Note: Descriptions are shown in the official language in which they were submitted.
CA 02204795 2005-11-02
1 WARMER DRAWER FOR A COOKING RANGE
2
3
4
b HACRGROUND OF THE INVENTION
7 FIELD OF THE INVENTION
8 The present invention pertains to domestic cooking
9 ranges and, more particularly, to domestic coo)cing ranges
to having a warming drawer adapted to receive and maintain
11 cooked hot food at an above-ambient temperature.
12 DESCRIPTION OF RELATED ART
13 Domestic cooking ranges traditionally include an open
14 space relatively beneath the oven which slidably receives a
storage drawer in which the user may store various
1.6 articles, such as cooking pots and/or pans. As such, the
17 conventional or prior art drawer is only useful for storage
1.8 purposes, and could not be used to heat or warm food.
19 The space occupied by the storage drawer has also, in
the past, been used as a broiling cavity which receives a
21 broiling tray. A broiling element is located relatively
2.2 above the broiling tray. The broiling element is operated
23 at high temperatures as required to accomplish the broiling
24 function.
The prior art references which include a broiling
26 element do not control energization of the broiling element
27 to only warm food contained on the broiling tray. Rather,
28 the broiling element is typically operated exclusively at
29 full power, as required for broiling. Due to the high-
energy or high-heat output of the broiling element,
CA 02204795 2005-11-02
maintaining food at an above-ambient temperature for warming
purposes, but still low enough so that further cooking does
not occur, is not possible.
Therefore, there exists a need in the art for a cooking
applicant which provides a warmer drawer in which heating or
warming of food is permitted. There also exists a need in
the art for a warming device wherein the temperature of the
food within the device is controlled such that further
cooking of the food, which may degrade the food quality,
does not occur.
SUMMARY OF THE INVENTION
In a first aspect, the present invention provides a
cooking appliance, comprising a cabinet, a lower heating
chamber adapted to receive a food receiving member, a
heating element disposed within said heating chamber, means
for controlling said heating element such that a temperature
within said heating chamber is maintained between a
predetermined minimum temperature and a predetermined
maximum temperature corresponding to a range of desired food
serving temperature, wherein said controlling means comprise
a temperature sensor and an infinite switch.
In another aspect, the present invention provides a
method for controlling a warmer drawer heating element to
maintain a temperature within a heating chamber between a
predetermined maximum and a predetermined minimum, said
warmer drawer heating element being disposed within said
heating chamber, comprising the steps of: moving a heater
control switch from an off position to a user-selected
position, said user selected position corresponding to a
duty cycle of heater element operation; energizing said
heater element at full power; sensing the temperature within
said heating chamber; terminating full power energization of
said heater element at said predetermined maximum
temperature; energizing said heater element at said
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predetermined duty cycle; terminating energization of said
heater element at said predetermined duty cycle at said
predetermined minimum temperature; energizing said heater
element at full power; and terminating full power
energization of said heater element at said predetermined
maximum temperature; resuming energization of said heater
element at said predetermined duty cycle.
In yet another aspect, the present invention provides a
cooking appliance, comprising: a cabinet; an oven wrapper
disposed within said cabinet, said oven wrapper having a
generally inverted u-shape including a pair of lateral side
walls; a warmer liner, comprising: a liner top wall disposed
generally between said lateral side walls; a liner bottom
wall disposed generally between said lateral side walls,
wherein said liner top wall and bottom wall cooperate with
said lateral side walls to define a heating chamber; a
warmer drawer adapted to be received within said heating
chamber; a heating element secured to said liner bottom wall
relatively beneath said warmer drawer; a temperature sensor
disposed within said heating chamber; and a control device
operable to control energization of said heating element to
maintain the temperature within said heating chamber between
a predetermined minimum temperature and a predetermined
maximum temperature corresponding to a range of desired food
serving temperatures, wherein said control device comprises
a user-adjustable infinite switch.
