Note: Descriptions are shown in the official language in which they were submitted.
1138S33
Background of the Invention
In microwave ovens, such as shown in Canadian Patent 1,125,378,
January 8, 1982, B. J. Weiss, microwave heating is supplemented by auxilliary
means such as an electric heating element positioned in the oven. However,
if gas burners are positioned in the oven in place of the electric resistance
heaters, it has been discovered that the microwave heating efficiency is very
substantially reduced since the microwave energy is absorbed by the gas
flame.
In addition, for cooking pattern uniformity it is desirable that
there be no auxilliary heating units in the cavity which can alter the pat-
tern of the modes in the cavity to reduce microwave heating pattern un;form-
ity.
If auxilliary gas heating means is positioned in a separate region
from the oven and vapor heated thereby is then circulated through the oven,
microwave energy may be coupled from the oven into the separate region and
may be absorbed by the gas flame. Microwave energy absorbed by the gas flame
in the separate region thereby rèduces the overall microwave oven efficiency.
1138S33
Summary of the Invention
This invention provides for a combined convection and micro-
wave oven in which the microwave energy is couplèd into a conduc-
tive enclosure while vapor is blown into the oven enclosure through
means for preventing escape of microwave energy from the enclosure.
More particularly, the vapor may be the products of combustion from
a gas fired burner. Such products of combustion are circulated
through the oven by a circulating blower through oven inlet and
outlet regions. In accordance with this invention, both the
inlet and outlet regions are formed of a plurality of apertures
whose diameters are less than a half wavelength of the free
space wavelength of the microwave energy and preferabIy less
than a tenth of a wavelength of said microwave energy.
Preferably, microwave energy is fed into the enclosure from
a different wall than that through which heated vapor is blown into
the oven. More particularly in accordance with this invention a
microwave oven has the microwave energy fed into the oven enclosure
through the bottom wall. Preferably, the microwave energy is
radiated through a rotating radiator in the enclosure. The radiato
may provide a plurality of separate directive radiation patterns
in the enclosure which are moved by rotation of said radiator and
which are directed toward a body to be heated. The rotating radiatt
is preferably covered with a transparent ceramic cover and the body
to be heated positioned on a support rack above the radiator. The
vapor heated by the products of combustion i5 directed into the ove
by the ~lower through a region either in the upp`er rear wall in
one embodiment of the invention or through a region in the top
wall in another embodiment of the invention and vapor is withdrawn
from the oven through a region in the lower portion of the enclosur~
1138533
In accordance with the present invention, there is provided in
combination: a conductive enclosure; means for supplying said enclosure with
microwave energy, and means for blowing a heated vapor into said enclosure
through means which prevents the escape of microwave energy from said enclosure.
In accordance with the present invention, there is further provided
a microwave oven comprising: a conductive enclosure having an access opening
and a closure member, a seal for said closure member comprising a microwave
choke section and a vapor seal section; means for directing separate patterns
of microwave energy into said enclosure through a rotating radiator; and means
for blowing a vapor heated by the products of combustion from a burner into
said oven through means which prevents the escape of microwave energy from
said enclosure.
In accordance with the present invention, there is further provided
an oven system comprising: a conductive enclosure having an access opening
and a closure member; means for supplying said enclosure with microwave energy
and a seal for said closure member; and a burner and means for recirculating
heated vapor comprising the products of combustion from said burner through
said oven through means for preventing escape of said microwave energy into a
region in which said vapor is heated while exhausting from said system a por-
tion of the vapor passing through said circulating means, said recirculating
means including means for blowing heated vapor into said enclosure through
said means for preventing escape of said microwave energy.
