System for controlling air-fuel ratio

Abstract

A system for controlling air-fuel ratio for a carburetor for an internal combustion engine having an intake passage, on air-fuel mixture supply device, a throttle valve, an exhaust passage, a detector such as an oxygen sensor for detecting the concentration of oxygen in the exhaust gases, an on-off type electromagnetic valve for correcting the air-fuel mixture and an electronic controller. The electronic controller comprises a comparing circuit for comparing the output signal of the detector with a reference, a proportional and integration circuit for producing a control signal connected to the comparing circuit, a triangular wave pulse generator, and a driving circuit for producing square wave pulses for driving the on-off type electromagnetic valve from the control signals of the proportional and integration circuit and of the triangular wave pulse, generator for controlling the air-fuel ratio to a valve approximately equal to the stoichiometric air-fuel ratio. A holding circuit for memorizing a voltage corresponding to the control signal during an idling operation connectable to the electronic controller. The holding circuit comprises a capacitor for, being charged with the voltage corresponding to control signal and an operational amplifier operated by the voltage charged in the capacitor. A first switch for connecting the capacitor to the electric controller, for charging the capacitor, a second switch for operative connection and disconnection, respectively, of the detector from the electronic controller circuit, and a third switch for connecting during a rapid deceleration that could cause misfiring the output of the amplifier to the electronic controller are provided.