In a fixed type constant velocity universal joint, an axial offset amount of a curvature center of each of track grooves of outer and inner joint members is set to 0. The track grooves of the outer and inner joint members are each inclined with respect to an axis line. The track grooves adjacent to each other in a circumferential direction are inclined in opposite directions. The track grooves of the outer and inner joint members that are opposed to each other are inclined with respect to the axis line in opposite directions. A chamfered portion is formed on a track inlet end of each of the track grooves of the outer joint member. When the cage and the inner joint member are inclined with respect to the outer joint member, balls are incorporated into two cage windows at the same time through the chamfered portions.

In a fixed type constant velocity universal joint, an axial offset amount of a curvature center of each of track grooves of outer and inner joint members is set to 0. The track grooves of the outer and inner joint members are each inclined with respect to an axis line. The track grooves adjacent to each other in a circumferential direction are inclined in opposite directions. The track grooves of the outer and inner joint members that are opposed to each other are inclined with respect to the axis line in opposite directions. A chamfered portion is formed on a track inlet end of each of the track grooves of the outer joint member. When the cage and the inner joint member are inclined with respect to the outer joint member, balls are incorporated into two cage windows at the same time through the chamfered portions.

A ball joint unit movable along guide grooves according to an embodiment of the present disclosure includes: a first member formed in a spherical shape, having axial lower end fixed to a fixed object, and having a first guide groove and a second guide groove perpendicularly crossing each other along longest circumferences thereof; and a second member extends downward at four sides to receive the first member therein, having four sides movably disposed on the first guide groove and the second guide groove, and supporting a moving object thereon.

A ball joint unit movable along guide grooves according to an embodiment of the present disclosure includes: a first member formed in a spherical shape, having axial lower end fixed to a fixed object, and having a first guide groove and a second guide groove perpendicularly crossing each other along longest circumferences thereof; and a second member extends downward at four sides to receive the first member therein, having four sides movably disposed on the first guide groove and the second guide groove, and supporting a moving object thereon.

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 bearing device for a wheel has a stem shaft of an outer joint member of a constant-velocity universal joint fit and inserted in a hole of a hub wheel, the stem shaft and hub wheel being coupled through an intermediation of a recess-projection fitting structure. Projections extending in an axial direction are provided on one of the stem shaft and an inner diameter surface of the hole of the hub wheel. The projections are press-fit into another of the stem shaft and the inner diameter surface of the hole along the axial direction. Recesses that adhere to and fit the projections are formed in the other. An end on an inboard side of the hub wheel is caulked to an outer diameter side to form a caulking section and preload is applied to a roller bearing by the caulking section.

A bearing device for a wheel has a stem shaft of an outer joint member of a constant-velocity universal joint fit and inserted in a hole of a hub wheel, the stem shaft and hub wheel being coupled through an intermediation of a recess-projection fitting structure. Projections extending in an axial direction are provided on one of the stem shaft and an inner diameter surface of the hole of the hub wheel. The projections are press-fit into another of the stem shaft and the inner diameter surface of the hole along the axial direction. Recesses that adhere to and fit the projections are formed in the other. An end on an inboard side of the hub wheel is caulked to an outer diameter side to form a caulking section and preload is applied to a roller bearing by the caulking section.

A constant-velocity universal joint includes: an outer joint member having a plurality of outer ball grooves; an inner joint member having a plurality of inner ball grooves; a plurality of torque transmitting balls; and a ball cage. The outer ball groove and the inner ball groove respectively have a double shape, and a ratio O/H of an offset value O which is a distance between an inflection point of the outer ball groove and a line connecting centers of the torque transmitting balls in a state that the outer joint member and the inner joint member form 0 angle and a distance H between a center line of the inner joint member and a center of the torque transmitting ball in a state that the outer joint member and the inner joint member form 0 angle is within a range of 0.07 to 0.11.

A constant-velocity universal joint includes: an outer joint member having a plurality of outer ball grooves; an inner joint member having a plurality of inner ball grooves; a plurality of torque transmitting balls; and a ball cage. The outer ball groove and the inner ball groove respectively have a double shape, and a ratio O/H of an offset value O which is a distance between an inflection point of the outer ball groove and a line connecting centers of the torque transmitting balls in a state that the outer joint member and the inner joint member form 0 angle and a distance H between a center line of the inner joint member and a center of the torque transmitting ball in a state that the outer joint member and the inner joint member form 0 angle is within a range of 0.07 to 0.11.