WHEEL BEARING DEVICE

PROBLEM TO BE SOLVED: To provide a wheel bearing device reducing looseness in the circumferential direction by preventing wear of a serration engagement face, reducing noise generated from the serration engagement face and improving controllability and stability. SOLUTION: In the wheel bearing device, an outer joint member 12 is integrally provided with a cup-shaped mouth part 13, a shoulder part 14 forming a bottom part of the mouth part 13 and a stem part 15 axially extended from the shoulder part 14 and internally fitted to a hub wheel 2 via a serration 16 so as to enable torque transmission, and with the shoulder part 14 abutting on an inner ring 3, the hub wheel 2 is axially detachably coupled to the outer joint member 12. The hub wheel 2 and serrations 5, 16 of the stem part 15 have predetermined quench-hardened layers formed thereon by induction hardening. A low friction film comprising hard chrome plating having predetermined film thickness is formed on the surface of the serration 16, and the film thickness on the tip side of the serration 16 is set thicker than that on the groove bottom side. COPYRIGHT: (C)2009,JPO&INPIT