Abstract:
A fuel tank and method of making the same having three polymeric sheet members arranged in a stacked relationship to define a first volume and a second volume. The first volume being separate from said second volume to provide a number of advantages, such as a barrier to prevent puncture, minimize vapor release, aid in cooling, define a reserve cavity, minimize fluid movement, and the like.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 09/770,097 filed on Jan. 24, 2001, which claims the benefit of U.S. Provisional Application No. 60/177,383, filed Jan, 24, 2000. This application further claims the benefit of U.S. Provisional Application No. 60/286,450, filed Apr. 27, 2001. The disclosures of the above applications are incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention generally relates to fuel storage apparatus and, more particularly, relates to a triple sheet thermoformed fuel tank with high performance aspects for use in light-duty vehicles.  
         BACKGROUND OF THE INVENTION  
         [0003]    It is well known in the art to provide fuel storage apparatus such as gas tanks to hold the fuel used by an engine adapted to propel a land vehicle. Two types of fuel tank are most common. A first type includes steel fuel tanks that generally comprise an upper shell half and a lower shell half joined by known manner to provide a steel storage fuel tank. The second type includes polymeric fuel tanks that are characteristically formed according to blow molding and, to a lesser extent, injection, and thermoform molding processes to provide a plastic fuel storage tank.  
           [0004]    In the past decade, global steel fuel tank production has experienced a significant decline while polymeric fuel tanks have enjoyed exceptional growth. Although steel fuel tanks are durable, they are also heavy weight, which increases fuel consumption. Polymeric fuel tanks are lightweight, relatively low cost and can be readily molded into complex shapes for optimum space utilization. Worldwide tailpipe emission limits and other competitive influences have finally caused automobile manufacturers to use polymeric fuel tanks in ever-greater numbers.  
           [0005]    Polymeric fuel tanks have problems. There are limitations imposed upon fuel tank apparatus by the molding equipment deployed for their manufacture. Improvements in the blow molding art are in particular required to meet new and more stringent light-duty vehicle emission limits. For example, fuel tank vapor emission limits represent new areas of heightened concern. The permeability of blow-molded fuel tanks has led some automobile manufacturers to reconsider the potential low permeability of hydro-formed steel fuel tanks to meet the more stringent fuel tank emission limits.  
           [0006]    Several potential areas of evaporative emission characterize fuel tanks. A first area of concern is permeability at a seam between two fuel tank halves in the case of steel and thermoformed fuel tanks, and along any seams of a blow-molded fuel tank. A second area of concern is emission at the openings at the tank interface with the external and internal fuel system components. The fuel system components generally include a Filler Pipe Assembly, a Vapor Control System, Engine Fuel and Vapor Lines, and a Sender Unit. Each of these fuel system components itself comprises an array of complex sub-components.  
           [0007]    The first problem area of permeability at a seam is greater in steel and thermoformed plastic fuel tanks than in blow molded fuel tanks. The art of blow molding is characterized by the expansion of a stream of thermoplastic within a hollow mold, as characterized by Boechker in Publication No. 2001/0013516 A1. The blow molding process yields a substantially seamless body. Multi layered streams of blow-molded plastic are also used for several aspects principally including impermeability.  
           [0008]    Seams are unavoidable characteristics of both steel and thermoformed plastic fuel tanks. Both processes contemplate the uniting of two fuel tank halves. The steel fuel tank industry is decreasing emissions at the seam with improved welding, adhesive, gasket, and coating technologies. The steel industry is also experimenting with steel blow molding. Thermoformed fuel tanks are now preferably composed of composite sheets that possess interior layers of non-permeable polymeric material, as set forth in International Publication No. WO 00/43230 to Sadr or U.S. Publication No. 2001/0045433 to Ellis. The composite sheet is co-extruded in known manner. The barrier layers are substantially thermally bonded together in a twin-sheet compression phase to provide a near non-permeable seam. Thus, permeability at the seam is less of a problem today than in the past.  
           [0009]    The second problem area of permeability at interfaces between a fuel tank and its fuel system components has lead to several advancements in polymeric fuel tanks in particular. For example, many of the fuel system components are integrated into the tank itself to reduce the number of openings and connections that contribute to fuel tank emissions. This approach is known as Ship-in-a-Bottle, and has been readily practiced in the steel fuel tank sector for some time. The Ship-in-a-Bottle (SIB) technique is particularly amenable in the thermoforming process. The SIB approach is problematic for blow molding, as described by Boechker in Publication No. 2001/0013516 A1. The SIB amenability of thermoforming will result in a relative decline of blow molded and a relative increase of thermoformed fuel tanks in the coming years. Although SIB has been demonstrated by technologically advanced blow molding practitioners, over-all economic factors favor a shift toward increased global thermoformed fuel tank production because of the ease with which the SIB technique may be implemented.  
           [0010]    The SIB technique has been adapted in recent years for a number of purposes. For example, in U.S. Pat. No. 6,138,859 to Aulph et al. an internal component-carrying cradle is adapted with baffle aspects that reduce the sloshing noises of moving fuel within the fuel tank. A cradle with baffle aspects and integral lines and connectors is also disclosed in Boechker in Publication No. 2001/0013516 A1.  
           [0011]    The SIB method has been practiced in the thermoforming industry for many years. For example, Spencer Industries Incorporated of Dale Ind. provides an eight-page brochure showing a “Door-In-A-Door” refrigerator door wherein it is written “During the twin sheet forming process, a three piece injection molded internal hinge assembly is inserted by means of a pick and place robot”. In the present case, the pick and place robot is positioned exteriorly adjacent the form station of a four-station Brown twin sheet thermoforming machine.  
           [0012]    In U.S. Publication No. 2002/0017745 to Vorenkamp et al. a hybrid thermoforming methodology is suggested providing a SIB function. Although it may be argued the thermoforming methodology is known in the art, such as in U.S. Pat. No. 3,779,687 to Alesi and U.S. Pat. No. 6,372,176 to Edendahl et al., the problem with the Vorenkamp method is that synchronization of two parallel lines would be problematic and far less productive, ultimately, than two conventional rotary style twin sheet thermoforming machines characteristic in the industry.  
