Note: Descriptions are shown in the official language in which they were submitted.
214 9 3 ~ 5 94-CON-013 (AP)
DUAL-ELEMENT HEATER CONTROL
BACKGROUND OF THE INVENTION
The present invention relates to systems for controlling electrical current to
resistance-type heating elements. The invention relates in particular to
controlling electrical current to heating elements employed in cooking appliances
5 as for example range top heaters or burners as they are often called. Typically
in such systems, a thermostatically responsive switch is em~oloyed to cycle
current to the heating element to prevent overheating and control the element
by regulation about the desired temperature for cooking.
Heretofore in range top applications, a separate cycling switch has been
10 required to control current for each heating element. This has resulted in
increased cost for dual-element burners which have become popular by virtue of
the wider range of sizes and content of cooking receptacles which may be
disposed upon the burner for cooking.
Where dual-elements have been employed for plural heat ranges of a single
15 burner location, parallel switching has been used for each of the heating
elements .
Parallel switching arrangements require a high resistance to be employed
for the thermal element, or heater, controlling the cycling switch because it isexposed to line voltage. Where a coil has been employed for the cycling switch
20 thermal element, the high resistance requirement has necessitated a very fineresistance wire for the coil; and, the fine wire has proven difficult to handle in
production and is prone to breakage and failure in service. In the event the
cycling switch thermal element coil breaks, the normally closed cycling switch
cannot be opened; and, if it is the only switch controlling one of the heating
25 elements, in such event, power cannot be cut off to the heating element.
Thus, it has been desired to provide a low cost, simple and reliable way of
controlling the current and heating of a dual-element electrical range top burner
and which presents no undue hazards.
2 21 ~ 9 3 ~ ~ 94-CON-013 (APJ
With reference to FIG. 3, a known single element range top burner system
is illustrated at 10 as having a user settable thermostatically operated infinitely
variable cycling switch indicated generally at 12 having a bimetal blade 14
which has a moveable contact 16 provided on the end thereof which is operable
to close against a stationary contact 18 connected to one side of a power line.
User adjustment of "Set" temperature, or temperature about which the thermally
responsive switch regulates is accomplished by user rotation of cam 32 for
varying the distance between contact 16,18, thus changing the temperature at
which the bimetal arm 14 opens switch 16. Moveable contac~ 16 is connected
through a heater 20 to one side of the "burner" heating element. The opposite
side of the "burner" heating element is connected to a stationary contact 22 of
a user-actuated selector switch indicated generally at 24. Switch 24 has a
moveable contact 26 on a blade arm 28 which is actuated by a user rotated
cam 30. Blade arm 28 is connected to the opposite side of the power line.
Upon user actuation of switch 24 closing contacts 26,22 power flows to
normally clGsed thermally responsive switch 12 (shown in the actuated or open
position) thus providing current to the element 21. Upon heating of the heater
20, switch 12 is opened thus breaking current flow to element 21. Upon
cooling of heater coil 20, switch 12 closes and repeats the cycle.
Referring to FIG. 4, a known dual-element range top "burner" system
utilizing parallel switching is illustrated at 34 as having an inner and outer
"burner" heating elements 36,38 controlled or regulated by a normally closed
thermostatic cycling switch 40. Switch 40 has the active or moveable blade
thereof denoted at 42 as formed of bimetal material which is heated by a
conductive heater 44 typically comprising a resistance wire coiled about the
bimetal blade 42 and having one end connected to the moveable contact 46 on
the end of the arm 42. The other side of heater coil 44 is connected to power
line L1. Contact 46 is also connected to connector terminal H2 which connects
to one side of the outer "burner" element 38. One side of the inner "burner"
element 36 is connected to connector terminal H2 and contact 46; whereas, the
other side of inner element 36 is connected to the side L1 of the power line.
- 3 ~ 119 3 5 ~ 94-CON-013 (AP)
Switch 40 is user-adjustable by rotation of cam 39 which varies the position of
the stationary contact 41 and thus the temperature of the "burner" element at
which the switch 40 opens.
