EP2017855B1 - Electrical control cable - Google Patents

Description

The present invention relates to electrical control cables, or power cables, used to transmit currents.

Such cables are used in various fields of the industry, such as for example the automotive industry, where they are assembled into bundles for the power supply of various equipment. These cables must thus be the lightest possible, and have a small footprint while maintaining good mechanical strength.

Such cables are conventionally formed by a plurality of copper strands, generally twisted to form a strand so as to increase the flexibility of the cable, and surrounded by an insulating sheath, obtained for example by extrusion. The figure 1 shows an example of such a cable 1, seen in cross section, and made from seven identical copper strands 20 surrounded by an insulating sheath 30 of circular section. To give an idea, the diameter of the cable is typically of the order of 1.6 mm and the copper strands 20 each have a diameter of the order of 0.3 mm.

Other cables of similar structure to that of the figure 1 but with a different number of copper strands, for example nineteen strands, are also known.

The advantages of a cable according to the preceding structure lie essentially in the simplicity of the manufacturing process, but also in the fact that it allows to have a reliable crimping of the connectors. Indeed, it suffices to locally strip the cable by removing a portion of the insulating sheath 30 where it is desired to place the connector, then mechanically compress a socket of the connector around the stripped cable section. In addition, copper intrinsically has a good mechanical strength to traction.

On the other hand, it has been found that the preceding cable uses a quantity of copper that is oversized compared to the real needs corresponding to the quantity of current to be transmitted by the cable. Specifically, near the half of the copper in the previous cable structure is used to increase the tensile strength of the cable, but also to ensure the effectiveness of crimping.

Copper is becoming increasingly expensive and it is important to find new cable structures that minimize the amount of copper used.

Various solutions of composite cables in which copper strands are combined with a core of non-conductive material are already known. In particular, the document US 7, 145, 082 describes a control cable in which a large amount of conductive son, for example copper, are stranded around a core or core core composed of a polymer mutlifilaments type aramid fibers.

This type of cable can significantly reduce the amount of copper used to the value just necessary for good signal transmission, while maintaining a very good mechanical strength to traction through the use of aramid. On the other hand, the number of strands of copper used remains very important compared to the solution of the figure 1 wherein the copper strands are arranged on a single layer concentric with the central copper strand.

The simple replacement of the central copper strand on the structure of the figure 1 by a multi-filament polymer core such as that described in the document US 7,145,082 is not possible because such a cable would not offer sufficient guarantee concerning the crimping operations. Indeed, once such a stripped cable for a crimping operation, the copper strands will deviate slightly with respect to each other, and some of the core polymer filaments may escape radially between two copper strands. This situation is illustrated schematically in figure 2 which shows a cross section of such a cable after stripping of a portion of the insulating sheath 30. As can be seen, certain filaments of the core 40 of multi-filament polymer are found outside the crown of copper strands 20 So when you just compress the socket of the connector around the stripped cable section, these filaments will come between the copper strands and the socket, thus reducing the contact area necessary for good transmission of the electrical signal.

On the other hand, the document is known EP 1 089 299 a cable structure in which a plurality of strands of conductive material are stranded concentrically around a core composed of a plurality of reinforcing fibers embedded in a metallic material. The manufacture of such a cable is expensive, especially because of the use of a matrix of metallic material for embedding the fibers.

Document is also known US 5, 159, 157 a control cable according to the preamble of claim 1, wherein the carbon fibers of the core are secured in a non-metallic unitary structure. More specifically, a petrolatum filling matrix fills all the cavities between the carbon fibers and the conductive material strands. Such a structure remains expensive to manufacture, because of the use of this filling matrix.

The present invention aims to provide a cable using the amount of conductive material, typically copper, just necessary for the transmission of the signal, distributed in a limited number of strands, while ensuring reliable crimping of a connector, and manufacturing is the least expensive possible.

• un coeur comprenant une pluralité de filaments en polymère ;
• une pluralité de brins en matériau conducteur s'étendant dans la direction longitudinale dudit coeur, répartis uniformément et de manière concentrique sur le pourtour dudit coeur, en contact deux à deux ainsi qu'avec ledit coeur, et
• une gaine externe isolante,

caractérisé en ce que lesdits filaments sont répartis en une pluralité de sous-ensembles, les filaments d'un même sous-ensemble étant toronnés en hélice, les sous-ensembles étant également toronnés entre eux pour former une hélice globale.This object is achieved according to the invention which relates to an electric control cable of the type comprising:

• a core comprising a plurality of polymer filaments;
• a plurality of conductive material strands extending in the longitudinal direction of said core, distributed uniformly and concentrically around the periphery of said core, in two-to-two contact as well as with said core, and
• an insulating outer sheath,

characterized in that said filaments are distributed in a plurality of subassemblies, the filaments of the same subassembly being stranded in helix, the subsets being also strung together to form a global helix.

