Excava-e

37RE 00 207/10.00

Modern Hydraulic Systems forWheeled and Crawler Excavators


Excavators with fully hydraulic working equipmenthave been around for the last 50 years or so. Mul-tiple circuit systems were built, initially with anumber of gear pumps which were deactivated asa function of pressure in order to achieve a formof power control. With the introduction of controlhydraulics and high pressure, standard excavatorscame to feature almost exclusively dual-circuitthrottle control systems with axial piston pumpsand motors. The power supply to the implementswas in most cases by means of a double pump inbent axis design, for instance the A8VO model, stillin use today in open centre systems on manyexcavators, cranes and similar machines.

The functionality of throttle control systems withtwo 4-spool MO control blocks and, later, the seriesM8 compact control blocks has been continuallyimproved over the years. However, with growingdemands for excavator controllability and optimumflow distribution to the individual actuators, manyleading excavator manufacturers took the decisionto go over to load sensing systems and variationsof these. Rexroth developed the LUDV system(load-pressure independent flow distribution) tomeet this need and has implemented it in severalmachines with varying requirements.

Fig. 1: Modern hydraulic systems for wheeled and crawler excavators

Min

i Exc

avat

or

Com

pact

Exc

avat

orCo

mpa

ct E

xcav

ator

Stan

dard

Exc

avat

or

Egon Rill / VMT1/HBrueninghaus Hydromatik GmbHHorb plantAxial piston unitsPhone +49 (0) 7451 / 92-14 63Fax +49 (0) 7451 / 92-82 21E-Mail: [email protected]

Gilles ChetailMannesmann Rexroth S. A.FranceControl technologyPhone +33 / 47878 -5248Fax +33 / 47878-5271E-Mail: [email protected]

Ralf Uhde / LVV-MLohmann + Stolterfoht GmbHWittenGear technologyPhone +49 (0) 2302 / 877-457Fax +49 (0) 2302 / 877-404E-Mail: [email protected]

Werner Herfs / RMH-V1Mannesmann Rexroth / LohrControl technologyPhone +49 (0) 9352 / 18-2380Fax +49 (0) 9352 / 18-2159E-Mail: [email protected]

Gnter Fertig / RMH-V1Mannesmann Rexroth / LohrControl technologyPhone +49 (0) 9352 / 18-2353Fax +49 (0) 9352 / 18-2159E-Mail: [email protected]

Helmut Funk / RMH-LMannesmann Rexroth / ParchimSteeringsPhone +49 (0) 3871 / 606-235Fax +49 (0) 3871 / 606-201E-Mail: [email protected]

Dirk van Aalst / VMT1/EBrueninghaus Hydromatik GmbHElchingen plantAxial piston unitsPhone +49 (0) 7308 / 82-25 63Fax +49 (0) 7308 / 53 38E-Mail: [email protected]

The special features, differences and possibilitiesoffered by hydraulic drive and control systems inthe different categories of excavators are describedbelow, with reference to the most popular sizes ofmachine worldwide (fig. 1).

38 RE 00 207/10.00


1. Control System for MiniExcavators

Mini excavators in the weight class from 2.5 toapprox. 5 metric tonnes are still predominantlyfitted with multiple circuit open centre systems. Toachieve the performance and manoeuvrability thatthe market demands, 3-circuit pump systems aremostly used (fig. 2).Double variable displacement pumps such as theA12VO and an attached gear pump for the slewdrive with a single suction port are widely used. Asecond gear pump with integral pressure reliefvalve serves the pilot oil circuit.The ever-more compact, modern design of todaysmini excavators with a high proportion of zero tailmodels calls for new solutions requiring less roomfor components and in particular for the pump andcontrol block.Unit numbers of mini excavators equipped with avariable displacement pump and closed centredirectional control valve have increased worldwidein recent years. Rexroth is one of the first hydraulicsmanufacturers to have developed this concept formini excavators, and the present-day-success of

Fig. 2: Throttle control three-circuit system

MCR(Slew drive)

GFT + A10VT(Travel drive)

SM 12(Control)

A12VO(Travel and implement hydraulics)

4TH5(Pilot control units)

this system is confirmation that we took the rightdecision (fig. 3).The mini excavator characteristics which themarket demands are importantly determined bythe features that are already taken for granted onstandard excavators: greater operation comfort improved precision control, manoeuvrability and

accuracy of the machines cost reduction by simplifying the hydraulic circuit increased reliabilityThe path more and more of our customers aretaking in order to achieve these performancecharacteristics is the Rexroth single-circuit LUDVsystem. This principally comprises the A10VO va-riable displacement pump and model SX12 closedcentre directional control valve with integral LUDVfunction.The swashplate medium-pressure pump A10VOseries 31 currently in use has been modified andin series 53 it now features an even more compactshape with a constant power control integrated

into the housing with no external piping (fig. 4).For some models the connecting plate has beendesigned to enable a special gear pump also to beattached to the through-drive, sharing a commonsuction port with the main pump (fig. 5).

