U.S. patent application number 10/546104 was filed with the patent office on 2007-01-11 for self-cleaning oven.
Invention is credited to Frank Carbonara, Theodore James Chmiola, Michael R. JR. Matthews, Gregory J. Tomko, John H. Wiker.
Application Number | 20070006865 10/546104 |
Document ID | / |
Family ID | 32927533 |
Filed Date | 2007-01-11 |
United States Patent
Application |
20070006865 |
Kind Code |
A1 |
Wiker; John H. ; et
al. |
January 11, 2007 |
Self-cleaning oven
Abstract
A self-cleaning, gas-fired tunnel oven is provided. One
embodiment of the oven provides a self-cleaning, gas-fired tunnel
oven for cooking food products. The oven includes a control system
that regulates oven temperature during a pyrolitic, self-cleaning
procedure for incinerating contaminants that accumulate inside; a
burner for cooking food products and incinerating contaminants; a
modulating air and fuel control system arranged for proportionally
delivering air and fuel to the burner; a plurality of convection
air fingers for directing heated air toward the food products; a
collapsible conveyor, capable of fitting into the oven when
collapsed, for passing the food products through the oven; a
plurality of blowers, each having a dedicated speed controller; a
floating cooking chamber; and a vent system that maintains a
negative pressure in the oven during the self-cleaning
procedure
Inventors: |
Wiker; John H.; (LOCKPORT,
IL) ; Carbonara; Frank; (Mount Juliet, TN) ;
Tomko; Gregory J.; (Elgin, IL) ; Matthews; Michael R.
JR.; (Crystal Lake, IL) ; Chmiola; Theodore
James; (Roscoe, IL) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH LLP
Two Prudential Plaza
180 North Stetson Avenue, Suite 2000
CHICAGO
IL
60601
US
|
Family ID: |
32927533 |
Appl. No.: |
10/546104 |
Filed: |
February 20, 2004 |
PCT Filed: |
February 20, 2004 |
PCT NO: |
PCT/US04/05153 |
371 Date: |
July 19, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60449545 |
Feb 21, 2003 |
|
|
|
Current U.S.
Class: |
126/21A |
Current CPC
Class: |
F24C 3/122 20130101;
F24C 14/025 20130101; A21B 1/245 20130101; F24C 15/322 20130101;
F24C 14/00 20130101; A21B 1/48 20130101; F24C 14/02 20130101 |
Class at
Publication: |
126/021.00A |
International
Class: |
F24C 15/32 20060101
F24C015/32 |
Claims
1. A conveyor oven comprising: a housing defining a cooking chamber
therein; and a conveyor having a main conveyor section positioned
substantially within the cooking chamber and first and second
conveyor extension sections releasably connected to the main
conveyor section at opposite ends of the main conveyor section, the
first and second conveyor extension sections extending at least
partially outside the cooking chamber during a cooking cycle of the
oven, wherein the first and second conveyor extension sections are
disconnected from the main conveyor section and placed
substantially within the cooking chamber during a self-cleaning
cycle of the conveyor oven.
2. The conveyor oven of claim 1, further comprising oven openings
on opposite sides of the housing through which the conveyor
extension sections extend during the cooling cycle and doors that
close the oven openings during the self-cleaning cycle.
3. A conveyor oven comprising: a housing defining a cooling chamber
therein; a blower having a high pressure side and a low pressure
side, the blower propelling air on the high pressure side into the
cooking chamber and drawing air from the cooking chamber into the
low pressure side; a vent tube in fluid communication with the high
pressure side, the vent tube providing a bypass route for air from
the high pressure side to the outside of the housing without
entering the cooking chamber; and a vent valve positioned within
the vent tube, the vent valve being closed during a cooking cycle
of the oven so that air from the high pressure side is
substantially directed into the cooking chamber and being opened
during a self-cleaning cycle of the oven so that at least some air
from the high pressure side is directed through the vent tube and
outside the oven housing.
4. The conveyor oven of claim 3, further comprising an inducer
blower in the venttube.
5. A conveyor oven comprising: a platform; an outer housing fixed
to the platform; and a cooking housing defining a cooking chamber
and positioned within the outer housing, the cooking housing being
supported by the platform and moveable with respect to the platform
to permit contraction and expansion of the cooking housing.
6. The conveyor oven of claim 5, wherein the cooking housing
includes a front wall, back wall, and two side walls, the back wall
being fixed with respect to the platform and the front wall and
side walls being permitted to move with respect to the
platform.
7. The conveyor of claim 5, further comprising insulation between
the outer housing and the cooking housing.
8. A conveyor oven comprising: a housing defining a cooking
chamber; an opening in a wall of the housing providing a passageway
from the exterior of the oven to the cooking chamber; a conveyor
positioned adjacent the opening; and a door moveable between a
first and second position, the door closing the opening in the
second position.
9. The conveyor oven of claim 8, wherein the conveyor includes a
main conveyor section and a conveyor extension section separable
from the main conveyor section, the conveyor extension section at
least partially extending outside the housing.
10. A conveyor oven comprising: a housing defining a cooking
chamber; a conveyor moveable through the cooking chamber; a burner
providing heat to the cooking chamber; a gas line providing gas to
the burner; a gas valve moveable to regulate the flow of gas
through the gas line; an air line providing air to the burner; and
an air valve moveable to regulate the flow of air through the air
line, wherein the movements of the gas and air valves are dependent
on each other.
