Abstract:
A control system for a cooking appliance enables a consumer to perform a complete cooking operation regardless of whether food is placed into an oven after a preheating operation or without initially preheating the oven. When the consumer does not intend to allow the oven to be preheated prior to inserting the food to be cooked therein, the consumer can select a no preheat operation wherein the lack of preheating is automatically compensated for, preferably by causing the oven to perform the cooking operation in two stages. Initially, the oven is operated at full output capacity for a first predetermined period and thereafter operated at various heat outputs during a subsequent plurality of stages until the cooking operation is complete. In this manner the food is completely cooked without the need to add additional time to the overall cooking operation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to the art of cooking appliances and, more particularly, to a control system for a cooking appliance which enables the appliance to perform a cooking operation without an initial preheat period. 
     2. Discussion of the Prior Art 
     Conventional cooking appliances generally perform cooking operations through radiant heat developed from bake and/or broil heating elements. Such types of cooking appliances can take various forms, mainly ranges and wall ovens. When utilizing a conventional cooking appliance, the oven is initially controlled to proceed through a preheat cycle in order to establish a desired cooking temperature. Oftentimes, a signal is provided to a user when the preheat cycle is complete in order to indicate when the food to be cooked should be placed in the oven. In some cases, both the bake and the broil elements are actuated during the preheat cycle. The oven preheat is typically required for short cook time items, such as packaged food items e.g. frozen pizza and TV dinners, as well as baked goods such as cookies, biscuits and the like. 
     Since their introduction, packaged food products have grown in popularity with modem consumers. Most, if not all, packaged food items have imprinted upon their labels preparation instructions that include time and temperature parameters. Typically, the preparation instructions also include an oven preheat requirement. That is, prior to placing the packaged food item into a cooking chamber of an oven, that oven must be preheated according to the preparation instructions. Generally, the preheat takes in the order of 10-15 minutes to bring the cooking chamber to or near a desired temperature. Therefore, in order to determine an overall preparation time, a consumer must add the preheat time to the actual cook time. Likewise, recipes for baked goods and other short cook time items establish cook time parameters based upon the oven being preheated. 
     Since cooking times set forth in recipes or other cooking instructions are established based on an oven being preheated, failure to preheat the oven directly affects the overall food preparation. Under such circumstances, the user must either mentally determine a supplemental cooking time period for the food item or, if the cook time is not altered, the food will be at least slightly undercooked. Thus, the consumer must take into account the preheat time of the oven when preparing a meal. However, due to haste, busy schedules or other time constraints, this additional time is not always allotted and, therefore, the consumer is faced with either consuming a partially undercooked meal or continually checking to see when the food item has cooked completely. In any case, unless the oven is preheated, the food item is not cooked in a satisfactory manner within the established time parameter. 
     Based on the above, there exists a need in the art for a system that will enable a consumer to readily perform a cooking operation within established time parameters without requiring that the oven be initially preheated. In other words, under conditions wherein a cooking operation is to be performed, it would be beneficial to enable the consumer to easily perform a cooking operation that automatically compensates for the lack of a preheat cycle while, at the same time, not extending the established time parameter. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a control system for a cooking appliance which enables a consumer to selectively perform a complete cooking operation in a standard mode or in a no preheat mode. More specifically, in the no preheat mode, the control system modifies operation of the oven so that the cooking operation is completed, despite placing a food item in a cold oven, within established time parameters, i.e., within a time period specified in on package label or as set forth in a recipe. The present invention is particularly adapted for use in connection with short cook time items, such as frozen pizzas, cookies, biscuits and the like, rather then long term items, such as roasts. 
     In accordance with the most preferred embodiment of the present invention, when the no preheat mode is selected, the cooking operation is performed using a two-stage process. Initially, the control system operates one or more heat sources at a maximum heat output for a first predetermined period. At the termination of a first period, the control system operates the heat source(s) at varying heat output levels for a second predetermined period. Preferably, the second period includes a plurality of stages, between which the operation and heat output of the heat source(s) is adjusted so as to match a level of heat capable of being absorbed by the food item. In this manner, the control system can complete the cooking operation within established time parameters without requiring the oven to be initially preheated. 
     Additional objects, features and advantages of the present invention will become more readily apparent 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 partial perspective view of an electric range incorporating a no preheat cooking system according to the invention; 
     FIG. 2 is a front view of a control panel, forming part of the range shown in FIG. 1, including a schematic illustration of a control arrangement that forms part of the no preheat cooking system; and 
     FIG. 3 is a graphical, linear interpolation representation illustrating various stages of operation of the no preheat system in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With initial reference to FIG. 1, the invention is illustrated for use in connection with an electric range, generally indicated at  2 . In the embodiment shown, electric range  2  includes a cabinet  5  within which is arranged an oven cavity  8  having top, bottom, rear and opposing side walls  9 - 13  that collectively define a cooking chamber  15 . Cooking chamber  15  has associated therewith a plurality of heat sources positioned to elevate a temperature of cooking chamber  15  during a cooking operation. In the embodiment shown, cooking chamber  15  includes a lower heating or bake element  20 , an upper heating or broil element  21 , a convection heating element  22  and a microwave emitter or magnetron  25 . Convection element  22  has associated therewith a convection fan  30  that, upon activation, circulates a heated airflow about cooking chamber  15 . Range  2  is also provided with a door  32 , shown in an open condition wherein access to cooking chamber  15  is permitted. This figure also illustrates the presence of a viewing window  33  in door  32 . In a manner known in the art, cabinet  5  is provided with a light switch  34  which functions to turn on a light (not shown in FIG. 1 but indicated at  35  in FIG. 2) to illuminate cooking chamber  15  upon the opening of door  32 . 
