WO1986001334A1 - Commutateur hybride de puissance - Google Patents

Commutateur hybride de puissance Download PDF

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Publication number
WO1986001334A1
WO1986001334A1 PCT/GB1985/000371 GB8500371W WO8601334A1 WO 1986001334 A1 WO1986001334 A1 WO 1986001334A1 GB 8500371 W GB8500371 W GB 8500371W WO 8601334 A1 WO8601334 A1 WO 8601334A1
Authority
WO
WIPO (PCT)
Prior art keywords
switch
contacts
hybrid
power
mechanical
Prior art date
Application number
PCT/GB1985/000371
Other languages
English (en)
Inventor
Allen David Muirhead
Original Assignee
Allen David Muirhead
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Allen David Muirhead filed Critical Allen David Muirhead
Publication of WO1986001334A1 publication Critical patent/WO1986001334A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
    • H01H9/54—Circuit arrangements not adapted to a particular application of the switching device and for which no provision exists elsewhere
    • H01H9/541—Contacts shunted by semiconductor devices
    • H01H9/542—Contacts shunted by static switch means
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
    • H01H9/54—Circuit arrangements not adapted to a particular application of the switching device and for which no provision exists elsewhere
    • H01H9/541—Contacts shunted by semiconductor devices
    • H01H9/542—Contacts shunted by static switch means
    • H01H2009/545—Contacts shunted by static switch means comprising a parallel semiconductor switch being fired optically, e.g. using a photocoupler

