EP2299453B1 - Electric line - Google Patents

Description

The invention relates to an electrical line, in particular signal line.

Electrical lines, such as signal lines, which are designed only for the transport of low currents, for example, up to 1 A and signal lines up to a maximum of 0.5 A, are used in a variety of areas, including. also in the automotive industry.

The document DE 69 819 056 T2 discloses a signal line.

Due to environmental considerations, weight-reduced cables and lines are being developed especially in the motor vehicle industry in order to ultimately be able to save fuel through the weight saving. For this purpose, for example, so-called outer diameter-reduced vehicle cables are used today, which are referred to as FLRY cables. FLRY lines are described, for example, in DIN 72551 (parts 5 and 6) or ISO 6722 (class A and B). In particular, the thickness of the insulation is reduced in these FLRY lines. Furthermore, the nominal cross sections of the electrical conductors have been reduced in recent years. For signal cables today the typical nominal cross-sections are about 0.35 mm ² .

Even this small cross section compared to previous cross sections is still significantly oversized with respect to the electrical requirement, i. the so-called current carrying capacity of such signal lines is significantly larger than required. So you are in principle suitable for higher currents, although this is not necessary. However, the requirements for mechanical stability as well as processing properties, for example during installation, determine the nominal cross-section finally chosen.

A reduction in the nominal cross-section is also of interest from a cost point of view because of the significantly higher price for copper, the typical conductor material, which has increased in recent years.

The invention has for its object to provide an electrical line, in particular signal line, which have a reduced conductor cross-section compared to the today's usual lines, especially the so-called FLRY lines, with the same or improved mechanical strength.

The object is achieved by an electrical line, in particular signal line, with an electrical conductor and a surrounding insulating sheath, wherein the sheath consists of a fiber-reinforced plastic and the plastic forms a matrix for this purpose, are embedded in the single-way and distributed short fibers. The conductor, preferably a multi-strand stranded wire, in particular of copper, is surrounded directly by the fiber-reinforced insulation jacket. Other layers or an additional cable sheath are usually not provided.

The line is usually designed for a given tensile stress, so it must be able to absorb a predetermined tensile force that may occur, for example, when laying the line.

By short fibers is meant here those fibers which are arranged as individual discrete short pieces, preferably homogeneously distributed in the matrix. The short fibers have lengths of up to 5 mm.

Due to the fiber reinforcement of the insulation jacket this assumes a mechanical task and has in comparison to non-fiber reinforced insulation coats in previous signal lines to a significantly higher tensile strength. This makes it possible to reduce the cross-section of the conductor, since the mechanical requirements are virtually split between the conductor and the insulation jacket. By this measure, the nominal cross section of the conductor is preferably by a factor of 1.5 to 3, partially over it, compared to previous lines, in particular so-called FLRY lines, reduced. Thus, for example, the nominal cross section of a conventional FLRY 0.35 line (that is, with a nominal cross section of 0.35 mm ² ) is reduced to approximately 0.15 mm ² . The one described here Signal line therefore generally has in comparison to a line with the same structure except for the use of the fiber-reinforced plastic, in particular a FLRY line eg according to DIN or ISO standard, with the same or improved mechanical (tensile) load by a factor of 1.5 to 3 reduced nominal cross section.

Of particular importance for the assumption of tensile forces through the fiber-reinforced insulation jacket is the special stress-strain behavior of the fiber-reinforced material of the insulation jacket. Decisive here is that the fiber-reinforced insulation material already at a relevant (low) strain, which shows the electrical conduction in a tensile stress, has sufficient tension. The relevant strain range is typically less than 10% strain and, for example, in the range of about 4% strain. That the insulation jacket already has the required tensile strength at these elongation values of <10% and in particular about 4%.

By introducing the short fibers into a suitable plastic for the insulation jacket, the fiber-reinforced material usually exhibits a special characteristic in the stress-strain curve with an initially steep increase in the expansion range of a few% until typically at least a local maximum in the relevant strain range is achieved.

As a conductor, a stranded conductor of a plurality of individual wires is usually used. For the low currents up to a maximum of about 1 A, stranded conductors with 7 or 19 individual wires (multicore conductors) are usually used. Alternatively, solid conductors (single-core conductor) can be used. The conductors in today's lines have a nominal cross section typically of about 0.35 mm ² , 0.5 mm ² or 0.75 mm ² .

According to an expedient development of the nominal cross-section of the conductor at a predetermined target current for which the line is designed, adapted to the extent required for the electrical conductivity. This means that the nominal cross section determined by the electrical requirements and at the same time It is also stipulated that therefore the nominal cross section is not chosen larger than is necessary due to the electrical requirements. The nominal cross section in this case is dependent, in particular, on the conductivity of the conductor and therefore on the choice of material and on the current intensity and voltage for which the conductor is provided in use.

