Patent attributes
In an electric power steering system, a motor drive controller that has an inverter circuit board and a control circuit board housed in a control case is provided so as to overlap a control case fixation surface formed at an end portion of a gear housing in the axial direction of a steering shaft, so that it is possible to reduce the projection in the axial direction of a motor as compared to the conventional one. In addition, a metallic board is used for the inverter circuit board and the inverter circuit board is fixed to the control case fixation surface so as to be in surface contact therewith, so that it is possible to efficiently dissipate the heat generated on the inverter circuit board into the gear housing and a fixation support plate.