A normally open user operated range or mode selector switch indicated
generally at 48 has a moveable blade 47 with a contact 49 mounted on the end
thereof disposed opposite the stationary contact 45. User rotation of the cam
43 is operative to move arm 47 to close contact 49 against contact 45 for
selecting as between the inner element and both elements. In operation, with
switch 4Ct in the normally closed position, closure of switch 48 by user rotation
of cam 43 causes current to flow through both "burner" elements 36,38 and
heater 44 which upon heating bimetal 42 opens switch 40 to cut off current to
the elements 36,38 and heater 44. With switch 48 in the open position and
switch 40 closed, current flows through heater 44 and element 36 only until the
heater heats the bimetal 42 and opens switch 40. The aforementioned prior art
device has the disadvantage that one of the dual "burner" heating elements
remains connected to the power line when the range or mode selector switch
48 is in the open or "OFF" position and relies solely on the cycling switch for
power shutoff. An open circuit failure of the heater 44, particularly where it is a
fine wire resistance coil heater, results in switch 40 going to the closed position;
and, power cannot be cut off to the "burner" heating element 36.
SUMMARY OF THE INVENTION
It is an object of the invention to control by regulation dual electric heating
elements or 'iburners" for cooking with a single thermostatic variable cycling
switch for regulation and a single user operated range or mode selector switch
for selecting operation of only one or both of the heating elements.
It is a further object of the invention to provide for control of such dual
heating elements with a single thermostatically operated variable cycling switchwith the cycling switch thermal element series connected to one of the heating
elements and a single range or mode selector switch.
214935S 94 CoN-o13(Ap)
It is another object of the invention to provide for control of dual heating
elements or "burners", for cooking with a single thermostatically operated
variable cycling switch having its thermal element series connected with one of
the "burner" heating elements and having the other heating element connected
5 through a single mode selector switch.
It is another object of the invention to provide for control of dual heating
elements or "burners" for cooking with a single thermostatically operated
variable cycling switch having its thermal element series connected with one of
the "burner" heating elements and a single mode selector switch having an
10 electrically separate set of switching contacts for switching power individually
to each of the dual "burner" elements.
~ 1 g 9 3 ~ ~ 94-coN-o13 (AP)
The present invention provides control of current to a dual-element heater
or "burner" of the type employed on a range top for cooking. The system of the
present invention employs a single thermally responsive infinitely variable setting
cycling switch for maintaining the selected temperature of the heating elements
5 for cooking. The system of the present invention utilizes a cycling switch
having a bimetal blade with a resistance heater preferably a strip of resistive
material for the blade which is series connected with one of the range top or
"burner" heating elements. The second range top heating element or "burner" is
connected through the moveable contact of the cycling switch but bypasses the
10 biade heater. In one embodiment a single user-actuated mode or range selectorswitch has "HIGH" and "LOW" operating positions for sequentially closing
separate sets of electrical contacts for selecting one or both heating elements
for cooking and an "OFF" or open position in which both sets of contacts are
open cutting off power to both range top elements.
In another lower cost embodiment the range mode selector switch utilizes a
single set of contacts to control only one of the dual "burner" heating elements,
with the other "burner" heating element controlled solely by the thermostatic
cycling switch.
Preferably the cycling switch has an ambient compensated bimetal for the
20 opposite blade of the switch. The present control system thus provides control
of dual range top heating elements with a single thermostatic infinitely variable
cycling switch, which has its thermally responsive element series connected
with one of the range top elements.
