US Patent 7464698 Air-fuel ratio control apparatus of internal combustion engine

There is provided an air-fuel ratio control apparatus of an internal combustion engine capable of learning an air-fuel ratio and performing purge at the same time. When purge is being performed, in an air-fuel ratio learning routine, an air-fuel ratio deviation between an air-fuel ratio detected by an air-fuel ratio sensor and a target air-fuel ratio is computed by the use of a fuel vapor concentration detected in a concentration detection routine and then a learning correction value flaf to correct the computed air-fuel ratio deviation is computed.