11. The conveyor oven of claim 10, further including a valve link
connecting the gas valve to the air valve, thereby moving the gas
valve and air valve together.
12. A conveyor oven comprising: a housing defining a cooling
chamber; a burner in fluid communication with the cooking chamber;
and a variable speed blower blowing air into the cooking chamber,
wherein the blower operates at a first speed during a cooking cycle
of the oven and at a second speed during a self-cleaning cycle of
the oven.
13. The conveyor oven of claim 12, wherein the speed of the blower
is controlled by a computer.
14. The conveyor oven of claim 12, wherein the first speed is
slower than the second speed.
15. A conveyor oven comprising: a housing defining a cooling
chamber; a burner in fluid communication with the cooking chamber;
and a variable speed blower blowing air into the cooling chamber,
wherein the blower operates at a first speed during a cooking cycle
of the oven and at a second speed during a start-up cycle of the
oven.
16. The conveyor oven of claim 15, wherein the speed of the blower
is controlled by a computer.
17. The conveyor oven of claim 15, wherein the first speed is
faster than the second speed.
Description
RELATED APPLICATIONS
[0001] The present patent application claims the benefit of prior
filed U.S. provisional patent application Ser. No. 60/449,545,
filed on Feb. 21, 2003, the entire contents of which are hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a gas-fired tunnel oven,
and particularly a gas-fired conveyor oven.
BACKGROUND AND SUMMARY OF THE INVENTION
[0003] Commercial, gas-fired tunnel ovens equipped with conveyors
produce, among other things, pizzas, cookies, bread, cakes and
donuts. Each oven routinely processes a large volume of food
products and, as a result, becomes rather dirty. Bits of the food
products themselves, burned food products, and soot from the
burners are typical sources of contamination that accumulate during
use.
[0004] Gas-fired tunnel ovens traditionally have been cleaned
manually with detergent and acid solutions. The oven must be taken
apart for cleaning by these methods. In addition to the oven walls,
roof, and floor, the conveyor used with the tunnel oven must be
cleaned, as well as any jet-impingement convection fingers,
convection blowers, and fired burners. Cleaning by the traditional
methods is tedious and expensive.
[0005] In theory, a gas-fired, commercially-sized tunnel oven might
be cleaned by installing electrical heaters at critical points to
raise the internal temperature to a range that reduces virtually
all contamination to ash. In practice, cleaning a gas-fired tunnel
oven by raising the temperature with electrical heaters requires an
estimated 50-100 amperes of electricity for each oven. Commercial
bakers do not normally have access to this much electrical current,
and the cost of installing high current electrical service is a
significant financial barrier for most bakers.
[0006] Accordingly, there is a need for a self-cleaning, gas-fired
tunnel oven suitable for use with a conveyor that can be cleaned
without need of disassembly, manual cleaning, or detergents.
Commercial bakers would welcome a self-cleaning, gas-fired tunnel
oven.
[0007] A self-cleaning, gas-fired tunnel oven that cleans by
pyrolysis is provided. The oven is used with a conveyor for food
products, which may be collapsed and placed inside the oven for
pyrolitic cleaning. The oven includes a control system that
regulates the oven temperature and duration of the self-cleaning
operation and deters people from opening the oven during the
self-cleaning operation.
[0008] The control system also modulates combustion air and heating
gas to one or more burners within the oven. A modulating control
system regulates the flow of air or heating gas to the burner or
burners. The ratio of airflow to heating gas flow is controlled
directly so that the ratio of air to fuel gas flowing to the burner
is approximately the same over a range of heating loads. The
control system that proportionally coordinates the flow of air and
fuel may be, for example, a mechanical linkage between the valves
or one or more electric or pneumatic controllers that send
positioning signals to the valves. With modulating control of
combustion air and heating gas, the oven operates cleanly and
efficiently over a wide range of heating loads.
[0009] The oven may be equipped with a plurality of convection
blowers, each of the convection blowers being subject to individual
speed control. The speed of one or more of the convection blowers
is varied during start-up operation to optimize fuel consumption,
during cooking operation to optimize the quality of food products
cooked in the oven, and during the self-cleaning operation to
control the rate of contaminant incineration, among other
reasons.
[0010] The oven includes a floating cooking chamber, which can
withstand pyrolitic cleaning temperatures and repeated pyrolitic
cleaning cycles without warping, cracking or developing metal
fatigue. Various components of the floating cooking chamber are
joined in a sliding fit that permits the floating cooking chamber
to expand and contract in response to temperature changes without
applying excessive mechanical stress to the components.
[0011] The oven also includes a vacuum exhaust system for
exhausting pyrolysis products. In one version, the convection
blowers are situated to deliver convection air to the oven and,
also, maintain the oven under a negative pressure with respect to
the kitchen. In another version, an inducer blower extracts the
exhaust air from the oven and delivers it to a disposal system. The
negative pressure prevents combustion products produced during the
self-cleaning process from escaping to the kitchen.
[0012] The oven is equipped with an active cooling system in which
air from the kitchen is passed through ducts that cool the exterior
surfaces of the oven. The oven includes heat-slingers to protect
the shafts of the convection blowers from overheating.
