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EP 1 085 199 B1 |
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EUROPEAN PATENT SPECIFICATION |
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Mention of the grant of the patent: |
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12.03.2003 Bulletin 2003/11 |
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Date of filing: 05.09.2000 |
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International Patent Classification (IPC)7: F02M 35/12 |
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Actively controlled induction noise using a quadrapole inlet
Aktiv gesteuertes Einlasslärm mir Quadripole-Einlassvorrichtung
Bruit d'admission contrôlé activement utilisant une admission quadripôle
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Designated Contracting States: |
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DE FR GB IT |
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Priority: |
14.09.1999 US 153721 P
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Date of publication of application: |
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21.03.2001 Bulletin 2001/12 |
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Proprietor: Siemens VDO Automotive Inc. |
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Chatham,
Ontario N7M 5M7 (CA) |
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Inventor: |
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- McLean, Ian R.
Chatham,
Ontario N7M 3V6 (CA)
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Representative: Condon, Neil et al |
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Siemens AG
P.O. Box 22 16 34 80506 München 80506 München (DE) |
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References cited: :
EP-A- 0 884 471 FR-A- 2 740 599
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WO-A-97/20307 US-A- 3 936 606
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Note: Within nine months from the publication of the mention of the grant of the European
patent, any person may give notice to the European Patent Office of opposition to
the European patent
granted. Notice of opposition shall be filed in a written reasoned statement. It shall
not be deemed to
have been filed until the opposition fee has been paid. (Art. 99(1) European Patent
Convention).
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[0001] The subject invention relates to an improvement in noise reduction capabilities of
an air induction system for an internal combustion engine.
[0002] Active noise attenuation has been used to reduce engine noise emitted through air
induction systems from the combustion chambers of internal combustion engines. One
such example is pending United States Patent Application Number 08/872,506 "Active
Noise Attenuation." Noise attenuation assemblies of this type are affixed inside an
air inlet duct leading to the engine combustion chambers. The inlet duct includes
an open end into which air is drawn for feeding the combustion chambers. The assembly
includes a loud speaker mounted upon an internal housing. The internal housing forms
an annular space with the inlet duct through which air travels.
[0003] A controller generates an electrical signal from input from a primary microphone
measuring a noise field emanating from the engine, and from an error microphone measuring
un-attenuated noise. The electrical signal is amplified and phase shifted from the
noise field and the signal is applied to the loudspeaker for broadcasting a sound
field phase shifted from the noise field. Preferably, the phase shift is 180°.
[0004] To generate a sound field strong enough to attenuate the noise field from the engine,
the speaker needed is large relative to the amount of space available inside the assembly.
Further, it is desirable to reduce vehicle mass and thus reduce the mass of components
such as the speaker be reduced to amounts a low as is practicable to perform the requisite
functions is a desirable goal. Therefore, it would be. desirable to provide apparatus
that can reduce the strength of the noise field, and enable the use of smaller, lighter,
and less powerful speaker.
[0005] In WO 97/20307 there is described a system and method for reducing noise from an
internal combustion engine using a duct housing receiving induction air flow to the
engine. A space is defined within the duct housing surrounding a speaker enclosure
associated with a speaker facing an open space upstream of the annular space. A sound
transducer at the axial location where the annular space opens into the open space
generates electrical signals corresponding to engine noise propagating through the
air induction ducting. The signals are amplified and phase shifted driving the speaker
to output canceling noises or sounds so as to at least reduce engine noise from the
annular space. The speak enclosure length is set to enhance speaker performance in
selected frequency bands of engine noise.
Summary of the invention and advantages
[0006] According to the invention there is provided an active noise attenuation assembly
for an air induction system of an internal combustion engine, said assembly comprising:
an air inlet duct leading to the engine having an open end into which air is drawn;
a fairing body mounted within said air inlet duct defining an annular space with said
inlet duct through which air travels; a loud speaker mounted on said fairing body
facing outwardly from said air inlet duct; a controller for generating an electrical
signal amplified and phase shifted from a noise field emanating from the engine and
applying the signal to said loudspeaker for broadcasting a sound field phase shifted
from the noise field thereby attenuating the noise field and characterised by; a transition
housing affixed to said open end of said inlet duct which forms a first pair of opposing
channels communicating with said speaker and a second pair of opposing channels communicating
with said annular space.
[0007] Preferably, the first and the second pair of channels terminate in an arrangement
having each of the first channels positioned adjacent to at least one of the second
channels.
