US3274361A

US3274361A - Thermal fuse utilizing an electrically conductive pellet

Info

Publication number: US3274361A
Application number: US446225A
Authority: US
Inventors: Gerald F Ebensteiner; Gregory J Rusinyak
Original assignee: United Carr Inc
Current assignee: United Carr Inc
Priority date: 1965-04-07
Filing date: 1965-04-07
Publication date: 1966-09-20
Anticipated expiration: 1983-09-20
Also published as: FR1475274A; GB1078245A; DE1563878A1

Description

Sepf- 20 1966 G. F. EBENSTEINER THERMAL FUSE UTILIZING AN ELECTRICALLY CONDUCTIVE PELLET Filed April 7, 1965 i v VW a Il Q ,QN v Q \\P Ev MY NVM Nm. Qw mm., NN

United States Patent Ofitice 3,274,361 Patented Sept. 20, 1966 3,274,361 THERMAL FUSE UTILIZING AN ELECTRICALLY CONDUCTIVE PELLET Gerald F. Ebenstciner and Gregory J. Rusinyak, Minneapolis, Minn., assignors, by mesne assignments, to United-Carr Incorporated, Boston, Mass., a corporation of Delaware Filed Apr. 7, 1965, Ser. No. 446,225 4 Claims. (Cl. 20D-123) This invention relates generally to circuit-breaking devices, and pertains mo-re particularly to a thermal fuse employing a temperature-sensitive pellet of electrically conductive material.

There are a number of situations in which it is necessary or at lea-st desirable that a circuit be opened when an excessive or abnormal temperature is experienced. This is for the purpose of protecting temperature-vulnerable equipment from damage in the region where the protective device is installed, For instance, it may be necessary to afford adequate protection to an electrical device, such as a motor, whereby such device is decnergized when it becomes overheated. Also, as a further illustration, liquid fuel may be in the process of being pumped and if a fire occurs, .it is essential that the pumping operation be immediately discontinued.

Accordingly, one object of the present invention is to provide a thermal fuse that will be highly reliable in breaking the electrical circuit in which it is located. More specifically, the invention has for an aim the providing of baflles that are instrumental in preventing the remaking or re-establishment of the electrical path once the excessive temperature has been reached. In this regard, a baille arrangement is incorporated into the fuse constructed in accordance witht-he teachings of the present invention so that there cannot be a bridging back by the molten fuse material.

Another object of the invention is to provide a theral fuse of the foregoing character that can be oriented in any position. Consequently, it is not necessary to exercise care in installing the thermal fuse, for it will function irrespective of the particular attitude in which it is mounted.

A further object is to provide a thermal fuse that can be connected directly in the primary circuit of the device that it is to control, it not being necessary to employ any relays. Stated somewhat differently, the invention envisages a thermal fuse that can carry a relatively high electrical current.

Still another object of the invention is to provide a thermal fuse that can be assembled easily and which does not require close tolerances other than those needed for affording the requisite amount of baffling action for the degree of reliability that is demanded by the particular installation. More specifically, the longitudinal dimensions are not critical, although the radial dimensions must be controlled within the ranges demanded for the particular degree of balllng that is to be provided.

Yet another object of the invention is to provide a thermal fuse that will be inexpensive to manufacture by virtue of the simple construction of the component parts constituting the structure.

These and other objects and advantages of our invention will more fully appear from the following description, made in connection with the accompanying drawing, wherein like reference characters refer to the same or similar parts throughout the several views and in which:

FIGURE l is a longitudinal sectional view taken through the center of a thermal fuse exemplifying the invention, the view showing the fuse prior to the fusible pellet becoming molten, and

FIGURE 2 is a longitudinal setcional view corresponding to FIGURE l but illustrating the position of the parts after the pellet has reached a predetermined ternperature which causes it to melt and allow the circuit to be interrupted.

Referring in detail to the drawing, the thermal fuse there depicted comprises a metallic casing or shell having a closed end 12 and -a cylindrical side wall 14. The cylindrical side wall 14 is formed with a shoulder at 16 and has an inturned or crimped flange 18 at the end thereof remote from the closed end -12.

Contained within the casing 10 adjacent the closed end 12 is a fusible pellet of an appropriate electrically conductive material for the maximum ambient temperature that is permissible for the device that is to be protected. For instance, if the permissible temperature is on the order of C., then indium proves very satisfactory. Of course, various alloys can be utilized and thereby obtain a circuit interruption at the proper temperature.