Definitions

  • the present invention relates to improvements in a hybrid electrical power switching device.
  • Unidirectional electronic switching devices exhibit more desirable switching characteristics, but cannot handle alternating voltages and thus are effectively open only during alternative half cycles. Thus, if the mechanical contacts pass through the portion of their travel in which arcing may occur whilst the electronic switch is effectively open, arcing will still occur.
  • the invention uses a single uni-directional device such as a silicon controlled rectifier (SCR) connected in parallel - 3 - with mechanical contacts whose switching period is less than one half cycle of the power line voltage waveform.
  • SCR silicon controlled rectifier
  • the SCR since it is a uni-directional device) has a much improved performance when switching inductive loads and is generally cheaper than a TRIAC with the same current carrying capability. If the SCR is fired at or near the zero crossing point of the voltage waveform and in particular at the same polarity transition (e.g. line positive to negative, depending on the orientation of the SCR) and is allowed to commutate at the next zero crossing transition, it will only "see" uni-directional current flow.
  • polarity transition e.g. line positive to negative, depending on the orientation of the SCR
  • a hybrid a.c. power switch for use with a power line of predetermined frequency comprises a hybrid a.c. power switch for controlling an a.c.
  • power supply comprising a mechanical switch having contacts moveable through an arcing zone from a first position in which said mechanical switch is in a closed state to a second position in which said mechanical switch is in an open state, mechanical switch operating means operable upon the mechanical switch to change the state thereof, an electronic switch in parallel with said mechanical switch and having an open state and a closed state, electronic switch operating means to change the state of said electronic switch, initiating means operable to initiate a change of state of said mechanical switch, control means operable between said initiating means and said operating means to control the operation of said operating means by said initiating means, sensing means responsive to a predetermined stat of said " power supply • and operable upon said control means upon 5 detection of said predetermined state to enable said operating means and said control means enabling said operating means to ensure passage of said contacts through said arcing zone with said electronic switch in a closed state.
  • Figure 1 is a schematic illustration of a hybrid switch, connected to a load.
  • Figure 2 is an illustration of the voltage waveform of the power line which is to be connected to a load by a power 15 switch.
  • Figure 3 is a representation of a zero-crossing detector output which is derived from the voltage of the power line. Each corner of the square waveform represents a zero-crossing of the power line voltage. 20.
  • Figure 4 is a schematic illustration of the output of the power control switch, there being a low or logic zero output when the switch is OFF and a high or logic 1 output when the switch is ON;
  • Figure 5 is an illustration graphically of the 25 condution periods of power through the uni-directional switch in a switch ON and a switch OFF operation.
  • the lower level indicating no power condution and the upper level indicating full conduction.
  • Figure 6 is an illustration of the conduction of power through the relay that controls the operation of the mechanical contacts, the lower level indicating no conduction and the upper level indicating condution to operate the relay to move the contacts to the closed position.
  • Figure 7 is an indication of the time sequence- of opening and closing of the mechanical switching contacts, the lower level indicating the open position and the upper level indicating the closed position.
  • Figure 8 is an illustration of the times during which power is supplied to the load, the lower level indicating no power and the upper level indicating substantially full power.
  • Figure 9 is a schematic illustration of a hybrid switch with an alternative relay operating means and uni-directional switch operating means to the one illustrated in Figure 1;
  • Figure 10 is an illustration of the voltage of the power line waveform for the arrangement of Figure 9;
  • Figure 11 is an illustration of the ON/OFF operation of the power control means for the embodiment of Figure 9;
  • Figure 12 is a representation of the output of the zero-crossing detector as supplied to the relay control means and electronics switch control means for the embodiment illustrated in Figure 9;
  • Figure 13 is an illustration of the logic state of the
  • Figure 14 is an illustration of the logic state of the Q output of flip flop 64 and D input of flip flop 66 of Figure 9;
  • Figure 15 is an illustration of the logic state of the Q output of flip flop 66 of Figure 9;
  • Figure 16 is an illustration of the conduction through the. electronic switch 72 of Figure 9;
  • Figure 17 is an illustration of the signal of the drive of the transistor 84 of relay 82 of Figure 9; the upper line indicating conduction through the transistor and relay and the lower line indicating when conduction is not taking place through the relay; and
  • Figure 18 is an illustration of the closed and open conditions of the mechanical contacts of the hybrid switch of Figure 9.
  • Figure 19 is a schematic diagram of a further embodiment of a hybrid switch.
  • Figure 1 is a schematic illustration of an a.c. power switch connected to a a.c. power source 10 to control the application of power from the source to a load 12 by the manipulation of an ON-OFF initiating switch 14.
  • a a.c. power switch connected to a a.c. power source 10 to control the application of power from the source to a load 12 by the manipulation of an ON-OFF initiating switch 14.
  • the uni-directional device 20 is connected in parallel with the mechanical switching contacts 16 and 18.
