US3352986A

US3352986A - Vibration resistant construction for thermally responsive electrical switches

Info

Publication number: US3352986A
Application number: US502807A
Authority: US
Inventors: Jr John Doherty
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1962-11-30
Filing date: 1965-10-06
Publication date: 1967-11-14
Anticipated expiration: 1984-11-14
Also published as: GB1032870A; DE1490749B1; NL287423A

Description

Nov. 14, 1967 J. DOHERTY, JR 3,352,936

I VIBRATION RESISTANT CONSTRUCTION FOR THERMALLY RESPONSIVE ELECTRICAL SWITCHES Original Filed Nov. 50, 1962 2 Sheets-Sheet 1 Inventor; rfokn ,Dokert y, rim, 5? W Atg United States Patent Ofifice Delaware Continuation of application Ser. No. 241,349, Nov. 30, 1962. This application Oct. 6, 1965, Ser. No. 502,807

4 Claims. (Cl. 200-138) This invention is a continuation of my earlier filed parent application, Ser. No. 241,349, filed Nov. 30, 1962, now abandoned, in the name of John Doherty, Jr., and assigned to the assignee of the instant invention.

This invention relates to thermally responsive electrical switches and in particular to such switches which are especially suited for miniaturized, hermetically sealed constructions.

Among the several objects of this invention may be noted the provision of new and improved thermally responsive electrical switches which permit fast response, and are adapted for miniaturization so as to be conveniently insertable into small spaces adjacent the heated parts to which a temperature response is to be made by the switch; the provision of such switches which are especially adapted for hermetically sealed constructions; the provision of such switches which are precise and relatively simple to calibrate; the provision of such switches which are accurate, compact and reliable in operation; the provision of such switches which provide for improved vibration and shock resistance and which are not position sensitive; and the provision of such switches which embody a minimum number of parts, are simple in construction and are economical to assemble and manufacture.

Other objects will be in 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 several of the various possible embodiments of the invention are illustrated:

FIG. 1 is a top plan view of a thermally responsive electrical switch according to the present invention;

FIG. 2 is a sectional view taken on line 22 of FIG. 1 showing the parts in a contacts closed position;

FIG. 3 is a fragmentary sectional view similar to FIG. 2 showing the parts in a contacts-open position;

FIG. 4 is a sectional view taken on line 44 of FIG. 2;

FIG. 5 is an exploded elevational view of the switch shown in FIG. 2;

FIG. 6 is a top plan view of a wave spring washer used in the switch shown in FIGS. 1-5;

FIG. 7 is a view taken on line 77 of FIG. 6;

FIG. 8 is a sectional elevational view of a headerterminal subassembly according to a second embodiment of the invention useful for the switch shown in FIGS. 1-5; and

FIG. 9 is a view taken on line 99 of FIG. 8.

Similar reference characters indicate corresponding parts throughout the several views of the drawings. Dimensions of certain of the parts, as shown in the drawings, have been modified and/or exaggerated for the purpose of clarity of illustration.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawpart apparent and in part 3,352,986 Patented Nov. 14, 1967 ings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

The switches of the present invention are of the type which employ a thermally responsive bimetallic snapacting disc for actuation of a pair of electrical contacts. Considerable ditiiculty is experienced in the manufacture of miniaturized versions of switches of this type. Many problems of fabrication and calibration are encountered with the miniaturized construction which either do not exist or are not as severe with the larger size switches of this type. Examples of such problems are: preventing actuation of the contacts by creep movement prior to the occurrence of snap action; calibration; mounting of the snap-acting member; hermetic sealing; and economical manufacture and assembly.

The present invention solves or at least minimizes these problems and provides a switch which affords additional advantages which will be described below.

Referring now to FIGS. 1-7, there is shown a first embodiment of the invention, generally referred to by numeral 10, and which takes the form of a hermeticallysealed, thermally responsive, snap acting, electrical switch.

Switch 10 includes a cup-shaped housing or casing 12 formed of a readily weldable good electrically and thermally conductive material such as, for example, cold rolled steel. Housing 12 also includes a peripherally extending annular flange 40. Disposed in supportive and electrically conductive engagement with the bottom of housing 12, is a wave spring washer 14 formed of a spring material having good electrically and thermally conductive properties. A suitable example is beryllium copper. Washer 14 has a diameter which closely approximates that of the interior diameter of the cup-shaped housing 12. As best seen in FIGS. 6 and 7, the spring washer 14 is undulated in form, the peaks being indicated at 15 and the valleys at 17.

