U.S. patent application number 12/500608 was filed with the patent office on 2010-01-14 for toaster oven.
This patent application is currently assigned to Breville Pty Limited. Invention is credited to Keith James Hensel, Edward Lai.
Application Number | 20100006561 12/500608 |
Document ID | / |
Family ID | 41504194 |
Filed Date | 2010-01-14 |
United States Patent
Application |
20100006561 |
Kind Code |
A1 |
Hensel; Keith James ; et
al. |
January 14, 2010 |
Toaster Oven
Abstract
A countertop toaster oven has an internal compartment heated by
at least four heating elements and a door for the compartment. At
least two of the heating elements are top elements, located
adjacent to a ceiling of the compartment. Two of the heating
elements are lower elements, located along a floor of the
compartment. At least one of the elements is controllable to
provide a variable wattage including one or more operational
wattages that are for at least a portion of the heating cycle,
intermediate between zero power and full power.
Inventors: |
Hensel; Keith James; (Lane
Cove, AU) ; Lai; Edward; (Glenfield, AU) |
Correspondence
Address: |
MICHAEL MOLINS;MOLINS & CO.
SUITE 5, LEVEL 6, 139 MACQUARIE ST
SYDNEY NSW
2000
AU
|
Assignee: |
Breville Pty Limited
Botany
AU
|
Family ID: |
41504194 |
Appl. No.: |
12/500608 |
Filed: |
July 10, 2009 |
Current U.S.
Class: |
219/483 ;
99/389 |
Current CPC
Class: |
A47J 37/0635 20130101;
A47J 37/0807 20130101 |
Class at
Publication: |
219/483 ;
99/389 |
International
Class: |
H05B 3/02 20060101
H05B003/02; A47J 37/08 20060101 A47J037/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 11, 2008 |
AU |
2008903560 |
Claims
1. A countertop toaster oven, comprising: an internal compartment
heated by at least four heating elements; a door for the
compartment; at least two of the heating elements being top
elements, located adjacent to a ceiling of the compartment; two of
the heating elements being lower elements, located along a floor of
the compartment; at least one of said elements being controllable
to provide a variable wattage including one or more operational
wattages that are for at least a portion of the heating cycle,
being intermediate between zero power and full power; the elements
being controlled as to variable wattage in accordance with one or
more user selected modes.
2. The toaster oven of claim i wherein: a fifth element is, in
operation of the toaster oven, controllable but not operated in
unison with the top elements in every mode; the fifth element being
positioned between the two top elements.
3. The toaster oven of claim 1 wherein: the lower elements are
regulated with triacs to vary a thermal output.
4. The toaster oven of claim 2 wherein: it is not possible to
operate the fifth element at the same time that the lower elements
are operated.
5. The toaster oven of claim 2 wherein: toasting is achieved
quickly by utilising four of the five heating elements at their
maximum wattage and not utilising the fifth element.
6. The toaster oven of claim 2 wherein: the toaster oven can
deliver, when toasting, the maximum allowable power from an
available power supply.
7. The toaster oven of claim 2 wherein: the fifth element is
physically protected by a radiation shield; various perforations
being provided along the length of the shield; the perforations are
irregularly spaced from one end to an other end, so that a central
portion of the fifth element is more shielded than the ends.
8. The toaster oven of claim 1 wherein: the lower elements have
shields located above and within the upward projected diameter of
each element.
9. The toaster oven of claim 1 wherein: the heating elements are
quartz elements each having an internal coil; a coil having, along
its length, regions of different pitch; a central portion having
the greater spacing between adjacent turns than an outer
portion.
10. The toaster oven of claim 1 wherein: a central part of the
ceiling is relatively flat and a curvature is provided in the
ceiling, both behind a rear element and in front of a front
element.
11. The toaster oven of claim 1 wherein: an interior floor of the
compartment is protected by a removable crumb tray having curved
reflective portions in front of a front lower heating element and
behind a rear lower heating element.
12. A user interface for a toaster oven having a plurality of
heating elements, the user interface comprising: a control module
coupled to the plurality of heating elements, the control module
adapted to independently control thermal output of one or more of
the heating elements; a plurality of user operable controls coupled
to the control module, wherein the plurality of user operable
controls includes: a first input element operatively associated
with selecting a mode of operation, a second input element
operatively associated with selecting a mode specific preference
indicative of cooking temperature or cooking intensity, and a third
input element operatively associated with selecting a mode specific
preference indicative of cooking time or cooking quantity; and a
display module coupled to the control module for indicating a
selected mode of operation.
13. A user interface according to claim 12, wherein the display
module includes a first display feature for displaying an indicator
of a selected mode of operation; a second display feature for
displaying an indicator of a selected mode specific preference
indicative of cooking temperature or cooking intensity; and a third
display feature for displaying an indicator of a selected mode
specific preference indicative of cooking time or cooking
quantity.
14. A user interface according to claim 13, wherein the first input
element is located in vertical alignment with the first display
feature; and wherein the second input element and the third input
element are vertically orientated with respect to the second
display feature and the third display feature.
15. A user interface according to claim 12, wherein the control
module is adapted to initially configure the display module to
present a default selected mode specific preference indicative of
cooking temperature or cooking intensity and a default selected
mode specific preference indicative of cooking time or cooking
quantity.
16. A user interface according to claim 12, wherein the first input
element, the second input element and the third input element are
each a rotary dial input element.
17. A user interface according to claim 12, wherein the control
module independently controls thermal output of one or more of the
heating elements in accordance with a selected mode of operation by
selectively suppressing cycles of an alternating current waveform
supplied to the one or more heating elements.
