EP0029898B1 - Variable resonators for noise attenuation - Google Patents

Variable resonators for noise attenuation Download PDF

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Publication number
EP0029898B1
EP0029898B1 EP80106229A EP80106229A EP0029898B1 EP 0029898 B1 EP0029898 B1 EP 0029898B1 EP 80106229 A EP80106229 A EP 80106229A EP 80106229 A EP80106229 A EP 80106229A EP 0029898 B1 EP0029898 B1 EP 0029898B1
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EP
European Patent Office
Prior art keywords
silators
struts
substruts
main frame
sub
Prior art date
Legal status (The legal status 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 status listed.)
Expired
Application number
EP80106229A
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German (de)
French (fr)
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EP0029898A2 (en
EP0029898A3 (en
Inventor
Oskar Dipl.-Ing.Dr. Bschorr
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Airbus Defence and Space GmbH
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Messerschmitt Bolkow Blohm AG
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Priority to AT80106229T priority Critical patent/ATE13232T1/en
Publication of EP0029898A2 publication Critical patent/EP0029898A2/en
Publication of EP0029898A3 publication Critical patent/EP0029898A3/en
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Publication of EP0029898B1 publication Critical patent/EP0029898B1/en
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    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/172—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using resonance effects

Definitions

  • DE-A-2 632 290 has made the basic training of resonating, volume-changing resonators - the so-called silators - known.
  • silators consist of two lenticularly curved sheet metal halves, which are joined together in a vacuum-tight manner, the space formed in the curvatures being evacuated in each case.
  • elements of this type have a natural frequency which can be set essentially by means of the wall thickness, curvature height and the diameter of the lenticular volumes.
  • the embodiments known primarily as Helmholtz resonators have a significantly higher volume and area requirement than the embodiment described above and can therefore only be used to a limited extent.
  • the present invention has for its object to reduce the area and volume requirements of silators in the order of magnitude.
  • FIG. 1a and 1b show in plan view and cross section I-I a silator element in the form of a base frame 1, which has a square shape in the exemplary embodiment shown.
  • This frame is stretched by the four side struts 2.
  • Sub-struts 3 are now attached in a lattice shape, the individual lattice connection points 4 being joined together.
  • the lower struts 3 are each slightly arched and therefore together form a pillow-shaped structure or contour. This is covered with a sheet metal or plastic jacket 5.
  • the volume thus formed is evacuated.
  • the arrangement and assembly of the lower struts 3 now form further square lower surfaces and the sheet metal 5 covering them again has a slight curvature, the dimensions of which range from 1/20 to 1/200 of the span.
  • the sheet 5 and the struts 2 and 3 are each formed from a material with a high modulus of elasticity and low specific weight. Examples of such materials are: beryllium, aluminum, sheet steel, glass or carbon reinforced plastic or ceramic materials.
  • the lower surfaces of the silators form resonators which have an impedance dip in the region of their resonance frequency and thus result in sound insulation.
  • the natural frequencies of the sub-surfaces of the so-called undersilators are set to different natural frequencies in order to ensure broadband sound insulation.
  • the lower struts 3 together form a silator, which can be set to a resonance frequency that is independent of the lower silencers.
  • the undersilators are expediently set to a high natural frequency and the silators to a lower natural frequency.
  • FIGS. 2a and 2b The exemplary embodiment according to FIGS. 2a and 2b is analogous to the previously described embodiment according to FIGS. 1a and 1b.
  • a silator 11 is spanned by a circular outer strut 12.
  • a weakly curved system of again circular struts 13 is supported on this.
  • the sheet metal jacket 15 is located above it.
  • Two halves 11 a, 11 b are combined to form a lenticular body, the interior 16 that forms being evacuated.
  • the effect of this embodiment is analogous to the square design.
  • the lower surfaces 15 spanned by the struts 13 form so-called undersilators.
  • the entire embodiment likewise likewise represents a silator. Here, too, the usable area has been doubled.
  • FIG. 3 now shows an embodiment with a triple hierarchical breakdown.
  • this shape is described using the example of a square plan shape.
  • the struts 22 again form the square planar base frame. This is divided by arched lower struts 23 and the latter are again divided by the lower struts 24. Over the entire system, the sheet metal jacket 25 then stretches. Each upper and lower half are joined together in the form of a pillow in a vacuum-tight manner and are so forming hollow space is evacuated.
  • This system consists of triple hierarchical silators. The natural frequencies of the silators are expediently set higher with increasing subdivisions.
  • the flat base frame is spanned by the struts 32.
  • Sub-struts 33 are based on this and all struts 32 and 33 are non-positively and torque-connected to one another at the nodes.
  • the lower struts 33 again have a curved contour, the curvature height being between 1/20 and 1/200 of the strut length.
  • the dimensions of the struts in length, width and height each have approximately the same relationships as for the sub-struts, sub-sub-struts, etc. thus the width and height are halved.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Laminated Bodies (AREA)
  • Control Of Motors That Do Not Use Commutators (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)

