Air-fuel ratio control device for an internal combustion engine

Claim 1

An air-fuel ratio control device for an internal combustion engine comprising: a first sensor provided in an exhaust passage for detecting the oxygen concentration of exhaust gas; a control circuit having means for comparing the output voltage from said first sensor with a reference voltage so that an air-fuel ratio of the mixture being introduced into the internal combustion engine is discriminated as rich or lean with respect to stoichiometric air-fuel ratio during all operating conditions of the engine; means for supplying fuel into an intake passage of the internal combustion engine, so that when the air-fuel ratio of the mixture is leaner than the stoichimetric air-fuel ratio the amount of fuel is increased and when the air-fuel ratio of the mixture is richer than the stoichiometric air-fuel ratio the amount of fuel is decreased; a second sensor for detecting the accelerating operating conditions of the internal combustion engine, said second sensor having an output signal indicating engine acceleration and comprising a diaphragm-type switch having a diaphragm which is actuated by vacuum pressure drawn from the intake passage downstream of a throttle valve, said diaphragm-type switch sends an accelerating signal to the control circuit when the absolute value of intake pressure is abruptly increased; and means, responsive to said output signal, for changing said reference voltage to a value different from a predetermined value so that the air-fuel ratio of the mixture being controlled is changed so as to be richer only when the internal combustion engine is in the accelerating operating conditions.