BACKGROUND 
       [0001]    The present invention relates to high pressure fuel supply pumps and in particular to damping pressure pulses arising from the reciprocation of a pumping piston that pressurizes fuel for discharge from such pump. 
         [0002]    An increasing number of fuel systems for on-road vehicles are adopting the so called “common-rail” configuration, whereby a fuel pump maintains a reservoir or “rail” at a pressure at or above that required for fuel injection, and a plurality of injectors are in fluid communication with the rail via respective injection valves that are electronically actuated, thereby controlling the timing and quantity of fuel delivered from the rail to each cylinder of the engine. The pumps typically contain at least one pumping piston that is reciprocated by a cammed connection to the engine drive shaft. Common rail systems no longer require direct synchronization of a plurality of pumping pistons or rotating hydraulic head, with the injection events. Instead, the pump need only maintain the rail at the desired pressure. As a consequence, designers now favor single piston pumps for a wide variety of operating regimes. 
         [0003]    The high pressure pump is typically fed from a low pressure feed line entering the charging line of the pump. Due to the high rate of piston reciprocation of a single piston to produce a sufficient number of discrete quantities of high pressure fuel discharged into the rail, the charging system of the pump can experience significant back pressure pulses which produce unwanted noise and wear on the pump internals. Although techniques are known for back pressure relief to a low pressure sink or auxiliary accumulator, vehicle manufacturers seeking to conserve space in the engine compartment and save cost, are increasingly requiring even single piston fuel pumps to have internal damping, i.e., without flow to a low pressure fuel reservoir or fuel accumulator. 
         [0004]    U.S. Publication 2008/0175735 “Inlet Pressure Attenuator for Single Plunger Fuel Pump” and U.S. Pat. Nos. 7,401,594 and 7,124,738 (both titled “Damper Mechanism and High Pressure Fuel Pump”) describe techniques for internal damping of pressure pulsations in the low pressure side of a high pressure fuel pump. Two metal diaphragms are joined together around the circumference to envelope an internal volume of pressurized gas (“double diaphragm”). One or two such double diaphragm assemblies are situated in a damping chamber upstream of the inlet valve for the high pressure pumping piston. 
         [0005]    The damper system of U.S. Pat. No. 7,124,738 has some inherent drawbacks. Firstly, two convoluted diaphragms are welded to each other on the outer periphery. This creates a condition where the weld strength is compromised. Because the diaphragms are made from a thin material, the resulting weld bead is of a small cross-section and the assembly (with thin capsule shaped diaphragms) has minimal hoop strength and resistance to flexing at the weld. This was overcome according to the &#39;738 patent by clamping the diaphragms with significant force inboard of the weld bead. Secondly, the damper will be overstressed and fail in the convolutions if excess pressure pulsations are encountered due to activation of the high pressure system overpressure relief valve. When this relief valve is functioning, pressure pulsations of two to three times normal operation are encountered. Finally, when one of the flexible diaphragms does fail, the common volume of gas shared by the two diaphragms becomes filled with fluid, causing both diaphragms to become inoperable. 
       SUMMARY 
       [0006]    It is an object of the present invention to provide a plurality of single metal diaphragms that are configured into a small diaphragm assembly for a fuel inlet damper assembly or mechanism, but without the inherent problems associated with the use of a “double diaphragm”. 
         [0007]    This is accomplished by joining two metal diaphragms to respective two sides of an imperforate central plate, thereby creating two closely spaced diaphragm dampers, each acting upon its own gas volume. 
         [0008]    In one aspect, the disclosure is directed to an inlet fuel pressure damper mechanism for a high pressure fuel pump, comprising a central metal plate and two flexible metal diaphragms each separately joined to respective opposite faces of the central plate, thereby trapping two separate gas volumes between the central plate and each of the metal diaphragms, whereby each diaphragm reacts to pressure pulsations by deflecting independently against its respective gas volume. 
