US2961958A - Thermal controlled arming device for a mine - Google Patents

Description

Nov. 29, 1960 J. F. TOOMEY ETAL Filed March 8, 1944 2,961,958 THERMAL CONTROLLED ARM'ING DEVICE FOR A MINE 4 Sheets-Sheet 1 Fl &

Nov. 29, 1960 J. F. TOOMEY ETAL 2,961,958

THERMAL CONTROLLED ARMING DEVICE FOR A MINE 1- Sheets-Sheet 2 Filed March 8, 1944 LOAD Nov. 29, 19 60 J. F. TOOMEY ETAL 2,961,958

THERMAL CONTROLLED ARMING DEVICE FOR A MINE Filed March 8, 1944 4 Sheets-Sheet 3 2T 43 W WWW I e?! i Nov. 29, 1960 J. F. TOOMEY EI'AL THERMAL CONTROLLED ARMING DEVICE FOR A MINE Filed March 8, 1944 4 Sheets-Sheet 4 MINE FIRING CONTROL MECHANISM P MINE FIRING l l l CONTROL MECHANISM I 9 k MINE n I 7 FIRING r 8 CONTROL MECHANISM THERMAL CONTROLLED ARMING DEVICE FOR A MINE John F. Toomey, Floral Park, N .Y., and Ellis M. Brown, Dallas, Tex.

Filed Mar. 8, 1944, Ser. No. 525,610

Claims. (Cl. 102-16) (Granted under Title 35, US. Code (1952), see. 266) a fusible alloy and thereby release an actuating member.

The device of the present invention is particularly adapted for use in controlling the firing mechanism of a mine by selective control of the electrical circuits connected thereto when a predetermined period of time has elapsed after the mine has been launched thereby to arm the mine in time delayed relation with respect to the launching thereof and to render the mine harmless or sterile, if desired, at the expiration of a substantially greater period of time after the mine has been launched in which there is no possibility of prematurely operating the contact actuating mechanism as the result of the violent shock received when the mine is planted from an aircraft in flight.

In arrangements heretofore proposed in which a relay having a movable magnetically responsive element is employed for arming a mine, or the mine is armed as the contacts of an arming clock are closed, the shock or excessive vibration caused by the impact of the mine against the surface of a target area may be sufiicient to operate the contact actuating mechanism or momentarily operate the arming clock contacts, as the case may be, and thus prematurely arm and fire the mine.

In the arrangement of the present invention, the contact actuating mechanism comprises a movable element having means operatively connected thereto for yieldably urging the movable element toward an operated position thereof, the element, however, being normally restrained from moving into the operated position by a sleeve or collar releasably bonded thereto by a fusible alloy whereby the movable element is locked in an initial or unoperated position at all times until the alloy has melted or softened sufficiently to permit relative movement of the movable element with respect to the collar. The device also includes a heater element or heater disposed adjacent the aforesaid fusible alloy and adapted to destroy the bond between the collar and the movable element by melting the fusible element in response to a flow of current through the heater. When this occurs, the contact actuating mechanism is moved to the operated position by any means suitable for the purpose such, for example, as a resilient spring and thereby operate the contact elements associated with the device, the circuit to the heater being invariably interrupted concurrently therewith.

One of the objects of the present invention is the pro vision of a new and improved circuit controlling device in which means are provided for preventing the operation of the contact actuating mechanism as a violent shock is received.

Another object is the provision of a new and improved thermal controlled device adapted to withstand a severe 2,961,958 Patented Nov. 29, 1960 shock or blow without being operated thereby and in which means are provided for actuating a mechanism operatively connected thereto in response to a predetermined flow of current received by the device.

Another object is to provide a thermal controlled relay in which means are provided for preventing movement of the contact actuating mechanism from an initial locked position until the thermal element has been heated to a predetermined temperature.

Another object is to provide a normally locked thermal relay in which the relay actuating element is prevented from moving from an initial locked position until the thermal element has been heated to a predetermined temperature and in which the relay is operated without an additional increase in the temperature of the thermal element.

