Note: Descriptions are shown in the official language in which they were submitted.
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RADIAL BYPRODUCT TRAP AND FILTER ASSEMBLY
FOR A COOKING APPLIANCE
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to the art of cooking appliances and,
io more particularly, to a radial cooking byproduct trap and filter
arrangement for a quick or rapid cook appliance.
2. Discussion of the Prior Art
In the art of cooking appliances, it has been heretofore proposed to
enable an appliance to operate in a self-cleaning mode. For example, in a
conventional range having a cooking cavity which can be heated by one
or more cooking elements arranged within the cooking cavity to perform
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at least baking and broiling functions, i t is known to operate one or more
of the cooking elements to perform a pyrolytic self-cleaning operation in
order to cleanse the walls of the cavity from grease and other food soils
developed during normal cooking operations. In such a cooking
arrangement, the cooking elements used to perfoi-m the cleaning process
are located entirely within the cooking cavity.
In addition, it is known to provide a catalytic self-cleaning oven.
In such an arrangement, the walls of the oven are coated with a catalytic
material which provides for self-cleaning of the oven cavity during
io cooking operations. In performing any self-cleaning function,
byproducts, including smoke, gases and other odorous fumes, are
inherently produced. A typical oven cavity will be vented to permit the
escape of these byproducts to the ambient surroundings. In some cases, a
catalytic oxidation unit is provided in the vent to react with the flowing
byproducts. In still other cooking appliance arrangements, a combination
of pyrolytic and catalytic cleaning is performed.
Regardless of the fact that various self-cleaning systems have been
proposed in the art, there still exists a need to fu.rther improve cleaning of
a recirculating air flow in a convection cooking appliance in order to
maximizes the elimination of byproducts, while also minimizing the
necessary operating time for any self-cleaning mode. Particular concerns
are raised in connection with the necessary operating time and byproduct
elimination in a rapid cook convection oven which essentially relies on a
heated flow of recirculating air and a microwave source for raising the
temperature in an oven cavity.
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SUMMARY OF THE IN'VENTION
The present invention is directed to trapping and filtering liquid
andJor solid cooking byproducts for purposes of cleaning a recirculating
air flow in a convection cooking appliance, particularly an appliance
including an air channel assembly which is defined by ducting extending
about portions of an oven cavity for directing the recirculating air flow
into and out of the oven cavity. The overall system utilizes various
heating elements to enhance the heating of the oven cavity, as well as the
catalyst in order to enhance the efficient elimination of developed smoke,
1o odor and other byproducts, and to effectively reduce the necessary
cleaning cycle time for the appliance.
In accordance with the present invention,l:he convection cooking
appliance particularly employs a radial byproduct trap and filter assembly
for use in a quick-cook type convection cooking appliance. Specifically,
the invention is concerned with using a concentric ring-type baffle filter
having two cylindrical sets of opposing air deflectors or baffles. As
recirculating air passes outwardly between two inner baffles, the air is
accelerated by a nozzle-type effect prior to impacting a center zone of an
outer baffle. This arrangement causes part of liquid and/or solid phases,
such as grease, fats, and moisture, of the air flow to be deposited or
trapped between the baffles. The air flow is then redirected back towards
the inner set of baffles where, once again, the air impacts a baffle that
leaves part of the byproducts in the air. Finally, the air exits between
certain baffles of an outer baffle.
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With this arrangement, the resulting separation of the liquid phase
byproducts functions to deposit some of the liquid/solid byproducts onto
an inside surface of an outer baffle, as well as on an outer surface of the
inside ring of baffles. Symmetrical spacing of inlet and outlet or exhaust
openings through each set of baffles generates a high uniform air flow
pattem around the annular baffle arrangement. The overall air flow
increases the effectiveness of the recirculation of the oven air system.