         [0009]    Preferably, the diaphragm assembly has (a) a rigid, relatively thick circular or polygonal central plate, (b) a first circular diaphragm having a rim portion sealingly secured as by welding to the plate and a relatively thin, flexible, convex portion projecting from one side of the plate and defining a first pressurized gas volume, and (c) a second circular diaphragm having a rim portion sealingly secured as by welding to the plate and a relatively thin, flexible, convex portion projecting from the other side of the plate and defining an independent second pressurized gas volume. 
         [0010]    The central plate does not flex during normal operation and acts as a stiffening member, thereby reducing the hoop stress and flexing of the weld. Additionally, the central plate can be configured with diaphragm stroke limiting features that reduce diaphragm flexing and stress when subjected to excess pressure pulsations as can arise when the high pressure system overpressure relief valve operates. 
         [0011]    In another aspect, the disclosure is directed to a pressure damper assembly for a fuel inlet passage in a single piston high pressure fuel pump, comprising an inlet fitting, a cover attached to the fitting and having a substantially cylindrical sidewall defining an internal chamber in fluid communication with the fuel inlet passage of the pump, and an open bottom with a bottom edge sealingly attached to the pump. At least one diaphragm assembly is supported within the damping chamber. Each diaphragm assembly includes first and second metal diaphragms having diaphragm rims sealingly secured to respective first and second sides of a central plate and convex central regions spaced from the central plate, thereby defining first and second independent closed gas volumes radially inward of a surrounding diaphragm assembly rim. In this way, feed fuel delivered to the pump through the inlet fitting flows through the damping chamber at a pressure that acts on the first and second diaphragms of each diaphragm assembly before entry into the inlet passage of the pump. 
         [0012]    A base plate can optionally be provided to close the bottom of the cover such that the damper unit is entirely independent of the pump except for attachment of the unit to the pump. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0013]    Embodiments of the invention will be described with reference to the accompanying drawing, in which: 
           [0014]      FIG. 1  is an overall schematic illustrating a fuel system for an internal combustion engine; 
           [0015]      FIG. 2  shows a first embodiment of the pressure damping diaphragm assembly of the present invention, which implements the function of the pressure damper of  FIG. 1 ; 
           [0016]      FIG. 3  shows a top view of the diaphragm assembly of  FIG. 2 ; 
           [0017]      FIG. 4  shows a second embodiment of the present invention; 
           [0018]      FIG. 5  shows one possible installation of the damper of  FIG. 4  within the pump described with respect to  FIG. 1 ; 
           [0019]      FIG. 6  shows a third embodiment of the present invention; 
           [0020]      FIG. 7  shows a pair of diaphragm assemblies according to  FIG. 3 , configured as a damper assembly; 
           [0021]      FIG. 8  shows the damper assembly of  FIG. 7  installed on a pump as an alternative embodiment to the configuration of  FIG. 5 ; and 
           [0022]      FIG. 9  shows another embodiment of a damper assembly according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  is an overall system schematic illustrating the fuel system for an internal combustion engine. The low-pressure pump  2  pressurizes fuel from the fuel tank  1 , and delivers it to the high pressure pump housing  3  through an inlet fitting. The fuel then passes through a pressure damper including diaphragm assembly  4 , and through a normally closed control valve  5 . Alternatively, the pressure damper could be upstream of the pump housing  3 . A normally open control valve is also applicable to such a fuel system. The fuel is then drawn into the pumping chamber  10 , where it is pressurized by the upward motion of the pumping piston  8  via the engine camshaft  9 . The control valve  5  is acted upon by the control valve spring  7  and solenoid  6  to control the quantity of fuel delivered by the high pressure pump. This is accomplished by the accurate timing of the control valve closing relative to the pumping piston upward travel position. When the fuel is pressurized, it then travels through the outlet check valve  11 , high pressure line  18 , and into the common rail  13  that feeds the engine fuel injectors  14 . Because the injectors  14  are fed from a common rail  13 , injector timing is flexible. Desired rail pressure is controlled by closed loop ECU  16  feedback and control of the high pressure fuel output via the solenoid  6  and control valve  5  compared to the rail pressure sensor  15  output signal to the ECU  16 . A pressure relief valve  12  is required to protect the high pressure system in case of a system malfunction. It is housed in a common fitting assembly  17 , which also houses the outlet check valve  11 . The pressure relief valve can also be used to control the maximum system pressure to a predefined limit to protect other fuel system components. 
