Information
-
Patent Grant
-
6734403
-
Patent Number
6,734,403
-
Date Filed
Thursday, April 19, 200123 years ago
-
Date Issued
Tuesday, May 11, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Colligan; John F.
- Rice; Robert O.
- Krefman; Stephen
-
CPC
-
US Classifications
Field of Search
US
- 219 483
- 219 486
- 219 490
- 219 492
- 219 497
- 219 506
- 219 508
- 219 391
- 219 395
- 219 398
- 126 39 R
- 126 41 R
- 126 39 BA
- 126 19 R
- 392 307
- 392 310
-
International Classifications
-
Abstract
An oven and a method for controlling the ambient temperature in an oven comprising a baking cavity that is preheated with respect to a user-selected temperature set point. The baking cavity can include a rack for supporting a pan that conceptually divides the cavity into an upper heating region and a lower heating region. A broil heating element and corresponding broil temperature sensor are disposed in the upper heating region of the baking cavity. A bake heating element and corresponding bake heating sensor are disposed in the lower heating region of the baking cavity. A controlled is provided to control the activation of the broil and bake heating elements in response to the sensed temperature of the upper and lower heating regions to maintain the entire oven at a temperature substantially equal to a target temperature set point, which is determined based on the user-selected temperature set point.
Description
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 corresponding to the sensed temperature if the sensed temperature is less than the corresponding heating element set point, and deactivating the heating element other than the heating element corresponding to the sensed temperature if the sensed temperature is less than the heating element set point. Preferably, only one heating element is activated at a time. Also, the activation of the bake and broil heating elements is preferably continued for a predetermined duty cycle as long as the other bake and broil element is deactivated.
The method can further comprise the step of detecting whether the oven is gas-based or electric based. If the oven is gas based, the method can include determining whether a purge time limit for the broil heating element has been satisfied.
The method can also comprise compensating the heating element set point based upon an initial heating condition of the baking cavity. The heating element set point is preferably increased in the compensation step. The compensation step can further comprise adjusting the heating element set point according to a predefined function, which is preferably a decreasing linear function.
In another aspect, the invention relates to an oven incorporating accurate ambient temperature control. The oven comprises a housing defining an enclosed baking cavity. At least one oven rack for supporting a pan is disposed within the cavity and conceptually divides the cavity into an upper heating region above the rack and a lower heating region below the rack. A broil heating element is mounted in the upper heating region of the baking cavity. Similarly, a bake heating element is mounted in the lower heating region of the baking cavity. A broil temperature sensor is mounted within the upper heating region adjacent to the broil heating element. Similarly, a bake temperature sensor is mounted within the upper heating region adjacent to the bake heating element. A controller is operably interconnected to a power source and to the broil heating element, bake heating element, the broil temperature sensor and the bake temperature sensor for selectively actuating the broil heating element and the bake heating element in response to the sensed temperatures of the upper and lower heating regions to maintain the temperature of the upper and lower heating regions substantially equal to a target temperature set point.
The controller preferably calculates the heating element set point comprising one of the broil set point and a bake set point derived from the target temperature set point. A sensor temperature signal comprising one of a bake temperature signal and a broil temperature signal is read from the corresponding heating element sensor comprising one of the bake temperature sensor and broil temperature sensor. The controller preferably compares the sensor temperature signal to the heating element set point. The controller deactivates the corresponding heating element if the sensor temperature signal exceeds the heating element set point. The controller also activates the corresponding heating element if the sensor temperature signal is less than the heating element set point. The controller can deactivate the heating element other than the corresponding heating element if the sensor temperature signal is less than the heating element set point.
Preferably, the controller includes a database comprising multiple target temperature set points and corresponding broil set points and bake set points, whereby the bake and broil set points can be selected from the table according to the target temperature set point. Preferably, the broil set point and the bake set point each comprise a range of temperature values delimited by a low temperature limit and a high temperature limit.
The controller deactivates one of the bake and broil heating elements if one of the bake and broil elements is activated and if the corresponding bake or broil temperature signal exceeds the corresponding bake or broil set point by a predetermined amount. The controller activates one of the bake and broil heating elements for a predetermined duty cycle as long as the other of the bake and broil heating elements is deactivated.
The controller can compensate the heating element set point based upon an initial heating condition of the baking cavity. The compensation increases the heating element set point. Preferably, the compensation adjusts the heating element set point according to a predefined function, which is preferably a decreasing linear function.
In yet another aspect, the invention relates to a method for maintaining an even temperature distribution in a baking cavity of an oven relative to a user-defined temperature set point. The baking cavity of the oven comprises a rack for supporting a pan, with the rack functionally dividing the cavity into an upper heating region above the rack and a lower heating region below the rack. A broil heating element is provided in the upper heating region along with a corresponding broil temperature sensor. A bake heating element is provided in the lower heating region along with a corresponding bake temperature sensor. The method comprises the steps of: providing a controller capable of actuating the broil and bake heating elements in response to the broil and bake temperature sensors; determining a target temperature set point for the oven cavity based on the user-selected temperature set point; sensing the temperature of the upper and lower heating region; comparing the sensed temperatures with the target temperature set point; and selectively actuating the broil and bake heating elements in response to the sensed temperatures to maintain the temperature of the upper and lower heating regions substantially equal to the target temperature set point.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1
is a perspective view looking into a prior art baking cavity of an oven with a door therefor shown in fragmentary perspective view, wherein the baking cavity has a single temperature sensor located near the upper end of the baking cavity;
FIG. 2
is a perspective view in the same orientation as
FIG. 1
but showing a baking cavity for an oven according to the invention having separate temperature sensors, one located adjacent a broil heating element at the top of the baking cavity and one located adjacent a bake heating element located at the bottom portion of the baking cavity;
FIG. 2A
is a perspective view of the baking cavity of
FIG. 2
wherein a food product in a baking pan is placed on the rack in the baking cavity and arrows show the general heat track around the baking pan and food product when the bake heating element is activated whereby a dead heating zone is defined above the food product;
FIG. 2B
is a perspective view of the baking cavity of
FIG. 2
wherein a food product in a baking pan is placed on the rack in the baking cavity and arrows show the general heat track around the baking pan and food product when the broil heating element is activated thus reducing the negative baking effects of the dead heating zone above the food product shown in
FIG. 2A
;
FIG. 3
is a block diagram showing the general components of the oven of
FIG. 2
configured for electric-based heating elements;
FIG. 4
is a block diagram showing the general components of the oven of
FIG. 2
configured for gas-based heating elements;
FIG. 5
is a flowchart for controlling the temperature of the baking cavity of the ovens shown in
FIGS. 2-4
, specifically showing the steps of gathering information from a user, determining specific parameters for the bake mode and preheating the baking cavity of the oven using those set parameters in proceeding to the flowchart shown in
FIG. 6
;
FIG. 6
is a flowchart continuing from point “A” of FIG.