In a further aspect, the present invention provides a
method for controlling an electrical warmer drawer heating
element to maintain a temperature within a lower heating
chamber, comprising steps of: providing a range for
placement on a floor, providing a cabinet to said range,
providing an oven wrapper disposed within said cabinet. and
at least partially defining an oven chamber, providing the
lower heating chamber relatively beneath said oven chamber,
providing a fixed panel defining a lower extent of the
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heating chamber, providing the electrical heating element
within said heating chamber, adjacent to the panel,
providing the warmer drawer slidably mounted in the lower
heating chamber, above the heating element and the panel,
providing a temperature sensor disposed within said heating
chamber and operable to sense temperature within said
heating chamber, and providing controlling means for
controlling said heating element such that a temperature
within said heating chamber is maintained between a
predetermined minimum temperature and a predetermined
maximum temperature corresponding to a range of desired food
serving temperatures; moving a heater control switch from an
off position to a user-selected position, said user selected
position corresponding to a duty cycle of heater element
operation; energizing said heater element at full power;
sensing the temperature within said heating chamber using
the temperature sensor; terminating full power energization
of said heater element at said predetermined maximum
temperature; energizing said heater element at said
predetermined duty cycle.
BRIEF DESCRIPTION OF THE DRAWINGS
Features of the present invention will be apparent with
reference to the following description and drawings,
wherein:
FIG. 1 is a perspective view of a cooking range with a
food warmer in a fully extended position;
FIG. 2 is a rear perspective view of a food warmer
drawer according to the present invention;
FIG. 3 is a front elevational view of a lower portion
of the cooking range shown in FIG. 1, with the food warmer
drawer removed therefrom;
FIG. 4a, 4b and 4c, are respectively, a front
elevational view, a top plan view, and a side elevational
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view of a front heat shield panel or grate according to the
present invention;
FIG. 4d is a cross sectional view of the front heat
shield as seen along line 4d-4d of FIG. 4a;
FIG. 5a, 5b and 5c are, respectively, a front
elevational view, a top plan view, and a side elevational
view of a rear heat shield panel according to the present
invention;
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1 FIG. 6a, Gb, and Gc are, respectively, a top plan
2 view, a front elevational view, and a side elevational view
3 of a lower heat shield panel according to the present
4 invention;
FIG. 7a, 7b, and 7c are, respectively, a bottom plan
6 view, a front elevational view, and a side elevational view
7 of ~n~upper heat shield panel according to the present
8 invention;
9 'FIGS. 8a, 8b, and 8c are, respectively, a front
elevational view, a top plan view, and a side elevational
11 view of a temperature sensor mounting brac)cet according to
12 the present invention;
13 FIGS. 9a, 9b, and 9c are, respectively, a front
14 elevational view, a top plan view, and a side elevational
view of a warmer drawer temperature sensor according to the
16 present invention;
17 FIG. 10 is a side elevational view of a warmer drawer
18 glide assembly according to the present invention;
19 FIG. 11 is an end elevational view of the warmer
drawer glide assembly shown in FIG. 10.
21 FIG. 12 is top plan view of a heating element
22 according to the present invention;
23 FIG. 13 is a perspective view of a heating element
24 mounting clip according to the present invention;
FIG. 14 is a front elevational view of an oven chassis
26 wrapper according to the present invention; and,
27 FIG. 15 is a schematic diagram illustrating a control
28 circuit for the warmer drawer heating element.
29 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
It should be noted that in the detailed description
31 which follows, identical components have the same reference
32 numeral, regardless are shown in different
of whether they
33 embodiments of the present invention.
It should also be
34 noted that, in order to clearly and concisely disclose the
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1 present invention, the drawings may not necessarily be to
2 scale and certain features of the invention may be shown in
3 somewhat schematic form.
4 With reference to FIG. 1, a household range 20
incorporating the present invention is illustrated. The
6 range includes a cabinet to which an oven door 22 is
7 secured so as to permit pivotal movement of the door about
8 its bottom edge. The cabinet includes a top panel which
9 includes surface heating elements (not shown). A control
panel 24 extends upwardly from adjacent a rear portion of
11 the top panel, and includes a plurality of control devices,
12 such as dials, switches, buttons, and/or knobs.
13 The control devices provided by the control panel
14 include a warmer drawer heater control switch 26, and
associated indicator light 28. Preferably, the warmer
16 drawer heater control switch 26 is rotatably mounted to the
17 control panel, and is movable in a push-and-turn fashion to
18 any user-selected position between an off position, and a
19 high heat position. More preferably, the warmer drawer
heater control switch 26 is an infinite switch wherein the
21 duty cycle (ratio of heater on-time to heater on-time plus
22 heater off-time) varies from zero, when the switch is set
23 to the off position, to one when the switch 26 is set to
24 the high position.
