Closed loop EPAS systems

1. A vehicle comprising a closed-loop electric power assisted steering (EPAS) system comprising a control unit configured to compute a desired reference torque (τref) incorporating a calculated artificial friction component, wherein the magnitude of the calculated artificial friction component is dependent upon and modified by a steering wheel angle (α), and wherein the EPAS system is configured to use the computed desired reference torque (τref) in providing an assistive torque to a steering system of the vehicle.

2. The vehicle according to claim 1 wherein the control unit is configured to receive a plurality of input parameters and input variables and is configured to execute a program to compute an hysteresis component of the desired reference torque (τref) that is dependent upon the steering wheel angle (α) and thereby incorporates said artificial friction component, the magnitude of which is dependent upon the steering wheel angle, into the desired reference torque.

3. The vehicle according to claim 1 wherein the control unit is configured to receive a plurality of input parameters and input variables and is configured to execute a program to compute a damping component of the desired reference torque (τref) that is dependent upon the steering wheel angle (α), thereby incorporating the artificial friction component, the magnitude of which is dependent upon the steering wheel angle, into the desired reference torque.

4. The vehicle according to claim 1 wherein the control unit is configured to refer to one or more look-up tables, which look-up tables comprise tuning parameters for various steering wheel angles and wherein the control unit is configured to reference said look-up tables and use said tuning parameters in determining the artificial friction component of the desired reference torque (τref) such that the magnitude of said artificial friction component is dependent upon the steering wheel angle (α).

5. The vehicle according to claim 4 wherein the one or more look-up tables are stored by the control unit.

6. A closed-loop electric power assisted steering (EPAS) system configured to carry out a computation of desired reference torque (τref), the computation comprising at least one function to generate an artificial friction component of the desired reference torque and wherein said at least one function for generating the magnitude of said artificial friction component is dependent upon steering wheel angle (α), and wherein the EPAS system is configured to use the computed desired reference torque (τref) in providing an assistive torque to a steering system of a vehicle.

7. The closed-loop EPAS system according to claim 6 comprising a control unit which is configured to receive a plurality of input parameters and input variables and is configured to execute a program to compute said desired reference torque (τref) that comprises an hysteresis component that is dependent upon the steering wheel angle (α) and/or that comprises a damping component that is dependent upon the steering wheel angle (α).

8. The closed-loop EPAS system according to claim 7 wherein the control unit is configured to refer to one or more look-up tables, which look-up tables comprise tuning parameters for various steering wheel angles and wherein the control unit is configured to reference said look-up tables and use said tuning parameters in determining the artificial friction component of the desired reference torque (τref).

9. The closed-loop EPAS system according to claim 8 wherein the one or more look-up tables are stored by the control unit.

10. A programmable unit for use in the EPAS system according to claim 6 for use in a vehicle, wherein the programmable unit is configured to determine a desired reference torque (τref) that includes computation of a magnitude of said artificial friction component that is dependent upon the steering wheel angle (α).

11. A method of operating a closed-loop EPAS system for a vehicle having a programmable control unit, the method comprising:

(i) collecting data at least relating to vehicle speed, steering wheel velocity, driver applied torque and steering wheel angle;

(ii) computing an artificial friction the magnitude of which is dependent upon a first steering wheel angle range, a second steering wheel angle range, or a third steering wheel angle range, wherein an upper boundary of the second steering wheel angle range is greater than an upper boundary of the first steering wheel angle range and an upper boundary of the third steering wheel angle range is greater than the upper boundary of the second steering wheel angle range;

(iii) computing a desired reference torque (τref) based upon the collected data and said artificial friction, wherein the artificial friction is fully applied in the first steering wheel angle range and only partially applied in the second steering wheel angle range and the third steering wheel angle range; and

(iv) instructing a motor of the EPAS system to provide an assistive torque to a steering system of the vehicle based on the computed desired reference torque (τref).

12. The method of operating a closed-loop EPAS system for a vehicle according to claim 11 wherein the step of computing an artificial friction comprises determining a functional relationship to use based upon one or more input variables or input parameters received by the control unit and operating that determined functional relationship on the input steering wheel angle signal to compute an intermediate signal that is combined with one or more other intermediate signals that are simultaneously and/or sequentially generated during the computation of a magnitude of the artificial friction.

13. A computerized control unit for an EPAS system, the control unit including a program configured to cause the control unit to compute a desired reference torque (τref) incorporating an artificial friction component, wherein the artificial friction component is dependent upon steering wheel angle (α), and a predetermined set of tuning maps are used to alter one or more characteristics of the artificial friction component and each of the tuning maps have a different function depending on a value of an input parameter, and further wherein the control unit instructs a motor of the EPAS system to provide an assistive torque to a steering system of a vehicle based on the computed desired reference torque (τref).

14. The computerized control unit according to claim 13 wherein the control unit is further configured to receive a plurality of input parameters and input variables and is configured to compute an hysteresis component of the desired reference torque (τref) that is dependent upon the steering wheel angle (α) and thereby incorporate the artificial friction component, that is dependent upon the steering wheel angle, into the desired reference torque.

15. The computerized control unit according to claim 13 wherein the control unit is further configured to receive a plurality of input parameters and input variables and is configured to compute a damping component of the desired reference torque (τref) that is dependent upon the steering wheel angle (α), thereby incorporating an artificial friction component into the desired reference torque that is dependent upon the steering wheel angle.

16. The computerized control unit according to claim 13 wherein the control unit is further configured to refer to one or more look-up tables, which look-up tables comprise tuning parameters for various steering wheel angles and wherein the control unit is configured to reference said look-up tables and use said tuning parameters in determining the artificial friction component of the desired reference torque (τref) such that the artificial friction component is dependent upon the steering wheel angle (α).

17. The computerized control unit according to claim 16 wherein, the one or more look-up tables are stored by the control unit.