Patent ID: 8924081

Claim:
An electric power steering apparatus adapted to detect steering torque applied to a steering shaft by a driver of a vehicle via a steering wheel, and apply an assist torque corresponding to the detected steering torque to the steering shaft by an electric motor via a speed reduction mechanism, the electric power steering apparatus comprising: an electric motor driving circuit constituted by a plurality of semiconductor power elements and controlling electric power supplied to an armature winding of the electric motor; a first switch element for opening and closing a connection between an input terminal of the electric motor driving circuit and an external power source, and a second switch element for opening and closing the armature winding, wherein: at least one of the first switch element and the second switch element is constituted by a semiconductor switch element; the armature winding is constituted by multi-phase AC windings; the electric motor driving circuit is constituted by a multi-phase bridge circuit constituted by the plurality of power elements; the plurality of power elements and the semiconductor switch element are mounted on a board attached to a metallic case; a plurality of boards form a discrete arrangement around a rotor shaft of the electric motor; each board of the plurality of boards contains at least two power elements of the plurality of power elements located thereon; and each board is attached to the metallic case, wherein: the plurality of power elements are mounted on different respective boards which each constitute an arm of a same phase as the multi-phase bridge circuit; and the respective boards on which the plurality of power elements are mounted are arranged radially around an axial center of the rotor shaft of the electric motor.