Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CONVECTION OVEN
TECHNICAL FIELD
[0001] This application relates generally to commercial cooking ovens
and, more
specifically, to convection ovens.
BACKGROUND
[0002] In commercial kitchens (e.g., found in restaurant, cafeteria and
retail
environments), convection ovens are used for cooking a large variety of food
items. Such
ovens may utilize heaters in the form of either gas-burners or electric
elements (e.g.,
resistive heaters) for generating heat, in combination with one or more fans
to move heated
air within the oven. Commercial kitchens are high volume cooking environments
in which
the door of the oven is repeatedly being opened and closed, which can result
in large
energy losses. Leakage past the oven door seals and through a steam vent in
the oven also
occur, even when the oven door is closed and the oven is simply idling (e.g.,
in a ready
state waiting for an operator to place an item to be cooked into the oven).
[0003] Typical convection ovens may have a high fan speed and a low fan
speed,
where the fan speed is manually controlled by an operator using a switch or
other input on
the oven interface. The higher the fan speed, the higher the volumetric flow
rate of air and,
thus, the higher the energy losses (e.g., due to higher leakage around door
seals etc.).
Operators commonly run the fan at high speed because the high speed tends to
produce a
more even bake. As a result, for efficiency rating purposes, the ovens are
also tested with
the fan at high speed, which adversely impacts efficiency.
[0004] Accordingly, it would be desirable to provide a convection oven
configured
to control fan speed in a more effective manner that increases oven
efficiency.
SUMMARY
[0005] In one aspect, a cooking oven includes a fan speed control that
reduces
energy losses by automatically switching a fan system to produce a lesser flow
rate under
one or more predefined oven conditions.
[0006] In another aspect, a convection cooking oven includes a cooking
cavity for
receiving food product to be cooked and a door movable between an open
condition and a
closed condition relative to the cooking cavity. The oven includes a heater
for heating air,
and a fan system for moving heated air within the cooking cavity, where the
fan system is
operable in a first mode for moving air at a first rate or in a second mode
for moving air at
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a second rate, wherein the first rate is higher than the second rate. A user
interface includes
a control input for manually selecting one of the first mode or the second
mode for
operation of the fan system. A fan system override control is configured such
that, when
the first mode is manually selected, the fan system is automatically switched
to operate in
the second mode based upon occurrence of a first predefined oven condition.
[0007] In still another aspect, a convection cooking oven includes a
cooking cavity
for receiving food product to be cooked, a door movable between an open
condition and a
closed condition relative to the cooking cavity and a heater for generating
heat. A fan
system is provided for moving heated air within the cooking cavity, the fan
system
operable in both a first mode in which air is moved at a first rate, and a
second mode in
which either (i) air is moved at a second rate, which is lower than the first
rate, or (ii) air is
not moved by the fan system. A fan system override control is configured such
that, when
the fan system is operating in the first mode, the fan system is automatically
switched to
operate in the second mode based upon occurrence of a first predefined oven
condition.
[0008] In yet another aspect, a convection cooking oven includes a
cooking cavity
for receiving food product to be cooked, and a heating system including a
heater and a fan
for moving heated air within the cooking cavity, the fan operable in a first
mode for
moving air at a first rate or in a second mode for moving air at a second
rate, wherein the
first rate is higher than the second rate. A user interface includes a control
input for
selecting one of the first mode or the second mode for operation of the fan
system. A fan
override is control configured such that, when the first mode is selected, the
fan
automatically switches to operate in the second mode based upon occurrence of
a
predefined oven condition.
[0009] The details of one or more embodiments are set forth in the
accompanying
drawings and the description below. Other features, objects, and advantages
will be
apparent from the description and drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Fig. 1 is a perspective view of a convection oven;
[0011] Fig. 2 is a schematic view of the oven interface;
[0012] Fig. 3 is a schematic view of the oven; and
[0013] Fig. 4 is an exemplary flow chart of oven operation.
DETAILED DESCRIPTION
[0014] Referring to Figs. 1-4, a convection cooking oven 10 includes an
external
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housing 12 and an internal housing 13 defining a cooking cavity 14 for
receiving food
product to be cooked. One or more doors 16 are movable between an open
condition and a
closed condition relative to the cooking cavity. One or more heaters 18 is
provided for
generating heat. Here, resistive heating elements are shown, but other heater
types (e.g.,
gas) could be utilized.
[0015] A fan system 20 is provided for moving heated air within the
cooking cavity
14 to more effectively and evenly heat loaded food product. Here, the fan
system 20 is
formed by a single fan 22 and fan motor 24 located along a back wall 26 of the
cavity 14,
in alignment with an opening 28 of the back wall. However, in other
embodiments,
multiple fans could be used. The fan system is operable in a first mode (e.g.,
high fan
speed) for moving air at a high rate or in a second mode (e.g., low fan speed)
for moving
air at a low rate. In the illustrated embodiment, operation of the fan 22
pulls air from the
oven cavity, moves the air past the heaters and alongside the exterior of the
cavity walls,
and then back into the cavity in a circulating manner. However, other
variations of
convection air flow are possible and within the scope of this application.
[0016] A user interface 30 includes a control input 32 (here a switch)
for manually
selecting one of the first mode or the second mode for fan system operation.
The
illustrated interface 30 also includes a temperature control knob 34, a timer
control knob
36, master switch 38 and a light control switch 40. In other embodiments, the
user
interface could be more advance, such as employing a touch-screen interface.
