AIR-FUEL RATIO CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

PURPOSE: To correct the reference output of an upper reaches sensor correctly by estimating the output characteristic of a lower reaches sensor during the operation of an engine to correct the output of the lower reaches sensor in the case of controlling the fuel injection quantity according to the output of the air-fuel ratio sensors disposed on the upper reaches and lower reaches of a three-way catalytic converter. CONSTITUTION: A linear output type first air-fuel ratio sensor 21 that can detect the air-fuel ratio degree of exhaust gas is disposed on the upper reaches of a three-way catalytic converter 9, and a step output type second air-fuel ratio sensor 22 suddenly changed in output voltage when an air-fuel ratio becomes near a stoichiometric air-fuel ratio is disposed on the lower reaches of the three-way catalytic converter 9. The fuel injection quantity is controlled so that the output of the upper reaches sensor 21 becomes the first output target value, and the reference output of the upper reaches sensor 21 to the stoichiometric air-fuel ratio is corrected on the basis of the difference between the output of the lower reaches sensor 22 and the second output target value. The output characteristic of the lower reaches sensor 22 is estimated during the operation of an engine, and the output of the lower reaches sensor 22 is corrected at the time of correcting the reference output of the upper reaches sensor 21.