Patent GB-1454419-A (GB)
Title: Pilot valve for use in an exhaust gas recirculation
IPC: F02M25/07
Filed: 1973-12-21
Abstract: 1454419 Exhaust gas recirculation control valve BENDIX CORP 21 Dec 1973 [26 Dec 1972] 59512/73 Heading F1B [Also in Division G3]  Exhaust gas recirculation system for I.C. engines comprises a pilot valve which includes first pressure differential responsive means adapted to be exposed to ambient air pressure and to a pressure which varies as a function of engine air-flow and which, in use, generates a first force, second pressure differential responsive means adapted to be exposed to pressure signals whose difference is representative of the circulated exhaust gas flowrate and which, in use, generates a second force, and means for summing said forces, said means being operative to wave a piston member and thereby modulate in accordance with the intensity of the combined forces a signal for controlling the relative opening and closing of an exhaust gas recirculating valve, the modulated control signal providing said valve with a regulation such that the volume of exhaust gas being recirculated to the engines intake manifold varies in a proportion related to the engine air-flow. Valve 20 has a connection 48 to the Venturi of carburetter 41 and a connection 115 to a point downstream of the Venturi and upstream of the throttle valve 46. Fig. 2 shows the exhaust gas recirculation passage which is connected to valve 20 by pipes 37 and 36 which communicate the pressures 52 and 53 in the passage and in a Venturi 35 respectively to the valve. A valve 38 controls the amount of exhaust gas recirculated and is actuated by a diaphragm 13, one side of which is subject to atmospheric pressure and the other side of which is subject to a pressure Sx in pipe 16 connected to valve 20, which regulates the amount of exhaust gas recirculated in a predetermined relationship to engine air-flow. Operation. When engine air-flow is small but increasing, pressure Si from the carburetter Venturi will be less than atmospheric and decreasing. This pressure acts on diaphragm 170, which is subject to atmospheric pressure on its other side, and through passageway 21c' on diaphragm 80. A spring 227 holds valve 225 against seat 226 at small air-flows, so that pressures Sy and S 1  are equal. As air-flow increases, diaphragm 80 is lifted and tends to close valve 27 against seat 92, thus closing off a passageway 91 which communicates with atmosphere through chamber 22d, below diaphragm 80, and passageway 21d'. The pressure Sx then tends more towards the manifold pressure Pw which is established in chamber 122 by connection 115, and pressure Sx acts on diaphragm 13 to open valve 18. Pressures S 2  and S 3 , of which S 3  will be the smaller act on opposite sides of diaphragm 60 and produce a downward force in addition to a downward force caused by the difference between pressures S 3  and Sy which act on opposite sides of diaphragm 70. This downward force tends to move valve 27 on to seat 93, thus reducing the influence of manifold pressure on Sx and tending to reduce the flow of recirculated exhaust gas. The rate of flow of exhaust gas is ultimately limited by an orifice 39 downstream of valve 18, the difference between pressures S 2  and S 3  is no longer sufficient to balance the forces on valve assembly 23 and valve 27 engages seat 92. The reservior 122 which includes check-valve 124 then acts to maintain pressure Sx at a low level, although manifold pressure may vary, thus maintaining the flow of recirculated exhaust gas. As engine air-flow continues to increase, diaphragm 170 is pulled down and valve member 235 engages seat 236, pressure Sy becomes equal to atmospheric pressure, via air opening 229 and passage 221c', valve member 27 closes on to seat 93 and pressure Sx becomes equal to atmospheric so that recirculation valve 18 closes. In a modification a bi-metal spring acts on valve assembly 223 to inhibit recirculation of exhaust gas at predetermined engine or engine bay temperatures.