[0017] A controller 50 is responsive to the user interface inputs. The
controller 50
may take on various forms, incorporating electrical and electronic circuitry
and/or other
components. As used herein, the term controller is intended to broadly
encompass any
circuit (e.g., solid state, application specific integrated circuit (ASIC), an
electronic circuit,
a combinational logic circuit, a field programmable gate array (FPGA)),
processor(s) (e.g.,
shared, dedicated, or group - including hardware or software that executes
code), software,
firmware and/or other components, or a combination of some or all of the
above, that
carries out the control functions of the machine or the control functions of
any component
thereof
[0018] Regardless of the exact configuration of the controller 50, the
controller is
configured with a fan system override control 52 that, in turn, is configured
such that, when
the first mode for the fan system is manually selected by use of the switch
32, the fan
system will automatically be switched to operate in the second mode based upon
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occurrence of a predefined oven condition. More specifically, the predefined
oven
condition is selected such that the fan system operates in the first mode
primarily when the
higher convection air flow rate is most needed, and switches to the second
mode when a
lower convection flow rate will not adversely impact the cooking operation.
[0019] By way of example, the predefined operating condition may be a
call for
heat condition of the oven (e.g., based upon whether the heater(s) are turned
ON or OFF).
In this example, when the first mode is selective or otherwise active, the
first mode will be
maintained while the oven is heating up (heaters on) and the second mode will
be
automatically triggered when the oven reaches the designated temperature set
point for the
cooking operation (at which point the heaters turn off). The fan system
override control 52
may include a relay, the state of which is controlled by current flow, or lack
thereof,
through the heaters 16, to achieve the override result. Thus, the fan system
override control
also automatically switches the fan system back to the first mode when
appropriate (e.g.,
when current flow the heater(s) resumes)).
[0020] Thus, the override operation allows the oven to operate with
reduced energy
losses when the higher convection flow rate is not actually needed for the
cooking
operation. The override reduces current draw during part of the cooking cycle
and during a
majority of the time the oven is in an idle state (running with no food in the
cavity). The
override also reduces the amount of air leakage due to the lower convection
flow rate.
Further, the switching between the convection flow rates beaks up standing
waves of air
flow in the oven, which improves overall baking consistency.
[0021] Various predefined oven conditions could be implemented for the
purpose
of the fan system override control. The predefined oven condition may be a
temperature
condition of the cooking cavity (e.g., indicated by temperature
sensor/thermostat 42). For
example, the temperature condition may be a temperature of the cooking cavity
reaching
either a temperature set point for cooking or a predefined temperature that is
below the
temperature set point for cooking. The flow chart 100 Fig. 4 depicts oven
operation when
the fan speed setting is either set to HI or LO. By way of example, the ON
condition 102
may be controlled by master switch, and the fan speed setting condition 104
may be
controlled by the switch 32. As depicted in the right side of the flow chart,
when the fan is
set to the HI mode, the fan runs at HI per 106, but can automatically switch
to the LO
mode, per 112, when the sensed temperature reaches the temperature set point,
per 108, and
the heater turns off per 110. In this case, the override of the fan speed
setting triggers off
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of the call for heat according to whether the actual oven temperature is at
the set point.
More generally, however, as used herein, a "call for heat condition" of the
oven
encompasses oven conditions in which the oven controller is configured to
activate the
heater(s), regardless of how the call for heat condition is determined to
exist (e.g., direct
sensing of temperature or sensing of current flow to the heater(s)). Once the
temperature
falls back below the set point, the heater is turned back on, per 114, and the
fan is switched
back to the HI mode, per 116. Notably, in this example, when the fan is set to
the LO
mode by the switch per 104, the LO mode is maintained and there is no override
that
switches the fan back to the HI mode, per 118, 120, 122 and 124.
[0022] As another example, the temperature condition may be a temperature
of the
cooking cavity remaining within a predefined range of a temperature set point
for at least a
set time period (e.g., actual temperature no less than ten degrees below the
set point for five
minutes or ten minutes). As another example, the temperature condition may be
a
temperature change condition (e.g., falling temperature triggers second mode,
rising
temperature returns to first mode). As another example, the temperature
condition may be
a rate of temperature change condition (e.g., as long as the rate of change is
below a set
threshold, the second mode is triggered). Other variations are also possible.
[0023] The first mode may result in a first effective (average) fan motor
operating
speed and the second mode may result in a second effective fan motor operating
speed,
where the first effective fan motor operating speed is faster than the second
effective fan
motor operating speed. Although a simple change in actual fan speed is
primarily
contemplated above as corresponding to the effective fan speeds, other
variations are
possible. For example, the effective speeds may be achieved by pulsed
operation of the fan
motor according to respective duty cycles for the first mode and the second
mode.
[0024] In another variation, the fan system may include multiple fans,
and in the
first mode two or more fans run, and in the second mode at least one of the
two or more
fans does not run.
[0025] It is to be clearly understood that the above description is
intended by way
of illustration and example only, is not intended to be taken by way of
limitation, and that
other changes and modifications are possible. For example, ovens which do not
include a
manual fan speed control input could also employ a fan system override control
as
contemplated above, with the fan system operating in the first mode at all
times when the
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predefined oven condition is not detected or present. As another example, in
the second
mode, the convection air flow may be stopped entirely. Other variations are
possible.
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