US2777034A - Thermal switch - Google Patents

Description

G. KING ETAL THERMAL SWITCH Jan. 8, 1957 Filed March 21, 1955 /NV,NTOR5. GILBERT KING CHfikLas E. Rosa/ens ROBERT \5. We.

@Y THE/R ATTORNEYS. HHRQ/S, KnscH, F05 Tue a HARRIS United States Patent THERMAL SWITCH Gilbert King, Los Angeles, Charles E. Roberts, Venice, and Robert S. Weil, Sherman Oaks, Calitl, assignors to Minitec, Los Angeles, Calif., a partnership Application March 21, 1955, Serial N 0. 495,683

13 Claims. (Cl. 200136) The present invention relates to new and improved thermal switch constructions.

For a large number of applications, it is desired to have switches which become operative at an elevated tempera'ture to ,pass current, which switches are distinguished by virtue of their extremely small size and ability to be used under extremely adverse conditions. It is an object of the present invention to produce thermal switches having these characteristics and qualities. Because they possess these properties, the thermal switches of the instant invention can be used for a wide variety of diverse applications. They can be used so as to cause the operation of motors, solenoids, or other devices at predetermined temperatures. Further, they can be used to give warning or advisory-type signals as by causing a current to flow through these switches and a light bulb, a bell, or like device. The thermal switches of the instant invention can also be utilized as a means of telemetering temperatures without the use of intermediate relays or amplifiers. They can also be employed as stand-by safety devices in connection with other more conventional equipment.

The thermal switches of the present invention can be defined in their broadest aspect as comprising a metal, can-like casing serving as an exterior electrode; a barrier member disposed within the bottom of such a casing; and aheaded interior electrode positioned within said casing so as to be insulated therefrom by means of a dielectric washer which serves to position the interior electrode within the center region of such a casing, with the head of said interior electrode bearing against both the dielectric washer and the barrier. In use of the device, means are normally provided either within the casing employed, as in one modification of the invention, or exteriorly of this switch, to normally force this head againstthe barrier utilized. The present invention is more precisely defined by the appended claims forming a part ofthis specification. Further details of the invention are best explained with reference to the accompanying drawings, in which:

Fig. 1 shows a cross-sectional view of a thermal switch ofthe present invention in a preferred operative position;

Fig. 2 shows a cross-sectional view of a modified thermal switch of the instant disclosure; and

Fig. 3 shows a cross-sectional view of'asecond'modified -thermal switch of the invention.

In the figures 'of the drawing like numerals are used to designate like parts.

In Fig. 1 a thermal switch of the invention is shown disposed between a conductive base member 12 and a pointed'end 14 of a conductive spring 16, an extremity of which isprovided with an aperture 18. This aperture '18 is held about an insulating washer 2t), which in turn is positioned about a screw 22, the threaded portion of which passes through a center opening 24 Within a standotl bushing 26, and is secured by means of threads within an opening 28 within the base member 12. The spring 16 is held in this position against a conventional terminal ice 30, which in turn is connected in a conventional manner to a wire lead 32. The head 34 of the screw 22 also holds a conventional terminal 36, of substantially the same construction as the terminal 30, against the insulating washer 20 so as to connect a wire lead 38 through the screw 22 to the base member 12. Thus, with this construction, the two wires 32 and 38 are connected in series with the thermal switch 10.

The construction of this thermal switch 10 is essentially very simple. It comprises a metal, can-like casing 40 within the bottom of which there is disposed a barrier member 42 so that the head 44 of an interior electrode 46 is in constant contact with this barrier 42. The position of the interior electrode 46 within the casing 40 is maintained by means of a ceramic or other dielectric washer 48 held within the casing 40 by means of a crimped-over top 50 of this casing. Thus, the head 44 is held against the washer 48, and the interior electrode 46 is held against the barrier 42 by means of the spring 16. As is seen in Fig. l the pointed end 14 of this spring 16 is normally located within a small depression 52 in the upper face of the electrode 46 so that there is substantially no chance of the thermal switch 10 slipping out from under the spring 16.

In Fig. 2 of the drawings, a related thermal switch construction 60 is shown, which differs from the construction of the thermal switch 10 primarily in the use of what is termed conventionally a Belleville washer 62. This Belleville washer is essentially a conventional washer which has been prestressed or bent so as not to lie flat, and so as to be capable of exercising spring pressure along a direction corresponding to the axis of the washer. Thus, the washer 62 is essentially a spring washer, and may be so termed. Other conventional spring washers can be employed as the washer 62, if desired. In the construction shown in Fig. 2, this spring washer 62 is located immediately above an insulating washer 64 or a conductive washer coated with a dielectric material, which in turn is positioned directly above a dielectric washer 66 corresponding generally to the washer 48 shown in Fig. 1. Immediately above the spring washer in the construction of Fig. 2, another dielectric washer 68 is positioned by means of a crimped-over top 50 of the casing 40 so as to normally hold the washer 62 under tension. Thus, in this construction, the washer 62 tends to urge the washer 66 and the adjacent interior electrode 46 against the barrier 42 by means of pressure exerted upon the head 44. It is obvious that with this specific construction the necessity of using the spring 16 is eliminated.

