Electrical shielded cable

Abstract

The invention relates to an electrical cable (1, 10, 20, 30) comprising a central electrical conductor (2) and a shielding layer (3) that surrounds the central conductor (2) and forms a tubular sheath accommodating the conductor (2), the shielding layer (3) comprising a plurality of strands (31, 32, 33, 34) which are helically wound about the central conductor (2) at a pitch greater than or equal to 100 mm so as to obtain a characteristic frequency greater than or equal to 1 MHz.

Description

[0001] DESCRIPTION

[0002] TITLE OF THE INVENTION: Electrical shielded cable

[0003] TECHNICAL FIELD

[0004] The invention relates to electrical cables with electromagnetic shielding and in particular those used in motor vehicles and more particularly those at high voltage, advantageously for voltages greater than 48 volts.

[0005] STATE OF THE ART

[0006] Shielded electrical cables are commonly used when connecting electrical components together. When there are a large number of electrical components, the cables are subject to severe electromagnetic stress and require shielding. In the case of high-voltage cables, the shielding must provide protection at high frequencies, above a characteristic frequency of 1 MHz, preferably between 1 MHz and 100 MHz.

[0007] In this field of application, the shielding covers the insulation surrounding an electrical core. This shielding is obtained by using a braid, a foil or a combination of braid and foil made of an electrically conductive material. A shield based on strands arranged in a helix is ​​not currently used in this field of application because it typically only provides protection up to 100 KHz. There is a need to optimize the shielding to maintain its mechanical stability, maintain a sufficiently low R0 (R0 characterizes the quality of the shielding when the cable is crossed by a direct current), ensure protection at high frequencies, above the characteristic frequency of 1 MHz and maintain the flexibility of the cable incorporating this shielding.

[0008] STATEMENT OF THE INVENTION The invention provides an electrical cable having optimized shielding performance.

[0009] To this end, the invention provides a high voltage electrical cable for voltages above 48 volts, the cable comprising a central electrical conductor and a shielding layer surrounding the central conductor forming a tubular envelope housing the conductor, the shielding layer comprising between 84 and 216 strands wound helically around the central conductor with a pitch of between 100 mm inclusive and 250 mm inclusive, the cable thus having a characteristic frequency of between 1 MHz and 100 MHz.

[0010] The invention is advantageously supplemented by the following characteristics, taken alone or in any of their technically possible combinations:

[0011] - the shielding layer (3) comprises between 59 and 836 strands, preferably between 84 and 216 strands or between 84 and 120 strands.

[0012] - the diameter of the strands of the shielding layer (3) is between 0.08 mm inclusive and 0.22 mm inclusive or between 0.1 mm and 0.22 mm, or between 0.1 and 0.15 mm.

[0013] - the shielding layer consists of 120 strands wound in a helix with a pitch of 250 mm, each strand having a diameter of 0.1 mm.

[0014] - the shielding layer comprises 84 strands wound in a helix with a pitch of 250 mm, each strand having a diameter of 0.15 mm.

[0015] - the shielding layer comprises 216 strands wound in a helix with a pitch of 250 mm, each strand having a diameter of 0.15 mm.

[0016] - it comprises a holding structure (5) surrounding the shielding layer (3).

[0017] - the holding structure consists of a holding cable (51) or ribbon (52) wound in a helix around the shielding layer (3).

[0018] - the holding structure comprises a combination of two holding cables (51) or two holding ribbons (52) or one holding cable (51) and one holding ribbon, crossed.

[0019] - the retaining rope or the retaining tape are made of polyester or polyethylene or polypropylene, or polyamide, or aramid or fiberglass

[0020] - it comprises a shielding screen wound in a helix around the holding structure (5), so as to completely cover the holding structure (5), the screen being made of an electrically conductive material, preferably an aluminum tape.

[0021] - the strands of the shielding layer are electrical conductors, preferably made of copper or aluminum or composites.

[0022] - the outer diameter of the electrical conductor (2) is between 1 mm and 35 mm, preferably between 3 mm and 22 mm, preferably 4 mm.

[0023] The present description also relates to an electrical cable comprising a central electrical conductor and a shielding layer surrounding the central conductor forming a tubular envelope housing the conductor, the shielding layer comprising a plurality of strands wound in a helix around the central conductor with a pitch greater than or equal to 100 mm so as to obtain a characteristic frequency greater than or equal to 1 MHz.

