| 摘要 |
PURPOSE:To prevent the deterioration of durability due to the thermal fatigue of a piston ring by forming the fin-shaped ribs onto the side peripheral edge part of a vacant part for feeding cooling oil which is formed onto the top wall part of a piston, thus preventing the concentration of thermal flow onto the outer peripheral wall part of the piston. CONSTITUTION:A vacant part 10 for feeding cooling oil is formed at the top wall part of a piston. Fin-shaped ribs 11 which extend in the radial direction of the piston and connect the wall surfaces opposed each other in the direction of the axis line of the piston are formed onto the side peripheral edge part of the vacant part 10. Therefore, heat can be transmitted from the top wall part to the piston boss part and the skirt part, and the concentration of thermal flow onto the outer peripheral wall part of the piston is prevented.
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