Internal combustion engine with electronic air-fuel ratio control

Abstract

An electronic air-fuel ratio control apparatus in an internal combustion engine provided with an oxygen sensor emitting an output voltage in response to an oxygen concentration including the oxygen in nitrogen oxides in an exhaust gas from the engine. The apparatus controls the air-fuel ratio of an air-fuel mixture by a feedback correction-control based on a fuel injection quantity in an on-off manner. By using an oxygen sensor having a nitrogen oxides-reducing catalytic layer, the detection of a theoretical air-fuel ratio is performed on a richer side compared to the output on the detection of a theoretical air-fuel ratio by an oxygen sensor without the nitrogen oxides-reducing function, and is not changed even through the nitrogen oxides concentration changes. Accordingly, the feedback air-fuel ratio control acts to decrease the amount of nitrogen oxides so as to stabilixe the air-fuel ratio control. A first target air-fuel ratio for the air-fuel ratio feedback control is changed to a second target air-fuel ratio, which is richer than the first target air-fuel ratio when a high nitrogen oxide conentration in the exhaust gas is detected, or which is leaner than the first target air-fuel ratio when a high imcompletely burnt component concentration in the exhaust gas is detected.