Supported on spring washer 14 is a snap-acting composite thermostatic bimetallic disc-type element 16 of the type disclosed, for example, in US. Patent No. 1,448,240. Disc 16 is provided with a non-developable or deformed portion responsible for its snap action and has a diameter substantially equal to that of spring 14. As best seen in FIG. 4, an electrical contact 18 is electrically connected and secured, as by welding, to the disc 16 at a central portion thereof for movement in response to snap movement of disc 16.

Switch 10 includes a header subassembly generally referred to by numeral 20 and best seen in FIGS. 2 and 5. Subassembly 20 includes a flanged metallic ring 22 formed of a readily weldable and good heat and electrically conductive material such as, for example, low carbon steel. Ring 22 includes an annularly extending flange 28 adjacent one end thereof as shown. An electrically conductive metallic tubular member 26, formed for example of a nickel-iron alloy, is embedded in and sealed to a glass filler or sealant 24 which is infused or sealed to ring 22 as shown.

The glass-to-metal hermetic seal for the header subassembly 20 may be of a so-called matched seal construction or a compression seal. If a matched seal construction is employed, the material for ring 22 and tube 26 would be selected so as to have a ooefiicient of thermal expansion similar to that of the glass sealant. Examples of such materials are Kovar and Rodar.

As best seen in FIG. 2, member 26 projects beyond the glass sealant 24 and ring 22, and is mounted in spaced, electrically insulated relation to ring 22.

Tube 26 telescopically receives an electrically conductive terminal member 30 formed of a good electrically conductive material such as, for example, a silver alloy. Member 30 is received with a tight sliding fit within tube 26 and provides an electrical contact 32 which is positioned for mating engagement with contact 18. Terminal member 30 is moved relative to tube 26 to adjust the relation between the bottom surface of contact 32- and an abutment surface 48 provided by ring 22 and also between

contacts

18 and 32 to exert a predetermined force against the center of disc- 16 (when the latter is in the FIG. 2 condition) to calibrate switch 10. Tube 26 is then deformed about terminal 30 as at 34, and peripherally welded to the terminal as at 36, to maintain the parts in final assembled calibrated position. If desired, calibrating terminal adjustment, deforming (as at 34) and welding (as at 36) may be carriedout automatically in a single combined operation. The excess tenminal portion projecting beyond tube 26 (indicated at 38 and in broken lines 1n FIG. 2) is removed and on welding (at 36) the end of terminal 30 flows over the end of tube 2 6 to provide a crowned effect (as seen in FIG. 2) which adds to the hermetically sealed integrity of switch 10.

As'best seen in FIG. 5, assembly of switch 10 can be accomplished by the following simple steps: dispose spring 14 in housing 12 so that it rests on the'bottom of the housing; insert disc 16 in housing 12 so that it rests on the spring 14 and contact 18 faces upwardly as seen in FIG. telescopically dispose terminal member 30 within tube 26; insert the header ring 22, glass sealant 24, tube 26, terminal 30 subassembly into the housing 12 and bond annular flange 28 to flange 40 as by welding circu mferentially about their entire periphery; thereafter move terminal member 30 within tube 26 into adjusted calibrated position; and then crimp and weld tube 26 to the terminal-30, respectively, as at 34 and 36 to maintainthe parts in the final assembled calibrated condition. The

weldbetween flanges

28 and 40 and between tube 26 and terminal 30 serves to complete the hermetic sealing of switch 10.

FIG. 2 shows switch in the final assembled calibrated and hermetically sealed condition. Switch 10 provides an electrically conductive current path leading from terminal 30 to contact 32, to contact 18, through thermostatic disc 16, to electrically conductive spring washer 14, to the electrically conductive housing 12. Housing 12 also provides a tab or projecting terminal extension 44 which is adapted for electrical connection to a lead 45 (see FIG. 2). Housing 12 and tab 44 maybe gold plated toimprove electrical conductivity.

Header ring 22," includes a skirt portion 46 which projects beyond the glass sealant 24 into the casing 12. The bottom edge of the skirt portion 46, provides an annularly extending stop or abutment 48 which overlies and is disposed adjacent the peripheral portion of disc 16 and is adapted for engagement therewith. Disc 16 also bears againststop 48 in snapping from the contacts-closed position shown in FIG. 2. to the contacts-open position shown in FIG. 3. Spring member 14 is at all times in annular engagement with and urges the peripheral portion of disc 16 for movement upwardly toward engagement with stop or abutment 48. Spring 14 by engaging the peripheral portion of the disc 16, does not significantly interfere with the snap acting characteristics and temperature of operation of the disc. Spring 14 is preferably of the type having a low spring rate so as to minimize the influence of the spring 14 on the snap-acting characteristics and operation of the disc 16 and to permit greater tolerance in spacing between the abutment 4S and the bottom of the cupshaped housing 12 which eliminates the need for expensive gauged selective assembly of parts. An example of a suitable spring rate is on the order of 5 to lbs. per inch.

