Air-fuel ratio control method for internal combustion engines

摘要

An air-fuel ratio control method for an internal combustion engine. The air-fuel ratio of an air-fuel mixture supplied to the engine is feedback-controlled to a desired air-fuel ratio dependent on operating conditions of the engine. When a transmission is being shifted or before a predetermined time period elapses after the shifting, the desired air-fuel ratio is held at a value assumed immediately before the shifting of the transmission. In another form of the invention, when the transmission is being shifted, or when the operating characteristics of at least one set of a set of intake valves and a set of exhaust valves have been not changed before the predetermined time period elapses after the shifting of the transmission, the desired air-fuel ratio is held at a value assumed before the shifting of the transmission.