US2907851A

US2907851A - Electrical switch structures

Info

Publication number: US2907851A
Application number: US736833A
Authority: US
Inventors: John O Moorhead; Raymond D Mulry
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1958-05-21
Filing date: 1958-05-21
Publication date: 1959-10-06
Anticipated expiration: 1976-10-06
Also published as: FR1224555A

Description

1959 10. MOORHEAD ETAL 2,907,851

ELECTRICAL SWITCH. STRUCTURES Filed May 21, 1958 2 Sheets-Sheet 1 72 lnventanis':

John 0. floorkeaai, Ra mand flfiulry,

0d. 6, 1959 Q, MOQRHEAD ETA k 2,907,851

ELECTRICAL SWITCH STRUCTURES Filed May 21, 1958 2 Sheets-Sheet 2 Inventors: rfoizn 0.Moorizead, Raymond D. Mulrzy,

United States Patent 2,907,851 ELECTRICAL SWITCH STRUCTURES John 0. Moorhead and Raymond D. Mulry, Lexington, -Ky., assignors to Texas Instruments, Incorporated,

Dallas, Tex., a corporation of Delaware Application May 21, 1958, Serial No. 736,833 14 Claims. (Cl. 200-138) This invention relates to electrical switch structures and, more particularly, to such switch structures which arethermally responsive.

Thermostatic or thermally responsive electrical switches, for one reason or another, are often required to be provided in the form of a hollow casing enclosing a thermal sensing element. For example, the interior of thermostatic switches for refrigerators in many cases must be sealed off from the circumambient atmosphere to prevent the entry of moisture-laden air thereby avoiding condensation on the internal parts of the switch and any resulting low electrical resistance path to ground along the surfaces of these parts and/ or corrosive action on these surfaces. The problem arises in such cases and in others of providing for the eflicient transfer of heat between the temperature-sensing element within the switch casing and the article whose temperature is to be sensed.

'Another difiiculty frequently encountered in the art of thermally responsive switches is that of providing for the efficient transfer of heat between an article: whose temperature is to be sensed and a thermally responsive element of, for example, the type formed from composite sheet material including layers having relatively different coefficients of thermal expansion; this particularly where the respective shapes of said element and said article are not compatible with each other so as to permit a substantial area of mutual contact therebetween.

.An object of this invention is to provide a novel thermally responsive switch structure which overcomes the above and other difiiculties.

1 Another object of this invention is to provide a new and improved switch structure of the class described which exhibits improved temperature-response characteristics.

A further object of this invention is to provide such a novel switch structure which is adapted for simple and reliable mounting on an article whose temperature is to be sensed.

A further object of this invention is to provide such anew and improved switch structure which is economical to produce and dependable in operation.

Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which one of the various possible embodiments of the invention is illustrated:

jFig. 1 is an elevational view in section of an electrical switch structure embodying the invention, the switch being shown mounted on a tube whose temperature is' to be sensed;

Fig. 2 is a sectional view taken along line 2-2 of Fig:1;-

Fig. 3 is a fragmentary elevational view on a slightly reduced scale of the cup-shaped member shown in Figs. 1 and 2;

Fig. 4 is a fragmentary plan view of the casing member as shown in Fig. 3 along with a sectional fragment of the other casing member to show structure of these parts by which they are mutually aligned;

Fig. 5 is a fragmentary view of the casing member as shown in Fig. 3 but rotated about its vertical axis;

Fig. 6 is a perspective view of the spring clip shown in Figs. 1 and 2; and

Fig. 7 is an enlarged fragmentary view illustrating the manner of and a tool for applying the spring clip of Fig. 6 to mount the thermally responsive switch on a tube whose temperature is to be sensed.

Referring to Fig. 1, an electrical switch structure embodying the invention is shown taking the form of a thermally responsive switch generally indicated by the reference numeral 10. Switch 10 includes a first hollow, cup-shaped casing member 12 formed of one of the customary moldable, electrically insulating, plastic materials and a second hollow, cup-shaped casing member 14 formed of a suitable sheet material having good thermal conductivity. The sheet material of which cup-shaped member 14 is formed is preferably aluminum, copper, bronze or the like in that these materials are not only thermally conductive but readily lend themselves to the conventional drawing and forming operations utilized to form'cup-shaped member 14 from fiat sheet stock. In the embodiment shown in the drawing, the sidewalls of

casing members

12 and 14 are cylindrical in form.