Conventional means for preventing undesirable contact actuation by. creep action prior to the occurrence of snap action as employed in larger snap-acting thermally responsive devices are generally not practical or useful with miniaturized constructions of this type. According to the present invention stop 48 is so spaced from the bottom of contact 32 so that disc 16 will not engage stop 48 in creeping from the contacts-closed toward the contacts-open position'which, along with the co-operation between disc 16 and spring 14, serves to prevent or inhibit the disc from opening

contacts

18 and 32 by creep action prior to the occurrence of snap action and renders switch 10 especially suitable for miniaturization. Switches of this invention have been made as small as 0.190 inch in diameter (excluding the extent of terminal tab 44) and 0.141 inch in height (excluding the height of terminal 30). The fact that a number of the elements of switch 10 serve multiple functions, contributes significantly toward providing a simple, minimum number of parts construction which is especially suited for miniaturization. For example, the header subassembly 20 in addition to serving the functions described above also co-operates with spring member 14 which constantly urges disc 16 for movement toward engagement with abutment 48, to maintain the

contacts

18 and 32 in a contacts-open or separated condition after the disc has snapped to the FIG. 3 (contactsopen) condition. This co-operation between spring 14, disc 16 and stop 48 additionally provides for improved and increased vibration and shock resistance of the switch 10; assures a maximum or atleast a substantial contactsopening gap when the disc is in the FIG. 3 condition;

serves to maintain desired contact pressure between

contacts

18 and 32 in the FIG. 2 contacts-closed condition; provides a good electrical connection between the disc 16 and the electrically conductive housing 12; provides a good heat transfer connection between housing 12 and disc '16 to afford a fast thermal response; and renders switch 10 relatively insensitive to position orientation.

The present invention avoids the necessity for fixedly securing the disc 16to any mounting means or supporting means, a factor which is particularly significant in a miniaturized construction, while providing a convenient means for calibration and preventing creep opening of the contactsprior to snap action. While a specific form of spring washer 14 has been described and shown, it will be understood that other forms of electrically conductive spring,

members may also be used for engaging the peripheral portion of the disc to urge the latter upwardly, as seen in FIGS. 2 and 3, toward engagement with the stop or abutment 48.

Calibration of the switch 10 may also be effected by precalibrating the header subassembly before it is welded to the can or housing 12. In FIGS. 8 and 9 is shown a second embodiment of a header subassembly generally designated by numeral 20 and which is useful for the switch. Header subassembly 20' is of the compression seal type and includes a ring 22 which is generally similar to ring 22 but has a substantially greater wall thickness than that of ring 22. The lower skirt portion 46 of ring 22' is beveled as at 70 to provide'a relatively narrow circumferentially or peripherally extending stop or abutment surface 48' which corresponds in function to stop 48 of ring It will be understood that a snap-acting thermostatic disc, such as herein contemplated, is one which snaps abruptly from one dished condition to an oppositely dished condition. Abrupt snapping occurs at least'in part because of temperature induced stresses set up in the disc, which upon change (e.g., increase) of temperature ultimately effects a very rapid and violent reversal of curvature, of the disc. The peripheral portion of the disc tends to restrain the remainder of the'disc from simply flattening out or flexing until the-temperature induced stresses become so high that the disc abruptly and violentlysnaps through the hoop-like peripheral portion. The amount of restraint to snapping presented by the peripheral portion of the disc will beinfluenced by the magnitude of forces exerted against the peripheral portion of the disc by the disc mounting or supporting means and also by the point of application of these forces to the disc. It will be clear that variation in the forces applied to the peripheral portion and in the point of application to the peripheral portion of the disc can affect the operating characteristics of the disc. The relatively narrow abutment surface 48' is thus preferred for minimizing the effect of stop 48 with the temperature of operation and the snap-acting characteristics of disc 16.

Assembly 20' also includes tube 26 and a terminal member 30 which provides contact 32 each of which is identical to their respective counterparts of subassembly 20. Assembly 20 also includes a glass sealant 24'. The glassto-metal seal between sealant 24, ring 22 and tube 26 is a so-called compression type seal which can be made by known convenient methods.