           [0013]    The cradle carrying the internal fuel system components is characteristically made of the same material as the inside walls of the fuel tank. The thermal plastic cradle may be fused in place within the fuel reservoir by compressing the cradle against a heated wall of the fuel tank in the process of twin sheet thermoforming, as in U.S. Pat. No.  6 , 138 , 859 . Alternatively, an adapter for welding the cradle to the fuel tank wall may be attached to the cradle for this purpose as in Vorenkamp Publication No. 2002/0020487. A second method to locate a cradle within the fuel tank is with a combination of recesses and projections, for example, as in U.S. Pat. No. 6,176,260 to Hahner et al.  
           [0014]    The described shift from blow molding to thermoforming has caused the blow molding industry to enjoin the threat posed by twin sheet thermoforming by advancing the art. For example, Schwochert in International Publication No. WO 00/48859 discloses a fuel tank with a molded polymeric cover providing a fuel vapor collection chamber. According to Schwochert&#39;s method, the exteriorly visible fuel system components and body seams are enclosed with a polymeric cover by way of secondary operations thereby trapping any fuel vapors that may escape from the body seams and the connections of the fuel system components. According to this remedial approach, deployed blow molding machinery may be kept in service with the aid of such auxiliary intervention. One problem with the Schwochert approach concerns the bond between the cover and the complex tank body. It is anticipated that the cover itself will be difficult to bond to the polymeric fuel tank, which could result in unacceptable vapor leaks at the cover seam.  
           [0015]    Although thermoforming is amenable to the Ship-in-a-Bottle advantage, thermoforming nonetheless is a relatively new fuel tank enabling technology and several problems have been identified. In particular, once the fuel system components have been enclosed within a twin sheet thermoformed structure, access for further manufacturing subassembly and in-field service and repair must be provided in order to implement a thermoformed fuel tank. As may be appreciated by referring to FIG. 3 of International Publication No. WO 00/74965, this is not a problem with blow molding techniques. The blow molding process can be readily adapted to provide threaded flange elements upon an exterior surface of the fuel tank body wherein the threaded flanges receive a removable cap or a developed cover for both assembly and service purposes.  
           [0016]    In U.S. Pat. No. 6,179,145 B1 a thermoformed fuel tank with an inspection tower receiving a threaded sealing cover is suggested. Unlike International Publication No. WO 99/56977, which disclosed a similar approach for a blow molded fuel tank, there is no suggestion in &#39;145 as to how this approach can be reduced to practice by a thermoforming practitioner. Although means for accessing internal fuel tank components for repair and service are clearly suggested, the approach of &#39;145 is found wanting in several ways. In particular, the inspection tower is provided so a service port can be opened and then later sealed by an in-field repair technician. This methodology does not contemplate using a service port to finally assemble and connect the fuel system components to the fuel tank body in the manufacturing stage. Therefore, these sub-assembly operations must occur before the fuel tank halves can be joined together in secondary operations, such as by the suggested method of welding. The &#39;145 scheme eliminates the inherent advantage of joining the heated sheets in an instant twin-sheet forming phase, and using a threaded inspection tower opening as means to access, sub-assemble, connect, inspect, service and seal the fuel system components associated with a thermoformed fuel tank.  
           [0017]    Thus, it may be appreciated through a review of the prior patent art and related non-patent publications that the thermoforming process provides several key advantages that may be readily adapted to thermoformed fuel tanks. These understood advantages include SIB, rapid twin sheet manufacture (a process which may be appreciated by referring to U.S. Pat. No. 3,925,140 to Brown), and the ready use of composite polymeric sheet with engineered properties. There are, however, several unknown thermoforming processes advantages that can be applied to fuel tank apparatus. It is therefore desirable to identify these unknown advantages so that the thermoforming art can be fully utilized as an enabling technology to provide high-performance fuel storage apparatus.  
         SUMMARY OF THE INVENTION  
         [0018]    It is, therefore, one objective of the present invention to provide high-performance fuel storage apparatus for light-duty vehicles. According to this object, advanced thermoforming technologies are adapted to provide fuel tanks having at least three composite polymeric sheets.  
           [0019]    According to this object, the fuel tank can be instantaneously thermoformed into a unitary article for a rapid production cycle. According to further aspects of this object, one or more composite polymeric sheets are provided enabling fuel tank improvements and enhanced functionality.  
           [0020]    It is another object of the present invention to provide a fuel tank with at least two hollow sections between at least three composite polymeric sheets. According to this object, one or more hollow sections are provided yielding advanced fuel tank characteristics.  
           [0021]    It is yet another object to provide one or more threaded elements upon at least one of the composite polymeric sheets forming a thermoformed fuel tank. According to an aspect of this object, the threaded elements enable post-forming sub-assembly operations to be completed most efficiently. Still according to this aspect, fuel system components are connected to threaded elements that may be readily serviced by in-field technicians.  
           [0022]    It is still another object to utilize a plurality of engineered composite polymeric sheet of greater or lesser thickness in cross-section, along with filler rigidified substrates, vapor barrier layers, RF transparency, intumescent surfaces, improved thermal bonding enhancements as well as other features and aspects. According to this aspect, more economical, technically sophisticated and emissions compliant fuel tanks with high-performance features may be used in light-duty vehicles.  