         [0024]      FIG. 2  shows the first embodiment of the present invention, which is directed to the diaphragm assembly  4  of the pressure damper of  FIG. 1 . Each single metal diaphragm  20  and  21  is welded at its outer periphery by welds  22  and  23  to the surface of center plate  19 , thereby trapping two separate gas volumes  25  and  26 . The gas volumes can be at the same pressure, or each at its own pressure level (including vacuum), as set during each of the welding operations. The three-part diaphragm assembly (diaphragm  20 , diaphragm  21  and center plate  19 ) is situated in a damping chamber. The diaphragm assembly  4  defines two distinct and independent diaphragms  20 ,  21  configured as a very space-efficient unit. Because the center plate is not acted upon by fluid pressure, and because it is shaped to be much stiffer in flexure and hoop than the diaphragms, the weld beads  22  and  23  see a low cyclic stress. Therefore the mounting or support of the diaphragm assembly within the damping chamber need not be designed to minimize stresses on the welds  22 ,  23 . 
         [0025]    Center plate  19  can be a flat plate, or can incorporate a series of raised features  24  which limit the diaphragm deflection to a defined distance ‘a’. The raised features can be designed to contact the diaphragm in one or more locations, i.e., the raised features can be circular or discrete dimples or the like. Cooperating feature  29  is an annular, internally directed groove on the diaphragms, aligned with and intended for contacting the raised features  24  on the center plate. Features  29  can likewise be discrete dimples or the like. The stroke limiting feature  24  can also be designed to work without the annular groove  29 . When distance ‘a’ is reduced to zero during operation (as can be the case when the high pressure relief valve is in operation), the annular groove  29  of diaphragms  20  and/or  21  becomes supported by the center plate, minimizing any added stress in the diaphragms and allowing the two diaphragms to survive. After the excessive pulsations, each diaphragm will return to normal function, operating without contacting the center plate. Another advantage of the present invention is the added benefit of a lower level of function if one diaphragm should fail. If diaphragm  20  should fail, and volume  25  fills with fluid, diaphragm  20  will become inoperable. However, the diaphragm assembly  4  will still function to a lesser degree because damper  21  and volume  26  will remain functional. The periphery or rim  27  of the center plate  19  extends radially outside the welds  22 ,  23  and can be used to locate and secure the diaphragm assembly  4  without contact against any of the diaphragms  20 ,  21  or welds  22 ,  23 . 
         [0026]      FIG. 3  shows the top view of the diaphragm assembly of  FIG. 2 . Although the diaphragm assembly can be circular, the preferred embodiment as shown has a plurality of lobes  27  at a relatively larger radius from the center alternating with a plurality of flats  28  at a relatively smaller radius from the center. The diaphragm assembly is preferably supported within the damping chamber by a fixture or retainer, at the lobes  27 . The flats  28  allow fuel flow between the outer side of the upper diaphragm  20  and the outer side of the lower diaphragm  21  when the diaphragm assembly  4  is situated in an infeed fuel path in the damping chamber. The flow feature  28  could be almost any shape that allows adequate flow area. 
         [0027]      FIG. 4  shows a second embodiment  4 ′ of the present invention. In this embodiment, the periphery of the circular diaphragms is at the same radius as the periphery of the circular central plate, so mounting rim  27  is eliminated. The mounting support of the diaphragm assembly can be over or adjacent to the welds  22 ′,  23 ′, and the flow features similar to  28  of  FIG. 3  can be incorporated into a mating component. 
