CA2149355A1 - Dual-element heater control - Google Patents

Abstract

A controller for a dual-element electrical range burner with a user-adjustable normally closed bimetal blade cycling switch having a resistance heater adjacentthe bimetal and connectable in series with one of the burner elements. In one embodiment, a user-actuated mode control switch sequentially closes a set of normally open contacts for connecting the other burner element to the power line. In a second embodiment, the mode switch has one set of contacts series connected with the heater for the blade and connectable with one of the burner elements. A second set of mode switch contacts is series connected with the cycling switch connectable with the other burner element and bypasses the blade heater. User actuation of the first set of mode switch contacts energizes one burner element and energizes the blade heater for effecting thermal opening of the cycling switch. Upon user actuation of the second set of contacts both burner elements are energized with the first set of contacts remaining closed.
With both burners energized the current flow through only the first burner element controls the cycling switch for regulating both burner elements.

Description

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.

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.

Claims (20)

1. A control system for connecting a dual-element electrical heater to a power source comprising:
(a) a first and a second resistive heating element;
(b) a user operated mode selector switch having a blade member user moveable between an "OFF" position, and a "HIGH" operating position, said selector switch member operative upon user movement to said "HIGH" position to close a set of power contacts for connecting said second heating element to said power source.
(c) normally closed cycling switch means series connected with said first heating element and said second heating element;
(d) thermally responsive means series connected with said first heating element and operative upon current flow therethrough to effect opening of said cycling switch means and breaking of the circuit between said power source and said first and second heating elements.

2. The system defined in claim 1, wherein said cycling switch means has one side thereof series connected with said thermally responsive means and also to said second heating element.

3. The system defined in claim 1, wherein said thermally responsive means includes a bimetal blade for said cycling switch means and a heater disposed adjacent thereto, said heater series connected to said first heating element.

4. The system defined in claim 1, wherein said thermally responsive means includes an active bimetal blade and a temperature compensating blade for said cycling switch means.

5. The system defined in claim 1, wherein said cycling switch is infinitely variable.

6. The system defined in claim 1, wherein said mode selector switch has a second set of contacts series connected with said first heating element.

7. The system defined in claim 1, wherein said mode selector switch has a second set of contacts series connected with said first heating element, said second set of contacts being subsequently closed after closure of said power contacts.

8. A method of controlling the temperature of a dual-element electrical heater comprising:
(a) series connecting a user actuable selector switch with one of said elements;
(b) providing a normally closed user variable cycling switch having a thermally responsive blade with a moveable contact thereon;
(c) disposing a blade heater proximate said blade and series connecting said heater with one of said dual-elements;
(d) series connecting said moveable contact with the other of said dual-elements; and, (e) connecting said switches to a source of power.

9. The method defined in claim 8, wherein said step of disposing includes disposing a strip of resistance material adjacent said blade.

10. The method defined in claim 8, wherein said step of providing a cycling switch includes providing a temperature compensated blade member.

11. The method defined in claim 8, wherein the step of series connecting a selector switch includes series connecting a switch with both of said dual elements.

12. A controller for a dual-element electrical range burner comprising:
(a) a user-actuated normally open mode selector switch having a first and second set of sequentially actuatable electrical contacts;
(b) a normally closed cycling switch including a thermally responsive member having a moveable electrical contact thereon and a user adjustable stationary electrical contact;
(c) heating means operable upon electrical energization to effect opening of said cycling switch contacts, said heating means adapted for series connection with one of said range burner elements and said first set of mode switch contacts, wherein upon connection of said mode switch and said cycling switch to a power source and user actuation of said mode switch to close said first set of contacts, one of said heating elements is energized to open said cycling switch and upon subsequent cooling of said heating element said cycling switch recloses; and, (d) said second set contacts is adapted for series connecting the other of said burner dual-elements with said moveable contact on said cycling switch such that upon said user sequential actuation of said second set of contacts current flows through both of said dual-elements.

13. The controller defined in claim 12, wherein said cycling switch moveable member includes a bimetal blade having said moveable contact thereon.

14. The controller defined in claim 12, wherein said cycling switch moveable member includes a bimetal blade; and, said heating means includes a heater strip adjacent to said blade.

15. The controller defined in claim 12, wherein said control switch is cam actuated.

16. The controller defined in claim 12, wherein said cycling switch is infinitely variable.

17. A controller for regulating a dual element heating unit comprising:
(a) a normally closed cycling switch having a user adjustable stationary contact blade and a thermally responsive moveable contact blade, said stationary blade adapted for connection to one side of a power line, said moveable contact blade adapted for connection to one side of one of said heating elements;
(b) a blade heater disposed to heat said moveable blade member and having one side thereof connected to said moveable contact blade and the other side adapted for connection to one side of the other of said heating elements; and, (c) a user-actuated normally open mode switch having a moveable contact blade adapted for connection to the opposite side of a power line from said cycling switch, and a stationary contact adapted for connection to the other side of said one heating element from said cycling switch wherein said blade heater is upon the aforesaid connection, electrically series connected to said one of said dual elements.

18. The controller defined in claim 17, wherein said cycling switch is infinitely variable by the user.

19. The controller defined in claim 17, wherein said cycling switch includes a rotatable cam for user adjustment

20. The controller defined in claim 17, wherein said mode selector switch is actuated by user movement of a cam.