Air-fuel ratio control system for use with internal combustion engine

Claim 1

System for effectively reducing oxides of nitrogen in exhaust gases emitted from a plurality of sequentially operative combustion chambers of an internal combustion engine, which system comprises: first means for generating a train of first pulses; second means for receiving said first pulses to count and to group the same every predetermined number of said first pulses, said predetermined number of said first pulses being in a prime relationship with the number of said plurality of sequentially operative combustion chambers; third means for generating a control signal indicative of an optimal air-fuel mixture to be supplied to the combustion chambers according to engine operating conditions; fourth means for reeiving both said control signal from said third means and said first pulses from said second means to generate a train of second pulses, each of said second pulses being generated within a time duration of said predetermined number of said first pulses in such a manner as to be modulated in width in dependence of said control signal; fifth means for controlling a fuel supply to the combustion chambers, which receives the train of said second pulses to alternatively supply a rich and a lean air-fuel mixture to each of the combustion chambers according to each of said second pulses.