US3753195A

US3753195A - Thermostatic switch

Info

Publication number: US3753195A
Application number: US00290570A
Authority: US
Inventors: L Woods
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1972-09-20
Filing date: 1972-09-20
Publication date: 1973-08-14
Anticipated expiration: 1990-08-14

Abstract

A thermostatic switch is disclosed comprising a dielectric housing having a first switch contact mounted within the housing. A thermoresponsive element having a central aperture is provided with a second switch contact mounted to the thermoresponsive element to make and break with the first switch contact upon actuation of the thermoresponsive element. A screw is screwed into the housing with a screw head disposed above an interior surface of the housing and a screw shank passing through the thermoresponsive element central aperture between the screw head and the housing interior surface. The central portion of the thermoresponsive element about the aperture is free to move along the screw shank between the screw head and housing interior surface. With this arrangement the screw provides means for adjusting the disposition of the thermoresponsive element while the screw head and housing interior surface limit movement of the central portion of the thermoresponsive element.

Description

United States Patent .1

Woods Aug. 14, 1973 THERMOSTATIC SWITCH Primary Examiner-Harold Broome [75] Inventor: Lee 0. Woods, Morrison, Ill. Attorney-John Stoudt et [73] Assignee: General Electric Company, Fort Wayne, Ind. ABSTRACT [22] Filed: Sept. 20, 1972 A thermostatic switch is disclosed comprising a dielectric housing having a first switch contact mounted [21] Appl' 290570 within the housing. A thermoresponsive element having a central aperture is provided with a second switch [52] U.S. Cl 337/347, 337/368, 337/94 Contact mounted to h herm responsive element to [51 Int. Cl. H01h 37/20 make and break h h first switch contact upon actu- [58] Field of Search 337/347, 368, 343, ation of the rm r pon i element. A screw is 337/363, 367, 89, 86, 94, 57 screwed into the housing with a screw head disposed above an interior surface of the housing and a screw [56] References Cit d shank passing through the thermoresponsive element UNITED STATES PATENTS central aperture between the screw head and the housing interior surface. The central portion of the thermogt g fi responsive element about the aperture is free to move 2 434 984 1/1948 Boleskfiiliffi II: 337/367 alng the Screw shank between the screw head and 3,1950 Bolesky 337/89 housing interior surface. With this arrangement the 2,543,040 2/1951 Mertler... 337 screw provides means for adjusting the disposition of 2,866,039 12/1958 Epstein 337/89 the thermoresponsive element while the screw head 2,967,920 1/1961 Harper, Jr. et al. 337/86 and housing interior surface limit movement of the cen- 3,0|3,l38 [2/1961 MOkSLI {It a]. 337/94 tra] portion of the thermoresponsive element 3,393,389 7/1968 Mawney et a1. 337/57 10 Claims, 4 Drawing Figures 1 l 53 5g 7 i I .5? 40 T 40 J 42 e 42 1 -.1 H i A I l I I0 I I /4 24 54 Patented Aug. 14, 1973 3,753,195

2 Sheets-Sheet 1 i, 86 3 EB Patented Aug. 14, 1973 3,753,195

2 Sheets-Sheet 2 THERMOSTATIC SWITCH,

BACKGROUND OFTI'IE INVENTION arcuate bimetallic sheets or discs. Usually, the disc is mounted within the switchzhousingby means of an ad'- justable screw or postpassing through an aperture in: the disc center. Upon heating the disc snaps bringing.

switchcontacts mounted onthe disc periphery into or our of engagement with: matingaswitchcontacts fixedly mounted. within the switch housing adjacent the disc.

Reciprocal movement occurs upon cooling. Disc heating may. be effected either by; changes in ambient-temperature or by means-of'anv electric heating elementmounted within the: switch housing adjacent the' disc.

Inorder for. the arcuate' bimetallic disc to snap and thereby reverse its curvature;.i.e. t have its concave surface becomeconverrand-itsconvexsurface become concave, both its central and peripheral: portions must" have some freedom of movement. This movement however mustube limited in order. for reversesnapactionto return-the: disc to" its. initialpositionfrom which it may subsequently bei-recycledl And=,.of.course;.the discmust be properly mounted within the switchhousing itself.