The series connection of the heater for the thermally responsive cycling
25 switch with one of the "burner" or range top heating elements allows the
cycling switch heater to be a very low resistance device, and thus more robust
than the cycling switch heaters of the prior art. This robustness of the cyclingswitch heater improves the service life and provides a heater less prone to
failure. This improved service life of the cycling switch heater raises the
30 reliability of dual range top element control systems employing parallel switching
with only one range top heating element switched by the separate mode
- 6 - ~ 1 4 9 ~ 5 ~ 94-CON-013 (AP)
selector switch, yet provides a system which achieves the manufacturing
economies of a range selector switch having only one set of contacts.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of one embodiment of the dual-element range top
5 heating element control system of the present invention utilizing a mode selector
switch having a set of contacts for individually switching power to each heatingelement;
FIG. 2 is a similar sGhematic of another embodiment of the invention
employing parallel switching with the mode selector switch controlling power to
10 only one of the dual range top heating elements;
FIG. 3 is a schematic of the prior art systems for single element heater
control; and,
FIG. 4 is a schematic of the prior art systems utilizing parallel switching for
dual element range top "burner" control.
15 DETAILED DESCRIPTION
Referring to FIG. 1, the control system of the present invention is shown
and has a controller indicated within the dashed outline by reference numeral 50and includes a power line connector L2 which is connected to an electrical
contact 52 attached to one end ol a blade arm 54 with the other end spring
20 suspended. The contact arm 54 in the present practice of invention is formed
of bimetal material to provide ambient temperature compensation for an active
bimetal as will hereinafter be described. The position of contact 52 is infinitely
adjustable by user rotation of an adjustment cam 53, which contacts a cam
follower 55 formed on blade arm 54. When cam 53 is rotated to the position
25 shown in dashed outline in FIG. 1, blade 54 is in the position shown in dashed
outline, which is the open or "OFF" position.
A second switch blade arm 56 formed of bimetal material is disposed in
generally spaced parallel arrangement with the blade arm 54. Blade arm 56 has
one end anchored to the base of controller 50 and has an electrical contact 58
-
-7- 21~9355 94-CON-013(AP)
disposed on the free end thereof directly opposite the contact 52 on blade arm
54. The arrangement of the blade arm 54 with contact 52 and blade arm 56
and contact 58 form a switch indicated generally at 60 which is a normally
closed switch with the moveable or cycling blade arm 56 in the position as
5 shown in dashed outline in FIG. 1 and shown in solid outline in the actuated or
open position. The contact 58 is connected to one end of an electric heating
strip formed typically of resistance material such as nickel-chromium or nickel-copper and which is disposed adjacent blade 56 on the surface of the blade
using techniques known in the art and which is denoted by reference numeral
62 in FIG. 1. In the presently preferred practice, heater strip 62 is formed of
material selected from the group consisting of 80% Ni--20% Cr, 45% Ni--
55/cCu, 22% Ni--78%Cu or 23% Ni--77%Cu; however, it will be understood
that other suitable resistive materials may be used. In the present practice of
the invention the strip heater is a low resistance device formed of material
having a resistance in the range 135-910 ohms per foot for typical range top
l1eating elements. A!ternatively, the strip 62 may be replaced by a coil of
resistance wire wrapped around or adjacent to blade arm 56.
The opposite end of heater 62 is connected to external connector terminal
H2 of the controller. The contact 58 on the end of blade arm 56 is also
connected via lead 64 directly to another external connector terminal H2A.
Referring to FIG. 1, another external power line connector terminal L1 is
adapted for connection to the opposite side of a power line as for example 240
Volts AC as is typical for household range power. The connector terminal L1 is
connected to one end of a switch blade arm 66 which forms a part of a
normally open user-actuated control or range or mode selector switch assembly
indicated generally at 68. The arm 66 has a cam follower 70 formed therein
with a moveable electrical contact 72 provided on the free end thereof. The
contact 72 is disposed directly opposite a stationary electrical contact 74 which
is connected to an external connector terminal H1A.
Switch 68, which is a normally open switch as shown in solid outline in
FIG. 1, has an auxiliary or secondary contact 76 provided thereon intermediate
-8- 2149355 94-CON-013(AP)
the stationary end of the blade 66 and the cam follower 70; and, contact 76 is
movably disposed directly opposite a second stationary electrical contact 78
which is connected to external connecting terminal H1. A user-actuated rotary
cam 80 is disposed adjacent the switch cam follower 70 such that upon rotation
of the cam 80 a first cam lobe 82 contacts follower 70 and moves the blade
arm 66 sufficiently to cause contact 76 to close against contact 78. Upon
further rotation of the cam 80 by the appliance user, a second cam lobe 84
contacts follower 70 and moves the blade 66 further in a downward direction to
the position shown in dashed outline in FIG. 1 whereupon contact 72 is closed
against the stationary contact 74. The switch cam 80 is typically connected to
a user control knob (not shown) and serves as a selector switch enabling the
user to select the desired mode of operation as will hereinafter be described.
