Note: Descriptions are shown in the official language in which they were submitted.
WO 00/64219 CA 02371147 2001-10-18 PCT/US00/10624
MULTI-SHELVED CONVECTION MICROWAVE OVEN
FIELD OF THE INVENTION
The present invention relates to a multi-shelved oven having multiple heating
means,
including convection, microwave and radiant food heating means.
BACKGROUND OF THE INVENTION
The oven disclosed herein relates primarily to ovens suitable for use in the
commercial food service industry, such as fast food restaurants, and other
food service
application where there is great variety in the food products prepared, the
need for speedy
thermalization of food and space constraints. While various oven designs are
known and
available for commercial food service applications, there still exists a need
for an efficient
and effective oven that allows for simultaneous cooking of different food
products requiring
different heat treatments. Single cavity ovens have been designed heretofore
that include
microwave and convection heat transfer cooking means. While such ovens meet
the needs of
certain commercial food service applications by providing rapid thermalization
and cooking,
the inability to cook different foods simultaneously with different heating
conditions and
cook cycles does not provide needed flexibility. Furthermore, known
combination ovens
often require mechanical means to stir the microwave or move the food product
in order to
achieve even microwave heat transfer to the food product.
The present invention provides an oven that meets a need in the food service
industry
for an oven provides rapid heating/cooking and the ability to cook multiple
food products
simultaneously under different conditions and cook cycles. Moreover, the ovens
of the
present invention provide a microwave heating means that does not require
mechanical
stirring of microwaves or movement of food products to achieve substantially
uniform
distribution of microwave energy into the cooking cavities of the oven.
SUMMARY OF THE INVENTION
The present invention provides a novel thermal food treatment system that
combines
multiple means of heating in a single system.
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In one aspect of the invention an oven is provided that includes a cooking
chamber, a
blower and a shelf disposed within the cooking chamber. The shelf has a unique
design in
that it has an inlet opening and cavity in fluid communication with the blower
and at least one
opening in fluid communication with the cooking chamber through which
temperature
controlled air can flow into the cooking chamber to cook food by convection
heating. In
another aspect of the invention, the oven further comprises a microwave
heating source for
heating food products within said cooking chamber, thereby providing multiple
heating
methods (convection and microwave).
In another aspect of the invention, the microwave heating means includes a
microwave source and wave guide through which microwaves travel. The wave
guide
includes a plurality of openings through which microwaves can pass into said
cooking
chamber. In a preferred aspect of the invention, the openings in the wave
guide are
positioned to correspond with the predetermined minima or maxima for the
microwave
wavelength propagating within the wave guide. That is the spacing of the wave
guide
openings occurs at multiples of predetermined minima and/or maxima for the
microwaves
within the guide generated by the microwave source, most commonly a magnetron.
In another aspect of the invention, a heating element can be mounted within
the
cooking chamber, providing an additional heating means. In a preferred
embodiment, a
movable, reflective stirrer is positioned above the heating element to reflect
heat from the
heating element toward a food product.
In yet another aspect of the invention the shelf includes a plurality of
louvers
protruding from the top surface of the shelf for supporting a food receptacle.
thereby allowing
air to flow freely beneath the food product or receptacle. The louvers have
openings that
direct temperature controlled air in a direction substantially parallel to the
top of the shelf.
In a preferred embodiment of the invention, the cooking chamber comprises a
first
cooking cavity and a second cooking cavity and includes a first shelf and a
second shelf. The
first shelf has an inlet opening and cavity in fluid communication with a
blower and the
second shelf has an inlet opening and cavity in fluid communication with a
blower. Further,
both the first and second shelves have at least one opening in fluid
communication with the
first cooking cavity and second shelf having at least one opening in fluid
communication with
said second cooking cavity, respectively. In a preferred aspect of this
embodiment,
microwave heating is provided in the first and second cavities through wave
guides,
preferably a pair of wave guides associated with each cavity. The preferred
wave guide
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arrangement again provides a wave guide having a predetermined minima and
maxima and
openings in the wave guide positioned to substantially correspond the minima
or maxima,
thereby providing efficient and even distribution of microwave energy into the
cooking
cavities along the length of the wave guide.
