Abstract: A shaft coupling includes a first coupling member, a second coupling member, and a cushioning member. The first coupling member includes first protrusions. The second coupling member includes second protrusions. The cushioning member includes a plurality of radiating portions. When the first coupling member and the second coupling member are arranged coaxially and the first coupling member and the second coupling member are in an unloaded state, predetermined paired facing surfaces have a minimum clearance angle present on a radially outer side with respect to a center of the radiating portion in a radiating direction. The predetermined paired facing surfaces are at least one of first paired facing surfaces and second paired facing surfaces.

Abstract: A worm reducer includes a worm shaft; a worm wheel; a housing that houses the worm shaft and the worm wheel; a bearing that holds the worm shaft inside the housing; a coil spring that contacts an outer peripheral surface of the bearing and applies an urging force toward the worm wheel; and a preload member that is screwed into and fixed to the housing and pressurizes the coil spring. A winding direction of the coil spring is different from a winding direction of a thread of the preload member, and contact resistance between the coil spring and the preload member is greater than contact resistance between the coil spring and the bearing.

Abstract: A shaft coupling includes a first coupling member, a second coupling member, and a cushioning member. The first coupling member includes first protrusions. The second coupling member includes second protrusions. The cushioning member includes a plurality of radiating portions. When the first coupling member and the second coupling member are arranged coaxially and the first coupling member and the second coupling member are in an unloaded state, predetermined paired facing surfaces have a minimum clearance angle present on a radially outer side with respect to a center of the radiating portion in a radiating direction. The predetermined paired facing surfaces are at least one of first paired facing surfaces and second paired facing surfaces.

Abstract: A worm reducer includes a worm shaft; a worm wheel; a housing that houses the worm shaft and the worm wheel; a bearing that holds the worm shaft inside the housing; a coil spring that contacts an outer peripheral surface of the bearing and applies an urging force toward the worm wheel; and a preload member that is screwed into and fixed to the housing and pressurizes the coil spring. A winding direction of the coil spring is different from a winding direction of a thread of the preload member, and contact resistance between the coil spring and the preload member is greater than contact resistance between the coil spring and the bearing.

Abstract: An urging member urges a first end of a worm shaft toward a worm wheel via a first bearing. The worm shaft includes a tooth flank forming portion and a non-tooth flank forming portion formed between the first end and the tooth flank forming portion. In a housing, a shaft housing portion that houses the worm shaft includes a substantially straight portion and a reduced diameter portion. The substantially straight portion has a substantially constant bore diameter, and extends in an axial direction of the worm shaft. The reduced diameter portion is arranged on the first end side with respect to the substantially straight portion, and has a bore diameter reduced from a position that overlaps tooth flanks in the axial direction to a position that overlaps the non-tooth flank forming portion in the axial direction.

Abstract: A first end portion of a worm shaft and a first bearing that supports the first end portion are housed in a first end housing portion in a housing. The first end portion is urged toward a worm wheel by an urging member. A rotation regulation portion housing recess is formed in a portion that defines the first end housing portion on an inner surface of the housing. An elastic member includes an arc-shaped buffer portion that is interposed between the portion that defines the inner surface and an outer peripheral surface of the first bearing, and a rotation regulation portion that extends from the buffer portion and is housed in the rotation regulation portion housing recess. The rotation regulation portion includes a hollow portion which suppresses load transmission from the rotation regulation portion to the buffer portion during rotation regulation.

Abstract: An urging member urges a first end of a worm shaft toward a worm wheel via a first bearing. The worm shaft includes a tooth flank forming portion and a non-tooth flank forming portion formed between the first end and the tooth flank forming portion. In a housing, a shaft housing portion that houses the worm shaft includes a substantially straight portion and a reduced diameter portion. The substantially straight portion has a substantially constant bore diameter, and extends in an axial direction of the worm shaft. The reduced diameter portion is arranged on the first end side with respect to the substantially straight portion, and has a bore diameter reduced from a position that overlaps tooth flanks in the axial direction to a position that overlaps the non-tooth flank forming portion in the axial direction.