Another object is the provision of a thermal relay having an actuating element normally locked in an initial position in which the actuating element is unlocked only in response to a predetermined fiow of current to a heater and in which means are provided for discontinuing the flow of current to the heater as the relay operates.

A further object is to provide a new and improved thermal controlled device which is economical to manufacture, compact in structure, reliable in operation, and which is suitable for a large variety of uses.

Still other objects, advantages, and improvements will be apparent from the following description taken in connection with the accompanying drawings of which:

Fig. l is a top plan view of a thermal relay in accordance with the present invention;

Fig. 2 is an end view of the device of Fig. 1;

Fig. 3 is a view somewhat enlarged taken along the line 3-3 of Fig. 1 and showing the device in an unoperated condition;

Fig. 4 is a view similar to Fig. 3 showing the device in an operated condition;

Fig. 5 is an enlarged sectional view taken substantially along the line 5-5 of Fig. 1;

Fig. 6 illustrates in diagrammatic form one of the many uses of the device;

Fig. 7 is a top plan view of an alternative form of the device;

Fig. 8 is an end view of the device of Fig. 7;

Fig. 9 is an enlarged sectional View taken along the line 9-9 of Fig. 7 and showing the device in an unoperated condition;

Fig. 10 is a fragmentary view partly in section showing the device of Fig. 9 in an operated condition;

Fig. 11 illustrates in diagrammatic form a circuit arrangement for the device of Fig. 7 suitable for sterilizing the firing control mechanism of a mine;

Fig. 12 illustrates in diagrammatic form a circuit arrangement for the device of Fig. 7 suitable for arming a mine; and, i

Fig. 13 illustrates diagrammatically still another circuit arrangement in which the device of Fig. 7 is employed to close a plurality of arming circuits and in part the firing circuit for a mine.

Referring now to the drawings for a more complete understanding of the invention, and more particularly to Figs. 1 to 5 thereof, there is shown thereon a thermal relay indicated generally by the numeral 19 comprising a casing 11 composed of material suitable for the purpose such, for example, as Bakelite or Lucite and provided with a cylindrical bore 12 therein. The casing is also threaded as at 13 thereby to receive a cap 14 and secure the cap to the casing. The cap is preferably knurled at 15 and provided with a shoulder 16 thereby to clamp a terminal connection 17 to the cap as the cap is secured to the casing. The cap is provided with a plunger 18 slideably arranged therein and continuously urged inwardly by a spring 19 in registered engagement with the shoulder 21 formed on the plunger and with the bottom of a well 22 within the cap. The plunger is also provided with a washer or stop member 23 secured to the outer end portion thereof and adapted to arrest the inward movement of the plunger by engagement with the cap as the relay operates.

The cap is also provided with a cylindrical recess 24 within which is arranged a spring 25, the spring being in registered engagement with a thrust plate or washer 26 and adapted to move the washer along the cylindrical recess 24 as the relay operates. The washer is composed of suitable insulating material such, for example, as Bakelite.

The opposite end of the casing 11 is provided with a thimble or sleeve 27 having flanged portions 28 and 29 adapted to secure the sleeve to the casing, a terminal member 31 being arranged between the flanged portion 29 and the casing. There is slideably arranged within the sleeve 27 a plunger or rod 32 having a cylindrical member 33 secured thereto, the cylindrical member being composed of insulating material suitable for the purpose such, for example, as molded Bakelite, the plunger 32 being preferably formed as at 34 and 35 to receive the molded Bakelite and strengthen the connection therebetween. The cylindrical member 33 includes a tapered portion 36 about which is formed a cap 37 composed of metal and having a projecting cylindrical portion 38 extending within the thrust plate 26 and adapted to engage the inner end of the plunger 18, a washer 39 being arranged between the end of the plunger 32 and the cap 37 to maintain the plunger electrically insulated from the cap. The cap 37 is also provided with a shoulder 41 in abutting relation with the thrust plate.