18. A user interface according to claim 12, wherein a mode of
operation is selectable from one of a set comprising: toast mode,
bagel mode, bake mode, roast mode, broil mode, pizza mode, cookies
mode, reheat mode, and warm mode; wherein the display module
displays a movable indicator for indicating a selected mode of
operation.
19. A user interface according to claim 13, wherein a mode of
operation is selectable from one of a set comprising: toast mode
and bagel mode; wherein the display module displays a movable
indicator for indicating a selected mode of operation, and wherein
when the selected mode of operation is toast mode or bagel mode as
indicated by the first display feature, the second input element is
operatively associated with selecting a darkness as indicated by
the second display feature, and the third input element is
operatively associated with selecting a number of portions as
indicated by the third display feature; and wherein during a
process according to a selected mode of operation, the third
display feature displays an indicator indicative of remaining
cooking time.
20. A user interface according to claim 12, wherein the plurality
of user operable controls further includes: a fourth input element
operatively associated with selecting a frozen food preference, for
enabling the control module to adjust cooking time to account for
frozen food.
Description
FIELD OF THE INVENTION
[0001] The invention relates to toaster ovens and more particularly
to a toaster oven with variable power heating elements and
versatile user control over the operation of those heating
elements.
BACKGROUND OF THE INVENTION
[0002] A toaster oven is used for a variety of cooking and food
heating tasks. A toaster oven will be used, for example, for
toasting a wide variety of breads (including frozen bread, bagels
and pizza), baking cakes, and broiling meats (grilling).
[0003] Handling the aforementioned tasks successfully requires
powerful heating elements and temperature control over these
heating elements that is sophisticated and versatile. In turn, easy
and versatile control over the heating elements is facilitated by a
user interface that permits a user to utilise the various functions
of the oven in a convenient and safe way.
[0004] Details in the construction of a toaster oven are contained
in the Applicant's co-pending Australian Provisional Application
No. 2008901884 which is incorporated herewith, in its entirety, by
reference.
OBJECTS AND SUMMARY OF THE INVENTION
[0005] It is an object of the invention to provide a toaster oven
having four or more heating elements that can be controlled to
perform a variety of tasks.
[0006] It is another object of the invention to provide a toaster
oven having heating elements that can be run at two or more power
settings.
[0007] It is a further object of the invention to provide a toaster
oven having an easy to use and intuitive user interface that
clearly distinguishes between the oven's toasting functions and its
other functions.
[0008] According, a toaster oven is provided with four or more
heating elements. At least some of the elements are controlled in
such a way that the power output of the elements can be varied.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0009] In order that the invention be better understood, reference
is now made to the following drawing figures in which:
[0010] FIG. 1 is a perspective view of a toaster oven in accordance
with the teachings of the present invention;
[0011] FIG. 2 is a schematic cross section of a toaster oven in a
toasting configuration;
[0012] FIG. 3 is a schematic cross section of a toaster oven in a
bake configuration;
[0013] FIG. 4 is a schematic cross section oven in a broil
configuration;
[0014] FIG. 5 is a front elevation detail of a toaster oven showing
a user interface and oven door details;
[0015] FIG. 6 are front elevation details of the interface
illustrating toast functions;
[0016] FIG. 7 is a front elevation detail of a portion of the
interface illustrating bake functions;
[0017] FIG. 8a is a schematic circuit diagram of a toaster oven in
accordance with the teachings of the present invention;
[0018] FIG. 8b is another schematic circuit diagram of a toaster
oven in accordance with the teachings of the present invention;
[0019] FIG. 9 is a perspective detail of the arrangement of the
oven's five heating elements;
[0020] FIG. 10 is an underside plan view of the top middle
element's shield;
[0021] FIG. 11 is a side view of the arrangement depicted in FIG.
9;
[0022] FIG. 12 is a detailed schematic diagram of the printed
circuit board depicted in FIG. 8;
[0023] FIGS. 13(a), (b) & (c) are schematic diagrams of the
cycles of AC power delivered to the elements in an oven according
to the teachings of the present invention;
[0024] FIGS. 14(a) and (b) are schematic diagrams illustrating
alternative AC wave shapes;
[0025] FIG. 15 is a graph illustrating oven temperature over a
duration associated with a bake mode;
[0026] FIG. 16 is a graph illustrating oven temperature over a
duration associated with toast mode cycles; and
[0027] FIG. 17 is a graph illustrating oven temperature over a
duration associated with several bagel mode cycles.
BEST MODE AND OTHER EMBODIMENTS
[0028] As shown in FIG. 1, a toaster oven 100 comprises a thermally
insulated housing 101 that defines an internal heating compartment
102. In this embodiment, the compartment 102 is accessed through a
door 103 with a transparent front panel 104. The door 103 is
hinged, horizontally, along its lower edge to a lower margin of the
compartment 102. The door's handle 105 is adapted to support the
door, when it is fully open, on the same horizontal surface that
the oven's legs 106 rest on. A vertical panel 107 on a front
surface of the housing and adjacent to the door 103 provides a user
interface comprising a graphic display 108 and a number of user
controls, as will be discussed below. The internal compartment
further comprises three opposing pairs of fixtures 109 for
supporting the one or more removable racks 110. Details in the
construction of a toaster oven are contained in the Applicant's
co-pending Australian Provisional Application No. 2008901884
(PCT/AU2009/000465) which is incorporated herewith in its entirety,
by reference.
[0029] In the embodiment depicted in FIG. 1, the internal
compartment 102 is heated by five quartz heating elements 120. As
will be explained, three of the quartz heating elements 120 are
located adjacent to the ceiling or top of the compartment 102 and
two of the elements are located along the floor or bottom of the
compartment 102. In this specification we refer to quartz heating
elements, but it will be noted that the invention can use many
types of heating element including stainless steel calrod,
tungsten, halogen etc.
