Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
2001-04-19
2004-05-11
Paik, Sang (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S490000, C219S391000
Reexamination Certificate
active
06734403
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
In one aspect, the invention relates to an oven having accurate temperature control including a baking cavity with independently-controlled bake and broil heating elements via separate temperature sensors located adjacent each of the corresponding heating elements. In another aspect, the invention relates to a method for independently controlling the bake and broil heating elements in the baking cavity of the oven during a bake cycle of the oven.
2. Description of the Related Art
Electric- and gas-based cooking ovens are old and well-known in the prior art. With reference to
FIG. 1
, these types of ovens
10
typically comprise an open-face housing defining a baking cavity
12
, with the open face enclosed by a hinged door
14
. The open face housing is formed by opposing top and bottom walls, opposing end walls, and a rear wall. A broil heating element
16
is mounted adjacent the upper wall of the baking cavity
12
and a bake heating element
18
mounted adjacent the lower wall of the baking cavity. The side walls
20
,
22
are provided with rack supports
24
extending generally in horizontal fashion depth-wise into the baking cavity
12
along the side walls
20
,
22
for supporting a baking rack
26
thereon.
In control methods for prior art ovens
10
, a single temperature sensor
28
is typically located a predetermined distance from each of the broil and bake heating elements
16
,
18
, respectively, such as along a medial horizontal plane of the baking cavity
12
as shown in FIG.
1
. This single temperature sensor
28
was typically used in bake and broil modes of prior art ovens
10
to control the activation and deactivation of the broil and bake heating elements
16
,
18
.
The use of a single temperature sensor
28
in prior art ovens
10
, especially such a sensor
28
spaced a great distance from the associated broil and bake heating elements
16
,
18
, has not shown to be an effective method by which to produce a constant and effective heating gradient across the vertical height of the baking cavity
12
since heat rises and because the heat differential across the vertical height of the baking cavity can be substantially affected by various types of food products placed on the cooking rack
28
(e.g., a frozen poultry product versus a room temperature mixture) and the shape and size of the pan holding the food product.
For example, the pan interferes with the vertical flow path of the heat air rising from the bake element. Typically, the larger the pan, the greater the interference. The interference results in the heated air building up along the bottom of the pan and flowing around the sides of the pan, which prevents an even distribution across the top of the pan, resulting in a region of lower temperature air above the pan and very heated air below the pan. The food product can exacerbate the low temperature region if the food product is at substantially lower temperature than the surrounding air, effectively functioning as a cooling point source. The end result is an undesirable temperature gradient on opposite sides of the pan.
It has been found that the location of a single temperature sensor
28
located at upper end of the baking cavity
12
is ineffective in providing input to a controller for activating and deactivating the broil and bake heating elements
16
and
18
in a manner capable of reducing or eliminating the temperature gradient across the pan.
There have been prior art attempts to install multiple temperature sensors
28
in the baking cavity
12
of an oven
10
, however, these prior art attempts have been to solve problems unrelated to the even heating along the height of the oven cavity.
For example, U.S. Pat. No. 5,723,846 to Koether, et al., issued Mar. 3, 1998, discloses the use of a pair of temperature sensors located adjacent heating elements both located on an upper wall of a baking cavity in a convection oven used for error detection purposes in sensing error conditions in the convection oven.
U.S. Pat. No. 5,791,890 to Maughan, issued Aug. 11, 1998, discloses a temperature sensor located adjacent each bake and broil heating element in a gas oven used for the purpose of detecting a positive proof of ignition in each of the gas-based heating elements.
U.S. Pat. No. 5,332,886 to Schilling et al., issued Jul. 26, 1994, discloses an electronic regulator for an electric oven having a controller provided with a fixed program to process data from a real temperature sensor and separate temperature sensors for producing error correction values on the ambient temperature in the baking cavity for converting the dependence between the temperature values of the real temperature sensor and the measuring temperature device into additional process data.
None of the dual sensor applications address the problem of accurately controlling the temperature of the oven baking cavity during a bake cycle of the oven to obtain an even heat distribution along the height of the oven.
SUMMARY OF THE INVENTION
The invention relates to a method for accurately controlling the ambient temperature in an enclosed baking cavity of an oven that is preheated with respect to a user-set temperature set point. The baking cavity of the oven comprises a broil heating element mounted to an upper portion of the baking cavity and a bake heating element mounted to a lower portion of the baking cavity, thereby defining a baking region therebetween. A broil temperature sensor is mounted within the baking cavity adjacent to the broil heating element. Similarly, a bake temperature sensor is mounted within the baking cavity adjacent to the bake heating element.
One method of controlling the oven comprises the following steps: providing a controller capable of actuating the broil and bake heating element in response to broil and bake temperature sensors; determining a target temperature set point for the oven cavity based on the user-set temperature set point; sensing the temperature of the baking region adjacent at least one of the bake and broil heat elements; comparing the sensed temperature with the target temperature set point; and, selectively actuating the broil and bake heating elements in response to the sensed temperature to maintain a vertical temperature distribution in the oven cavity that is substantially equal to the target temperature set point.
The steps in determining a target temperature set point can comprise calculating the heating element set point comprising one of a broil set point and a bake set point derived from the target temperature set point. The calculation of the bake and broil element set points preferably comprises selecting the one of the bake and broil set points from a data table containing a list of target temperature set points and a corresponding list of at least one of the bake and broil set points. The bake and broil set points preferably comprise a range of temperature values delimited by a low temperature limit and a high temperature limit.
Alternatively, the calculation of the broil and bake set points can comprise selecting a temperature differential value corresponding to the target temperature set point and summing the temperature differential value with the selected at least one of the bake and broil set points to calculate the other of the at least one of the bake and broil set points. The temperature differential value can be either negative or positive.
The step of sensing the temperature preferably comprises reading a sensor temperature signal comprising one of a bake temperature signal and a broil temperature signal read from the corresponding bake temperature sensor and broil temperature sensor.
The selective actuation of the broil and bake heating elements preferably comprises alternately activating the bake and broil heating elements. The alternate activation typically includes deactivating the heating element corresponding to the sensed temperature if the sensed temperature exceeds the corresponding heating element set point, activating the heating element corre
Baker Richard L.
Lockwood John W.
Pyles James A.
Thompson Daniel E.
Colligan John F.
Krefman Stephen
Paik Sang
Rice Robert O.
Whirlpool Corporation
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