5
and shows a main set of steps for checking the temperature sensors shown in
FIG. 2
adjacent each of the bake and broil heating elements and calling subprocesss in
FIGS. 7
,
8
,
9
and
10
as indicated by subprocess calls “B”, “D”, “E”, and “G”, respectively;
FIG. 7
is a flowchart showing the method steps performed if subprocess “B” is called from
FIG. 6
;
FIG. 8
is a flowchart showing the method steps performed if subprocess “D” is called from
FIG. 6
;
FIG. 9
is a flowchart showing the method steps performed if subprocess “E” is called from
FIG. 6
;
FIG. 10
is a flowchart showing the method steps performed if subprocess “G” is called from
FIG. 6
; and
FIG. 11
is a flowchart showing a compensation routine for various temperature set points employed in the method steps of
FIGS. 6-10
for compensation of temperature set points relating to the bake and broil heating elements due to a typical overshooting of the desired oven cavity temperature during preheating of the oven whereby the compensation steps of
FIG. 11
artificially increase the target set points of both the broil and bake heating elements to prevent extended idle control times during the controlled heating of the oven cavity during a bake mode.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings and to
FIGS. 2-4
in particular, the oven
10
is shown in
FIGS. 2-3
configured for electric-based heating elements and in
FIG. 4
for gas-based heating elements in which a broil temperature sensor
30
is located adjacent to a broil heating element
16
and a bake temperature sensor
32
is located adjacent a bake heating element
18
. The broil temperature sensor
30
and the bake temperature sensor
32
are interconnected to a controller
34
.
It will be understood that the oven
10
shown in
FIGS. 2-4
having common elements with the prior art oven in
FIG. 1
are referred to with common reference numerals, i.e., the baking cavity
12
, door
14
, heating elements
16
,
18
, side walls
20
,
22
, rack supports
24
, and baking rack
26
are all referred to with the same reference numerals in
FIGS. 2-4
as they were in FIG.
1
.
FIGS. 3-4
show block diagrams of electric-and gas-based ovens,
10
, respectively, since the particular mechanical interconnection and assembly of the elements of the block diagrams shown in
FIGS. 3-4
are not critical to the invention and any of the well known components making up prior art ovens will suffice as this invention relates to the method of controlling the broil temperature sensor
30
and the bake temperature sensor
32
.
With reference to
FIGS. 3-4
, the general components making up the oven
10
according to the invention include an oven chassis
36
that supports the components making up the oven
10
on a floor
38
. An anti-tip bracket
40
, mechanically couples the chassis
36
to either the floor or the wall to prevent the oven from tipping when a large weight is placed on the door
14
. The door
14
is typically mounted to the chassis
36
by a hinge
42
and maintains the integrity of the baking cavity
12
by a seal
44
that is preferably effective in preventing heat from escaping the cavity
12
.
A warming/storage drawer
46
is typically provided at a lower portion of the chassis
36
and mounted thereto by conventional glides
48
permitting slidable movement of the warming/storage drawer
46
relative to the chassis
36
. The warming/storage drawer
46
is typically provided with its own heating element
50
interconnected to the controller
34
and actuated by the controller
34
via a signal from a temperature sensor
52
located within the warming/storage drawer
46
.
The oven
10
can also include a conventional cooktop
54
typically comprising several cooktop burners or elements
56
. In the electric-based oven
10
shown in
FIG. 3
, the cooktop burners/elements
56
are interconnected to an electric power supply
58
via a switch
60
as is conventionally known. In the gas-based oven
10
shown in
FIG. 4
, the cooktop burners/elements
56
are interconnected to a gas supply line
62
via a regulator
64
and several valves
66
also as is conventionally known. In both the embodiments of
FIGS. 3-4
, the power supply
58
is also interconnected to the controller
34
to supply power thereto.
A latch
65
is also mounted on the chassis
36
and preferably interconnected to the controller
34
and the door
14
. A user
67
manually actuates the latch
65
to latch the door to the chassis
36
to lockably enclose the cavity
12
. Further, the controller
34
can send a signal to the latch
65
to automatically lock the door
14
to the chassis
36
enclosing the cavity during oven cleaning operations thus preventing the user
67
from opening the door
14
.
In the electric-based oven
10
shown in
FIG. 3
, the broil heating element
16
and the bake heating element
18
are directly interconnected to the controller
34
, which controllably supplies power from the power supply
58
to selectively heat the cavity
12
in a controlled fashion. In the gas-based version shown in
FIG. 4
, the broil heating element
16
and the bake heating element
18
are interconnected to the controller
34
via a gas control assembly
68
that comprises a spark module
70
(i.e., an igniter) for passing a spark to an electrode
72
which, in turn, interacts with a volume of gas released by a solenoid valve
74
that is interconnected to the gas supply line
62
via the regulator
64
.
The controller
34
is interconnected to a control panel
76
mounted to the chassis
36
that contains among other things, actuator devices such as control knobs that allow the user
67
to set, among other things, the particular heating mode of the oven
10
(e.g., BAKE, BROIL, CLEAN, etc.) and, to the extent the user has selected either the bake or broil heating modes, a target temperature set point at which the user desires to cook food products in the baking cavity
12
.
For the purposes of the flowcharts describing the inventive method herein of
FIGS. 5-11
, it is assumed that the user
67
has accessed the control panel
76
and set the heating mode of the oven to BAKE and actuated another of the control knobs thereon to set a target temperature set point (i.e., the desired temperature to which the baking cavity
12
is to be heated and closely controlled and maintained at that temperature during the BAKE cycle).
