US3930215A

US3930215A - Nonresettable thermally actuated switch

Info

Publication number: US3930215A
Application number: US527973A
Authority: US
Inventors: Ronald E Senor
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1974-11-29
Filing date: 1974-11-29
Publication date: 1975-12-30
Anticipated expiration: 1992-12-30

Abstract

A nonresettable thermal switch comprises a conductive case, a first lead connected to the case, a second lead having a stop, and an insulator with a bore receiving the second lead and with an end engaging the stop securing and insulating the second lead relative to the case. A cup-shaped separator is disposed within the case, and a normally solid body of fusible material is disposed in the separator. A force spreader is slidable in the cup-shaped separator and a deformable connector is disposed between the force spreader and the second lead. Spring means bias the separator for pressing the spreader member via the body of fusible material into engagement with the connector for holding the deformable connector in electrical engagement with the second lead and with the case when the fusible material fuses, the force spreader slides into the cup-shaped separator which deforms the connector away from the inside surface of the case to break the circuit.

Description

United States Patent 1191 Senor Dec. 30, 1975 NONRESETTABLE THERMALLY Prima'ry'ExaminerG. Harris ACTUATED SWITCH Attorney, Agent, or FirmJames P. McAndrews; John [75] Inventor: Ronald E. Senor, North Attleboro, Haug; Russell Baumann Mass.

[73] Assignee: Texas Instruments Incorporated, ABSTRACT Dallas A nonresettable thermal switch comprises a conduc- [22] Filed; N 29, 1974 tive case, a first lead connected to the case, a second lead having a stop, and an insulator with a bore receiv- [211 Appl' 527973 ing the second lead and with an end engaging the stop securing and insulating the second lead relative to the 52 US. Cl 337 407; 337 409 9889- A 9 m Separator is disposed Within the 51 Int. c1. 110111 37/76 case, and a normally solid y of fusible material is ield of Search 337/403 404 405 407 disposed in the separator. A force spreader is slidable 337/403 409 in the cup-shaped separator and a deformable connector is disposed between the force spreader and the second lead. Spring means bias the separator for [56] References Cited pressing the spreader member via the body of fusible UNlTED STATES PATENTS material into engagement with the connector, for hold- 3 727 164 ing'the deformable connector in electrical engagement 3:78l'737 5: 3;? et 24232 with the second lead and with the case when the fus- 3,s20:0s0 6/1974 Tyler i Liz III..............I::::: 337/408 lble material fuses the force Spread" Slides the FOREIGN PA cup-shaped separator which deforms the connector TENTS OR APPLICATIONS away from the inside surface of the case to break the l,l64,589 9/1969 United Kingdom 337/409 circuit.

8 Claims, 3 Drawing Figures 65 27 /7 a 39 N3 3 29 3e 45 5 5 n e 6, I I 2/ U.S. Patent Dec. 30, 1975 3,930,215

a 65 63 f f NONRESETTABLE THERMALLY ACTUATED SWITCH I BACKGROUND OF THE INVENTION This invention relates to a thermally actuated switch, and more particularly to a one-time or nonresettable thermally actuated switch.

Generally, such one-time switches are used to protect a motor, transformer, or other electrical apparatus from operating in ambient temperature which exceed a predetermined maximum safe level. Such one-shot switches are typically used as backup devices for protecting electrical apparatus which may also have current sensing devices or other thermostatic switches or the like adapted to provide normal overload protection for the apparatus, the switch of this invention functioning where the normally relied upon devices might fail. For example, sucha one-shot switch may be serially connected to the windings of a motor so as to protect the motor by interrupting the power supplied thereto in the event that, because of overheating of the motor winding or for any other reason, the ambient temperature level to which the switch and motor are exposed exceeds a level which could cause damage to the motor. These switches are often relatively small (e.g., 0.50 inches or 1.27 cm. long and 0.135 inches of 0.34 cm. in diameter) so they may be readily incorporated in the apparatus they are to protect to be responsive to the ambient temperatures to which the apparatus is exposed. Such switches utilize a fusible material which rapidly undergoes a change of state when heated to a predetermined temperature (i.e., the fusible material melts) to effect breaking of the circuit. Reference may be made to U.S. Pat. Nos. 3,180,958, 3,291,945, 3,309,481, 3,505,630 and 3,519,972 which show such one-time thermally actuated switches.

SUMMARY OF THE INVENTION Among the several objects of this invention may be noted the provision of a one-time thermally actuatable switch which effects a more positive interruption of an electrical circuit upon the switch being heated above a predetermined temperature; and provision of such a switch which is convenient and inexpensive to manufacture, which is reliable in operation, and which utilizes a more economical manner of securing and electrically insulating one of the power leads of the switch relative to the switch case. Other objects and features will be in part apparent and in part pointed out hereinafter.

