AIR-FUEL RATIO CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

PURPOSE: To avoid the temporary change of the air-fuel ratio to the lean and the rich so as to prevent the lowering of transformation efficiency with three way catalyst by correcting the increase quantity in response to a difference between the air-fuel ratio just before the switching and the stoichiometric air-fuel ratio at the time of switching the target air-fuel ratio from the lean to the theoretical value with a change of the engine operation condition. CONSTITUTION: Operation condition whether an engine 1 is operated at the lean air-fuel ratio or the stoichiometric air-fuel ratio is decided on the basis of the detecting signal such as the engine speed detected by a crank angle sensor 8, the cooling water temperature detected by a water temperature sensor 6, the intake air quantity detected by an air flowmeter and a load or the like. A control unit 16 performs the computing on the basis of the program in response to the detecting signal from these sensors. Consequently, at the time of the lean air-fuel ratio, the fuel injection quantity is computed on the basis of the allocation coefficient, and drive is controlled. In the condition except for the lean, a difference between the value detected by the air-fuel ratio sensor 14 and the theoretical value is computed, and the air-fuel ratio is switched from the lean, and increase quantity is corrected, and as a result thereof, after switching an A/F specifying flag, the real air-fuel ratio is quickly condensed, and comes close to the stoichiometric air-fuel ratio.