In yet another aspect of the invention, the blower which supplies temperature
controlled air to the cooking chamber has an exhaust opening in its housing
through which a
portion of the temperature controlled air is exhausted from the system. In
this arrangement,
the oven further includes an ambient air intake opening in fluid communication
with the
blower whereby the blower draws airs through the intake opening to replace the
exhausted
air.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is front view of the oven (three cavity configuration);
FIG. 2 is a front view of the interior cooking chamber of the oven (three
cavity
configuration);
FIG. 3 is a front perspective view of the interior cooking chamber and
portions of the
convection heat transfer and microwave heat transfer systems of the oven
(three cavity
configuration);
FIG. 4 is a front perspective view of the interior cooking chamber and
portions of the
convection heat transfer and microwave heat transfer systems of the oven
(three cavity
configuration);
FIG. 5 is a front perspective view of the interior cooking chamber and
portions of the
convection heat transfer system of the oven (three cavity configuration),
including the food
product shelf;
FIG. 6 is a view of the interior cooking chamber depicting the electric
heating element
within the cooking chamber;
FIG. 7 is a left side view of the oven with the left panel of the exterior
cabinet
removed to show portions of the convection heating system of the oven (three
cavity
configuration);
FIG. 8 is a perspective view of the food shelf which serves as a conduit
through which
temperature controlled air into the cooking chamber of the oven;
FIG. 9A is a perspective view of an alternative embodiment of the shelf;
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FIG. 9B is a cross section view of the alternative embodiment of the shelf
depicted in
FIG. 9A;
FIG. 10 is a perspective view of a product support rack;
FIG. 11 is a perspective view of an embodiment of an air delivery duct for the
convection heat transfer system of the oven;
FIG. 12 is a perspective view of a preferred alternative embodiment of an air
delivery
duct for the convection heat transfer system of the oven;
FIG. 13A is a front view of a filter assembly for filtering air exiting the
cooking
chamber;
FIG. 13B is side view of the filter assembly of FIG. 13A;
FIG. 13C is schematic depiction of the accordion fold 'filter plate of the
filter
assembly of FIG. 13A;
FIG. 14 is a side view of a bracket for supporting the filter assembly of FIG.
13A on
the side wall of the interior cooking chamber of the oven;
FIG. 15 is schematic depiction of a control system for the oven of the present
invention (three cavity configuration);
FIG. 16 is a perspective view a two cavity configuration of the oven;
FIG. 17 is a partial perspective view of the interior cooking chamber and
microwave
heating system for the oven (two cavity configuration);
FIG. 18 is a perspective view of the microwave heating system for the oven
(two
cavity configuration);
FIG. 19 is a partial perspective view of the cooking chamber and oven
configuration
with partial exhaust of temperature controlled air stream;
FIG. 20 is a partial perspective view of the ambient air intake and partition
chamber
aspects of a preferred embodiment of the two cavity configuration of the oven;
and
FIG. 21 is a perspective view of the reflective stirrer of the present
invention.
WO 00/64219 CA 02371147 2001-10-18 PCT/US00/10624
DETAILED DESCRIPTION OF THE INVENTION
The description of the invention provided below is made with reference to the
drawings attached hereto. The drawings have been consecutively numbered as
FIGS. 1-23.
In FIG. 1, there is shown one embodiment of the oven 10 of the present
invention.
5 Oven 10 includes an exterior cabinet 12 defined by exterior side walls,
exterior top and
bottom walls and an exterior rear wall. Preferably said walls are constructed
of a stainless
steel material. Hingedly secured to the front of the oven is door 14 which
permits food
products to be placed in and out of the interior of the oven. A handle 16 with
latching means
is secured to door 14 to allow the door to be secured in a closed position
during cooking. The
door 14 is designed by known conventional means for preventing microwave
leakage from
the chamber 18 while the door is closed. Referring to FIGS. 2-4, 16-17 and 19,
chamber 18
is defined by interior side walls 19 and 21, back wall 23, top wall 25 and
bottom wall 27
(collectively the oven chamber interior walls). Preferably said oven chamber
interior walls
are constructed of a stainless steel material. As depicted in FIGS. 1 and 5
(three cavity oven)
and FIGS. 16-17 and 19 (two cavity oven), chamber 18 further comprises a
plurality of
cooking cavities 18a.
Referring to the three-cavity oven of FIGS. 1-5, disposed within the chamber
18 of
the oven are upper shelf 20, intermediate shelf 22 and lower shelf 24,
preferably constructed
of a stainless steel material. Shelves 20 and 22 are movably mounted within
the oven
chamber 18 and are positioned atop brackets to hold the shelves in position.
Bottom shelf 24
can rest on the bottom of the oven chamber or, if desired, can rest on a
bracket as well. Said
brackets are generally shown by reference numeral 30 and are secured to the
interior side
walls of the oven cavity on opposite sides of the cavity walls. By providing
removable
shelves they can be more easily cleaned.