39RE 00 207/10.00


Fig. 3: 1-circuit LUDV system

MCR(Slew drive)

GFT + A10VT(Travel drive)

9SX12(Control)

A10VO(Travel and implement hydraulics)

4TH5 2TH6R 4TH5(Pilot control units)

MHSTE(Pilot oil supply)

Fig. 4: A10VO for mini excavator

A10VO/53

Size ________________ 10...85

Nominal pressure pN _____ 250 bar

High pressure pmax ___ 315 bar

Fig. 5: A10VO with integral gear pump

Technical data:A10VO 28 DFLR/53Size 28 + 8Nominal pressure: 250 barPeak pressure: 315 bar single suction port pressure controller flow controller constant power control

40 RE 00 207/10.00


A10VO series 53 also offers electro-proportionalpump control (EP) for nominal sizes 28, 45, 60 and85 (fig. 6). The swivel angle control isproportionately adjustable via an electric current,thus expanding the control range for the A10VOpump.Internal mechanical swivel angle feedback ensurespermanent transient load adjustment of the forcesupplied via the proportional solenoid valves.The mechanical/hydraulic pressure and volumecontroller can also be attached to the pump andis effective below the electrical flow limitingsystem.EP controller can be upgraded to speed-sensingcontrol by recording the diesel engine drive speedand pedal position (fig. 7).This means that when the diesel engine is underload and the diesel engine speed is under strain,the input power of the pump is adjusted byreducing the flow volume.The advantage is that the power of the dieselengine is used as efficiently as possible at all times.Although electronic speed-sensing control stillaffects the cost of a mini excavator at present, newregulations on exhaust and noise emissions andreduced energy consumption could makeelectronic speed-sensing control cost-effective ifenergy costs continue to rise.

Fig. 6: A10VOEP series 53

Fig. 7: A10VOEP with speed sensing control GLB

Controlblock SX

Diesel engine

/

max

EP

1

0 I/Imax 1

A10VO...EPDF/53

Gearbox

Microcontroller

Speed sensor

Accelerator pedal position

41RE 00 207/10.00


The good controllability of the machines isachieved through volume flow control in thedirectional control valve SX12. The characteristicsof this remain optimal irrespective of the loadpressure (fig. 8). The LUDV function allows the flowdistribution desired by the driver to be guaranteedindependently of the combination of machinemovements. Even if the pump volume flow isinsufficient, the speed of the movements initiatedremains constant with respect to one another.On the tracked excavator, straight-line travel is stillensured even if several operating functions areactivated at the same time.Moreover, the improved and simplified operationof the controls makes it easier to learn how tooperate the machine, an additional advantage withregard to the growth of the hire market.The patented design principle of the Rexroth valveswith the directly controlled LUDV pressurecompensator enables the necessary functions, suchas control, pressure selection and pressurecompensation, to be implemented in a simple andhence a reliable way.The single-circuit LUDV system simplifiesinstallation (the directional control valve comprisesa single inlet component) and componentassembly.The pump has no need for the costly cross-sensingcontroller that has to be used in a multiple pumpcircuit.The whole system requires fewer components andis less expensive than a comparable open centremultiple circuit system.Optimisation of the directional control valve spoolsalso includes an extension of the fine control range.The improved pilot properties are for exampleachieved by reducing the dead strokes (effect onthe chain between the operating angle on the pilotcontrol and the actuator speed).The 4-spool control system in the closed centredesign allows faster optimisation of the controlcharacteristics of each individual directional controlvalve piston in comparison with the conventional6-spool valve (open centre). This is a significantadvantage if the shorter development lead-timesexpected for new machine models are to beachieved. The LUDV principle also allows differentspeeds to be set for each actuator spool anddirection of movement. This enables theexcavators movement sequence to be precisely co-ordinated.The power requirements made of the slew drivefunction are also derived from the standardexcavator class.

Fig. 8: 9SX12 LUDV-control block

Fig. 9: Section of SX12

By means of a specially developed slew drive pistonco-ordination system, we are able to offer idealsolutions according to the machine manufacturersrequirements and machine size.Unlike conventional 3-circuit systems, the slewdrive does not have full priority. Sub-priorityachieved via the pressure compensator gives themini excavator satisfactory function.Furthermore, the LUDV load sensing conceptprovides the necessary flexibility for the adding ofextra functions.The SX12 directional control valve, designed for aflow volume of 120 l/min at the pump inlet and80 l/min per directional control valve element, canbe used for mini excavators from 1.5 t to about 6 twith an operating pressure up to 250 bar.

42 RE 00 207/10.00


Drive torqueT2

The 4TH5 pilot control unit (fig. 10) is a newdevelopment which has considerably improved thecontrollability of mini excavators. The reduction inthe operating forces and reduced powerfluctuation when the lever is operated improve theconditions of use and increase convenience ofoperation.With regard to triggering the crawler travelfunction, the new 4TH6NR foot pedal unit (fig. 11)in monobloc construction with integral dampingfunction provides a further improvement inconvenience of operation. Even jerky movementsof the levers, for instance when returning to neu-tral, are damped, thus avoiding oscillation.The 4TH6NR unit is more compact than twoindividual 2TH6R units fitted side by side and theuse of a single fastening plate simplifies installationon the machine. The valve can be equipped withvarious pedals according to the customersrequirements.Mini excavators offer various possibilities for pilotoil supply. With the MHSTE model pilot oil unit(data sheet RD/E 64571) the pilot oil is drawn offthrough a pressure-reducing valve connected withthe main circuit and the pressure is limited by apressure-limiting valve. Two electrically operatedswitching functions can also be integrated into theunit. One is designed for the safety function of thearmrest position, and the other, which is optional,serves to switch the 2-step travel motors.The scope which Rexroth offers for supplying acomplete system from a single source representsa further advantage in terms of machine planningthanks to a co-ordinated range of components.