The plunger 32 is also provided with a sleeve 42 slideably arranged thereon and releasably bonded thereto by a fusible alloy 43 composed of low fusing metals such as lead, tin and antimony in such proportions as will allow the alloy to be melted at a temperature of substantially 210 degrees Fahrenheit and adapted to be melted in response to heat received from a heat coil or heater 44 disposed about the sleeve 42. The heater comprises a number of turns of resistance wire, one end of the wire being connected at 45 to the sleeve 42 and the other end connected as by the flexible conductor 46 to the cap 37 to which the end of the conductor is secured as by soldering the parts together. The cylindrical member 33 is provided with a slotted portion 47 within which the conductor 46 is arranged thereby to facilitate movement of the cap 37 as the relay operates. The plunger 32 is thus locked in an initial position by the sleeve 42 by reason of the engagement of one end of the sleeve with the flanged portion 28 of the thimble 27, and with the outer end of the plunger substantially flush with the outer surface of the casing 11.

The casing 11 is attached to a support 48 as by the screws 49, the support having a bent up portion 51 to which is attached as by the screws 52 a spring pile-up indicated generally by the numeral 53, the pile-up comprising a pair of movable contact springs 54 connected together as by the insulating member 55 and adapted to engage the contact springs 56 as the member 55 is moved to the operated position by the plunger 32. The contact springs 54 and 56 are electrically insulated from each other and from the support 48 by spacing members 57. The casing 11 is also provided with a pair of bores 58 adapted to receive the bolts 59 and thereby attach the device to a mounting plate or base 61, Fig. 5.

The device is adapted to a variety of uses such, for example, as connecting a load to a source of electrical power in response to the closure of a control key, such an arrangement being shown in Fig. 6 in which the device is adapted to be connected to a battery B when the switch S is moved to a closed position. When this occurs, the heater 44 is energized by current from the battery B thereby melting the fusible alloy and releasing the plunger 32. The plunger is now actuated by the spring 25 into engagement with the member 55 thereby moving the contact springs 54 connected thereto into engagement with the contact springs 56 and concurrently therewith interrupting the circuit to the heating coil at 62, corresponding to the point of engagement of the plunger 18 with the end of the cap 37. As the contact springs 54 engage the contact springs 56 the load is connected to the battery B. Whereas in Fig. 6 the load is shown in diagrammatic form, it will, of course, be understood that this is by way of illustration only as the load may comprise various control circuits and mechanisms therefor such, for example, as the mechanisms and circuits employed with mines in which the detonation of the mine is accomplished by closing a firing circuit to an electroresponsive detonating device.

On Figs. 7 to 10 is shown an alternative form of the device in which the plunger 32 is preferably set back slightly from the surface of the casing 11. The spring pile-up indicated generally by the numeral 63, however, comprises two contact elements 64 and 65 adapted to be moved to an operated position by the plunger 32 by reason of the provision of a spacing member 66 of suitable insulating material disposed between the contact springs. The contact spring 64 is provided with a contact element 67 adapted to be engaged by the plunger 32 and establish an electrical circuit therebetween as the relay operates. As the plunger 32 moves to the operated position, the contact spring 65 is moved into engagement with the contact element 68 and engages the contact element 68 with sufficient force to cause the element 68 to be moved into engagement with and be arrested by the stop member 69. The contact springs 64, 65, 68 and the stop member 69 are normally electrically insulated from one another and from the support 48 by reason of the provision of the insulating spacing members 71.

The relay of Fig. 7 is arranged such that the contact spring 64 is prevented from being brought into engagement with the plunger 32 prior to the release of the plunger from the initial locked position thereof by reason of the provision of a relatively small recessed portion 72 within the casing 11 within which the bearing support for the plunger 32 is arranged. As illustrated in dashed outline on Fig. 7, the spring 64 is adapted to be arrested by the casing 11 as the spring is set into vibration or suddenly moved from an initial position as the result of a violent shock received before the spring has moved through a distance sufficient to engage the rod 32.

