Patent ID: 8794843

Claim:
A rotation support device for a pinion shaft that supports the pinion shaft with a pinion gear provided on one end, inside a housing, comprising: a pair of rolling bearings for supporting the pinion shaft that are separated from each other in the axial direction such that the pinion shaft can rotate freely and can support an axial load from both directions; wherein: the rolling bearing on the pinion gear side is a tandem double-row angular contact ball bearing that is capable of supporting an axial load that acts on the pinion shaft in a direction from the pinion gear side to the side opposite from the pinion gear side, and the rolling bearing on the side opposite from the pinion gear side is a single-row angular contact ball bearing that is capable of supporting an axial load that acts on the pinion shaft in a direction from the side opposite from the pinion gear side to the pinion gear side; when the radius of curvature of the outer raceway of this single-row angular contact ball bearing is taken to be Ro, the diameter of the balls is taken to be Bd, and the contact angle between the outer raceway and inner raceway and the balls is taken to be α, the relationships 0.52<Ro/Bd≦0.56 and 35°≦α being satisfied; and of both ball rows of the tandem double-row angular contact ball bearing, the pitch-circle diameter of the ball row on the pinion gear side is larger than the pitch-circle diameter of the ball row on the side opposite from the pinion gear side, and the radial clearance of the ball row on the pinion gear side is less than the radial clearance of the ball row on the side opposite from the pinion gear side.