US2313072A

US2313072A - Thermal responsive device

Info

Publication number: US2313072A
Application number: US363521A
Authority: US
Inventors: Hotchkiss Clifford
Original assignee: Perfex Corp
Current assignee: Perfex Corp
Priority date: 1940-10-30
Filing date: 1940-10-30
Publication date: 1943-03-09
Anticipated expiration: 1960-03-09

Description

March 9, 1943. c. Ho'rcHKlss THERMAL RESPONSIVE DEVICE Filed oct. so. 1940 Patented Mar. 9, `1943 UNITED STATES PATENT OFFICE 2,313,072 THERMAL RESPONSIVE DEVICE Clifford Hotchkiss, Milwaukee, Wis.. assignor to l Perfex Corporation, Milwaukee, Wis., a corporation of Wisconsin Application October 30, 1940, Serial No. 363,521

18 Claims. (Cl. 20G-137) This invention relates in general to thermal responsive devices but more particularly to\a thermal device adapted for operation as a safe.

running period, or ignition failure upon start-` ing, in order that hazardous conditions may be obviated. l

It is an object of the invention to provide an improved combustion responsive and heat sensitive device for controlling the operation of a burner in which the thermalv element is responsive to radiant heat or energy emanating from the furnace combustion chamber.

In the past, it hasl been common to form radiant heat operated combustion responsive devices of a diaphragm exposed to radiant-heat from the name and restrained from expanding at its edges, the diaphragm thus buckling uponv the presence of combustion and unbuckling when combustion ceases. Usually such diaphragms operate a combustion switch through a slip friction mechanism of some sort. One disadvantage of such arrangements is that `they are under some conditions too responsive said often ycause opening and closing of the combustion switch when the burner is rst started, even though a real iiame failure does not occur. One cause for this is a shifting in position of the burner iiame as the combustion chamber warms up.: Thus when the burner is rst started the flame may be near the control while later, due to increased draft caused by heating of the chimneyy' the iiame may move toa different position. A

It is an object of this invention to provide a thermal responsive arrangement of this general type with means compensating for the unstable nature of the flame when the burner is rst started. y

In accordance with my invention, the responsive device is formed of a diaphragm and a ring 'attached to the edges thereto. Both the diaphragm and ringare `equally subjected to the radiant heat and the diaphragm s formed of a Y material having a high coeiiicient of expansion relatively small, thereby making it more sensitive to reversals in temperature. This constitutes a further object of the invention.

When a device of this character is used on certain types of burners, or under certain conditions, the .diaphragm may nse in temperature at a Yrate considerably faster than the ring. When the ring and diaphragm begin equalizing in temperature, the diaphragm may unbuckle causing reverse movement of the combustion switch even though no ame failure has occurred. This reverse action of the diaphragm however is compensated for by the present invention.

It is accordingly another object of this irivention to provide a thermal responsive device having a pair of elements which change in temperature at different rates with means for preventing reversals in operation due to unequal rates of heating.

A further object is to provide an improved combustion responsive device of the disc or diaphragm type, this device responding to the ra- I diant heat from the furnace and operating a switch through a slip friction mechanism,- the latter mechanism serving to cause actuation of the switch immediately upon reversalsA in movement of the diaphragm, and permitting unrestricted diaphragm movement after the switch is actuated.l

A further object is to provide novel means for adjustably4 supporting the thermal responsive device upon a furnace to provide for any Varithe iiame in the com- Fi/g. 1 shows a cross sectional side elevation of the thermal responsive device and associated switching mechanism mounted on a burner tube; I

Fig. 2 is a top view of the switching mechanism;

Fig. 3 is an end view of the thermal responsive devicel taken along the line 3-3 of Fig. 1; l

Fig. 4 is an end view of a modified form of the thermal responsive device;

Fig. 5 is a cross sectional side view of Fig. 4'-

Fig. 6 is a fragmentary view of a gun type of burner installation on a furnace to which the invention is applied; while Fig. 7 is a fragmentary view of a spinner type of burner to which the invention is applied.

