Patent Publication Number: US-7223944-B2

Title: Oven temperature control system

Description:
Priority for this nonprovisional patent application is claimed on the basis of and from U.S. Provisional Patent Application No. 60/559,088, filed Apr. 1, 2004. 

   The present invention relates to residential cooking ovens and, in particular, to a system for more accurately monitoring and controlling the temperature within the oven and providing specific heating modes and temperatures for different modes of cooking. 
   Residential cooking ovens are normally provided with a top heating element at the ceiling of the oven cell and a bottom heating element at the bottom wall of the oven cell with a control system for activating one or both of the heating elements for a particular mode of cooking. For example, for cake baking only the bottom heating element might be activated, for steak broiling normally only the top element would be activated, and for cooking a meat roast both elements might be activated. In addition, some modern residential ovens also include a convection heating element on the back wall of the oven cell and a fan for circulating the heated air throughout the oven cell, with the oven control also activating the top and/or bottom heating elements. Some top and bottom heating elements may be comprised of two separate elements with the oven control activating one or both elements for low or high heating, respectively. The heating elements are cycled on or off for maintaining the desired temperature as set by a temperature control for the oven which is responsive to a temperature sensor probe positioned in the oven. However, all portions of the oven are not at the same temperature and therefore the temperature control is merely a result of a representative temperature at the location of the temperature sensor probe. 
   The present inventors have found that better temperature control within the oven cell improves the precision with which foods are cooked within the oven. Moreover, the present inventors have found that certain cooking modes for cooking certain foods are improved by sensing the temperature within the oven at different locations for controlling the cooking process. 
   It is a principle object of the present invention to provide an oven temperature control system wherein a plurality of temperature sensors are positioned at different locations in the oven cell and the temperatures sensed by such plurality of sensors are proportionally averaged for providing the control temperature for the oven. A further object of the present invention is to provide such an oven temperature control system wherein the proportional averaging of the sensed temperatures is varied or weighted among the plurality of sensors based on the cooking mode selected. A still further objective of the present invention is to provide such an oven temperature control system wherein the selected cooking mode determines which of the heating elements are to be activated and controlled by the proportional averaging of the temperatures sensed by the plurality of temperature sensors. 

   
     Other and more detailed objects and advantages of the present invention will become more apparent to those skilled in the art from the following description and drawings of a preferred embodiment, wherein: 
       FIG. 1  is a perspective view of a typical cooking oven for residential use incorporating the present invention; 
       FIG. 2  is a sectional elevation view taken substantially on the line  2 — 2  in  FIG. 1  for illustrating the interior of the oven; 
       FIG. 3  is a diagrammatic front view of the oven of  FIG. 1  showing the preferred locations of the plurality of temperature sensing probes for one embodiment of the control system of the present invention; 
       FIG. 4  is a diagrammatic side view of the oven of  FIG. 3  showing the locations of the temperature sensing probes; 
       FIG. 5  is a diagrammatic front elevation view of the oven similar to  FIG. 3  but illustrating a different number and locations of the plurality of temperature sensing probes in another embodiment of the control system of the present invention; 
       FIG. 6  is a diagrammatic side elevation view similar to  FIG. 4  of the oven of  FIG. 5  but illustrating different locations for the temperature sensing probes; and 
       FIG. 7  is a chart of an algorithm matrix for the heating elements and temperature sensors for a variety of cooking modes for the oven. 
   