Abstract

A noise reducing resonator, herein referred to as a silator due to its noise silencing quality, is made up of primary struts forming a main frame and secondary struts forming at least one subframe enclosed by a vacuum tight cover to enclose a vaulting evacuated volume. Each frame has a given span width and a vaulting height corresponding to 0.005 to 0.05 times the respective span width. The frames are arranged in a hierarchic order which means that a larger main frame holds a smaller subframe which in turn holds a still smaller subframe and so on. The resonance frequency increases with the number of subframes held in a main frame. Interconnected silators may cover entire surface areas for noise reduction or absorption.

Description

Durch die DE-A-2 632 290 ist die Grundausbildung von mitschwingenden, volumenändernden Resonatoren - den sogenannten Silatoren - bekanntgeworden. Diese Silatoren bestehen aus zwei linsenförmig gewölbten Blechhälften, die miteinander vakuumdicht zusammengefügt sind, wobei der sich in den Wölbungen gebildete Raum jeweils evakuiert ist. Wie eingehend erläutert ist, weisen derartige Elemente eine Eigenfrequenz auf, die im wesentlichen durch Wandstärke, Wölbungshöhe und dem Durchmesser der linsenförmigen Volumina einstellbar ist.DE-A-2 632 290 has made the basic training of resonating, volume-changing resonators - the so-called silators - known. These silators consist of two lenticularly curved sheet metal halves, which are joined together in a vacuum-tight manner, the space formed in the curvatures being evacuated in each case. As explained in detail, elements of this type have a natural frequency which can be set essentially by means of the wall thickness, curvature height and the diameter of the lenticular volumes.

Die vorwiegend als Helmholtz-Resonatoren bekannten Ausführungsformen weisen gegenüber der vorbeschriebenen Ausführungsform einen wesentlich höheren Volumen- und Flächenbedarf auf und sind daher nur begrenzt einsetzbar.The embodiments known primarily as Helmholtz resonators have a significantly higher volume and area requirement than the embodiment described above and can therefore only be used to a limited extent.

Der vorliegenden Erfindung liegt die Aufgabe zugrunde, den Flächen- und Volumenbedarf von Silatoren größenordnungsmäßig zu verringern.The present invention has for its object to reduce the area and volume requirements of silators in the order of magnitude.

Diese Aufgabe wird durch die in den Ansprüchen niedergelegten Maßnahmen gelöst. Die Beschreibung erläutert in Ausführungsbeispielen die vorgeschlagenen Maßnahmen und die Zeichnung zeigt in schematischer Darstellung diese Ausführungsformen. Durch die vorgeschlagene hierarchische Untergliederung der Silatoren, wobei in einem Silator der ersten Stufe mehrere Subsilatoren integriert sind, gelingt bereits eine doppelte Flächenausnutzung. Bei n-facher Untergliederung ergibt sich resultierend auch ein n-facher Ausnutzungsgrad für die Fläche. In der Zeichnung zeigt

