Patent Publication Number: US-6222163-B1

Title: Gas oven incorporating auxiliary electric heating element

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to the art of cooking and, more particularly, to the incorporation, mounting and control of an auxiliary electric heating element within a gas oven. 
     2. Discussion of the Prior Art 
     Hybrid ovens have been proposed in the art of cooking appliances. More specifically, it has been previously proposed to provide a combination gas/electric oven wherein gas and electric heating elements can be used independently or simultaneously as heat sources for the oven. Typically, the electric heating element is utilized only for certain periods, i.e., during particular modes of operation of the appliance. For example, U.S. Pat. No. 2,463,712 discloses a hybrid cooking appliance incorporating an electric heating element which is particularly used for broiling purposes, but the electric heating unit can also be used when the oven cavity is to be heated above a predetermined temperature during a baking mode of operation. However, during the baking operation, once the oven has reached a desired temperature condition, a thermostat functions to automatically cut off the electric heating element such that the oven temperature is maintained through operation of the gas alone. 
     In another exemplary arrangement as disclosed in U.S. Pat. No. 3,423,568, upper and lower electric heating elements can be used by themselves or simultaneously with upper and lower gas burners to heat an oven cavity. However, the oven is primarily intended to be used with gas for normal cooking purposes, while the electric heating elements are particularly adapted for use during oven cleaning periods. 
     Regardless of these prior arrangements, there still exists a need in the art for a combination gas and electric cooking appliance wherein an electric heating element is effectively used during various modes of operation of the appliance. More specifically, there exists a need for a cooking appliance incorporating an electric heating element which is constructed and mounted within an oven cavity in a manner that enables the electric heating element to be efficiently utilized during baking, broiling and/or cleaning modes of operation. 
     SUMMARY OF THE INVENTION 
     The present invention is concerned with incorporating an electric eating element at a top portion of a gas oven cavity. That is, the oven cavity includes a lower gas burner unit, an upper gas burner unit and an upper, auxiliary electric heating element. The electric heating element is preferably arranged in a substantially horizontal plane at a position no closer to a top wall portion of the oven cavity than the ports associated with the upper gas burner unit in order to minimize any flame impingement upon the electric heating element. The electric heating element can be utilized during various modes of operation of the cooking appliance, such as during baking, broiling and cleaning operations. 
     More specifically, the most preferred form of the invention has the electric heating element operating in unison with the lower gas burner unit to pre-heat the oven cavity for a baking operation and then the electric heating element is cycled on and off while the lower gas burner unit is operated in a full state during the baking mode. During a broiling operation, the electric heating element preferably operates on full with the upper gas burner unit in order to establish a substantial uniform temperature throughout the oven cavity. During a cleaning operation, the electric heating element is preferably, initially operated to pre-heat the oven cavity at a controlled rate prior to operation of the upper and lower gas burner units. A controller is used to regulate the operation of each of the gas burner units and the electric heating element in the manner set forth above based on signals received from at least one temperature sensor and operator input controls. 
     Additional objects, features and advantages of the present invention will become more fully apparent below from the following detailed description of a preferred embodiment when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a gas oven incorporating an auxiliary electric heating element and a related control system in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     As shown in FIG. 1, an oven  2  includes a cavity  5  defined by top, bottom, rear and side walls  8 - 12  respectively. Cavity  5  is adapted to be closed by means of a door  15  that is illustrated to include tempered glass section  17 . In accordance with the invention, oven  2  can constitute a portion of a range or part of an oven wall unit. In either case, to develop heat within oven cavity  5  for cooking food items placed therein, oven  2  includes a first gas burner or baking unit  21 , a second gas burner or broiling unit  22  and an electric heating element  25 . 
     More specifically, first gas burner unit  21  generally takes a form known in the art and therefore includes an elongated manifold  27  that is provided with various gas emitting ports  29 . Ports  29  generally open towards a flame spreader plate  31  that extends on opposing sides of manifold  27  and which takes the form of a flattened V-shape piece. As clearly shown in this figure, first gas burner unit  21  is preferably mounted beneath bottom  9  of oven cavity  5 . In a similar manner, second gas burner unit  22  includes a flame spreader  35 , that generally takes a flattened V-shape, and a manifold  37  having a plurality of gas emitting ports  39 . The actual construction and general operation of first and second gas burning units  21  and  22  is actually well known in the art, does not form part of the present invention and therefore will not be discussed further herein. 
