Air-fuel ratio control system

An air-fuel ratio control system for providing a required amount of air to a carburetor of an internal combustion engine, the carburetor having fuel passage means, including a fuel passage and means for receiving air from the atmosphere into the fuel passage for mixing fuel received in the fuel passage with the air for forming a combustible air-fuel mixture, which air-fuel ratio control system comprises:

• a catalytic converter installed on an exhaust passageway leading from the engine to the atmosphere;
• means, including a composition sensor provided on the exhaust passageway at a location between the engine and the catalytic converter, for sensing and producing a first output signal, proportional to the concentration of a component contained in exhaust gases emitted from the engine, which concentration is a function of the air-fuel mixing ratio of the combustible mixture combusted in the engine;
• first air passage means, communicating with the fuel passage, for feeding air from the atmosphere to the fuel passage;
• first actuator means for controlling the flow of air fed into the fuel passage by said first air passage means;
• means, responsive to said first output signal, for producing a second output signal representative of a desired duty ratio;
• duty ratio control means, responsive to said second output signal, for controlling the duty ratio of said first actuator means such that the duty ratio of said first actuator means equals said desired duty ratio;
• second air passage means, communicating with the atmosphere, for feeding air from the atmosphere to the fuel passage;
• second actuator means for controlling the flow of air fed into the fuel passage by said second air passage means;
• and
• air bleed control means, responsive to said second output signal, for controlling said second actuator means to open said second air passage means to permit the flow of air to the fuel passage means through said second air passage means together with the air flowing through said first air passage means when said second signal reaches a level indicating that said required amount of air exceeds a predetermined value.

An air-fuel ratio control system for providing a required amount of air to a carburetor of an internal combustion engine, the carburetor having fuel passage means, including a fuel passage and means for receiving air from the atmosphere into the fuel passage for mixing the fuel received in the fuel passage with the air for forming a combustible air-fuel mixture, which air-fuel ratio control system comprises:

• a catalytic converter installed on an exhaust passageway leading from the engine to the atmosphere;
• means, including a composition sensor provided on the exhaust passageway at a location between the engine and the catalytic converter, for sensing, and producing a first output signal proportional to, the concentration of a component contained in exhaust gases emitted from the engine, which concentration is a function of the air-fuel mixing ratio of the combustible mixture combusted in the engine;
• first air passage means, communicating with the fuel passage, for feeding air from the atmosphere to the fuel passage;
• first actuator means for controlling the flow of air fed into the fuel passage by said first air passage means;
• means, responsive to said first output signal, for producing a second output signal representative of a desired duty ratio;
• duty ratio control means, responsive to said second output signal, for controlling the duty ratio of said first actuator means such that the duty ratio of said first actuator means equals said desired duty ratio;
• second air passage means, communicating with the atmosphere, for feeding air from the atmosphere to the fuel passage;
• second actuator means for controlling the flow of air fed into the fuel passage by said second air passage means;
• and
• air bleed control means, responsive to said second output signal, for controlling said second actuator means to open said second air passage means to permit the flow of air to the fuel passage means through said second air passage means together with the air flowing through said first air passage means when said second output signal reaches a level indicating that said desired duty ratio exceeds a predetermined value.