Referring to FIGS. 2, 5 and 8, the shelves 20, 22 and 24 shall be described in
greater
detail. Each shelf is designed to not only support a food product but is also
designed as a
conduit through which temperature-controlled (e.g. heated) gas (preferably
air) passes and
provides convection heating to food products within each oven cavity 18a. As
shown in the
above referenced figures, each shelf has a top portion 31, a bottom portion
32, side portions
34 and 36, rear portion 38 and front portion 40, defining shelf cavity 41.
Front portion 40 is
disposed within the chamber of the oven adjacent interior oven chamber side
wall 19.
Further, the front wall 40 of each shelf has openings 42 and 44 through which
temperature
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controlled air can pass into the shelf cavity 41. After the temperature
controlled air is
disposed into the shelf cavity, the air then passes through openings 52 in
louvers 50 which
project from the top portion 31 of each shelf. The louvers 50 are positioned
at spaced areas
and permit air to exit via openings in the louvers in a direction
substantially parallel to the top
portion of the shelf, at least as it initially exits a louver 50. The openings
on louvers 50 are
best seen in FIGS. 5 and 8 and are represented by reference numeral 52. When
temperature
controlled gases exit openings 52 into the oven cavity, food products disposed
within the
oven cavity are heated via connective heat transfer. One advantage of the
louvered openings
projecting from the shelf is that when a pan or other food receptacle is
placed on the shelf,
heated air travels freely beneath the pan and between the louvers providing
very effective
connective heat transfer.
In an alternative embodiment of the shelf design, the louvers are inverted and
do not
project from the top of the shelf, but instead project into the shelf cavity.
In this
configuration the louvers act like scoops within the shelf cavity. While this
configuration
does not allow air to flow freely beneath a food tray disposed over the
openings, a wire rack
900 (FIG. 10) may be placed on the shelf to lift the food receptacle (or food)
from the top
surface of the shelf, thereby providing satisfactory convection heat transfer.
In yet another alternative embodiment of the shelf shown in FIGS. 9A and 9B,
the top
surface of the shelf 31a has vertically extending protrusions SOa, recessed
areas or surfaces
46 and openings 48 disposed in the recesses areas. The arrows shown in FIG. 9B
generally
depict the direction of air travel into the shelf cavity 41 a and through
openings 48. Like the
louver configuration (noninverted) described above, one advantage of the shelf
design
depicted in FIGS. 9A and 9B is that when a pan or other food receptacle is
placed on the
shelf, heated air travels freely beneath the pan and between the louvers
providing very
effective connective heat transfer.
Temperature controlled air is delivered into each shelf by blower assemblies
60 (FIG.
4). As shown in FIG. 4, each blower assembly 60 comprises a blower housing 64,
a blower
wheel 66 and a shaft 68 operably connected to a motor which rotates each
blower wheel. In
the preferred embodiment of the invention, each blower wheel is turned by a
single axle 68
which is operably connected to a motor means. A 1/10 horsepower motor has been
found to
be adequate. A blower wheel of the forward inclined type has also been found
to be
adequate. Air is drawn into the blower housing and is disposed into tapered
ducts 62 which,
as shown, are disposed between the cabinet side wall and the oven chamber side
wall 19.
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In FIG. 4, specific reference numerals are provided only with respect to the
tapered
duct which is in fluid communication with the lower shelf. However, the
features of the
lower blower and duct assemblies are essentially identical to the middle and
upper blower
and duct assemblies and therefore descriptions for the latter are not
repeated. As shown in
FIG. 4, each tapered duct has a proximal end 162 and a distal end 168. An
inlet opening is
provided at proximal end where temperature controlled gas from blower 60
enters the duct
(i.e., inlet opening 164 is in fluid communication with the blower assembly
associated with
the duct). Further, each tapered duct 62 has an elongated opening 70 at the
bottom inward
facing wall and also has a plurality of orifices 72. As shown in this
embodiment, the orifices
72 and elongated opening 70 are formed in the side wall 19 of the oven chamber
18 (FIG. 12)
with the remainder of the duct 62 being formed by two tapered side walls and a
top wall.
