HANDS-ON/-OFF DETECTION IN A STEER-BY-WIRE SYSTEM

Abstract

A steer-by-wire steering system may include a steering adjuster that is electronically controlled depending on driver input, a feedback actuator transmitting feedback from a road, and a control unit that actuates the feedback actuator and the steering adjuster. The control unit comprises an estimator including a monitor and a model of the feedback actuator. The estimator may estimate a driver's steering torque based on measurement values of the feedback actuator and with the model and the monitor, then providing the driver's steering torque as a result. The control unit further comprises a filter unit that analyzes the measurement values of the feedback actuator by determining the damping of amplitudes of predetermined frequency ranges and to provide the result. The control unit further comprises a decision unit that decides whether a driver's hand is in contact with a steering wheel by using the results of the filter unit and the estimator.

Claims

1.-13. (canceled)

14. A steer-by-wire steering system for a motor vehicle, the steer-by-wire steering system comprising: a steering adjuster that acts on steered wheels of the motor vehicle and is electronically controlled based on a driver's steering demands; a feedback actuator that transmits feedback effects of a road to a control; and a control unit that actuates the feedback actuator and the steering adjuster, the control unit comprising an estimator that has a monitor and a model of the feedback actuator, wherein the estimator estimates a driver's steering torque based on measurement values of the feedback actuator and the model and the monitor and provides the driver's steering torque as a result, a filter unit that analyzes the measurement values of the feedback actuator by determining damping of amplitudes of predetermined frequency ranges and that provides a result, and a decision unit that decides whether a driver's hand is in contact with a steering wheel based on the results of the filter unit and the estimator.

15. The steer-by-wire steering system of claim 14 wherein the filter unit comprises a Goertzel algorithm.

16. The steer-by-wire steering system of claim 14 wherein the monitor is an extended Kalman filter.

17. The steer-by-wire steering system of claim 14 wherein depending on an accuracy of the determination of the damping in the filter unit, the decision unit is configured to send a test signal to the feedback actuator, wherein via the test signal, the filter unit, and the estimator the decision unit determines whether the driver's hand is in contact with the steering wheel.

18. A method for determining a contact state between a driver of a motor vehicle with a steer-by-wire steering system and a steering wheel of the steer-by-wire steering system, wherein the steer-by-wire steering system comprises a steering adjuster that is electronically controlled based on a driver's steering demands, a feedback actuator that transmits feedback effects of a road to the steering wheel, and a control unit that actuates the feedback actuator and the steering adjuster, the method comprising: determining a frequency spectrum of movement signals detected by sensors of the feedback actuator; analyzing the frequency spectrum by determining damping of amplitudes of predetermined frequency ranges; and estimating a driver's steering torque with a monitor of the feedback actuator, a model of the feedback actuator, and the movement signals.

19. The method of claim 18 wherein if the analysis of the frequency spectrum exceeds a predetermined level of accuracy, the method comprises determining the contact state by analyzing estimated driver's steering torque, the frequency spectrum, and the damping of amplitudes of the predetermined frequency ranges.

20. The method of claim 19 wherein if the analysis of the frequency spectrum fails to exceed the predetermined level of accuracy, the method comprises outputting a test signal to the feedback actuator prior to performing the steps of determining the frequency spectrum, analyzing the frequency spectrum, estimating the driver's steering torque, and determining the contact state.

21. The method of claim 18 wherein analyzing the frequency spectrum comprises comparing the determined frequency spectrum with a stored reference frequency spectrum.

22. The method of claim 18 comprising filtering the determined frequency spectrum, wherein analyzing the frequency spectrum is performed depending on a filtered frequency range of the frequency spectrum.

23. The method of claim 22 wherein the filtering utilizes a Goertzel algorithm.

24. The method of claim 18 wherein the monitor is an extended Kalman filter.

25. The method of claim 18 wherein the model of the feedback actuator contains at least one of inertia, damping/friction, stiffness, non-uniformity, or dead time of the steer-by-wire steering system.

26. The method of claim 18 wherein the movement signals comprise an angle of rotation of a steering shaft that is measured by the feedback actuator and a torque that is measured by the feedback actuator.

Description

[0028] Preferred embodiments of the invention are described in detail below using the drawings. Similar or equivalent components are denoted in the figures by the same reference characters. In the figures:

[0029] FIG. 1: shows a schematic representation of a steer-by-wire steering system,

[0030] FIG. 2: shows a block diagram of a controller of the steer-by-wire steering system, and

[0031] FIG. 3: shows a block diagram with a control unit and a feedback actuator.

