WO1999067862A1

WO1999067862A1 - Fuse element for electrical installations

Info

Publication number: WO1999067862A1
Application number: PCT/EP1999/003542
Authority: WO
Inventors: Rainer Mäckel; Thomas Schulz
Original assignee: Daimlerchrysler Ag
Priority date: 1998-06-19
Filing date: 1999-05-22
Publication date: 1999-12-29
Also published as: DE19827374C2; DE19827374A1

Abstract

The invention relates to a fuse element for electrical installations, comprising a conductor area to be protected which serves as current path for an electric current. Connected in series with the conductor area (11) to be protected, the fuse element comprises a reference conductor (9) which outside the current path has at least one fusible area (13) containing a fuse material whose melting point is below the melting point of a safety-relevant element (12) of the conductor area (11) to be protected. Means for reducing the current (14, 15, 16, 23, 24) in the conductor area (11) to be protected are provided for in the fusible area (13) which can be connected at least when the melting temperature of the material is exceeded.

Description

Fuse element for electrical systems

description

The invention relates to a fuse element for electrical systems, in particular for vehicles.

In electrical systems, in particular in motor vehicle electrical systems, fuses are usually used to protect electrical lines. Fusing with fuses has the disadvantage that, with a reasonable design, these fuses cannot provide complete line protection.

When short-term overcurrents occur, an electrical line in the vehicle can carry much more current than the fuse due to the high thermal capacity of the electrical conductor, so that a conventional fuse is under-dimensioned for short-term high overcurrents. In the area of long-lasting small overcurrents, on the other hand, the fuse switches off too late, so that in this case an electrical line and / or consumer is not adequately protected. With an overcurrent of e.g. 35% of the fuse's nominal tripping current can take up to half an hour for a fuse to actually trip. With an overcurrent of 250%, which corresponds to 3.5 times the nominal tripping current of the fuse, it can still take 5 seconds until the fuse is tripped.

From DE 195 03 808 AI an arrangement is known in which the current-carrying line can be disconnected with the aid of an explosive device. Here, the detonator is connected on one side to the positive battery terminal and on the other side to a second line that envelops the first line. If mechanical damage to the cable results in contact between the vehicle earth and the second conductor, the detonator is triggered and disconnects the connection between the battery and the first line. However, this has the disadvantage that the costs for the first line are increased by the sheathing with the second line. The separation by a blasting element makes sense only for lines with a large cross-section, ie high Current carrying capacity, suitable. Furthermore, this method only protects the case of mechanical damage, but not the case of thermal overheating of the cable.

The invention has for its object to provide a fuse element for electrical systems, in particular for on-board networks of motor vehicles, which protects electrical lines of the electrical system from thermal overload.

The object is solved by the features of the independent claim. Further and advantageous refinements can be found in the subclaims and the description.

A fuse element according to the invention has, at least adjacent to the line area to be protected, a reference material arranged outside the current path, which is used at least in one of its physical and / or chemical properties for comparison with physical and / or chemical properties of a security-relevant element of the line area to be protected, at least If a predetermined change in at least one physical and / or chemical property of the reference material is exceeded, means are provided for current reduction with which the current in the line area to be protected can be reduced.

The reference material is preferably non-metallic, particularly preferably an insulator.

A safety-relevant element is expediently an electrical insulation of the line area to be protected.

It is advantageous. if the reference material covers a reference conductor at least in some areas. Is expedient. when the fusible material surrounds the reference conductor like an insulating jacket. The reference conductor is preferably connected in series with the line area to be protected.

A preferred fuse element has a reference conductor, which outside the direct current path, which is formed by the line region to be protected, has at least one melting material as reference material, the melting point of which lies below the melting point of the insulation of the conductor region to be protected, means for providing in the region of the melting material Current reduction in the line area to be protected can be activated at least when the melting temperature of the melting material is exceeded.

