US2720623A - Thermoelectric generators - Google Patents

Description

United States Patent Office Patented Dot. 1!, 1955 THERMOELECTRIC GENERATORS Paul L. Betz, Baltimore, Md., assignor to Baltimore Gas and Electric Company, a corporation of Maryland Application December 9, 1952, Serial No. 324,989 Claims. (c1. 322-2 This invention relates to thermoelectric generators suitable for use with safety or other devices for controlling fuelburners, and one aspect thereof is directed particularly to improvements in such generators which decrease the time required for operation of the associated device following extinction of the flame which activates the generator. The present invention has useful characteristics in other respects than rapid decrease in electrical output upon cooling, and is therefore adapted to other applications than those involving the direct control of fuel burners.

By way of example, thermoelectric generators and their associated safety devices for gas burners of the character heretofore commercially available are, in general, restricted to use in installations where reasonably prompt operation of the safety device is acceptable following extinction of the flame applied to the thermoelectric generator. With these devices, operation usually occurs in about 50 to 60 seconds after flame failure; and in many appliances, such as Water heaters and residential heating furnaces, as well as in some commercial applications, a time delay of this magnitude between flame failure and safety operation is not objectionable. However, there are many commercial types of gas burning apparatus, and certain domestic installations, to which thermoelectric safety devices have not been applied because of the need for faster operation than is obtainable with such devices as previously developed.

It is therefore one of the principal objects of the present invention to provide improved forms of thermoelectric generators which are capable of effecting more rapid operation of the associated thermoelectrically controlled devices following interruption of heating than can be achieved by use of the thermoelectric generators .of the prior art.

in conventional safety control systems for gas burners, a thermoelectric generator, such as a thermocouple,.may be positioned closely adjacent to a pilot burner that is associated with a burner to be controlled so that the hot junction of the thermocouple is subjected to the heat of the pilot flame, and its cold junctions are connected to the energizing winding of an electromagnetic safety device which, when energized by the thermoelectric current produced by the generator, holds an armature in attracted position. The armature is connected to a valve or other control mechanism which is thereby maintained in running position to permit the flow of gas to the controlled burner. In such an installation, When the pilot flame is extinguished, the hot junction of the thermoelectric generator cools by radiation, conduction and natural convection, augmented, in some instances, by .the cooling effect of the stream of unignited gas flowing from the pilot burner. Cooling of the hot junction results in a gradual, although relatively rapid, reduction in the output voltage of the generator and a consequent reduction in the thermoelectric current supplied to the winding of the electromagnetic safety device. When the output current reaches a predetermined, relatively low value, the electromagnet releases the armature of the safety device and permits the latter and its associated control mechanism to move to safety position and cut off the flow of gas to the controlled burner. As indicated above, when using thermoelectric generators of the character heretofore available, a period of approximately 50 to 60 seconds elapses between failure of the pilot 'flame and operation of the safety device. Other conventional arrangements include those in which the thermoelectric generator is heated by the flame at the burner controlled by the safety device, and those in which the flow of gas to the pilot burner as well as to the controlled burner is interrupted by the safety device upon cooling of the generator.

The improved thermoelectric generators of the present invention are characterized by the inclusion of elements having thermoexpansive or thermostatic characteristics which are employed to decrease or interrupt the output thermoelectric current of the generator and thereby effect deenergization of the control or other device more rapidly than would result from the decrease in thermoelectric current due to normal cooling of the hot junction of the generator.

The improved thermoelectric generators of the present invention may also be arranged so that the thermoexpansive or thermostatic elements will decrease or interrupt the output thermoelectric current of the generator upon heating of the thermostat above a predetermined value, in contrast with the use in which the output current is decreased or interrupted upon cooling of the generator thermostat. This arrangement is hence one in which an upper limit control action is provided. In other applications of the invention the desired characteri'stic'may be the switching action by which the generator may be disconnected from associated circuits when the temperature of the thermostat of the generator is either above or below. a predetermined value depending on the arrangement of the thermoexpansive or thermostatic elements.

