Patent ID: 8545337

Claim:
A fixed type constant velocity universal joint, comprising: an outer joint member having a radially inner surface in which eight track grooves extending in an axial direction are formed; an inner joint member having a radially outer surface in which eight track grooves extending in the axial direction are formed; eight torque-transmission-ball tracks formed by the track grooves of the outer joint member and the track grooves of the inner joint member in correspondence with the track grooves of the outer joint member; eight torque transmission balls arranged in the torque-transmission-ball tracks, respectively; and a cage including pockets for retaining the torque transmission balls, wherein the fixed type constant velocity universal joint is an undercut-free type including a curved portion and a straight portion which are both provided on a bottom surface of each of the track grooves of the outer joint member and a bottom surface of each of the track grooves of the inner joint member, wherein under a state in which an operating angle of the joint is 0°, when a straight line including an axis of the outer joint member and an axis of the inner joint member is referred to as a joint center axis and a plane including a center of each of the torque transmission balls and being orthogonal to the joint center axis is referred to as a joint center plane, a center of curvature of each of the track grooves of the outer joint member and a center of curvature of each of the track grooves of the inner joint member (a) are respectively spaced from the joint center plane on both sides thereof in the axial direction and (b) are offset so as to be positioned away from the joint center axis on a radially opposite side thereof relative to the track grooves, and wherein a center of an outer spherical surface of the cage and a center of an inner spherical surface of the cage correspond to each other, and wherein in a case where Rt represents a distance between the center of each of the torque transmission balls and the center of curvature of each of the track grooves of the outer joint member or the center of curvature of each of the track grooves of the inner joint member, and F represents an axial distance between the joint center plane and the center of curvature of each of the track grooves of the outer joint member or the center of curvature of each of the track grooves of the inner joint member, a ratio R 1 =F/Rt is set to satisfy 0.044≦R 1 ≦0.071, and, wherein in a case where fr represents a radial offset amount as a distance between the joint center axis and the center of curvature of each of the track grooves of the outer joint member or the center of curvature of each of the track grooves of the inner joint member, a ratio R 3 =fr/Rt is set to satisfy 0.07≦R 3 ≦0.19, whereby the ratio R 1 and the ratio R 3 are set to values that ensure durability at normal angles and improve torque capacity at a high operating angle.