System for controlling air-fuel ratio

Abstract

A system for controlling the air-fuel ratio for an internal combustion engine having an induction passage, an exhaust passage, a choke valve in the induction passage, an automatic choke device comprising a positive temperature coefficient (PTC) heater and a bimetal element connected to the choke valve, a detector for detecting the concentration of a constituent of exhaust gases passing through the exhaust passage, an electronic control circuit, an on-off type electromagnetic valve actuated by the output signal from the electronic control circuit for correcting the air-fuel ratio of the air-fuel mixture supplied by an air-fuel mixture supplier, and means for actuating the on-off type electromagnetic valve at a fixed duty ratio during cold engine operation. The electronic control circuit comprises a vacuum sensor for converting the amount of the induced air to an electric quantity, an engine temperature detector for converting the engine temperature to an electric quantity, a first calculating circuit for producing a proper desired air-fuel mixture ratio signal from the output signals of the vacuum sensor and of the engine temperature detector, and a second calculation circuit for producing an actual air-fuel ratio signal from output signals of the vacuum sensor and of the PTC heater. A summing circuit for summing the proper air-fuel ratio signal and the actual air-fuel ratio signal produces a pulse duty ratio correcting signal which is applied to the electronic control circuit for correcting the fixed duty ratio.