Air-fuel ratio control system for an automotive engine

Claim 1

An air-fuel ratio control system for an automotive engine, comprising: an O 2 -sensor for detecting oxygen concentration of exhaust gas and for producing a feedback signal; first means responsive to the feedback signal for producing an air-fuel ratio signal; second means for producing a deviation signal representing the air-fuel ratio dependent on the air-fuel ratio signal from a desired air-fuel ratio; a first lookup table storing a plurality of basic fuel injection pulse widths from which one of pulse widths is derived in accordance with engine operating conditions; a second lookup table storing a plurality of maximum correcting quantities for correcting a derived basic fuel injection pulse width in order to correct deviation of air-fuel ratio due to change of a characteristic of a device used in the engine; third means for producing a necessary correcting quantity by multiplying a learning coefficient and a derived maximum correcting quantity; fourth means for producing a desired fuel injection pulse width in accordance with the necessary correcting quantity and the derived basic fuel injection pulse width; fifth means for updating the learning coefficient with a correcting value when deviation represented by said deviation signal is out of an allowable range; said correcting value being gradually reduced at every updating.