The invention comprises generally the combination of a thermal responsive device indicated at 5 and a control device or switching mechanism associated therewith indicated at 6, both elements being arranged for example upon a burner as indicated in Fig. 6. The thermal vresponsive device 5 is arranged within an enclosing chamber or casing preferably in the form of a casting 1, having fairly thick walls including a at bottom wall 8 through which a bolt 9 passes and is threaded into the side wall l0 of the blast tube of a burner for supporting the casting 1. A pair of downwardly projecting legs, one of which is shown at II, straddle the tube I0 and serve to space the bottom wall 8 from direct thermal contact vwith the tube I0. The

' casing 1 has semi-circular side and top walls and is provided with an opening I2 inthe front thereof. The upper portion of the wall extending toward the opening I2 is gradually sloped downward as indicated at I3. The opening I2 is arranged so as to face the combustion chamber of a furnace as shown in Fig. 6. 'I'he rear or opposite end of the casing 1 is arranged with a cylindrical wall I4 having a shoulder portion -formed therein to providea seat for a at metal position in the associated slot.

tube I6 passing through an opening in the disc I5. An operating rod or-shaft I1 passes axially through the tube I6 and projects outwardly Y from the front end thereof. The condition rephragm I8 is preferably constructed of material having a relatively high thermal coefi'icient of expansion. I have found the best results to be obtained by using .0000202 cms. per cm. per de# gree centigrade. This material may be stainless steel comprising 18 to 25% chromium and 8 to 12% nickel. It is bowed outward toward the opening I2 a slight amount as a result of a shoulder 20 on the shaft I1 engaging the same and applying a slight amount of pressure to the diaphragm. The shaft I1 aswill be hereinafter pointed out is normally spring urged in a direction toward the diaphragm I8. Arranged upon the peripheral front edge of the diaphragm I8 is a confining means -takng the shape of an annularjring 2| preferably made of a material having a somewhat smaller coeiicient of heat expansion than the material of which the dia` phragm I8 isv constructed. I prefer to use a material for this' ring having a coeflicient. of

per degree centigrade. 'Ihis part may be formed of Inconel comprising 78 to 80% nickel, 12 to 14% chromium and 6 to 8% iron. The ring 2I is thicker than the diaphragm and preferably spot welded at recurring intervals to the periphery of the diaphragm. The diaphragm I 8 upon being subjected to elevated temperatures such as caused by radiant heat waves bows or bulges outward as indicated by the dotted lines in Fig. 1, while the annular ring 2| expands circumferentially at a somewhat slower rate thanrthe diaphragm. The end of the shaft I1 loosely projects through a hole in the center of the diaphragm so as to guide and support the end of the shaft.

Rigidly secured to and arranged upon the front end of the supporting tube I6 is an annular iiat metal-disc 2Ia positioned directly bel hind the diaphragm I8. This disc 2Ia serves as a support for a' plurality of bimetallic at strips 22 illustrated more clearly in Fig. 3. The bimetal strips 22 are attached at one end by rivets as shown to the disc 2Ia. The opposite ends of 'the bimetal strips are provided with reduced portions 23 which project loosely through slots provided in the ange I9 of the diaphragm I8. rIn assembling the thermal responsive element upon the end of the supporting tube I6 one or 4more of the reduced portions 23 of the bimetal blades 22 are inserted in the corresponding slots in the iiange I9 of diaphragm I8 and then each portion of the flange I9 between the remaining bimetal blades 22 is pressed inwardly so that the remaining projection 23 may be snapped into The bimetal blades 22 are thereby securely locked in position so as to support the diaphragm I8 upon the end of the shaft I1. Ihe bimetal strips are each so constituted that upon a temperature rise they will bow their free ends in the direction indicated by the arrows in Fig. 1 so as to move the diaphragm I8 outwardly for a purpose which will be hereinafter pointed out. It will be noted that the bimetal strips 22 being arranged behind the diaphragm I8 are shielded by the diaphragm from direct contact with the radiant heat waves passing through the opening I2. The bimetal strips 22 therefore are activated as the result of the heat transmitted by conduction from the diaphragm through the fiange I9 and by the convection from the 'rear surface of the diaphragm.

4 In order to prevent any cooling Aair currents from passing through the tube I6 to the rear side of the diaphragm I8 and also to the bimetal blades 22, an enclosing means is provided for closing the end of the tube I6. This enclosing means includes a washer 24 axially disposed upon the shaft I1 and covering ythe open end of the expansion of approximately .0000161 cms. per cm.

tube. A light spring 25 extends between the washer 24 and the shoulder 20 of the shaft I1 so as to at all times urge and hold the washer against the open end of the tube. 'Ihis spring 25 is light enough so as to have no appreciable effect upon the operation of the diaphragm I8.