One of the main objects of the invention is therefore to provide a-novel form of thermoelectric generator which includes thermoresponsive or thermostatic means formodifying the output of thermoelectric current from the generator.

A further object is to provide an improved control system'for fuel burners which includes both a thermoelectric generator subject to the heat produced by the flame of a main or pilot burner for supplying current to an electromagnetic control device and a thermostat also directly subject to the heat from the burner associatedwith the thermoelectric generator for controlling the flow of thermoelectric current from the generator to the control device.

.Another object is toprovide a thermoelectric generator ofnovel, unitary construction in which is incorporated thermostatic means for very quickly reducing the output current of the generator upon extinction of the flame or other source of heat by which it is heated or upon heating of the generator beyond a predetermined temperature.

Stillanother object of the present invention is to employ, in combination with a thermoelectric generator, a thermoresponsive or thermostatic means adapted 'to promptly decrease the effective thermoelectric current output upon discontinuance of heating of said generator and means, which combination also provides the less rapid normal decrease in thermoelectric current output from the generator in the event that the thermoresponsive or thermostatic means becomes inoperative.

These and other objects, including the provision of a quick-acting thermoelectric generator of simple construction embodying commercially available thermoelectric and thermostatic elements, will appear more fully upon consideration of the following detailed description of the several diiferent embodiments of the invention which have been illustrated in the accompanying drawing. It is to be expressly understood, however, that this drawing is exemplary only and is not to be construed as defining the limits of the invention, for which latter purpose reference should be had to the appended claims.

In the drawing, wherein like reference characters indicate like parts throughout the several views:

Fig. 1 is a schematic representation of one form of improved thermoelectric generator embodying the invention wherein a thermostat of conventional form is connected in parallel with the output circuit of a conventional open type thermocouple, the generator being applied to a control system for fuel burners;

Fig. 2 is a similar schematic illustration of a modification of the arrangement shown in Fig. 1 wherein the thermostat is connected in series with the thermocouple output circuit;

Fig. 3 is a longitudinal sectional view of a closed type thermoelectric generator with built-in thermostat constructed in accordance with the present invention, certain of the parts thereof being shown in full and the associated burner and control device being illustrated diagrammatically;

Fig. 4 is a sectional view similar to Fig. 3 showing a modified form of closed type generator wherein the thermostatically controlled contacts are in series, instead of in parallel, with the thermocouple output circuit;

Fig. 5 is a schematic view of the generator portion of a system similar to that illustrated in Fig. 1 embodying a thermopile, instead of a thermocouple, as the generator; and

Fig. 6 is a schematic view similar to Fig. 5 of a series arrangement of thermopile and thermostat comparable to the system of Fig. 2.

In each figure of the drawing, the thermostatically actuated contacts are shown in the position occupied when the control system is in its normal running condition with the burner flame fully ignited and heating the thermoelectric generator and the thermostat in normal manner.

Referring now to Fig. 1, there is shown therein a thermoelectric generator 12 positioned closely adjacent to a fuel burner 11 so as to be subject to the heat produced by the flame thereof and an electromagnetic control device 13 having a magnetizable core 14, an energizing winding 15 adapted to receive thermoelectric current from the generator 12 through output leads 16 and 17, and an armature 18 to which is connected an operating member 19. Operating member 19 serves in known manner to move an associated control mechanism, such as a valve (not shown), to a released position when winding 15 is deenergized, whereby one of the following actions may be accomplished: (a) flow of fuel is discontinued to burner 11, in which case burner 11 is the main burner; (b) flow of fuel is discontinued to a main burner (not shown) but continued to pilot burner 11; (c) flow of fuel is discontinued to a main burner (not shown) and also to pilot burner 11, this action being commonly known as 100 percent shutoff. In the embodiment illustrated, the thermoelectric generator 12 consists of an open type thermocouple having thermoelements 20 and 21 connected together at one end to form a hot junction 22, the opposite ends of the thermoelements forming the cold junctions 23 and 24, respectively. Cold junctions 23 and 24 are also referred to herein as output terminals and are connected to output leads 16 and 17, respectively. Thermoelements 2t) and 21 may be made of any suitable conductive metals having dissimilar thermoelectric properties, such as 18-8 stainless steel and constantan or Copel, while the electromagnetic control device 13 and the associated control mechanism may conform to any of the various constructions now known to the art.

