| 摘要 |
The present invention discloses a crankcase scavenging internal combustion engine (1) having a transfer passage (8) interconnecting the crankcase (3) and the cylinder (2) via a conventional transfer port (20). An air supply tube (16) is connected to the transfer passage (8) via a reed valve (17). The transfer passage has a volume which is an appreciable percentage of the swept volume of the cylinder. When the crankcase is depressurized, air enters via the reed valve (17) and scavenges the transfer passage (8). When the crankcase is pressurized and the transfer port opens, the air remaining in the transfer passage which is substantially free of fuel is used to scavenge the cylinder. Some of this air enters the exhaust port (7) and some remains in the cylinder to form part of the combustion gases. The fuel free air remaining in the cylinder enables the quantity of oil in the gasoline/oil fuel mixture to be reduced. Provision of a decompression valve (30), preferably adjacent the exhaust port (7) enables a fuel mixture enriching effect, equivalent to choking, to be achieved at starting.
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