Patent Abstract:
A portable food warmer is provided with a powered heating element, includes an enclosure, formed from an outer shell and an inner layer, with the powered heating element positioned between the outer shell and the inner layer. A steel rack is provided to support food items contained therein. The powered heating element preferably is in the form of a carbon fiber ribbon, wrapped around the enclosure, between the outer shell and inner layer.

Full Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates in general to devices for maintaining materials at a desired temperature above ambient, and particularly for such devices as are used in the transportation and delivery of prepared pre-cooked food products. 
         [0003]    2. The Prior Art 
         [0004]    Many methods and devices exist for the transportation of already-prepared “hot” food products. Some of these methods and devices rely simply on attempting to contain and prevent heat loss from the prepared food, through the use of insulated containers (e.g., Styrofoam “coolers”, insulated bags having metalized surfaces, vacuum bottles and containers using air gaps as insulation). Such unpowered systems eventually lose heat to their ambient surroundings, leading to loss of temperature in the prepared food products. 
         [0005]    Other food product transportation systems may employ pre-heated elements installed in the walls of a container, such as pre-heated ceramic discs. However, these systems also will eventually lose heat, leading to heat loss in the food products. 
         [0006]    Powered containers and systems exist for maintaining food at an elevated temperature; however, such powered systems tend to be too large in scale to be readily portable. 
         [0007]    It would be desirable to provide an apparatus and system for transporting prepared “hot” food products, which does not suffer from continual heat loss, and which is readily portable. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention comprises in part a food warmer. In an embodiment of the invention, the food warmer comprises a box having an internal cavity, an opening defined in a face thereof, and a movable cover cooperating with the opening, to enable access to the internal cavity. The box may include an outer shell; an innermost facing layer; an insulation layer disposed between at least portions of the outer shell and at least portions of the innermost facing layer; and a powered heating system disposed at least in part, along inwardly-facing surfaces of at least portions of the insulation layer. 
         [0009]    The present invention also comprises a method for fabricating a food warmer, comprising the steps of: 
         [0010]    providing a box, having an internal cavity, an opening defined in a face thereof, and a movable cover cooperating with the opening, to enable access to the internal cavity, the step of providing a box further including the steps of 
         [0011]    forming an outer shell; 
         [0012]    placing an insulation layer within the outer shell; 
         [0013]    providing a powered heating system disposed at least in part, along inwardly-facing surfaces of at least portions of the insulation layer; 
         [0014]    placing an innermost facing layer within the outer shell, so that the insulation layer is disposed between at least portions of the outer shell and at least portions of the inner facing layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view of a food warmer according to an embodiment of the invention. 
           [0016]      FIG. 2  is a top view of the food warmer of  FIG. 1 . 
           [0017]      FIG. 3  is a front view of the food warmer of  FIG. 1 . 
           [0018]      FIG. 4  is a side elevation of the food warmer of  FIG. 1 . 
           [0019]      FIG. 5  is a top view of a heating element assembly, according to an embodiment of the invention. 
           [0020]      FIG. 6  is a perspective exploded view thereof. 
           [0021]      FIG. 7  is a front exploded view thereof. 
           [0022]      FIG. 8  is an enlarged fragmentary sectional view, taken along line  8 - 8  of  FIG. 4 . 
           [0023]      FIG. 9  is a schematic illustration of the electrical circuitry for a food warmer according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    While this invention is susceptible of embodiment in many different forms, there is shown in the drawings, and described in detail herein, one embodiment, with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated. 
         [0025]    The following description and drawings are illustrative and are not to be construed as limiting. Numerous specific details are described to provide a thorough understanding of the disclosure. However, in certain instances, well-known or conventional details are not described in order to avoid obscuring the description. References to one or an embodiment in the present disclosure can be, but not necessarily are, references to the same embodiment; and, such references mean at least one of the embodiments. 