[0030] For toasting and where maximum power is desired, an element
or combination of all or some elements may be run at its full
capacity. When, for example, baking or warming temperatures are
required, an element or combination of some or all elements need to
deliver lower power in a way that is consistent with the needs of
e.g. baking. The present technology is adapted to deliver, at a
macroscopic level (one that can be sensed by a person, e.g. seen or
felt) intermediate power. This means the technology creates, for at
least a period of time that can be observed by a user, an
appearance of a continuous power level that is somewhere between
full and off. This is to be distinguished from other oven element
powering configurations where an element is cycled or turned on and
off from full power to no power throughout a cooking cycle. This
common prior art method achieves a form of intermediate heating,
but the quality of e.g. baked goods suffers because of the
intensity of the full power portion of the cooking cycle. The prior
art form of intermediate heating also produces undesirable thermal
overshooting of the desired target temperature. In particularly
preferred embodiments, the gentle, continuous, even heating
preferred by bakers (for example in the baking of cakes) can be
achieved throughout all (or a significant or visible portion of) a
cooking time by reducing the amplitude of or "chopping" the AC wave
form, or by omitting or deleting or suppressing cycles of the AC
waveform of the power supplied to the heating elements, using
triacs or cycling relays or other electronic components in the
circuitry associated with some or all heating elements (but not
necessarily the top central element 220). In this way, at least at
a macroscopic or sensory level, the element appears to be
delivering what is defined here as true intermediate power, a level
of heat that is, for a user appreciable time, intermediate--less
that the full power output of the element but more than zero power.
This true intermediate power can be combined with full power, no
power and other true intermediate power settings during a cooking
cycle. True intermediate power is akin to electronic dimming of the
heating element, as seen in lighting devices.
[0031] As shown in FIG. 2, the internal compartment 102 contains
five quartz heating elements. The ceiling 200 of the internal
compartment is configured to optimise even toasting. The central
part 201 of the ceiling is relatively flat. A curvature is provided
in the ceiling, both behind 202 the rear element 203 and in front
of 204 the front element 205. The front curvature 204 extends
downwardly toward a small flat strip 206 that is lower than the
central flat area 201. A short bevelled section 207 extends across
the top edge of the opening into the compartment, terminating at
the strip 206. The bevelled portion 207 makes user access into the
interior of the compartment easier.
[0032] FIG. 2 also illustrates that the interior floor 208 of the
compartment is protected by a removable crumb tray 209. The crumb
tray 209 also includes curved reflective portions in front of the
front lower heating element 210 and behind the rear lower heating
element 211. The crumb tray 209 is preferably flat between the
forward curved reflective portion 212 and the rear curved
reflective portion 213.
[0033] As will be further explained, an optimisation of the oven's
versatility and performance is achieved by providing five heating
elements and utilising at variable wattages according to the mode
of operation. (In smaller or more economical versions of the oven
of the present invention, the optional top central element may be
omitted). In the present examples, the device is presumed to be
running on 120 volt AC. It will be understood that values expressed
in these examples, in watts, need to be adjusted accordingly when
other line voltages are used. In the example provided in FIG. 2 it
can be seen that the oven has a top set of three heating elements
being, a top front element 205, a top central element 220 and a top
rear element 203. The top front and rear elements are preferably
operated in unison. In some embodiments, the top front and rear
elements 205, 203 are 450 watts and the middle element 220 is 550
watts. In other embodiments, better performance is achieved by
installing a 520 watt element in the top front position 205, a 380
watt element in the top rear position 203 and a 550 watt element in
the top central position 220. In preferred embodiments, both of the
lower heating elements 210, 211 are 450 watts and operated in
unison. As will be explained, the top central element 220 and the
bottom elements 210, 211 may be shielded. In particularly preferred
embodiments, the lower elements and the top elements (but not
necessarily the central element 220) are current controlled or
regulated with triacs to further vary the thermal output of the
elements. In order to address safety and regulatory concerns (and
as will be explained with reference FIG. 8) it is preferably not
possible to operate the oven's top central element 220 at the same
time that the bottom elements 210, 211 are operated. When the top
central element 220 is on, both lower elements 210, 211 are off.
When the lower elements 210, 211 are on, the top central element
920 is off.
Toast Configuration
[0034] As shown in FIG. 2, uniform toasting of a wide variety of
breads is achieved quickly by utilising four of the five heating
elements 121.
[0035] In the example of FIG. 2, all of the oven's elements are on
except for the top central element 220. The other four elements
205, 203, 210, 211 are operated at their maximum wattage. This
produces the maximum glowing radiation for effective toasting. When
used as a toaster, the oven's rack 110 is located in the middle
position. As suggested by FIG. 5, instructions for using the rack
in the middle position are printed on or adjacent to a
corresponding location 501 on the oven's door.
[0036] In preferred embodiments the toaster oven uses the maximum
available wattage, limited by local regulatory or power
limitations. In the US and Canada this is 1800 watts of power,
shared equally between the top and bottom elements. In Australia
this is 2400 watts.
Bake Configuration
[0037] As shown in FIG. 3, the toaster oven 100 may be used as an
oven or convection oven. When used as an oven, the top central
heating element 220 is not used but other heating elements 205,
203, 210, 211 are. In this configuration or mode, the rack 110 is
preferably located in the lowest rack setting. The motorised
convention fan 301 is preferably set to a default state of "on"
although it may be defeated according to the operation of the user
controls on the control panel 107. In particularly preferred
embodiments, the gentle heating preferred by bakers (for example in
the baking of cakes) can be achieved by reducing the amplitude of
or "chopping" the AC wave form, or by omitting or deleting or
suppressing cycles of the AC waveform of the power supplied to the
heating elements, using triacs or cycling relays or other
electronic components in the circuitry associated with both of the
top and bottom heating elements (but not necessarily the top
central element 220). This form of true intermediate power can be
used continuously through a cooking cycle or used intermittently
with another true intermediate or zero power interval or combined
with, for example, a pre-heating portion of a cooking cycle using
full power for an initial time, to bring the oven up to the correct
cooking temperature.
