Electric power steering control system and method for controlling the electric power steering control system

• US 20020026270A1
• Filed: 08/20/2001
• Published: 02/28/2002
• Est. Priority Date: 08/30/2000
• Status: Active Grant

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Kifuku, Takayuki, Kurishige, Masahiko, Nishiyama, Ryoji, Tsutsumi, Kazumichi, Inoue, Noriyuki
• Granted Patent: US 6,459,971 B1
• Time in Patent Office: Days
• US Class Current: 701/41
• CPC Class Codes: B62D 15/0245 Means or methods for determination of the central position of the steering system, e.g. straight ahead position
• CPC Class Codes: B62D 5/0466 for returning the steering wheel to neutral position

Abstract

In the conventional electric power steering control system, a steering force applied by a driver to a steering wheel is detected and a torque of a motor is determined on the basis of the detected steering force. In such a prior system, at the time of going round a gentle curve, going round an intersection at an extremely low speed or the like, any steering wheel return torque is not generated unless the driver returns the steering wheel, and drive feeling is not improved. First, a road surface reaction torque estimator 15 estimates a road surface reaction torque on the basis of a steering wheel angle. A neutral point learning unit 24 and a neutral point compensator 25 learn a neutral point of the steering wheel on the basis of the road surface reaction torque with respect to the steering wheel angle. A return torque for returning the steering wheel to the neutral point is computed from a difference between a current angle of the motor and the learned neutral point. As a result, the steering wheel returns to the neutral point under the current driving condition without application of any force to the steering wheel by the driver.

Claims

1. An electric power steering control system comprising:

a motor for applying an assisting torque to a steering wheel used for manipulating running wheels of a vehicle;

steering torque detecting means for detecting a torque applied to said steering wheel by a driver of said vehicle as a steering torque;

motor angle detecting means for detecting a rotating angle of said motor;

road surface reaction torque estimating means for estimating a road surface reaction torque of said running wheels using said steering torque;

and

neutral point learning means for learning a neutral point of the steering wheel under the actual driving condition from said estimated road surface reaction torque and the rotating angle of said motor.

2. The electric power steering control system according to claim 1 further comprising:

steering angle compensation means for computing are turn torque to return said steering wheel to said neutral point from a difference between the rotating angle of said motor and said learned neutral point and for converting said return torque into an electric current of said motor, whereby said return torque is applied to said steering wheel whenever said steering wheel is turned from said neutral point.

3. The electric power steering control system according to claim 1 further comprising:

speed detecting means for detecting speed of the vehicle; and

means for stopping operation of the neutral point learning means when said vehicle speed detected by said speed detecting means is smaller than a predetermined value.

4. The electric power steering control system according to claim 3 further comprising rotating direction detecting means for outputting different codes according to the rotating direction of the motor,

wherein the neutral point learning means learns a neutral point in left steering and a neutral point in right steering respectively according to the codes outputted by said rotating direction detecting means at the time of learning the neutral point and subsequently learns a neutral point by computing an average of said neutral point in left steering and said neutral point in right steering.

5. The electric power steering control system according to claim 3 further comprising rotating direction detecting means for outputting different codes according to the rotating direction of the motor,

wherein the neutral point learning means learns a neutral point on the basis of a value obtained by subtracting or adding a preliminarily stored friction torque of a steering mechanism according to said rotating direction from or to the estimated road surface reaction torque.

6. The electric power steering control system according to claim 5 further comprising rotating speed detecting means for detecting a rotating speed of the motor or angular acceleration detecting means for detecting a rotating angular acceleration of the motor,

wherein the neutral point learning means learns a neutral point when at least one of said rotating speed and said rotating angular acceleration of said motor is smaller than a predetermined value and does not learn the neutral point when the rotating speed or the rotating angular acceleration of the motor is larger than said predetermined value.

7. The electric power steering control system according to claim 5, wherein the steering angle compensating means comprises a limiter for limiting an output of the steering angle compensating means to be within a predetermined level.

8. The electric power steering control system according to claim 4 further comprising:

speed detecting means for detecting a vehicle speed;

a damping compensator for compensating a damping on the basis of speed of the motor; and

an inertia compensator for compensating an inertia on the basis of acceleration of said motor;

wherein said damping compensator and said inertia compensator work when said vehicle speed exceeds a predetermined level, and said damping compensator and said inertia compensator stop working when the vehicle speed does not exceed said predetermined level.

