Protective hose with electromagnetic shielding

Description

[0001] The invention relates to a protective hose whose diameter can be elastically expanded according to the preamble of claim 1.

[0002] Such protective conduits are used, for example, to protect electrical cables from the influence of electromagnetic interference. One area of ​​application is automotive engineering, particularly vehicle wiring. In this case, the situation often arises where the protective conduit must be pulled over a connector that is not detachably connected to the electrical line or cable. Important in this context is the resilience of the protective conduit, i.e., its ability to shrink back to a diameter adapted to the diameter of the line or cable after passing through the connector.

[0003] A protective hose is known, for example, from EP 1 348 247 B1. The known protective hose is designed as a braided hose, in which, in addition to the threads made of electrically conductive material, plastic threads are also used, which ensure the protective hose's elastic recovery after expansion. In practice, however, it has been shown that the known protective hose has a lower shielding capacity against electromagnetic interference in lengths in which it remains expanded when installed, for example, in a length directly adjacent to a connector, than in lengths in which it has been able to fully contract.

[0004] Furthermore, document WO-A-03013208 discloses a braid comprising a first and a second group of fibers, each arranged in a first and a second direction. One of the two groups of fibers is wrapped with a metal foil, so that the braid can exhibit electromagnetic shielding properties. Due to the arrangement of the fibers or groups of fibers, the braid also exhibits elastic properties.

[0005] Furthermore, a protective sheath with electromagnetic shielding properties is known from document JP-H-1064353 A. The protective sheath comprises a magnetic and a conductive layer. The magnetic layer is composed of a mix of elastomer and magnetic powder. The protective sheath disclosed therein is slit on one side parallel to its longitudinal axis.

[0006] From US-A-4375009 a protective hose with electromagnetic shielding is known, into which cables to be insulated can be inserted, or which can be knitted and / or braided around cables to be insulated.

[0007] Furthermore, the documents JP-A-2004190194, WO-A-0142702, US-A-2012148772, EP-A-2112731, JP-H-1070808 A, EP 1 348 247 B1, WO 2008 / 043 948 A2, US 4 376 229 A, US 2011 / 083 879 A1, EP 2 128 212 A2, DE 41 16 591 A1 and US 4 452 279 A are mentioned.

[0008] It is therefore an object of the present invention to further develop the generic protective tube in such a way that, in the expanded state, it has an improved shielding capacity against electromagnetic interference effects, in particular electromagnetic interference radiation, at least in a frequency range from 10 kHz to 30 MHz.

[0009] This object is achieved according to the invention by a protective tube according to claim 1. The sheathing made of the elastically stretchable material ensures that the threads from which the protective tube is made remain reliably in contact with one another at the points where they touch each other during expansion, so that the eddy currents induced by the electromagnetic interference effects can circulate essentially unhindered, regardless of the expanded state of the protective tube, and thus can exert their shielding effect essentially unhindered. In particular, an EMC test (EMC - electromagnetic compatibility) shows that the shielding against electromagnetic radiation with a frequency of 10 kHz to 30 MHz is almost identical both in the unexpanded and expanded state of the protective tube.

[0010] Silicone, for example, can be used as an elastically stretchable material. However, polyurethane, polyurethane-based materials, natural rubber, or elastomers in general are also possible. A silicone, for example, available under the trade name Elastosil®< LR 3003 / 20 from Wacker Chemie AG, can be used.

[0011] At this point, it should be noted that the provision of a sheath made of an elastically stretchable material for protective hoses with exclusively mechanical and / or thermal protection functions is known per se. However, since these protective hoses are made exclusively of threads without any electrical conductivity, these protective hoses do not suggest to the person skilled in the art that such a sheath could also improve the shielding properties against electromagnetic interference.

[0012] According to the invention, the protective hose is a braided protective hose. A knitted protective hose (not according to the invention) for such a use will also be described as an example.

[0013] In the case of a braid, the expandability can be achieved through the so-called scissor effect of the braided threads. According to the first inventive aspect, a flat braiding angle, i.e., a braiding angle measured relative to the longitudinal direction of the protective tube of less than 45°, preferably less than 30°, is provided.

[0014] In contrast, in the case of a knitted fabric, the expandability can be achieved by keeping the knitted fabric under tension in the longitudinal direction of the protective tube while covering it with the elastically stretchable material, so that the stitches of the knitted fabric are stretched. In this way, the stretched shape of the stitches can be virtually "frozen" by the elastically stretchable sheathing. According to the second inventive aspect, the stitch sections running in the longitudinal direction of the protective tube run essentially parallel to one another. However, due to the elastic extensibility of the sheathing, the tube can be expanded without the stitches shifting relative to one another, because the sheathing fixes the thread sections touching each other at the stitch points.

