Method for operating a power steering system

Abstract

Method for operating a power steering system (10), in which a servo motor (30) is controlled by a control unit (26) to superimpose a superimposed torque, and wherein the servo motor (30) is excited with a high-frequency signal which causes a high-frequency motor torque, characterized in that a check is carried out on the basis of a resulting torsion bar torque (50) to determine whether the applied motor torque is effective.

Description

[0001] The invention relates to a method for operating a servo or auxiliary power steering system according to the preamble of claim 1, such a servo steering system and a computer program and a computer program product for carrying out the method.

[0002] Power steering systems, also known as servo steering systems, are designed to reduce the amount of effort required by the driver to steer. This allows for the most direct steering possible with minimal effort. A servo motor is used for this purpose. During operation, sensors register the steering torque applied by the driver and the steering speed. This information is transmitted to a control unit, which then calculates the required steering assistance or servo torque and controls the servo motor accordingly.

[0003] The servomotor transmits the calculated servo torque, e.g., via a worm or epicyclic gear, to the torsion bar and pinion, and thus to the rack. It should be noted that the servomotor can be installed in different ways. In a parallel-axis power steering system, the servomotor is mounted parallel to the rack.

[0004] The transmission concept of the parallel-axis servo or electric steering system consists of a belt and a ball screw drive (BSD) that transmits the servo motor's assist torque. During operation, the steering system can stiffen, with an unfavorable arrangement of the balls in the BSD making the steering stiff. This leads to customer complaints, which must be avoided at all costs.

[0005] It should be noted that constructive solutions lead to increased costs or conflict with other quality criteria, such as acoustic assessment.

[0006] From the generic DE 198 01 982 C2, for example, a method for operating a power steering system is known in which a servo motor is controlled by a control unit to superimpose a superimposed torque, and wherein the servo motor is excited with a high-frequency signal which causes a high-frequency motor torque.

[0007] The object of the invention is to remedy or prevent the hardening or blockage of the steering by suitable measures.

[0008] Against this background, a method for operating a power steering system according to claim 1 and such a power steering system with the features of claim 8 are presented. Further details are set out in the dependent claims.

[0009] In this process, a servomotor is controlled by a control unit to superimpose a superimposed torque. The servomotor is excited or controlled with a high-frequency signal that generates a high-frequency motor torque. The resulting torsion bar torque is used to check whether the applied motor torque is effective.

[0010] The method can be used to detect and / or prevent a locking and / or to release a locking of the steering.

[0011] Furthermore, it can be provided that the applied engine torque is determined taking into account a limit curve.

[0012] The excitation signal can be a sinusoidal signal. Furthermore, the signal can be in a frequency range of 10 - 25 Hz.

[0013] In the design of the procedure, a wheel rotation speed is taken into account.

[0014] The power steering system of a motor vehicle presented here is used, in particular, to implement the method described above. It comprises a control unit for calculating engine torque and a servo motor for applying the engine torque. The control unit is configured to excite the servo motor with a high-frequency signal.

[0015] Implementing the discussed procedure shows that high-frequency excitations of the servo motor are suitable for relieving the steering stiffness or loosening the locking balls of the ball joint. However, the driver should not perceive these additional excitations as disturbing. It is known from the compensation of steering wheel vibrations that the driver can only perceive steering wheel vibrations above a certain limit curve. Even if the conservative limit curve is slightly violated to prevent or resolve steering stiffness, this would only be perceived briefly as a vibration of the steering wheel, for example, due to the road surface, and not as a measure to resolve a potentially safety-critical steering lock.

[0016] If, in the case of hardening, it is detected that engine torque below the perceived threshold is insufficient to relieve the hardening, the engine torque can be increased above the perceived threshold, at least temporarily. This is usually not perceived by the driver as a measure to counteract the hardening, but rather as an external disturbance. In all other cases, the measure to counteract the hardening is not perceived by the driver.