As will be described more fully hereafter, rotation of
26 the'w~rmer drawer heater control switch 26 between the
27 various user-selected positions varies the duty cycle of a
28 warmer drawer heating element 32. It is believed that
29 operation of infinite switches is well known to one skilled
in the art and, therefore, will not be further discussed
31 hereinafter.
32 With reference to FIG. 2, the warmer drawer 34
33 according to the present invention is illustrated. The
34 warmer drawer preferably includes a pair of lateral side
walls 36, a rear wall 38, a bottom wall 40, and a front
36 wall 42 which cooperate to define a receptacle adapted to
37 receive food stuffs to be maintained at an acceptable
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1 above-ambient serving temperature.
2 The front wall 42 includes a front panel 44 from which
3 a handle extends (FIG. 1). Each of the lateral side walls
4 36 had a first portion 47 of a glide assembly 48 secured
thereto, as will be described more fully hereafter.
6 The. front wall and panel 42, 44 extend or project
7 laterally and vertically outboard and perpendicular to the
8 lateral side walls 36 and bottom wall 40 of the drawer. An
9 annuhar heat seal member or gasket 50 is attached to a
rearward facing surface of the front wall 42 and surrounds
11 the lateral side walls 36 and bottom wall 40, as
12 illustrated. When the drawer is in,a retracted or closed
13 position, the heat seal member 50 limits the escape of heat
14 from within the warmer drawer 34 and heating chamber 54, to
be described hereafter. Preferably, the heat seal member
16 is formed from material commonly used to seal the periphery
17 of the oven door to the cabinet.
18 The heat seal member 50 does not prevent air from
19 being drawn through slotted openings 56 in the grate 52, as
is desirable to supply supplementary combustion air to a
21 lower burner of a gas range. As will be apparent to one
22 skilled in the art, the front grate 52 may be modified and
23 the usable heating chamber height increased accordingly for
24 electric ranges, since supplementary combustion air is not
required.
26 . The walls of the warmer drawer 34 are preferably
27 formed from steel, and have a porcelainized inner surface.
28 A porcelain inner surface of the warmer drawer is
29 preferable over a painted surface for a number of reasons.
These reasons include heat tolerance, resistance to
31 scratches and wear, ease of cleaning, and aesthetic
32 continuity with other surfaces of the oven. The warmer
33 drawer 34 may receive one or more racks (not shown) which
34 support foodstuffs in a spaced relationship to the bottom
wall 40.
36 With reference to FIG. 3, the range cabinet provides
37 an open space between the bottom of the cooking oven (not
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1 shown) and the floor. The open space is defined, in part,
2 by lateral sidewalls 60 of an oven chassis wrapper 58,
3 which is illustrated in FIG. 14. The oven chassis wrapper
4 58 is generally of an inverted U-shape, and defines the
lateral and top walls of the cooking oven. A bottom oven
6 wall (not shown) and rear oven wall (not shown) are
7 mechanically attached, such as by welding, to the oven
8 chassis wrapper to define the cooking oven.
9 A base portion of the oven chassis wrapper lateral
walls 60 defines the lateral extent of the open space. A
11 warmer drawer liner assembly is attached to the cabinet in
12 the open space and cooperates with the lateral walls 60 to
13 define the heating chamber which receives the warmer drawer
14 34.
The warmer drawer liner assembly includes, in addition
16 to the front panel or grate 52, an upper panel 62, a lower
17 panel 64, and a rear panel 66.
18 The front panel or grate 52 is secured to the upper
19 panel 62, as will be described more fully hereafter and,
with reference to FIGS. 4a-4d, includes a front wall 68, a
21 bottom wall 70, and a pair of upper tabs 72. The front
22 wall 68 has the slotted openings 56 formed therein, as
23 discussed hereinbefore. The bottom wall 70 and the upper
24 tabs 72 extend rearwardly from the front wall 68.
Each of the upper tabs 72 includes an opening 74
26 through which a mounting screw is inserted to secure the
27 front panel 52 to a front chassis wall of the range 20
28 (FIG: 1). The lower wall 70 has a proximal portion 76
29 adjacent the front wall and a distal portion 78 spaced from
the front wall. The proximal portion 76 includes a pair of
31 openings 80 underlying the upper tabs 72 through which
32 access to the tabs may be gained for insertion/removal of
33 the mounting screws.
