Backho-e

83RE 00 207/10.00

New Power Management Concepts in conjunctionwith LUDV Technology and Closed Centre Steering Units

in Backhoe Loaders

New Power Management Concepts inConjuction with LUDV Technology andClosed Centre Steering Unitsin Backhoe Loaders

2.1 Horse power control ortorque limiting

As long as a hydraulic pump without powercontrolling device is considered, the decision onthe pumps displacement is based on the cornerpower (power at maximum displacement andpressure) taken up. Corner power should notexceed power available from the diesel engine.Exceeding the available power the diesel enginewill stall, not using all the power available resultsin insufficient machine performance.The power controlling device restricts the torquetaken up and enables installation of pumpsregardless of their corner power. This permits largerflows of oil at lower pressures and smaller flowsof oil at higher pressures (see Figure 1), thuspreventing the diesel engine from beingoverloaded or even stalled. This also producessignificant advantages in terms of machinebehaviour:

greater handling power as a result ofhigher corner power- faster working speeds through higher oil flow rates- higher forces through higher pressures

better utilisation of diesel engineoutput- greater fuel economy- lower noise emission- better exhaust emission behaviour, i.e. meeting the most stringent of emission standards

maximum handling convenience- no overloading of diesel engine- no stalling of diesel engine- machine easier to control

The A10 standard horse power control (DFLR, seealso figure 2) limits the pumps discharge pressuredepending on its displacement. The horse powercontrol valve (or torque limiter) is a pressure reliefvalve connected to the swivel cradle via twosprings. Its opening pressure is therefore governedby the position of the swivel cradle - when deliveryfrom the A10 variable displacement pump is low,opening pressure is high, when delivery from theA10 variable displacement pump is high, openingpressure is low. It is piloting the flow regulator (orin cases that LUDV blocks are used a separatedregulator) and limits pressure in the LS-line. Sincethe control oil is delivered through a nozzle, thepower regulating valve is able to generate apressure drop in the control line as soon as itsopening pressure is attained, thus influencing theflow regulator in such a way that the pump swivelsinto position (please also note, that once the horsepower control is active the flow regulator becomes

1. Introduction

The excavator loader is an all-round machinesuitable for many different applications. Employinga tractor as its base, it unites the functions of anexcavator and a loader. Robust and easy to operateas you would expect, its hydraulic system is ratedfor medium pressure.As development of this machine type hasadvanced, so too have the requirements anddemands placed on it. Today, attention must bepaid more than ever before to efficiency andcontrollability. Besides, ergonomic operation, fueleconomy, reduced exhaust and noise emission areexpected. A satisfactory emergency operation ismandatory.These targets can only be achieved with a modernhydraulic drive system based on the technologyalready presented during last MOBILECONFERENCE in 1997 steering unit LAG, LUDVblock SX 14, joy sticks 4TH, variable displacementpump A10VO further developments of thecomponents were carried out. The new option thatare now available form even better systems, thatcover the whole range from basics to benchmarkperformance.

2. Power managementconcepts

Only in few cases the available power, usuallyprovided by a diesel engine, is sufficient to drivethe hydraulic pump used for the implements at fulldisplacement against the maximum pressure level.A variable displacement pump in conjunction withthe adequate control offers the possibility to ma-nage the installed power. Depending on thedesired quality of control the A10VO, axial pistonpump in swashplate design for medium pressurelevels, can be selected with different regulatoroptions.

EckleistungCorner power

p

Q (Vg)

(+)

(+)

figure 1: advantage horse power control

A10VO 74 DFLR/31

figure 2: A10VO DFLR

Detlef van BrachtBrueninghaus HydromatikHorb PlantPhone +49 (0) 74 51 92 14 41Fax +49 (0) 74 51 8221

Philippe FillonMannesmann Rexroth S.A.Division Sigma InternationalPhone +33 (0) 4 78 78 52 52Fax +33 (0) 4 78 78 52 71

Dr. Udo HakerRexroth HydraulicsParchimPhone +49 (0) 38 71 606-236Fax +49 (0) 38 71 606-201

84 RE 00 207/10.00

New Power Management Concepts in conjunctionwith LUDV Technology and Closed Centre Steering Unitsin Backhoe Loaders

a remote pressure controller). The flow rate isreduced as the pump swivels into position,increasing the opening pressure (control pressure)and thus keeping pump drive torque constant.