[0017] As a solution to the hardening problem, a sinusoidal, high-frequency engine torque in the frequency range of 10-25 Hz is proposed, which creates a torsion bar torque below the driver's perception threshold. The torsion bar torque checks whether the set engine torque is effective or whether the steering is jammed. To vary the excitation frequency and thus the vibration frequency, the frequency can be varied according to the wheel rotation speed.

[0018] The described computer program comprises program code means for carrying out all steps of a method as described above when the computer program is executed on a computer or a computing unit.

[0019] The described computer program product comprises these program code means stored on a computer-readable data carrier.

[0020] The computer program can be stored as a computer program product on a computer-readable data storage medium, such as a floppy disk, CD, DVD, hard disk, USB memory stick, or similar, or on an internet server. From there, the computer program can be transferred to a memory element of the control unit.

[0021] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0022] It is understood that the aspects mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or in isolation, without departing from the scope of the present invention.

[0023] The invention is illustrated schematically in the drawing using exemplary embodiments and is described in detail below with reference to the drawing. Fig. 1 shows an embodiment of the power steering according to the invention. Fig. 2 shows an embodiment of the presented method.

[0024] In Fig. Figure 1 shows an embodiment of the power steering system, designated overall by reference numeral 10. The illustration shows a steering wheel 12, a steering column 14, a torsion bar 16, a pinion 18, a rack 20, a steering linkage 22, and wheels 24.

[0025] Also shown is a control unit 26 connected to a sensor system 28. This sensor system 28 can detect the steering angle, steering torque, and steering speed applied via the steering wheel 12. The control unit 26 controls a servomotor 30, which in turn transmits a superimposed torque to the steering linkage 22 via a gear unit 32, so that the steering torque applied by the driver is superimposed.

[0026] In Fig.Figure 2 shows a possible sequence of the described method. A high-frequency signal is applied to the servomotor, and a resulting torsion bar torque 50 is detected, the amplitude of which is calculated in a block 52. An absolute value analysis is performed in a further block 54, and a subsequent block 56 checks whether a threshold has been exceeded. If this is not the case, a hardening flag 58 is set, meaning that hardening of the steering is detected.

[0027] To ensure that the high-frequency excitation is not perceived as disturbing, a limit curve 60 is considered, which represents the perceived amplitude (ordinate 62) of the torsion bar vibration over the frequency (abscissa 64). The input variable is the wheel rotation frequency 66.

[0028] A virtual, subjectively imperceptible torsion bar torque is determined via a function generator 70, from which a vibration torque 74 results via an inverse steering model G(z) 72. A variation of the excitation frequency and vibration frequency is achieved by varying the frequency according to the wheel rotation speed or frequency 66.

Claims

[1] Method for operating a power steering system (10), in which a servo motor (30) is controlled by a control unit (26) to superimpose a superimposed torque, and wherein the servo motor (30) is excited with a high-frequency signal which causes a high-frequency motor torque, characterized by that a resulting torsion bar torque (50) is used to check whether the applied engine torque is effective. [2] Method according to claim 1, which is used to detect a blockage of the power steering (10). [3] Method according to claim 1, which is used to prevent blocking of the power steering (10). [4] Method according to claim 1, which is used to release a blockage of the power steering (10). [5] Method according to one of claims 1 to 4, in which the applied engine torque is determined taking into account a limit curve (60). [6] Method according to one of claims 1 to 5, wherein the signal lies in a frequency range of 10 - 25 Hz. [7] Method according to one of claims 1 to 6, in which a wheel rotation speed or wheel running frequency (66) is taken into account. [8] Power steering of a motor vehicle for carrying out a method according to one of claims 1 to 7 with a control unit (26) for calculating an engine torque, a servo motor (30) for introducing the motor torque, wherein the control unit (26) is designed to excite the servo motor (30) with a high-frequency signal. [9] Computer program with program code means for carrying out all the steps of a method according to one of claims 1 to 7 when the computer program is executed on a computer or a corresponding computing unit. [10] Computer program product with program code means stored on a computer-readable data carrier for carrying out all the steps of a method according to one of claims 1 to 7 when the computer program is executed on a computer or a corresponding computing unit.

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