  • the device 20 is preferably a silicon controlled rectifier (SCR) that has a gating contact 22 which permits the rectifier to close and conduct when gating voltage is applied and the voltage bias is in the appropriate direction. Continued application of the voltage bias in the same direction maintains the SCR conducting even if the gating voltage is removed. Upon application of a reverse voltage across the SCR, the SCR opens and prevents further conduction.
  • SCR silicon controlled rectifier
  • Other suitably rated uni-directional devices such as transistors could be used in place of the device 20.
  • the resistor 24 and capacitor 26 are components of a snubber network to limit the applied dv/dt and prevent ungated turn-on.
  • the contact 18 is mounted on an armature and moves between open and closed positions with respect to the contact 16 under the influence of a relay indicated by the numeral 26.
  • relay 26 When relay 26 is activated the armature moves to the closed position to close the contacts as illustrated in solid lines.
  • the relay is de-activated the armature moves to the dotted line position illustrated in the drawings.
  • Numeral 27 refers to a voltage source for operating the relay 26 and the exclusive-or gate generally indicated by numeral 28 of the control circuit for the rectifier 20.
  • Control means are provided between the initiating switch 14 and electronic switch 20 for applying a voltage to the control gate 22 of the silicon control rectifier 20 only during the first negative going half cycle of the power supply after the control switch 14 has been closed or opened. In this way, the electronic switch can conduct electricity to the load only during this half cycle.
  • the armature that carries the mechanical contact 18 into and out of electrical connection with the contract 16 has a period of operation which is no longer than the period of conduction of rectifier 20 during the one half cycle of the voltage of the power supply so that as the connectors 16 and 18 are opening and closing, there is an alternative path for power through the silicon controlled rectifier.
  • a zero-crossing detector 30 operates as a sensing device to detect a predetermined condition (i.e. zero crossing) of the power supply and has an electrical output similar in form to Figure 3 wherein each high corner of the square waveform corresponds to a zero-crossing point of the voltage of the applied power waveform.
  • the zero-crossing detector output voltage is in anti-phase with the voltage of the applied power waveform.
  • a similar arrangement using an in phase zero crossing detector could be used in which case the conducting direction of the SCR 20 would be reversed.
  • the output of the zero-crossing detector 30 is applied to the clock input 35 of the D-type flip flop 32 which controls operation of the relay 26 and gating contact 22.
  • Flip Flop 32 is designed to transfer the logic from its D input 34 to its Q output 36 on the occurrence of the first positive going pulse produced by the output of the crossing detector following a change of logic at the D input 34.
  • the logic 1 will be transferred to the O output 36 upon the occurrence of the first positive going signal from the crossing detector 30 following the application of the logic 1 to the input 34.
  • closing of the switch 14 to initiate closing of the contact 18 changes the D input 34 of the flip flop 32 from a no voltage, logic zero, to an applied voltage, logic one.
  • the iniating signal from the switch 14 is transferred by an opto isolator 38 to the D input 34.
  • a d.c. control voltage of about 15 volts controlled by rectifier 50 is applied across the terminals 40 and 42 with the switch 14 closed to energise a light emitting diode 44.
  • a photo transistor 46 responds to the emission of the LED 44 to provide a high signal at input 34.
  • Numeral 48 is a current limiting resistor.
  • the control voltage across the contacts 40 and 42 can conveniently be between three to thirty volts and can be derived from the power line.
  • relay 26 It starts and maintains the flow of current through the relay 26 by applying a gating voltage to the gate 55 of transistor 52. Thus, it puts relay 26 into operation and maintains it in operation as long as the logic 1 appears at the Q output terminal 36 of the flip flop.
  • relay 26 When relay 26 is in -operation, the mechanical contacts 16 and 18 are drawn towards each other to the closed solid line position.
  • the appearance of a logic 1 at the Q output terminal 36 of the flip flop 32 also causes a difference of voltage to appear across the terminals 51 and 53 of the exclusive-or gate 56 for a period of time determined by the time constant of resistor 58 and capacitor 60.
  • This time constant is made less than the period of one half cycle of the power line waveform so that the output of gate 56 is a pulse of duration determined by the time constant.
  • the contacts 16 and 18 have fully closed due to relay action without arcing and are themselves then able to carry full load current.
  • the period of closure of the contacts is less than one half cycle of the power supply so that closure takes place during the time that power is supplied to the load 12 through the silicon control SCR 20.
  • FIG. 5 and 10 show the operation of the electronic SCR 20 and the mechanical switching contact 16 and 18.
  • the electronic switch 20 becomes operative during the first positive going output of the zero-crossing detector and stays operative until the end of the first half cycle.
  • An examination of Figure 8 shows that power to the load is continuous from the appearance of the logic 1 signal at the Q output of the output terminal 36 of the flip flop 32, being first through the SCR 20 and subsequently through the mechanical contacts 16 and 18.
  • the switch 14 is opened the logic 1 reverts to logic 0 at the D input 34 of the flip flop 32.
  • the device includes means for generating from the power supply, the voltage 27 for operating the relay 26, the d.c. control voltage across 40 and 42 for operating the flip flop and for the zero-crossing device.
  • These voltages can be derived by any one of several available well-known means not referred to in detail.
  • the period of operation of the mechanical contacts 16 and 18 of the relay is less than one half cycle of the power supply and during the half cycle in which the "• • relay opens provision is made for conducting the supply of power to the load around the contacts and through a uni-directional electronics device.