With reference to FIG. 1, connector terminal H2A is illustrated as
connected to a first range heating element 86 with the opposite side of the
element 86 connected to connector terminal H1A. A second heating element
88 is disposed typically adjacent and sometimes concentrically with the element
86; and, element 88 has one side connected to connector terminal H2 and the
opposite side of the element 88 connected to connector terminal H1. It will be
understood that the electrical leads for interconnecting the elements 88,86 to
the controller 50 are provided external to the controller 50 and disposed withinthe cooking appliance as desired by the appliance manufacturer. Typically,
controller 50 is located remotely from the elements 88,86 which form a single
range top "burner" location indicated generally at 90; and, the controller 50 may
be located on a control console provided on the cooking appliance.
If desired, an optional contact 92 may be provided for making contact with
the blade 66 which contact 92 is connected to an indicator lamp 94 for
indicating the state of actuation of the switch 68.
In operation, with the controller 50 connected to power lines at L1 and L2,
upon the user rotating cam 53 to the position shown in solid outline positioningcontact 52 to the position shown in solid outline (for the N.C. condition of
switch 60) and upon user actuation of the cam 80 to a first position for a
9- 21~935~ 94-coN-o13(Ap)
"LOW" level selected mode of operation, switch contact 76 is closed against
contact 78; and, with the switch 60 in its normally closed position, current
flows through heater strip 62 and heating element 88 of "burner" 90. When the
heating element 88 has reached a desired temperature, the current flow through
heater strip 62 has caused sufficient heating of bimetal blade 56 to move the
blade to the position shown in solid outline so as to open switch 60. Upon
cooling of strip 62 and blade 56, switch 60 is again closed and the cycle
repeated to thereby provide temperature regulation of heating element 88. It
will be understood that cam 53 is connected to an unshown temperature control
selector knob which is calibrated to position contact 52 in the appropriate
position for causing switch 60 to open at the temperature selected by the
positioning of cam 53. If desired cam 53 and cam 80 may be mounted on an
unknown common user rotated knob or shaft.
Upon the user rotating cam 80 to a second position for "HIGH" level
selected mode of operation cam lobe 84 contacts the follower 70 and closes
contact 72 against contact 74; and, current is caused to flcw through the outer
heating element 86 of "burner" 90. It will be understood that with the cam lobe
84 in a position to cause cam follower 70 to close contact 72 against contact
74 that closure of contact 76 against contact 78 is maintained; and, current
continues to flow through the heating element 88 thus giving the additional
heating effect of both elements 86 and 88. It will be understood that one of theadvantages of the present controller is in the arrangement of the connection of
the outer burner heating element 86 with contact 58 such that the current flow
through element 86 does not significantly affect the bimetal blade 56.
The cycling of switch 60, caused by the heating of bimetal element 56, is
thus due to the current flow through burner element 88 only, yet switch 60
serves as an infinitely variable thermostatic cycling control switch for both
heating elements 88 and 86.
Referring to FIG. 2, another embodiment of the invention is in~icated at
100 and employs a dual element range top cooking unit or "burner" indicated
generally at 102 which has an inner heating element 104 and an outer heating
- 10 - ~14 9 3 ~ ~ 94-CON-013 (AP)
element 106 disposed adjacent thereto and sometimes concentrically therewith.