  • Fig. 1a eine Draufsicht auf ein Silatorelement mit zweifacher Stufenhierarchie in schematischer Darstellung;
  • Fig. 1b einen Querschnitt entlang der Linie I-I gemäß der Ausführungsform nach Fig.la in schematischer Darstellung;
  • Fig. 2a eine Draufsicht eines Silatorelementes mit kreisförmiger Fläche mit zweifacher Stufenhierarchie in schematischer Darstellung;
  • Fig. 2b einen Querschnitt entlang der Linie 11-11 der Ausführungsform gemäß Fig. 2a in schematischer Darstellung;
  • Fig. eine Draufsicht auf ein Silatorelement mit quadratischem Grundriß und dreifacher Stufenhierarchie in schematischer Darstellung;
  • Fig. 4 eine Draufsicht auf ein Silatorelement mit dreieckförmigem Grundriß und zweifacher Stufenhierarchie in schematischer Darstellung.
This object is achieved by the measures set out in the claims. The description explains the proposed measures in exemplary embodiments and the drawing shows these embodiments in a schematic representation. The proposed hierarchical subdivision of the silators, with several subsilators being integrated in a silator of the first stage, already enables a double use of space. With an n-fold subdivision, the result is an n-fold utilization rate for the area. In the drawing shows
  • FIG. 1a shows a top view of a silator element with a double level hierarchy in a schematic representation;
  • Figure 1b shows a cross section along the line II according to the embodiment of Fig.la in a schematic representation.
  • 2a shows a schematic top view of a silator element with a circular surface with a double step hierarchy;
  • 2b shows a cross section along the line 11-11 of the embodiment according to FIG. 2a in a schematic illustration;
  • Fig. A plan view of a silator element with a square plan and triple hierarchy hierarchy in a schematic representation;
  • Fig. 4 is a plan view of a silator element with a triangular plan and two-tier hierarchy in a schematic representation.

Die Fig. la und 1b zeigen in Draufsicht und Querschnitt I-I ein Silatorelement in Form eines Grundrahmens 1, der in dem gezeigten Ausführungsbeispiel quadratische Form aufweist. Durch die vier Seitenstreben 2 wird dieser Rahmen aufgespannt. Darin sind nun Unterstreben 3 gitterförmig angebracht, wobei die einzelnen Gitterverbindungspunkte 4 miteinander zusammengefügt sind. Die Unterstreben 3 sind jeweils schwach gewölbt und bilden daher zusammen eine kissenförmige Struktur bzw. Kontur. Diese ist mit einem Blech- oder Kunststoffmantel 5 belegt. Das so gebildete Volumen wird evakuiert. Durch die Anordnung und Zusammenfügung der Unterstreben 3 bilden sich nun weitere quadratische Unterflächen und das diese überdeckende Blech 5 erhält wieder eine schwache Wölbung, deren Ausmaße von 1/20 bis 1/200 der Spannweite betragen. Das Blech 5 und die Streben 2 bzw. 3 sind jeweils aus einem Material mit hohem Elastizitätsmodul und geringem spezifischen Gewicht gebildet. Als Beispiele für solche Materialien seien genannt: Beryllium, Aluminium, Stahlblech, glas- oder kohlenstoffverstärkter Kunststoff oder auch keramische Stoffe.1a and 1b show in plan view and cross section I-I a silator element in the form of a base frame 1, which has a square shape in the exemplary embodiment shown. This frame is stretched by the four side struts 2. Sub-struts 3 are now attached in a lattice shape, the individual lattice connection points 4 being joined together. The lower struts 3 are each slightly arched and therefore together form a pillow-shaped structure or contour. This is covered with a sheet metal or plastic jacket 5. The volume thus formed is evacuated. The arrangement and assembly of the lower struts 3 now form further square lower surfaces and the sheet metal 5 covering them again has a slight curvature, the dimensions of which range from 1/20 to 1/200 of the span. The sheet 5 and the struts 2 and 3 are each formed from a material with a high modulus of elasticity and low specific weight. Examples of such materials are: beryllium, aluminum, sheet steel, glass or carbon reinforced plastic or ceramic materials.