[0015] With regard to the extensibility of the knitted protective tube, the invention provides that, in the non-expanded state of the protective tube, the ratio of the length of the mesh sections running in the longitudinal direction of the protective tube to the length of the mesh sections running in the circumferential direction of the protective tube is at least 2. Preferably, this ratio can be at least 3, more preferably at least 5.

[0016] According to the invention, at least one of the threads, preferably all of the threads, comprises a plurality of fibers, at least some of which, preferably all, are made of electrically conductive material. The provision of a plurality of fibers made of electrically conductive material per thread has the advantage that the fibers of two adjacent threads are arranged such that both threads have a flattened cross-sectional area. This increases the number of fibers in contact with one another, which in turn has a positive effect on the circulation of the eddy currents induced by the electromagnetic interference and thus on the shielding effect. The fibers are preferably arranged next to one another due to the flattening. If all fibers of all threads are made of electrically conductive material, the best possible shielding effect is also achieved.The sheathing made of elastically stretchable material ensures that the fibers of the threads do not clump together when the protective sleeve expands, but rather that the juxtaposition of the fibers and thus the quality of the shielding effect is maintained. In addition to or as an alternative to fibers with a circular cross-sectional area, fibers with a flattened cross-section can also be used to improve the shielding effect.

[0017] It should be noted at this point that a fiber made of an electrically conductive material can also be referred to as a "wire." However, in the context of the present invention, the term "fiber" will nevertheless be used.

[0018] To improve the shielding effect, it is further advantageous if at least one thread, preferably each thread, and / or at least one fiber, preferably each fiber, is / are made of copper, preferably tinned or silvered copper. Copper is advantageous because of its high conductivity. Tinning can also improve the corrosion resistance and / or solderability of the protective tube. However, for high conductivity, the copper fibers can also be silvered.

[0019] To improve the expandability of the protective tube, according to the invention, the elongation at break of the elastically stretchable material is more than 200%, preferably more than 500%, and more preferably at least 800%. The "elongation at break" is determined by stretching a material strip of a predetermined length until it tears. The length of the material strip immediately before it tears, divided by the predetermined length, results in a dimensionless value referred to as the "elongation at break." The value of the elongation at break of the elastically stretchable material can be selected depending on the extensibility of the protective tube, in particular the braided or knitted fabric.

[0020] If the sheathing is designed to be perforated, as proposed by the invention, the protective hose has, on the one hand, very good recovery properties when expanded, since the sheathing contracts again over its entire surface after expansion. On the other hand, the perforation-free sheathing can also provide protection against moisture. Furthermore, a perforation-free sheathing ensures uniform expansion of the protective hose. Finally, it enables the protective hose to be colored throughout. Such continuous coloring, particularly in signal orange, is required, for example, in electric and hybrid vehicles for the cables carrying the drive current.

[0021] According to the invention, the sheath adheres to the threads at least on the side facing the outer peripheral surface of the hose. Complete embedding of the threads or fibers in the elastically stretchable material is not necessary. Rather, it is sufficient to bond the threads or fibers together in such a way that they remain in contact with each other when the protective hose expands. This can also be done only from the outside of the threads or fibers.

[0022] The invention will be explained in more detail below with reference to an exemplary embodiment of the invention, which is shown in the accompanying drawing. Figure 1 shows a partially sectioned view of a protective tube according to the invention; Figure 2 shows a schematic representation of a measuring setup for determining the shielding attenuation of the Figure 1 shown protective hose; Figures 3 and 4 show the results of the shielding attenuation measurement on the Figure 1shown protective hose using the Figure 2 shown measurement setup, in the unstretched state ( Figure 3 ) and in the stretched state ( Figure 4 ); and Figure 5 shows a roughly schematic representation of a knitted fabric which can be used to produce a further embodiment of a protective hose according to the invention.

[0023] In Figure 1 is a protective hose designed as a braided hose, generally designated 20. The braided hose 20 is formed from a plurality of intersecting threads 22 and 24. The braiding angle α of the threads 22, 24, measured relative to the longitudinal direction L of the protective hose 20, is at most 45°. As in Figure 1As indicated at 26, each of the threads 22, 24 comprises sixteen fibers or wires made of tinned copper, each with a diameter of 0.10 mm. In the unexpanded state, the protective tube 20 has a diameter of approximately 20 mm. A layer 28 of silicone available under the trade name Elastosil®< LR 3003 / 20 from Wacker Chemie AG, between approximately 0.5 mm and approximately 1.0 mm thick, is applied to the protective tube 20. The protective tube 20 produced in this way is temperature-resistant for at least 3,000 hours in a temperature range from -40°C to +150°C and for at least 1,500 hours in a temperature range from -40°C to +175°C.