The control device which is actuated by the operation of the thermal responsive device 5 is shown, for example, in. the form of a switch mechanism 6. This switching mechanism is suitably enclosed in a rectangular shaped metal casing or housing 26 which is supported by means of an angular U-shaped bracket 21 and `screws 28 upon the top of the blast tube I0 of the burner. The bracket 21 comprises a pair of legs,.one of which is shown, which straddle the tube I0 and have their lower ends bent to conform to the cylindrical shape of the tube and are securedv thereto by the screws 29. This screw 29 passes through a slot 30 of each bracket ment the element supporting tube I6 and the thermal device may be laterally positioned within the casing 1 at any desired location either closer or further away from the opening I2 of the casing 6, depending upon the intensity of the burner ame within the combusition chamber so that the correct response of the thermal elment may be more accurately and reliably gauged. In the case of a very hot fire the thermal device 5 would be positioned further away from the opening I2 whereas in the type of burner in which a lower flame would exist the thermal device 5 would be adjusted closer to the opening I2.

A sheet metal enclosing cover 3| is provided for protecting the switching mechanism 6. It is adjustably attached to the blast tube I0 by means of a screw 32 on each side riding in a slot 33 so that the cover 3I may be shifted whenever the switching mechanism is adjusted. The casing 26 is provided at one end with an opening in which a conduit connection or a rubber grommet 34 may be inserted as shown. This serves for the purpose of providing an ventry for the electrical connecting' wires 35. A cover plate 36 for enclosing the casing 26 is provided which is held on the casing by means of a screw 31. The screw 31 threads into a protecting plate 38 arranged immediately above the switching mechanism and which is secured to the sides. of the easingy 26 by means of screws 39, one of. which is shown; A projecting edge of the plate 38 extends through an opening 40 in the side of the casing to further support the plate 38.

The plate 38 thereby serves to protect a portion of the mechanism and likewise serves as a securing means for the screw 31. One sido wall of the casing 26 has a threaded projecting portion 4I formed integral therewith and into which the end of tube I6 is threaded. A lock nut 42 threaded on the tube I6 and tightened against the side wall of the casing 26 rigidly secures and locks the thermal device 5 and the switching mechanism 6 in associated operative relationship. 'Ihis threaded engagement provides a calibration or adjustment of the thermal device 5 within the casing 1 and 'of the switching me'chanism. A compression spring 43 encircles the E, outside of the supporting tube I6 and exerts its force between the lock nut 42 and the rear of the shielding disc I5. The purpose of this spring 43 is to at all times hold and maintain the disc I5 in its set position upon the shoulder formed in the cylinder I4 of casing' 1. The disc I5 will remain on its seat and close the end of casing 1 regardless of the position to which the switching mechanism 6 may be longitudinally shifted when an adjustment of the position of the thermal device 5 is made. Y

Arranged in spaced relation to the bottomwall of the switch casing 26 is a fiat insulating plate 44, the general shape of which is shown in detail in Fig. 2. The plate 44 is supported by means of a number of bushings 45 riveted at one end to the-bottom of casing 26 and screws 46 threading into the bushings.

so-called slip friction type. that is. the contact structure is operated immediately upon initial movement of the mechanism and upon continued progressive movement a slipping action takes place between the elements while the contacts remain closed. By this arrangement the contact mechanism is actuated immediately upon reversals of the switching mechanism caused by temperature changes. In the embodiment illustrated this switching mechanism is preferably of the type illustrated in the-Homer E. Malone copending application, Serial No. 363,431, filed October 30, 1940, in which this structure is described in greater detail and claimed therein. The slip friction mechanism comprises generally a lever means including a pair 'of identically shaped and oppositely disposed lever arms 41 and 48 which are pivoted together for movement about the pivot pin 49 which is supported on the insulatirg plate 44. A second .pivot pin 50 connecting the lever arms 41 and 48 together passes through a movable element or link 5|.