T ~ VG x p P ~ T x n ~ Q x p = const.

2.2 Dual horse power controlor dual torque limiting

It is in a backhoeloaders nature to be used eitheras excavator or loader. Since nearly all diesel enginepower can be used for the implement hydraulicwhen excavating, but only partial diesel enginepower when loading here the power basicallyhas to be shared between the transmission andimplement hydraulic , the possibility to shiftbetween a high and a low setting is highlydesirable (figure 3).

Excavation implement hydraulic only high settingLoading implement hydraulic plusdriving low setting

On the base of A10 standard horse power controlthis capability is fairly easily achieved. Simply andRexroth patented the horse power controlbecomes a dual horse power control (figure 4).Byutilising the power control valvesdependency on the rate of control oilflowit is possible to modify the power output setting.Increasing the rate at which control oil is deliveredto the power control valve raises pressure in thecontrol line and increases the power output setting(also refer to Standard power control).Delivering a lower rate of control oil flow will bringpressure down and reduce the power outputsetting.By feeding back the LS-pressure signals over dif-ferent orifice sizes the control oil flow can beinfluenced (within limits). Using a

Larger orifice higher setting BackhoeSmaller orifice lower setting Loader

dual horse power control is simply and costeffective achieved.

In some loader operating conditions, for examplelifting the loader boom at machine standstill, oronly to leave the machine operator the last choicefull diesel engine power could be applied to theimplement hydraulic. For these cases dual horsepower control is optional available electricalshiftable.

Regardlessly, which type of dual horse powercontrol is used, the setting can now be controlledinside limits, i.e. the A10 variable displacementpump takes up the power available to it - to meetthe operating status of the excavator loader.Whereas setting the standard power regulatordemanded a compromise between excavator andloader operation, the advantages of power controlare now utilised to the full extent for bothoperating modes. Moreover, it is possible to adjustthe power output setting to the particular dieselengine speed (diesel engine power output). Thisis, for example, welcomed in residential areaswhere machines may only be operated at reducedspeed for noise reasons.

p

Q

BaggerBackhoe

LaderLoader

Loader Backhoe

DFR1

LR

smallerorifice

largerorifice

figure 3: power sharing - (dual) horse power control

engine characteristic

Torque

enginespeed

lowidle

highidle

pump

transmission

torqueavailable

low pumpsetting

pumponly

high pumpsetting

BackhoeLoader

LR

DFR1

figure 4: A10 VO dual horse power control

85RE 00 207/10.00


in Backhoe Loaders

2.3 Speedsensing powercontrol or variable torquelimiting

The latest development on cost effective controlsof the A10VO is the EP control electroproportionaldisplacement control (figure 5). The pumpsdisplacement is governed by an electric currentapplied to the controls solenoid. Its unique designis compact and directly connected via a pilot spoolto the displacement control cylinder. It acts like anadjustable maximum displacement stop andallows the optional combination with flow andpressure control, enabling the use of LS- or LUDVmobile blocks. As the current applied isdetermining the pumps maximum displacement,flow and pressure control still can control thepumps displacement from maximum to minimum a speed-sensing power control can be built up(figure 6).

Speed controlled diesel engines are commonlyused in Backhoeloaders, i.e. the drop of dieselengine speed reflects the load on it. Detecting theposition of the gas pedal or the stroke of theinjection pump (WS) equals the power available.Sensing the actual diesel engine speed (ID) equalsthe load on the diesel engine. Both signals arecompared and processed in a microcontroller (RC2)determining the utilisation of the diesel enginepower.

If the drop of diesel engine is too high, the dieselengine is overloaded. The microcontroller willreduce the solenoid current of the A10VOs EPcontrol bringing the pump to a smallerdisplacement. Decreasing the displacement willreduce the load on the diesel engine allowing itto recover.If the drop of diesel engine speed is too low, thediesel engine power is not fully utilised. Themicrocontroller will increase the solenoid currentof the A10VOs EP control bringing the pump to alarger displacement. The larger displacement willincrease the load on the diesel engine using all thepower that is available.

