Air-fuel ratio control system for internal combustion engine

摘要

During an air-fuel ratio feedback control based on an oxygen concentration in exhaust gases which converges an air-fuel ratio toward a target ratio suitable for a satisfactory purifying efficiency of a catalyst, the air-fuel ratio is coercively deflected so as to make a fuel mixture richer and leaner alternatively. An extent of deflection of the air-fuel ratio is set larger before the catalyst has not yet been activated sufficiently.