| 摘要 |
<P>PROBLEM TO BE SOLVED: To form a communication passage and openings by machining, while preventing peeling, and expansion of the peeling, of a joint surface in the periphery of an opening in a piston in which a ring for forming a piston cooling flow passage is embedded. Ž<P>SOLUTION: The ring 10 for forming a piston cooling flow passage to be casted in the piston is formed with a thin part 12a in the peripheral edge thereof at an opening forming position 12, and formed into a shape easy to be opened by machining and weak in mechanical strength. The thin part 12a is therefore easily broken by a drill blade, and opened. The force in a direction for peeling the ring 10 for forming a piston cooling flow passage from a joint surface with a piston body becomes small. Further, since mechanical strength in the thin part 12a is weak, the thin part is easily deformed. Outward expansion of peeling inside the thin part 12a is thereby prevented. Even if one drill blade is used continuously, peeling of the joint surface is prevented in the periphery of the opening and expansion of peeling is prevented, and efficient drilling work is enabled without changing a drill blade. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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