  • This embodiment has two flip flops 64 and 66, an exclusive-or gate 68, a transistor 70 and a silicon controlled rectifier 72 which is in parallel to the mechanical switch contacts 74 and 76.
  • One of the flip flops 64 acts to control the operation of the SCR 20 and relay 82 and the other 66 acts to generate a pulse output for the SCR gate.
  • the load 78 is -- similarly supplied from an a. c. supply 80 and a relay 82 connects through a transistor 84 with the Q output of flip flop 64 and D2 input 88 of flip flop 66.
  • the output of the zero-crossing detector 90 connects to the clock input CK of each of the flip flops 64 and 66.
  • the d.c. control voltage is similarly applied as in Figure 1 from terminal similarly numbered 40 and 42.
  • Trie occurrence of the logic 1 at the output of flip flop 64 and input of flip flop 66 causes operation of the relay 82 through the gating of transistor 84 as indicated in Figure 17 and the consequent commencement of closure of the mechanical switch contacts 74 and 76.
  • a similar sequence of events occurs as the d.c. control voltage is removed.
  • a logic zero is applied to the input of flip flop 64, transferred to the output to commence flow through the relay 82 and render the silicon controlled rectifier 72 conductive by reason of the difference in output and input on the flip flop 66.
  • the input and output of flip flop 66 is made to have the same zero logic and gating current to the SCR 72 is terminated. By this time, the relay has opened without arcing.
  • Hybrid switching devices are commonly used for loads of about 40 amperes but can be used for loads of any reasonable magnitude.
  • FIG. 1 through 18 illustrate a hybrid swith in which the mechanical contact has a switching period less than a half cycle of the supply. This enables the firing of the SCR and the relay to be accomplished simultaneously.
  • a modification of the embodiments illustrated above may be used to ensure that arcing of the contacts does not occur.
  • the gating voltage to the silicon controlled rectifier is supplied such that the SCR will be closed during passage of the contacts through an arcing zone, which is a zone in which there is the potential for arcing to occur..
  • movement of the contacts can be initiated prior to closing of the SCR as the switch moves from an open to a closed position.
  • FIG. 19 An embodiment of a hybrid switch for use with a mechanical switch having a closing period greater than one half cycle is shown in Figure 19.
  • similar components to those shown in Figures 1 and 9 will be identified with like reference numerals with a suffix "a" added for clarity of description.
  • the output of zero crossing detector 30A is also passed through a pulse generator in the form of an exclusive OR-GATE 100 having one terminal 102 connected directly to the output of
  • 15 flop 110 is the outpu t 36A of the Q terminal of the flip flop 32A.
  • the Q output o f flip flop 35A is transf erred to the Q output of the flip flop 110 .
  • the Q output of flip flop 110 is connected to one inpu t of an AND gate 112 , the o ther input of which i s
  • the purpose of the fl ip flop 110 is to provide a delay
  • the delay provided by the D type flip flop can be increased by utilising a number of flip flops in s eries wi th each one being clocked by the output of the exclusive OR-GATE 100 and the receiving as its D input the Q output from the preceding flip flop.
  • the clock input 35A from the zero crossing detector provides a clocking pulse , i . e . a positive going edge every cycle.
  • the output from the zero crossing detector provides a change of state every half cycle and as a result the inputs 102, 104 to exclusive OR-GATE 100 d iffer each half cycle .
  • the output from exclusive OR-GATE is a positive going pulse each half cycle so that each of the D type flip flops 110 employed will provide a delay of one half cycle.
  • the open state of the SCR 20A has been maintained for a further one half cycle relative to the initiation of the movement to the contacts of the switch 18 and the silicon controlled rectifier 20A is closed permitting conduction of the current during the latter part of the movement of the contacts of switch 18 so that as they pass through the arcing zone the current is carried by the. silicon controlled rectifier 20A.
  • the D input to flip flop 34A goes low and upon the next clocking pulse from the zero crossing detector 30A the Q output of flip flop 32A also goes low. This terminates the control signal to relay 26A and so initiates movement of the contacts of switch 18 from a closed to an open position.
  • the delay may be adjusted by employing an appropriate number of flip flops 110. Also, the output of the zero crossing detector may be inverted or reversed as appropriate to shift the initiation of the relay by one half cycle.
  • the circuit of Figure 19 has also been modified to ensure that upon failure of the SCR 20A the switch 18 cannot be closed. This is accomplished using a reset signal derived from the open pole indicated at 114 of the mechanical switch 18.
  • the open pole 114 is connected through a signal line 116 to the reset terminals of each of the D type flip flops 32A and 110.
  • the open pole 114 is also connected through a high value resistor 120 to the load 12A and through capacitor 122 to the line 10A.
  • live line 10A serves as a zero volt reference line for the d.c. supply under normal conditions the relative voltage in the signal line 116 is low. This allows the D type flip flops to operate in the normal manner.
  • This signal line may also be utilised in the embodiments of Figures 1 and 9 by employing a normally closed contact of the relay as a reset line.
  • a simple hybrid switch takes advantage of a uni-directional switching characteristics of the silicon controlled rectifier and ensures that the contacts of the mechanical switch are not subjected to arcing.
  • the hybrid switch can be used with switching periods greater than one half cycle if necessary and also may incorporate a safety feature to inhibit operation of the switch in the event that the SCR fails as shown in the embodiment of Figure 19.

