Patent ID: 8459402

Claim:
An electric power steering system, comprising: a worm shaft that has a first end portion and a second end portion, and that is connected to an electric motor; a worm wheel that meshes with the worm shaft, and that is connected to a steering mechanism; a housing that houses the worm shaft and the worm wheel; a first bearing that rotatably supports the first end portion, and that has an inner ring having a raceway groove, an outer ring having a raceway groove, and rolling elements interposed between the raceway grooves, wherein curvature radii of the raceway grooves in the first bearing are each larger than 50% of a diameter of each of the rolling elements, whereby the worm shaft is allowed to pivot about the first end portion, and the first bearing is opposed, in an axial direction of the worm shaft, to an opposed portion provided at the housing or the worm shaft and is movable relative to the opposed portion in the axial direction; a second bearing that rotatably supports the second end portion; a first elastic member that elastically urges the second bearing in a direction in which an inter-axis distance between a central axis of the worm shaft and a central axis of the worm wheel decreases; an annular pressing member that is fitted on an outer peripheral face of the outer ring and radially presses the first bearing to cause the raceway groove of the inner ring, the raceway groove of the outer ring, and the rolling elements to press against each other; and a second elastic member that is arranged between the opposed portion and the first bearing and elastically deforms as the worm shaft moves relative to the housing in the axial direction, wherein the pressing member is comprised of metal, the pressing member and the first bearing are assembled into a sub-assembly, and the pressing member is fitted in a retention hole, formed in the housing, through clearance fit.