The short fibers expediently have a length in the range of a maximum of a few millimeters, preferably a maximum of 10 mm and in particular a maximum of 2 mm. The diameter of the fibers is typically in the range of a few 1 .mu.m to a few 100 .mu.m. Such short fibers can be easily processed manufacturing technology.

Conveniently, the insulation sheath is produced by extrusion of a plastics material in which the short fibers are already contained prior to extrusion. The insulating jacket therefore nestles directly against the electrical conductor. Due to the extrusion, the fibers have a preferred direction in the longitudinal direction of the conduit in an expedient embodiment. Due to this forced orientation of at least a majority of the fibers, the tensile strength in the longitudinal direction of the line is positively influenced.

Preferably, the proportion of the fibers is in the range of 0.5 vol.% To a maximum of 10 vol.%, Preferably up to a maximum of about 5 vol% based on the total volume of the insulating material. This allows a good tensile strength while still achieving good insulation properties.

The fiber material used is preferably glass fibers with a diameter in the μm range. In addition, other fibers, such as polymer fibers, cellulose fibers, carbon fibers, etc. may be provided. For example, when glass fibers are used, their content is preferably in a range of about 0.5 to 10% by volume.

Preferably, the insulation jacket takes over a range of 20 to 80% and in particular more than 40% of the predetermined tensile stress, ie it is for the inclusion of a comparatively large proportion of the predetermined tensile stress designed. Preferably, the insulating jacket takes over a greater proportion than the electrical conductor The remaining residual tensile stress carries the electrical conductor itself. The predetermined tensile stress is for example up to 500 N and in particular at only about 70 N, ie the line must have a tensile force of 500 N or max Maximum 50 - 100 N can withstand. This means that it must not experience any mechanical damage in such a tensile stress - with the appropriate safety tolerances. The line therefore deforms substantially elastically, only a slight plastic deformation is allowed. This high mechanical tensile strength shows the insulation jacket already in particular in the relevant strain range of less than 10% elongation.

• Die Leitung ist für einen Strom kleiner 1A und vorzugsweise als Signalleitung für einen Signalstrom kleiner 0,5 A ausgelegt;
• der Nennquerschnitt des Leiters beträgt maximal 2 mm² und liegt vorzugsweise unter 1 mm², bei der Verwendung für Signalleitungen und Kupfer als Leitermaterial liegt er vorzugsweise im Bereich von unter 0,25 mm²;
• der Außendurchmesser der Leitung beträgt maximal 1 bis 4 mm und liegt vorzugsweise bei maximal 1 bis 2 mm. Je nach Anwendungsfall kann hierbei vorgesehen sein, dass zusammen mit der Reduzierung des Leiterquerschnitts auch der Gesamt-Außenquerschnitt reduziert wird. Alternativ kann jedoch auch der Außenquerschnitt beibehalten werden, beispielsweise für den Einsatz bei Durchführungen mit definierten Öffnungsdurchmessern, um den Außendurchmesser also an vorgegebene Loch-Geometrien anzupassen. In diesem Fall wird dann die Reduzierung des Leiterquerschnitts durch eine größere Wanddicke des Isolationsmantels kompensiert;
• die Wanddicke des Isolationsmantels liegt im Bereich typischerweise bis maximal 0,7 mm und vorzugsweise bei lediglich 0,2 bis 0,3 mm;
• als Kunststoffmaterial wird ein extrudiertes Material, insbesondere ein PVC, verwendet. Bevorzugt werden derartige Isolationsmaterialien eingesetzt, die neben den Fasern keine hohen Anteile weiterer Füllstoffe, insbesondere mineralische Füllstoffe, wie beispielsweise Flammschutzmittel, enthalten. Dadurch ist der Füllstoffgehalt, d.h. der Anteil der in der Kunststoff-Matrix eingebetteten Fasern, Partikel und sonstiger Stoffe, gering gehalten, um die Isolationseigenschaften nicht negativ zu beeinflussen.

The low current line typically further preferably exhibits at least a number of the following features, preferably all features in combination:

• The line is designed for a current less than 1A and preferably as a signal line for a signal current less than 0.5 A;
• the nominal cross-section of the conductor is a maximum of 2 mm ² and is preferably less than 1 mm ² , when used for signal lines and copper as a conductor material, it is preferably in the range of less than 0.25 mm ² ;
• the outer diameter of the pipe is a maximum of 1 to 4 mm and is preferably at most 1 to 2 mm. Depending on the application, it may be provided that, together with the reduction of the conductor cross-section, the overall external cross-section is also reduced. Alternatively, however, the outer cross section can be maintained, for example, for use in bushings with defined opening diameters, so as to adapt the outer diameter to predetermined hole geometries. In this case, the reduction of the conductor cross-section is then compensated by a greater wall thickness of the insulating jacket;
• the wall thickness of the insulation jacket is in the range typically up to a maximum of 0.7 mm and preferably only 0.2 to 0.3 mm;
• As plastic material, an extruded material, in particular a PVC, is used. Preferably, such insulation materials are used, the in addition to the fibers no high levels of other fillers, especially mineral fillers, such as flame retardants included. As a result, the filler content, ie the proportion of embedded in the plastic matrix fibers, particles and other substances, kept low, so as not to negatively influence the insulation properties.

