The present invention relates to a tapered roller bearing which is used in differentials for motor vehicles and industrial machines, a tapered roller bearing apparatus which utilizes the tapered roller bearing and an automotive pinion shaft supporting apparatus which utilizes the tapered roller bearing apparatus.
Since tapered roller bearings are characterized in that they have a high load capacity and a high rigidity, compared to ball bearings, the tapered roller bearings are used in automotive pinion shaft supporting apparatuses in differentials and transaxles of motor vehicles.
In the tapered roller bearing, conventionally, in order to reduce a sliding friction between a large diameter side end face of a tapered roller and a large rib portion of an inner ring so as to reduce the running torque of the tapered roller bearing, the large diameter side end face of the tapered roller was formed into a convexly curved surface. In forming the convexly curved surface, in order to increase the lubricity between the large diameter side end face of the tapered roller and the end face of the large rib portion of the inner ring, the radius of curvature of the large diameter side end face and the radius of curvature of the end face of the large rib portion of the inner ring were normally made to be substantially equal to each other. In machining the tapered rollers, +/−(plus/minus) tolerances were permitted (for example, when Ra represents the radius of curvature of the large diameter side end face, a plus side tolerance permitted was Ra×0.04, while a minus side tolerance permitted was Ra×0.1).
In the aforesaid case, however, when a tapered roller is machined with the plus side tolerance, since a contact position between the large diameter side end face of the tapered roller and the end face of the large rib portion of the inner ring becomes high (the value of e in FIG. 1 increases), the lubricity between the large diameter side end face and the end face of the large rib portion was deteriorated, and as a result, there was caused a problem that the large diameter side end face of the end face of the large rib portion tended to get seized easily.