           [0023]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    The present invention will become more fully understood from the detailed description and the accompanying drawings wherein:  
         [0025]    [0025]FIG. 1 is a flow chart illustrating a method of manufacturing a three-sheet high-performance fuel tank according to the principles of the present invention;  
         [0026]    [0026]FIG. 2 is a cross-sectional schematic view illustrating a three-sheet assembly high-performance fuel tank having a double-walled bottom half according to the principles of the present invention;  
         [0027]    [0027]FIG. 3 is a cross-sectional schematic view illustrating the three-sheet assembly high-performance fuel tank having a double-walled top half;  
         [0028]    [0028]FIG. 4 is a cross-sectional schematic view illustrating the three-sheet assembly high-performance fuel tank having a double-walled top half and bottom half;  
         [0029]    [0029]FIG. 5 is a cross-sectional schematic view illustrating a two-sheet fuel tank according to the prior art;  
         [0030]    [0030]FIG. 6 is a cross-sectional schematic view illustrating the three-sheet assembly high-performance fuel tank having a double-walled bottom half and reserve cavity;  
         [0031]    [0031]FIG. 7 is a cross-sectional schematic view illustrating the three-sheet assembly high-performance fuel tank having a double-walled bottom half and baffle feature;  
         [0032]    [0032]FIG. 8 is a cross-sectional schematic view illustrating the three-sheet assembly high-performance fuel tank having a double-walled top half and dual cavity arrangement;  
         [0033]    [0033]FIG. 9 is a cross-sectional schematic view illustrating the three-sheet assembly high-performance fuel tank having a double-walled top half and cooling feature;  
         [0034]    [0034]FIG. 10 is a cross-sectional view illustrating a thermoforming mold having a single sheet thereon;  
         [0035]    [0035]FIG. 11 is a cross-sectional view illustrating a thermoforming mold having a double sheet thereon;  
         [0036]    [0036]FIG. 13 is an exploded cross-sectional view illustrating the fuel tank of the present invention;  
         [0037]    [0037]FIG. 12 is a partial cross-sectional schematic view illustrating the three-sheet assembly high-performance tank having multiple layers of separate materials all applied thereto and formed simultaneously;  
         [0038]    [0038]FIG. 14 is a cross-sectional schematic view illustrating the three-sheet assembly high-performance fuel tank having a double-walled top half and a fuel system component;  
         [0039]    [0039]FIG. 15 is a cross-sectional schematic view illustrating the three-sheet assembly high-performance fuel tank having a double-walled top half and noise barrier feature;  
         [0040]    [0040]FIG. 16 is a cross-sectional schematic view illustrating the three-sheet assembly high-performance fuel tank having a double-walled top half and a system component;  
         [0041]    [0041]FIG. 17 is a cross-sectional schematic view illustrating the three-sheet assembly high-performance fuel tank having a double-walled bottom half and a system component;  
         [0042]    [0042]FIG. 18 is a diagrammatic view showing the manufacturing process employed with the present invention;  
         [0043]    [0043]FIG. 19 is a perspective view illustrating an exemplary fuel storage apparatus;  
         [0044]    [0044]FIG. 20 is a perspective view illustrating the top half of the exemplary fuel storage apparatus;  
         [0045]    [0045]FIG. 21 is a perspective view illustrating the interior sheet of the exemplary fuel storage apparatus;  
         [0046]    [0046]FIG. 22 is a perspective view illustrating the bottom half of the exemplary fuel storage apparatus;  
         [0047]    [0047]FIG. 23 is a flow chart illustrating a method of manufacturing a three-sheet high-performance fuel tank;  
         [0048]    [0048]FIG. 24 is a perspective view illustrating another exemplary fuel storage apparatus;  
         [0049]    [0049]FIG. 25 is a perspective view illustrating the top half of the exemplary fuel storage apparatus;  
         [0050]    [0050]FIG. 26 is a perspective view illustrating the interior sheet of the exemplary fuel storage apparatus; and  
         [0051]    [0051]FIG. 27 is a perspective view illustrating the bottom half of the exemplary fuel storage apparatus. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0052]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0053]    The recently invented apparatus and methods of Triple Sheet Thermoforming are unknown to the practitioners of the most current Twin Sheet Thermoforming arts. The apparatus and methods of triple sheet thermoforming are described in the present inventor&#39;s co-pending U.S. patent application Ser. No. 09/377,792, entitled Triple Sheet Thermoformed Apparatus, Methods and Articles, filed Aug. 20, 1999, now U.S. Pat. No. 6,294,114. Further preferred embodiments of the methods of triple sheet thermoforming will be known by referring to other co-pending U.S. patent applications in the present inventor&#39;s name. These other applications are entitled “Thermoformed Apparatus Having a Communications Device”, originally filed Jan. 24, 2000 as U.S. Provisional Application No. 60/177,383; and “Thermoformed Platform”, originally filed Apr. 11, 2000 as U.S. Provisional Application No. 60/196,127; and “Triple Sheet Thermoforming Apparatus”, a continuation-in-part application filed Jul. 5, 2001 as U.S. patent application Ser. No. 09/898,457. These patent application references are incorporated herein in their entireties by such reference.  
         [0054]    Thus, it may be appreciated that the method of triple sheet thermoforming involves a process whereby three composite polymeric sheets are successively heated in three ovens, separately thermoformed over three co-acting mold surfaces and sequentially compressed together between two opposed platens in both twin and triple sheet phases. The triple sheet process yields an instant unitary article comprising three sheets of plastic, whereby a third continuous sheet is between a first sheet forming a first fuel tank half and a second sheet forming a second fuel tank half. The method sequence may be understood by referring to FIG. 1. It should be understood, however, that the invention is not intended to be limited by the specific sequence described therein, but may include other sequences as preferred by the triple sheet practitioner and described in the referenced art.  
         [0055]    A number of different fuel storage tank configurations may be used in the design and construction of triple sheet fuel tanks. A triple sheet fuel tank enables several improvements over twin sheet fuel tanks as will be described below. Three such configurations according to the principles of the present invention are set forth in FIGS. 2, 3 and  4 . A prior art twin sheet fuel tank is illustrated in FIG. 5.  