Additional objects, features and advantages of the present
invention will become more fully apparent below with reference to a
io preferred embodiment of the invention, when taken in conjunction with
the drawings wherein like reference numerals refer to corresponding parts
in the several views.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective, partial sectional view of a convection
cooking appliance constructed in accordance with the present invention;
Figure 2 is a cross-sectlonal side view of the cooking appliance of
Figure l ;
Figure 3 is a schematic side view, similar to that of Figure 2, of the
cookirig appliance;
Figure 4 is a block diagram illustrating a control arrangement used
in a self-cleaning system employed in the cooking appliance of Figure 1;
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Figure 5 depicts a graph illustrating a time versus temperature
curve followed in accordance with operation of the cooking appliance
during a self-clean operation;
Figure 6 is a perspective, partial cross-sect:ional view
corresponding to that of Figurel, while depicting a radial trap and filter
arrangement incorporated into the cooking appliance in cross-section; and
Figure 7 is an enlarged cross-sectional view of the radial trap and
filter arrangement of Figure 6.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENT
With initial reference to Figures 1-3, a cooking appliance 1 is
schematically shown in the form of a wall oven. Appliance 1 includes an
oven cavity 5 generally defined by a bottom wall 8, a top wall 9, a rear
wall 10 and a pair of side walls, one of which is indicated at 11. Oven
cavity 5 also has associated therewith an access opening 13 for food items
to be placed into or withdrawn from cavity 5. About access opening 13 is
provided a frontal plate 16. In a manner known in the art, frontal plate 16
is adapted to be mounted against a substantially vertical wall such as in
the kitchen of a residential home, and would have a door (not shown)
pivotally attached thereto for selectively sealing off access opening 13.
Extending generally along top, bottom and rear portions of cavity 5
is an air channel assembly 26 defined by ducting that leads into and out of
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cavity 5. More specifically, air channel assembly 26 includes a lower air
return section 29, an upper air delivery section 30 and a rear air transfer
section 31. Lower air return section 29 is open into cavity 5 through a
substantially central return air outlet 33 formed in bottom 8. In the most
preferred form of the invention, return air outlet 33 is constituted by a
generally circular insert provided with various spaced holes (not shown).
In a similar manner, upper air delivery section 30 includes a discharge or
delivery inlet 35 formed in top wall 9. Although only partially shown in
Figure 1, inlet 35 is also preferably constituted by a generally circular-
io shaped insert which is attached to the remainder of upper air delivery
section 30 and which is provided with a plurality of holes 37.
As will become more fully evident below, the particular
construction of cooking appliance I can significantly vary in accordance
with the present invention. However, as shown, cooking appliance 1
includes an air channel assembly, such as that discussed above with
reference to assembly 26, as well as a blower assembly, such as that
generally indicated at 40, for use in generating a circulating flow of air
through oven cavity 5. Although not considered a part of the present
invention, a preferred construction for oven cavity 5 and air channel
zo assembly 26 can be found in U.S. Patent No. 6,373,037 entitled "OVEN
CAVITY CONSTRUCTION".
In the preferred embodiment shown, cooking appliance I
constitutes an electric appliance and, more specifically, a combination
convection, microwave and radiant cooking device. As shown in this
figure, cooking appliance 1 is provided with an annular filter basket 46,
having a multitude of circumferentially spaced holes 47, which is
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positioned within lower air return section 29 and through which the air
flowing from cavity 5 through return air outlet 33 is directed. Arranged
below filter basket 46 is a microwave generator unit 48 incorporating a
magnetron (not specifically shown).
Encircling at least a portion of filter basket 46 is a first electric
heating element 52. Heating unit 52 is shown as constituted by a
sheathed electric resistance heating element having upper and lower
interconnected legs 53 and 54. First electric heating unit 52 is preferably
provided to heat return air flowing from oven cavity 5, through outlet 33
io and filter basket 56 prior to the air reaching a catalyst indicated at 57.
'The present invention is particularly directed to the structure and
operation of catalyst 57 as will be detailed more fully below. However,
in general, catalyst 57 functions to eliminate smoke and the like from the
air stream. As shown, catalyst 57 extends partially within a rotatable
blower element 60 which forms part of blower assembly 40. Although
blower element 60 can take various forms while performing the desired
air flow generating function, blower element 60 preferably constitutes a
centrifugal unit arranged at the juncture of lower air return section 29 and
rear air transfer section 31. In general, blower element 60 is secured to a
shaft member 62 that is rotatably mounted through a bearing assembly
64. Shaft member 62 also has attached thereto, for non.-relative rotation,
a sheave 66 which is adapted to receive a belt (not shovrn) for use in
rotating blower element 60 through shaft member 62 in combination with
an electric motor (also not shown). As illustrated, sheave 66 is preferably
arranged within a housing extension 68 which projects from rear air
transfer section 31.
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Preferably mounted in upper air delivery section 30 adjacent rear
transfer section 31 is a second electric heating element arrangement 70
that is preferably constituted by a bank of heating coils. Although not
pertinent to the present invention, second heating unit 70 can be defined
by a single electric coil that runs back and forth across upper air delivery
section 30 or multiple, separately controllable coil elements. In any
event, second heating unit 70 functions to further heat the air flowing
through channel assembly 26 prior to the air reaching discharge inlet 35.
