Specifications

Service Training
Page 4.2
Section 24
09.04
POWER LIMITER, ANTI-STALL DEVICE
The drive is provided with a power limiter to prevent any overload on the engine by the travel drive.
This device controls the swashplate angle of the variable-displacement pump and the variable-displacement
motors depending on the high pressure so that the product of flow volume Q x working pressure P does
not exceed the available engine power at any time.
EXPLANATION
When an accelerator pedal is depressed, the higher pilot pressure at Z or Y goes via the activated
preselector valve (29) to pressure reducing valve (30), while the working pressure of the closed circuit
goes through valve (29) to the high-pressure modulator (31). After the selected engine power is achieved
(Q
max
and approx. 170 bar), valve (30) is activated via the high-pressure modulator (31), thus reducing the
differential pressure between Y and Z. This causes the pump to downstroke from Q
max
towards Q
min
, thus
reducing the oil flow. At the same time the hydraulic motors stroke up from Q
min
to Q
max
, increasing the
torque at the traction wheels.
Any additional power requirements by the working and steering hydraulics cannot be served by the power
limiter. This overloads the engine and, if the power requirement continues, reduces its speed. If the engine
speed drops until the differential pressure between Y and Z is reduced to 4 bar, the pump will downstroke
to zero delivery, thus preventing the engine from stalling.
4.2.2.3 BRAKING
When the accelerator pedal is released, the pressure for the engine speed control cylinder is first reduced
and then the differential pressure between Y and Z so that the hydraulic motors stroke from Q
min
to Q
max
and the pump from Q
max
to zero output. This reduces truck speed, braking the truck.
4.2.2.4 AUXILIARY BRAKE
Due to the reversal of power when braking (tractive power converted to pushing power), the hydraulic
motors drive the pump, which is coupled to the engine, so that the engine speed must rise as a result. When
a determined engine speed is reached, the auxiliary brake is applied, preventing the engine speed from
rising too high. The maximum braking force is determined by the pressure-relief valve in the high-pressure
circuit.