Fuel line purging device
BACKGROUND AND SUMMARY 
     The invention relates to fuel supply systems for fuel injected internal combustion engines, and particularly to a device for purging gases, including air and vapor, from the system. The purging device may be used in combination with the fuel injection systems shown in my co-pending application Ser. No. 808,135, filed Dec. 12, 1985, and U.S. Pat. No. 4,699,109. 
     In a fuel injection system, a fuel pump draws fuel from a fuel tank and delivers pressurized fuel through a pressure line to one or more fuel injectors. At initial start-up, the high pressure fuel line and the fuel pump may be devoid of fuel, particularly after a long lay-off or when the fuel system has run dry. The fuel injection system may have difficulty in pumping such air and/or vapor, and in any event requires longer engine cranking and difficult starting, as well as poor initial performance. 
     The present invention provides a simple and effective device for purging gases from the high pressure fuel line. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically shows a fuel injection system. 
     FIG. 2 is a cross-sectional view of a purging device in accordance with the invention, in an open position. 
     FIG. 3 is a view like FIG. 2, but showing a closed position. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a fuel injection system for an internal combustion engine having a fuel pump 2 communicating with and drawing fuel from a fuel tank 4 through a float bowl or a vapor separator 6 such as shown in my above noted co-pending application Ser. No. 808,135. Fuel pump 2 delivers pressurized fuel through a pressure line 8 to one or more fuel injectors 10, with a return fuel loop provided through a pressure regulator 12 controlling the fuel pressure in line 8. Purging device 14 has an inlet 16 connected to high pressure fuel line 8, and has an outlet 18 for venting gases, including air and vapor, to the atmosphere or returning same to vapor separator 6 or fuel tank 4. 
     Referring to FIG. 2, purging device 14 has a housing 20 with the noted inlet 16 and outlet 18. A pressure responsive valve 22 in the housing is movable between an open position, FIG. 2, permitting flow from inlet 16 to outlet 18, and a closed position, FIG. 3, blocking flow from the inlet to the outlet. A first branch passage 24 communicates between inlet 16 and one side 26 of valve 22. A second branch passage 28 communicates between inlet 16 and the other side 30 of valve 22. Restriction means in branch passage 28 is provided by a plug 32 with a central axially extending orifice 34 therethrough. The orifice restriction is selected to provide a fuel pressure drop thereacross but not substantially dropping air and/or vapor pressure thereacross. Pressurized fuel in inlet 16 from pressure line 8 is transmitted through branch passages 24 and 28 to the respective sides 26 and 30 of valve 22 and causes a higher pressure on side 26 than on side 30, to close valve 22 by moving it leftwardly to the closed position, FIG. 3. Air and/or vapor in inlet 16 from line 8 is transmitted through branch passages 24 and 28 to the respective sides 26 and 30 of valve 22 but does not cause sufficient pressure differential across valve 22 to close same, such that valve 22 is in the rightward open position, FIG. 2. 
     Biasing means are provided by a compression spring 36 biasing valve 22 rightwardly to the open position such that valve 22 is normally open. The force of spring 36 is overcome by the differential pressure across valve 22 responsive to fuel pressure. Valve 22 is provided by a flexible diaphragm 38 and an attached plate 40, to be described. 
     In operation at start-up with the fuel system filled with air and/or vapor, the fuel pump starts to pump air and/or vapor which exits through device 14. Valve 22 is held open by spring 36, whereby the air and/or vapor may escape fuel line 8, allowing fuel pump 2 to draw fuel from tank 4 and become primed. As the pump is primed and fuel enters the fuel loop and line 8, the fuel pressure rises. The increasing fuel pressure acts on the diaphragm and moves it leftwardly to close branch passage 28 and hence shut off flow to outlet 18, FIG. 3. Fuel pressure acts on both sides 26 and 30 of the diaphragm. Orifice 34 restricts fuel flow and causes the noted pressure drop, such that for a given fuel line pressure the right side 26 of the diaphragm is acted on by full pressure and the left side 30 of the diaphragm is acted on by a lower pressure, which in turn causes a differential pressure across the diaphragm, thus causing the diaphragm to move leftwardly to the closed position. The fuel injection system is now purged of air and vapor, and device 14 does not further affect operation of the fuel injection system. 
     Housing 20 includes a cavity 42. Flexible diaphragm 38 and its attached plate 40 divide cavity 42 into a first chamber 44 on the right side of diaphragm 38 and a second chamber 46 on the left side of diagraphm 38. Right chamber 44 is separated and sealed from left chamber 46 in cavity 42 by diaphragm 38. Right chamber 44 communicates with first branch passage 24. Left chamber 46 communicates with second branch passage 28 through restriction orifice 34 and also communicates with outlet 18. Diaphragm 38 is mounted between and forms a sealing gasket between right and left housing sections 48 and 50, and has an aperture therethrough aligned with branch passage 24. 
     Diaphragm 38 and plate 40 move leftwardly to block branch passage 28 to provide the noted closed position of valve 22 in response to fuel pressure responsive pressure differential overcoming compression spring 36 such that fuel flow from inlet 16 and branch passage 28 is blocked from reaching left chamber 46 and outlet 18. Fuel flow from inlet 16, branch passage 24 and right chamber 44 is blocked by diaphragm 38 from reaching left chamber 46 and outlet 18. Diaphragm 38 and plate 40 move rightwardly to open branch passage 28 to provide the noted open position of valve 22 in response to air and/or vapor in fuel pump 2 causing insufficient pressure differential across the diaphragm. In this open position, the gases, including air and vapor, flow from inlet 16 through branch passage 28 and restriction orifice 34 and through left chamber 46 to outlet 18. 
     Housing 20 includes an annular wall 52 defining branch passage 28 centrally therein and having an axial right end 54 engaged by plate 40 in the leftward closed position of diaphragm 38, FIG. 3. Compression spring 36 is disposed concentrically around annular wall 52 and bears between diaphragm 38 at plate 40 and housing wall section 56. Restriction plug 32 has a threaded outer surface 58 threadingly engaging the inner surface 60 of annular wall 52 defining branch passage 28 and is leftwardly screwed thereinto from axial end 54 engageable with plate 40 of diaphragm 38. 
     As above noted, valve 22 is in a normally open condition, allowing the purging of air and/or vapor. Spring 36 biases valve 22 to move in the same direction as flow through branch passage 28. Fuel pressure in right chamber 44 causes valve 22 to move in a direction opposite to the direction of flow through branch passage 28. 
     It is recognized that various alternatives and modifications are possible within the scope of the appended claims.