As thus far described, the arrangement of Fig. 1 is conventional and operates in known manner. As previously pointed out, it usually takes about 50 seconds or more after extinction of the flame from burner 11 for the ordinary thermocouple to cool sufliciently to effect operation of the control device. In order to reduce this time interval, commonly referred to as the dropout time, the present invention combines with the above described conventional type of control system thermoresponsive or thermostatically operated means for deenergizing the electromagnet winding of the control device more rapidly than would result from normal cooling of the hot junction of the thermocouple following flame failure.

In the embodiment illustrated in Fig. l, a thermostat indicated schematically at 25 is connected in parallel with the output terminals 23 and 24 of thermocouple 12 and is positioned closely adjacent burner 11 so that the thermoresponsive element of the thermostat is subject directly to the heat of the burner flame. For purposes of illustration, thermostat 25 may comprise a fixed contact arm 26 and a movable, bimetallic contact arm 27 carrying contacts 28 and 29, respectively, which are closed when the thermostat is cold, bimetallic arm 27 being so positioned with respect to burner 11 and fixed contact arm 26 that, when heated by the normal burner flame, the bimetallic arm assumes a position in which the movable contact 29 is separated from fixed contact 28. Contacts 28 and 29 are connected to the thermocouple output leads 16 and 17, respectively, through the arms 26 and 27 and conductors 30 and 31.

Thermostat 25 is of the quick-acting type and is so designed or adjusted that it effects closure of contacts 28, 29 promptly after extinction of the burner flame and before release of armature 18 with normal cooling of hot junction 22. When contacts 28, 29 are closed, a portion of the thermoelectric current generated by thermocouple 12 is shunted through the circuit comprising conductors 3t 31, contact arms 26, 27 and contacts 28, 29, thereby reducing the current flowing through output leads 16, 17 to the winding 15 of control device 13 due to the inherent voltage regulation of thermocouple 20. The electrical characteristics of the two circuits are so selected that the decrease in current flow through winding 15 upon closure of contacts 28, 29 is suflicient to eflfect release of armature 18 and permit the release of operating member 19. Provision of the shunt circuit thus materially shortens the dropout time for control device 13 as compared with operation of the conventional system. When the burner 11 is reignited, thermostat 25 operates to open contacts 28, 29 to permit the thermoelectric current generated by thermocouple 12 to build up to a value at which the winding 15 of control device 13 is sufliciently energized to maintain armature 13 in its attracted, running position.

The system illustrated in Fig. 2 is identical with that of Fig. 1 except that the contacts 28, 29 of thermostat 25' are connected in series, rather than in parallel, with the output circuit of thermocouple 12, and the arms 26, 27 of the thermostat are so constructed and arranged that the contacts 28', 29 are closed, rather than open, when the thermostat is heated normally by the flame of burner 11. With this arrangement, extinction of the burner flame results in the prompt opening of thermostat contacts 28, 29' which thereby interrupts the flow of thermoelectric current from thermocouple 12 to the winding 15 of control device 13 long before the hot junction 22 of the thermocouple has cooled sufliciently to effect release of armature 18 in the conventional manner.

The thermoelectric generator illustrated in Figs. 1 and 2 is of the open type in which both thermoelements are exposed to the action of combustion products from the burner flame at the hot junction. In many instances, such exposure may shorten the life of one of the thermocouple elements more rapidly than the other, in which Case it is desirable to protect the more susceptible thermoelement'. The closed type of structure illustrated in Figs. 3 and 4 has therefore been provided to protect the more susceptible thermoelement from exposure to combustion products by enclosing it within a hollow thermoelement made from the material that isthe more resistant of the two to the action of such products. These structures are also characterized by the incorporation of builtin thermostatic means for controlling the thermoelectric current output in the same manner as that accomplished by the arrangements of Figs. 1 and 2.

