Abstract:
A fluid pulse damper having increased dynamic range and sensitivity, being especially useful in suppressing pulsations in the fuel supply rail of an internal combustion engine. The damper is a longitudinal gas-filled plastic pillow having walls formed by opposed flexible short sides and opposed flexible long sides, and includes at least one internal self-contact element, and preferably a plurality of such elements. As the short sides flex, the elements make contact internally, shifting the damper into a different compression regime and extending the pressure/response over an increased range of pressures. A feature of some embodiments is that the inner surface within the contact elements is shifted into tension after the elements make contact, thereby stiffening the damper and increasing the damper&#39;s resistance to further deformation. The damper is formed of a plastic such as ultra-high molecular weight polyethylenes, high flow polyetherimides, or tubing grade polyphthalamides.

Description:
TECHNICAL FIELD 
   The present invention relates to fuel rails for internal combustion engines; more particularly, to devices for damping pulses in fuel being supplied to an engine via a fuel rail; and most particularly, to an improved fuel rail internal damper having increased dynamic range. 
   BACKGROUND OF THE INVENTION 
   Fuel rails for supplying fuel to fuel injectors of internal combustion engines are well known. A fuel rail is essentially an elongate fuel manifold connected at an inlet end to a fuel supply system and having a plurality of ports for mating with a plurality of fuel injectors to be supplied. 
   Fuel rail systems may be recirculating, as is commonly employed in diesel engines. Fuel rails are more typically “returnless” or dead ended, wherein all fuel supplied to the fuel rail is dispensed by the fuel injectors. 
   A well-known problem in fuel rail systems, and especially in returnless systems, is pressure pulsations in the fuel itself. It is known that fuel system damping devices are useful in controlling fuel system acoustical noise and in improving cylinder-to-cylinder fuel distribution. Various approaches for damping pulsations in fuel delivery systems are known in the prior art. 
   For a first example, one or more metal spring diaphragm devices may be attached to the fuel rail or fuel supply line. These provide only point damping and can lose function at low temperatures. They add hardware cost to an engine, complicate the layout of the fuel rail or fuel line, can allow permeation of fuel vapor, and in many cases simply do not provide adequate damping. 
   For a second example, the fuel rail itself may be configured to have one or more relatively large, thin, flat metal sidewalls which can flex in response to sharp pressure fluctuations in the supply system, thus damping pressure excursions by energy absorption. This configuration can provide excellent damping over a limited range of pressure fluctuations but it is not readily enlarged to meet more stringent requirements for pulse suppression. 
   For a third example, a fuel rail may be configured to accept an internal damper comprising a sealed metal pillow typically having a flat oval cross-section and formed of thin stainless steel. Air or an inert gas is trapped within the pillow. The wall material is hermetically sealed and impervious to gasoline. Such devices have rigid sidewalls supporting and separating relatively large, flat or nearly-flat flexible diaphragm sides that can flex in response to rapid pressure fluctuations in the fuel system. The flexing absorbs the energy of the pressure spike and reduces the wave speed of the resultant pressure wave, thereby reducing the amplitude of the pressure spike. Internal dampers have excellent damping properties, being easily formed to have diaphragm-like walls on both flat sides, and can be used in rails formed of any material provided the rail is large enough to accommodate the damper within. An internal damper may be advantageous over the wall-formed damper, in that mechanical failure of the damper results only in flooding of the damper itself and not in an external fuel leak. 
   The damping characteristics of a prior art internal damper are a function of the thickness of the diaphragm wall, the total wall area, the volume of captive air, and the mechanical characteristics of the metal. To increase the damping capability of an internal damper by applying prior art technology requires an increase in the captive air volume, a thinner wall, or increased area of the walls. 
   Reducing wall thickness is not desirable because it reduces the functional margin between stress and yield. Increasing the diaphragm wall area is feasible provided that a) the resulting damper is flexible enough to achieve the desired minimum change in volume for a given change in pressure without approaching the material yield point; b) the resulting damper will withstand cyclic fatigue; and c) the resulting damper is still small enough to fit into the fuel rail. Increasing the size of a fuel rail to accommodate a damper having a larger diameter or longer length is highly undesirable because the space adjacent the engine in a vehicle is already highly congested and limited, and because a new fuel rail design or layout increases the cost of manufacturing an engine. 