[0024] This example is advantageously supplemented by the following characteristics, taken alone or in any of their technically possible combinations:

[0025] - the winding pitch of the shielding layer is less than or equal to 1000 mm, preferably equal to 250 mm;

[0026] - the shielding layer comprises between 59 and 836 strands;

[0027] - the diameter of the strands of the shielding layer is between 0.08 mm inclusive and 0.22 mm inclusive;

[0028] - the cable includes a holding structure surrounding the shielding layer;

[0029] - the holding structure consists of a cable or a holding tape wound in a helix around the shielding layer;

[0030] - the holding structure comprises a combination of two holding ropes or two holding tapes or one holding rope and one holding tape, crossed;

[0031] - the retaining rope or the retaining tape are made of polyester or polyethylene or polypropylene, or polyamide, or aramid or fiberglass;

[0032] - the cable comprises a shielding screen wound helically around the holding structure, so as to completely cover the holding structure, the screen being made of an electrically conductive material, preferably an aluminum tape;

[0033] - the strands of the shielding layer are electrical conductors, preferably made of copper or aluminum or composites;

[0034] - the outer diameter of the electrical conductor is between 1 mm and 35 mm, preferably between 3 mm and 22 mm, preferably 4 mm.

[0035] Thus, the cable of the invention has a shielding which is better than that obtained with a braid because it has a lower linear mass, without crossing or interlacing between the strands to improve resistance to bending, faster to produce and easier to disassemble to simplify its recycling.

[0036] Wrapping or helical winding of the strands for the shielding layer allows the same cable shielding performance to be achieved with less material than a braided cable. It is therefore possible to use a less electrically conductive material such as aluminum, a recycled material, or a composite material.

[0037] The wrapping allows for optimized shielding sizing to be as close as possible to a target electromagnetic compatibility (EMC) template. This has the effect of reducing the amount of shielding material required.

[0038] PRESENTATION OF FIGURES

[0039] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0040] - figure 1, figure 2, figure 3, figure 4 illustrate a longitudinal view of a cable according to several embodiments of the invention;

[0041] - Figure 5 illustrates the transfer impedance (ohm / m) as a function of frequency for several cables #1, #2, #3, #4;

[0042] - Figure 6 illustrates the transfer impedance Zt (mQ / m) on a #2 cable with an electrical conductor section of 4mm 2 with aluminum tape after irradiation having undergone successive bends with a radius of 3 times the diameter of the cable (3D) then 5 times the diameter of the cable (5D); - figure 7 illustrates the screen attenuation of a shielding layer on a cable #2 having an electrical conductor section of 4 mm 2 with aluminum tape after crosslinking having undergone successive bends with a radius of 3 times the diameter of the cable (3D) then 5 times the diameter of the cable (5D);

[0043] - Figure 8 illustrates the transfer impedance Zt (Q / m) on a #5 cable with a shielding layer on an electrical conductor with a cross-section of 35 mm 2 without tape after crosslinking having undergone successive bends with a radius of 5 times the diameter of the cable (5D);

[0044] - Figure 9 compares the transfer impedance of a braid and a covering with a similar RO. We note that at frequencies above 1 MHz, we observe that the curves remain relatively comparable, the shielding performances are therefore similar.

[0045] In all figures, similar elements have identical references.

[0046] DETAILED DESCRIPTION

[0047] Figure 1 illustrates a longitudinal view of an electrically shielded cable 1 according to a first embodiment.

[0048] The electrical cable 1 comprises an electrical conductor 2 consisting of a conductive core 21 covered with an insulator 22 and a layer 3 of electromagnetic shielding surrounding the electrical conductor 2.

[0049] The shielding layer 3 has a cylindrical shape inside which the conductor 2 extends along an axis X of symmetry of revolution of the cable 1. The shape of the shielding layer 3 and therefore of the cable 1 thus defines an axial direction DA along which the axis of cylindrical symmetry X extends and a radial direction DR. An outer sheath 4 surrounds the shielding layer 3. The outer sheath 4 made of electrically insulating material, preferably incorporating a polymer (e.g.: polyolefins, PET, etc.)

[0050] The conductive core 21 is made of an electrically conductive material such as copper and the outer sheath 4 is made of an electrically insulating material.

[0051] Advantageously, the conductive core 21 is made up of one or more conductive cores (copper, aluminum, CNT, SN and composites, etc.) individually insulated with a single-layer or multi-layer electrical insulating material 22 (for example XLPO, PE, PP, PET, RPET, etc.).

[0052] The electrical conductor 2 is preferably of circular geometry.

[0053] Furthermore, the outer diameter of the electrical conductor 2 is between 1 mm and 35 mm, preferably between 3 mm and 22 mm.

[0054] Alternatively, the conductive core 2 may be of annular geometry.

[0055] The shielding layer 3 comprises metal strands 31, 32, 33, 34 wrapped or helically wound around the electrical conductor 2. The shielding layer 3 advantageously comprises between 59 and 836 strands.

[0056] The strands 31, 32, 33, 34 of the shielding layer 3 are advantageously bare electrical conductors (tinned copper or aluminum).