• la figure 1, déjà décrite, illustre une section transversale d'un câble à sept brins de cuivre connu de l'art antérieur ;
• la figure 2, déjà décrite, illustre une section transversale après dénudage, d'un câble dans lequel le brin central de cuivre a été remplacé par un coeur en polymère mutlifilaments ;
• la figure 3 illustre la structure d'un autre câble connu ;
• la figure 4 illustre la structure unitaire non métallique d'un coeur pour un câble selon le mode de réalisation de l'invention.

The invention and the advantages it provides will be better understood from the following description given with reference to the appended figures, in which:

• the figure 1 , already described, illustrates a cross section of a known seven-strand copper cable of the prior art;
• the figure 2 , already described, illustrates a cross section after stripping, of a cable in which the central strand of copper has been replaced by a polymer core mutlifilaments;
• the figure 3 illustrates the structure of another known cable;
• the figure 4 illustrates the nonmetallic unitary structure of a core for a cable according to the embodiment of the invention.

The figure 3 represents a portion of a cable 1, the end has been stripped to show the internal structure of this cable.

Just like the cable of the prior art described in the document US 7, 145, 082 , cable 1 of the figure 3 comprises a plurality of strands 20 of conductive material, for example copper, extending in the longitudinal direction of a core or central core 40 of mutlifilament polymer, and an outer sheath 30 of insulating material.

However, the number of strands 20 used is reduced here since these strands are distributed uniformly and concentrically around the periphery of said core 40, in contact two by two as well as with said heart. In the non-limiting example shown, these strands 20 are six in number. For other sections of the core and the strands, the total number of copper strands will of course have to be adapted to surround on a single layer the periphery of the core.

The filaments of the polymer core 40, for example aramid, have been joined together in a non-metallic unitary structure obtained by a simple adhesive coating, glue type, external. Such a step in the manufacturing process is very simple to perform, and therefore does not overly burden the total cost of manufacturing the cable. In addition, by removing a portion of the sheath 30 for a crimping operation of a connector, there is no risk that the filaments of the core 40 come to interpose between the strands 20 and the connector, even if the strands 20 come away slightly.

In another embodiment not shown, the non-metallic structure is secured by stranding the helical filaments and wrapping the helix with a matrix or a sheath of non-metallic material. The manufacturing process is a little more complex than the simple coating of an adhesive, but however uses well-known techniques for winding several helical wires followed by sheathing, for example by extrusion.

The figure 4 illustrates finally a non-metallic unitary structure 40 according to the embodiment of the invention. Here, the filaments of the heart have been divided into a plurality of subsets (three subsets in the non-limiting case of the figure 4 ). Each subassembly is formed by a plurality, preferably seven filaments 41, helically stranded and placed inside a sheath 42 of insulating material. The three subassemblies thus obtained are then also stranded together to form a global helix. Preferably, as illustrated on the figure 4 , it will be chosen to wind the subsets in a global helix of pitch inverted with respect to the pitch of the helices forming each subgroup. This further reduces the risk that some filaments may escape during a crimping operation of a connector. As an alternative to the use of the sheath 42, each subset is embedded in a matrix of non-metallic material prior to the formation of the overall helix. In another variant, each subassembly is glued.

In all the exemplary embodiments, the core polymer may be aramid, or high performance polyester, or polyamide, or polyester naphthalate.

Claims (5)

1. An electric control cable (1) of the type including:

   - a core (40) comprising a plurality of polymeric filaments;

   - a plurality of strands (20) in a conductive material extending in a longitudinal direction of said core, uniformly and concentrically distributed on the perimeter of said core (10), two by two in contact as well as with said core, and

   - an insulating external sheath (30),
   characterized in that said filaments are distributed into a plurality of subsets, the filaments (41) of a same subset being helically twisted, the subsets being also twisted with each other in order to form a global helix.
2. The control cable (1) according to claim 1, characterizing that the pitch of the global helix of the subsets twisted together is inverted relatively to the pitch of the helices of each subset.
3. The control cable (1) according to any of claims 1 or 2, characterized in that each subset is either embedded in a non-metal material, or covered with a sheath (42) in a non-metal material, or sized.
4. The control cable (1) according to any of the preceding claims, characterized in that the conductive material is copper.
5. The control cable (1) according to any of the preceding claims, characterized in that the polymer of the core (40) is aramide or a high performance polyester, or polyamide, or naphthalate polyester.

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