As shown in Fig. 3, an elongated thermoelement 32 made ofa material to be protected from exposure to the action of combustion products, suchas constantan or Copel, is enclosed within a hollow thermoelement 33 of a difierent, more resistant material, such as 18-8 stainless steel. The hot junction between the two thermoelements may be formed by a plug 34 of preferably, although not necessarily, the same material as, and closing the upper end of, hollow element 33. The junction between the upper end of thermoelement 32 and plug 34 may be made by welding the two members together in any suitable manner. Plug 34 may be also fixed to hollow thermoelement 33 by welding, as indicated at 33'.

Fixed to the lower open end of hollow element 33, as

by brazing, is a conductive sleeve 35 which serves as one of the output leads of the thermoelectric generator. The lower end of sleeve 35 is connected, also by brazing, to a tubular lead member 36 which is concentric with respect to an inner conductor 37. Conductor 37 is fixedly positioned within tubular lead member 36 in coaxial relation therewith and electrically insulated therefrom and mechanically fixed in any suitable manner as-by means of fixed supporting blocks 38 and 39 of nonconducting material having forced fits within member 36. The upper end of' conductor 37 is electrically connected to the lower end of inner thermoelement 32 by a flexible conductor 49, the latter comprising the other output lead. The lower ends of tubular member 36 and the coaxially arranged conductor 3'7 are connected to the energizing winding of electromagnetic control device 13 in any suitable manner, as by leads 16' and 17 which, if desired, may bearranged coaxially as continuations of member 36 and conductor 37, respectively. With this construction, the central portions of concentric leads 36, 37 may be bent, if desired, to facilitate installation without disturbing the rest of the structure or the electrical connections between the conductive elements thereof.

In order toprovide the device of Fig. 3 with the improved thermostatic control of the present invention,

there is also housed within the outer hollow thermoelement 33, closely adjacent-to inner thermoelement 32, an elongated thermostatic member 41 fixed at its upper end to plug 34 in good thermal contact therewith, as by welding, and carrying at its lower end an electrical contact 42 adapted to cooperate with a similar contact 43 fixed to the lower end of inner thermoelement 32. In the embodiment'illustrated, member 41 consists of a bimetallic-thermostatic arm to which the contact 42 is connected, but from which it is electrically insulated, by a suitable connector 44 of non-conducting material. Movable contact 42 is electrically connected to sleeve in any suitable manner, as by a flexible conductor 45. Since fixed contact 43is mounted directly on inner thermoelement 32, it will be evident that the two contacts with conductor 45 are connected in parallel with the output leads of the thermoelectric generator represented by sleeve 35 and conductor 40.

As indicated in Fig. 3, the generator structure is adapted to be mounted'closely adjacent to burner 11 so that the upper end thereof, particularly plug 34 which is part of the hot junction between the two thermoelements 32 and 33 and is also in good thermal contact with bimetallic arm 41, is subjected directly to the heat of the burner flame. The bimetallic arm 41 isso positioned with respect to the rigidly fixed inner thermoelement 32 that,

when the burner flame impinges the upper end of the generator, the heat conducted through plug 34 to the bimetallic arm causes the latter to assume a position in which the movable contact 42 is separated from the fixed contact 43 carried by thermoelement 32. At the same time, heating of the hot junction between inner and outer thermoelements 32 and 33 generates thermoelectric current which flows through the circuit comprising inner thermoelement 32, flexible conductor 40, conductor 37, lead 17 winding 15, lead 16', tubular lead member 36, sleeve 35, outer thermoelement 33 and plug 34.

When the burner flame is extinguished, thermostatic member 41 cools and moves to a position wherein the contacts 42, 43 are closed, whereupon a portion of the current generated by thermoelements 32- and 33 is shunted through the circuit comprising flexible conductor and contacts 42, 43, and the current flowing through leads 16, 17' is reduced below the value required to maintain the armature 18 of control device 13 in attracted or running position by the inherent voltage regulation of thermocouple 32, 33. As in the case of Figs. 1 and 2, the thermo-' static means of Fig. 3 are so designed or may be so adjusted that contacts 42, 43 are closed within the desired time period after the burner flame is extinguished so that the control device functions much more quickly than it would were it dependent solely upon normal cooling of the hot junction of the thermocouple for reduction of the thermoelectric current output.

