Abstract:
A cooking or food warming appliance having a heated heat sink plate situated in a vacuum environment within an outer shell. A food vessel intimately engages the heat sink plate along a food contacting surface thereof by virtue of the vacuum. The vacuum eliminates air gaps between the food contacting surface of the food vessel and the heat sink plate so as to provide instantaneous and uniform heating of the food vessel. The vacuum environment also provides thermal insulation for the heat sink plate whereby heat loss by convection is virtually eliminated.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of co-pending U.S. application Ser. No. 11/245,478 filed Oct. 6, 2005, and is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to electric cooking appliances and, more particularly, to an electric cooking or food warming appliance having a thin food contacting surface, preferably of stainless steel, that intimately engages a thicker heat conductive core or heat sink plate of copper or aluminum by means of a vacuum to maximize heating uniformity and minimize heat loss. 
     2. Description of Related Art 
     Briefly stated, the invention disclosed in parent application Ser. No. 11/245,478 is directed to a composite griddle plate comprising a core consisting of a metal plate having a high coefficient of thermal conductivity such as copper or aluminum. The core plate is faced at least with an upper sheet of a metal such as stainless steel or titanium which defines the cook surface of the griddle plate. The interface between the core plate and upper sheet is under the reduced pressure of a vacuum so as to cause intimate contact between the core and cook surface which increases the thermal conductivity to the cook surface and, thus, reduces the thermal recovery time of the griddle. 
     Various additional embodiments of the original invention are also disclosed in the parent application. For example, the griddle plate of one such embodiment comprises a high heat conductivity core of copper or aluminum having upper and lower sheets of stainless steel in intimate contact with the core. The entire perimeter of the griddle plate is sealed as by welding and the interior is under a permanently sealed vacuum. Another such embodiment utilizes an upper sheet of stainless steel or other metal having a non-stick coating applied thereto. The upper sheet is removably secured to the heat conductive core plate under vacuum utilizing a high temperature gasket or adhesive sealant to maintain the vacuum. The upper sheet may be mechanically secured by bolts or the construction may be placed under a constant vacuum using a vacuum pump. When the non-stick surface ages and/or otherwise loses its non-stick properties, such as with a PTFE-type non-stick coating, the upper sheet can be easily replaced with a freshly non-stick coated upper sheet and the vacuum reestablished. 
     SUMMARY OF THE INVENTION 
     The present invention incorporates several aspects of the invention disclosed in parent application Ser. No. 11/245,478, namely, the attachment of a thin metal cook surface to a thicker core layer or heat sink by way of a vacuum to ensure uniform surface contact between the cook surface and the heat sink which provides instant heating as well as uniform heating over the entire cook surface. The subject parent application also discloses the removability of the cook surface from the heat sink through the use of a vacuum pump and high temperature gasket sealing around the perimeter of the cooking surface. The removability feature is particularly beneficial when a non-stick PTFE type surface is present on the cook surface since it permits periodic replacement of the cook surface and its non-stick surface. 
     Briefly stated, a presently preferred embodiment of the present invention comprises a heat sink plate with heating means associated therewith. The heat sink is surrounded by a vacuum when in use so as to provide a heat insulating environment for the heat sink so as to minimize heat loss and maximize energy efficiency. A food vessel tightly engages the heat sink along the cook surface thereof by virtue of the vacuum. In preferred embodiments, the invention contemplates that the heat sink is enclosed by a metal pot-shaped shell which communicates with a vacuum pump. The invention includes sealing means to contain the vacuum between the shell and the food vessel. 
     The food vessel is removable from vacuum engagement with the shell and heat sink to permit easy cleaning thereof. When the food vessel is so removed, the heat sink may be preheated or maintained at temperature under vacuum through the use of a lid which engages the sealing means and maintains the vacuum within the shell and around the heat sink. When the food vessel is prepared and loaded with ingredients for cooking, the vacuum is halted to permit removal of the lid and insertion of the food vessel in the shell. The vacuum is again established around the heat sink for heat insulation of the heat sink and for tight engagement between the heat sink and the cook surface of the food vessel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of the construction of one presently preferred embodiment of the vacuum cooking appliance of the present invention; and 
