Cylinder having a first plurality of intake ports and a second plurality of intake ports at respective first and second distances from a crankshaft

摘要

A combustion chamber of an internal combustion engine 150 has primary intake ports 158 located a first distance from a crankshaft (92, fig 1) and secondary intake ports 160 located a second distance from the crankshaft. One or more unidirectional valves, such as reed valves 174 & 176, are place in an intake duct 204 upstream of the primary intake ports 158. The valves prevent backflow from the cylinder into the intake when the pressure in the cylinder exceeds that of the intake. The backflow into the intake is reduced by having valves in the intake; therefore scavenging efficiency is improved. Furthermore, the asymmetry between the intake and exhaust port timing may be reduced by providing such valves. Additionally, the total intake port area can be increased with two sets of intake ports 158, 160 and valves 174 disposed in the primary ports 158, thereby improving the volumetric efficiency in spite of the pressure drop presented by the valves.