DEVICE AND METHOD FOR DETECTING INTER-CYLINDER AIR-FUEL RATIO VARIATION ERROR

According to a first aspect of the present invention, there is provided an apparatus for detecting variation abnormality in an air-fuel ratio between cylinders comprising a wide-range air-fuel ratio sensor (42) and an Osensor (56) provided in an exhaust passage upstream of an exhaust gas purifying apparatus (40) arranged in the exhaust passage (38) for an internal combustion engine (10) having a plurality of cylinders, air-fuel ratio controlling means for performing air-fuel ratio control for a predetermined period in such a manner as to make an exhaust air-fuel ratio be equal to a stoichiometric air-fuel ratio based upon output from the wide-range air-fuel ratio sensor (42), and abnormality detecting means for detecting variation abnormality in an air-fuel ratio between cylinders based upon output from the Osensor (56) for the predetermined period when the air-fuel ratio control is performed.