Vehicle electric power assist steering system and method using velocity based torque estimation

• US 6,425,454 B1
• Filed: 02/16/2000
• Issued: 07/30/2002
• Est. Priority Date: 02/16/2000
• Status: Expired due to Term

• Current Assignee: Ford Motor Company
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Chabaan, Rakan C., Wang, Le Yi
• Primary Examiner(s): Olszewski, Robert P.
• Assistant Examiner(s): Fischer, Andrew J.
• Application Number:
  US09/505,373
• Time in Patent Office: 895 Days
• Field of Search: 180/443, 180/444, 180/446, 180/422, 701/41, 701/42
• US Class Current: 180/443
• CPC Class Codes: B62D 5/0463 calculating assisting torque from the motor based on driver input
• CPC Class Codes: B62D 6/10 characterised by means for sensing or determining torque

Abstract

A steering system (10) and method (70) for controlling the steering of a vehicle having a steering wheel (12), a steering column (14)connected to the steering wheel (12), and an electric motor (20) operatively engaged with the steering column (14) for supplying torque assist. A velocity detector is employed for detecting an angular velocity {dot over (θ)}_m of the electric motor (20). The system has a torque estimator (40) for determining an estimated torque signal T_dest as a function of the detected motor velocity {dot over (θ)}_m, and a motor controller (30) for generating a motor control signal (U) as a function of the estimated torque. Accordingly, the present invention reduces the complexity and cost of the electric power assist steering system by eliminating the need for a conventional pinion torque sensor, without sacrificing vehicle steering performance.

Claims

1. An electric power assisted steering system for a vehicle, comprising:

a steering assembly including a steering wheel connected to a steering column;

an electric motor operatively engaged with said steering assembly for supplying steering torque assist;

a velocity detector detecting an angular velocity of said electric motor;

a torque estimator calculating an estimated driver torque applied to the steering wheel by a driver as a function of said detected angular velocity; and

a controller generating a motor control signal as a function of said estimated torque for controlling the electric motor.

2. The system as defined in claim 1, wherein said torque estimator determines said estimated torque signal further as a function of the motor control signal input to the electric motor.

3. The system as defined in claim 2, wherein said torque estimator determines the estimated torque signal further as a function of one or more steering system transfer functions.

4. The system as defined in claim 1, wherein said torque estimator estimates a driver torque signal and a pinion torque signal.

5. The system as defined in claim 1, wherein said controller includes a feedback controller and a feedforward controller.

6. The system as defined in claim 5 further comprising a friction compensation filter coupled to said feedforward controller.

7. The system as defined in claim 1, wherein said steering assembly further includes a shaft operatively coupled to the steering column and further connected to a rack and pinion assembly, wherein said electric motor is coupled to said shaft.

8. The system as defined in claim 1, wherein said system is provided without a pinion torque sensor.

9. A control system for controlling electric motor torque assist to an electric power assisted steering system for a vehicle having a steering assembly including a steering wheel connected to a steering column and an electric motor operatively engaged with the steering assembly for supplying steering torque assist, wherein said control system comprises:

a velocity detector detecting an angular velocity of the electric motor;

a torque estimator estimating a driver torque applied to the steering wheel by a driver as a function of said sensed angular velocity of the electric motor; and

a controller generating a motor control signal as a function of said estimated torque for controlling the electric motor.

12. The control system as defined in claim 9, wherein said torque estimator estimates a driver torque signal and a pinion torque signal.

10. The control system as defined in aim 9, wherein said torque estimator determines said estimated torque signal further as a function of the motor control signal input to the electric motor.

11. The control system as defined in claim 10, wherein said torque estimator determines the estimated torque signal further as a function of one or more steering system transfer functions.

13. A method of controlling an electric power assisted steering system having a steering assembly including a steering wheel connected to a steering column for a vehicle and an electric motor operatively coupled to the steering assembly, said method comprising the steps of:

sensing an angular velocity of the electric motor;

estimating a driver torque applied to the steering wheel by a driver as a function of said sensed angular velocity of the electric motor;

generating a motor control signal as a function of said estimated torque for controlling an electric motor; and

applying said motor control signal to an electric motor to generate a controlled amount of steering torque assist.

14. The method as defined in claim 13, wherein said step of estimating a torque signal further comprises estimating the torque signal as a function of the motor control signal input to the electric motor and one or more predetermined transfer functions.

15. The method as defined in claim 13, wherein said step of estimating a torque signal further comprises estimating a driver torque signal and estimating a pinion torque signal.

16. The method as defined in claim 13, wherein said step of generating a motor control signal includes generating a feedforward signal and a feedback signal.

17. The method as defined in claim 13, wherein said step of estimating a torque signal is performed without employing a pinion torque sensor.