| 摘要 |
PROBLEM TO BE SOLVED: To set the position and the form of a cooling hollow provided around a cavity, in order to improve the reliability of a cavity lip provided on the top surface of a piston. SOLUTION: A cooling hollow 30 is provided in a circular form, at the head part 12 of a piston 10, in order to surround a cavity 20 provided on the top surface 16 of the piston 10. In this case, the cooling hollow 30 is formed in an elliptical form, and its shorter diameter is fitted in the extending direction of a piston pin, and the longer diameter is fitted in the thrusting direction orthogonal to the pin direction. In the pin direction, the wall thickness L between the cooling hollow 30 and the outer peripheral surface of the piston 10 is made thicker and the rigidity is made larger, and the deformation of a lip part 22 by an explosion stress to be an outer stress is suppressed. The wall thickness L is made thinner in the thrusting direction, and the rigidity is reduced, and the deformation of the lip part 22 by a thermal stress to be an inner stress is also suppressed.
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