On a typical control knob for setting the target temperature set point TARGET_TEMP, the user
67
is typically allowed to select from various temperatures in 25-50 degree increments in degrees F. such as 200, 250, 300, 325, 350, 400, 450, 475, etc. The method of controlling the temperature of the baking cavity
12
at the user selected target temperature set point TARGET_TEMP in the BAKE mode is shown at
100
in FIG.
5
. Once these parameters are set by user at step
100
processing moves to step
102
wherein further bake mode parameters are determined by the controller
34
from a database
104
. The database
104
can be any simple look-up table or a relational database that supplies data to the controller
34
based upon the make and/or model of oven
10
employed. An example of the database
104
appears in the following Table 1.
TABLE 1
|
|
Bake Method Temperature and Time Set Points (all Temperatures in degrees F. and times in seconds)
|
Preheat
Broil
Bake
Broil
Bake
|
D
F
H
I
J
K
|
Temp
A
B
C
Set
E
Set
G
Cycle
On
Cycle
On
L
|
Band
Target
Broil
Bake
Point
Amplitude
Point
Amplitude
Time
Time
Time
Time
Delta
|
|
LOW
200
230
230
188
1
182
1
60
15
60
60
6
|
250
280
280
238
1
232
1
60
15
60
60
6
|
300
330
330
288
1
282
1
60
15
60
60
6
|
325
355
355
313
1
307
1
60
15
60
60
6
|
MID
330
360
360
314
1
302
1
60
35
60
60
12
|
350
380
380
334
1
322
1
60
35
60
60
12
|
400
430
430
384
1
372
1
60
35
60
60
12
|
440
470
470
424
1
412
1
60
35
60
60
12
|
HIGH
450
470
470
434
1
420
1
60
40
60
60
14
|
475
495
495
459
1
445
1
60
40
60
60
14
|
|
The example database
104
shown in Table 1 has twelve columns labeled consecutively by letters A-L. Column A in Table 1 corresponds to the target temperature set point TARGET_TEMP set by the user
67
on the control panel
76
. Table 1 contains several rows each corresponding to the typical temperature settings on a control knob on the control panel
76
for setting the desired target temperature set point TARGET_TEMP. Table 1 shows several rows corresponding to these typical values in degrees F. including 200, 250, 300, 325, 330, 350, 400, 440, 450 and 475. It should be known that this invention is not limited by the values shown in Table 1 as these should be interpreted as merely an example of the data used by the controller
34
and should not be limiting on the invention.
Table 1 also includes a first column which breaks down the rows of Table 1 into low, mid, and high temperature bands wherein the low temperature band ranges from 200-325° F., the mid temperature band ranges from 330-440° F. and the high temperature band ranges from 450° F. and higher. These groupings were made by trial selection. It has been found that particular heating ranges such as the low, mid and high temperature bands shown in Table 1 each exhibit common characteristics which allow certain equations to be attributed individually to the two target temperatures falling within these target temperature bands as will be further described below.
Columns B and C of the database
104
shown by example in Table 1 include target set temperature points for the broil heating element
16
and the bake heating element
18
, respectively. These values represent the desired targets to have the broil temperature sensor
30
and the bake temperature sensor
32
read during preheating of the oven
10
. It will be noted that the preheat broil target temperature of column B and the preheat bake target temperature of column C exceed the target temperature of column A by 30, 30 and 20 for the low-, mid- and high-temperature bands, respectively.
It should not be limiting to this invention that the preheat, broil, and preheat bake target temperatures are shown as equal values as it is equally contemplated that these values could differ under a different oven preheating cycle. Further, the “overshoot” differences, i.e., the amount the preheat broil and preheat bake target temperatures of columns B and C of the database
104
of Table 1 exceed the target temperature set point of Column A, can also be selected as different values without departing from the scope of this invention as those values shown are by example and not by limitation.
Columns D-E and F-G of the database
104
shown by example in Table 1 contain a target set point and range amplitude for the broil heating element
16
and the bake heating element
18
as to be detected by the broil temperature sensor
30
and the bake temperature sensor
32
, respectively, during the BAKE mode as selected by the user
67
for a particular target temperature set point TARGET_TEMP. These values permit the controller
34
to calculate low temperature limit and high temperature limit set points for the broil heating element
16
and the bake heating element
18
.
For example, at a particular target temperature set point TARGET_TEMP selected by the user
67
, the database
104
looks up a corresponding value in Column A and sets a variable BROIL_SET to the value in Column D (e.g., 334° F. at a desired target temperature TARGET_TEMP of 350° F.). The controller
34
then calculates a broil heating element low temperature limit BROIL_LTL by subtracting the amplitude in Column E from the set point temperature in Column D and calculates a broil heating element high temperature limit BROIL_HTL by adding the amplitude in Column E to the broil set point temperature in Column D.
For example, at a particular target temperature set point TARGET_TEMP selected by the user
67
, the database
104
looks up a corresponding value in Column A and sets a variable BAKE_SET to the value in Column F (e.g., 322° F. at a desired target temperature set point TARGET_TEMP of 350° F.). The controller
34
then calculates a bake heating element low temperature limit BAKE_LTL by subtracting the amplitude in Column G from the set point temperature in Column F and calculates a bake heating element high temperature limit BAKE_HTL by adding the amplitude in Column G to the bake set point temperature in Column F.
Columns H and I define the duty cycle for the broil heating element
16
, i.e., the length of time comprising the normal heating cycle of the broil heating element
16
and the length of time (in seconds) that the broil heating element
16
is on during that time. Column H represents the length of time BROIL_CYCLE that the broil heating element
16
stays on upon a signal to activate the broil heating element
16
from the controller
34
. Column I represents the amount of time in seconds BROIL_ON that the broil heating element is actually emitting heat during the BROIL_CYCLE. For example, at a desired target temperature of 350°, the broil heating element
16
has a total cycle time of 60 seconds (Column H at a target temperature set point of 350° from Column A) and the broil heating element stays on approximately 35 seconds out of that 60-second time (Column I at a desired target temperature set point of 350° in Column A).
