Measurement of Driver Torque and Steering Angle in a Torque Overlay Steering System

Abstract

A method for determining a driver torque of a power steering assembly for an electrohydraulic power steering system of motor vehicles, includes an input shaft for introduction of a driver torque, an output shaft for driving a steering linkage and a torsion bar between the input shaft and the output shaft for actuation of a rotary slide valve, an electric drive for electrical steering assistance, and a control unit for controlling the electric drive. The power steering assembly has a sensor arrangement on the torsion bar for actuation of the rotary slide valve. An actual torque is determined with the aid of the sensor arrangement. The control unit determines a driver torque with the aid of the actual torque.

Claims

1.-20. (canceled)

21. A method for determining a driver torque of a power steering assembly for an electrohydraulic power steering system of a motor vehicle, comprising: providing the power steering assembly with an input shaft for introducing the driver torque, an output shaft for driving a steering linkage and a torsion bar between the input shaft and the output shaft for actuating a rotary slide valve, an electric drive for electrical steering assistance, and a control unit for controlling the electric drive; determining, via a sensor arrangement of the power steering assembly, an actual torque using the torsion bar for actuating the rotary slide valve; and determining, via the control unit, the driver torque based on the actual torque.

22. The method as claimed in claim 21, wherein the driver torque is also determined based on an assistance torque output by the electric drive.

23. The method as claimed in claim 21, wherein the sensor arrangement uses a torque and angle sensor (TAS) system for determining the actual torque.

24. The method as claimed in claim 23, wherein the TAS system comprises a torque sensor for determining the actual torque and/or an absolute angle sensor.

25. The method as claimed in claim 21, wherein the sensor arrangement uses only one sensor for determining the actual torque, the sensor being embodied as an angle sensor, and wherein determining the driver torque is determined from data from the angle sensor and data from a motor sensor, included in the electric drive, for monitoring an electric motor of the electric drive.

26. The method as claimed in claim 21, wherein the sensor arrangement detects the actual torque in a redundant manner.

27. The method as claimed in claim 21, wherein the sensor arrangement is configured such that the actual torque is determined using a differential angle.

28. The method as claimed in claim 21, wherein the sensor arrangement detects a differential angle between the input shaft and the output shaft for calculating the actual torque.

29. The method as claimed in claim 21, wherein the sensor arrangement detects a differential angle between a motor shaft of an electric motor of the electric drive and the output shaft for calculating the driver torque.

30. The method as claimed in claim 21, wherein the sensor arrangement detects a differential angle between a shaft of a gear mechanism of the electric drive and the output shaft for calculating the driver torque.

31. The method as claimed in claim 30, wherein the gear mechanism comprises a worm gear mechanism.

32. The method as claimed in claim 21, wherein the sensor arrangement detects a differential angle between a motor shaft of an electric motor of the electric drive and the input shaft for calculating the driver torque.

33. The method as claimed in claim 21, wherein the electric drive, for steering assistance, exerts a motor torque on the input shaft by engaging with the input shaft.

34. The method as claimed in claim 33, wherein the control unit also determines the driver torque based on the motor torque.

35. The method as claimed in claim 33, wherein the control unit ascertained the motor torque based on a measurement of a motor current that operates the electric drive.

36. The method as claimed in claim 21, wherein the sensor arrangement detects a steering angle with multiturn capability from the angle of a motor shaft of an electric motor of the electric drive and the angle of the output shaft.

37. The method as claimed in claim 21, wherein the sensor arrangement uses a computer module for calculating the driver torque.

38. The method as claimed in claim 21, wherein the sensor arrangement passes on detected measurement values to a module which is present in the motor vehicle for calculating the driver torque.

39. A power steering assembly for an electrohydraulic power steering system of motor vehicle, comprising: an input shaft for introducing a driver torque; an output shaft for driving a steering linkage and a torsion bar between the input shaft and the output shaft for actuating a rotary slide valve; an electric drive for electrical steering assistance; a control unit for controlling the electric drive; and a sensor arrangement which is configured to determine an actual torque with the aid of the torsion bar for actuating the rotary slide valve, wherein the control unit is configured to determine a driver torque based on the actual torque.

40. A low-floor vehicle comprising a power steering assembly according to claim 39.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 is a schematic diagram of a first design variant of a power steering assembly according to the invention for executing the method according to the invention; and

[0040] FIG. 2 is a schematic diagram of a second design variant of the power steering assembly according to the invention for executing the method according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1 shows a first design variant of the power steering assembly for transmitting a steering movement from a steering wheel (not illustrated) to a steering linkage (likewise not illustrated). This design variant in FIG. 1 can also execute the method according to the invention.