     In a manner also known in the art, side walls  11  and  12  of oven cavity  5  are preferably provided with a plurality of fore-to-aft extending and vertically spaced runners, one of which is indicated at  44 . The runners  44  are arranged in associated pairs on side walls  11  and  12  in order to support an elongated rack  46  that extends across substantially the entire width of oven cavity  5 . Of course, elongated rack  46  can be supported upon any respective pair of runners  44  such that rack  46  can assume various vertical positions within cavity  5 . For the sake of simplicity of the drawing, runners  44  have been shown to be vertically spaced quite a distance on each of sides  11  and  12  when actually, additional runner  44  would be provided such that the spacing would be much less than that shown. In any event, the arrangement and mounting of rack  46  within cavity  5  is not considered part of the present invention such that it will not be discussed further herein. Instead, the present invention is particularly directed to the inclusion of electric heating element  25 , its particular mounting arrangement relative to second gas burner unit  22  and the manner in which electric heating element  25  is operated in conjunction with one or more of first and second gas burner units  21  and  22 . 
     In accordance with the most preferred form of the invention, electric heating element  25  generally takes a U-shaped form, including fore-to-aft legs  53  and  54  and a connecting leg  56 . Electric heating element  25  is preferably constituted by a sheathed electric resistance element similar to those typically found in a conventional electric range. Although not particularly shown in the drawing, each of legs  53  and  54  would be provided with a terminal connector that projects through rear wall  10  of oven cavity  5 , with the connectors being attached to wires for activating/de-activating electric heating element  25 . As shown, electric heating element  25  is mounted in a position spaced below top wall  8  of oven cavity  5 . More specifically, manifold  37  of second gas burner unit  22  extends in a generally horizontal plane which is spaced below top wall  8  of oven cavity  5 . Electric heating element  25  is preferably mounted within oven cavity  5  at a position no closer to top wall  8  than ports  39  of manifold  37 . During operation of second gas burner unit  22 , the flames extending from manifold  37  would be directed onto flame spreader  35  in order to enhance the distribution of heat generated within oven cavity  5 . The mounting of electric heating element  25  relative to ports  39  in the manner described above avoids direct impingement of legs  53 ,  54  or  56  by the flames. Furthermore, the relative mounting of second gas burner unit  22  and electric heating element  25  has been found to minimize any affect of the heat generated by electric heating element  25  on the combustion of gas associated with second burner unit  22 . As will be discussed more fully below, this mounting, as well as the configuration of electric heating element  25 , balances hot and cold spots that can be generated within oven cavity  5  during operation thereof. 
     At this point, it should be understood that electric heating element  25  can take various shapes and can be mounted in numerous ways, such as through the use of hanging brackets which extend around portions of legs  53 ,  54  and  56  and are secured to top wall  8  of cavity  5 . The actual wattage rating of electric heating element  25  would depend on the supplied amperage to oven  2 . That is, a typical electric range would include an oven cavity having a fairly uniform size in the art, but the power hook-up can generally vary between 15 and 20 amps circuits. In a 20 amp circuit for oven  2 , electric heating element  25  preferably constitutes a 1400 watt element that works on 120 volts. In a 15 amp circuit, a 1250 watt element is preferably utilized. For the lower amp circuit, a higher wattage element could be utilized. Regardless, such minor changes in the overall system is considered well within one of ordinary skill in the art. For the sake of completeness, electric heating element  25  is preferably utilized in the embodiment shown with second gas burner unit  22  which constitutes a natural gas broiler having a 14,000 BTU/hr rating. 
     The cooking appliance in accordance with the present invention also incorporates a controller  62  that is used to regulate the operation of each of first gas burner unit  21 , second gas burner unit  22  and electric heating element  25 . In general, controller  62  receives signals from a temperature sensor  66 , which is arranged to sense the temperature within oven cavity  5  in a manner known in the art, as well as input signals from operator controls as generally indicated at  69 . These operator controls  69  are widely known in the art and include such selections as the particular operating mode for oven  2 , i.e., baking, broiling, cleaning and the like modes, a desired temperature setting for a cooking operation and, as now found on more modern ranges, a desired cooking time. Again, since these types of controls are widely known in the art and do not form part of the present invention, they have not been separately shown in the figure. Instead, operator input controls  69  are generically represented and it is to be understood that the associated selectors can take the form of knobs, buttons, etc. as is common in the art. 
