Stratified scavenging two-cycle engine
A stratified scavenging two-cycle engine that has a simpler structure than conventional stratified scavenging two-cycle engines and that has an excellent blow-by prevention effect etc. In an air intake stroke, lead air passes a lead-air port ( 12 ) etc. to flow into an inner space of a piston ( 6 ) during a period from the instant at which a lateral groove ( 21 b ) starts to superpose on the lead-air port ( 12 ) until the superposing between the lateral groove ( 21 b ) and the lead-air port ( 12 ) disappears after the piston ( 6 ) passes its top dead center. Further, in a scavenging stroke, lead air passes a scavenging path ( 17 ) etc. to flow into a cylinder ( 4 ) from a scavenging port ( 18 ) during a period from the instant at which a scavenging connection opening ( 20 ) and a scavenging inflow opening ( 19 ) start to superpose on each other until the superposing between the scavenging connection opening ( 20 ) and the scavenging inflow opening ( 19 ) disappears after the piston ( 6 ) passes its bottom dead center. Then, a mixture gas passes the inside of the piston ( 6 ) to flow into the cylinder ( 4 ) from the scavenging port ( 18 ).
1. A stratified scavenging two-cycle engine, comprising:
a piston;
a lead air flow channel provided in the piston for causing lead air to flow from outside into an inner space of the piston, the inner space communicating with a crank chamber;
a scavenging communication port provided in a side portion of the piston; and
an exhaust port, a lead air port, a scavenging port, and a scavenging inflow port provided in an inner circumferential surface of a cylinder;
wherein:
the scavenging port and the scavenging inflow port are air-tightly connected by a scavenging passage;
the scavenging communication port is formed in a position such that the scavenging communication port overlaps the scavenging inflow port when the piston is located close to a bottom dead center;
the lead air flow channel is formed in a position such that an end portion at one side of the lead air flow channel overlaps the lead air port of the cylinder when the piston is located close to a top dead center;
in an intake process, while the end portion at one side of the lead air flow channel overlaps the lead air port, the lead air flows into the inner space of the piston via the lead air port and the lead air flow channel; and
in a scavenging process, while the scavenging communication port and the scavenging inflow port overlap, the lead air located in the inner space of the piston flows from the scavenging port into the cylinder via the scavenging communication port, the scavenging inflow port, and the scavenging passage and then an air-fuel mixture located in the crank chamber flows from the scavenging port into the cylinder via the inside of the piston, the scavenging communication port, the scavenging inflow port, and the scavenging passage.
2. The stratified scavenging two-cycle engine according to claim 1 , wherein:
the lead air flow channel comprises a groove formed in an outer circumferential surface of the piston and a lead air inflow port communicating with the inner space of the piston;
the groove is formed in an L-like shape comprising a vertical groove and a transverse groove extending transversely from the lower end of the vertical groove;
the lead air inflow port is formed at an upper end of the vertical groove; and
an end portion of the transverse groove is formed in a position such that the end portion overlaps the lead air port when the piston is located close to the top dead center.
3. The stratified scavenging two-cycle engine according to claim 1 , wherein a rib for inhibiting an air flow in an up-down direction is formed inside the piston.
4. The stratified scavenging two-cycle engine according to claim 2 , wherein the lead air inflow port is configured so as to be open in a tangential direction of the inner circumferential surface of the piston.
5. The stratified scavenging two-cycle engine according to claim 1 , wherein two of the lead air flow channels are provided in the piston.
6. The stratified scavenging two-cycle engine according to claim 2 , wherein two of the lead air flow channels are provided in the piston.