The link member 5| is adapted to freely rotate a limited amountabout the pin 5I between the two lever arms and is provided with an axial bore into which the operating shaft |1` loosely projects. The lever arms 41 and 48 are connected together at one end by a pin 52 to which one end of a tension spring. 53 is connected. The other end of spring 53 is connected'to a supportin'gbracket 54 suitably secured to the bottom of the casing 26 as shown. The foregoing arrangement of elements is such that the Spring 53 normally exerts a pull upon the lower end of levers 41 and 4.8 as viewed in Fig. 2 and tends to urge the lever arms about pivot pin 49 so that the link 5I transmits this spring force longitudinally to the operating shaft I1. The shaft I1 as a result urges its shoulder `2l against the rear side of diaphragm I8 thereby bulging it slightly outward at its center. From this'arrangement it is seen that the diaphragm I8 upon being subjected to heat and as a result bowing outward permits the lever arms 41 and 48 to swing their upper ends in a clockwise direction as viewed in Fig. 2 and upon a drop in temperature aiecting -the diaphragm I8 the iiaphragm forces the shaft I1 in a left hand direction to rotate the lever arms 41 and 48 clockwise against the action of the spring 53.

The slip friction mechanism proper includes a relatively thin steel blade 55 pivoted at one end .to pin 49 and having a polished surface on both sides which is in intimate contact with a separate graphite disc 56 arranged on each side of the blade 55. Each graphite disc 56 is held in position on the blade 55 with tension by means of a thin spring blade 51 which is supported at each end in slotted openings in eachlever 41 and 48.

In order to adjust the degree of friction between the discs 56 and the blade 55, an adjusting screw 58 threads between the ends of the lever arms 41 and 48. By turning this screw the desired friction or compressive eifort of the friction discs is obtained. The adjusting screw 58 is of suflicient length so as to serve as a stop for the lever arms by engaging the sides of a recess 59 formed in the insulating plate 44.

A switching arm 66 made of insulating material is secured to the friction plater55 by means of rivets 6I as shown. 'I'he switch arm 60 at its free end carries a bracket arranged to support amovable contact 62 supported upon a thin pressback spring blade 62a as shown. The movable contact 62 is arranged in cooperative relationship with a iixed contact 63 which in tum is carried upon ari angular metal bracket 64' attached to the insulating plate 44 byscrews such as 65. 'AI'he bracket 64 has a slotted-opening in its turned up portion through which a reduced portion 66 of the switch arm 60 projects. This 'slotted opening serves as a guide and slidable.. support for the end of the switch arm 60. An

adjusting and stop screw 61 threaded through a Vprojecting end of the bracket 64 is adapted to engage one edge ofthe switch arm 68 when the arm is in contact opening position. They adjusting screw 61 enables the switch arm to be adjusted to operate with any desired degree of movement.v The bracket 64 is also provided with a terminal screw 68 to which one of the wires 35 is attached to establish a circuit path for the fixed contact 63. A second bracket 69 is supported as shown to the insulating plate 44 and carries a terminal screw 18 for attachment ofA vthe other connecting wire 35. The bracket 69 has a pig tail connection passing underneath the insulating plate 44 and connecting with the spring blade of. the movable contact 62.

Figs. 4 and 5 disclose a modified form of the thermal responsive device of the invention. In

this form a, thin diaphragm 1I of the same general shape as the diaphragm I8 of Fig. 1 is provided with a peripheral flange 12 extending rearwardly therefrom. Upon the front of the diaphragm 15 there is suitably spot welded an annular ring 13 having angular projecting por- 'tions 14 and 15 formed thereon and projecting disposed projections 18 which are arranged to.

loosely fit into associated slots so` as to straddle the projecting portion 15 of ring 13. The other end of the bimetal blade 16 has a series of shoulders formed thereon including a tongue-shaped projection 19 which passes through an associated slot formed in the projecting portion 14 of ring 13. A washer 24 and retaining spring 25 close the opening of tube I6 in the same manner as in Fig. 1.

