| 摘要 |
PURPOSE:To provide a scavenge hole to spread its area and to prevent stress from its concentration to a boss part, by forming a recessed cut large curving toward the axial direction of the boss part so as to communicate with the scavenge hole, which communicates with the inside and the outside of a piston, in the peripheral part of the boss part of a piston pin. CONSTITUTION:A piston P, in which both sides in the axial direction of a boss hole H are opened in a reverse U-shape from the vicinity of a bottom side ring groove 1 over a bottom skirt part, opens the first scavenge port 2. While the piston P forms its piston pin boss part 3 symmetrically in the longitudinal direction to be reinforced by each boss supporting rib 4A-4C integrally molded with the piston P, further a rib surface provides the second scavenge ports 5 to be drilled laterally symmetrically interposing the boss part 3 and communicating with the inside of the piston P. Here the piston forms n recessed cuts 3A to be curved toward the axial direction of the boss part 3 in its peripheral part so as to communicate with the second scavenge port 5. In this way, the piston attains the second scavenge port 5 to spread its area and the prevention of stress from its concentration to the boss part 3.
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