Abstract:
The present invention relates to a connection assembly and method suitable for high-pressure applications. Specifically, end fittings securable to a fuel line may be configured to reduce the stress concentration factor between the fuel line and the end fitting. The end fitting is spherical and the mating structures have conical surfaces contacting the spherical end fitting to increase the assembly&#39;s tolerance of misalignments between the end fitting and mating fitting.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a high-pressure connection assembly for a fuel line with end fitting designed to allow for angular misalignment of a high pressure fuel line to a mating fitting in the connection so as to reduce the stress concentration factor between the end fitting and fuel line.  
       BACKGROUND OF THE INVENTION  
       [0002]     A high-pressure fuel line may be used to connect various components in a high-pressure fuel system (seeing pressures up to 180 bar), see  FIG. 1 . These fuel systems often utilize a metal-to-metal seal between mating components  16 ,  18  for robust sealing in various environmental conditions. Some end fittings  16  are designed with a flat backside  35  and a frontside  22  shaped as a half sphere, with offset radius center points A and B, to seal against the 60-degree conical surface  19  of a mating fitting  18 . A tube nut  8  is then used to fasten the fuel line  9 , which may be flexible, to the mating fitting with enough clamp force as to seal the metal-to-metal connection. The tube nut applies a force to the end fitting through a flat backside  35  of the end fitting  16  which is configured to interface with the mating fitting  18  at a 90 degree angle.  
         [0003]     Misalignments between end fitting and mating fitting may be accommodated by a flexible fuel line which includes crimp joints between the tubing of the fuel line and its end fitting.  
       SUMMARY OF THE INVENTION  
       [0004]     What is desirable is a high-pressure connection assembly for a fuel line with end fitting and mating fitting configured to reduce the stress concentration factor between the end fitting and fuel line. The connection assembly includes a mating fitting and retention structure and uses two less joins, i.e., eliminating the flexible line crimp joints.  
         [0005]     The end fitting has a spherical frontside and backside which complement the conical inner surfaces respectively of the mating fitting and retention structure.  
         [0006]     In one embodiment of the invention, the conical mating surfaces of the retention structure and the mating fitting define a 60 degree conical surface.  
         [0007]     Another aspect of this invention includes a fuel line assembly, having a fuel line configured to transport fluid at a high pressure and a connection assembly with an end fitting securable to the fuel line. The connection assembly defines a cavity into which the end fitting is fittable and which has facing bi-conical surfaces that cooperate with the end fitting to effect a seal.  
         [0008]     Another aspect of the invention includes a method of reducing misalignment-induced stress concentration in a high pressure fuel line assembly which includes a fuel line, end fitting, mating fitting and retention structure. The method includes configuring an inner cavity between the mating fitting and the retention structure with angular walls, configuring the end fitting with a backside and frontside respectively co-operable with the mirrored angular walls of the mating fitting and retention structure and positioning the end fittings in the cavity between the mirrored angular walls so that at least one of the backside and frontside are in sealing contact with at least one of the mirrored angular walls.  
         [0009]     More specifically, the present invention includes a high pressure connection assembly for a fuel line, having a mating fitting with a first connecting surface; an end fitting securable to the fuel line and matable with the mating fitting; and a retention structure for connecting the end fitting to the mating fitting and having a second connecting surface. The end fitting defines an orifice configured to permit fuel to flow from the fuel line to the matable fitting. Moreover, the end fitting defines a frontside and backside. The frontside is configured to sufficiently abut the mating fitting in a manner to effect a seal therebetween. The backside of the end fitting, in cooperation with the second connecting surface of the retention structure, is angularly or spherically configured with respect to the second connecting surface to complement the seal between the frontside of the end fitting and the mating fitting in a manner so as to reduce the stress concentration factor between the fuel line and the end fitting.  
