Patent ID: 8899019

Claim:
An air-fuel ratio control apparatus which controls an air-fuel ratio of an internal combustion engine based on an output of an upstream air-fuel ratio sensor provided in an exhaust passage to be located upstream, with respect to an exhaust gas flow direction, of an exhaust purification catalyst for purifying exhaust gas discharged from cylinders of said engine and based on an output of a downstream air-fuel ratio sensor provided in said exhaust passage to be located downstream of said exhaust purification catalyst with respect to said exhaust gas flow direction, said air-fuel ratio control apparatus being characterized by comprising: a determination section configured so as to determine whether or not said output of said downstream air-fuel ratio sensor falls within a predetermined range whose center corresponds to a target value corresponding to a stoichiometric air-fuel ratio; a reverse direction correction introducing section, operable when said output of said downstream air-fuel ratio sensor falls within said predetermined range, configured so as to temporarily introduce an air-fuel ratio correction in a reverse direction opposite to a direction requested by said output, wherein said reverse direction correction introducing section is configured so as to introduce a rich spike in a case where said output of said downstream air-fuel ratio sensor shifts to a rich side so that an air-fuel ratio correction in a lean direction is requested, and so as to introduce a lean spike in a case where said output of said downstream air-fuel ratio sensor shifts to a lean side so that an air-fuel ratio correction in a rich direction is requested; and a fuel injector operable to inject an amount of fuel based on the requested air-fuel ratio correction.