| 摘要 |
An extendable shaft (5) has an outer shaft (13, 13A, 13B, 13C, 13D) and an inner shaft (14, 14A, 14B, 14C, 14D, 14E, 14F). Rolling bodies (15) are elastically held between raceway grooves (16, 17) of the outer shaft and the inner shaft by elastic restoring force of the outer shaft. An outer peripheral surface (141) of the inner shaft includes at least a par of flat sections (21, 22, 41, 42, 43, 44, 45, 46) that are parallel to each other. An inner peripheral surface (131) of the inner shaft includes at least a pair of flat restriction sections (31, 32, 71, 72, 73, 74) that are parallel to each other. Each of the restriction sections (31, 32, 71, 72, 73, 74) engages with corresponding each of the flat sections (21, 22, 41, 42, 43, 44, 45, 46) to restrict the amount of relative rotation of the outer shaft and the inner shaft. A deformation promotion section (33, 33A, 33B, 33C, 33D, 33E, 33F, 33G, 33H, 330) for promoting deformation of the outer shaft is provided in a predetermined region in the circumferential direction of the outer shaft. The predetermined region is a region between a plane (C1) and the restriction sections (31, 32, 71, 72, 73, 74), the plane (C1) including the curvature center (A2) of the outer shaft raceway groove (16) and the center axis (A1) of the outer shaft. |
