Note: Descriptions are shown in the official language in which they were submitted.
06
This invention relates to gas-firea radiant
generators and more particularly to a griddle-topped
food cooking unit having one or more gas fired radiant
heat generators.
Radiant gas generators for cooking
applications have been proposed in various combinaticns
incluuing deep fryers (U.S. patent no. 4,397,29&) and
ovens (U.S. patent no. 4,480,628). The burners or
generators in these combinations are of the tyDe in
which the burner surface is defined by a ceramic tile
structure including a plurality of parallel perforations
in the tile structure an~ wherein a fuel gas mixture is
burned at the upper surfzce of the tile structure to
generate the radiant heat used in the cooking process
Whereas the radiant heat burners of the ceramic tile
type have been generally satisfactory for general
cooking applications, the" su fer rclr ~he diszdvantage
that the generated heat tends tc peak at the geometric
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center of the tile surface so that the overlying heating
surface is relatively hot adjacent the center of the surface
and relatively cool adjacent the perimeter of the surface
with the result that the cooking performance of the heating
surface varies considerably across the expanse of the
heating surface. While this may not represent a problem in
deep fryers and ovens, it may present considerable use
problems in cooking on a griddle, especially in large batch
quantities.
This invention is directed to the provision of a
radiant gas burner assembly in which the temperature of a
cooking surface heated by the burner is substantially
uniform over the surface area thereof.
The radiant gas burner assembly of the invention
comprises a griddle member defining a heat utilization
surface; generator means defining a source of radiant heat
spaced below the griddle member; a housing defining a closed
chamber above the generator and below the heat utilization
surface; and means for drawing heated effluent by convection
to peripheral areas of the chamber beneath the griddle
thereby to supplement or boost griddle temperature at the
edges and corners for temperature uniformity. This
arrangement has the effect of drawing the hot combustion
effluent beneath the peripheral portions of the heat
utilization surface to minimize the temperature gradient
across the heat utilization surface.
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According to a further feature of the invention,
the radiant heat burner surface is constructed so as to have
a non-radiating center area so as to minimize the
concentration of radiant energy in the central region of the
griddle positioned to receive the energy and thereby reduce
the heat gradient across the expanse of the heat utilization
surface.
According to a further feature of the invention,
the annular burner surface is defined by a ceramic tile
structure including parallel perforations wherein the
perforations adjacent the central region of the tile
structure are blocked or non-existent, leaving the
peripheral perforations open to define the actual radiating
area.
According to a further feature of the invention,
a plenum chamber is positioned below the ceramic tile
structure; the casing is rectangular and coacts with the
plenum chamber and upper planar member to define a sealed
volume; a mixing tube passes through the front wall of the
plenum chamber and constitutes the only entrance to the
sealed volume; and openings are provided in a wall or walls
of the housing, preferably adjacent the front and/or rear
corners of the housing and constitute the only exit or exits
from the sealed volume through an opening or openings which
may be positioned to draw the hot effluent of combustion to
griddle areas requiring heat boost for temperature
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uniformity. With this arrangement, an air/fuel mixture
enters the sealed volume through the mixing tube and flows
upwardly through the perforations in the ceramic tile
structure for combustion at the upper face of the ceramic
tile structure, whereafter the combustion effluent leaves
the sealed volume through the exhaust openings of the
casing. Hot combustion effluent is thus moved continuously
and efficiently in the areas needed, under the heat
utilization surface, to minimize the temperature gradient
across that surface.
In one disclosed emodiment of the invention, the
upper planar member comprises a griddle sealing the open
upper end of the housing; the ceramic tile structure
includes a plurality of individual perforated tiles
positioned in side by side relation with the perforations in
the central portion of the tile area blocked to define an
annular burner surface at the perimeter of the tiles; and an
exhaust conduit extends along the rear side wall of the
casing and communicates with the two rear corners of the
combustion chamber to facilitate the continuous removal of
effluent from the combustion chamber through appropriate
areas suitably positioned. In another embodiment, tiles are
arranged in a closed figure around a central steel plate so
that, again, the central portion of the overall burner area
is non-radiating.
In the drawings,
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FIGURE 1 is a perspective view of a gas fired
radiant heat griddle according to the invention with the
griddle plate exploded upwardly;
FIGURE 2 is a fragmentary cross-sectional plan
view of the griddle of FIGURE 1;
FIGURES 3 and 4 are cross-sectional views taken
respectively on lines 3-3 and 4-4 of FIGURE 2;
FIGURE 5 is a schematic view of the control
circuit for the griddle;
FIGURE 6 is a perspective view of an igniter
assembly with a ground screen;
FIGURE 7 is a plan view of an alternative
generator surface arrangement; and
FIGURE 8 is a circuit diagram for a device having
a low temperature "hold" selector.
