Electric power steering control system

• US 6,431,307 B2
• Filed: 03/12/2001
• Issued: 08/13/2002
• Est. Priority Date: 03/15/2000
• Status: Expired due to Fees

• Current Assignee: Koyo Seiko Co., Ltd. (Toyota Motor Corporation)
• Original Assignee: Koyo Seiko Co., Ltd. (Toyota Motor Corporation)
• Inventors: Yoshida, Kazuyuki
• Primary Examiner(s): Lerner, Avraham
• Assistant Examiner(s): LUBY, MATTHEW D
• Application Number:
  US09/802,874
• Publication Number:
  US 20010022249A1
• Time in Patent Office: 519 Days
• Field of Search: 180/443, 180/446, 701/41-42
• US Class Current: 180/446
• CPC Class Codes: B62D 5/0463 calculating assisting torque from the motor based on driver input

Abstract

A control system for an electric power steering system which generates a steering assist force by an electric motor driven on the basis of a steering torque applied to an operation member. The control system includes: a target current determining circuit for generating a target current value according to the steering torque; a compensation value determining circuit for generating a compensation current value according to a time-based differential value of the steering torque; a waveform transforming circuit for performing a waveform transformation to convert the compensation current value into a modified compensation value which sinusoidally changes with time; a circuit for generating a control command value by superimposing the modified compensation value obtained through the waveform transformation on the target current value; and a motor driving circuit for driving the electric motor on the basis of the control command value.

Claims

1. A control system for an electric power steering system adapted to generate a steering assist force by an electric motor driven on the basis of a steering torque applied to an operation member, the control system comprising:

a target current determining circuit for generating a target current value according to the steering torque;

a compensation value determining circuit for generating a compensation current value according to a time-based differential value of the steering torque;

a waveform transforming circuit for performing a waveform transformation to convert the compensation current value generated by the compensation value determining circuit into a modified compensation value which sinusoidally changes with time;

a circuit for generating a control command value by superimposing the modified compensation value generated by the waveform transforming circuit on the target current value determined by the target current determining circuit; and

a motor driving circuit for driving the electric motor on the basis of the control command value.

2. A control system as set forth in claim 1, wherein the compensation value determining circuit generates the compensation current value in a digital data form on the basis of the time-based differential value of the steering torque in a digital data form.

3. A control system as set forth in claim 1, wherein the waveform transforming circuit performs the waveform transformation so that a pulse indicative of the compensation current value for a minimum value of the time-based differential value of the steering torque is converted into a digital signal having a stepwise sinusoidal waveform expressed by at least three discrete values.

4. An electric power steering system comprising:

an electric motor for generating a steering assist force; and

a control system for driving the electric motor on the basis of a steering torque applied to an operation member,

the control system comprising;

a target current determining circuit for generating a target current value according to the steering torque;

a compensation value determining circuit for generating a compensation current value according to a time-based differential value of the steering torque;

a waveform transforming circuit for performing a waveform transformation to convert the compensation current value generated by the compensation value determining circuit into a modified compensation value which sinusoidally change with time;

a circuit for generating a control command value by superimposing the modified compensation value generated by the waveform transforming circuit on the target current value determined by the target current determining circuit; and

a motor driving circuit for driving the electric motor on the basis of the control command value.

5. An electric power steering system as set forth in claim 4, wherein the compensation value determining circuit generates the compensation current value in a digital data form on the basis of the time-based differential value of the steering torque in a digital data form.

6. An electric power steering system as set forth in claim 4, wherein the waveform transforming circuit performs the waveform transformation so that a pulse indicative of the compensation current value for a minimum value of the time-based differential value of the steering torque is converted into a digital signal having a stepwise sinusoidal waveform expressed by at least three discrete value.