Tapered roller bearing

1. A tapered roller bearing, comprising:

an outer ring having a tapered raceway surface on an inner periphery thereof;

an inner ring having a tapered raceway surface on an outer periphery thereof, and comprising a large-collar surface on a large-diameter side of the tapered raceway surface;

a plurality of tapered rollers arrayed between both of the tapered raceway surfaces so as to be freely rollable; and

a cage configured to receive the tapered rollers,

wherein each of the tapered rollers has a large end side including an end surface chamfer, a relief portion, and a large end surface located between the end surface chamfer and the relief portion, the large end surface to be held in contact with and guided by the large-collar surface of the inner ring during use of the bearing,

wherein when R represents a set curvature radius of the large end surface of each of the tapered rollers, and R BASE represents a base curvature radius from a vertex of a cone angle of each of the tapered rollers to the large-collar surface of the inner ring, the base curvature radius R BASE is 100 mm or less, and a ratio R/R BASE of the set curvature radius R to the base curvature radius R BASE is set to 0.90 or less,

wherein the large end surface of each of the tapered rollers is formed by an annular surface centered on a tapered roller centerline and has two arc-shaped convex cross sections in a vertical cross section of the tapered roller, the two arc-shaped convex cross sections each having an actual curvature radius R ACTUAL that is smaller than the set curvature radius R in the vertical cross section of the tapered roller, and

wherein the actual curvature radius R ACTUAL is defined as a radius of an arc curve passing through three points of each of the two arc-shaped convex cross sections, which are a connection point between the large end surface and the end surface chamfer, a connection point between the large end surface and the relief portion, and a midpoint between the connection points, in the vertical cross section of the tapered roller, and a ratio R ACTUAL /R of the actual curvature radius R ACTUAL to the set curvature radius R is a value exceeding 0.5.

2. The tapered roller bearing according to claim 1 , wherein the ratio R/R BASE of the set curvature radius R to the base curvature radius R BASE is set within a range of from 0.70 to 0.90.

3. The tapered roller bearing according to claim 1 , wherein the large end surface of each of the tapered rollers and the large-collar surface of the inner ring are superfinished surfaces.

4. The tapered roller bearing according to claim 1 , wherein the large-collar surface of the inner ring has a relief surface.

5. The tapered roller bearing according to claim 1 ,

wherein the tapered raceway surface of the inner ring and the tapered raceway surface of the outer ring each have a straight shape or a full-crowning shape having an arc, and

wherein the tapered rollers each have a rolling surface with a logarithmic crowning shape.

6. The tapered roller bearing according to claim 5 , wherein at least one of the inner ring, the outer ring, and the tapered rollers has a nitrogen-enriched layer, and a depth of the nitrogen-enriched layer is 0.2 mm or more.

7. The tapered roller bearing according to claim 5 , wherein at least one of the inner ring, the outer ring, and the tapered rollers has a nitrogen-enriched layer, and a grain size number of austenite crystal grain in the nitrogen-enriched layer is larger than No. 10.

8. The tapered roller bearing according to claim 1 , wherein the tapered roller bearing is used for a transmission or a differential for an automobile.