ELECTRIC POWER STEERING SYSTEM

摘要

An EPS includes a first rack and pinion mechanism that converts rotation of a pinion shaft due to a steering operation, to reciprocating motion of a rack shaft; and a steering force assist device that applies a motor torque of a motor as an assist force by using a second rack and pinion mechanism; and an ECU that controls an operation of the steering force assist device. Rack teeth of the rack shaft constituting the first rack and pinion mechanism are formed so that a steering gear ratio is changed depending on a steering angle. The ECU computes a motor neutral point by subtracting a conversion value from a motor angle detection value. The conversion value is computed based on a steering angle detection value by referring to a conversion map that is set taking into account the steering gear ratio corresponding to the steering angle.

主权项

1. An electric power steering system comprising:
a rack and pinion mechanism that converts rotation of a pinion shaft due to a steering operation, to reciprocating motion of a rack shaft; a steering force assist device that applies an assist force to a steering system by converting rotation of a motor to the reciprocating motion of the rack shaft by using a conversion mechanism other than the rack and pinion mechanism; a steering sensor that detects a steering angle of a steering wheel as an absolute angle; a relative angle sensor that detects a motor angle of the motor as a relative angle; and a control device that controls an operation of the steering force assist device, wherein rack teeth of the rack shaft constituting the rack and pinion mechanism are formed so that a steering gear ratio is changed depending on the steering angle, and wherein the control device computes a motor neutral point that is a value of the motor angle at a steering neutral position, by using a motor angle detection value detected by the relative angle sensor, and a conversion value that is computed based on a steering angle detection value detected by the steering sensor taking into account the steering gear ratio corresponding to the steering angle.