         [0028]      FIG. 5  shows one possible installation of the damper  4 ′ of  FIG. 4  within the pump  3  described in  FIG. 1 . Item  31  is an inlet fitting of the high pressure pump. Item  30  is a cover defining the damping chamber, which is closed by the pump housing  35 . Retainers  32 ,  33  and spacer  34  locate and provide feed fuel flow to the pair of diaphragm assemblies  4 ′. The retainer assembly  32 ,  33 , and  34  is compressed between an oblique or horizontal portion of the cover  30  and a substantially horizontal surface of the pump housing  35 . Retainer  32  is has a rim portion  32   a  that bears on and biases the top of the rim of the upper diaphragm assembly, retainer  33  has a rim portion  33   a  that bears on and biases the bottom of the rim of the lower diaphragm assembly, spacer  34  has a radially outwardly directed rim portion  34   a  that bears on and biases the bottom of the rim of the upper diaphragm assembly, and spacer  34  has a radially outwardly directed rim portion  34   b  that bears on and biases the top of the rim of the lower diaphragm assembly. The second retainer  33  fits within and is laterally fixed in position by a recess  38  in the pump that is in fluid communication with the fuel inlet passage  37 . 
         [0029]    The upper retainer  32  has a convex upper portion  32   b  including a plurality of cut outs or spaces  32   c  and the lower retainer  33  also has a convex lower portion  33   b  including a plurality of cut out or spaces  33   c.  The spacer is substantially ring shape, with spaced apart holes  34   c.  The cutouts, spaces, and/or holes in the retainers and spacers provide flow paths from all directions onto all four of the diaphragms. 
         [0030]    When the bottom edge  30   a  of the cover is welded to the top of the pump  35 , the compressed, biased condition of the rims of the diaphragm assemblies  4 ′ maintains the diaphragm assemblies in place within the damping chamber. Inlet flow path  36  provides communication with the low pressure pump  2  and outlet flow path  37  provides communication with the pump control valve. 
         [0031]      FIG. 6  shows a third embodiment  4 ″ of the present invention, as a variation of the diaphragm assembly of  FIG. 4 . The welds  22 ″ and  23 ″ are not located at the outer periphery of the diaphragms and center plate, but are instead through-welds on the diaphragm rims, which penetrate into the rim of the center plate. 
         [0032]      FIG. 7  shows a pair of diaphragm assemblies  4  according to  FIG. 3 , configured as a damper assembly  39 , and  FIG. 8  shows such damper assembly installed in a damping unit  40  on a pump as an alternative to the configuration of  FIG. 5 . 
         [0033]    The center plate  27  of each diaphragm assembly  4  has substantially flat upper and lower surfaces and a peripheral edge, with the upper and lower surfaces extending two dimensionally with a maximum radial span S 1  defined by the lobes  27  and a minimum radial span S 2  defined by flats  28 . The plate minimum span is at least equal to the radius R of the diaphragm rims, preferably greater, so the diaphragm rims are bonded to the plate inside the minimum span. Each diaphragm assembly  4   a,    4   b  is supported in the damping chamber  41  transversely to its plate  20 , at portions of the upper and lower plate surfaces that are outside the rims of the diaphragms, and each diaphragm assembly is laterally supported in the damping chamber, at portions of the peripheral edge of the plate. Preferably, each diaphragm assembly is supported in the damping chamber transversely to the plate, at upper and lower surfaces of the lobes  27 . The diaphragm assembly can be laterally supported in the damping chamber, at the peripheral edges of the lobes, or as shown, at the peripheral edges of the flats  28 . The upper and lower support can be at or include the weldments  22 ,  23  to the lobes. Whereas the diaphragms preferably have a circular circumference, the plate can be any regular geometric shape, such as a circle or polygon, and preferably substantially triangular with lobes at the corners. 
