EP0625284A1

EP0625284A1 - Flat fuse for high rated currents

Info

Publication number: EP0625284A1
Application number: EP92904874A
Authority: EP
Inventors: Jean-Michel Saulgeot; Gilles Pittion
Original assignee: Dav SA
Current assignee: Dav SA
Priority date: 1991-01-16
Filing date: 1992-01-13
Publication date: 1994-11-23
Also published as: WO1992013356A1; US5373278A; CA2100782A1; JPH06504875A

Abstract

Il est du type comprenant un boîtier dans lequel est logé en partie un organe conducteur (5, 6, 9, 10) pourvu de deux languettes de connexion plates (5, 6) dont les extrémités libres (7) sont situées hors du boîtier, lesdites languettes de connexion étant reliées à l'intérieur du boîtier par une partie fusible plate (8) sur au moins une face de laquelle et sensiblement au centre est déposée une goutte de métal (13) de surface de contact prédéterminé, et il est caractérisé en ce que la partie fusible comprend une zone calibrante centrale (9) de largeur (l1) plus petite que la largeur (l2) des zones latérales adjacentes (21) de liaison avec les languettes de connexion, la surface de contact de ladite goutte (13) étant au moins supérieure à la moitié de la zone calibrante (9). Application notamment à l'équipement automobile.It is of the type comprising a casing in which is partly housed a conductive member (5, 6, 9, 10) provided with two flat connection tabs (5, 6) whose free ends (7) are located outside the casing, said connection tabs being connected inside the case by a flat fuse part (8) on at least one face of which and substantially in the center is deposited a drop of metal (13) of predetermined contact surface, and it is characterized in that the fuse part comprises a central calibrating zone (9) of width (l1) smaller than the width (l2) of the adjacent lateral zones (21) for connection with the connection tabs, the contact surface of the said drop ( 13) being at least greater than half of the calibrating zone (9). Application in particular to automobile equipment.

Description

FLAT FUSE FOR HIGH NOMINAL CURRENTS

The present invention relates to a flat fuse for nominal currents greater than or equal to 20 Amps, and more particularly to a flat fuse for cars.

Increasingly, flat fuses are used in the equipment of automobiles, for reasons of space, qualities of protection and convenience of plugging. Such fuses generally include a housing or insulating body in which is partially mounted a conductive member constituted by two pluggable flat connection tabs, and joined by a fusible or calibrating part.

A fuse of this type is described in US-A-3,909,761 OR FR-A-82 13,847.

However, the structure and nature of the materials used for the manufacture of these flat fuses were chosen for a nominal current flowing in the fuse part and the connection tabs of less than 30 amperes.

For higher nominal currents of up to 100 Amperes and more, the fusible part can bend and come into contact with one of the internal faces of the insulating body or case. As the material used for the housing is a plastic material, it follows that bringing the fusible part into contact is likely to melt the plastic material and would cause complete deterioration of the housing. The phenomenon of deflection generally occurs at the center of the calibrating part because, it is there that the hottest point is located when the temperature curve is plotted. The solutions that have been recommended to resolve the problem of deflection have been either to reduce the section of the calibrating part in the hot spot area, or to deposit a drop of metal in the center of said calibrating part when it is constituted by a metal wire, or to provide an orifice in the hot spot area and to deposit, on either side of said orifice, a drop of metal. All these solutions are described in GB-A-2 090 081 and US-A-4 635 023. In the solution retained with drops of tin placed on either side of the central orifice, it is necessary to choose the structural parameters as a function of the nominal current of the flat fuse. This is why the length, width and thickness of the fuse part are not the same for a 40 amp flat fuse and a 60 amp flat fuse, which is a serious drawback for mass production. . In addition, it may be necessary to change the location of the tin drops and therefore their receiving orifices as a function of the length of the fuse part.