[0008] The arrangement of the channels at the inlet end of the housing facilitates the transfer
of particulate matter between the first and second pairs of channels. Because the
sound fields are out of phase, particulate matter is pushed and pulled between the
first and second pairs of channels at the inlet end of the housing. The transfer of
the particulate matter between the channels dampens the noise field reducing the output
requirements of the loudspeaker for attenuating the noise field. Reduced output requirements
allows for the reduction in the size and power of the loudspeaker resolving the problems
associated with the prior art.
[0009] According to the invention there is also provided a method of attenuating noise emanating
from an internal combustion engine and travelling through a fresh air inlet opening
of an air induction assembly comprises the steps of: providing a loudspeaker concentrically
mounted within said assembly facing outwardly of said assembly; detecting the noise
field emanating from the engine for determining the phase of the noise wave; broadcasting
a sound field from said speaker out of phase of the noise field for attenuating the
noise field, characterised by; separating the noise field emanating from the engine
into a first pair of opposing channels and separating the sound field broadcast from
the loudspeaker into a second pair of opposing channels, wherein said first and said
second pair of channels terminate in an arrangement having each of said first channels
positioned adjacent each of said second channels.
Brief description of the drawings
[0010] Other advantages of the present invention will be readily appreciated as the same
becomes better understood by reference to the following detailed description when
considered in connection with the accompanying drawings wherein:
Figure 1 is a partial sectional view of an embodiment of the invention showing the
adjacent opposing channels;
Figure 2 is an end view of the frame shown in Figure 1; and
Figure 3 is a partial sectional view of an embodiment of the invention showing the
filter cell attached;
Figure 4 is a view in direction of section 4-4 in Figure 1 showing the channels at
the outlet end of the transition housing of an embodiment of the invention; and
Figure 5 is a view in direction of section 5-5 in Figure 1 showing the channels at
the inlet end of the transition housing of an embodiment of the invention.
Detailed description of the preferred embodiment
[0011] Referring to the Figure 1, an active noise attenuation assembly is generally shown
at 10. The assembly 10 includes an air inlet duct 12, which leads to an internal combustion
engine 14. Air is channeled through the duct 12 into internal combustion chambers
(not shown) within the engine 14 as is known in the art of internal combustion engines.
The duct 12 includes an open end 16 into which air is drawn. The duct 12 is widest
at the open end 16 and narrows as it approaches the engine 14.
[0012] A fairing body 18 is concentrically mounted within the air inlet duct 12 and defines
an annular space 20 with the inlet duct 12 through which the air travels. The fairing
body 18 is hollow and generally contoured to the shape of the duct 12. A loudspeaker
26 is mounted on the fairing body 18 facing outwardly from the air inlet duct 12.
[0013] As best shown in Figure 2, the duct 12 includes a frame 22 for affixing the fairing
body 18 to the duct 12. The frame 22 includes equally spaced radial bars 24 so as
to allow maximum air flow through the annular space 20. The frame 22 includes spaced
apertures 28 for receiving fasteners (not shown) to mount the loudspeaker 26 to the
fairing body 18. The fairing body 18 is affixed to an inner ring 30 of the frame 22
by a series of tabs 32. The loudspeaker 26 is arranged to broadcast in an opposite
direction of the air flow. The loudspeaker 26 forms a closed-chamber 34 with the fairing
body 18. A controller 36 is secured inside the chamber 34 to the fairing body 18.
[0014] The controller 36 generates an electrical signal amplified and phase shifted (preferably
by, 180°, but other shifts come within the scope of this invention) from a noise field
emanating from the engine 14. The noise field travels from the combustion chambers
of the engine through the duct 12 in the opposite direction of the air flow. The controller
36 drives the loudspeaker 26 by applying the signal to the loudspeaker 26. Therefore,
the loudspeaker 26 broadcasts a sound field that is phase shifted from the noise field.
Phase shifting the sound field from the noise field attenuates the noise field generated
by the engine
14 as is known in the art of active noise control. Again a 180° shift is most preferred,
but shifts approximately equal to 180°, but shifts approximately equal to 180° are
also capable of performing a good deal of benefits of this invention.
[0015] The noise field is detected by a primary microphone 38. The primary microphone 38
signals the controller 36 with the measured noise field from which the controller
36 determines the phase of the noise field. The primary microphone 38 is affixed to
the duct 12 in a location determined to measure the noise field prior to being attenuated
by the loudspeaker 26. Thus, the optimum location is between the fairing body 18 and
the engine 14.
