Air-fuel ratio control apparatus of internal combustion engine and method thereof

Abstract

The present invention has an object to provide an air-fuel ratio control apparatus of an internal combustion engine and a method thereof, for estimating with high accuracy an oxygen adsorption amount in an exhaust purification catalyst, and controlling the oxygen adsorption amount in the exhaust purification catalyst at an optimum amount, thereby enabling to maintain high exhaust purification efficiency. To this end, in the present invention, there is stored a catalyst model that receives an oxygen amount which is not used for the oxidization/reduction in an exhaust purification catalyst disposed on an exhaust passage of an engine, and outputs an oxygen concentration in an exhaust gas downstream of the exhaust purification catalyst, the oxygen amount which is not used for the oxidization/reduction in the exhaust purification catalyst is calculated based on the oxygen concentration in the exhaust gas upstream of the exhaust purification catalyst and an engine intake air amount, parameters of the catalyst model are sequentially estimated based on the calculated oxygen amount and the oxygen concentration in the exhaust gas downstream of the exhaust purification catalyst, an oxygen adsorption amount in the exhaust purification catalyst is calculated using the estimated parameters of the catalyst model, thereby feedback controlling an air-fuel ratio upstream of the exhaust purification catalyst so that the calculated oxygen adsorption amount reaches an optimum oxygen adsorption amount.