Stratified scavenging two-stroke engine

A stratified scavenging two-stroke engine comprising:

• a piston;
• a cylinder that houses the piston in a manner allowing reciprocation;
• a crankshaft that is connected to the piston via a connecting rod;
• a crankcase that houses the crankshaft in a manner allowing rotation;
• a mixture gas passage that introduces mixture gas into the crankcase;
• a scavenging passage that extends between a scavenging intake that opens into the crankcase and a scavenging port that opens into the cylinder;
• an air passage that is connected to an intermediate position of the scavenging passage for introducing air into the scavenging passage;
• a first check valve for preventing a flow of the scavenging passage toward the scavenging intake, wherein the first check valve is disposed within a section of the scavenging passage between the scavenging intake and the intermediate position where the air passage is connected;
• and
• a crankcase-cover that is fixed to the crankcase and defines at least a part of the scavenging passage between the crankcase and itself,
• wherein the crankcase comprises a flat face contacting the crankcase-cover,
• wherein the flat face is parallel to an axis of rotation of the crankshaft, and is tilted downward to form an angle within 0 to 30 degrees with, respect to a longitudinal axis of the cylinder, and
• wherein, in a part of an upward stroke period during which the piston moves to an opposite side with respect to the crankcase, the crankcase in which negative pressure is generated connects to the scavenging passage via the scavenging port.