GB2062981A - Miniature electric fuse - Google Patents

Abstract

A miniature electric fuse (1) having variable thermal capacity and improved arcing characteristic. The fuse has a base (5) and body, a fuse cover (3) and a pair of electrically conductive terminals (7, 7') protruding from the base and partially embedded in the body. The fuse body comprises a pair of opposed, spaced apart generally crescent- shaped members (9, 9'), each having an outer curved surface (11, 11'), generally flat top (13, 13') and bottom surfaces and a generally perpendicular inner wall (15, 15') spaced apart from that of the other in parallel facing relation. The embedded ends of the electrically conductive terminals are disposed midway in each member. A groove (19, 19') extends in each member from the top surface to midway down the members and thereafter angled horizontally relative to the inner walls of the members. A fusible element (21) extends between the terminals with its end portions resting on the bottom of said grooves and are soldered therein. A metal plate of desired thickness may be placed on the top of the solder for improved thermal capacity. <IMAGE>

Description

SPECIFICATION Minature electric fuse The present invention relates to minature electric fuses.

Quick acting miniature electric fuses have been widely used in various electric and electronic circuits. In most of these fuses, the fusible element is either soldered to the ends of lead wires or it is simply secured thereto mechanically.

One type of miniature fuse is described in United States Patent No. 3,227,841, issued to Adens J. Gaia on January 4, 1966. This fuse comprises a hollow housing made of an insulating material such as a refractory material, an electrically non-conductive disc also made of a refractory material and mounted in said housing and a pair of electrically conductive terminals extending through a pair of spaced openings in said disc mounting. The two terminals are partially enclosed in the housing and a fusible conductor stretches between the enclosed ends of said terminals and is soldered thereto at both ends.

Another type of fuse comprises a housing which includes a base made of an insulating material and a pair of lead wires passed through the base partially into the housing. Each tip of the lead wires is bent and a fusible conductor stretches between these tips with the ends of the fusible elements secured to the respective tips of the lead wires by means of an electrically conductive paste.

These prior fuses, however, are extremely unstable since the length of the fusible element is sub jest to variations, and the evaporation of the electrodes due to arcing heat tends to prolong the arcing time. Accordingly, these fuses have not been entirely satisfactory.

In another type of fuse which is described in British Patent No. 969,654, published on September 16, 1964, the fuse comprises an integral fuse body through which extends a pair of spaced lead wires projecting beyond opposite ends of the fuse body, and a fusible element between the two ends of the lead wires in the fuse body. The fusible element and the lead wires are wholly embedded in a solid, arc-quencing filler made of epoxy resin and an imperforate cup-shaped cap is fitted over the fuse body to encase the fusible element, the lead wire portions in the fuse body and the epoxy resin filler.

The difficulty with fuses using epoxy fillers, however, is that, the heat generated by the passage of electric current causes thermal expansion with subsequent contraction when current flow is interrupted. Repeated thermal expansions and contractions often cause breakdown of the fusible element.

Accordingly, it is an object of this invention to provide a miniature electric fuse which is substantially free from the aforesaid inherent drawbacks of the prior fuses.

It is a further object of this invention to provide a miniature electric fuse which is quick acting and has improved arc-extinguishing characteristics.

It is also an object of this invention to provide such a fuse which also exhibits improved stability and thermal capacity.

According to the present invention there is provided a miniature electric fuse comprising a fuse base and body, a fuse cover and a pair of electrically conductive lead wires partially embedded in said fuse base and body and protruding from said base, said fuse body comprising a pair of opposed, spaced apart, generally crescent-shaped members, each of said members being defined by an outwardly curved surface, substantially flat top and bottom surfaces and an inner wall substantially perpendicular to said bottom surface, which inner walls are spaced apart from and face one another, an end portion of one of said lead wires being embedded in a respective one of said crescent-shaped members; a groove in each of said crescent-shaped members which extends perpendicularly from the top surface thereof a finite distance therein corresponding to the top ends of the embedded portions of said lead wires and thereafter parallel to said bottom surface in said crescentshaped member perpendicularly to said inner walls; and a fusible element extending between said embedded ends of said lead wires, said fusible element being securely positioned on the bottom of said groove and soldered therein.

Thus, a miniature electric fuse is provided which, due to its unique construction and arrangement of its component parts, exhibits improved thermal stability and capacity, and superior arc-quenching characteristics. The fuse comprises a fuse base and body, a fuse cover which is fitted on to the fuse body and base, and a pair of electrically conductive lead wires protruding from the fuse base and partially embedded in the fuse body. The fuse body comprises a pair of opposed, spaced apart, generally crescent-shaped members, each member being defined by an outwardly curved surface, generally flat top and bottom surfaces and generally perpendicular inner wall, wherein each of said inner walls is spaced apart and is in parallel facing relation; to the other. The embedded ends of the electrically conductive lead wires are disposed midway in each of the respective members of the fuse body.A groove is cut in each of said members from the top surface thereof to approximately midway in each member and thereafter is angled horizontally relative to said perpendicular inner walls of said members. A fusible element is stretched between said terminals and has its end portions resting on the bottom of said grooves and are soldered therein.

