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.

A constant velocity joint comprises an outer joint part with a longitudinal axis and first and second outer ball tracks. The outer joint part comprises an attachment side and an aperture side. An inner joint part has a longitudinal axis and first and second inner ball tracks. with a torque transmitting ball 14 in each pair of tracks, and a ball cage 15 with cage windows 18 in which the balls 14 are held. In each angular position of the constant velocity joint 11 an opening angle is enclosed between an outer tangent and an inner tangent at the ball. At least one of the first and second pairs of tracks is designed such that, within a small articulation angle range comprising at least the joint central plane, at at least an articulation angle, an opening angle amounts to zero, and within a greater articulation angle range, an aperture-side opening angle of a first pair of tracks widens in the opposite axial direction relative to the aperture-side opening angle of a second pair of tracks.

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.

An axle assembly for a driving wheel of a vehicle allows a wheel-side joint and a shaft to be rotated separately from a boot while driving so as to prevent generation of friction noise of the boot. The axle assembly includes the shaft rotated by receiving driving force from a powertrain; an axle housing disposed to pass through a center of a steering knuckle connected to a steering apparatus; a wheel bearing mounted between the steering knuckle and the axle housing; a joint bearing mounted on an outer part of the shaft; and a boot unit configured to have a first end coupled to an outer race of the joint bearing and a second end coupled to an outer race of the wheel bearing so as to form a space filled with a lubricant outside the shaft.

A forging apparatus includes an ironing mechanism and a phase alignment mechanism. The ironing mechanism includes: a punch set, which is fitted into a cylindrical portion of a pre-processing material to be formed into the outer joint member, and is radially expandable and contractible, the cylindrical portion having grooves formed in an inner peripheral surface thereof; and a die having a hole into which the cylindrical portion is press-fitted. The phase alignment mechanism is configured to align phases of the grooves in the inner peripheral surface of the pre-processing material and phases of track groove portion forming surfaces of the punch set with each other before the pre-processing material is fitted to the punch set.

A universal joint or other vehicle driveline assembly includes an inner race, an outer race, and bearings positioned between the races. In some embodiments, the components of the universal joint that are in contact with the bearings are selectively processed to be harder than the other non-contact surfaces of the component.

A double-offset plunging type constant velocity universal joint includes inner and outer joint members each having six linear track grooves extending along an axial direction. The inner joint member has a coupling hole at a center portion thereof for coupling a shaft. Six torque transmission balls retained by a cage are incorporated between the linear track grooves of the inner and outer joint members. A ratio T.sub.CAGE/D.sub.BALL of a minimum thickness (T.sub.CAGE) of the cage to a diameter of the torque transmission ball (D.sub.BALL) is from 0.225 to 0.245, wherein a ratio D.sub.BALL/D.sub.S of a diameter (D.sub.BALL) of the torque transmission ball to a spline large diameter (D.sub.S) of the coupling hole of the inner joint member is from 0.79 to 0.85, and wherein a ball contact ratio (ψ) of the torque transmission ball is from 1.08 to 1.12.

A fixed type constant velocity universal joint (3) includes an outer joint member (31), an inner joint member (32), eight balls (33), and a cage (34). A diameter (D.sub.31c) of the outer joint member (31) at an opening end of an inner peripheral surface (31c) is set larger than an outer diameter (D.sub.34b) of the cage (34) at a center portion in a circumferential direction of pockets (34a) when the cage (34) is seen from an axial direction of the joint. A bottom surface (31f) of a mouth section (31a) of the outer joint member (31) is arranged so as to interfere with an imaginary spherical surface (Q) being an extension of the inner peripheral surface (31c) of the outer joint member (31) toward a deep-side.

A fixed type constant velocity universal joint (3) includes an outer joint member (31), an inner joint member (32), eight balls (33), and a cage (34). A curvature center (O.sub.31d) of track grooves (31d) of the outer joint member (31) and a curvature center (O.sub.32e) of track grooves (32e) of the inner joint member (32) are offset to opposite sides in an axial direction of the joint with respect to a joint center (O(f)) by an equal distance. A ratio (PCD.sub.BALL/D.sub.BALL) of a pitch circle diameter (PCD.sub.BALL) of the balls (33) to a diameter (D.sub.BALL) of each of the balls (33) is set from 3.70 to 3.87. A ratio (T.sub.C/D.sub.BALL) of a radial thickness (T.sub.C) of the cage (34) to the diameter (D.sub.BALL) of each of the balls (33) is set from 0.22 to 0.25.

A constant velocity joint includes an outer joint portion with a first longitudinal axis, a first attaching end, an aperture end and outer ball tracks on an inner circumferential surface, an inner joint portion with a second longitudinal axis, a second attaching end, an inner face facing towards the outer joint portion and inner ball tracks on its outer circumferential surface, balls for torque transmission between the outer and inner joint portions, an annular ball cage between the outer and inner joint portions with several cage windows in which the balls are guided. The inner and outer joint portions are arranged so that one outer ball track and one inner ball track are in each case arranged opposite to each other to form three different types of track pairs to receive one respective balls. The balls have different controlling behaviors due to different track geometries.