US2719199A - Thermostat - Google Patents

Description

Sept. 27, 1955 G. l. HOLMES THERMOSTAT Filed Sept. 29,' 1950 IN V EN TOR.

Holm es United States Patent THERMOSTAT Gilford I. Holmes, Waukesha, Wis., assignor to Milwaukee Gas Specialty Company, Milwaukee, Wis., a corporation of Wisconsin Application September 29, 1950, Serial No. 187,539

8 Claims. (Cl. 200139) This invention relates, in general, to thermostats, and has particular relation to thermostats of the type which comprise thermostat elements having different coeliicients of expansion.

While the particular device which I shall describe hereinafter in connection with the drawing is adapted for use for regulating automatically the temperature produced by a heating apparatus, and more particularly for maintaining the temperature of a room or other space at a definite degree, it is to be understood that the device may be used for controlling other devices, or for making, breaking, or changing the connections in one or more electric circuits for heaters or other devices as suitable or desired.

In prior practice, thermostats of the bi-metallic type have commonly comprised strips of different metals welded or brazed together and operated by distortion of such strips caused by unequal expansion of the metals with increase in temperature, The manufacture of such thermostats has involved hot rolling and pressing operations, which have been complicated and expensive and have required considerable skill. Moreover, it has been necessary to make such thermostats relatively long to provide the desired action. Their mass has been relatively large, and they have not been as small compact, and sensitive as may be desired.

One of the main objects of the present invention is to provide an improved thermostat which will overcome shortcomings of prior bimetallic thermostats, and more particularly a thermostat wherein the thermostat elements may be shorter than the usual prior art bimetal elements; also of less mass and higher action, and of smaller, more compact and more sensitive character.

Another and more specific object of the invention is to provide a thermostat in which the active elements are joined in spaced relation and shaped as beam sections, and have flexible hinge portions.

Another object of the invention is to provide a thermostat in which the hinge portions of the active elements are disposed adjacent to one of the locations where the elements are joined in spaced relation.

Another object of the invention is to provide a thermostat in which the spaced active elements shaped as beam sections and having iiexible hinge portions may operate either in compression or in tension.

Another object of the invention is to provide a thermostat in which the portions of the spaced active elements which are shaped as beam sections move about the hinge portions by differential elongation and shortening of the active elements upon a rise and drop in temperature.

Another object of the invention is to provide a thermostat in which the spaced active elements shaped as beam sections and having flexible hinge portions may be stamped from sheet or strip stock and joined in spaced relation without hot rolling or pressing; also active elements'of the character described which may be similarly formed to permit use, for example, of the same stamping or forming means for the diierent active elements.

Another object of the invention is to provide active elements of the class described which are shaped to permit nesting of such elements for further compactness of the device.

Another object of the invention is to enable making the active elements of different sensitive metals, alloys or other materials having good strength and high coeiiicients of thermo-expansion; also to enable the use of active elements having different coeiiicients of expansion combined with generally similar moduli of elasticity.

Another object of the invention is to provide a thermostat in which the active elements may be spaced diiferently to provide diiierent sensitivities and different output forces for a given change in temperature.

Another object of the invention is to eliminate shear forces such as are present in bimetal thermostats where the neutral axis is welded, whereby to enable a further reduction in size of the thermostat.

Another object of the invention is to enable the use of highly stressed and extremely thin active elements further to increase the sensitivity of the device.

Further objects and advantages and numerous adaptations or" the invention will appear from the following detailed description, taken in connection with the accompanying drawing.

In the drawing:

Figure l is a front elevational view of one form of thermostat embodying the present invention, with the front cover removed;

Figure 2 is a vertical sectional view taken on the line 2 2 of Figure l;

Figure 3 is a detail section taken on the line 3 3 of Figure 2;

Figure 4 is a fragmentary elevational view showing the pivoting of a magnet on one of the contact arms; and

Figure 5 is a fragmentary sectional View showing a modification incorporating sealed contacts.

Referring now to the drawing, the particular embodiment of the invention selected for illustration comprises a base plate 1 which may be mounted, for example, upon a wall 2 or other support.

