Air/fuel ratio control system including means to well time start of feedback

Claim 1

A control system for feedback control of the air/fuel ratio of an air-fuel mixture supplied to an internal combustion engine, the control system comprising: an oxygen sensor which is disposed in an exhaust passage of the engine and comprises a first solid electrolyte cell having an oxygen ion conductive solid electrolyte layer provided with a reference electrode on one side thereof and a measurement electrode on the opposite side, reference means for maintaining a reference gas atmosphere containing a given amount of oxygen such that said reference electrode is exposed to said reference gas atmosphere, measurement means for defining a space which provides access to said measurement electrode for gases and restrictively admitting a fraction of the exhaust gas of the engine into said space and a second solid electrolyte cell having an oxygen ion conductive solid electrolyte layer provided with a pair of electrodes in such an arrangement that an externally supplied pumping current flows through the solid electrolyte layer to cause migration of oxygen ions therethrough and to thereby cause a change in the partial pressure of oxygen in said space; sensor means to detect the temperature of the engine; means for outputting a detection start signal after the lapse of a predetermined length of time from the start of the engine, said predetermined length of time being based upon the temperature of the engine, received from said sensor means, and decreasing as the detected temperature of the engine increases; detection means for supplying said pumping current to said second solid electrolyte cell in said oxygen sensor while controlling said pumping current so as to render the output voltage of said first solid electrolyte cell equal to a target value and producing an air/fuel ratio signal which is representative of the magnitude of the controlled pumping current, said detection means comprising means for suspending the supply of said pumping current to said second solid electrolyte cell in said oxygen sensor until receiving said detection start signal from said means for outputting a detection start signal; and control means for producing and outputting an air/fuel mixing ratio control signal based on said air/fuel ratio signal, said control means comprising discrimination means for ascertaining whether or not said output voltage is within a predetermined tolerance range containing said target value and suspension means for suspending outputting said air/fuel mixing ratio control signal if said output voltage is outside said predetermined tolerance range.