Internal combustion engine secondary air control system

Claim 1

A relief valve for use in an internal combustion engine having an exhaust system and means for injecting secondary air for treating the exhaust gas, said relief valve comprising: a casing having a valve seat and a bore therethrough in communication with a source of secondary air that is pressurized by an air pump; a movable valve stem having a valve head that defines a pressure receiving area at one end thereof in opposition to said valve seat, said valve head being arranged with respect to said valve seat such that the pressure receiving area of said valve changes when said relief valve is open; a valve body having a bore therein for slidably receiving said valve head; a cap secured to said valve body, said cap including a central extension having a bore therein for receiving said valve stem and a first air bleed hole formed through the wall of said extension, said first air bleed hole being fully opened when said valve head is in engagement with said valve seat and said relief valve is fully closed, said first air bleed hole being closed by said valve stem when said valve head moves out of engagement with said valve seat, said bore in said extension, in combination with said valve stem, defining an air damping chamber; and spring means extending between said cap and said valve head for normally biasing said valve head against said valve seat; whereby relieved air pressure is not applied against said valve head when said relief valve is opened and the air damping chamber is operable to absorb the vibration due to the pulsating action of the air pressure caused by the output pressure of the air pump when the valve is opened.