Patent ID: 7520815

Claim:
A constant velocity universal joint comprising: an inner race having an outer peripheral face on which inner grooves are formed; an outer race having an inner peripheral face on which outer grooves are formed; a plurality of balls, each engaging with a pair of an inner groove and outer groove; an annular cage disposed between the outer peripheral face of the inner race and the inner peripheral face of the outer race and including window portions for retaining respective balls, each window portion being formed so as to penetrate through the cage; wherein a coefficient of sliding friction between each of said balls and a rolling face on the inner groove of the inner race with which the ball is in contact, and a coefficient of sliding friction between the respective ball and a rolling face on the outer groove of the outer race with which the ball is in contact are larger than a coefficient of sliding friction between the respective ball and a sliding face on the window portion with which the ball is in contact, wherein an amorphous hard carbon film is formed on the rolling face on the inner or outer grooves, and another amorphous hard carbon film is formed on the sliding face.