Air-fuel ratio control system

Claim 1

An improved air-fuel ratio control system for a vehicle powered by an internal combustion engine having an induction passage, air-fuel mixture supply means, an electromagnetic valve for correcting the air-fuel ratio of the air-fuel mixture supplied by said means, an O 2 sensor for detecting oxygen concentration in exhaust gases, a first conparator for comparing the output of said O 2 sensor with a reference value and for producing an output signal relative to the comparison, and a feedback control circuit responsive to the output of said comparator for producing a control output signal for driving said electromagnetic valve for correcting the air-fuel ratio; wherein the improvement comprises means comprising an air-fuel ratio deviation detecting circuit responsive to the output signal of said first comparator for producing an output signal when the output signal of said comparator exceeds a predetermined condition at a transient state of the driving of said vehicle; means responsive to said output signal of said air-fuel ratio deviation detecting circuit for changing circuit constants of said feedback control circuit so as to expedite the operation of the feedback control circuit, a driving condition detecting circuit for disabling said air-fuel ratio deviation detecting circuit at a predetermined driving condition, said driving condition detecting circuit comprises a circuit responsive to ignition pulses of the engine for producing an engine speed signal, first comparator means for producing an engine low speed when the engine speed signal is lower than a predetermined value, and means responsive to said engine low speed signal for disabling said air-fuel ratio deviation detecting circuit.