         [0026]      FIGS. 1-4  illustrate a food warmer according to the principles of the present invention. Food warmer  20  includes a parallelepiped box  22  (or other three dimensional shape), having a hinged front wall  24 , and top wall  26 , bottom wall  28 , back wall  30 , and side walls  32 ,  34 . Referring, by way of example, to  FIG. 8 , which is an enlarged fragmentary sectional view of side wall  32 , taken along line  8 - 8  of  FIG. 4 , each of the walls is preferably fabricated from a plastic or fabric (e.g., corrugated polypropylene, molded thermoplastic, canvas, nylon, etc) shell layer  40  for strength and light weight, with an innermost facing layer  42  being, in embodiments of the invention, a laminate of aluminum foil  44  and polyester film  46 . An insulation layer  48  of, e.g., polystyrene foam, preferably having a relatively high R value (e.g., R&gt;4), is disposed between the outer shell layer  42  and the inner wall layer  44 , along all of the top, bottom, side and rear walls of box  22 , and may be disposed between the outer shell layer  42  and inner wall layer of the front wall of box  22 , to maximize containment of heat within food warmer  20 . 
         [0027]    Hinged front wall  24  may be held in place in a closed position by any suitable method, such as by simple friction, small projections on the door mating with recesses in structure surrounding and defining front opening  23  of box  22  or by any suitable latching method, such as by magnetic catches, snaps and straps, mechanical latches (generally shown at  25  in  FIG. 1 ), etc. 
         [0028]    To provide the heating effect, a heating element  50  is placed between the insulation sheet  48  and the inner wall layer  44 . Heating element  50 , in embodiments of the invention, includes flattened carbon fiber strip  52 , and is wound around the interior of the warmer  20 , as suggested by the broken lines in  FIG. 4 . Heating element  50  is provided, for most of its length with a protective and insulative cover for carbon fiber strip  52 , in the form of thermoplastic sleeve  53 . In an embodiment, the heating element may be as shown and described in U.S. Pat. No. 7,247,822 that is incorporated herein by reference. Power for heating element  50  is provided via car power outlet adapter  54 , connected to cord  56 . Cord  56  is electrically connected to heating element  50  by connection  58 , which is illustrated in detail in  FIGS. 5-7 . 
         [0029]    In an embodiment of the invention, suitably mounted, preferably vertical/linear carrying handles  36  may be mounted to the wire rack to bear the forces of the contents and protrude through the outer shell layer of top  26 . In an alternate embodiment, handles may be mounted to the outer shell with appropriate strain relief. Feet  38  (preferably rubber) may be provided in embodiments of the invention, to elevate food warmer  20  above any flat surfaces upon which food warmer  20  may be placed, to prevent marring thereof. 
         [0030]    A metal rack  39 , having a plurality of shelves  41 , is provided. Preferably, rack  39  will be configured to support a substantial weight, e.g., on the order of 90 pounds. 
         [0031]    Connection  58 , which interconnects cord  56  to heating element  50 , includes first connection element  60  and second connection element  62 . First connection element  60  includes one or more locator pins  64  (four in the illustrated embodiment of  FIG. 6 ), as well as an array of fixation elements  66  or energy directors. Second connection element  62  includes one or more locator apertures  68  corresponding to the one or more locator pins  64  of first connection element  62 , as well as an array of fixation elements  70 , which correspond to and align with fixation elements  66  of first connection element  62 . Connection  50  is formed by placing an end of heating element  50 , in which carbon fiber strip  52  is exposed, between first and second connection elements  62 ,  64 , respectively. An end of cord  56 , in which the insulation  72  has been removed to expose the conductor  74 , is positioned adjacent the exposed portion of carbon fiber strip  52 . Locator pin(s)  64  is/are aligned with locator aperture(s)  68 , and first and second connection elements  62 ,  64  are pressed together, and exposed to sonic/ultrasonic waves of sufficient force, frequency and duration, to cause a number of fixation elements  66  and/or  70  to pass through carbon fiber strip  52 , and abut and fuse to one another, effectively welding first and second connection elements  62 ,  64  together, and holding the exposed end of conductor  74  in tight electrical contact with the exposed portion of carbon fiber strip  52 . 
