Stratified scavenging two-stroke engine

A stratified scavenging two-stroke engine comprising:

• an intake passage that supplies a gaseous mixture of fuel and air to an inside of a crankcase;
• a first scavenging passage that extends from a first scavenging intake that opens to the inside of the crankcase to a scavenging port that opens to an inside of a cylinder according to movement of a position of a piston;
• a second scavenging passage that branches from the first scavenging passage and extends to a second scavenging intake that opens to the inside of the crankcase, wherein the second scavenging passage has one end communicating with the inside of the crankcase via the second scavenging intake and the other end connected to the first scavenging passage to communicate with the inside of the cylinder via the scavenging port;
• an air passage that supplies air for pre-scavenging into the first scavenging passage at a position closer to the first scavenging intake than a position at which the second scavenging passage branches from the first scavenging passage;
• a first check valve that inhibits a flow of air from the first scavenging passage to the inside of the crankcase during an upward stroke of the piston;
• and
• a second check valve that inhibits a flow of air and the gaseous mixture from the first scavenging passage toward the air passage during a downward stroke of the piston,
• wherein the engine is configured so that during the upward stroke of the piston, the gaseous mixture is supplied from the intake passage to the inside of the crankcase, and the air, that has been supplied from the air passage, flows into the first and the second scavenging passages, and
• wherein the engine is configured so that during the downward stroke of the piston, the air, that has entered into the first and the second scavenging passages during the upward stroke of the piston, flows through the scavenging port to the inside of the cylinder, so that the gaseous mixture inside of the crankcase is supplied through the first and the second scavenging passages and the scavenging port to the inside of the cylinder.