WO1998043252A1 - Ensemble de cablage electrique ameliore - Google Patents

Ensemble de cablage electrique ameliore Download PDF

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Publication number
WO1998043252A1
WO1998043252A1 PCT/GB1998/000908 GB9800908W WO9843252A1 WO 1998043252 A1 WO1998043252 A1 WO 1998043252A1 GB 9800908 W GB9800908 W GB 9800908W WO 9843252 A1 WO9843252 A1 WO 9843252A1
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Prior art keywords
mhz
wires
layer
frequencies
enclosed
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Ceased
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PCT/GB1998/000908
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English (en)
Inventor
Ian Paul Atkins
David Crofts
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Raychem Ltd
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Raychem Ltd
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Filing date
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Publication of WO1998043252A1 publication Critical patent/WO1998043252A1/fr
Anticipated expiration legal-status Critical
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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B11/00—Communication cables or conductors
    • H01B11/02—Cables with twisted pairs or quads
    • H01B11/12—Arrangements for exhibiting specific transmission characteristics
    • H01B11/14—Continuously inductively loaded cables, e.g. Krarup cables
    • H01B11/146—Continuously inductively loaded cables, e.g. Krarup cables using magnetically loaded coatings

Definitions

  • This invention relates to a method of improving an electrical wiring assembly incorporating a twisted pair of wires or passive components such as filters, to the resulting improved wiring assembly, and to automotive electrical components, for example ABS sensors or actuators for automotive air bags or seat belt pre-tensioners, with such improved wiring assembly connected thereto for electrical actuation in use.
  • Twisted pairs of wires are traditionally used to reduce parasitic signals generated in those wires when exposed to electromagnetic interference (EMI).
  • EMI electromagnetic interference
  • Passive components such as filters are traditionally used to reduce transients such as electro static discharges being transmitted along wires.
  • ESD electrostatic discharge
  • the invention is especially useful in combatting parasitic signals caused by electrostatic discharge (ESD) at frequencies below 100 MHz, especially 50-100 MHz or 1 - 10 MHz, in which ranges lie many of the electrical events which may interfere with electrical sensors (e.g. ABS braking systems) or threaten accidental discharge of pyrotechnic actuators in vehicles.
  • ESD electrostatic discharge
  • each wire of the said untwisted pair is at least partly enclosed as aforesaid.
  • the inner layer hereinafter referred to for convenience as the PVDF layer without necessarily excluding other suitably high-dielectric materials
  • the lossy layer may be formed by coatings extruded along the wire(s) by known wire-coating techniques.
  • the presence of the PVDF layer has been found especially advantageous for the aforementioned automotive uses of the invention.
  • the lossy layer is preferably a ferrite-filled polymeric material, for example a thermoplastic elastomer, preferably fluorinated, those available under the Trade Mark "Viton" being particularly preferred.
  • the jacket layer may be made of any suitable polymeric material, for example cross-linked ethylene/tetrafluoroethylene (ETFE) copolymers, or preferably polyester for lower cost.
  • ETFE ethylene/tetrafluoroethylene
  • a recommended form of such wires is available under the Trade Mark "Electroloss Filterline” from Raychem Corporation.
  • Suitable lossy materials are described, for example, in US-A-3309633 and US-A-3191132, and high-frequency- attenuating wire and cable structures are described, for example, in EP-A-0053036 (MP0750), the disclosures of all of which are incorporated herein by reference.
  • wiring assemblies from which twisted pairs of wires are eliminated according to the present invention can achieve attenuation of the parasitic signals to levels at least comparable with those achieved by the twisted pairs, without the cost and efficiency disadvantages associated with the additional wire twisting operation. It may also be possible to eliminate some or all of the known series-connected passive components such as filters and/or ferrite beads possibly used with the twisted pairs, while maintaining acceptable levels of attenuation in the lossy layers of the untwisted wires according to the present invention.
  • the series filters and beads may in any case be less than desirably effective at frequencies above 100 MHz.