Hollow casing member 12 encloses an electrical contact arrangement of any desired form which, in the embodiment shown in the drawing, includes a bridging contact member 16 disposed in operative relationship to spaced

stationary contacts

18 and 20. According to the particular embodiment shown in the drawing, a compression spring 22 has one end in abutment with casing member 12 and its opposite end biased against a springretaining member 24, the latter being engaged with bridging contact member 16 whereby spring 22 resiliently biases contact member 16 from contacts-open position to the contacts-closed position shown in Fig. 1. Each of

stationary contacts

18 and 20 is carried by a

terminal

26 and 28, respectively, which extends through the casing to the exterior thereof.

Cup-shaped casing member 14 provides, adjacent its open end, two annular, inwardly extending ledges or

steps

30 and 32 about its inner periphery, the step 30 nearer the open end of the cup-shaped member extend-- ing outwardly of the other step 32.

Switch 10 includes a thermally responsive member 34 formed of composite, thermally responsive material. The thermally responsive material of which element 34 is formed comprises at least two

layers

36 and 38 having mutually different coeflicients of thermal expansion and joined together. Thermally responsive element 34 is provided with a deformation or dished shape capable of changing its shape suddenly with a snap motion from the position shown in full lines in Figs. 1 and 2 to the broken-line position shown in Fig. 1 when heated or cooled, as the case may be, to a predetermined temperature. For certain applications, the material of layer 36 will have a greater coefficient of thermal expansion than that of layer 38 whereby element 34 will snap from the full-line (contacts-closed) position to the broken-line smaller coeificient of thermal expansion than that of layerv 38 whereby element 34 will snap position to the contacts-open position upon cooling" from the contacts-closed (rather than heating, as before) of this element to a predetermined temperature. Element 34 resets itself by snapping back to the contacts-closed position upon cooling or heating to a predetermined temperature depending, of course, upon whether this element snaps to the contactsopen position upon heating or cooling, respectively; It will be apparent, however, that the invention is .applicable as well to other thermally responsive elements such, for example, as those similar to element 34 but designed with a reset temperature above or below, as the case may be, the temperature range to which the element Will be expected normally to encounter whereby resetting thereof must be accomplished manually.

A motion transfer member 40 formed of electrical insulating material is provided having one end bearing against thermally responsive element 34 at substantially the central portion thereof and its other end adjacent and engageable with bridging contact member 16. It will be apparent, that, upon snapping of thermally responsive element 34 from the full-line to the broken-line position shown in Fig. l, motion transfer member 46 will be moved upwardly as viewed in Figs. 1 and 2 against bridging contact member 16 to move the latter against the bias of spring 22 to contacts-open position. Upon snapping of thermally responsive element 34 fromj'the broken-line to the full-line position shown in Fig. 1, the bridging contact member will be moved into contactsclosed position with respect to

stationary contacts

18 and 20 under the resilient bias exerted by spring 22.

According to the embodiment shown in the drawing, thermally responsive element is circular in shape. The outer, annular marginal periphery of thermally responsive element 34 is engaged with and supported by interionin wardly extending step 32, and the annular open end of casing member 12 is in abutting engagement with internal, inwardly extending step 30. The open end of easing member 112 extends inwardly of step 30 to overhang the latter at 42 whereby the outer margin of the thermally responsive element 34 is confined between step 32 on one side and the overhanging portion 42 of casing member 12 on the other side. A slight clearance is provided between overhanging portion 42 of the open end of easing member 12 and the adjacent outer marginal portion of the thermally responsive element to permit unrestricted movement of the latter between its two positions of stability as depicted in Fig. 1. Accordingly, a continuous, annular area of engagement between step 32 and the thermally responsive element is effected by the construction according'to the embodiment shown in the drawing.