Heretofore, the just discussed: requirements have been met mostfrequently. by means of screwsor bolts which,.for thepurpose of'this application and concluding claims, are considered equivalents. The screw is passed loosely througha central aperture in the bimetallicdisc with the threaded shank portionscrewed'into the housing orinto anut. Thescrew head'itself or a terminalfastener'has served to limitdisc' movementin one direction. Movement in the opposite" direction away fromthe screw-head has been limited by-flanges formed integrally on the screw shank or secured thereto. In other cases such opposite'disc movementhas beenlimited by compression sprin'gs disposed about the shank in contact with ahousingsurface; In still other cases eyelets and arbor forming'collars have been secured to such shanks, or, inthe case of nonadjustable' discs, to posts formed integrally with the housing. Each of these implements'haveincluded components which, in addition to the disc. itself, have had: to be secured-to the screw and carefully adjusted'in calibratingvthe switch. As these thermostaticv switches are often quite small and manufactured in large quantities, the. necessity for carefully securing such limits or stops has proven costly.

In thermostaticv switches of the type just described the peripheral portionsi of the thermoresponsive'element mustalso havelimited freedom of movement'in order to actuate the switch contacts associated therewith. Thus, theperipheral portion ofthe element is usually disposed withinacavity or void within theswitch housing. When an internal heating element is employed such heater is also disposed withinthis-cavity adjacent the thermoresponsive element. To the walls encompassing, and frequently definingthe cavity itself, are

mounted the switch terminals which extendto the exte-- rior of the switch housing. Frequently, one or more switch contacts are mounteddirectly to a portion of these terminals which protrude into the cavity. The

housing is typically formed of a molded phenolic resin. The metallic terminals are securedto' the housing by means of a thermosetting adhesive=such= as an epoxy resin. During-manufacture it is difficultto' control fully the" flow of the thermosetting adhesive; Thus,'it often happens that a portion of the adhesive fiows down into the cavity and onto a portion of the heating element. This, of course, is not desired insomuch as the resultant adhesive bridge fromthe housing to the heater creates a thermally conductive path for heat to flow to the housing rather than be radiated and convected to the thermoresponsive disc. This tends to place the thermostatic switch out'ofi operational adjustment. In addition, adhesiveupon the heater'tends to be vaporized during heater operation, which vaporized adhesive may condense upon the cooler switch contacts and otherwise contaminate the switch interior.

Accordingly, it is a general'object of the present invention to provide an improved thermostatic switch of the type employing a snap-acting thermoresponsiveelement.

More specifically, it is an object of the invention to provide'a thermostatic switch having improved means for adjustably mounting and limiting movement of a snap-acting thermoresponsive element.

Another'object of the invention is to provide a thermostaticswitch having a'snap-acting thermoresponsive element with improvedmeans'for positioninga heating element within the switch housing adjacent the snapacting thermoresponsive element.

SUMMARY OF THE INVENTION In one form of the present invention a thermostatic switch is provided comprising adiel'ectric housing having a first switch contact mounted within the housing. A thermoresponsive element having a central'aperture is provided with a second switch contact mounted to the thermoresponsive element to make andbreakwith the first switch contact upon actuation of the thermoresponsive element. A screw is screwed into the housing I BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a top plan view of a thermostatic switch em-' bodying principles of the present invention in one form with most of the housing cover removed to reveal internal components of the switch. I

FIG. 2 is a cross-sectional view of the switch show in FIG. 1 taken along plane 2-2 with selected switch terminals, contacts, and an adjustable screw shown in elevation. I

- FIG. 3 is a topplan view of the switch housingcover shown in FIG. 2.

FIG. 4 is a top plan view of the switch housing base shownin FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE DRAWING Referring now in more detail to the drawing, there is shown a thermostatic switch comprising a dielectric housing having a molded phenolic base member and a molded phenolic cover member 12. The two housing members are secured together along mating, planar member surfaces by four screws 14 extending through aligned holes 16 in the two housing members, and by four nuts 18.,Alternatively, rivits or eyelets may be substituted for these screws and nuts. The interior of base 10 may, by reference to FIG. 4, be seen to be so molded as to have three walls 20 peripherally disposed about a cavity floor 22. Three steps 24 rise above floor 22 with the top surface of the steps extending between walls 20 to the base exterior. Each step has a recess 26 in the top surface as well as a trough 28 extending downwardly from the recess towards the cavity floor.

