| 摘要 |
PROBLEM TO BE SOLVED: To prevent increase in oil consumption even if low tension is generated with an expander by forming at least one side which abuts on a diameter direction surface of a ring groove, in a smooth curved surface whose top surface is formed in the vicinity of a center having the thickness of a side rail. SOLUTION: In the case where a side surface 13 of a side rail 10 is formed in a smooth curved surface whose top point 13a is formed in the vicinity of the middle of thickness (t) direction, the side surface 13 is brought into linear contact with a diameter direction surface 8 of a ring groove 9 at all times at the top point 13a formed in a nearly center with large surface pressure. Even if tension of an expander 1 is reduced, in the vicinity of a top dead point changed from a raising process to a falling down process, a lubricating oil which radially flows to the outside passing by the side surface 13 of the side rail 10 is intercepted by large plane pressure, and a flow passage of the lubricating oil is narrowed locally. It is thus possible to reduce oil consumption.
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