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 the 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 first scavenging port that opens to the inside of a cylinder according to movement of the position of a piston;
• a second scavenging passage that extends from a second scavenging intake that opens to the inside of the crankcase to a second scavenging port that opens to the inside of the cylinder according to movement of the position of the piston;
• a communicating portion through which the first scavenging passage and the second scavenging passage communicate with each other;
• an air passage that supplies an air for pre-scavenging into the first scavenging passage at a position closer to the first scavenging intake than the communicating portion;
• 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 through the air passage to the outside 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 through the air passage into the first scavenging passage, flows through the communicating portion into the second scavenging passage, 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 first and the second scavenging ports 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 first and the second scavenging ports to the inside of the cylinder.