  • the invention is thus especially useful in wiring assemblies wherein the original twisted pairs of wires replaced by the untwisted pairs of wires according to the invention are connected in use to an automotive pyrotechnic device for actuation thereof, especially for use in automotive air bags or seat belt pre-tensioners. Protection of such pyrotechnic devices against parasitic currents caused by coupling of the wires with an ESD or the filelds generated by it, or possibly with EMI fields generated by mobile telephones or their roadside base stations, is especially desirable, the lossy wires preferably being at least 30 cm in length.
  • the untwisted lossy wires of the present invention are capable of attenuation levels ranging from 20dB/m up to more than 25 dB/m, more than 27dB/m, or even more than 30dB/m.
  • ESD in vehicles may occur for many reasons, such as wind friction or passenger contact with static-generating materials.
  • the major source of RF energy inside the passenger compartment of a vehicle is the mobile phone, especially the hand portable with the antenna radiating inside the vehicle. Glass mounted antennae should produce a lower field inside the car than hand portable phones, but fields of greater than 30V/m inside one vehicle have been shown to be the result of transmissions from other vehicle(s).
  • the types of phone may be fixed-installation or hand-portable, and analogue or digital. Frequency ranges for such phones include 890 MHz to 1000 MHz for DCS 900 ETACS; 1100 MHz to 1300 MHz for ORANGE; and 1710 MHz to 1785 MHz for DCS 1800.
  • GSM Global System for Mobile Communications
  • Power outputs of the phones vary, but GSM allows up to 20W to be used for Transmitters (43 dBm), and such phones use typically 8W for GSM 900 Class 2 (39 dBm); 2W for GSM 900 Class 4 handheld (33 dBm); 1W for DCS 1800 Handheld (30 dBm); and 500mW for Analogue Handheld (27 dBm).
  • These figures exclude transmission from amateur transceivers that can be of the order of 70W (48 dBm) at 430 MHz and 144 MHz. These transmissions are not considered legitimate by the regulatory bodies in the EEC and do not form part of the directive for auto EMC.
  • the EEC directive for EMC in vehicles stipulates a field strength of 30V/m, at which all electronic systems must appear unaffected and operate normally. It has been demonstrated that a class 2 GSM 8W transceiver can produce a field of 33V/m inside a vehicle, 3V above the maximum allowed in the EEC directive. It is clear that higher- power GSM transceivers, if and when they are introduced, and amateur transceivers will produce fields well in excess of the limit.
  • a typical wiring harness as previously known for vehicle pyrotechnic actuators is constructed as follows :-
  • Length lm 2 cores multistrand black PVC believed to be 24 gauge; Load end terminated in two crimp terminals to accept pins from load; Load pins insulated with orange heatshrinkable tubing; Both wires assembled into a 5mm dia black PVC tube; 75 mm from one load pin is an in-line inductor measured as 8 ⁇ H; Inductor believed to be Siemens type (Siemens Matsushita); A high-frequency filtering inductor is spliced into one wire and is covered by black heat shrink tubing.
  • the Siemens Matsushita data sheets B82144, B78108-S and B78148-S show inductors of the above value (nominally 6.8 ⁇ H) to be resonant at 80 MHz (LBC), 75 MHz (BC), and 40 MHz (SBC) where LBC is large bobbin core, BC is bobbin core and SBC is small bobbin core and are Siemens designations of the component used, the impedance above these frequencies dropping away dramatically (typically by two orders of magnitude per decade of frequency). This means that the inductors will have little effect in the higher (for example mobile phone) frequency bands. Ferrite beads only add 250nH of inductance per line per bead and a considerable number of beads would be required to approach ideal performance.
  • a harness according to the present invention is constructed to the same dimensions as the above, but with the wire containing the inductor completely replaced with a one- metre length of Raychem's Electroloss Filterline wire, comprising a stranded metal conductor enclosed in successive layers of (a) radiation-cross-linked PVDF, (b) ferrite- filled lossy layer, and (c) radiation-cross-linked modified ETFE copolymer.
  • the measurements taken are the signal level at the load on the 'high' and 'low' sides of the load with respect to ground.
  • the load is a pure resistor, i.e. it has negligible inductance and capacitance, there is no phase change across the load from the signal and the resultant differential mode signal can be calculated from the two common mode measurements.
