Patent ID: 8249793

Claim:
An air-fuel ratio control apparatus for an internal combustion engine, comprising: an air-fuel ratio adjustment mechanism that adjusts an air-fuel ratio of the internal combustion engine; an exhaust gas air-fuel ratio detection unit that detects an air-fuel ratio of an exhaust gas; an ammonia sensor disposed in an exhaust system of the internal combustion engine; a catalyst disposed in the exhaust system to be located upstream of the ammonia sensor; an oxygen sensor disposed downstream of the catalyst; a first feedback portion that subjects the air-fuel ratio adjustment mechanism to a first feedback control such that the air-fuel ratio of exhaust gas becomes close to a target air-fuel ratio in a neighborhood of a stoichiometric air-fuel ratio, wherein the exhaust gas air-fuel ratio detection unit includes an air-fuel ratio sensor disposed upstream of the catalyst, and the first feedback portion performs the first feedback control on a basis of an output of the air-fuel ratio sensor; a second feedback portion that subjects the air-fuel ratio adjustment mechanism to a second feedback control based on an output value of the ammonia sensor; a third feedback portion that subjects the air-fuel ratio adjustment mechanism to the second feedback control based on an output value of the oxygen sensor or the output values of the ammonia sensor and the oxygen sensor, and a second feedback selection portion that selectively actuates the second feedback portion and the third feedback portion.