Additionally, the oven includes self-cleaning fingers for a
jet-impingement convection system that also clean the conveyor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a perspective view of a self-cleaning oven with
both first and second conveyor extension sections extended, each of
the conveyor sections being depicted without its mesh belt for
clarity;
[0014] FIG. 2 is a partial perspective view of the oven of FIG. 1
showing a drive shaft, a main conveyor section and the first and
second conveyor extension sections, each of the conveyor sections
being depicted without its mesh belt for clarity;
[0015] FIG. 3 is a side view of the oven of FIG. 1 with one of the
side walls removed, showing one of the blower and motor assemblies
and two air-impingement fingers;
[0016] FIG. 4 is a perspective view of the oven of FIG. 1 with the
first conveyor extension section extended and the second conveyor
extension section retracted, the first conveyor extension section
being shown without its mesh belt for clarity;
[0017] FIG. 5 is a view of the oven of FIG. 1 with the front access
door removed, showing both conveyor extension sections in their
retracted positions;
[0018] FIG. 6 is a front elevation view of the oven of FIG. 1 with
both conveyor extension sections retracted;
[0019] FIG. 7 is an overhead perspective view of the oven of FIG. 1
with the ceiling and overhead insulation removed, showing a
roof-mounted burner assembly, two blower and motor assemblies, and
a vent arrangement;
[0020] FIG. 8 is a close-up perspective view of the burner assembly
of FIG. 3 showing a gas shut-off valve, a gas valve, an air valve,
a valve link that coordinates the action of the gas valve with the
action of the air valve, and a burner;
[0021] FIG. 9 is a rear perspective view of the oven of FIG. 1
showing the two blowers and the vent arrangement; and
[0022] FIG. 10 is a perspective view of walls and a tubular frame
support surrounding a cooking chamber of the oven of FIG. 1.
[0023] FIG. 11 is a partial perspective view of the oven of FIG. 1
showing a drive shaft, the main conveyor section and the first
conveyor extension section, each of the conveyors depicted without
its mesh belt for clarity.
[0024] FIG. 12 is a an overhead view of the oven of FIG. 1 with the
ceiling and overhead insulation removed, showing a roof-mounted
flame tube assembly and two blower and motor assemblies.
[0025] FIG. 13 is a view of the main conveyor section through an
oven opening with one of the conveyor extension sections
removed.
[0026] FIG. 14 is a view of the main conveyor section and its
connection to the front wall of the oven depicted in FIG. 1.
[0027] FIG. 15 is a view of one of the conveyor extension sections
separated from the oven of FIG. 1.
[0028] FIG. 16 is a side view of the mesh belt of one of the
conveyor extension sections.
DETAILED DESCRIPTION
[0029] According to one embodiment, a pyrolytically self-cleaning,
gas-fired, conveyor oven 10, as shown in FIG. 1, includes an oven
housing 12 supported on four legs 14. The oven housing 12 surrounds
a cooking chamber 16 through which food products are passed on a
conveyor assembly 18. The oven 10 also includes a front access door
40 that can be opened using a front access door handle 41.
[0030] As best seen in FIG. 2, the conveyor assembly 18 includes
powered rollers 20 that drive a wire mesh conveyor belt (not shown
in the Figures) that conveys. food through the cooling chamber 16.
The powered rollers 20 can be driven in either direction so that,
as viewed in FIG. 2, the conveyor belt can convey food through the
cooking chamber 16 from left-to-right or right-to-left. Food
products can be transported by the conveyor assembly 18 into a
first oven opening 37 and out of a second oven opening 38 or,
alternatively, into the second oven opening 38 and out of the first
oven opening 37. In either case, the motion of the conveyor drive
motor (not shown) and, consequently, the motions of the conveyor
assembly 18 are precisely and continuously controlled in order to
provide the optimum cooking time for the food products. The speed
and direction of the conveyor assembly 18 are input by an operator
through a control station (not shown).
[0031] As the oven 10 is shown in FIGS. 1 and 2, it is configured
for cooking food products. That is, the conveyor assembly 18
extends out of the cooking chamber 16 at both ends. Food is placed
on the conveyor assembly 18 at either end of the oven 10 and is
carried through the cooking chamber 16 to the other end of the oven
10. As best seen in FIG. 2, the conveyor assembly 18 includes a
main conveyor section 30 and first and second conveyor extension
sections 32, 34 extending out of the cooking chamber 16. Over time,
as food products travel back and forth over the conveyor assembly
18, the various sections 30, 32, 34 of the conveyor assembly 18
clog with food debris and otherwise become dirty. Additionally,
food particles that drop onto various surfaces and components
within the cooking chamber 16 become dirty. To clean the oven 10,
the first and second conveyor extension sections 32, 34 can be
disconnected from the main conveyor section 30 and inserted into
the cooking chamber 16.
[0032] The main conveyor 30 is driven by a direct current electric
motor operating through a gear reducer. A pulse-controlled conveyor
drive motor (not shown) turns a drive shaft 86 which is rigidly
attached to a drive gear 88, which are depicted in FIG. 11. The
drive motor sends well-defined pulses of electrical energy to move
the drive shaft 86 in either a clockwise or counterclockwise
direction. Each electrical pulse of the motor moves the drive shaft
86 a reproducible increment. For example, a single pulse may be
adjusted to advance the drive shaft 86 by a predetermined number of
angular degrees. The frequency of electrical pules determines the
speed of the drive shaft 86, and consequently the speed of the
conveyor assembly 18, in either direction. The drive gear 88 turns
the main conveyor section 30 and the first and second conveyor
extension sections 32, 34 by means of follower gears 90, 92 (only
one is shown for the first conveyor extension section 32). The
follower gears 90, 92 cause conveyor axles 110 to turn, which
creates the conveyor motion. The speed of all the conveyor
sections, and ultimately, the cooking time of food products
traveling through the oven 10, is regulated by the drive motor. The
drive motor for oven 10 is controlled by a digital control unit
(not shown).