     Cabinet  5  is also provided with an associated range top  40  which supports various spaced surface heating elements  42 - 45  in a manner known in the art. At an upper rear portion, cabinet  5  is provided with a control panel  48 . Control panel  48  includes a plurality of knobs  56 - 59  for use in selectively activating and deactivating surface heating elements  42 - 45  respectively. In addition, control panel  48  is shown to include a central display  64 , such as an LED or LCD display unit (also see FIG.  2 ). Furthermore, control panel  48  is provided with a number pad, generally indicated at  66 , having buttons for the numbers zero ( 0 ) through nine ( 9 ), with the zero ( 0 ) button also functioning as a reset control button. 
     Although the particular features incorporated into electric range  2  could vary greatly within the scope of the present invention, for the sake of completeness in describing a preferred form of the invention, control panel  48  of range  2  is also shown to include a lower row of control buttons, generally indicated at  68 , which are provided to select various operational modes for range  2 . For instance, the row of control buttons  68  can be used to select bake, broil, microwave and clean modes for range  2  through respective buttons  69 - 72 . In the particular embodiment shown, an additional convection baking mode, which is essentially defined by a baking mode with the further activation of convection fan  30 , can be selected through button  73 . 
     In another form of the invention, the user may program the operation of range  2  through the use of the lower row of control buttons  68 , control button  73  and numeric pad  66 , as well as timer buttons  75  and  76 . Furthermore, buttons  78  and  79  are provided to enable a consumer to set desired countdown and clock times, in combination with numeric pad  66 , respectively. Button  80  performs a stop or clear control function, while button  81  enables a consumer to turn on light  35  without opening door  32  such that cooking chamber  15  can be selectively viewed through window  33 . Button  90  is provided to initiate the no preheat mode in accordance with this invention as will be described below. Finally, an Auto Set button  92  is provided and can be used to perform various programming functions as will also be discussed below. Of course, although various buttons are described for use on control panel  48 , other types of control members, including a wide range of switches, could equally be employed. In addition, although the invention is being described with reference to range  2 , it should be recognized that the invention is applicable to various types of cooking appliances, including wall ovens and the like. 
     FIG. 2 shows control panel  48  including an associated CPU  95  for controlling fan  30  and heat sources  20 - 22 ,  25  and  42 - 45  of range  2 . CPU  95  also includes a no preheat circuit  98  which is activated through no preheat selector button  90  as will be more fully discussed below. As the operation of light  35  and heating elements  42 - 45  is performed in a manner known in the art and does not constitute part of the present invention, they will not be discussed further here. However, it will be mentioned that Auto Set button  92  can be used to assist the user in programming a cooking operation for range  2 . For example, if bake button  69  is selected, the operating temperature can be set directly through number pad  66  or by pressing Auto Set button  92  once for a certain starting temperature, e.g. 350° F. (177° C.), and subsequently for adding a set temperature value, e.g. 25° F. (14° C.), upon each further depression of button  92 . If a broil operation is selected through button  70 , Auto Set button  92  can be used to toggle between “Hi” and “Low” settings for heating element  21 . In any event, this operation is known in the art and only provided for the sake of completeness. Instead, the present invention is particularly directed to the manner in which CPU  95  is programmed to cause heating of cooking chamber  15  upon the selection of the no preheat mode by a user through button  90 . More particularly, no preheat circuit  98  of CPU  95  operates in accordance with the present invention to assure that a complete cooking operation is performed on a food item placed within cooking chamber  15  even though cooking chamber  15  is not initially preheated. 
     In using range  2 , a consumer may select a desired cooking function or operational mode through control buttons  69 - 71  and  73 , while also establishing an operating time period for the respective heat source(s) utilizing numeric pad  66  and timer buttons  75  and  76 . Again, numeric pad  66  or Auto Set button  92  can be used to set certain operating parameters as well. In one embodiment, the selected operation will be shown by illuminating key words or symbols in central display  64 . The preceding description corresponds to the structure described in U.S. Pat. No. 6,153,858, the entire disclosure of which is herein incorporated by reference. 
