Abstract:
A bottom electric heating element for an oven wherein the electric heating element is positioned in a recessed portion in the oven bottom and comprises at least one corrugated ribbon of conductive material partially embedded in an insulating base. A glass panel is positioned over the recessed portion and on a compressible heat resistant gasket. The glass panel is transparent or semi-transparent, high temperature resistant and high impact resistant. A frame extends around the glass panel and fastens it to the oven bottom while partially and resiliently compressing the gasket to support the glass panel.

Description:
RELATED APPLICATION 
   This is a continuation of U.S. patent application Ser. No. 10/817,258, filed Apr. 1, 2004 now U.S. Pat. No. 6,949,720, the disclosure of which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to ovens with electric heating elements and to electric heating element systems. 
   Electric cooking ovens for residential use normally have an electric heating element along the bottom wall of the oven and an electric heating element along the top wall or ceiling of the oven, although a recent innovation has employed a gas broiler for the top heating element in an electric oven, as shown in U.S. Pat. No. 5,909,533. Electric cooking ovens are desirable for many reasons, such as the ability to be self-cleaning by developing an extremely high temperature. Conventionally the electric heating element for the bottom of a residential oven has been a Calrod which is supported by a wire frame a short distance above the bottom surface of the oven. The Calrod is an electric resistance heater rod and, when activated, begins to glow and produce heat and some infrared light waves. The Calrod heating element may be open to the oven or in some oven constructions is placed below a steel sheet coated with porcelain enamel that provides a bottom surface of the oven that may be wiped clean without removing the calrod heating element. In older ovens the Calrod element can be removed for cleaning the bottom of the ovens where the Calrod heating element is exposed. However, the porcelain enamel coating often cracks under the high temperatures to which it is subjected, such as by the self-cleaning cycle. 
   Recently, a ribbon-type heating element has been used as both the top and bottom heating elements in residential ovens because of the more rapid increase in temperature and higher temperature that may be achieved by such a ribbon-type element but the ribbon is susceptible to damage so it must be covered. While a high temperature glass has been used to cover and protect the ribbon-type heating element when used as the upper element, the porcelain enamel metal sheet that is used to protect the ribbon type bottom heating element is highly susceptible to cracks. Moreover, the porcelain enamel coated metal sheet illuminates infrared heating from the bottom element and is a poor heat conductor. 
   Both as a practical matter and to meet modern safety requirements, the bottom heating element in an electric oven must successfully resist liquid spills and impacts from pans, which has led to the use of the porcelain enamel coated sheet immediately above the bottom heating element which creates the inefficiencies and potential failures noted above. Heretofore a glass cover over the bottom electric heating element has been unacceptable because of the inability to meet the required impact resistance requirements and, to a lesser extent, the liquid spill resistance requirements. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to an electric heating element system having an electric heating element positioned on a bottom wall with a compressible, nonbonding and heat resistant gasket positioned on the wall and a glass panel removably positioned over the electric heating element and on the gasket. A frame is arranged on an upper surface of the glass panel about its perimeter. The frame extends outwardly over an adjacent portion of the wall. 
   In a first separate aspect of the present invention, the frame has fasteners mounting the frame to the wall. The fasteners cause the frame and glass panel to partially compress the gasket for resilient support of the glass panel. 
   In a second separate aspect of the present invention, the frame has a sheet having inner and outer peripheral portions bent downwardly with fasteners mounting the frame to the wall between the inner and outer peripheral portions. 
   In a third separate aspect of the present invention, a bottom wall is included with a central recessed portion in the electric heating element system. The gasket is positioned on the wall about the periphery of the central recessed portion. 
   In a fourth separate aspect of the present invention, the foregoing separate aspects are contemplated to be in combination with an oven including an enclosure with top, sides, and rear walls, the bottom wall and a open front wall with a door. 
   In a fifth separate aspect of the present invention, any of the foregoing separate aspects are contemplated to be combination to further advantage. 
