Abstract:
An internal pulse damper for use in a fuel rail for an internal combustion engine. The damper is formed from a length of tubular metal stock having a flat oval cross-section and ends flattened by crimping to form a captive-air pillow. The end crimps are improved through use of tooling to eliminate a creased sidewall area vulnerable to stress failure in prior art pulse dampers. Such tooling includes constraints to prevent the tubing sides from flaring out and forming a longitudinal crease adjacent the end crimp during squeezing-shut of the tube end

Description:
TECHNICAL FIELD  
       [0001]     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 an improved end crimp for extending the useful life of the damper.  
       BACKGROUND OF THE INVENTION  
       [0002]     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 one or more ports for mating with one or more fuel injectors to be supplied.  
         [0003]     Fuel rail systems may be recirculating, as is commonly employed in diesel engines. Fuel rail systems are more typically “returnless” or dead ended, wherein all fuel supplied to the fuel rail is dispensed by the fuel injectors.  
         [0004]     A well-known problem in fuel rail systems, and especially in returnless systems, is pressure pulsations in the fuel itself. Therefore, damping devices are useful for controlling fuel system acoustical noise and for improving cylinder-to-cylinder fuel distribution. Various approaches for damping pulsations in fuel delivery systems are known in the prior art.  
         [0005]     For a first example, one or more 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.  
         [0006]     For a second example, the fuel rail itself may be configured to have one or more relatively large, thin, flat sidewalls which can flex in response to sharp pressure fluctuations in the supply system, thus damping pressure excursions by 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. Further, the thin sidewall can be accessible to accidental puncture.  
         [0007]     For a third example, a fuel rail may be configured to accept an internal damper comprising a sealed pillow, or metal bladder, 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 relatively large, flat or nearly-flat sides that can flex in response to rapid pressure fluctuations in the fuel system. 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.  
         [0008]     In simplest form, a prior art damper is produced by simply crimping together the ends of a flat oval steel or stainless steel tube to form a flat section. A hermetic seal is created by welding the resulting seam. The crimping process causes the sides to widen out in a gradual manor from the flat-oval section to the flattened area. This results in an adequate end sealing method that will withstand pressure cycling for small dampers. However, this type of end form is inadequate for applications wherein larger dampers are required. The cyclic motion of the damping surfaces transfers the motion along the transition and can fatigue the material where it is bent over on itself. In this area, the material is stressed by the crimping operation. One solution is to fold the sides inward prior to flattening, forming thereby a “milk carton” type closure, as disclosed in commonly owned U.S. Pat. No. 6,655,354, which stiffens the ends and isolates from motion the areas wherein the material is bent over onto itself. This approach adds cost to the manufacturing process.  
         [0009]     What is needed in the art is an improved method of sealing the end of a pulse damper to produce a seal that can withstand working pressure cycles over the expected working lifetime of a pulsation damper.  
         [0010]     It is a principal object of the present invention to extend the working life of a pulsation damper in a liquid medium.  
       SUMMARY OF THE INVENTION  
       [0011]     Briefly described, an internal pulse damper in accordance with the invention is formed from a length of tubular metal stock having a flat oval cross-section and ends flattened by crimping to form a captive-air pillow. The end crimps are improved through use of improved tooling to eliminate a creased area of the sidewall that is vulnerable to stress failure in prior art pulse dampers. The crimp is made by altering the tooling to prevent the sides from flaring out as a result of the crimping operation. This results in stiffening of the end and changes the point where cyclic bending occurs during pulse damping. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0013]      FIG. 1  is a transverse cross-sectional view of a prior art pulse damper;  
         [0014]      FIG. 2  is a first longitudinal cross-sectional view of the prior art pulse damper shown in  FIG. 1 ;  
         [0015]      FIG. 3  is a second longitudinal cross-sectional view of the pulse damper shown in  FIGS. 1 and 2 , taken at 90° to the view shown in  FIG. 2 ;  
         [0016]      FIG. 4  is a transverse view of the damper shown in  FIGS. 2 and 3 , taken along line  4 - 4  in  FIG. 3 ;  
         [0017]      FIG. 5  is a first longitudinal cross-sectional view of portions of two adjacent pulse dampers in accordance with the invention during manufacture thereof, being crimped in tooling in accordance with the invention;  
         [0018]      FIG. 6  is a second longitudinal cross-sectional view of one of the portions shown in  FIG. 5 , taken at 90° to the view shown in  FIG. 5 ;.  
         [0019]      FIG. 7  is a transverse cross-sectional view taken along line  7 - 7  in  FIG. 6 ; and  
         [0020]      FIG. 8  is a cutaway view of a fuel rail, showing in cross-sectional view a pulse damper in accordance with the invention mounted within the fuel rail in an internal combustion engine. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     Referring to  FIGS. 1 through 4 , 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. The shown cross-sectional shape is known in the art, and referred to herein, as a “flat oval.” Pillow  12  is provided with first and second diaphragm sides  14  separated and connected by longitudinal rigid short sides  16  of height  17  (typically about 3.41 mm) which are typically curved as shown such that the cross-sectional shape is a flat oval. Sides  14  are joined at the ends of pillow  12 , as by compression of sides  14  (pinching) to form a crimp, defined by a flattened region  15  as shown in  FIG. 2 , and then welding  19  of sides  14  together as shown in  FIGS. 2 and 3 , 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  FIGS. 1 through 4  but similarly to improved damper  10 ′ disposed in a fuel rail  20  in an internal combustion engine  70  as shown in  FIG. 8  and discussed below). The aspect ratio of pillow  12 , that is, the ratio of the typical height of sides  16  (4.8 mm) to the typical width of sides  14  (17.2 mm) is about 4.8/17.2=0.28.  