[0016] A transition housing 40 is mated to the duct 12. The transition housing 40 includes
an outlet end 42 and an inlet end 44. The outlet end 42 is mated to the open end 16
of the inlet duct 12. The housing forms a first pair of opposing channels 46 and a
second pair of opposing channels 48. The channels 46, 48 terminate at the inlet end44
in an arrangement positioning each of the first channels 46 adjacent each of the second
channels 48 (Figure 1). The structure of the channels 46, 48 is shown schematically
in Figure 1. The first pair of opposing channels 46 communicates with the loudspeaker
26. The second pair of opposing channels 48 communicates with the annular space 20.
The noise field emanates through the annular space 20 into the second pair of opposing
channels 48 against the flow of air.
[0017] The loudspeaker 26 broadcasts the sound field through the first pair of opposing
channels 46 phase shifted from the noise field emanating from the engine 14 through
the second pair of opposing channels 48. The sound field emanating from the loudspeaker
26 through the first pair of opposing channels 46 attenuates the sound field emanating
from the engine 14 through the second pair of opposing channels 48 at the inlet end
44. Locally attenuating the noise field in this manner prevents the noise field from
traveling far away from the source.
[0018] The adjacent arrangement of the channels 46, 48 at the inlet end 44 facilitates the
transfer of particulate matter between the first and second channels 46, 48 due to
the proximity of each of the first channels 46 to the second channels 48. Additionally,
the 180° phase shift between the noise field and the sound field increases the amount
of particulate matter transferred between the channels 46, 48 by pushing and pulling
the particulate matter between the channels 46, 48. The strength of the noise field
is significantly dampened by the transfer of particulate matter. Thus, the size and
power requirements of the loudspeaker 26 that is necessary to attenuate the noise
field is significantly reduced.
[0019] An error microphone 49 is positioned adjacent the outlet end 42 for detecting un-attenuated
noise. The error microphone 49 senses both the noise field and the sound field and
signals the controller 36 to adjust the phase of the sound field to improve the attenuating
properties of the sound field.
[0020] As shown in Figure 3, a filter cell 50 is affixed at the inlet end 44 of the transition
housing 40 for filtering air entering the inlet end 44. The filter cell 50 includes
filter media 52 through which the air is drawn into a central cavity 54. The error
microphone 49 is located in or near the cavity 54. The noise field is attenuated in
the cavity 54 before it can leave the filter cell 50 through the media 52.
[0021] As best shown in Figures 4 and 5, the first channels 46 form a twisting path from
the inlet end 44 of the housing 40 to the speaker 26. The second channels 48 form
a twisting path from the inlet end 44 of the housing 40 to the annular space 20. As
seen in Figure 4, the first channels 46 combine to form a circular space to mate with
the speaker 26, while the second channels 48 combine to form a concentric ring around
the first channels 46 to mate with the annular space 20. As seen in Figure 5, the
first channels 46 are positioned in an opposing relationship being separated by the
second channels 48 at the inlet end 44 of the housing 40. When oriented in this manner,
each of the first channels 46 is adjacent at least one of the second channels 48 to
facilitate the transfer of particulate matter between the first and second channels
46, 48.
[0022] The invention has been described in an illustrative manner, and it is to be understood
that the terminology which has been used is intended to be in the nature of words
of description rather than of limitation.
[0023] Many modifications and variations of the present invention are possible in light
of the above teachings. It is, therefore, to be understood that within the scope of
the appended claims, wherein reference numerals are merely for convenience and are
not to be in any way limiting, the invention may be practiced otherwise than as specifically
described.
1. An active noise attenuation assembly (10) for an air induction system of an internal
combustion engine (14), said assembly comprising:
an air inlet duct (12) leading to the engine (14) having an open end (16) into which
air is drawn;
a fairing body (18) mounted within said air inlet duct (12) defining an annular space
(20) with said inlet duct (12) through which air travels;
a loud speaker (26) mounted on said fairing body (18) facing outwardly from said air
inlet duct (12);
a controller (36) for generating an electrical signal amplified and phase shifted
from a noise field emanating from the engine (14) and applying the signal to said
loudspeaker (26) for broadcasting a sound field phase shifted from the noise field
thereby attenuating the noise field and characterised by;
a transition housing (40) affixed to said open end (16) of said inlet duct (12) which
forms a first pair of opposing channels (46) communicating with said speaker (26)
and a second pair of opposing channels (48) communicating with said annular space
(20).