         FIG. 2  is a cross-sectional view of another embodiment of the vacuum cooking appliance of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Food preparation with an electrical cooking device represents certain advantages such as portability and versatility, and certain drawbacks such as lack of ease of cleaning, evenness of heating, and safety. The present invention provides an electrical cooking apparatus with unique features in construction and performance that addresses the shortcomings of the traditional electrical cooking apparatus. The central feature of this appliance is the use of vacuum as both an insulator and as a means of attaching the cooking vessel to the heat source.  FIGS. 1 and 2  schematically depict several generic arrangements of the apparatus of the present invention. 
     The vacuum cooking appliance  10  shown in  FIG. 1  is suitable for use as a food cooking or warming apparatus and particularly as a slow cooker corn popper or similar device. The appliance  10  includes an outer shell  12 , an inner food contacting vessel  14 , and a heat sink plate  16  supported within the shell  12  by support legs  18 . A resistance heater  20  is associated with the heat sink plate  16  having an external power cord and plug  22  associated therewith to supply electrical energy thereto. A ring-shaped gasket  24  positioned between outwardly flared flanged rims of the shell  12  and food vessel  14  provides a vacuum tight seal between the shell and vessel when the interior space  30  between shell  12  and food vessel  14  is evacuated by a vacuum pump  32 . The vacuum pump  32  communicates with the interior space  30  by way of a conduit  34  and passage  36  formed through the wall of the shell  12 . Controls include a thermostat  40 , solenoid  42  and vacuum switch  44 . A lid  50  is also preferably included to cover the food vessel  14  when in use and also during preheat. 
     Overview 
     A vacuum is created in the interior space  30  defined between the outer shell  12  and the food vessel  14  by the vacuum pump  32 . The high temperature seal  24  is somewhat compressible which allows the bottom wall or cook surface  15  of the food vessel  14  to come into intimate contact with the heat sink  16  as vacuum builds in space  30 . The heat sink  16  is a thicker plate of metal (copper, aluminum, steel, etc.) which is intended to store latent energy from the resistance heater  20 , then deliver that energy in a rapid and even manner to the cook surface  15  of the food vessel  14 . The mass of the heat sink plate  16  is adjusted to fit the application of the apparatus  10 . The heat sink plate  16  is preferably one of aluminum or copper. 
     The temperature of the heat sink  16  is controlled by the thermostat  40  which has a probe connected directly to the heat sink or by means of a non-contact sensing device. The elements of the resistance heater  20  may be mechanically attached to the heat sink  16  or may be cast into the heat sink. The wattage of the resistance heaters is adjusted according to the application of the apparatus  10 . The lid  50  is provided which securely fits the outer shell  12  as well as the food preparation vessel  14 . During a pre-heat period, the lid  50  is placed on the high temperature gasket  24  without the food vessel placed in the outer shell. The vacuum pump  32  is turned on and the resulting vacuum that is developed in the interior space defined between the lid  50  and shell  12  insulates the heat sink plate  16  during the heat-up period. To start the cooking cycle, the solenoid  42  opens and vents the evacuated space between the outer shell  12  and lid  50  so that the lid may be removed and the food vessel  14  put in place inside the shell  12 . The vacuum switch  44  turns on the vacuum pump  32  and the thermostat  40  turns on the resistance heaters  20  as energy flows to the food vessel. The legs  18  which support the heat sink  16  provide a spaced gap between the bottom of the heat sink  16  and the outer shell  12 . The height of the legs is adjusted to place the heat sink  16  in contact with the surface  15  of the vessel  14  so as to provide maximum clamping force between the food vessel  14  and heat sink  16  when the vacuum is applied. This great clamping force is possible by virtue of the fact that the space  30  is under vacuum while the space above the food vessel is at atmosphere. The resultant net force acting to press the surface  15  against the heat sink  16  may be well in excess of 1,000 pounds. The lid  50  which was used to maintain the vacuum during the pre-heat period fits the food vessel  14  and can be used as a lid during the cooking cycle. 
