1. Field of the invention
The present invention relates to an air fuel ratio controller for internal combustion engine, wherein an oxygen density in exhaust gas of an internal combustion engine is detected by an oxygen density sensor (hereinafter called "O.sub.2 sensor"), an air fuel ratio of a mixed gas to be supplied to the internal combustion engine is subjected to a feedback control, for example, to a theoretical air fuel ratio or around.
2. Description of the Prior Art
A prior art way of controlling an air fuel ratio is disclosed in Japanese Patent Laid-Open No. 140021/1976, wherein an O.sub.2 sensor output corresponding to an O.sub.2 sensor output voltage is integrated in consideration of an output characteristic of an O.sub.2 sensor installed on an exhaust system of an internal combustion engine to an air fuel ratio, and a fuel quantity is corrected according to the integration output, thus when actual air fuel ratio is disordered appreciably from a theoretical air fuel ratio, the fuel quantity is quickly adjusted, and when actual air fuel ratio approximates the theoretical air fuel ratio, the fuel quantity is gradually adjusted.
Meanwhile, such mode of control as disclosed above is still based on the condition that the output characteristic of the O.sub.2 sensor to air fuel ratio is always constant, however, the output characteristic fluctuates due to a deterioration of the O.sub.2 sensor practically, therefore a controllability desired on initial design cannot be maintained at the time of change in O.sub.2 sensor, thus causing a deterioration of emission.
Accordingly, an object of the invention is to provide an air fuel ratio controller for internal combustion engine capable of ensuring a control precision satisfactory to a desired air fuel ratio regardless of a change arising in the output characteristic of the O.sub.2 sensor due to deterioration or the like thereof.