Air intake side secondary air supply system for an internal combustion engine

Claim 1

An air intake side secondary air supply system for an internal combustion engine having a carburetor and intake air passage with a throttle valve, comprising: an air-fuel ratio detection means for detecting an air-fuel ratio from an oxygen concentration of an exhaust gas of the engine and producing an air-fuel ratio signal; a first air intake side secondary air supply passage leading to the intake air pasage on downstream side of the carburetor and the throttle valve; an air control valve disposed in said first air intake side secondary air supply passage and adapted to vary a sectional area of the first air intake side secondary air supply passage in accordance with a magnitude of a pressure supplied to a pressure chamber thereof; a second air intake side secondary air supply passage leading to the intake air passage on downstream side of the carburetor and the throttle valve; a first open/close valve disposed in said second air intake side secondary air supply passage and opening and closing same in accordance with a content of said air-fuel ratio signal; a first air supply delay means disposed in said second air intake side secondary air supply passage on upstream side of said first open/close valve; a pressure supply passage for providing communication between said pressure chamber of the air control valve and a part of said second air intake side secondary air supply passage between said first open/close valve and said first air supply delay means; and a pressure control means responsive to a predetermined operating condition of the engine, for supplying a pressure capable of reducing an opening degree of said air control valve into said part of second air intake side secondary air supply passage between said first open/close valve and said first air supply delay means when the engine is operating under said predetermined operating condition.