  • the highest of the common mode signals can be taken as representing the largest common mode threat to the load, energy flow from the bridgewire through the compound and the capacitance to ground.
  • FIG. 1 shows the attenuation provided by the harness to the signal injected at the drive end when the load is looked at as the receiving end.
  • the very peaky nature of the inductor harness can be explained by resonance of the harness and by the lack of effect of the inductor.
  • the harness is 1 metre long and can be expected to have resonance's spaced at multiples of ⁇ /4 i.e. 70 to 100 MHz range spacing.
  • the impedance offered by the inductor over the range shown taken from the Siemens data sheet is less than 100 ohm and given that the typical characteristic impedance of the line is in the 100 to 300 ohm range the attenuation offered by the inductor is probably less than 3 dB.
  • the attenuation shown for the inductor harness is largely as a result of signal cancellation and normal harness losses at these frequencies.
  • the large dips in signal are due to cancellation of signal at the load.
  • the Filterline wire example shows a much more controlled response over the frequency spectrum with the large majority of resonance damped out.
  • the peaks of signal indicate that the inductor harness attenuates for much of the band by as little as 15 dB, whilst the Filterline wire is always better than 27dB, i.e. the Filterline wire reduces the signal through the load by a factor 16 times greater than the inductor harness. Further, in the 1200 to 1300 MHz band the inductor harness reduces the signal by the same amount as before, 15dB, whereas the Filterline wire harness is always better than 33dB. Unfortunately it is not possible to keep the deep troughs of resonant cancelling without the peaks of signal transmission, as they are part and parcel of the same process.
  • Figure 2 shows the net signal level in common mode at the load.
  • the signal level for the Filterline wire can be seen to be significantly lower than that for the inductor harness.
  • the effect of this signal level is that energy will flow from the bridgewire through the explosive to local ground plane. It is probable that this, or significantly less, energy flowing in this mode will cause a response from the explosive compound.
  • the Filterline wire reduces the power level by between 20 and 25dB, in comparison with the inductor harness generally reducing the power level by less than 20dB. Power levels in the 1200 to 1300 MHz band are reduced by the Filterline by at least 30dB.
  • the inductor harness reduces the power level by a about lOdB. This indicates that the Filterline wire has an advantage in power reduction of at least two decades over the inductor solution.
  • Figure 3 and 4 show the same information for the DCS 1800 band of frequencies. Apart from the resonant cancellation of signal at 1700 MHz, the Filterline wire is clearly a better solution.
  • the Filterline wire attenuation and the level of signal at the load in the Filterline harness was always below the noise floor of the measurement for this set-up. Accordingly, the attenuation of the differential mode signal (that which could operate the detonating bridgewire) is typically 25dB greater in the case of the Filterline wire, i.e. 300 times less signal across the bridgewire in this case.
  • a typical wiring harness used to connect ABS braking sensors incorporate twisted pairs of wires that reduce parasitic transients.
  • An alternative wiring harness using the Filterline as described above can be shown to be equivalent or superior to the traditional twisted pair whilst having the manufacturing advantages of a pair of parallel wires. Results are shown in figs 5 - 8 that demonstrate the superior or equivalent performance of the Filterline construction.
  • fig 5 the attenuation of a typical ESD transient by both a standard twisted pair and the Filterline harness is shown. It can be seen that the total energy in the pulse is reduced to a tenth (20db power reduction).
  • Bulk Cable Injection demonstrates the reduction of parasitic signals.
  • a high frequency transient is induced onto the cable under test and the resulting parasitic induced voltage is measured.
  • Fig 6 shows that the induced current is less than that for the twisted pair.
  • the level of an induced parasitic signal induced by a radiated field is shown in fig. 7.
  • the harnesses are radiated in a stripline at a field strength of 30 volts per meter as specified in many specifications such as the EC directive on EMC.
  • the results shown in fig. 7 show that the induced voltage from the field is to some extent reduced at higher frequencies and that the performance of both systems is broadly equivalent.
  • the final test measures the strength of the emissions radiated from the test wires conducting parasitic transients.
