US2688677A - Lag fuse - Google Patents

Description

Sept 7, 1954 G. F. LAING 2,688,677

LAG FUSE Filed April 16, 1952 fllig/1111144 45 Patented Sept. 7, 1954 LAG FUSE Gordon F.'Laing, Delavan, Wis., assignor to Economy -Fuse and Manufacturing Co., Chicago, Ill., `a corporation of Illinois Application April 16, 1952, Serial No. 282,602

(Cl. 20D-123) Claims. l

VThis invention .relates to time lag fuses, and

,more especially to such fuses of the dual element type applicable to low amperage circuits,

as, for example, ratings below three amperes,

although it is not necessarily limited thereto.

v.In certain o'f its aspects, fuses of this invention follow the considerations of construction and operation rpresented in my contemporary 'United States 'Patent No. 2,543,245, issued on February 27, 1951, and No. 2,613,297, issued to me on October 7,1952, respectively.

In the main, the present invention combines ,the positive-acting massive, relatively-movable,

non-fusible heat storage elements ofthe latter patent, with an improved positive heater means assembly as disclosed in the kformer patent, for communicating heat to said heat storage elements.

There results from this an improved fuse which maybecritically adapted to open circuit upon attainment of preselected current-time relationships without encountering objections of uncertainty and imprecision attributed to earlier embodiments, including those of the iusible type.

Other objects and advantages will become apparent hereinafter `when the fol-lowing description is read in conjunction with the accompanying drawings, in which- Figure 1 is a mid-sectional plan view of a fuse k.cxmstructionzin accordance lwiththe present in- -vention :shown with its Aparts in closed circuit position;

Figure 2 is a side elevational view of the device of Figure 1, shown partly in section, with the parts in open circuit position; and

Figure 3 is a modication of the heating unit employed in the foregoing embodiment.

Referring now to Figures 1 and 2, there is provided the usual insulator casing I0 of nber or other suitable material, having metal cap terminals I2 and I4 which close the ends thereof, and at least one internal partition I6, which divides the interior of the casing into two chambers.

As viewed in Figures 1 and 2, the right hand chamber contains a fuse link I8 which extends from the terminal I4 to which it is soldered, through the partition I6, into the left hand chamber, where it is bent 90 degrees, and is staked to one of the massive electric conductors 20. The right hand chamber containing the fuse link I8 is preferably lled with quenching power I9 in the usual way.

A metal plunger'1 element 22 is arranged in telescoping relation with the conductor 20 and is adapted to reciprocate back and forth with respect thereto so as to extend over to a metallicsleeve 24, to which it is secured by means Yoi solder 26, preferably oi a eutectic alloy of predetermined melting point.

A resistance wire or heater coil 28 is soldered to kthe terminal cap i2 at its outer end and is soldered to the plunger 22 at the point where its Vterminal convolution passes through an aperture inthe metallic sleeve 2d provided therefor. All of these parts are soldered to the plunger so as 'to provide a union that is eiiicient in transmitting both electrical energy and mechanical energy expressed as heat.

Concentrically arranged between the coil 28 and the metallic sleeve 24 is an insualting lining 30, which is of material, such as porcelain, that is capable of conducting heat while at the same --time is an insulator to electricity. The liner 30 electrically isolates the coil 28 from the metallic sleeve 24 to `prevent the coil from becoming short-circuited, and also spaces the sleeve from the terminal I2 by a projecting end portion 32 provided for this purpose.

With the parts in closed circuit position, the plunger 22 is held in engagement with the metallic sleeve 24 by the eutectic alloy solder placed at points 26 and 21 against the bias of a tension spring 34 which tends to urge the plunger away iro-inthe metallic sleeve 42li and into open circuit position, as shown in Figure 2.

Where a surge of current passes through the fuse that exceeds the capacity of the fuse link I8, the latter is adapted instantaneously to blow out. On the other hand, where the overload is of a magnitude which can be immediately tolerated, but is greater than the intended circuit capacity over prolonged periods oi time, and is less than will cause instantaneous failure of the fuse link I8, the current passing through the wire coil 28 gradually heats the latter. The heat in the coil is communicated through the porcelain lining 30 to the metalic sleeve 24, where it is collected and transmitted to the plunger and associated parts until the temperature thereof exceeds the melting point of the eutectic solder.

