AN ELECTRIC FUSE COMBINED WITH A CONNECTOR

Abstract: The invention relates to electric fuse and solves the problem of providing a fuse which is cheap to manufacture, has an insignificant space requirement but still is capable of operating at relatively high rated current intensities, such as of the order of magnitude of 100 A. This makes it practically feasible to protect by use of a fuse also such electric circuits which normally are unprotected, such as the current supply circuit of the electric cranking motor of a vehicle engine. A fuse according to the invention does not have a separate holder or mounting device. It does insted form an integrated unit consisting of a central melt bridge (3) between end portions (1, 2) for connection of the fuse in an electric circuit. To preserve the mechanical shape and integrity of the fuse also upon melting its end portions (1, 2) are held together by a central jacket (8). Preferably, the jacket is constituted in a way permitting ocular observation of bridge (3) through the jacket wall.

Description: An electric fuse combined with a connector In several contexts, especially at motor vehicles, only current-consuming units having a relatively low rated current intensity are provided with fuses, whereas loads operating at considerably higher rated current intensities lack fuse protection. A typical example is the arrangement of the cranking motors of motor vehicles. Trucks and other working vehicles do in addition to the starter motor often comprise one or more further electric motors operating at high current intensities and lacking fuse protection. This has turned out to be a serious disadvantage, especially when such an electric motor has a location which is exposed from a collision point of view. This applies to for example lift motors for tailgate lifts. It has been found that also a relatively minor collision damage often causes serious and expensive secondary damages in the way that the insulation around the connector cable from the positive pole of the battery is damaged. This in turn causes a short-circuit to earth which by overheating or spark formation can generate a fire. While, naturally, the corresponding problem can be solved by the use of conventional fuses, plugs or cartridges, this solution has practically never been used in the vehicle industry, the reason for this being the relatively high costs and the comparatively high space requirement. The object of the invention is to provide a fuse solving the above-mentioned problem in a manner satisfactory in all respects. Consequently, the fuse should be cheap to manufacture and have an insignificant space requirement. It will appear from the following description how this object can be realized according to the invention but, in few words, the subject of the invention can be defined as a fuse lacking a separate, stationary holder. This means that it can form a portion of a current conductor which portion is integrated with the conductor from an electrical and a mechanical point of view. The current conductor does typically extend between on the one hand a current source, a storage battery or a generator, and on the other an electric load which typically but not exclusively is constituted by a electric motor installed in a vehicle. Three embodiments of the invention will now be described with reference to the drawing, all figures of which are perspective views. Fig. 1 illustrates the principle of a fuse member according to the invention. Fig. 2 shows a complete fuse for connection between a cable and a threaded bolt. Fig. 3 corresponds to Fig. 2 but shows a fuse unit arranged for connection between a cable and the pole bolt of a battery. Fig. 4 illustrates a second shape of the fuse member shown in Fig. 1. Fig. 5 corresponds to Fig. 4 but illustrates a third fuse member shape . The fuse member shown in Fig. 1 has two end portions 1 and 2 and an intermediate, narrow bridge portion 3 which will melt when the fuse is activated. The bridge portion consists of a metal having a relatively low melting point and, at the end portions of the unit, the bridge ends have coatings 4, 5 consisting of a material of high electrical conductivity, preferably copper, and intended to reduce the transition resistance between the fuse and the components to which it is connected. To facilitate such connection the end portions have through holes 6, 7. Fig. 2 shows a complete fuse unit the melt bridge of which can be shaped as shown in e.g. Fig. 1, Fig. 4 or Fig. 5. If one would use just the melt bridge and connect it between e.g. a bolt through hole 6 and the end of a flexible cable connected to end portion 5, melting of bridge 3 would cause end portions 1 and 2 to separate and, due to the flexibility of the cable, its separated end could fall down and, when connected to a voltage source, get into contact with earth or with some other component. This risk is eliminated in a complete fuse as shown in Fig. 2 since the bridge is there surrounded by a supporting jacket 8 of an insulating material, preferably a plastic. The jacket is secured to both end portions, in this case by inbossments 9 engaging corresponding depressions in the end portions. It should however be underlined that the necessary form-stable connection between the jacket and each of the two end portions can be achieved in many other ways, such as by the use of guide pins. For the purpose of making it possible conveniently to determine whether the fuse has been activated or not jacket 8 is provided with a central window 10 permitting direct observation of bridge 3. The only difference between Fig. 3 and Fig. 1 or 2 is that in Fig. 3 one of the end portions is shaped like a cable shoe 11 for connection to the pole bolt of a accumulator battery. The fuse member illustrated in Fig. 4 does, on each side of melt bridge 3, exhibit through holes 12 for guide pins securing the jacket. Also according to the embodiment of Fig. 5 there are such holes 12 and, additionally, a central hole 13 in bridge 3. As is understood, the effective current-conducting cross- sectional area of the bridge will depend on the diameter of hole 13. In other words, by variation of the diameter of hole 13 it is possible, using one and the same fuse member of a predetermined, standardized size, to vary the rated current intensity of the fuse within a relatively wide interval, for example 50-400 A. This possibility is an advantage further reducing the manufacturing and marketing costs of fuses according to the invention. According to such embodiments of the invention it is suitable to provide the jacket 8 with information concerning the actual rated current of the fuse. Such information can be presented in many different ways, for example by variation of the colour of jacket 8 or by providing it with figures or symbols. In certain applications, for example when the fuse is mounted inside a closed space adjacent to a accumulator battery, it can be gas sealed so that the spark formation occurring upon melting is prevented from igniting gas assembled inside the confined space. If in such cases one wishes to preserve the possibility of determining by direct observation whether bridge 3 has melted or not one does not use an open window 10 as shown in Figs. 2 and 3 but does instead use a jacket 8 consisting of a transparent material. It is to be understood that it is not necessary for one of the ends of the fuses to be connected directly to a current source or to an electrical load. Instead, one or more components or conductor sections can intervene making such connection indirect. It is however equally true that, for the reasons above explained, such direct connection as a rule represents the optimal way of taking advantage of the positive properties of the fuse according to this invention.

