Method and device for the compensation of steering wheel rotary oscillations in a steering system

1. A method of compensating for steering wheel rotary oscillations due to imbalances on wheels of a vehicle during operation of a steering system in said vehicle, said steering system comprising an activatable torque actuator,

the method comprising:

determining a current torsion bar torque;

determining a compensation torque as a function of the current torsion bar torque; and

activating the torque actuator as a function of the compensation torque;

wherein the torsion bar torque or a first variable determined as a function of the torsion bar torque is fed to a variable-frequency disturbance variable and state variable calculator which contains a model of a sinusoidal disturbance of steering wheel rotary oscillations and a model of a transmission behavior from a torque of the torque actuator; and

wherein the compensation torque is determined by the variable-frequency disturbance variable and state variable calculator using the model of the sinusoidal disturbance of steering wheel rotary oscillations.

2. The method according to claim 1 , wherein an amplitude and a phase of the steering wheel rotary oscillation are taken into account by the variable-frequency disturbance variable and state variable calculator when determining the compensation torque.

3. The method according to claim 1 , wherein a component of the steering wheel rotary oscillations that has already been compensated is taken into account when determining the compensation torque.

4. The method according to claim 3 , wherein the compensation torque is fed back to the variable-frequency disturbance variable and state variable calculator.

5. The method according to claim 1 , wherein the model of the transmission behavior describes the transmission behavior at least in a frequency range relevant to the steering wheel rotary oscillations with regard to an amplitude response and a phase response.

6. The method according to claim 1 , further comprising testing for existence of said steering wheel rotary oscillations, and wherein the compensation torque is determined when said existence of said steering wheel rotary oscillations is deduced from said testing.

7. The method according to claim 6 , wherein the existence of said steering wheel rotary oscillations is deduced if a vehicle speed, a wheel speed or a variable correlating with the wheel speed is within a predefinable range and the steering system is being operated at least substantially in a straight-ahead position.

8. The method according to claim 6 , wherein said testing comprises evaluating a current amplitude of the torsion bar torque, said current amplitude being determined as an estimate.

9. The method according to claim 1 , further comprising filtering the detected torsion bar torque and the filtered torsion bar torque is fed to the variable-frequency disturbance variable and state variable calculator to determine the compensation torque.

10. The method according to claim 9 , wherein said filtering is performed by a variable bandpass filter, and an excitation frequency is formed as a function of a vehicle speed, a wheel speed or a variable correlating with the wheel speed, and a center frequency of the variable bandpass filter is selected as a function of the excitation frequency.

11. The method according to claim 1 , wherein the variable-frequency disturbance variable and state variable calculator is parameterized with regard to at least one parameter variable and an adaptation of at least one function of the variable-frequency disturbance variable and state variable calculator in order to compensate deviations in series production and/or in order to compensate an aging of the steering system is performed by modifying the at least one parameter variable.

12. The method according to claim 11 , wherein the at least one parameter variable is modified as a function of a determined compensation quality.

13. The method according to claim 12 , wherein the compensation quality is determined by evaluating an amplitude of a remaining residual oscillation in the torsion bar torque.

14. The method according to claim 1 , wherein the variable-frequency disturbance variable and state variable calculator is configured as an inseparable module which determines the compensation torque as a function of the torsion bar torque, wherein the variable-frequency disturbance variable and state variable calculator comprises the model of the transmission behavior.

15. A device for compensating for steering wheel rotary oscillations due to imbalances on wheels of a vehicle during operation of a steering system in said vehicle, wherein the steering system comprises an activatable torque actuator and means for determining a current torsion bar torque, and wherein the device comprises:

a variable-frequency disturbance variable and state variable calculator for determining a compensation torque, and which contains a model of a sinusoidal disturbance of steering wheel rotary oscillations and a model of a transmission behavior from a torque of the torque actuator;

means for activating the torque actuator as a function of the compensation torque;

wherein the torsion bar torque or a first variable determined as a function of the torsion bar torque is fed to the variable-frequency disturbance variable and state variable calculator; and

wherein the compensation torque is determined by the variable-frequency disturbance variable and state variable calculator using the model of the sinusoidal disturbance of steering wheel rotary oscillations.

16. The device according to claim 15 , configured to implement a method comprising:

determining a compensation torque as a function of the current torsion bar torque; and

activating the torque actuator as a function of the compensation torque.