Patent ID: 7360468

Claim:
An electric power steering device to transmit an auxiliary power by an electric motor to a steering mechanism of a vehicle via a speed reduction gear mechanism, the speed reduction gear mechanism comprising: a driven gear, that is a resin gear, having a resin part with gear teeth formed on an outer peripheral surface thereof and integrally formed on the outside of a metal core; a drive gear that meshes with the driven gear; and grease present at least between the driven gear and the drive gear, wherein the resin part of the resin gear is composed of a resin composition having a polyamide resin, as a base resin, containing 10 to 50% by weight of glass fiber having a diameter in the range of from 5 to 9 μm, and the grease is composed of a base oil formed mainly of at least one oil selected from mineral oil, poly α-olefin oil, and alkyl polyphenyl ether, a thickener, and 3 to 10% by weight of a wax having a melting point or softening point in the range of from 70 to 130° C.