ES2620382T3 - Coaxial cable - Google Patents

Abstract

Coaxial cable (100) comprising: - a central conductive unit (1) intended to carry a signal, - a shield (4) a plurality of wires (40) arranged as a mesh, intended to be connected to a ground in order to protect the central conductive unit, - a dielectric material (2) arranged between the central conductive unit (1) and the shield (4) to insulate the central conductive unit (1) from the shield (4), and - an insulation cover ( 5) arranged around the shield (4), in which the central conductive unit (1) and the shield (4) comprise a plurality of wires (10, 40) made with an aluminum core (11, 41) covered with a copper cladding (12, 42) characterized in that the wires (40) of the shield (4) comprise an outer tin cladding (43).

Description

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DESCRIPTION

Coaxial cable

The present industrial invention patent application refers to a coaxial cable.

] As is known, a coaxial cable comprises a central conductor wire intended to carry an electrical signal, a peripheral shield intended to be connected to a ground to protect interference on the central conductor wire, a dielectric material interposed between the central conductor wire and Peripheral shielding to insulate the central conductor wire of the peripheral shielding, and an insulating envelope surrounding the peripheral shielding. Peripheral shielding is generally composed of conductive wires that form a mesh, also called a "junction bridge."

The central conductor wire and the coaxial cable junction bridge cables that are commercially available are generally made of pure copper.

The use of solid copper for the central conductor wire and the junction bridge cables guarantees the best performance of the product due to the excellent capacity of the copper to be crossed by a signal. In fact, copper has a high conductivity, and therefore a low electrical resistance and a low ohmic loss. However, a solid copper conductor wire implies very high production costs due to the high price of copper and its huge uncontrollable fluctuations (especially in the short term).

In order to overcome the problem of high costs, other types of coaxial cables are known, which are provided with a central conductor wire and / or junction bridge wires made of pure aluminum. Due to its lower specific gravity, aluminum has a considerably lower price than copper, but at the same time it has a lower performance due to its low oxidation resistance and high electrical resistance (low conductivity and therefore high ohmic loss) . In addition, aluminum wire, which is less ductile than copper, does not have the same versatility because its minimum stretch dimensions are greater than that of a copper wire, which is not appreciated by the market in view of the growing trend towards miniaturization

Copper clad aluminum conductor wires (CCA) are known to solve these problems, at least partially.

EP1469486A1 describes a conductive wire in which the core and mass are made of concentric sheets of CCA folded in tubular form. This type of cable finds a special application in the television industry (therefore static applications) and cannot be applied in dynamic consumer sectors, such as the automotive industry, due to a series of factors related to the complexity of the production process and The mechanical properties of tubular conductive wires made with curved copper sheets. In fact, this type of cable is too expensive, has limited flexibility and is subject to breakage during flexion tests.

Document GB1310334A describes a coaxial cable in which the central conductor wire is made with a single wire that can be made of CCA, isolated from the external metal sheet, which represents protection, by means of a series of plastic discs. This type of cable cannot be applied to the standard connectors of the automotive industry without making very high investments to modify the connectors.

This solution is mechanically very weak and prevents the cable from connecting with other elements, such as clips (which deform the internal structure of the cable when the clip is pulled), or other connections due to the union operation (element that maintains the cables together) occurs with tensions and tractions that change the geometry of the cable, thereby altering its performance.

This type of coaxial cable is not suitable for the automobile sector and is typically used for static applications that require low resistance in repeated bending cycles.

US 6265667B1 describes a coaxial cable with a central conductor unit and a joint bridge made of multiple CCA cables. In particular, the central conductor unit may comprise multiple CCA twisted cables. The patent document describes how to prevent the oxidation of the metals used for the cable. While the product's life is extended on one side (which can be stored for a long time and transported in extreme conditions), on the other hand the antioxidant substance limits the electrical conductivity and weldability of the metal parts that must be properly cleaned before being machined to obtain the best qualitative result for a special operation such as welding. The process is expensive and is affected by quality problems for products that need to be assembled in large quantities.

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The purpose of the present invention is to remedy the drawbacks of the prior art by providing a coaxial cable that is efficient, effective and at the same time cheap and simple to manufacture.

This objective is achieved in accordance with the invention, with the features claimed in the independent claim 1 attached.

Advantageous embodiments appear from the dependent claims.

The coaxial cable of the invention comprises:

- a central conductive unit intended to carry a signal,

- a shield, comprising a plurality of wires arranged as a mesh, intended to be connected to a ground in order to protect the central conductive unit,

- a dielectric material arranged between the central conductive unit and the shield to insulate the central conductive unit from that of the shield, and

- an insulation cover placed around the shield.

The central conductive unit and the shield comprise a plurality of wires made of an aluminum core coated with a copper coating.

The shield wires comprise an external tin coating.