The embodiment of the invention shown in the
drawing includes a griddle plate 10; a housing 12;
independently controllable left and right generator
assemblies 14 and 16; an exhaust conduit assembly 18; and a
control assembly 20.
Griddle plate 10 includes a left portion lOa and
a right portion lOb dividied by a central rib lOc and
including an outer peripheral lip or flange lOd extending
totally around the griddle and defining a downwardly opening
peripheral seat or groove lOe. Griddle 10 is preferably
formed as a heavy cast aluminum member.
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Housing 12 is preferably formed of 20 gage
aluminized steel and includes a front side wall 12a, a left
side wall 12b, a back side wall 12c, a right side wall 12d,
a bottom wall 12e, and a central partition 12f dividing the
housing into a left compartment 12g and a right compartment
12h. Groove 10e of flange portion 10d of griddle plate 10
fits sealingly over the upper edge 12i of the side wall of
the casing and partition portion 10c sealingly engages
housing partition 12f so that the griddle plate sealingly
encloses the open upper end of the housing. To insure a
good seal which is essential to the operation, a gasket 15
of woven ceramic tape is applied to the upper surfaces of
12a, 12b, 12c, 12d and to the central partition 12f. Gasket
15 or a seal of equal effectiveness is necessary to insure a
positive draft in the burner venturi 26 hereinafter
described and to avoid back pressure above the burner.
Generator assemblies 14 and 16 are identical and
are respectively disposed in the bottom wall of compartments
12g and 12h, Only generator assembly 16 will be described
and it will be understood that assembly 14 may be identical
to or the mirror image of assembly 16.
Generator 16 includes a plurality of contiguous
and coplanar ceramic tiles 22, a plenum chamber 24, and a
venturi mixing tube 26. Tiles 22 are arranged in side by
side abutting relation and each include a plurality of
perforations 27 (Figure 4) extending from the bottom surface
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to the top surface of the tile. There may, for example, be
200 perforations per square inch of tile surface with each
perforation having a diameter of .05 inches so that
approximately 1/3 of the surface area of the tile
constitutes open area. The central area of the assembled
tiles is blocked by a layer of ceramic cement 28 applied in
paste form to the undersurface of the assembled tiles so as
to preclude upward movement of fuel air mixture through the
perforations of the central area of the assemblied tiles and
allow the fuel air mixture to move upwardly through the
perforations in the annular perimeter 22a of the assembled
tiles; i.e., the only active burner area of the tiles is a
rectangular perimeter strip 22a about 1 1/4 inches in width
around the outside of the composite of tiles. It may be
advantageous to vary the rectangular surface in certain
instances or designs to obtain the required temperature
uniformity. As a first alternative, the portions of the
tiles which make up the blocked area may be left
unperforated. As a second alternative, rectangular tiles
may be placed around a central steel plate.
Plenum chamber 24 is defined as a dish like sheet
metal structure underlying the assembled tiles and including
a bottom wall 24a, side walls 24b, and an upper lip portion
24c coacting with the bottom 12e of the casing to define a
groove 24d receiving peripheral flange portions 22b
selectively provided at the external peripheries of the
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assembled tiles.
Mixing tube 26 extends through the front side
wall of plenum chamber 24 and includes a main body portion
26a receiving a gas supply line 28 and a venturi portion 26b
positioned within the plenum chamber and beneath the
assembled tiles. Clearly, other forms of introducting the
gas/air mixture into the burner can be used. Such, for
example, as pressurized air mixing.
Exhaust conduit assembly 18 is formed of a
suitable sheet metal material and includes a conduit 18a
extending across the rear wall 12c of the housing and a
central exhaust vent or stack 18b communicating centrally
with conduit 18a. Conduit 18a communicates with the rear
corners of griddle chamber 12h through openings 12j and 12k
and with the rear corners of griddle chamber 12g through
openings 121 and 12m. Conduit 18a further includes corner
portions 18c and 18d respectively wrapping around the left
rear corner of griddle chamber 12g and the right rear
corner of griddle chamber 12h. Conduit portion 18c
communicates with the left rear corner of chamber 12g
through an opening 12n in casing side wall 12b, and conduit
portion 18d communicates with the right rear corner of
griddle chamber 12h through an opening 12p in casing side
wall 12d. The ducts are not necessarily limited in position
to that shown. They may be disposed as desired to obtain
the uniform temperature distribution desired and their
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location ties in with the shape and size of the radiant area
to achieve the maximum uniformity.