[0057] The helical geometry of shielding layer 3 is advantageously defined so as to maintain efficient shielding at high frequencies, i.e. frequencies above 100 KHz.

[0058] Preferably the sheathing pitch (distance between each turn of the helix or length of cable over which the helix makes a complete turn) is greater than or equal to 100 mm so as to obtain a characteristic frequency greater than 1 MHz. The characteristic frequency is the frequency from which the performance of the shielding sheath deteriorates.

[0059] Preferably, the wrapping pitch is less than 1000 mm so as to ensure sufficient mechanical support between the strands of the shielding. Indeed, the helically wound strands must move little when the cable is deformed by bending.

[0060] Preferably, the number of strands is defined to obtain a covering coverage rate of 100%. In this way, the conductive element 2 is perfectly covered over its entire length, the shielding layer 3 then being well distributed over the entire surface of the electrical conductor 2. Preferably, the thickness of the shielding layer 3 is between 0.08 mm and 0.22 mm. Such a thickness can be obtained either by a single layer formed of strands having a diameter preferably between 0.08 mm and 0.22 mm or in several layers provided that the two layers have the thickness preferably between 0.08 mm and 0.22 mm. In a complementary manner, the shielding layer 3 adheres to the electrical conductor 2 via a bonding layer (not shown). Such a bonding layer is for example an adhesive.

[0061] Figure 2 illustrates a longitudinal view of a shielded electrical cable 10 according to a second embodiment.

[0062] In addition to the characteristics of the first embodiment, this cable 10 comprises a holding structure 5 which here comprises a holding cable 51, for example made of polyester, wound in a helix around the shielding layer 3 but with a smaller pitch as can be seen in FIG. 2. This holding structure

[0063] 5 allows the strands of the shielding layer 3 to be held underneath and in particular it allows the strands of the shielding layer 3 to be held against each other. Alternatively, the holding structure is a polyester tape 52 as illustrated in figure 4.

[0064] The sheath 4 finally covers the support structure 5.

[0065] Figure 3 illustrates a longitudinal view of a shielded electrical cable 20 according to a third embodiment.

[0066] In addition to the features of the second embodiment, this cable 20 comprises a polyester retaining tape or an aluminum shielding screen.

[0067] 6 surrounding the holding structure 5. This screen or ribbon 6 helically surrounds the holding structure 5 below so as to cover it completely. In particular, it is wound, partially overlapping from one turn to the next. It has a rectangular section with a width preferably between 1 and 10 mm.

[0068] Figure 4 illustrates a longitudinal view of a shielded electrical cable 30 according to a fourth embodiment.

[0069] In addition to the characteristics of the second embodiment, this cable 30 is such that the holding structure 5 comprises, in addition to a polyester rope 51, a holding tape 52, for example made of polyester. The holding tape 52 and the holding tape 51 are wound in a helix around the shielding layer 3 in opposite directions so as to cross. This promotes the holding of the shielding layer 3. The holding tape 52 has a rectangular section with a width preferably between 1 and 10 mm.

[0070] Additionally, a cable can be provided which is the combination of the third and fourth embodiments. Examples

[0071] Several electrical cables comprising a 3-layer shielding were manufactured and characterized.

[0072] Figure 5 illustrates the transfer impedance (ohm / m) as a function of frequency in [MHz] for several cables #1, #2, #3, #4 whose characteristics are reported in the table below.

[0073] Transfer impedance is a measure characterizing the performance of a shield. It indicates the voltage induced in the electrical conductor linked to the current flowing in the shielding layer. The measurement is made according to the IEC 62153-4-16 standard. In this figure 5 we see that with a pitch of 250 mm for cables #2,

[0074] #3, #4, we obtain a transfer impedance well below the template (desired objective). On the contrary, with a long strand installation (equivalent to an infinite pitch) (cable #1), the strands are not sufficiently maintained to ensure 100% coverage and the transfer impedance is above the template. This gives an indication of the length of the pitch which must not be too long.

[0075] It is also noted that for a pitch of 250 mm, the addition of a holding structure 5 comprising both a holding cable 51 and a polyester holding tape 52 also makes it possible to improve the transfer impedance. Thus the curve for cable #4 is below the curve for cable #3 (without polyester holding tape 52 but only with a polyester holding cable 51).

[0076] Figure 6 illustrates the transfer impedance Zt (mQ / m) of cable #2 with a cross-section of the electrical conductor core of 4mm 2 with a shielding screen 6 consisting of an aluminum ribbon wound in a helix with a pitch of 250mm after crosslinking and having undergone successive curvatures with a radius of 3 times the diameter of the cable (3D) then 5 times the diameter of the cable (5D). It is specified that crosslinking is the creation of new bonds by bombardment. This is electronic irradiation.