The conductor material used is preferably copper. Alternatively, other conductor materials can be used, in particular those with copper increased tensile strength.

The object is further achieved according to the invention by a method according to claim 11, which provides that is reduced in the design of an electrical line, the nominal cross-section of the conductor compared to a comparable line without fiber-reinforced plastic, taking into account that at least part of a predetermined tensile load is taken over by the fiber-reinforced plastic. In this case, a comparable line is understood to mean that the two lines are designed for comparable, in particular the same mechanical (tensile) loads and show the same structure with regard to their architecture / structure. The line differs from the comparable line in particular only by the insulating jacket (fiber-reinforced) and by the reduced conductor and preferably also cable diameter.

Fig. 1

zeigt eine vereinfachte, schematische Querschnittsdarstellung einer Leitung, insbesondere einer Signalleitung und

Fig. 2

zeigt ein beispielhaftes Zugkraft-Dehnungs-Diagramm.

An embodiment of the invention will be explained in more detail with reference to FIGS.

Fig. 1

shows a simplified, schematic cross-sectional view of a line, in particular a signal line and

Fig. 2

shows an exemplary tensile-strain diagram.

An electrical line 2 comprises in the embodiment according to FIG. 1 an electrical stranded conductor 4, which is formed from a total of seven individual wires 6. For this purpose, the individual wires 6 are stranded with one another and consist, for example, of copper. The stranded conductor 4 is surrounded by an insulating jacket 8, in which - here only greatly simplified and shown schematically - short fibers 10 are embedded in a plastic matrix 12. If a smooth outer surface without fiber content is desired or required, a fiber-free plastic skin is preferably provided around the insulation jacket 8 or an additional jacket. The line is preferably formed in the variant shown in the figure as a single round cable without further elements, such as additional strain relief threads, etc. The signal line shown is laid, for example, together with other lines within a motor vehicle electrical system.

Alternatively, several of these lines may already be prefabricated surrounded by a common protective sheath.

The cable 2 described here with the insulating sheath reinforced by the embedded short fibers 10 has several advantages in comparison with the previous such cables without a fiber-reinforced insulation sheath. Thus, furthermore, the copper which is particularly suitable with regard to the electrical properties can be used with its good conductivity. By reducing the nominal cross section to the level required for the electrical properties, a significant cost reduction is achieved at the same time. The mechanical function of the tensile strength is in fact transferred from the expensive copper material to the comparatively inexpensive fiber-reinforced plastic. Furthermore, the line can be manufactured and processed by the usual methods. Both the extrusion process is easily possible with the fibers. The laying of the cable, the connection of plugs, etc. does not require any new process technologies, since only the conductor cross-sections are reduced. There are therefore no problems due to a technology change, for example, in the contact, such as corrosion, etc. expected. Since when connecting a contact element, for example, via a crimp connection this also engages the insulation jacket, a mechanical force is automatically transmitted via the crimp connection in the insulation jacket.

In the in the FIG. 2 the diagram shown is the interaction between the insulating jacket 8 and the stranded conductor 4 outlined in terms of the assumption of traction. In the diagram, the applied tensile force is plotted on the vertical axis and the elongation on the horizontal axis. The lower curve shows the force-elongation behavior of an exemplary insulation jacket 8 made of a thermoplastic thermoplastic elastomer (TPE) with a minimum wall thickness of about 0.2 mm, which surrounds a stranded conductor with a nominal cross-sectional area of about 0.22 mm ² , so that the total cross-sectional area of the insulation jacket is approximately 0.5 mm ² . The middle curve shows the force-strain behavior of an exemplary copper stranded conductor with a nominal cross-section of 0.22 mm ² . This curve shows the typical stress-strain behavior of copper, whose tensile strength is usually about 230 N / mm ² . The uppermost curve shows a mathematical superimposition of the two curves for the stranded conductor 4 and for the insulation jacket 8.

Typical requirements require that such a line 2 must withstand a tensile force of 70 N. As can be seen from the upper superimposed curve, this is achieved by the interaction of the insulation jacket 8 with the stranded conductor 4 without problems at a relevant expansion range of about 5%. This therefore shows that, due to the special choice of the insulating jacket 8 and its good mechanical properties with regard to the tensile strength, a clear reduction in the cross section of the conductor 4 is achieved from the nominal cross sections of 0.35 mm ² customary today.