9. An electric power steering control system comprising:

a motor for applying an assisting torque to a steering wheel used for manipulating running wheels of a vehicle;

steering torque detecting means for detecting a torque applied to said steering wheel by a driver of said vehicle as a steering torque;

motor angle detecting means for detecting a rotating angle of said motor;

motor current setting means for setting a target value of an electric current flowing in said motor by receiving a torque command signal;

motor current detecting means for detecting a value of the electric current flowing in said motor;

road surface reaction torque estimating means for estimating a road surface reaction torque of said running wheels using said steering torque and the current of said motor;

neutral point learning means for learning a neutral point of said steering wheel under the current driving condition from said estimated road surface reaction torque and the rotating angle of said motor; and

steering angle compensation means for computing a return torque to return said steering wheel to said neutral point from a difference between the rotating angle of said motor and said learned neutral point and outputting the return torque to said motor current setting means, whereby the return torque is applied to said steering wheel whenever said steering wheel is turned from said neutral point.

10. The electric power steering control system according to claim 9 further comprising:

speed detecting means for detecting speed of the vehicle; and

means for stopping operation of the neutral point learning means when said vehicle speed detected by said speed detecting means is smaller than a predetermined value.

11. The electric power steering control system according to claim 10 further comprising rotating direction detecting means for outputting different codes according to the rotating direction of the motor,

wherein the neutral point learning means learns a neutral point in left steering and a neutral point in right steering respectively according to the codes outputted by said rotating direction detecting means at the time of learning the neutral point and subsequently learns a neutral point by computing an average of said neutral point in left steering and said neutral point in right steering.

12. The electric power steering control system according to claim 10 further comprising rotating direction detecting means for outputting different codes according to the rotating direction of the motor,

wherein the neutral point learning means learns a neutral point on the basis of a value obtained by subtracting or adding a preliminarily stored friction torque of a steering mechanism according to said rotating direction from or to the estimated road surface reaction torque.

13. The electric power steering control system according to claim 12 further comprising rotating speed detecting means for detecting a rotating speed of the motor or angular acceleration detecting means for detecting a rotating angular acceleration of the motor,

wherein the neutral point learning means learns a neutral point when at least one of said rotating speed and said rotating angular acceleration of said motor is smaller than a predetermined value and does not learn the neutral point when the rotating speed or the rotating angular acceleration of the motor is larger than said predetermined value.

14. The electric power steering control system according to claim 12, wherein the steering angle compensating means comprises a limiter for limiting an output of the steering angle compensating means to be within a predetermined level.

15. The electric power steering control system according to claim 11 further comprising:

speed detecting means for detecting a vehicle speed;

a damping compensator for compensating a damping on the basis of speed of the motor; and

an inertia compensator for compensating an inertia on the basis of acceleration of said motor;

wherein said damping compensator and said inertia compensator work when said vehicle speed exceeds a predetermined level, and said damping compensator and said inertia compensator stop working when the vehicle speed does not exceed said predetermined level.

17. The method for controlling an electric power steering control system according to claim 16 further including:

a step of detecting a vehicle speed; and

a step of stopping an operation of the step of learning a neutral point when said vehicle speed is lower than a predetermined value.

18. The method for controlling an electric power steering control system according to claim 16 further including:

a step of detecting a rotating direction in which different codes are outputted according to the rotating direction of the motor; and

a step of learning a neutral point by learning a neutral point in left steering and a neutral point in right steering respectively according to the codes of the rotating direction outputted at the time of learning the neutral point and subsequently computing an average of said neutral point in left steering and said neutral point in right steering.

16. A method for controlling an electric power steering control system including:

a step of detecting a motor angle in which a rotating angle of a motor for applying an assisting torque to a steering wheel used for manipulating running wheels of a vehicle is detected;

a step of estimating a road surface reaction torque in which a road surface reaction torque is estimated using a steering torque applied to said steering wheel by a driver of said vehicle and a current signal of said motor;

a step of learning a neutral point in which a neutral point of said steering wheel is learned from said road surface reaction torque and the rotating angle of said motor; and

a step of compensating a steering angle in which a torque for returning said steering wheel to said neutral point is computed from said neutral point and the rotating angle of said motor.