         [0010]     The full spherical end of the fuel line fitting eliminates the stresses in the fuel line caused by angular misalignment between the fuel line and the mating fitting. The spherical end allows easier assembly when angular misalignment exists between the spherical end of the fitting and its mating conical fitting. The lower stresses and easier assembly accommodates more misalignment between mating components and may avoid the need for flexible fuel lines.  
         [0011]     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a schematic side sectional view, partly in elevation, of an end fitting with a flat backside and a frontside configured substantially as a half sphere to interface with a mating fitting at a 90 degree angle;  
         [0013]      FIG. 2  is a schematic side sectional view, partly in elevation, of a substantially full spherical end fitting with a backside substantially spherically configured in accordance with this invention to interface with the mating fitting in a manner so as to improve the stress concentration factor between the end fitting and a fuel line;  
         [0014]      FIG. 3  is a fragmentary perspective view of the substantially spherical end fitting on a high pressure fuel line isolated from the mating fitting;  
         [0015]      FIG. 4   a  is a schematic perspective view of a high pressure fuel line with a retention structure relatively rotatably connected and secured to the end fitting; and  
         [0016]      FIG. 4   b  is a schematic perspective view of a high-pressure fuel line with the improved substantially spherical end fitting and without the retention structure shown in  FIG. 4   a.    
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Referring to the drawings,  FIGS. 2 through 4   b , wherein like characters represent the same or corresponding parts throughout the several views there is shown in  FIG. 2 a  schematic sectional side view of a high-pressure connection assembly  10  for a fuel line  12  with end fitting  14  having a substantially spherical outer surface  15 . Fundamentally, the present invention includes a high pressure connection assembly  10  for a fuel line  12 , having a mating fitting  18  with a first connecting surface  19 ; an end fitting  14  securable to the fuel line and matable with the mating fitting; and a retention structure or tube nut  28  for connecting the end fitting to the mating fitting and having a second connecting surface  34  (as shown in  FIG. 2 ). The end fitting  14  defines an orifice  30  configured to permit fuel to flow from the fuel line  12  to the mating fitting  18 . Moreover, the end fitting  14  defines a frontside  20  and backside  36 . The frontside  20  is configured to sufficiently abut the mating fitting  18  in a manner to effect a robust seal therebetween. The backside  36  of the end fitting  14 , in cooperation with the second connecting surface  34  of the retention structure  28 , is angularly configured with respect to the second connecting surface  34  to complement the seal between the frontside  20  and the mating fitting  18  in a manner so as to reduce the stress concentration factor between the fuel line  12  and the end fitting  14 . The term “angularly configured with respect to” refers to the two surfaces having a relative angle (i.e. not parallel), such as a spherical surface positioned against a conical surface, as described herein.  
         [0018]     In high-pressure applications the end fitting must be securely sealed to the mating fitting  18  to prevent fuel from seeping out. Moreover, the end fitting and mating fitting  18  should be substantially sealed to maintain the desired pressure level within the fuel line  12 . The upper and lower portions,  24  and  26  respectively, of the frontside  20  of the end fittings  14  and  16  define substantially semi-spherical surfaces, the two portions ( 24  and  26 ) have slightly offset radius center points (A for the upper portion and B for the lower portion, respectively). The retention structure or tube nut  28  is fastened to the fuel line  12  for relative rotation with respect to the end fitting  14  and the threaded mating fitting  18  to provide a clamp force sufficient to seal the mating fitting  18  to the end fitting  14 . The end fitting  14  defines an orifice  30  to enable fuel to pass from the fuel line  12  to the mating fitting  18 . The mating fitting  18  also defines an orifice  32  which directs the fuel in the desired direction at a predetermined pressure.  