   Referring now in detail to  FIGS. 1 and 2  of the drawings, the oven  10  incorporating the present invention is shown diagrammatically as an oven cell with six insulated walls, namely, a top wall  12 , a bottom wall  14 , a right side wall  16 , a left side wall  18 , a rear wall  20  and a front wall  22 . The front wall  22  is provided with a door  24  that is tightly sealed in the door opening  25  in the front wall  22  when the door  24  is closed, as shown in  FIG. 2 . 
   The interior of each of the side walls  16  and  18  is provided with a conventional grate rack  28  for supporting a rod type grate  30  at any desired level within the oven for in turn supporting a pan  32  or the like for receiving the food to be cooked. 
   A bottom heating element  36  is provided along the interior of the bottom wall  14  and a top heating element  38  is provided along the interior of the top wall  12 . The heating elements  36  and  38  may be of a conventional type, either gas or electric, but electric heating elements are preferred for use with the oven temperature control system of the present invention. Further, it is also preferred that the heating elements  36  and  38  each have two separate elements that may be separately activated for either high (two elements) or low (one element) heating. Still further, it is preferred that the heating elements  36  and  38  each be comprised of two separate ribbon-like electric conductors (not shown) embedded on edge in a ceramic insulating material because of the rapid rise in temperature developed by such heating elements. The inventors have found that electric heating elements sold under the trademark “CERAMASPEED” by Ceramaspeed, Inc. of Kidderminster, England are well suited for the top and bottom electric heating elements  36  and  38  for the oven using the present invention, although any similar heating elements by any other manufacturer that has similar characteristics would be acceptable. The CERAMASPEED heating elements include two separate corrugated metallic ribbons that may be separately activated, with one metallic ribbon formed in a serpentine arrangement to cover most of the area (an “inner” element) and the second metallic ribbon arranged in loops extending around the periphery of the unit (an “outer” element). The metallic ribbons of the bottom and top heating elements  36  and  38  preferably are covered and protected by a plate of high temperature and impact resistant glass (not shown) which preferably also is transparent or at least semi-transparent for allowing the transmission of infrared light for heating. Two such glass plates have been found acceptable, namely, CERAN-HIGHTRANS and ROBAX by the Schott Corporation, Technical Glass Division, Appliance Products Group, Yonkers, N.Y. 
   The oven  10  may also be provided with a conventional convection oven assembly, generally designated  40 , on the rear wall  20 . The convection oven assembly  40  includes a fan  42  driven by an electric motor  44  and surrounded by a heating element  46  for drawing air from the interior of the oven through a metal screen filter  48  mounted in the front of an enclosure  49 . The fan  42  discharges the air heated by the element  46  into the oven cell through the right and left ends of the enclosure  49 . The convection oven assembly  40  may be operated in the conventional manner and for purposes of the chart set forth in  FIG. 7 , the heating element  46  is the “Rear Element” and the fan  42  is the “Conv. Fan”. 
   Referring now to  FIGS. 1–4 , one preferred arrangement of a plurality of temperature sensing probes is illustrated. Specifically, a probe P 1  is positioned in the upper right hand corner adjacent top wall  12  and right side wall  16 , probe P 2  is positioned adjacent the left hand wall and about midway between the top wall  12  and bottom wall  14 , probe P 3  is positioned adjacent the right hand wall  16  and about midway between the top wall  12  and bottom wall  14 , and probe P 4  is positioned in the lower left corner adjacent the left side wall  18  and bottom wall  14 , as best shown in  FIG. 3 . In this embodiment each of the probes P 1 , P 2 , P 3  and P 4  are adjacent the rear wall  20 , as shown in  FIG. 4 . 
   In another preferred embodiment of the temperature sensing probe arrangement of the present invention as shown in  FIGS. 5 and 6 , the temperature probes P 1 , P 2 , P 3  and P 4  are positioned with respect to the top, bottom and side walls in the same pattern described with respect to  FIG. 3 , as shown in  FIG. 5 . However, temperature probes P 1  and P 4  are spaced from the rear wall  20  toward the front wall  22 , as shown in  FIG. 6 . Moreover, a fifth temperature sensing probe P 5  is provided adjacent the top wall  12  midway between the side walls  16  and  18  and at the rear wall  20 , as shown in  FIGS. 5 and 6 . In this embodiment of  FIGS. 5 and 6 , the temperature within the oven cell is not sensed solely along the rear wall  20  for thereby providing a more representative temperature within the oven cell. While two patterns of locations for multiple temperature probes are shown in  FIGS. 3–6 , it is to be understood and will readily appear to those skilled in the art that numerous other patterns of more or fewer temperature probes may be provided for more or fewer samplings of the temperatures throughout the oven cell during operation. 