Operation YThe combination control, including the thermal responsive device 5 and the switching mechanism 6, is arranged as a unitary struc-g ture supported as has been pointed out upon the sides of a cylindrical blasttube I8 of an' oil burner installation 8| in-the position indicated in Fig. 6.. The unit is supported in such a manner 4that the opening I2 will be exposed and point into the combustion chamber of a furnace indicated generally at 82. The name 83 produced by the operation'of the burner 8| projects into the fire pot of the furnace in the general manner indicated and the opening I2 isso arranged that radiant heat emanating from the ilame can pass through the opening I2 and 'impinge upon the front surface of the diaphragm I8. The diaphragml8 is therefore so positioned in the assembly of the device as to be directly exposed tothe temperature of the ame to which itis arranged to respond. Fig. l shows the switching mechanism including contacts 62 and 63in their closed or "cold position and if the re is now started by the burner 8| in the Well known manner, and combustion rproduced in the furnace 82, the diaphragm I8 will rapidly become heated by radiant heat from the flame and tend to expand. Circumferential expansion of the diaphragm I8 is restricted because of its intimate association with the annular ring 2| which'does not heat up as fast as the diaphragm and which also expands a lesser amount than the diaphragm even when heated to the same temperature as the diaphragm. As a result the center portion or apex of the diaphragm `I8 bulges outwardly. 'This action takes place almost immediately in response to combustion conditions in the furnace because the da: phragm is constructed of relatively thin material and absorbs the heat immediately. The outward movement of the apex of the diaphragm I8 permits the shaft I1 to follow this movement due-to the followfup movement of the levers 41 and 48 caused by the tension of the coil spring 53. 'I'he spring 53` at all times maintains a relatively close intimate relationship between the levers 41 and 48, the rod I1 and the diaphragm I8 so that no lost motion can exist in the linkage. Upon the initial movement of the levers 41 and 48 about the'pin 49 the friction blade 55 is caused to effect a movement also about pivot pin 49 by reason of the force exerted upon the blade by the friction discs 56 which carry the blade along when the levers are rotated. 'Ihe switch arm 60 is thereby swung in a clockwise direction as viewed in Fig. 2 so that the normally closed contacts 62 and 63 are immediately opened.

The action of opening the contacts 62 and 63 produces a change in the circuit operating conand the contacts remain in their open position.

The diaphragm I8 however may continue to lbuckle outward as a consequence of greater elevated temperatures to which itmay be subjected as the flame in the combustion chamber acquires greater intensity. As a result the spring 53 continues to exert a pivoting movement of the lever arms 41 and 48 about pivot pin 49. The friction blocks 56 on each side of Afriction blade 55 can now frictionally slip across the surface of the blade 55 without causing further motion of the blade 55 and without straining any of the mechanism.

When the burner is rst started up, the combustion chamber is relatively cool and similarly the air within the housing 5 is also relatively cool. The radiantv heat in striking the diaphragm causes it to be heated above its surroundings and it thus buckles as set forth above to actuate the l' combustion switch. In some types of burners or in some installations the ame is somewhat unstable when the burner rst starts, that is, the llame shifts in position. Thus at times, the radiant heat supply to the diaphragm falls olf, and the diaphragm due to being surrounded by air which. is cooler than itself, cools o to some extent, thus unbuckling slightly. Due to the action of the slipfriction mechanism,l this movement would tend to cause actuation of the combustion switch even though no flame failure has occurred. Such action, however, is compensated for by the bimetal elements 22. When the burner rst starts, these elements are in their cold positions. As the burner operates, the temperature in housing gradually rises even though the flame may be unstable, this causing the elements 22 to progressively move the entire diaphragm assembly to the iight as seen in Fig. 1. .This movementI l continues while the combustion chamber is heating up and has the same effect on push rod I1 as buckling movement of the diaphragm. Thus when the diagram moves in unbuckling direction due to an unstable flame, this movement is compensated for by the progressive movement of the bimetal elements 22 and the pushrod I'I remains stationary or may even continue to move to the right. As a result, unstable flame conditions occurring when the burner is rst started are comy be apparent that due to both the diaphragm and ring being formed o'f expansible material, the degree of buckling of the diaphragm is partly determined by the difference in temperature between these elements. If the diaphragm reaches its maximum temperature while the ring is still relatively cool. the diaphragm will be buckled a greater 'amount than when the diaphragm and ring are at the same temperature. Thus under such conditions, the diaphragm will actually unbuckle while the ring is heating up, and the unbuckling might be sumcient to actuate the com- I bustion switch, but for the action of the bimetal velements 22. It will be noted that these elements are rising in temperature at the same time that the diaphragm and ring are equalizing in temperature. 'I'hus the movement of the diaphragm v and ring by the bimetal elementsA counteracts such unbuckling movement of the diaphragm and the combustion switch remains in its hot position.

