Method for compensating the play in the gearing between a steering wheel and a steering valve

1. An operating method for a hydraulic servo steering system of a motor vehicle including the following steps: applying a supporting force to a steering gearing by a steering cylinder integrated into a hydraulic circuit by means of a steering valve, a steering valve opening of which specifies the supporting force, setting the supporting force is set by the steering valve in accordance with a steering torque applied to a steering wheel, by means of a gearing having play, wherein an actuator is acting on the gearing having play in order to cause relative adjustment thereof, wherein the operating method includes a compensation step in which, provided that a steering direction reversal is detected, the gearing having play is adjusted by means of the actuator in a direction opposite a prior engagement direction of the gearing for a predefined duration or a predefined adjustment distance.

2. The operating method according to claim 1 comprising at least one further step, wherein a variation of valve characteristics is performed by means of the actuator and the gearing.

3. The operating method according to claim 1 , wherein an adjustment distance, an adjustment duration, or an adjustment speed is selected depending on steering parameters including a current steering angle, and a current or prior steering torque, or a current steering speed.

4. The operating method according to claim 1 , wherein an adjustment distance, or an adjustment duration, or an adjustment speed is selected depending on steering parameters including a current vehicle speed and a current yaw rate.

5. The operating method according to claim 1 , wherein the compensation step is not provided unless a steering angle is above a certain predefined value.

6. The operating method according to claim 1 , wherein a detection step is provided in which the play of the gearing is detected.

7. The operating method according to claim 1 , wherein a steering angle present during steering direction reversal is measured and saved in a detection, and a maximum adjustment distance of the actuator is selected in a subsequent compensation step proportional to a difference between a current steering angle and a saved steering angle.

8. The operating method according to claim 1 , wherein detection of a steering direction reversal is done by a steering angle sensor, which directly detects a rotational direction of an input shaft having torque-proof connection to a steering wheel.

9. The operating method according to claim 1 , wherein the steering valve is provided with at least one planetary gearing to vary valve characteristics by means of the actuator.

10. The operating method according to claim 1 , wherein the actuator is an electromechanical actuator.

11. The operating method according to claim 1 , wherein the predefined adjustment distance is set steadily by means of the actuator.

12. The operating method according to claim 1 , wherein the servo steering system further includes a rack and a pinion engaging in the rack as well as a pinion shaft having torque-proof connection to the pinion and that the gearing is provided between the steering valve and the pinion shaft.

13. A hydraulic servo steering system comprising: a hydraulic circuit, a steering cylinder integrated into the hydraulic circuit applying a supporting force to a steering gearing, a steering valve integrated into the hydraulic circuit which sets the supporting force in accordance with a steering torque applied to the steering wheel, by means of a gearing having play, wherein the steering system further includes an actuator that acts on the gearing in order to cause relative adjustment thereof as well as a control unit, wherein the control unit the hydraulic circuit, the steering cylinder, the steering gearing, the steering valve, the steering wheel and the actuator are configured to perform the operation method according to claim 1 .