PURPOSE: To improve cooling effect by forming an oil inlet at one edge and an oil outlet at the other edge on the undersurface of a hollow part which spreads in the direction of transverse section at the top part of a piston and allowing a rib which smoothly connects the oil inlet and the oil outlet to protrude downward on the ceiling wall surface of the hollow part.
CONSTITUTION: A hollow part 16 which spreads in the direction of transverse section of a piston is formed at the top part 11 of the piston, and an oil inlet 21 is formed at one edge and an oil outlet 22 is formed at the other edge on the undersurface 19 of the hollow part so that both ports are drilled symmetrically to the center axis line of the piston. On the ceiling surface 18 of the hollow part 16, a center rib 24 which rectilinearly connects the oil inlet 21 and the oil outlet 22 and the right and left ribs 25 in symmetrical form which extend in circular form on both sides of the center rib 24 are formed.
KANDA MUTSUMI
INOUE TOKUTA
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