Method for controlling the air-fuel ratio of an internal combustion

Abstract

Engine parameter signals indicative of the operating condition of the engine and an air-fuel ratio signal indicative of whether the air-fuel ratio condition of the engine is on the rich side or the lean side relative to a stoichiometric condition are produced. When the engine operates under a predetermined state, the fuel feeding rate to the engine is controlled in response to the engine parameter signals and the air-fuel ratio signal, by a closed loop control operation, in order to determine a learning control correction factor F.sub.G. In the closed loop control operation, a feedback correction factor F.sub.B is calculated depending upon the air-fuel ratio signal, and the fuel feeding rate is corrected depending upon the calculated factor F.sub.B, so as to control the air-fuel ratio condition to a condition close to the stoichiometric condition. At the same time, the learning control correction factor F.sub.G is adjusted, so as to settle the feedback correction factor F.sub.B within a predetermined range while at the same time maintaining the air-fuel ratio condition close to the stoichiometric condition. After the closed loop control operation is completed, the fuel feeding rate is controlled, by open loop in response to the engine parameter signals and the adjusted learning control correction factor F.sub.G, so as to control the air-fuel ratio condition at a desired condition which is different from the stoichiometric condition.