A movable contact element has been denoted generally by the reference numeral 22 and is formed with a flat head 24 and an integral shank 26. A sleeve member designated generally by the numeral 28 has a tubular baille portion 30` encircling the shan-k 2-6, there being preferably only a sufficient amount of clearance between the shank and portion 30 to permit free sliding movement of the shank relative to the portion 30 when the pellet 20 beco-mes molten. The sleeve member 28 also includes a radially extending flange 32 that forms a shoulder between the tubular baflle portion 30 and a larger diameter ltubular portion 34. Still further, at the free end of the larger diameter portion 34 is an outwardly directed flange 36 that abuts against the shoulder 16 of the cylindrical side wall 414. Actually, the cylindrical portion 34 is press/fitted into the cylindrical side wall 14 and itis the flange 36 that longitudinally positions the sleeve member 28 within the casing 10. An annular knife edge 38 is formed on the flange 36 and performs a function described below.

-The larger diameter tubular portion 34, which is somewhat cup-shaped, accommodates therein a rubber bushing 40 formed with a smaller bore portion 42 and a larger bore portion 44. At this time, it will be perceived that during assembly the annular knife edge 3-8 cuts through part of the rubber bushing 40 s-o as to provide what amounts to a detached annular flange 46 that provides an effective moisture seal at this end of the casing 10.

Describing now the specific configuration of the xed Contact element, which has been identified by the reference numeral 48, it will be seen that this element constitutes a plurality of spaced spring 4fingers 50 that are integral with a shank 52.

Circumscribing the shank 52 and projecting somewhat from the right end of the casing 10 is a high temperature insulator 54 which can be of appropriate plastic or cerramic material. Thus, during assembly, the flange 18 is crimped or spun against the insulator 54 so as to prevent detachment of the parts contained within the casing 10.

An additional sleeve member 56 -has a tubular barrier portion 57 and a radially directed flange 58. The tubular barrier portion 57 encircles the previously-mentioned tubular barrier portion 30 and has only a slight clearance with respect thereto which allows the sleeve member 56 to move relative to the sleeve member 28. ln other words, there is only a sliding fit between the

tubular barrier portions

30 and 57.

A coil spring 60 has one end thereof bearing against the flange 58 and its opposite end bearing against the flange or shoulder 32. Consequently, the coil spring 60 biases the movable contact 22 against the fusible pellet 20 and in a direction such as to cause the shank 26 to be urged in a direction away from the fixed contact element 48. More specifically, the free end of the shank 26 is only frictionally engaged with the contact element 48 via the spring lin-gers 5t). When tlhe pellet 20 becomes suiciently molten, then the shank 26 moves to the left under the influence of the coil spring 40 so as to separa-te the

contact elements

22 and 48.

It will be noted that the enlarged head 24 on the movable contact element 22 has a diameter somewhat lless than the dia-meter of the bore of the casing 10. Therefore, an annular space exists which functions as a pasw sage for the ow of the material when it becomes uid due to a suiciently high temperature. The space to the right of the head 24 forms a chamber or compartment 62 of suficient size to accommodate all of the material constituting the pellet 20. rThus, the material forming the pellet 2()` is displaced from its original position and flows into the chamber 62. 'From what has been described, it will be manifest that a tortuous path is pre sented to Ithe owing material by reason of the close t between :the barrier port-ions and 57` Even if any molten material does enter between these barrier portions, it still must traverse a very small clearance path between `the shank 26 and the barrier portion 30. Sti-ll further, the fact that the rubber bushing 40' has a -smaller bore portion 42, which when not distended can be slightly smaller than the cross section of the shank 26, presents still a further resistance to any material entering into the larger bore portion 44 of the bushing 40. Therefore, it is virtually impossible for any of the material of which the pellet 20 is composed to pass into the region between the

contact elements

22 and 48. In this way, assurance is given that there will not be a bridging back which will re-establish the electrical path that `is normally formed between the

contact elements

22 and 48.

Although not important lto a practicing of the invention, the drawing shows a rst conductor 64 having a buttonlike head or flange 66 thereon which is welded or ybrazed to the closed end 12 of the casing 10. Somewhat similarly, a second conductor 68 is attached or connected to the shank 52 of the lixed contact 48, a portion of .the conductor 68 being encompassed by the insulator 54.

