Electronic air-fuel ratio control apparatus in internal combustion engine.

摘要

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 same in nitrogen oxides in an exhaust gas from the engine controls an 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 the oxygen sensor having the nitrogen oxides-reducing catalytic layer, the detection of a theoretical air-fuel ratio is performed on a richer side comparing with 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 though the nitrogen oxides concentration changes. Accordingly the feedback air-fuel ratio control effects to decrease the amount of nitrogen oxides so as to omit mounting of EGR control system and to stabilize the air-fuel ratio control. In order to avoid changing of the controlled air-fuel ratio to the too much lean side when the engine is accelerated and then the injected fuel for the acceleration reaches in a certain delay period to an combustion chamber of the engine or in the driving state where the nitrogen oxides conversion of a ternary catalyst disposed in the exhaust system of the engine is unstable because of the disposition and the deterioration of parts, 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 at least when the high nitrogen oxide concentration in the exhaust gas is detected.