking systems
Modern Vehicle Systems Design – Dr. A. Sorniotti
Revision – Tyre Behaviour
Interaction between longitudinal and lateral force
Rear wheel locking Oversteer
Front wheel locking Understeer
Modern Vehicle Systems Design – Dr. A. Sorniotti
Revision – Tyre Behaviour
Interaction between longitudinal and lateral force
Key concept: friction ellipse
Elliptical envelope
Modern Vehicle Systems Design – Dr. A. Sorniotti
Revision – Tyre Behaviour
Interaction between longitudinal and lateral force
Revision – Tyre Behaviour
Modern Vehicle Systems Design – Dr. A. Sorniotti
The effect of camber is
much less significant
than the one related to
slip angle
Revision – Tyre Behaviour
Modern Vehicle Systems Design – Dr. A. Sorniotti
Tyre rolling resistance
Undriven wheel in conditions of constant speed
Rolling resistance is caused by the fact that the resultant vertical force is
applied to the frontal part of the contact patch
𝜔
𝐹𝑧 −𝐹𝑧
𝐹𝑅𝑜𝑙𝑙
∆𝑥
𝑅𝑤,𝑙𝑎𝑑𝑒𝑛
𝐹𝑅𝑜𝑙𝑙𝑅𝑤,𝑙𝑎𝑑𝑒𝑛 = 𝐹𝑧∆𝑥
∆𝑥 = 𝑓𝑅𝑤,𝑙𝑎𝑑𝑒𝑛
𝐹𝑅𝑜𝑙𝑙 = 𝑓𝐹𝑧 −𝐹𝑅𝑜𝑙𝑙
Modern Vehicle Systems Design – Dr. A. Sorniotti
Revision – Tyre Behaviour
Tyre rolling resistance
Exercise – What would the free body diagram be for a driven wheel?
𝑓 = 𝑓0 + 𝑓1𝑉 + 𝑓2𝑉2
The rolling resistance coefficient is a function of speed:
Typical values are:
𝑓0 = 0.011 [−] 𝑓1 = 0 [𝑠/𝑚] 𝑓2 = 6.5 10−6 [𝑠2/𝑚2]
Modern Vehicle Systems Design – Dr. A. Sorniotti
Revision – Tyre Behaviour
Tyre rolling resistance
Effect of slip angle on rolling resistance
𝐹𝑥
𝐹𝑦
𝑉
𝐹𝑅𝑜𝑙𝑙
𝐹𝑅𝑜𝑙𝑙 = 𝐹𝑥 cos 𝛼 + 𝐹𝑦 sin 𝛼
𝐹𝑅𝑜𝑙𝑙 ≅ 𝐹𝑥 + C𝛼2
If 𝐹𝑦 ≅ Cα (small slip angle) then:
𝛼
Calculation of the Wheel Loads
•Vehicle dynamics is significantly influenced by the variation of
the vertical load between each tyre and the road as a function
of braking and cornering forces;
•In general, the lower is the load transfer, the better are vehicle
dynamics;
•It is necessary to achieve a good understanding of the
mechanisms which provoke load transfers in order to have an
acceptable evaluation of vehicle dynamics
Modern Vehicle Systems Design – Dr. A. Sorniotti
Calculation of the Wheel Loads
ya
xa LFzF ,
Vehicle parameters
RFzF ,
RRzF ,
LRzF ,
Roll angle V
Modern Vehicle Systems Design – Dr. A. Sorniotti
Prediction of the Vertical Load
in Static Conditions
a b
mg
CG
L
a = front semi-wheelbase
b = rear semi-wheelbase
L = wheelbase
FSTATICzF ,, RSTATICzF ,,
O
Modern Vehicle Systems Design – Dr. A. Sorniotti
Prediction of the Vertical Load
in Static Conditions
L
mgaFF RRSTATICzLRSTATICz
2,,,,
L
mgbFF RFSTATICzLFSTATICz
2,,,,
mgbLF FSTATICz ,,
Moment balance equation about point O
L
mgbF FSTATICz ,,
mgFF RSTATICzFSTATICz ,,,,
Force balance equation (vertical direction)
L
mga
L
bmgFmgF FSTATICzRSTATICz
1,,,,
Combining the former equations, it is:
Modern Vehicle Systems Design – Dr. A. Sorniotti
Prediction of the Vertical Load
in Static Conditions
In the case of race cars it is easy to change the static load distribution
during the vehicle design phase
62% 38% Excluding driver
Modern Vehicle Systems Design – Dr. A. Sorniotti
Prediction of the Vertical Load
in Static Conditions
Modern Vehicle Systems Design – Dr. A. Sorniotti
In this case the mass distribution is shifted
towards the front axle
Prediction of the Effect of the