   Thus, it is a principle object of the present invention to provide a system for using a glass cover on a bottom electric heating element in a wall. The system is of particular applicability for an oven. Other objects and advantages will become apparent hereafter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a typical oven having the bottom electric heating element system of the present invention; 
       FIG. 2  is a perspective view of the bottom pan of the electric oven with the bottom electric heating element system of the present invention; 
       FIG. 3  is an exploded view of the bottom electric heating element system illustrated in  FIG. 2 ; and 
       FIG. 4  is a sectional elevation view of the bottom electric heating element system of the present invention taken substantially on the line  4 - 4  in  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIG. 1 , a typical residential oven  10 , such as the type that is wall mounted separate from a cooktop, is illustrated but it will be understood that the present invention is applicable to any form of residential cooking oven including ovens combined with a cooktop range, warming ovens or other cooking ovens. The oven  10  includes an open front wall closeable by a door  12  and walls forming a top or ceiling (unnumbered), sides  14 , rear  16  and bottom  18 . The top wall of the oven  10  may include a broiler-heating element that may be either gas or electric. The sidewalls  14  will include ledges (not shown) for supporting horizontal racks (not shown) that in turn support the cooking pans. The bottom wall  18  includes the bottom electric heating element system, generally designated  20 , of the present invention. 
   Referring now to  FIGS. 2-4 , the bottom electric heating element system  20  is mounted in a bottom pan  22  that forms the bottom wall  18  of the oven  10 . The bottom pan  22  and bottom electric heating element system  20  are shown separate from the remaining components of the oven  10  for the convenience of illustration. Further, the bottom pan  22  is shown with only a pair of flanges  24  along two edges for attaching to the other components of the oven  10  and it is to be understood that the other two edges of the bottom pan  22  also will be provided with flanges or other means for securing the bottom pan  22  in the oven  10  but the size, shape or extent of any such attachment means on the bottom pan  22  are not relevant to the present invention. 
   A major portion of the bottom pan  22  in the central area has a recessed portion  26  of a size and depth to accommodate the components of the bottom electric heating element system  20  of the present invention. An upwardly facing ledge  28  is provided around the perimeter of the upper end of the recessed portion  26  and spaced downwardly below the upper surface  22   a  of the bottom pan  22 . 
   An electric heating element assembly, generally designated  30 , is provided in the recessed portion  26  of the bottom pan  22 . The electric heating element assembly  30  preferably includes two separate heating elements  32  and  34  that preferably are formed of a corrugated metallic ribbon, although other forms of heating elements may be used. Also, a single or more than two heating elements may be used, as will readily appear to those skilled in the art. 
   The first heating element  32  comprises a single length of metallic ribbon that is formed in a serpentine arrangement to cover most of the upper surface of the electric heating element assembly. The two ends  32   a  and  32   b  of the ribbon-like element  32  extending into the rear wall of the assembly  30  where each is separately joined to an electrical connector, such as connector  36  shown in  FIG. 4 . 
   The second electric heating element  34  is also comprised of a corrugated ribbon-like element and preferably is formed into multiple loops extending around the internal periphery of the electric heating element assembly  30  with two such loops shown in the preferred embodiment in  FIG. 2 . The two ends  34   a  and  34   b  of the ribbon-like element  34  also extend into the rear wall of the electric heating element assembly  30  and are joined to separate electrical connectors  36 . 
   The ribbon-like electric heating elements  32  and  34  are embedded in a ceramic insulating material  38  which is formed to provide a peripheral wall portion  38   a  of a sufficient height to protect the heating elements  32  and  34 . The insulating material  38  is of a sufficient thickness vertically that the bottom wall  26   a  of the recessed portion  26  of the bottom pan  22  does not become over heated. The inventors have found that an electric heating element assembly  30  sold under the trademark “CERAMASPEED” by Ceramaspeed Ltd. of Kidderminster, England is well suited for use in the bottom electric heating element system  20  of the present invention, although any similar assembly  30  by any other manufacturer that has similar characteristics would be acceptable. 
   In the preferred assembly  30 , the electric heating elements  32  and  34  have a 3100 watt rating with element  32  having a 1600 watt rating and element  34  having a 1500 watt rating, which provides excellent and rapid heating for the oven  10 , although it is to be understood that any wattage ratings may be used. By separately operating electric heating element  32  without operating electric heating element  34 , a lower heating rate and maximum temperature may be provided. If even greater control over the heating rate and maximum temperature were desirable, three or more separate heating elements may be provided in the assembly  30 . 
   A separate insulating wall  40  is provided and encircles the electric heating element assembly  30  to minimize the heat transfer from the assembly  30  to the vertical wall  26   b  of the recessed portion  26  of the bottom pan  22 . A gasket  42  is provided on the ledge  28  surrounding the recessed portion  26  of the bottom pan  22 . A glass panel  44  is supported on the gasket  42  and ledge  28 . 