Temperature controlled gases entering each duct 62 exit through openings 72
into the
respective oven cavities to heat the food product contained within said
cavities. Further, as
shown, a portion of the air entering each duct 62 also exits through opening
70 and flows
respectively into the shelf cavities 18a of shelves 20, 22 and 24. In other
words, each tapered
duct feeds a separate shelf (20, 22, 24) and also feeds temperature controlled
air through
orifices 72 above each shelf (20, 22, 24). Accordingly, as described above,
convective heat
transfer is achieved by the present oven design through orifices located in
the oven cavity
side wall above each shelf and also through the shelves themselves through the
louvers
disposed on the top portion of each shelf. In an alternative arrangement, the
oven would not
include orifices 72 and therefore all heated gas would flow from ducts 62 into
the shelf
associated with the duct.
Referring to FIGS. 4-7, air return openings 90 are provided in side wall 19
within
each cooking cavity 18a for the return of gas from each cooking cavity to
blowers 60. By
providing air return ports within each cavity 18a, each cavity can function as
an independent
convection oven, thereby allowing cooking of different foods at different
temperatures and on
different cycles. In an alternative embodiment of the invention (FIGS. 13A-C
and 14), the air
return openings 90 may be covered by a filter assembly 300 mounted to side
wall 19 by a
bracket 302 or other known means to prevent food particles, grease and other
materials from
escaping the cooking cavity through the return openings. A preferred filter
assembly 300 is
shown in FIGS. 13A-C and 14 and comprises a filter frame 304 which supports a
perforated
metal plate 306 that is folded in an accordion fashion thereby providing a
greater surface area
over which return air passes before exiting the cooking chamber through the
return openings.
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The temperature of the circulated air or gas can be controlled by any known
means.
One suitable means to heat and control the temperature of the air is by well
known electric
heating rods 80 (i.e., Calrod) (FIG. 7) or "gas burner" (not shown). Heating
rods 80 can be
disposed in any suitable location. In the preferred embodiment, heat rods are
placed as
shown in FIG. 7 in the return air path for the oven. FIG. 7 shows just one
heating rod placed
between the upper and middle ducts 62 in the area between the exterior cabinet
side wall and
the cavity side wall 19. Preferably, a heating element is placed above each
duct 62 through
the openings 82 shown in FIG. 7.
As it relates to the tapered duct design, duct 62 may have a constant taper
from
proximal end 162 to distal end 168 as shown in FIGS. 3-5 and 7 or may have
multiple
degrees of taper as shown by the dashed lines in FIG. 11. As shown in FIG. 11
and denoted
by the cross hatched lines, duct 62 may have a dual taper configuration, which
has been
found to provide even air flow from the orifices along the length of the duct.
More particularly,
in the dual taper configuration of duct 62, said duct has a first horizontal
tapered portion 160
adjacent proximal end 162 and inlet opening 164 (i.e., the opening where air
from the blower
enters the duct) and a second horizontal tapered portion 166 adjacent the
distal end 168. As
shown, the first horizontal tapered portion 160 has a greater angle of taper
than the second
horizontal tapered portion 166 which has a lower slope. Preferably, the first
horizontal tapered
portion 160 extends approximately one-quarter to one-half of the length of the
duct. The degree
of taper in the first and second horizontal tapered portions may vary.
Preferably, the first
horizontal tapered portion tapers down 1 inch for every 1 to 3 inches of
length and the second
horizontal tapered portion tapers 1 inch for every 7 to 16 inches of length.
By providing a dual
taper, it has been found that the air is distributed more evenly along the
length of the duct
from proximal end 162 to distal end 168. In a most preferred embodiment of the
duct 62
shown in FIG. 12, said duct not only includes the dual taper horizontally
along its length
described above, but also includes a vertically tapered portion 170 adjacent
proximal end 162
to further enhance air flow into the duct and even distribution of heated air
into the oven
chamber along the length of the duct.
After the temperature controlled air enters the oven cavity 18a through the
above-
described orifices 72 (optionally) and shelves, air is returned to the blower
housing through
return openings 90 in the oven cavity side wall 19 (i.e, the cavity wall
adjacent each duct 62)
(see FIGS. 2-5). The air returning through openings 90 is heated by heating
element 80
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before entering the blower housing where the heated air is recirculated into
the oven cavity
through the ducts 62.
Optionally, an electric heating element 101 (e.g., Calrod heating elements)
may also
be disposed adjacent the top of the oven cavity so as to provide a means for
broiling food
products disposed on the upper shelf (see FIGS. 1, 2 and 6).
The present oven also provides means for heating food product via microwave
energy. In one embodiment of the invention shown in FIGS. 2 and 3, microwaves
are
disposed into the oven cavity through microwave openings 200 formed in the
side wall 21 of
the oven cavity. Side wall 21 is disposed opposite of oven cavity side wall
19. As shown in
the preferred embodiment, there are three series of openings 200, each being
served by a
separate magnetron assembly 210. The type (i.e. power) of magnetron used is a
matter of
choice and is based on well known selection factors. Use of 2450 MHz
magnetrons were
found suitable in the embodiment shown in FIGS. 16-18.
