US Patent 7270119 Air/fuel ratio control device for internal combustion engine

An air-fuel ratio control apparatus for an internal combustion engine, implementing integral correction of the air-fuel ratio by an integral term edfii obtained by multiplying an integrated difference between a target air fuel ratio and the actual air-fuel ratio by an integral gain, wherein the upper and lower limit values of the integral term are set based on the actual intake air amount and the actual air-fuel ratio. This limits the range of the integral term edfii to prevent it from being set at an excessively high or low level removed from the realities of the intake air amount and the air-fuel ratio, and thereby to prevent erroneous air-fuel ratio correction by the integral term.