Additional steered axle straight-running stability, function

W46.60-1003-05

Schematic of auxiliary steered axle

(Leading axle)

1 Front axle steering gear

2 Drag links

3 Idler lever

4 Hydraulic lines

5 Steering cylinder

5.1 Cylinder chamber (auxiliary steered axle, right steering angle)

5.2 Cylinder chamber (auxiliary steered axle, left steering angle)

6 Hydraulic pump

7 Electric cables

A54 ZL control unit

B86 Front axle steering angle sensor

B87 Auxiliary axle steering angle sensor

Y67 Auxiliary steered axle hydraulic control block

W46.60-1004-05

Schematic of auxiliary steered axle

(Trailing axle)

1 Front axle steering gear

2 Drag links

3 Idler lever

4 Hydraulic lines

5 Steering cylinder

5.1 Cylinder chamber (auxiliary steered axle, right steering angle)

5.2 Cylinder chamber (auxiliary steered axle, left steering angle)

6 Hydraulic pump

7 Electric cables

A54 ZL control unit

B86 Front axle steering angle sensor

B87 Auxiliary axle steering angle sensor

Y67 Auxiliary steered axle hydraulic control block

Function

When driving straight-ahead the front axle steering angle sensor (B86) on the front axle steering linkage measures steering angle as "zero".

The auxiliary axle steering angle sensor (B87) measures the instantaneous position of the auxiliary steered axle (steering direction and steering angle).

The ZL control unit (A54) calculates the specified value for the position of the auxiliary steered axle from the measured value of the front axle. If the measured value of the auxiliary steered axle is in the tolerance window the hydraulic control does not intervene.

The ZL control unit (A54) now constantly compares the measured values of the front axle, auxiliary steered axle and the calculated specified value for the auxiliary steered axle.

If the measured value of the auxiliary steered axle goes out of the tolerance window due to external influences, the hydraulic control intervenes.

The proportioning valve in the auxiliary steered axle hydraulic control block (Y67) is actuated depending on the deviating angle.

As a result corresponding pressure and volume flow is supplied to the steering cylinder (5). The steering cylinder (5) operates the steering linkage of the auxiliary steered axle.

The auxiliary axle steering angle sensor (B87) again measures the actual value of the auxiliary steered axle and passes this on to the control unit (A54), if the specified/actual value correspond again, the proportioning valve returns to its position of rest.

Function check while driving

The steering angle zero point is checked while driving under certain conditions.

For this the auxiliary steered axle is activated briefly when driving straight-ahead (v > 55 km/h). Due to the caster the auxiliary steered axle positions itself straight-ahead and from this a correction of the zero point position is determined in the control unit if necessary.