Electric power steering system

摘要

A reduction gear (19) coupled to an electric motor (18) includes: a first bearing (31) that rotatably supports a first end portion (22) of a worm shaft (20) such that the worm shaft (20) is allowed to oscillate in an oscillation direction (A1) about the first end portion (22); and a first elastic member (36) that elastically urges a second bearing (32) in such a direction (B2) that an axis-to-axis distance (D1) between the worm shaft (20) and the worm wheel (21) reduces. The first end portion (22) and an output shaft (18b) of the electric motor (18) are coupled by a joint (50). A second elastic member (64) located between the joint (50) and the first end portion (22) elastically urges the worm shaft (20) toward a second end portion (23) and applies a preload on the first bearing (31). An outer ring (31 b) of the first bearing (31) is interposed in an axial direction (S1) by the third elastic member (83) and the fourth elastic member (87).