From the central portion of the cavity floors extends a generally conic projection 30 having a center bore 32 into which a screw may be screwed and thereby form threads within the bore. The conic projection is truncated to have an annular, planar apex surface 34. Near this projection apex surface bore 32 flares as shown by conic surface 36. As seen by reference to FIG. 3, cover 12 is molded with walls 38 formed to matewith the walls of base 10. When so mated upon switch assembly wall extensions 39 project partially down over the extensions of steps 24 between base walls 20 thereby forming three slots which pass through the mated walls to the switch exterior.

Referring now to FIGS. 1 and 2 the thermostatic switch is seen to have three generally planar terminals 40 extending from the exterior of the switch housing through the just described slots and onto the top of steps 24 between shoulders 25. To the exposed tops of two of these terminals are secured two stationary or fixed switch contacts 42. A heater wire 44 is secured to the third terminal and to one of the contact supporting terminals. The heater wire partially encircles projection 30 in spaced relation with both it and floor 22 of the cavity in which it is disposed. Terminal tabs 46 extend downwardly into recesses 26 within steps 24. A thermosetting adhesive, such as a translucent epoxy resin, is poured into recesses 26 as indicated at 48. Once set the adhesive firmly secures terminals 40 atop steps 24 and thus to the housing base. During manufacture excess adhesive flows down through troughs 28 to cavity floor 22. The quantity of adhesive in excess to the volumetric capacity of recesses 26 is ordinarily slight and certainly insufficient to cover floor 22 and thereby build upwardly towards heater wire 44. Being below the top surface of the terminals there is also little danger in any of the adhesive flowing onto contacts 42.

With continued reference to FIGS. 1 and 2, a thermoresponsive element in the form of a generally disc shaped sheet of bimetal 50 is seen to be mounted within the switch housing by means of a screw having a screw head 52 and a screw shank 54. One of two unitary tail portions 51 of the disc are positioned between two posts 53 which prevent the disc from rotating. An unthreaded portion of the screw shank passes loosely through a central aperture 56 in the bimetallic disc. The central aperture is in the shape of a four leaf clover which serves to provide the disc with good snap action characteristics during actuation. A threaded portion of the screw shank is screwed into the walls of bore 32 within projection 30 until screw head 52 engages the bi-metallic disc with mobile switch contacts 58 secured beneath peripheral portions of the disc in engagement with fixed contacts 42. The screw may then be screwed further down into bore 32 for switch operational adjustment. As this action progresses screw head 52 forces the central portion of disc towards annular surface 34 atop projection 30 whereupon a smaller increase in the temperature of the disc will cause the disc to snap to the position shown in phantom lines 50'. Such snap action in turn causes switch

contacts

42 and 58 to break. Subsequent cooling of the disc forces the disc to snap back to its initial position 50 thereby causing the fixed and mobile contacts to remake.

From the above description it should be noted that screw head 52 limits movement of the central portion of the bimetallic disc upwardly, as viewed in FIG. 2, while annular surface 34 atop conic projection 30 limits downward movement of this portion of the disc. Thus, screw head 52 and annular surface 34 function as stops. Simultaneously, screw head 52 serves as disc mounting and adjustment means, and annular surface 34 as a part of the female screw receiving and switch housing structure. This unique combination of elements renders simplicityv and economy to the switch.

It should be understood that the just described embodiment merely illustrates principles of the invention. Obviously, many modifications may be made thereto without departure from the spirit and scope thereof as set forth in the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A thermostatic switch comprising a dielectric housing; at least one fixed contact mounted within said housing; a conductive snap-acting thermoresponsive element having a centrally located aperture; at least one mobile switch contact mounted to said conductive snap-acting thermoresponsive element to make and break with said fixed switch contact; and a screw secured to said housing and having an exposed screw shank portion extending from an interior surface of said housing through said thermoresponsive aperture to a screw flange portion extending over a portion of said thermoresponsive element adjacent said thermoresponsive element aperture, said exposed screw shank portion being dimensioned to permit the central portion of said thermoresponsive element to move there-, along between said housing interior surface and said screw flange portion; whereby the screw provides means for adjusting the disposition of the conductive snap-acting thermoresponsive element, and the interior housing surface and screw flange portion limit movement of the central portion of the conductive snapacting thermoresponsive element along the exposed shank portion of the screw.

