Patent ID: 8219285
Filing Date: 2012-07-10
Classification: B62D

Abstract:
1. An electric power steering system comprising: a torque sensor having a torsion bar that couples a steering-side input shaft and a tire-side output shaft, the torque sensor measuring a torque applied to the torsion bar based on a twist of the torsion bar; and a motor generating assist torque, wherein the electric power steering system further comprises: a self-aligning torque determiner that determines a self aligning torque created by a tire; and a commanded-torque generator that: determines a value of an assist ratio based on a predetermined relationship between the self aligning torque and the assist ratio, the assist ratio representing a ratio of share of torque by the motor for compensating the self aligning torque; and generates, based on the self aligning torque and the value of the assist ratio, a commanded torque, and wherein the assist torque to be generated by the motor is determined based on the commanded torque generated by the commanded-torque generator; a stabilizing controller that calculates, based on the torque measured by the torque sensor, a compensation, the compensation being to stabilize a whole of the electric power steering system including: the torque measured by the torque sensor with respect to torque inputted to a steering wheel, and a speed of the motor, wherein a commanded value for the assist torque is determined based on a basic assist request value and the compensation calculated by the stabilizing controller, the basis assist request value being obtained as a product of the value of the assist ratio and the self aligning torque, and the stabilizing controller changes the compensation depending on the value of the assist ratio; wherein the stabilizing controller comprises: a first compensator that calculates, based on the torque measured by the torque sensor, a value of the compensation as a minimum compensation value assuming that the value of the assist ratio is a preset minimum value; a second compensator that calculates, based on the torque measured by the torque sensor, a value of the compensation assuming that the value of the assist ratio is a preset maximum value; and a linear interpolator that determines, using linear interpolation, the value of the compensation corresponding to the value of the assist ratio determined by the commanded-torque generator.