The fiber-reinforced material used for the insulation jacket 8 generally shows a maximum in the expansion range <15% and - especially at a high fiber content - even at elongation values of well below 10%, a maximum in the stress-strain behavior. Together with a high modulus of elasticity at low strains in the range for example up to 5% elongation, a very good mechanical stress-strain behavior of the insulation jacket 8 is achieved overall.

Thus, the fiber-reinforced insulation material shows a significantly different characteristic behavior to conventional non-fiber reinforced insulation materials such as PVC, which has a continuous increase in tensile strength up to its elongation at break at about 300% elongation. In the strain region of <10% relevant for the cable 2 with regard to the tensile strength, such a conventional insulation material shows only a fraction of its maximum tensile strength.

In general, the relation holds that with increasing fiber content, the maximum tensile stress of the fiber-reinforced material increases while the elongation at break decreases. Investigations have shown that a good compromise between a sufficient elongation at break and the best possible tensile stress can be achieved with already low elongation values with low fiber contents.

About the special properties of each selected fiber-reinforced insulation material and its cross-sectional area (ie, the choice of the wall thickness of the insulating jacket 8) can be a traction-absorbing capacity of the insulating jacket 8 set according to the respective requirements and in particular also in dependence of the selected conductor cross-section. For example, assuming a given tensile force of 70 N and the use of a copper stranded conductor with 0.13 mm ² cross-sectional area, the stranded conductor 4 at the typical copper tensile strength of 230 N / mm ² only about 29, Take 9 N of traction. The rest must therefore be taken over by the insulation jacket.

Claims (11)

1. Electric line (2), in particular signal line, comprising an electrical conductor (4) and an insulating sheathing (8) directly surrounding the latter, characterized in that the line (2) is designed for a rated current intensity up to a maximum of 1 ampere and for a predetermined tensile stress that can be at least partially absorbed by the insulating sheathing (8), which for this purpose is formed from plastic in the form of a matrix (12) with milled fibres (10) of a length in the range of a maximum of several millimetres embedded therein in an individual and distributed manner.
2. Line (2) according to Claim 1, in which the nominal cross section of the conductor (4) under the predetermined rated current intensity for which the line (2) is designed is limited to the nominal cross section required for the electrical conductivity.
3. Line (2) according to Claim 1 or 2, in which the length of the milled fibres (10) is a maximum of 10 mm, preferably a maximum of 2 mm.
4. Line (2) according to one of the preceding claims, in which the milled fibres (10) are aligned in the longitudinal direction of the line (2).
5. Line (2) according to one of the preceding claims, in which the insulating sheathing (8) is formed by extrusion of a plastics compound with milled fibres (10) already contained therein.
6. Line (2) according to one of the preceding claims, in which the proportion of the milled fibres (10) lies in the range from 0.5% by volume to a maximum of 10% by volume with respect to the total volume of the insulating sheathing (8).
7. Line (2) according to one of the preceding claims, in which the insulating sheathing (8) is designed for a tensile stress in the range from 20 to 80% of the predetermined tensile stress.
8. Line (2) according to one of the preceding claims, which is designed for a predetermined tensile stress of up to approximately 500 N and in particular of approximately 50 to 100 N.
9. Line (2) according to one of the preceding claims, which has the following features in combination:

   - it is designed for a current lower than 1 A,

   - the nominal cross section of the conductor is a maximum of 2 mm² and is preferably below 1 mm²,

   - the outside diameter is a maximum of 1 to 4 mm and preferably a maximum of 1 to 2 mm,

   - the insulating sheathing (8) has a wall thickness that lies in the range up to a maximum of 0.7 mm,

   - an extrudable material is used as the plastic, for example a thermoplastic, in particular a PVC.
10. Method for designing an electric line (2) for a rated current intensity up to a maximum of 1 ampere, comprising an electrical conductor (4) and an insulating sheathing (8) directly surrounding the latter, of a fibre-reinforced plastic with milled fibres (10) of a length in the range of a maximum of several millimetres embedded therein in an individual and distributed manner, the line (2) being designed for a predetermined tensile loading that can be partially absorbed by the insulating sheathing (8) and the nominal cross section of the conductor (4) being reduced with respect to an FLRY line conforming to DIN 72551 (Parts 5 and 6) or ISO 6722 (Classes A and B) that is comparable with regard to the structure and the mechanical load-bearing capacity, but without fibre-reinforced plastic.
11. Use of a line (2) according to one of Claims 1 to 10 or of a line (2) designed according to Claim 11 in a motor vehicle.

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