WO1998037566A1

WO1998037566A1 - Improved fusible link

Info

Publication number: WO1998037566A1
Application number: PCT/US1998/005333
Authority: WO
Inventors: Siebang Oh; James J. Beckert
Original assignee: Littelfuse, Inc.
Priority date: 1997-02-21
Filing date: 1998-02-20
Publication date: 1998-08-27
Also published as: AU6472098A

Abstract

An improved fusible link (18), comprising a length of a metal or metal alloy having a melting temperature of 450 °C or less, such as zinc alloy metal, which link may be shortened to increase the amperage rating of that fusible link. The improved fusible link (18) typically comprises a length of metal or metal alloy having two opposite ends (22, 24), and which has been coined along a portion of its length and between its two ends. The coining creates a flattened portion (36) of increased diameter. Between one and three holes may be placed in that flattened portion (36) and the flattened portion may be trimmed of excess material. The improved fusible link (18) may have a circular cross section, and preferably has a diameter of between 0.100'-0.500'.

Description

IMPROVED FUSIBLE LINK

DESCRIPTION

Technical Field

The invention relates to fusible links that may be used, under current overload conditions, to interrupt the current in an electrical circuit. By virtue of its construction, the fusible link of the present invention can be made for a wide range of amperage ratings, using a minimum of fusible link wire diameters.

Related Applications

This invention is a continuation-in-part of U.S. Application No. 08/697,337, filed on August 22, 1996.

Background Of The Invention

Fusible links are commonly used to interrupt current in electrical circuits. These fusible links may take the form of relatively large (up to Vø') diameter metal wire that melts upon current overload occurring over pre-designated spans of time. They may also take the form of thin, fusible pieces of metal that form a bridge between terminals or terminal extensions, such as the thin fusible link that appears in the ATO®. MINI® or MAXI® fuses manufactured and sold by the assignee of the present invention. For the purpose of this application, these two types of fusible link- containing units shall be referred to. respectively, as "wire links" and "blade fuses."

Prior art wire link devices are commonly made of copper or tin- plated copper, and are generally insulated with a polymeric or rubber-based insulating cover. Such insulated copper wire links have been generally satisfactory for their intended purposes, but have certain deficiencies that make them less than ideal. For example, copper wire links have very high melting temperatures, i.e.. approximately 1083 ° C. The insulating cover cannot withstand such temperatures and. under certain excessive current conditions, will melt, split, burn or separate from the wire long before the copper wire link melts. Accordingly, there is a perceived need for a fusible link to replace copper wire links in such applications, which would melt at temperatures lower than the deformation or burning temperatures of the insulation, even under conditions which could cause insulation deformation or burning with copper links.

Prior art fuse links are also limited in their flexibility. Particularly, a given fuse link diameter is generally limited to a particular amperage rating. Hence, it is desirable to determine a means for enabling a limited number of fuse link diameters to act as a suitable link for a wide variety of amperage ratings.

Summary Of The Invention The invention comprises an improved fusible link, having a length of a metal or metal alloy with a melting point of 450° C. or less, which link may be shortened to increase the amperage rating of that fusible link. The improved fusible link typically comprises a length of zinc alloy metal having two opposite ends, and which has been coined along a portion of its length and between its two ends. The coining creates a flattened portion of increased diameter. Between one and three holes may be placed in that flattened portion, and the flattened portion may be trimmed of excess material. The improved fusible link may have a circular cross- section, and preferably has a diameter of between 0.100"-0.500".

By virtue of its construction, the fusible link of the present invention can have a wide variety of amperage ratings, using a minimum of fusible link wire diameters. Brief Description Of The Drawings

FIG. 1 is a perspective view of a first embodiment of the invention, which comprises a length of zinc alloy metal, covered by an insulating cover, and crimped to a pair of terminals. FIG. 2 is a side view of the embodiment of FIG. 1.

FIG. 3 is a side and partially sectioned view of a second embodiment of the invention, which comprises a length of zinc alloy metal having two opposite ends, and which has been coined along a portion of its length and between its two ends, thereby creating a flattened portion of increased diameter. FIG. 4 is a side view of the embodiment of FIG. 3, but turned 90° about its lengthwise axis.

FIG. 5 is a cross-sectional view of a portion of the embodiment of FIG. 3, taken along the axis of that embodiment, particularly, along lines 5-5 of FIG. 3. FIG. 6 is a perspective view of a battery, starter, or alternator cable for an automobile, and incorporating as its fusible link the first embodiment of the invention, i.e.. the invention of FIG. 1.

FIG. 7 is a side view of the battery or starter cable of FIG. 6.

Detailed Description Of The Preferred Embodiment

Two embodiments of the invention are described in the present application. In both cases, the fusible link is made of a metal or metal alloy with a melting point of 450° C. or less, most preferably a zinc alloy. The first embodiment of the invention is shown in FIGS. 1 , 2. 6 and 7, and may have an elongated, generally cylindrical construction with a uniform cross-section. The second embodiment of the invention is shown in FIGS. 3-5. The cross-section of most of this embodiment is also cylindrical. A portion of this embodiment is flattened by coining or another similar process, providing an oblong cross-section along a part of its length.

Turning first to the embodiment of FIGS. 1, 2, 6 and 7, FIG. 1 shows the improved fusible link 10, which comprises a length of zinc alloy metal. The zinc alloy used in the present invention has a composition of 99.9% zinc, with the remainder being impurities. The zinc alloy used in connection with this invention is a product of Platt Brothers, and is available under Alloy No. 220.

The zinc alloy metal used in connection with this invention has the advantage of melting at a much lower temperature than copper or tin-coated copper wire links. Particularly, the zinc alloy metal of the present invention melts at 420° C.