Briefly, a nonresettable thermally actuated switch of this invention comprises a case of electrically conductive material, a first power lead electrically connected to the case, a second power lead, and an insulator for securing the second lead relative to the case and for electrically insulating it from the case. A rigid cupshaped separator member of insulating material having an open end and having a rim or edge around the open end is disposed within the case, and a normally solid body of material which is fusible at a selected temperature is disposed within the cup-shaped member. in

addition, a force spreader member of a size slidable in the cup-shaped member is disposed in engagement with the body of fusible material at the open end of the cup-shaped member. A resilient deformable connector of electrically conductive material is disposed between the force spreader member and the second lead. Spring means are arranged within the case to bias the cupshaped member for normally pressing the spreader member via the body of fusible material into engagement with the connector, thereby to hold the connector in electrical engagement with the second lead and to normally hold the connector in resilient electrical engagement with the case to complete a circuit while the fusible material is in solid condition. When the switch is subjected to a selected temperature so that the fusible material fuses, the force spreader member is permitted to slide into the cup-shaped member and the spring means bias the cup-shaped member into surrounding relation to the connector to the point where the cup rims abuts against the insulator which secures the second lead relative to the case. In this way, the cupshaped member deforms the connector away from the inside surface of the case and encloses the connector to assure that it is electrically isolated from the case to break the circuit. The insulator which secures the second lead relative to the case has a central bore therethrough for reception of the second lead and the second lead has a stop formed thereon engaging an inner face of the insulator. In this arrangement, the insulator and second lead are insertable into one end of the case to engage an end of the second lead with the connector,

thereby to compress the spring means via the force spreader member, the solid body of fusible material, and the cup-shaped member to establish a desired preload condition in the spring means. The insulator is then secured relative to the case to maintain the spring means in the desired preload condition.

BRIEF DESCRIPTION OF THE DRAWINGS BRIEF DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings and more particularly to FIG. 1, a vnoriresettable (or one-time) thermally actuated switchof'this invention, generally indicated at 1, is shown to comprise a cylindric case or housing 3 of electrically conductive material, such as formed from silver-plated red brass or the like. One end of the case is closed, as indicated at 5, and a first power lead or terminal 7 is secured in electrical contact with the closed end 5 of the case. A second power lead 9 is electrically insulated from the case and secured thereto by insulator and securement means 11. This second lead extends into an open end of the housing opposite closed end 5. A deformable connector 13 of electrically conductive material, such as silver sheet material or the like, is normally in electrical contact with an inside surface 15 of case 3 and in electrical contact with the inner end of lead 9. As generally indicated at 17, means are provided which are actuable in response to being heated above a predetermined ambient temperature of deforming (i.e., bending) connector 13 away from inside surface 15 of case 3 and for electrically insulating the connector from the case thereby to break the circuit.

More particularly, lead 7 is shown to have a flange 19 adjacent its end and a short portion 21 extending beyond the flange insertable through an opening 23 in end of case 3. Once inserted through opening 23, portion 21 is upset, as indicated at 25, with flange 19 abutting end 5 of the case so as to positively secure the lead to the case in electrical contact therewith and to seal the case end.

Connector 13, as best shown in FIG. 3, is a starshaped contact member having 8 bendable legs or contact portions 27 and a center portion 29. The legs are each bent, as indicated at 31, from the plane of the center portion so that only the outer peripheral edges 33 of the legs contact the inner surface of case 3 thereby to provide electrical contact between the case and connector 13. The center portion 29 of connector 13 is adapted to bear against the inner end of connector of power lead 9 thereby to complete the circuit between case 5 and lead 9. As the span of connector .13 between opposed outer edges 33 is somewhat greater than the inside dimensions of case 3 and because its legs 27 are resilient, the legs bend inwardly upon being inserted in the case and thus are resiliently biased into contact with inside wall 15 of case 3 to provide good electrical contact between the case and the connector. While connector 13 is shown as star-shaped to provide readily deformable legs, it will be understood that connectors of other configurations, such as a cup-shaped, radially slotted connector may be used.

