Abstract:
A control system for an oven includes a temperature sensor configured to detect a cavity temperature within the cavity, and a controller operatively coupled with the sensor. The oven includes a body having a cavity defined therein and at least one heater positioned within the cavity. The controller is also configured to receive a signal from the sensor, to calculate a rate of temperature change of the cavity temperature, and to adjust a power level of the heater based on the cavity temperature and the calculated rate of temperature change.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to ovens and, more particularly, to control systems for ovens to facilitate more even cooking.  
         [0002]     In thermal/convection ovens, the food is cooked by the air in the cooking cavity, which is heated by a heat source. Standard thermal ovens do not have a fan to circulate the hot air in the cooking cavity. Some convection ovens use the same heat source as a standard thermal oven, but add a fan to increase cooking efficiency by circulating the hot air around the food. Thermal/convection ovens can be used to cook a wide variety of foods.  
         [0003]     Evenness of cooking is desirable for the ovens. Some known ovens monitor the cavity temperature, and turn on/off the heat source when the monitored temperature is below/above a predetermined value. However, known ovens inject a considerable amount of energy into the cooking cavity in a relatively short time period, such that the cavity temperature may not be timely and precisely controlled. Therefore, at least some known ovens have a cavity temperature variation of more than 20 degrees Fahrenheit, which may lead to uneven cooking and causes variation in browning and a darkening around the edges in baked products.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0004]     In one aspect, a control system for an oven is provided. The oven includes a body having a cavity defined therein and at least one heater positioned within the cavity. The control system includes a temperature sensor configured to detect a cavity temperature within the cavity, and a controller operatively coupled with the sensor. The controller is also configured to receive a signal from the sensor, to calculate a rate of temperature change of the cavity temperature, and to adjust the power level of the heater based on the cavity temperature and the calculated rate of temperature change.  
         [0005]     In another aspect, an oven is provided. The oven includes a body having a cavity defined therein, an upper heater and a lower heater positioned within the cavity, a temperature sensor positioned between the upper and lower heaters, the sensor configured to detect a cavity temperature within the cavity, and a controller operatively coupled with the sensor and the heaters. The controller is configured to receive a signal from the sensor, to calculate a rate of temperature change of the cavity temperature, and to adjust the power levels supplied to the upper heater and the lower heater based on both the cavity temperature and the calculated rate of temperature change.  
         [0006]     In still another aspect, a method for assembling an oven is provided. The method includes providing a body having a cavity defined therein, positioning at least one heater within the cavity, positioning a temperature sensor within the cavity, the sensor configured to detect a cavity temperature within the cavity, and operatively coupling a controller with the sensor and the heaters. The controller is configured to receive a signal from the sensor and calculate a rate of change of temperature of the cavity temperature. The controller is also configured to adjust the power levels supplied to the heater based on the cavity temperature and the calculated rate of change of temperature. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a cutaway view of an exemplary electric range including an oven.  
         [0008]      FIG. 2  is a diagram illustrating a cavity temperature curve for known ovens heating to a predetermined temperature.  
         [0009]      FIG. 3  is an enlarged view of section A of the temperature curve shown in  FIG. 2 .  
         [0010]      FIG. 4  is a diagram illustrating a cavity temperature curve for the oven shown in  FIG. 1  heating to a predetermined temperature.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]      FIG. 1  is an embodiment of an exemplary electric range  100  having an oven  142  in which the present invention may be employed. While a free standing electric range is shown, it will be understood that the present invention is equally applicable to other oven products as well. Examples of other oven products include a speedcooking oven, a gas fired oven, a wall oven, and an over the range oven.  
         [0012]     Range  100  includes an outer cabinet  102  having a top cooking surface  126  including individual surface heating elements  122 . Positioned within cabinet  102  is a cooking chamber or cavity  134  formed by a box-like oven liner having vertical side walls  112 , top wall  104 , bottom wall  116 , rear wall  110  and a front opening drop door  118 . Cavity  134  is provided with two heating elements, a bake heating element  114  positioned adjacent bottom wall  116  and a broil heating element  108  positioned adjacent top wall  104 . In one embodiment, heating elements  108 ,  114  are electrical heating elements. It is contemplated, however, that gas fired heating elements and other suitable heating elements known in the art may be employed in alternative embodiments.  