[0024] The shielding capacity of this protective conduit 20 can be described by the degree of so-called shielding attenuation. This shielding attenuation is the ratio of the interference power in the room to the maximum power generated within the line / cable surrounded by the protective conduit. More precisely, the shielding attenuation is the ratio of the electric field strength outside the conduit to the electric field strength inside the conduit. It is specified in "dB." The shielding attenuation can be determined using the parallel wire method according to VG 95214-6 with the Figure 2 shown structure.

[0025] In this case, test specimen 5 was the inner conductor of a coaxial cable whose shielding had previously been removed and replaced with the protective tube according to the invention. Test specimen 5 was connected to two measurement fixtures 4 and 6, which in the specific test setup were formed by two brass plates with soldered N-type sockets. The inner conductor of the coaxial cable ran through the N-type sockets, while the protective tube was electrically connected to the N-type sockets using screw clamps. A parallel wire 8, serving as an interference source, also ran between measurement fixtures 4 and 6.

[0026] The interference power was fed to parallel wire 8 from a network analyzer 1 (RF generator from Rohde & Schwarz, type SMA100C, identification no. 2.81.01, calibrated 06 / 2012; and test receiver from Rohde & Schwarz, type ESU8, identification no. 2.70.05, calibrated 09 / 2011) via a power divider 2 and the measurement pickup 6. Furthermore, the parallel wire 8 was connected to the measurement pickup 4 with a terminating impedance 10 (from Spinner, type 50Ω / 25W, identification no. 5.10.01, calibrated 10 / 2012). The test object 5 was connected to the measuring fixture 6 via a shielding tube 7 with a shielding housing 9, which was provided with a terminating impedance (Rosenberger, type 50Ω / 0.25W, identification no. 5.10.16, calibrated 10 / 2012), and to the measuring fixture 4 via another shielding tube 7 with a shielding housing 3, via which the signal induced in the test object 5 was fed to the network analyzer 1.If necessary, a power amplifier a can also be provided between the shielding housing 3 and the network analyzer.

[0027] The measurements were performed on a wooden table in a shielded test booth. Shielding attenuation was measured in the frequency range from 10 kHz to 30 MHz.

[0028] Firstly, the measurement was carried out in the unstretched basic state of the protective tube according to the invention, in which it had a diameter of 20 mm. The corresponding measurement result is shown in Figure 3 Secondly, the measurement was carried out in the expanded state of the protective tube according to the invention, in which it had a diameter of 45 mm. The corresponding measurement result is shown in Figure 4As can easily be seen, the two measurement results are practically identical, which means that the shielding effect of the protective tube according to the invention in its unstretched basic state and its shielding effect in the stretched state are essentially identical.

[0029] In Figure 5 A knitted fabric 30 is shown that is suitable for producing a second embodiment of a protective tube according to the invention. In particular, the stitches 32 of the knitted fabric 30 are elongated in the longitudinal direction L of the protective tube, with the stitch sections 32a extending in the longitudinal direction L of the protective tube extending substantially parallel to one another and being considerably longer than the stitch sections 32b extending in the circumferential direction U of the protective tube.

Claims

1. Protective hose (20) with electromagnetic shielding, said hose being elastically expandable in its diameter, which is manufactured using threads (22, 24) made at least partially of electrically conductive material, wherein the protective hose (20) is braided, characterised in that it is sheathed with a layer (28) of an elastically expandable material, wherein the sheath (28) of the elastically expandable material adheres to the thread (22, 24) at least on its side facing towards the outer circumferential surface of the hose (20), and specifically so that the threads are bonded to one another at the points where they contact one another in such a way that they remain reliably in contact with one another during expansion, that the sheath (28) of the elastically expandable material is formed free of perforations, that the braiding angle (α) is less than 45° is that the elongation at break of the elastically stretchable material is more than 200%, and that at least one of the threads (22, 24) comprises a plurality of fibres, at least some of which are made of electrically conductive material, wherein the fibres are configured such that the fibres of two adjacent threads are arranged in such a way that both threads have a flattened cross-sectional area, so that the number of fibres in contact with each other increases, which in turn has a positive effect on the circulation of the eddy currents induced by the electromagnetic interference effects and thereby on the shielding effect.

2. Protective hose according to claim 1, characterised in that at least one thread and / or at least one fibre is / are made of copper or tin-plated copper.

3. Protective hose according to claim 1 or 2, characterised in that at least one thread and / or at least one fibre is / are made of aluminium.