Aerodynamic Forces and Moments
DRAGCAERODYNAMIF _
FRESISTANCEROLLINGF ,_ RTRACTIONF ,
FCAERODYNAMIzF ,,
CG
CGH
Constant velocity
Rear wheel driven vehicle (like our FS vehicle)
RCAERODYNAMIzF ,,
YCAERODYNAMIT ,
L
O
DOWNFORCECAERODYNAMIF _
Modern Vehicle Systems Design – Dr. A. Sorniotti
Prediction of the Effect of the
Aerodynamic Forces and Moments
Moment balance equation about point O
LT
L
bF
L
HFF
YCAERODYNAMIDOWNFORCECAERODYNAMI
CGDRAGCAERODYNAMIFCAERODYNAMIz
1,_
_,,
YCAERODYNAMIDOWNFORCECAERODYNAMI
CGDRAGCAERODYNAMIFCAERODYNAMIz
TbF
HFLF
,_
_,,
Modern Vehicle Systems Design – Dr. A. Sorniotti
Prediction of the Effect of the
Aerodynamic Forces and Moments
2
__2
1VSCF DOWNFORCECAERODYNAMIDOWNFORCECAERODYNAMI
2
_2
1VSCF DRAGDRAGCAERODYNAMI
2
,,2
1LVSCT YTYCAERODYNAMI
32.1m
kg
Modern Vehicle Systems Design – Dr. A. Sorniotti
S frontal area of the vehicle
air density
Prediction of the Effect of the
Aerodynamic Forces and Moments
2
,,
,,,,
RCAERODYNAMIz
LRSTATICzRRzLRz
FFFF
2
,,
,,,,
FCAERODYNAMIz
LFSTATICzRFzLFz
FFFF
0_,,,, DOWNFORCECAERODYNAMIFCAERODYNAMIzRCAERODYNAMIz FFF
Modern Vehicle Systems Design – Dr. A. Sorniotti
Prediction of the Effect of the
Aerodynamic Forces and Moments
DRAGCAERODYNAMIF _
RRESISTANCEROLLINGF ,_FTRACTIONF ,
FCAERODYNAMIzF ,,
CG
CGH
Constant velocity
Front wheel driven vehicle
RCAERODYNAMIzF ,,
YCAERODYNAMIT ,
L
DOWNFORCECAERODYNAMIF _
Modern Vehicle Systems Design – Dr. A. Sorniotti
Prediction of the Effect of the
Aerodynamic Forces and Moments Typical Data Sets (passenger cars)
Vehicle CDRAGS [m2] CDRAG S [m2]
Renault 5 0.67 0.37 1.80
Opel Kadett 0.60 0.32 1.88
Ferrari Testarossa 0.61 0.33 1.85
Alfa Romeo GTV 0.71 0.40 1.77
Mercedes 190 E 0.65 0.34 1.89
Mercedes 200 0.60 0.29 2.07
Modern Vehicle Systems Design – Dr. A. Sorniotti
Load Transfer during
Traction/Braking
L
HmaF CGx
az x ,
xazF ,xazF ,
If the vehicle is braking or accelerating, there is an additional load transfer which, in a
very first approximation, without considering the effect of suspension stiffness and the
anti-dive, anti-lift and anti-squat designs of the suspensions, can be computed in the
following way:
CG xma
CGH
RTRACTIONF ,FRESISTANCEROLLINGF ,_
Modern Vehicle Systems Design – Dr. A. Sorniotti
Load Transfer during
Traction/Braking
22
,,,
,,,,XazFCAERODYNAMIz
LFSTATICzRFzLFz
FFFFF
22
,,,
,,,,XazRCAERODYNAMIz
LRSTATICzRRzLRz
FFFFF
Modern Vehicle Systems Design – Dr. A. Sorniotti
Load Transfer during Braking
xa
XazF ,
Vertical load
1.5 g
Formula Student vehicle (for an assigned V)
XazF ,
Rear axle
Front axle
Modern Vehicle Systems Design – Dr. A. Sorniotti
Load Transfer during Braking
xa
XazF ,
Vertical load
1.1 g
Typical Passenger Car (for an assigned V)
XazF ,
Rear axle
Front axle
Modern Vehicle Systems Design – Dr. A. Sorniotti
The vertical load
distribution
significantly changes
during braking
Equations for the Prediction of the Load
Transfer during Traction/Braking
Static load distribution 50:50,
centre of gravity height 0.5 m
• Load distribution during braking at 1.1g and 100 km/h?
• What happens for a different number of passengers?
Modern Vehicle Systems Design – Dr. A. Sorniotti
• Load distribution at 130
km/h (constant velocity)?