Exhaust gas recirculation system

An exhaust gas recirculation (EGR) system for use with an internal combustion engine having intake and exhaust manifolds, a carburetor induction passage having a venturi and a pressure sensing port adjacent the venturi for sensing the vacuum level therein, the system comprising;

• an EGR duct connecting the gases from the exhaust manifold to the engine intake manifold, and a one-piece integral assembly of a spring closed sonic flow EGR valve means in the duct normally closing the duct to prevent recirculation of gases and movable to open positions in response to a signal pressure acting thereon and a fluid pressure actuated servo means connected to the valve means for moving the valve means in response to the signal pressure,
• the servo means comprising a housing having a pair of annular flexible diaphragm means spaced from one another and together partitioning the housing into a plurality of fluid chambers, means connecting a first one of the chambers at all times to the venturi port, means connecting a second diaphragm means to the EGR valve means, and means subjecting the second diaphragm means to the actuating signal pressure for actuating the EGR valve means, a second one of the chambers having an air bleed valve assembly operably associated therewith to bleed the actuating pressure at times, the assembly including an air vent and a spring closed air bleed valve movably associated with the vent to control flow through the same, a part of the assembly being movable with the first diaphragm means to control the bleed of air to control the movement of the EGR valve means as a function of the change in venturi vacuum;
• the EGR valve means consisting of an essentially conical pintle mounted for a reciprocating movement into and out of a stationary cooperatively shaped nozzle valve seat to define convergent-divergent flow paths at all open positions of the pintle for the flow of exhaust gases therethrough, the valve means being so designed and constructed to provide sonic flow through the valve means over essentially the entire vacuum operating level of the engine to thereby establish a constant rate of flow of exhaust gases through the valve means at each open position of the valve means, the rates of flow through the valve means thereby varying solely as a function of the area opening of the valve means as determined by the position of the pintle in response to the change in venturi vacuum level controlling the signal pressure acting on the servo means and being independent of the pressure level variations adjacent the valve means;
• the bleed valve including a subhousing secured to the second diaphragm means and having a hole therein defining the air vent, a valve movably mounted in the subhousing, spring means biasing the latter valve into the hole to block the same, the second diaphragm means also having a vent therethrough into the chamber defined by the subhousing connecting the signal pressure at all times to the subhousing chamber.