AIR-FUEL RATION CONTROL DEVICE FOR ENGINE

An air-fuel ratio control device for an engine comprises a three way catalyst arranged in the exhaust passage, an upstream-side air-fuel ratio sensor arranged in the exhaust passage upstream of the three way catalyst, and an downstream-side air-fuel ratio sensor arranged in the exhaust passage downstream of the three way catalyst. A first feedback correction coefficient is calculated on the basis of an output of the upstream-side sensor to make the air-fuel ratio equal to the stoichiometric air-fuel ratio. A smoothed value is calculated on the basis of an output of the downstream-side sensor, the absolute value of a changing rate of the smoothed value being smaller than the absolute value of the changing rate of the output of the downstream-side sensor. A second feedback correction coefficient is calculated on the basis of a deviation of the output of the downstream-side sensor from the smoothed value. The first feedback correction coefficient is corrected using the second feedback correction coefficient. An amount of fuel to be fed to the engine is corrected using the corrected first feedback correction coefficient.