A10VO...EPDF/53Mikrocontroller RC2

figure 5 A10VO EP

The power taken up by the implement hydraulic isautomatically adjusted to the power that isavailable regardless what power is used by thegearbox (see also figure 7), whereas with (dual)horse power the controller setting is always acompromise. Tests have proven that therefore,especially in loader operation, even a smaller sizedpump with EP control can lead to machineperformance set out by a larger sized pump with(dual) horse power control. Besides,

figure 6 speed sensing power control

RC2

MobilBlock

SX

WS

ID

A10VO...EPDF/53

Gear BoxDiesel-Engine

figure 7 sharing - speed sensing power control

engine characteristicTorque

enginespeed

lowidle

highidle

pump

transmission

torqueavailable

Pu

mp

Dis

pla

cem

en

t

Solenoide Current

B

X

S LL1

86 RE 00 207/10.00


automatic compensation of weak diesel engines- tolerances- low idle- high altitude operation

automatic compensation of load taken up byother components, for example gear pumps,air conditioning compressors, alternators, etc.

programmable machine operation modes diagnosis feature

become state of the art and all benefits of (dual)horse power controlled pumps are furtherimproved.The new EP control of A10VO pumps combines thestrength of the electronics (controlling) with thestrength of hydraulics (power transmission). Itsunique and cost effective design and the conceptof speedsensing without any electronic pressuretransducer will bring the power management inBackhoeloaders into the next generation.

3. A10VO flow control thelink to LUDV-, LS-blocks

In addition to the capability to manage the power,the variable displacement pump in conjunctionwith LS or LUDV systems enables to benefit fullyfrom the advantages provided by the pumps flowcontrol over a fixed displacement pump. The maindifference between a system with a flow-controlledvariable displacement pump and an otherwiseidentical system with fixed-displacement pump liesin the fact that a system with flow-controlled va-riable adjustment pump delivers just as much oilas is required whereas in a system with fixed-displacement pump the flow of oil is governed bythe pump drive speed and pump size. In the lattercase, excess oil flow must be throttled back againstpump pressure, resulting in high amounts of energybeing lost in the form of heat (see figure 8).

Oil flow delivered = oil flow requiredThis means no energy is lost throughexcess flows of oil.

This produces the following direct advantages forbackhoeloaders: better fuel economy lower operating costs environmentally friendly lower cooling capacity requirement smaller radiator smaller tank and thus less fluid exposure of fluid to lower temperatures longer service life

constant displ. pump

corner power

A10 variable displ.pump /DFR

corner powerp

Q

p

Q

A10VO...DFR/52

figure 8: advantages A10VO DFR

The enhanced utilisation of primary energyprovides more power at partial load for the traveldrive in loader mode.

87RE 00 207/10.00


in Backhoe Loaders

pump displacement installed. Most commonlyused today are pump displacement of 74 cm3/rev..

The new A10VO 85 and especially its speed sen-sing power management option in combinationwith the SX14 will allow you to improve themachines in this direction,of course for the smallermodels the A10VO 74 with power managementbased on horse power control version is alwaysgood to consider and for the more price sensitivemodels the SX14 can work with a gear pump stillbringing the advantages listed in fig 9.

The other field of improvement is the ergonomyand the comfort ; at that point it is interesting toconsider what other machines are competingagainst the back hoe loaders. The 7 tons wheeled excavator in combination witha small /medium loader is probably the classic al-ternative to a backhoe loader, if one looks at thecontrols used on those machines, it will be veryobvious that in the comfort and ergonomicaldepartment the backhoe is still lacking a little bitof it, with its long, out of reach, hudgedisplacement levers, it is certainly not the bestreference as far as operators comfort is concerned.

Again the controls of the back hoe loaders are anheritage of what the machine was in the past : atractor to which some attachments were addedlater on ; The levers directly mounted on the valveswere in this respect the best and probably onlysolution .Also because of the lack of controlability and theimpossibility to perform several movementssimultaneously there was little improvement to beexpected by only changing the type of control.

