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 passage 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 communicating said pressure chamber of said air control valve with 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; a second air supply delay means disposed in said pressure supply passage; and a pressure control means for supplying an air pressure for reducing an opening degree of said air control valve into said pressure supply passage between said second pressure supply delay means and said pressure chamber of the air control valve, during a predetermined operating condition of the engine.