In use, the conductors 64, 68 are connected in circuit with the electrical device to =be protected or shut down, as the case may be, and when the pellet 20 melts due to it reaching a prescribed temperature, then the biasing action of the spring 60 takes over so as to urge the movable contact element 22 to the left. In other words, the movable contact element 22 shifts from the position in which it is pictured in FIGURE 1 to that illustrated in FIG-URE 2, thereby separating or disengaging the contact ele-ment 22 from the contact element 48. As can be discerned from FIGURE 2, the shank 26 is no longer within the contines of the spring lingers and the circuit is completely broken.

Although not mentioned herein, it will be appreciated that the thermal fuse constituting the present invention can have the various parts thereof appropriately plated.

Therefore, Whereas the thermal fuse normally passes current from one conductor 64 to the other conductor 68, doing so through the pellet 20, it does not do this when Ithe pelle-t 20 thas melted. Consequently, complete assurance is provided that the thermal fuse structure will perform its safeguarding role.

It Iwill, of course, be understood that various changes may be made in the form, details, arrangements and proportions of the parts without departing from `the scope of our invention as set forth in the appended claims.

What is claimed:

1. A thermal fuse comprising an elongated casing, a fusible -pellet of electrically conductive material disposed within said casing at one end thereof, a fixed electrical contact element disposed within said casing at the other end thereof, a movable contact element having an enlarged head engaging said pellet and a shank having its free end engaging said fixed contact, .a fixed sleeve member having a tubular baille portion closely encircling said shank, said shank being free `to slide relative to said bafe portion, a movable sleeve member having a tubular batiie portion closely encircling said first bathe portion provided with a flange abutting said enlarged head, said second battle portion being free to slide relative to said lirst baffle portion, and a coil spring acting against said flange so as tobias said movable contact element toward said pellet and away from said fixed contact to effect separation of said contact elements when said pellet becomes molten due to a suflicient rise in temperature.

2. A thermal fuse in accordance with claim 1 in which said lixed sleeve member is formed with an outwardly directed liange and an enlarged cup-shaped portion engaged Iwithin the interior of said casing adjacent the end thereof containing said fixed contact element, the other end of said coil spring abutting against sand last-mem tioned flange` 3. A thermal -fuse in accordance with claim 2 including a resilient bushing contained in the cup-shaped por tion and having a lirst bore yportion tightly but releasably encircling said shank and a second bore portion encircling a portion of said lixed contact.

4. A thermal fuse in accordance with claim 3 in which Said fixed contact element includes a plurality of spring fingers frictionally engaging said shank.

References Cited by the Examiner UNITED STATES PATENTS 513,796 1/1894 Lewers 200-142 1,645,201 10/1927 McBrien 200-142 1,753,846 4/1930 Brand 20D-142 2,883,492 4/1959 Landers 200-142 2,931,874 4/1960 Leaman ZOO-61.08 X 2,934,628 4/1960 Masser et al. 20G-123- X 2,955,179 10/1960 Milton et al 200-142 2,999,912 9/1961 Kincaid et el. 200-142 3,180,958 4/1965 Mer-rill 20G- 142 BERNARD A. GILHEANY, Primury Examiner. H. B. GILSON, Assistant Examiner.

Claims

1. A THERMAL FUSE COMPRISING AN ELONGATED CASING, A FUSIBLE PELLET OF ELECTRICALLY CONDUCTIVE MATERIAL DISPOSED WITHIN SAID CASING AT ONE END THEREOF, A FIXED ELECTRICAL CONTACT ELEMENT DISPOSED WITHIN SAID CASING AT THE OTHER END THEREOF, A MOVABLE CONTACT ELEMMENT HAVING AN ENLARGED HEAD ENGAGING SAID PELLET AND A SHANK HAVING ITS FREE END ENGAGING SAID FIXED CONTACT, A FIXED SLEEVE MEMBER HAVING A TUBULAR BAFFLE PORTION CLOSELY ENCIRCLING SAID SHANK, SAID SHANK BEING FREE TO SLIDE RELATIVE TO SAID BAFFLE PORTION, A MOVABLE SLEEVE MEMBER HAVING A TUBULAR BAFFLE