Broil or Grill Configuration
[0038] As shown in FIG. 4, the toaster oven 100 of the present
invention may be used as a broiling or grilling device. In this
configuration or mode, the rack 110 is preferably located in the
uppermost position within the cavity 102. When the grilling or
broiling cycle is selected by a user, all three top elements are
used, preferably at their full power setting. However, any and all
top element can be triac controlled, in unison, to provide more
precise power delivery. As previously mentioned, the top central
element may be omitted in smaller or more economical embodiments.
As will be further explained, it is preferred that the top central
element 220 (if present) be shielded. Accordingly, a perforated
metal shield 401, is interposed between the element 220 and the
food below it. In preferred embodiments, the rack 110 is higher in
the broil position than in the toast position. The utilisation of
three heating elements above the rack assists in providing an even
spread of heat. With only two elements, the oven would have a cool
spot toward the middle of the rack. The utilisation of the third
element 220 enables the delivery of an even heat. The use of the
perforated shield allows some direct radiation to pass through it.
In special cooking configurations or modes such as for melting
cheese on toast, the intensity of the elements, particularly the
forward and rear upper elements can be reduced by using triacs and
the supply of true intermediate power (as previously explained) so
that, for example, the toast doesn't burn before the cheese is
melted. Further details concerning the various cooking modes will
be provided below.
User Interface
[0039] A user interface panel 107 is provided on the front of the
toaster oven too. The user interface panel further comprises a
graphic display area 502 and various user operable controls 503. In
preferred embodiments, the user controls are located directly below
the graphics display 502.
[0040] The graphics display area 502 comprises a vertically
arranged list of cooking modes 504 and a moving arrow or indicator
505 that tells the user which mode has been selected. In the
example of FIG. 5, the modes include toast, bagel, bake, roast,
broil, pizza, cookies, re-heat and warm. The various modes and
their functions will be explained below. The graphics display area
502 also comprises a toast shade selection indicator 506. The
indicator 506 shows schematic representations of toasted bread, one
light 507 and one dark 508. The user selections are, in this
example, seven in number and small icons 509 in conjunction with a
moving arrow or indicator 510 provide visual feedback to the user
of the selected toast shade. The display area 502 further comprises
an upper alphanumeric portion 511 and a lower alphanumeric portion
512. The upper alphanumeric portion 511 is used to indicate, for
example, a numeric value of the toast shade selected by the user
(when the toast mode has been selected) or, an oven temperature
(for example when the bake function has been selected). The lower
alphanumeric portion 512 can be used to indicate the number of
slices of bread that the user has selected (when the toast mode has
been user designated), a pizza size, or the time remaining in a
cooking cycle (for example when the bake mode has been user
selected).
[0041] The user operable controls 503 provide the user with an easy
way to make selections or preferences, and provide inputs to the
oven's processor in respect of the various modes and user
preferences within modes. Importantly, the primary modes designated
in the vertical list 504 are selectable by a rotary dial 513 which
is located in vertical alignment and preferably below the list 504.
Rotation of the mode dial 513 changes the oven's functionality and
the selected mode is indicated by the moving arrow 505. In this
example, the start/cancel button 514 is located directly below the
display area 502 and adjacent to the mode dial 513. The mode dial
513 allows the user to select one of a number of different modes or
functions. However, within each of these modes, the user is able to
express various preferences. Thus, the two largest rotary selection
dials are the temperature/darkness control dial 515 and below it, a
time/load size dial 516. The upper dial 515 allows the user to
adjust the cooking temperature, for example, adjusting the default
temperature associated with any particular mode upward or downward.
This same dial 515 allows a user to select the selected shade or
darkness of toast when the unit is in a toast mode. When the toast
mode has been selected with the dial 513, rotation of the upper or
temperature/darkness selecting control 515 results in the
appropriate movement of the arrow or indicator 510. Rotation of the
lower or time/load size control 516 allows the user to adjust,
before or at the inception of a cooking cycle or during it, a
selected time or the default time specified by the unit's
microprocessor. However, when the user selected function is the
pizza or toast function, rotation of the time/load size dial 516
results in commensurate changes to the lower alphanumeric indicator
512 that relate to load size, such as number of slices or pizza
size. In preferred embodiments, the temperature/darkness dial 515
and the time/load size 516 are of equal size and located in
proximity. Both may be operated during a cooking cycle so as to
make adjustment mid-cycle. The interface panel 107 also includes a
button or control 520 for the user selection or de-selection of the
convection fan feature. The convection fan feature preference is
only available in certain modes. The interface panel 107 also
includes a control or button 521 that allows the user to toggle any
displayed temperature from Fahrenheit to centigrade or centigrade
to Fahrenheit. A frozen food control or button 522 is also
provided. As will be explained, selection of the frozen food
preference allows the total cooking time to account for frozen
foods (when this feature is enabled in a mode).
[0042] Examples of the way information is displayed in the graphics
display area 502 are depicted in FIGS. 5 and 6. As shown in FIG. 6,
the function list 504 in conjunction with the indicator 505 show
the user that the toast mode has been selected. The upper
alphanumeric area 511 in conjunction with the symbolic display 506
indicates that the user has selected a darkness or shade of 4. The
lower alphanumeric area 512 indicates that the user has selected
four slices using the time/load size dial 516. Once the mode and
preferences have been established, the user presses the
start/cancel button 514 and the display changes accordingly. The
resulting display, particularly the lower alphanumeric display area
512 displays the remaining cooking time 601 rather than the number
of slices that have been selected. If the user had also selected
the frozen food control button 522 the lower alpha numeric display
area 602 would show the user that more time had been added to the
toasting cycle. A graphic icon and the word "frozen" 605 within the
display area 502 also provide feedback to the user that the frozen
food preference had been selected by use of the frozen food control
or button 522.