The melting material is particularly preferably formed from a PVC material whose melting point is below that of a PVC jacket of the line area to be protected.

It is particularly favorable that the means for reducing the current have at least one parallel current path to the line area to be protected. This reduces the current in the line area to be protected. The parallel current path is preferably of lower resistance than the line area to be protected. It is particularly advantageous to arrange the melting material as insulation between an electrical contact point to the parallel current path and an electrical contact point to the protective line area.

In a particularly expedient embodiment, a metallic fuse is arranged in series with the reference conductor. A high current flows when the melting area melts, so that the metallic fuse melts. One advantage is that the fuse does not have to have high requirements for tripping accuracy.

A design of the fuse element is particularly expedient, in which the means for reducing the current in the line region to be protected have a spring element, so that an electrical one when the melting temperature of the melting region is exceeded Contact point of the parallel current path with spring force can be brought into contact with an electrical contact point of the conductor area to be protected. The contacting is particularly reliable and can be made very simple and inexpensive.

A further favorable embodiment is to provide the reference conductor having a bore in which engages a stopfenfb ^'rmiges melting material. Is low, electrical and / or mechanical contact means of the parallel current path for contacting the reference conductor through the stopfenfb ^{'melting-shaped} material to space. The advantage is that only a small amount of the melt material is required. It is also favorable that the shape of the reference conductor can be used to generate a higher electrical power loss in the melting area than in the line area to be protected, so that melting of the melting material begins at a temperature which is safely below a critical temperature for the line area to be protected lies.

It is particularly expedient to make the reference conductor and / or contact means permeable to molten material in the melting range. It is thereby achieved that the electrical contact can be produced simply and reliably without molten or re-solidified melting material interrupting the electrical contact.

A further advantageous embodiment consists of designing means for reducing the current as an interruption point in the reference conductor.

It is favorable to provide means for monitoring the electrical conductivity and / or the dielectric constant and / or the magnetic susceptibility and / or the mechanical strength and / or the hardness of the reference material.

Further advantages and refinements of the invention emerge from the further claims and the description. The invention is described below with reference to a drawing, wherein

1 is a schematic diagram of a fuse element according to the invention, Fig. 2 shows in detail an embodiment of a securing element according to the invention, Fig. 3a, b further embodiments of a securing element according to the invention, and Fig. 4 shows a further embodiment of a securing element in section.

The invention is described below using examples for use in a motor vehicle. However, the invention is not limited to this use, but is particularly suitable for use in which a cable to be protected is to be protected against thermal overload.

A favorable embodiment of a securing element according to the invention is shown in Fig. 1 as a schematic diagram. A fuse element 10 is connected between a battery 1 with a positive pole 2 and a negative pole 3, which is connected to ground 4, and the line area 11 to be protected. The fuse element 10 has a reference conductor 9 with an insulating sleeve 13, which surrounds the reference conductor 9, and additionally a metallic fuse with a connection 7 and a connection 6, between which a fuse element 8 is arranged. The insulating sleeve 13 serves as a reference material. The reference conductor 9 is preferably detachably connected to the line region 11 to be protected. The battery-side connector 6 of the metallic fuse is connected to the positive pole 2 of the battery 1 via the connection 5. In an analogous manner, the reference conductor 9 can be arranged on the battery side of the metallic fuse. In this case, the reference conductor 9 would be connected to the battery 1 and the fuse would be connected to the line area 11 to be protected. The metallic fuse can be a conventional fuse or an active fuse, preferably an active fuse, which can be triggered by an additional thermal and / or electrical and / or another ignition mechanism.