Control assembly 20 includes a control panel 30;
a main solenoid valve 32; a left solenoid valve 34; a right
solenoid valve 36; a left igniter assembly 38; a right
igniter assembly 40; a left burner toggle switch 42; a right
burner toggle switch 44; a main switch 46; and a ~unction
box 48 receiving outside power through a suitable cable 50.
Each igniter assembly 38,40 includes an igniter
electrode 52 positioned over the exposed annular burner
surface 22a of the assembled tiles, a ground electrode 54,
and a frame probe or sensor electrode 56 also positioned
over the annular burner surface 22a.
If the burning area of the tile is severely
llmited with respect to the total area, the ground area can
conveniently be increased by putting an Inconel mesh screen
57 over the electrode wire ends and grounding it to the
housing with sheet metal screws as shown in Figure 6.
Exclusive of the screen 57, the igniter assembly 52, 54, 56
is a known device in which an alternating voltage of about
60 volts is applied between the electrode 56 and ground.
The presence of a flame ionizes the air surrounding the
electrode and rectifies the current flow to ground. This
rectified dc current is sensed and employed to hold a relay
open which continues gas flow. The screen 57 adds to the
ground plane and improves the operation of the flame sensor
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12~35~06
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during low temperature operation just after ignition.
In use, the griddle assembly is positioned within
a suitable countertop (not shown) with the upper surface of
the griddle plate 10 positioned generally flush with the
countertop and with the control panel 30 positioned beneath
the forward edge of the counter.
In operation, and assuming that it is desired to
use the right hand griddle unit, main switch 46 is actuated
and rigth hand burner control switch 44 is actuated to open
solenoid valve 36 and supply gaseous fuel under pressure
from a fuél source 58 through line 28 and nozzle 29 to
mlxlng tube 26 where it unites with air flowing under
natural aspiration through the annular entry space defined
between the mixing tube and the nozzle and flows through
venturi portion 26b into the plenum chamber beneath the tile
assembly 22. The gas and air mixture then flows upwardly
through the exposed perforations 27 in the annular burner
area 22a to the top surface of the tiles where it is ignited
by igniter electrode 52 coacting with ground wire 54.
Ultimately the flame heats the tile cherry red to produce a
radiant flame surface throughout the annular burner surface
area 22a; i.e., the center is unheated and does not radiate.
The heat generated by the exposed burner surface
22a radiates upwardly to heat griddle portion lOb. The
annular burner surface 22a underlying the griddle surface
lOb has the effect of minimizing the temperature gradient
lZ85Z06
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across the griddle surface as compared to the gradient that
would be established with a total area burner tile surface
since the radiation intensity is a trigonometric function
with the highest intensity occurring directly geometrically
over the flame front and the intensity lessening in a
direction away from the location immediately over the flame
front by an amount corresponding to the cosine of the angle
between the ray emanating directly upwardly from the fla~.e
and the ray emanating to the particular point in question on
the griddle surface. Thus, rather than having a very high
temperature in the center of the grill and a significant
temperature gradient in all directions moving away from the
center of the grill, the described annular burner surface
has the effect of establishing a relatively uniform
temperature across the expanse of the griddle surface.
The combustion effluents moving upwardly from the
tile surface move rearwardly by convection beneath the
griddle surface and exit from the chamber 12h through corner
openings 12;, 12k and 12p for entry into conduit 18a and
discharge through stack 18b. The hot effluents moving
beneath the griddle surface and outwardly through the
corners of the chamber 12h have the effect of boosting the
heat at the perimeter and corner portions of the griddle to
mlnimize the temperature gradient across the expanse of the
griddle.
It will be seen that the housing 20, griddle 10,
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and plenum chamber 24 coact to define a sealed volume having
only a single inlet constituted by the mixing tube 26 and a
single outlet through the rear corners of the combustion
chamber. This arrangement facilitates control of the
combustion process and also has the effect of creating a
srong, directed convection current flow beneath the griddle
and out of the direct openings of the combustion chamber.
Griddles constructed in accordance with the
present invention and incorporating the annular burner
surface in combination with the described convection current
flow provide a temperature gradient across the griddle
surface of no more than 3 degree F. as opposed to prior art
designs in which temperature gradients of 50 degrees F. or
more are commonly encountered across the expanse of the
griddle surface.