Upon assembly of

casing members

12 and 14 as shown in Fig. 1, cup-shaped member 14 is inwardly deformed at 44 about its periphery to retain the casing members in assembled relationship. Prior to assembly of the

casing members

12 and 14, casing member 14 is indented at 46 to provide an inwardly extending projection 48 which interfits with a complementary-shaped recess 50 provided by the adjacent outer surface of easing member 12 as shown in Figs. 2 and 4. In this manner, alignment of

casing members

12 and 14 with each other during assembly is facilitated and relative rotation thereafter between these casing members is prevented.

With

casing members

12 and 14 assembled as shown in Fig. 1, a pair of leads 45, 47 covered except at their end portions with electrical insulation are inserted through respective apertures provided in the sidewall of easing member 14 (see the portion of aperture 49 for lead 45 as shown in Fig. 1), and leads 45, 47 are welded to

terminals

26 and 28, respectively. The interior of switch may be sealed from the circumambient atmosphere by depositing a suitable sealing compound 51 to fill cupshaped member 14 between the internal surface thereof and the external, otherwise exposed surfaces of casing member 12, leads 45 and 47 and the insulation within member 14 which covers these leads. In addition, a boot 52' formed of rubber or the like may be disposed about that of surface 94 and between the latter recess and.

casing member 12 and adjacent the upper end of easing member 14 as viewed in Fig. 1, with sealing compound 54 disposed between the adjacent portions of the boot and casing member 14, all as shown in Fig. 7.

Sealing compounds

51 and 54 may be any suitable, electrically insulating, thermosetting resin material which effectively bonds to the surfaces contiguous therewith.

Cup-shaped member 14 is further provided with

indentations

56 and 58 to provide a pair of external shoulders 61 and 62, respectively, for the reception and retention of the inturned

ends

64 and 66 of a U-shaped clip 68. U-shaped clip 68 is formed of relatively stiff, springy material such as 18-8 stainless steel.

The bottom of cup-shaped member 14 is provided with a recess 70 conforming to the shape of an article such as a tube 72 whose temperature is to be sensed by the thermally responsive element 34. The yoke 74 of U shaped clip 68 is likewise provided with a depression or recess/76 configured to conform to the shape of the article whose temperature is to be sensed by the thermally responsive element. Each of the portions of U-shaped clip. 68 between recess'76 and the inturned

ends

64 and 66 is provided with an

aperture

78, 80, respectively, and a

surface

82, 84, respectively, for the application of pressure to assemble the clip to cup-shaped member 14 with the article 72' therebetween. By virtue of

apertures

78 and 86, a pair of outwardly facing

abutments

79 and 81 are provided by the spring clip, each of these abutments lying between recess 76 and one of inturned ends 64 and 66.

A description, now to follow, of the manner in which clip 68 is applied to mount thermally responsive switch. 10 in good heat-conductivity relation with article 72 will serve to indicate, in part, the improved and advantageous characteristics of the invention. Referring to .Fig. 7, a tool generally indicated by the reference numeral 86 is provided carrying a stud 88 grooved at 90. Tool 86 further includes a pressure foot or pressure-applying surface 92. To mount cup-shaped member 14 of switch 10 tightly and securely on and against tube 72, cupshaped member 14 is placed in assembled relationship with tube 72 as shown in Fig. 7 whereby recess 70 of member 14 is engaged in interfitting relationship with the tube. One of the inturn'ed ends of U-shaped clip 68 (inturned end 64 as shown in Fig. 7) is disposed in engagement with one of external shoulders 60, 62 (shoulder 60 as shown in Fig. 7) as provided by cup-shaped member 14. The other inturned end 66 of clip 68 is' placed in engagement with a cam surface 94 provided by cup-shaped member 14 between recess 72 and external shoulder 62. Tool 86 is juxtaposed with clip 68 as shown in Fig. 7 whereby abutment 79 provided by aperture 78 is disposed in groove 90 of stud 88, and pressure foot 92 is in engagement with surface portion 84' of the clip. By swinging handle 96 of the tool in a generally counterclockwise direction fromthe full-line to the broken-line position shown in Fig. 7, it will be apparent that a combination of forces is applied to the spring clip including a generally laterally directed force by stud 88fiand a generally upwardly directed force ap plied by pressure foot 92. The combination of these forces in concert with the action of end 66 of the spring. clip moving against cam surface 94 of the-cup-shaped member results in the stressing of the spring clip and movement thereof to the broken-line position shown in. Fig. 7; this broken-line position corresponding to the full-line position shown in Figs. 1 and 2.

