Abstract:
A system for wiring a heating element in an electrical appliance to a conventional thermostat switch in a new manner and a new thermostat for supporting the new wiring system. The new wiring system avoids switching the full heating element current for both hot power leads of a split-phase power system to reduce the amount of wiring needed to wire the thermostat switch to a heating element and a pilot lamp showing that current is being provided to the heating element.

Description:
BACKGROUND OF THE INVENTION 
   This application relates to a system for wiring a heating element in an electrical appliance to a thermostat switch in a new manner and a new thermostat switch for supporting the new wiring system. 
   Residential and light commercial cooking appliances often utilize 240 volt split-phase systems, which are a 3-wire, single-phase, mid-point neutral 240 volt power system that is typically provided for residential and light industrial use in the United States. Such a system has two live hot conductors (terminals), and a neutral conductor (terminal). Each live conductor provides a voltage of about 120VAC with respect to the neutral conductor (which is typically grounded), whereas the hot terminals provides a voltage of about 240VAC with respect to each other. Of course, the actual voltages might vary from utility to utility and place to place, such as between 200VAC and 260VAC (100VAC to 130VAC). 
   Heating appliances, and in particular electric stoves, will typically utilize the 240VAC split-phase power in order to reduce the current draw on the home wiring system, and thus avoid the use of overly thick conductors. Thus, such appliances must be connected to both hot terminals of the power supply, utilizing the split-phase system. Modern appliances also tend to include 120VAC components as well, such a light fixtures or control systems, and thus such appliances will also be connected to the neutral terminal of the power supply as well. In such a case, only one of the hot terminals, along with the neutral terminal, need be utilized to provide the 120VAC power. Furthermore, the neutral conductor is often utilized for safety reasons as well. 
   Conventionally, thermostats having connections to both hot terminals of the power supply have been utilized in such heating appliances. Often, an “infinite switch”  10  such as the one shown in a simplified schematic in  FIG. 2  is utilized as a thermostat switch in the manner shown in the wiring diagram of  FIG. 1 , or the additional wiring as shown in  FIG. 3  may be used. The connections to the power supply and the heating element, and SW 1  and SW 2 , must all carry the maximum heating element current, and thus must be sized for substantial current loads. However, such wiring is wasteful, complicated, and utilizes much more wire than might otherwise be necessary for some appliances. Furthermore, the infinite switch  10  is more complicated than it needs to be. 
   Desired is a means of reducing this thermostat complexity, and/or reducing the amount of wasteful and/or complicated wiring. 
   SUMMARY OF THE INVENTION 
   Provided is a system for wiring a heating element in an electrical appliance to a thermostat (infinite) switch in a new manner and/or a new thermostat switch for supporting the new wiring system. 
   This can be provided by a plurality of embodiments of the invention, including, but not limited to, a circuit for controlling an electrical heating element in an appliance. The circuit comprising: a heating element including a first element terminal and a second element terminal; a pilot light including a first pilot terminal and a second pilot terminal; and a thermostat switch. 
   The thermostat switch includes: an element contact electrically connected to the second element terminal; at least one power contact, a pilot contact connected to a first pilot terminal, a sensing device for detecting a temperature of the heating element, an element switch, a pilot switch; a control device, and a sensing device. 
   The element switch is for intermittently electrically connecting and disconnecting one of the at least one power contact to the element contact. 
   The control device is adapted for receiving a temperature setting of a desired temperature of the electrical heating element, wherein the control device controls the element switch based on a temperature detected by the sensing device and also based on the temperature setting, wherein the control device is also adapted for preventing the element switch from making electrical contact between the one of the at least one power contact and the element contact when the control device is set in an off position. 
   The pilot switch is for electrically connecting the one or an additional one of the at least one power contact to the pilot contact when the control device is not in an off position and disconnecting the one or the additional one of the at least one power contact from the pilot contact when the control device is in the off position. 