[0043] As shown in FIG. 7, when the user selected bake mode has
been requested, the default temperature of 350 degrees Fahrenheit
is displayed in the upper alphanumeric display area 511 and a
default time, e.g. 30 minutes is displayed in the lower area 512.
In preferred embodiments, utilisation of the bake function results
in a default selection of the convection feature and the same is
indicated within the display area by an icon and/or text 701.
Circuitry
[0044] FIGS. 8a and 8b show typical schematic circuit diagrams 800
for implementation of the electronic control of the elements and
fan. In this example, the oven's functions are controlled by an
integrated circuit 801. In this example, separate sub-circuits are
provided for both of the bottom elements 802, the middle top
element 803, the fan 804 and the front and rear top elements 805.
An overload or storm protection sub-circuit 806 is provided across
the input power leads. The sub-circuit 806 includes an optional
thermal fuse 840, a noise filter capacitor 841, a varistor 807 to
absorb power surges and a PCB fuse 808 as a back-up against the
failure of the varistor 807. In the sub-circuit 802 associated with
the bottom elements, a triac 807 is protected by a heat sink 858.
The triac is used as an electronic relay and current controller
(e.g. for delivering true intermediate power) in the control and
regulation of both of the bottom heating elements 800, 810. A
resistor and capacitor 811, in series, and located across the
outputs of the triac 807 absorb high frequency noise that may be
produced from the operation of the triac. The triac 807 can be used
to switch the bottom elements on and off as well as regulating
their current draw and thermal output with methods such as
"chopping" or suppressing the AC wave form, many times a second
(for true intermediate power, or otherwise) to reduce the effective
or average wattage, as required. The sub-circuit 805 for the top
elements is similar to the sub-circuit for the bottom elements 802.
The sub-circuit 803 for the middle top element 820, in this
embodiment does not use a triac, but it may. Instead or as well as
a triac or other current regulator, it uses a relay 821 so as to
create a toggling between the operation of the top middle element
and the pair of bottom elements 809, 810. Thus, it becomes
impossible (in this configuration) to operate both the middle top
element 802 and the bottom elements 800, 810 together. This
optional toggling feature eliminates the need for a current fuse.
The e.g. 20-60 watt fan 830 for the convention feature is operated
with a triac 831 but does not require a high frequency noise
filter.
[0045] A thermistor 870 located in the oven provides temperature
feed back information to the processor 801. Thus the processor can
compensate or adjust (by reduction) the time calculated to cook
based on the internal oven temperature of the oven at the time when
the Start button 514 is pressed. This happens for automatic
functions such as Toast, Bagel, and Pizza as will be explained. The
thermistor 870 is preferably located behind a thin aluminium
pressed shell or bubble at an upper portion of the back or sides of
the oven, and is embedded in heat-sink paste.
[0046] An alternative circuit is depicted in FIG. 8b. In this
example, a single triac 807 or other current regulating device is
used to control either the top middle element or the bottom
elements. This is done by routing the regulated output 880 of the
triac 807 to the relay 821. Thus operation of the relay delivers
the regulated output to either the bottom elements 809, 810 or the
top middle element 820 (but not both the bottom elements and the
top middle element).
Elements and Shielding
[0047] As shown in FIG. 9, each of the oven's five quartz heating
elements is protected from accidental breakage. For example, the
front and back top elements are located between and above a pair of
stainless steel rods 903. The top middle element 904 is physically
protected by a radiation shield 905. The shield 905 is formed from
metal and is shaped as a generally "U" shaped or arcuate channel.
As better shown in FIG. 10, various perforations 1000 are provided
along the length of the shield 905. The perforations 1000 are
provided in three longitudinal rows 1001, 1002 and 1003. The rows
1001, 1003 along the edges 1004 of the shield are generally equally
spaced and equally sized and provide only modest blocking of the
intense radiant energy emitted by the heating element. In the
example of FIG. 10, the perforations of the middle row 1002 are
equally sized but irregularly spaced. The centre group 1005 of
perforations are further apart when approaching the centre of the
shield. The middle row's outer perforations 1006, 1007 are spaced
together more closely than the middle perforations 1005 and are
preferably evenly spaced. Thus, the central portion of the heating
element is more shielded than the ends. This prevents a formation
of a hot spot underneath the middle of the top middle element
905.
[0048] Because of the combined effects of the radiant and
convection output of the lower elements, special shielding has been
devised to provide physical protection of the elements in
combination with the elimination of hot spots associated with the
lower elements. As shown in FIG. 11, the lower heating elements
1101, 1102 are both located below and laterally of an adjacent
stainless steel rod 1103. In addition, the lower elements 1101,
1102 are physically protected by an inverted "U" shaped,
unperforated shield 1104. In this example, the shield 1104 of the
lower elements is located above and within the upward projected
diameter of each element. The shields 1104 are canted so that one
lower back or rear side edge 1105 is closer to the adjacent element
than an upper front side edge 1106.
[0049] It will be appreciated that within the confines of a
relatively small oven compartment, a heating element that produces
uniform heat across its length will produce a distribution of
temperature within the compartment that is uneven. Particularly
with regard to shorter cooking times, operation of a uniform
heating element will produce a temperature in the middle of the
oven that is hotter than the temperature close to the side walls.