Today with the flow sharing giving to the backhoeloader a controlability comparable to modernexcavators it is probably the opportunity to improvealso the way the control is made by using remotecontrols and locate them in the armrests of theseats to come closer to the excavators ergonomy.

There are 2 main possibilities to control avalve with remote controls : hydraulic controls electronic controls

The choice between the 2 technologiesdepends on many factors : costs packaging space available to run pipes remote controls as option or serie type of functions to be controlled number of functions to be controlled etc etc

Since its creation the SX14 our flow sharing valvewas available with mechanical and hydrauliccontrols ; in 2000 it will be available as well withelectronic control (see fig 10).

4. LUDV technology

The load sensing flow sharing concept improvesthe standard. Load sensing by giving to the systeman independance to the load variations but alsoto the flow availibility.

This possibility is obviously a break through in theattempt to make the machines more user friendlyand more performant.

Since 1997 thousands of machines equiped withSX14 flow sharing were delivered to themarket,the feed back we have had confirms thepoints we were listing back in 97 (see fig 9),thebest compliment we ve had was given by a pro-fessional operator who said "the machine is soeasy to operate that nobody will need meanymore".

Obviously this operator will still be needed becausethe performances of the machine being improvedin such a drastic way by the flow sharing meansthat he will be able to perform quicker and better.

What are the next improvements that operatorswill expect from their machines ?

Because the flow sharing allows to give to theoperator a perfect control even at maximum enginespeed, limitation in speed is now given by the

figure 9 SX14 - flow sharing system

88 RE 00 207/10.00


5. Joysticks-control

With regards to the joysticks Rexroth has in itsrange all necessary joysticks in hydraulic or inelectronic version (see fig 11):

In hydraulic version :-4TH6 (heavy duty) 4TH5 (light duty) for theexcavator side (see data sheet: RE 64555)-4THF6 with electric detents for float & returnto dig on the loader side (see data sheet :RE 64553).

figure 10 SX14 - flow sharing system

figure 11a Joystick 4TH6 and M Control

In electronic version :-M control signal control joystick(see data sheet RE 29882).-4THE6 power control joystick(see data sheet: RE 29711).

Because a joystick can only control 2 axis and thebackhoe loader control requires a minimum of 5proportionnal functions : Boom, arm, bucket,slew, telescopic, Rexroth has created the EC3000handle (see fig 11a) that will provide aproportionnal electrical slider and 4 on offswitches, this handle is available on any of theRexroth joysticks hydraulic or electronic versionand will provide a third proportionnal control tothe joysticks.As said previously there are 2 main solutions toperform a remote control but obviously there are

also many possible combinations between all typesof controls (mechanical,hydraulic,electrical on off,electrical proportional) that can be usedsimultaneously on the same machine to take inaccount the different impositions given to machinedesigners.

To summerize ,the next improvements allowed bythe flow sharing are : the increase of speed andthe improvement of the ergonomy,there are alsosome possibilities to make simpler ,more costeffective and more flexible option controls(see fig 12) . Also the flow sharing technology givesthe possibility not to use a priority flow divider tofeed the power steering with the only impositionto use a power steering and steering cylinders thatcan accept the system working pressure.

figure 11b Joystick EC 3000

AB

AP1

Pr

T

AB

A

B

Bv

figure 12 LUDV-komplete system

4TH6

M Controller

89RE 00 207/10.00


in Backhoe Loaders

Two types of hydrostatic steering are used inbackhoe loaders: Open centre Non reactionand Closed centre Non reaction. The forcesacting on the steered wheels are not felt by thedriver via the steering wheel. The trend is currentlytowards closed-centre steering systems (Fig. 13).

As Fig. 14 shows, the closed-centre steering unitsare supplied by a pump with constant or variabledisplacement via a priority valve. Since the priorityvalve is controlled via a load-sensing (LS) signal,it ensures that the steering unit is supplied asrequired.

Other hydraulic actuators can also be connectedto the priority valve; these are then supplied at thesecond level.

The following actuators may be connected:

Implement functions with pressures up to250 bar

Remotely powered braking system Fan drive Pilot oil supply Feed functions

Further information on the open-centre andclosed-centre steering units can be found in datasheets RE 14 365/01.98. The LPS priority valvesare described in more detail in data sheetRE 27 548/10.98.