[0032] A steer-by-wire steering system 1 is shown in FIG. 1. A steering angle sensor that is not shown is attached to a steering shaft 2 and detects the driver's steering torque that is applied by rotating the steering wheel 3. Furthermore, a feedback actuator 4 that is attached to the steering shaft 2 is used to transfer the feedback effects from the road 70 to the steering wheel 3 and thus give the driver feedback about the steering behavior and the driving behavior of the vehicle. The driver's steering demand is transferred to a control unit 5 via signal lines by means of the angle of rotation of the steering shaft 2 that is measured by the steering angle sensor. The control unit 5 actuates an electrical steering adjuster 6 that controls the position of the steered wheels 7 depending on the signal of the steering angle sensor and other input variables, such as for example the speed of the vehicle, the yaw rate and similar. The steering adjuster 6 acts indirectly on the steered wheels 7 via a steering transmission 8 and track rods 9 and other components.

[0033] FIG. 2 shows the relationship between the feedback actuator 4, the control unit 5 and the steering adjuster 6. The feedback actuator 4 comprises the angle of rotation-sensor, a torque sensor and a motor 10. The feedback actuator 4 communicates with the control unit 5, which comprises an estimator 11. As shown in FIG. 3, the estimator 11 receives signals from the feedback actuator 4 representing a steering angle and a torque applied to the feedback actuator 4.

[0034] The steering angle from the feedback actuator 4 measured by means of the steering angle sensor and the torque measured by means of the torque sensor are thus the input variables for the estimator 11.

[0035] The estimator estimates from said measurement values a steering torque of the driver or a driver's steering torque; the torque that the driver applies to the steering wheel. For this the estimator uses a model 12 of the feedback actuator 5 and a Kalman filter as the monitor.

[0036] As the input for the state model 12 of the feedback actuator 4, inter alia the following physical properties are taken into account: the inertia, damping/friction, stiffness, non-uniformity and dead time of the system.

[0037] The concept of a Kalman filter concerns a method for estimating the temporal development of linear systems, by means of which noise can be removed from a measurement signal. The filter requires a model of the system to be estimated for this.

[0038] Non-linear relationships are preferably taken into account, so that the estimator is based on an extended Kalman filter and a non-linear model of the feedback actuator.

[0039] In addition to the estimated driver's steering torque, the damping of amplitudes of predefined frequency ranges is determined by means of a filter 13 from the steering angle and torque measured by the feedback actuator.

[0040] If the driver is grasping the steering wheel 3, then vibrations are partly absorbed because of the new overall mechanical system and the changed damping properties. The frequency spectra of the steering wheel when not being held differ characteristically from those of the steering wheel that is being held. The difference between the hands-on and the hands-off states can thus be seen in the frequency spectrum of the measured sensor signals of the feedback actuator 4.

[0041] In this case, it is advantageous if only certain frequency ranges are used. Thus it is known for example that characteristic vibrations can be detected in higher frequency ranges, which are made up of vibrations from the surroundings of the steering wheel. If the steering wheel is now grasped, then said frequency ranges change accordingly, which can then be detected.

[0042] A Goertzel algorithm preferably only analyzes certain frequency ranges, using which steering wheel monitoring is carried out.

[0043] There are thus two almost mutually independently conducted estimations that are combined with each other in a final analysis step of a decision unit 14 to reliably determine whether hand contact or a driver's steering torque is applied to the steering wheel or not.

[0044] If the vibrations occurring in the driving mode are not sufficient for the determination of the damping of the amplitudes in the predefined frequency ranges, a test signal 15 of a defined intensity and amplitude is introduced into the feedback actuator 4 by means of the feedback motor 10 and a symmetrical oscillation is produced at the steering wheel 3. Thereupon, using the estimated driver's steering torque and by means of frequency analysis of the Goertzel filter, the effect on the feedback actuator 4 of touching the steering wheel 3 is detected and hence the current operating state (hands-on/off) is determined.

[0045] If the vehicle is cornering and a hands-off situation at the steering wheel 3 is determined, it can be necessary to move the steering wheel 3 back to the neutral position in order to enable straight-ahead travel. When restoring the steering wheel 3 to the neutral position, the steering feel on the steering wheel 3 is adjusted. Adjusted means that smooth resetting is enabled by means of a higher adjustable friction or damping depending on the speed of the vehicle and the steering angle rate and the steering direction, and the driver is thus provided with a highly natural steering feel in the event of a new hands-on situation.