Columns J and K define the duty cycle for the bake heating element
18
, i.e., the length of time comprising the normal heating cycle of the bake heating element
18
and the length of time (in seconds) that the bake heating element
18
is on during that time. Column J represents the length of time BAKE_CYCLE that the bake heating element
18
stays on upon a signal to activate the bake heating element
18
from the controller
34
. Column K represents the amount of time in seconds BAKE_ON that the bake heating element
18
is actually emitting heat during the BAKE_CYCLE. For example, at a desired target temperature of 350° the bake heating element
18
has a total cycle time of 60 seconds (Column J at a target temperature set point of 350° from Column A) and the bake heating element
18
stays on approximately 35 seconds out of that 60-second time (Column K at a desired target temperature set point of 350° in Column A).
Column L is an optional column in the database which is essentially used as a tool to conserve memory in the controller
34
by creating a value DELTA in Column L which defines the relationship between the bake set point in Column F and the broil set point in Column D., i.e., DELTA in Column L represents the number of degrees F. by which the broil set point of Column D exceeds the bake set point in Column F. Thus, if the DELTA value in Column L is employed, one of the broil set points in Column D and the bake set point BAKE_SET in Column F is unnecessary as the other of these two values could be calculated by adding or subtracting the DELTA value in Column L to either Column D or Column F.
Thus, memory can be conserved by employing the fewer bits to represent the DELTA value in Column L rather than the larger number of either Column D or Column F (BROIL_SET or BAKE_SET) which requires more bits to store this value. While this memory saving may not be a concern with controllers
34
with large amounts of RAM or ROM, this memory saving technique can be significant for controllers
34
with smaller amounts of memory.
In summary, when the user sets the desired target temperature set point TARGET_TEMP and selects the bake mode on the control panel
76
at step
100
, the processing moves to step
102
where the controller
34
looks up and calculates the following bake parameters from the database
104
shown by example in Table 1. All values in Table 1 are shown in degrees F. and all times are shown in seconds. Also, in the following equations, a capital letter shown in parentheses (e.g., (D)) represents a value from the column identified by the letter in parentheses at the intersection of the row corresponding to the desired target temperature set point TARGET_TEMP set by the user
67
on the control panel
76
.
BROIL_SET=(D) (or) (F)+(L);
BROIL_LTL=BROIL_SET−(E);
BROIL_HTL=BROIL_SET+(E);
BAKE_SET=(F) (or) BROIL_SET−(L);
BAKE_LTL=BAKE_SET−(G);
BAKE_HTL=BAKE SET+(G);
BROIL_CYCLE=(H);
BROIL_ON=(I);
BAKE_CYCLE=(J);
BAKE_ON=(K); and
DELTA (if used)=(L).
The database
104
can also be used to look up the preheating target set point temperatures BROIL_PRE=(B) and BAKE_PRE=(C).
It is important to note that the parameters and the corresponding values shown in Table 1 are illustrative and not limiting to the invention. The particular values for each of the parameters can vary depending on the particular oven characteristics, such as, for example: baking cavity volume, broiler heating output, oven heating output, and desired response time in the case of the initial temperature overshoot. The particular values for a given oven can be determined by standard testing procedures.
Once these values are established, processing moves to step
106
in which the oven is preheated using the parameters looked up in the database
104
in step
102
. The preheat routine is relatively simple and relates to selectively actuating the broil heat element
16
until the broil temperature sensor
30
reads an excess of BROIL_PRE and selectively actuating the bake heating element
18
until the bake temperature sensor
32
reads an excess of BAKE_PRE. It is preferred that the broil heating element
16
and the bake heating element
18
be actuated independently of each other so that at no time the broil heating element
16
is on the same time as the bake heating element
18
since the actuation of both heating elements
16
and
18
at once can cause the rate of ambient temperature rise in the baking cavity
12
to increase dramatically, often beyond the ability of the controller
34
to compensate for this increase. It will also be understood that the broil heating element
16
and the bake heating element
18
are preferably actuated according to their duty cycles defined in columns H-I and J-K by the BROIL_CYCLE, BROIL_ON, BAKE_CYCLE and BAKE_ON parameters determined in step
102
by a look up to the database
104
.
Once the oven has preheated, typically by overshooting the desired target temperature TARGET_TEMP, processing moves to a connecting flowchart in
FIG. 6
via connector “A”.
An overview of the control process will be useful in understanding the detailed operation. After the setting of the control parameters (FIG.
5
), the broil and bake heating elements
16
and
18
are activated to maintain the temperature of the cavity adjacent the corresponding broil and bake temperature sensors
30
and
32
between the high and low temperature limit set points, respectively (FIG.
6
).
It is preferred that neither the bake or the broil element are simultaneously activated (
FIGS. 7-10
) and priority is given to the bake element (FIG.
7
). In other words, if both the bake and broil heating elements require activation, the bake element is activated even if the broil element must be turned off.
The benefits of alternate actuation of the bake and broil heating elements (
18
and
16
) can be seen from an examination of
FIGS. 2A and 2B
.
FIG. 2A
is a perspective view of the baking cavity
12
of
FIG. 2
wherein a food product
80
in a baking pan
82
is placed on the rack
26
in the baking cavity
12
. As can be seen from
FIG. 2A
, arrows show the general heat track around the baking pan
82
and food product
80
when the bake heating element
18
is activated. Since the heat from the bake heating element
18
generally tracks around the baking pan
82
and food product
80
and then generally rises vertically, a dead heating zone
84
is defined above the food product
80
where the heat from the bake heating element
18
does not effectively cook the food product
80
. In the case of a low temperature item such as frozen poultry, this dead heating zone
84
can cause significant detriment to the cooking of the food product
82
.
This invention addresses this problem by periodically activating the broil heating element
16
based upon signals from the broil temperature sensor
30
in addition to the periodic activation of the bake heating element
18
based upon signals from the bake temperature sensor
32
. This causes heat to be applied to the food product
80
from above as well as shown in FIG.
2
B. The arrows in
FIG. 2B
show the general heat toward the food product
80
from the broil heating element
16
directly through the dead heating zone
84
thus reducing the negative baking effects of the dead heating zone
84
above the food product
80
.
