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Industrial Hydraulics

Electric Drivesand Controls

Linear Motion andAssembly Technologies Pneumatics

ServiceAutomation

MobileHydraulics

Bosch Rexroth AG

Mobile Hydraulics

Glockeraustraße 4

89275 Elchingen, Germany

Tel. +49 (0) 73 08-82 0

Fax +49 (0) 73 08-72 74

[email protected]

www.boschrexroth.com/brm

Printed in Germany

RE 98300/06.03

Easy Machine Operation with

Rexroth Automotive Drive and

Anti Stall Control

The Drive & Control Company

Rexroth_DA_GB_RZ 25.6.03 25.06.2003 14:37 Uhr Seite 22

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tens habet hos numeratque.

Interdum volgus rectum videt, est ubi pec-

cat. Si veteres ita miratur laudatque poe-

tas, ut nihil anteferat, nihil illis comparet,

errat. Si quaedam nimis antique, si pera-

que dure dicere volgus rectum videt, est

ubi peccat. Si veteres ita miratur laudatque

poetas, ut nihil anteferat, nihil illis compa-

ret, errat. Si quaedam nimis antique, si pe-

raque dure dicere arto stipata theatro

spectat Roma potens; habet hos numerat-

que poetas ad nostrum tempus Livi scrip-

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laudatque poetas.

Pressure sensing capabilities of the

DA-system allow precise and efficient

drive behavior since in the lower and

intermediate engine speed range, the

tractive effort is varied by the diesel

engine speed. Telescopic handlers, for

instance, thus allow sensitive positioning.

When wheels get blocked, the tractive

effort is controlled via the diesel engine

speed, however, without heating up the

system.

32 Rexroth Automative Drive and Anti Stall Control | Features and Functions

The Features

Both features can be realized without any direct link betweenpump and accelerator pedal. Thereis no requirement for any controlrod or electronics. The pump controller works fully automatically.

The DA control is a well provencontrol system, produced for manyyears. Thousands of different machines, e.g. fork lift trucks,municipal vehicles, wheel loadersor other vehicles are proof of thereliability, durability, and uniqueness of this concept.

The Functions

An A4VG pump with Drive and Anti Stall Control DA as well as an integrated inching

valve ensures a smooth drive characteristic. This allows careful handling of goods with

maximum drive comfort as well as quick acceleration and thus high turnover speeds of

the handled material.

Automotive Drive Control

allows the operator to run a machinewith a hydrostatic transmission similar to a passenger car with automatic transmission: The morethe accelerator pedal is moveddown, the more the transmissionpump increases its delivered flow,i.e. speeds up the vehicle.

Anti Stall Control

ensures that the pump adjusts itsconsumed power to the poweravailable from the diesel engine.In any overload situation, the AntiStall Control reduces the pump’sflow rate to a value that preventsthe engine from stalling.

The Automotive Drive and Anti Stall Control (DA) is a pure hydro-mechanical controlfor closed loop transmissions which provides two main features: Automotive Drive Control and/or Anti Stall Control. Additional options provide servo override controlsand enhanced braking.

Automotive Drive Control makes the

pump displacement follow the engine

speed:

• Pushing down the accelerator pedal leads to an increase in engine speed.

• The difference in engine speed also causes a different pump speed. Since the boost pump is integrated in the transmission pump it also shows a different flow rate.

• The boost pump’s flow rate is measured within the transmission pump’s speed sensing valve.

• The more flow travels through the speed sensing valve, the more the pump goes on stroke and thus delivers more flow.This in turn increases the vehicle speed.

The travel direction is selected by an integrated forward-neutral-reverse valve.The selected hydraulic motor can be eitherof constant displacement (e.g. A2FM)or variable displacement (e.g. A6VM).


4 Rexroth Automative Drive and Anti Stall Control | Applications 5

The Applications

The working characteristic of a DA-controlled vehicle can be displayed within a three dimensional diagram shown onthis page. The x-axis describes the travel speed which corresponds to the flow rate of the transmission pump.The y-axis shows the tractive effort which is proportional to the drive pressure. Eventually, the z-axis displays the engine speed which is mainly determined by the accelerator pedal position.All working points of a vehicle with Automative Drive and Anti Stall Control are located on a three dimensional surface within this diagram. Looking at three typical day to day travel situations, the working principle becomes clear:

Accelerating Vehicle

A vehicle, e.g. a wheel loader, accelerating on plain ground shows a

certain characteristic travel path within this diagram. The working

points at the different states are:

At standstill, the engine runs at low idle. The DA pump stays at

zero flow at this stage.

Slightly pushing the accelerator pedal causes the engine to

speed up. The DA pump senses the increased engine speed

and starts to build up pressure. However, due to the vehicle’s

friction, it does not yet move.

The vehicle overcomes the sticking forces and starts to move.

Steadily pushing the accelerator pedal speeds up the engine.

The DA pump continuously increases its stroke and thus

delivers increased flow. The vehicle speeds up.