In application DE-A-2 500 364, a flat fuse is described comprising a fuse part produced in one piece with the connection tabs, but which is partially hollowed out in the central part so as to produce a thinned zone d 'thickness and constant section, only the thinned zone constituting a calibrating zone.

In application PCT / US88 / 0924, the calibrating part of the fusible part comprises cutouts intended to provide cooling zones capable of generating a delaying effect on the deflection. seed of said calibrating part.

The present invention aims to remedy the aforementioned drawbacks and to provide a flat fuse comprising a flat fuse part and flat connection tabs in which the temperature communicated to the connection tabs is reduced before blowing.

The present invention relates to a flat fuse, of the type comprising a housing in which is housed in part a conductive member provided with two flat connection tabs, the free ends of which are located outside the housing, said connection tabs being connected to the inside the housing by a flat fusible part on one face of which a drop of metal is deposited, and which is characterized in that the fusible part comprises a central calibrating zone of width smaller than the width of the adjacent lateral zones of connection with the connection tabs, the contact surface of said drop being at least greater than half the surface of the calibrating zone.

An advantage of the present invention is to allow the drop of metal to extend over almost the entire calibrating zone without risk of contact with the connection tabs.

Another advantage of the present invention lies in the fact that the calibrating part has a reduced length and a possibility of constant thickness whatever the nominal current or rating of the flat fuse.

According to another embodiment of the invention, the fuse part comprising two calibrated zones in parallel mounted, of which at least one of said zones is provided, approximately, in the center of at least one drop of metal . Other advantages and characteristics of the present invention will emerge more clearly on reading the description of the embodiments, as well as the appended drawings in which:

FIG. 1 is a plan view of the flat fuse comprising a protective box in which the conductive member shown in FIG. 2 is arranged,

FIG. 2 is a plan view of the conductive member according to an embodiment of the invention,

FIG. 3 is an enlarged sectional view along III-III of FIG. 2,

FIG. 4 is an enlarged sectional view along IV-IV of FIG. 2,

FIG. 5 is a partial top view of the grading zone shown in FIG. 2, with blades folded over the drop of metal,

FIG. 6 is an elevation view of the trapezium-shaped expansion limiting blades,

- Figure 7 is a plan view of the conductive member according to a second embodiment according to the invention.

The box 1 shown in Figure 1 can be of the one-piece type or in two parts, the front part or cover 2 being mounted by crimping or other means on the rear part or body-support 3, for example as described in FR- A-87 04 382.

A conductive member 4 according to the invention, shown in FIG. 2, is mounted in the housing 1.

The member or conductive element comprises two connection tabs 5 and 6, the ends 7 of which are bevelled to allow easy insertion into corresponding housings provided in various receiver assemblies such as interconnection boxes. A fuse part 8 is mounted between the connection tabs 5 and 6 and it is connected to the internal sides 5a, 6a of the latter.

According to a preferred form of the present invention, the fusible part 8 is for the same rating, of constant thickness and it is constituted by at least one central calibrating zone 9 made of zinc alloy (approximately 99.7% of zinc), arranged between two lateral zones 10 and 11 intended to be connected to the connection tabs 5 and 6 respectively. Calibrating the central area 9 has a width W smaller than the width 1 ₂ of the adjacent zones 10,11 so as to provide flanges 12, while the length La. Of the calibrating zone is less than or equal to two thirds of the length L_ > of the fuse part (fig. 4).

A drop of metal 13, preferably a tin-silver or tin-lead alloy, is deposited on the calibrating zone 9. The drop 13 is in contact on the calibrating zone 9 along a contact surface S which is at less than half of the surface S _a , of the face of the calibrating zone receiving said drop. Preferably, the contact surface Sx is substantially equal to that S_. of the calibrating zone.

Means for limiting the expansion of the drop 13, during the melting of the latter, are provided on the calibrating zone 9. The limiting means are constituted by at least one blade of low height, and preferably by two blades 14 and 15 which are each connected to a longitudinal side 16, 17 of the calibrating zone 9, and in a plane perpendicular to the plane containing said calibrating zone (fig. 4).