   The system also includes a split-phase power supply including: a first voltage source electrically connected to the first element terminal bypassing the thermostat switch, a second voltage source electrically connected to the one of the at least one power contact, and a neutral terminal electrically connected to the second pilot terminal. 
   Also provided is a circuit for controlling an electrical heating element in an appliance, with the circuit comprising: a heating element including a first element terminal and a second element terminal; a pilot light including a first pilot terminal and a second pilot terminal; and a thermostat switch. 
   The thermostat switch includes: a first element contact electrically connected to the second element terminal; a second element contact not electrically connected to the first element terminal; a first power contact, a second power contact; a pilot contact connected to a first pilot terminal, a sensing device for detecting a temperature of the heating element; an element switch for intermittently electrically connecting and disconnecting the second power contact to the element contact; a control device, and a pilot switch. 
   The control device is adapted for receiving a temperature setting of a desired temperature of the electrical heating element, wherein the control device controls the element switch based on a temperature detected by the sensing device and also based on the temperature setting, wherein the control device is also adapted for preventing the element switch from making electrical contact between the second power contact and the element contact when the control device is set in an off position. 
   The pilot switch is for electrically connecting the first power contact to the pilot contact when the control device is not in an off position and disconnecting the first power contact from the pilot contact when the control device is in the off position. 
   A split-phase power supply is utilized for the system, with the supply including: a first voltage source electrically connected to the first element terminal utilizing a wire sized to carry a current to power the heating element, wherein the first voltage source is also connected to the second power contact using a wire sized for a current substantially less than the current to power the heating element, a second voltage source electrically connected to the first power contact, and a neutral terminal electrically connected to the second pilot terminal. 
   Still further provided is a method of using a thermostat switch to control the temperature of a heating element, the thermostat switch comprising: a first element contact; at least one power contact, a pilot contact, a sensing device for detecting a temperature of the heating element, an element switch for intermittently electrically connecting and disconnecting one of the at least one power contact to the element contact; a control device adapted for receiving a temperature setting of a desired temperature of the electrical heating element, wherein the control device controls the element switch based on a temperature detected by the sensing device and also based on the temperature setting, wherein the control device is also adapted for preventing the element switch from making electrical contact between the one of the at least one power contact and the element contact when the control device is set in an off position, and a pilot switch for electrically connecting the one or an additional one of the at least one power contact to the pilot contact when the control device is not in an off position and disconnecting the one or the additional one of the at least one power contact from the pilot contact when the control device is in the off position; 
   The method comprises the steps of:
         1) electrically connecting the first element contact to a first element terminal of the heating element;   2) electrically connecting a second element terminal of the heating element to a first voltage source bypassing the thermostat switch;   3) electrically connecting the one of the at least one power contact to a second voltage source;   4) electrically connecting the pilot contact to a first terminal of a pilot light; and   5) electrically connecting a second terminal of the pilot light to a common neutral terminal of the first and second voltage supplies.       

   Also provided are additional embodiments of the invention, some, but not all of which, are described hereinbelow in more detail. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which: 
       FIG. 1  shows a simplified conventional thermostat and heating element wiring scheme; 
       FIG. 2  shows a conventional thermostat for supporting a heating device; 
       FIG. 3  shows another embodiment of the conventional thermostat and heating element wiring scheme; 
       FIG. 4  is a simplified diagram showing possible modifications of the conventional thermostat and heating element wired in a new manner; 
       FIGS. 5A and 5B  are diagrams showing additional embodiments of the conventional thermostat and heating element each wired a in new manner; 
       FIG. 6  shows an embodiment of a infinite switch designed to support the new wiring scheme; 
       FIG. 7  is a diagram showing an embodiment of the infinite switch of  FIG. 6  and a heating element wired in the new manner; 
       FIG. 8  is a diagram showing another embodiment of the infinite switch of  FIG. 6  and a heating element wired in the new manner. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a simplified diagram showing one conventional means of wiring a conventional infinite switch  10  used as a thermostat switch into a heating element circuit, including a heating element E with a first element terminal E 1  and a second element terminal E 2 . The conventional infinite switch  10 , shown in more detail in the simplified schematic of  FIG. 2 , has a first element contact H 1  for electrically connecting to the first element terminal E 1 , and a second element contact H 2  for electrically connecting to the second element terminal E 2 . The infinite switch  10  connects to a split-phase power supply via first supply contact A 1  which is electrically connected to the first hot voltage supply L 1  (at about 120VAC above neutral), and second supply contact A 2  which is electrically connected to the second hot voltage supply L 2  (also at about 120VAC above neutral, but at about 240VAC with respect to L 1 ). 
