| 摘要 |
PROBLEM TO BE SOLVED: To shorten a clearance between a rack shaft and a back-up ring inner circumferential surface so as to prevent invasion of foreign matters by arranging grooves which are not penetrated in an axial direction at a prescribed clearance of a circumferential direction, on an inner circumferential surface of the back-up ring. SOLUTION: A clearance between a back-up ring 3 and the surface of a rack shaft 11 is shortened so as to reduce a sliding resistance. Namely, a contact area with the surface of the rack shaft 11 is reduced by grooves 3b arranged on the inner circumferential surface of the backup ring 3, the grooves 3b are arranged in an axial direction, and thereby, a sliding resistance is reduced. Since the grooves 3b are not penetrated in the axial direction, foreign matters such as dust, rust, and the like which are generated between the inner circumferential surface of the back-up ring 3 and the surface of the rack shaft 11 are stored in the grooves 3b so as to prevent the foreign matters from invading in a cylinder. Even if the back-up ring 3 is expanded in a radial direction, a sliding resistance between the inner circumferential surface and the surface of the rack shaft 11 is not much increased. |