Means 17 for deforming connector 13 is shown to comprise a solid body 35 of fusible material, a force spreader member 38 engageable with the fusible body and with the center portion 29 of the connector 13, a rigid, cup-shaped separator member 37 of ceramic or other electrically insulating material, and a spring 39. The fusible material is preferably an organic compound or the like of a type well known in the art (see the patents previously noted) which remains solid upon being heated to a predetermined temperature but then rapidly changes state from a solid to a liquid with very small additional increase in temperature. Separator member 37 is spaced from connector 13 by the fusible body 35 and by the force spreader member 38 while the fusible body is in its solid preformed shape (i.e., before it melts). Separator member 37 has an edge 41 engageable with connector 13 for deforming the connector (i.e., for bending legs 27 of the connector) so as to break electrical contact between the legs and the inside surface of the case. Spring 39 is a compression coil spring interposed between end 5 of case 3 and the inner end of separator member 37 to bias the separator member, the fusible body 35, the force spreader member 38 and the connector 13 to hold the connector in positive current-carrying engagement with the inner end of lead 9, this inner end of lead constituting an abutment for connector 13. Separator member 37 is a generally cylindric cup-shaped member having outer dimensions somewhat less than those of the inside of case 3. In this arrangement the separator is freely mov able longitudinally within the case from a retracted position (see FIG. 1) in which the fusible material and the force spreader member maintain it spaced from connector 13 and an advanced circuit-breaking position (see FIG. 2) in which its rim or edge 41 is moved between the case and the connector 13 and deforms the latter to break the circuit. Preferably as shown in FIG. 2, the cup-shaped separator member 37 has sufficient depth for permitting the edge 41 of the cupshaped member to engage the insulator and securement means 11 when the body 35 has been fused. Separator member 37 is movable from its retracted position (see FIG. 1) to its circuit-breaking position by spring 39 upon fusible member 35 melting. It will be understood that with the separator in its retracted position, coil spring 39 is compressed in a preloaded position and contains sufficient stored energy to move the separator forward to deform legs 27 of connector 13 and to break the circuit.

Separator member 37 has a central bore or recess 43 having a base wall 45 at its inner end facing fusible member 35, has cylindric side walls 46, and has an edge 41. The separator member 37 also has a shoulder 49 against which one end of spring 39 bears and a central hub portion 51 extending into the coil spring.

Fusible body 35, like separator member 37 is cylindric and has a generally flat face 53 engageable with the force spreader member 38. As shown, the fusible body 35 is preferably proportioned to fit entirely within the cup-shaped member 37. The force spreader member 38 preferably comprises a disc of metal such as copper which is of selected thickness to rest on the fusible body 35 to extend a short distance out of the cup-shaped separator member 37 and which is of selected size or diameter slightly smaller than the inner dimensions of the cup-shaped member to substantially fill the open cup end and to be freely slidable in the cup-shaped member while permitting the fusible material of the body 35 to flow around the member 38 when the body melts. In this way, the spreader member 38 assures that the forces between the connector 13 and the fusible body 35 are distributed over a large area of the fusible body to avoid significant penetration of the body and to minimize the occurrence of any localized initial melting of the fusible body, such as might permit creep-like movement of the connector, when the body is heated close to the temperature at which the body material fuses.

Insulator and securement means 11 comprises an integral collar or stop 57 formed on lead 9 and spaced from the inner end of the lead. Means 11 further comprises an insulator ring 59 of a ceramic or other relatively rigid insulator material, such as is commercially available under the trade designation ALSIMAG 645 from American Lava Corporation of such as teflon, having a central aperture or opening 61 therethrough for reception of lead 9. The outer diameter of insulator 59 is only slightly less than the inner diameter of the open end of case 3 so as to be conveniently insertable into the open end of case 3. An inwardly projecting abutment or shoulder 63 within case 3 is engageable with the outer periphery of the inner face of the insulator upon inserting the insulator into the case and thus serves as a locating stop for the insulator to prevent inward movement of the insulator into the case beyond a desired point. Lead 9 with insulator 59 thereon is inserted endwise into the open end of case 3 until the inner end of lead 9 is positioned within the case such as is shown in FIG. 1. The outer end of the case is crimped, as indicated at 65, adjacent the back or outer face of insulator 59 thereby to positively secure and to electrically insulate lead 9 relative to the case. If desired, an epoxy potting or sealing compound 69 is disposed around the lead 9 for sealing the lead in the case 3. In this way, hermetic sealing of the device is achieved.

