Patent ID: 8175771

Claim:
A control apparatus that controls a motor of an electric power steering system to assist a steering effort of an operator, comprising: a sensor configured to detect a current value of a steering parameter expressing a condition of a steering operation of the operator; a parameter computer configured to: store therein a mathematic model expressing, as a plurality of equations, at least a part of the electric power steering system based on the steering parameter and a plurality of physical parameters that express a physical characteristic of the electric power steering system; and compute, using an online identification method, a current value of at least one of the plurality of physical parameters based on the mathematic model and the current value of the steering parameter; a target torque computer configured to: store therein a relationship between change in the at least one of the plurality of physical parameters and a gain for returning a current steering feeling of the operator to a preset steering feeling; determine a value of the gain based on the relationship and a difference between the current value of the at least one of the plurality of physical parameters and a default value; and compute, based on the determined value of the gain, a target torque of the motor which compensates for the difference between the current value and the default value of the at least one of the plurality of physical parameters; and a motor driver configured to drive the motor to generate the target torque so that the steering feeling of the operator is maintained at the preset steering feeling.