  • the dielectric constant of plastic materials varies with the frequency. Materials with high dielectric constants are polar and have pairs of opposite charges. A pair of opposite charges separated by a small distance forms a dipole. This dipole is free to rotate to align itself with an alternating electric field. The response to the field will be of the relaxation type with the rotation of the dipole lagging further behind the phase of the applied field.
  • Kynar (Trade Mark) PVDF given in the literature are as follows at the indicated frequencies: 1kHz 8.1, 10kHz 8.0, 100kHz 7.8, 1MHz 6.8, 10MHz 5.8.
  • compositions it may be preferable to use a small amount of fillers such as barium titanate or other similar fillers to increase the dielectric constant of PVC or other polymer systems.
  • fillers such as barium titanate or other similar fillers to increase the dielectric constant of PVC or other polymer systems.
  • Very high loadings, above 50% by weight, are needed to move the dielectric constant above 10, which loadings may be impracticable for processing, but the use of lower levels of the inorganic fillers to raise the value higher than that of the base polymer is often beneficial.
  • Raychem's Filterline low susceptibility wire is a unique three-layer construction that provides the necessary electrical properties to act as a low-pass-band distributive filter.
  • the Raychem wire has an inner layer made from a high-dielectric- constant material, preferably polyvinylidene fluoride.
  • the second layer is preferably a rubber material filled with 80% , by weight of the whole layer, of a ferrite material with very high initial permeability at low frequencies ( ⁇ 50 MHz).
  • the outer layer provides the wire with a tough outer insulating jacket. With this construction adequate performance can be obtained without the use of an additional screening layer.
  • the three-layer combination provides a lower operating frequency than constructions with just one active layer that is filled with a ferrite. This is because the inner layer provides the capacitance term of the wire that can be considered as a distributive filter.
  • the second layer is filled with a ferrite whose high initial permeability at low frequencies combined with low resistivity provides the inductive term. This unique combination ensures that the wire is effective at attenuating high speed pulses such as those caused by electro static discharges whose energy is concentrated in the 30MHz region.
  • the outer layer provides the insulating layer.
  • Ferrites are magnetic ceramic materials consisting mainly of iron oxide that is blended with other metallic oxides. The choice of these other metals determines the permeability and the operating frequency of the ferrite layer. A second variable is that of the shape of the ferrite particle to ensure maximum coupling to the magnetic field. Raychem has selected a ferrite whose magnetic properties and shape factor combine to give the highest values of permeability and permittivity for the second layer of its low-susceptibility wire at low frequencies.
  • the outer layer can be made of any suitable polymeric material, preferably of either fluorinated ethylene propylene (FEP) for high temperature uses ( > 200°C) or polyesters such as poly butylene terephthalate for intermediate temperatures such as 150°C. These materials have little, if any, influence on the magnitude of any currents flowing down the central conductor the wire, firstly because they have dielectric constants of only between 3 and 4, and secondly because they are not sufficiently close to the conductor.
  • FEP fluorinated ethylene propylene
  • polyesters such as poly butylene terephthalate for intermediate temperatures such as 150°C.
  • a seat belt Pretensioner system has been tested in the EMC laboratories in Swindon to the requirements of the GM International Specification GM1 12559R. Two designs were tested, the first with a ferrite chock spliced into the interconnection cable and the second using Raychem ElectroLoss wire.
  • the GM specification GM1 01301 gives the requirements of the Seat Belt Buckle Pretensioner and in this document the only EMC test is for ESD.
  • GME 12 550 that covers the requirements for Squibs for Airbags again only ESD is specified.
  • GMI 12559 covers all systems and subsystems and is the master specification for the requirements of EMC. This specification covers all aspects of EMC in the car and its systems and not all parts are applicable to the seat belt pretensioner system. An study was made of the specification to select the relevant sections applicable and the rational for these are given in this report. The specifications do not, however, specify the test levels and these have been chosen from the requirements of the new Automotive EMC Directive 72/245 and from similar specifications from other OEMs.
  • Electromagnetic immunity off vehicle radiation source, vehicle requirement. This section covers the radiation testing of the whole vehicle to the requirements of the relevant EC directive and as such has to be carried out on the complete vehicle with the seat belt pretensioner installed and is hence outside the scope of this qualification.