As will be understood, the switch 1 as illustrated in FIG. 1 is adapted to be serially connected in an electrical circuit by connecting the leads 7 and 9 into the circuit. Upon switch 1 then being heated above a predetermined ambient temperature level, member 35 melts. Melting of the fusible material 35 permits the material to flow around the edge 'of the force spreader member 38 and permits spring 39 to rapidly move the separator member 37 from its retracted position shown in FIG. 1 to its circuit-breaking position shown in FIG. 2. As separator 37 moves forward, its leading edge 41 engages legs 27 of connector 13 and forces the connector to bend to move the outer edges33 of the connector away from the inner face l5. of case 3. At the same time, the spreader member 38 is moved to the bottom of the cup-shaped separator. Upon continued further movement of separator member 37 by'spring' 39, separator edge 41 moves the connector 'legs 27'c ompletely away from the inner surface l5of'the "case' (i.e., to move radially inwardly toward lead 9) to interrupt the switch circuit. Edge 41 of thes eparator then moves into engagement with the insulator ring 59 and thus provides a hard stop for the separator. With the separator in its circuit-breaking position, a portion of the insulator is interposed between the connector and the inside surface of the case thereby to positively insulate the connector and lead 9 from the case. Further, the insulating separator 37 and the insulating ring 59 completely enclose the connector for assuring complete electrical isolation of the connector from the case even if the switch circuit should be subjected to unusually high potentials. It will be understood that upon melting of the organic material of member 35, the melted organic material will merely pool (not shown in FIG. 2) in the lower portion of case 3 and does not prohibit separator 37 from moving from its retracted to its circuit-breaking position. It will further be understood that the fusible material is not electrically conductive.

In assembling a nonresettable thermally actuated switch of this invention, spring 39, separator 37, member 35, force spreader 38 and connector 13 are in serted in the above-stated order into the open end of case 3, such as shown in FIG. 1. Insulator ring 59 with lead 9 received in center bore 61 is inserted into the open end of the case until the inner face of the ring engages stop shoulder 63. With the outer face of collar 57 on lead 9 in engagement with the inner face of insulator ring 59, spring 39 is compressed to a desired preload position via connector 13, force spreader 38, member 35 and separator 37 as the insulator ring and lead 9 are inserted into case 3. When insulator ring 59 is in engagement with shoulder 63, spring 39 is compressed to its desired preload condition. The case 3 on the outer side of the insulator is then deformed or crimped around the insulator 59, as indicated at 65, to grip the insulator and to thus secure the insulator relative to the case and to maintain spring 39 in its desired preload condition. The sealant compound 69 is then added over the insulator as will be understood.

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

As various 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.

I claim: 1

1. A nonresettable thermally actuated switch comprising a case of electrically conductive material, first power lead means electrically connected to saidcase, second power lead means, means securing said second lead means relative to said case in electrically insulated relation to said case, a deformable connector of electrically conductive material in electrical engagement with said second lead means and normally in electrical engagement with said case to complete the electrical circuit between said first and second lead means, a cup shaped separator of rigid electrically insulating material having an open end and an edge around. said open end, a normally solid body of material fusible at a "selected temperature disposed in said cup-shaped separator, a'force spreader member of a size slidable in said cup-shaped separator normally disposed in engagement with said solid body of fusible material at said open end of said cup-shaped separator, and spring means biasing said separator to normally press said force spreader member via said fusible body against said connector to permit said connector to maintain said circuit while said fusible body is solid and for moving said separator when said fusible material is heated to said selected temperature to allow said force spreader member to move into said separator and to move said separator edge into engagement with said connector to deform and to separate said connector from said case to break said circuit.

2. A switch as set forth in claim 1 wherein said force spreader member normally extends a selected distance into said open end of said separator.

3. A switch as set forth in claim 2 wherein said force spreader member is of a size to substantially fill said open separator end while permitting said fusible material to move around said force spreader member when said fusible material is heated to said selected temperature. I

4. A switch as set forth in claim 1 wherein said cupshaped separator has a selected cup depth for permitting movement of said separator in response to bias of said spring means to abut said separator edge with said second lead securing means for enclosing said connector in said separator to isolate said connector from said case in breaking said circuit.

5. A switch as set forth in claim 1 wherein said means securing said second lead means relative to said case comprises a stop formed on said second lead and an electrical insulator having a central bore therethrough for reception of said second lead, said insulator having an inner face engageable by said stop thereby to prevent movement of said second lead in outward direction relative to said insulator, said insulator and said second lead being insertable in one end of said case so that the end of the second lead extends into said case beyond the inner face of said insulator and engages said connector means and compresses said spring means via said force spreader member, said fusible body and said separator to a selected preload condition, said insulator being secured relative to said case in position therewithin to maintain said spring means in said preload condition.

6. A nonresettable thermally actuated switch as set forth in claim 5 wherein the case includes an abutment there-within engageable with said insulator for preventing inward movement of the insulator beyond a selected position within the case.

7. A nonresettable thermally actuated switch as set forth in claim 6 wherein said case is deformed inwardly adjacent the outer face of said insulator thereby to positively secure the insulator in said selected position within the case.

