Patent ID: 8226489

Claim:
A constant velocity universal joint, comprising: an outer joint member comprising a cup portion opening at one end thereof; an inner joint member positioned in an interior of the cup portion; balls interposed between the outer joint member and the inner joint member to transmit torque; and a cage retaining the balls, wherein the outer joint member comprises track grooves disposed in an inner surface of the cup portion and along which the balls are capable of rolling, a tapered relief surface extending continuously from the inner surface of the cup portion to an opening end surface, and a boot groove disposed in an outer surface of the cup portion and in which a boot is capable of being attached, the outer surface of the cup portion being continuous to the opening end surface, wherein the constant velocity universal joint is an undercut-free constant velocity universal joint in which each of the track grooves comprises a circular-arc portion and a straight portion each having a hardened layer formed by induction quenching, and wherein the opening end surface protrudes by a protruding amount t in an axial direction from a center in a width direction of the track grooves in the relief surface so as to form a protruded portion, the protruding amount t satisfying a relation of t=0.037d to 0.185d when a diameter of each of the balls is represented by d; the opening end surface in the protruded portion and the outer surface of the cup portion continuous to the opening end surface comprise an unhardened layer free from hardening by quenching; the unhardened layer extends to the relief surface; and the hardened layer extends to the relief surface.