FIG. 6
represents the main control routine for controlling the temperature in the baking cavity
12
of the oven
10
. Processing then moves to step
108
in which the controller accepts a signal BAKE_TEMP from the bake temperature sensor
32
, which is indicative of the temperature in the cavity
12
at the sensor
32
location. Processing moves to decision point
110
where it is determined whether BAKE_TEMP exceeds the desired high temperature limit for the bake heating element BAKE_HTL. If so, processing passes to the subprocess shown in
FIG. 7
via connector “B” in FIG.
6
. If not, processing moves to decision point
112
.
At decision point
112
, it is determined whether the value of the signal BAKE_TEMP emitted by the bake temperature sensor
32
is less than the desired lower temperature limit for the bake heating element
18
BAKE_LTL. If so, the subprocess shown in
FIG. 8
is called via the connector “D” shown in FIG.
6
. If not, processing moves to step
114
.
At step
114
, the controller
34
receives a signal from the broil temperature sensor
30
corresponding to the temperature BROIL_TEMP read by the broil temperature sensor
30
. It should also be noted that processing returns from the subprocess noted by “B” and the subprocess identified by “D” to the method step shown in
FIG. 6
by the connector shown as “C” which returns the processing of these subprocesss to step
114
as well.
Processing then moves to decision point
116
. At decision point
116
, the controller
34
determines whether the value BROIL_TEMP read in step
114
exceeds the desired high temperature limit for the broil heating element
16
BROIL_HTL. If so, the subprocess shown in
FIG. 9
is called as indicated by connector “E” in FIG.
6
. If not, processing passes to decision point
118
.
At decision point
118
, the controller
34
determines whether the value read by the broil temperature sensor
30
BROIL_TEMP is less than the desired lower temperature limit for the broil heating element
16
BROIL_LTL. If so, the subprocess of
FIG. 10
is called as indicated by connector “G” on FIG.
6
. If not, processing passes to the intermediate point indicated by connector “F” in FIG.
6
. At which time processing loops back to step
108
.
It should also be noted that the subprocess of
FIG. 9
as indicated by connector “E” on FIG.
6
and the subprocess of
FIG. 10
indicated by connector “G”, each return their processing to the connector indicated as “F” on
FIG. 6 and
, thereby, also loop back to step
108
for continued processing of the main loop shown in FIG.
6
.
FIG. 7
represents the subprocess called by decision point
110
if the temperature signal BAKE_TEMP read in step
108
exceeds the desired high temperature limit for the bake heating element
18
BAKE_HTL. Processing then moves to decision point
120
at which point the controller
34
determines whether the bake heating element
18
is OFF. If the bake heating element is OFF, the subprocess merely loops back via the connector shown as “C” whereby processing is returned to step
114
of FIG.
6
.
If the bake heating element
18
is ON, processing moves to step
122
where the controller deactivates the bake heating element
18
. Processing then returns to step
114
of
FIG. 6
via the connector shown at “C”. The net effect of this subprocess is to turn off the bake heating element
18
if the bake temperature sensor
32
reads a temperature BAKE_TEMP in excess of the high temperature limit BAKE_HTL as determined in the database
104
.
FIG. 8
represents the method steps performed when decision point
112
determines that the temperature signal emitted by the bake temperature sensor
32
BAKE_TEMP is less than the desired lower temperature limit for the bake heating element
18
BAKE_LTL. Processing then moves to decision point
124
where the controller
34
determines whether the broil heating element
16
is currently deactivated, i.e., in all OFF state. If so, processing moves to step
126
where the bake heating element is activated for its predefined duty cycle as determined by the controller
34
in the database
104
.
Specifically, the duty cycle activates the bake heating element
18
for a cycle of BAKE_CYCLE seconds of which the bake heating element
18
is on for BAKE_ON seconds of that total cycle time at a temperature of BAKE_SET degrees F. It should be noted that the duty cycle of the bake heating element
18
is started at step
126
and is continuing as processing is returned via the connector “C” to step
114
in FIG.
6
.
The net effect of the subprocess steps of
FIG. 8
is, once a determination is made that the bake temperature sensor
32
is reading a temperature BAKE_TEMP less than the desired lower temperature limit for the bake heating element
18
BAKE_LTL, the duty cycle for the bake heating element
18
is initiated but only after deactivating the broil heating element
16
to ensure that the broil and bake heating element
16
and
18
are not actuated at the same time which can cause sudden uncontrolled temperature increases in the baking cavity
12
.
FIG. 9
represents the subprocess called by decision point
116
if the temperature signal BROIL_TEMP read in step
116
exceeds the desired high temperature limit for the broil heating element
16
BROIL_HTL. Processing then moves to decision point
128
at which point the controller
34
determines whether the broil heating element
16
is OFF. If the broil heating element
16
is OFF, the subprocess merely loops back via the connector shown as “F” whereby processing is returned via connector “F” to FIG.
6
. If the broil heating element
16
is ON, processing moves to step
130
where the controller
34
deactivates the broil heating element
16
. Processing then returns to
FIG. 6
via the connector shown at “F”. The net effect of this subprocess is to turn off the broil heating element
16
if the broil temperature sensor
30
reads a temperature BROIL_TEMP in excess of the high temperature limit BROIL_HTL as determined in the database
104
.
FIG. 10
represents the subprocess called a decision point
118
when the controller
34
determines that the temperature signal BROIL_TEMP sent by the broil temperature sensor
30
is less than the desired lower temperature limit for the broil heating element
16
BROIL_LTL. If so, processing moves along connector “G” from
FIG. 6
to
FIG. 10
to decision point
132
.
At decision point
132
, the controller
34
determines whether the bake heating element
18
is currently activated, i.e., in an ON state. If so, processing returns to
FIG. 6
via connector “F” which thereby returns processing to step
108
in FIG.
6
. If the bake heating element
18
is not currently ON, processing moves to decision point
134
where the controller checks whether this is an electric-based oven
10
or a gas-based oven
10
. If a gas-based oven
10
is detected (i.e., the test whether the oven is electric fails), processing moves to decision point
136
. At decision point
136
, the controller
34
determines whether the broil heating element
16
burner purge time has been satisfied (gas-based systems require a certain amount of time to elapse before a heating element may be reactivated).
If the burner purge time has not been satisfied, processing moves to step
138
at which time the gas-based broil heating element
16
is purged in a manner that is well known in the art. After which, processing moves to step
140
.
