WHEEL BEARING DEVICE, AND MANUFACTURING METHOD OF WHEEL BEARING DEVICE

摘要

PROBLEM TO BE SOLVED: To provide a wheel bearing device in which heat treatment of an inner shaft whose inner peripheral surface is formed with a gear can be carried out adequately, and strength degradation and lifetime deterioration can be suppressed as the whole device.SOLUTION: A wheel bearing device comprises an inner shaft 2 formed with a small diameter part 6 to which an inner wheel member is externally fitted. On an inner peripheral surface of the inner shaft 2, a gear 10 is formed. A difference between a radius of an outer peripheral surface 6a of the small diameter part 6 in the inner shaft 2 and the outmost radius of a group of the tooth bottoms 10a of the gear 10 formed on the inner peripheral surface of the inner shaft 2 is set to 2.5 mm or more. On the outer peripheral surface 6a and the gear 10, hardened layers L2, L3 are formed by induction hardening. An unhardened layer is provided between the second hardened layer L2 formed on the outer peripheral surface 6a of the inner shaft 2 and the third hardened layer L3 formed on the gear 10, to secure fracture toughness of the inner shaft 2.