Patent ID: 8540582

Claim:
A bearing device for a wheel, comprising: a bearing comprising double-row rolling elements arranged between outer raceways and inner raceways opposed to each other; a hub wheel for attachment to a wheel; a constant velocity universal joint; and a recess-projection fitting structure through which a shaft section of an outer joint member of the constant velocity universal joint is integrated with the hub wheel, the shaft section being inserted in a fitting manner into a hole portion of the hub wheel, wherein the recess-projection fitting structure comprises: projecting portions extending in an axial direction provided on one of an outer surface of the shaft section of the outer joint member and an inner surface of the hole portion of the hub wheel, the projecting portions being press-fitted along the axial direction into another of the outer surface of the shaft section of the outer joint member and the inner surface of the hole portion of the hub wheel; and recessed portions formed through the press-fitting of the projecting portions in the another of the outer surface of the shaft section of the outer joint member and the inner surface of the hole portion of the hub wheel such that the projecting portions bite into the another of the outer surface of the shaft section of the outer joint member and the inner surface of the hole portion of the hub wheel and transfer a shape of the projecting portions onto the another of the outer surface of the shaft section of the outer joint member and the inner surface of the hole portion of the hub wheel, the projecting portions and the recessed portions being held in close contact with each other in a fitting manner throughout an entire region of fitting contact regions therebetween, wherein a hardness of at least press-fitting start end portions of the projecting portions is set to be higher than a hardness of a recessed-portion forming region into which the projecting portions are press-fitted, and a hardness difference therebetween is set to be equal to or larger than 20 points in HRC, and wherein an end of each of the projecting portions on a side from which the press-fitting is started is formed as an edge that is not chamfered.