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  • Relay Circuits (AREA)

Abstract

Commutateur hybride de puissance pour courant alternatif utilisé avec une alimentation de fréquence prédéterminée, comportant des contacts mécaniques de commutation (16, 18) capables de supporter la puissance nominale de charge et de fonctionner entre une position d'ouverture et une position de fermeture, ainsi qu'un commutateur électronique (20) caractérisé par un flux de courant unidirectionnel normalement ouvert et connecté électriquement en parallèle aux contacts mécaniques de commutation (16, 18). Un dispositif de commande électrique (32) du commutateur hybride de puissancepermet de fournir un signal de mise sous tension et un signal de mise hors tension pour déclencher le mouvement des contacts (16, 18) entre les positions d'ouverture et de fermeture. L'actionnement du dispositif de commande électrique (32) rend le commutateur électronique (20) conducteur pendant la durée de déplacement des contacts (16, 18) à travers une zone où il peut se produire un amorçage d'arc. Si la durée de commutation des contacts mécaniques (16, 18) reste inférieure à la durée de conduction dudit commutateur électronique (20) devenu conducteur pendant une demi-période de tension de secteur, le mouvement des contacts (16, 18) et la fermeture du commutateur électronique (20) se déclenchent simultanément. En revanche, si la durée de commutation excède une demi-période, la synchronisation relative entre le déclenchement de la fermeture des commutateurs électronique et mécanique est réglée de sorte que les contacts (16, 18) se déplacent à travers la zone d'amorçage d'arc lorsque le commutateur électronique (20) est conducteur.
PCT/GB1985/000371 1984-08-20 1985-08-20 Commutateur hybride de puissance WO1986001334A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8421070 1984-08-20
GB848421070A GB8421070D0 (en) 1984-08-20 1984-08-20 Power switching device

Publications (1)

Publication Number Publication Date
WO1986001334A1 true WO1986001334A1 (fr) 1986-02-27

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ID=10565556

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1985/000371 WO1986001334A1 (fr) 1984-08-20 1985-08-20 Commutateur hybride de puissance

Country Status (4)

Country Link
EP (1) EP0190304A1 (fr)
AU (1) AU4727885A (fr)
GB (1) GB8421070D0 (fr)
WO (1) WO1986001334A1 (fr)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3627017A1 (de) * 1986-08-09 1988-02-18 Licentia Gmbh Hochspannungs-halbleiterschuetz
US4745511A (en) * 1986-10-01 1988-05-17 The Bf Goodrich Company Means for arc suppression in relay contacts
US4760483A (en) * 1986-10-01 1988-07-26 The B.F. Goodrich Company Method for arc suppression in relay contacts
WO1994013000A1 (fr) * 1992-11-30 1994-06-09 A. Ahlstrom Corporation Procede pour commander un commutateur electronique et commutateur electronique
US5473202A (en) * 1992-06-05 1995-12-05 Brian Platner Control unit for occupancy sensor switching of high efficiency lighting
EP1023765A1 (fr) * 1997-10-15 2000-08-02 Reliance Electric Industrial Company Procede et dispositif de reduction de la perte de puissance dans des circuits de conversion de tension
WO2004032168A1 (fr) * 2002-10-03 2004-04-15 Electroheat Plc Procede et appareil de commutation electrique
EP1573762B1 (fr) * 2002-12-17 2010-10-06 Intel Corporation Architecture de commutation utilisant des commutateurs mems et des commutateurs a semi-conducteur en parallele
US9337880B2 (en) 2012-08-30 2016-05-10 Motorola Solutions, Inc. Method and apparatus for overriding a PTT switch to activate a microphone
EP3288056A4 (fr) * 2015-04-20 2019-01-02 Sony Corporation Dispositif de commutation

