Method and apparatus for “hands-on” identification on steering systems

1. A method for hands-on identification on a steering system having at least two subsystems which are connected to one another by at least one elastic connection, in which the at least one elastic connection has at least one respective static friction state and one respective sliding friction state for a respective set of external state variables, the method comprising:

exciting the steering system by an excitation vibration, which is generated by a controllable vibration generator and has a respective excitation amplitude and a respective excitation frequency, for a respective set of external state variables,

taking the respective excitation amplitude and the respective excitation frequency from a table for a currently present set of external state variables;

controlling the vibration generator based on the respective excitation amplitude and the respective excitation frequency,

measuring a reaction torque to the excitation vibration using a sensor,

calculating a phase difference between the excitation vibration and the reaction torque, and

either identifying a hands-off state by a value of the phase difference that is between 0° and 90°, or identifying a hands-on state by a value of the phase difference that is between 90° and 180°.

2. The method as claimed in claim 1 , further comprising:

providing the table, which contains the respective excitation amplitude and the respective excitation frequency for the respective set of external state variables by determining the respective transition region between the static friction state and the sliding friction state of the at least one elastic connection of the steering system, by way of the respective excitation frequency being selected from the respective frequency range between a first transition region for a steering system which is held by a driver and a second transition region for the steering system which is not held by the driver, and

ascertaining the respective excitation amplitude for a respective static friction level of the held steering system and a respective sliding friction level of the non-held steering system for the respective excitation frequency, and

selecting a respective table value for the respective excitation amplitude between the ascertained respective static friction and sliding friction levels.

3. The method as claimed in claim 1 , in which the respective excitation frequency is selected in the table for the respective set of external state variables between a natural system frequency for a steering system which is not held by a driver and a natural system frequency for a steering system which is held by the driver.

4. The method as claimed in claim 1 , in which the respective set of external state variables is compiled from the following list: temperature, age, wear, and/or service interval.

5. The method as claimed in claim 1 , in which the steering system includes a steering wheel, steering column and torsion bar.

6. An apparatus for hands-on identification on a steering system, said apparatus comprising:

a vibration generator, a vibration sensor and at least two subsystems, wherein the at least two subsystems are connected to one another by at least one elastic connection, wherein the at least one elastic connection has at least one respective static friction state and one respective sliding friction state for a respective set of external state variables,

wherein the apparatus is configured to (i) excite the steering system by an excitation vibration, which is generated by the controllable vibration generator and has a respective excitation amplitude and a respective excitation frequency, for a respective set of external state variables, (ii) take the respective excitation amplitude and the respective excitation frequency from a table for the currently present set of external state variables and to control the vibration generator with the respective excitation amplitude and the respective excitation frequency, (iii) measure a reaction torque to the excitation vibration using the vibration sensor, (iv) calculate a phase difference between the excitation vibration and the reaction torque, and (v) either establish a hands-off state by a value of the phase difference of between 0° and 90°, or establish a hands-on state by a value of the phase difference of between 90° and 180°.

7. The apparatus as claimed in claim 6 , wherein the apparatus is further configured to:

(vi) provide the table which contains the respective excitation amplitude and the respective excitation frequency for the respective set of external state variables by determining the respective transition region between the static friction state and the sliding friction state of the at least one elastic connection of the steering system,

(vii) select the respective excitation frequency from the respective frequency range between a first transition region for a steering system which is held by a driver and a second transition region for the steering system which is not held by the driver, and

(viii) ascertain the respective excitation amplitude for a respective static friction level of the held steering system and a respective sliding friction level of the non-held steering system for this respective excitation frequency, and

(ix) select a respective table value for the respective excitation amplitude between the ascertained respective static friction and sliding friction levels.

8. The apparatus as claimed in claim 6 , which is configured to select the respective excitation frequency for the respective set of external state variables between a natural system frequency for a steering system which is not held by a driver and a natural system frequency for a steering system which is held by a driver.

9. The apparatus as claimed in claim 6 , in which the respective set of external state variables is compiled from the following list: temperature, age, wear, and/or service interval.

10. The apparatus as claimed in claim 6 , in which the steering system comprises a steering wheel, steering column and torsion bar.