Patent ID: 6435171
Filing Date: 2002-08-20
Classification: F02D,Y02T

Abstract:
An air-fuel ratio control apparatus comprising:an air-fuel ratio detection device, provided in the exhaust system of an internal combustion engine, and outputs a signal approximately proportional to the concentration of oxygen in the exhaust; a lean operating determination device for determining whether the operating state of the internal combustion engine is in a predetermined lean fuel mixture region; a lean fuel mixture control device for controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine so as to be a leaner air-fuel ratio than the stoichiometric air-fuel ratio when it is determined by the lean fuel mixture region determination device that the operating state of the internal combustion engine is in the lean fuel mixture region; a check operating region determination device for determining whether or not the operating state of the internal combustion engine is in a predetermined region; a malfunction check device for checking for a malfunction of the air-fuel ratio detection device based on the output of the air-fuel ratio detection device when the operating state of the internal combustion engine is in the check region; and a malfunction check interruption device for interrupting the malfunction check when the check operation region determination device determines during an malfunction check by the malfunction check device that the operating state of the internal combustion engine is not in the check region and for prohibiting at the same time the lean fuel mixture control for a predetermined period of time.