The manner in which the device of Fig. 7 may 'be employed for rendering a mine harmless when a predetermined period of time has elapsed after the mine has been launched, is illustrated on Fig. 11 of the drawings in Which a mine firing control mechanism is adapted to be operatively connected to a source of electrical power BA in response to the closing of the contacts of an arming clock AC, means in the firing control mechanism being provided for closing a firing circuit to the detonator D in response to the movement of a vessel within the eifectivc zone of destruction of the mine. In the event, however, that the detonator is not operated within a predetermined period of time, the contacts of a sterilizing clock SC are closed thereby completing a circuit from the battery BA to the heat coil 44 of the thermal relay. When the fusible alloy has become heated sufliciently to disengage the plunger 32 from the sleeve 42, the plunger is moved by the spring 25 into electrical engagement with the contact spring 64 thereby short circuiting the battery BA. Concurrently therewith the spring 65 is moved into engagement with the contact element 68 thereby short circuiting the detonator D. The mine is thus rendered harmless or sterile by discharging the battery, accidental or incidental firing of the mine concurrently therewith being prevented by the short circuit across the detonating device D as the result of the engagement of contact spring 65 with the contact element 68. As the rod 32 moves to the operated position thereof the circuit to the heater coil is interrupted at 62 by the cap 37 moving out of engagement with the end of the plunger 18.

On Fig. 12 is shown an arrangement in which the device of Fig. 7 is employed for arming a mine in response to the operation of an arming clock AC. When the contacts of the arming clock close, the heater 44 isenergized thereby causing the plunger 32 to be released and moved into engagement with contact spring 64. Contact spring 64 is electrically connected to contact spring 65, and as contact spring 65, therefore, engages contact element 68, negative battery is applied to conductor 73 and concurrently therewith negative battery is also applied to conductor 74 extending to the mine firing control mechanism to which positive battery is connected as by the conductor 75. The mine is now armed and in readiness to fire the detonator D in response to the movement of a vessel within the vicinity of the mine. As the plunger 32 moves to the operated position, the current through the heater coil is discontinued by reason of the interruption of the heater circuit at 62 thereof.

Still another arrangement for arming a mine is shown on Fig. 13 in which the thermal device is employed to close an arming circuit and concurrently therewith to close in part the firing circuit to the detonating device D in response to the operation of the contacts of the arming clock AC. When the heater coil 44 has been energized sufficiently to release the plunger 32, negative potential from the battery BA is applied by way of the plunger 32 and contact element 64 to conductor 76 extending to the mine firing control mechanism, the positive terminal of the battery being connected to the mine firing control mechanism by way of conductor 77. As contact spring 65 moves into engagement with contact element 68, conductor 78 is brought into electrical connection with conductor 79 extending to the detonator D, from whence the circuit is continued by way of conductor 81 to the mine firing control mechanism thereby closing in part a firing circuit to the detonator D as the thermal relay operates.

Whereas in Figs. 1 and 7 respectively there is disclosed a thermal relay having two pairs of normally open contacts adapted to be closed as the relay operates, it will be understood that this is by way of example only as various other combinations of contacts and various other spring pile-ups including pile-ups having one or more pairs of normally closed contacts may be employed with the thermal control release mechanism disclosed herein for various purposes in which a control connection or a plurality of control connections are made effective in response to a predetermined flow of current through the heater element. Furthermore, the contact control ele ments may be operated in predetermined time delayed relation over a considerable range of time intervals in accordance with the selected resistance of the heater circuit including the heater element and the voltage applied thereto. In any case, however, the plunger rod is prevented from moving from an initial locked position until sufficient heat has been applied to a fusible alloy to cause the fusible alloy to soften and release a locking member fused thereto. When this occurs, the plunger is. moved quickly and positively by a source of energy stored within the device to the operated position thereof without the necessity of additionally heating the fusible alloy. As the plunger moves to the operated position, the contact elements are actuated thereby and the flow of current to the heater coil is invariably interrupted.

An arrangement is thus provided in which, by employing a fusible alloy bonded to the actuating element in the manner disclosed, the actuating element is prevented from being moved from an initial locked position as the result of a shock received, the actuating element remaining locked until the fusible alloy has softened sufficiently to release the bond in response to a predetermined degree of heat applied thereto by the heater.

