US2668887A - Mechanical indicating current limiter - Google Patents

Description

Feb. 9, 1954 M, LAZAR 2,668,887

MECHANICAL INDICATING CURRENT LIMITER Filed NOV. 14. 1952 Mz'ckaelllhgzp Patented Feb. 9, 1954 UNITED sures Michael: D: Lazai', New York-ivh'ilt -assignor to- Burn'd-y; Engineering! Company-Inez, acorpora tion :of New *Yorls Application Newman- 14, 195'2, Serial'Not 320M53 My invention relates to current Iinriter'S and more particulars} t'o' the indicating: v'arietyz Previous efforts have been largely confinedilt) the*"peep'-ho1e'type through' the window of: which the parted fusible wire of the blown limiter could: be" detected: Shel-'1 construction was" not satisfactory f 111* many circumstances;

In'most installations? the limite'rs' are installed side by sideii'n a box-s The box itselris' usually moufiteu with other 'equipmentl These crowded conditions; plus the fact that th'ere is: usually poor lighting in 1 the 1 area; make it very difficult to detect a blown liiniteri In additiomxdetecting a' b'lown umiter becomes immeasurably more' difficult *if "the 'limiter 'haippens to' h'ave been blown by a relatively low: current flowing for a long time: 'lli'ese conditions will causeaveryi small section of thefusiiztle wire to melt without the discoloring explosion-or arcing wh ich' would-make foreasier detection;

Another phase of the problem is i the need for completely covering the fusible wire: and filling the limiter chamber with: roc'kwool quartzge or some such suitable:material; This is to quench the a'rc and suppress thezusuai explosion; which occurs when the limiter blows under very: high current; Thesuppressing: material=,-. however; interferes with visual indication: of the fuse condition.

ficcording1y-,uthe principal object of myrinventionto provide: an explosion-proof.- limiter which is not dependent uponpeep-hole's; or dis"- coloration for" indicating? itscondition.

Gther: objects are: to provide such a limiter thatz is:- light weight: and suitable: foraircraft where excess weight= means a diminished fuel capacity; to-provide a limiter which will-possess the: same operating; characteristics at elevations of: 50;000feet--as i it does at sea-level; to provide aelimiter with operatingcharacteristics that-wi11 permit a controlled: heat dissipation to allow certain overloading. faults to be cleared; to provide a limiter;that will permit its condition to be indicated by touch to permit ready detection in -dark -areasr. to provide an' indicating lirr'iit'er the-fuse ofwhich can-beimhedded in' a're'suppression material; and to provide an-indicating limiter-havingthe foregoing characteristics which is sma-ll of sturdy construction,relativel"? in"- expensive and capable of being, massproducedf v I accomplish these and'other objects 'and ob tainmy. new results as-will be-apparent'iromthe device described in the following" specification, particularly pointed out 'irf'the claims; and mustratedsin the accompanying drawing, in" which:

Fig; lis a front elvatioifo'ithe"indicating r'espectiv nous; g adjacent the indicator illustrating a n iedifiaitiblf thereon I aceomplis'h the variousobj cots: of myinvennew by providing a limiter Illhaving: a plunger H whicli' ex'ternally projected;- as shown in Fig- 5 1 when the limiter is -blowni Thus-the condition of the limiter can be detected both visually and by touch. n

The operating: mechanism: is contained in a housing comprising: two halves-I 2- and l 2a made of insulating atid fire resisting material molded into thedesired shape; V

The housingi half 12 is provided I with a fuse chamber 1 3; and an indicator containing cham- Her it for housing: the fuse assembly- I5 and the indicaton assembly: I 8, respectively.- x

The fu'seassembly l5-- comprises: two blades preferablyU-shaped-piecesofsheet metal 11 and I8, folded overan end of the fuse wire l9. The indicator assembly i6--com-prise s-two metal contacts: 20 and-- 2+ preferably made; of fol dd over pieces of sheet A material to each? of-' which is attached one-end of a wire 22 made of high resistance metal suchas Nichi'ome. The" Nichrome wire '22 isof sufiicient length'ahd'sti'ength to hold a coiled spring 23 compressed intermediate two insulating washers 23d positioned adjacent to thetwo coiitacts2'0" and" 2i: The plunger! 1 "forming the-indicator; extends'thro'ugh the coiled" pr ng 23' and abutsthe contact 2-1 at" one endwhilethe other-'end-is securely fastened to the contact 20; the Nichron'ie wire- 22? extending alongside 1 the plunger and secured a't one' en'd to the: plunger andcontact 2fl a'nd to the othen endlby contact 2 I; if made discontinuous as shown in Fig.- 2, permits the coiled springs 23- to drive the plunger and connected contactaway) from the remaining contact; The two contacts are prevented mm e'scaping from theindicating" chamber" by?" the housingsbarrier 24' and 'its corresponding barrier 24?: in-the' half I211. The plunger llf is"; posttion'ed, however; in themoutlrfi oftlie barrier 24 through which it "outwardly"moves"for afdi's t'ance equal to" the" movement of contact" 2' the chamber lfl u'ndr propulsion ot slirifig 2 v Tofjreduce"the"cost"of manuraeburegthe housl 2-ma'y-becoiistructed ideirtic'cally'- tt half l2a. By providing interlocking symmetry to each side about axis AA, the pattern is furnished for the mating of the two identical parts. Thus the post of housing half l2a, corresponding to post 25, fits into the post hole 21, to center and give lateral securement to the two halves i2 and 12a. Similarly the counterpart ridge 28a in the opposing half 12a of ridge 28 encircling one half the margin of the fuse chamber I3 is seated in groove 29 forming the remainder of the periphery.

