Patent ID: 6913540

Claim:
A constant velocity universal joint for use with a propeller shaft comprising: a cup-shaped outer ring having a plurality of straight track grooves extending axially on a cylindrical inner peripheral surface, an inner ring having a plurality of straight track grooves formed on a convex spherical outer peripheral surface, the track grooves being opposite to the track grooves of the outer ring, wherein the track grooves of the inner and outer rings are elliptical or Gothic arched in cross-sectional shape, a plurality of balls, interposed between the track grooves of the inner and outer rings, for transmitting torque, a cage, accommodated in an annular space between the inner and outer rings, for holding the balls, the constant velocity universal joint provided with a stub shaft having a shaft portion inserted from an open end portion of the outer ring to mate with the inner ring to enable torque transmission and provided with a boot, attached to the open end portion of the outer ring and the shaft portion of the stub shaft, respectively, for sealing the joint, wherein a distal end surface of the inner ring is capable of abutting a bottom of the outer ring upon press fitting of the shaft portion of the stub shaft, wherein a track groove is formed on each of the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring so as to intersect each other; a ball is placed at an intersecting portion of both grooves; and the ball is interposed between the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring and held with the cage having a concave spherical inner peripheral surface, wherein the ball is made of a heat resisting steel and tempered after having been subjected to quenching or carbonitriding the ball has a surface hardness of 58 or more in HRC after having been tempered; and the maximum size of a carbide grain is 8 μm or less, and wherein at least a ratio of a groove radius of curvature at a contact point between the track groove of the inner ring and the ball to a radius of the ball is 1.05 to 1.10.