Electric power steering unit and method for vehicle

• US 6,360,151 B1
• Filed: 09/28/2000
• Issued: 03/19/2002
• Est. Priority Date: 10/19/1999
• Status: Expired due to Fees

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Suzuki, Toru, Suzuki, Yoshiaki
• Primary Examiner(s): Nguyen, Tan
• Assistant Examiner(s): Tran, Dalena
• Application Number:
  US09/671,257
• Time in Patent Office: 537 Days
• Field of Search: 701/41, 180/446, 180/443, 180/400, 180/412, 180/413, 318/432, 318/433, 318/430, 318/434
• US Class Current: 701/41
• CPC Class Codes: B62D 5/046 Controlling the motor

Abstract

An electric power steering unit includes an electric motor that applies assisting force with respect to a rotating operation of the steering wheel. In one embodiment, the steering torque TM detected by a steering torque sensor is converted into a command current value I* for the electric motor by a controller. The controller controls the driving of the electric motor in accordance with the command current value I*. The controller can calculate a differential value of the steering torque TM. Based on the calculated differential value, the inertia compensation control amount TM′ is added to the steering torque TM, thus reducing the steering operation load of the steering wheel at the start of a steering operation. The steering speed also can be detected. The inertia compensation control amount TM′ can be decreased with an increase in detected steering speed, thus avoiding an uncomfortable steering feel due to the difference in the steering speeds.

Claims

1. An electric power steering unit for a vehicle comprising:

an electric motor which applies an assisting force with respect to a rotating operation of a steering wheel;

a torque detector which detects a steering torque of the steering wheel;

a steering speed detector which detects a steering speed of the steering wheel; and

a rotational force controller that generates an initial inertia compensation control amount to offset an inertia force of the electric motor, corrects the initial inertia compensation control amount in accordance with the steering speed detected by the steering speed detector, and controls a rotational force of the electric motor based on the steering torque detected by the torque detector and the corrected inertia compensation control amount.

2. The electric power steering unit according to claim 1, wherein:

the controller corrects the initial inertia compensation control amount so as to decrease with an increase in the detected steering speed.

3. The electric power steering unit according to claim 1, wherein:

the steering speed detector calculates the steering speed of the steering wheel based upon a terminal voltage and a drive current of the electric motor.

4. The electric power steering unit according to claim 1, wherein:

the controller differentiates the detected steering torque, and generates the initial inertia compensation control amount corresponding to the differential value.

5. The electric power steering unit according to claim 4, wherein:

the initial inertia compensation control amount generated by the controller decreases as the differentiated value increases.

6. The electric power steering unit according to claim 1, further comprising:

an angular velocity detector which detects an angular acceleration of the steering wheel, and

the controller generates the inertia compensation control amount in accordance with the detected angular acceleration.

7. The electric power steering unit according to claim 1, wherein the controller calculates a steering signal by adding the corrected inertia compensation control amount to the detected steering torque, and converts the calculated steering signal into a command current value to command a current amount supplied to the electric motor.

8. The electric power steering unit according to claim 1, wherein the controller converts the detected steering torque into a command current value to command a current amount supplied to the electric motor, and adds a compensation current value to the command current value based on the corrected inertia compensation control amount.

9. The electric power steering unit according to claim 1, wherein the steering speed detector comprises:

a steering angle detector which detects a steering angle caused by a rotating operation of the steering wheel; and

a steering speed calculator which calculates the steering speed based on the detected s angle.

10. An electric power steering unit for a vehicle comprising:

an electric motor which applies an assisting force with respect to a rotating operation of a steering wheel;

a torque detector which detects a steering torque of the steering wheel; and

a rotational force controller that generates an inertia compensation control amount to offset an inertia force of the electric motor, controls a rotational force of the electric motor based on the detected steering torque and the generated inertia compensation control amount, and limits the inertia compensation control amount when the detected steering torque and the generated inertia compensation control amount act in opposite directions;

wherein the rotational force controller inhibits the limiting of the inertia compensation control amount in accordance with vehicle speed.

11. The electric power steering unit according to claim 10, wherein the controller differentiates the steering torque detected by the torque detector, and generates the inertia compensation control amount corresponding to a differential value of the steering torque.

