Patent ID: 6854262

Claim:
An air-fuel ratio control apparatus of an internal combustion engine, comprising: an exhaust purification catalyst disposed on an exhaust passage of said engine; a first oxygen concentration detecting section detecting an oxygen concentration in an exhaust gas, on an upstream side of said exhaust purification catalyst; a second oxygen concentration detecting section detecting the oxygen concentration in the exhaust gas having passed through said exhaust purification catalyst, on a downstream side of said exhaust purification catalyst; an intake air amount detecting section detecting an engine intake air amount; a storage section storing a catalyst model that receives an oxygen amount which is not used for the oxidization/reduction in said exhaust purification catalyst and outputs the oxygen concentration in the exhaust gas downstream of said exhaust purification catalyst; a calculating section calculating the oxygen amount which is not used for the oxidization/reduction in said exhaust purification catalyst, based on the oxygen concentration in the exhaust gas upstream of said exhaust purification catalyst and the engine intake air amount, estimating parameters of said catalyst model, based on the calculated oxygen amount and the oxygen concentration in the exhaust gas downstream of said exhaust purification catalyst, and calculating an oxygen adsorption amount in said exhaust purification catalyst using the estimated parameters of said catalyst model; and a feedback control section feedback controlling an air-fuel ratio upstream of said exhaust purification catalyst based on the calculated oxygen adsorption amount.