Abstract: An apparatus for purifying an exhaust gas on the basis of a single three-functional catalyst capable of oxidizing hydrocarbons and carbon monoxide, and simultaneously reducing nitrogen oxides, where a fuel-controlling means is provided for dividing driving conditions into an accelerating stage as zone I, a steady running stage as zone II, and a slowing-down and idling stage as zone III, and controlling an air-fuel mixture to be fed from a carburetor to a reducing state of the three-functional catalyst in zone I, a three-functional state in zone II, and an oxidizing state in zone III.

Abstract: A variable stage type carburetor having a throttle valve and a movable venturi vane cooperative with the throttle valve. This carburetor further includes a negative pressure responsive device for forcedly shifting the venturi vane in a direction to be closed, irrespective of an opening of the throttle valve, when the negative pressure in the venturi portion is lowered to less than a given value, and an accelerator pump for additionally supplying fuel to an intake passage commensurate to the opening action of the throttle valve. The accelerator pump is effectively operated when the opening of the throttle valve remains at an angle no more than a given degree, while the negative pressure responsive device is effectively operated, when the opening of the throttle valve is at an angle no less than a given degree.

Abstract: A gas mixture feed system provided therein with an exhaust gas recirculating passageway. The gas mixture feed system comprises: a throttle valve; a movable vane operationally associated with the throttle valve to regulate Venturi negative pressure; a variable stage type carburetor provided therein with a fuel metering device controlled by the movable vane; and an exhaust gas recirculating passageway for recirculating part of the exhaust gas of the internal combustion engine to the carburetor. The exhaust gas recirculating passageway has an opening within an intake passageway disposed between the movable vane of the carburetor and the throttle valve, whereby intake air and recirculating exhaust gas are uniformly mixed. Mounted in the exhaust gas recirculating passageway is a control valve which is mechanically connected to the movable vane so as to change the area of opening in accordance with the movement of the movable vane.