PURPOSE: To prevent blow by of a mixture and perform stable combustion, by scavenging internally of a cylinder with intake air in a scavenging passage at the beginning of a scavenging stroke and then introducing the mixture into the cylinder.
CONSTITUTION: When a piston 3 is moved from the bottom dead center to the top dead center, a crank chamber 12 becomes negative pressure, and air is sucked to a scavenging passage 7 via an air throttle valve 15, check valve 11 and passage 9. If an air suction hole 10 is communicated to the crank chamber 12, a mixture is sucked to the crank chamber 12 through a mixer 13 and a mixture throttle valve 14. That is, the scavenging passage 7 becomes a condition, sucked with air, from a position about a scavenging hole 5. Then if the piston lowers from the top dead center, an exhaust port 6 is firstly opened to discharge exhaust gas, successively the scavenging hole 5 is opened to perform scavenging with air in the scavenging passage 7, and then a mixture in the crank chamber 12 inflows. Totalized volume of this scavenging passage 7 and the scavenging hole 5 is arranged to at least 20% the displacement, and scavenging can be fully performed, then blow by of a mixture can be prevented.
JIYO SHIYAKUKOU
OONISHI SHIGERU