  • Electromagnetic immunity Electromagnetic immunity, direct radiation, absorber lined chamber, component test.
  • This test measures the immunity of a system to high frequency radiated fields.
  • the frequency range is above that that can be achieved with the stripline test. No levels or frequency ranges are given in the specification but in the EC 75/245 a test level of 30 Volts/meter is specified and a normal frequency range is 30MHz to 1GHz.
  • Tests were therefore carried out at 50V/m to provide a safety margin between 30MHz and 1GHz in the Raychem screened room using a bipolar antenna at 1 meter for the frequency range 30MHz to 210 MHz and a log periodic antenna from 210MHz to 1GHz.
  • This test is widely used to evaluate the immunity of systems to the effects of radiated fields.
  • the test is not specified in the standard, however, the test is limited by injection coils to between 200kHz and 450MHz.
  • the injected current level is specified in the EC 75/245 at 60milliamps , however, most OEM specifications use lOOmilliamps over a frequency range 1MHz to 450 MHz and that was used in this qualification. 5.5 Electromagnetic immunity, stripline, component test.
  • This test is used to evaluate the immunity of a system to radiated fields in the range 1 to 200 MHz.
  • the specification provides no details, however the EC 75/245 would use 60 V/m and normal field strengths from most OEMs is lOOV/m. Tests were carried out at 100 V/m over the frequency range 1 to 200 MHz.
  • test pulses are specified in ISO 7637-1 and cover a total of 5 pulse types. These cover all the likely transients that can occur in a vehicle and a study of their causes and sources is required to select the relevant pulses to use. Some of the transient pulses have more energy in them than the pulse used to fire the squib. It has been assumed that the seat belt pretensioner is isolated from the battery power supply and that transients associated with load dumps and battery changes are not applicable especially since the transients are above the power levels required to fire the squib.
  • ISO 7637 Test Pulse No. 1 simulates the disturbance caused by the disconnection of the inductive load supply and is a double exponential pulse of 2 ms width 100 volts and 10 amps. This pulse fires the squib and is not applicable to this qualification since the total system has to be isolated by design from this transient.
  • ISO 7637 Test Pulse No. 2 simulates the disturbance caused by a sudden interruption of current in an inductance in series and is a double exponential pulse of 50us width 100 volts and 10 amps
  • This pulse fires the squib and is not applicable to this qualification since the total system has to be isolated by design from this transient.
  • ISO 7637 Test Pulse No 3 simulates the transients caused by switching, due to capacitances and inductances along the wiring harness. This transient is a double exponential 100ns in width, 150 volts and 3 amps. This is the typical transient that occurs on vehicle harnesses and is relevant to this qualification. Section 10.4 species that the most severe level is -150 volts, however, it does not specify the number of pulses. The usual number is 10,000 at a repetition rate of 10Hz to represent the life of the vehicle. A pulse of opposite polarity is also specified but at + 100 volts and again the number of pulses applied was 10,000.
  • ISO Test Pulse No 4 and the deviations specified again simulate transient due to sudden load dumps and have sufficient energy to cause the squib to fire and these transients are not applicable to this qualification since the total system has to isolated by design from these transients.
  • Two termination systems were evaluated, one (Previously-known System) with a ferrite choke in series with the squib and the second (The Invention) with the input line to the squib being of Raychem Filterline ElectroLoss (Trade Mark) 55FA0511-22-7L wire.
  • the samples were supplied to Raychem by AlliedSignal as completed assemblies marked 673- 1L,2L & 3L for those using the ferrite choke and 673-lR,2R & 3R for those using the ElectroLoss cable.
  • the plastic connector was removed from the end of the T300 harness and the two wires terminated in a BNC coaxial connector to facilitate testing.
  • Electromagnetic immunity Electromagnetic immunity, direct radiation, absorber lined chamber.
  • the sample under test was supported 5cms above a ground plane in the screened room and radiated from lmetre.
  • the applied field strength was measured using a field probe.
  • the samples were terminated in a short between the input and output wires.