   The damping response of a prior art metal damper is essentially linear and has a limited linear range of response. Thus, a damper having excellent low-amplitude damping characteristics also has a relatively short range of amplitude-damping response capability. What is needed in the art is a fuel rail internal damper that can be tuned to meet fuel system pressure requirements having a variable, non-linear, and progressive stiffness to accommodate a greater range of pressure fluctuations in a given damper volume. 
   It is a principal object of the present invention to provide a greater range of pulse amplitude-damping capability in a fuel rail internal pulse damper while requiring no change in the size of a fuel rail accepting the damper. 
   SUMMARY OF THE INVENTION 
   Briefly described, an improved internal pulse damper in accordance with the invention has increased dynamic range and sensitivity. The pulse damper is useful in suppressing pulsations within any fluid body, whether moving or still, and is especially useful in suppressing pulsations in the fuel supply rail of an internal combustion engine. 
   The improved damper is a longitudinal gas-filled pillow having a modified flat oval cross-sectional profile, with two long, flat flexible sides (the “diaphragm” sides) and two short non-flat flexible sides connecting the two long sides. The damper includes at least one internal self-contact element, and preferably a plurality of such elements, formed on the inner surface of the long sides. 
   As the long sides flex inwards, and the short sides also flex, at a predetermined level of pressure the one or more self-contact elements make contact internally, thereby shifting the damper into a different compression regime. Additional pressure can cause additional internal contact elements to make contact, thus shifting the damper into yet another one or more compression regimes, as only the diaphragm sides can undergo further deformation. The result is that the pressure/response performance of such a damper can be tuned by varying the shape and thickness of the walls and contact elements and is extended over a much greater range of pressures than can be obtained with a simple pillow as in the prior art. 
   Further, a damper in accordance with the invention is formed preferably of a plastic polymer having much higher compliance than the stainless steel used in prior art dampers. Typical classes of plastics suitable for use in an improved damper are, among others, ultra-high molecular weight polyethylenes, high flow polyetherimides, and tubing grade polyphthalamides. 
   A damper in accordance with the invention may assume any of several cross-sectional shapes permitting opposed sides to self-contact, thus increasing the stiffness and minimizing the resultant stresses during high pressure events. 
   In a preferred embodiment, the inner surfaces of the opposed long sides are each provided with two opposing longitudinal internal contact points which, when they meet, divide the internal space into a central chamber within the contact points and two peripheral chambers outboard of the contact points within the short sides. Further pressure causes further compression of the central chamber. An important element in providing the extended compression range in some embodiments is that the inner surface within the contact points is shifted into tension after the points make contact, thereby stiffening the damper and increasing the damper&#39;s resistance to further deformation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is a cross-sectional view of a prior art pulse damper; 
       FIGS. 2 through 7  are schematic cross-sectional views of six exemplary embodiments of variable-stiffness dampers in accordance with the invention; 
       FIG. 8  is a cross-sectional view of a currently-preferred embodiment of a variable-stiffness damper, shown disposed within a fuel rail in an engine; 
       FIG. 9  is an isometric wire drawing of the damper shown in  FIG. 8 ; 
       FIGS. 10 through 16  are cross-sectional views of the damper shown in  FIGS. 8 and 9 , taken over a range of external pressures to show the: progressive compression and distortion of the damper; and 
       FIG. 17  is a graph showing tensile stress in the damper at points A and B, as shown in  FIG. 10 , as a function of the pressure range shown in FIGS.  10  through  16 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , a prior art internal pulsation damper  10  for inclusion within a fuel rail for an internal combustion engine is formed as an elongate pillow  12 ,  FIG. 1  showing a transverse cross-sectional view thereof. Pillow  12  is provided with walls  13  having first and second flexible diaphragm sides  14  separated and connected by longitudinal rigid short sides  16  of height  17  (typically about 5.0 mm) which are typically curved as shown such that the cross-sectional shape is referred to in the prior art as a “flat oval.” Sides  14  are joined (not shown) at the ends of pillow  12 , as by compression of sides  14  (pinching) and welding of sides  14  together, to form a sealed chamber  18  within pillow  12 . Chamber  18  is filled with a gas, preferably air. Pillow  12  is disposed within a fuel rail (not shown in  FIG. 1  but similarly to improved damper  700  shown disposed in a fuel rail  760  in FIG.  8 ). The aspect ratio of pillow  12 , that is, the ratio of the typical height of sides  16  (5.0 mm) to the typical width of sides  14  (18 mm) is about 5.0/18=0.28. 
