| 摘要 |
A structure in which two worm wheels are disposed across a worm provides an increase in locking reliability while maintaining stable operation during rotation. At the time of rotation, respective rotating fulcrums set at both end portions in an axial direction of a worm 50 are supported by bearing portions 510, 520. At the time of locking, a locking fulcrum set at an eccentric position on one end portion in the axial direction of the worm 50 is supported by one bearing portion 510, while on the other end portion in the axial direction, the rotating fulcrum is supported by the other bearing portion 520 as is. As a result, the angle of advance of the worm supported by the pair of bearing portions 510, 520 is changed between the time of rotation and the time of locking and becomes smaller at the time of locking than at the time of rotation, whereby an increase in locking reliability can be achieved. |