Additional features of the invention will appear evident from the detailed description that follows and which refers to the attached drawings, which have an illustrative, non-limiting purpose, in which:

Figure 1 is a partially sectioned perspective view of the coaxial cable according to the invention;

Figure 2 is a perspective view of the coaxial cable core of Figure 1;

Figure 3 is a cross-sectional view of the coaxial cable of Figure 1;

Figure 3A is an enlarged view of a detail of Figure 3, showing a single core conductor wire; Y

Figure 3B is an enlarged view of a detail of Figure 3, showing a single conductor wire of the joint bridge.

With reference to the figures, the coaxial cable of the invention is described and generally indicated by the reference number (100).

With reference now to Figures 1 and 3, the coaxial cable (100) comprises:

- a central conductive unit (1),

- a dielectric material (2) placed around the central conductive unit (1),

- a shield (4) placed around the dielectric material (2) and

- an insulation cover (5) arranged around the shield (4).

The coaxial cable (100) optionally comprises a second shield (3) between the dielectric material (2) and the first shield (4).

The central conductive unit (1) is intended to carry electrical signals. The central conductive unit (1) comprises a plurality of conductive wires (10) suitably arranged (10).

Referring to Figure 3A, each conductive wire (10) of the central conductive unit is made with copper clad aluminum (CCA) technology and comprises an aluminum core (11) and a copper cladding (12).

The conductive wire (10) has a total diameter that can vary from 0.1 mm to 1 mm, preferably 0.27 mm, according to

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the application. The aluminum core (11) has a diameter of 90-97%, preferably 95% of the total diameter of the wire and the thickness of the copper coating is 10-7%, preferably 5% of the total diameter of the wire.

Optionally, each wire of the central conductor wire can be additionally covered with an outer layer of tin (13) with a thickness equal to 0.5% - 2% of the total wire diameter. The outer layer of tin (13) is used to make the conductive wire immune to oxidation and keep its weldability characteristics unchanged over time.

As shown in Figure 2, the central conductor unit (1) is composed of a straight central conductor wire (10a) and a plurality of peripheral conductor wires (10b) wound around the central conductor wire (10a) in a spiral beam. The spiral beam formed by the peripheral conductor wires (10a) is developed by winding along the straight central conductor wire (10a) using as the axis of the spiral.

The figures illustrate an embodiment of the central conductive unit (1) comprising seven wires, that is, a core wire and six peripheral wires

The peripheral wires (10b) are wound in the central wire (10a) forming a spiral beam with a winding degree of 15-20 mm. The winding degree of the spiral can have different values, according to the dimensions of the wire and the number of wires used to make the central conductive unit (1).

Said manufacturing technique of the central conductive unit (1) can be industrially automated with the use of suitable machines and with low production costs.

Such arrangement of the conductive wires (10) of the central conductive unit is used to improve the mechanical behavior of the central conductive unit (1). In fact, a solid single-wire conductive wire or a linear wire of parallel wires cannot withstand a large number of repeated curves of the coaxial cable (100), which occur due to the handling, production and installation required in special applications, as in the automotive sector.

The coaxial cable (100) of the invention, in which the central conductor wire (1) is obtained with said manufacturing technique, is more flexible, more resistant to bends in any direction and easier to compress during crimping of the connectors

It should be noted that the central conductive unit (1) of the coaxial cable according to the invention is not provided with twisted wires, that is, wires that mutually twist along the entire length of the cable. The central conductor unit (1) of the multi-wire type is obtained with a procedure according to which the remaining threads are arranged around a central wire by means of bending, without twisting. This allows to obtain a compact bundle of cables and avoid the presence of air between the cables.

The dielectric material (2) is made of polyethylene or expanded polypropylene, and has a diameter between 1.5 and 3 mm, preferably 2.1 mm.

Referring to Figures 1 and 3, the coaxial cable (100) advantageously has two levels of protection (4, 3).

The first shield (4) comprises a plurality of twisted conductive wires (40) such that they form a mesh intended to be connected to a ground. For this reason, the first shield (4) is also known as a union bridge (4).

Referring to Figure 3B, each conductive wire (40) of the junction bridge is of the CCA type and comprises an aluminum core (41), an intermediate copper coating (42) and an outer tin coating (43).

The joint bridge (4) is composed of a set of threads (40) that are twisted with a suitable degree of torsion. Each wire (40) can have a total diameter which, according to the specific application, can vary between 0.1 mm to 0.2 mm with a thickness of the copper coating (42) equal to 6% of the total diameter. The copper layer (42) is additionally covered with the tin layer (43) in a percentage that can vary between 0.5% to 2% of the total diameter of the wire according to the specific application.

The tin coating (43) applied to the CCA cables of the junction bridge is necessary when the cable is exposed to extremely severe work environments, such as places with humid heat conditions, salt fog or repeated intense heat. The tin coating (43) allows to maintain the resistivity of the constant wire over time, without any impedance and alteration of attenuation. In addition, being free from oxidation, tin guarantees the perfect weldability of the joint bridge over time.