The active elements 3 and 4 of the thermostat are shaped as beam sections and, by such construction, can operate either in compression or tension. The present invention is not limited to the particular beam section configuration shown in the drawing, but contemplates other forms of beam sections within the scope of the appended claims.

As best shown in Figure 3, the beam sections selected for illustration are of longitudinally extending, generally channel form, having angular longitudinally extending flanges 5 and a connecting web 6. The connecting web 6 0f each element 3 and 4 extends at 7 beyond the flanges 6 at one end of the thermostat (i. e., at the lower end as the device is shown in the drawing). ln the absence of the anges 5 along the extending ends 7 of the webs 6, these extending web ends 7 are liexible and constitute a liexible hinge for the active elements 3 and 4, as will presently appear.

The outer or upper ends of the elements 3 and 4, as the device is shown in the drawing, are spaced apart by a spacer 8 rigidly fixed between the webs 6 of the elements 3 and 4. The inner or lower ends of the elements 3 and 4 are spaced apart by a spacer 9 rigidly fixed between the extending ends 7 of the webs 6. The spacers S and 9 may be of the same thickness to provide equal spacing of the active elements 3 and 4 throughout their extent. The elements 3 and 4 may be rigidly joined at the spacers 8 and 9 by welding, brazing, soldering, screwing or riveting them together with the spacers 8 and 9 rigidly secured therebetween, or they may be joined in any other suitable or desired manner.

The elements 3 and 4 may be formed of any suitable or preferred metals, alloys, or other thermostat materials having different coefficients of expansion. Thermosensitive metals having good strength and high coecients of expansion are preferably employed. As an example and cured at their ends or other spaced locations, the Invar element 3 may be associated with an element 4 of alumi num or brass or, preferably, stainless steel which has a coeiicient of expansion corresponding to some brasses, and thereforeditferent from the coeicient of expansion of the Invar element. At the same time the stainless steel element has a modulus of elasticity similar to Invar.

The spaced extending ends 7 of the webs 6 are secured with the spacer 9 therebetween, for example, to a flange 10 at the outer end of a channel-shaped bracket 11, for example, by a rivet 12 or by a screw, or by welding, soldering, brazing, or otherwise as desired. The inner end of the bracket 11 has, for. example, anotherflange 13 secured to the base plate 1, for example, by a rivet 14, or by a screw, or otherwise as desired.

The angular anges 5 of the beam sections of the active elements 3 and 4 terminate short of the attachment of the elements 3 and 4 to the bracket 11 to form the hinge 15 about which the elements 3 and 4 rotate or move in the operation `of the thermostat. As the temperature of the room or other space, or other temperature affecting the elements 3 and 4, rises, the element 4 elongates, whereby tne elements 3 and 4 assume different lengths to cause rotation or movement of the elements 3 and 4 in the direction of the arrow 16 (Figure 2) about the hinge 15. Upon a drop in temperature, the element 4 contracts or shortens differentially relative to the element 3, and the elements 3 and 4 rotate or move about the hinge 15 in the opposite direction.

The active elements 3 and 4 may be stamped from sheet or strip stock, and are joined in spaced relation without hot rolling or pressing operations. Moreover, the active elements may be similarly formed and shaped to permit use, for example, of the same stamping or forming means for the different active elements 3 and 4. Moreover, the r shape of the elements 3 and 4 to form the beam sections permits nesting of the elements 3 and 4 as shown in Figure 3 for further compactness of the device.

In the manufacture of thermostats embodying the pres-v ent invention it is contemplated to provide different spacings between the active elements 3 and 4 and to join these elements in their different spaced relations to provide different sensitivities and different output forces for a given change in temperature.

The active elements 3 and 4 of the present invention may be shorter than the usual prior art bimetal elements;

also of less mass and higher or more powerful output action, and of smaller, more compact, and more sensitive character. While the present invention is not limited thereto, it has been found by experiments with Invar and #302 stainless steel of .005 of an inch thickness spaced .O20 of an inch apart and 21/2 inches long sensitive elements that an operating differential of approximately 1/2 of a degree F. is obtained at 3 grams contact pressure. It is contemplated that the spaced metalsthermostat of the present invention will be projected to thermostats which may be totally enclosed so that even thinner, and hence more thermally sensitive elements may be employed.

