PURPOSE: To aim at improvement in thermal efficiency as well as in exhaust emission control, by controlling liquid fuel flowing an inner wall of a crank chamber or the like, while separating a thick air-fuel mixture inclusive of the liquid fuel from any other rare air-fuel mixture, and feeding the inside of a cylinder with each of them through each individual scavenging hole, respectively.
CONSTITUTION: During a compression stroke, when a suction port 11 opens with a piston 4 going up, an air-fuel mixture passed through a carburetor 13 flows into the inside of a crank chamber 8. And, when the mixture is circulated under being stirred with rotation in a crank 9, a part of liquid fuel sticks to the inner wall surface of a crankcase 7, turning to a wall surface stream. In this case, since a flow passage 20 of the wall surface stream is installed in the inner wall surface of the crankcase 7, the wall surface stream is guided by the flow passage and runs toward an opening 19 at the crank chamber side. And, during a scavenging stroke, it flows inside a cylinder 3 by way of a pair of scavenging passages 18 for thick air-fuel mixture use and a scavenging port 16 while forming the thick mixture. At this time, a rare air-fuel mixture is led into the cylinder 3 from an exclusive scavenging port 15 in advance, thus combustion gas is scavenged up.
OONISHI SHIGERU
JIYO SHIYAKUKOU