When the burner 8| is shut down or in the` event of combustion failure during a running period, the ame 83 in the combustion chamber ceases to exist. 'Ihe drop in temperature is immediately manifested upon the diaphragm I8 which senses the reversal or change in temperature and because of its thinness begins to move immediately toward a flat position, as shown in Fig. 1. This movement of the diapragm I8 is passed to the shaft II by means of the shoulder 20 engaging the rear of the diaphragm.A 'I'he shaft II causes levers 41 and 48 tov rotate against the tensionof spring 53. 'I'he initial movement of levers 41 and causes the friction blade to move the switch arm GII into contact closing position awai7 from stop screw 61. Continued inward buckling of the diaphragm I8 causes the friction blocks 56 to slip on the blade 55 after contacts' 62 and 63 establish contact so that the mechanism can continue to move without straining the same. The bimetal blades 22 return slowly to their straight unwrped conditiony as shown at this time but do not prevent the immediate revers action of the diaphragm.

In the event that the thermal responsive device 5 should develop a defect, burn off or become affected by any abnormal conditions the device is arranged to move into a fail safe position.

That is, upon the automatic operation of the burner the device would operate under control oi ,the tension spring 53 to cause opening of contacts 62 and 63 which would enable the burner 8l to start, but upon the automatic stoppage of the burner and the consequent extinguishment of the flame in the burner, the diaphragm or associated mechanism which is disabled would fail to restore the contacts to their closed position with the result that a lock out condition would occur in the burner circuit in the well known manner and prevent the further operation of the burner. The device therefore is arranged to provide for this fail safe feature in a simple and reliable manner.

It is contemplated in the present structure that the device may be utilized in a circuit arrangement in which the contacts 62 and 63 may be normally opened instead of closed as shown. This may be accomplished by simply reversing the position of the contacts and the adjusting stop screw 61. Under certain conditions an arrangement of this type is desirable and to produce a. fail safe condition with this arrangement similar conditions would prevail as pointed out.

It is further contemplated that the unitary structure comprising the thermal responsive device 5 and the slip friction mechanism 6 be mounted in other positions than the top of the blast tube as illustrated in Fig. 6. For example it may be mounted on the side ofthe blast tube I0 or any other position.- Under these conditions and that in which it is shown in Fig. 6 the sloped portion I3 on the casing 'I is arranged'to intercept the radiant heat which emanates from the edge of the flame within the burner. This portion of the ilame does not produce a stable condition but vwavers considerably and if it were permitted to transmit its heat rays to the diaphragm I8 erratic operation may result. Therefore the opening I2 of the casing 5 is so arranged as to point toward the most intense or most stable portion of the flame in the combustion chamber and permit only the rays from this portion of the *I I flame to pass' to the diaphragm I8. y

In Fig. 7 there is illustrated an adaptation of the combination thermal and switching mechanism for use in connection with a rotary or spin'- ner type of burner. The motor for this burner is indicated generally at 86 and is suitably positioned in the bottom of a furnace casing 85 with the rotary spinner 86 positioned in the combustion chamber. ,The operation of the motor 84 results in the burning fuel being sprayed outwardly from the periphery of the disc 86 as indicated a.; 8l. The thermal responsive unit 5 is positioned in the wall of the furnace casing 85 immediately below the ilame 81 where the direct rays may aifect the same. The unit is mounted within the casing by means of a.y sleeve member 88 to which it is attached by means of a set screw 89 engaging the supporting tube I6. A supporting plate- 90 to which the sleeve 88 is suitably secured is carried by screws as shown upon a tubular enclosing member 9I extending from the outside ofthe furnace into the combustion chamber. The switching mechanism 6 is supported below the plate 90 as shown. The foregoing illustrates the adaptability of the control unit for mounting in various types of burners. The action and operation of the saine in producing the desired switching operations are similar in this arrangement as that described in connection with Fig. 6. However. since the ame 81 is propagated in a direction at right angles to the thermal responsive element 5 it is not necessary to provide a case such as at 1 in Fig. 1. The

thermal element 5 is adjustably positioned by means of screw 89 closer or further away from the iiame 81 as desired.

