Electronic closed loop air-fuel ratio control system

Claim 1

A mixture control system for an internal combustion engine having an exhaust gas sensor for generating a signal representative of the concentration of a predetermined constituent of the exhaust gases from said engine, said signal having high and low voltage levels depending on the concentration of said constituent gas when said gas sensor is above a nominal operating temperature and having said low voltage level when said sensor is below said nominal operating temperature, and means for supplying mixture to said engine in response to a feedback control signal derived from said exhaust gas sensor, comprising: first means for detecting when said exhaust gas sensor is below said nominal operating temperature; second means for clamping the magnitude of said feedback control signal to a predetermined voltage level in response to said first means; and third means responsive to said first means for generating a plurality of unipolar electrical pulses during a single uninterrupted open loop period of operation which vary periodically between first and second voltage levels, the first voltage level corresponding to said predetermined voltage level of said clamped signal, said second voltage level corresponding to enrichment of said mixture, said electrical pulses fed to said mixture supplying means.