The GFT track drives for this application arecharacterised by remarkable compactness andexpand the product range for mini excavators(fig. 12).Such compactness is achieved in particular by theuse of hydraulic motors specially developed for thisapplication, which function as an integral part ofthe driving gear and thus form an ultra-compactdrive in conjunction with the planetary gearconstruction.By adapting the carrying axle inner contour to therequirements of the hydraulic motor, there is noneed to use a separate motor housing.The result of this coordinated componentdevelopment between LST and BHY is a productrange from GFT 3 to GFT 9 with the followingcharacteristics: compact, space-saving two-stage planetary

construction rugged bearings

Fig. 11: 4TH6NR foot pedal remote controlvalve for track drive

Fig. 12: HYDROTRAC GFT travel drive for mini excavators

integral medium-pressure hydraulic two-stepmotors in swashplate design

counter balance valve and secondary relief valveintegrated into the motor plate

integrated multiple-disc parking brake(not GFT 3)

high starting efficiency simple assembly simple oil change low-noise running

Fig. 13: Table of HYDROTRAC driving gear for mini and compact excavators

Driving gear Two-step motorcapacity

Excavatorweight

GFT 3 *

GFT 4 *

GFT 7

GFT 9

3000

4000

7000

9500

18

28

28

45

3

5

6

9

Vg max Vg mincm3

9

14

14

22,5* in preparation

Development work continues with the aim ofadapting the MCR type radial piston motors to thespecial requirements of the slew drive in the miniexcavator class. It will then be possible to createthe entire hydraulic system with components madeby Rexroth.

Fig. 10: 4TH5 Joystick

43RE 00 207/10.00


Fig. 14: 7 tonne tracked excavator

Fig. 15:1-circuit LUDV-system

GFB + A10FD(Slew drive) A6VM + MHB

(Travel drive)9SX14

(Control)

A11VO / A10VO + G2(Travel and implement hydraulics)

4TH6N 2TH6R 4TH6N(Pilot control units)

MHSTE(Pilot oil supply)

Brake Steering

2. Compact Excavators, 7 toApproximately 10 Tonnes

The compact excavator class is a growing marketsegment, because: mini excavators under 5 tonnes do not deliver

sufficient power standard excavators over 10 tonnes are too big

and thus not manoeuvrable enough for urbanuse

the excavator-loaders still widely used in manycountries are losing market share to specialisedmachines like excavators and wheel loaders.

Compact excavator manufacturers vary in theirviews of how an excavator in this weight classshould work. Such differences are due in part to: manufacturers extending their product range

downwards from the standard excavator classor

mini excavator manufacturers expanding theirexisting product line upwards.

44 RE 00 207/10.00


Fig. 16: 6SX14 Fig. 17: 4M6-15

Fig. 18: A10VO Fig. 19: A11VO

Rexroth rises to these different challenges withstandard products perfectly matched to marketrequirements.The existing components that can be used in thisexcavator class are the SX14 or M6-15 valves, bothwith LUDV technology.The pumps used are the A10VO up to a pumppressure of 280 / 315 bar or the A11VO up to 350/ 400 bar.

It is important to consider at the design stage whatoutlay (cost) corresponds to what power andoperability, especially as regards the slew drive.The solution illustrated is a system comprising anA11VO or A10VO pump with constant power andflow controller and a series SX14 sandwich controlblock suitable for high pressure for a sectionvolume of approximately 150 l/min.The primary (1) and LS pressure cut-off valves (2),LS flow controller (3) and unloading valve (4)needed for a 1-circuit LUDV are implemented inthe combined inlet and slew control element.Moreover, the slew drive has priority supply via theconnection as a LS function to the rest of the LUDV.The LS meter-in pressure compensator (5) and thetorque control valve (6) for fine control and loss-free acceleration are housed in the combinationelement (7). The directional function for the slewdrive is implemented using a standard SX14sandwich element (8), but the LUDV pressurecompensator is not fitted.

Fig. 20: LUDV block for crawler excavator

A10VOor

A11VO

MHSTE

Pilotpressure

Swin

g1

2

3

4

68

5

7

45RE 00 207/10.00


3. Standard Excavators(Wheeled and Tracked),12 to 24 Tonnes

We do not propose to discuss the single-circuitLUDV system in detail with respect to standardexcavators. Naturally, Rexroth can supply thenecessary components for crawler and wheeledexcavators, as may be seen from the system circuitdiagram in fig. 21.What we would like to do is discuss the newproducts and features and look at some of theimportant details of various components used inLUDV systems.In the 1.5-circuit and single-circuit LUDV systemRexroth uses the A11VO swashplate type pump forthe open circuit. This pump has special featuresthat offers advantages to both the manufacturerand the operator of the excavator. The A11VOpump will be described more fully below.In the 1.5 circuit the slew drive makes use of theA10VO already described in the open circuit or theA4VG high-pressure pump for the closed circuit.The control of the A4VG has been further refinedand the size range now also additionally includesnominal sizes 90 to 250.Fig. 23 shows the available nominal sizes of theaxial piston units used in excavators. The provenbent axis variable displacement motor type A6VMfor long travel drives in the wheeled excavator isnow available with brake pressure dependentadjustment for more efficient braking ondownward slopes.

