| 摘要 |
PROBLEM TO BE SOLVED: To provide an oil return passage structure capable of inexpensively forming an oil return passage. SOLUTION: In a piston 10 equipped with a land part 11 on which an oil ring groove 20 to be fitted with an oil ring 50 is formed on its periphery, a skirt part 14 provided in the lower part of the land part 11, and side wall parts 13 provided on partial parts of the skirt parts 14 at both ends of a piston boss part 12 so as to be positioned on the further axial center side of the piston than the periphery of the land part 11 while forming a step part 11a between it and the land part 11, the oil return passage 21 passing through the oil ring groove 20 is provided in the step part 11a.
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