Patent ID: 7654252

Claim:
An air-fuel ratio control system for an internal combustion engine, which is applied to an internal combustion engine that includes: a catalyst that is provided in an exhaust passage of the internal combustion engine and that has a property of storing oxygen; an air-fuel ratio sensor that is provided upstream of the catalyst in the exhaust passage and that outputs a value corresponding to the air-fuel ratio of exhaust gas entering the catalyst; and an electromotive force type oxygen concentration sensor that is provided downstream of the catalyst in the exhaust passage and that outputs a value corresponding to the air-fuel ratio of exhaust gas flowing out of the catalyst, wherein the air-fuel ratio control system comprises: output value estimation means for estimating the output value of the oxygen concentration sensor using a catalyst model that estimates an oxygen storage amount of the catalyst, and an oxygen concentration sensor model that estimates the output value of the oxygen concentration sensor based on the estimated oxygen storage amount; integral value calculation means for calculating an integral value of deviation which is updated by integrating a difference between an actual output value of the oxygen concentration sensor and the estimated output value; correction value calculation means for calculating, based on at least the integral value of deviation, a feedback correction value for correcting a value corresponding to the output value of the air-fuel ratio sensor and/or a target air-fuel ratio; and air-fuel ratio control means for performing a control so that the air-fuel ratio of the exhaust gas entering the catalyst is equal to the target air-fuel ratio by controlling a first deviation to be zeros, the first deviation being obtained by correcting a difference between a detected air-fuel ratio detected based on the output value of the air-fuel ratio sensor and the target air-fuel ratio, using the feedback correction value.