34 The distal portion 78 has a series of short slots 82
formed therein which separates the distal portion of the
36 lower wall into an alternating series of first tabs 84 and
37 second tabs a6. The first tabs 84 are generally co-planar
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1 with the proximal portion 76 of the bottom wall, while the
2 second tabs 86 are bent upwardly at an angle to the common
3 plane of the first tabs 84 and the proximal portion 76, as
4 illustrated.
. The second or angled tabs 86 have openings 88 formed
6 therein through which screws are inserted to secure the
7 upper panel 62 to the front panel or grate 52. As will be
8 described more fully hereafter with reference to assembly
9 of the front panel to the upper panel, the upper panel 62
is inserted relatively above the first tabs 84 and
11 relatively below the second tabs 86, and screws are
12 inserted through the openings in the second tabs 86 and
13 through the upper panel 62 to secure the upper panel 62 to
14 the front panel 52.
The upper panel 62 is secured to the front panel or
16 grate 52, as described hereinbefore, and to the lateral
17 walls 60 of the oven chassis wrapper 58. The upper panel
18 is located rearwardly relative to the front panel or grate,
19 and defines an upper extent of the heating chamber.
With reference to FIGS. 7a-7c, the upper panel 62
21 includes a generally planar plate 90 from which a rearward
22 flange 92 and a pair of lateral flanges 94 are downwardly
23 bent. The lateral flanges 94 include openings through
24 which screws are inserted to secure the upper panel to the
lateral walls 60 of the oven chassis wrapper 58. The front
2G edge of the upper panel is slidably inserted between the
27 first and second tabs 84, 86 of the front panel, and
28 includes openings through which screws are inserted to
29 secure the upper panel 62 to the front panel 52, as
discussed hereinbefore.
31 The lower panel 64 is secured to the rear panel 66 and
32 to lateral walls 60 of the oven chassis wrapper, and
33 defines a lower extent of the heating chamber 54. With
34 reference to FIGS. 6a-6c, the lower panel 64 includes a
plate member 96 from which a rear flange 98 and a pair of
36 lateral flanges 100 extend.
37 The rear flange 98 is bent generally perpendicular to
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1 the plate member 96, and is secured to the rear panel 66 by
2 means of a screw. The lateral flanges 100 are generally Z-
3 shaped in cross section, and define openings through which
4 screws extend to secure the lateral flanges to the lateral
walls 60 of the oven chassis wrapper 58.
6 The plate member 96 also provides a pair of mounting
7 tabs 102 and a series of dimpled mounting openings 104.
8 The mounting tabs 102 are bent upwardly from the plate
9 member 96 and define pockets for receipt of a temperature
~0 sensing and circuit enabling/disabling assembly,
11 hereinafter referred to as the temperature sensing
12 assembly. The mounting tabs 102 slidably, yet resiliently,
13 receive the temperature sensing assembly thereunder, as
14 will be described hereafter. The dimpled mounting openings
104 are provided to facilitate securing heating element
16 mounting clips 106 (FIG. 13) to the lower panel 64, as will
17 be described hereafter.
18 The rear panel 66 is secured to the lower panel 64 and
19 to the lateral walls 60 of the oven chassis wrapper 58, and
extends between rearward edges of the upper and lower
21 panels 62, 64, and between the lateral walls of the oven
22 chassis wrapper. The rear panel defines a rearward extent
23 of the heating chamber 54.
24 ~ With reference to FIGS. 5a-5c, the rear panel 66
includes a plate 108 from.which a lower flange 110 and a
26 pair of lateral flanges 112 extend. The lateral flanges
27 112 extend generally rearwardly of the plate 108, and
28 include openings to assist in mechanical securement of the
29 lateral flanges to the lateral walls 60 of the oven chassis
wrapper. The lower flange 110 has a generally inverted-L
31 shape, and is adapted to extend out over, and in front of
32 the rear flange 98 of the lower panel 64. A vertical face
33 114 of the lower flange 110 includes an opening through
34 which a mounting screw extends to secure the lower flange
110 to the rear flange 98.
36 As such, the panels 52, 62, 64, 66 cooperate with
37 the oven chassis wrapper 58 to define the heating chamber;
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1 which is closed at its lateral sides, rear side, upper
2 side, and lower side, and open at the front. The warmer
3 drawer 34 is slidably inserted into the heating chamber 54,
4 and's~lidably removed from the heating chamber, by means of
the glide assembly 48, to be described further hereafter.
