ELECTRIC POWER ASSISTED STEERING SYSTEMS

• US 20140277944A1
• Filed: 10/29/2012
• Published: 09/18/2014
• Est. Priority Date: 10/27/2011
• Status: Active Grant

• Current Assignee: Jaguar Land Rover Limited (TATA Motors Limited)
• Original Assignee: Jaguar Land Rover Limited (TATA Motors Limited)
• Inventors: Bean, Alex, Pucci, Paolo
• Granted Patent: US 9,815,493 B2
• Time in Patent Office: Days
• US Class Current: 701/41
• CPC Class Codes: B62D 1/16 Steering columns
• CPC Class Codes: B62D 15/02 Steering position indicators ; Steering position determination; Steering aids
• CPC Class Codes: B62D 15/021 Determination of steering angle
• 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 5/0463 calculating assisting torque from the motor based on driver input
• CPC Class Codes: B62D 6/002 computing target steering angles for front or rear wheels B62D7/159 takes precedence
• CPC Class Codes: B62D 6/008 Control of feed-back to the steering input member, e.g. simulating road feel in steer-by-wire applications
• CPC Class Codes: B62D 6/10 characterised by means for sensing or determining torque

Abstract

A vehicle comprising an electric power assist steering (EPAS) system, wherein the EPAS system is configured to receive a detected value of steering wheel angle and/or steering wheel angular velocity and wherein the EPAS system is configured to improve the accuracy of the detected value of steering wheel angle and/or steering wheel angular velocity by compensating for any one or more of an angular phasing of the joint between any two linked components of the steering mechanism and the effect on steering wheel angle of the deflection across a torque sensor at least substantially due to the stiffness of that torque sensor.

Claims

1. A vehicle comprising an electric power assist steering (EPAS) system, wherein the EPAS system is configured to receive a detected value of steering wheel angle and/or steering wheel angular velocity and wherein the EPAS system is configured to improve the accuracy of the detected value of steering wheel angle and/or steering wheel angular velocity by compensating for any one or more of:

(i) an angular phasing of the joint between any two linked components of the steering mechanism and/or drive mechanism by carrying out a computation to derive an improved value of steering wheel angle and/or steering wheel angular velocity from the detected value of steering wheel angle and/or steering wheel angular velocity, which computation accounts for an angle at a joint (δ

₅) between the two linked components; and

(ii) the effect on steering wheel angle of the deflection across a torque sensor at least substantially due to a low stiffness of that torque sensor.

2. A vehicle according to claim 1 wherein the EPAS system is configured to use the improved value of steering wheel angle and/or steering wheel angular velocity to compute the amount of assistive torque supplied by a motor of the EPAS system.

3. A vehicle according to claim 1 wherein a sensor for detecting the angle of rotation of the steering wheel is disposed within the steering mechanism and is not directly connected to the steering wheel.

4. A vehicle according to claim 1 wherein the EPAS system is configured to compensate for the effect of angle phasing of the joint between two linked components of the steering mechanism using any one or more of the following relationships:

5. A vehicle according to claim 4, wherein the EPAS system is configured to compensate for the effect of angle phasing of the joint between two linked components of the steering mechanism using a computation that includes an approximation and/or equivalent function or value for any one or more of:

(i) the cosine and/or sine of the angle between the two linked components (cos δ

₅ and/or sin δ

₅);

(ii) the square of the cosine of the angle input to the joint (cos² α

₅);

(iii) the square of the sine of the angle between the two linked components (sin² δ

₅);

(iv) the cosine and/or sine of the angle input to the joint (cos α

₅ and/or sin α

₅);

(v) the arctangent in the range of −

π

/2 and π

/2 of the sine of the angle input to the joint and of the cosine of the angle between the two linked components multiplied by the cosine of the angle input to the joint; and

(vi) the arctangent in the range of −

π

/2 and π

/2 of the sine of the angle output from the joint (sin β

₅) and of the quotient of the cosine of the angle output from the joint and the cosine of the angle between the two linked components (cos β

₅/cos δ

₅).

6. A vehicle according to claim 5 wherein the computation that includes an approximation and/or equivalent function or value uses a Taylor Series expansion or a Euler Series Expansion and/or references an approximate or equivalent value from a look-up table.

