Device for improving combustion efficiency of mixture in four cycle internal combustion engine

摘要

A device for improving combustion efficiency of mixture in a four cycle internal combustion engine is disclosed in which burnt gas is introduced, upon the intake stroke, into a combustion chamber from an exhaust passage to generate a swirl whereby fresh mixture supplied from an intake port to the combustion chamber is disturbed to form a strong swirl. To this end, the valve opening periods of intake and exhaust valves are partially overlapped with each other and a swirl generating guide wall is formed around an exhaust port and extends inwardly from the combustion chamber wall so that a part of burnt gas flows back, upon the intake stroke, into the combustion chamber through the exhaust port unclosed by the exhaust valve to impinge against the guide wall thereby to generate a swirl. A portion of the exhaust passage leading to the exhaust port may extend in a direction offset from the center of the combustion chamber so as to promote the generation of a swirl. Two exhaust ports may be provided instead of a single exhaust port.