| 摘要 |
PURPOSE:To specify the outer peripheral pressure of a side rail throughout the whole periphery, by a method wherein an in inner peripheral crest part is higher in the direction of an axis than an outer peripheral crest part, and an expander, in which a number of slits, extended alternately from an outer and an inner periphery, are formed, is provided. CONSTITUTION:An outer peripheral crest part 16 and an inner peripheral crest part 18 of an expander 12 are bent, in a direction extended toward the inside side and the outside, respectively, over a flat part 14, and the inner peripheral crest part 18 is so formed as to be higher by about a size about equal to the thickness of a side rail 10 than the outer peripheral crest part 16. In order to annularily bend the whole of the expander, slits 20, all widths of which amount to about 10% of that of the whole periphery, are formed in the expander 12. This constitution enables the outer peripheral surface pressure of the side rail 10 and a surface pressure to the upper surface of a piston ring groove to be uniformized throughout the whole periphery, and reduces wear of the expander 12. |