According to one embodiment (fig. 3), each blade 14, 15 has a rounded profile and it is provided substantially at equal distance from the internal edges of the connection zones (18) formed on the connection tabs 5, 6. The fuse part 8 is electrically welded. or on the dial on the underside of the connection tabs 5, 6 when the plan view of FIG. 2 is considered, and it preferably, but not necessarily, has a small thickness so that a housing 20 for the drop 13 is formed between the calibrating zone 9 and the internal edges 18 of the connection tabs 5,6.

The portion 21 of each connection zone 10, 11 comprised between the rim 12 and the corresponding welding zone 22 also constitutes an additional heat dissipation zone which will be discussed later.

By drop of metal is meant a very small mass of metal which can have any regular shape or not, such as spherical, parallelepipedic. The metal drop is joined to the calibrating zone by fusion or any other suitable means.

Preferably, each blade 14, 15 whose height is substantially equal to or greater than the corresponding dimension of the drop 13, has an upper free part 23, 24 which is foldable over the drop 13 so as to further trap said drop, the expansion is limited both upwards because of the parts 23, 24, after folding, and laterally because of the blades. As a result, the drop 13, when it is traversed by a strong electric current which produces a fusion of said drop 13, is forced to conform to the shape of the blades 14, 15 and can only spread towards the edges 12 In fact, experiments have shown that the drop 13 takes the form shown in FIG. 5, that is to say that it presents at its ends a sort of meniscus 25.

According to another embodiment of the blades shown in Figure 6, the blades 14 and 15 present tent a trapezoid shape whose upper free edge 40 is substantially straight with rounded ends 41 and 42 rounded.

On each side of each central part 26,27 of the connection tabs 5,6 to which a lateral zone 10,11 of the fuse part 8 is connected, there are provided heat dissipation fins 28,29 which are separated from the middle part 26, 27 by two notches 30, 31, the role of which is to delimit the ailet¬ 28, 29 for cooling the connection tabs 5, 6 and the four fixing points of said connection tabs on the housing 1, shown in figure 1.

The connection tabs 5,6 each have two orifices 32,33 for their mounting by crimping on pins provided for this purpose in the support body 3 of the protective housing 1.

Each connection tab 5,6 comprises, on the external side 5b, 6c, opposite the internal side 5a, 6a, a cutout or notch 34,35, intended to allow during continuous production, in the form of a strip, to accommodate the conductive member 4 in the housing 1.

In operation, the passage of an electric current through the fuse part 8, by means of the connection tabs 5, 6, creates a hot spot which is situated substantially in the center of the calibrating zone 9.

At the nominal intensity I _N , recorded for example on the housing 1, the alloy of the drop 13 is in a solid state and the temperature in the calibrating zone is lower than the eutectic point of the alloy.

For low current overloads (1.35 x IN for 30 minutes) the drop 13 goes to the liquid state while remaining centered on the hot point, but the alloy of which it is made diffuses into the material of the calibrating zone 9 in zinc. Temperature of fusion of the calibrating zone 9 is located between that of the alloy of the drop 13 and that of the zinc. In this way, the temperature communicated to the connection tabs 5, 6 is reduced during very slow fusion, the reduced length of the calibrating zone eliminating any risk of contact with the housing 1 for said low overload.

For medium overloads (from 2 to 3.5 x IN), the melting time of drop 13 is relatively short, of the order of a few seconds, and the molten alloy of said drop does not have time to diffuse in the zinc of the calibrating zone. The melting temperature is close to that of zinc because the rupture takes place essentially on the thickness of zinc. Thus, there is a rapid rupture on one of the sides of the drop and the calibrating zone is maintained in the same state with a slight deflection without however coming into contact with the case.

For heavy loads (up to 800 Amps), ^• one alloy of the drop remains 1'état solid and the calibrating zone 9 is sectioned randomly on one side or the other of said drop, without fléchis¬ ment out of the fuse part plane.

