| 摘要 |
PURPOSE:To provide a three-piece type combined oil ring improved in the follow-up performance of side rails to the deformation of a bore. CONSTITUTION:In a combined oil ring 31 where a spacer expander 17 is disposed between two, upper and lower side rails 13, 15, plural notches 13a are formed at designated intervals on the inner peripheries of the side rails 13, 15. Ion nitriding treated layers 21 are formed only on the outer peripheral surfaces of the side rails 13, 15 so as to improve the durability while the embrittlement of the side rails is prevented.
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