| 摘要 |
PURPOSE:To enable increase of the open area of a scavenging port and to improve improvement of the output of an engine, by a method wherein a recessed part is formed in the top surface of a piston along a peripheral edge positioned facing the scavenging port, and a suddenly-rising stepped part is formed on the exhaust port side of the recessed part. CONSTITUTION:A 2-stroke engine 1 has a combustion chamber 1d surrounded with a cylinder 1a, a piston 1b, sliding on the interior of the cylinder, and a cylinder head 1c covering the top part of the cylinder 1a. A suction port 2, scavenging ports 3, and an exhaust port 4 are open to the inner wall of the cylinder 1a, and the scavenging ports 3 are disposed adjacent to both sides of the exhaust port 4. With this constitution, a recessed part 6 is formed in the top surface of the piston 1b along the peripheral edge positioned facing the scavenging ports 3. A stepped part 6a is formed in the end part on the exhaust port 4 side of the recessed part 6. This reduces blow-by of fresh air even when the scavenging ports 3 approach the exhaust port 4, and enables increase of the opening area of the scavenging port 3.
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