Method for controlling an electric power steering system

• US 7,398,854 B2
• Filed: 04/06/2005
• Issued: 07/15/2008
• Est. Priority Date: 05/06/2004
• Status: Expired due to Fees

• Current Assignee: Robert Bosch Automotive Steering GmbH (Robert Bosch GmbH)
• Original Assignee: ZF Lenksysteme GmbH (Robert Bosch GmbH)
• Inventors: Heilig, Arnulf, Bischofberger, Michael
• Primary Examiner(s): Morris; Lesley D.
• Assistant Examiner(s): YEAGLEY, DANIEL S
• Application Number:
  US11/100,919
• Publication Number:
  US 20060000662A1
• Time in Patent Office: 1,196 Days
• Field of Search: 180/446, 701/41, 701/42
• US Class Current: 180/446
• CPC Class Codes: B62D 15/0215 by measuring on the steering column
• CPC Class Codes: B62D 15/0235 by measuring or deriving directly at the electric power steering motor
• CPC Class Codes: B62D 5/0484 for reaction to failures, e.g. limp home
• CPC Class Codes: B62D 6/10 characterised by means for sensing or determining torque

Abstract

A method for controlling an electrical power steering system for a vehicle includes an electrical servomotor, a steering device for entering a reference value (θ_S) of a steering angle into a control andlor regulation device, a moment sensor and an angle sensor for the steering device, a device for estimating the moment (M_v) at the steering device and an angle sensor for determining the angle (θ_A) of a power take-off of the electrical servomotor. In order to control the electrical power steering system, which makes a non-critical behavior possible in the event of a malfunction or failure of a moment sensor at the steering device, provisions are made so that an offset value (Δ_θ) is constantly formed from the reference value (δ_S) of the steering angle and the actual value θ_I of the steering angle, and a virtual moment (M_v) of the steering device is determined on the basis of the offset value (Δ_θ) and is used to control the electrical servomotor.

Claims

1. Method for controlling an electrical power steering for a vehicle comprising an electrical servomotor, having a power take-off, a control and/or regulation device, a steering device for entering a reference value (θ

_S) of a steering angle into the control and/or regulation device, a moment sensor and a first angle sensor for the steering device, an estimating device for estimating the moment (M_v) at the steering device, a second angle sensor for determining the angle (θ

_A) of the power take-off of the electrical servomotor, an offset value (Δ

_θ

) being determined constantly from the reference value (δ

_S) of the steering angle and an actual value (θ

_I) of the steering angle and a virtual moment (M_v) of the steering device being determined on the basis of the offset value (Δ

_θ

).

2. The method of claim 1, wherein the virtual moment (M_v) of the steering device is determined by the control and/or regulation device from the steering angle actual value (θ

_I), the angle (θ

_A) of the power take-off of the electrical servomotor, the offset value (Δ

_θ

), and the stiffness of the kinematics of the electrical power steering.

3. The method of claim 1, wherein in the event of a malfunction or a failure of the moment sensor of the steering device, a moment (M_S) of the electrical servomotor is reduced by the control and/or regulation device by way of a transition function (F), as a function of the virtual moment (M_v) of the steering device, the actual value (θ

_I) of the steering angle and a steering velocity (v_L) specified by the steering device.

4. The method of claim 3, wherein the transition function (F) is a ramp function.

5. The method of claim 3, wherein the transition function (F) is a strictly monotonously decreasing function.

6. The method of claim 3, wherein the moment (M_S) of the electrical servomotor is reduced by the control and/or regulation device by way of the transition function (F), if the virtual moment (M_v) of the steering device has decreased to a specifiable limiting value (lim_Mv).

7. The method of claim 6, wherein the limiting value (lim_Mv) of the virtual moment (M_v) at the steering device is approximately 2 Nm.

8. The method of claim 6, wherein the electrical servomotor is switched off by the control and/or regulation device when the virtual moment (M_v) of the steering device has changed its sense of direction, while simultaneously exceeding the specifiable limiting value (lim_Mv).

9. The method of claim 1, wherein the electrical servomotor is switched off by the control and/or regulation device when an error at the first or second angle sensors is detected by the control and/or regulation device.

10. The method of claim 1, wherein the electrical servomotor is switched off by the control and/or regulation device when the steering angle actual value (δ

_I) is less than a specifiable limiting value (lim<sub>δ

I</sub>) and an error occurs at the first angle sensor for the steering device or an error occurs at the moment sensor at the steering device.

11. The method of claim 10, wherein the limiting value (lim_δ

I) is approximately 10°

.

12. The method of claim 1, wherein the electric servomotor is switched off by the control and/or regulating device when the steering speed (V_L) exceeds a specifiable limiting value (lim_vI).

13. The method of claim 12, wherein the specifiable limiting value (lim_vL) is approximately 100°

/s.