It should also be noted that should the test at decision points
134
and
136
be satisfied in the affirmative, i.e., there is an electric-based oven
10
at issue or the broil heating element
16
purge time has been satisfied, processing also moves directly to step
140
. Also, the cycle can be optimized for either an electric or gas oven, instead of the illustrated process that checks for the type of oven. If optimized for one type of oven, the process steps specific to the non-optimized oven can be dropped.
At step
140
, the duty cycle for the broil heating element
16
is initiated in the same manner as described with respect to the bake heating element
18
duty cycle described in step
126
of FIG.
8
. Specifically, a duty cycle of a total cycle time of BROIL_CYCLE seconds of which the broil heating element
16
is activated and emitting heat for BROIL_ON seconds of that total cycle time.
After the duty cycle for the broil heating element
16
is initiated at step
140
, processing returns along the connector “F” to its corresponding connection point “F” at
FIG. 6
which thereafter returns processing to step
108
to repeat the steps of FIG.
6
.
The net effect of the steps shown in
FIG. 10
, once it is established that the temperature BROIL_TEMP detected by the broil temperature sensor
30
is less than the desired lower temperature limit BROIL_LTL of the broil heating element
16
, is to leave the bake heating element
18
on if it is currently on when the subprocess of
FIG. 10
is called. Otherwise, if the bake heating element
18
is off, the duty cycle for the broil heating element
16
is immediately initiated at step
140
for an electric-based oven as determined at decision step
134
. For a gas-based oven
10
, the controller
34
ensures that the broil heating element
16
purge time has been satisfied and only then initiates the duty cycle for the broil heating element at step
140
.
As stated above, once the duty cycle is initiated at step
140
, processing returns via connector “F” to
FIG. 6
where the cycle of
FIG. 6
repeats until the bake time is reached or canceled by the user. The broil and bake heating elements
16
and
18
are activated by the controller
34
as needed with priority given to the bake heating element
18
.
It is believed that the basic invention disclosed herein is the concept of employing a pair of temperature sensors, i.e., the bake temperature sensor
32
located adjacent the bake heating element
18
and the broil temperature sensor
30
located adjacent the broil heating element
16
to independently control the corresponding heating elements. Because the broil and bake temperature sensors
30
,
32
are located relatively close to their respective broil and bake heating elements
16
,
18
, respectively, the temperature sensors
30
,
32
are available to allow the broil and bake heating elements
16
,
18
to be independently controlled based upon a signal from the corresponding temperature sensor
30
,
32
. The signal from the sensors is also more indicative of the local temperature of the oven cavity corresponding to the location of the respective heating element. Thus, greater temperature control and accuracy can be achieved within the baking cavity
12
of the oven
10
.
The relative spacing of the sensor and corresponding element can vary from what is disclosed in the drawings without departing from the invention. If the spacing is great enough some of the high and low element set points might need to be altered to maintain the desired even temperature distribution throughout the oven cavity. What is important to the invention is that the broil element is used to control the local temperature of the portion of the oven above a pan in the oven cavity, the bake element controls the local temperature below the pan, and the elements collectively control the overall temperature of the entire oven cavity through the independent localized temperature control.
It has been found that this invention has equal applicability and value for implementation on both electric-based and gas-based ovens as described previously with respect to
FIGS. 3 and 4
, respectively. It will be understood that the broil heating element
16
and bake heating element
18
can be any of well-known heating elements such as wire-or coil-based heating elements as are typically used in electric-based ovens or gas-based burners typically employed in gas-based ovens.
The example database
104
shown in Table 1 illustrates that different temperature set points, i.e., BROIL_SET and BAKE_SET are established for the corresponding broil temperature sensor
30
and the bake temperature sensor
32
which can be a function of the location of the particular temperature sensor
30
,
32
to its corresponding heating element
16
,
18
, respectively. It should also be noted, as previously described, that the preheat temperatures BROIL_PRE and BRAKE_PRE are preferably greater than the corresponding desired target temperature TARGET_TEMP set by the user
67
on the control panel
76
at the initiation of the BAKE mode heating cycle of the oven
10
. Additionally, the duty cycles of the broil heating element
16
and the bake heating element
18
can be initiated at different duty cycles as defined by the BROIL_CYCLE, BROIL_ON, BAKE-CYCLE, and BAKE_ON as corresponding to the particular target temperature set point TARGET_TEMP for the broil heating element
16
and bake heating element
18
as determined by the target set points for each heating element, i.e., BROIL_SET and BAKE_SET, respectively.
In the example shown in Table 1, the broil heating element
16
is cycled according to a certain pre-set duty cycle for the defined low, mid and high temperature bands of operation and the bake heating element
18
is operated at a different duty cycle for each of these temperature bands. In the example shown in Table 1, the bake heating element
18
is operated at a 100% duty cycle for each of the temperature bands, i.e., BAKE_CYCLE=BAKE_ON thus defining that the bake heating element is activated for the entire length of the total cycle time of the duty cycle for the bake heating element
18
.
A compensation method is also contemplated by the inventive method described herein since, during preheating of the baking cavity
12
of the oven
10
, the temperature of the baking cavity typically overshoots the desired temperature TARGET_TEMP set by the user
67
on the control panel
76
. Accordingly, after the preheating cycle completes, there is typically an idle period wherein the actual ambient temperature within the baking cavity
12
of the oven
10
falls from its overshoot position above the desired temperature TARGET_TEMP set by the user
67
toward the desired temperature TARGET_TEMP set by the user.
The compensation routine contemplated by this invention includes a compensation subprocess which can be called by any of the steps of
FIGS. 6-10
to modify any of the target set points of the method steps and decision points herein (e.g., BROIL_SET, BROIL_HTL, BROIL_LTL, BAKE_SET, BAKE_HTL and BAKE_LTL). The modification of these values, generally upwardly, prevents the actual temperature of the baking cavity
12
of the oven
10
from falling too quickly since the cooling rate of the baking cavity
12
corresponds to the difference between the actual oven temperature (such as the overshot oven temperature after the preheating cycle) and the desired target temperature for which the broil heating element
16
and the bake heating element
18
will be idle during this overshot period.
The compensation method is detailed in FIG.