Recesses 3G and 3! are provided in the housing for the fuse blades il and I8 respectively, and recesses 32 and 33 form pockets for connecting contact springs 34 and 35 which electrically connect blade I? to the end of Nichrome Wire 22 at its contact 20, and blade l8 to contact 2| respectively.

The blades may be notched at 35 to fit tongue 3'! of the housing to interlock the parts, and prevent accidental movement which might affect the fuse wire l9.

In assembling the parts, the fuse chamber 13 is filled with the arc quenching and explosion suppressing materiallQa, as for instance rockwool, and the grooves 29 and 29a filled with any suitable cement which will caus the two halves to be sealed and securely cemented, when properly applied to each other. The indicator chamber M may be filled with a silicon heat resisting grease which will permit a seal of the parts dur ing movement when the Nichrome wire is blown. The silicon grease ma be obtained from Dow Corning Corporation under the designation D04.

Thus when the two matinghalves i2 and We are secured together, the limiter is sealed from the outside atmosphere, even in the indicator chamber, and will retain at all times its normal atmospheric characteristics until blown.

The limiter is externally shaped to provide finger grips 38. The limiter when blown will cause the plunger to project through one of the finger grips, interfering with its function, as is shown in Fig. 1. Thus the limiter may indicat its con- I dition simply by placing the fingers on the grips. Below the finger grips insulating barriers 39 of the housing extend alongside one edge of the blades to prevent accidental contact with the current during installation. The housing may be externally bridged as at 40 to accommodate the fuse chamber Without weakening the wall thereof.

The plunger may be made of insulating material that can accept a fluorescent red dye to facilitate visual inspection.

Finally a plug il may be cemented in the mouth a of the counterpart half after insertion of the silicon grease into the indicator chamber M to seal the chamber.

In operation, the limiter is inserted into a standard base where the blades make contact with spring clips of well-known construction and not shown here. The current flowsfrom .blade to blade, through the fuse wire made of relatively low resistance material such as silver. The fusible element is designed to melt when a certain combination of current intensity and time of fiow is reached in the circuit, which, if continued .longer would endanger the circuit. If the path of least resistance is broken, the current will be shunted through contact springs 34 and to the Nichrome wire which being of high resistance will instantly release spring 23. This action causes the projection of plunger II to the outside of fin- 4 ger grip 38 and through mouth 25, as is shown in Fig. 2.

The plunger does not interfere with removal of the limiter for it is resiliently held in position by the spring 23 which will be recompressed to permit the plunger to be pushed back in its chamber upon fingering the grips 38.

In Fig. 4, I have provided a protective sealing cover for the plunger whereby a flexible mem-- brane ii: sealed as at 43 to the housing "i4 is outwardly positioned when the plunger 15 is released by the spring not shown. The usual cement may be used to seal off the parts, allowing the flexible but non-permeable plastic membrane to be outwardly driven by the plunger to furnish the desired indication, as shown by the dot-dash lines.

In the foregoing specifications I have described I an explosion-proof limiter which is not dependent upon transparent walls to permit its condition to be detected.

My limiter is exceptionally easy to assemble for the indicator forms a sub-assembly and with the blade and fuse sub-assembly enables the few parts to be quickly installed in manufacture.

The use of silicon grease enables me to seal off the moving parts when the Nichrome wire melts, thus reducing the fire hazard and maintainin the electrical characteristics of the limiter.

When a battery of my limiters are placed in stack formation, by running ones finger alongside the grips, the blown fuse may be instantly located even in a darkened fuse box.

I have thus described my invention, but I desire it understood that it is not confined to the particular forms or uses shown and described, the same being merely illustrative, and that the invention may be carried out in other ways without departing from the spirit of my invention, and, therefore, I claim broadly the right to employ all equivalent instrumentalities coming within the scope of the appended claims, and by means of which, objects of my invention are attained and new results accomplished, as it is obvious that the particular embodiments herein shown and described are only some of the many that can be employed to attain these objects and accomplish these results.

I claim:

1. In a current indicating limiter comprising ahousing, a pair of connecting members having outside contacts, a fuse connected thereto, and a chamber for said fuse; an indicator chamber positioned outside of said fuse chamber, conducting means positioned outside the fuse chamber for shunting the current from the connecting members to the indicator chamber, a plunger for movement outside the limiter, means operated by said shunt current for actuating the plunger whereby an external indication will be produced when the limiter has been blown.

2. In the current limiter of claim 1, wherein the housing is provided with finger grips, and means for allowing the plunger to emerge from the housing so as to interfere with the finger grip.

3. In the current limiter of claim 1, wherein the connecting members are provided with longitudinally extending fuse blades, and the housing is provided with longitudinally extending finger grips for enabling the limiter to be handled with the fingers, said housing having insulation barriers positioned between the finger grips and the blades to prevent accidental contact therewith.

the current limiter of claim 1, wherein the housing is made of two identical parts, and contains the fuse and indicator chambers, said parts having interlocking means adapted to be cemented to each other.

5. In the current limiter of claim 1, wherein the housing contains both fuse chamber and indicator chamber each of which is provided with a seal to prevent escape of the heated contents of the chambers.

6. In the current limiter of claim 1, wherein the means for actuating the plunger comprises a spring in the indicator chamber, and a wire having a higher resistance than the fuse, for releasing the spring.

7. In the current limiter of claim 5, wherein the indicating chamber is provided with two openings, one for the plunger and the other for filling the chamber with a sealing material.

8. In the current limiter 01 claim 5, wherein the indicating chamber is sealed with a silicon rease.

9. In the current limiter of claim 6, a unitary assembly consisting of the plunger, th spring and the wire.

MICHAEL D. LAZAR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,343,224 Powell Feb. 29, 1944 2,421,658 Strang et a1 June 3, 1947 FOREIGN PATENTS Number Country Date 706,243 France Mar. 24, 1931

Images