[0033] FIGS. 1 and 2 depict both the first conveyor extension
section 32 and the second conveyor extension section 34 in an
extended and locked position, the conveyor extension sections 32,
34 being both collapsible and extendable. The first conveyor
extension section 32 is accompanied by a first insulated door 35
and the second conveyor extension section 34 is accompanied by a
second insulated door 36. Both the first and second conveyor
extension sections 32, 34 can be separated from the oven housing 12
and inserted into a first oven opening 37 and a second oven opening
38, respectively. After the conveyor extension sections 32, 34 have
been inserted into the oven housing 12, the first insulated door 35
can be shut to close the first oven opening 37 and the second
insulated door 36 can be shut to close the second oven opening
38.
[0034] FIG. 11 is a partial perspective view of oven 10 in which
only selected components are shown in order to better communicate
the invention. FIG. 11 shows the relationship of the main conveyor
section 30 to the first conveyor extension section 32 when the
first conveyor extension section 32 is in the extended position.
The first and second conveyor extension sections 32, 34 (only one
is shown in FIG. 11) each include an upper notch 78, sized and
shaped to receive an upper peg 80, which is attached to an inside
wall of the oven (not shown in FIG. 11). The first and second
conveyor extension sections 32, 34 also each include a lower notch
82 for receiving a lower peg 84, which is also attached to the
inside wall (not shown). Lifting the first and second conveyor
extension sections 32, 34 causes them to rotate about the upper
pegs 80 until the lower pegs 84 disengage from the lower notches
82.
[0035] With the lower notches 82 disengaged, the first and second
conveyor extension sections 32, 34 can be separated from oven 10
and inserted into the first and second oven openings 37, 38 so that
the first and second insulated doors 35, 36 close the first and
second oven openings 36, 38, as shown in FIG. 6.
[0036] In order to assemble the conveyor assembly 18 for baking,
the first conveyor section 32 is partially inserted into the first
oven opening 37 and locked in an extended position with respect to
the main conveyor section 30. The first conveyor section 32 is
locked by inserting the pair of upper notches 78 formed by the
sides of the first conveyor section 32 under a pair of upper pegs
80 mounted in the oven 10. A pair of lower notches 82 also formed
by the sides of the first conveyor extension 32 are then rotated
onto a pair of lower pegs 84 mounted in the oven 10. The second
conveyor extension section 34 is similarly inserted into the second
oven opening 38 and locked in an extended position with respect to
the main conveyor section 30.
[0037] The first conveyor extension section 32 is separated from
the oven 10 in FIG. 13, providing a close-up view of the first oven
opening 37 and the main conveyor section 30. The drive shaft 86 of
the main conveyor section 30 extends between two side plates 96,
although only one of the side plates 96 is visible in FIG. 13. FIG.
13 also depicts five of the six drive sprocket wheels 100 attached
to the conveyor axle 110 of the main conveyor section 30. A mesh
belt 102 is shown as an endless chain engaged with the drive
sprocket wheels 100. One of the upper pegs 80 and one of the lower
pegs 84, which cooperate for locking the first conveyor section 32
(not shown in FIG. 13) in an extended position, are also visible in
FIG. 13.
[0038] The sixth of the six drive sprocket wheels 100 of the main
conveyor section 30 is shown in FIG. 14 along with one of the two
side plates 96. A bracket 106 extends from one of the side plates
96 and is fastened to the front wall 66 for supporting the main
conveyor section 30. The front wall 66 also supports one of the
upper pegs 80 and one of the lower pegs 84.
[0039] A close-up, partial perspective view of the first conveyor
extension section 32 is presented in FIG. 15. The mesh belt 102 of
the first conveyor extension section 32 tends to sag if not
supported, as illustrated in FIG. 16. FIG. 15 depicts four guides
108, which are provided to support the mesh belt 102. The guides
108 are in turn supported by guide supports 98, which extend the
width of the first conveyor extension section 32. FIG. 15 also
shows the conveyor axle 110 and the six drive sprocket wheels 100
for the first conveyor section, which are used to facilitate the
progress of the mesh belt 102.
[0040] FIG. 4 shows the second conveyor extension section 34
inserted into the cooling chamber 16 and a second insulated door 36
closed to seal off the second oven opening 38 through which the
second conveyor extension section 34 previously extended.
[0041] FIG. 5 further illustrates that the main conveyor section 30
supports the first conveyor extension section 32 when the first
conveyor extension section 32 is inserted into the first oven
opening 37. Inserting the first conveyor extension section 32 into
first oven opening 37 allows the first insulated door 35 to close
the first oven opening 37. Similarly, the main conveyor section 30
supports the second conveyor extension section 34, when the second
conveyor extension section 34 is inserted into the second oven
opening 38 so that the second insulated door 36 can close the
second oven opening 38. With the insulated doors 35, 36 closed, the
cooling chamber 16 of the oven 10 is completely sealed, as shown in
FIG. 6. The cooking chamber 16 can then be superheated to
approximately 900.degree., turning all food debris in the oven 10
to ash. When the food debris has been burned and turned to ash, the
front access door 40 can be opened using the front access door
handle 41 and the ash can be cleaned from the oven 10.