6. Steering units High axial loads and kinematic conditions producecorrespondingly high steering pressures inbackhoe loaders. The standards and regulationsgoverning a machines steerability including itsemergency steering when the steering unitoperates as hand pump also apply for backhoeloaders. To meet these specifications, it may benecessary to use steering units with speedreduction in emergency operation.

P

EF

LS

CFWorkingHydraulic

LS conected with Tank

High Pressure (unmetered)Low PressureSuction PresureEntrapped OilAmbient Pressure

Fig. 13: LAGC und LAGC../LD

LAGU

LAGZ

Fig. 15: LAGU and LAGZ

Fig. 14: Steering circuit with dynamic load sensing

90 RE 00 207/10.00



Working Hydraulic

Priority Valve

P

CF EFLS

P


v

The LAGU steering units with chamber isolationand the LAGZ steering units with rotor blockdisconnection have been specially developed forthese applications (Fig. 15).

Operation of the LAGU and LAGZ units is no dif-ferent from that of other steering units in servooperation, but the delivery rate is reducedautomatically in emergency operation. Thisreduces the drive energy (= manual force appliedto the steering wheel) by roughly 50% or more incomparison to a conventional steering unit.

In the LAGU units, individual chambers of the rotorblock are connected to the tank in emergencymode (Fig. 16) so that only 50% of the flow ratein servo mode is now routed to the steeringcylinder.

Two rotor blocks operate in the LAGZ in servomode. One of these is disconnected completely inemergency mode (Fig. 17), thus permitting furtherreductions in addition to the 50% reduction in flowrate.

Further information on the LAGU and LAGZsteering units can be found in data sheetsRE 11 867/09.98 and RE 11 868/04.00.

Fig. 16: LAGU in emergency mode

Fig. 17: LAGZ in emergency mode

91RE 00 207/10.00


in Backhoe Loaders

These steering units deliver the same flow rate inservo operation (160 cm3 per revolution of thesteering wheel).Figure 18 shows the achievable steering pressureover the steering torque for the various units.

For the operator, the LAGU and LAGZunits offer a number of advantages overthe LAGC units:

Lower steering torque with the same steeringpressure in emergency operation.

Better ergonomic conditions for the driverdue to:- fewer turns of the steering wheel from end to end in servo mode- smaller steering wheel

Cost savings for the manufacturer due to:- smaller steering cylinders- no supplementary equipment required (emergency steering pump) Fig. 18: Emergency steering torque over steering pressure of LAGU and LAGZ units as compared

with LAGC

Dru

ck

Lenkmoment

LAGZ

LAGU

LAGC

The flow rate is reduced in the LAGU and LAGZunits if the auxiliary energy fails

7. Summary

Based on proven technology - steering unit LAG,LUDV block SX 14, joy sticks 4 TH, variabledisplacement pump A10VO Rexroth can offer alarge variety of products to be used inBackhoeloaders. These products are underconstant development to adapt the hydraulicscomponents even better for the optimumutilisation in Backhoeloaders. The new options,which are available now, will not only furtherimprove efficiency and controllability but alsoopens new opportunities for futureBackhoeloaders.The new power management concept of speed-sensing on the base of an electroproportionaldisplacement controlled A10VO EP guaranteesoptimum diesel engine power utilisation at anytime without overlaoding or stalling. In conjunctionwith SX14 LUDV technology the full hydraulicpower can be controlled at operators convenienceenabling him to operate the Backhoeloader evenbetter and quicker. The electric actuation of SX 14combined with the newly design EC3000 handleof 4TH joy sticks allows to operate three propor-tional axis. Afuture development on the closedcentre steering unit LAG will prove if the priorityflow divider will become unnecessary by employingflow sharing. The steering with optional chamber

switch off can be mounted in confined spaceproviding sufficient steering flow in emergencyoperation.At the end of the day, decision upon the hydraulicsystem will be based on cost of products comparedto the operating cost and performance.Optimum machine utilisation keeps operatingcosts down, also making this system an attractiveoption compared with the costs of the technicallyinferior fixed displacement pump.

Steering torque

Pres

sure

92 RE 00 207/10.00


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