| 摘要 |
A ring groove for a two-piece oil ring of a piston is provided that has ring body equipped with a coil expander, wherein the ring body has an upper outer surface and a lower outer surface, both orthogonal to the axial direction of the piston. The ring groove also has an upper inner surface and a lower inner surface, both orthogonal to the axial direction of the piston; a radially inward-most, bottom surface connecting the upper and lower inner surfaces; and oil drain holes, each having an opening thereof located on the bottom surface. The ring groove has an axial width slightly greater than the width of the two-piece oil ring. The ring groove has a radially inward ends of the upper and lower surfaces of the ring groove, respectively, located radially inwardly apart by a first predetermined distance from the radially inward ends of the upper and lower outer surfaces of the ring body when the oil ring is mounted within the ring groove so that the outer circumferential surface of the ring body is in contact with the inner circumferential surface of a cylinder which is engaged with the piston.
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