At such point, the plunger 22 is released and the spring 34 causes it to retract from the metallic sleeve 24 into the massive metallic member 2U, to open the circuit. In this relationship, the parts appear as shown in Figure 2.

In Figure 3, there is illustrated a modified form of the invention. Here the wire coil is replaced by a wire 38 of higher resistance, inasmuch as it is straight and thus offers a shorter path of now to the current than in the case of the coil 28. The metallic sleeve 40 may be made tubular in form without regard to cupping or :daring the ends, except for the flange 42, which is soldered to the plunger 22 in a manner similar to that previously described.

It is preferred that the resistance Wire 38 be accommodated in a recessed portion 44 in the head of the plunger 22 so as to afford maximum contact with the latter, after passing through which the end of the wire projects through an opening in the sleeve as at 46, similar to the construction previously described.

All of these parts are soldered together. The Wire 38 joins the terminal I2 with the plunger, but is electrically isolated from the sleeve 40 by the heat conducting, electrically-insulating liner 48, which abuts against the plunger at one end,

but Which projects sufficiently beyond the sleeve at its other end to maintain clearance between the terminal I2 and the end of the sleeve, as is indicated at 50.

This modied embodiment of heater is applied to the other parts as shown in Figures 1 and 2 in the manner and for the purpose previously described, whereby it is unnecessary to repeat the description pertaining thereto.

Fuses constructed in accordance with the present 'invention have the advantage of affording a positive source of heat from the heater unit which may be made effectively to control the operating conditions and periods of time in which the lag elements will be activated to open circuit position.

The heat generated in the heater unit upon overload is efficiently collected and transmitted to the massive members 28 and 22, which are adapted to store predetermined amounts of sensible heat before the temperature of all of the parts attains the fusion point of the eutectic alloy solder.

Great accuracy of performance and precision of control of circuit conditions are thus realized, Which have not heretofore been possible in functionally similar fuse constructions known to the prior art.

I claim:

1. A lag fuse construction comprising a pair of terminals, a heater connected to one terminal, a fuse link secured to the other terminal, a pair of massive relatively movable heat and electric current conductors, a spring associated with said conductors, fusible material holding said conductors in expanded condition against the bias of said spring in bridging relation between said heater and fuse link, said heater comprising a resistance Wire extending between the adjacent terminal and conductor, a non-metallic heat transmitting envelope for said wire, and means in surrounding relation to said envelope for collecting and transmitting heat resident in said envelope to said adjacent conductor.

2. The invention of claim 1, in which said resistance wire is in the form of a coil.

3. The invention of claim 1, in which said envelope is an electrical insulator.

4. The invention of claim 1, in which said envelope is porcelain.

5. The invention of claim 1, said collecting means comprising a metallic sleeve of high heat conductive properties.

6. A lag fuse comprising a pair of terminals, a fuse link connected to one terminal, a heater link connected to the other terminal, a spring l actuated plunger extending between said links and connected to one of them by fusible material, said heater link comprising a resistance Wire extending lbetween the terminal and plunger, a heat conductive ceramic sleeve surrounding said wire, and a metallic envelope enclosing said sleeve in electrically insulated relation to said terminal and wire detachably joined to said plunger in heat transmitting contact with the latter and with said ceramic sleeve.

7. The invention according to claim 6, in which the detachable joint between said envelope and plunger is comprised of a eutectic solder of predetermined low melting point.

8. The invention according to claim 7, said resistance wire being in the form of a coil coaxially disposed in said sleeve and envelope.

9. The invention according to claim 8, said fuse link being permanently electrically connected to said plunger.

10. The invention according to claim 9, said ceramic sleeve being of a porcelain-like material which is an insulator for electricity and conductor of heat.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 546,475 Potter Sept, 17, 1895 1,265,576 Wright May 7, 1918 2,281,795 Pittman et al. May 5, 19,42

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