Steering Device and Method of Controlling a Steering Device

Abstract

A steering device for a motor vehicle is described, the steering device comprising a steering element for steering the motor vehicle, and an actuating element by means of which wheels of the motor vehicle are adjusted as a function of an actuation of the steering element. The steering element has a steering assist unit associated with it, in particular an electronic steering assist unit for active return of the steering element, the steering assist unit comprising a motor and an open- and closed-loop control unit which drives the motor for generating an assist torque. The open- and closed-loop control unit receives data from a first sensor which directly senses the position of the actuating element, and drives the motor as a function of the position of the actuating element. Further described is a method of controlling a steering device.

Claims

1. A steering device for a motor vehicle, the steering device comprising a steering element for steering the motor vehicle, and an actuating element by means of which wheels of the motor vehicle are adjusted as a function of an actuation of the steering element, the steering element having a steering assist unit associated therewith for active return of the steering element, the steering assist unit comprising a motor and an open- and closed-loop control unit which drives the motor for generating an assist torque, the open- and closed-loop control unit receiving data from a first sensor which directly senses a position of the actuating element, and driving the motor as a function of the position of the actuating element.

2. The steering device according to claim 1, receives data from a second sensor which senses a velocity of the actuating element.

3. The steering device according to claim 1, wherein the open- and closed-loop control unit receives data from a third sensor which senses a speed of the motor vehicle.

4. The steering device according to claim 3, wherein the open- and closed-loop control unit includes a reference generator which calculates a reference velocity of the actuating element.

5. The steering device according to claim 1, wherein the open- and closed-loop control unit comprises a calculating unit, a limiting unit, and a damping unit which receives data from at least one sensor on the steering element.

6. The steering device according to claim 1, wherein the steering device is an electrically powered or electrically assisted steering device.

7. A method of controlling a steering device according to claim 1, wherein: a) the open- and closed-loop control unit senses the position of an actuating element by means of the first sensor, and b) the open- and closed-loop control unit calculates an assist torque of the motor for returning the steering element as a function of the position of the actuating element.

8. The method according to claim 7, wherein a second sensor senses a velocity of the actuating element and transmits the velocity to the open- and closed-loop control unit, which uses the velocity to calculate the assist torque of the motor.

9. The method according to claim 8, wherein a third sensor senses a vehicle speed and transmits the vehicle speed to the open- and closed-loop control unit, which uses the vehicle speed to calculate the assist torque of the motor.

10. The method according to claim 9, wherein on a basis of values sensed by the first, second and third sensors, a reference velocity of the actuating element is generated in a reference generator of the open- and closed-loop control unit.

11. The method according to claim 7, wherein a damping factor is calculated in a damping unit of the open- and closed-loop control unit.

12. The method according to claim 7, wherein a maximum assist torque of the motor is calculated in a limiting unit of the open- and closed-loop control unit.

13. The steering device according to claim 2, wherein the first and second sensors are adapted to be configured in a sensor unit.

14. The steering device according to claim 4, wherein the reference velocity of the actuating element is calculated as a function of signals from the first, second and third sensors.

15. The steering device according to claim 6, wherein the steering device is an electrically powered or electrically assisted steer-by-wire steering device.

16. The method according to claim 11, wherein the damping factor is calculated in the damping unit of the open- and closed-loop control unit as a function of the position, the speed and the torque of the steering element.

17. The method according to claim 12, wherein the maximum assist torque of the motor is calculated in the limiting unit of the open- and closed-loop control unit as a function of the damping factor determined by the damping unit and of the motor vehicle speed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 shows a schematic representation of a steering device according to the invention; and

[0026] FIG. 2 shows a schematic representation for illustrating the method according to the invention for controlling a steering device.

DETAILED DESCRIPTION OF THE INVENTION

[0027] FIG. 1 schematically illustrates a steering device 10 for a motor vehicle, the steering device comprising a steering element 12, which includes a steering wheel 14 and a steering shaft 16 arranged thereon, and an actuating element 18 which has a pair of wheels 20 of the motor vehicle directly coupled thereto by means of track rod arms 21. Depending on the design of the steering device 10, steering arms and steering knuckles may also be provided.

[0028] An electronic steering assist unit 22, which may generally be configured to assist the steering device 10, is arranged between the steering element 12 and the actuating element 18. This may include an active adjustment of the actuating element 18 and a generation of torques in the steering element 12 to create an improved perception on the part of the driver. The electronic steering assist unit 22 may, in addition, actively return the steering element 12 when the vehicle transitions from a cornering to traveling straight.

[0029] FIG. 1 only shows those components of the electronic steering assist unit 22 which are necessary for the active return of the steering element 12 to its neutral position.

[0030] Thus, the electronic steering assist unit 22 includes an open- and closed-loop control unit 24 which, as the central element of the steering assist unit 22, drives an electric motor 26 which actively returns the steering element 12 to its neutral position.