Subassembly 20' also differs from subassembly 20 in that prior to securing the subassembly to the housing 12, the terminal 30 is set and fixed in adjusted calibrated position by spacing the lower surface of contact member 32 a predetermined distance (indicated at A in FIG. 8) from the abutment surface 48'. The depth of insertion of abutment member 48 within casing 12 is fixed and limited by engagement between header flange 28' and housing flange 40. This depth is selected so that the distance between the abutment 48' and the bottom of the housing will provide the multiple functions described above for the cooperation between spring 14, disc 16 and stop 48 (or 48). Also distance A is so selected that when the precalibrated subassembly 20' is inserted into and secured to the housing -12, stationary contact 32 Will mate with movable contact 18 (in the FIG. 2 condition) to provide the desired contact pressure therebetween and to stress disc 16 (in the FIG. 2 condition) to provide the required thermostatic response at the desired temperature of operation and to provide the advantages of preventing undesirable contact separation by creep action prior to the occurrence of snap action as described above for the FIGS. 1-7 embodiment. Calibration, crimping (as at 34) and welding (as at 36) can be conveniently performed by automated means.

In view of the above, it will objects of the invention are tageous results attained.

As many changes could be made in the above construcbe seen that the several achieved, and other advan- .tions 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, and it is also intended that the appended claims shall cover all such equivalent variations as come Within the true spirit and scope of the invention.

I claim:

1. A calibrated thermally-responsive electrical switch comprising a cup-shaped housing having an open end and having an electrically and thermally conducting bottom portion; a header sleeve mounted in telescoping relation within said housing spaced from the bottom of said housing; a tube mounted in electrically insulating relation to said housing within said sleeve; a terminal rod having a contact at a selected location within said housing for calibrating said switch; electrically and thermally conducting spring means disposed within said housing against said housing bottom; and a composite dish-shaped, snapacting bimetallic member having a contact centrally supported thereon, said member being engaged near its periphery by said spring means to hold said member contact in firm electrical engagement with said terminal contact for closing a circuit between said housing bottom and terminal rod, said member being responsive to selected temperature conditions to move into inverted dish-shape with snap-action to disengage said member contact from said terminal contact for opening said circuit and to engage an additional portion of said member periphery with said header sleeve so that, while said circuit is open, said member is firmly held at its periphery between said spring and sleeve.

2. A sealed and calibrated thermally-responsive electrical switch comprising a cup-shaped housing having an open end and having an electrically and thermally conducting bottom portion; a header sleeve sealed in telescoping relation within said housing spaced from the bottom of said housing; a tube; a material sealed to said tube and sleeve mounting said tube in electrically insulating relation to said housing; a terminal rod having a contact at one end disposed with a sliding fit in said tube, said rod being sealed in said tube to hold said terminal contact at a selected location within said housing for calibrating said switch; electrically and thermally conducting spring means disposed Within said housing against said housing bottom; and a composite, dish-shaped, snapacting bimetallic member having a contact centrally supported thereon, said member being engaged near its periphery by said spring means to hold said member contact in firm electrical engagement with said terminal contact for closing a circuit between said housing bottom and terminal rod, said member being responsive to selected temperature conditions to move into inverted dishshape with snap-action to disengage said member contact from said terminal contact for opening said circuit and to engage an additional portion of said member periphery with said header sleeve so that, while said circuit is open, said member is firmly held at its periphery between said spring and sleeve.

3. A thermally-responsive electrical switch mechanism adapted to be calibrated and sealed, said switch comprising a cup-shaped housing having an open end and having an electrically and thermally conducting bottom portion; a header sleeve sealed in telescoping relation within said housing with an end of said sleeve spaced from the b0ttom of said housing; a tube; a material sealed to said tube and sleeve mounting said tube in electrically insulating relation to said housing; a terminal rod having a contact at one end, said rod being disposed with a sliding fit in said tube and being adapted to be sealed in said tube to hold said terminal contact at a selected location within said housing for calibrating said switch; electrically and thermally conducting spring means disposed Within said housing against said housing bottom; and a composite, dish-shaped, snap-acting bimetallic member having a contact centrally supported thereon, said member being engaged near its periphery by said spring to hold said member contact in electrical engagement with said terminal contact for closing a circuit between said housing bottom and terminal rod, said member being responsive to selected temperature conditions to move into inverted dish-shape with snap-action to disengage said member contact from said terminal contact for opening said circuit and to engage an additional portion of said member periphery with said header sleeve so that, while said circuit is open, said member is firmly held at its periphery between said spring and sleeve.