[0042] As seen in FIGS. 13-16 each of conveyors includes endless
stainless steel mesh belts 102 capable of travelling in either
direction and at variable speeds. Crumb trays (not shown) are
removably installed underneath the first and second conveyor
extension sections 32, 34.
[0043] As food travels through the cooking chamber 16, it is cooked
by the impingement of hot air that is directed at the main conveyor
section 30 through nozzles 22 located on fingers 24. As shown in
FIGS. 2 and 3, the depicted conveyor oven 10 includes two fingers
24, a lower finger having nozzles 22 directing air upward at the
bottom of the conveyor assembly 18 and an upper finger having
nozzles 22 (not seen in FIG. 2) directing air downward at the top
of the main conveyor section 30. The fingers 24 contain an inner
distributor plate (not shown) and a perforated outer plate
containing the nozzles 22 that collimate the heated air and evenly
distribute the heated air across the main conveyor section 30 on
which the food products ride. The oven 10 depicted in FIG. 3
includes two fingers 24 (one above the conveyor and one below),
however, the oven 10 can accommodate a number of bottom fingers 24
and top fingers 24. Any combination or deletion of fingers may be
employed.
[0044] The hot air directed through the fingers 24 is heated by a
burner assembly 42 (best seen in FIGS. 7 and 8) located under an
instrument panel 39 (FIG. 1) on the front of the oven 10. The
burner assembly 42 creates the heat used by the oven 10 during both
cooking (baking) and self-cleaning. The burner assembly 42 heats
the hot air that flows through the fingers 24 to cook food products
passing along the conveyor assembly 18. The burner assembly 42
burns a gas and air mixture at a burner 44, which shoots a flame
down a flame tube 46. The flame heats the air contained in the
flame tube 46, and the heated air exits the flame tube through an
outlet 47 and into a plenum 94, as seen in FIG. 12. The open space
of the plenum 94, located in front of the back wall 70 of the oven
10, provides the hot air with a directed passageway toward a blower
housing 74 where it will be circulated throughout the cooking
chamber 16.
[0045] Because the burner 44 is called upon to satisfy a wide range
of heat output requirements, it is necessary to control the flow of
gas and air supplied to the burner 44. While the burner 44 is
operating, the flow of both air and heating gas to the burner 44 is
modulated by a combined control system. With this combined
modulating control system for combustion air and heating gas,
optimum combustion conditions within the burner 44 can be
maintained approximately constant over a range of heat outputs.
With this combined modulating control system, the ratio of
combustion air flow to heating gas flow can be optimized and
maintained so that combustion is thermally efficient and
environmentally sound, producing a minimum of objectionable
byproducts.
[0046] The ratio of combustion air to heating gas can be optimized
to produce, for example, environmentally clean burning and the
ratio will remain close to the optimum value whether the
programmable controller (not shown) calls for high heat or low
heat. Alternatively, the ratio may be optimized for optimal fuel
consumption, optimal heat-up time or any other results that the
operator desires and the ratio will not vary substantially with
heat output. This modulating control system for combustion air and
heating gas over a range of heat output is especially advantageous
for a self-cleaning oven, such as the oven 10, where a range of
heat outputs is required.
[0047] The burner assembly 42 includes an actuator 48 that operates
an air valve 50 that regulates the amount of air entering the
burner 44 from a combustion air blower 52. The actuator 48 controls
the position of the air valve 50 based on signals received from
other control instruments and sensors (not shown) included in oven
10. A valve link 54 coordinates the movement of the gas valve 56
with that of the air valve 50. The gas valve 56 receives gas from
an automatic gas shut-off valve 57 and modulates the flow of this
gas so that the ratio of heating gas to combustion air is
relatively constant for a wide range of heating loads. The valve
link 54 connects the air valve 50 to the gas valve 56 so that as
the actuator 48 opens and closes the air valve 50, the gas valve 56
is correspondingly opened and closed, proportionally mixing the air
and gas as they enter the burner 44. The air and gas mixture is
then ignited inside the burner 44 and a flame shoots down the flame
tube 46.
[0048] One of the advantages of modulating air and gas control, as
provided by the valve link 54, is that the amount of excess air in
the flame tube 46 remains substantially the same during high and
low heating load periods. This advantage is particularly important
in a self-cleaning, pyrolitic oven, which exhibits a significantly
higher heating load during self-cleaning than conventional cooling
heating loads. Although the valve link 54 depicted in FIGS. 6, 7
and 8 is mechanical, it is also contemplated that the positions of
an air valve and a gas valve in modulating air and gas control
systems may alternatively be coordinated by, for example, utilizing
electronically-controlled actuators for each of the valves and
coordinating their positions by means of one or more electronic
controllers.
[0049] The burner 44 may be mounted anywhere in the oven.
Preferably, the burner 44. is roof-mounted as shown and sends its
flame along the inside of the flame tube 46 mounted adjacent the
ceiling of the oven 10. During operation of the oven 10,
contaminants tend to accumulate most heavily on and near the oven
floors. Thus, the roof-mounted burner system is more likely to
progressively incinerate and less likely to ignite the floor
accumulation as compared to conventional floor-mounted and
wall-mounted burner configurations.
