Stratified scavenging two-cycle engine
Provided is a laminar-scavenging two-cycle engine, which can have a higher laminar-scavenging effect than that of the laminar-scavenging two-cycle engine of the prior art and which can expect drastically excellent effects on the stabilization of combustion and on the blow-by prevention. The laminar-scavenging two-cycle engine is characterized in that a scavenging passage ( 4 ) is constituted to include a portion (or a crankcase side portion ( 4 a )) extending along a crankcase ( 9 ) and a portion (or a cylinder side portion ( 4 b )) extending along a cylinder ( 10 ) and to have a length larger than the sum of the diameter and stroke of the cylinder ( 10 ), in that an ambient air introducing passage ( 11 ) for introducing the leading air into the scavenging passage ( 4 ) is connected to an intermediate portion of the scavenging passage ( 4 ), and in that a notch ( 8 a ) for opening a scavenging port ( 7 ) to the side of the crankcase ( 9 ) when a piston ( 8 ) is near the top dead center is formed in the piston ( 8 ).
1. A stratified scavenging two-cycle engine comprising:
a cylinder;
a piston;
a crank chamber;
a scavenging channel including a crank-chamber side portion that extends along the crank chamber and a cylinder-side portion that extends along the cylinder;
an external air introduction path for introducing lead air into the scavenging channel, the external air introduction path being connected to an intermediate position of the scavenging channel; and
an opening portion formed in the piston;
wherein:
the opening portion and a scavenging port are relatively positioned such that when the piston is located close to top dead center, the scavenging port is opened via the opening portion so that the crank chamber communicates with the scavenging channel via the opening portion and the scavenging port; and
the engine comprises communication-preventing means for preventing communication between the crank chamber and the crank-chamber-side portion of the scavenging channel through a starting point of the scavenging channel that is open to the crank chamber, when the piston is located close to top dead center, such that an air-fuel mixture remaining in the cylinder-side-portion of the scavenging channel is pushed out by the lead air introduced via the external air introduction path and caused to flow into the crank chamber via the scavenging port when the piston is located close to top dead center.
2. The stratified scavenging two-cycle engine according to claim 1 , wherein the external air introduction path is connected to a position of the cylinder-side portion of the scavenging channel that is closest to the starting point of the scavenging channel that is open to the crank chamber.
3. The stratified scavenging two-cycle engine according to claim 1 , wherein a length of the scavenging channel is larger than a sum of a diameter and stroke of the cylinder.
4. The stratified scavenging two-cycle engine according to claim 1 , wherein the opening portion comprises a cutout.
5. The stratified scavenging two-cycle engine according to claim 1 , wherein the opening portion comprises a hole.
6. The stratified scavenging two-cycle engine according to claim 1 , the communication-preventing means comprises a crank weight that rotates in the crank chamber to close the starting point of the scavenging channel that is open to the crank chamber.