In accordance with the present invention, there is further provided
a microwave oven comprising: a conductive enclosure having an access opening
and a closure member, a seal for said closure member comprising a microwave
choke section and a vapor seal section; means for supplying said enclosure with
microwave energy; means for recirculating heated vapor through said oven and a
vapor heating region including means for blowing said heated vapor into said
oven through means for preventing microwave energy in said enclosure from
entering said vapor heating region; said oven and said vapor heating region
~eing separated by said means for preventing the escape of microwave energy
from said oven into said recirculating means.
-~ - 2a -
113~S33
Brief Description of the Drawings
Other and further embodiments of ~he invention will become
apparent as the description thereof progresses, reference being
had to the accompanying drawings wherein:
FIG. 1 illustrates a partially broken away side elevation
view of an oven embodying the invention;
FIG~ 2 illustrates a transverse sectional view of the micro-
wave radiator structure of FIG. 1 taken along line 2-2 of FIG. l;
FIG~ 3 illustrates a transverse sectional view of a blower
portion of the oven of FIG. 1 taken along line 3-3 of FIG. 1.
FIG. 4 illustrates a sectional view of the burner portion of
the oven of FIG. 1 taken along line 3-3 of FIG. 1 and showing
burner details;
FIG. 5 illustrates a vertical sectional view of an oven illus-
trating an alternate embodiment of the invention; and
FIG. 6 is a transverse sectional view of the burner and blower
portion of the oven of FIG. 5 taken along line 6-6 of FIG. 5.
1138533
Description of the Preferred Embodiment
Referring now to FIG.'s l through 4 there is shown a combi-
nation gas convection and microwave stove 10 comprising an oven
cavity 12 closed by a door 14.
Cavity 12 has elongated inlet region 16 through which
heated vapor is directed into the oven 12. In accordance with
this invention inlet region 16 provides means comprising apertures
20 for preventing the escape of microwave energy from cavity 12
and is preferably located in the back wall of the oven adjacent
the top oven wall so that the hottest vapor enters adjacent to
the top of the oven. Two vapor outlet regions 13 in approximately
the middle of the back wall of oven 12 contain apertures 20 for
preventing the escape of microwave energy and through which the
vapor is drawn out of the oven. Apertures 2~ preferably have
maximum dimension which are less than a half wavelength of the
free space wavelength of the microwave energy radiated into
cavity 12, and preferably are holes whose diameters are less
than a tenth of the free space wavelength of the microwave energy.
Microwave energy is fed into oven cavity 12, which is a
conductive enclosure, by a rotating.radiator 22 which may
comprise, for example., a plenum 24 whose upper surface is a plate
26 which contains a plurality of apertures 28 through which
microwave energy is radiated upwardly into enclosure 12. A
central conductor 30 of a coaxial line 32 supports plenum 24 by
being attached to the center of plate 26. Conductor 30 extends
downwardly from the lower end of coaxial line 32, through a
waveguide 34, and through a microwave choke 36 having bearing
assembly 38. An extension of conductor 30 is connected to motor
40 below waveguide 34 which rotates radiator 22 through central
conductor 30.
1138533
Microwave energy from a magnetron 42 is fed through waveguide 34,
coaxial line 32, and plenum 24 to be radiated upwardly from slots 28 into
enclosure 12 as a plurality of separate directive radiation patterns. A
cover 44 of microwave transparent material is supported over radiator 22 on
bumps 46 on the bottom of enclosure 12 to prevent food juices or other ma-
terial from being dropped on radiator 22.
Door 14 contains a microwave choke region surrounded by a high tem-
perature vapor seal so that most of the microwave energy is prevented from
being absorbed from the high temperature vapor seal. However, microwave en-
ergy passing through the choke section is substantially absorbed by the hightemperature vapor seal thereby preventing stray radiation from the oven.