While the invention has been described in connection with two mechanisms which are adapted for the uses set forth in the description, it is to be understood that the reference to such uses shall not limit the invention thereto and that various changes may be made in the mechanism employed within the principles of this invention, and that any words of description that may be imported to the claims from the specification are not to be considered as words of limitation.

The invention herein described and claimed may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In a device of the character disclosed for arming a mine, in combination, a source of electrical power, a thermal element on said device, circuit means including a pair of normally closed contacts for connecting said element to said source of power, locking means within said thermal element and adapted to be heated thereby, an actuating member on said device and movable from an initial cocked position to a released position, said normally closed contacts being arranged to be operated by said actuating member during initial movement thereof thereby to deenergize said thermal element, means for moving said actuating member, means fusibly bonded to the actuating member and to the locking means for releasably locking the actuating member in said initial position, a mine firing control mechanism, and means on said device for connecting the mine firing mechanism to said source of power during movement of the actuating member from said initial position to the released position.

2. A thermal controlled arming device for a mine having an actuating member movable from an initial locked position to a released position, means for moving the actuating member, means including a fusible element bonded to the actuating member for releasably locking the actuating member in said initial position, a heat coil adapted to increase the temperature of said fusible element sufiiciently to release the actuating member from said locking means, a source of electrical power, an anning circuit for connecting the heat coil to said source of power, a pair of normally closed contacts in said arming circuit adapted to be disengaged during the movement of the actuating member from said initial position to the released position thereby to disconnect the heat coil from the source of power when the actuating member has been released, a mine firing mechanism, and means controlled by the actuating member for connecting the mine firing mechanism to said source of power as the actuating member moves into said released position.

3. In a thermal controlled arming device for a mine, a control element adapted to be moved from an initial cocked position to a final position, means for actuating said control element, means including a fusible alloy bonded to the control element for releasably locking the control element in said initial position, an electroresponsive heater adapted to melt the fusible alloy sufficiently to release the control element from said locking means, a source of electrical power, circuit means including a pair of normally closed contacts for energizing said heater from said source, said normally closed contacts being arranged to be opened by said control element during initial movement thereof thereby to deenergize said heater, an arming circuit for connecting the source of power to said heater and to the control element, a mine firing mechanism having a plurality of control circuits connected thereto, a contact element adapted to be engaged by said control element during the movement of the control element into said final position and thereby connect one of said control circuits to the source of power, and means including an additional contact element on said device for connecting another of the control circuits to said source of power as the control element moves into said final position.

4. In a system for a mine having an explosive charge therein, an electroresponsive device for detonating said charge, a firing control mechanism, a firing circuit connected to said detonating device and adapted to be closed by said firing control mechanism, an arming circuit for the firing control mechanism, a source of electrical power, a thermal device having an electrical heater controlled element adapted to be connected to said source of electrical power, means for closing said arming circuit in response to a predetermined flow of current applied to said heater element by the source of electrical power, and means on said thermal controlled device for closing in part said firing circuit in response to said predetermined flow of current.

5. In a system for a mine having an explosive charge therein, an electroresponsive detonator adapted to fire the charge, a firing control mechanism, a firing circuit for said detonator adapted to be closed by the firing control mechanism, a source of electrical power, a thermal controlled disarming device having an actuating element movable from an initial locked position to a released position, means adapted to move said actuating element, means including a fusible alloy bonded to the actuating element for releasably locking the actuating element in said initial position, means including a heater adapted to melt the fusible alloy suificiently to release the actuating element from said locking means in response to a predetermined flow of current from said source of power, means for connecting the heater in circuit with the source of electrical power when a predetermined period of time has elapsed after the mine has been planted, a normally closed switch in said heater circuit arranged to be opened by said actuating element during the initial movement thereof, means on said disarming device for short circuiting the source of electrical power as the actuating element moves into said released position, and contact closing means on the disarming device operatively connected to said firing circuit and adapted to short circuit the detonator when the actuating element is in said released position.

