| 摘要 |
PURPOSE:To facilitate manufacture by providing longitudinal grooves extending in the direction perpendicular to the piston ring grooves on the thick-wall part of cylindrical inner surface part continuously provided beneath a piston top plate, and further forming these longitudinal grooves at the time when the piston raw material is made by casting or forging. CONSTITUTION:A piston 1 has a cylindrical part 2 which is loosely fitted in the cylinder bore, a top plate 3 which closes one end thereof, and in the cylindrical part 2 a boss 4 for supporting a piston pin. Further, on the upper inner surface of the piston 1 a thick-wall part 1a reduced in diameter is provided, and on the outer circumference of the piston 1 a pressure ring groove 5 and an oil ring groove 6 are provided. In the above piston 1, a plural number of longitudinal grooves 8 extending in the axial direction from the B side of a piston skirt part to the oil ring groove 6 are provided on the thick-wall part 1a, and the bottom parts of these longitudinal grooves are communicated with the inside of the oil ring groove 6. And these longitudinal grooves 8 are formed simultaneously at the time when the piston raw material is made by casting or forging. |
