Method and apparatus for controlling the air-fuel ratio in an internal combustion engine

Claim 1

An air-fuel ratio control method of an interal combustion engine having at least one fuel injection valve, an exhaust gas sensor for detecting the concentration of a predetermined component in the exhaust gas and for generating a voltage signal which represents the detected concentration, and an electrical digital computer, said method comprising the steps of: intermittently sampling the voltage signal from said exhaust gas sensor to produce a first electrical signal indicative of the sampled voltage; detecting the operating condition of the engine to produce a second electrical signal indicative of the : detected operating condition; finding the maximum value and the minimum value of said first electrical signal; producing a maximum signal and a minimum signal by means of said digital computer in accordance with said maximum value and said minimum value, respectively, said producing step being performed only when said first electrical signal resulting in said maximum value is greater than a first setpoint and said first electrical signal resulting in said mimimum value is less than a second setpoint; calculating, by means of said digital computer, a reference value in accordance with said maximum and minimum signals by using a predetermined algebraic function; comparing, by means of said digital computer, the magnitude of the reference value with said first electrical signal to produce a third electrical signal indicative of the comparison result; calculating, in response to said second and third electrical signals, the fuel feeding rate to the engine to produce a fourth electrical signal indicative of the calculated fuel feeding rate, by means of said digital computer; converting said fourth electrical signal into a pulse signal having a variable pulse width which corresponds to said fourth electrical signal; and actuating, in response to said pulse signal, said fuel injection valve.