| 摘要 |
PROBLEM TO BE SOLVED: To easily form a machining reference face in a piston structure, having a thinned skirt part and omitting a rib formed over the overall circumference by forming projection parts protruded toward the radial inside to the circumference direction of the skirt part inner circumferential face and forming planes being flush with each other on the lower faces of the respective projection parts. SOLUTION: In two opposed position which mutually face orthogonal to the axial direction of a pin hole 5 on the inner circumferential face of a skirt part 2, which is thinned so as to be deformed by a lateral pressure for dispersing and absorbing stress, projection parts 7 protruded toward the radial inside of the skirt part 2 are formed partially. In addition, using sufficient thickness secured by the projection parts 7, machining reference face 4 being flush with each other are easily formed on the lower faces of the projection parts 7. The respective projection parts 7 are scatted in the circumferential direction of the inner circumferential face of the skirt part 2, so that problems such as occurrence of excessive deformation stresses due to strong thrusts against a lateral pressure applied to the skirt part 2 and increase in collision force to a cylinder liner can be avoided in advance.
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