The device illustrated in Fig. 4 is of substantially the same construction as that of Fig. 3 except that the contacts 42', 43' are so arranged that, when closed, they are in series, rather than in parallel, with the output circuit of the thermoelectric generator. To this end, the thermostatic arm 41 is so designed that contacts 42, 43 are closed, instead of open, when the upper end of the structure is heated in normal manner by the flame of burner 11, the flexible conductor 45 connects movable contact 42' to the upper end of conductor 37, instead of to sleeve 35, andthere is no permanent electrical connection between fixed contact 43 and conductor 37. With the arrangement of Fig. 4, contacts 42, 43 form part of the circuit through which the thermoelectric current is supplied to the control device as long as the burner is heating in normal fashion. However, upon flame failure, contacts 42, 43' are opened promptly as determined by the design or adjustment of the thermostatic means due to the cooling of thermostatic member 41' and thereby open the thermoelectric circuit and effect operation of the control device much more quickly than would be possible in the absence of the thermostatic control.

Figs. 5 and 6 illustrate diagrammatically how the invention may be applied to systems wherein the thermoelectric generator consists of a thermopile instead of a thermocouple. As shown in Fig. 5, a thermopile 46, having a series of thermoelements 47 and 48 of suitable dissimilar metals connected together to form hot junctions 49 and cold junctions 49a, is mounted in any convenient manner on a support 50 and is positioned closely adjacent to burner 11 so that the hot junctions 49 are all subjected to the heat produced by the burner flame. The end thermoelements of the thermopile are connected to output termnials 51 and 52, which in turn are connected to output leads 16 and 17, respectively, the latter being adapted to supply the thermoelectric current generatedby the thermopile to a control device (not shown) of the same character asthat indicated in Fig. l, for example.

Also mounted on support 50 is a thermostat 25 which, like that shown in Fig. 1, may comprise a fixed contact arm 26 and a movable, bimetallic contact arm 27 carrying contacts 28 and 29, respectively, which close when the thermostat cools, bimetallic arm 27 being so positioned with respect to burner 11 and fixed contact arm 26 that, when heated by the burner flame, the bimetallic arm assumes a position in which the movable contact 29 is separated from fixed contact 28. As in the system illustrated in Fig. 1, thermostatic contacts 28 and 29 are connected to the thermopile output leads 16 and 17, respectively, through the arms 26 and 27 and conductors 3t) and 31, thus placing the circuit through contacts 28, 29 in parallel with that by which the thermoelectric current is supplied to the the control device through leads 16, 17. Inasmuch as the operation of the arrangement illustrated in Fig. 5 is the same as that of Fig. 1 except for the use of a thermopile, instead of a thermocouple, as the generator, a detailed description of said operation would appear unnecessary.

The device represented by Fig. 6 is identical with that of Fig. 5 except that the contacts 28', 29' of thermostat 25' are connected in series, rather than in parallel, with the output of thermopile 46, and the arms 26, 27 of the thermostat are so constructed and arranged that the contacts 28', 29' are closed, rather than open, when the thermostat is heated normally by the flame of burner 11. The arrangement of Fig. 6 is thus directly comparable to that of Fig. 2 and operates in the same manner as the latter.

It is to be expressly understood that the drawings are schematic and that thermostat 25 in Figs. 1 and 5, thermostat 25' in Figs. 2 and 6, and thermostats 32, 41 and 32, 41' in Figs. 3 and 4, respectively, may be provided with suitable contact adjusting means whereby the time for operation of said thermostats may be adjusted with respect to the cooling rate of the associated thermocouple or thermopile.

For purposes of illustration the drawings exemplify the use of the present invention to hasten the operation of an associated control device upon interruption of heating of the hot junction or junctions and of the thermostat. It is to be expressly understood, however, that the thermostats may be arranged to reduce or interrupt the thermoelectric output current when heating exceedsa predetermined value.