11
and can essentially be called as a subprocess from any of the decision points and method steps to modify the values discussed above. Processing begins in the compensation method at step
142
wherein the compensation method receives various parameters as outlined in data box
144
.
The data box
144
contains the parameters necessary for the compensation method of
FIG. 11
including: TIMER representative of a clock count between zero seconds or minutes and MAX_TIME representative of the total length of time of the compensation method of FIG.
11
. The data box
144
also contemplates a parameter titled MAX_COMP_FACTOR corresponding to the maximum amount that a particular temperature point will be compensated. Finally, the compensation method of
FIG. 11
is provided with a value TEMP_SET representative of, or as an element of, one of the temperature values indicated above, i.e.,
Once the compensation method of
FIG. 11
has the required parameters at step
142
processing moves to step
146
at which the controller
34
determines the fraction of the total compensation cycle time (MAX_TIME) elapsed during this cycle of the compensation method by calculating:
FRACTION=TIMER/MAX_TIME
Processing then moves to step
148
where the maximum compensation factor MAX_COMP_FACTOR is adjusted according to the fraction of the compensation cycle time remaining, i.e., (1−FRACTION) as calculated in step
146
. Thus, an example of a linear MAX_COMP_FACTOR reduction formula which linearly reduces the amount of adjustment to MAX_COMP_FACTOR along the length of the compensation cycle would be indicated by:
COMP_FACTOR=(1−FRACTION)·MAX_COMP_FACTOR
Processing then moves to step
150
where the temperature value target set point TEMP_SET passed to the compensation method of
FIG. 11
is calculated based upon the compensation factor COMP_FACTOR calculated in step
148
according to whatever linear or non-linear function is desired or employed at step
148
(a linear function is shown, but any non-linear or other function can be employed at step
148
without departing from the scope of this invention). The new target set point TEMP_SET is calculated as:
TEMP_SET=TEMP_SET·(1+COMP_FACTOR).
Processing then moves to step
152
where the compensation method of
FIG. 11
returns the adjusted TEMP_SET value calculated at step
150
in whatever decision point or step that called the compensation method of FIG.
11
.
For example, if the compensation method of
FIG. 11
employed a 48-minute timer, i.e., MAX_TIME=48 minutes or 2,880 seconds and TIMER represents an integral value between 0 and MAX_TIME, the controller
34
would also store a value for MAX_COMP_FACTOR such as 0.04 for a 4% upward adjustment in the set point TEMP_SET passed to the compensation method of FIG.
11
. In the linear compensation routine proposed at step
148
by the example in
FIG. 11
, the value FRACTION would, calculated as a value between 0.00 and 1.00 based upon the ratio of TIMER to MAX_TIME would cause the value COMP_FACTOR to be a reducing linear value between MAX_COMP_FACTOR at TIMER=0 and 0.00 at TIMER=MAX_TIME. The value temp set would then be multiplied by this calculated value to upwardly adjust the value TEMP_SET to the compensated amount.
It has been found that the overshooting of the desired target temperature TARGET_TEMP of the baking cavity
12
as well as the location of the broil temperature sensor
30
and the bake temperature
32
closely adjacent to the broil heating element
16
and the bake heating element
18
creates this need for the compensation algorithm of
FIG. 11
to control the temperature in the baking cavity
12
even more closely than that contemplated by the steps of
FIGS. 6-10
. This compensation method of
FIG. 11
prevents the temperature variance or rate of change of the temperature in the baking cavity
12
from changing radically and far reduces the temperature variance between the high temperature experienced and the low temperature experienced at a particular desired target temperature TARGET_TEMP.
While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.
Claims
- 1. A method for accurately controlling the ambient temperature in an enclosed baking cavity of an oven that is preheated with respect to a user-selected temperature set point, the baking cavity of the oven having 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 defining a baking region therebetween, a broil temperature sensor is mounted within the baking cavity adjacent to the broil heating element, a bake temperature sensor is mounted within the baking cavity adjacent to the bake heating element, the method comprising:providing a controller operably interconnected to a power source and to the broil heating element, bake heating element, the broil temperature sensor and the bake temperature sensor for selectively actuating the broil heating element and the bake heating element in response to the sensed temperature of one or both the broil temperature sensor and the bake temperature sensor; determining a target temperature set point for the oven cavity based on the user-selected temperature set point by calculating a heating element set point comprising both a broil set point and a bake set point derived from the target temperature set point; sensing the temperature of the baking region adjacent at least one of the bake and broil heating elements; comparing the sensed temperature with the target temperature set point; and selectively actuating the broil heating element and the bake heating element in response to the sensed temperature of the baking region to maintain a vertical temperature distribution in the oven cavity that is substantially equal to the target temperature set point.
- 2. The method of claim 1, wherein the step of calculating the one of the bake and broil element set points 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 the one of the bake and broil set points.
- 3. The method of claim 2, wherein the broil set point and the bake set point each comprise a range of temperature values delimited by a low temperature limit and a high temperature limit.
- 4. The method of claim 3, wherein the step of calculating the broil and bake set points further comprises 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.
- 5. The method of claim 4, wherein the temperature differential value can be either negative or positive.
- 6. The method of claim 5, wherein the step of sensing the temperature 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.
- 7. The method of claim 1, wherein the step of selectively actuating the broil and bake heating elements comprises alternately activating the bake and broil heating elements.
- 8. The method of claim 7, wherein the step of alternately activating the broil and bake heating elements comprises at least one of the following steps:deactivating the heating element corresponding to the sensed temperature if the sensed temperature exceeds the corresponding heating element set point; activating the heating element corresponding to the sensed temperature if the sensed temperature is less than the corresponding heating element set point; and deactivating the heating element other than the heating element corresponding to the sensed temperature if the sensed temperature is less than the heating element set point.
- 9. The method of claim 1, wherein the step of selectively activating the bake and broil heating elements comprises the step of deactivating one of the bake and broil heating elements if the one of the bake and broil heating elements is activated and if the sensed temperature is less than the corresponding bake or broil set point by a predetermined amount.
- 10. The method of claim 9, and further comprising the step of activating the other of the bake and broil heating elements for a predetermined duty cycle as long as the one of the bake and broil heating elements is deactivated.
- 11. The method of claim 1, and further comprising the step of detecting whether the oven is gas-based or electric-based.