Thesimilarly formed` spaced metals permit of a shorter .t

stat for the reason that the main axis formed, for example, by the Invar element with an expansible element has no shear forces therein as in the case of a bimetal thermostat where the neutral axis is welded. This enables further reduction in size of the thermostat and, as a result, an exceedingly compact device is provided.

The use of highly stressed and extremely thin elements is permitted, and this further increases the sensitivity of the device. Moreover, neither element need be made of more metal than the other element to allow for a difference to which one metal will roll down as compared with the other metal as in bimetal thermostats where the metals are hot rolled and pressed in brazing or welding them together.

The mounting tang. or flange 10 may, if desired, be of a character to be turned or twisted with a pair of pliers or other suitable tool to get the end of the thermostat properly located.

An insulating pusher or actuator 18 is carried by the active elements 3 and 4 adjacent to the spacer 8 for actuating a controlled device by movement of the active elements 3 and 4 aboutthe hinge 15. The actuator 18 may be secured to the elements 3 and 4, for example, .by a rivet 19 which rigidly joins these elements with the spacer S therebetween or otherwise as desired.

ln the illustrated embodiment of the invention the controlled device is shown in the form of a switch comprising a pair of switch blades 20 'and 21 mounted on an insulating block 22 which, in turn, may be secured to an insulating base block 23. The base block 23 may be suitably secured to the base plate 1, for example, by screws, one of which is shown at 24.

Thel contact arm or blade2i) 'may carry a small magnet, such as a bar magnet 25, upon a friction pin 26 so that it maybe turned or adjusted angularly about the pin 26and with respect to an armature 27 'Carried by the switch blade .21. Figure 4 shows one position of the bar magnet 25'in full lines, and'another position in dotted lines. In the full line position a greater area of the bar magnet 25 cooperates with the armature 27 than in the dotted line position. Other positions of the bar magnet 25 about the pin 26 will provide greater or less areas of cooperation with the armature 27 as desired. Friction cooperation of the bar magnet 25' with the pin 26 retains the bar magnet in any of its adjusted positions.

The base plate 1 is provided with an opening 28 through which conductors 29, 29 may pass. 29 are fastened in contact with conductor plates 30 which in turn are connected as by wires or conductors 31, 31 to the lower extensions Aof the switch blades 20 and 21.'

Where-the thermostat is used, for example, for regulating automatically the temperature produced by heating apparatus, and more particularly for maintaining the temperature of a room or other space, the conductors '29 may, for example, connect an electroresponsive valve in the gas or other fuelV supply line to a source of electric power (not shown), so that when the contacts 32 and 33' on the switch blades 20 and 21 are in Contact the valve will be energized to open and be retained in open position` for the supply of gaseous fuel to the burner. When contact 32 is separated from contact 33 the circuit'is opened andthe valve moves to closed position to shut off the supply of fuel to the burner. The foregoing aspects are merely illustrative. The thermostat mayalso be usedin-connection 4with cooling systems and for controlling .any electric circuits, or elsewhere as suitable or desired.

TheswitchA blades 20 and21 are of suitable electric conducting spring stock, and are biased away from each other or arranged with the blade 20 biased away from the blade 21 with enough tension to break the magnet 25 away fromthe armature 27 and separate contacts `32 and 33 even-in theirmost favorable positions with respect to the magnetand armature combination. By turning the, magnet- 25..on its pivot 26 theattraction of the magnet for The conductors 29,

the armature may be adjusted to the break away tension in the switch blades and 21 or for adjusting the break away tension required in the switch blades.

A struck-in neck 34 on the base plate 1 may be internally threaded at 35 to receive an adjustment screw 36 which is fixed at 37 to turn with a rotatable adjustment dial 38. An insulating adjusting screw 39 is screwed at in the screw 36 and constitutes a factory adjustment screw with the dial set at 70, for example, in a 70 ambient, and the screw 39 backed into the screw 36 so that contacts 32 and 33 will just make contact. The dial 38 projects peripherally through an opening 41 in a member 42 carried by the base plate 1, and has temperature markings 43 on its outer surface which are adapted to be moved into register with a pointer 44 on the member 42 to set the device for the desired temperature to be maintained.