   The infinite switch  10  also has a pilot contact B 1  for electrically connecting to a pilot lamp P, and a first switch SW 1  for electrically connecting a first pilot terminal P 1  of the pilot lamp P to the first hot voltage supply L 1 , and also for electrically connecting the first element terminal E 1  to the supply L 1 . Note that the second pilot terminal P 2  is electrically connected to the split-phase power supply neutral terminal. A second switch SW 2  intermittently connects the second element terminal E 2  to the second hot voltage supply L 2 . The infinite switch  10  also has a sensing device S 1  for detecting the temperature of the element E, either directly by utilizing the heat put off by the element E, or indirectly by measuring the current flow through the element E in some manner (such as by the combination a heater and a bimetal device, for example). A control device C 1  operates with the sensing device S 1  for providing temperature control, and typically also to turn the element E off (i.e., disconnect the element from the voltage source). First switch SW 1  works in conjunction with second switch SW 2 , the sensing device S 1 , and the control device C 1  to ensure the following:
         1) The temperature of the heating element E is controlled by a setting of the control device C 1 ;   2) The first pilot terminal P 1  and the first element terminal are both electrically connected to the first hot terminal L 1  of the split-phase power supply by the first switch SW 1  whenever the control device C 1  is set to provide a heating temperature for the heating element E (i.e., the control device C 1  (or some other on/off switch) is not set to an off position);   3) The sensing device S 1  works in conjunction with the control device C 1  and the second switch SW 2  to intermittently connect the second element terminal E 2  to the second hot terminal L 2  to maintain a desired temperature of the heating element E by controlling the current flowing through the heating element E (such as by pulse-width-modulating the current, for example); and   4) Both SW 1  and SW 2  are sized to at least carry the maximum current capability of the heating element (e.g., for maximum heating), as are the conductors connecting the thermostat switch to the first and second hot terminals L 1  and L 2 .       

   The manner of operation of such a thermostat switch is known in the art, and need not be specified here in any detail. For example, similar such thermostat switches are discussed in U.S. patent application Ser. No. 10/058,350 and U.S. Pat. Nos. 6,111,231 and 6,093,014, incorporated herein by reference. Additional types of thermostat switches can also be utilized. 
     FIG. 3  is another wiring diagram showing the infinite switch  10  installed in a consumer cooking device, such as a stovetop. The thermostat  10  is shown schematically represented by two portions,  10 A utilizing the first switch SW 1 , and  10 B utilizing the second switch SW 2 . 
   The conventional infinite switch  10  can be used in an improved wiring harness wired in a new manner to save a substantial amount of wire length.  FIG. 4  shows a simplified diagram showing two different options that can be used for an improved wiring scheme. Either (1) a lower gauge wire  15  can be used to connect the first supply contact A 1  to the first hot supply L 1  to power the pilot light, or (2) a jumper  16  can connect the first supply contact A 1  to the second supply contact A 2  to utilize the second hot supply L 2  to power the pilot light. The first option is used where, because of the arrangement and/or installation of the switch, the jumper  16  is not feasible. Note that in no case should both the low gauge wire  15  and jumper  16  be used in the same wiring scheme, as this would short out the power supplies L 1  and L 2 . 
