Motor-driven power steering system for vehicles

• US 4,735,271 A
• Filed: 01/06/1987
• Issued: 04/05/1988
• Est. Priority Date: 01/14/1986
• Status: Expired due to Term

• Current Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Original Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Inventors: Shimizu, Yasuo
• Primary Examiner(s): Love, John J.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/000,907
• Time in Patent Office: 455 Days
• Field of Search: 180/79.1, 180/142, 364/424, 364/424.1, 318/432, 318/489, 318/624
• US Class Current: 180/446
• CPC Class Codes: B62D 5/0466 for returning the steering wheel to neutral position

Abstract

A motor-driven power steering system for vehicles includes a control device which is responsive to output signals from a torque detector mechanism which detects a steering torque acting on an input shaft, for applying a driving signal to an electric motor to produce an assistive torque to be imposed on the output shaft. The power steering system further includes a device for detecting a freely returning state of a steering wheel to produce a motor damping signal and a motor damping device for damping the electric motor in response to the motor damping signal.

Claims

1. A motor-driven power steering system for a vehicle, comprising:

an input shaft operatively coupled to a steering wheel;

an output shaft operatively coupled to a dirigible wheel;

an electric motor for applying an assistive torque to said output shaft;

torque detecting means for detecting a steering torque imposed on said input shaft;

control means responsive to output signals from said torque detecting means for applying a driving signal to said electric motor;

freely returning state detecting means for detecting a freely returning state of the steering wheel to generate a motor damping signal; and

damping means responsive to the motor damping signal for damping said electric motor.

2. A motor-driven power steering system according to claim 1, wherein said freely returning state detecting means comprises said torque detecting means and a rotational speed detecting means for detecting a rotational speed of said steering wheel, and wherein said freely returning state detecting means generates said motor damping signal when said steering torque is smaller than a presecribed steering torque and said steering speed is larger than a prescribed steering speed.

3. A motor-driven power steering syatem according to claim 2, wherein said freely returning state detecting means further includes a neutral position detecting means for detecting the condition that a said steering wheel is in the vicinity of a neutral position, and wherein said freely returning state detecting means generates said motor damping signal when said steering wheel passes in the vicinity of the neutral position.

4. A motor-driven power steering system according to claim 3, wherein said neutral position detecting means comprises a means for detecting a steering angle of said steering wheel.

5. A motor-driven power steering system according to claim 3, wherein said neutral position detecting means comprises a means for detecting the condition that a steering aceleration of said steering wheel is negative.

6. A motor-driven power steering system according to claim 2, wherein said prescribed steering torque has a relatively small value and said prescribed steering speed has a relatively large value.

7. A motor-driven power steering system according to claim 1, wherein said freely returning state detecting means comprises said torque detecting means and a rotational speed detecting means for detecting a rotational speed of said electric motor, and wherein said freely returning state detecting means generates said motor damping signal when said steering torque is smaller than a prescribed steering torque and said rotational speed of said electric motor is larger than a prescribed motor speed.

8. A motor-driven power steering system according to claim 7, wherein said freely returning state detecting means further includes a neutral postion detecting means for detecting the condition that said steering wheel is in the vicinity of a neutral position, and wherein said freely returning state detecting means generates said motor damping signal when said steering wheel passes in the vicinity of the neutral position.

9. A motor-driven power steering system according to claim 8, wherein said neutral position detecting means comprises a means for detecting a steering angle of said steering wheel.

10. A motor-driven power steering system according to claim 8, wherein said neutral position detecting means comprises a means for detecting the condition that a rotational acceleration of said electric motor is negative.

11. A motor-driven power steering system according to claim 7, wherein said prescribed steering torque has a relatively small value and said prescribed motor speed has a relatively large value.