Secondary air supply system for the exhaust system of an internal combustion engine

Claim 1

A secondary air supply system for the exhaust system of an internal combustion engine, comprising a source of compressed air, an air control valve which supplies a part of the air delivered from said source to the exhaust system of the engine while relieving the rest of the air, an oxygen detector for detecting residual oxygen contained in the exhaust gases flowing through the exhaust system, a source of actuating fluid pressure different from atmospheric pressure, a change-over valve for said actuating fluid pressure, a controller which changes over said change over valve in accordance with the output of said oxygen detector, said air control valve having an inlet port for receiving air from said source of compressed air, an outlet port for supplying a part of the air received to the exhaust system, a relief port for relieving the rest of the air received, a first passage which connects said inlet port and said outlet port, a second passage which connects said inlet port and ssaid relief port, a valve element which reciprocally controls the openings of said first and second passages, first and second diaphragm chambers selectively supplied with either said actuating fluid pressure or atmospheric pressure by way of said change-over valve, at least one diaphragm which defines said individual diaphragm chambers and is connected with said valve element, first and second springs which are separate from said diaphragm and which reciprocally operate to balance said valve element at a neutral position where a predetermined opening ratio of said first passage to said second passage is established, said change-over valve having a first change-over position wherein it connects said first diaphragm chamber to said source of actuating fluid pressure while it connects said second diaphragm chamber to the atmosphere and a second change-over position where it connects said second diaphragm chamber to said source of actuating fluid pressure while it connects said first diaphragm chamber to the atmosphere, and throttle means for throttling only either one of two flows of fluid, one of which is the flow of fluid which flows through said change-over valve between said source of actuating fluid pressure and said diaphragm chambers, and the other of which is the flow of fluid which flows through said change-over valve between the atmosphere and said diaphragm chambers, wherein said diaphragm or diaphragms are adapted so as to shift said valve element against the balancing force of said first and second springs in the direction to increase the opening of said first passage and to decrease the opening of said second passage when the fluid pressure in said first diaphragm chamber is lower than the fluid pressure in said second diaphragm chamber, and so as to shift said valve element against the balancing force of said first and second springs in the direction to increase the opening of said second passage and to decrease the opening of said first passage when the fluid pressure in said second diaphragm chamber is lower than the fluid pressure in said first diaphragm chamber, said spring and said throttle means cooperating each time said change-over valve is actuated, to rapidly return said valve element to said neutral position by said first and second springs and to maintain said element for a while at said neutral position due to the delay of fluid flow caused by said throttle means and thereafter to gradually shift said element in one of said two directions in accordance with the fluid pressure in said first and second diaphragm chambers.