6. A thermal control device of the character disclosed comprising, in combination, a tube of non-conducting material having an inturned flange forming an axial opening at one end thereof, a sleeve of conducting material disposed within said opening and secured to said flange, a conductor ring secured between said sleeve and flange, an actuating rod arranged for sliding movement within said sleeve from an initial locked position within said tube to a moved position extending outwardly of said flange, a tube of conducting material sleeved about said rod and arranged in abutting engagement with said sleeve, a fusible bond for releasably locking said rod to said conducting tube with the rod arranged in said initial position thereof, an electric heat coil mounted on said conducting tube in heat transfer relation therewith and having one end of the coil electrically connected thereto, a piston connected to the other end of said rod and arranged for sliding movement within said non-conducting tube, a contact carried by said piston in axial alignment with said rod and electrically connected to the other end of said coil, a conducting cap secured to the other end of said non-conducting tube and having an inwardly extending hub portion, a contact ring secured between said cap and said non-conducting tube, said hub portion having a central bore in axial alignment withisaid rod, a contact rod arranged for sliding movement within said central bore and initially arranged with one end thereof in electrical engagement with said piston contact thereby to complete a circuit for energizing said coil when said contact rings are connected to a source of electrical energy, a coil spring sleeved about said hub portion between said piston and said cap for moving said rod to said moved position thereof when the coil has been energized sufliciently to diffuse and break said bond, a stop member carried by the other end of said contact rod and arranged to engage said cap upon limited follow-up movement of the contact rod with respect to said actuating rod, and a coil spring sleeved on said contact rod and arranged to yieldably urge the contact rod into said follow-up engagement with said piston contact whereby energization of the coil is maintained until said stop member engages the cap.

7. A thermal control device of the character disclosed comprising, in combination, a non-conducting tube, an actuating rod arranged for sliding movement within one end of said tube for movement from an initial locked position to a moved position, means including a fusible bond for releasably locking said rod in said initial locked position, a conducting sleeve on said rod, a heater coil mounted on said sleeve in heat transfer relation with respect thereto for breaking said bond when the coil is energized, one end of the coil being electrically connected to said sleeve, a contact electrically connected to the other end of said coil and carried by said rod for movement therewith, a contact rod arranged for sliding movement within the other end of said tube and arranged initially in electrical engagement with said contact whereby the coil is energized when said contact rod and said sleeve are connected across a source of electrical power, a coil spring arranged within the tube to move said actuating rod to said moved position thereof, a stop member carried by said contact rod and arranged to engage the tube upon limited follow-up movement of the contact rod with respect to the actuating rod, and a coil spring arranged to yieldably urge the contact rod into said follow-up engagement with said contact whereby energization of the coil is maintained until said stop member engages the tube.

8. A thermal control relay of the character disclosed comprising, in combination, a tube of non-conducting material having an inturned flange forming an axial opening at one end thereof, a sleeve of conducting material disposed Within said opening and secured to said flange, a conductor ring secured between said sleeve and flange, circuit controlling means supported on said tube and including a plurality of spring contacts arranged in axial alignment with said opening, an actuating rod for said contacts composed of conducting material and arranged for sliding movement within said sleeve, a tube of conducting material sleeved about said rod and arranged in abutting engagement with said sleeve, 21 fusible alloy for releasably bonding said rod to said conducting tube with one end of the rod arranged in spaced relation with respect to said contacts suflicient to prevent engagement tlierebetween in response to a shock received by the relay, an electric heat coil mounted on said conducting tube and having one end thereof connected electrically thereto, a non-conducting piston connected to the other end of said rod and arranged for sliding movement within said non-conducting tube, a contact carried by said piston in axial alignment with said rod and electrically connected to the other end of said coil, a conducting cap secured to the other end of said non-conducting tube and having an inwardly extending hub portion, a contact ring secured between said cap and said non-conducting tube, said hub portion having a central bore in axial alignment with said rod, a contact rod arranged for sliding movement within said central bore and initially arranged with one end thereof in electrical engagement with said piston contact thereby to complete a circuit for energizing said coil when said contact rings are connected to a source of electrical energy, a coil spring sleeved about said hub portion between said piston and said cap for moving said rod to engage and actuate said plurality of contacts when the coil has been energized sufliciently to diffuse said bond,

