Steering: Description and Operation

SERVOTRONIC



Components:

Electronic speedometer

Control unit (installed in A pillar)

Electro/hydraulic converter (bolted on steering gear)


Design:

The speed signal from the speedometer is evaluated in the control unit and put out to the converter in form of electric pulses. The converter regulates the flow of oil out of the reaction chambers into return flow.


Description:

Turning the steering wheel clockwise causes the right valve piston (6) to move. This lets the oil flow into the right cylinder chamber (12) as well as via the right check valve (8) into the right reaction chamber (4).

When the car is in "parking" state (there are no speed signals from the speedometer), converter valve (3) remains closed and the oil continues to flow via both orifices (10 and 11) to the left reaction chamber (5). The closed left check valve (9) prevents the oil from flowing into the pressureless left cylinder chamber (13) which is connected with return flow. Since there is equal pressure in both reaction chambers (4 and 5). there is no counterforce (no reaction) on the steering wheel. The steering wheel is easy to turn.

When driving fast on "highways", the converter valve is wide open and the oil flows from the pressurized right cylinder chamber (12) via the right check valve (8), right orifice (10) and converter (3) to return flow. The right reaction chamber (4) then has full pressure, while the left reaction chamber (5) is without pressure. This produces a left-turning torque, which tries to force the valve pistons back into neutral position (maximum reaction). The steering wheel is hard to turn.

When driving at medium speed, converter valve (3) is opened only partially. The reduced arm pressure is transmitted to the left reaction chamber (5), while the right reaction chamber (4) has maximum pressure. The counterforce acting on valve pistons (6 and 7) is lower accordingly.




Cross Section Drawing of Valve in Worm Head







1. Speedometer

2. Control Unit

3. Electro/hydraulic converter

4. Reaction chamber, right

5. Reaction chamber, left

6. Valve piston, right

7. Valve piston, left

8. Check valve, right

9. Check valve, left

10. Orifice, right

11. Orifice, left

12. Cylinder chamber, right

13 Cylinder chamber, left