- 12. The method of claim 11, and further comprising the step of determining whether a purge time limit for the broil heating element has been satisfied when the oven is gas-based/powered.
- 13. The method of claim 12, and further comprising the step of purging the broil heating element if the purge time limit has not been satisfied and if a gas-based oven has been detected.
- 14. The method of claim 1 and further comprising the step of compensating the heating element set point based upon an initial heating condition of the baking cavity.
- 15. The method of claim 14 wherein the heating element set point is increased in the compensation step.
- 16. The method of claim 15 wherein the compensating step further comprises adjusting the heating element set point according to a predefined function.
- 17. The method of claim 16 wherein the function is a decreasing linear function.
- 18. An oven incorporating accurate ambient temperature control comprising:a housing defining an enclosed baking cavity; at least one oven rack for supporting a pan is positioned within the baking cavity and conceptually dividing the cavity into an upper heating region above the rack and a lower heating region below the rack; a broil heating element mounted in the upper heating region of the baking cavity; a bake heating element mounted in the lower heating region of the baking cavity; a broil temperature sensor mounted within the upper heating region adjacent to the broil heating element; a bake temperature sensor mounted within the lower heating region adjacent to the bake heating element; a controller configured to calculate a heating element set point comprising both a broil set point and a bake set point derived from the target temperature set point and operably interconnected to a power source and to the broil heating element, bake heating element, the broil temperature sensor and the bake temperature sensor for selectively actuating the broil heating element and the bake heating element in response to the sensed temperatures of the upper and lower heating regions to maintain the temperature of the upper and lower heating regions substantially equal to the target temperature set point.
- 19. The oven of claim 18, wherein a sensor temperature signal comprising one of a bake temperature signal and a broil temperature signal is read from a corresponding heating element sensor comprising one of the bake temperature sensor and broil temperature sensor.
- 20. The oven of claim 19, wherein the controller compares the sensor temperature signal to the heating element set point.
- 21. The oven of claim 20, wherein the controller deactivates the corresponding heating element if the sensor temperature signal exceeds the heating element set point.
- 22. The oven of claim 21, wherein the controller activates the corresponding heating element if the sensor temperature signal is less than the heating element set point.
- 23. The oven of claim 22, wherein the controller deactivates the heating element other than the corresponding heating element if the sensor temperature signal is less than the heating element set point.
- 24. The oven of the claim 19, controller deactivates one of the bake and broil heating elements if the one of the bake and broil heating elements is activated and if the corresponding bake or broil temperature signal exceeds the corresponding bake or broil set point by a predetermined amount.
- 25. The oven of claim 24, wherein the controller activates the one of the bake and broil heating element for a predetermined duty cycle as long as the other of the bake and broil heating elements is deactivated.
- 26. The oven of claim 18, wherein the controller includes a database comprising multiple target temperature set points and corresponding broil set points and bake set points whereby the bake and broil set points can be selected from the table according to the target temperature set point.
- 27. The oven of claim 26, wherein the broil set point and the bake set point each comprise a range of temperature values delimited by a low temperature limit and a high temperature limit.
- 28. The oven of claim 18, wherein the controller compensates the heating element set point based upon an initial heating condition of the baking cavity.
- 29. The oven of claim 28, wherein the compensation increases the heating element set point.
- 30. The oven of claim 29, wherein the compensation adjusts the heating element set point according to a predefined function.
- 31. The oven of claim 30, wherein the function is a decreasing linear function.
- 32. A method for maintaining an even temperature distribution in a baking cavity of an oven relative to a user-selected temperature set point, the baking cavity of the oven having rack for supporting a pan, with the rack functionally dividing the cavity into an upper heating region above the rack and a lower heating region below the rack, a broil heating element and a corresponding broil temperature sensor are provided in upper heating region, and a bake heating element and a bake temperature sensor are provided in the lower heating region, the method comprising the steps of:providing a controller operably connecting a power source to the broil heating element, the bake heating element, the broil temperature sensor and the bake temperature sensor for selectively actuating the broil heating element and the bake heating element in response to the temperature of the upper and lower heating regions; determining a target temperature set point for the oven cavity based on the user-selected temperature set point by calculating a heating element set point comprising both a broil set point and a bake set point from the target temperature set point; sensing the temperature of the upper and lower heating regions; comparing the sensed temperature of the upper and lower heating regions with the target temperature set point; and selectively actuating the broil heating element and the bake heating element in response to the sensed temperature of the upper and lower heating regions to maintain the upper and lower heating regions substantially equal to the target temperature set point.
- 33. The method of claim 32, wherein the step of calculating the one of the bake and broil element set points 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 the one of the bake and broil set points.
- 34. The method of claim 33, wherein the broil set point and the bake set point each comprise a range of temperature values delimited by a low temperature limit and a high temperature limit.
- 35. The method of claim 34, wherein the step of calculating the broil and bake set points further comprises 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.
- 36. The method of claim 35, wherein the temperature differential value can be either negative or positive.
- 37. The method of claim 32, wherein the step of sensing the temperature 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.
- 38. The method of claim 32, the step of selectively activating the broil and bake heating elements comprises alternately activating the bake and broil heating elements.
- 39. The method of claim 38, wherein the step of alternately activating the broil and bake heating elements comprises at least one of the following steps:deactivating the heating element corresponding to the sensed temperature if the sensed temperature exceeds the corresponding heating element set point; activating the heating element corresponding to the sensed temperature if the sensed temperature is less than the corresponding heating element set point; and deactivating the heating element other than the heating element corresponding to the sensed temperature if the sensed temperature is less than the heating element set point.
- 40. The method of claim 38, wherein the step of alternately activating the bake and broil heating elements comprises activating one of the bake and broil heating elements for a predetermined duty cycle as long as the other of the bake and broil heating elements is deactivated.
- 41. The method of claim 32, further comprising the step of compensating the heating element set point based upon an initial heating condition of the baking cavity.
- 42. The method of claim 41, the heating element set point is increased in the compensation step.
- 43. The method of claim 42, wherein the compensating step further comprises adjusting the heating element set point according to a predefined function.
- 44. The method of claim 43, wherein the function is a decreasing linear function.
US Referenced Citations (13)