7. A vehicle according to claim 6 wherein the EPAS system is configured to compensate for the effect of angle phasing of a joint between two linked components of the steering mechanism to improve the accuracy of the steering wheel angle (α

) and/or the steering angle velocity by conducting a computation in which reference is made to one or more look-up tables to locate one or more stored values approximating said relationships between the detected variable and/or the angle(s) of the joint between the two linked components.

8. A vehicle according claim 1, wherein the EPAS system is configured to compensate for the effect of the deflection across the steering wheel torque sensor, by determining a displacement angle (Δ

α

) and off-setting the detected steering wheel angle (α

) by a factor at least proportional to that displacement angle (Δ

α

).

9. A vehicle according claim 1, wherein the EPAS system is configured to compensate for the effect of the deflection across the steering wheel torque sensor, by determining a displacement angle (Δ

α

) and then subtracting that displacement angle (Δ

α

) from the detected steering wheel angle (α

).

10. A vehicle according claim 1, wherein the EPAS system is configured to receive a detected value of steering wheel torque and is configured to improve the accuracy of the detected value of steering wheel torque by compensating for an angular phasing of a joint between any two linked components of the steering mechanism.

11. A vehicle according claim 1, wherein the EPAS system is configured to use at least an approximation of a torque contribution (Tweight) to the steering wheel torque caused by the presence of one or more weights disposed in the steering wheel in an off-centre position to compensate for that torque contribution (Tweight) by computing a corrected value of steering wheel torque from a detected value of steering wheel torque and/or to compensate for that torque contribution (Tweight) by computing a corrected value of assistive motor torque.

17. An electric power assist steering system for use in a vehicle according to claim 1.

12. (canceled)

13. An electric power assist steering (EPAS) system for a vehicle, the system being configured to receive a detected value of steering wheel angle and/or steering wheel angular velocity and to improve the accuracy of the detected value of steering wheel angle and/or steering wheel angular velocity by compensating for any one or more of:

(i) an angular phasing of the joint between any two linked components of the steering mechanism and/or drive mechanism by carrying out a computation which accounts for an angle at a joint (δ

₅) between the two linked components; and

(ii) the effect on steering wheel angle of the deflection across a torque sensor at least substantially due to a low-stiffness of that torque sensor.

18. A controller for use in an electric power assist steering system according to claim 13, wherein the controller is configured to receive a detected value of steering wheel angle and/or steering wheel angular velocity and is configured to improve the accuracy of the detected value of steering wheel angle and/or steering wheel angular velocity by compensating for any one or more of:

(i) an angular phasing of the joint between any two linked components of the steering mechanism and/or drive mechanism by carrying out a computation which accounts for an angle at a joint (δ

₅) between the two linked components; and

(ii) the effect on steering wheel angle of the deflection across a torque sensor at least substantially due to the low stiffness of that torque sensor.

14. A method of assisting the steering of a vehicle, the method comprising:

(a) providing an electric power assist steering (EPAS) system having a controller configured to adjust a detected variable value used by the controller of the EPAS system;

(b) receiving a detected value of steering wheel angle or steering wheel angular velocity;

(c) adjusting the detected value of steering wheel angle or steering wheel angular velocity by compensating for any one or more of;

(i) a phasing of a joint between any two linked components of a steering mechanism; and

(ii) the effect on steering wheel angle of the deflection across a torque sensor at least substantially due to the low-stiffness of that torque sensor; and

(d) using the adjusted value of steering wheel angle or steering wheel angular velocity in computations to calculate the amount of assistive torque to be supplied by a motor of the EPAS system.

16. A controller for use in an EPAS system of a vehicle, the controller including a program containing one or more algorithms for carrying out the method of claim 14 such that when running, the program is configured to compensate for an inaccuracy in the detected steering wheel angle and/or detected steering wheel angular velocity, the program configured to receive a detected value of steering wheel angle and/or steering wheel angular velocity and configured to adjust the detected value to compensate for any one or more of:

(i) an angular phasing of a joint between any two linked components of the steering mechanism and/or drive mechanism by carrying out a computation which accounts for an angle at a joint (δ

₅) between the two components; and

(ii) the effect on steering wheel angle of the deflection across a torque sensor at least substantially due to a low-stiffness of that torque sensor.

15. (canceled)