The heat dissipation fins 28 and 29 of the connection tabs 5 and 6 receive an imprint 22a during the passage of the welding wheel between the fuse part 8 and said connection tabs and, more precisely, between the parts 10, 11 of the fuse part and said connection tabs.

Another embodiment of the conductive member is shown in FIG. 7. In this embodiment, the fusible part comprises two cali¬ brantes zones 9a and 9b which are mounted in parallel but located in the same horizontal plane , slightly lower laughing at that containing the connection tabs 5,6; each calibrating zone 9a, 9b having the dimensional characteristics of the calibrating zone 9 as defined above. A drop of metal 13a is deposited on at least one of the calibrating zones 9a or 9b and, if necessary, on each calibrating zone, as shown in FIG. 7. Likewise, one or both calibrating zones 9a, 9b are provided expansion limiting blades shown in one of Figures 2 to 7. The droplet (s) 13a are made of tin-silver alloy. The calibrating zones 9a, 9b are not tinned on both sides and have a thickness of approximately 0.30 mm. As the calibrating zones 9a, 9b are made of zinc alloy (about 99.7% zinc), such a thickness is best suited for the formation of the tin-silver / zinc alloy.

The metal drops 13a come either from a welding wire with incorporated flux flux, or from a pre-dimensioned element, in the form of a piece as shown in FIGS. 2 to 6. In addition, one of the calibrating zones 9a, 9b or both can or can include the expansion limiting means 14, 15 described with reference to FIGS. 2 to 6.

The passage of an electric current in the connection tabs 5, 6 then in the fuse part 8 creates, in the center of each calibrating zone 9a and 9b, a hot spot. At the nominal current IN of the flat fuse, for example 50 amperes, the drops of metal 13Aa are in a solid state because the temperature of the hot spots is less than approximately 221 ^β C.

For low current overloads, up to 1.35 x I for 30 minutes maximum, the metal drops 13a pass to a liquid state, the temperature at the hot spots then being above 221 ^* C, and below the melting temperature of the calibrating part 9a without drop. Therefore, the temperature communicated to the connection tabs 5 and 6 is reduced and the thermal resistance of the housing 3 is achieved and the risk of contact of the calibrating zones 9a, 9b with the walls of the housing is avoided. When the calibrating zones are deformed due to a rise in temperature, the rupture of one of them causes the instantaneous rupture or breakdown of the other, the cutting of the calibrating zones being able to intervene either on the right or on the left of the solder drop.

For medium overloads, of the order of 2 × IN, the metal drops 13a delay the rise in temperature of the hot spots and spread out randomly on one side or the other, or on both sides. other, hot spots. The breakdown time being short, around 10 seconds, the tin-silver / zintane alloy has no time to form. The calibrating zones 9a and 9b then cut in the vicinity of the hot spots, that is to say substantially at their center.

For heavy overloads, much higher than

4 x IN, the metal drops 13a do not have time to melt. This then results in a random sectioning of the calibrating zones, generally at the point where the section is the smallest.

Finally, the various constituent elements of the fuse according to the two embodiments described above easily lend themselves to mass production in the form of strings so as to be able to be wound up in the form of coils. For this purpose, the elements of the housing are provided with lateral fasteners, not shown, which connect the supports together and the covers together. Likewise, the electrical components, i.e. the connection tabs and the cali- brante, are also produced in the form of chape¬ lets. The installation of the various constituent parts of the fuse can then be carried out very easily according to appropriate sequences, after which, the fuses terminated are separated by cutting the side connections.