a coil spring sleeved on said contact rod and arranged to yieldably urge the contact rod into follow-up engagement with said piston contact during initial movement of the actuating rod, and a stop member carried by the other end of said contact rod and arranged to engage said cap to stop said follow-up movement of the contact rod following said initial movement of the actuating rod thereby to interrupt said circuit to the coil.

9. A thermal control relay for operating the control circuits of a marine mine comprising, in combination, a tube of non-conducting material having an inturned flange portion forming an axial opening on one end thereof, a conducting cap secured to the other end of said tube and having a central bore in alignment with said opening, a metallic pin slidably arranged Within said bore, means for yieldably urging said pin inwardly of said tube, a nonconducting piston slidably arranged within said tube, a metallic extension secured to said piston and initially abutting said pin to form an electrical connection therebetween, a conducting rod secured to said piston and slidably arranged within said tube opening, means for yieldably urging said extension out of abutting engagement with said pin and said rod outwardly of the tube, a metallic sleeve arranged about said rod and arranged in abutting engagement with the flange portion of the tube, a fusible alloy for releasably bonding said sleeve to said rod, an electroresponsive heating coil mounted upon said sleeve in heat transfer relation therewith and having one end thereof connected to said extension and the other end connected to said sleeve whereby the coil is energized through said extension and pin when said cap and sleeve are connected to a source of power thereby to release the rod from the sleeve for said sliding movement thereof, a stop member carried by said pin and disposed outwardly of the cap, means for yieldably urging said pin into engagement with said extension and said stop member into engagement with the cap thereby to disengage said pin from the extension to deenergize the coil upon further movement of the extension with the rod, and a plurality of circuit control elements included in said mine circuits and normally spaced from said rod suificiently to prevent engagement therewith in response to a shock received by the mine, said circuit control elements being adapted to be operated by said rod during said further movement of the extension and rod.

10. A thermal control relay of the character disclosed comprising, in combination, a non-conducting tube, a plu rality of spring contacts supported on said tube and having the contact elements thereof arranged coaxially of the tube, an actuating rod for said contact springs slidably supported in one end of said tube and arranged in spaced relation with respect to the contact springs suflicient to prevent engagement of the contact springs therewith in response to a shock received by the relay, means including a fusible bond for releasably locking said rod in said spaced relation with respect to the contact springs, a conducting sleeve on said rod, a heater coil mounted on said sleeve in heat transfer relation with respect thereto for diffusing and breaking said bond when the coil is energized, one end of the coil being electrically connected to said sleeve, a contact electrically connected to the other end of said coil and carried by said rod for movement therewith, a contact rod arranged for sliding movement within the other end of said tube and arranged initially in electrical engagement with said contact whereby the coil is energized when said contact rod and said sleeve are connected across a source of electrical power, a coil spring arranged within the tube to move said actuating rod to actuate said contact springs when the rod is released, a stop member carried by said contact rod and arranged to engage the tube upon limited follow-up movement of the contact rod with respect to the actuating rod, and a coil spring arranged to yieldably urge the contact rod into said follow-up engagement with said contact whereby energiz-ation of the coil is maintained until said stop member engages the tube.

References Cited in the file of this patent UNITED STATES PATENTS 588,206 Williams Aug. 17, 1897 738,803 Hoglund Sept. 15, 1903 833,425 Stigberg Oct. 16, 1906 1,265,576 Wright May 7, 1918 1,273,158 Dickinson July 23, 1918 1,382,374 Maxim June 21, 1921 1,548,826 Currier Aug. 11, 1925 1,689,210 McBrien Oct. 30, 1928 1,924,014 Appel Aug. 22, 1933 2,352,226 Ronning June 27, 1944 FOREIGN PATENTS 241,941 Great Britain 1925

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