A fixed type constant velocity universal joint includes an outer joint member, an inner joint member, eight balls, and a cage. The fixed type constant velocity universal joint has a ball retaining mechanism. A ratio of an axial length from a joint center to an opening-side end surface of the outer joint member to a diameter of each of the balls is within a range of 0.35 to 0.52. A ratio of a width of the cage to the diameter of each of the balls is within a range of 1.63 to 1.80. The ball retaining mechanism includes a cylindrical shaft portion at an end portion of a shaft and an angle restriction stopper surface of the outer joint member.

A fixed type constant velocity universal joint includes an outer joint member, an inner joint member, eight balls, and a cage. The fixed type constant velocity universal joint has a ball retaining mechanism. A ratio of an axial length from a joint center to an opening-side end surface of the outer joint member to a diameter of each of the balls is within a range of 0.35 to 0.52. A ratio of a width of the cage to the diameter of each of the balls is within a range of 1.63 to 1.80. The ball retaining mechanism includes a cylindrical shaft portion at an end portion of a shaft and an angle restriction stopper surface of the outer joint member.

A constant velocity joint includes an outer part having a connecting portion and an opening portion and a plurality of axial grooves forming outer raceways, and an inner part having a plurality of axial grooves forming inner raceways. Each outer raceway and inner raceway form a raceway pair, a ball being disposed in each raceway pair. Each raceway pair defines a region in axial cross-section with respect to a groove longitudinal axis conceptually divided into four quadrants. The outer raceway is in the first and second quadrants and the inner raceway is in the third and fourth quadrants. With torque transmission in a first direction, the ball has two contact points in the first quadrant and/or two contact points in the third quadrant, and with torque transmission in a second direction, the ball has two contact points in the second quadrant and/or two contact points in the fourth quadrant.

A constant velocity joint includes an outer part having a connecting portion and an opening portion and a plurality of axial grooves forming outer raceways, and an inner part having a plurality of axial grooves forming inner raceways. Each outer raceway and inner raceway form a raceway pair, a ball being disposed in each raceway pair. Each raceway pair defines a region in axial cross-section with respect to a groove longitudinal axis conceptually divided into four quadrants. The outer raceway is in the first and second quadrants and the inner raceway is in the third and fourth quadrants. With torque transmission in a first direction, the ball has two contact points in the first quadrant and/or two contact points in the third quadrant, and with torque transmission in a second direction, the ball has two contact points in the second quadrant and/or two contact points in the fourth quadrant.

A constant velocity universal joint includes an inner ring and an outer ring. A cage is disposed between an outer spherical surface of the inner ring and an inner spherical surface of the outer ring, and has windows in which respective balls are received. The cage has ball contact surface areas with which the balls come into contact, and includes soft portions that are lower in hardness than the ball contact surface areas. The soft portions are formed by local heat treatment at portions of the windows that are kept out of contact with the balls or surface portions around the windows.

A power transmission mechanism (2) includes left and right drive shafts (3L, 3R) that transmit rotational torque from a drive source to drive wheels provided on left and right sides of a vehicle. In the right drive shaft (3R) and the left drive shaft (3L), the numbers of rolling elements (23, 33) included in plunging type constant velocity universal joints (6L, 6R) are different from each other.

A power transmission mechanism (2) includes left and right drive shafts (3L, 3R) that transmit rotational torque from a drive source to drive wheels provided on left and right sides of a vehicle. In the right drive shaft (3R) and the left drive shaft (3L), the numbers of rolling elements (23, 33) included in plunging type constant velocity universal joints (6L, 6R) are different from each other.

A speed-reducing or -increasing apparatus, with first and second crown gears facing one another, with a cam unit that causes the first crown gear to incline with respect to the second crown gear so that the first crown gear meshes with the second crown gear, that causes the first crown gear to precess in such a manner as to move the meshing position, and couples to an input or output shaft. A rolling element is between the cam unit and the first crown gear, and the cam unit includes a first member that couples to the input or output shaft and a second member made of steel and including a rolling element rolling portion where the rolling element rolls, the second member configured to be incapable of rotating relatively to the first member, and at least part of the first member having a lower specific gravity than the second member.

A speed-reducing or -increasing apparatus, with first and second crown gears facing one another, with a cam unit that causes the first crown gear to incline with respect to the second crown gear so that the first crown gear meshes with the second crown gear, that causes the first crown gear to precess in such a manner as to move the meshing position, and couples to an input or output shaft. A rolling element is between the cam unit and the first crown gear, and the cam unit includes a first member that couples to the input or output shaft and a second member made of steel and including a rolling element rolling portion where the rolling element rolls, the second member configured to be incapable of rotating relatively to the first member, and at least part of the first member having a lower specific gravity than the second member.

A constant velocity universal joint has an outer joint member and an inner joint member that transmits torque while permitting angular displacement due to balls between the inner and outer joint members. An attaching and detaching mechanism for attaching and detaching a power transmission shaft to and from the inner joint member is provided between the inner joint member and the power transmission shaft such that torque can be transmitted between the two. The attaching and detaching mechanism has a cylindrical member that fits over the power transmission shaft, a retaining ring that is radially movable, and an annular member that is axially movable. By using a boot band to fixedly tighten, to the power transmission shaft, a small diameter end portion of a boot closing an opening portion of the outer joint member, the axial position of the annular member is restricted by the small diameter end portion.