[0050] During baking and self-cleaning operations, the flame tube
46 becomes very hot and radiates heat energy throughout the
inventive oven 10. It is contemplated that a diffusing tube (not
shown) may be employed around the burner for processing food
products that tend to discolor or otherwise deteriorate when
subjected to intense radiant heat.
[0051] The oven 10 has two relatively large blowers 26, 27 (see
FIG. .7) to move the heated air created by the burner 44 through
the fingers 24 and onto the product so that the most efficient bake
is achieved for each food product processed in the oven 10. More
specifically, the oven 10 employs collimated, vertical air streams
to give uniform and intensive heating. The collimated, vertical
streams of air that emerge from the fingers 24 provide an
exceptional heat transfer rate and generally bake foods faster and
at lower temperatures than in conventional convection hot air or
infrared heating ovens.
[0052] The hot air is circulated through the oven 10 by the two
blowers 26, 27 located at the back of the oven 10 (see FIG. 9). The
two convection blowers 26, 27 are located in the blower housing 74
(see FIG. 10). The blowers 26, 27 are each powered by a blower
motor 75 (only one is shown in FIG. 9), which is mounted on the
back wall 70, and connected to the blowers 26, 27 by a shaft (not
shown). In order to protect the shafts from the pyrolitic
temperature of the self-cleaning operation, the shafts may be
fitted with heat-slingers (not shown) or other cooling apparatuses.
A heat slinger is a type of fan arrangement mounted on the shaft.
Each blower motor 75 may be equipped with a dedicated speed
controller (not shown), preferably including an electrical power
inverter. With the benefit of individual speed control, the blowers
26, 27 can be individually accelerated and decelerated to optimize
electrical current inrush, the burner 44 firing or convective heat
loss. The speed of the blowers 26, 27 may also be individually
controlled in order to create distinguishable heating zones within
the oven 10 to optimize the baking of particular food products.
[0053] In another embodiment, the blowers 26, 27 may be variable
speed blowers that are controlled together so that their speeds,
while variable, are always the same as each other.
[0054] There are also two cooling fans 13, 15 located on the front
of oven 10 as depicted in FIGS. 1, 4, 6, and 7. These fans blow
cool air in through the machinery compartment and out the side
walls. The cooling fans 13, 15 draw air from the surroundings
through the instrument panel 39 for cooling the instruments located
behind the instrument panel 39. A portion of the discharge air from
the cooling fans 13, 15 may enter the combustion air blower 52 and
be delivered to the burner 44 as combustion air. The remainder of
the discharge air from cooling fans 13, 15 enters passages that
extend between the external sheeting of the oven 10 and an inside
wall, which supports insulation. The flow of air in these passages
serves to cool the external sheeting of the oven 10 below
preferably about 125 degrees F.
[0055] Referring to FIG. 9, a vent arrangement 58 is located at the
back of the oven 10. The vent arrangement 58 includes a vent valve
60 that is positioned between a vent tube 62 and a T-shaped tube 64
that communicates with the high-pressure sides of the blowers 26.
During a normal cooking cycle, the vent valve 60 is closed so that
no air passes through the vent valve 60 into the vent tube 62. In
this way, during cooking, air that is heated is directed solely
into the cooking chamber 16 for efficient cooking of food in the
cooking chamber 16. However, when it is desired to clean the oven
10, the vent valve 60 is opened and the oven openings 37, 38 are
closed, as discussed above. By opening the vent valve 60, enough
heated air is exhausted through the vent tube 62 to maintain a
slight negative pressure within the cooking chamber 16. In this
way, the smoke and soot that develops during a self-cleaning cycle
is exhausted through the vent tube 62 and the passage of smoke and
soot through small openings and cracks in the oven housing 12 is
prevented.
[0056] As shown in FIG. 10, the cooking chamber 16 is bounded by a
front wall 66 and two side walls 68 that are connected to a back
wall 70. The front wall 66, two side walls 68, and back wall 70 are
all screwed together to form a box surrounding the cooking chamber
16. The back wall 70 of this box is fixed to a tubular frame 71,
which is connected to a platform 72. However, while the back wall
70 of the box is fixed to the tubular frame 71, the front wall 66,
and two side walls 68 are free-floating. That is, the front wall 66
and two side walls 68 are connected to the back wall 70, but are
not connected to the tubular frame 71. The perimeters of the front
wall 66 and the two side walls 68 include lips 73 that sit on the
various members that make up the tubular frame 71, but are not
fixedly connected to those members. In this way, the front wall 66
and two side walls 68 are free to move relative to the tubular
frame 71 so that during cooking, and particularly during
self-cleaning when the temperatures in the cooking chamber 16 are
relatively high, the front wall 66 and side walls 68 of the cooking
chamber 16 are free to expand and slide on the members of the
tubular frame 71, thereby preventing buckling and warping of the
walls of the cooking chamber 16.
[0057] A unified display control station (not shown) for the oven
10 can include a blower selector, a heat selector, a conveyor
selector, two or more conveyor speed controllers and a digital
temperature controller. Additionally, a machinery compartment
access panel safety switch disconnects electrical power to the
controls and the blowers when the machinery compartment access
panel is opened.