From the foregoing description it isfperceived that an improved thermal responsive element is disclosed in combination with'associated switching mechanism in which the mechanism is of simple construction, extremely reliable in operation andis arranged to safeguard its operation in a number of diierent instances. By combining the thermal element 5 and the switching mechanism 6 into a single unitary structure, a reduction in the wiring and installation costs is effected as well as a simplification of the testing, assembly and matching of the units. While the invention is illustrated in a preferred and modied form, it is contemplated that various modifications in the same may be made without -departing from the spirit of the invention and it is therefore to be understood that the invention is `not limited to th precise construction illustrated,

but only by the scope of the appended claims.

What is claimed is:

1. In a thermostatic mechanism, the combination of a control device having a movable element. first thermal responsive means comprising two portions subjected to a variable temperature and arranged to change in temperature therewith at different rates, said thermal responsive means actuating said movable element, and a second thermal responsive means also subjected to said variable temperature and varying the movement of said movable element caused by said rst mentioned thermal responsive means.

2. In a thermostatic mechanism, the combination of a control device having a movable element, first thermal responsive means comprising two portions subjected to a variable temperature and arranged to change in temperature therewith at different rates, said thermal responsive means actuating said movable element, and a second thermal vresponsive means also subjected to said variable temperature, said second thermal responsive means being arranged to oppose the eiect of said first thermal responsive means caused by the diierent rates at which said two portions change in temperature. v

3. In a thermostatic control mechanism, the combination bf a control device having a movable element, thermal responsive means comprisy ing two portions subjected to a variable tempersive means also subjected to said variable temperature. and innuencing the actuation of said movableelement by said first mentioned thermal responsive means.

4. In a thermostatic control apparatus, the

different rates whereby said thermal responsive means may reverse its initial movement following a change in said variable temperature due to equalization in temperature of the two portions, and means for substantially preventing -such reversal in movement of said thermal responsive means from being transmitted to said actuator. 5. In a thermostatic control mechanism, the combination of a control device having a movable element, thermal responsive means comprising two portions subjected to variable temperature and arranged to change in temperature therewith at different rates, whereby said thermal responsive means may reverse its initial movement following a change in said-variable temperature due to equalization of the'temperatures of said two portions, a slip friction motion transmitting means for transmitting motion from said thermal responsive means to said movable element, and means for substantially preventing a reversal in motion of s'aid thermal responsive means caused by the different rates of temperature change of said portions from being transmitted from said thermal responsive means to said slip friction motion transmitting means.

6.- In a thermostatic control apparatus, the

` combination of, a control mechanism comprising combination of, a control mechanism comprising L a control device and an actuator therefor including a slip friction mechanism, a thermal responsive means for causing movement of said actuator and hence said control device, said thermal responsive means comprising two portions subjected to a variable temperature and arranged to change in temperature therewith at a control device and an actuator therefor including a slip friction mechanism, a thermal responsive means for causing movement of said actuator and hence said control device, said thermal responsive means comprising two portions subjected to a variable temperature and arranged to change in temperature therewith at different rates whereby said thermal responsive me 11193Y reverse its initial movement following aaglsige in said variable temperature due to equalization in temperature of thetwo portions, and meansx for substantially preventing such reversal in movement' of said thermal responsive means from being transmitted to said actuator, said last mentioned means comprising a thermal responsive compensating device.

7. In a thermostatic control apparatus, the combination of, a control mechanism comprising a controldevice and an actuator therefor including a slip frictionmechanism, a thermal responsive means for causing movement of said actuator and hence said control device, said thermal responsive means comprising two portions subjected to a variable temperature and arranged to change in temperature therewith at different rates whereby said thermal responsive means may reverse its initial'movement following a change in said variable temperature due to equalization in temperature of the two portions, and means for substantially preventing such reversal in movement of said thermal responsive means from being transmitted to said actuator, said last mentioned means comprising a thermal responsive device also subjected to said variable temperature and arranged to change in temperature therewith at a relatively slow rate.

8. In a thermostatic control mechanism, the combination of, a control device having a movable element, thermal responsive means comprisingv l two portions subjected to a variable temperature and arranged to change in temperature therewith at diierent rates, means /including a slip friction device for transmitting reversals in motion of said thermal responsive` means to said movable element, and a physical condition responsive device for cooperating with said thermal responsive 9. In a thermostatic mechanism, the combination of a thermal responsive device formed of a relatively thin plate-like member adapted to change in temperature relatively rapidly, confining means for opposite edges of said member whereby said member buckles or unbuckles upon changes in a variable temperature to which the thermal responsive device is subjected, a control device having a movable element actuated by the thermal responsive device, and a second'thermal responsive device subjected to said variable temperature for cooperating with said first thermal Y responsive device in positioning said movable element.

