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.

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.

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.

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.

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 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 hub-bearing unit is provided with: a rotatable hub, with an axially outer flange portion configured for engagement with a rotatable element of a motor vehicle, a bearing unit provided with a fixed radially outer ring, configured for engagement with a fixed element of the motor vehicle, a first, axially outer, crown of rolling bodies, and a second, axially inner, crown of rolling bodies, interposed between the radially outer ring and the hub. The hub also assumes the function of the radially inner ring of the bearing unit and the bell of a constant velocity joint. The hub-bearing unit is designed so that the axial distance between the center of the axially inner crown of rolling bodies and the rolling center of the constant velocity joint lies within a predetermined range according to the following formula:

[00001]$\{\begin{array}{cc}\mathrm{with}.Math..Math.L\ge 0,& 0.4\le \frac{P_B}{S+A+L}\le 4\\ \mathrm{with}.Math..Math.L<0,& 0.5\le \frac{P_B}{S+A}\le 4.Math.\end{array}\hspace{1em}$

Apparatus, such as a propeller shaft, includes an outer circumferential portion or outer race to rotate as a unit with an internal shaft (serving as the propeller shaft), an inner circumferential member or inner race to rotate as a unit with an external shaft and a plurality of balls disposed between the outer race and inner race, for transmitting rotation therebetween. A sleeve rotating as a unit with the inner race includes an inside cavity for receiving the external shaft. The sleeve is coated with a coating formed on an inside circumferential surface.