Looking now to Figure 7 an alternative embodiment
of the invention particularly useful in connection with very
large griddle surfaces is disclosed. In the Figure 7
embodiment one half of a double griddle arrangement is shown
to comprise a housing 60 having an interior horizontal
bulkhead 62 into which is sealingly installed a rectangular
pattern 64 of individual rectangular or square burner tiles.
The center area 66 is made of sheet steel just as the
bulkhead floor area 64 is constructed of sheet steel. In
this embodiment a good seal must be maintained around the
entire peripheries, both inside and outside, of the pattern
85;~06
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64. Area 68 of the pattern 64 is perforated to permit the
flow of the fuel air mixture through from the plenum which,
as will be understood from the previous description lies
below the plane of surfaces 62 and 66, through the burner
tiles. Areas 70 are blocked off by paste as previously
described. Area 71 is left unblocked to provide a location
for the igniter and flame sensor electrodes 52, 54, 56.
The housing 60 further comprises walls 72, 74, 76
and 78 to define exhaust ports 80, 82, 84 and 86 of which
ports 80 and 82 are located at the rear corners and ports 84
and 86 are located at the front corners. Again the location
of the exhaust ports, although shown diagrammatically, is
apparent from the planned view and differs from the
foregoing embodiment primarily in the fact that ports 84
and 86 are located in the front corners of casing 60.
Referring now to Figure 8 a second embodiment of
the control circuitry is disclosed, the principal
differences between the circuit of Figure 8 and the circuit
of Figure 5 lying in the provision of a "hold" mode of
burner operation wherein a low or intermediate temperature
is maintained between full-on cooking times.
In this connectlon it will be noted that neither
of the embodiments of Figure 5 nor 8 provides temperature
control through gas valve modulation. Of course, the
invention may be incorporated into a unit having such
temperature control but it is believed preferable in certain
~85~06
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applications to provide simple preset gas flow controls such
that operator responsibility is reduced to the decision as
to whether to turn the unit on or off or, in the case of the
embodiment of Figure 8, to place the unit in the low or
intermediate temperature "hold" mode.
Looking specifically to the circuit diagram of
Figure 8 it will be noted that the switch 90 is a double
throw double pole switch with center "OFF" position and is
provided with switch elements 92 and 94. It will be
appreciated that switch 90 corresponds in physical location
with either of switch 42 or switch 44 of Figure 1. Element
96 can be moved from the "off" position shown to a "cook"
position where it contacts terminal 96 and to a "hold"
position where it contacts terminal 100. Switch element 94
can be moved from the "off" position shown to a "cook"
position corresponding to terminal 98 and to a "hold"
position corresponding to terminal 102. Switch elements 92
and 94 are tied together so that they must move in
synchronism.
The embodiment of Figure 8 further includes the
circuit board 104 which is essentially a sequencer to
provide internal connections to the various elements of the
circuit, and a timer 106. Additional elements which differ
from the circuit of Figure 5 include the "hold" light 108
which comes on when the switch 90 is placed in the "hold"
position. A "purge" light 110 is provided to indicate that
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the sequencer of the circuit board 104, a known device, is
in the 10 second purge mode; i.e., after the switch 90 is
placed in either of the cook or hold positions, a relight
sequence including a 10 second purge of the combustion
chamber and a subsequent activation of the igniter
electrodes 52, 54 and 56 is carried out in a manner well
known and well understood by those skilled in the art. A
light 112 is provided to show that the gas valve is actually
open and the unit is heating.
When the switch 90 is in the "cook" position
power is supplied directly to the circuit board 104 through
terminal 98 and line 114. Accordingly the circuit board
operates to perform the purge cycle and thereafter supplies
power to the igniter and maintains the gas valve in the open
position as previously described. When the switch 90 is
placed in the "hold" position, power is applied through
terminal 100 to the timer 106 through line 116 and, from the
timer 106 to the switch at terminal 102 to terminal 94 and
thence, as before by line 114 to circuit board 104.
Accordingly, in the "hold" position the circuit board 104
receives power only through the timer 106 and it is the
function of the timer to establish a base cycle and to allow
the gas valve and the burner to function only for a portion
of the base cycle. For example, a base cycle 130 seconds
may be established and a portion of 20 seconds may be set
aside for activation of the burner, leaving 10 seconds for
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the purge as previously described. As a result the burner
is on for 20 seconds out of every 130 seconds and this is a
form of temperature control using time duration modulation.
Whereas preferred embodiments of the invention
have been illustrated and described in detail, it will be
apparent that various changes may be made in the disclosed
embodiments without departing from the scope or spirit of
the invention.
.~