         [0056]    In FIG. 2, three composite polymeric sheets  22 ,  24  and  26  are molded and instantly compressed together to provide fuel tank body  28  comprising a single walled top-half  30  and a double-walled bottom half  32 . In the present embodiment, sheet  26  is adapted to preserve the fuel containing integrity of an interior sheet  24  of the fuel tank body  28 . Other advantages are discussed below in further reference of the present description.  
         [0057]    Referring now to FIG. 3, three composite polymeric sheets  42 ,  44  and  46  are molded and compressed together to provide an instant fuel tank body  48  comprising a double walled top-half  50  and a single walled bottom half  52 . The top-half  50  comprises exterior top member  54  and interior top member  56 . In the present embodiment of FIG. 3, sheet  42  is adapted to provide protection preserving the fuel containing integrity of an interior sheet  44  of the fuel tank body  48 . Other advantages are discussed below in further sections of the present description.  
         [0058]    Referring now to FIG. 4, four composite polymeric sheets are thermoformed to provide fuel tank  60 . Fuel tank  60  is manufactured according to a quadruple sheet thermoforming methodology involving four sheets, at least three ovens, four molds on two shuttle systems and two moving platens. The four sheets in the present embodiment of FIG. 4 may be represented by sheets  54  and  56  forming the double walled top half  50  and sheets  34  and  36  forming the double walled bottom half  32 . It should be understood, however, that the invention is not intended to be limited by the specific composite sheets described herein, but may include other polymeric composite sheets as may be preferred by the triple sheet practitioner.  
         [0059]    In regards to composite polymeric sheets of the FIGS. 2, 3, and  4 , it would be advantageous to provide a number of different composite polymeric sheets having certain desirable properties and functionality. The composite polymeric sheets would comprise a plurality of layers of engineered polymeric materials. A composite polymeric sheet may comprise at least one layer selected from a group of layers consisting of the following compositions or functionality:  
         [0060]    a) An intumescent composition  200  (FIG. 2) suitable for deflecting fire and heat of fire away from the combustible fuel contained within the fuel tank body. Such intumescent compositions may be known by referring to U.S. Pat. Nos. 5,834,535 and 6,184,269, both to Abu-Isa et al., and 5,984,126 to Gordon, which are incorporated herein by such reference.  
         [0061]    b) A fuel barrier composition  202  (FIG. 2) suitable for inhibiting the escape of fuel vapors through the body of the fuel tank. The barrier composition may comprise materials such as ethylene vinyl alcohol copolymer (EVOH) or any other materials that would substantially inhibit the passage of hydrocarbon vapor through the walls and seams of a fuel tank.  
         [0062]    c) An electrically conductive composition  204  (FIG. 3) ensuring static electricity does not build up and assisting in grounding the fuel tank. The electrically conductive composition may include carbon materials, although other materials are envisioned as well, which carbon materials may also aid in the ultra-violet stability of exteriorly exposed fuel tank surfaces.  
         [0063]    d) An electroplateable composition  206  (FIG. 3).  
         [0064]    e) An adhesive agent composition  208 , the adhesive agent composition being suitable for bonding, such as for example thermally or chemically, dissimilar compositions during the sheet extrusion and/or thermoforming phases of fuel tank manufacture.  
         [0065]    f) A polyolefin composition  210  comprising any thermoplastic resins from a group of resins comprising at least polyethylene, polypropylene and including modified polyolefin with predetermined functionality. The polyolefin composition, in particular any high density polyethylene composition, being a relatively inexpensive, readily moldable and rugged material providing a substantial portion of the polymeric sheet composition as will be described.  
         [0066]    g) A filled polyolefin composition  212  (FIG. 2) comprising any filler from a group of fillers comprising talc, silica, glass fibers or beads, cellulose, natural fibers, organic matter, a thermosetting resin, carbon, a pigment, metallic particles, nano-compounds or fire retardant substances including organophosphates and any other functional filler as may be preferred by the thermoforming practitioner. The filled polyolefin composition providing improved physical properties selected from a group of properties including impact resistance, hardness, flexural stiffness, tensile strength and modulus, elongation at break, tear strength, chemical resistance, environmental stress crack resistance, thermal shock resistance, color, ultra-violet stability, fire resistant, and any other physical property that may be envisioned.  
         [0067]    h) A regrind composition  214  comprising post-industrial, post-consumer or any combination of the compositions listed above generated as a byproduct of the thermoformed fuel tank manufacturing operation. The regrind composition being beneficially used to reduce industrial waste and lower the over-all cost of fuel tank manufacture.  
         [0068]    i) A Radio Frequency amenable composition  215  that will permit communications devices residing within the structure to receive and send data signals. Such a composition, for example may omit carbon or other conductive materials that provide UV stability or other functionality.  
         [0069]    It is to be understood that any of the listed compositions may be included in any combination in any one of the single polymeric composite sheets that may be used to construct a triple sheet thermoformed fuel tank.  
         [0070]    Thus, it may be appreciated that the methodologies of triple and quadruple sheet thermoforming may be utilized to provide multi-cavity fuel tanks comprised of multi-layer multi-purpose composite polymeric sheets. An important advantage of either of the triple or quadruple sheet methodologies is that a selectively double walled fuel tank can be instantly thermoformed in a single and rapid manufacturing operation for maximum production efficiency.  
         [0071]    In the following descriptive sections below, the purposes, end uses, and functionality of the different aspects of double walled and multi-cavity fuel tanks is described so that as an enabling technology, triple sheet thermoforming can be used to provide high-performance fuel tank apparatus options for the automotive designer. It should be understood, however, that the invention is not intended to be limited by the specific arrangements described and shown, but may include other arrangement as preferred by the triple sheet practitioner. For example, the over-laying seams  20  of the three conjoined sheets may be configured vertically rather than horizontally, as seen in proceeding FIGS. 2, 3, and  4 . In this alternative arrangement, the fuel tank may comprise one or more double walled side halves rather than top and bottom halves.  