In a preferred embodiment of the invention, in order to improve the thermal capacity of the fuse, and to prevent the solder from scattering about in the event of a fuse blowout, a metal plate (e.g., a brass plate) is placed on top of the solder surface and is preferably bonded thereto for added safety.

Embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which like reference numerals are employed to designate like parts, and in which Figure 1 is a perspective view of an embodiment of a fuse of this invention capped and ready for installation; Figure 2 is a perspective view of the fuse shown in Figure 1 with fuse cover removed; Figure 3 is a plan view of the fuse shown in Figure 2 before a fusible element is stretched between the electrodes; Figure 4 is a view similar to Figure 3 afterthe fusible element is stretched between the electrodes and soldered; Figure 5 is a sectional view taken along the line 5-5 in Figure 4; and Figure 6 is a sectional view taken along the line 6-6 of Figure 4.

Referring first to Figure 1, there is shown a miniature electric fuse generally, designated as 1 comprising a fuse cap or cover 3 capping a fuse base 5, and a pair of electrodes 7,7' protruding from the fuse base 5. As shown in Figures 5 and 6 and as will be more fully described hereinafter, the electrodes 7,7' are embedded in the fuse base and body.

With reference to Figure 2, the fuse body comprises a pair of generally crescent-shaped substantially identical, opposed spaced apart members 9,9' which are defined by curved outer surfaces 11,11', relative ly flat top surfaces 13,13' and bottom surfaces (not shown) and inner facing walls or surfaces 15,15' which are spaced apart and substantially parallel to one another Each of the electrodes 7,7' extend through the respective members 9,9' terminating at terminals 17,17' approximately midway therein as shown in Figures 5 and 6.

As is further shown in Figures 2 to 4, each of the members 9,9' has a groove 19,19' cut therein from the top surface 13,13' down to approximately the middle of each member and then at a right angle toward their respective inner walls 15,15'. A fusible element 21, e.g., an electrically conductive wire, is stretched between the terminals 17,17' of the electrodes 7,7' with the ends of the fusible elements positioned at the bottom of the respective grooves and are soldered to said electrodes as shown at 23.

Due to the unique construction of the miniature fuse of this invention and the layout of the fusible element in said grooves, there is less tendency to arcing when an overload current passes through the fuse, and whenever arcing occurs because of excessive current overload, it can be extinguished more rapidly.

As is further shown in Figures 4 to 6, a relatively flat brass plate 25 of desired thickness is placed on the surface of the solder 23, in intimate contact therewith, and may, for example, be bonded thereto.

The provision of the brass plate 25 (or any other equivalent plate) on the solder surface as described serves the dual function of imparting greater thermal capacity to the fuse so as to achieve quicker melting of the fusible element, and affords a safety factor in that it prevents the solder from spraying when the fuse blows due to passage of excessive electric current.

The lead wire portions in the fuse body, the solder material and the brass plates are completely encased within an insulating wall 27 which is a part of the fuse base.

Thus, in accordance with this invention, there is provided an improved quick acting fuse having superior performance characteristics than the hitherto employed fuses for similar applications. As was previously mentioned, the unique layout of the electrically conductive terminals 7,7' and the fusible element 21 substantially reduces arcing due to current overload through the fuse, and whenever arcing occurs due to the passage of excessive current, it can be extinguished more rapidly. Furthermore, the thermal capacity of the fuse may be increased or decreased by varying the thickness of the plate 25 which also serves to prevent the solder from scattering in the event of a blowout.

Claims (5)

1. A miniature electric fuse comprising a fuse base and body, a fuse cover and a pair of electrically conductive lead wires partially embedded in said fuse base and body and protruding from said base, said fuse body comprising a pair of opposed, spaced apart, generally crescent-shaped members, each of said members being defined by an outwardly curved surface, substantially flat top and bottom surfaces and an inner wall substantially perpendicular to said bottom surface, which inner walls are spaced apart from and face one another, an end portion of one of said lead wires being embedded in a respective one of said crescent-shaped members; a groove in each of said crescent-shaped members which extends perpendicularly from the top surface thereof a finite distance therein corresponding to the top ends of the embedded portions of said lead wires and thereafter parallel to said bottom surface in said crescentshaped member perpendicularly to said inner walls; and a fusible element extending between said embedded ends of said lead wires, said fusible element being securely positioned on the bottom of said groove and soldered therein.

2. A fuse as claimed in claim 1 wherein each of said electrically conductive lead wires extends approximately midway into its respective crescentshaped member and wherein each of said grooves is cut to approximately midway of said crescentshaped member before angling relative to said inner walls.

3. A fuse as claimed in claim 1 or 2 further comprising a metal plate securely positioned on the top surface of the solder.

4. A fuse as claimed in claim 3 wherein said plate is made of brass.

5. An electric fuse substantially as herein described with reference to and as illustrated in the accompanying drawings.