Patent ID: 7874143

Claim:
An air-fuel ratio control apparatus of an internal combustion engine, comprising: a catalyst arranged in an exhaust passage of the internal combustion engine; a downstream side air-fuel ratio sensor which is arranged in the exhaust passage downstream of the catalyst and outputs a value indicative of an air-fuel ratio of gas flowing out from the catalyst; a catalyst upstream air-fuel ratio estimating device which estimates an estimated upstream side estimated air-fuel ratio corresponding value which corresponds to the air-fuel ratio of gas discharged from a combustion chamber of the internal combustion engine into the exhaust passage based on an operating state of the internal combustion engine and a combustion state of the internal combustion engine; and an air-fuel ratio control device which controls, during a steady state operation, the air-fuel ratio of gas flowing into the catalyst based on the estimated upstream side estimated air-fuel ratio corresponding value and the output value of the downstream side air-fuel ratio sensor, wherein the estimated upstream side estimated air-fuel ratio corresponding value is obtained by: dividing a value representing an in-cylinder intake air quantity by a value representing a fuel injection quantity to obtain a result; and multiplying the result by a combustion rate coefficient to obtain the estimated upstream side estimated air-fuel ratio corresponding value, the combustion rate coefficient being calculated as a function of a speed of the internal combustion engine, the in-cylinder intake air quantity and a coolant temperature.