A pin 45, which projcts into an arcuate slot 46 in the dial 38 and limits the rotation or turning movement of the dial in opposite directions, may friction engage the sides of the slot 46 to retain the dial in its adjusted position. The pin 45 may be carried by the base plate 1 or otherwise supported in fixed position.

The front of the device may be covered by a cover 43 secured, for example, at its upper end to the member 42 by a screw 49. The lower end of the cover 43 is shown secured, for example, by a screw 50 to an angular member 51, which in turn is secured by a screw 52 to a forwardly projecting marginal flange 53 on the base plate 1. rhese details may, of course, vary widely within the scope of the present invention.

in the operation of the device, when the temperature aiecting the active elements v3 and 4' of the thermostat rises above the temperature for which the device is set (i. e., 70 as shown in Figure 2) the element 4 elongates, whereby elements 3 and 4 assume different lengths to cause rotation or movement of the active elements 3 and 4 in the direction of the arrow 16 about the hinge 1S. This removes the pressure of the pusher or actuator 18 against the switch blade 20 which holds the Contact 32 in contact with contact 33, and, as a result, the blade 20 springs, by its own bias or resilience, away from blade 21 and separates contact 32 from contact 33. This shuts off the heating action, for example, by shutting otl the ow of fuel to the burner.

Upon a drop in temperature, the element 4 shortens more than element 3, and the elements 3 and 4 are caused to rotate or move in the opposite direction to press the contact 32 into Contact with the contact 33. This starts the heating action, for example, by establishing a ow of fuel to the burner.

The active elements 3 and 4 may be highly stressed, with the stresses concentrated at the hinge 15. in existing thermostats, a differential of about 3 may be obtained without heat anticipation. With the active thermostat elements 3 and 4 of the present invention, it has been found that a differential of less than 1 is obtainable, particularly with low contact pressure of the order of approximately 3 to 6 grams.

While only a single pair of nested active elements 3 and 4 are shown in the drawing, it is to be understood that a plurality of sets of such nested elements may be employed within the scope of the present invention.

In the modified form of the invention shown in Figure 5, the contacts 32 and 33', carried by the switch blades 20 and 21 respectively, are enclosed within an enclosure formed, for example, by a pair of flexible cups 56 secured, for example, between the contacts 32 and 33 and the respective switch blades 20' and 21 and joined marginally at 57. The enclosure members 56 may be formed, for example, of neoprene, which is a synthetic rubber, or of other suitable material.

In this latter embodiment of the invention, the pusher or actuator 18 is in the form of an angular insulating member secured at 58 to the outer ends of the active elements 3 and 4. In this form of the invention the switch blades 20 and 21 project outwardly of the contacts 32 and 33', and the actuator 18 cooperates with the switch blade 20 outwardly of the contact 32'. The dial 38 is fixed to turn with a screw 36', and screw 39' is screwed into the screw 36 and cooperates with the projecting end of the switch blade 21'. The switch blades 20' and 21' are mounted on an insulating block 22', which in turn may be secured to an insulating block 23' as in the preceding embodiment of the invention.

The embodiments of the invention shown in the drawing are for illustrative purposes only, and it is to be expressly understood that said drawing and the accompanying specification are not to be construed as a denition of the limits or scope of the invention, reference being had to the appended claims for that purpose.

I claim:

l. A thermostat comprising a pair of active elements of substantially equal length and coextensive, said elements having different coeiicients of expansion and shaped as beam sections with the beam section of one element extending to one end of said element and the beam section of the other element extending to the adjacent end of the other element, the beam sections of both said elements terminating short of one pair of adjacent ends of said elements to form at protruding end tabs flexible transversely to form ilexible hinge portions, spacer means interposed between said end tabs outwardly beyond said exible hinge portions and between the beam sections at the opposite ends of said elements and acting to space said elements substantially uniformly throughout their entire extent to reduce heat transfer from one of said elements to the other element, xed means joining said end tabs together outwardly beyond said beam sections to form by said exible tabs hinge portions between said fixed means and the adjacent ends of said beam sections, and means joining the beam sections at the opposite ends of said elements and the spacer means together whereby differential elongation and shortening of the elements when equally subjected to changes in temperature of the surrounding medium causes swinging movement of said elements about said hinge portions.

