Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2002-05-31
2003-05-27
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S411000, C219S412000, C219S492000
Reexamination Certificate
active
06570136
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
In one aspect, the invention relates to an oven for baking food items, and more specifically, to an oven capable of selectively browning a food item.
2. Description of the Related Art
Electric and gas cooking ovens are old and well-known. They comprise a chassis in which is located a baking cavity having one or more racks for supporting a food item. Such ovens initially used a single heating element located in the bottom of the baking cavity, which is known as the bake heating element. The heat from the bake heating element would travel to the top of the baking cavity, predominately by convection. A disadvantage of the single element was that a temperature gradient can develop between the bottom and the top of the oven because of the time that it took for the heat to travel to the top of the cavity. The magnitude of the temperature gradient is exacerbated by the use of a cooking dish which typically covered a large portion of the baking cavity cross section and disrupted the flow of heat from the bottom to the top of the baking cavity. The presence of the pan tended to create an airflow stagnation location at the bottom of the pan and forced the heated air to the perimeter of the baking cavity, which resulted in a dead heating zone directly above the dish where the air has a lower temperature. The temperature gradient with and without the dish was often substantial enough to adversely affect the baking performance of the oven.
One popular solution to eliminating the temperature gradient was to use a second heating element in the top of the oven. Such heating elements are also used to broil foods by directly radiating heat onto the upper surface of the food item. These heating elements are generally referred to as “broil heating elements” even when used during baking because of their initial historical use for broiling.
A disadvantage of the using the broil heating element during baking is that the food item receives a much larger amount of directly radiated heat (top heat) from the broil heating element. The amount of radiated heat is attributable to the close proximity of the broil heating element to the upper surface of the food item, and the upper surface of the food item is not protected from direct radiation like the bottom surface, which is normally protected by a pan or some other covering to prevent dripping.
The extra top heat increases the rate and degree of browning of the food item as compared to when only the bake heating element is used. The extra top heat, while greatly beneficial for maintaining a more even temperature distribution in the oven resulting in a reduced temperature gradient and in better baking performance, is not useful for food items that require browning, like pies, cookies and the like.
There is still a need for an oven that has the even temperature distribution associated with dual heating elements yet maintains the browning performance of the single heating element.
SUMMARY OF INVENTION
The invention solves the problem of providing user control of the top-heat radiated by an oven by permitting the user to selectively increase or decrease the radiated top heat. The decrease in radiated top heat is especially important in enhancing the browning performance problem of a dual-heating-element oven. The invention relates to an oven for baking food according to a bake cycle, which typically has a user select time and temperature parameters. The oven comprises a housing that defines an open-faced baking cavity, which is formed by opposing top and bottom walls, opposing sidewalls that extend between the top and bottom walls, and a rear wall opposing the open face. A door is movably mounted to the housing for movement between an opened to a closed position to thereby selectively close the baking cavity open face. A bake heating element is positioned adjacent the bottom wall for introducing heat energy (“bottom heat”) into the baking cavity. A broil heating element is positioned adjacent the top wall for introducing heat energy (“top heat”) into the top of the baking cavity. A controller is provided for controlling the activation of the top heating element by cycling the broil heating element ON and OFF to implement the bake cycle. The controller has a user-operable switch, the selection of which reduces/increases the top heat radiated by the broil heating element while the switch is selected. The deselection of the switch terminates the reduced/increased top heat. The selection and deselection of the switch permits the user to selectively control the top heat and thus control the browning performance of the oven.
The controller can control the activation of both the broil and the bake heating elements by cycling the broil and bake elements ON and OFF according to a predetermined protocol to implement the bake cycle according to the user-selected time and temperature. The selection of the user-operable switch reduces/increases the top heat radiated by the broil heating element relative to top heat output according to the predetermined protocol.
The reduction/increase of the top heat radiated by the broil heating element can be accomplished in a variety of different ways. For example, the selection of the user-operable switch can reduce/increase the overall time that the broil heating element is on relative to the overall time the broil heating element would be on under the predetermined protocol. The reduced/increased time that the broil heating element is on can be accomplished by either reducing/increasing a broil temperature set point for the broil heating element or reducing/increasing the duty cycle for the broil heating element, as compared to the duty cycle under the predetermined protocol. The reduction/increase of the broil temperature set point and the duty cycle can be combined to reduce/increase the top heat output of the broil heating element.
The invention also relates to a method for controlling the browning performance of an oven comprising a baking cavity having a broil heating element positioned near the top wall of the oven cavity for radiating top heat into the baking cavity, a bake heating element positioned near a bottom wall of the baking cavity for radiating bottom heat into the baking cavity, and a controller for actuating the bake and broil heating elements ON and OFF. The method comprises implementing a baking cycle that maintains a temperature of the baking cavity at a predetermined bake temperature by controlling the cycling of the bake and broil heating elements and selectively reducing/increasing the cumulative top heat radiated by the broil heating element for at least part of the bake cycle in response to a user input.
The top heat radiated by the broil heating element can be reduced/increased for the entire bake cycle in response to the user input. Also, the predetermined bake temperature is typically selected by the user.
The implementation of the bake cycle comprises having a broil temperature set point corresponding to the predetermined bake temperature. The selective reduction/increase of top heat can be accomplished by reducing/increasing the broil temperature set point. Also, the implementation of the bake cycle can further comprise adding a duty cycle for the broil heating element based on the predetermined bake temperature.
The duty cycle can vary as a function of the magnitude of the predetermined bake temperature. The predetermined bake temperature can also be limited to at least two temperature ranges, with the duty cycle varying as a function of the temperature range. The reduction of the broil temperature set point can also vary as a function of the temperature range.
In another aspect, the invention relates to an oven for baking food according to a bake cycle having user selected time and temperature parameters. The oven comprises a housing that defines a baking cavity in which a bake heating element is positioned adjacent a lower portion of the baking cavity for introducing bottom heat into the baking cavity and a broil heating element positioned adjacent
Cook Madelyn A.
Embury Karen M.
Hodson Barbara A.
Lockwood John W.
Pyles James
Colligan John F.
Rice Robert O.
Roth Thomas J.
Whirlpool Corporation
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