SizesImplement hydraulic Medium pressure A10VO...DFLR 28 45 60 85 (mini- and compact excavators)pump High pressure A11V/L)O...LE2S2 40 60 75 95 130 190 260

Slew pump Closed circuit A4VG...DWD 28 40 56 71 90 125 180 250Slew motor Swashplate A10FD... 45 85

Bent axis A2FE...192 28 32 45 56 63 80 90 107 125 160 180

Track drive motor Integral version A10VT...HZ 18 28 45 (mini- and compact excavators)Plug-in version A6VE...HZ3 55 80 107 160

Axle drive motor A6VM...HA1 55 80 107 140 160

GFB + A10FD(Slew drive)

A6VM + BVD(Travel drive)

A11VO(Travel and implement

hydraulics)TH6(Pilot control units)

1M7 + 5M7 + 1M7(Control)

Fig. 22: Axial piston units for Excavators

A4VG...DWD

GFT+A10VT

A2FE...192

A6VE...HZ3...22

A6VM...380K+BVD

A10VO...DFLR/53

A11VO...LE2S2

GFB+A10FD

Fig. 21: 1-circuit LUDV-system

Fig. 23: Nominal sizes of axial piston units

46 RE 00 207/10.00


3.1 A11VO as LS Pump inthe LUDV System

The A11VO swashplate type pump for the opencircuit (fig. 24) was designed in the form shownspecifically for LUDV systems. The diesel engineflange and the pump housing are one component.This gives the pump as a whole a very short, rigidconstruction. The flat-design controller lies in thecontour of the pump body and does not pretrudebeyond the end of the pump. The controller hasonly a small number of ports and these lie parallelto the pump to save space. The drain and bleedports are arranged in such a way that the pumpcan be fitted in any desired position in theexcavator. This construction allows considerablepossibility in the design of the oil tankcompartment and position.Demand for higher power makes larger dieselengines necessary in some cases. The more strin-gent noise emission regulations mean that moreroom is needed for encapsulation of the IC engineand pump. This increasingly eats into the spaceavailable for mounting the pump, so that acompact pump such as the A11VO is needed.In addition, diesel engine speeds are reduced dueto pollutant emissions. This in turn calls for largerpumps in order to main comparable flows. Astreamlined pump compartment together with thecompact A11VO allow larger pump sizes to beachieved, as well as making assembly and serviceeasier.The A11VO pump comprises three main groups(fig. 25): the one-part housing with the integrally cast

diesel engine flange, containing the rotarygroup,

the port plate with the positioning cylinderchambers and machining for the through-drive,

the one-part flat-design controller, which isbolted directly on to the port plate.

All the sealing points between these main groupsare, without exception, sealed by O-rings. Thisguarantees a dry pump and ensures a perfect sealis maintained even when components are replaced.The longitudinally arranged positioning cylindersproject into the port plate, where they are suppliedwith positioning oil through channels. All the supplychannels are securely housed in the stable port plate.This eliminates the need for external pipes, whichcould be a possible leak source.The housing incorporates two stable, adjustablestops for Vg min and Vg max. This allows the necessaryspecific flow volume to be adjusted as desired fromoutside, without having to dismantle or open up thepump.

Fig. 26: Constant power controller with electric override

Constant powercontroller withelectric override

Load-sensingcontroller withdifferentialpressure lowering

X (Load-sensing)

Fig. 24: Variable displacement pumpA11VO...LE2S2

Fig. 25: Variable displacement pumpA11VO...LE2S2 - section

When using the A11VO pump in the LUDV systemwe recommend the LE2S2 controller design(fig. 26). This controller comprises the hyperbolicconstant power controller with electric override viaa directly mounted round solenoid. The hyperbolicconstant power controller enables very goodpower use in any power mode. As a result,electronic speed-sensing control is not absolutelynecessary in a single-circuit system. In the absenceof electronic function both in power mode and inspeed-sensing control, the hyperbolic constantpower controller offers very good emergencyoperating functions.The mounted solenoids avoid the need for controlpipes and separate pressure reducing valves, andcan be operated directly from the cab. The round

solenoids can be rotated at will, enabling the castcables to be positioned in the optimumarrangement.The differential pressure setting override on theload-sensing controller is implemented in a similarway with a round solenoid, again saving many ad-ditional components and much installation work.A shuttle orifice is fitted inside the controller in thepump positioning oil channel. This is accessiblefrom the outside in order to optimise the sizeselection. The pump response time can thus bematched to the system.

47RE 00 207/10.00


Fig. 27: Variable displacement pump A11VOLE2S circuit diagram

X

M A G

S M1

Vg max Vg min

R T1 T2

1

2

3

4

5 6

7

8

9

A11VO basic pump for constant powercontroller

LE2S2 controller

Mechano-hydraulic-hyperbolic constantpower controller

Power adjusting spring

Power override with proportional solenoid

Shuttle orifice for adjusting time control

Load-sensing controller

Differential pressure setting spring

Differential pressure override with solenoid

1

2

3

4

5

6

7

8

9

LE2

I

S2

Ope

ratin

g pr

essu

re p

B (b

ar)

Power reduction

Fig. 28: Displacement pump A11VOLE2S performance curve

Pilot current I (mA)

pLS

(ba

r)

Volume flow qV (L/min)