For example, a wire (40) of the joint bridge with a total diameter of 0.13 mm in the cable (100) has the following structure:

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Maximum diameter of the aluminum wire (41) = 0.12 mm,

Maximum thickness of the copper coating (42) = 0.004 mm,

Minimum thickness of the tin coating (43) = 0.001 mm.

The joint bridge (4) is made of a twisted wire mesh (40). The threads are grouped into spindles of 5 threads each. A total of 16 spindles are used to make the mesh. Each spindle is made of 5 threads with the diameter of 0.13 mm (each thread). The torsion degree of the spindles to make the mesh is 28 mm.

The second shield (3) surrounds the dielectric material (2). The second shield (3) is composed of a sheet of material made of aluminum with a thickness of 0.05 mm. Advantageously, the second shield (3) comprises a multilayer sheet comprising a polyester film interposed between two layers of aluminum.

The dielectric material (2) and the second shield (3) (if present) have a percentage of optical coverage greater than 90%.

The outer cover (5) is made of lead-free anti-migration PVC.

The cable (100) of the invention has the following mechanical characteristics:

- Minimum static radius of curvature 5 times the outside diameter; Y

- Dynamic radius mm of curvature 15 times the outside diameter.

The cable (100) passes the following laboratory tests:

- 3000 hours of exposure to temperatures of + 85 ° C / -40 ° C; Y

- reliability of 30,000 curvature cycles in accordance with ISO 14572.

The coaxial cable (100) of the invention has the following advantages:

1) The copper coating (12, 42) applied on the aluminum core (11, 41) of the wires (10, 40) of the central conductive unit and the joint bridge protects the aluminum from oxidation and considerably increases the conductive capacity of the thread.

2) The tin coating (13, 43) of the copper coating (12, 42) of the wires (10, 40) of the central conductive unit and of the joint bridge provides stability over time to contact resistance, especially during connection of the connecting bridge (4) to a connector; therefore, said tin coating is more advantageous especially on the threads of the joint bridge (4) that are more severely exposed to the external operating environment.

3) In addition, this innovation allows to reduce the total weight of the product because, having a specific gravity three times less than copper, the CCA has a weight of 60% lower than solid copper, thus satisfying the demand for lightness of the automotive market .

4) The quotes in the aluminum market, which represents practically the total volume in a CCA wire, are more stable than those of copper. Also, with the same volume, which has a specific gravity that is three times less, weighs less and therefore costs less than a solid copper wire.

Accordingly, the cable (100) of the invention has the same electrical performance and the same corrosion resistance as a coaxial cable with core and joint bridge made of solid copper and advantageously has a considerably lower total weight, as well as lower costs of production.

Claims (10)

5 10 fifteen twenty 25 30 35 40 Four. Five 1. Coaxial cable (100) comprising: - a central conductive unit (1) intended to carry a signal, - a shield (4) a plurality of wires (40) arranged as a mesh, intended to be connected to a ground in order to protect the central conductive unit, - a dielectric material (2) arranged between the central conductive unit (1) and the shield (4) to insulate the central conductive unit (1) from the shield (4), and - an insulation cover (5) arranged around the shield (4), wherein the central conductive unit (1) and the shield (4) comprise a plurality of wires (10, 40) made of an aluminum core (11, 41) coated with a copper cladding (12, 42) characterized because the wires (40) of the shield (4) comprise an outer lining of tin (43). 2. The coaxial cable (100) of claim 1, wherein the thickness of the outer sheathing of tin (43) ranges from 0.5% to 2% of the total diameter of the shield wiring (4). 3. The coaxial cable (100) of claim 1 or 2, wherein the wires (10) of the central conductive unit (1) comprise an outer sheath of tin (13). 4. The coaxial cable (100) of claim 3, wherein the thickness of the outer sheathing of tin (13) ranges from 0.5% to 2% of the total wire diameter of the central conductive unit (1). 5. Coaxial cable (100) according to any of the preceding claims, wherein the wires (10) of the central conductor unit (1) comprise a straight central conductor wire (10a) and a plurality of coiled peripheral conductor wires (10b) around the central conductor wire (10a) in a spiral beam. 6. Coaxial cable (100) according to any of the preceding claims, which also comprises a second shield (3) interposed between the dielectric material (2) and the shield (4) for grounding. 7. The coaxial cable (100) of claim 6, wherein the second shield (3) comprises an aluminum-based composite sheet. 8. The coaxial cable (100) of claim 7, wherein the second shield (3) comprises a multilayer sheet comprising a polyester film interposed between two layers of aluminum. 9. Coaxial cable (100) according to any of the preceding claims, wherein the thickness of the copper cladding (12) ranges from 7% to 10% of the total wire diameter of the central conductive unit (1). 10. Coaxial cable (100) according to any of the preceding claims, wherein the thickness of the copper cladding (42) ranges from 7% to 10% of the total diameter of the shield wiring (4).