[0077] Figure 7 illustrates the shield attenuation of shield 3 (AS) on cable #2 having a cross-section of the electrical conductor core of 4 mm 2 with aluminum tape wound in a helix with a pitch of 250mm after crosslinking and having undergone successive bends with a radius of 3 times the diameter of the cable (3D) then 5 times the diameter of the cable (5D).

[0078] Shielding attenuation describes the effectiveness of the shielding and is expressed in dB. It corresponds to the ratio between the power sent into the cable and the radiated power. The measurement is made according to the IEC 62153-4-16 standard.

[0079] Figures 6 and 7 show that the shielding does not degrade following bending following crosslinking.

[0080] Figure 8 illustrates the transfer impedance Zt (Q / m) on cable #5 having a shielding layer 3 on an electrical conductor 2 having a core cross-section of 35 mm 2without retaining tape or shielding screen (aluminum tape) after crosslinking and having undergone successive bends with a radius of 5 times the diameter of the cable (5D).

[0081] This figure shows that the shield degrades as the cable is flexed. This therefore highlights the importance of the polyester retaining tape in its ability to hold the strands and provide 100% coverage without degradation of the shield.

[0082] Figure 9 compares the transfer impedance of a braid and a covering with a similar RO for cable #2. We note that at frequencies above 1 MHz, we observe that the curves remain relatively comparable, the shielding performances are therefore similar.

[0083] Cables with the characteristics shown in the table below were tested. In particular, cables according to the invention called Shielded were compared with cables of the prior art called Braid.

[0084] On a cable with a 4mm conductive section 2 with a shielding layer, we measure a flexibility of 9 N. This is better than with a cable with a braid which gives a flexibility of 10.3 N. In the same way, on a cable with a conductive section of 35 mm 2 with a shielding layer, we measure an average flexibility of 33 N compared to 49 N for a cable with a braid.

[0085] It is also shown that the covering allows to reduce the weight of the shielding in comparison with a braid by having an RO comparable to the braid.

Claims

CLAIMS 1. High voltage electrical cable (10, 20, 30) for voltages above 48 volts, the cable (1, 10, 20, 30) comprising a central electrical conductor (2) and a shielding layer (3) surrounding the central conductor (2) forming a tubular envelope housing the conductor (2), the shielding layer (3) comprising between 84 and 216 strands (31, 32, 33, 34) wound helically around the central conductor (2) at a pitch of between 100 mm inclusive and 250 mm inclusive, the cable (1, 10, 20, 30) thus having a characteristic frequency of between 1 MHz and 100 MHz.

2. Cable (1, 10, 20, 30) according to claim 1, wherein the shielding layer (3) comprises between 59 and 836 strands, preferably between 84 and 216 strands or between 84 and 120 strands.

3. Cable (1, 10, 20, 30) according to one of claims 1 to 2, in which the diameter of the strands of the shielding layer (3) is between 0.08 mm inclusive and 0.22 mm inclusive or between 0.1 mm and 0.22 mm, or between 0.1 and 0.15 mm.

4. Cable according to one of claims 1 to 2, in which the shielding layer comprises 120 strands wound in a helix with a pitch of 250 mm, each strand having a diameter of 0.1 mm.

5. Cable according to one of claims 1 to 2, in which the shielding layer comprises 84 strands wound in a helix with a pitch of 250 mm, each strand having a diameter of 0.15 mm.

6. Cable according to one of claims 1 to 2, in which the shielding layer comprises 216 strands wound in a helix with a pitch of 250 mm, each strand having a diameter of 0.15 mm.

7. Cable (10, 20, 30) according to any one of claims 1 to 6, comprising a holding structure (5) surrounding the shielding layer (3).

8. Cable (10, 20) according to claim 7, in which the holding structure (5) consists of a holding cable (51) or ribbon (52) wound helically around the shielding layer (3).

9. Cable (30) according to the preceding claim, in which the holding structure (5) comprises a combination of two holding cables (51) or two holding tapes (52) or one holding cable (51) and one holding tape (52), crossed.

10. Cable according to claim 8 and / or claim 9, in which the retaining rope or the retaining tape are made of polyester or polyethylene or polypropylene, or polyamide, or aramid or fiberglass.

11. Cable (20) according to one of claims 7 to 10, comprising a shielding screen (6) wound in a helix around the holding structure (5), so as to completely cover the holding structure (5), the screen being made of an electrically conductive material, preferably an aluminum tape.

12. Cable (1, 10, 20, 30) according to any one of claims 1 to 11, wherein the strands (31, 32, 33, 34) of the shielding layer (3) are electrical conductors, preferably made of copper or aluminum or composites.

13. Cable (1, 10, 20, 30) according to any one of claims 1 to 12, in which the outer diameter of the electrical conductor (2) is between 1 mm and 35 mm, preferably between 3 mm and 22 mm, preferably 4 mm.

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