In accordance with this invention circulation of vapor through en-
closure 12 is produced by centrifugal blowers 48 which draw vapor out of cav-
ity 12 through apertures 20 in regions 18 and blows it into plenums 50 sur-
rounding blowers 48 supplying apertures 20. The upper ends of plenums 50
have an opening to a vent 52 through which a small portion of the output of
blowers 48 is blown and is mixed with the air blown by a second set of blow-
ers 54 driven by motors 56. Blowers 54 draw cool air in from the back of the
oven 12 to cool the motors 56 and to mix with vapor from vent 52. The cooled
vent vapor then exits through a screened aperture 58 in the top of the oven.
1138533
A burner system 60 is positioned at the bottom of oven 10
in a compartment adjacent the microwave generator and comprises a
horizontal apertured tube 62 extending substantially the entire
width of the oven 10. Tube 62 is fed a gas fuel and primary air
mixture at one end by a vertical tubular member 64 whose lower
end is supplied with air and with gas through a solenoid operated
gas valve 66 and a pressure regulator 68. An electrically energize~
ignitor 70 ignites the mixture coming from the apertures in tube
62 in the presence of secondary air to produce flue gas products
in burner plenum 72. The flue gas products are drawn into the
region of the stove between blowers 48 and oven outlet regions 18
where the combustion products are mixed with vapor drawn from enclo
sure 12. The burner i5 preferably run with excess air so that the
temperature of the products of combustion is below 3,000 F, for
example, between 1,200 F and 2,000 F, so that combustion is sub-
tantially complete. This heated oxidizing atmosphere contacting
vapor drawn from the enclosure 12 substantially immediately oxidize
organic components of food vapors so that when they are blown back
into the enclosure through region 1~ or up the vent 52 into
the room they are substantially clean. The slight pressure
differential between the inlet and outlet of the blowers 48 causes
a slight negative pressure in combustion plenum 72 which accurately
regulates the excess air in the gas-air mixture drawn into the
combustion plenum 72.
A rack 74 made, for example, of steel rods is supported
on bumps formed in the side walls of the enclosure 12 so that
the position of ~he rack may be changed in accordance with well-
known oven practice. Positioned below rack 74 is rotatable
microwave energy radiator 22 which directs microwave energy up
through the apertures in rack 74 and through microwave transparent
1138S33
plate 76 positioned in the middle of rack 74 and microwave trans-
parent dish 78 to a food body 80 such as a roast of meat.
A plurality of top gas burners 82 are provided which
operate as convention gas surface burners in accordance with
well-known practice. Thermal insulation 84 is provided around
the oven 12 and around the burner plenum 72 to reduce loss of
energy from the oven. The entire oven has a skin 86 of, for
example, sheet metal surrounding the oven 12, the blower, burner,
and microwave supply regions.
During operation, the temperature of the enclosure vapor is
sensed by a temperature bulb 88 mounted, for example, in the enclo
sure 12 on a bracket below the vapor inlet region 16. The posi-
tioning of temperature sensor 88 is preferably chosen so that it
is not directly in the entering hot vapor stream from region 16
but rather measures the temperature of the vapor eddying around
in the enclosure 12. Its location may be selected so that the
oven heating cycles have reasonable time periods for burner on
and burner of and the temperature range fluctuates large amounts.
When the oven burner blown into the oven at velocities of 500 to
1,000 feet per minute is energized, heat is delivered in the
form of hot vapor along the top surface of enclosure 12 and a
substantially uniform convection heating pattern occurs.
The power level and time of the microwave energy may be
controlled, for example, by a control panel 90 containing a
manually set timer 92 and a manually set power level 94. In addit
a light 96 may be positioned outside enclosure 12 illuminating
enclosure 12 through a light transparent high temperture ceramic
plate and microwave shielding screen 98.
113~s33
Description of an Alternate Embodiment
Referring now to FIG.'s 5 and 6 there is snown a combination
gas convection and microwave stove 100 illustrating an alternate
embodiment of the invention. Stove 100 comprises an oven cavity
102 of conductive me'al closed by a door 104.