         [0013]     A temperature probe or sensor  106  is mounted to project into cavity  134  and senses a temperature within cavity  134 . In one embodiment, sensor  106  is positioned between broil heating element  108  and top wall  104 . It is contemplated, however, that sensor  106  may be disposed at other positions within cavity  134  in alternative embodiments, such as being positioned between broil and bake heating elements  108 ,  114 . In one embodiment, sensor  106  is positioned at a center of cavity  134 . In another embodiment, multiple sensors  106  are positioned within cavity  134 .  
         [0014]     A door latch handle  120  is used for locking door  118  in a closed position during a self-cleaning operation. A control knob  130  extends outwardly from a control panel  132 , which is supported from a back splash  140  of range  100 . Control panel  132  also includes a controller  144  for controlling the operation of range  100  and oven  142  according to an operator&#39;s selection.  
         [0015]     Controller  144  is operatively coupled to sensor  106  for receiving signals representative of the detected cavity temperature from sensor  106 , and is also operatively coupled to heating elements  108 ,  114  for controlling the operation thereof. In one embodiment, controller  144  is coupled to heating elements  108 ,  114  through relay outputs (not shown) to provide discreet control of heating elements  108 ,  114 . In another embodiment, controller  114  is coupled to heating elements  108 ,  114  through a triac output (not shown) to provide a continuous power output to heating elements  108 ,  114 . In one embodiment, controller  14  is a proportional integral derivative (PID) based controller.  
         [0016]      FIG. 2  is a diagram illustrating a cavity temperature curve  150  when known ovens heating to a predetermined temperature, such as for example, in a preheating process. When heating cavity  134 , a considerable amount of energy is introduced into cavity  134  in a relatively short time period, such that the cavity temperature deviates about the predetermined temperature and cannot be kept constant.  
         [0017]      FIG. 3  is an enlarged view of a section A of temperature curve  150  shown in  FIG. 2 . In order to facilitate precisely adjusting the cavity temperature, temperature curve  150  within a predetermined time period is divided into several regions by four dividing lines  152 ,  154 ,  156 , and  158 . In the exemplary embodiment, dividing lines  152 ,  156  are respectively defined at temperatures of 0.5 degree Fahrenheit above below the predetermined temperature, and dividing lines  154 ,  158  are respectively defined at temperatures of 1 degree Fahrenheit above/below the predetermined temperature. As such, temperature curve  150  within the predetermined period is divided into ten regions. It is contemplated, however, that the temperatures of the dividing lines, the number of the dividing lines, and the number of the divided regions may be varied in alternative embodiments. In the exemplary embodiment, controller  144  (shown in  FIG. 1 ) accesses a look-up table to control the cavity temperature An exemplary look-up table is shown below:  
                                                                   TABLE 1                           Look-Up Table            Region   Rate   Error   Bake %   Broil %                    1   0   10   0   0.5   25   10       2   0   10   0.5   1   15   5       3   −10   10   1   100   0   0       4   −10   0   0.5   1   0   0       5   −10   0   0   0.5   0   0       6   −10   0   −0.5   0   0   0       7   −10   0   −1   −0.5   0   0       8   −10   10   −150   −1   65   20       9   0   10   −1   −0.5   50   15       10   0   10   −0.5   0   35   15                    
         [0018]     The look-up table pertains to region, rate, error, and power level of heating elements, and each region corresponds to a data group. Each data group includes a range of rate, such as a range of rate of temperature change of the cavity temperature, a range of error, or a temperature difference range with respect to a predetermined temperature, and power level values.  
         [0019]     The range of rate and the range of error of each region described in Table 1 correspond to the same region shown in  FIG. 3 . For example, in region “1” the temperature difference is from 0 to 0.5 degree Fahrenheit above the predetermined temperature, and the rate of temperature change is from 0 to 10 degrees per second i.e. the cavity temperature keeps constant or increases. In region “7”, the temperature difference is from 0.5 to 1 degree Fahrenheit below the predetermined temperature and the rate of temperature change is from −10 to 0 degrees per second, temperature decreases or keeps constant.  
