Abstract:
A fuel tank has a neck into which a flange of a level sender unit is to be sealed. A seal gasket surrounds the neck and is received between converging seal surfaces, one on the neck and the other on the flange, and the outside of the neck. A flange nut is provided to clamp the flange to the neck, thus compressing the gasket between the seal surfaces to effect a seal.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates to a fuel tank neck seal arrangement in which a gasket is used to provide a seal effective to seal a fuel tank against the escape of gasoline molecules from the tank.  
         BACKGROUND OF THE INVENTION  
         [0002]    Many new vehicles feature the use of blow-moulded plastic fuel tanks for a variety of reasons. The primary reason is often to maximise the volume of fuel that a vehicle may carry. The plastic tank enables this by virtue of the fact that it may be moulded into shapes that steel tanks may not be capable of, therefore effectively increasing the storage capacity of the same vehicle when compared to a steel tank.  
           [0003]    However, simple plastic fuel tanks bring with them other problems, primarily to do with emissions as molecules of gasoline are able to percolate through the polymeric structure of the material used for blow moulded fuel tanks (eg: high density polyethylene—HDPE).  
           [0004]    Fuel tank manufacturers have developed methods of minimising this percolation process. One method is to convert the inside skin of the tank by a chemical process called fluorination and another method is to ‘co-extrude’ another material with the HDPE such that a barrier is set up rather like an onion skin inside the main material of the tank wall (this barrier layer being a type of nylon).  
           [0005]    Once emissions from the main tank structure have been minimised, there still remains the problem of minimising emissions from the elastomeric seals that are used on some of the connections to the tank. One of the seals is that used on the so-called ‘level sender flange’.  
           [0006]    This flange is used to close an aperture in the fuel tank where the fuel level sender and the vehicle&#39;s electric fuel pump are assembled into the fuel tank.  
           [0007]    Many configurations of gasket have been seen in use to seal this opening, and many have deficiencies associated with, for example: manufacturing, product assembly and cost.  
           [0008]    [0008]FIGS. 1 and 2 show a typical flange-to-tank neck sealing arrangement such as found in many existing European vehicles. A tank neck  10  with an external thread  12 , a level sender edge flange  14  and a flange retaining nut  16 . A gasket  18  is fitted between the neck  10  and the flange  14 . The gasket has a significant influence on the variability of the nut tightening torque and applied load during assembly, and also influences the ease with which the assembly may be serviced.  
         SUMMARY OF THE INVENTION  
         [0009]    The proposed solution identifies a simple gasket arrangement that utilises a minimum of material, a low cost material, an improved initial assembly condition and an improved service condition. The gasket or seal method also affords an improvement to vehicle hydrocarbon emissions.  
           [0010]    According to the invention, there is provided a fuel tank neck seal arrangement in which a flange is to be sealed against the neck, the arrangement comprising a seal gasket surrounding the neck and received between converging seal surfaces, one on the neck and the other on the flange, with separate means being provided to clamp the flange to the neck, thus compressing the gasket between the seal surfaces to effect a seal.  
           [0011]    The seal surface on the neck is preferably moulded integrally with the tank, and the seal surface on the flange is preferably integral with the flange. The flange may be of metal or plastic.  
           [0012]    The converging seal surfaces can approach one another at a variety of different angles. Preferably both surfaces converge with each other at the same angle. Preferably the included angle between the surfaces is in the range between 5° and 25°. However any angle greater than 0° could be used.  
           [0013]    The seal gasket preferably has a D-shaped cross-section, and the flat part of the D-shaped cross-section will then fit against the neck between the converging seal surfaces. The seal gasket will be constrained on three sides but may be unconstrained on a fourth side.  
           [0014]    The seal gasket will be made of an elastomeric material which is impervious to gasoline molecules. Suitable materials will be well known to those skilled in the art.  
           [0015]    The flange can be clamped to the neck by a threaded nut which engages with an external thread on the neck. The external thread on the neck can be below the converging seal surface on the neck, so that the nut covers and protects the seal gasket.  
           [0016]    Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The invention will now be further described, by way of example, with reference to the accompanying drawings, in which  
         [0018]    [0018]FIG. 1 shows schematically a motor vehicle fuel tank;  
         [0019]    [0019]FIG. 2 is a section through a flange-to-neck joint in a prior art fuel tank;  
         [0020]    [0020]FIGS. 3 and 4 show a section through a flange-to-neck joint in accordance with the invention, in loose and tightened positions; and  
         [0021]    [0021]FIG. 5 shows the joint of FIG. 4 in additional detail. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    [0022]FIGS. 1 and 2 also show a conventional moulded plastics fuel tank with an irregular shape  20 , and a fuel filler neck  22 . The tank also has a level sender unit  24  installed through a neck  26  on the top surface. The sender unit  24  may be combined with fuel flow connections  28 , and will have a socket  30  for connection of electrical cables through which a fuel level signal can be sent to the driver&#39;s instrumentation.  