In accordance with the invention, an apertured convection vapo
inlet region 106 is preferably located in the top wall of oven
cavity 102 so that vapor is directed downwardly from the top of
the oven. Oven vapor outlet region 108 is an apertured region in
the bottom of the back wall of oven cavity 102. A rack 110 is
provided made, for example, of steel rods supported on bumps 112
formed in the side walls of the oven.
Positioned below rack 110 is a rotatable microwave energy
radiator 114 which directs a plurality of separate microwave
energy patterns up through the apertures in rack 110, through a
microwave transparent support plate 116 positioned in the middle
of rack 110 and through a microwave transparent dish 118 to a
food body 120. Apertures in regions 106 and 108 have maximum
dimensions substantially less than a half ~7avelength of the free
space wavelength of said microwave energy which may have a
fre~uency, for example, of 2.45 KMH and preferably said apertures
are less than a tenth of the free space wavelength of the microwave
energy. Door 104 has a microwave choke and vapor seal like that
disclosed in the preferred embodiment, and hence microwave energy
is prevented from escaping from oven 102.
Radiator 114 may comprise, for example, a plenum whose
upper surface contains a plurality of apertures through which
microwave energy is radiated upwardly into oven 102. A central
conductor of a coaxial line supports radiator 114 by beinq
attached to the center of the upper plate and by extending down-
113~S33
wardly through a waveguide to be supported by a choke and bearing
assembly, An extension of the central conductor is rotated
by a motor below the waveguide while microwave energy from a
magnetron is radiated through the waveguide, the coaxial line and
the radiator 114 into the oven 102. A cover 122 of microwave
transparent material is supported over radiator 114 to prevent
food juices or other material from being dropped on the radiator.
Such a radiator with its feed and drive assembly is similar to
that described in the preferred émbodiment.
In accordance with this invention, recirculation of vapor
within the oven 102 is achieved by a motor 124 driving a centri-
fugal blower 126 through a belt 128. Blower 126 sucks vapor from
the oven 102 through region 108 and blows the vapor out through
ducts 130 into the oven 102 through the apertures in top wall vapor
inlet region 106. A small portion of the output of blower 126 is
blown outwardly through outlet duct 132 to an exhaust duct where
it is mixed with cool the air drawn in through vents 134,in the
back of the stove 100 to cool the air in duct i32 which then
exits through a screened aperture 136 in the top back of the stove.
A burner system 138, positioned at the bottom of stove 100,
comprises a horizontal apertured tube 140 extending substantially
the entire width of the oven and fed at one end by a vertical
tubular member 142 whose lower end is supplied with air from
vent 144 and with gas from a gas jet 146 controlled by a gas
control valve 148 supplied with gas through a pressure regulator
150. An electrically energized ignitor 152 ignites the air-gas
mixture emanating from the apertures in tube 14~ causing a flame
in burner plenum 154 to produce flue gas products which are drawn
through the blower 126 along with vapor drawn from the oven throug~
3~ vapor outlet apertured region 108 and the hea~ed output of blower
1138533
126 is blown into the oven.
An example of power levels for effective food body cooking
or browning may be microwave energy applied at a rate of 500-800
watts or around 2,000-3,000 BTU's per hour and a gas burner sup-
plying at a rate of 5,000-15,000 BT~'s per hour. Such power
levels will cook and/or brown a cake in a few minutes. Since
microwave energy is prevented from entering the burner plenum
154, the burner can be operated while microwave energy is being
supplied to the oven.
This completes the description of the embodiments of the
invention illustrated herein. However, numerous modifications
thereof will be apparent to one having ordinary skill in the
art without departing from the spirit and scope of the invention.
For example, the oven may be fed through apertures located in
regions other than the top or back walls, the circulating blower
may be inside the oven, and other systems for supplying microwave
energy to the oven may be used. In addition, other types of
burners such as ribbon or power burners may be used. Accordingly,
it is intended that this invention be not limited to the embodi-
ment of the invention described herein except as defined by the
appended claims.
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