[0058] In order to start up the oven 10, an operator confirms that
the front access door 40 is closed. The operator then turns the
blower and conveyor selectors to the "on" position. If necessary,
the operator adjusts the conveyor speed setting by pushing
appropriate selectors on the conveyor speed controller. The
operator adjusts the temperature controller to a desired
temperature and selects normal operation. A heat switch on a
control station (not shown) of the oven 10 activates the combustion
air blower 52. The burner 44 is a direct ignition burner. The main
gas valve 57 is opened while starting. a spark in the burner 44. A
sensor then monitors whether a flame is present within the burner
44. If a flame is not detected within 6 seconds, the main gas valve
57 is shut down, the burner 44 is purged, and the ignition cycle is
repeated. Referring to FIGS. 7 and 8, a gas bypass tube 76 provides
enough gas to the burner 44 to maintain a minimum flame even when
the gas modulation valve 56 is closed.
[0059] The oven 10 will typically heat to a desired heating
set-point temperature within a matter of minutes. While the oven 10
is heating, the control station (not shown) displays the actual
temperature. One or more thermocouples (not shown) in the interior
of the oven 10 send signals to a programmable controller (not
shown) that controls the actuator 48. If the programmable
controller (not shown) calls for more heat, the actuator 48 rotates
to open the air valve 50 and more combustion air is permitted to
pass from the combustion air blower 52 to the burner 44.
Simultaneously, the valve link 54 moves under the influence of the
actuator 48 to further open the gas valve 56, permitting more
heating gas to pass from gas line 55 to the burner 44. If the
programmable controller (not shown) calls for less heat, the valve
link 54 causes the air valve 50 and the gas valve 56 to close
simultaneously and proportionally. Consequently, the ratio of
combustion air flow to heating gas flow entering the burner 44
remains approximately constant over a range of heat output.
[0060] As mentioned, the speed of the blowers 26, 27 can be varied.
For example, the speed of the blowers may be two-thirds full speed
during start-up and self-cleaning cycles and full speed during a
cooking cycle to promote heating efficiency during each of the
cycles. For heating the oven 10 to baking or self-cleaning
temperatures, one or both of the blower motors 75 (only one is
shown in FIG. 9) start and routinely ramp up to a desired operating
speed in a programmable period of time. Programming the start-up
time of convection blower motors 75 makes firing of the burner 44
more reliable and promotes better combustion, among other things.
When the blowers 26, 27 are turning, the burner 44 is initially
fired with a minimum heat output and ramped up to the baking or
self-cleaning heat output over a period of time by, for example, a
programmable controller (not shown). When the desired heat output
has been achieved, the blower motors 75 are accelerated to
operating speed in a programmable period of time.
[0061] The start-up procedure (i.e., ramping up the speed of one or
both of the blowers 26, 27) prevents an objectionable current
inrush situation that is observed in conventional ovens, which
commonly start two or more blower motors at full speed
simultaneously. This startup procedure is also quieter, and
requires less electricity and heating gas, than the startup of
conventional ovens. Because the blowers 26, 27 draw more electrical
current when the oven is cold and the air in the oven is relatively
dense, operating both blowers at low speed during heat-up
(start-up) saves electricity. Also, because increased convection on
the inside surfaces of the oven walls promotes heat loss to the
kitchen, operating only one of the convection blowers during
heat-up saves heating gas.
[0062] Preferably, each of the blowers 26, 27 is equipped with an
electrical power inverter (not shown), which alters the frequency
and/or voltage of the electrical current to control the speed of
the blower 26 or 27. In that case, the blower motor 75 can be
either ramped up to operating speed over a programmable period such
as, for example, about thirty minutes, or held at an optimal
intermediate speed until the oven 10 reaches baling or cleaning
temperature and then accelerated. These variations conserve still
more energy by providing appropriate programmable blower speeds
depending on the current operation of the oven 10. When the oven 10
is, for example, baking (cooking), self-cleaning, warning up, or
cooling down, the blowers 26, 27 can operate at specific speeds
best suited for each individual activity.
[0063] Furthermore, for baking, the speed of the blower motors 75
(only one is shown in FIG. 9) may be separately adjusted to create
two or more different heating zones (not shown) within the oven 10.
These heating zones (not shown) can be created at will and utilized
to optimize the baking process and, consequently, the finished
quality of a particular food product. The oven 10 may be equipped
with two or more thermocouples (not shown) or other temperature
sensors to individually monitor and adjust these heating zones (not
shown). The manner in which the signals from these thermocouples
(not shown) are averaged or otherwise interpreted by the
programmable controller can be varied to suit the food product.
[0064] In order to shut down the blowers 26, 27, the operator
selects standby on the control station. The blowers 26, 27 will
remain in operation until the oven 10 has cooled to below 200
degrees F. and then cease turning.
[0065] When it is determined that the oven 10 should be cleaned, it
is cooled to a temperature below about 140 degrees F. The operator
then disengages the first conveyor extension section 32 and
withdraws the first conveyor extension section 32 from the first
oven opening 37. The first conveyor extension section 32 is then
inserted into the first oven opening 37 so that the first conveyor
extension section 32 is supported by the main conveyor section 30
and the first insulated door 35 closes the first oven opening 37.
The second conveyor extension section 34 is similarly separated
from the oven 10 and inserted into the second oven opening 38 and
the second insulated door 36 is closed. Because the first and
second conveyor extension sections 32, 34 are inserted into the
interior of the oven I0, they are cleaned by pyrolitic heat during
the self-cleaning cycle. The vent valve 60 (best seen in FIG. 9) is
opened and the blowers 26, 27 are then brought up to operating
speed and the burner 44 is fired to raise the oven 10 to
self-cleaning temperature. During the self-cleaning cycle, oven 10
operates under the control of temperature sensors and controllers
(not shown) that are specifically designed to operate in the range
of about 650-1000 degrees F. These may be the same sensors and
controllers used for baling (not shown) or a separate set.
