Feedback control apparatus for internal combustion engine

A feedback control apparatus for internal combustion engines comprising:

• an exhaust gas sensor for generating a detection signal indicative of the concentration of one component of the exhaust gases from an engine;
• an amplifier circuit for amplifying said detection signal, the gain of the amplifier circuit being variable;
• a first-comparator circuit for comparing an output of said amplifier circuit with a predetermined first reference value;
• a gain computing circuit responsive to the comparison result of said first comparator circuit to vary the gain of said amplifier circuit and thereby to maintain a maximum value of the output of said amplifier circuit substantially constant;
• a second comparator circuit for comparing the output of said amplifier circuit with a variable second reference value, the output signal of said second comparator circuit being a pulse signal having a variable time width which feedback controls the air-fuel ratio of said engine;
• a third comparator circuit for comparing an integrated value of the detection signal of said exhaust gas sensor with a third reference value corresponding to a predetermined air-fuel ratio;
• and
• a reference setting circuit responsive to an output of said third comparator circuit to vary said second reference value.