AIR-FUEL RATIO CONTROL SYSTEM OF SUPERCHARGED LEAN-BURN GASOLINE INTERNAL COMBUSTION ENGINE

摘要

PURPOSE:To raise air density so as to enhance combustion efficiency for carrying out stable lean combustion by reducing the capacity of a small turbo charger in the area where proper supercharging effects at the boundary area between a lean air-fuel ratio area after a supercharging means exhibits supercharging effects and a theoritical air-fuel ratio operating area are weak though not zero. CONSTITUTION:A supercharged condition detecting means B detects a state in which supercharging is substantially carried out by a supercharger A. A lean air-fuel ratio setting means C sets air-fuel ratio to one leaner than theoritical air-fuel ratio, the air-fuel ratio being obtained from an engine when a supercharged condition detecting means B detects operation in which supercharging is carried out substantially. Thereafter, a boundary area identifying means E identifies a boundary area after setting of the air-fuel ratio is switched from basic to lean air-fuel ratio. Then a variable capacity mechanism control means F controls a variable capacity mechanism D so that the capacity of the supercharger A is reduced at the boundary area.