         [0020]     The power level values of each data region are corresponding to the power levels supplied to heating elements  108 ,  114  (shown in  FIG. 1 ), and each power level value is defined as a percentage of the full power level that could be supplied to heating element  108 ,  114 . The power level values are predetermined based on several factors of oven  142  (shown in  FIG. 1 ), such as for example, heater power capacity, oven size, oven airflow, rate of oven heat loss, etc. It is contemplated that the power level values may be varied based on different oven factors in alternative embodiments. In the exemplary embodiment, two data groups having identical temperature difference ranges and different changing rate ranges, such as for example, regions “2” and “4”, have different power level values.  
         [0021]     In operation, controller  144  (shown in  FIG. 1 ) operates heating elements  108 ,  114  (shown in  FIG. 1 ) to heat cavity  134  (shown in  FIG. 1 ) to a predetermined temperature upon the operator&#39;s selection, and receives signals representative of the cavity temperature from sensor  106  (shown in  FIG. 1 ). Controller  144  calculates a temperature difference between the detected cavity temperature and the predetermined temperature and a rate of temperature change of the cavity temperature. Controller  144  then accesses a look-up table, such as the one described in Table 1, compares the calculated temperature difference and the calculated rate of temperature change with the data groups described in Table 1, and adjusts heating elements  108 ,  114  according to the power level values described in Table 1.  
         [0022]     Specifically, if both the temperature difference and the rate of temperature change are within the temperature difference range and the range of rate of temperature change of one of the data groups, controller  144  (shown in  FIG. 1 ) determines that the cavity temperature is within the corresponding region of temperature curve  150 , and adjusts heating elements  108 ,  114  (shown in  FIG. 1 ) according to the power level values of that region. In one embodiment, controller  144  adjusts the power levels supplied to heating elements  108 ,  114  to different values, respectively. In another embodiment, the power levels of heating elements  108 ,  114  are adjusted identically. It is contemplated, however, that each data group may include only one power level value, and controller  144  may only operate one of heating elements  108 ,  114  to heat cavity  134  (shown in  FIG. 1 ) and adjust that heating element according to the only power level value in alternative embodiments.  
         [0023]     In the exemplary embodiment, controller  144  (shown in  FIG. 1 ) adjusts heating elements  108 ,  114  (shown in  FIG. 1 ) based on both the calculated temperature difference and the calculated rate of temperature change. Such as for example, when the temperature differences are both 0.8 degree Fahrenheit above the predetermined temperature, but the rates of temperature change are opposite, controller  144  may pick up the different power level values from regions “2” and “4”, respectively. As such, the power level supplied to each heating element  108 ,  114  may be different when the rates of temperature change are different. In addition, in region “3” or “8”, the rate of temperature change is from −10 to 10 degrees per second, i.e., whether the cavity temperature decreases, increases, or keeps constant, it falls within the range of the rate of regions “3” and “8”. As such, when the temperature difference is far beyond/below the predetermined temperature, controller  144 , in one embodiment, respectively de-energizes/energizes heating elements  108 ,  114 , regardless of the rate of temperature change.  
         [0024]      FIG. 4  is a diagram illustrating a cavity temperature curve  160  controlled by controller  144  (shown in  FIG. 1 ) when oven  142  (shown in  FIG. 1 ) heats to a predetermined temperature, such as for example, in a preheating process.  
         [0025]     By adjusting heating elements  108 ,  114  (shown in  FIG. 1 ) based on both the temperature difference and the rate of temperature change, controller  144  (shown in  FIG. 1 ) facilitates anticipating the future need of oven  142  (shown in  FIG. 1 ) and timely and precisely controls the cavity temperature. As such, in one embodiment, upon oven  142  reaching a steady state condition, controller  144  keeps the cavity temperature within five degrees Fahrenheit of the steady state temperature. In another embodiment, upon oven  142  reaching a steady state condition, controller  144  keeps the cavity temperature within three degrees Fahrenheit of the steady state temperature. In a further embodiment, upon oven  142  reaching a steady state condition, controller  144  keeps the cavity temperature within one degree Fahrenheit of the steady state temperature. Controller  144  reduces thermal gradients within oven cavity  134 , facilitates evenness of cooking, and avoids variation in browning and darkening in cooked products.  
         [0026]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.