Patent ID: 8677957

Claim:
An internal combustion engine system comprising: a spark ignited internal combustion engine having a cylinder, a piston which reciprocates in said cylinder, a cylinder head which is arranged over said cylinder and forms a combustion chamber together with said cylinder and an upper surface of said piston, and an intake valve capable of shutting off air flowing into said combustion chamber; a fuel injector which directly injects fuel into said combustion chamber; a spark plug which is arranged on said cylinder head and makes a spark in said combustion chamber; an intake valve closing timing varying mechanism which varies a closing timing during a cylinder cycle of said intake valve; and a controller configured to control said intake valve closing timing varying mechanism to: vary a closing timing of said intake valve to regulate air charged in said combustion chamber in accordance with engine operating conditions; and in a first engine operating condition where a least volume of air is required to be charged into said combustion chamber, retard a closing timing of said intake valve to a most retarded crank angle which is after bottom dead center during a cylinder cycle and satisfies the following formulas such that an effective compression ratio is lowered to 6.1 or smaller: α≧−0.2685×ε0 2 +10.723×ε0+15.815; and ε0≧11.0 where: α is said most retarded crank angle which is expressed by a crank angle in degrees of deviation of said most retarded crank angle from a closest bottom dead center; and ε0 is a geometric compression ratio of said engine.