         [0023]    [0023]FIG. 3 shows a section through the neck  26  and a flange  32  of the sender unit  24 . A flange nut  34  has an internal thread at  36  which screws onto an external thread  38  of the neck  26 . An annular seal ring  40  surrounds the neck  26  and is received between an upwardly sloping rib  42  on the neck, and a downwardly sloping outer portion  44  of the flange  32 .  
         [0024]    The seal ring  40  is D-shaped in cross-section, and the flat portion of the seal ring circumference lies against the outer wall of the neck  26 .  
         [0025]    When the flange nut  34  is tightened, (see FIG. 4) the seal ring  40  is compressed between the outer wall of the neck  26 , the rib  42  and the flange outer portion  44 , to complete a seal between the interior and the exterior of the tank.  
         [0026]    The seal ring or gasket  40  is in a contained seating when fully compressed.  
         [0027]    The contained seating is constructed from an outer diameter on the neck of the fuel tank&#39;s sender aperture opening and two inclined faces, one face adjoins the outer diameter and the other face is constructed on the flange used to close the fuel sender opening.  
         [0028]    The ‘D’ section gasket  40  assembles over an outside diameter of the fuel tank neck  26  onto which it is a transition fit such that the tank may be reasonably handled during assembly without the seal simply falling off.  
         [0029]    The ‘D’ section seal is seated onto a face which forms an angle of somewhat less than 90° with the outside diameter mentioned above.  
         [0030]    The fuel level sender flange  32 , which closes the aperture in the fuel tank, also has an angled face, again of somewhat less than 90°, on its underside, where the ‘D’ section seal comes into contact with it.  
         [0031]    When the flange retaining nut  34  is driven down the thread on the fuel tank opening neck, the two angled faces (one on the neck, the other on the flange) contact the seal and the force vectors generated load the elastomer gasket inward toward the tank neck, deforming the seal to tend to fill the trapezium-shaped containment volume created by the tank neck and the level sender flange.  
         [0032]    Thus, the flange retaining nut, when driven home, abuts a combination of solid features (flange plus tank neck) and the drive torque required to complete the assembly suffers from far less variability than in systems where the elastomeric seal forms a component of the abutment of the flange nut assembly.  
         [0033]    Also, since the seal is housed in a containment volume of relatively precise proportions (when compared to other seals) and capable of close dimensional control, the seal is compressed by a known amount which suffers from minimal variability, allowing better choice of material type and sectional area, also bringing cost advantages.  
         [0034]    Service use is also benefited as any swelling of the seal which may take place due to exposure to hydrocarbons is minimised due to the very small contact available with the hydrocarbon via the mating face gap between the level sender flange and the tank neck upper face. Once swelling is minimised, no radical change in flange nut torque will be experienced. This is not the case where the gasket forms a component of the abutment of the flange nut assembly.  
         [0035]    [0035]FIG. 5 shows the solid abutment area, which also serves to limit liquid fuel exposure to the elastomeric seal, and the load vectors used to contain the ‘D’ section seal. The regions indicated at  46  represent the sealing surfaces; the arrows  48  represent the load vectors on the gasket; the heavy arrow  50  represents the gasket load onto the tank neck  26 , and the distance  52  represents the abutment of the flange  32  to the tank neck  26 . This abutment prevents overstressing of the gasket.  
         [0036]    This gasket/seal method may contribute to the emissions performance of the total vehicle in PZEV (Partial Zero Emissions Vehicle), ZEV (Zero Emissions Vehicle) and LEV (Low Emissions Vehicle) applications.  
         [0037]    Although this disclosure has been aimed at the use of this method of sealing in conjunction with blow-moulded plastic fuel tanks, the method could equally well be utilised with steel fuel tanks having a typical ‘cam lock’ method of retention for the fuel level sensor/fuel pump closing flange.  
         [0038]    The foregoing discussion discloses and describes preferred embodiments of the invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that changes and modifications can be made to the invention without departing from the true spirit and fair scope of the invention as defined in the following claims. The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words and description rather than of limitation.