Electric power assisted steering (EPAS) systems

• US 9,108,669 B2
• Filed: 10/29/2012
• Issued: 08/18/2015
• Est. Priority Date: 10/27/2011
• Status: Expired due to Fees

• Current Assignee: Jaguar Land Rover Limited (TATA Motors Limited)
• Original Assignee: Jaguar Land Rover Limited (TATA Motors Limited)
• Inventors: Bean, Alex, Pucci, Paolo
• Primary Examiner(s): Trammell, James
• Assistant Examiner(s): SMITH-STEWART, DEMETRA R
• Application Number:
  US14/354,591
• Publication Number:
  US 20140303848A1
• Time in Patent Office: 1,023 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: B62D 5/0463 calculating assisting torque from the motor based on driver input
• CPC Class Codes: B62D 5/0472 for damping vibrations
• 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 capable of receiving a detected value of steering wheel torque and wherein the EPAS system is operable to improve the accuracy of the detected value of steering wheel torque by compensating for a weight imbalance present in the steering wheel.

Claims

1. A vehicle comprising an electric power assisted steering (EPAS) system wherein the EPAS system is configured to use at least an approximation of a torque contribution (Tweight) to a steering wheel torque caused by the presence of one or more weights disposed in a steering wheel of the vehicle in an off-center position to compensate for that torque contribution (Tweight) by computing at least one of a corrected value of steering wheel torque from a detected value of steering wheel torque that is then used to determine an amount of assistive motor torque to be applied by the EPAS system, or a corrected value of assistive motor torque to be applied by the EPAS system, thereby accounting for the presence of the one or more weights in the steering wheel in the determination of an assistive motor torque to be applied by the EPAS system.

2. A vehicle according to claim 1 wherein the corrected value of steering wheel torque is computed by the EPAS system by subtracting the at least an approximation of the torque contribution (Tweight) from the detected value of steering wheel torque as follows:

SensorTorqueCorrected=SensorTorque−

Tweight.

3. A vehicle according to claim 1 wherein the corrected derived assistive motor torque is computed by the EPAS system by subtracting a scaled value of the at least an approximation of the torque contribution (Tweight) from a derived value of assistive motor torque (T₁) as follows:

MotorTorqueDemandCorrected=MotorTorqueDemand (T₁)−

Tweight*k₁/k₂.

4. A vehicle according to claim 1 wherein the at least an approximation of the torque contribution (Tweight) used by the EPAS system is calculated or is referenced from a look-up table of measured values.

5. A vehicle according to claim 1 wherein the EPAS system is configured to compute the torque contribution (Tweight) by at least one of:

approximating a weight imbalance as one or more point masses;

approximating an angular position of the mass;

approximating a radial position of the mass;

or approximating an angular position of the steering wheel relative to a horizontal plane as follows;

Tweight[Nm]=W[kg]·

R[m]·

g·

sin(α

+β

),

wherein, the weight imbalance is treated as a single point mass (W), disposed at an angle (β

) from a straight ahead position, at a radius (R) from the center of the steering wheel, for a steering wheel angle of rotation (α

) and factor (g) is an acceleration due to gravity.

6. A vehicle according to claim 5 wherein the factor (g) is taken to be between 9 m/s² to 10 m/s²⁻

.

7. A vehicle according to claim 6 wherein the factor (g) is taken to be 9.81m/s².

8. A vehicle according to claim 5 wherein the computation further includes a term to account for the steering wheel being positioned at an angle (δ

) relative to a notional horizontal plane, the computation at least approximating the torque contribution (Tweight) as follows;

Tweight[Nm]=W[kg]·

R[m]·

g·

sin(α

+β

)·

sin(δ

).

9. A vehicle according to claim 1 wherein the EPAS system is configured to compensate for the torque contribution (Tweight) of any weight imbalance present in the steering wheel by computing a corrected value of steering wheel torque from a detected value of steering wheel torque or a corrected value of assistive motor torque (T₁), and wherein the EPAS system is configured to refer to a look-up table comprising a series of values of torque contribution (Tweight), each torque contribution for a given angle of rotation of the steering wheel, and wherein the EPAS system is configured to compensate for the torque contribution (Tweight) by conducting a real-time linear, quadratic, other polynomial or exponential interpolation of the torque contribution (Tweight) from the look-up table against the angle of rotation of the steering wheel.

