Electric power steering apparatus

• US 7,188,702 B2
• Filed: 05/16/2003
• Issued: 03/13/2007
• Est. Priority Date: 07/02/2002
• 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: Yoneda, Atsuhiko, Kuribayashi, Takashi, Takagi, Masanori
• Primary Examiner(s): BOEHLER, ANNE MARIE M
• Application Number:
  US10/439,606
• Publication Number:
  US 20050045414A1
• Time in Patent Office: 1,397 Days
• Field of Search: 180/443, 180/444, 180/446, 701/41, 701/42
• US Class Current: 180/446
• CPC Class Codes: B62D 5/046 Controlling the motor
• CPC Class Codes: B62D 5/0463 calculating assisting torque from the motor based on driver input
• CPC Class Codes: H02P 21/22 Current control, e.g. using a current control loop

Abstract

An electric power steering apparatus is provided, which has a first device for detection of steering torque, a motor, a motor drive unit, a second device for determining a target current based upon at least a signal of steering torque, a third device for detection of a motor current, and a control unit for generating a signal for motor drive based upon at least a deviation between the target current and motor current and transmitting the signal for motor drive to the motor drive unit. The apparatus has a feature that the control unit includes a fourth device for weakening a magnetic field within the motor according to the deviation or a value computed based upon the deviation.

Claims

1. An electric power steering apparatus comprising:

a first device for detection of steering torque of a steering line;

a motor for exerting assist steering torque on the steering line;

a motor drive unit for driving the motor;

a second device for detection of a motor current running through the motor; and

a control unit including a third device for determining a target current to be supplied to the motor based on at least a signal of steering torque delivered by the first device and means for generating a signal for motor drive based on at least a deviation between the target current and the motor current and for transmitting the signal for motor drive to the motor drive unit, said target current being based on a compensation current being added to a command current where the command current is determined based on a function of the steering torque and where the compensation current is based on a function of the motor current and not based on a deviation of the target current and motor current,

wherein the signal generating means also comprises means for weakening a magnetic field within the motor according to the motor current.

2. The apparatus of claim 1, wherein said magnetic field weakening means executes a conversion in accordance with:

C2=G2(Iqr)

where C2 is the compensation current and G2 is the function of motor current, and

where C2=0 for a range of large q-axis actual said motor current Iqr and C2 ≠

0 when said Iqr is smaller than said range of large said Iqr wherein for this latter case said magnetic field is weakened.