The insulating sleeve 13 on the reference conductor 9 is a melting material with a

Melting temperature, which is preferably below the melting temperature of the insulation 12 of the line region 11 to be protected. The insulating sleeve 13 is preferably formed from a plastic. It is favorable to use a similar type of reference material Plastic as for the insulation 12 of the conductor area 11 to be protected, in particular PVC (polyvinyl chloride), in which the melting temperature can be influenced very easily, preferably by means of fillers and / or chain lengths and / or degree of crosslinking in the plastic. However, it is also favorable to use waxes as insulation material 13, with which very precise monitoring of the temperature is possible, since these have a precisely controllable melting point. The insulating material of the melting area 13 is preferably selected so that the melting point of the material lies below that of the insulation of the line area 11 to be protected.

The advantage is that the reference conductor 9 covered with melting material simulates the thermal cable behavior of the line region to be protected by a combination of conductor and insulation material. The behavior of the insulation reference material 13 is now checked within the area of the reference conductor 9.

Since, in the event of thermal overheating of a cable, as a rule only the insulation material is damaged, it is expedient to monitor the insulation material 13 on the reference conductor 9. In this area, the insulation material is damaged by the heat generated by the current flow or changes its physical parameters such as electrical conductivity, capacitance, relative dielectric constant, permeability, physical state, flowability, thermal conductivity, temperature and others in such a way that a loss of the insulation effect is to be expected , it can be assumed that the insulation of the line region 11 to be protected also threatens to be damaged. In this case, means are provided which at least reduce the current flow in the line area 11 to be protected. The metallic fuse 6, 7, 8 is triggered by a trigger mechanism and the current flow in the line area 11 to be protected is interrupted.

For this purpose, a contact 15 is pressed against the insulation 13 of the reference conductor with a spring element 14. If a large current now flows through the cable 11 and thus through the reference conductor 9, the ohmic resistance results in a temperature increase in the conductor 9 and thus also in the insulation layer 13. This temperature increase leads to a change in the physical parameters and thus also to damage the insulation layer 13. Both the material of the insulation layer 13 can be chosen so that the melting point is lower compared to that of the insulation material 12 in the line region 11 to be protected, or the reference conductor 9 can be adjusted by shape or material so that the ohmic resistance is higher there than in the conductor 11, so that the greatest heat development takes place in the region of the reference conductor 9 and the melting region 13 is warmer than the insulation 12 of the line region 11 to be protected.

Is e.g. modified the melting material 13 accordingly, the temperature limit for the damage to the insulation layer 13 is below the corresponding limit value of the insulation material 12 of the line region 11 to be protected. Accordingly, the layer 13 will first show a change in its physical parameters. The change is preferably softening and / or melting and dripping of the insulation layer 13 from the reference conductor 9.

When softening or dripping, the contact 15 and the spring element 14 make electrical contact with the vehicle ground by bringing a low-resistance parallel current path to ground 16 into contact with the reference conductor 9. The current flow through the line region 11 to be protected is greatly reduced because its ohmic resistance is higher than that of the parallel current path. In addition, the current flow through the melting element 8 is significantly increased and the metallic fuse is triggered. Since the limit value for the damage to the insulation layer 13 is lower than the limit value for the insulation layer 12, the cable 11 is protected by this arrangement. If the insulation material 13 has the same or very similar physical and chemical properties as the insulation material 12 except for the melting point, aging effects and previous damage are largely taken into account in the securing behavior.

Another possibility is that the insulation materials for the melting area 13 and the insulation 12 are the same, and the design of the reference conductor 9 ensures that the temperature in the reference conductor 9 is a few degrees higher than in the line 11. The very similar structure of the reference conductor 9 and line 11 results in comparable current carrying capacity characteristics of the fuse element 10 according to the invention and the line area 11 to be protected. Complete cable protection can thus be achieved, the current carrying capacity of the cable 11 being used as well as possible.

In the event that the battery 1 can not provide sufficient current to open the melting element 8, the cable 11 is relieved by the current path connected in parallel consisting of the reference conductor 9, the contact 15 and the spring 14 and thereby protected.