2. An assembly (10) as set forth in claim 1 wherein each of said first pair of channels
(46) are positioned adjacent at least one of said second pair of channels (48) at
an end opposite (44) said open end (16) of said inlet duct (12).
3. An assembly (10) as set forth in claim 2 wherein said speaker (26) broadcasts said
sound field through said first pair of opposing channels (46) phase shifted from the
noise field emanating from the engine (14) through said second pair of opposing channels
(48).
4. An assembly (10) as set forth in claim 3 wherein said sound field emanating from said
speaker (26) through said first pair of opposing channels (46) attenuates the noise
field emanating from the engine (14) through said second pair of opposing channels
(48).
5. An assembly (10) as set forth in claim 4 wherein the strength of the noise field emanating
from the engine (14) through said second pair of opposing channels (48) is dampened
by transfer of particulate matter between said first (46) and said second (48) pairs
of opposing channels.
6. An assembly (10) as set forth in claim 4 wherein said air inlet duct (12) includes
a primary microphone (38) for detecting the phase of the noise field emanating from
the engine (14) and signaling said controller (36).
7. An assembly (10) as set forth in claim 6 including an error microphone (49) for measuring
both the noise field and the sound field and signaling said controller (36) to adjust
the phase of the sound field to improve attenuation the noise field.
8. An assembly (10) as set forth in claim 1 wherein said fairing body (18) forms a closed
chamber with said speaker (26).
9. An assembly (10) as set forth in claim 8 wherein said controller (36) is disposed
within said chamber formed by said fairing body (18) and said speaker (26).
10. A method of attenuating noise emanating from an internal combustion engine (14) and
travelling through a fresh air inlet opening of an air induction assembly comprises
the steps of:
providing a loudspeaker (26) concentrically mounted within said assembly facing outwardly
of said assembly;
detecting the noise field emanating from the engine (14) for determining the phase
of the noise wave;
broadcasting a sound field from said speaker (26) out of phase of the noise field
for attenuating the noise field, characterised by;
separating the noise field emanating from the engine (14) into a first pair of opposing
channels (46) and separating the sound field broadcast from the loudspeaker into a
second pair of opposing channels (48), wherein said first (46) and said second pair
of channels (48) terminate in an arrangement having each of said first channels positioned
adjacent each of said second channels.
11. A method as set forth in claim 10 further including the step of dampening the noise
field emanating from the engine (14) by passing particulate matter between said first
pair (46) and said second (48) pair of opposing channels.
12. A method as set forth in claim 11 further including the step of detecting both the
noise field and the sound field and adjusting the phase of the sound field to improve
attenuation the noise field.
1. Eine aktive Geräuschdämpfungs-Baugruppe (10) für das Lufteinlasssystem eines Verbrennungsmotors
(14), welche Folgendes umfasst:
ein Lufteinlasskanal (12), der zum Motor (14) führt und ein offenes Ende (16) besitzt,
in das Luft eingesaugt wird;
ein strömungsführendes Formteil (18), das in den besagten Lufteinlasskanal (12) eingebaut
ist und zusammen mit diesem eine ringförmige Zone 20 begrenzt, durch welche die Luft
strömt;
ein Lautsprecher (26), der an dem besagten strömungsführenden Formteil (18) so befestigt
ist, dass er von dem besagten Lufteinlasskanal (12) aus nach außen weist;
eine Steuereinheit (36) zum Erzeugen eines von dem vom Motor (14) ausgehenden Störschall
abgeleiteten verstärkten und phasenverschobenen elektrischen Signals und zum Anlegen
dieses Signals an den Lautsprecher (26), um ein in der Phase gegenüber dem Störschallfeld
verschobenes Kompensationsschallfeld abzustrahlen und dadurch den Störschall abzuschwächen;
gekennzeichnet durch
ein am besagten offenen Ende (16) des besagten Einlasskanals (12) befestigtes Übergangsgehäuse
(40), welches ein erstes Paar gegenüberliegender, mit dem besagten Lautsprecher (26)
akustisch verbundener Kanäle (46) sowie ein zweites Paar gegenüberliegender, mit der
besagten ringförmigen Zone (29) akustisch verbundener Kanäle (48) bildet.
2. Eine Baugruppe (10) gemäß Anspruch 1, wobei an einem dem besagten offenen Ende (16)
des besagten Einlasskanals (12) gegenüberliegenden Ende (44) jeder der Kanäle des
besagten ersten Kanalpaars (46) mindestens einem der Kanäle des besagten zweiten Kanalpaars
(48) benachbart platziert ist.