[0066] In either case, the programmable control system actuates a
set of safety interlocks adapted for cleaning temperature
operation. For example, the oven overrides the baling cycle high
temperature shutdown limits, which are typically set at values less
than 600 degrees F. As another example, the programmable control
system actuates door locks that deter people from opening the oven
doors during the pyrolitic self-cleaning cycle.
[0067] The programmable controller also initiates corrective action
if unsafe or undesirable conditions are detected. For example, upon
detecting excessively high temperatures, high smoke levels or low
oxygen levels within the oven, the programmable controller shuts
down the burner 44 and the blowers 26, 27.
[0068] As mentioned, during cleaning, the interior of the oven 10
is kept under a negative pressure compared to the surrounding
atmospheric pressure. In the illustrated embodiment the opening of
the vent valve 60 and the operation of the blowers 26, 27 create
the negative pressure in the interior of the oven 10. As mentioned
earlier, when the vent valve 60 is opened and the blowers 26, 27
are operating, enough circulating hot air escapes through the vent
valve 60 to create the negative pressure inside the cooking chamber
16 necessary to force the smoke and soot created during the
cleaning cycle through the vent tube 62. In another embodiment, an
inducer blower (not shown) maintains the interior of the oven 10
under a negative pressure during cleaning as compared to the
surrounding atmospheric pressure. The inducer blower creates this
negative pressure by drawing air from the blower housing 74. The
blowers 26, 27 actually assist the inducer blower in creating this
negative pressure because the discharge flow from the blowers 26,
27 is impelled directly into the inducer blower. The combined
effect is similar to that of a two-stage blower. The discharge flow
from the inducer blower is sent to the vent arrangement 58.
[0069] The inducer blower could also take suction from the interior
of the oven 10 during normal baking. The entry of the inducer
blower opens directly into the blower housing 74. The inducer
blower may be positioned directly in the path of the discharge air
flow from each of the blowers 26, 27 so that the two sets of
blowers work in tandem to reduce the pressure in the interior of
the oven 10. Alternatively, the inducer blower may be mounted
anywhere in the interior of the oven 10. The discharge flow of air
from the inducer blower is sent to the vent arrangement 58 for
disposal.
[0070] Maintaining negative pressure in the interior of the oven 10
during both cooking and self-cleaning enhances energy efficiency
and safety. Maintaining negative pressure in the interior of the
oven 10 during the cooking and self-cleaning operations insures
that little or no heated air escapes to the kitchen. Minimizing
heated air loss makes the oven 10 more energy efficient. Any loss
or discharge of heated air from the interior of the oven 10
necessitates the combustion of additional heating gas. By directing
all exhaust flows from the oven 10 to the vent arrangement 58 and
ultimately the vent tube 62, the loss or discharge of heated air
can be better controlled and minimized. Also, the negative pressure
system promotes safety because negative pressure retains burning
gases in the interior of the oven 10 rather than permitting them to
escape into the kitchen. Additionally, maintaining negative
pressure in the oven 10 tends to prevent any smoky residue from
building up on the exterior of the oven 10 during normal cooking
and self-cleaning operations. The exterior surfaces of the oven 10
remain clean longer because they are not subjected to smoke, which
commonly escapes from the atmospheric cooking chambers of
conventional ovens.
[0071] The blowers 26, 27 turn at a relatively low speed during a
first incineration period of the cleaning cycle. This low speed
uniformly distributes heat throughout the interior of the oven 10
while minimizing convective heat loss through the walls of the oven
10. The first incineration period generally continues for about one
hour, although it may be longer or shorter based on factors such as
the cleaning temperature and the amount and type of contamination
in the oven 10.
[0072] During a second incineration period, which is generally
about one to three hours in duration, the blowers 26, 27 operate at
a relatively higher speed to promote complete incineration of the
contamination or debris accumulation. The temperature of the oven
10 is increased to a peak temperature at least once during the
second incineration period.
[0073] After the incineration periods, the programmable controller
cools the oven, disengages the safety interlocks and arranges the
control system for cooling operation. Due to the combination of
high temperature and convective air flow in the inventive oven
during the self-cleaning cycle, any contamination accumulation that
is in the oven is reduced to harmless and sterile ash. This ash may
be collected on drip pans provided for that purpose, which can be
accessed through the front access door 40 and carried away to
disposal. Alternatively, the ash may be collected in a vacuum
cleaner system that is built into or independent of the inventive
oven.
[0074] It is contemplated that collection of the ash from the lower
fingers may be facilitated by constructing the mesh belt 102 of the
main conveyor section 30 so that it is close to or touching the
perforated plates of the lower fingers 24. The mesh belt 102 thus
pushes or scrapes the ash from the lower fingers 24 for collection
by a drip pan or vacuum system. Preferably, the perforations are
formed so that the lower fingers 24 present a nonabrasive surface
to the mesh belt 102.
[0075] Although the invention has been described in detail with
reference to certain preferred embodiments, variations and
modifications exist within the scope and spirit of the invention as
described and defined in the following claims.
* * * * *