Electric power steering system

摘要

The surface roughness (Ra) of tooth surfaces (25) of teeth (21) of a worm wheel (20) is greater than or equal to 0.1 µm and less than or equal to 0.5 µm and, more particularly, less than or equal to 0.3 µm. The worm wheel (20) is produced by forming a resin member (22) on which the teeth (21) are to be formed, using a resin composition that contains reinforcing fiber; forming the teeth (21) by performing a gear-cutting process; and adjusting the surface roughness (Ra) of the tooth surfaces (25) by performing a running-in machining process on the teeth (21).