Abstract:
A permeation barrier fuel tank for a vehicle includes a tank shell having a wall formed from a plurality of layers. The layers include at least an inner layer, an outer layer, a fuel permeation barrier layer disposed between the inner layer and the outer layer and a nanocomposite outer layer disposed adjacent to the outer layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S)  
       [0001]    The present invention claims the priority date of copending U.S. Provisional Patent Application Ser. No. 60/172,567, filed Dec. 18, 1999. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates generally to fuel tanks for vehicles and, more particularly, to a permeation barrier fuel tank for a vehicle.  
         BACKGROUND OF THE INVENTION  
         [0003]    It is known to provide a fuel rank such as a plastic fuel tank in a vehicle to hold fuel to be used by an engine of the vehicle. In some vehicles, the plastic fuel tank is made from polymers that are typically multi-layer structures in which one or more barrier polymer layers are introduced to prevent unacceptable loss of fuel to atmosphere because of permeation through walls of the fuel tank. For example, a fuel tank may be composed of high-density polyethylene (HDPE) in which a layer of a barrier polymer, such as a polyamide or an ethylene-vinyl alcohol copolymer has been fabricated.  
           [0004]    Fuel tanks made by either blow molding or other thermoforming methods will possess a seam where the barrier layer is extremely thin or sometimes the barrier layer is incomplete. In these areas, there is a significant increase in fuel permeation to the atmosphere.  
           [0005]    One commercial approach to resolve this concern regarding permeation is to thicken the walls of the fuel tank, which increases the weight, cost and reduces fuel capacity of the fuel tank. Another commercial approach is to add metal sheets or shields to the fuel tank, which increases the weight and cost of the plastic fuel tank.  
           [0006]    Therefore, it is desirable to provide a fuel tank for a vehicle that has a more effective fuel permeation barrier to prevent evaporative emissions. It is also desirable to provide a permeation barrier fuel tank for a vehicle that significantly reduces evaporative emissions, weight and cost of the fuel tank.  
         SUMMARY OF THE INVENTION  
         [0007]    It is, therefore, one object of the present invention to provide a new permeation barrier fuel tank for a vehicle.  
           [0008]    It is another object of the present invention to provide a fuel tank that significantly reduces evaporative emissions without unduly increasing weight and cost.  
           [0009]    To achieve the foregoing objects, the present invention is a fuel permeation barrier fuel tank for a vehicle including a tank shell having a wall formed from a plurality of layers. The layers include at least an inner layer, an outer layer, a fuel permeation barrier layer disposed between the inner layer and the outer layer and a nanocomposite layer disposed adjacent to the outer layer.  
           [0010]    One advantage of the present invention is that a permeation barrier fuel tank is provided for a vehicle that has improved performance in reducing volatile fuel component emissions into the atmosphere from a seam or “pinch off” areas of the fuel tank. Another advantage of the present invention is that the permeation barrier fuel tank incorporates a nanocomposite polymer outer layer, resulting in cost savings of the fuel tank. Yet another advantage of the present invention is that the permeation barrier fuel tank significantly improves performance by reducing volatile fuel emissions Into the atmosphere from a body of the fuel tank. Still another advantage of the present invention is that the permeation barrier fuel tank has improved resistance to burning in the event of an external fire using a non-halogenated material. A further advantage of the present invention is that the permeation barrier fuel tank can still be manufactured using existing thermoforming processes.  
           [0011]    Other objects, features and advantages of the present invention wilt be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a perspective view of a permeation barrier fuel tank, according to the present invention.  
         [0013]    [0013]FIG. 2 is a sectional view taken along line  2 - 2  of FIG. 1.  
         [0014]    [0014]FIG. 3 is a fragmentary elevational view of a pinch off area of the permeation barrier fuel tank of FIG. 1. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    Referring to the drawings and in particular FIGS. 1 and 2, one embodiment of a permeation barrier fuel tank  10 , according to the present invention, is shown for a vehicle (not shown). The permeation barrier fuel tank  10  includes a tank shell  12 . In the embodiment illustrated, the tank shell  12  is of a generally rectangular type. The tank shell  12  includes a first or lower half shell  14  and a second or upper half shell  16 . The lower half shell  14  has a base wall  18  and a side wall  20  around a periphery of the base wall  18  and extending generally perpendicular thereto. The side wall  20  has a flange  22  extending outwardly and generally perpendicular thereto. The upper half shell  16  has a base wall  24  and a side wall  26  around a periphery of the base wall  24  and extending generally perpendicular thereto. The side wall  26  has a flange  28  extending outwardly and generally perpendicular thereto. The flanges  22  and  28  of the lower half shell  14  and upper half shell  16 , respectively, are joined together to form a seam by suitable means such as by thermoforming, compression molding or friction welding. The lower half shell  14  and upper half shell  16  are made of a rigid material such as a thermoformable plastic.  
         [0016]    Referring to FIGS. 1 and 2, the permeation barrier fuel tank  10  has the base walls  18 ,  24 , side wails  20 ,  26 , and flanges  22 ,  28  formed from a plurality of layers  30 ,  32 ,  34 ,  36 . The first or inner layer  30  is made from a thermoformable polymer such as a high density polyethylene (HDPE) or similar polyolefin, which is a conventional material known in the art. The inner layer  30  has a predetermined thickness of approximately two millimeters (2.00 mm).  
         [0017]    The second or fuel permeation barrier layer  32  is made from a barrier polymer as a barrier layer between the inner layer  30  and an outer layer  34  to be described. The barrier polymer is a polymer material such as a polyamide or an ethylene-vinyl alcohol (EVOH) copolymer which is a conventional material known On the art. The fuel permeation barrier layer  32  has a predetermined thickness of approximately 0.1 mm to approximately 1.0 mm.  
         [0018]    The third or outer layer  34  is made from a thermoformable polymer such as a high density polyethylene (HDPE) or similar polyolefin, which is a conventional material known in the art. The outer layer  34  has a predetermined thickness of approximately two millimeters (2.00 mm).  
         [0019]    The fourth or nanocomposite outer layer  36  is made from a nanocomposite polymer as a barrier layer adjacent the outer layer  34 . The nanocomposite polymer is a polymer material such as high density polyethylene (HDPE) in which a small quantity from about 0 wt. % to about 15 wt. % of a platy filler material has been uniformly dispersed. The platy filler material has particles with a high aspect ratio of about two hundred (200) to about one thousand (1000) where the thickness is of the order of one nanometer (1 nm) . The nanocomposite outer layer  36  is about 0% to about 15% of the total thickness of the layers.  
         [0020]    In manufacturing the permeation barrier fuel tank  10 , several conventional processes such as extrusion, lamination, etc., may be used. Preferably, the permeation barrier fuel tank  10  is formed by a conventional thermoforming process wherein the nanocomposite outer layer  36  can be thermoformed along with the outer layer  34  by heat and pressure. The presence of the platy filler material presents an efficient obstacle to the transport, i.e. diffusion, of penetrant molecules, such as those normally found in fuels. It should be appreciated that the incorporation of a polymer nanocomposite as the external layer for the nanocomposite outer layer  36  in a fuel tank provides a significant improvement in preventing permeation of fuel to the atmosphere. It should also be appreciated that nanocomposite polymer of the nanocomposite outer layer  36  provides an effective barrier to permeation both in the body of the fuel tank and in the seam or “pinch off” areas as illustrated in FIG. 3. It should further be appreciated that the nanocomposite polymer provides improved flame resistance over conventional unfilled polymers.  
         [0021]    The present invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation.  
         [0022]    Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced other than as specifically described.