Electric power steering apparatus and method for controlling the electric power steering apparatus

• US 7,845,459 B2
• Filed: 06/06/2007
• Issued: 12/07/2010
• Est. Priority Date: 06/06/2006
• Status: Expired due to Fees

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Kasai, Eiji
• Primary Examiner(s): Boehler; Anne Marie M
• Assistant Examiner(s): YEAGLEY, DANIEL S
• Application Number:
  US12/096,649
• Publication Number:
  US 20080277191A1
• Time in Patent Office: 1,280 Days
• Field of Search: 180/443, 180/407, 318/139, 318/400.02, 318/488, 318/489, 323/234, 323/282
• US Class Current: 180/443
• CPC Class Codes: B62D 5/046 Controlling the motor

Abstract

An electric power steering apparatus includes an electric power supply device that includes a main electric power unit that supplies high-tension electric power and a sub-electric power supply unit that supplies low-tension electric power, the main electric power unit and the sub-electric power supply unit being connected to each other in parallel, and that supplies electric power to the electric motor from one of the main electric power supply unit and the sub-electric power supply unit. An assist ECU calculates a correction coefficient based on which a d-axis target current increases with a decrease in voltage output from the electric power supply device, and calculates a final corrected d-axis target current by multiplying the d-axis target current by the correction coefficient.

Claims

1. An electric power steering apparatus, comprising:

a steering mechanism that steers steering wheels in response to a steering operation of a driver'"'"'s steering wheel;

an electric motor that is fitted to the steering mechanism and that rotates using electric power supplied from an electric power supply device to generate a force used to assist the steering operation; and

a motor control unit that controls an operation of the electric motor based on a manner in which the steering operation of the driver'"'"'s steering wheel is performed,

wherein

the electric power supply device includes at least two electric power supply units connected in parallel, which are a main electric power supply unit and a sub-electric power supply unit that outputs a voltage lower than a voltage output from the main electric power supply unit, the electric power supply device being structured such that electric power is supplied to the electric motor from one of the main electric power supply unit and the sub-electric power supply unit, and

the motor control unit includes;

a vector control unit that controls rotation of the electric motor by executing vector control indicated by a two-phase rotating flux coordinate system where a direction in which the electric motor rotates is used as a q-axis and a direction perpendicular to the direction in which the electric motor rotates is used as a d-axis; and

a motor speed compensation unit that increases, when electric power is supplied to the electric motor from the sub-electric power supply unit, a d-axis current used as a field-weakening control current by a larger amount than when electric power is supplied to the electric motor from the main electric power supply unit so that a decrease in a motor speed due to a decrease in a voltage output from the electric power supply device is suppressed.

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

a sub-electric power output line of the sub-electric power supply unit is provided with a switching unit that permits or shuts off electric power supply through the sub-electric power output line, and a protection circuit that is provided between the switching unit and the sub-electric power supply unit and that prevents an increase in a voltage of the sub-electric power output line.

3. The electric power steering apparatus according to claim 2, wherein

the main electric power supply unit includes a high-tension battery having a first voltage and a voltage-decreasing circuit that decreases the first voltage output from the high-tension battery, and outputs a voltage obtained by decreasing the first voltage,

the sub-electric power supply unit includes a low-tension battery having a second voltage that is lower than the voltage that is obtained by decreasing the first voltage output from the main electric power supply unit, and outputs the second voltage, and

electric power is supplied to the electric motor from one of the main electric power supply unit and the sub-electric power supply unit.

4. The electric power steering apparatus according to claim 3, further comprising:

an electric power supply unit change-over control unit that starts an operation of the voltage-decreasing circuit of the main electric power supply unit and turns off the switching unit of the sub-electric power supply unit when electric power is supplied to the electric motor from the main electric power supply unit, and that stops the operation of the voltage-decreasing circuit of the main electric power supply unit and turns on the switching unit of the sub-electric power supply unit when electric power is supplied to the electric motor from the sub-electric power supply unit.

5. The electric power steering apparatus according to claim 1, further comprising:

a supply voltage detection unit that detects a voltage output from the electric power supply device,

wherein

the motor speed compensation unit controls a supply amount of d-axis current used as the field-weakening control current based on the voltage detected by the supply voltage detection unit.

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

a magnetic force decrease prevention unit that sets an upper limit value for the d-axis current to prevent a decrease in a magnetic force of a permanent magnet of the electric motor.

7. A method for controlling an electric power steering apparatus including a steering mechanism that steers steering wheels in response to a steering operation of a driver'"'"'s steering wheel;

an electric motor that is fitted to the steering mechanism and that rotates using electric power supplied from an electric power supply device to generate a force used to assist the steering operation; and

a motor control unit that controls an operation of the electric motor based on a manner in which the steering operation of the driver'"'"'s steering wheel is performed, comprising

supplying electric power to the electric motor from one of at least two electric power supply units which are included in the electric power supply device, which are connected in parallel, and which include a main electric power supply unit and a sub-electric power supply unit that outputs a voltage lower than a voltage output from the main electric power supply unit;

controlling, using the motor control unit, rotation of the electric motor by executing vector control indicated by a two-phase rotating flux coordinate system where a direction in which the electric motor rotates is used as a q-axis and a direction perpendicular to the direction in which the electric motor rotates is used as a d-axis; and

increasing, using the motor control unit, when electric power is supplied to the electric motor from the sub-electric power supply unit, a d-axis current used as a field-weakening control current by a larger amount than when electric power is supplied to the electric motor from the main electric power supply unit so that a decrease in a motor speed due to a decrease in a voltage output from the electric power supply device is suppressed.