An electric power steering apparatus comprising a torque sensor for detecting
the steering torque applied on the steering member of a vehicle; the first control
unit for outputting the first control signal to drive a motor for steering assist,
based on the steering torque detected by the torque sensor; the steering angle
sensor for detecting the steering angle of the steering member; the norm steering
unit for outputting a norm steering angle, based on a norm steering model which
defines the relation between the steering torque and the norm steering angle; the
second control unit for outputting the second control signal to drive the motor
in order to reduce the difference between the norm steering angle outputted from
the norm steering unit based on the steering torque and the detected steering angle;
and the changing unit for switching between the first control signal and the second
control signal, thereby being capable of switching between the driving at the steering
torque determined regardless of the conditions of the road surface and the driving
at the steering torque of the conventional steering assist.