         [0072]    Referring again to FIGS. 2, 3, and  4 , the exteriorly exposed sheets  26  or  42  forming the exterior walls  34  or  54  may be adapted to provide a thermoformed fuel tank with integral barrier characteristics. The barrier characteristics may include any one or combination of barrier characteristics from the following list of characteristics:  
         [0073]    a) A puncture resistant barrier  220  (FIGS. 6 and 8) provided to reduce the penetration of external objects or other vehicle components through the interior sheets  36  or  56  containing the fuel stored within the apparatus. The problem may be better understood by referring to International Publication No. WO 01/00433 to Detourneay et al. Two layers of composite sheet can be fused together to provide a thicker wall in cross section or offset to limit distortion, to overcome the condition problematic in U.S. Pat. No. 6,294,127 issued to Huse.  
         [0074]    b) A heat resistant barrier  222  (FIG. 8) provided to deflect the high heat associated with vehicle components, such as, by way of example, exhaust pipes, and return fuel lines, away from thermally conductive polymeric composite sheets  36  and  56  containing the combustible fuel and fuel vapor. The problems may be appreciated by referring to International Publication No. WO 99/44851 to Butler or U.S. Pat. No. 6,268,037 to Butler et al.  
         [0075]    c) A scuff resistant barrier  224  (FIG. 15) provided to reduce the wear and tear associated with abrasion of vehicle components flexing upon the fuel tank body as well as the wear and tear associated with the operation of the light-duty vehicle under off-road driving conditions. A scuff resistant barrier may comprise a high-density material with a low co-efficient of friction or a low-density material with a comparably high co-efficient of friction, as preferred.  
         [0076]    d) A noise-dampening barrier  226  (FIG. 15) provided to insulate the sloshing sounds associated with fuel movement. The problem may be known by referring to U.S. Pat. No. 6,293,420 to Richter et al or International Publication No. WO 98/36929 to Keller.  
         [0077]    e) An anti-deflection barrier  228  provided to rigidify the interior sheets  36  and  56  preventing said interior sheets from deflecting toward each other when pressures within the fuel tank are generated by fuel system components and operation. The problem may be understood by referring to International Publication No. WO 00/47437 to Sadr, or U.S. Pat. No. 6,338,420 to Pachciarz et al.  
         [0078]    f) A secondary vapor barrier  230  further reducing the escape of environmentally hazardous fuel vapors from the fuel storage cavity.  
         [0079]    g) An intumescent barrier  232  (FIG. 8) that reacts with fire to form a char or inorganic ceramic-like insulator that will extend the length of time before the fuel and fuel vapor within the apparatus combusts.  
         [0080]    Although the aforementioned barriers have been suggested for use in conjunction with the exterior members  34  and  54 , it is to understood that any of the listed barrier characteristics may be used in any combinations to construct a high-performance thermoformed triple sheet fuel tank.  
         [0081]    In addition to the exemplary barrier characteristics listed above, the triple and quadruple sheet thermoforming methodologies may also be used to provide a number of functional aspects that have heretofore been difficult to implement with known blow molding and twin sheet thermoforming practices. The functional aspects may include any one or combination of the functional aspects from the following list of functional aspects:  
         [0082]    a) A segmented fuel reserve aspect  240  (FIG. 6). As may be appreciated by referring to FIG. 6, sheet  24  forming interior member  36  may be adapted to provide a fuel reserve  70 , which is defined by fuel reserve cavity  72 , formed between exterior sheet  26  and interior sheet  24 . In this arrangement, it may be appreciated that a fuel reserve cavity is instantly thermoformed as an integral aspect of the fuel storage apparatus, the arrangement thus reducing the costs associated with supplying and installing a separate fuel reserve device within a single-walled fuel tank. It may alternately be suggested that the fuel reserve cavity can be incorporated into a suitably adapted double walled top fuel tank half. In other words, the tank of FIG. 6 could be rotated 180°. The benefits and advantages of the present arrangement may be appreciated by referring to U.S. Pat. No. 6,176,260 to Hahner; U.S. Pat. No. 6,223,526 to Wissler et al.; or WO 99/14485 to Siekmann.  
         [0083]    b) A baffle aspect  242  (FIG. 7). As may now be appreciated by referring to FIG. 7, sheet  24  forming interior member  36  may be adapted to provide baffling aspects  74  obstructing excessive fuel movement and the sloshing noise of moving fuel within the fuel storage apparatus. The baffle elements  76  may be orientated extending from one side of the vehicle to the other, extending from the front of the vehicle to the back or in both directions. The baffle elements  76  may also be advantageously offset (as suggested in broken line) with respect to one and the other to provide a network of movement limiting interior obstructions.  
         [0084]    c) A dual-cavity storage aspect  244  (FIG. 8). Referring now to FIG. 8, an embodiment of a dual-cavity fuel storage tank  90  is suggested. This arrangement is particularly suitable for two-stroke internal combustion engines with an additional engine-oil lubricating system. Dual-cavity fuel storage apparatus may become useful in respect to future engine fuel technologies and hybrid fuel mixtures. As can be seen the cavities of the dual fuel storage apparatus may be segmented in a proportionate aspect consistent with expenditure of the fuel mixtures, herein designated A and B.  
         [0085]    d) Fastening aspects  246  (FIG. 9). Referring now to FIG. 9, it may be appreciated that the double walled construction of any of the preferred embodiments of a thermoformed fuel tank may be developed to provide fastening aspects  78 . In order to secure a twin sheet fuel tank to the undercarriage of the light-duty vehicle, a more secure combination of straps and fasteners is contemplated, as in U.S. Publication No. 2001/0020622. As may be fully appreciated by referring to FIG. 9 a fastener receiving hollow standoff  80  is seen formed between exterior sheet  42  and interior sheet  44 . In this arrangement, a fastener can be used without penetrating the interior sheet  44 , which could result in the escape of environmentally hazardous fuel vapors. It may also be appreciated that a plurality of hollow stand-offs with slotted openings may be incorporated into the fuel tank apparatus to provide for the attachment of numerous vehicle and fuel system components.  