   Each of the temperature sensing probes, such as probes P 1 –P 4  in  FIGS. 3 and 4  and probes P 1 –P 5  in  FIGS. 5 and 6 , is connected to a control means  50  for supplying the temperature sensed by that temperature probe to the control means  50 . The temperature sensing probes are preferably of the resistance temperature device (“RTD”) type, although other types may be used. An RTD has two wires and one wire of each may be connected in series with other RTDs although it is preferred that not all of the RTDs be connected in series to avoid a complete failure of temperature sensing if only one sensor fails. Thus, at least one sensor is separately connected to the control means  50 . The control means  50  includes a microprocessor for calculating a proportional average temperature in the oven cell as the single temperature preselected by the control means  50  as the desirable temperature that the heating elements  36 ,  38  and/or  46  will maintain in the oven cell. For each selected mode of cooking, the control means  50  develops a proportionally averaged or combined temperature as the overall sensed temperature by adding a percentage of each temperature sensed by the plurality of probes to then comprise the oven temperature. For example, if each of the four temperatures from probes P 1 –P 4  were assigned an equal weight of 25%, then the resultant oven temperature would be the mathematical average of those four temperatures, i.e. the four temperatures added together and divided by 4. On the other hand, for a given cooking mode, it may be preferable to average the sensed temperatures in different proportions, such as 0% for P 1 , 40% for P 2 , 40% for P 3  and 20% for P 4  or any other proportions including, for example, 100% for P 4  for broiling for achieving the maximum temperature because P 4  is located at the bottom of the oven. 
   Referring now to  FIG. 7 , a chart of different cooking modes illustrates the heating elements to be activated and the temperature sensing probes to be used in the proportional averaging of the oven temperature. As a representative example for a description of an application of the control system of this invention to an oven, the aforedescribed preferred oven with two separate heating circuits (corrugated ribbons) in each of the top and bottom heating elements  38  and  36 , respectively, and convection oven assembly  40  will be used although it will be understood that the invention is equally applicable to other oven constructions having more or fewer heating elements. For convenience, three cooking modes have been selected as representative but numerous other cooking modes will normally be included in the control system. A brief description of the cooking mode is set forth in the left-hand column of  FIG. 7  under “Mode”. The next eight columns refer to operating modes of the various components and an “X” means that the component is operated in that mode. In some cooking modes the component may be pulsed or operated intermittently. For the next eight columns from left to right the legends have the following meanings: 
   “Pre-Heat” means that a preheat cycle is used for that cooking mode; 
   “Element-Top Inner” means the inner of two heating elements in the top heating element  38 ; 
   “Element-Top Outer” means the outer of the two heating elements in the top heating element  38 ; 
   “Rear-Element” means heating element  46  in the convection oven assembly  40 ; 
   “Conv. Fan Lo” means the fan  42  of the convection oven assembly  40  is operated at a low speed; 
   “Conv. Fan Hi” means the fan  42  of the convection oven assembly  40  is operated at a high speed; 
   “Element-Bottom Inner” means the inner heating element of the two elements in bottom heating element  36 ; and 
   “Element-Bottom Outer” means the outer of the two heating elements in the bottom heating element  36 . 
   The next four columns in the chart of  FIG. 7  under the legend “Temp Sensor %” represent in columns  1 ,  2 ,  3  and  4  the percentage of weight to be given to the temperature sensed by the temperature probes P 1 –P 4 , respectively, which temperature probes are located in the oven cell in the positions shown in  FIGS. 3 and 4  as also indicated in the small diagram above the chart in  FIG. 7  as a front view. For example, for the first Mode “Surround Bake” the temperature probe P 1  will be given 10% weight, the temperature probe P 2  will be given 40% weight, the temperature probe P 3  will be given 40% weight and the temperature probe P 4  will be given 10% weight to determine the proportional average temperature in the oven cell. For the second Mode “Pure Convection” the temperature probes P 1  and P 4  will be given 0% weight and temperature probes P 2  and P 3  each will be given 50% weight. For the third Mode “Broil” the temperature probe P 4  is given 100% weight while probes P 1 , P 2  and P 3  are given 0% weight. 
   The next column in the chart of  FIG. 7  headed “Jump-In Temp” provides the desired temperature to be used during that cooking mode and would be displayed as the preselected temperature. The next column headed “Temp Range” indicates the desired temperature range to be maintained above and below the preselected desired temperature in the oven cell for that Mode. 
   Thus, as described above, the present invention allows a more precise measurement and representation of the actual temperature in an oven cell at or near the location in the oven cell that is most significant to the mode of cooking that is being used by proportionally averaging the temperatures sensed by a plurality of temperature sensing probes. The precise percentages for proportional averaging of the temperatures set forth in  FIG. 7  are merely representative and may be selected by any desirable criteria. The percentages for proportional averaging of the temperatures may be varied by other criteria, such as the weight or type of item being cooked, for any given cooking mode if that is found to be desirable. Moreover, the cooking mode, desired temperature, time period, item weight, or the like may be selected from a menu on the control means  50  and displayed for verification by the operator. The display also may include a touch screen for ready selection of all of the cooking criteria.