Also shown in this figure is a third electric heating unit 72 which,
io in a manner similar to first electric heating unit 52, is preferably
constituted by a sheathed, resistance-type heating element. Third electric
heating unit 72 preferably extends adjacent top wall 9 and constitutes an
additional heat source for cavity 5 of cooking appliance 1. The particular
manner in which first, second and third electric heating units 52, 70 and
72 are utilized during operation of cooking appliance 1 for a cooking
mode of operation is not considered to constitute part of the present
invention. Instead, these details can be found in U.S. Patent No.
6,291,808 entitled "HEATING SYSTEM FOR A COOKING
APPLIANCE': .
As represented in Figure 4, each of blower assembly 40,
microwave generator 48 and first, second and third electric heating units
52, 70 and 72 are linked to an appliance controller or CPU 73. Controller
73 also receives signals from operator input controls 74, as well as from a
temperature sensor 75 which is preferably arranged in upper air delivery
section 30, between heating unit 70 and delivery inlet 35. The present
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invention is particularly directed to the manner in which cooking
appliance 1 is operated through a cleaning mode.
When an operator selects a cleaning mode through input controls
74, heating units 52 and 70 are initially activated, along with blower
assembly 40, for preheating of oven cavity 5. At the same time, during
this preheat phase, heating unit 72 is maintained deactivated. This
operational stage enables the oven cavity 5 to be heated in a substantially
exponential manner as represented by the portion A of the
tirne/temperature curve shown in Figure 5. This arrangement is designed
io to provide for a relatively short preheat time period, while assuring that
early stage self-clean byproducts will flow to the catalyst for effective
elimination. That is, it is this initial time period that substantial amounts
of smoke, odors and other byproducts will be developed due to the
burning off of grease and the like remaaining in the oven cavity 5. By
maintaining heating unit 72 deactivated, it has been found that an
optimum preheat rate is established, with the temperature rise being based
on the flow of heated air directed through the oven cavity 5.
When the temperature in oven cavity 5 reaches point B on the
curve shown in Figure 5 as conveyed through temperature sensor 75,
2o blower assembly 40 and heating unit 70 are deactivated, while heating
unit 52 remains activated and heating unit 72 in oven cavity 5 is also
activated, through controller 73. With blower element 40 deactivated, the
air flowing through air channel assembly 26 is based on natural
convection only. This switchover phase results in a short, generally
steady state time period wherein the temperature within oven cavity 5
remains substantially constant. However, electric heating unit 72 is
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preferably a high wattage element which rapidly heats such that the
temperature within oven cavity again rises exporientially, as represented
by portion C in Figure 5. In fact, as clearly shovm, portion C has an even
higher associated slope than portion A. With this overall control
arrangement, the preheat phase is performed at a rate which assures that
the developed byproducts are effectively eliminated and vented through
catalyst 57, while the subsequent rapid heating o:f oven. cavity 5 with
heating unit 72 enables the time needed to perform the overall self-
cleaning operation to be minimized.
In accordance a preferred cleaning operation of cooking appliance
l, a maximum cleaning algorithm which is configured to provide
maximum energy to clean oven cavity 5 plus maintain specified surface
temperatures. The algorithm employs timed periods of very high thermal
and forced air energy to maximize BTU delivery onto the surfaces of
is oven cavity 5. With this arrangement, consumption of the cooking
deposits can be maximized. In general, the process is based on the
chemical and thermodynamic principles that reactions increase in rate as
the temperature increases.
More specifically, the self-clean algorithm starts with a catalyst
2o heating sequence designed to eliminate smoking of various components
during thermal start-up of the self-clean operation. This start-up phase
directly corresponds to that described above. After the start-up phase, a
moderately high presoak operation is performed to essentially burn off
various light molecular weight hydrocarbons and the like. In accordance
25 with the most preferred form of the invention, the presoak operation
establishes a temperature in the order of 750 F.
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In essence, the start-up and presoak phases are precursors to the
main cleaning stages. In a first main stage, maximum thermal heat is
applied with maximum air flow to drive the surface temperatures within
oven cavity 5 to high levels. In accordance with the most preferred form
of the invention, this stage operates at approximately 990 F and a 4,800
rpm blower speed for 10 to 15 minutes. This established temperature
provides the energy necessary to convert the majority of the cooking
byproducts into water and carbon dioxide.
Following this first main stage, a timed cool down sequence is
io employed. In this cool down stage, the thermal input is reduced,
preferably to approximately 930 F which represents a desired minimum
cleaning temperature, and the air flow is reduced. Most preferably, the
air flow is reduced in half by decreasing the speed of blower assembly 40
to approximately 2,400 rpm. With this arrangement, thermal heating/time
relationships are used to minimize the effects of the first main cleaning
stage. This cool down stage is preferably maintained for in the order of
10 to 15 minutes.