Other contemplated uses of the present invention include applications in which the switching action of the improved thermoelectric generator is the desired function in that the generator may disconnect itself from associated circuits when the temperature of the thermostat is above or below a predetermined temperature depending on the arrangement of the thermostat.

There is thus provided by the present invention a new and improved form of thermoelectric generator which may be used with control devices for fuel burning apparatus, as well as with other devices, and which materially decreases the time interval between interruption of heating of the generator and operation of the associated control or other device. The improvement resides primarily in the combination with a thermoelectric generator of thermostatic means controlled by the same flame or other source of heat as that to which the generator is subjected whereby the output of thermoelectric current from the generator is either decreased or interrupted promptly after failure of the heat source and operation of the control or other device is effected more rapidly than would result from the decrease in thermoelectric current due to normal cooling of the hot junction or junctions of the generator. The invention also provides a structurally novel thermoelectric generator of the closed type having a builtin thermostatic control for the purposes above indicated.

Although several specifically different forms of the invention have been described and illustrated in detail, it is to be expressly understood that these devices are intended for puiposes of illustration only, and that the inventive concept is capable of a variety of mechanical embodiments. For example, it is obvious that any appropriate type of thermostat may be used in lieu of the bimetallic thermostats illustrated in the drawing, that the thermoelectric generator may incorporate any combination of dissimilar metals having suitable thermoelectric properties, and that the generator may be used with other forms of control device, or for other purposes, than that herein represented. It is equally evident that the specific character and construction of the heat source with which the generator is associated is not material as long as it simultaneously heats both the generator and the thermostatic control sufliciently to maintain an adequate output of thermoelectric current. In this connection, it will be understood that the generator may be used with electrical as well as fuel burning sources of heat. It will also be recognized that the generic concept of the present invention may be embodied in devices wherein the therrnoelements of a thermoelectric generator themselves also possess thermostatic characteristics, as is the case with the structures disclosed in my copending application Serial No. 324,990, filed contemporaneously herewith. Furthermore, if oxidation or the presence of foreign matter is apt to interfere with proper operation of the open contacts of Figs. 1, 2, 5 and 6, it will be understood that the latter may be enclosed in any suitable manner, as by a bellows arrangement of the type shown in my above identified copending application.

Various other changes, which will now suggest themselves to those skilled in the art, may be made in the mechanical construction, arrangement, electrical characteristics and use of the device, without departing from the inventive concept. Reference is therefore to be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

l. A thermoelectric generator comprising a pair of conductors of dissimilar metals having one end of each connected to one end of the other and their other ends separated from one another, the first of said conductors being hollow and forming at least part of an enclosure for the second conductor, a pair of contacts within said enclosure, one of said contacts being carried by said second conductor, a lead conductor insulated from said first conductor, a conductive connection between said lead conductor and one of said contacts, and thermostatic means also enclosed within said first conductor for closing and opening said contacts.

2. A thermoelectric generator comprising a pair of conductors of dissimilar metals having one end of each connected to one end of the other and their other ends separated from one another, the first of said conductors being hollow and forming at least part of an enclosure for the second conductor, a first contact electrically connected to said second conductor, a thermostatic element within said enclosure carrying a second contact positioned closely adjacent and adapted to cooperate with said first contact, a conductive connection between said second contact and said first conductor, a lead conductor insulated from said first conductor, and a conductive connection between said first contact and said lead conductor.

3. A thermoelectric generator comprising a pair of conductors of dissimilar metals having one end of each connected to one end of the other and their other ends separated from one another, the first of said conductors being hollow and forming at least part of an enclosure for the second conductor, a first contact electrically connected to said second conductor, a thermostatic element within said enclosure carrying a second contact positioned closely adjacent and adapted to cooperate with said first contact, said second contact being insulated from said first conductor, a lead conductor also insulated from said first conductor, and a conductive connection between said second contact and said lead conductor.

4. A thermoelectric generator comprising a first thermoelement of hollow construction, a second thermoele ment housed within said first thermoelement and connected at one end to the latter to form a hot junction, first and second output conductors for connecting said first and second thermoelements to a utilization circuit, and thermostatic means also housed within said first thermoelement for controlling the output of thermoelectric current to said output conductors.