Approaching maximum speed, the pressure slightly decreases

again since there is no further acceleration necessary. The

vehicle only needs to overcome the frictional drag forces.

1

2

3

Vehicle Getting into Stall Mode

Another typical situation is a vehicle driving at medium speed and getting

stalled out. This may be for instance a loader entering a pile of gravel with

its shovel.

Driving at medium speed across a plain ground yields a certain

pressure level that delivers the necessary tractive effort to overcome

all drag.

Touching the first gravel increases the required tractive effort. The

system pressure goes up. At the same time the pressure sensitive

DA-pump already reduces the flow to not overload the engine.

Fully digging into the pile of gravel further increases the system

pressure. The engine sees increased loading. This loading leads to

an engine speed decrease.

If the system pressure exceeds preset values (given by hydraulic

component’s pressure rating), the DA-pump’s pressure cut-off

function reduces the pump’s flow rate. The pump adjusts its

displacement to maintain full system pressure (i.e. maximum tractive

effort) without heating up the system.

4

3

2

1

Vehicle Entering a Slope

A vehicle traveling at full speed on plain ground enters an uphill slope.

This obviously requires an increased tractive effort. The working points in

the three dimensional diagram are:

Vehicle traveling at max. speed on plain ground: The pump is at full

stroke and delivers maximum flow. The established pressure level

corresponds to the vehicle’s drive resistance (rolling-, air

resistance) in this operation condition.

Entering the slope causes the tractive effort to increase. This

yields increasing hydraulic system pressure. The diesel engine lugs

due to increased power requirement. The pressure sensing rotary

group swivels back and balances hydraulic and engine power

according to the increased system pressure.

2

1

4

5

Anti Stall Control protects the

engine from stalling:

The pressure sensing capability ofthe transmission pump’s rotarygroup is the main feature of the AntiStall Control. Increasing pressuremay be caused by the vehicle gettinginto heavy ground conditions, or bydriving up a hill.• Increasing pressure in the

transmission pump’s working lines lead to a reduction in pump displacement.

• With the reduced displacement the pump delivers less flow and adapts its power intake to the engine power capabilities. It thus protects the engine from stalling.

In case of additional power requirements from other consumers(e.g. steering systems, implement hydraulics), the transmission pumpautomatically adjusts its displacementto balance the power of engine (output) and hydraulics (input).Depending on the application, theAnti Stall Control may allow the installation of smaller diesel enginessince they are now protected againststalling.

Well balanced rotary

group technology

features power self

control to serve as

engine stalling

protection

The Functions

Characteristic of the Rexroth Automative Drive and

Anti Stall Control


7

The Service

Rexroth Power Brakes with integrated inching valve

If the vehicle includes a hydraulic power brake system, inchingcan be realized cost effectively by using the Rexroth power brake valve LT 31 with integrated inching function (see technicaldata sheet RE 66 227). The function is similar to the versionwith brake pressure inching valve described on the far left.

Rexroth Power

Brake Valve LT31

with integrated

inching function

Rexroth application engineers are ready to assist you inthe right selection of components and controls thatbest suit for your application. All pumps equippedwith the Automotive Drive and Anti-Stall Control arefactory set and fully tested according to specification tomeet your engine and application requirements.

Servo Override Controls

The Automotive Drive and/or Stall Control can be combined with all servo displacement controls. This allows both enjoyingthe ease of operation of an automotive drive when operating on the road and the load independent precision of servo displacement control in the working mode. Frequently used servo displacement controls with Automotive Drive and/or AntiStall Control (DA) are mechanical proportional (HW), hydraulical proportional (HD) or electrical proportional (EP). See the Rexroth A4VG and A10VG pump data sheets RA/RE 92 003 and RA/RE 92 750 for reference.

6 Rexroth Automative Drive and Anti Stall Control | Options and Service

The Options

Brake pressure inching valve

The brake pressure inching valve works simultaneouslywith the service brake. This is therefore the best solutionwhen inching shall support the service brake to reduce brake pad wear.Application example: To slow down a wheel loader, theoperator pushes down the brake pedal. Pushing gently means hydrostatic braking only, pushing harder meanshydrostatic and service braking simultaneously.The pump’s control device is hydraulically connected withthe service brake circuit. Increasing pressure in the servicebrake system causes the transmission pump to destroke.

Rotary inching valve for low speed operations

Rotary Inching Valve is the preferred solution when inching shall be separated from braking. This is typicallythe case when certain operations require high enginespeeds while the travel speed is very low.Application example: Sweeping machines when the brushsystem requires full hydraulic oil flow from the implementpump while the travel speed is low.The pump’s control device is hydraulically connected to theremotely installed rotary inching valve. The inching valvein turn is mechanically operated by either a hand lever or apedal. Pushing the lever or pedal and thus increasing theangle of the rotary inching valve’s lever causes the trans-mission pump to destroke.

The DA-pumps offer various options of override controls for specific braking and inching functions:


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