[0042] The driver torque is introduced via the steering wheel into the power steering assembly by the input shaft 2. The gear mechanism 7 of the electric drive 10 is connected to the input shaft 2, the gear mechanism 7 being a worm gear mechanism here. The electric drive 10 further comprises the electric motor 3 having a motor shaft 4 and a motor sensor 8 here. The torsion bar 5 connects the input shaft 2 to the output shaft 1 in such a way that it permits a certain rotational movement between the two. This is necessary since the input shaft 2 and the output shaft 1 form a rotary slide valve, which serves to control the hydraulic steering assistance system (not illustrated here). Owing to rotation of the input shaft 2 in relation to the output shaft 1, valves which actuate the hydraulic steering assistance system are actuated. As soon as the input shaft 2 and the output shaft 1 have a differential angle of substantially 0?, the steering linkage is in the position desired by the driver and the hydraulic steering assistance system does not introduce any more force into the power steering assembly. The sensor arrangement 6 is located at the interface between the input shaft 2 and the output shaft 1, the sensor arrangement detecting, by way of example, the differential angle between the input shaft 2 and the output shaft 1 here, this differential angle in turn being used to determine the driver torque.

[0043] The exemplary embodiment depicted in FIG. 2 shows the power steering assembly, which is substantially identical to that in FIG. 1, with the difference that the sensor arrangement comprises only one angle sensor whichin contrast to the sensor arrangement 6 in FIG. 1 that detects the differential angledetects the absolute angle of the output shaft 1.

[0044] It is true for both exemplary embodiments that the driver of the vehicle operates the steering system in a manual driving mode. For this purpose, the driver turns the steering wheel in order to specify the desired direction of travel of the vehicle. This rotational movement of the steering wheel is transmitted to the input shaft 2. As a result, the electric drive 10 also rotates at the same time. Owing to the movement of the electric drive 10, the angle of the motor shaft 4 and therefore also the angle of the input shaft 2, taking into consideration the transmission ratio of the gear mechanism 7, can be determined by the motor sensor 8. Therefore, the position in which the steering wheel is located is known and the direction that the driver wishes to steer the vehicle is known.

[0045] In addition to the applied driver torque, the electric motor 10 can apply a motor torque. The motor torque can be directed such that the rotational movement by the driver is assisted, or it can be directed oppositely, so that the driver has to apply an increased torque. The steering sensation for the driver can be influenced in this way.

[0046] Owing to the rotation of the input shaft 2, a differential angle between the input shaft 2 and the output shaft 1 is initially established since the torsion bar 5 elastically connects the input shaft 2 to the output shaft 1, and the output shaft 1 generally counteracts the rotation by, for example, frictional forces of the wheels. The differential angle is established depending on the steering resistance of the wheels or the steering mechanism, which is directly connected to the output shaft 1.

[0047] In the exemplary embodiment of FIG. 1, the differential angle is directly detected by the sensor arrangement 6. In the exemplary embodiment of FIG. 2, the differential angle is ascertained by way of the angle of the input shaft 2 also being known by the motor sensor 8, in addition to the absolute angle of the output shaft 1 being known by the sensor arrangement 6. Since the input shaft 2 and the output shaft 1 are connected by means of the torsion bar 5 in both exemplary embodiments, the actual torque can be determined in both cases of the torsion bar 5.

[0048] The greater the driver torque in connection with the torque of the electric drivethat is to say the motor torque , the greater is this differential angle too. The rotation of the input shaft in relation to the output shaft leads to the hydraulic valves opening, so that a hydraulic steering assistance system introduces an additional torque into the power steering assembly and assists the driver in turning the steering wheel. The hydraulic steering assistance system intervenes at a point downstream of the torsion bar 5, such as the output shaft 1 for example. The magnitude of the hydraulically introduced torque depends significantly on the size of the differential angle. As soon as the hydraulic steering system has rotated the output shaft 1 to such an extent that the differential angle becomes smaller, the hydraulic valves close again and the hydraulic torque becomes lower. If the differential angle is close to zero, the valves are also substantially closed and the hydraulic steering assistance is no longer provided.

[0049] The magnitude of the electrically introduced motor torque can initially be controlled freely of the control system of the electric drive 10. However, during manual operation, it is advisable to use control taking into consideration the differential angle and also the measurement variables of the motor sensor 8. The magnitude of the motor torque can be determined by means of the motor sensor 8 by way of the motor voltages or motor currents for operating the electric motor 3 being detected. This motor torque can be offset together with the detected actual torque of the sensor arrangement 6, so that the driver torque can be determined. The torques now known can then be used to draw conclusions about the extent to which the electrical steering assistance system should intervene.

[0050] In an autonomous driving mode, the hydraulic steering assistance system reacts and assists in the same way as in the manual mode. The required differential angle for controlling the hydraulics system is again achieved by rotating the input shaft 2 relative to the output shaft 1, but the electrically introduced torquethat is to say the motor torqueacts on the input shaft 2 and leads to a differential angle. The driver torque is not present and the electric drive 10 can operate the steering system without action by the driver and the movements of the electric drive are assisted by the hydraulic steering assistance system.

LIST OF REFERENCE SIGNS

[0051] 1 Output shaft [0052] 2 Input shaft [0053] 3 Electric motor [0054] 4 Motor shaft [0055] 5 Torsion bar [0056] 6 Sensor arrangement [0057] 7 Gear mechanism [0058] 8 Motor sensor [0059] 9 Control unit [0060] 10 Electric drive