A constant velocity joint includes: an outer race having outside ball grooves; an inner race having inside ball grooves; and balls interposed between the outside and inside ball grooves that cooperate to constitute groove portions. The groove portions include first and second groove portions. In the first groove portion, a radial distance between the outside and inside ball grooves is increased in a direction toward an opening end of the outer race when a joint angle is 0 degree. In the second groove portion, a radial distance between the outside and inside ball grooves is reduced in a direction toward the opening end of the outer race in the reference state. A radius of a second outside arc of the outside ball groove of the second groove portion is larger than a radius of a first outside arc of the outside ball groove of the first groove portion.

A first constant velocity joint is equipped with a cup part made of a light alloy. First ball grooves that receive a torque from torque transmitting members are formed on an inner wall of the cup part. A high hardness layer made of ceramic or cermet as a principal component thereof is formed on an inner surface of the cup part including at least inner surfaces of the first ball grooves.

Outer ball grooves of an outer joint member of a constant velocity joint each have a first ball groove for allowing a ball to roll therein when the constant velocity joint operates, and a second ball groove having a ball groove radius larger than a ball groove radius of the first ball groove. The second ball groove has a curved line and a connecting line. The curved line is connected to a groove bottom end of the first ball groove located closer to an opening of the outer joint member and is curved radially outward in a concave manner. The connecting line connects the curved line and the opening. The curved line is curved with a curvature center that is located closer to the opening than the groove bottom end of the first ball groove and that is located radially inside the outer joint member.

A joint-center-fixed constant velocity joint configured to be provided in a vehicle includes an outer joint member, an inner joint member, a first ball, a second ball, and a cage. While a center of the first ball is moving to a position of the maximum use angle on an opening side from a joint center, a first open angle faces the opening side. While a center of the second ball is moving to a position of the maximum use angle on a bottom side from the joint center, a second open angle is not reversed from a state where the second open angle faces the bottom side to a state where the second open angle faces the opening side.

In a constant velocity joint, a center locus of a first ball rolling on a first outer central portion is inclined such that a distance from a central axis of an outer joint member decreases toward a bottom side of the outer joint member. A center locus of a second ball rolling on a second outer central portion is formed in a linear shape and inclined such that a distance from the central axis of the outer joint member increases toward the bottom side of the outer joint member. A center locus of the second ball rolling on the second outer bottom side portion is formed in an arc shape and disposed in the outer joint member at a position radially inwardly from a tangent at a connecting position between the second outer central portion and the second outer bottom side portion.

In a constant-velocity joint, a center locus of a ball rolling on a first outer large-diameter portion has an arc shape having an arc center, and a center locus of the ball rolling on a second outer large-diameter portion has an arc shape having an arc center. Center loci of the ball rolling on an outer extension portion are positioned, throughout their lengths, in a region inducing a tangent line to an opening-side end portion of the center locus of the ball rolling on the second outer large-diameter portion, the region being positioned outward of the tangent line in a radial direction of the outer joint member. An opening-side end portion of the center locus of the ball rolling on the outer extension portion is positioned outward of the tangent line in the radial direction of the outer joint member.

Provided is a method of manufacturing an outer joint member of a constant velocity universal joint, which is constructed by forming a cup section having track grooves, and a shaft section, and by welding a cup member and a shaft member, the method including: forming the cup member and the shaft member of medium carbon steel; preparing a cup member having a cylindrical portion and a bottom portion integrally formed by forging, and a joining end surface in a machining step; preparing a shaft member having a joining end surface formed in a machining step; bringing the joining end surface of the cup member and the joining end surface of the shaft member into abutment against each other; welding the cup member and the shaft member by radiating a beam; and performing, after the welding, an ultrasonic flaw detection-inspection step.

Provided is a method of manufacturing an outer joint member of a constant velocity universal joint, which is constructed by forming a cup section having track grooves, and a shaft section, and by welding a cup member and a shaft member, the method including: forming the cup member and the shaft member of medium carbon steel; preparing a cup member having a cylindrical portion and a bottom portion integrally formed by forging, and a joining end surface in a machining step; preparing a shaft member having a joining end surface formed in a machining step; bringing the joining end surface of the cup member and the joining end surface of the shaft member into abutment against each other; welding the cup member and the shaft member by radiating a beam; and performing, after the welding, an ultrasonic flaw detection-inspection step.

A constant velocity universal joint is assembled as a crown ball meshed within a housing socket for rotation about respective rotational axes. The outside diameter of the crown ball is greater than the inside diameter of the socket. A plurality of channels, equally spaced around the crown ball perimeter are cut into the crown ball surface generally along or parallel with the crown ball drive axis. An arcuate cup is cut into each crown ball channel to confine a respective torque transfer element. A number, corresponding to the number of crown ball channels, of partial cylinder channels are cut into the inside surface of the housing socket. One of opposite side walls for each housing channel is given an arcuate radius corresponding to that of the force transfer elements. Ridges between adjacent crown ball channels mesh with ridges between adjacent housing socket channels. Torque transfer elements confined within said crown ball cups engage the partial cylinder wall of the housing channels to transfer drive forces between the crown ball and socket housing through a departure angle between the respective rotational axes.

A fixed type constant velocity universal joint of a track groove crossing type has track grooves of an inner joint member formed so as to be mirror-image symmetrical with the paired track grooves of an outer joint member with respect to a joint center plane at an operating angle of 0. The track grooves of both the joint members each have a length corresponding to a maximum operating angle required for a rear-wheel drive shaft. Further, each axial clearance between the inner joint member and the cage is set larger than an axial clearance formed by a ball track clearance between each of balls and each track groove.