Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
1999-07-13
2002-01-08
Paschall, Mark (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S506000, C219S413000, C219S508000, C099S331000
Reexamination Certificate
active
06337468
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to ovens and more particularly, to apparatus and methods for controlling oven operation in response to temperature drift.
Some known ovens include microcomputers that typically utilize single level logic to control the oven temperature. The microcomputer energizes and deenergizes the oven bake and broil heating elements based on simple thermostat temperature set point limits. That is, the oven microcomputer uses the oven set point temperature plus an overshoot allowance to trigger deenergization of the bake and broil heating elements, and the microcomputer uses the oven set point temperature minus an undershoot allowance to trigger energization of the bake and broil heating elements. The temperature band defined by the set point limits may be referred to as the tolerance band.
If the oven door is opened, the oven temperature, i.e., the temperature in the oven cooking cavity, falls substantially below the tolerance band. Such events which result in the oven temperature falling substantially below the lower limit of the tolerance band are sometimes referred to herein as drift events. The occurrence of numerous drift events, particularly if the cooking operation requires a lengthy cook time, e.g., 30 minutes or more, can adversely affect oven operations in that even though an operator may expect that a food item will be completely cooked at the end of the timed period, the food item may not be completely cooked since the selected oven temperature was not maintained throughout the cooking operation.
It would be desirable to control oven operations so that upon the completion of a timed cooking operation, the food item is likely to be completely cooked even if numerous drift events occur during the operation. Of course, in providing such control, the cost and complexity of the oven should not be significantly increased.
BRIEF SUMMARY OF THE INVENTION
In an exemplary embodiment of the invention, an oven controller differentiates between normal temperature cycling and a drift event in which the temperature drops below a lower set limit, sometimes referred to herein as the rapid recovery entry temperature. Such differentiation enables the oven microcomputer to use differentiated heating modes to rapidly bring the oven temperature back to within a tolerance band or range upon the occurrence of a drift event.
Particularly, and in connection with an oven including a microcomputer, a relatively low heat rate mode is used to maintain the oven temperature within the tolerance band or range during normal operations. Upon the occurrence of a drift event, e.g., opening of the oven door, causing the temperature to fall below the lower set limit, a relatively high heat rate mode is utilized to quickly return the oven temperature back to within the tolerance band or range.
In one specific embodiment, the microcomputer is programmed so that during operation in the normal bake mode, the oven temperature is controlled by the user set point temperature and offsets. Power cycling of the bake and broil heaters is controlled according to timing defined by prestored parameters for the normal bake mode. If the temperature in the oven cooking cavity drops below the lower set limit, e.g., the user set temperature minus a rapid recovery offset, rapid recovery is initiated. In the rapid recovery mode, the bake heating element is energized at a 100% duty cycle to quickly raise the oven temperature back within the tolerance range.
The rapid recovery mode facilitates operation of an oven so that upon the completion of a timed cooking operation, the food item is likely to be completely cooked even if numerous drift events occur during the operation. In addition, such rapid recovery can be implemented with components currently utilized in known ovens and without much additional cost.
REFERENCES:
patent: 4282423 (1981-08-01), Volz
patent: 4913038 (1990-04-01), Burkett et al.
patent: 5038676 (1991-08-01), Davis et al.
patent: 5528017 (1996-06-01), Wollf
patent: 5767488 (1998-06-01), Barger et al.
Able Douglas A.
Gray Steven J.
Lenhart, Jr. Brian P.
Worthington Timothy
Armstrong Teasdale LLP
General Electric Company
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