6 It should be noted that the illustrated warmer drawer
7 liner assembly is intended for an electric range. On gas
8 ranges, the rear panel is not used, and the rearward extent
9 of the heating chamber is defined by a vertical wall which
has control devices for the lower gas burner assembly
11 mounted thereto. The vertical wall and control devices are
12 conventional and, therefore, are not specifically
13 illustrated.
14 Each of the lateral walls 60 of the oven chassis
wrapper have a second portion 46 of the drawer glide
16 assembly 48 secured thereto. The first and second portions
17 47, 46 of the glide assembly 48 cooperate with one another
18 to permit the drawer 34 to be slidably inserted into the
19 heating chamber, and slidably removed from the heating
chamber. Also, the first and second glide portions 47, 46
21 may be disengaged from one another to permit the warmer
22 drawer 34 to be completely disconnected and removed from
23 the range 20, as would be desirable for cleaning and/or
24 maintenance purposes. It is understood that numerous glide
assemblies are known in the art, and various other glide
26 assemblies may be substituted for the illustrated glide
27 assembly 48 without departing from the scope and spirit of
28 the present invention.
29 The heating element 32 (FIG. 12) and temperature
sensing assembly (FIG. 3) are disposed within the heating
31 chamber 54 and secured to the lower panel 64. The heating
32 element 32 preferably comprises a tubular, electrical
33 resistance-type heating element which is fastened to the
34 lower panel 64 via the mounting clips 106 (FIG. 13) and a
mounting bracket 118 (FIG. 8a-8c). The mounting clips 106
36 are attached to the mounting openings 104 in the lower
37 panel and clamp the heating element 32 to the lower panel
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1 64. Naturally, more or less than the illustrated four
2 mounting clips 106 may be used to secure the heating
3 element 32 to the lower panel 64, if desired.
4 A mounting plate 116 of the heating element 32 is
secured to the mounting bracket 118 of the temperature
6 sensing assembly, as will be described hereafter. The
7 heating element 32 is electrically connected to a
8 temperature sensor 30, and is powered in accordance with
9 the user-selected setting of the control switch 26 and as
needed to maintain the temperature within the heating
11 chamber 54, as sensed by the temperature sensor 30, within
12 a predetermined desired range of operating temperatures, as
13 will be described hereinafter with reference to the control
14 circuit illustrated in FIG. 15.
The temperature sensing assembly includes the
16 temperature sensor 30 and the mounting bracket 118. The
17 temperature sensor 30 is secured to the mounting bracket
18 118 in an elevated position, as illustrated in FIG. 3, and
19 is operable to sense the temperature within the heating
chamber 54.
21 . kith reference to FIGS. 8a-8c, the mounting bracket
22 118 includes a body member 120 from which a base flange 122
23 extends rearwardly. The base flange is slidably received
24 under the mounting tabs 102 and mechanically attached,
preferably by a screw, to the lower panel G4. The body
26 member 120 defines an elongated opening 123 which receives
27 the temperature sensor 30, and includes a plurality of
28 openings through which fasteners extend to secure the
29 temperature sensor 30 and the heating element mounting
plate 116 to the mounting bracket 118.
31 The temperature sensor 30 has a forwardly projecting
32 sensor portion 126, a mounting flange 128, and a rearwardly
33 extending connector portion 130. The mounting flange 128
34 includes a pair of lateral openings through which fasteners
extend to secure the temperature sensor 30 to the mounting
36 bracket 118. The temperature sensor 30 is inserted through
37 the elongated opening 123 in the mounting bracket body,
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1 such that the sensor portion 126 faces toward the warmer
2 drawer 34 and the open front of the heating chamber 54 and
3 the connector portion 130 faces toward the rear panel 66.
4 The connecting portion 130 is electrically connected, via
suitable conductors, to the control switch 26 and the
6 heating element 32.
7 The location of the sensor 30 and mounting bracket 118
8 gives the control circuit its ambient compensation
9 characteristics. For example, and as will be apparent from
the description to follow, relatively more heat may have to
11 be input into the heating chamber to reach the
12 predetermined maximum temperature during low ambient
13 conditions than during high ambient conditions. Putting
14 more heat into the heating chamber during low ambient may
help reduce cycling as the time required to reach the
16 minimum temperature will be extended. Moreover, the
17 temperature within the warmer drawer corresponding to the
18 predetermined maximum heating chamber temperature may be
19 relatively higher during low ambient conditions than during
~ high ambient conditions. For high ambient conditions, less
21 heat may be required to reach the predetermined maximum
22 heating chamber temperature, and less heat is lost to
23 atmosphere, so temperature within the heating chamber and
24 the warmer drawer may be relatively more uniform and
static.