8. A nonresettable thermally actuated switch comprising a generally cylindrical case of electrically conductive material, having an open end and a closed end, a first power lead electrically connected to said case, a second power lead having a stop portion intermediate the ends of said second lead, an insulator ring having a central bore receiving said second lead and having a face engaging said second lead stop, said ring being disposed in said open case end with said face facing inwardly of said case, said case being deformed at said open case end for securing said ring relative to said case disposing said second lead in electrically insulated relation to said case, a deformable connector of electrically conductive material in electrical engagement with said second lead and normally in electrical engagement 8 with said case to complete a circuit between said first and second leads, a cup-shaped separation of rigid electrically insulating material having an open end, having an edge around said open end and having a selected depth disposed within said case, a normally solid body of material fusible at a selected temperature disposed in said separator, a force spreader member of a size slidable in said separator normally disposed in engagement with said solid body of fusible material at said open end oftsaid separator, and spring means disposed between said separator and said closed case end biasing said separator to normally press said force spreader member via said fusible body against said connector to permit said connector to maintain said circuit while said fusible body is solid and for moving said separator when said fusible material is heated to said selected temperature to allow said force spreader member to move into said separator and to move said separator edge between said connector and case to abut said ring to deform said connector and to isolate said connector from said case to break said circuit.

Claims

1. A nonresettable thermally actuated switch comprising a case of electrically conductive material, first power lead means electrically connected to said case, second power lead means, means securing said second lead means relative to said case in electrically insulated relation to said case, a deformable connector of electrically conductive material in electrical engagement with said second lead means and normally in electrical engagement with said case to complete the electrical circuit between said first and second lead means, a cup-shaped separator of rigid electrically insulating material having an open end and an edge around said open end, a normally solid body of material fusible at a selected temperature disposed in said cup-shaped separator, a force spreader member of a size slidable in said cup-shaped separator normally disposed in engagement with said solid body of fusible material at said open end of said cupshaped separator, and spring means biasing said separator to normally press said force spreAder member via said fusible body against said connector to permit said connector to maintain said circuit while said fusible body is solid and for moving said separator when said fusible material is heated to said selected temperature to allow said force spreader member to move into said separator and to move said separator edge into engagement with said connector to deform and to separate said connector from said case to break said circuit.

3. A switch as set forth in claim 2 wherein said force spreader member is of a size to substantially fill said open separator end while permitting said fusible material to move around said force spreader member when said fusible material is heated to said selected temperature.

4. A switch as set forth in claim 1 wherein said cup-shaped separator has a selected cup depth for permitting movement of said separator in response to bias of said spring means to abut said separator edge with said second lead securing means for enclosing said connector in said separator to isolate said connector from said case in breaking said circuit.

5. A switch as set forth in claim 1 wherein said means securing said second lead means relative to said case comprises a stop formed on said second lead and an electrical insulator having a central bore therethrough for reception of said second lead, said insulator having an inner face engageable by said stop thereby to prevent movement of said second lead in outward direction relative to said insulator, said insulator and said second lead being insertable in one end of said case so that the end of the second lead extends into said case beyond the inner face of said insulator and engages said connector means and compresses said spring means via said force spreader member, said fusible body and said separator to a selected preload condition, said insulator being secured relative to said case in position there-within to maintain said spring means in said preload condition.

8. A nonresettable thermally actuated switch comprising a generally cylindrical case of electrically conductive material, having an open end and a closed end, a first power lead electrically connected to said case, a second power lead having a stop portion intermediate the ends of said second lead, an insulator ring having a central bore receiving said second lead and having a face engaging said second lead stop, said ring being disposed in said open case end with said face facing inwardly of said case, said case being deformed at said open case end for securing said ring relative to said case disposing said second lead in electrically insulated relation to said case, a deformable connector of electrically conductive material in electrical engagement with said second lead and normally in electrical engagement with said case to complete a circuit between said first and second leads, a cup-shaped separation of rigid electrically insulating material having an open end, having an edge around said open end and having a selected depth disposed within said case, a normally solid body of material fusible at a selected temperature disposed in said separator, a force spreader member of a size slidable in said separator normally disposed in engagement with said solid body of fusible material at said open end of said separator, and spring means disposed between said separator and said closed case end biasing said separator to normally press said force spreader member via said fusible body against said connector to permit said connector to maintain said circuit while said fusible body is solid and for moving said separator when said fusible material is heated to said selected temperature to allow said force spreader member to move into said separator and to move said separator edge between said connector and case to abut said ring to deform said connector and to isolate said connector from said case to break said circuit.