10. A vehicle according to claim 1 wherein an angle of rotation of the steering wheel (α

) is a detected variable and the EPAS system;

(i) uses the detected angle of rotation of the steering wheel in a computation of the torque contribution (Tweight) or uses the detected angle of rotation of the steering wheel in a look-up table referencing of the torque contribution (Tweight);

or

(ii) improves an accuracy of the detected angle of rotation of the steering wheel by compensating for a phasing of one or more joints between any two linked components of a steering mechanism and uses the improved value of steering wheel angle in a computation of the torque contribution (Tweight) or in referencing a look-up table of the torque contribution (Tweight);

or

(iii) improves the accuracy of the detected angle of rotation of the steering wheel by compensating for an effect on steering wheel angle of deflection across a torque sensor due to a low-stiffness of the torque sensor and uses the improved value of steering wheel angle (α

) in a computation of the torque contribution (Tweight) or in referencing a look-up table of the torque contribution (Tweight).

11. A vehicle according to claim 1 wherein the EPAS system is further capable of receiving a second detected variable value or deriving a variable value from a second detected variable value and is configured to improve an accuracy of that second detected or derived variable value to at least partially eliminate any discrepancy between an actual variable value and the second detected or derived variable value and wherein the second detected or derived variable is one of:

steering wheel angle, steering wheel angular velocity and motor angle.

12. A vehicle according to claim 11 wherein the EPAS system is configured to improve an accuracy of the second detected or derived variable value by compensating for any one or more of:

(i) an angular phasing of joints between any two linked components of a steering mechanism; and

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

13. A vehicle according to claim 12 wherein the EPAS system is configured to compensate for the effect of angular phasing of the joints between two linked components of the steering mechanism using any one or more of the following relationships:

14. A vehicle according to claim 11 wherein the second detected variable value is a angle of rotation of the steering wheel, and wherein the EPAS system is configured to compensate for an influence of the steering wheel torque sensor to improve the accuracy of the angle of rotation of the steering wheel used by the EPAS system to compute the amount of assistive torque supplied by the motor by determining and subtracting a displacement angle (Δ

α

) from the detected angle of rotation of the steering wheel.

15. A vehicle comprising an electric power assisted steering (EPAS) system, wherein the EPAS system is capable of receiving a detected value of steering wheel torque and wherein the EPAS system is configured to improve the accuracy of the detected value of steering wheel torque by compensating for a weight imbalance present in the steering wheel or by compensating for a weight imbalance present in the steering wheel and steering wheel column, and to then use the compensated value of the steering wheel torque to determine an assistive motor torque to be applied by the EPAS system thereby accounting for the presence of the imbalance in the steering wheel or the steering wheel and steering wheel column in the determination of an assistive motor torque to be applied by the EPAS system.

16. A vehicle according to claim 15 wherein the EPAS system is configured to derive an assistive motor torque (T₁) to be supplied by a motor of the EPAS system and wherein the EPAS system is configured to compensate for the influence of a weight imbalance present in the steering wheel by adjusting the derived assistive motor torque (T₁) using a torque correction that is dependent upon steering wheel angle (α

).

17. A controller for use in an electric power assist steering (EPAS) system of a vehicle, the controller configured to determine or use at least an approximation of a torque contribution (Tweight) to a steering wheel torque caused by the presence of one or more weights disposed in a steering wheel of the vehicle in an off-center position to compensate for that torque contribution (Tweight) by computing at least one of a corrected value of steering wheel torque from a detected value of steering wheel torque that is then used by the controller to determine an amount of assistive motor torque to be applied by the EPAS system or a corrected value of assistive motor torque to be applied by the EPAS system, thereby accounting for the presence of the one or more weights in the steering wheel in the determination of an assistive motor torque to be applied by the EPAS system.