         [0086]    e) A heat exchange aspect  248  (FIG. 9). Referring again to FIG. 9 it may be known by referring to International Publication No. WO 00/64694 that approximately one-third of the fuel pumped from the tank to the engine is returned to the fuel tank. A relatively high return fuel temperature, usually of the order of 80° C., in high volumes relative the quantity of fuel remaining in a tank may produce unwanted results. Fuel temperature may exceed the heat deflection temperature of the interiorly exposed polymeric surfaces, causing resin precipitation, composition destruction or lasting deformation of the tank body. According to this problem, one or more cavities may be formed between at least two of the polymeric sheets forming the fuel tank apparatus wherein one or more cavities  92  are developed to receive and cool the returning high temperature fuel before its re-entry into a fuel reserve  94 . A complex heat exchange channel  96  may be formed in a cavity to assist the control methodology. A return fuel cavity  92  may be positioned adjacent the bottom of the fuel tank to have the benefit of low ambient external temperature, or adjacent the top of the fuel tank to offer insulating distance between a cavity wall and the fuel reserve. It may also be appreciated that the fuel vapor control apparatus and vapor ducts of U.S. Pat. No. 6,276,387 to Pachciarz et al. may be reproduced in functionality through the triple sheet thermoforming method.  
         [0087]    f) A fuel system component aspect  250  (FIG. 16). For example, a discreet chamber may be provided to receive a fuel vapor filter/condenser unit. In the case of a deep draw fuel tank, the EVOH barrier layer thins, and permeating vapors are captured before escaping through the exterior barrier into the environment.  
         [0088]    Although the aforementioned aspects have been suggested for use in conjunction with one of the fuel tank halves shown, it is to be understood that any of the listed aspects may be used in any combination or re-arrangement to construct a high-performance thermoformed triple sheet fuel tank.  
         [0089]    Thus, it may now be appreciated that fuel tank apparatus may be instantly thermoformed out of three or more polymeric sheets to yield fuel tanks having a plurality of engineered sheet compositions, a plurality of integral barrier characteristics, and a plurality of functional aspects that in combination yield high-performance fuel storage apparatus.  
         [0090]    Referring now to another enabling aspect of triple sheet thermoforming technology, it has been suggested that fuel tanks must be sub-assembled for final integration into the light-duty vehicle and serviceable in the field by repair technicians. Two approaches characterize a solution to this requirement. In a first approach, which may be known by referring to International Publication No. WO 00/43230, an aperture is provided on the tank body and a fitting is welded adjacent the aperture to accomplish desired means. Although this first approach has been used with some measure of success, the methodology requires post-molding intervention that adds cost and operational complexity. In a second approach, which has been identified in connection with earlier reference International Publication No. WO 99/56977, a blow molded fuel tank is provided with an integral flange that may be opened and sealed for both sub-assembly and in-field repairs. The second approach is preferable because integral flange means are enabled in an instant blow molding operation. The means is used in manufacturing sub-assembly and in-field service and repair.  
         [0091]    A plurality of integral external and internal flange means may also be advantageously provided in the practice of triple and quadruple sheet thermoforming. Turning now to FIGS. 10 through 18, it may be understood how integral flanges can be incorporated into high-performance thermoformed fuel storage apparatus.  
         [0092]    Referring to FIG. 10, a segment of a thermoforming mold  100  with a recess  102  is seen. The recess  102  is annular, but could take many different shapes as preferred. In one preferred thermoforming machine arrangement and method sequence, a shuttle delivery system positioned externally adjacent a form station delivers an injection molded polymeric flange plate  104  for receipt within the recess  102 . Next, polymeric composite sheet  106 , after suitable heating, is displaced over the mold  100  and the flange plate  104  with the aid of differential pressure. When a heated surface  108  of sheet  106  is compressed upon the exposed surface  110  of the flange plate  104 , the surfaces  108  and  110  auto-genously fuse together through molecular cross-linking to form a bond area  112 . (It being understood the polymeric compositions of the surfaces  108  and  110  contain compatible polyolefin resin amounts.) In the present arrangement, although the bond area of the surfaces will be substantially permanent, a creep resistant gasket  109  or barrier material may be received within a channel interposed between the surfaces to inhibit permeation of fuel vapors through bond area  112 . The arrangement would be appreciated by referring to U.S. Pat. No. 6,305,568 to Suzuki et al.  
         [0093]    When sheet  106  is sequentially ejected from the mold the flange plate  104  is recognized as an integral feature of the intended end product. In post-molding operations, an aperture  120  is made in sheet  106  adjacent an interior wall  118  of the flange plate. The aperture  120  provides access to an interior of a fuel tank for sub-assembly. The interior wall  118  may include a threaded aspect  119 . The threads receive a bushing  121  to that compresses a plate  122  against the interior wall to close the aperture. The arrangement is seen in FIG. 13. The aperture plate  122  includes electrical connector aspects  123  and hose connector aspects  125 . The aperture plate is provided with integral electrical and hose connectors to minimize the number of openings in the body of the fuel tank. As there will be several apertures in the plate, it cannot be rotated in a threading manner. The compression bushing threads over the plate, which remains substantially stationary. It should also be noted that the flange plate  104  is interiorly disposed upon the surface of the intended end product to reduce the vertical space occupied by the apparatus. This is in marked contrast to the inspection tower of U.S. Pat. No. 6,179,145, which is exteriorly disposed upon a fuel tank surface.  
         [0094]    Furthermore, one or more flange plates having different insert receiving aspects may be employed to provide a plurality of inter-connection points as suggested by the different fuel system components. On such flange plate would be offered for specifically connecting the fuel filler assembly to the fuel tank. Additionally, a plurality of flange plates may be integrally fused in the thermoforming process to a plurality of the polymeric sheets forming the fuel tank. One or more shuttle carriages would therefore be adapted to place flange plates upon mold or molded recesses for final integration onto the polymeric sheets forming a fuel tank.  
