Apparatus and method for controlling air-to-fuel ratio in engine

摘要

If the output of an O2 sensor located downstream of a catalyst deviates from a predetermined range, the air-to-fuel ratio upstream of the catalyst is over-corrected to be a leaner value or a richer value beyond the predetermined purification-efficiency range when the output of the O2 sensor downstream of the catalyst indicates rich or lean, respectively, so that the output of the O sensor downstream of the catalyst returns within a predetermined range as soon as possible.