Air-fuel ratio control system for an internal combustion engine

Abstract

A fuel supply apparatus for an internal combustion engine comprises an air valve disposed in an intake air conduit upstream of a throttle valve and caused to rotate in accordance with the quantity of intake air through the intake conduit, a fuel supply source for supplying fuel under a substantially constant pressure through a fuel feed conduit to a fuel discharge port opened to the intake conduit, and a fuel metering device including a variable slit provided in the fuel feed conduit and interlocked with the air valve to be controlled such that the flow area of the variable slit may be proportional to the quantity of intake air and a fuel differential device for maintaining pressure difference across the variable slit at a predetermined value. The fuel pressure differential device comprises a first pressure chamber applied with a fuel pressure prevailing at the downstream side of the variable slit, a second pressure chamber having a constant pressure difference relative to the first pressure chamber and a constant differential pressure valve disposed in the fuel feed conduit downstream of the variable slit for controlling the pressure at the downstream side of the variable throttle passage to have the aforementioned pressure difference relative to the second pressure chamber. Further the pressure of the second pressure chamber is arranged to be automatically varied dependent on environmental and operating conditions of the engine such as atmospheric pressure, ambient temperature, engine temperature, acceleration and deceleration of the engine, whereby the pressure difference across the variable slit is varied so as to correct the air-fuel ratio.