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.

Constant-velocity ball joint, having at least a joint outer part with an axis of rotation and with outer ball tracks and with outer center lines, a joint inner part with inner ball tracks and inner center lines, and a large number of torque-transmitting balls which are each guided in mutually associated outer ball tracks and inner ball tracks.

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 constant-speed universal joint includes: an outer ring; an inner ring; a plurality of balls that engages with the outer-ring ball grooves and the inner-ring ball grooves; and a holder that is interposed between an inner spherical surface of the outer ring and an outer spherical surface of the inner ring and in which a holding window for holding the plurality of balls is formed. A chamfered portion is formed in the inner ring. The chamfered portion includes a linear section portion that is formed in a linear shape in a section perpendicular to a moving locus of the center of the corresponding ball and an arc section portion that is formed in a protruding arc shape in the section perpendicular to the moving locus of the center of the corresponding ball.

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.

A fixed type constant velocity universal joint has outer joint member track grooves each with a raceway center line that includes an arc-shaped portion having a curvature center that has no offset with respect to a joint center in an axial direction. The track grooves are formed such that adjacent track grooves are inclined in opposite directions. The joint also has inner joint member track grooves that are each formed to be mirror-symmetric with a corresponding one of the outer joint member track grooves with a plane including the joint center and being orthogonal to the axis of the joint at an operating angle of 0°. When at a large operating angle, an operating angle at which a torque transmission ball loses contact with the inner joint member track groove is larger than that at which the torque transmission ball loses contact with the outer joint member track groove.

A fixed ball type joint for a vehicle, which reduces the friction between a cage and an outer race and friction between the cage and an inner race by changing shapes of an inner spherical diameter of the outer race and an outer spherical diameter of the inner race. The fixed ball type joint for a vehicle includes an inner race, an outer race installed at the outside of the inner race, a plurality of balls for transmitting rotational power of the inner race to the outer race, and a cage for supporting the balls. A first inner spherical radius of the outer race is set to be smaller than a second inner spherical radius of the outer race. A first outer spherical radius of the inner race is set to be larger than a second outer spherical radius of the inner race.

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.

A tripod constant-velocity joint includes: an outer joint member having a cavity elongated in a longitudinal direction and three roller tracks; an inner joint member having a center body and three journals outwardly radially protruded from the center body; and three roller assemblies respectively coupled to the journal in a state of being respectively disposed in the roller tracks. The respective roller assembly comprises: an inner race which is connected to the journal and is provided with a first inner ball groove and a second inner ball groove on both lateral sides thereof; a first ball array and a second ball array respectively having a plurality of balls which are respectively disposed in the first inner ball groove and in the second inner ball groove; and a ball cage which restricts movements of the first ball array and the second ball array in a longitudinal direction thereof.

A protrusion shaft portion is provided on an end surface of a shaft on a joint fitting side, and a recess into which the protrusion shaft portion is fitted is formed in an inner surface of a bottom wall of the mouth section of the outer joint member. The recess allows angular displacement of the shaft to a predetermined operating angle, and the protrusion shaft portion is brought into contact with a wall surface of the recess at the predetermined operating angle so that angular displacement exceeding the predetermined operating angle is regulated. Allowable angular displacement in the recess is within a range of preventing the shaft from being brought into contact with an opening portion of the mouth section.