This dilemma may be addressed by varying the pitch or spacing of
the coils within the quartz heating element in the manner disclosed
by FIG. 12. As shown in that figure, a quartz heating element's
internal coil 1200 may contain, along its length, regions of
different pitch or turn spacing. In the example of FIG. 12, the
length of the coil 1200 can be thought of as having been subdivided
into six portions of generally equal length 1201, 1202, 1203, 1204,
1205 and 1206. The outer most portions 1201, 1206 have the smallest
or finest pitch (tightest spacing between adjacent turns). The
central two portions 1203, 1204 have the greatest spacing between
adjacent turns and may have equal pitches. The intermediate
portions 1202, 1205 having turn spacing that is closer than the
central portions 1203, 1204 but farther (greater or coarser pitch)
than the outer portions 1201, 1206.
Further Discussion of the Toaster Oven's Modes
[0050] Toast Mode
[0051] The toast mode is user selectable with the mode dial 513.
The toast mode is intended to be used with the rack 110 in the
middle position. In preferred embodiments, the top middle element
220 is not used but the other elements are. The fan is not used and
full power (preferably 1800 watts or 2400 W where allowed by local
authorities) is delivered to the remaining four elements. The
time/load size dial 516 can be used to receive a user preference of
between 1 and 6 slices. The default setting is preferably four
slices. Using the aforementioned wattage, toasting times vary
between about 165 seconds for 1 slice (at the lowest browning
setting) to about 420 seconds (for six slices at the maximum
browning setting). The convection feature is turned off and the
circuitry does not allow the user to activate the convection
feature. When the frozen food function is selected with the frozen
food button 522 extra time is added to the normal cycle time. By
way of example, fifteen seconds is added for one or two slices.
Twenty seconds is added for three slices or four slices. Thirty
seconds is added for five slices and thirty five seconds is added
for six slices.
[0052] The thermistor 870 in the oven may provide oven temperature
feed back information that allows the processor 801 to compensate
for the internal temperature of the oven, by reducing the cooking
time as required.
[0053] Bagel Mode
[0054] When the bagel function has been selected, the cooking cycle
is subdivided. A first portion of the cooking cycle (e.g. two
minutes and 30 seconds) is cooked using 1800 watts of power.
Thereafter, the power is reduced, for example, to 1450 watts. In
the first portion of the cycle, all of the elements are used except
for the top middle element. Thereafter, all of three top elements
are used but the bottom elements are not used. In the bagel mode,
the defaults are four slices and a browning setting of 4 (out of
7). Cooking times vary from about 205 seconds (for one bagel half
at the lowest setting) to about 375 seconds (for six bagel halves
at the highest browning setting). When the frozen food preference
is selected, extra time is added to the normal cooking time. For
example, 25 seconds is added for one bagel half and an additional
five seconds is added for each additional half, resulting in an
additional 50 seconds when six slices or bagel halves are selected.
When using the bagel function, the convection feature preferably
deactivated and prevented from being selected.
[0055] The thermistor 870 in the oven may provide oven temperature
feed back information that allows the processor 801 to compensate
for the internal temperature of the oven, by reducing the cooking
time as required.
[0056] Bake Mode
[0057] The maximum cooking time when the bake mode has been
selected is about 2 hours. In the bake mode, the convection fan
default is "on". The top middle element is preferably "off" and a
total power of about 1440 watts is delivered evenly to the other
four elements. Because the convection fan is generally "on", the
total power consumption may reach 1500 watts. In the bake mode, the
default temperature is 350 Fahrenheit (optionally delivered at
least in part by true intermediate power) and the default cooking
time is 30 minutes. Both of these values may be subsequently
adjusted by the user, even in mid-cycle. In the bake mode, the
frozen food selector control may be disabled and the displayed
symbol 605 may be caused to flash to indicate than an improper
selection has been made. In some embodiments, the delivery of power
may be biased toward the bottom elements for all or a portion of
the cooking cycle. When the Start button is pressed in Bake mode,
the oven preheats until the selected temperature has been reached.
PREHEATING flashes on the display, and an audible sound then
indicates that the oven has reached the selected temperature, and
the timer starts to count down automatically.
[0058] Roast Mode
[0059] When the roast mode has been selected, power is preferably
delivered evenly to all of the heating elements except for the top
middle which is off. When the Start button is pressed in the Roast
mode, the oven preheats until the selected temperature has been
reached. PREHEATING flashes on the display, and an audible sound
then indicates that the oven has reached the selected temperature,
and the timer starts to count down automatically. The power
delivery to the elements 1440 watts and utilisation of the 60 watt
convection fan results in a total power consumption of about 1500
watts. Power may be biased toward the bottom elements during all or
a part of the cooking cycle. In the roast mode, the default
temperature is 350 degrees Fahrenheit (optionally delivered at
least in part by true intermediate power) and the default roasting
time is 60 minutes. Both of these values may be adjusted by the
user pre or mid-cycle. The maximum time permitted in the roast mode
is two hours. In the roast mode, the frozen food function is
disabled and the display symbol 605 may be caused to flash so as to
indicate that an improper selection has been made. In preferred
embodiments, the default for the convection fan is "on".
[0060] Broil Mode
[0061] Three different broil preferences may be set using the
temperature/darkness dial 515. If the user sets the broil to (e.g.)
300 degrees Fahrenheit, power delivery to the top front and top
rear elements is set to about 310 watts each. The top middle
element will be cycled with the triac or relay to achieve an
average of about 380 watts. This results in an overall power
delivery of about 1000 watts. The default time is set to 15 minutes
with a maximum time of 20 minutes. The frozen food preference
control is disabled. The default for the convection feature is
"off" but a user can use the convection control 520 to activate it.
Cooking times are not adjusted by the microprocessor if the
convection feature is selected.