Die Unterflächen der Silatoren bilden Resonatoren, die im Bereich ihrer Resonanzfrequenz einen Impedanzeinbruch aufweisen und so eine Schalldämmung ergeben. Je nach Herstellungsgenauigkeit sind die Eigenfrequenzen der Unterflächen der sogenannten Untersilatoren auf verschiedene Eigenfrequenzen eingestellt, um so eine breitbandige Schalldämmung zu gewährleisten. Darüber hinaus bilden auch die Unterstreben 3 zusammen einen Silator, der auf eine unabhängig von den Untersilatoren eigene Resonanzfrequenz eingestellt werden kann. Zweckmäßigerweise werden die Untersilatoren auf eine hohe und die Silatoren auf eine tiefere Eigenfrequenz eingestellt. Durch die hierarchische Überlagerung gelingt es nun, die Fläche mittels des vorbeschriebenen Ausführungsbeispiels doppelt auszunutzen.The lower surfaces of the silators form resonators which have an impedance dip in the region of their resonance frequency and thus result in sound insulation. Depending on the manufacturing accuracy, the natural frequencies of the sub-surfaces of the so-called undersilators are set to different natural frequencies in order to ensure broadband sound insulation. In addition, the lower struts 3 together form a silator, which can be set to a resonance frequency that is independent of the lower silencers. The undersilators are expediently set to a high natural frequency and the silators to a lower natural frequency. The hierarchical overlay now makes it possible to utilize the area twice by means of the exemplary embodiment described above.

Das Ausführungsbeispiel gemäß den Fig. 2a und 2b ist analog zu der vorbeschriebenen Ausführungsform gemäß den Fig. 1a und 1b. Ein Silator 11 wird durch eine kreisförmige Außenstrebe 12 aufgespannt. Darauf stützt sich ein schwach gewölbtes System von wieder kreisförmigen Unterstreben 13 ab. Darüber befindet sich der Blechmantel 15. Je zwei Hälften 11 a, 11 b sind zu einem linsenförmigen Körper zusammengefaßt, wobei der sich bildende Innenraum 16 evakuiert wird. Die Wirkung dieser Ausführungsform ist analog zu der quadratischen Ausgestaltung. Die durch die Unterstreben 13 aufgespannten Unterflächen 15 bilden sogenannte Untersilatoren. Ebenso stellt die gesamte Ausführungsform ebenfalls einen Silator dar. Auch hier ist die Nutzungsfläche verdoppelt worden.The exemplary embodiment according to FIGS. 2a and 2b is analogous to the previously described embodiment according to FIGS. 1a and 1b. A silator 11 is spanned by a circular outer strut 12. A weakly curved system of again circular struts 13 is supported on this. The sheet metal jacket 15 is located above it. Two halves 11 a, 11 b are combined to form a lenticular body, the interior 16 that forms being evacuated. The effect of this embodiment is analogous to the square design. The lower surfaces 15 spanned by the struts 13 form so-called undersilators. The entire embodiment likewise likewise represents a silator. Here, too, the usable area has been doubled.

Die Fig. 3 zeigt nun ein Ausführungsbeispiel mit dreifacher hierarchischer Untergliederung. Um das Ausführungsbeispiel in einfacher Weise verdeutlichen zu können, wird diese Form am Beispiel einer quadratischen Grundrißform beschrieben. Die Streben 22 bilden wieder den quadratischen planen Grundrahmen. Dieser ist durch bogenförmig gewölbte Unterstreben 23 unterteilt und letztere werden wieder unterteilt durch die Unter-Unterstreben 24. Über das ge samte System spannt sich sodann der Blechmantel 25. Je eine Ober- und Unterhälfte sind in Form eines Kissens vakuumdicht miteinander zusammengefügt und der sich so bildende Hohlraum wird evakuiert. Dieses System besteht also aus dreifach hierarchisch gegliederten Silatoren. Zweckmäßigerweise werden mit größer werdenden Untergliederungen die Eigenfrequenzen der Silatoren höher eingestellt.3 now shows an embodiment with a triple hierarchical breakdown. In order to be able to clarify the exemplary embodiment in a simple manner, this shape is described using the example of a square plan shape. The struts 22 again form the square planar base frame. This is divided by arched lower struts 23 and the latter are again divided by the lower struts 24. Over the entire system, the sheet metal jacket 25 then stretches. Each upper and lower half are joined together in the form of a pillow in a vacuum-tight manner and are so forming hollow space is evacuated. This system consists of triple hierarchical silators. The natural frequencies of the silators are expediently set higher with increasing subdivisions.