12. The electric power steering unit according to claim 11, wherein the inertia compensation control amount generated by the controller is corrected in accordance with vehicle speed.

13. The electric power steering unit according to claim 10, further comprising:

an angular velocity detector which detects an angular velocity of the steering wheel under a rotating operation, wherein the controller generates the inertia compensation control amount in accordance with the detected angular velocity.

14. The electric power steering unit according to claim 13, wherein the inertia compensation control amount generated by the controller is corrected in accordance with vehicle speed.

15. The electric power steering unit according to claim 10, further comprising:

an angular velocity detector which detects a rotational angular velocity of the electric motor, wherein the controller generates the inertia compensation control amount in accordance with the detected rotational angular velocity.

16. The electric power steering unit according to claim 10, wherein the controller calculates the inertia force of the electric motor, and generates the inertia compensation control amount in accordance with the calculated inertia force.

17. The electric power steering unit according to claim 10, wherein the controller calculates a steering signal by adding the inertia compensation control amount to the detected steering torque, and converts the calculated steering signal into a command current value to command a current amount supplied to the electric motor.

18. The electric power steering unit according to claim 10, wherein the controller converts the detected steering torque into a command current value to command a current amount supplied to the electric motor, and adds a compensation current value to the command current value based on the inertia compensation control amount.

19. An electric power steering unit for a vehicle comprising:

an electric motor which applies an assisting force with respect to a rotating operation of a steering wheel;

a torque detector which detects a steering torque of the steering wheel; and

a rotational force controller that generates an inertia compensation control amount to offset an inertia force of the electric motor, controls a rotational force of the electric motor based on the detected steering torque and the generated inertia compensation control amount, and limits the inertia compensation control amount when the detected steering torque and the generated inertia compensation control amount act in opposite directions;

wherein the rotational force controller limits the inertia compensation control amount when an absolute value of the steering torque is larger than a predetermined torque.

20. An electric power steering unit for a vehicle comprising:

an electric motor which applies an assisting force with respect to a rotating operation of a steering wheel;

a torque detector which detects a steering torque of the steering wheel; and

a rotational force controller that generates an inertia compensation control amount to offset an inertia force of the electric motor, controls a rotational force of the electric motor based on the detected steering torque and the generated inertia compensation control amount, and limits the inertia compensation control amount when the detected steering torque and the generated inertia compensation control amount act in opposite directions;

wherein the rotational force controller limits the inertia compensation control amount to zero when the detected steering torque and the generated inertia compensation control amount act in opposite directions.

21. An electric power steering unit for a vehicle comprising:

an electric motor which applies an assisting force with respect to a rotating operation of a steering wheel;

a torque detector which detects a steering torque of the steering wheel; and

a rotational force controller that generates an inertia compensation control amount to offset an inertia force of the electric motor, controls a rotational force of the electric motor based on the detected steering torque and the generated inertia compensation control amount, and limits the inertia compensation control amount when the detected steering torque and the generated inertia compensation control amount act in opposite directions;

wherein the rotational force controller limits the inertia compensation control amount to be in a range between a predetermined upper limit and a predetermined lower limit when the detected steering torque and the generated inertia compensation control amount act in opposite directions.

22. A method of controlling an electric motor that applies an assisting force with respect to rotating operation of a steering wheel in an electric power steering unit for a vehicle, the method comprising:

detecting a steering torque of the steering wheel;

detecting a steering speed of the steering wheel;

generating an initial inertia compensation control amount to offset an inertia force of the electric motor;

correcting the initial inertia compensation control amount in accordance with the detected steering speed; and

controlling a rotational force of the electric motor based on the detected steering torque and the corrected inertia compensation control amount.

23. A method of controlling an electric motor that applies an assisting force with respect to rotating operation of a steering wheel in an electric power steering unit for a vehicle, the method comprising:

detecting a steering torque of the steering wheel;

generating an inertia compensation control amount to offset an inertia force of the electric motor; and

controlling a rotational force of the electric motor based on the detected steering torque and the generated inertia compensation control amount;

wherein the inertia compensation control amount is limited when the detected steering torque and the generated inertia compensation control amount act in opposite directions and the limiting of the inertia compensation control amount is inhibited in accordance with vehicle speed.