         [0095]    Finally, a flange plate may be inserted into a molded recess formed in a first polymeric sheet and a subsequent molded polymeric sheet could than be compressed against the first sheet over the flange plate to provide an enclosed flange plate accessible through two apertures opened in fuel tank. The arrangement is enabled in fuel tank  500 .  
         [0096]    It may thus be appreciated that a first aperture is provided so that second apertures can be opened as suggested by the means of flange plates. It should be understood, however, that the invention is not intended to be limited by the specific sequences, flange plates, inserts and multiple locations described herein, but may include other such embodiments as preferred by the triple sheet practitioner.  
         [0097]    The flange plates facilitate SIB advantages. Triple sheet fuel tanks facilitate multiple SIB aspects. Multiple flange plates facilitate access to multiple SIB aspects. As suggested in FIGS. 14, 15,  16 , and  17 , fuel system components  140  may be interiorly positioned in a fuel reserve section  142  and or a component section  144  of a triple or quadruple sheet fuel tank. It may also be noted here that the fuel system components would be sub-assembled upon a component cradle  146  as means for delivery and pre-placement of the subsystem between first and second or second and third sheets by an external shuttle apparatus adjacent a form station. This apparatus is described below and in the aforementioned references toward triple sheet thermoforming apparatus. Therefore, one or more fuel system component packages  140 A and  140 B can be advantageously positioned within a first or second interior cavity of the triple sheet article. Access to the interior packages is provided by an external aperture  120  and an internal aperture  146 , it being understood internal aperture includes a second flange plate  104 . Although four SIB configurations are suggested, other triple and quadruple sheet adaptations can be made and these fall within the scope of present invention.  
         [0098]    The shuttle apparatus employed to deliver the packages into a fuel tank is suggested to advantage in FIG. 18. A plan view of one triple sheet thermoforming machine  300  suitable for the manufacture of a triple sheet fuel tank is shown. The machine conforms to a (four or six station) rotary machine configuration, although a linear machine configuration and parallel operating machines, as suggested in U.S. Publication No. 2002/0017745 to Vorenkamp et al., fall within the scope of the present invention. A machine comprises a machine frame  302  upon which is suspended a frame support  304 . The frame support involves clamp frames  306 , and each clamp frame carries one polymeric composite sheet as the frame support is indexed forward in desired increments. The frames advance successive sheets through at least three ovens  308 ,  310 , and  312  to a form station  314 . At the form station a plurality of heat deformable sheets are sequentially molded and instantly compressed together between opposed platens  316  and  318  to yield a unitary article. Although the arrangement suggests a four station rotary configuration, the five and six station rotary configurations fall within the scope of the present invention.  
         [0099]    Apparatus external to the machine frame is provided to enable the manufacture of a triple sheet fuel tank. A sheet loading shuttle system  320  is deployed to sequentially deliver sheet selected from an inventory of polymeric composite sheets A and B to the frames. Although a two-sheet, delivery system is suggested, single or multiple sheet delivery systems fall within the scope of the present invention. A SIB loading shuttle system  322  is deployed adjacent the form station  314 . A first shuttle and track system  324  projecting into the form station uses a carriage  333  to sequentially deliver externally supplied flange plates and sub-assembled packages for incorporation into the intended end product. Cooperating with the shuttle and track system is a sub-assembly delivery track sub-system  326 . The present sub-system suggests three SIB packages C, D, and E on a five-segment sub-track  328 , although both single and multiple segmented sub-tracts fall within the scope of the invention. Additionally, the shuttle track system projects into the form station in a position intermediate the wheel and a lower platen  318 , however, an upper shuttle track system with elements projecting intermediate the wheel and an upper platen  316  also falls within the scope of the invention. The upper shuttle track system may be developed to deliver insert packages into the form station, or the upper shuttle track system may be developed to provide a plug assist function to distribute the heat deformable sheet material more uniformly upon a mold surface. This arrangement may in fact be preferred to prevent over-thinning of a composite layer or barrier material such as  202 . According to this concern, a lower platen shuttle system, as in the upper platen shuttle system  330 , which moves two molds  332  and  334  into and out of the platen  316 , may be employed to provide a reciprocating lower platen molding tool and plug assist shifting apparatus. Therefore, a plurality of lower and upper shuttle systems may be used to deliver multiple packages or provide assisting means, and all such derivations fall within the scope of the invention.  
         [0100]    Adjacent a load and unload station  336  is intermediate apparatus  338  delivering ejected articles through an external cooling region  340  characterized by known controlled cooling apparatus and procedures. The ejected articles travel through the cooling region to a 5-axis CNC trimming station  342 . CNC routers remove recyclable process materials from the body of the thermoformed articles and open apertures for further final sub-assembly operations.  
         [0101]    The machine  300  is configured to manufacture the fuel storage apparatus indicated by  400  and  500  in the following figures, which are provided for illustration purposes of the flexibility of the triple sheet thermoforming processes. The fuel storage apparatus indicated by fuel tank  400  is represented in FIGS. 19 through 22, and is described below.  
         [0102]    Fuel tank  400  represents a detailed embodiment of fuel tank  28  characterized with a double walled bottom  432  and a single walled top  430 . The bottom comprises sheets  424  and  426 . Sheet  426 , constituting sheet B, is thermoformed to provide the exterior bottom wall  436 . Sheet B, as the present case so admits, is distinguished from sheet A, which is intended to contain the fuels of the intended apparatus. Sheet A 1  forms the top  430  of the fuel tank and sheet A 2  forms the inside wall  434  of the fuel tank. The A sheet is characterized as having composition  202  contained therein for vapor barrier purposes.  
