Air/fuel ratio feedback control system adapted to temporary open-loop control under transient conditions

Claim 1

A control system for feedback control of the air/fuel ratio of an air-fuel mixture supplied to an internal combustion engine, the control system comprising: air/fuel ratio detection means for detecting actual values of air/fuel ratio in the engine from concentratins of oxygen in the exhaust gas of the engine; warm-up detection means for detecting a degree of warm-up of the engine; transient condition detection means for detecting predetermined transient operating conditions of the engine; control means for performing feedback control of the feed of at least one of fuel and air to the engine based on the detected actual values of the air/fuel ratio, said control means comprising shift means for shifting said feedback control to temporary open-loop control when any of sad predetermined transient operating conditions is detected; and timing means for variably determining the duration of said temporary open-loop control of the air/fuel ratio according to the detected degree of warm-up of the engine, said timing means comprising means for memorizing a set of values of said duration respectively assigned to different degrees of warm-up of the engine and means for making a selection from said set of values based on the degree of warm-up of the engine detected by said warm-up detection means; said shift means shifting said open-loop control to said feedback control after the lapse of a time the length of which has a predetermined relation to said duration determined by said timing means; wherein said set of values of said duration comprises a first set of values which are to be employed when the detected transient operating condition of the engine is an accelerating condition and a second set of values which are to be employed when the detected transient operating condition is a decelerating condition.