     FIG. 5A  shows another embodiment of how the conventional infinite switch  10  can be utilized in a similar manner as discussed in the first option for  FIG. 3 . This figure illustrates a wiring harness change to eliminate a wiring harness between terminal H 1  on the surface unit switch and terminal  2 A on the element shown in the conventional harness in  FIG. 3 . 
   The wire  15  electrically connecting L 1  to the first switch SW 1  can be reduced in wire gauge size from 14 gauge to 20 gauge because it will only serve the pilot light circuit. 
   An additional jumper is used to connect terminal  2 A of the temperature limit switch (which, in an example embodiment, is part of the element E) to terminal  1 B of the Hot Surface Sense Switch. In the example embodiment, this will add approximately 24 inches of wire to this portion of the harness. The Hot Surface Indicator light will come on whenever the glass surface temperature becomes sufficiently hot to close the contacts in the Hot Surface Sense Switch. This switch is typically physically mounted on the heating element E and can be an integral part of the element itself. 
   The Hot Surface Sense Switch is a type of safety switch whose primary function is to prevent damage to the glass cooktop due to overheating condition. If the surface temperature exceeds the specified level this switch will “open” and interrupt the L 1  power feed to the element thereby turning it off until the surface cools sufficiently to allow the switch contacts to close. 
   The resulting change in the wire harness of the example embodiment will eliminate approximately 141.5 inches of wire as well as four terminal ends that plug onto H 1  at the switch in the example embodiment. After deducting additional length from the L 1  harness to the element E, the net savings will be approximately 117.5 inches of 16 gauge type  33  wire for a four unit surface stove. For example, in the typical configuration there is already an existing L 1  wire on the body of the surface heating element that feeds the “Hot Surface Indicator” circuit. By increasing the gauge of this wire slightly and using it to also provide L 1  power to the element directly one can eliminate the wire and terminal ends from the switch SW 1  to the element E. 
     FIG. 5B  shows another embodiment of how the conventional infinite switch  10  can be utilized in a similar manner as discussed in the second option for  FIG. 3 . The first element terminal E 1  can be electrically connected to the first hot supply terminal L 1  in a manner shown in the diagrams, rather than being switched by the first switch SW 1  of the infinite switch  10 . Thus, the first element contact H 1  need not be utilized in this new wiring scheme. A jumper  16  is used to connect the first supply contact A 1  of the conventional infinite switch  10  to the second supply contact A 2 , which is, as in the conventional wiring, electrically connected to the second hot supply terminal L 2 . Thus, both supply contacts A 1  and A 2  are electrically connected to the same voltage supply source. Finally, the second element contact H 2  and pilot contact B 1  are electrically connected to the infinite switch  10  as in the conventional wiring scheme, except that the pilot contact P 1  is now electrically connected to the second hot supply terminal L 2  via first switch SW 1  (rather than connecting to the other voltage supply L 1 , as in the conventional scheme). Accordingly, in this usage, the first switch SW 1  of the infinite switch no longer has to carry the element current, and need carry only the pilot current. 
   Such an improved wiring scheme of  FIG. 5B  allows the elimination of wires that previously connected the first element contact H 1  with the first element terminal E 1 , as well as an elimination of the wiring that connected the first hot supply L 1  with the first supply contact A 1  of the infinite switch  10 . This option also provides a substantial savings in wire. 
   Such new wiring schemes as described above might also be utilized by conventional thermostats (infinite switches) that have different configurations than that shown in  FIG. 2 . 