         [0103]    The fuel tank  400  is manufactured on the machine  300  according to the following method sequence of FIG. 23, which machine sequence functions relate in the present restricted case to the method sequence functions at the form station and adjacent the form station. The process sequence is upside down from the view of the FIGS. First, the flange plate  104  is positioned onto the first mold. The flange plate, indicated by package C, includes an integral plastic grid  450  that supports a plurality of flange plates for one-step insertion onto the mold. For example, one flange plate  452  is provided for installation of the fuel filler assembly  454 . Second, the first sheet  422  is thermoformed over the first mold and the plastic grid  450 , the grid permanently fusing to the first sheet. The first molded sheet is retracted from a sheet line by movement of the lower platen  318 . While the lower platen is retracted, the carriage  333  of the shuttle system  324  delivers a second package D comprising fuel system components supported upon cradle  146 . The cradle is deposited upon a visible surface of the first molded sheet. Simultaneously, a second sheet is thermoformed over a second mold supported upon the upper platen  316 . The package-delivering shuttle may carry packages below and include plug assist apparatus above to assist in the formation of a catenary sheet. Fourth, the lower platen is extended into the upper platen compressing the first sheet against the second sheet in a twin-sheet phase, the first and second sheets being permanently fused together where they communicate and cross-link at temperature and pressure. (The package D is enclosed between two composite polymeric sheets.) Fifth, after a dwell period, a frame releases the second sheet allowing the lower platen to retract while carrying the twin-sheet subassembly. Simultaneously, the upper platen retracts a fixed distance and the second mold is replaced with a third mold, by means of the upper platen shuttle system  330 . Concurrently and optionally, package E is offered for delivery upon the second sheet. Sixth, the third sheet is thermoformed over the third mold supported upon the upper platen. Seventh, the lower platen is extended into the upper platen compressing sections of the visible surface of the second sheet of the twin-sheet assembly against sections of the third sheet in a triple-sheet phase, the second and third sheets being permanently fused together where they communicate and cross-link. Finally, the platens retract and a frame holding the instant third sheet indexes the triple-sheet assembly to the load/unload station for further processing as anticipated in the prior description. A triple sheet article  400  is thus provided.  
         [0104]    In the process of thermoforming the sheets over their respective mold surfaces certain barrier characteristics and functional aspects can be incorporated into the design of one such fuel storage apparatus  400 . As seen in FIG. 21 these characteristics and aspects include baffles  242  and fuel reserve  240 . It may now also be appreciated that a segment  458  of the fuel reserve  70  communicates with molded sheet  422 , fusing together (in the area  459  suggested in broken line detail) to provide a sealed fuel reserve cavity  72 . Details  460  are provided to provide fuel passage from the fuel supply to the fuel reserve. As seen in connection with FIG. 22, the exterior sheet  426  comprises heat-shielding compositions  462  adjacent a tail pipe and fastening aspects  246  for receiving straps and the like supporting the fuel tank upon the light-duty vehicle. It is advantageous to provide localized barrier properties, such as for the heat sensitive area  462  by adding a barrier laminate upon a surface of a composite sheet as would be suggested in FIGS. 19 and 20 of co-pending U.S. Pat. No. 09/770,097. Such an arrangement would increase the efficiency of the article by reducing its overall use of potentially expensive material costs.  
         [0105]    Moving on, fuel tank  500 , represented in FIGS. 24, 25,  26  and  27 , has a double-walled top  550  and single walled bottom  552  as in the fuel tank  48  of FIG. 3. The top comprises exterior composite polymeric sheet  554  and interior composite polymeric sheet  556 . The bottom comprises composite polymeric sheet  558 .  
         [0106]    The fuel tank  500  is manufactured on the machine  300  according to the method sequence of FIG. 23. A second package  140 A comprising flange plates  104 B and  104 C and fuel system components is laid to rest upon sheet  554 . The second sheet  556  is sequentially compressed upon the flange plates and the surrounding sheet, to encapsulate the flange plates between two composite polymeric sheets. A post-molding aperture  120  is opened in the fuel tank by removing overlaying sections of the recognized work pieces upon the CNC trimmer  342 . The flange plate  104 B includes interior threads that are exposed when the apertures are made to receive the members of a lid assembly  560 . The aperture of sheet  556  provides access to a third package  140 B of fuel system components within the interior fuel reserve.  
         [0107]    In the process of thermoforming the sheets of fuel tank  500  over their respective mold surfaces certain barrier characteristics and functional aspects can be incorporated into the design of fuel storage apparatus. A vapor fuel filter canister  562  is provided to re-circulate fuel vapors permeating into the component section  144  from the fuel reserve section  142 . The filter canister is accessible through flange plate  104 A. Details  460  are opened through sheets  554  and  556  for connecting the fuel filler assembly  454  to provide fuel passage from the fuel supply to the fuel reserve. The top exterior sheet  554  has composition  200  also providing heat resistant barrier  222 . The plate  122  of the lid assembly  560  includes electrical and hose connector aspects  123  and  125 , respectively to provide the necessary connector means of the apparatus.  
         [0108]    Another advantage of providing a three-sheet fuel storage tank is so that fuel tank instrumentation can be accommodated. For example, a wireless communications devise may be deposited between the sheets for remote or local communication objectives. A hydrocarbon sensor may record hydrocarbon levels and communicate data indicative of these records automatically by remote communication, or in reply to local inquiry. A fuel quality sensor may be used to regulate ownership compliance. A fuel vapor filter sensor may be used to schedule maintenance wirelessly. Communications and Information Technology systems are deployed to assure tank emission compliance and renew licenses where required.  
         [0109]    Furthermore, with particular reference to blow molding technology, the present invention provides a number of advantages. Specifically, the present invention, being thermoformed, is more economical than blow molding since thermoforming is capable of producing multiple pieces simultaneously, while blow molding is merely capable of producing a single shot at a time. Furthermore, as seen in FIG. 12, the thermoformed fuel tank of the present invention could include multiple layers (i.e. 18 for example) of separate material. It would be unlikely to arrange eighteen extrusion lines to blow mold a triple layer fluid container with a top member, a bottom member, and a middle member having a hole.  
         [0110]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.