The zinc alloy fusible link of FIG. 1, without the insulation 12 which overlays that link and the terminals 14 and 16 which are crimped to its ends, has a length of approximately 4". A wide range of diameters may be used in connection with the present invention, and this range will provide protection for various amperage ratings. It has been found that four fusible link wire diameters will enable the manufacture of fusible links for a broad spectrum of amperage ratings. The particular fusible link wire diameters which are preferred for the invention are 0.125", 0.167". 0.250" and 0.300". The fusible link wires having the following diameters are suitable for the following amperage ratings. Diameter, in. Rating, amperes

0.125 80 - 125

0.167 125 - 150

0.250 150 - 225

0.300 225 - 300 The amperage rating of the fusible links having each of these diameters may be varied by any number of methods. First, the length of the fusible link may be shortened. Second, a central portion of the fusible link may be coined. Third, a part of the metal in the coined part of the fusible link may be trimmed away. Fourth, one or more holes may be placed in the coined portion of the fusible link.

Shortening the fusible links, without making any other changes to those links, increases the amperage rating of that fusible link. For example, if a 4" fusible link has a rating of approximately 100 amperes, it is expected that shortening that same link to 3" will change the rating of that link to approximately 125 amperes. Coining a central portion of the fusible link, without changing any other aspect of that link, results in an effectively thinner link, decreasing the amperage rating of that link. Trimming away a portion of the coined part of the fusible link removes material from the cross-sectional area of the coined part, which further decreases the amperage rating of that link. Placing holes in the coined part of the fusible link also removes material from the cross-sectional area of the coined part, and similarly decreases the amperage rating of the link.

Referring now to the second embodiment of the present invention. FIG. 3 shows a fusible link like that of FIG. 1, but which has been coined. This second embodiment of the invention is also made of a zinc alloy fusible link 18. Like the embodiment of FIGS. 1-2, the fusible link 18 is enclosed in an insulating cover 20. The fusible link 18 has two opposite ends 22 and 24. A pair of terminals 26 and 28 are crimped onto the opposite ends 22 and 24 of the fusible link 18. respectively. As may be seen in FIGS. 3 and 4, a central portion 30 of the fusible link 18 has been coined. The coining operation distorts, along the central portion 30 of the fusible link 18, the normally circular cross-section of the fusible link 18. The effect of coining on the cross-section of the fusible link 18 may best be understood by holding the outside of a piece of pliable, hollow rubber tubing, with the fingers positioned on the tubing wall 180° apart. When the tubing is squeezed, the cross- section of the tubing at the portion of the tubing being squeezed changes from circular to oval in shape. Coining has this same effect on the rigid, non-pliable fusible link 30, as shown in FIG. 5. In FIG. 5, the coined part of central portion 30 is depicted by cross-hatching. In effect, coining causes one part 32 of the central portion 30 to be effectively enlarged (FIGS. 3 and 5), and another part 34 of the central portion 30 to be effectively narrowed (FIGS. 4 and 5). The coining creates a flattened portion 36 of effectively increased "diameter," this effectively increased diameter corresponding to the length of the bracket corresponding to part 32 in FIG. 5.

Prior to either insulating the fusible link 18, or placing the terminals 26 and 28 on the ends 22 and 24 of fusible link 18, any combination of three operations may be performed. First, the coining operation can be done to create the cross-section of FIG. 5, and to create the flattened portion 36. Second, between one and three holes 38, 40 and 42 may be placed in that flattened portion. Third, the flattened portion 36 may be trimmed of excess material as, for example, along the bulging part of the flattened portion shown in FIG. 3. Each of these operations has the effect on amperage rating noted above.

FIGS. 6 and 7 depict a battery, starter or alternator cable incorporating the fusible link of FIGS. 1 and 2. The fusible link 46 is again enveloped by an insulating cover 48. and one of its ends 50 is crimped to a terminal 52. The other end 54 of the fusible link 46 is crimped, by means of a union 56. to a cable 58 of length, gauge and material that is appropriate to its application. It will be understood, however, that the fusible link 10 and the corresponding assembly of FIGS. 1 and 2 may be used to protect a circuit or cable exactly as shown in FIGS. 1 and 2, without the need for the auxiliary cable of FIGS. 6 and 7.

Claims

CLAIMSWhat I claim is:

1. An improved fusible link, comprising a length of metal or metal alloy with a melting point of 450┬░ C. or less.

2. The improved fusible link of Claim 1 , wherein said link has been shortened to increase the amperage rating of said fusible link.

3. The improved fusible link of Claim 1. wherein said metal or metal alloy is a zinc alloy.

4. An improved fusible link, comprising a length of metal or metal alloy with a melting point of 450┬░ C. or less, and having two opposite ends, and which has been coined along a portion of its length and between its two ends, said coining creating a flattened portion of increased diameter.

5. The improved fusible link of Claim 4. wherein said metal or metal alloy is a zinc alloy.

6. The improved fusible link of Claim 4, further comprising at least one hole in said flattened portion.

7. The improved fusible link of Claim 4. further comprising three holes in said flattened portion.

8. The improved fusible link of Claim 4. said flattened portion having been trimmed of excess material.

9. The improved fusible link of Claim 4, wherein said link has been shortened, to thereby increase the amperage rating of said link.

10. The improved fusible link of Claim 3, wherein said length of zinc alloy metal is cylindrical, and has a diameter of between 0.125" and 0.300".

11. The improved fusible link of Claim 5, wherein said length of zinc alloy metal is cylindrical, and has a diameter of between 0.125"-0.300".