With the construction in Fig. 2, the spring washer is preferably formed of such dimensions so that at no time does this washer electrically connect the interior electrode 46 and the casing 40. .It is possible with this construction to omit either or both of the washers 64 or 68. If the washer 68 is omitted the washer 62 is thus held directly against the casing 40. If the washer 64 is omitted the washer 62 is directly held against the washer 66. It is also possible with the construction of Fig. 2, to form the crimped-over top 50 in such a manner as to serve the same function as the spring washer 62, although this construction is not preferred because of difiiculties in manufacturing the thermal switch 60.

A very important feature of the instant invention is the barrier 42. This barrier is normally nonconductive in mally preferred .to form this barrier 42 of a semiconducting material, which, under normal conditions, exercises an exceedingly high resistance, and which, at elevated temperatures, passes current. The precise conductive characteristics of the thermal switch can with such semiconductive materials be varied within wide limits so as to obtain various special current passing characteristics at different temperatures.

Suitable semiconductive materials for use with the invention in obtaining specialized effects are such materials as arsenic doped germanium, either nor n-type silicon, or various p-n junctions formed with these or other similar semiconductive materials. When a p-n junction is utilized in a thermal switch of the instant invention, the junction itself should be disposed generally parallel to the bottom of the can-like casing 40. The literature at the present time is filled with references to a number of semiconductors which could be utilized with the instant invention to obtain specialized effects, and those skilled in the arts should have no difiiculty in locating suitable materials for any given application.

The barrier materials which are usually utilized with the instant invention tend to melt and flow to a limited extent at the temperature within which the switches of the instant invention are usually designed to be used. For this reason, the thermal switch constructions of the instant invention employ means such as are indicated above which are adapted to normally force the head 44 of the interior electrode 46 at all times towards the barrier 42 in order to establish the desired amount of electrical contact with the interior electrode 46 and the casing 45). This casing serves as an outer electrode for the thermal switch constructions herein described. Many of the semiconductive materials applicable for use with the instant invention are of a generally paintdike character comprising various scmiconductive ingredients such as por n-silicon disposed within a suitable binding vehicle of a thermoplastic resinous character. A suitable material for this purpose is conventional paraffin.

It is obvious that the instant invention may incorporate barriers formed out of other than the particular class of materials discussed above. Thus, it is possible to utilize within the thermal switch constructions of the invention a small thin layer of a thermoplastic resin, such as, for example, a suitable grade of polyethylene, polyvinylchloride, or the like. When such resinous materials are used with the invention, electrical contact between the inner electrode and the casing is established purely by movement of the inner electrode into engagement with the casing. Under these circumstances, the barrier is forced by the head 44 from its normal location.

The instant invention has a number of distinct advantages over the prior art thermal switch constructions. The thermal switches described herein as presently being manufactured are exceedingly small in dimension. As an example of this, a complete thermal switch and holder as illustrated in Pig. 1 of the drawings normally consumes a base area of approximately Mr it Me". Further, these thermal switches of the present invention are unaffected by various corrosive environments, or by moisture, and thus may be utilized in locations where the prior art thermal switches, as a general rule, could not be employed. Because of the simplicity of the constructions, they are very inexpensive to manufacture. Further, because of the construction illustrated, they can be utilized under conditions where they are subject to a great deal of shock of either a thermal or physical category.

it is possible to produce a modified thermal switch 69 of the invention, as shown in Fig. 3 of the drawings. The construction shown in Fig. 3 includes an outer canlike casing 71? of a metal upon the bottom of which is placed a barrier layer 72. formed of any of the barrier materials previously discussed. Within the can-like casing there is held a movable metal contact member '74 including a rounded lower surface '76 and projecting edge portions 78 which are designed to be engaged by means of a metal spring washer 80 of the same broad category as the spring Washer 62. A boss 82 formed upon the Cit movable contact 74 is held within the center of the spring washer and within a depression 84 within a terminal 86 in such a manner that sidewise movement of this movable contact into engagement with the can-like casing 70 is prevented. This terminal 86 is located so as to project out through an open end 88 of the can-like casing 70. The terminal 86 includes a circular flange 90 against which the spring washer St is normally biased so as to be in constant electrical communication therewith.