         [0022]     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 sides and compressing the gas consumes the energy of a pulse. The damping characteristics of pillow  12  are limited, in part, by the volume of chamber  18 .  
         [0023]     A problem with a damper formed in accordance with the prior art is that the flat oval shape is compressed at each end by a press (not shown) to form the flattened region  15 . As short sides  16  are subjected to a progressively smaller radius, the long sides  14  are caused to freely flare outwards  21  until near and at region  15  the sidewall material collapses and is forced into a folded crease  23  along each side  16 . Such creasing deforms and weakens the structure of the metal of the tube and predisposes the metal to fatigue failure along the crease. It is a primary object of the invention to prevent the formation of a fatigue-inducing crease at the extremities of sides  16 .  
         [0024]     Referring to  FIGS. 5 through 7 , an improved internal pulsation damper  10 ′ is formed in a fashion similar but not identical to prior art damper  10 . A portion of a first improved damper  10 ′ a  is shown in  FIG. 5  along with a portion of a second improved damper  10 ′ b  in preferred tooling in accordance with the invention as described below. The improvement consists in providing lateral constraint elements  30  for preventing sides  16  from freely flaring out in a first transverse direction  31  during compression of the tube in a second transverse direction  33  and thereby forming creases  23  as in the prior art. Constraint elements  30  preferably comprises posts  32  spaced apart by essentially the long outer diameter of the raw tubing from which a damper is to be formed. Posts  32  may be connected by a cross-member  34  to provide a rigid U-shaped structure resistant to flaring forces generated during compression of the tubing. Preferably constraint elements  30  are rounded on the tube-bearing surface  36  to facilitate deformation of the tube into a crimp  37  without a sharp crease. Preferably, a loose-fitting trough  38  having sides  40  and a bottom  42  is provided for holding the raw tubing of the damper during deformation of the ends thereof in accordance with the invention.  
         [0025]     In preferred tooling, posts  32   a  and  32   b  are spaced apart longitudinally of the dampers adjacent an anvil  44  having an anvil surface  46  of a length preferably greater than the combined length of compressed regions  15   a  and  15   b  such that a portion  15   x  may be cut from the crimped material in a subsequent step (not shown, as by conventional punching) wherein adjacent pulse dampers are separated from each other. Anvil  44  may be reciprocable  45 . Such length extends the working life of a reciprocable  47  hammer  48  by requiring hammer  48  to have an equivalent length  50  greater than the length required simply to compress regions  15   a,   15   b.  Preferably, length  50  is selected to be less than the spacing of posts  32   a,   32   b  such that a distortion zone  52   a,   52   b  is created between the posts and the anvil/hammer, allowing the folding of the damper ends into a crimp  37  to proceed as follows without creating a crease  23 .  
         [0026]     As hammer  48  engages the raw tubing against anvil  44 , the tubing begins to flatten as in the prior art. Being constrained from free flaring as in the prior art, however, by posts  32 , the tubing becomes flattened against the posts, forming shoulders  54  as the distance between walls  14  diminishes and creating a quasi-rectangular cross-sectional shape, as shown in  FIG. 7 . The thus-planarized sidewalls  16  then flare out abruptly between the posts and the anvil/hammer by bending about the posts through an angle  56  of preferably about 45°. Simultaneously, walls  14  progressively approach each other in a smooth deformation  58 , ultimately forming region  15 . Thus, region  15  is formed as a transformation of the raw tubing “flat oval” profile without creating a longitudinal crease  23 . The folding is very similar to the “gable end” of a milk carton, as is well known in the prior art, except that the sidewalls flare radially outward to form region  15  as simply two thicknesses of material, rather than folding radially inward and then being tucked between walls  14  to form a complex region having both two and four thicknesses of material.  
         [0027]     In operation, lengths of raw metal tubing are provided having the proper diaphragm characteristics in walls  14  and support characteristics in walls  16 . The flat oval tubing has a short inner width  100 , a short outer width  102 , a long inner width  104 , and a long outer width  106 . Such lengths may be, for example, about 20 feet and sufficient to form a plurality of dampers  10 ′. The tubing is inserted into trough  38  with a first end of the tubing extending between posts  32   a  and across anvil surface  46 . Hammer  48  is engaged, forming a first closed end preferably having an extended region  15  including a region  15   x.  The hammer is retracted and the tubing is advanced along trough  38  past posts  32   a,   32   b  by a distance equal to the desired length of a pulsation damper plus region  15   x.  The hammer is again advanced to compress region  15   a,   15   x,   15   b,  completing the closure of a first damper  10 ′ a  and the initial closure of a second damper  10 ′ b.  This sequence is repeated until the length of tubing is exhausted. As noted above, subsequently each region  15   x  is chopped from the string of attached dampers  10 ′ to sever them and form a region  15  on the end of each, the regions  15   x  being discarded or recycled. The damper ends are then hermetically sealed as by welding, soldering, or brazing, and preferably by welding  19 .  
         [0028]     Referring to  FIG. 8 , improved damper  10 ′ may be suspended and secured in fuel rail  20 , for use in an internal combustion engine  70 , by capturing the pinched ends  15  of damper  10 ′ in mounts  60  disposed in the fuel rail, which may be attached to engine  70  as by brackets  72 .  
         [0029]     An internal fuel rail damper in accordance with the invention has a greatly extended working life when compared to a prior art damper. In an over-stress bench test, the improved damper was functional for more than 10 6  cycles, whereas the prior art damper failed in fewer than 10 3  cycles.  
         [0030]     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.