     It is preferable to employ some type of audible or visual indicator to the consumer when certain time periods have expired or certain temperatures have been reached. This function is performed by incorporating a piezoelectric buzzer or the like as indicated schematically in FIG. 2 at  100 . For instance, as with a conventional cooking appliance, buzzer  100  is preferably used to indicate the end of a cooking operation. In addition, when range  2  is used in a more conventional mode wherein cooking chamber  15  is permitted to preheat prior to the placing of food therein for cooking, buzzer  100  can signal a user at the end of the preheat stage. 
     Of course, as indicated above, it is not uncommon for a consumer to place food into an oven for a predetermined cook time without first enabling the oven to reach a preheat temperature. Since cooking times set forth in recipes or other cooking instructions for short cook time items such as frozen pizzas, cookies, biscuits and the like, are established based on an oven being preheated, failure to preheat the oven directly affects the overall food preparation. However, in accordance with the present invention, the user need only press no preheat selector button  90  after programming a cooking operation wherein the user is not going to allow cooking chamber  15  to preheat. Therefore, a signal is sent to CPU  95  that no preheat circuit  98  is to be utilized in connection with the selected cooking operation. In general, when the no preheat mode is selected, the heat source(s)  20 - 22 ,  25  is operated in such a manner as to match heat input to cooking chamber  15  with a level of heat that the food item is capable of absorbing. No preheat circuit  98  incorporates a control algorithm which functions to determine the required heat output and cycles time parameters of each of the heat sources  20 - 22 ,  25  associated with cooking chamber  15 . These parameters are then used to establish a particular cooking operation so as to completely cook the food item in the established time period. That is, in the case of a prepackaged food item, the food item will be completely cooked within the time period listed on the package label. In the case of a recipe, the food item will be completely cooked in the time period set forth in the recipe. In either case, the consumer can input the time period for cooking and either elect to wait for cooking chamber IS to be preheated before placing the food item therein for the set time period or activate no preheat control circuit  98  through button  90  to allow the food item to be immediately placed in cooking chamber  15  and fully cooked in the same time period. 
     By way of an example as shown in FIG. 3, if biscuits are recommended to be cooked at 350° F. (177° C.) for 14 minutes and no preheat selector button  90  is pressed, the cooking operation enters a first period where CPU  95  would operate one or more of heat elements  20 - 22 , perhaps even with fan  30  and/or microwave  25  heat sources, in a first or rapid heat mode during which time the heat sources are operated to produce as much heat as the oven can deliver. During this initial period, an insulation barrier, resulting from a temperature differential between the food item and oven ambient air, substantially prevents the food item from absorbing the heat. Thus, the oven can be operated at these high heat input levels without fear that the food item will be adversely affected. After a period of time, for example 3 minutes for the biscuits, the cooking operation enters a second period where CPU  95  controls the heat sources in a manner so as to produce a series of managed heat generation stages to prevent the food item from burning while the temperature of cooking chamber  15  is reaching package or recipe temperature. That is, the wattage output is adjusted during the managed heat generation stages to balance an amount of top and bottom heat both in radiated energy and ambient oven air temperature. For example, during an initial stage of the second period, CPU  95  operates bake element  20  at 50% power, e.g., either by operating bake element  20  at half of the available power level or at full power level for half the established time, broil element  21  at nearly 100% power and convection element  22  is off, for a period of approximately 2.5 minutes. In stage II, CPU  95  operates bake element  20  at nearly 100% power, broil element  22  is off and convection element  22  at approximately 20% power, for a period of approximately 1.0 minutes. Finally, in stage III, CPU  95  operates bake element  20  at approximately 95% power, while broil element  21  and convection element  22  are off, for a period of approximately 7.5 minutes during which time cooking chamber  15  reaches the set temperature. With this arrangement, at the completion of 14 minutes, the food item (biscuits) is completely cooked to the same level as if cooking chamber  15  was initially preheated. 
     The actual number of stages and adjustments made are dependent upon the physical limitations of the oven and the set temperature, but can be adjusted to work in any oven, preferably an oven having a required total energy availability according to the relationship A/B≅1270 Watts/ft 3 , where A is the required minimum total wattage of heating elements in range  2  and B is the total volume of cooking chamber  15 . In any event, at the termination of the managed heat generation stages, the food item is completely cooked within the predetermined or listed time parameters without preheating cooking chamber  15 . 
     In any case, it should be understood that the present invention is focused on preparing short cook time items, for example frozen pizza, cookies and biscuits, with a no preheat mode of operation. The advantageous features of this invention do not necessarily lend themselves to long cook time items such as roasts, whole chickens and turkey which are not generally affected by failing to preheat the oven. Although described with reference to a preferred embodiment of the present invention, it should be readily apparent to one of ordinary skill in the art that various changes and/or modifications can be made to the invention without departing from the spirit thereof. In addition, the particular operation and cycling of the heating element(s) within each particular stage or managed heat generation step could vary based upon the physical limitation of the appliance. Also, the particular programming established through the control panel is but one example as the present invention would work equally as well with a wide array of control panels. Finally, it should be understood that the particular number and type of heating elements could vary in accordance with the present invention. In general, the invention is only intended to be limited to the scope of the following claims.