2. A thermostat according to claim l wherein the beam sections of the active elements are of channelshaped configuration, with the channel-shaped beam section of one element nested within the channel-shaped beam section of the other element throughout its longitudinal extent.

3. A thermostat according to claim l wherein the protruding end tabs at the adjacent ends of one pair of active elements are xedly secured to a stationary support, the spaced beam sections at opposite ends of said elements carrying a pusher cooperable by swinging movement of said elements with one of a pair of contact arms to move a contact thereon into engagement with a cooperating contact on the other contact arm, said pusher releasing said contact arm for separation of said contacts upon swinging movement of the elements in the opposite direction.

4. A thermostat according to claim l wherein the protruding end tabs at the adjacent ends of one pair of active elements are iixedly secured to a stationary support, the spaced beam sections at the opposite ends of said elements carrying a pusher cooperable by swinging movement of said elements with one of a pair of contact arms to move a contact thereon into engagement with a cooperating contact on the other contact arm, said pusher releasing said contact arm for separation of said contacts upon swinging movement of the elements in the opposite direction, an armature on one of said contact arms, and a cooperating magnet on the other contact arm.

5. A thermostat according to claim 1 wherein the protruding end tabs at the adjacent ends of one pair of active elements are iixedly secured to a stationary support, the spaced beam sections at the opposite ends of said-elements ycarrying 1a pusher cooperable by swinging movement of said elements with one of a pair of contact arms to move Ya contact thereoninto engagement with a cooperating;v contact on'the other contact arm, saidl pusher releasing lsaid contact arm` for separation of said contactswupon swinging movement of the elements in arms -to move a contact thereon'into engagement with a cooperatingcontact on the, other contact arm, said pusher releasing said contact arm for separation of said contacts upon swinging movement of the elements in the opposite direction, an adjustment screw having screwed-engagement with a fixed threaded support adjacent to said other Contact arm, and an adjusting screw independently adjustable in said adjustment screw and cooperating with said other contact arm to constitute a factory adjustment for the thermostat.

7. A thermostat according to claim 1 wherein the protruding end tabs at the adjacent ends of one pair of active elements are xedly secured to a stationary support, the spaced beam sections at the opposite ends of said `elements carrying a pusher cooperable by-swinging n movement of said elements with one of a pair of contact arms to move a contact thereon into engagement with a cooperating 'contact on the other contact arm, said pusher releasing said contact arm for separation of said contacts upon'swinging movement of the elements in the opposite direction, and a sealed enclosure enclosing the contacts and comprising flexible cups carried by the contact arms and joined peripherally.

8. In a device of the class described, in combination, a pair of contact arms having contacts thereon, a thermostat operable to move one of said contacts into cooperation with the other contact, one of said arms being biased to position away from its contact with the other contact, an adjustment screw having screwed engagement with a fixed threaded support adjacent to said other contact arm, and an adjusting screw independently adjustablein said adjustment screw and cooperating directly with said other contact arm to constitute a factory adjustment for the thermostat.

References Cited in the file of this patent UNITED STATES PATENTS 1,116,534 Baker Nov. 10, 1914 1,511,055 Entwhistle Oct. 7, 1924 1,706,523 Churcher Mar. 26, 1929 1,801,736 Greenwood Apr. 21, 1931 1,940,300 Gerdien et al. Dec. 19, 1933 2,040,919 Caldwell May 19, 1936 2,204,791 Davis June 18, 1940 2,248,666 Fischer July 8, 1941 2,349,577 Dean May 23, 1944 2,412,483 Warrington Dec. 10, 1946 2,418,647 Jordan Apr. 8, 1947 2,420,078 Higley May 6, 1947 2,473,789 Crise June 21, 1949 2,519,025 Crise Aug. 15, 1950 FOREIGN PATENTS 109,273 Switzerland Apr. 11, 1924

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