| 摘要 |
PURPOSE:To aim at improvement in scavenging efficiency with a crankcase compression ratio raised as well as to increase the quantity of air charge in this way while keeping the negative pressure inside a crankcase higher, by separating a scavenging passage from the crankcase via rotary valve members being secured to a crankshaft. CONSTITUTION:Rotary valve members 71 and 81, which rotate, being secured to a crankshaft 10, between a crankcase C and an opening 16 at the crankcase side of a scavenging passage 13 are installed. When suction air is compressed inside the crankcase, the opening 16 is blocked up by crank webs 71 and 81 so that capacity of the crankcase C is decreased and the crankcase compression ratio goes up whereby scavenging air pressure becomes increased. As a result, scavenging efficiency can be improved. In addition, since a possibility that some reflective waves could affect the inside of the crankcase C is checked and suction pressure inside the crankcase C is kept higher, augmentation of the charging quantity can be much expected. |
