ELECTRIC POWER STEERING APPARATUS

• US 20080114515A1
• Filed: 11/15/2007
• Published: 05/15/2008
• Est. Priority Date: 11/15/2006
• Status: Abandoned Application

• Current Assignee: NSK Limited
• Original Assignee: NSK Limited
• Inventors: HARA, Takeshi
• Application Number:
  US11/940,351
• Publication Number:
  US 20080114515A1
• Time in Patent Office: Days
• US Class Current: 701/42
• CPC Class Codes: B62D 5/0466 for returning the steering wheel to neutral position

Abstract

There is provided an electric power steering apparatus in which an electric motor for imparting a steering assist force to a steering mechanism is controlled based on a current control value which is operated from a steering assist command value which is operated based on a steering torque and a vehicle speed and a motor current, including a road surface reaction force detection unit for detecting a road surface reaction force, an angular velocity detection unit for detecting an angular velocity of the motor, and a return angular velocity control unit for operating a return angular velocity control signal based on the road surface reaction force, the angular velocity, the steering torque and the vehicle speed, wherein the steering assist command value is corrected by the return angular velocity control signal.

Claims

1. An electric power steering apparatus comprising:

an electric motor which imparts a steering assist force to a steering mechanism, and is controlled based on a current control value;

a road surface reaction force detection unit which detects a road surface reaction force;

an angular velocity detection unit which detects an angular velocity of the motor; and

a return angular velocity control unit which operates a return angular velocity control signal based on the road surface reaction force, the angular velocity, the steering torque and the vehicle speed, wherein

the current control value is calculated from a motor current and a steering assist command value which is operated based on a steering torque and a vehicle speed, and

the steering assist command value is corrected by the return angular velocity control signal.

2. The electric power steering apparatus as set forth in claim 1, wherein

the road surface reaction force detection unit is a road surface reaction force detector.

3. The electric power steering apparatus as set forth in claim 1, wherein

the road surface reaction force detection unit is SAT (Self-Alignment Torque) estimation unit, and

an SAT estimation value that is estimated by the SAT estimation unit is made to constitute the road surface reaction force.

4. The electric power steering apparatus as set forth in claim 1, wherein

the angular velocity detection unit is made to detect or estimate the angular velocity based on an inter-terminal voltage and the motor current.

5. The electric power steering apparatus as set forth in claim 1, wherein

the return angular velocity control unit comprises:

a motor angular speed target value setting unit which sets a motor angular velocity target value based on the road surface reaction force;

a first gain adjustment unit which outputs a first gain according to the vehicle speed;

a subtracter unit for obtaining a deviation between the angular velocity and a value obtained by multiplying the motor angular velocity target value by the first gain, and

a third gain adjustment unit which outputs a third gain according to the steering torque, and

wherein the return angular velocity control signal is made up by multiplying the deviation by the third gain.

6. The electric power steering apparatus as set forth in claim 1, wherein

the return angular velocity control unit comprises:

a motor angular speed target value setting unit which sets a motor angular velocity target value based on the road surface reaction force;

a first gain adjustment unit which outputs a first gain according to the vehicle speed;

a second gain adjustment unit which outputs a second gains according to the vehicle speed;

a subtracter unit which obtains a deviation between the angular velocity and a value obtained by multiplying the motor angular velocity target value by the first gain; and

a third gain adjustment unit which outputs a third gain according to the steering torque, and

wherein the return angular velocity control signal is made up by multiplying the deviation by the second gain and multiplying the resultant value from the multiplication by the third gain.

7. The electric power steering apparatus as set forth in claim 5, wherein

the motor angular velocity target value is set by a gain which varied in accordance with the road surface reaction force.