| 摘要 |
PROBLEM TO BE SOLVED: To prevent abrasion and seizure caused by biting of a middle ring into an outer ring by forming the outer peripheral edge part in the small diameter side end part of the middle ring into a cross-sectional circular arc shape. SOLUTION: At unoperated time, there is a case where respective rings rotate while inclining in the optional direction in an idly rotating state. In this case, since a middle ring 14 relatively rotating with an outer ring 13 is different in the inclination, the edge part of the small diameter side end part easily hitches on the inner peripheral surface side of the outer ring 13, particularly, a lubricating groove 13d formed on the inner peripheral surface. However, since the outer peripheral edge part 14d corresponding to the small diameter side edge part of the middle ring 14 is formed in a cross-sectional circular arc shape, the outer peripheral edge part 14d of the small diameter side end part of the middle ring 14 does not hitch on the lubricating groove 13d on the inner peripheral surface of the outer ring 13 so as to prevent biting of the moddle ring 14 into the outer ring 13 to thereby prevent abrasion and seizure caused by biting of the middle ring 14 into the outer ring. |