[0031] The open- and closed-loop control unit 24 receives data from a first sensor 28 which senses the position of the actuating element 18, and from a second sensor 30 which senses the velocity of the actuating element 18. The two sensors 28, 30 may be embodied in one single sensor unit 32 here, so that they are realized in a space-saving manner.

[0032] The open- and closed-loop control unit 24 further receives data from a third sensor 34 which senses the vehicle speed.

[0033] In addition, the open- and closed-loop control unit 24 may acquire data from a further sensor 36 which is arranged on the steering element 12, in particular on the steering shaft 16, and transmits data such as the angular position of the steering shaft, the rotational velocity of the steering shaft, and the steering shaft torque to the open- and closed-loop control unit 24.

[0034] Using the three sensors 28, 30, 34, the open- and closed-loop control unit 24 can calculate an assist torque of the motor 26, which acts on the steering element 12 so as to give the driver the impression of an active return of the steering element 12 to the neutral position as is known from steering devices that are not electronically assisted.

[0035] The data sensed by the further sensor 36 furthermore serves for a kind of fine adjustment of the assist torque of the motor 26.

[0036] The mode of operation of the steering device 10, and in particular the control of the steering assist unit 22 are described with reference to FIG. 2.

[0037] FIG. 2 schematically illustrates how the data received from the individual sensors 28, 30, 34, 36 are processed in the open- and closed-loop control unit 24 of the electronic steering assist unit 22 in order to drive the motor 26 of the electronic steering assist unit 22 such that a particular assist torque is generated by the motor 26, as a result of which the steering element 12 is actively returned.

[0038] To this end, the open- and closed-loop control unit 24 includes a reference generator 38, a damping unit 40, a calculating unit 42, and a limiting unit 44, each of which receives data from the different sensors 28, 30, 34, 36 and processes it as described below.

[0039] Based on the sensor signals of the first three sensors 28, 30, 34, the reference generator 38 generates a reference velocity of the actuating element 18, at which the actuating element 18 is to move back to its neutral position. The reference generator 38 transmits this reference velocity to the calculating unit 42.

[0040] Additionally, the calculating unit 42 receives the respectively measured data directly from the sensors 28, 30, 34. Accordingly, the calculating unit 42 receives the reference velocity of the actuating element 18 as generated by the reference generator 38, the vehicle speed sensed by the third sensor 34, the actual velocity of the actuating element 18 as sensed by the second sensor 30, and the position of the actuating element 18 as sensed by the first sensor 28.

[0041] Furthermore, the calculating unit 42 receives a damping factor which has been calculated in the damping unit 40 as a function of the data sensed by the further sensor 36. The damping factor here is a variable from which conclusions are drawn to the activity of the driver since the data sensed by the further sensor 36 are measured directly at the steering element 12, which is operated by the driver. By means of the damping factor, the assist torque to be generated by the motor 26 can be adapted to the activity of the driver.

[0042] On the basis of the data previously mentioned, a preliminary assist torque of the motor 26 is now calculated in the calculating unit 42. The open- and closed-loop control unit 24 can compare the reference velocity generated by the reference generator 38 with the actual velocity of the actuating element 18 here and can appropriately adjust the preliminary assist torque of the motor 26. This method step can be carried out iteratively, with an adjustment of the reference velocity calculated in the reference generator 38 also being possible.

[0043] The preliminary assist torque calculated in the calculating unit 42 can, in conclusion, be limited in the limiting unit 44. To this end, the damping factor calculated by the damping unit 40, the vehicle speed sensed by the third sensor 34 and the preliminary assist torque calculated by the calculating unit 42 are provided to the limiting unit 44.

[0044] Based on the incoming variable, the limiting unit 44 calculates a limitation of the preliminary assist torque and limits the latter in certain vehicle situations, so that it is ensured that the assist torque of the steering assist unit 22 as generated by the motor 26 will not lead to any unsafe vehicle situation. Here, in particular the vehicle speed and the behavior of the driver are taken into account.

[0045] The electric motor 26 may be a separate motor which is only provided for actively returning the steering element 12. Alternatively, the motor 26 may be that motor which also adjusts the actuating element 18 during a steering process. This depends on the type of steering device 10. For example, if a steer-by-wire steering device is involved, which has no mechanical connection between the steering element 12 and the actuating element 18, two separate motors are provided. If, on the other hand, the steering device is an electronically assisted steering device which may feature a mechanical connection, all in all, only one motor may be provided.

[0046] The steering device 10 according to the invention and the method according to the invention of controlling a steering device make sure that the assist torque of the electronic steering assist unit 22 can be determined independently of the vehicle topology, so that a safe vehicle operation and an active return of the steering element 12 are ensured.

[0047] In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.