Air-fuel ratio control apparatus

Abstract

An air-fuel control apparatus comprises an air-fuel ratio sensor comprising a gap portion for introducing exhaust gas generated from an engine, a solid electrolyte oxygen pump for controlling a partial pressure of oxygen in the gap portion and a solid electrolyte oxygen sensor producing an electromotive force in response to a proportion of the partial pressure of oxygen in the gap portion and a partial pressure of oxygen in other than the gap portion. The air-fuel control apparatus is further provided with an electronic control device including a pump current stopping means which controls a pump current from the solid electrolyte oxygen pump so that the electromotive force generated by the solid electrolyte oxygen sensor is maintained at a constant value, and controls not to feed the pump current when the engine is stopped, and a control device which operates the optimum quantity of fuel supply to thereby effect an air-fuel control by a gas mixture producing mean in an operational condition that the engine is not subjected to a feed-back control on the basis of an output signal from the air-fuel ratio sensor, and controls not to feed a pump current by the actuation of the pump current stopping means when the revolution number of the engine is determined to be lower than a predetermined value, i.e. the engine is stopped in an operational condition that the engine is subjected to the feed-back control on the basis of the pump current.