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3430063A (en) * 1966-09-30 1969-02-25 Nasa Solid state switch
US4225895A (en) * 1977-11-28 1980-09-30 Hjertman Bengt N V Device for closing or interrupting an electric alternating current arising on a line
GB2090702A (en) * 1981-01-05 1982-07-14 Gen Electric Method and circuit for controlling the switching of an inductive load
FR2525386A1 (fr) * 1982-04-15 1983-10-21 Anectron Dispositif de commutation de charges electriques du type resistif et selfique alimentees en courant alternatif
US4466038A (en) * 1982-02-01 1984-08-14 Hewlett-Packard Company Hybrid power switch

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3430063A (en) * 1966-09-30 1969-02-25 Nasa Solid state switch
US4225895A (en) * 1977-11-28 1980-09-30 Hjertman Bengt N V Device for closing or interrupting an electric alternating current arising on a line
GB2090702A (en) * 1981-01-05 1982-07-14 Gen Electric Method and circuit for controlling the switching of an inductive load
US4466038A (en) * 1982-02-01 1984-08-14 Hewlett-Packard Company Hybrid power switch
FR2525386A1 (fr) * 1982-04-15 1983-10-21 Anectron Dispositif de commutation de charges electriques du type resistif et selfique alimentees en courant alternatif

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3627017A1 (de) * 1986-08-09 1988-02-18 Licentia Gmbh Hochspannungs-halbleiterschuetz
US4745511A (en) * 1986-10-01 1988-05-17 The Bf Goodrich Company Means for arc suppression in relay contacts
US4760483A (en) * 1986-10-01 1988-07-26 The B.F. Goodrich Company Method for arc suppression in relay contacts
US5473202A (en) * 1992-06-05 1995-12-05 Brian Platner Control unit for occupancy sensor switching of high efficiency lighting
WO1994013000A1 (fr) * 1992-11-30 1994-06-09 A. Ahlstrom Corporation Procede pour commander un commutateur electronique et commutateur electronique
EP1023765A4 (fr) * 1997-10-15 2001-07-18 Reliance Electric Ind Co Procede et dispositif de reduction de la perte de puissance dans des circuits de conversion de tension
EP1023765A1 (fr) * 1997-10-15 2000-08-02 Reliance Electric Industrial Company Procede et dispositif de reduction de la perte de puissance dans des circuits de conversion de tension
WO2004032168A1 (fr) * 2002-10-03 2004-04-15 Electroheat Plc Procede et appareil de commutation electrique
GB2409771A (en) * 2002-10-03 2005-07-06 Electroheat Plc Electrical switching method and apparatus
GB2409771B (en) * 2002-10-03 2006-05-31 Electroheat Plc Electrical switching method and apparatus
EP1573762B1 (fr) * 2002-12-17 2010-10-06 Intel Corporation Architecture de commutation utilisant des commutateurs mems et des commutateurs a semi-conducteur en parallele
US9337880B2 (en) 2012-08-30 2016-05-10 Motorola Solutions, Inc. Method and apparatus for overriding a PTT switch to activate a microphone
EP3288056A4 (fr) * 2015-04-20 2019-01-02 Sony Corporation Dispositif de commutation
US10811203B2 (en) 2015-04-20 2020-10-20 Sony Corporation Switching device

Also Published As

Publication number Publication date
GB8421070D0 (en) 1984-09-26
AU4727885A (en) 1986-03-07
EP0190304A1 (fr) 1986-08-13

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