         [0034]    In many embodiments the periphery of the diaphragms is smaller than the periphery of the plate. The rim of each diaphragm is welded to the plate, such that symmetric portions of the plate extend radially outside the weld of the diaphragms to the plate. Support of the diaphragm assembly can be at the lobes, at radial positions that are optionally outside the rims of the diaphragms, on the periphery of the rims of the diaphragms outside the welds, over the welds, or inside the welds. 
         [0035]    In the embodiment of  FIG. 8 , each of the upper and lower diaphragm assemblies  4   a,    4   b  is supported within the damping chamber by a retainer assembly. A first retainer  42  of the retainer assembly has a rim portion  42   a  that bears on and biases the upper surface of one plate  27 , a second retainer  43  has a rim portion  43   a  that bears on and biases the lower surface of the other plate, and a spacer  44  has an inwardly directed portion  44   a  that bears on and biases the lower surface of the one plate and another inwardly directed portion  44   b  that bears on and biases the upper surface the lower plate. The upper and lower retainers have outwardly angled tabs  45  that snap vertically into slots  46  formed between the spacer  44  and the flats  28 . This holds the parts together as a unit  39  and restrains lateral displacement of the upper and lower diaphragm assemblies, respectively. 
         [0036]    Another embodiment with the diaphragm assemblies of the type shown in  FIG. 4  or  6  is shown in  FIG. 9 . The damper unit  47  is also attached to the pump  35  as a separate system. As with the other embodiments, a pair of upper and lower diaphragm assemblies is supported within the damping chamber  48  by a retainer assembly  49  that is somewhat similar to that shown in  FIG. 5 . A first retainer  50  has a portion that bears on and biases the top of the rim of the upper diaphragm assembly, a second retainer  51  has a portion that bears on and biases the bottom of the rim of the lower diaphragm assembly, and a spacer  52  has a radially outwardly directed portion that bears on and biases the bottom of the rim of the upper diaphragm assembly, and another radially outwardly directed rim portion that bears on and biases the top of the rim of the lower diaphragm assembly. The cover  53  retains a base plate  54  such that the damping chamber  48  is defined within the cover independently of the pump. When welded to the body, the cover  53  compresses the damper assembly  49  and thereby effectuates the biases among the first retainer, second retainer, spacer, and pair of diaphragm assemblies. The base plate  51  has an exit port alignable with the fuel inlet passage  37  of the pump. 
         [0037]    In  FIG. 9 , the upper and lower retainers  50 ,  51  have obliquely inwardly directed prongs  56  that engage the outer edges of the spacer  52 , thereby capturing and retaining the rims of the diaphragm assemblies. Another feature of the embodiment shown in  FIG. 9 , is that the retainer assembly  49  is radially restrained (i.e., substantially centered) within the cover  53 , by contact between the retainers  50 ,  51  and the sidewall of the cover. 
         [0038]    Alternatively, the retainer assembly  49  can be entirely self-supporting within the damping chamber, by a clamp or the like (not shown) provided between the base plate  54  and the first retainer  50  to compress the unit and thereby effectuate the biases among the first retainer, second retainer, and coil spring between a pair of diaphragm assemblies, without using the installation force of the cover  53 . In this and other embodiments, the spacer  52  can alternatively comprise a coil spring that urges the upper diaphragm assembly upward and the lower diaphragm assembly downward against respective upper and lower retainers.
A damper assembly for a fuel pump includes at least one diaphragm assembly formed by joining two metal diaphragms to respective two sides of an imperforate central plate, thereby creating a pair of closely spaced diaphragms, each acting upon its own gas volume. Preferably, the diaphragm assembly has (a) a rigid, relatively thick circular or polygonal central plate, (b) a first circular diaphragm having a rim portion sealingly secured as by welding to the plate and a relatively thin, flexible, convex portion projecting from one side of the plate and defining a first pressurized gas volume, and (c) a second circular diaphragm having a rim portion sealingly secured as by welding to the plate and a relatively thin, flexible, convex portion projecting from the other side of the plate and defining an independent second pressurized gas volume.