[0062] If the user sets the broil setting of (e.g.) 400 Fahrenheit
using the temperature/darkness control 515, only the top elements
are used. The front and back elements are powered to 390 watts and
the top middle element is cycled to achieve an average power of 470
watts. This results in an average power delivery of 1250 watts. The
default cooking time is 15 minutes with a maximum time of 20
minutes. The frozen food and convection features operate the same
as when the user sets the broil to 300 Fahrenheit.
[0063] The user may also select a third discreet broil temperature
of (e.g.) 450 or 500 degrees Fahrenheit. Thus, it will be
appreciated that the user is effectively presented with three broil
settings, effectively being low broil, medium broil and high broil,
each designated by a different display of temperature. The display
can be configured accordingly to display e.g. Low, Medium or High
instead of a specific temperature. In the high broil setting, all
three top elements are used and each is used to its maximum power
rating. The bottom elements are not used. The total power delivery
is thus about 1450 watts. The default and maximum times, frozen
food and convection features are handled in the same way as the
other broil settings.
[0064] Pizza Mode
[0065] When the pizza mode has been selected, the user can select a
number of different pizza sizes (diameters) using the time/load
size dial 516. For example, a user may be able to select from 6
inch, 8 inch, 10 inch, 12 inch or 13 inch pizza sizes. The 12 inch
size is the preferred default. The default cooking time for the 12
inch default pizza is 15 minutes with no oven preheating. Cooking
times vary, for example, from 12 minutes for a six inch pizza
through to 15 minutes, 30 seconds for a 13 inch pizza. The frozen
food setting default is "on" for pizza. If the user elects to
disable the frozen food setting by pressing the frozen food button
522, the cooking time is adjusted downward, for example, by two
minutes. In the pizza mode, the convection default is "on". When in
the pizza mode, the top middle element is off but the other
elements are on and powered equally. In preferred embodiments, each
element is powered to 360 watts (optionally delivered at least in
part by true intermediate power) and because the 60 watt fan is on,
the total power consumption is about 1500 watts. The maximum
cooking time allowed in the pizza mode is 40 minutes. The default
cooking temperature in the pizza mode is 450 degrees
Fahrenheit.
[0066] The thermistor 870 in the oven may provide oven temperature
feed back information that allows the processor 80i to compensate
for the internal temperature of the oven, by reducing the cooking
time as required.
[0067] When the Start button is pressed in the Pizza mode, the oven
preheats until the selected temperature has been reached.
PREHEATING flashes on the display, and an audible sound then
indicates that the oven has reached the selected temperature, and
the timer starts to count down automatically.
[0068] Cookies Mode
[0069] When the cookies mode has been selected by a user, the top
middle element is off but the other elements are powered equally to
about 360 watts. With the inclusion of the convection fan, the
total power consumption is about 1500 watts. The default cooking
temperature for cookies is 350 degrees Fahrenheit (optionally
delivered at least in part by true intermediate power)but this can
be modified by the user. In the cookies mode, the default baking
time is 12 minutes (after the oven preheats to the selected cooking
temperature). The preheat time is typically five minutes. If the
frozen food preference is selected by the user, the cooking time is
adjusted upward by about 2 minutes.
[0070] When the Start button is pressed in the Cookies mode, the
oven preheats until the selected temperature has been reached.
PREHEATING flashes on the display, and an audible sound then
indicates that the oven has reached the selected temperature, and
the timer starts to count down automatically.
[0071] Reheat Mode
[0072] When the reheat mode has been selected by a user, the top
middle element is off and the other elements are powered equally to
approximately 360 watts each. Because the convection fan is
defaulted to "on" the total power consumption is about 1500 watts.
In the reheat mode, the default cooking time is 15 minutes with a
maximum setting of one hour. The default temperature in the reheat
mode is 350 degrees Fahrenheit (optionally delivered at least in
part by true intermediate power).
[0073] Keep Warm Mode
[0074] When a user selects the keep warm mode, the top middle
element is off and the other elements are powered equally to 360
watts each. The default warming temperature is 160 degrees
Fahrenheit and the default warming time is 60 minutes. The maximum
keep warm time is two hours. In the keep warm mode, the frozen food
function is disabled. The convection default is off but may be
activated by the user.
[0075] The thermistor 870 in the oven may provide oven temperature
feed back information that allows the processor 801 to compensate
for the internal temperature of the oven.
[0076] As shown in FIG. 12 the printed circuit board 1201
previously disclosed with reference to FIG. 8 may contain zero
crossing sensor circuitry 1202. The zero crossing sensor 1202 uses
a diode and transistor arrangement with suitable resistors and
capacitors so as to provide a signal 1203 to the oven's integrated
circuit type controller 1204 every time the wave of the 12 AC power
supply to the PCB reaches zero volts. This provides the controller
1204 with signal information from which the frequency of the input
power can be determined. Given the zero crossing signal, the
controller 1204 can then drive the triacs and associated circuits
to manipulate the wave form of the AC power that is supplied to the
one or more heating elements that are dimmed, that is, adapted to
deliver true intermediate power. Schematic representations of the
AC wave forms that result in dimming or true intermediate power
1205, as supplied by the PCB 1202 to the elements are exemplified
in FIGS. 13 and 14.
[0077] As shown in FIG. 13(a), the wave form of the AC power
supplied to the top element 1301 and to the bottom element 1302,
during toasting, is uniform and generally represents the maximum
power available to an element at any given time. In a bread
toasting mode, it is advantageous to supply the maximum available
power so that the bread browns quickly without drying out.
[0078] In FIG. 13(b) wave forms are illustrated for the top element
1303 and the bottom element 1304 during, for example, a bake mode.