3. Eine Baugruppe (10) gemäß Anspruch 2, wobei der besagte Lautsprecher (26) den besagten
Kompensationsschall durch das besagte erste Paar gegenüberliegender Kanäle (46) hindurch
abstrahlt und wobei der besagte Kompensationsschall gegenüber dem vom Motor (14) ausgehenden,
über das besagte zweite Paar gegenüberliegender Kanäle (48) weitergeleiteten Störschall
phasenverschoben ist.
4. Eine Baugruppe (10) gemäß Anspruch 3, wobei der vom besagten Lautsprecher (26) durch
das besagte erste Paar gegenüberliegender Kanäle (46) hindurch abgestrahlte besagte
Kompensationsschall den vom Motor (14) ausgehenden, über das besagte zweite Paar gegenüberliegender
Kanäle (48) weitergeleiteten Störschall abschwächt.
5. Eine Baugruppe (10) gemäß Anspruch 4, wobei die Stärke des vom Motor (14) ausgehenden,
über das besagte zweite Paar gegenüberliegender Kanäle (48) weitergeleiteten Störschalls
durch das Verlagern von Partikelmaterial zwischen dem besagten ersten (46) und dem
besagten zweiten Kanalpaar (48) gedämpft wird.
6. Eine Baugruppe (10) gemäß Anspruch 4, wobei der besagte Lufteinlasskanal (12) ein
Hauptmikrofon (38) enthält, um die Phase des vom Motor (14) ausgehenden Störschalls
zu messen und an die besagte Steuereinheit (36) weiterzumelden.
7. Eine Baugruppe (10) gemäß Anspruch 6, wobei zusätzlich ein Kontrollmikrofon (49) vorhanden
ist, um sowohl den Störschall als auch den Kompensationsschall zu messen und an die
besagte Steuereinheit (36) weiterzumelden, um die Phase des Kompensationsschalls so
nachzustellen, dass der Störschall besser abgeschwächt wird.
8. Eine Baugruppe (10) gemäß Anspruch 1, wobei das besagte strömungsführende Formteil
(18) zusammen mit dem besagten Lautsprecher (26) eine geschlossene Kammer bildet.
9. Eine Baugruppe (10) gemäß Anspruch 8, wobei die besagte Steuereinheit (36) innerhalb
der besagten, von dem besagten strömungsführenden Formteil (18) zusammen mit dem besagten
Lautsprecher (26) gebildeten geschlossenen Kammer platziert ist.
10. Ein Verfahren zum Abschwächen des von einem Verbrennungsmotor (14) ausgehenden und
durch eine Frischluft-Einlassoffnung einer Lufteinlassbaugruppe hindurch austretenden
Störschalls, bestehend aus folgenden Schritten:
Einbauen eines konzentrisch in der besagten Baugruppe und von dieser in Richtung nach
außen orientiert befestigten Lautsprechers (26);
Messen des vom Motor (14) ausgehenden Störschalls und Ermitteln der Phase dieses Störschalls;
Abstrahlen eines gegenüber dem Störschall phasenverschoben Kompensationsschalls durch
den besagten Lautsprecher (26), um den Störschall abzuschwächen:
gekennzeichnet durch
getrenntes Einleiten des vom Motor (14) ausgehenden Störschalls in ein erstes Paar
von gegenüberliegenden Kanälen (46) und getrenntes Einleiten des vom Lautsprecher
abgestrahlten Kompensationsschalls in ein zweites Paar gegenüberliegender Kanäle (48),
wobei die besagten ersten (46) und zweiten (48) Kanalpaare in einer Anordnung enden,
bei der jeder der besagten ersten Kanäle jedem der besagten zweiten Kanäle benachbart
ist.
11. Ein Verfahren gemäß Anspruch 10, wobei ein zusätzlicher Schritt enthalten ist, in
welchem der vom Motor (14) ausgehende Störschall dadurch gedämpft wird, dass sich
Partikelmaterial zwischen dem besagten ersten (46) und dem besagten zweiten (48) Paar
gegenüberliegender Kanäle bewegt.
12. Ein Verfahren gemäß Anspruch 11, wobei ein zusätzlicher Schritt enthalten ist, in
welchem sowohl der Störschall als auch der Kompensationsschall gemessen werden und
die Phase des Kompensationsschalls so nachgestellt wird, dass der Störschall besser
abgeschwächt wird.