2 shows a favorable embodiment. Here, the spring 14 is realized by the prestressed bracket 24. A wedge 23 presses against the insulation layer 13, and as soon as it dissolves or becomes soft, an electrical contact is made between the reference conductor 9 and the vehicle ground 16 via the wedge 23. The melting element 8, which is not shown in the figure, then triggers and interrupts the current flow through the conductor 11, which is also not shown separately in the figure. This version is particularly simple and inexpensive.

In addition to making mechanical contact between the reference conductor 9 and the parallel current path, other methods (e.g. also in combination with active switching elements, active fuses) are possible. For example, the electrical conductivity of the insulation material 13 is measured and used from the triggering criterion, in which a parallel current path is connected or switched to the reference conductor 9. Likewise, other physical parameters of the insulation material 13 can be determined and used to trigger the fuse element.

3 shows a detailed view of a further advantageous embodiment of the securing element according to the invention. The structure of the arrangement essentially corresponds to that in FIG. 1. In the embodiment according to FIG. 3, however, the reference element 9 has a bore into which the melting material 13 is inserted as a stopper. This can be seen in plan view in FIG. 3a. 3b is a side view of the arrangement 3 a, in which the effect of the means for contacting the parallel current path can be seen. The plug-shaped melting material 13 projects beyond the conductor cross section of the reference conductor 9 and serves as a spacer to a connecting means 17, which represents a low-resistance connection to the vehicle ground. The connecting means 17 is pressed against the melting material 13 by the spring force of a spring 14. As soon as it softens and / or melts at elevated temperature, the electrical contact between the connecting means 17 and the reference element 9 is established. The melted material can flow out of the contact area through the bore, so that the electrical connection is as large as possible and reliable and is not contaminated by molten insulation material. It is advantageous if the connecting means 17 forms a cup-shaped cavity, the opening of which faces the bore. The electrical contact then takes place over the rim of the pot. Molten insulation material 13 can then be accommodated in the interior of the cup-shaped cavity. It is also favorable to provide the pot base of the connecting means with bores or also to form it as a network through which the melt of the insulation material can pass, so that the electrical contact points are not contaminated by the melt.

Another inexpensive embodiment is to place the plug-shaped melting material between the reference conductor 9 and the connecting means 17, the reference conductor being perforated so that when the melting point of the melting material is exceeded, it can flow through the perforation of the reference conductor 9.

Another expedient arrangement is shown in FIG. 4 as a lateral section through a favorable reference element 9. The reference conductor 9 itself is used here as an opener for the current path through the conductor 11 and is formed by two sections 9.1, 9.2, which are pressed together in the manner of a shrink tube by their sheathing, which is formed by a melting material 13. The sections form an electrical contact at their contact point. The contact point can also be provided with an electrically conductive adhesive and / or a solder in order to make the electrical contact, but the mechanical connection is mainly produced by the melting material 13. As soon as the casing 13 becomes soft or melts, the two sections 9.1, 9.2 of the reference conductor 9 come apart. In this case, an additional fuse in the fuse element 10 can be dispensed with, since no parallel current path has to be connected. It is advantageous to connect one of the sections or both sections 9.1, 9.2 with a spring in order to additionally tear them apart when the melting material 13 melts. It is also possible to provide the two sections 9.1, 9.2 with a pretension which brings about the same effect. This prevents the sections 9.1, 9.2 of the reference conductor 9 from undesirably welding to one another, for example by sparking, and not separating from one another.

It is particularly favorable that the fuse element according to the invention does not require any complex encapsulation, since the temperatures which are necessary for melting the melting material 13 are considerably lower than those of metallic fuses.

The short circuit to the vehicle mass produced in preferred embodiments allows the use of inexpensive slow-acting metallic fuses, which also do not have to be particularly precise, since the triggering of the metallic fuse is reliably forced by the short-circuit current when the melting material 13 melts.

