Air-fuel ratio control apparatus of internal combustion engine

An air-fuel ratio control apparatus of an internal combustion engine, comprising:

• oxygen storage amount estimating means for estimating an oxygen storage amount of an exhaust purifying catalyst located on an exhaust path of the internal combustion engine, based on a history of an oxygen adsorption/desorption amount calculated from an air-fuel ratio of said internal combustion engine;
• downstream exhaust air-fuel ratio detecting means located downstream of said exhaust purifying catalyst on said exhaust path, for detecting an exhaust air-fuel ratio downstream of said exhaust purifying catalyst;
• maximum oxygen storage amount estimating means for estimating a maximum oxygen storage amount, based on an oxygen storage amount estimate estimated when the exhaust air-fuel ratio detected by said downstream exhaust air-fuel ratio detecting means is a predetermined air-fuel ratio;
• air-fuel ratio target setting means for setting a target of a controlled air-fuel ratio, based on the maximum oxygen storage amount estimate;
• and
• wherein said oxygen storage amount estimating means estimates the oxygen storage amount, based on a quantity of fuel supplied into a cylinder, which is predicted according to a fuel behavior model taking account of fuel attaching onto an internal surface of an intake path of the internal combustion engine.