Differential pressure reduction

Spring force

Pilot current I

Fig. 27 shows the circuit diagram of pump A11VOwith controller LE2S2.In fig. 28 the upper diagram shows the powercurve with LE2 controller design.The top start of control (basic setting) is achievedby the initial force of the control start spring. Asthe current at the override solenoid increases, thespring force and hence the start of control isreduced. The pump is thus set to a lower powercurve. In the event of power failure or a brokencable, the pump goes over to the highest powercurve specified by the mechanical setting.This controller design has a number of specialfeatures in relation to speed-sensing control:If the diesel engine is overloaded, the engine speeddrops. This signal is picked up by the micro-controller and reduces the start of control andhence the power input. If, for instance, the pumpis at Vg max and the operating pressure suddenlyrises, the A11VO pump is adjusted to a smallerswivel angle by means of the integral mechanicalconstant power controller and the rising pressure.In this case, the speed-sensing controller does nothave to respond at this stage. Only when additio-nal power is drawn from the diesel engine doesthe speed-sensing controller alter the start ofcontrol and set the A11V0 constant powercontroller to a new value.With other speed-sensing control systems, thepump swivel angle is altered by the control signal.In this case, if the pump is at max. flow volume, asudden high pressure increase causes the powerto rise, up to the corner power. This is when thespeed of the diesel engine has to be reduced sothat a signal is generated via the speed-sensingcontroller to swivel back the pump. Heavyoverloads may occur briefly.Speed-sensing control based on the hyperbolicconstant power controller produces stable controlbehaviour, less overloading and less speedfluctuation for the diesel engine.Differential pressure adjustment on the load-sen-sing controller of the variable displacement pumpis achieved by means of an adjustable spring force(fig. 28, bottom). This mechanical setting can bereduced to a lower differential pressure value withthe aid of a solenoid located opposite. Here too,the advantage of the directly mounted solenoid isevident, in avoiding the need for piping andenabling precision control from the cab.Fig. 29 top shows the influence of differentialpressure override. The effect of reducing the diffe-rential pressure setting is that each individualactuator is limited in the same percentageproportion in the maximum flow volume. This doesnot impair movement harmony, but only slows

down the movements so that all the controlledactuators are affected equally.Fig. 29 bottom shows the influence of differentialpressure reduction on precision controllability. Asdescribed above, in case of differential pressurereduction the maximum flow volume for thecontrolled actuators is reduced. The effect of thisis that if an excursion of the joystick, a smallervolume is now allocated to the actuator. Finecontrol is thus enhanced. The start of movementof the actuator, in relation to the excursion of thejoystick, is not altered and remains independentof the high pressure.

qV max

qV

qV red

max

x%

x%x%

x%

IIIIII

Fig. 29: Displacement pump A11VOLE2S differential pressure shifting

Lever stroke

Actuator

Flow reduction

Fine control expansion

p= x bar

p= < x bar

This fine mode enables lifting work or otheroperations where increased fine controllability isrequired to be performed very successfully.The A11VO pump is also available with a swivelangle sensor. This allows the momentary positionof the pump or the momentary flow volume to berecorded via an electrical signal. This makes itpossible in an excavator system for instance tocontrol the engine idle speed.

48 RE 00 207/10.00


Fig. 32

As a rule each A11VO pump is machined forthrough-drive attachment (fig. 30). This allows sim-ple retrofitting of through-drive parts of size SAE-A to through-drives for pumps of the same nomi-nal size. Many machine manufacturers are alreadymaking use of this possibility, frequently withvarying requirements as regards the pumpequipment.The symmetrical construction the flange can beturned through 90 - enables the pressure andsuction port of the attached pump to be arrangedin the optimum position. This cuts down on pipingand assembly.The availability of a large number of through-drivesgives the machine manufacturer a flexible choiceof attached pumps.

3.2 Slew DriveThe A2FE fixed displacement motor in bent axisdesign with integral one-stage or two-stagepressure valves is available for the slew drive.One new development is the swashplate fixeddisplacement motor model A10 FD 85, designedspecifically for slew drives in the open circuit.In conjunction with another new development, theMobilex GFB 17 T2 slew drive gearbox, a 1.5-litredrive is thus available for the 13 18 tonneexcavators (fig. 31).This slew drive is a combination of an ultra-compact 2-stage planetary gear with anA10 FD 85 medium-pressure transmission (Pnom =320 bar / Pmax = 350 bar).The driving gear features the proven short-designoutput housing. The bearings used for the outputshaft are high-capacity tapered roller bearings. Themultiple-disc parking brake, which was part of thedriving gear in the slew drives with A2FE motorspreviously presented, is now mounted on thecylinder in this rotary group to save space. The frontflange of the motor housing is conceived as thegearbox cover. In this design, all necessary valvesare integrated into the motor port plate.This includes: pressure relief valves with damping (prevents

overloading of the motor, pipes and valves dueto pressure peaks, while two-stage opening ofthe pressure relief valves prevents load peaksfor the transmission and boom whenaccelerating)

anti-cavitation valves (to prevent leakage oilcavitation when braking)

brake release valve (electrically or hydraulicallyoperated, to actuate the release pressure to themultiple-disc parking brake)

anti-reaction valve (prevents the upper bodyswinging back when decelerating).

Fig. 30: Variable displacement pump A11VO through-drive

Through-driveflange

Through-drivehub

Fig. 31: Mobilex GFB slew drive gearbox

There is thus no need for the conventional pipingwith this integrated drive solution (fig. 32). Itcovers a transmission range from 17.3 to 23.6 : 1.The next-smallest size of motor at 45 cc is designedto expand the slew gear series downwards inconjunction with an appropriately adaptedgearbox. The construction and valve gear willcorrespond to that of the GFB 17 T2 describedabove.

3 5

1

4

2

Pressure relief valve withdampingAnti cavitation valveBrake release valveAntireaction valveParking brake

PortsA,B Hydraulic portsL Case drain portPB Brake release pressure portMA, MB Measuring ports