A ceramic washer 92 is employed to position the terminal 86 within the casing 70 so that it also cannot move into engagement with the can-like casing 70. As is best seen in Fig. 3 of the drawing, the flange 90 is in engagement with this ceramic Washer 92. Ifdesired, conven- -tional resinous materials can be employed over the ceramic Washer 92 in order to waterproof the entire unit, or in order to supplement the action of the ceramic Washer 92. The ceramic washer may, of course, be replaced by an appropriately molded dielectric resinous Washer of similar construction.

The terminal 86 shown in Fig. 3 presents an improvement over the terminal 46 in that it is provided with an upper cylindrical recess 94 which is designed in such a manner that it may be crimped about a wire (not shown) placed within this recess so as to establish electrical communication with this wire. The casing 70 may with this modification of the invention be mounted by any convenient means, and various conventional terminal elements may be soldered, welded, or formed by metal-working techniques upon the casing 70.

With the construction shown in Fig. 3 of the drawings, the terminal 86 remains in a fixed position and may be securely sealed to the washer 92 so as to prevent the ingress of moisture into the unit. Such seal is not possible Where this terminal or the washer has to reciprocate during the operation of the device. The only movement within the construction shown in Fig. 3 is on the part of the movable contact member 74, and is created by virtue of the inherent action of the spring Washer 80.

It will be obvious from the above discussion that the constructions of the instant invention may be modified in a number of different manners, Which, it is thought, will be apparent to those skilled in the art. The present invention is, therefore, not to be limited to the precise shape, dimensions, or constructions shown, but, instead, is to be limited solely by the appended claims.

We claim as our invention:

1. A new and improved thermal switch of the class described, which comprises: a metal, can-like casing serving as an exterior electrode, said casing having a bottom; a barrier member whose electrical conductivity varies with temperature located within said casing upon said bottom; a dielectric washer held within said casing; and an interior electrode projecting into said casing through said washer, said interior electrode heaving against said barrier member.

2. A thermal switch as defined in claim 1, wherein spring means are disposed within said casing so as to normally force said interior electrode against said barrier towards said casing.

3. A thermal switch as defined in claim 1, wherein said interior electrode is adapted to be mounted in contact with spring means positioned eXteriorly of said thermal switch, said spring means tending to force said interior electrode against said barrier member and towards the bottom of said casing.

4. A new and improved thermal switch construction, which comprises: a metal, can-like casing; a barrier member positioned on the bottom of said casing; a dielectric washer held within said casing; and an interior electrode positioned so as to pass through said dielectric Washer, said interior electrode including a headed member held against said dielectric washer and said barrier member.

5. A thermal switch as defined in claim 4, wherein said barrier member comprise a thermoplastic dielectric resin.

6. A thermal switch as defined in claim 4, wherein said barrier member comprises a semioonductive material.

7. A thermal switch as defined in claim 4, wherein said barrier member comprises a semiconductive material disposed within a thermoplastic resin binder.

8. A new and improved thermal switch, which comprises: a metal, can-like casing having a bottom; a barrier member disposed on the bottom of said casing; a dielectric washer held within said casing; and a headed interior electrode located within said casing so as to pass through said dielectric washer with said head of said interior electrode positioned against said dielectric washer and against said barrier member.

9. A thermal switch as defined in claim 8, including spring means held within said casing bearing against said dielectric washer so as to normally force said head of said interior electrode against said barrier and towards aid bottom of said casing.

10. A thermal switch as defined in claim 9, wherein said spring means comprises a spring washer.

11. A thermal switch as defined in claim 8, wherein said interior electrode is provided with means adapted to engage an end of a spring mean positioned externally of said thermal switch, said spring means serving to force said interior electrode against said barrier member and towards said metal, can-like casing.

12. A new and improved thermal switch construction which comprises: a metal, can-like casing; a barrier member positioned inside said casing on the bottom thereof; a dielectric washer held within said casing adjacent to the top thereof, said washer including an opening formed therein; an electrically conductive member passing through said opening, said member including a passage formed therein adjacent to said barrier member; a movable contact held within said passage so as to be capable of movement with respect to said member; and spring means urging said contact against said barrier member.

13. A thermal switch construction as defined in claim 12 wherein said spring means comprises a spring washer.

References Cited in the file of this patent UNITED STATES PATENTS 794,497 Gould July 11, 1905 796,904 Fiske Aug. 8, 1905 1,175,432 Garretson Mar. 14, 1916 2,516,964 Derby et al Aug. 1, 1950

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