Air-fuel ratio feedback control system having a single air-fuel ratio sensor downstream of a three-way catalyst converter

摘要

In an air-fuel ratio feedback control system including a single air- fuel ratio sensor downstream of a three-way catalyst converter, the coarse-adjusting term and the O.sub.2 adjusting term are calculated in accordance with the air-fuel ratio sensor, and a proportional amount of said O.sub.2 adjusting term is reduced in accordance with a degree of a deterioration of said catalyst converter, when the catalyst converter is deteriorated, to thus improve the drivability of a vehicle.