Die Fig.4 zeigt nun ein Ausführungsbeispiel mit dreieckförmigem Grundriß der Silatoren und zweifacher Untergliederung. Der plane Grundrahmen wird durch die Streben 32 aufgespannt. Darauf stützen sich Unterstreben 33 und alle Streben 32 bzw. 33 sind an den Knotenpunkten kraft- und momentschlüssig miteinander verbunden. Die Unterstreben 33 weisen wieder eine gewölbte Kontur auf, wobei die Wölbungshöhe zwischen 1/20 und 1/200 der Strebenlänge beträgt.4 now shows an exemplary embodiment with a triangular outline of the silators and two subdivisions. The flat base frame is spanned by the struts 32. Sub-struts 33 are based on this and all struts 32 and 33 are non-positively and torque-connected to one another at the nodes. The lower struts 33 again have a curved contour, the curvature height being between 1/20 and 1/200 of the strut length.

Abschließend sei noch gesagt, daß die Abmessungen der Streben in Länge, Breite und Höhe jeweils ungefähr die gleichen Relationen aufweisen, wie bei den Unterstreben, Unter-Unterstreben usw. Das heißt: ist beispielsweise eine Unterstrebe nur halb so lang, wie ihre zugeordnete Strebe, so halbiert sich bei ihr auch Breite und Höhe.Finally, it should be said that the dimensions of the struts in length, width and height each have approximately the same relationships as for the sub-struts, sub-sub-struts, etc. thus the width and height are halved.

Durch die vorgeschlagenen Silatoren bzw. deren hierarchische Gliederung ist nun eine optimale Flächenausnutzung gegeben.Due to the proposed silators and their hierarchical structure, an optimal use of space is given.

Claims (5)

1. Co-vibrant volume-changing resonators (so- called silators) for the reduction or absorption of noise, characterised in that a base frame (1,11) is spanned on both sides by substruts (3, 13) and, where appropriate, sub-substruts (24), in which .the entire strut system has a ratio of arch height to total span width of between 1/20 and 1/200 and is covered over with a vacuum-tight arched jacket (5, 15) of sheet metal, plastics material or similarly-natured materials and the lower half (1a, 11a) and upper half (1b, 11b) are joined together in vacuum-tight manner and the thereby formed inner volume (1 c, 11 c) is evacuated.
2. Silators according to claim 1, characterised in that the struts (2, 24) and the jacket (5) consist of a material having the highest possible modulus of elasticity and lowest possible specific weight, such as aluminium, beryllium, ceramics, sheet steel or fibrereinforced plastics materials, and are connected in force-locking and moment- locking manner at the common nodal points (4).
3. Silators according to claim 1 and 2, characterised in that the inherent frequencies of the silators rise with increasing hierarchical subordination.
4. Silators according to claims 1 to 3, characterised in that the individual silators are combined to form a surface bracing.
5. Silators according to claims 1 to 4, characterised in that the cross-sectional dimensions of the struts (2, 22, 32 etc.), substruts (3, 23), sub-substruts (24 etc.) and so forth are substantially in accordance with the free span widths thereof.
EP80106229A 1979-11-22 1980-10-14 Variable resonators for noise attenuation Expired EP0029898B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT80106229T ATE13232T1 (en) 1979-11-22 1980-10-14 VOLUME CHANGING RESONATORS FOR NOISE REDUCTION.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE2947026 1979-11-22
DE2947026A DE2947026C2 (en) 1979-11-22 1979-11-22 Silators to reduce noise

Publications (3)

Publication Number Publication Date
EP0029898A2 EP0029898A2 (en) 1981-06-10
EP0029898A3 EP0029898A3 (en) 1981-08-26
EP0029898B1 true EP0029898B1 (en) 1985-05-08

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EP80106229A Expired EP0029898B1 (en) 1979-11-22 1980-10-14 Variable resonators for noise attenuation