4. A sealed and calibrated thermally responsive electrical switch comprising a cup-shaped electrically and thermally conducting metallic housing 'having an open end and having a radially extending flange around the rim of said open cup end; a metallic header sleeve disposed in telescoping relation within said housing said sleeve having a radially extending flange at one end welded in sealed relation to said housing flange and having an opposite end spaced from the bottom of said housing; a metallic tube; a glass material sealed to said tube and sleeve mounting said tube in coaxial, electrically insulating relation to said housing;

cally and thermally conducting spring of undulating shape disposed Within said housing against said housing bottom; and a composite, dish-shaped snap-acting bimetallic memher having a contact centrally supported thereon, said member being engaged near its periphery by said spring to hold said member contact in firm electrical engagement with said terminal contact for closing a circuit between said housing and terminal rod, said member being responsive to selected temperature conditions to move ino inverted dish-shape with snap-action to disengage said member contact from said terminal contact for opening said circuit and to engage an additional portion of said member periphery with said opposite end of said header sleeve so that, while said circuit is open, said member is firmly held at its periphery between said spring opposite sleeve end.

References Cited UNITED STATES PATENTS Satchwell 200-166 Spencer 200--122 Gillespie 200-438 Cataldo et al. ZOO-115.5 Hasselhorn 20O-118 Romine 200-138 Heidorn 200--138 Broadley et a1 200-422 BERNARD A. GILHEANY, Primary Examiner.

and 15 A. LEWITTER, Assistant Examiner.

Claims

4. A SEALED AND CALIBRATED THERMALLY RESPONSIVE ELECTRICAL SWITCH COMPRISING A CUP-SHAPED ELECTRICALLY AND THERMALLY CONDUCTING METALLIC HOUSING HAVING AN OPEN END AND HAVING A RADIALLY EXTENDING FLANGE AROUND THE RIM OF SAID OPEN CUP END; A METALLIC HEADER SLEEVE DISPOSED IN TELESCOPING RELATION WITHIN SAID HOUSING SAID SLEEVE HAVING A RADIALLY EXTENDING FLANGE AT ONE END WELDED IN SEALED RELATION TO SAID HOUSING FLANGE AND HAVING AN OPPOSITE END SPACED FROM THE BOTTOM OF SAID HOUSING; A METALLIC TUBE; A GLASS MATERIAL SEALED TO SAID TUBE AND SLEEVE MOUNTING SAID TUBE IN COAXIAL, ELECTRICALLY INSULATING RELATION TO SAID HOUSING; A TERMINAL ROD HAVING A CONTACT AT ONE END DISPOSED WITH A SLIDING FIT IN SAID TUBE, SAID ROD BEING WELDED IN SEALED RELATION TO SAID TUBE TO HOLD TERMINAL CONTACT AT A SELECTED LOCATION WITHIN SAID HOUSING FOR CALIBRATING SAID SWITCH; AN ANNULAR, ELECTRICALLY AND THERMALLY CONDUCTING SPRING OF UNDULATING SHAPE DISPOSED WITHIN SAID HOUSING AGAINST SAID HOUSING BOTTOM; AND A COMPOSITE, DISH-SHAPED SNAP-ACTNG BIMETALLIC MEMBER HAVING A CONTACT CENTRALLY SUPPORTED THEREON, SAID MEMBER BEING ENGAGED NEAR ITS PERIPHERY BY SAID SPRING TO HOLD SAID MEMBER CONTACT IN FIRM ELECTRICAL ENGAGEMENT WITH SAID TERMINAL CONTACT FOR CLOSING A CIRCUIT BETWEEN SAID HOUSING AND TERMINAL ROD, SAID MEMBER BEING RESPONSIVE TO SELECTED TEMPERATURE CONDITIONS TO MOVE INTO INVERTED DISH-SHAPE WITH SNAP-ACTION TO DISENGAGE SAID MEMBER CONTACT FROM SAID TERMINAL CONTACT FOR OPENING SAID CIRCUIT AND TO ENGAGE AN ADDITIONAL PORTION OF SAID MEMBER PERIPHERY WITH SAID OPPOSITE END OF SAID HEADER SLEEVE SO THAT, WHILE SAID CIRCUIT IS OPEN, SAID MEMBER IS FIRMLY HELD AT ITS PERIPHERY BETWEEN SAID SPRING AND OPPOSITE SLEEVE END.