Inner element 104 has one side thereof connected to junction 108 which is
connected to side L1 of a power line; and, the other side of element 104 is
connected to terminal H2 which is connected to one side of a thermal element
or heater strip 1 10 provided adjacent the moveable contact blade 1 12 of a
thermally responsive cycling switch indicated generally at 114. Contact blade
arm 112 has a contact 116 attached to the end thereof which is disposed
directly opposite the corresponding stationary contact 118 disposed on a
stationary contact blade 120 of the switch 1 14. The heater 1 10 has its
opposite end connected to the end of contact blade 112 which is formed of
bimetal material. The end of blade l 12 is also connected directly through lead
122 to connector terminal H2A which is adapted for connection to one side of
the outer heating element 106. A user rotatable adjustment cam 124 is
provided for adjusting the position of the stationary contact 118 by movement
1 5 of the blade 1 20.
Outer heating element 106 has its opposite side connected through lead
126 to connector terminal H1 A which is connected to a stationary contact 128
of a range or mode selection switch indicated generally at 130. Switch 130 has
a moveable contact blade 132 having a moveable contact 134 attached to the
- 20 end thereof and disposed directly opposite contact 128 for closure thereagainst
upon actuation of the switch 130. The opposite end of moveable blade arm
132 is connected to the side L1 of the power line through lead 136 and junction
108. Switch 130 is user-actuated by rotation of a cam 138 which contact a
cam follower provided on moveable blade arm 132. If desired a separate
stationary contact 140 may be provided for switch 130 for connection through
terminal P and lead 142 to an indicator lamp 144 for indicating the condition ofswitch 130.
In operation, the cam 124 is initially in the position shown in dashed outline
in FIG. 2 with blade 120 moved to the position shown in dashed outline such
that contact 1 18 is spaced from contact 1 16 thereby cutting off power to
burner element 104 and element 102. Upon user rotation of cam 124 to a
11 ~1 9 9 3 ~ 5 94-CON-013 (AP)
desired selected temperature setting as indicated in solid outline in FIG. 2, blade
120 is moved to a position causing contact 118 to close against contact 116
plus placing switch 114 in its normally closed condition.
Closure of switch 1 14 causes current to flow through element 104 and
heater strip 1 10. As strip 1 10 heats the bimetal arm 1 12 at the desired
temperature of burner 104, bimetal blade 1 12 is operative to open switch 1 14
cutting off power to the burner and heater 1 10. As heater 1 10 and blade 1 12
cool, switch 114 returns to its normally closed condition re-energizing the
burner element 104 and strip 110 and thus repeating the cycle. If the user
desires additional heating of burner ï02, switch cam 138 is rotated to the
position shown in dashed outline FIG. 2 which position effects closing of switch130 and energization of burner element 106 which is then subsequently also
cycled by switch 114. It will be understood that the embodiment of FIG. 2
nrovides for a lower cost system inasmuch as switch 130 requires only a single
set of contacts and eliminates the additional wiring associated therewith for
controlling the inner heating element. The embodiment of FIG. 2 thus relies
upon the thermally responsive cycling switch 114 to control power to inner
heating element 104; however, the series arrangement of heater 110 permits
the heater to be a low resistance device and thus more robust and provides
greater reliability to the cycling switch 1 14.
The present invention thus provides for a reliable and economical controller
for a range top "burner" having dual heating elements such that one or both
heating elements may be employed for cooking as desired by the user. The
heating elements controlled by a single thermostatically operated infinitely
variable cycling control switch 60 having the thermal element series connected
to one of the range top heating elements which permits the thermal element to
be a low resistance robust element for improved reliability and service life. The
present invention utilizes a single range or mode selector switch which in one
embodiment has two sets of contacts, one set for controlling each heating
element to insure that power to both elements can be cut off by the user
separately and independently of the cycling switch. In another embodiment
-12- ~1~935~; 94-CON-013(APJ
parallel switching is employed utilizing a lower cost singie contact set for themode selector switch which controls power to one of the range top elements;
and, the cycling switch employs a series connected strip for the thermally
responsive element which provides a robust low resistance heater for improved
5 reliability of the cycling switch.
Although the invention has hereinabove been described with respect to the
illustrated embodiment, it will be understood that the invention is capable of
modification and variation and is limited only by the following claims.
