Additional steered axle pressure control, function

W46.60-1012-12

Pressure control (schematic of auxiliary steered axle hydraulic control block)

7 Pressure limiting valve

8 Pressure relief valve

9 Filter element

373 Oil level switch

403 Oil pressure sensor

404 Proportioning valve solenoid A

405 Proportioning valve solenoid B

406 Ram pressure switch

407 Reservoir charge valve

408 Activate valve

A Steering cylinder connection

B Steering cylinder connection

DA Oil pressure sensor connection

P Hydraulic pump pressure-side connection

P1 Pressure reservoir

S Hydraulic pump suction-side connection

SP Pressure reservoir connection

T Reservoir

Y67.1 Proportioning valve

Pressure build-up and control

The system is always in a safe state when the engine is being started (driving switch "On").

In this situation the oil supplied by the hydraulic pump is pumped round depressurized, the two chambers of the steering cylinder are connected to each other by the activate valve (408).

Pressure is controlled by the interaction of the control unit and auxiliary steered axle hydraulic control block.

The pressure sensor (403) records the prevailing system pressure. If the pressure is below the parameterized cut-in threshold, the control unit reacts and closes the reservoir charge valve (407).

The system pressure increases up to the parameterized cut-out threshold, the reservoir charge valve (407) is opened again and the hydraulic pump again delivers in the depressurized circuit.

The system pressure is maintained by the pressure reservoir (P1) behind a non-return valve.

In normal operation pressure control is a function which represents an independent control circuit and is not directly influenced by other control circuits of the auxiliary steered axle.

If the pressure sensor (403) fails, the control unit switches over to substitute value control, i.e. the reservoir charge valve (407) is closed as soon as steering movements are sensed.

The pressure limiting valve (7) controls the maximum operating pressure.

The system pressure is passed on to the steering cylinder depending on the position of the proportioning valve (Y67.1).

A dirty or blocked filter (9) is recognized via the ram pressure switch (406) and conveyed to the control unit. (Can be read out via measured/binary value)

Pressure reduction

By means of a load-reducing procedure the pressure still prevailing in the pressure reservoir is reduced after terminal 15 is switched off. This opens the activate valve (408) and solenoids A and B (404, 405) of the proportioning valve (Y67.1) are actuated. As a result a safe state is achieved for maintenance and repair work.

For further protection a manually operated pressure relief valve (8) is attached to the hydraulic unit.