     The food vessel  14  can be made from a food grade material such as stainless steel or a less expensive material which is coated with a synthetic material such as a PTFE (non-stick). A multi-ply bonded material of stainless steel-aluminum-stainless steel, for example, would also be useful as a material for the food vessel  14  to promote heat flow to the vessel and to conduct heat throughout the vessel. 
     The wires to the resistance heater  20  and the thermostat  40  must pass through the outer shell  12 , such as through port  36 , without allowing loss of vacuum. This is accomplished through the use of appropriate gaskets and sealants. The vacuum port  36  to the outer shell can also double as the entry point for these wires to minimize the number of possible vacuum leakage points in the outer shell  12 . Energy consumption is minimized by the design of the apparatus as outlined below. 
     A. Convection loss is minimized by the evacuation of the space  30  surrounding the heat sink  16  during the heat-up period. Convection loss is minimized during the cooking cycle by reestablishing the vacuum after the lid has been removed and the food vessel  14  has been put in place in a sealed relationship at gasket  24  with the outer shell  12 . 
     B. Conduction losses are minimized by using a low conductivity material for the heat sink support legs  18  such as stainless steel or ceramics to space the heat sink plate  16  from the shell  12 . Also, the contact points for the legs  18  are kept to a minimum. Hence, loss of heat by conduction from the heat sink plate  16  to the shell  12  is minimized. 
     C. Radiant losses are minimized by providing a smooth reflective surface for the heat sink  16 , the interior and the exterior of the outer shell  12 . 
     Operation 
     With the food vessel  14  removed from the outer shell  12 , the lid  50  is placed on the vacuum seal  24  that is located at the top flange of the outer shell  12 . The apparatus  10  is turned on and the lid  50  is drawn down by the differential between the atmospheric pressure outside the lid and the vacuum beneath the lid, and the heat sink  16  begins to heat by virtue of the resistance heater  20 . When the apparatus has achieved the pre-set vacuum level (approximately 23 inches of mercury) and the desired pre-set temperature, both the vacuum pump  32  and resistance heater  20  turn off. When desired, the operator switches the solenoid valve  42  which vents the evacuated space between the food vessel and the outer shell to atmosphere to free the lid. The lid is removed from the outer shell and the food vessel  14  with the food to be cooked thereon is placed inside the outer shell  12  with the upper flange of the food vessel  14  resting on the high temperature seal  24 . Vacuum is reestablished and a tight clamping force is generated between the cook surface  15  of the food vessel  14  and the heat sink  16 . When the cooking cycle is finished, the food vessel  14  is removed and the unit is either turned off or the lid is replaced on the vacuum seal to maintain the heat in the heat sink  16 . 
     Advantages 
     Among the advantages provided by the present invention are the following: 
     A. Preheat—The time to preheat is separate from the cooking cycle. The apparatus can be left turned on and ready to cook but in an idle mode that is consuming little energy because the heat sink is surrounded by a vacuum. 
     B. Even Heating—The heat delivered to the cook surface  15  of the food vessel  14  is completely evenly distributed throughout the heat sink  16 . The high clamping force of atmospheric pressure eliminates air gaps between the heat sink  16  and the cook surface  15  to thus assure well distributed delivery of the latent energy in the heat sink to the cook surface. 
     C. Speed—The delivery of heat energy to the cook surface  15  of the food vessel  14  is instantaneous. 
     D. Accuracy—The thermostatically controlled heater  20  in the heat sink  20  delivers no more and no less than the desired temperature. 
     E. Easy Cleaning—The detachable food vessel  14  is easily removed for cleaning. 
     F. Simplicity—The technology of the apparatus is very simple and involves no complicated electronics. 
     G. Energy Efficiency—The design of this apparatus minimizes consumption of energy. When cooking, the energy yielded from the heat sink is conducted straight to the food being processed. 
     H. Safety—When used in a situation such as a buffet serving dish, there is no hot water or fuel container to present a safety hazard. There are no high frequency electromagnetic waves that could affect biomedical devices. 
     Possible Applications: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Chafing Dishes 
                 Panini Press 
               
