Electric power steering apparatus

Abstract

An electric power steering apparatus for generating a PWM signal based on a calculated steering assist command value, PWM-controlling a motor via a motor drive circuit including switching elements, and assist-controlling a steering system that a motor relay is inserted between the motor drive circuit and the motor, comprises a steering status detecting section that detects a steering status of a steering wheel, outputs a longtime steering holding signal when detecting that the steering status is a longtime steering holding status, and outputs a normal steering signal when detecting that the steering status is a normal steering status, and a motor current control section that determines a motor current control value for controlling a motor current flowing in the motor relay in accordance with the longtime steering holding signal or the normal steering signal.

1 . An electric power steering apparatus for calculating a steering assist command value based on a steering torque and a velocity, generating a PWM signal based on said steering assist command value, PWM-controlling a motor via a motor drive circuit comprised of switching elements, and assist-controlling a steering system that an electromagnetic type motor relay is inserted between said motor drive circuit and said motor, comprising:
 a steering status detecting section that detects a steering status of a steering wheel, outputs a longtime steering holding signal when detecting that said steering status is a longtime steering holding status, and outputs a normal steering signal when detecting that said steering status is a normal steering status, and   a motor current control section that determines a motor current control value for controlling a motor current flowing in said electromagnetic type motor relay in accordance with said longtime steering holding signal or said normal steering signal that is outputted from said steering status detecting section,   wherein said steering status detecting section detects a steering status at a time that a given time elapses from a time of determining that said steering status is a steering holding status as said longtime steering holding status.   
     
     
         2 . An electric power steering apparatus according to  claim 1 , wherein when said longtime steering holding signal from said steering status detecting section is inputted into said motor current control section, via said motor current control section, in accordance with said motor current control value corresponding to said longtime steering holding signal, control so as to decrease said motor current to a maximum limit desired value within a motor current decline time based on a given decrease rate,
 when said normal steering signal from said steering status detecting section is inputted into said motor current control section, via said motor current control section, in accordance with said motor current control value corresponding to said normal steering signal, control so as to increase said motor current that is decreased to said maximum limit desired value and recover.   
     
     
         3 . An electric power steering apparatus according to  claim 2 , wherein an increase rate in control of said motor current is more than a normal time. 
     
     
         4 . An electric power steering apparatus according to  claim 3 , wherein said motor is a three-phase brushless DC motor.