5. A thermoelectric generator comprising a first thermoelement of hollow construction, a second thermoelement housed within said first thermoelement and connected at one end to the latter to form a hot junction, first and second output conductors for connecting the other ends of said first and second thermoelements to a utilization circuit, and means for controlling the output of thermoelectric current from said generator including a thermostat also housed within said first thermoelement, and a pair of contacts actuated by said thermostat for controlling the flow of thermoelectric current from said second thermoelement to said second output conductor.

6. A thermoelectric generator comprising a first thermoelement of hollow, elongated construction, a second elongated themoelement housed within said first thermoelement and extending substantially parallel to the surrounding wall thereof, means at one end of said first thermoelement forming a hot junction between said first thermoelement and one end of said second thermoelement, first and second output conductors for connecting the other ends of said first and second thermoelements to a utilization circuit, a thermostatic element also housed within said first thermoelement, and a pair of contacts actuated by said thermostatic element for controlling the flow of thermoelectric current through said output conductors.

7. A thermoelectric generator comprising a first thermoelement of hollow, elongated construction, a second elongated thermoelement housed within said first thermoelement and extending substantially parallel to the surrounding wall thereof, means at one end of said first thermoelement forming a hot junction between said first thermoelement and one end of said second thermoelement, first and second output conductors for connecting the other ends of said first and second thermoelements to a utilization circuit, a thermostatic element also housed Within said first thermoelement and in thermal contact with said hot junction forming means, and a pair of contacts actuated by said thermostatic element for controlling the flow of thermoelectric current through said output conductors, one of said contacts being carried by said second thermoelement and the other contact being carried by said thermostatic element.

8. A thermoelectric generator comprising a first thermoelement of hollow, elongated construction, a second elongated thermoelement housed within said first thermoelement and extending substantially parallel to the surrounding wall thereof, means closing the upper end of said first thermoelement and forming a hot junction between said first thermoelement and the upper end of said second thermoelement, first and second output conductors for connecting the lower ends of said first and second thermoelements to a utilization circuit, an elongated bimetallic thermostat also housed within said first thermoelement adjacent and extending substantially parallel to said second thermoelement and in thermal contact at its upper end with said hot junction forming means, and a pair of contacts actuated by said thermostat for controlling the flow of thermoelectric current through said output conductors, one of said contacts being carried by the lower end of said second thermoelement and the other contact being carried by the lower end of said thermostat.

9. A thermoelectric generator comprising a first thermoelement of hollow, elongated construction, a second elongated thermoelement extending substantially parallel to said first thermoelement, means at one end of said first thermoelement forming a hot junction between said first thermoelement and one end of said second thermoelement, first and second output conductors for connecting the other ends of said first and second thermoelements to a utilization circuit, means for controlling the output of thermoelectric current from said generator including a thermostat and a pair of contacts actuated by said thermostat for controlling the fiow of thermoelectric current from said thermoelements to said output conductors, and means including said first thermoelement forming an enclosure for said second thermoelement, said thermostat and said contacts.

10. A thermoelectric generator comprising a first thermoelement of hollow, elongated construction, a second elongated thermoelement extending substantially parallel to said first thermoelement, means at one end of said first thermoelement forming a hot junction between said first thermoelement and one end of said second thermoelement, first and second output conductors for connecting the other ends of said first and second thermoelements to a utilization circuit, an elongated bimetallic thermostat adjacent and extending substantially parallel to said second thermoelement and in thermal contact with said hot junction forming means, a pair of contacts actuated by said thermostat for controlling the flow of thermoelectric current from said thermoelements to said output conductors, one of said contacts being carried by said second thermoelement and the other contact being carried by said thermostat, and means including said first thermoelement forming an enclosure for said second thermoelement, said thermostat and said contacts.

References Cited in the file of this patent UNITED STATES PATENTS 2,385,530 Paille Sept. 25, 1945 2,449,185 Unger Sept. 14, 1948 FOREIGN PATENTS 680,611 Germany Sept. 2, 1939

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