     In addition to the particular mounting arrangement between second as burner unit  22  and electric heating element  25 , the manner in which electric heating element is operated during use of oven  2  in various modes, including baking, broiling and cleaning operational modes, is an important aspect of the present invention as will now be described in full. During a baking operation in a conventional gas oven, only the first or lower gas burner unit  21  would be operated. However, in accordance with the present invention, electric heating element  25  is also activated during a baking operation to improve baking performance. In general, it would not be desirable to operate second gas burner unit  22  during a baking operation since it would have to operated intermittently and this would create certain issues related to combustion of gas and proper burner performance. In the most preferred form of the invention, controller  62  cycles electric heating element  25  on and off while operating first gas burner unit  21  at a full operating state. Most preferably, controller  62  cycles electric heating element  25  on and off at less than full capacity during the baking mode, with the off-cycle period for electric heating element  25  being multiple times greater than the on-time period. In the most preferred form of the invention, an on/off duty cycle of ten second on to 50 seconds off is utilized and has been found during testing to significantly enhance the overall cooking performance. Of course, the duty cycle ratio can be varied in accordance with the present invention, although it is desired to have a longer off-cycle period than the on-time period. 
     During a typical baking operation, oven cavity  5  can reach a temperature which would warrant cutting off all heat sources, or at least greatly reducing the capacity thereof. In the most preferred form of the invention, controller  62  functions to de-activate electric heating  25  when first gas burner unit  21  is cycled off or operated at lower than it full state. Furthermore, electric heating element  25  is preferably fully activated with first gas burner unit  21 , as regulated by controller  62 , during a pre-heating stage for oven cavity  5 . After the preheating stage, electric heating element  25  is then operated on the on-off duty cycle discussed above whenever first gas burner unit  21  is on full. Cycling electric heating element  25  in this fashion has been found to enhance not only the overall cooking of the food items, but also advantageously performs a browning function. 
     During a broiling operation in a conventional gas oven, it is not uncommon to generate certain hot and relatively cold spots. The inclusion of electric resistance heating element  25  has been not only found to increase the broiling area within oven cavity  5 , but also creates a substantially uniform temperature for the broiling operation. In one test conducted on this invention wherein a goal temperature of 170° F. was desired for oven cavity  5 , the zones within oven cavity  5  which are maintained within 5° F. of the goal temperature was increased from 33% (no use of electric heating element  25 ) to 66% (combination of second gas burner unit  22  and electric heating element  25 ) during a broiling operation. Therefore, during a broiling operation, electric heating element  25  can be advantageously utilized to provide added heat and to balance hot and cold spots within oven cavity  5 . Preferably, both electric heating element  25  and second burner unit  22  are operated in fully activated states during a broiling mode, with electric heating element  25  being de-activated in unison with second burner unit  22 . 
     Electric heating element  25  can also be utilized during a self-cleaning mode of operation for oven  2 . Although electric heating element  25  could simply not be used during self-cleaning such that oven  2  could be self-cleaned in a manner found in many gas cooking appliances, it is preferable to utilize electric heating element  25  initially to pre-heat oven cavity  5  at a controlled rate, either with or without second burner unit  22 , prior to the operation of first burner unit  21 . That is, if operated simultaneously, first and second gas burner units  21  and  22  would raise the temperature of oven cavity  5  at a fairly rapid rate which could have the tendency to develop rather strong odors as grease and other items are burned during the cleaning process. Operating electric heating element  25  at a controlled rate, either with or without second burner unit  22 , to pre-heat oven cavity  5  prior to the operation of first gas burner unit  21  can advantageously minimize the amount of smoke and odors generated during this initial phase of the cleaning process wherein grease and the like are baked off the walls  8 - 12  of oven cavity  5 . Once first gas burner unit  21  is fully activated to perform a pyrolysis operation, it is preferred that electric heating element  25  be simply de-activated, along with the second burner unit  22 . 
     Based on the above, it should be readily apparent that electric heating element  25  is mounted in an advantageous manner relative to second burner unit  22  and is controlled in such a way to produce synergistic results with at least one of the first and second burner units  21  and  22  during baking, broiling and/or cleaning modes so as to enhance the overall performance of oven  2 . Although described with respect to a preferred embodiment of the invention, it should be readily understood that various changes and/or modifications can be made to the invention without departing from the spirit thereof. In general, the invention is only intended to limited by the scope of the following claims.