| 摘要 |
In a three-piece combined oil ring comprising a pair of side rails and provided between them a spacer expander, the side rails are each provided in the inner edge thereof with a plurality of cutouts at given intervals, thereby providing a combined oil ring improved in its conformable property to any deformation of a cylinder bore. A nitrided layer is formed by plasma nitriding on each side rail only at its outer edge face, thereby preventing embrittlement of the side rails and improving the durability.
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