Claims: Claims 1. An electric fuse unit which is combined with a connector in the way that its one end permits direct connection to either a current source, especially an accumulator battery of a motor vehicle, or to an electric load, especially an electric motor installed in a vehicle, whereas its opposite end is adapted to be connected to a current conductor, such as a flexible cable, c h a r a c t e r i z e d in that the fuse unit does not have a separate, stationary holder and does substantially consist of an elongate member comprising a central melt bridge (3) between two end portions (1, 2) which have greater cross- sectional area than that of the bridge and are adapted to serve as connecting means, a supporting jacket (8) of an electrically insulating material, preferably a plastic, surrounding and interconnecting said end portions (1, 2) whereby, also upon melting of bridge (3)', a fuse unit is mechanically held together, replacement of the fuse upon activation thereof requiring exchange of the complete unit. 2. A fuse unit as claimed in Claim 1 , c h a r a c¬ t e r i z e d in that the supporting jacket (8) is constituted in a way permitting direct observation of the melt bridge (3) through the jacket wall, e.g. in the way that the jacket, in a manner known per se, either has a central window (10) or consists of a transparent material. 3. A fuse unit as claimed in Claim 2, c h a r a c¬ t e r i z e d in that the supporting jacket encloses the melt bridge as a gas-sealed enclosure. 4. A fuse unit as claimed in Claim 2 or 3, c h a r a c¬ t e r i z e d in that the support jacket (8) carries information about the rated current of the fuse, such information being represented by the colour of the jacket or by figures or symbols in its surface. 5. A fuse unit as claimed in any of Claims 2-4, c h a r a c t e r i z e d in that at least one of its end portions (1, 2) does on one or both sides have a layer (4, 5) of a relatively soft material of high electrical conductivity, preferably copper, for the purpose of reducing the transition resistance of the corresponding connection and increasing the effective current carrying cross-sectional area of the end portion. 6. A fuse unit as claimed in any of Claims 1-5, c h a r a c t e r i z e d in that the size and basic shape of the melt bridge (3) is the same in fuses with different rated current intensities, the effective current carrying cross-sectional area being matched to those rated values by the bridge portion being provided with holes.

Inventors: LENFELDT LARS, SVANBERG BOERJE, LENFELDT, LARS, SVANBERG, BOERJE
Applicants: Z LYFTEN PROD AB, Z-LYFTEN PRODUKTION AB
Application year: 1987
Main classification: H01H85
IPC codes: H01H85