Patent 7249892 was granted and assigned to NSK Ltd. on July, 2007 by the United States Patent and Trademark Office.
When a minimum thickness of a part where an outer ring raceway is provided on a middle portion in the axial direction of an outer ring is h, and a diameter of each rolling element is Da, the relationship 0.4 Da≦h 0.8 Da is satisfied. As a result, even when the outer ring 4a is fixed in a transmission case of low-rigidity, elastic deformation of the outer ring can be prevented without needlessly increasing the thickness h of the outer ring.