Operating pressureS Boost port

1

2345

49RE 00 207/10.00


BLTTERN

MODE

F M

ManE

qp

maxmin

v u

RESET

Fig. 33: Working attachements

3.3 Multi-Function Elementfor Standard Excavators

As an addition to the 1.5-circuit and the single-circuit LUDV system, work has forged ahead ondeveloping a multi-function element for theoperation of various working attachments. The ideaof developing this multi-function element aroseas a result of repeated market demands and thegrowing variety of options for standard classexcavators.The Rexroth multi-function element offers andfulfils, in different stages of extension, all therequirements made of a modern multi-functionmachine such as the excavator.This applies not only to wheeled excavators butalso to tracked excavators in the standard class,which are tending to be used more and more forall sorts of jobs. Faster ground speeds and theassociated increase in the flexibility of the crawlerexcavator have played their part in this.Rexroth has developed a modular principle in orderto fulfil the varying requirements with the mosteffective solution in each case.The remit was to permit easy preselection of theflow and pressure for the particular attachment,such as a hammer, scrap shears, mower, generatorfor a magnet plate, etc. via the on-board computer.This renders obsolete all the solutions currently inuse, such as mechanical stroke limiters on thedirectional control valve, externally adjustablepressure valves, etc., most of which cannot beadjusted from the cab but require the use of tools.Furthermore, the flow and pressure settings haveconsiderable tolerances, as both these values aredifficult to verify in the field. The cost of thesesolutions is appreciable.As a rule the multi-function element is designedas an LS valve with meter-in pressure compensator.This operating principle permits the priority desiredfor many attachments with sufficient accuracy.A choice of 3/4 SAE or 1" SAE actuator ports allowsuse on the M7-20 and the M7-22 valve.In the basic or standard version, the multi-functionelement has been designed for a hammer. As isusual with the hammer, the valve spool is operatedat one side. The supply pressure available at thepst-port via a hydraulic remote control valve (joy-stick) is limited electrically by means of a propor-tional pressure valve (1) to the pilot pressurecorresponding to the volume.Pressure limiting is effected via a fixed secondarypressure relief valve (2).The reason Rexroth has chosen a pressure-freereturn flow to the tank (3) for the hydraulichammer via the control block is evident from thenext stage of extension.

Concrete cutter

Scrap shear Magnet plate

Display

Hammer

Fig. 34: Hammer element for single-circuit LUDV system

1

2

3

Semi priority

Sandwich design

Section flow adj. electrically

Port relief adj. manualy

Pressure free return flow

1

2

3

Slew

M7-20 or M7-22

50 RE 00 207/10.00


Fig. 35: M7-20 Multi-function element

If other double-acting working attachments arerequired as well as the hammer, the solution weoffer does not need a separate, costly hammerreturn line. All that is necessary is to fit two highpressure lines (5) via the boom and stick to thefront end of the equipment.To prevent the oil, which in the case of wornhammers is often contamination, from returningto the tank via the control block and to keep theback pressure below 5 bar, the hammer returnvalve (6) is electro-hydraulically actuated in thehammer preselection.Secondary relief valves (7) and anti-cavitationvalves (8) are included for port A and B. If a fixedsetting of the pressure valves does not provide therequired convenience of operation, the pressuresetting can be freely selected by means of a pro-portional pressure relief valve (9).When using the multi-function element adistinction has to be made between use in a 1.5-circuit or in a single-circuit LUDV system. The se-parate slew circuit in the 1.5-circuit system rulesout any influence between the slew drive and theoptional function.In the single circuit with the LS slew drive solutionalready described, measures have been taken toco-ordinate the LS slew drive and the LS multi-function element.Differently set pressure compensators (10) and(11) give priority to the attachment over the slewdrive.In practice, the parallel connection of slew driveand option is barely discernible, since with anattachment in full operation the slew drive is onlyactuated in the fine control range, if at all.Most working attachments can therefore beoperated efficiently with the system arrangementshown.If the priority for the working attachment has tobe increased further, a priority valve (12) is installedto further reduce the volume of oil allocated to theLUDV block.The priority valve compares the current LS pressurein the option spool with the pump pressure. If thedifference between the pump and the LS dropsbelow the value set on the spring (13), adjustingenergy is drawn from the pump circuit and thecurrent pressure in the LS line to the LUDV blockis increased. The effect of this increase is to reducethe control differential pressure at the orifices inthe LUDV block, and hence the volume, in favourof the LS actuator.100% priority, for example to a generator, can beachieved by means of:

Fig. 36: M7-20 Multi-function element with priority valve

9

45

68

74

Semi priority

Section flow

High pressure lines

Hammer return valve

Port relief valves

Anti cavitation valves

Port relief setting electrically

5

6

7

8

9

4

10

11

Semi priority

LS inlet compensator

Priority valve

Priority valve spring setting

10

Slew

M7-20 or M7-22

Slew

a second priority valve, so that the slew drivepressure compensator is down controlled earlier,or

pilot pressure reduction on the slew drive.

Both solutions ensure that the volume is reducedin favour of the option spool.M6-15 sandwich elements using LUDV technologycan also be mounted on the multi-functionelement for actuators with a smaller section flowof up to about 180 l/min.The components and system solutions describedare a fresh demonstration of the flexibility andadaptability of the Rexroth LUDV system.

11

13

13

12

12

51RE 00 207/10.00


Fig. 38: Emergency operation LAGU

Fig. 37: LAGU and LAGZ

3.4 Steering Systems forWheeled Excavators

Hydrostatic steering systems in open centre nonreaction or closed centre non reactionconstruction are used in wheeled excavators. Nonreaction means that the driver does not feel theforces acting on the wheels at the steering wheel.Closed centre steering units are supplied by meansof a constant or variable displacement pump via apriority valve. The priority valve supplies the flowdemanded via the meter in orifice to the steeringgear according to the LS signal.Secondary actuators can be connected to thepriority valve, but are subordinate to the supply tothe steering gear:Wheeled excavators are subject to standards andregulations relating to the steerability of theexcavator as well in emergency operation, whenthe steering assembly is acting as a hand pump.With excavators of about 15 tonnes and upwardsoverall weight, predetermined axle loads andkinematic conditions produce corresponding

steering pressures which make steering units withemergency mode speed reduction necessary.Rexroth LAGU steering gear with chamberdisconnection and LAGZ with rotor assemblydisconnection were developed for theseapplications. In servo mode there is no differencebetween the function of LAGU and LAGZ and othersteering gear.In emergency mode, if the power supply fails, theflow volume is reduced automatically. As a result,the necessary drive energy = manual effort on thesteering wheel is halved compared to aconventional steering unit.In LAGU steering systems, in emergency modeindividual rotor assembly chambers are connectedto the tank, such that only, say, 50% of the servomode flow volume is sent to the steering cylinder.With LAGZ, two rotor assemblies operate in servomode. In emergency operation, one disengagescompletely. Different reduction ratios for the tworotor assemblies enable the flow volume and themanual effort required in emergency mode to beoptimally matched to the particular machine.

