For an internal combustion engine for a vehicle, comprising an exhaust manifold, a catalytic converter mounted to said exhaust manifold, an intake manifold, and a carburetor comprising a fuel jet;
- an air/fuel ratio control system, comprising:
- an oxygen sensor, mounted within said exhaust manifold, which detects the oxygen present within said exhaust manifold and produces a sensor output signal;
- a means for computing a corrective signal for controlling the amount of air for air bleeding and secondary air injection based upon said sensor output signal;
- a means for supplying secondary air to said exhaust manifold in an amount corresponding to an input signal;
- a means for supplying bleed air to said jet of said carburetor in an amount corresponding to an input signal;
- a means for feeding said corrective signal to said secondary air supply means and said air bleeding means;
- a vehicle road speed sensor which detects whether the road speed of the vehicle is at or above a predetermined first value which indicates that the vehicle is not in a heavily loaded condition;
- an engine cooling water temperature sensor which detects whether the temperature of the cooling water of the engine is at or above a predetermined second value which indicates that the engine is in a warmed up condition;
- an intake manifold vacuum sensor which detects whether the manifold vacuum is at or above a predetermined third value which indicates that the engine is in idling operation;
- a first engine rotational speed sensor which detects whether the rotational speed of the engine is at or above a predetermined forth value which indicates that the engine is at least in stable idling operation;
- a second engine rotational speed sensor which detects whether the rotational speed of the engine is at or above a predetermined fifth value which indicates that the engine is above the idling condition;
- and,
- a catalyst temperature sensor which detects whether the temperature of the catalytic converter is within a safe temperature range;
- wherein said corrective signal feeding means comprises:
- an air bleed signal cutoff device which intercepts the feeding of said corrective signal to said air bleeding means unless the road speed of the vehicle is at or above said predetermined first value and the temperature of the cooling water of the engine is at or above said predetermined second value;
- and,
- a secondary air signal cutoff device which intercepts the feeding of said corrective signal to said secondary air supply means when at least one of the following four conditions is encountered:
- (a) the temperature of the catalytic converter is out of said safe temperature range;
- (b) the temperature of the cooling water of the engine is at or above said predetermined second value, the manifold vacuum is at or above said predetermined third value, and the rotational speed of the engine is at or above said predetermined fifth value;
- (c) the temperature of the catalytic converter is within said safe temperature range, and the rotational speed of the engine is at or above said predetermined fourth value but is lower than said predetermined fifth value;
- and,
- (d) the temperature of the cooling water of the engine is below said predetermined second value, and the vehicle is not being decelerated and provided further that the following two conditions are met:
- that the manifold vacuum is at or above said predetermined third value and that the rotational speed of the engine is at or above said predetermined fifth value but not concurrently.