         [0019]     One technical advantage of the present invention is that the end fitting  14  is configured in a manner to compensate for angular misalignments between the fuel line and mating fitting and thereby reduce the stress concentration factor, if any, in the fuel line  12 . Therefore, joint performance is not compromised by moderate misalignment between the mating fitting  18  and the end fitting  14  due to the full spherical outer surface  15  as shown in FIGS.  2  though  4   b . In particular and with reference to  FIGS. 2 and 3 , the end fitting  14  has a substantially spherical frontside  20  and backside  36 . This configuration enables the end fitting  14  and fuel line  12  to accommodate moderate misalignments between the fuel line and the mating fitting  18  whereby to reduce the stress concentration factor between the end fitting  14  and fuel line  12 . The complementary spherical surface on the backside  36  of the end fitting  14 , like the frontside, also has upper and lower portions ( 24  and  26  respectively) which are formed by radii having similar offset centers. However, the offset is minimized so that the outer surface of the end fitting  14  is more circular. The outer surface of the end fitting  14  is configured to be compatible with the inner conical surfaces  19  and  34  of the mating fitting  18  and the retention structure  28 . Each of the fitting  18  and retention structure  28  approximately defines a 60 degree conical surface  19  and  34  respectively. Together they form a cavity  27  with facing bi-conical surfaces  19  and  34 . Such mirrored angular walls cooperate with the spherical end fitting to effect a seal when the end fitting is sandwiched between the conical surfaces. The substantially spherical surfaces  20  and  36  of end fitting  14  are designed to complement these conical surfaces. The retention structure  28  is threaded at  40  to fasten to the mating fitting  18 .  
         [0020]     The retention structure  28 , as shown in  FIG. 4   a , applies a force to the backside  36  of the spherical end fitting  14  through the conical inner surface  34 . The retention structure  28  reinforces and secures the seal or connection between the end fitting  14  and the mating fitting  18  for the fuel line  12 . An end fitting  14  and retention structure  28  are relatively rotatably fittable to each other at each end of fuel line  12  as shown in  FIGS. 4   a  and  4   b.    
         [0021]     The assembly  10  may rely on a two-fold sealing system as shown in  FIG. 2 . Primary sealing is provided through the contact between the angled surface  36  of the end fitting  14  and conical surface  34  of the retention structure  28 . If the primary seal is compromised—e.g., spherical surfaces  20  misaligning with conical surfaces  19 —a secondary seal may be desirable. An optional flexible sealing member  44  may also be included in the assembly  10 , as shown in  FIG. 2 , to prevent fuel from leaking outside of the assembly and to maintain the desired pressure level therein. The sealing member  44  (or as it may commonly be referred to the “o-ring”) is fittable between the mating fitting  18  and the retention structure  28 . The sealing member  44  acts as a secondary seal, sealing the threaded portion  40  of the mating fitting  18  from the right side  46  of the retention structure  28 .  
         [0022]     Another benefit of the present invention is that the connection assembly  10  requires less parts than the prior art assembly  42 . Specifically, the fuel line  12  has two fewer flexible line crimp joints between end fittings  14  and fuel line  12  than prior high pressure fuel connections. Moreover, the end fitting  14 , mating fitting  18 , and retention structure  28  are preferably made of stainless steel so as to reduce corrosion of the assembly parts under repetitious contact with various fuels.  
         [0023]     A method of reducing misalignment-induced stress concentration in a high pressure fuel line assembly requires configuring an inner cavity  27  between the mating fitting  18  and the retention structure  28  with mirrored angular walls  19 ,  34  and configuring the end fitting  14  with a backside  36  and frontside  20  which cooperate with the mirrored angular walls  19 ,  34  of the mating fitting  18  and the retention structure  25 . The positioning of the end fitting in the cavity  27  between the mirrored angular walls is such that at least one of the backside and frontside are in sealing contact with at least one of the mirrored angular walls.  
         [0024]     The reduction of stress in the fuel line  12  resulting from the end fitting  14  enables the connection assembly  10  to be operable in 100% of all six sigma stack-up conditions. Though each production part (end fitting  14 , fuel line  12 , mating fitting  18  and retention structure  28 ) may vary within certain tolerances the end fitting  14  is configured to accommodate part variations so that the performance of the pressure line connection assembly  10  is not compromised.  
         [0025]     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.