   Because the infinite switch  10  utilized in the new wiring schemes of  FIGS. 4 ,  5 A, and  5 B no longer require two external contacts (i.e., A 1  and H 1 ), and because the first switch SW 1  no longer need carry the large maximum heating element current in the new scheme, an improved infinite switch design can be provided to support the new wiring scheme.  FIG. 6  shows such an improved infinite switch  20 , while  FIGS. 7 and 8  show such a switch in diagrams analogous to those in  FIGS. 4 and 5 . Note, however, that the jumper  16  electrically connecting A 1  and A 2  in  FIG. 5B  reflects an externally wired connection for electrically connecting A 1  and A 2  together for infinite switch  10  (and line  15  in  FIG. 5A  is an external wire as well), whereas in  FIG. 8 , the broken line  25  electrically connecting A 3  of  20 A to A 3  of  20 B (or the solid line  25  shown in  FIG. 7 ) merely represents that these are the same connector, or represent an internal jumper, in the new infinite switch  20 . 
   In one embodiment, the improved infinite switch  20  eliminates at least two external contacts. Thus, this infinite switch  20  only requires one element connector H 3  for electrically connecting to the second element terminal E 2 . Only one hot power connector A 3  is provided for electrically connecting to the second hot supply terminal L 2 . The hot power connector A 3  is further electrically connected, typically internally, to both the first switch SW 3  and the second switch SW 4 , and the current carrying capacity of the first switch SW 3  can be reduced compared to the second switch SW 4  (and the conventional infinite switch  10  switches SW 1  and SW 2 ). Only the second switch SW 4  need carry the full maximum heating element current, whereas the fist switch SW 3  need only carry a current sufficient to power the pilot lamp P. A pilot contact B 3  is provided such that the first switch SW 3  connects the pilot contact B 3  to the second hot power terminal L 2  in a manner similar to that discussed for the conventional design (except it is connected to the other voltage source), but now the first switch SW 3  is no longer utilized to connect the heating element E to the any hot terminal. 
   The improved infinite switch  20  has a control device C 2  and a sensing device S 2  that can be similar in operation and/or design to the respective C 1  and S 1  of the conventional design. The infinite switch  20 , however operates in the following unique manner:
         1) The temperature of the heating element E is controlled by a setting of the control device C 2 ;   2) The first pilot terminal P 1  of the pilot light P is electrically connected to the second hot supply terminal L 2  of the split-phase power supply by the first switch SW 3  whenever the control device C 2  is set to provide a current to the heating element E (i.e., the thermostat is not set to an off position); and   3) The sensing device S 2  works in conjunction with the control device C 2  and the second switch SW 4  to intermittently connect the second terminal E 2  of the heating element E to the second hot terminal L 2  to maintain a desired temperature of the heating element E in a manner similar to the conventional thermostat operation (except that the heating element current need not flow through the first switch SW 3 ).       

   Accordingly, the improved infinite switch does not require any contact for electrically connecting to the first hot supply terminal of the split-phase power supply, and it requires only a single element contact to connect to the heating element (and thus two contacts are eliminated from the infinite switch  20 ). Furthermore, the pilot light is now powered off the second hot terminal rather than the first hot terminal. This allows the first switch SW 3  of the infinite switch  20  to carry a lower current, and thus to save on material costs in its design. 
   A three-terminal thermostat switch that is similar to that described above, except that it is not designed to utilize a split-phase system, is found in U.S. Pat. No. 4,968,963, incorporated herein by reference. 
   These improved wiring schemes and thermostat switches are particularly useful for Smooth/Glass top consumer ranges, where the power terminals of the heating elements are not exposed to the consumer. Thermostat switches that sense the heating element temperature using various different means can be utilized, such as switches that indirectly sense temperature (via direct or indirect current measurement), or even direct temperature measurement, could be used. The examples shown herein are for illustrative purposes. 
   The invention has been described hereinabove using specific examples and embodiments; however, it will be understood by those skilled in the art that various alternatives may be used and equivalents may be substituted for elements and/or steps described herein, without deviating from the scope of the invention. Modifications may be necessary to adapt the invention to a particular situation or to particular needs without departing from the scope of the invention. It is intended that the invention not be limited to the particular implementations and embodiments described herein, but that the claims be given their broadest interpretation to cover all embodiments, literal or equivalent, disclosed or not, covered thereby.