   In operation, pillow  12  is surrounded by fuel  22  being pumped from a source to fuel injectors (not shown) connected to the fuel rail. Hydraulic pulses being transmitted through fuel  22  are absorbed by inward/outward flexure of diaphragm sides  14  and corresponding compression/expansion of gas in chamber  18 . The work done in flexing the diaphragm sides and compressing the gas consumes the energy of a pulse. 
   Referring to  FIGS. 2 through 7 , schematic cross-sectional views of several exemplary embodiments of an improved internal pulsation damper in accordance with the invention are shown. For simplicity, in  FIGS. 2 through 5 , the wall thickness is omitted. All of these embodiments preferably are formed, as by extrusion, of a durable organic polymer, as described in more detail below, rather than of stainless steel as in the prior art. Each embodiment is formed as a modified flat oval generally similar in size and outer dimensions at rest to prior art damper  10 . 
   Referring to  FIG. 2 , embodiment  100  is formed having walls  113  having a plurality of accordion pleats  150  in short sides  116  separating diaphragm sides  114 . Sides  114  are of uniform thickness. Damping results from progressive compression of pleats  150  in response to pressure applied to sides  114 . Different ones of pleats  150  may be formed to have different thicknesses or otherwise differing flexural  20  characteristics such that resistance to compression of embodiment  100  increases progressively rather than linearly in accordance with Boyle&#39;s Law. Sides  116  are formed such that flexuring occurs at the inner  152  and outer  154  creases in pleats  150 . As the pleats progressively collapse and self-contact by flexing at creases  152 , 154 , both within and without chamber  118 , resistance progressively increases. As accordion pleats  150  become progressively compressed, diaphragm sides  114  undergo continued deformation to extend the dynamic range of the damper. 
   Referring to  FIG. 3 , embodiment  200  is similar to embodiment  100 , having walls  213  including generally pleated short sides  216  and diaphragm sides  214 ; sides  214  are of uniform thickness. However, pleats  250  are more general folds  252 , 254  rather than sharp creases  152 , 154  and stiffness is controlled by variable curvature of the pleat portions between the folds. This design can allow the damper to completely collapse some of the side walls at various pressure levels by self-contacting, thus increasing the stiffness and minimizing the resultant stresses during high-pressure events. 
   Referring to  FIG. 4 , self-contacting within a damper may be fostered and controlled by inclusion of one or more internal contact elements. In embodiment  300 , a self-contact element  302  extends from a first diaphragm side  314 - 1  of wall  313  across chamber  318  toward the second diaphragm side  314 - 2  of wall  313 . The length of element  302  is selected to provide a predetermined amount of flexure in sides  316  before element  302  makes contact with side  314 - 2 . After such contact has occurred, embodiment  300  becomes essentially two half-size mirror-image dampers  300 - 1 ,  300 - 2 , each having different pressure response characteristics than damper  300 . Thus the damper is moved into a different pressure/response regime. 
   Referring to  FIG. 5 , embodiment  400  shows that multiple self-contact elements  402  may be employed, and by careful selection of their various lengths, a progressive and controlled collapse of embodiment  400  may be produced in response to increasing pressure, first by flexure of short sides  416  followed by flexure of diaphragm sides  414 - 1 ,  414 - 2  of walls  413 . 
   Referring to  FIG. 6 , in embodiment  500 , walls  513  having diaphragm sides  514  have significant thickness, and taper in thickness from center to edge. Sides  514  can flex inwards under pressure. Under a predetermined external pressure, sides  514  self-contact. Due to the cross-sectional shape, the self-contact will initiate closer to the sides of the damper and work its way progressively towards the center of the damper as pressure continues to increase. This embodiment provides a continuously variable damper response characteristic. 
   Referring to  FIG. 7 , embodiment  600  is similar to embodiment  500  in having walls  613  including tapered diaphragm sides  614 , but short sides  616  are thinned down to provide greater flexure by providing first and second side galleries  620 - 1 ,  620 - 2  further defining first and second contact elements  602 - 1 ,  602 - 2 . As pressure is applied to embodiment  600 , not only do sides  614  flex inwards, but sides  616  also flex outwards until the contact elements meet, at which point the damper consists of three separate chambers: one central chamber and two lateral chambers formed from galleries  620 - 1 ,  620 - 2 . 