Further details about the LAGU and LAGZ steeringgear can be found in data sheets RE 11 867 andRE 11 868.The use of open centre steering gear is prevalentin excavator applications. In view of the scope forseries connection with our hydraulic power brakevalves and/or the pilot oil supply, it offers aninexpensive solution for various excavator sub-systems.

P

CF EF LSAuxiliary hydraulicsPriority valve

High pressure (regulated)

Low pressure

Suction pressure

Chamber oil

Ambient pressure

52 RE 00 207/10.00


Fig. 39: Emergency operation LAGZ

Fig. 40: Sub-system: wheeled excavator block diagram

In the system illustrated, a constant displacementpump (1) supplies the power brake, e.g. LT 17 orLT 13. The system is designed and optimised so thatthe braking system is supplied as first priority viathe integral priority piston (2). The orifice (3) isarranged so that only part of the total pump flowis used to charge the accumulator. The remainingoil flow via the N port of the compact brake to theopen centre steering unit has to be dimensionedsuch that servo steerability is guaranteed even atlower diesel engine speeds.

P

High pressure (regulated)

Low pressure

Suction pressure

Chamber oil

Ambient pressure

Brake lightswitch

LAGCSteering unit Accumulator

pressurewarningswitch

2 circuit brake valve

Parking brake valve

Accumulator charchingvalve

1

23

53RE 00 207/10.00


Fig. 41: Crawler excavator

Fig. 43: 1-circuit LUDV system diagram

P LST S K

HZ HZ

Fig. 42: Dragline excavator

3.5 LUDV Systems in CrawlerMachines

The two machines shown a crawler excavatorand a dragline excavator demonstrate theexisting LUDV systems and components for thesetypes of machines.Fig. 43 shows a conventional 1-circuit LUDVsystem of the kind used for crawler excavators upto a machine size of about 24 tonnes.The whole control system is supplied by a load-sen-sing controlled main pump. The familiar M7 LUDVcontrol block comprises all the control andregulating functions. The single-circuit LUDVsystem has already been described in detail inprevious presentations (see attached). The mainemphasis of this chapter will be on the track drive.Since with the 1-circuit system the main pump flowdistribution to the track motors is via the LUDVsystem, special demands are made of the technicalimplementation of straight-line travel. Varyingmotor leakages, mechanical tolerances and controltolerances have to be compensated for to enableeach track motor to take 50% of the drive power.If this is not the case, in other words different flowsare available to the two drive motors, then thechain with the greater section flow takes over thedriving and the second chain is pulled along.In the worst case the meter-in pressure can dropso much that the counter balance valve of thepulled track closes. The drive pressure of the drivingchain continues to increase and the pumpdestrokes along power curve.The result is that: the speed of travel falls and the excavator starts to corner

This problem is overcome by means of an internalbypass system downstream of the pressurecompensator for both track drive control spool inthe LUDV control block. The flow differences arecompensated for and both track drive motorstransmit the drive torque non-positively. The sizeof the bypass system is determined in theprototype.To enable the excavator to be run up to maximumtorque without a break, the long travel drive isoverridden by a shift valve which is dependent ontravel pressure. This switches the travel motor tothe maximum or minimum swivel angle. A diffe-rential surface in the shift valve distinguishesbetween the respective shift pressures, in otherwords creates a deliberate hysteresis, in order toensure stable travel behaviour.

Option Arm Bucket Boom Slewleft rightTrack

Fig. 44: Travel shift valve

54 RE 00 207/10.00


Fig. 46: 1-circuit LUDV control block

Another criterion for assessing long travel drive iscornering. In the single circuit the system-relateddifferential pressures, multiplied by the flow goingto the more slowly revolving chain, is a power loss.By way of alternative fig. 45 shows a 2-circuitLUDV system. The circuit diagram shows thehydraulic system of a tracked crane or draglineexcavator. The two main pumps are switched toeither the 1-circuit or the 2-circuit system by meansof an electro-hydraulic proportionally controlleddirectional control valve. The original idea ofpowering winch drives with high differentialpressures in the 2-circuit system on the draglineexcavator in order to minimise power losses canbe transmitted to the track.As may be seen from the diagram, all the additio-nal functions necessary, such as double pressurecut-off, primary valve and LS relief, separation ofpump and LS line are integrated into the controlblock.The electro-hydraulic actuation of the mainfunctions, already widely used in tracked cranes,improves convenience of operation of the machine.The electronics offer considerably greater scope foroptimisation of both individual and overriddenmovements.The design differences in the control block systemand associated circuit diagrams may be seen fromthe figures 46 and 47.

