Air-fuel mixture control for automobile engine having fuel injection system

Claim 1

An air-fuel ratio control system for an internal combustion engine of a type having a fuel injection system, said control system comprising, in combination: a fuel intake passage means for the introduction of air into said engine; a throttle valve disposed in said fuel intake passage means for regulating the flow of air flowing therethrough towards said engine; a fuel injection nozzle disposed in said fuel intake passage means for injecting a mist of fuel thereinto for the preparation of a combustible mixture with said air flowing therethrough; an exhaust passage means for the discharge of exhaust gases from said engine towards the atmosphere; an EGR passage means communicating between said exhaust passage means and said intake passage means for recirculating a portion of said exhaust gases from said exhaust passage means into said intake passage means; an EGR control valve means disposed in said EGR passage means for controlling the rate of recirculation of that portion of said exhaust gases which flow through said EGR passage means; a detecting means for detecting the rate of flow of air through said intake passage means in dependence on at least two of signals which are respectively indicative of engine speed, an opening of said throttle valve and a negative pressure developed inside said intake passage means at a position downstream of said throttle valve with respect to the direction of flow of said mixture towards said engine; a setting means operable during said recirculation of that portion of said exhaust gases and in response to an output signal from said detecting means for setting the rate of flow of fuel to be injected to a value which is required to lean said combustible mixture to such an extent as to be compensated for by the rate of flow of said exhaust gases recirculated into said engine in dependence on said detected rate of flow of said air; a first means for controlling the rate of flow of fuel to be injected in response to an output from said setting means; a composition sensor disposed in said exhaust gas passage means for detecting the concentration of a component of said exhaust gases which is a function of the air-fuel mixing ratio of said combustible mixture burned in said engine; a second means for controlling the opening of said EGR control valve means in response to an output signal from said composition sensor, said output signal from said composition sensor being supplied only to said second controlling means so as to enable said second controlling means to control said EGR control valve means so as to allow the passage of said exhaust gases recirculated at a rate of flow which is required to adjust said mixing ratio to a required value; and an EGR control means and a memory means for controlling said EGR control valve means in dependence on a control value which is stored in said memory means by detecting a transit operating condition of said engine, said transit operating condition including acceleration and deceleration of said engine.