26 The warmer drawer 341of the present invention is
27 located relatively above the heating element 32 and,
28 therefore, the present invention takes advantage of the
29 natural tendency of relatively hot air to rise. ~s such,
the food stuffs contained within the drawer 34 are in a
31 relatively hot portion of the heating chamber 54. As
32 mentioned briefly hereinbefore, it may be desirable to
33 place one or more removable racks within the drawer 34 to
34 space the foods being warmed away from the bottom wall 40
of the drawer. Spacing of the food from the bottom wall 40
36 permits warm air to flow beneath the food and facilitates
37 more even heating thereof. Spacing of the food from the
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1 bottom wall 40 also prevents localized over-heating of the
2 food at the interface with the bottom wall, since the
3 bottom wall will be relatively hot, as compared to air
4 within the heating chamber 54, due to the proximity of the
bottom wall to the heating element 32.
6 With reference to FIG.~15, a control circuit 131 for
7 the warmer drawer heating element 32 is illustrated. The
8 circuit 131 generally includes an oven self-cleaning cycle
9 lock=out switch 132, the heater control switch 26, the
~0 warmer indicator light 28, the temperature sensor 30, the
11 warmer drawer heating element 32, and a diode 134. The
12 heater control switch 26 provides first and second pairs of
13 contacts 26a, 26b. The first pair of contacts 26a are
14 closed whenever the switch 26 is turned on. The second
pair of contacts open and close when the switch 26 is
16 turned on, the frequency of opening and closing depending
17 upon the angular position of the switch 26 to vary or
18 adjust the duty cycle of heater operation. For example,
19 when the heater control switch 26 is turned to "high", the
second pair of contacts 26b are mechanically locked in a
21 closed position whereas, when the switch 26 is turned to
22 the "low" position, the second pair of contacts 26b will be
23 closed only a portion of the time (e.g., 20%) and will be
24 open the rest of the time. It is considered that the
above-described operation of the switch 2G is well known in
26 the infinite switch art.
27 The lock-out switch 132 opens and thereby de-activates
28 or renders inoperable the warmer drawer heating element 32,
'29 and the heater control switch 26, when the oven is operated
in a self-cleaning mode and, therefore, prevents
31 energization of the heating element 32 during a self-
32 cleaning cycle.
33 The first pair of heater control switch contacts 26a
34 are connected in series with the lock-out switch 132. The
warmer indicator light 28 is connected in parallel with the
36 warmer heating element 32 and a heating element
37 energization control circuit 136 and, therefore, is
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1 illuminated whenever the heating element 32 is powered to
2 provide visual indication to the user that the warmer
3 heating element 32 is operating.
4 The temperature sensor 30 provides a thermally-
actuated switch 30a which is normally-closed. The warmer
6 element energization circuit 136 includes the diode 134 and
7 the second pair of heater control switch contacts 2.6b in
8 parallel with the temperature sensor switch 30a, as
9 illustrated. Therefore, when the heater control switch 26
is turned from "off" to any position, the series
11 combination of the second pair of heater control switch
12 contacts 26b and the diode 134 is shorted by the parallel
13 branch due to the normally-closed temperature sensor switch
14 30a.
The heating element 32 is therefore in series with the
16 temperature sensor switch 30a, and full power is applied to
17 the heating element 32. At this point, no current flows
18 through branch of the energization circuit 136 containing
19 the diode 134 and the second pair of heater control switch
contacts 36b. This period of operation is referred to
21 herein as the preheating cycle during which the heating
22 element 32 is operated at full power to more quickly bring
23 the warmer drawer 34 up to the maximum operating or peak
24 preheat temperature. When the temperature within the
heating chamber 54 reaches the predetermined maximum
26 desired temperature or peak preheat temperature, the
27 temperature sensor switch 30a opens and control of the
28 heating element energization is given over to the heater
29 control switch 26. The time required to reach the
predetermined maximum temperature depends upon a number of
31 factors, including the size, temperature, and type of food
32 being warmed,~and the ambient temperature.
