A raceway surface (3a) of an outer ring (3) of a tapered roller bearing (1) includes a composite crowning surface. The composite crowning surface includes a center curve (3a1), which is formed at a center portion in a generating-line direction, and end portion curves (3a2 and 3a3), which are formed on both sides of the center curve (3a1) in the generating-line direction. The raceway surface (3a) of the outer ring (3) is entirely subjected to superfinishing. Each of a ratio (R.sub.2/R.sub.1) of a curvature radius (R.sub.2) of the end portion curve (3a2) to a curvature radius (R.sub.1) of the center curve (3a1) and a ratio (R.sub.3/R.sub.1) of a curvature radius (R.sub.3) of the end portion curve (3a3) to the curvature radius (R.sub.1) is set to 0.02 or more. Each of drop amounts of the end portion curves (3a2 and 3a3) is set to 0.07 mm or less.

A value of R/R.sub.BASE is not smaller than 0.75 and not greater than 0.87 where R represents a reference radius of curvature of a larger end face of a roller and R.sub.BASE represents a distance from an apex of a cone angle of the roller to a larger flange surface of an inner ring 13. A distance from an outermost surface of at least any one of an outer ring, the inner ring, and a plurality of rollers to a bottom of a nitrogen enriched layer is not shorter than 0.2 mm. A crowning profile is formed on a rolling surface of the roller.

This bearing device (1) for vehicle wheels comprises: an inner undercut part (8) provided in a portion at which an inner rolling surface (3d) formed on the inner side of an inner member (3) and an inner flange surface (3m) of the inner rolling surface (3d) intersect; an outer undercut part (9) provided in a portion at which an inner rolling surface (3c) formed on the outer side of the inner member (3) and an outer flange surface (3n) of the inner rolling surface (3c) intersect; and a vehicle wheel installation flange (3e) provided at a portion adjacent to the inner rolling surface (3c) formed on the outer side of the inner member (3), wherein, when the radius of curvature of the inner undercut part (8) is Ri, and the radius of curvature of the outer undercut part (9) is Ro, the relationship of Ri<Ro is satisfied.

In a tapered roller bearing, a cage includes a plurality of trapezoidal pockets and the pockets accommodate and hold a plurality of rollers. A notch having a width is provided in a post on a smaller width side of the pocket of the cage from a boundary between a smaller annular portion and a post toward a larger annular portion. Lubricating oil which flows from an inner diameter side of the cage toward an inner ring is quickly discharged through the notch toward an outer ring on an outer diameter side. A distance from an outermost surface of at least any one of the outer ring and the inner ring of the roller and a plurality of rollers to a bottom of a nitrogen enriched layer is equal to or longer than 0.2 mm. A rolling surface of the roller is provided with a logarithmic crowning profile.

Vehicle input shafts are disclosed. The vehicle input shafts include a bearing boss, a spline portion, a cylindrical shaft body portion and a drive end. The spline portion includes spline teeth and spline grooves that do not exit directly onto the shaft body. Instead, the spline grooves include blend out fillets that interrupt the spline grooves by providing additional material near the shaft body. The bearing boss includes an increased diameter at a central point along its axial length and decreased diameters at its first and second boss ends.

A double-row self-aligning roller bearing has rollers interposed, in two rows aligned in a bearing width direction, between an inner ring and an outer ring. The outer ring has a spherical raceway surface. Each of the rollers has an outer circumferential surface having a cross-sectional shape that matches the raceway surface of the outer ring. The rollers have lengths equal to each other and maximum diameters equal to each other, and have different distances from centers of the roller lengths to positions at which the maximum diameters are obtained.

In a linear motion guide unit, in order to prevent direct collision of a roller, or a rolling element, with an end portion of a carriage, an extending portion of a spacer of an end cap is disposed at the end portion of the carriage for absorbing impact resulting from collision of the roller. The spacer has the extending portion which protrudes from the spacer at a position adjacent to an inner circumferential surface of a turnaround passage and which has a wall surface continuous from the inner circumferential surface of the turnaround passage. The wall surface of the extending portion serves as a collision receiving surface for receiving a colliding roller. The carriage has a housing recess which is formed at an end of a raceway groove thereof and to which the extending portion is fitted.

Vehicle input shafts are disclosed. The vehicle input shafts include a bearing boss, a spline portion, a cylindrical shaft body portion and a drive end. The spline portion includes spline teeth and spline grooves that do not exit directly onto the shaft body. Instead, the spline grooves include blend out fillets that interrupt the spline grooves by providing additional material near the shaft body. The bearing boss includes an increased diameter at a central point along its axial length and decreased diameters at its first and second boss ends.

A tapered roller bearing includes inner and outer rings including raceway surfaces having tapered shapes on their outer and inner peripheries, respectively, tapered rollers between the raceway surfaces, and a retainer configured to receive the tapered rollers. At least the raceway surface of the inner ring includes cut crowning of a complex curve including a center curve and end portion curves formed on both sides of the center curve each have a curvature radius smaller than a curvature radius of the center curve. The tapered rollers each have a rolling surface including a straight portion and logarithmic crowning portions formed on both sides of the straight portion. When the raceway surface of the inner ring has an effective raceway surface width represented by LG, and the straight portion of the rolling surface of the tapered roller has a width represented by LW1, 0.7LW1/LG<0.95 is satisfied.

A raceway surface (3a) of an outer ring (3) of a tapered roller bearing (1) includes a composite crowning surface. The composite crowning surface includes a center curve (3a1), which is formed at a center portion in a generating-line direction, and end portion curves (3a2 and 3a3), which are formed on both sides of the center curve (3a1) in the generating-line direction. The raceway surface (3a) of the outer ring (3) is entirely subjected to superfinishing. Each of a ratio (R.sub.2/R.sub.1) of a curvature radius (R.sub.2) of the end portion curve (3a2) to a curvature radius (R.sub.1) of the center curve (3a1) and a ratio (R.sub.3/R.sub.1) of a curvature radius (R.sub.3) of the end portion curve (3a3) to the curvature radius (R.sub.1) is set to 0.02 or more. Each of drop amounts of the end portion curves (3a2 and 3a3) is set to 0.07 mm or less.