In the embodiment shown in FIGS. 2 and 3, each magnetron 210 feeds microwaves
into and through a conduit 212 associated with the particular magnetron
assembly and
through the openings 200 and into the oven cavity. The openings 200 and
conduit structure
212 are arranged such that a more uniform dispensing of microwave is provided
within the
oven cavity. A preferred configuration for the openings 200 is shown in the
figures. Other
configurations may also be determined and will vary according to the design
and dimensions
of the cooking cavity. As shown in the figures, each cavity 18a has its own
independent
microwave source (i.e., magnetrons assemblies). Thus, heating of food products
disposed in
different cavities can be provided at different rates and on different cycles
by separately
controlling each magnetron. A schematic representation of the heating controls
for the
embodiment of FIGS. 1-5 is shown in FIG. 15.
In a preferred embodiment of the invention shown in FIGS. 16-20 (two cavity
design), microwave energy from magnetrons 410 is fed into each oven cavity 18a
through a
pair of wave guides 400, 402 (i.e., conduits) disposed above each cavity.
Thus, each cavity
18a has its own independent microwave source. Each wave guide includes a
plurality of
openings 404, preferably slots, through which the microwaves travel into the
cooking cavity.
The slots 404 are spaced to provide substantially even microwave distribution
along the
length of the wave guide. Specifically, the slots are spaced approximately at
multiples of the
calculated minima or maxima for the microwaves generated by the microwave
source, i.e.
magnetron. The minima and maxima for a particular wave guide and magnetron are
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calculated by known means. Microwave maxima and minima for various wave guide
designs
and microwave frequencies also can be readily determined by reference to
tables published
by magnetron suppliers, such as Continental Microwave & Tool Co., Inc,
Hampton, New
Hampshire. As shown, slots 404 are preferably disposed at angles in relation
to the length of
5 wave guides which run generally from the back towards the front of each
cavity. Further, as
shown in FIGS. 17-18, blowers assemblies 500 are preferably provided to cool
the
magnetrons 410 during operation.
In a preferred embodiment of the invention reciprocating reflective stirrers
600 are
disposed above the heating elements at the top of heating chamber 18 for
reflecting heat from
10 the heating element toward the shelf below. Preferably the stirrers are
made of a material that
is also microwave reflective so that enhanced stirring of microwaves is
achieved, thereby
promoting evenness of cooking. A suitable stirrer material is stainless steel.
As shown, the
reflective stirrer 600 is operably connected to bearing 602 which is moved by
link 604, which
in turn is connected to a drive link 606 driven by motor 608.
I S In the embodiment of the invention shown in FIGS. 16-20, it should be
noted that
chamber 18 comprises two cooking cavities 18a and that two doors 700 are used
to seal the
oven. Another feature of an embodiment of the invention provides for the
exhausting of a
portion of the temperature controlled cooking air from the blower housing.
Referring to
FIGS. 17-19, there is shown a exhaust opening 702 in blower housing 64 through
which a
portion of the temperature controlled gas is exhausted from the oven via stack
(or conduit)
704. The exhausting of air from the system induces ambient air to be drawn
through intake
opening 706 disposed at the back of the oven. Ambient air is then drawn into
partition
chamber 708 disposed between the upper and lower cavities 18a. Air from
partition chamber
708 is then drawn through openings 710 to both the upper and lower blower
assemblies 60
which are in fluid communication with the partition chamber. Exhaust air flow
and "make
up" ambient air flow into the system is depicted by the arrows in FIGS. 19 and
20. The
location of the partition chamber between the cooking cavities of the oven is
particularly
advantageous since the heat from the cooking cavities heats the air in the
partition chamber,
thus acting as a heat exchanger to preheat ambient air.
FIGS. 1 and 16 generally depict the control panel (or controller) 450 for the
embodiments described herein. Preferably, the controller 450 has the
capability to control
microwave heating power and cook cycle times, and is capable of being
programmed for
particular food cooking applications. Likewise, it also is preferable that the
controller 450
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control the convective heat transfer aspects of the invention (e.g., blowers
60 and heating
elements) and the reflective stirrers described above.
The present invention is not limited to the examples illustrated above, as it
is
understood that one ordinarily skilled in the art would be able to utilize
substitutes and
equivalents without departing from the present invention.
