To minimize frictional loss generated at a sliding part with a piston by providing a cylinder wall with appropriate temperature distribution without the increase of machining cost in engine cooling structure with a water jacket formed at a cylinder block so as to surround the outer periphery of a cylinder bore.
A large number of ribs 17 extending parallel with the axis of a cylinder are formed on the wall surface, positioned on the cylinder bore 12 side, of a water jacket 16 formed at a cylinder block 11. The rib 17 comprises an upper rib 17a positioned on the top dead center side of a piston, and a lower rib 17b positioned on the bottom dead center side of the piston. The height Ht of the upper rib 17a is almost constant in the axis direction of the cylinder, and the height Hb of the lower rib 17b is increased from the top dead center side of the piston toward the bottom dead center side of the piston.
SUGIMOTO MITSURU
YAMAMOTO KAZUHIRO
MIYAO MASAKATSU
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