ELECTRIC POWER STEERING DEVICE

• US 20110166750A1
• Filed: 09/02/2009
• Published: 07/07/2011
• Est. Priority Date: 09/11/2008
• Status: Active Grant

• Current Assignee: Honda Motor Co., Ltd. (Honda Motor Company)
• Original Assignee: Honda Motor Co., Ltd. (Honda Motor Company)
• Inventors: Nakano, Yasuhiro
• Granted Patent: US 8,606,462 B2
• Time in Patent Office: Days
• US Class Current: 701/41
• CPC Class Codes: B62D 5/046 Controlling the motor
• CPC Class Codes: H02P 21/0089 using field weakening
• CPC Class Codes: H02P 21/06 Rotor flux based control involving the use of rotor position or rotor speed sensors
• CPC Class Codes: H02P 25/024 controlled by supply frequency

Abstract

There is provided a electric power steering device which can perform torque control through a simple arithmetic process using a synchronous reluctance motor having a nonlinear current/torque characteristic. A target torque is transmitted from an EPS control unit 41 to a motor control unit 51. The motor control unit 51 calculates a target-current effective value I and a target-current phase θ from the input target torque. Based on the calculated target-current effective value I and target-current phase θ, calculation is changed whether to perform calculation so that the maximum torque (the maximum torque obtainable at the minimum current effective value) can be obtained, or to perform calculation so that the maximum output (the maximum output obtainable at the minimum current effective value) can be obtained in accordance with a duty ratio of an output by a PWM converting unit 57 comprising a three-phase inverter. Next, a three-phase biaxial converting unit 53 calculates a target q-axis current Iq and a target d-axis current Id from the target-current effective value I and the target-current phase θ, and the PWM converting unit 57 performs duty control in order to control the torque of a motor 58.

Claims

1. A electric power steering device which drives a synchronous motor based on a signal from a steering input detecting unit and which assists a steering, the electric power steering device comprising:

a target-torque calculating unit that calculates a target torque output by the synchronous motor based on at least a steering input signal; and

a target-current calculating unit that calculates a target current to the synchronous motor based on a signal from the target-torque calculating unit, wherein

the target-current calculating unit calculates a motor-current effective value and a motor-current phase which are necessary for generating a target torque value and the synchronous motor is driven by calculating a d-axis current and a q-axis current based on the motor-current effective value and the motor-current phase.

2. The electric power steering device according to claim 1, wherein the target-current calculating unit includes a map for calculating the motor-current effective value and the motor-current phase from the input target torque value, and the map includes at least two maps which are a normal range map and a high-output range map.

3. The electric power steering device according to claim 2, wherein the map is changed from the normal range map to the high-output range map when a duty ratio of driving power output to the synchronous motor is equal to or larger than a predetermined value.