   Referring to  FIGS. 8 and 9 , a currently-preferred embodiment  700  is a refinement of embodiment  600  in that sides  716  of walls  713  are thinned still further to provide ready flexure at low pressures. Thus, at low pressures, embodiment  700  behaves much like embodiments  100 , 200 , 300 , 400  wherein short-wall flexure absorbs most of the energy in low-pressure fluctuations. When pressure is sufficient to cause first and second contact elements  702 - 1 ,  702 - 2  to touch, a central chamber  718  ( FIG. 12 ) is formed, and further energy absorption occurs principally by inward deformation of diaphragm sides  714 . The damper is thus an essentially two-stage device wherein the thin, curved&#39;side walls  716  respond to low-amplitude pressure waves, and the diaphragm walls  714  respond to high-amplitude pressure waves. 
   Embodiment  700  shown in  FIG. 9  is shown as open-ended, but of course that is simply a representative longitudinal portion of an actual damper, which would have ends  730 - 1 , 730 - 21  closed as by separate end pieces (not shown) or by being crimped and fused shut to capture gas within the damper in known fashion. 
   Referring to  FIGS. 10 through 16 , a finite element analysis of embodiment  700  shows deformations of sides  714  and  716  at various external pressures between 0 MPa ( FIG. 10 ) and 1 MPa (FIG.  16 ). It is seen that contact elements  702 - 1 ,  702 - 2  touch at about 170 kPa (FIG.  12 ). At pressures below that level, diaphragm sides  714  are urged toward one another almost without deformation by decreasing the radius of curvature of sides  716 . Once the contact elements meet, forming lateral chambers  720 - 1  and  720 - 2 , sides  716  participate very little in further pressure absorption. Embodiment  700  is shifted to a second pressure/response regime wherein deformations of sides  714  are accompanied by changes in volume in central chamber  718  (FIGS.  12 - 16 ). 
   Embodiment  700  introduces a new factor, variable tension in the structure itself, into the overall pressure absorption of a damper. Referring to  FIGS. 10 and 17 , it is seen that tensile stress in sides  716  (as measured at point B and shown as curve B) increases, as might be expected, at imposed pressures up to about 170 kPa, as the radius of sides  716  is progressively reduced. However, once the internal self-contact occurs, the stress at point B abruptly decreases. On the other hand, the tensile stress at point A (shown as curve A) increases essentially linearly up to about 600 kPa, and then decreases at still higher pressures. Finite element analysis shows that the reason for the continuation in stress at point A is the flattening of the arch  750  formed in each side  714  whereby the polymer molecules along the inner surface of the arch are drawn into extension. 
   Referring again to  FIG. 8 , in a currently-preferred configuration of embodiment  700 , as may be suitable for insertion into a fuel rail  760  of an internal combustion engine  770  for damping operating pulses in fuel  22  being supplied via fuel rail  760  to the combustion chambers (not shown) of engine  770 , overall height  780  may be about 5 mm; width  782  between the contact points, about 11 mm; height  784  of the gap between opposed contact points, about 0.8 mm; maximum height  786  between arches  750 , about 3 mm; thickness  788  of sides  716 , about 0.3 mm; and radius  790  of sides  716 , about 2.5 mm. 
   Materials suitable for forming a pulsation damper in accordance with the invention may be selected from a wide range of classes of organic polymers, including, but not limited to, polyimide, polyamide-imide, polyetherimide, polyphenylene sulfide, polysulfone, polyethersulfone, polytetrafluoroethylene, Ethylene Tetrafluoroethylene (ETFE), Per Fluoro Alcoxy (PFA), Fluorinated Ethylene Propylene (FEP), polyetheretherketone, partially or completely aromatic polyamides (PA6T/6I, PA6T/XT, PA6T/6I/66, etc.), aliphatic polyamides (PA6, PA66, PA612, PA46, PA11, PA12, etc.), acetal, ultrahigh molecular weight polyethylene, polypropylene, copolymers of polypropylen, polyethylene, metalocene polymers, polyurethane (i.e., isoplast), syndiotactic polystyrene, and aliphatic polyketone. Preferably, the yield strain of the polymer is around 10% or higher. For use in fuel rails, the polymer must have a high resistance to hydrocarbon and ethanol fuels and a temperature stability from about −40° C. to about 120° C. 
   A currently preferred polymer is a polyetherimide, available as GE Ultem 1010 from General Electric Corp., Schenectady, N.Y., USA. 
   While the embodiments shown were described as dampers used in fuel rails, it is understood, that a damper in accordance with the invention is not limited to fuel rails. A damper in accordance with the invention can be used in any fluid-containing vessel (liquid or gas) for the purpose of absorbing pressure excursions by energy absorption. 
   While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.