  • the sample was radiated using a bi-conical antenna from 30 MHz to 210 MHz in steps of 5Mhz with the power to the antenna being increased until the field strength was 50 volts/meter. For the frequency range 210 MHz to 1GHz the frequency steps were 10MHz.
  • the samples were supported 5cms above the return of the strip line which was 1 meter long with a height of 50 cms and a width of 40 cms. Again a field probe was used to measure and control the field strength to 100 Volts per meter. The test was carried out between 1 and 200 MHz using increment steps of 1 MHz from 1 to 20 MHz, MHz from 20 to 200 MHz. Two tests were carried out, the first with the input and output wires short circuited to maximize the circulating current and the connected to the input of a spectrum analyzer to measure the voltage generated into 50 ohms.
  • Typical voltages compared to a control sample are shown in fig. 9.
  • the injection coils are calibrated by determining the power required to drive 100 milli amps into a 50 ohms calibration jig. This power is then used to inject current onto the input wire to the squib with both the input and output shorted together to from a loop. The induced current on the wires is monitored with a second coil.
  • a typical result for a harness and a control sample is shown in fig. 10.
  • a pulse generator was connected to the input line of the sample under test and the specified pulse injected into the harness at a repetition rate of 10 Hz.
  • the wave form was monitored using an oscilloscope across the input terminals.
  • the pulse was applied in 4 modes :-

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Abstract

L'invention concerne un procédé d'amélioration d'un ensemble de câblage électrique destiné à un dispositif tel qu'un actionneur pyrotechnique de coussins gonflables de sécurité pour véhicules consistant à remplacer la paire de fils torsadés habituels par une paire de fils non torsadés offrant une plus grande facilité de construction du faisceau de fils électriques, tout en maintenant ou en augmentant l'atténuation des signaux parasites étant donné qu'au moins un des fils non torsadés est au moins partiellement protégé (de préférence entièrement protégé) dans: a) une couche intérieure d'une composition polymère à diélectrique élevé, de préférence PVDF, laquelle couche intérieure est au moins partiellement protégée (de préférence entièrement protégée) dans b) une couche à forte atténuation de recouvrement au moins partiellement composée d'une matière polymère organique, de préférence un élastomère thermoplastique et/ou un ferrite, et ladite couche à forte atténuation est au moins partiellement protégée (de préférence entièrement protégée) dans c) une couche de gaine polymère électro-isolante de recouvrement, de préférence de l'ETFE (éthylène/tétrafluoroéthylène) ou un polyester. Lesdites couches sont capables de faire office de filtres parallèles atténuant (de préférence de plus de 20 dB par mètre, idéalement d'au moins 25 dB par mètre) les signaux parasites i) à des fréquences de décharge électrostatique inférieures à 300 MHz, de préférence aussi à des fréquences inférieures à 200 MHz, idéalement aussi à des fréquences situées dans la plage inférieure à 100 MHz, notamment la plage comprise entre 50 et 100 MHz ou 1 et 10 MHz, ou ii) à des fréquences d'interférences électromagnétique supérieures à 300 MHz, de préférence aussi à des fréquences supérieures à 500 MHz, idéalement aussi à des fréquences supérieures à 1000 MHz.
PCT/GB1998/000908 1997-03-26 1998-03-25 Ensemble de cablage electrique ameliore Ceased WO1998043252A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB9706418.2A GB9706418D0 (en) 1997-03-26 1997-03-26 Improving electrical wiring assembly
GB9706418.2 1997-03-26

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WO1998043252A1 true WO1998043252A1 (fr) 1998-10-01

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0061247A1 (fr) * 1981-03-23 1982-09-29 Allied Corporation Procédé pour fabriquer un câble-ruban à diaphonie minimale
US4371742A (en) * 1977-12-20 1983-02-01 Graham Magnetics, Inc. EMI-Suppression from transmission lines

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4371742A (en) * 1977-12-20 1983-02-01 Graham Magnetics, Inc. EMI-Suppression from transmission lines
EP0061247A1 (fr) * 1981-03-23 1982-09-29 Allied Corporation Procédé pour fabriquer un câble-ruban à diaphonie minimale

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