Patent ID: 6988486

Claim:
An air-fuel ratio control apparatus for a multiple cylinder engine, comprising: an exhaust passage into which exhaust gas from a plurality of cylinders in the multiple cylinder engine flows; a catalytic converter provided in said exhaust passage; air-fuel ratio detecting means, provided upstream of said catalytic converter in said exhaust passage, for generating a detection output corresponding to an exhaust air-fuel ratio; exhaust air-fuel ratio variation determining means for determining that there is a variation in exhaust air-fuel ratio between one cylinder and other cylinder when an output for one cylinder from said air-fuel ratio detecting means indicates one of a rich side and a lean side twice in succession, and in the meantime, an output for the other cylinder from said air-fuel ratio detecting means indicates other one of the rich side and the lean side from the air-fuel ratio indicated by the detection value for the one cylinder; and combustion air-fuel ratio control means for controlling the fuel injection quantity according to a detention output from said air-fuel ratio detecting means to adjust an average air-fuel ratio of exhaust gas flowing into said catalytic converter to about a stoichiometric air-fuel ratio, and for, when said exhaust air-fuel ratio variation determining means determines that there is a variation in the exhaust air-fuel ratio, compensating for the fuel injection quantity to reduce the variation.