The cool down stage is followed by an intermediate high
temperature and blower timed stage. Most preferably, the established
temperature for this stage is approximately 960 F, with a blower speed of
3,600 rpm. This stage is preferably preset for 10 minutes and is followed
by a repeat of the cool down or cooling stage as set forth above.
Thereafter, this intermediate high temperature and blower timed stage and
following cool down stage combination is continuously repeated until the
total self-clean time set by the user is completed.
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Even if a dedicated, self-cleaning cycle is employed, it is still
desirable to cleanse an air flow which recirculates during the operation of
convection cooking appliance 1. To this end, in accordance with the
present invention, cooking appliance 1 incorporates a trap and filter unit
85, as shown in each of Figures 6 and 7, for trapping and filtering liquid
andlor solid cooking byproducts from a recirculating air flow. In the
most preferred form of the invention, trap and filter unit 85 is used in
place of filter basket 46 and constituted by a concentric ring-type baffle
filter element including inner and outer, concentric, generally cylindrical
io air baffles 88 and 89. Inner air baffle 88 is composed of a plurality of
annularly spaced inner deflectors 95 which are spaced by inner, air inlet
gaps 98. Each inner deflector 95 includes a radially innermost base
portion 100 and angled first and second end portliions 102 and 103. Each
of first and second end portions 102 and 103 preferably projects radially
outward at an angle in the range of 30-60 , most preferably about 45 ,
from base portion 100.
In a similar manner, outer air baffle 89 is composed of a plurality
of annularly spaced outer deflectors 110 which are spaced by outer, air
exhaust gaps 112. Each outer deflector 110 includes a radially outermost
2o base portion 120 and angled first and second end portions 122 and 123.
Each of first and second end portions 122 and 123 preferably projects
radially inward at an angle in the range of 30-60 , most preferably about
45 , from base portion 120. Inner and outer baffles 88 and 89 are
interconnected by upper and lower rings 125 and 126. As shown, each
outer deflector 110 spans and annularly overlaps the inlet gap 98 between
respective, adjacent inner deflectors 95. In fact, each base portion 120
preferably has a length which is greater than each inlet gap 98.
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Therefore, first and second end portions 122 and 123 are located within
the confines of respective, juxtapose inner deflectors 95. At the same
time, each of first and second end portions 122 and 123 is both annularly
and radially spaced from a respective first and second end portion 102,
103 so as to define internal openings or gaps 128.
With this construction, as recirculating air passes outwardly
through the inlet gap 98 between two inner baffles 88, the air is
accelerated by a nozzle-type effect prior to impacting a center zone of
base portion 120. This arrangement causes part of liquid and/or solid
io cooking byproducts, such as grease, fats, and moisture, of the air flow to
be deposited or trapped on the outer baffles 89. The air flow is then
redirected back towards the inner baffles 88 where, once again, the air
impacts a respective base portion 100 in order to separate part of the
byproducts from the remainder of the air flow. Therefore, the redirection
rs of the air flow causes a rapidly reduced air velocity between baffles 88
and 89 which occurs faster than heavy cooking byproducts, including
liquid fats and moisture, can respond. Instead, these heavy byproducts
get deposited at the base portions 100 and 120 as discussed above.
Finally, the air is led to a respective outlet gap 112 where the
2o recirculating air exits trap and filter unit 85. In this manner, the air
takes
a generally serpentine or sinusoidal path through trap and filter unit 85.
With this arrangement, the resulting separation of the liquid phase
byproducts functions to deposit some of the liquid/solid byproducts onto
the inside surfaces (not labeled) of outer baffles 89, as well as on the
25 outer surfaces (not labeled) of inner baffles 88. Inlet and outlet or
exhaust gaps 98 and 112 are symmetrically located so as to generate a
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high uniform air flow pattem around the overall baffle arrangement. The
overall air flow increases the effectiveness of the recirculation of air
through air channel assembly 26, as well as oven cavity 5. Of course, any
collected byproducts will be subjected to the high heat levels discussed
above during self-clean cycles. If desired, trap and filter unit 85 can be
removed for cleaning or replacing.
Although described with respect to a preferred embodiment of
the invention, it should be readily understood that various changes and/or
modifications can be made to the invention without departing from the
io spirit thereof, For instance, although trap and filter unit 85 is stated to
replace filter basket 46, it is possible to utilize these components in
combination, with trap and filter unit 85 being anranged either radially
inwardly or outwardly of filter basket 46. In any event, the invention is
only intended to be limited by the scope of the following claims.
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