33 The heating chamber temperature corresponds to the
34 warmer drawer temperature (i.e., food temperature), so that
sensing of the heating chamber temperature is an accurate
36 guide to the warmer_ drawer temperature and, as will be
37 apparent from the following description, the sensed heating
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1 chamber temperature is used to control energization of the
2 heating element 32 to maintain the warmer drawer
3 temperature within a range of desired food serving
4 temperatures.
Due to the diode 134, only half-wave rectified current
6 flows through the heating element 32 which, therefore, is
7 limited to half maximum power if the warmer switch is set
8 to "high". As noted hereinbefore, the duty cycle of the
9 heating element operation is controlled by the angular
position of the heater control switch 2G which, in turn,
11 corresponds to the rate or frequency of opening/closing of
12 the second pair of heater control switch contacts 26b.
13 The duty cycle controls the amount of power dissipated
14 in the heater element 32 which, in turn, affects the amount
of heat energy added to the warmer drawer heating chamber
16 54 and, hence, the warmer drawer 34. The rate at which the
17 heating chamber temperature falls (from the maximum
18 temperature at the end of the preheat cycle) is affected by
19 the food load within the warmer drawer, the ambient
temperature, and the user-selected duty cycle of the warmer
21 drawer heating element 32 (i.e., the angular position of ,
22 the switch 26).
23 For example, at a given ambient temperature, if a
24 relatively large, cool item of food is placed in the warmer
drawer 34 and the warmer switch 2G is set to the "low"
26 position (which corresponds to a small duty cycle, e.g.,
27 .20), the temperature within the heating chamber 54 and the
28 warmer drawer 34, following the preheat cycle, will fall
29 faster than if a similarly sized but hotter item of food is
placed in the warmer drawer and the warmer switch 26 is set
31 to high (i.e., full one-half power, switch duty cycle
32 equals 1.0). Similarly, if a small, hot food item is
33 placed in the warmer drawer 34 in a low ambient environment
34 and the warmer switch 26 is set to "medium", the
temperature within the heating chamber 54 and the warmer
36 drawer will fall faster than if an item of similar size and
37 temperature is placed in the warmer drawer in a high
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1 ambient environment and the warmer switch is set to the
2 "medium" position.
3 If the heating chamber temperature drops below a
4 predetermined minimum desired temperature (which
corresponds to a minimum desired serving temperature within
6 the warmer drawer), the temperature sensor contacts close,
7 shorting the branch of the energization circuit 136
8 containing the diode 134 and the second pair of heater
9 contrbl switch contacts 26b, and full power is again
applied to the heating element 32 until the heating chamber
11 temperature exceeds the maximum desired temperature
12 (corresponding to the maximum desired serving temperature
13 within the warmer drawer), at which point the temperature
14 sensor contacts open and control is returned to the heater
control switch 26 at the user-selected duty cycle.
16 Accordingly, the warmer drawer temperature is maintained
17 between maximum and minimum desired serving temperatures.
18 As should be apparent from the foregoing, control over
19 energization of the heating element 32 alternates between
full power when the temperature sensor contacts close
21 (preheat cycle and low heating chamber/warmer drawer
22 temperature) and the user-selected duty cycle. As noted
23 hereinbefore, the heat input into the heating chamber to
24 reach the maximum desired heating chamber temperature will
vary depending at least upon ambient temperature.
26 Similarly, the rate at which the heating chamber
27 temperature falls to the predetermined minimum desired
28 heating chamber temperature will vary depending at least
29 upon ambient temperature, food size and type, and user
selected setting of the control switch 26.
31 It is also noted that the maximum and minimum warmer
32 drawer temperatures may vary in dependence upon ambient
33 temperature. For example, the maximum warmer drawer
34 temperature may be relatively higher in low ambient
conditions than in high ambient conditions. Similarly, the
36 minimum warmer drawer temperature may be relatively higher
37 in low ambient conditions than in high ambient conditions.
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CA 02204795 1997-OS-08
1 Since relatively more heat is lost to the environment in
2 low ambient conditions than in high ambient conditions, the
3 noted temperature compensation feature reduces cycling of
4 the heater element between the user-selected duty cycle and
full power cycle than would otherwise occur. The maximum
6 and minimum warmer drawer temperatures fall within a range
7 of desired food serving temperatures.
g While the preferred embodiment of the present
9 invention is shown and described herein, it is to be
understood that the same is not so limited but shall cover
11 and include any and all modifications thereof which fall
12 within the purview of the invention.
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