As suggested by FIG. 13(b) an AC wave group comprising seven full
and uninterrupted waves 1305 is followed by an interruption
equivalent to a duration of two wave lengths 1306 during which the
controller 1204 reduces the power output to zero. Thus out of a
duration of nine consecutive wave lengths, only seven continuous
wave lengths are provided. In preferred embodiments, the top
element uses this scheme 1303 while the scheme 1304 of the bottom
element has eight continuous full power waves 1307 followed
immediately by a one wave length duration interruption in power
1308. Accordingly, the bottom element is producing more true
intermediate power than the top element.
[0079] As suggested by FIG. 13(c) the bottom element in a roasting
mode is supplied with a continuous maximum power wave form 1309. In
this same roasting mode, the wave form of the top element 1310
comprises a wave group of seven continuous AC cycles 1311 followed
by an interval equivalent to three wave lengths of power
interruption 1312. Accordingly, the bottom element can be seen
operating in full power while the top element only receives seven
out of every ten cycles of AC power.
[0080] A typical cooking cycle associated with a bake mode is
illustrated in FIG. 15. As suggested by this graph, the oven's
(actual or inferred cavity) temperature begins at room temperature
1501 and rises evenly until the oven's thermistor detects a
temperature that is equivalent to an oven 72a target oven centre
temperature 1502. In this example, the target temperature 1502 is
210c. During this pre-heating phase 1503 both the upper and lower
elements are on at a true intermediate power. In this example, the
top elements are using 720 W and the bottom elements are consuming
720 W giving a total power draw of 1440 W, for example, provide
gentle heat and to conform to regulatory requirements. When the
measured oven cavity temperature reaches the target temperature
1504 the top and bottom elements cycle on and off together,
providing an average centre temperature, over time that equates to
the target temperature 1502.
[0081] As shown in FIG. 16, a typical toasting cycle begins with
the thermistor measured (inferred) oven cavity temperature being at
room temperature 1601. During toasting, two top elements and two
bottom elements are at full power delivering a total of 1800 W
until this first toast cycle finishes 1602. The duration of the
first toast cycle 1603 is determined by the oven's microprocessor
in a predictive manner taking into account user inputs relating to
the number of pieces of toast (oven load), the initial oven cavity
temperature and the level of colour or darkness selected by the
user. The graph in FIG. 16 also shows the fall in oven cavity
temperature 1604 that occurs when the door is opened and the cooked
toast is removed. In this example, a second toast cycle 1605 is
commenced with an initial over cavity temperature 1606 that is
higher than room temperature. This second cycle also provides 1800
W of cooking power, delivering full power to two top and two bottom
elements. This full power phase of the toast cycle continues until
the oven cavity temperature reaches a pre-established first
threshold that is programmed into the microprocessor. In this
example, the first threshold temperature is 210 C. When this first
threshold is exceeded, the power to the two top and two bottom
elements is reduced to a total power of 1620 W, divided equally
between the top and the bottom elements. The duration of this
second user initiated toasting cycle is determined by the oven's
microprocessor, in a predictive matter, taking into account the
oven's starting temperature, the number of slices requested by the
user (oven load) and the level of darkness or colour requested by
the user. This reduced power phase 1606 continues until the oven
centre temperature reaches a level just short of a second threshold
1607. In this example, the second threshold is 250 C. Just before
the second threshold temperature, the top elements begin to turn on
and off, simultaneously, at a time interval ranging between 5 and
20 seconds so as to keep the oven centre temperature below the
second threshold. In this way, overcooking the toast in a hot oven
is prevented while still providing some degree of radiant energy to
continue the bread toasting or colouration process.
[0082] The graph of FIG. 17 illustrates aspects of the bagel mode.
Cooking bagels in a bagel mode occurs over a time duration 1701
that is determined by the microprocessor, in a predictive manner,
taking into consideration the number of bagel pieces being cooked
(oven load), the initial temperature (initially room temperature)
and the level of colour or darkness requested by the user. The
first bagel cooking phase in the cooking cycle 1702 occurs for
approximately 150 seconds with full power being delivered to two
top elements and two bottom elements. This provides a maximum power
cooking phase delivering 1800 W. At the end of the first phase 1703
(about 150 seconds) the bottom elements are turned off and the top
elements continue cooking at an increased combined power of 1440 W
using a third element. This second phase continues until the end of
the first cycle 1705. The graph of FIG. 17 then illustrates the
drop in oven centre temperature 1706 caused by the opening of the
oven door and the removal of the bagels from within. In this
example, a second bagel toasting cycle begins at a temperature that
is elevated from room temperature 1707. Initiation of the second
cycle causes a phase similar to the first phase of the first cycle
1702, that is, about 150 seconds with the two top and two bottom
elements delivering a total of 1800 W, that is, the top pair and
the bottom pair of elements each delivering 900 W per pair. The
duration of the second bagel toasting cycle is also determined by
the microprocessor, in a predictive manner taking into account the
initial oven centre temperature 1707, the oven load and the
darkness selected by the user. A third bagel toasting cycle is
shown as beginning at an initial temperature 1708 that is higher
again than the starting point for the second toasting cycle.
However, in a bagel mode toasting cycle where the oven centre
temperature reaches a predetermined threshold 1709, the bottom
elements are turned off and the top elements continue cooking at
power of 1440 W using the fifth oven element. Thus, the first phase
1710 of this third cycle is truncated, terminating when the
threshold temperature 1709 is achieved. In this example, the
threshold temperature is 210 C. Where the cooking cycle is long,
for example, when the oven load is high and the darkness setting is
high the three top elements (or two top elements if there are only
two) will cycle from on to off every 5-20 seconds to keep the oven
centre temperature below a second predetermined threshold 1711. In
this example, the second threshold 1711 is 250 C.
[0083] While the present invention has been disclosed with
reference to particular details of construction, these should be
understood as having been provided by way of example and not as
limitations to the scope or spirit of the invention.
* * * * *