Claims

1. Flat fuse for high nominal currents, of the type comprising a housing (1) in which is partially housed a conductive member (5,6,9,10) provided with two flat connection tabs (5,6) whose ends free (7) are located outside the housing, said connection tabs being connected to the interior of the housing by a flat fuse part (8) on at least one face of which and substantially in the center is deposited a drop of metal (13) of predetermined contact surface, characterized in that the fusible part comprises at least one central calibrating zone (9) of width (l) smaller than the width (1_.) of the adjacent lateral zones (21) connecting with the tongues of connection, the contact surface (31) of said drop (13) being at least greater than half the surface of the calibrating zone (9).

2. Flat fuse according to claim 1, characterized in that the contact surface (Sx) of the drop (13) is substantially equal to the surface (S_.) Of the calibrating zone (9).

3. Flat fuse according to one of claims 1 or 2, characterized in that the length (Lx) of the calibrating zone (9) is less than or equal to two thirds of the length (L ₂ ) of the fuse part (8 ).

4. Flat fusion according to one of claims 1 to 3, characterized in that it comprises at least means (14,15) for limiting expansion of the drop of metal (13), said limiting means being perpendicular to - res at the contact surface (S ₂ ) of the calibrating zone

(9).

5. Flat fuse according to claim 4, characterized in that the limiting means consist of at least one blade of low height.

6. Flat fuse according to claim 4, characterized in that the limiting means consist of two blades of low height, arranged on either side of the metal drop.

7. Flat fuse according to one of claims 5 or 6, characterized in that at least one of the blades has an upper free part (23, 24) foldable suscep¬ tible to be folded over the drop of metal (13) .

8. Flat fuse according to claim 7, characterized in that each blade has a trapezoid shape.

9. Flat fuse according to claim 1, characterized in that the fuse part is connected to the connection tabs so as to provide a housing (20) for the metal drop.

10. Flat fuse according to claim 1, characterized in that the lateral zones (10) of the fuse part also partly constitute heat dissipation zones.

11. Flat fuse according to one of the preceding claims, characterized in that the calibrating zone (9) has a length which is less than or equal to two thirds of the length of the fuse part.

12. Flat fuse according to claim 1, characterized in that at least one of the connection tabs comprises a heat dissipation fin (28,29).

13. Flat fuse according to one of claims 1 or 12, characterized in that each connection tab comprises two heat dissipation fins (28,29) arranged on either side of a central part (26) connecting the fuse part.

14. Flat fuse according to claim 13, characterized in that the heat dissipation fins and the central connection part are separated by notches (30).

15. Flat fuse according to claim 1, characterized in that each connection tab comprises, on the external side (5b, 6c) which is opposite to the side (5a, 6a) of connection of the fuse part, a recess (34.35 ) suitable for allowing the strip 1 to be manufactured in strips.

16. Flat fuse according to any one of claims l to 15, characterized in that the metal drop (13) is a tin-silver alloy.

17. Flat fuse according to any one of the preceding claims, characterized in that the metal drop (13) is a tin-lead alloy whose melting temperature is between 180 ^e C and 420 ° C.

18. Flat fuse according to any one of the preceding claims, characterized in that the connection between the fuse part (8) and the connection tabs (5,6) is produced by electrical welding.

19. Flat fuse according to any one of claims 1 to 18, characterized in that the connection between the fuse part (8) and the connection tabs (5,6) is produced by continuous welding with the knurl.

20. Flat fuse according to one of claims 12 or 13, characterized in that the heat dissipation fins (28,29) of the connection tabs (5,6) receive an imprint (22a) during the passage of a wheel making a connection between the fuse part and the connection tabs.

21. Flat fuse according to one of the preceding claims, characterized in that the fuse part (8) comprises two calibrating zones (9a, 9b), has a drop of metal (13a) being disposed substantially in the center of at least one of said calibrating zones.

22. Flat fuse according to claim 21, caracté¬ ized in that a drop of metal (13a) is disposed on one face of each calibrating zone.

23. Flat fuse according to one of claims 21 or 22, characterized in that means (14, 15) for limiting the expansion of the metal drop (13a) are provided on at least one of the calibrating zones (9a, 9b).