Fig. 45: 2-circuit LUDV system diagram

P LS KP LS T

Aux.winch

Trackright

Mainwinch

Winch

Slew

Boomwinch

Trackleft

The basic block of the 1-circuit LUDV system is a5-spool M7 monobloc nominal size 20 or nomi-nal size 22 with scope for mounting individualelements at both sides for additional functions orslew drive (fig. 46).The optional 1-circuit or 2-circuit LUDV controlconcept is based on a 3-spool M7 monobloc no-minal size 22 (fig. 47). In this construction, theslewing module 1M7-20LS is mounted at one sideof the control block. On the other side is thedividing plate with functions integrated asappropriate for the 1-circuit or 2-circuit solution

and further mounting of sandwich elements. Thedividing plate lies between the two travel axes. Itis also possible as an option to fit a sandwichelement between the 3-spool monobloc and thedividing plate.Possible solutions for tracked excavators with dif-ferent LUDV systems are shown. When choosingbetween a 1-circuit and 2-circuit system, besidesthe technical performance the cost-effectivenessshould be considered as a decision criterion.

55RE 00 207/10.00


1,5 2,0 2,5 3,5 4,5 6,0 8,0 10 12 15 18 21 25 30 35 45 55 65 75 90 100

Gross Vehicle Weight (t)Gear Sizes

GFT 3 T2

GFT 4 T2

GFT 7 T2

GFT 9 T2

GFT 17 T3

GFT 24 T3

GFT 28 T3

GFT 36 T3

GFT 50 T3

GFT 60 T3

GFT 80 T3

GFT 110 T3

GFT 160 T3

Driving gear Excavator weight (t)

Fig. 48: HYDROTRAC driving gear/excavator weight chart

Fig. 47: 2-circuit LUDV control block

Irrespective of the decision as to a 1-circuit or 2-circuit system, Hydrotrac GFT travel gear issuccessfully in use in many tracked excavators witha wide range of operating weights.The range of applications varies, as alreadyindicated, from the mini excavator with a machineweight of approximately 3 tonnes to standardexcavators through to the large hydraulicexcavators, known as mining excavators, with anoperating weight of around 500 tonnes.The table (fig. 48) shows the driving gear sizesdesigned for use as an excavator track drive in theweight class up to about 80 tonnes.As the design of these driving gears depends onsuch parameters as overall weight, traction, trackdiameter, working pressure, etc., this table isprovided purely as a guide to planning themachine. Due to the large number of differenttransmission versions, in conjunction with variousmotor nominal sizes, the machine manufacturersrequirements can as a rule be fulfilled sufficientlyaccurately according to the modular principle.

56 RE 00 207/10.00


Fig. 49: Motor / driving gear combination

Fig. 50: Mounting arrangement

Fig. 51: Hydrotrac GFT travel drive

For hydraulic excavators of an overall weight of10 tonnes and upwards, a variety of crawler drivegears are available, starting with GFT 17 T3(17,000 Nm) with a variety of motor/driving gearcombinations.The plug-in two-step motor in bent axis design,model A6VE, has the brake valve and brakeactuating valve function integrated in the portplate. This compact, high-performance motor isused as a plug-in motor in larger trackedexcavators.The illustration of the fitting arrangement (figs. 49and 50) highlights the advantages of VEC/VTtechnology when fitting the complete drive unit inthe chassis.Driving gear systems with bent axis motors (A2FE,A6VE) need to be separated for fitting in the spaceavailable in the chassis. Driving gear systems withswashplate motors can be fitted directly in thechassis, as all the radial dimensions of the motorconnecting plate in relation to the motor axis arewithin the centring diameters of the driving gearcontact area.Fig. 51 shows the interior construction of thedriving gear in combination with the A2FE motor.High-capacity tapered roller bearings, high-qualityaxial face seal, integrated multiple-disc parkingbrake and the use of case-hardened, sun andplanetary wheels are but a few characteristics ofthese track drives.

HYDROTRAC GFTwith bent axis motor

HYDROTRAC GFTwith integral swashplate motor

57RE 00 207/10.00


Fig. 52: 250 tonne mining excavator Fig. 53: 320 tonne mining excavator

Fig. 54: Hydrotrac GFT travel drive for miningexcavators

3.6 Mining Excavators

For mining excavators Rexroth can supply pumps,control blocks and motors designed for thedemands of pit and quarry applications.Lohmann & Stolterfoht have for years beensupplying drives for these severe demands that arein use worldwide.As in the case of lower-powered hydraulicexcavators, crawler track drives in the GFT form ofconstruction are flanged on to the chassis at oneside. These transmit the torque generated byhydraulic motors via the crawler track drivesflanged on at the output side to the chain, andtransmit the externally acting reactive forces to thechassis frame structure.The use of this type of construction depends on theuse of correspondingly dimensioned torsion-resistant chassis designs. These have to a largeextent replaced the GFA style crawler drive gears(track drive hub bearing-mounted in the chassis onboth sides, torque transmission between trackdrive hub and flange-mounted driving gear viaseparate plug-in shaft).Standard constructions such as the GFT 330 areused nowadays in mining excavators up to175 tonnes. Special constructions like the GFT 600and GFT 800, comprising 2-stage planetary gearswith preliminary spur gear, plate-type brake andtwo-motor drive are currently used in 255 tonneand 320 tonne hydraulic mining excavators. Traveldrives up to GFT 1300 have been designed to date.The rotary drives used in these large machines arespecially tailored to the requirements profile ofmining plant and are based on a 2-stage planetaryconstruction in conjunction with an integral plate-type brake at the driving gear inlet. To keep thegearbox dimensions compact, the necessary

superstructure torque is achieved by the use of upto three rotary driving gears, depending on design.The much longer service life expected of a miningexcavator compared to conventional excavators istaken into account when designing the travel androtary driving gear.

58 RE 00 207/10.00


Index

Documents

Excava-e