2. A thermostatic switch in accordance with claim 1 wherein said screw flange portion comprises the, head of said screw.

3. A thermostatic switch in accordance with claim 1 wherein said interior surface of said housing is annular.

4. A thermostatic switch in accordance with claim 1 wherein said dielectric housing comprisesa base having an interior floor and a centrally located projection extending from said floor; and wherein said interior surface of said housing is the apex of said projection.

5. A thermostatic switch in accordance with claim 4 wherein said base comprises a plurality of steps extendin g from said floor in spaced relation with said centrally located projection; and a plurality of walls extending between said steps to form a cavity within said base bounded on the outside by said walls and steps and on the inside by said centrally located projection.

6. A thermostatic switch in accordance with claim 5 comprising a plurality of terminals mounted atop said plurality of steps, and a heater wire disposed within said cavity adjacent said conductive snap-acting thermoresponsive element and electrically connected to two of said terminals.

7. A thermostatic switch comprising: a dielectric housing; a first switch contact mounted within said housing; a thermoresponsive element having a central aperture; a second switch contact mounted to said thermoresponsive element to make and break with said first switch contact upon actuation of said thermoresponsive element; a screw screwed into said housing and having a screw head disposed above an interior surface of said housing and a shank passing through said thermoresponsive element central aperture between said screw head and said housing interior surface with the central portion of said thermoresponsive element about said aperture being free to move along said shank between said screw head and said housing interior surface; whereby said screw provides means for adjusting the disposition of said thermoresponsive element and wherein said screw head and housing interior surface limit movement of said thermoresponsive element.

8. A thermostatic switch in accordance with claim 7 wherein said dielectric housing includes a base having a centrally located projection into which said screw is screwed, and wherein the apex of said projection forms said housing interior surface.

9. A thermostatic switch in accordance with claim 8 wherein said housing interior surface is the annular apex of a truncated conic projection into which said screw is screwed.

10. A thermostatic switch in accordance with claim 9 wherein said housing base has a plurality of peripheral walls disposed about said centrally located projection at least partially defining a cavity, and wherein said thermostatic switch further comprises means for heating said thermoresponsive element mounted within said cavity in spaced relation with said walls and said projection. I

* i i I k

Claims

1. A thermostatic switch comprising a dielectric housing; at least one fixed contact mounted within said housing; a conductive snap-acting thermoresponsive element having a centrally located aperture; at least one mobile switch contact mounted to said conductive snap-acting thermoresponsive element to make and break with said fixed switch contact; and a screw secured to said housing and having an exposed screw shank portion extending from an interior surface of said housing through said thermoresponsive aperture to a screw flange portion extending over a portion of said thermoresponsive element adjacent said thermoresponsive element aperture, said exposed screw shank portion being dimensioned to permit the central portion of said thermoresponsive element to move therealong between said housing interior surface and said screw flange portion; whereby the screw provides means for adjusting the disposition of the conductive snap-acting thermoresponsive element, and the interior housing surface and screw flange portion limit movement of the central portion of the conductive snap-acting thermoresponsive element along the exposed shank portion of the screw.

2. A thermostatic switch in accordance with claim 1 wherein said screw flange portion comprises the head of said screw.

4. A thermostatic switch in accordance with claim 1 wherein said dielectric housing comprises a base having an interior floor and a centrally located projection extending from said floor; and wherein said interior surface of said housing is the apex of said projection.

5. A thermostatic switch in accordance with claim 4 wherein said base comprises a plurality of steps extending from said floor in spaced relation with said centrally located projection; and a plurality of walls extending between said steps to form a cavity within said base bounded on the outside by said walls and steps and on the inside by said centrally located projection.

10. A thermostatic switch in accordance with claim 9 wherein said housing base has a plurality of peripheral walls disposed about said centrally located projection at least partially defining a cavity, and wherein said thermostatic switch further comprises means for heating said thermoresponsive element mounted within said cavity in spaced relation with said walls and said projection.