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US (1) US4325461A (en)
EP (1) EP0029898B1 (en)
AT (1) ATE13232T1 (en)
DE (1) DE2947026C2 (en)

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DE3020830A1 (en) * 1980-06-02 1981-12-10 Messerschmitt-Bölkow-Blohm GmbH, 8000 München COINCIDENCE SILENCER
DE3217784C2 (en) * 1982-05-12 1985-12-19 Messerschmitt-Bölkow-Blohm GmbH, 8000 München Sound-absorbing element with resonators
DE3217783C2 (en) * 1982-05-12 1985-12-19 Messerschmitt-Bölkow-Blohm GmbH, 8000 München Sound-absorbing and sound-absorbing element with resonators
DE3241932A1 (en) * 1982-11-12 1984-05-17 Transformatoren Union Ag, 7000 Stuttgart TRANSFORMER WITH OIL-COOLED ACTIVE COMPONENT AND SOUND ABSORBING RESONATORS
DE3347827A1 (en) * 1983-05-10 1985-03-07 Metzeler Kautschuk GmbH, 8000 München Resonating, variable-volume resonator in the form of a silator
DE3317103C2 (en) * 1983-05-10 1986-08-07 Metzeler Kautschuk GmbH, 8000 München Resonant, volume-changing resonator in the form of a silator
DE3330471A1 (en) * 1983-08-24 1985-03-14 Metzeler Kautschuk GmbH, 8000 München Covibrating, variable-volume resonator in the form of a silator
US5267321A (en) * 1991-11-19 1993-11-30 Edwin Langberg Active sound absorber
DE19626167C1 (en) * 1996-06-29 1997-09-04 Coldewey Maik Volume-alternating resonator component
GB0304867D0 (en) * 2003-03-04 2003-04-09 Rickards M J A sound barrier vacuum panel
CN1830020A (en) * 2003-05-29 2006-09-06 理音株式会社 Sound insulation/absorption structure, and structure having these applied thereto
DE10332833B4 (en) * 2003-07-18 2005-07-28 Siemens Ag Silencer with surface membrane
DE102011006242A1 (en) 2011-03-28 2012-10-04 BSH Bosch und Siemens Hausgeräte GmbH Refrigerant circuit component and refrigeration device
US8752667B2 (en) 2011-10-06 2014-06-17 Hrl Laboratories, Llc High bandwidth antiresonant membrane
CN103137118B (en) 2011-11-30 2016-07-06 香港科技大学 Acoustic energy absorption metamaterial
CN102951795A (en) * 2012-03-21 2013-03-06 戴长虹 Vacuum glass without extraction opening and support and preparation method thereof
US8616330B1 (en) 2012-08-01 2013-12-31 Hrl Laboratories, Llc Actively tunable lightweight acoustic barrier materials
US11021870B1 (en) * 2013-03-14 2021-06-01 Hrl Laboratories, Llc Sound blocking enclosures with antiresonant membranes
US8869933B1 (en) 2013-07-29 2014-10-28 The Boeing Company Acoustic barrier support structure
US8857563B1 (en) 2013-07-29 2014-10-14 The Boeing Company Hybrid acoustic barrier and absorber
US9222229B1 (en) 2013-10-10 2015-12-29 Hrl Laboratories, Llc Tunable sandwich-structured acoustic barriers

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DE2739075A1 (en) * 1976-09-02 1978-03-16 Saurer Ag Adolph SOUND-INSULATING, WALL-LIKE COMPONENT AND ITS USE
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DE2758041A1 (en) * 1977-12-24 1979-06-28 Fraunhofer Ges Forschung Sound-damping laminate used as wall-covering - made of polyethylene sheet with noise-absorbing depressions sealed by smooth covering polystyrene foil

Also Published As

Publication number Publication date
ATE13232T1 (en) 1985-05-15
US4325461A (en) 1982-04-20
DE2947026C2 (en) 1981-10-01
EP0029898A2 (en) 1981-06-10
DE2947026B1 (en) 1980-11-27
EP0029898A3 (en) 1981-08-26

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