US Patent 9249716 Stratified scavenging two-stroke engine

A two-stroke engine is provided with a scavenging passage that extends between a scavenging intake that opens into a crankcase and a scavenging port that opens into a cylinder, and an air passage that is connected to an intermediate position of a scavenging passage for introducing air into the scavenging passage. A first check valve that is disposed within a section of a scavenging passage between a scavenging intake and the intermediate position. A second check valve that is disposed within the air passage. The section of the scavenging passage between the intermediate position and the scavenging intake, the air passage, and a mixture gas passage are arranged in a substantially same direction with respect to a longitudinal axis of the cylinder.