| 摘要 |
PROBLEM TO BE SOLVED: To provide a combined oil control ring having a superior abrasive resistance and an anti-sludge characteristic so as to prevent a single rotation of a side rail.SOLUTION: This invention relates to a combined oil control ring comprising a pair of ring-like side rails having abutments and a spacer expander present between the side rails and having ears at its inner peripheral part for pressing against the inner peripheral surfaces of the side rails. When the side rail pressing surfaces of the ears are formed with either one or a plurality of grooves extending substantially in an axial direction and the pressing surfaces of the side rails including the grooves are formed with a nitrided layer, it is adjusted to satisfy a relation of 0.05≤1000×d/(h×t)≤0.45, where d (μm) is a depth of the groove, h (a micro Vickers hardness, HV0.1) is a surface hardness of the nitrided layer, and t (μm) is a thickness of the nitrided layer having a hardness of 700 or more. |