An advantageous embodiment of the invention is that physical and / or chemical properties of the reference material 13 are monitored and if the properties change beyond a predetermined permitted level, means for reducing the current in the line area 11 to be protected intervene. A parallel current path can be switched on as well as a circuit breaker can be actuated. It is favorable to monitor easily accessible material parameters and, for example, to determine the electrical conductivity and / or the capacity of the reference material 13. If the behavior of the material parameters with increasing temperature is known, the current reduction in the line area 11 to be protected can be triggered when a predetermined amount of change in at least one monitored parameter is exceeded. The reference material 13 can be used as part of a reference conductor 9, can also be connected directly to the line region 11 to be protected, and electrical and / or chemical properties can be monitored directly on the cable 11 to be protected. It is advantageous to connect a reference conductor 9 as an additional, detachable line part to the cable 11 to be protected. Such an element can be easily replaced.

Claims

claims

1. Fuse element for electrical systems with a line area to be protected as a current path for electrical current, characterized in that the fuse element (10) at least adjacent to the line area to be protected (11) has a reference material (13) arranged outside the current path, which at least in one its physical and / or chemical properties are used for comparison with physical and / or chemical properties of a safety-relevant element (12) of the line area (11) to be protected, at least when a predetermined change is exceeded, at least one physical and / or chemical property of the reference material ( 13) Means for current reduction (9.1, 9.2, 14, 15, 16, 17, 23, 24) are provided, with which the current in the line area (11) to be protected can be reduced.

2. Security element according to claim 1, characterized in that the reference material (13) is non-metallic.

3. Fuse element according to claim 1, characterized in that the safety-relevant element (12) is an electrical insulation of the conductor area to be protected (11).

4. Fuse element according to claim 1, characterized in that the reference material (13) covers a reference conductor (9) at least in regions.

5. Fuse element according to claim 1, characterized in that the reference conductor (9) is connected in series with the line region (11) to be protected.

6. Fuse element according to claim 4, characterized in that the reference conductor (9) as the reference material (13) has a melting material whose melting point is below the melting point of the insulation (12) of the conductor region (11) to be protected and the means for current reduction (14th , 15, 16, 23, 24) in the line area (11) to be protected in the area of the melting material (13) can be switched on at least when the melting temperature of the material is exceeded.

7. Fuse element according to one of claims 4 to 6, characterized in that a metallic fuse (6, 7, 8) is arranged in series with the reference conductor (9).

8. Fuse element according to claim 1, characterized in that the means for current reduction (14, 15, 16, 23, 24) have at least one parallel current path to the line region (11) to be protected, which is lower-resistance than the line region (11) to be protected .

9. Fuse element according to claim 1, characterized in that the reference material (13) as insulation and / or spacer between electrical and / or mechanical contact means (14, 15, 16, 17, 23, 24) with an electrical contact point to a parallel current path and an electrical contact point to the line area (11) to be protected is arranged.

10. Fuse element according to claim 6 or 8, characterized in that the means for current reduction (14, 15, 16, 23, 24) have a spring element (14) so that when the melting temperature of the melting material (13) is exceeded, an electrical contact point of the Parallel current path with spring force can be brought into contact with an electrical contact point of the conductor region (11) to be protected.

11. Fuse element according to claim 4, characterized in that the reference conductor (9) is provided with a bore into which a stopper-shaped reference material (13) engages.

12. Fuse element according to claim 4, characterized in that the reference conductor (9) is designed to be permeable to molten material in the region of the melting material (13).

13. Fuse element according to claim 9, characterized in that the contact means (17) in the region of the melting material (13) are designed to be permeable to molten material.

14. Fuse element according to claim 1, characterized in that means for current reduction (9.1, 9.2) are designed as an interruption point in the reference conductor (9).

15. Fuse element according to claim 1, characterized in that means for monitoring the electrical conductivity and / or the dielectric constant and / or the magnetic susceptibility and / or the

Temperature and / or the hardness and / or the mechanical strength of the reference element (13) are provided.