               
                   
                 Slow Cookers 
                 Waffle Maker 
               
               
                   
                 Rice Makers 
                 Fun Foods (popcorn, cheese melt) 
               
               
                   
                 Commercial Warming Trays 
                 Commercial Braziers 
               
               
                   
                 Grill tops 
                 Coffee Makers 
               
               
                   
                 Electric Fry Pans 
                 Various Serve Ware 
               
               
                   
                 Two-sided Grill 
                 Soup Tureens 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLES OF INVENTION 
     Example 1 
     Popcorn Maker 
     An apparatus  10 , as depicted in  FIG. 1 , with an outer shell  12  of approximately 10″ circular diameter is fitted with a high temperature gasket  24  of a compressible nature around the top rim. A strong and well-insulated lid  50  is placed on the rim without the presence of a food vessel  14  and the apparatus is turned on for preheating. The preset temperature (350° F.) and vacuum (23 inches Hg) are quickly achieved and the vacuum pump  32  and resistance heater  20  automatically shut off. The apparatus sits in an idle state at temperature and under vacuum until cooking is desired. At that time, a food vessel  14  has ½ cup of vegetable oil and 1 cup of popcorn placed therein. The vacuum is vented to atmosphere by way of solenoid valve  42 , the lid  50  is removed and the food vessel  14  with the oil and popcorn therein is placed on the vacuum seal  24 . The vacuum pump  32  is then restarted. The lid that was previously on the outer shell during preheat is now placed on the food vessel  14  as the vacuum in the sealed-off space  30  between the food vessel  14  and the outer shell  12  increases. The vacuum condition forces the cook surface  15  to forcibly engage the heat sink plate  16 . Energy rapidly conducts to the cook surface  15  of the food vessel and then to the oil and popcorn. The popcorn is processed in less than 2 minutes, leaving no unpopped kernels. After releasing the vacuum, the food vessel  14  is removed and the lid is put back on the outer shell rim. The vacuum and heat sink temperature are reestablished to the idle state where the temperature of 350° F. is maintained in the heat sink plate  16 . The popping cycle is repeated with very little heat loss and minimized energy consumption. After use, the food vessel  14  may be completely immersed in water for ease of cleaning. 
     Example 2 
     Griddle 
     The apparatus depicted in  FIG. 2  with reference to Example 2 has generally the same structural elements as the apparatus shown and described in  FIG. 1 . Accordingly, like elements will be designated with the same numerals, but with prime symbols added in  FIG. 2 . 
     As shown in  FIG. 2 , an apparatus  10 ′ of the same generic construction as Example 1, but with an outer shell  12 ′ of rectangular shape, for example, measuring 12 inches by 16 inches, is fitted with a strong, well-insulated lid  50 ′ that will withstand the atmospheric pressure without collapsing under vacuum during the preheat period. The plane of the heat sink  16 ′ is only ⅛″ below the plane of the top of the vacuum seal  24 ′ in its uncompressed state. The apparatus reaches preset heat and vacuum levels and idles. When desired, the vacuum is broken and the lid  50 ′ is removed and replaced with a flat thin sheet of stainless steel or titanium which acts as a food vessel  14 ′ in the form of a griddle cooktop  15 ′. Atmospheric pressure secures the stainless sheet defining food vessel  14 ′ in place at the seal  24 ′ and on the heat sink plate  16 ′. The latent energy from the heat sink  16 ′ allows meat, such as hamburger patties, to be cooked rapidly and evenly across the griddle plate cooktop  15 ′. By way of example, the heat sink plate  16 ′ may be an aluminum plate about 0.75 inches thick and the food vessel  14 ′ may be a sheet of 304 stainless steel having a thickness of about 0.017 inches. The preheat lid  50 ′ fits over the stainless sheet  14 ′ to promote cooking, minimize heat loss and prevent splatter. Since the griddle cooktop  15 ′ is in intimate contact with the heat sink plate  16 ′ by virtue of the vacuum condition within the interior  30 ′, the cooktop  15 ′ will remain at a constant temperature over its entire surface and will also experience almost instantaneous thermal recovery when cold or frozen food is placed on the surface of cooktop  15 ′. This is particularly advantageous in commercial griddles where frozen hamburger patties are cooked. Thus, the invention ensures uniform and safe cooking in a commercial food preparation environment. 
     Example 3 
     Two-Sided Grill/Waffle Maker 
     Two outer shells (not shown, but similar in concept to shell  16 ) are attached by a hinge in a “clam shell” type of arrangement. Both halves are equipped with a heat sink  16  and a port  36  to a vacuum pump  32 . When the two halves are closed on each other, high temperature seals  24  around the perimeter of each shell contact the other. In other words, the clam shell is closed and the vacuum seal of each half contacts the other half. Vacuum is established and the heat sinks  16  in each half are preheated to a desired temperature. When desired, the vacuum is vented to atmosphere and the claim shell is opened. Grill vessel plates  14  which may include cast aluminum with a non-stick coating are placed against the vacuum seals  24  and vacuum is established in each of the two halves. When the clam shell is closed again, it may be used as a waffle maker, a two-sided grill, a panini press, or any other two-sided heat source application. The usage is determined by the plates or sheets  14  which are vacuum attached to the heat sinks  16  within the outer shells  12 . 
     Example 4 
     Warming Pan/Chafing Dish 
     This example is similar to Example 1, however, the outer shell  16 , food preparation vessel  14  and lid  50  may be shaped in a rectangular configuration (in plan view) to assume the general size and configuration of a commercial warming tray or chafing dish. In such commercial settings, it is important to maintain the already cooked food at a holding/serving temperature between about 167° F.-185° F. This temperature range is of importance because bacteria will grow at temperatures below 167° F. and cooking will continue at temperatures above 185° F. The operation of the food warming device of this example is the same as that set forth in the previous examples except that the temperature of the heat sink plate is maintained between 167° F.-185° F. so that precooked food placed in the food vessel  14  remains at a safe temperature during holding/serving without being overcooked.