A cam surface 98 is provided by cup-shaped member 14 which may be identical to surface 94, but, as shown in the drawings, on the opposite side of recess 70 from the remaining parts of switch 10 are firmly mounted;

' yoke 74 of the spring clip, respectively,

on article 72, and, due to the provision of

recesses

70 and 76 in the bottom of cup-shaped member 14 and in rotation of cupshaped member 14 relative to tube 72 is effectively resisted. .Also, it is to be noted that the innermost edges of inturned ends 64 and 66 of the spring clip are concavely curved and that the indented portions of cupshaped member 14 adjacent thereto are convexly curved whereby the latter respectively fit one within the curved portion of each of said inturned ends. With this construction, movement of the spring clip in the directions toward and away from the viewer as shown in Fig. 1 and relative to cup-shaped member 14 is resisted.

It will be clear that with the construction as shown in Figs. 1 and 2, tube 72 is in good heat-transfer relation with cup-shaped member 14 for the conduction of heat along acomparatively large area of mutual contact therebetween. Also, a comparatively large area of mutual engagement is provided between thermally responsive element 34 and cup-shaped member 14 whereby a high degree of heat conductivity between these parts obtains. The result is that a good heat-transfer relationship exists between tube 72 and thermally responsive member 34 whereby changes in the temperature of the tube, due, for example, to the flow of refrigerant therethrough (the starting and stopping of which flow may be controlled by opening and closing of bridging contact member 16 with respect to contacts 18 and 20) are quickly and effectively reflected by snapping of the thermally responsive element between its respective positions of stability. The desirable result is achieved with the embodiment as shown in the drawings, that the flow of heat to and from the thermally responsive element is substantially uniform along the outer marginal portion of the latter toward and away from the center thereof. It will be apparent that the invention permits sealing off the thermally responsive element from the circurnambient atmosphere while providing for the effective heat transfer characteristics described above. Furthermore, the manner of mounting the thermally responsive switch on the tube 72 according to the invention is greatly superior to that, for example, of bolting-on from standpoints such as ease and cost of mounting and minimal time required therefor. Along with these advantages, the cost of the parts of switches embodying the invention compares most favorably with those of prior constructions.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

Dimensions of certain of the parts as shown in the drawing have been modified for the purposes of clarity of illustration.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

We claim:

1. An electrical switch structure including a pair of electrical contacts and a thermally responsive member, a hollow casing enclosing said contacts and said thermally responsive member, said thermally responsive member being operatively connected to open and close said electrical contacts, said casing including a member formed of heat-conductive material, and said last-named member being configured to conform to the shape of an article whose temperature is to be sensed by said thermally responsive member means on said last-named member having portions for releasably retaining a spring clip adapted to engage portions of an article whose temperature is to be sensed and retain said switch structure thereagainst.

2. An electrical switch structure comprising a hollow casing, a pair of electrical contacts and a thermally responsive element disposed within said casing, said to open and close said contacts, said casing including a cup-shaped member formed of heat-conductive ma-. terial, said cup-shaped member being configured to com form to the shape of an article against which the cup-,

shaped member is to be mounted, means on said cup: shaped member for releasably retaining a spring clip adapted to engage portions of said article and retain said switch structure thereagainst.

3. A unitary cup-shaped member for mounting a thermally responsive element of an electrical switch in good heat transfer relation to an article whose temperature is to be sensed by the switch, a part of said cup-shaped member providing inwardly extending shoulder means for supporting the thermally responsive element within the cup-shaped member, the external surface of said cup-shaped member being configured at one portion thereof to conform to the shape of said article, and the external surface of said cup-shaped member having indented portions at opposite sides thereof for thereception of a clip to retain said article firmly against said one portion of the cup-shaped member.