1. Ensemble d'atténuation active de bruit (10) pour un système d'admission d'air d'un
moteur à combustion interne (14), l'ensemble comprenant :
une conduite d'entrée d'air (12) menant au moteur (14) et ayant une extrémité ouverte
(16) dans laquelle de l'air est aspiré ;
un corps caréné (18) monté à l'intérieur de la conduite d'entrée d'air (12) et définissant
avec la conduite d'entrée (12) un espace annulaire (20) dans lequel de l'air se déplace
;
un haut-parleur (26) monté sur le corps caréné (18) et dirigé vers l'extérieur par
rapport à la conduite d'entrée d'air (12) ;
un régulateur (36) pour générer un signal électrique amplifié et déphasé par rapport
à un champ parasite émanant du moteur (14) et appliquant le signal audit haut-parleur
(26) pour diffuser un champ acoustique déphasé par rapport au champ parasite, atténuant
ainsi le champ parasite et
caractérisé par :
une enveloppe de transition (40), qui est fixée à l'extrémité ouverte (16) de la conduite
d'entrée (12) et qui forme une première paire de canaux opposés (46) communiquant
avec le haut-parleur (26) et une secondaire paire de canaux opposés (48) communiquant
avec l'espace annulaire (20).
2. Ensemble (10) selon la revendication 1, dans lequel chaque canal de la première paire
de canaux (46) est positionné de manière adjacente à au moins un canal de la seconde
paire de canaux (48) au niveau d'une extrémité opposée (44) à l'extrémité ouverte
(16) de la conduite d'entrée (12).
3. Ensemble (10) selon la revendication 2, dans lequel le haut-parleur (26) diffuse le
champ acoustique dans la première paire de canaux opposés (46),de manière déphasée
par rapport au champ parasite émanant du moteur (14) dans la seconde paire de canaux
opposés (48).
4. Ensemble (10) selon la revendication 3, dans lequel le champ acoustique émanant du
haut-parleur (26) dans la première paire de canaux opposés (46) atténue le champ parasite
émanant du moteur (14) dans la seconde paire de canaux opposés (48).
5. Ensemble (10) selon la revendication 4, dans lequel la force du champ parasite émanant
du moteur (14) dans la seconde paire de canaux opposés (48) est amortie par le transfert
de matière particulaire entre la première paire (46) et la seconde paire (48) de canaux
opposés.
6. Ensemble (10) selon la revendication 4, dans lequel la conduite d'entrée d'air (12)
comprend un microphone primaire (38) pour détecter la phase du champ parasite émanant
du moteur (14) et pour le signaler audit régulateur (36).
7. Ensemble (10) selon la revendication 6, comprenant un microphone d'erreur (49) pour
mesurer à la fois le champ parasite et le champ acoustique et pour signaler audit
régulateur (36) d'ajuster la phase du champ acoustique pour améliorer l'atténuation
du champ parasite.
8. Ensemble (10) selon la revendication 1, dans lequel le corps caréné (18) forme une
chambre fermée avec le haut-parleur (26).
9. Ensemble (10) selon la revendication 8, dans lequel le régulateur (36) est disposé
à l'intérieur de la chambre formée par le corps caréné (18) et le haut-parleur (26).
10. Procédé d'atténuation du bruit émanant d'un moteur à combustion interne (14) et se
propageant par une ouverture d'entrée d'air, frais d'un ensemble d'admission d'air
comprenant les étapes consistant à :
prévoir un haut-parleur (26) monté concentriquement à l'intérieur de l'ensemble et
dirigé vers l'extérieur de l'ensemble ;
détecter le champ parasite émanant du moteur (14) pour déterminer la phase de l'onde
parasite ;
diffuser depuis le haut-parleur (26) un champ acoustique déphasé par rapport au champ
parasite pour atténuer le champ parasite, caractérisé par :
la séparation du champ parasite allant du moteur (14) dans une première paire de canaux
opposés (46) et la séparation du champ acoustique diffusé depuis le haut-parleur dans
une seconde paire de canaux opposés (48), la première paire (46) et la seconde paire
(48) de canaux se terminant en un agencement ayant chacun des premiers canaux positionné
de manière adjacente à chacun des seconds canaux.
11. Procédé selon la revendication 10, comprenant en outre l'étape consistant à amortir
le champ parasite émanant du moteur (14) en faisant passer la matière particulaire
entre la première paire (46) et la seconde paire (48) de canaux opposés.
12. Procédé selon la revendication 11, comprenant en outre l'étape consistant à détecter
à la fois le champ parasite et le champ acoustique et à ajuster de la phase du champ
acoustique pour améliorer l'atténuation du champ parasite.