Patent ID: 8191528

Claim:
An internal combustion engine comprising: a cylinder; a piston which reciprocates within said cylinder; a cylinder head which defines a combustion chamber in cooperation with said cylinder and piston; a spark plug which is provided in said cylinder head; and an intake valve and an exhaust valve each having a valve head which closely contacts with a corresponding valve seat of said cylinder head to seal said combustion chamber, wherein: said internal combustion engine has a valve overlap period for allowing both said intake and exhaust valves to be opened during the course of a cylinder cycle, and a geometric compression ratio of 13.0 or greater, said internal combustion engine being designed to satisfy, at a center timing of said valve overlap period, a conditional expression: S 1 ≧S 2 , where: S 1 is a cross-sectional area of said combustion chamber taken along any selected one of a plurality of mutually parallel hypothetical cutting-planes each of which extends parallel to a linear reciprocating direction of at least one of said intake and exhaust valves and passes through the valve head of said at least one of said valves; and S 2 is an effective opening area defined between the valve head of said at least one of said valves and the corresponding valve seat in a region on an outward side of said combustion chamber relative to said selected hypothetical cutting-plane.