10. In a flame detecting device for fuel burners, the combination of, a control device, a relatively thin plate-like member for actuating said control device, said member being located in a region spaced from the flame and adapted tol receive radiant heat from the flame, and means for preventing reversal in action of said member due to an unstable ame when the burner is first started; said means comprising a thermal responsive device which rises in temperature when the burner is placed in operation, movement of said thermal responsive device counteracting the eiTect of simultaneous movement of said member toward its cold position. 11. In a flame detecting device for fuel burners, the combination of, a housing having an open end and adapted to be aimed at the liame, the opening of the housing being of reduced cross sectional area as compared with the interior of the housing,v a rst thermal responsive device comprising a relatively thin plate-like member extending transversely of the housing and arranged to receive radiant heat passingthrough said opening, confining means for opposite edges of said member whereby said member buckles or unbuckles upon occurrence and discontinuance of said flame, a control device actuated by said member, and a second thermal responsive device for cooperating with said first thermal' responsive device in positioning said control device.

12. In a flame detecting device for fuel burners, the combination of a housing having an open end and adapted to be aimed at the fiame, the opening of the housing being of reduced cross sectional area as compared with the interior of the housing, a relatively thin plate-like member extending transversely'of the housing and arranged to receive radiant heat passing through said opening, a control device, said member buckling and unbuckling upon presence or absence of flame for actuating said control device, and means for adjustably positioning said member at ,different distances from said opening to vary. the amount of radiant heat received by said diaphragm.

13. In a control mechanism, a thermal responsive device comprising a diaphragm member and a ring member associated therewith, both of said members subjected to variable temperatures and arranged to respond thereto at different rates to actuate said control mechanism, and a second thermal responsive device comprising a bimetallic 14. In a controlmechanism, a thermal responsive device comprising a diaphragm member and a ring member arranged upon the periphery of said diaphragm member, said members subjected to variable temperatures and arranged to respond thereto atA different rates, connecting means extending from one of said members to said control mechanism whereby the control.'l mechanism is operated, and means for supporting said members, said supporting means comprising a bimetallic means subjected to said variable temperatures and arranged to respond thereto at a different rate than said members for bodily shifting said members.

15. In a control mechanism, a thermal responsive device comprising a diaphragm meinber and a ring member arranged upon the periphery of said diaphragm member, a connecting shaft extending from the center of said diaphragm member to said control mechanism whereby said control mechanism is operated when said members are subjected to variable temperatures, a supporting tube through which said connecting shaft extends, a plurality of bimetallic blades supported at one of their ends from said supporting tube and supporting the diaphragm and ring members from their other ends.

16. In a control `mechanism, a thermal reponsive device including a diaphragm member, a connecting shaft extending from the diaphragm member to said control mechanism for operating the same when the thermal responsive device is actuated in response to variable temperatures, a supporting tube through which said connecting shaft extends and having one end arranged adjacent said diaphragm member, a second thermal responsive device arranged upon the supporting tube end, said second thermal responsive device blade associated with said iirst thermal responsive device, said bimetallicblade arranged to respond to said variable temperatures at a different supporting said first-thermal responsive device from 'the end of said supporting tube, and means arranged between the end of said supporting tube and said diaphragm member for closing the tube opening to prevent passage of air through said tube.

17. In a thermostatic control mechanism, the combination of, a control device having a movable element, thennal responsive means comprising two portions subjected to a variable temperature and arranged to change in` temperature therewith at different rates', means including a -slip friction device for transmitting reversals in motion of said thermal responsive means to said` movable element, and a second thermal responsive means arranged to bodily shift said first thermal responsive means from one position to another.

18. In a thermostatic mechanism, the combination of, a thermal responsive device formed of a relatively thin plate-like member adapted to change in temperature relatively rapidly, conlining means for opposite edges of said member adapted to change in'temperature at a relatively slower rate whereby said member buckles or unbuckles upon changes in a variable temperature to which the thermal responsive device is subjected, a control device having a movable element actua/ted by the thermal responsive device. and a second thermal responsive device subjected to said variable temperature for bodily shifting said first thermal responsive device from one position to another.

CLIFFORD HOTCHKISS.