Patent ID: 7047824

Claim:
An electric power steering system for steering a vehicle wheel, comprising: a torque sensor for detecting torsion torque to be supplied to a first shaft and a second shaft, the torque sensor including a resilient member disposed between and fixed to the first and second shafts so that the first shaft, the resilient member and the second shaft are coaxially in alignment with one another, a ferromagnetic member for producing a magnetic field and connected to one of the resilient member and the first shaft, a soft magnetic member connected to one of the second shaft and the resilient member, the soft magnetic member positioned within the magnetic field and forming a magnetic circuit, and a magnetic sensor for detecting the magnetic flux density generated in the magnetic sensor; a steering mechanism to which steering torque is applied, one end of the steering mechanism is connected to one of the first and second shafts; steering power transmission mechanism whose one end is connected to the wheel and whose other end is connected to the other of the first and second shafts; an electric motor connected to the steering power transmission mechanism and in circuit with the magnetic sensor of the torque sensor; and a control circuit for generating control current to be supplied to the electric motor in response to a detected output of the magnetic sensor, wherein the electric motor gives a drive force to the steering power transmission mechanism in response to the control current for assisting the steering torque applied to the steering.