4. An electrical switch structure comprising in combination: a hollow base having an open end anden-- casing a pair of electrical contacts; a thermally responsive element operatively connected for opening and closing said contacts; a unitary cup-shaped member closing said open end of the base, said cup-shaped member being formed of heat-conductive sheet material and including, at opposite sides thereof, a first laterally extending por-;

tion providing an internal shoulder engaging said thermally responsive element and a second laterally extending portion providing an external shoulder; and a portion ofv said cup-shaped member being configured to conform to the shape of an article whose temperature is to be sensed by the thermally responsive element.

5. The electrical switch structure as set forth in claim I 4 including a U-shaped clip having inturned ends; each article whose temperature is to be sensed by the thermally responsive element.

7. The electrical switch structure as set forth in claim 4 wherein said internal shoulder extends in engagement with the thermally responsive element throughout the inner periphery of said cup-shaped member.

8. A unitary cup-shaped member for closing an open end of an electrical switch casing member, said cupshaped member being formed of a sheet of heat-conductive material, the sidewall of said cup-shaped member adjacent the open end thereof providing two inwardly extending shoulders about its inner periphery, one of said shoulders being adapted to engage the open end of said casing member and the other of said shoulders being adapted to engage the outer marginal portion of a thermally responsive element, a portion of the cup-shaped member being recessed to conform to the shape of an article against which the cup-shaped member is to be mounted, and the outer periphery of the sidewall of the cup-shaped member being inwardly indented at opposite sides of the cup-shaped member for the reception of a clip to retain said portion of the cup-shaped member firmly against said article.

9. In combination: a hollow switch casing member having an open end, a pair of electrical contacts mounted within said casing member, a cup-shaped member providing two inwardly extending steps about its inner periphery, the one of said steps nearer the open end of the cup-shaped member extending outwardly of the other step, the open end of said casing member lying against said one step and extending inwardly thereof to overhang the latter, a thermally responsive member having its outer marginal portion disposed between said other step and the overhanging portion of the end of said .casing member, said thermally responsive member being operatively connected to open and close said con tacts in response to change in temperature of the thermally responsive member, a portion of said cup-shaped member being recessed to conform to the shape of an article whose temperature is to be sensed by the thermally responsive member, said cup-shaped member being indented at opposite sides thereof, and a U-shaped spring clip for-straddling said article, said clip having inturned ends each of which is engaged with one of said indents for firmly biasing said article against the recessed por-' tion of said portion of the cup in good heat-transfer relation through the cup-shaped member to said thermally responsive element.

10. In combination, a unitary cup-shaped member for mounting a thermally responsive element of an electrical switch in good heat transfer relation to an article whose temperature is to be controlled by the switch, said cup-' shaped member including inwardly extending shoulder means for mounting the thermally responsive element within the cup-shaped member and spaced indented portions, the external surface of said cup-shaped member being configured at a portion thereof to conform to the shape of said article, a U-shaped spring clip having inturned ends received in said indented portions for retaining said article firmly against said portion of the cup-shaped member, and said cup-shaped member providing a cam surface adjacent one of said indented portions for camming one of the inturned endsof said spring clip into reception with said one indented portion while the other end of said spring clip is received in the other of said indented portions. 1

11. The combination as set forth in claim' 10 wherein said inturned ends of the U-shaped spring clip are concavely curved and the respective surfaces of said cupshaped member adjacent thereto are con'vexly' curved and" fit one within the curved portion of each of said in turned ends. 12. The combination as set forth in claim. 10. wherein ;said spring clip provides an outwardly extending abutand the thermally responsive element; said casingincluding a cup-shaped member formed of heat conductive sheet material and providing an annular shoulder in engagement with the thermally responsive element along the outer margin of the latter; the bottom of the cupshaped member being recessed to conform to the shape of an article against which the cup-shaped member is to be mounted, and the outer periphery ofthe sidewall of they cup-shaped member being inwardly indented at opposite sides of the cup-shaped member for the reception of a clip to retain said bottom of the cup-shaped member firmly against said article. I

References Cited in the file of this patent UNITED STATES PATENTS Moorhead -1 Feb. 18,