         [0032]      FIG. 9  is a schematic illustration of the electrical circuitry  90  for warmer  20 . In an embodiment of the invention, V in =13.8 VDC  (typical rated voltage for a motor vehicle interior power outlet), F 1 = 10 A (fuse typically located in a motor vehicle adapter  54 ) and R (representing a typical load for the heating element)=1.9 ohms. Thermostat  76  will be positioned in warmer  20  at a suitable location (which may be on the inner surface of innermost facing layer  42 , or between insulation layer  48  and innermost facing layer  42 ), and operably inserted electrically between adapter  54  and heating element  50 , so as to provide automatic control of the temperature within warmer  22 , to maintain warmer temperature  22  within a desired, predetermined temperature range. The numerical values provided in  FIG. 9  are provided merely by way of example, and the invention is not intended to be limited thereof. 
         [0033]    The walls of box  22  may be fabricated using suitable known fabrication methods, in order to ensure that no heat leakage spots are created, especially along the edges and corners where two or three walls meet. Fabrication of warmer  20  may be accomplished by first forming the outer shell  40  of box  22 . Heating element  50  is first attached to the insulation layer  48 . Then innermost facing layer is applied over this assembly. Next, this assembly is formed and placed within the outer shell  40 . Rack  39  (which in embodiments of the invention may be removable, e.g., for cleaning) will then be positioned in the inner cavity of box  22 . 
         [0034]    As an alternative to hinged front wall  24 , a completely removable cover (not shown) may be provided, which can be inserted into (or placed over) front opening  23 , to enable controlled access to the interior of box  22 . Such a removable cover may still be fabricated in a manner similar to that of the rest of box  22 , having an outer shell layer, an inner facing layer, and an insulation layer therebetween. In more complex embodiments of the invention, heating elements may be provided in either hinged front wall  24  or in a removable cover, though additional power transmission cords would be required to connect such heating elements to the electrical circuitry in the rest of box  22 . 
         [0035]    It is to be understood that the foregoing numerical values are provided simply by way of example, and that other embodiments of the invention may be provided with components having other numerical values, without departing from the scope of the invention. 
         [0036]    Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments. 
         [0037]    The terms used in this specification generally have their ordinary meanings in the art, within the context of the disclosure, and in the specific context where each term is used. Certain terms that are used to describe the disclosure are discussed above, or elsewhere in the specification, to provide additional guidance to the practitioner regarding the description of the disclosure. For convenience, certain terms may be highlighted, for example using italics and/or quotation marks. The use of highlighting has no influence on the scope and meaning of a term; the scope and meaning of a term is the same, in the same context, whether or not it is highlighted. It will be appreciated that same thing can be said in more than one way. 
         [0038]    Consequently, alternative language and synonyms may be used for any one or more of the terms discussed herein, nor is any special significance to be placed upon whether or not a term is elaborated or discussed herein. Synonyms for certain terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only, and in no way limits the scope and meaning of the disclosure or of any exemplified term. Likewise, the disclosure is not limited to various embodiments given in this specification. 
         [0039]    Without intent to limit the scope of the disclosure, exemplary instruments, apparatus, methods and their related results according to the embodiments of the present disclosure are given below. Note that titles or subtitles may be used in the examples for convenience of a reader, which in no way should limit the scope of the invention. Moreover, certain theories may be proposed and disclosed herein; however, in no way, whether they are right or wrong, should they limit the scope of the disclosure so long as the disclosure is practiced according to the disclosure without regard for any particular theory or scheme of action 
         [0040]    Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. In the case of conflict, the present document, including definitions will control. 
         [0041]    The term “proximate” shall mean at or near the object being modified by the term “proximate”. Any numerical values provided herein are given by way of example and the scope of the claimed invention is not intended to be limited in any way thereby. 
         [0042]    The foregoing description and drawings merely explain and illustrate the invention, and the invention is not limited thereto, except as those skilled in the art who have the present disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.

Technology Classification (CPC): 8