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

(i) providing an electronic power assisted steering (EPAS) system having an EPAS control unit and a steering wheel torque sensor;

(ii) configuring the EPAS control unit to use at least an approximation of a torque contribution (Tweight), caused by the presence of one or more weights disposed within the steering wheel in an off-center position; and

(iii) configuring the EPAS control unit to use said torque contribution (Tweight) to compute at least one of a corrected value of steering wheel torque that is then used to determine an assistive motor torque to be applied by the EPAS system;

or

a corrected value of assistive motor torque to be applied by the EPAS system, thereby accounting for the presence of the one or more weights in the steering wheel in the determination of an assistive motor torque to be applied by the EPAS system.

19. A method according to claim 18 wherein the corrected value of steering wheel torque is computed by subtracting said torque contribution (Tweight) from the detected value of steering wheel torque as follows:

SensorTorqueCorrected=SensorTorque −

Tweight.

20. A method according to claim 18 wherein the corrected derived assistive motor torque is computed by subtracting a scaled value of said torque contribution (Tweight) from a derived value of assistive motor torque (T₁) as follows:

MotorTorqueDemandCorrected=MotorTorqueDemand (T₁)−

Tweight*k₁/k₂.

21. A method according to claim 18 further comprising the step of determining the torque contribution (Tweight) by a computation that comprises at least one of:

approximating a weight imbalance as one or more point masses;

approximating an angular position of the mass;

approximating a radial position of the mass;

or approximating the angular position of the steering wheel relative to a horizontal plane and wherein the step of determining the torque contribution (Tweight) comprises the following calculation;

Tweight[Nm]=W[kg]·

R[m]·

g·

sin(α

+β

),

wherein, the weight imbalance is treated as a single point mass (W), disposed at an angle (β

) from a straight ahead position, at a radius (R) from the center of the steering wheel, the steering wheel having an angle of rotation (α

) and factor (g) is an acceleration due to gravity.

22. A method according to claim 21 wherein the calculation further includes a term to account for the steering wheel being positioned at an angle (δ

) relative to a notional horizontal plane, the computation at least approximating the torque contribution (Tweight) as follows;

Tweight[Nm]=W[kg]·

R[m]·

g·

sin(α

+β

)·

sin(δ

).

23. A method according to claim 18 further comprising the step of determining the torque contribution by:

referring to a look-up table comprising a series of values of the torque contribution (Tweight), each torque contribution for a given angle of rotation of the steering wheel, and the method including controlling the amount of assistive torque applied to an electric motor by conducting a real-time interpolation of the torque contribution (Tweight) from the look-up table against the angle of rotation of the steering wheel.

24. 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 18 such that when running, the program is configured to at least approximately determine the torque contribution (Tweight) or to reference an at least approximate torque contribution stored in a look-up table, caused by the presence of one or more weights disposed within the steering wheel in an off-center position.

25. A controller according to claim 24 wherein the program is capable of receiving a detected value of steering wheel torque and is configured to improve an accuracy of the detected value of steering wheel torque by subtracting the determined or referenced torque contribution (Tweight) from the detected value of steering wheel torque as follows:

SensorTorqueCorrected=SensorTorque−

Tweight; and

wherein a corrected derived assistive motor torque is computed by subtracting a scaled value of the determined or referenced torque contribution (Tweight) from a derived value of assistive motor torque (T₁) as follows;

MotorTorqueDemandCorrected=MotorTorqueDemand(T₁)−

Tweight*k₁/k₂.

26. An electric power assisted steering (EPAS) system for a vehicle, the system being configured to use at least an approximation of a torque contribution (Tweight) to a steering wheel torque caused by the presence of one or more weights disposed in a steering wheel in an off-center position to compensate for that torque contribution (Tweight) by computing at least one of a corrected value of steering wheel torque from a detected value of steering wheel torque that is then used to determine an amount of assistive motor torque to be applied by the EPAS system or a corrected value of assistive motor torque to be applied by the EPAS system, thereby accounting for the presence of the one or more weights in the steering wheel in the determination of an amount of assistive torque to be applied by the EPAS system.