   The glass panel  44  is held in place by a metal frame  46  surrounding the upper peripheral surface of the glass panel  44  and overlapping a portion of the upper surface  22   a  of the bottom pan  22 . The frame  46  has outer and inner peripheral edge portions  46   a  and  46   b , respectively, that are bent downwardly a small amount from the main portion of the frame  46  extending between those edge portions. The frame  46  is provided with a plurality of holes  48 , eight of which are shown in  FIGS. 2 and 3 , through which fastening screws (not shown) are provided for securing the frame to the bottom pan  22 . The holes  48  are between the downwardly bent edge portions  46   a  and  46   b  of the frame  46  so that the tightening of the screws flexes the frame  46  to resiliently apply a downward mounting force to the glass panel  44 . In turn, the glass panel  44  resiliently compresses the gasket  42 , whereby the glass panel  44  is resiliently supported in this bottom electric heating element system  20 . The glass panel  44  also engages the upper end of peripheral wall portion  38   a.    
   The resilient support arrangement for the glass panel  44  allows for the different rates of thermal expansion of the various components and assists in absorbing impacts to the glass panel  44  without breakage. In the assembled condition, the upper surface of glass panel  44  is approximately level with the upper surface  22   a  of the bottom pan  22 . 
   While various forms and compositions of the gasket  42  may be acceptable for use in the bottom electric heating element system  20  of the present invention, a so-called “Clip Gasket” oven seal made by Davlyn Manufacturing Co., Inc. is preferred. This Clip Gasket oven seal is conventionally used around the periphery of the front opening of an oven and has been found to successfully resist the high oven temperatures and provide excellent sealing. The Clip Gasket is comprised of a braided ECG fiberglass tube surrounding a knitted stainless steel wire tube or spring that retains its resiliency even in the high temperatures associated with a cooking oven. Thus, the glass panel  44  is effectively supported by a resilient, tubular spring in the gasket  42 . The gasket  42  is held in place on ledge  28  by a plurality of stainless steel wire clips  50  that are spaced along and protrude from the gasket  42  for inserting through holes  52  provided in the ledge  28  of the bottom pan  22 . 
   The glass panel  44  is comprised of a high temperature and impact resistant glass that preferably is transparent or at least semi-transparent for allowing the transmission of infrared light for heating the oven. One such glass panel  44  that has been found acceptable is sold under the trademark CERAN-HIGHTRANS by Schott Corporation, Technical Glass Division, Appliance Products Group, Yonkers, N.Y. and it is either a black or orange-brown color, resists thermal stress with a temperature differential of about 1200° F., and resists thermal stress fracture by shock up to about 1200° F., such as by dousing with cold water. The black CERAN-HIGHTRANS glass has a pleasing black appearance but when the electric heating elements  32  and  34  are activated they are readily visible as glowing ribbons that provide an immediate visual indication that the oven is in a heating mode. Another high temperature and impact resistant glass that is also suitable for glass panel  44  is sold under the trademark ROBAX by the Schott Corporation, which is a clear and transparent glass. 
   The above-described bottom electric heating element system  20  of the present invention overcomes the disadvantages of prior art bottom electric heating elements in that the conventional porcelain enamel coated steel cover over the heating element is eliminated to thereby allow more efficient heat transfer from the heating elements to the oven cavity as well as providing infrared heating. The glass panel  44  is not susceptible to deterioration and cracking as is the porcelain enamel coating on a steel panel and may be easily cleaned. 
   The resilient supporting arrangement for the glass panel  44  as provided by the resilient gasket  42  and the resilient mounting frame  46  enhances the impact resistance of the glass panel  44  and avoids any problems of differential rates of thermal expansion of the components. While the frame  46  with its outer edge  46   a  engaging the upper surface  22   a  of the bottom pan  22  and its inner edge  46   b  engaging the glass panel  40  resists the intrusion of any liquid spills into the recessed portion  26  of the bottom pan  22 , any such spillage that bypasses the frame  46  will be absorbed by the gasket  42  or excessive leakage will merely drain to the bottom of the recessed portion  26 . In the unlikely event that there is a malfunction in the electric heating element assembly  30  or the glass panel  44  breaks, maintenance may be readily performed by merely removing the frame  46  from the bottom pan  22  by removing the mounting screws (not shown) and then lifting the various components out of the recessed portion  26  of the bottom pan  22 . In the heretofore conventional bottom electric heating element systems any such malfunctioned usually required replacement of the entire oven cavity walls. 
   Although a specific, preferred embodiment of the present invention is described above, it is to be understood that various modifications of that preferred embodiment will readily appear to those skilled in the art and yet fall within the scope of the present invention as defined by the following claims.