Abstract: A first end portion of a worm shaft and a first bearing that supports the first end portion are housed in a first end housing portion in a housing. The first end portion is urged toward a worm wheel by an urging member. A rotation regulation portion housing recess is formed in a portion that defines the first end housing portion on an inner surface of the housing. An elastic member includes an arc-shaped buffer portion that is interposed between the portion that defines the inner surface and an outer peripheral surface of the first bearing, and a rotation regulation portion that extends from the buffer portion and is housed in the rotation regulation portion housing recess. The rotation regulation portion includes a hollow portion which suppresses load transmission from the rotation regulation portion to the buffer portion during rotation regulation.

Abstract: In a worm reducer, an elastic member urges a worm shaft housed in a housing toward a worm wheel. In a method for manufacturing the worm reducer, the elastic member is arranged in a recess formed on the inner face of the housing. Then, a jig is inserted into the housing, and the elastic member is compressed by the jig. In the state in which the elastic member is compressed by the jig, the worm shaft is inserted into the housing. Then, the jig is removed from the housing.

Abstract: In a worm reduction gear, a second bearing that supports a second end of a worm shaft and a guide member are housed in a holding hole in a housing. A bias member biases the second end of the worm shaft toward the worm wheel (in a second direction). The guide member is elastically fitted in the holding hole in the housing to guide movement of the second end via the second bearing. A slit is fanned in the guide member. Stress is relieved which is exerted on the guide member when the guide member is elastically fitted in the holding hole.

Abstract: An electric power steering system includes an electric motor and a worm speed reducer. The worm speed reducer includes a worm shaft, a worm wheel, and a ring member. The worm wheel includes an annular tooth portion and an annular support formed of a material that is softer than a material of a shaft. The ring member includes an outer periphery press-fitted with the annular support so as to form plastically deformed portions in part of the annular support, and an inner periphery with which the shaft is press-fitted. The ring member is formed of a material with a hardness equivalent to a hardness of the material of the shaft.

Abstract: A shaft coupling structure includes a rotating shaft, a worm shaft, a first member, a second member, and an intermediate member that is an elastic member. The intermediate member is interposed between the first member and the second member. Coupling protrusions of the first member that extend in an axial direction are each inserted between second radial protrusions of the intermediate member and between a plurality of first radial protrusions of the second member. Protruding portions of the first radial protrusions engage with the corresponding recessed portions of the second radial protrusions in the axial direction. When a relative rotation angle between the first member and the second member is smaller than a predetermined angle, ends of each of the second radial protrusions in a circumferential direction each projects in the circumferential direction with respect to a corresponding end of the corresponding first radial protrusion in the circumferential direction.

Abstract: In a worm reduction gear, a second bearing that supports a second end of a worm shaft and a guide member are housed in a holding hole in a housing. A bias member biases the second end of the worm shaft toward the worm wheel (in a second direction). The guide member is elastically fitted in the holding hole in the housing to guide movement of the second end via the second bearing. A slit is fanned in the guide member. Stress is relieved which is exerted on the guide member when the guide member is elastically fitted in the holding hole.

Abstract: A worm reduction gear includes a bias member that biases a second end of a worm shaft in such a direction that the second end approaches a worm wheel. A guide member that guides movement of the second end is held in a holding hole in a housing. The holding hole has an opening at an end of the housing. The guide member includes a ring portion fitted in the holding hole to guide movement of the second end and a closing portion that closes an end of the ring portion and thus an opening of the holding hole.

Abstract: An electric power steering system includes an electric motor and a worm speed reducer. The worm speed reducer includes a worm shaft, a worm wheel, and a ring member. The worm wheel includes an annular tooth portion and an annular support formed of a material that is softer than a material of a shaft. The ring member includes an outer periphery press-fitted with the annular support so as to form plastically deformed portions in part of the annular support, and an inner periphery with which the shaft is press-fitted. The ring member is formed of a material with a hardness equivalent to a hardness of the material of the shaft.