| 摘要 |
A rotation preventing mechanism is composed of a thrust ball bearing including a first race section having an annular shape, a second race section disposed at an eccentric position in confrontation with the first race section at intervals and thrust balls interposed between the first and second race sections. The first and second race sections have ball accommodating grooves formed at the confronting surfaces thereof, respectively. Each of the ball accommodating grooves includes a central portion and a groove bottom portion around it. When the radius of curvature of each thrust ball is represented by RB, the radius of curvature of the groove bottom portion on an inner side is represented by Rin and the radius of curvature thereof in an outer side is represented by Rout, and the ball accommodating groove has a shape satisfying a formula RB</=Rin<Rout. |
