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JP2015172370

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DESCRIPTION JP2015172370
Abstract: The present invention provides an active noise control system which is particularly
compact and which requires only a small space in the undercarriage of a vehicle provided with
an internal combustion engine. An active noise control system for a vehicle provided with an
internal combustion engine Sound generator 1 is disclosed. The sound generator 1 comprises a
first casing 10 having at least one exhaust gas inlet 11 and at least one exhaust gas outlet 12
different from the at least one exhaust gas inlet 11 and a sound according to the electrical
control signal. And at least one electro-acoustic transducer 20 configured to generate. The at
least one electroacoustic transducer 20 is located inside the first casing 10 or directly attached to
the first casing 10. Furthermore, an active noise control system including the sound generator 1
and a vehicle including the active noise control system are disclosed. [Selected figure] Figure 1A
Active design of exhaust noise
[0001]
The present invention relates to the active design of exhaust noise for vehicles operating with an
internal combustion engine. The internal combustion engine may be part of a hybrid drive unit.
The invention relates in particular to affecting the overall acoustic pattern of the exhaust noise.
[0002]
The operation of internal combustion engines, regardless of their specific design, such as
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reciprocating engines, rotary engines without pistons, or free piston engines, such as intake and
compression of the mixture, combustion, and exhaust of the combustion mixture, etc. , A certain
process is performed as repetition of each process implemented. The sound generated thereby
partially propagates through the engine directly as solid-borne sound. Another portion of the
generated sound exits the engine exhaust system with the combustion gases as airborne sound.
In the exhaust pipe of the exhaust system, the flow noise of the combustion gas is superimposed
on the air propagation sound. The sound produced as a result of this superposition is called
exhaust sound. Finally, the rest of the generated sound exits through the engine's intake system.
[0003]
Sound propagating in the internal combustion engine as solid-borne sound can generally be
isolated well by means of suitable sound insulation in the engine compartment of the vehicle.
[0004]
In order to reduce the acoustic emission that leaks with the exhaust gas, a sound absorber is
usually arranged in the exhaust duct.
Such a sound absorbing device is called a muffler. The muffler can operate, for example,
according to the principle of absorption and / or reflection. Furthermore, it is known to provide
the muffler with a resonance chamber that is harmonically tuned so that destructive interference
occurs where the opposite sound waves cancel out.
[0005]
Such a system has the disadvantage of increasing the back pressure of the exhaust gas flowing in
the exhaust gas system and thus reducing the efficiency of the combustion engine. Such systems
also suffer from the disadvantage that the sound actually coming out of the exhaust gas system is
not attractive to the user, especially in the case of modern diesel vehicles and vehicles with
hybrid drive systems.
[0006]
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Therefore, an active sound system capable of artificially generating exhaust noise for use in an
exhaust system of a vehicle has been developed. The corresponding system uses connector
components in the exhaust pipe of the internal combustion engine to superpose the
electroacoustically generated sound waves on the sound waves generated by the combustion
process in the engine or generated by the flow of exhaust gas in the exhaust gas system. Have an
electro-acoustic transducer connected by In this way, the exhaust noise of the vehicle can be
intentionally corrected. The electrical input signal of this converter is generated by the controller
as a so-called control signal, taking into account the current values of the engine parameters,
such as the engine speed and the ignition sequence. The electro-acoustic transducer requires
additional space in the undercarriage of the vehicle as it is housed in a separate housing from the
exhaust piping.
[0007]
Active sound systems can be used, for example, not only as a substitute or supplement to the
muffler but also as an anti-noise system. The antinoise system superimposes the
electroacoustically generated antinoise on the airborne noise generated by the internal
combustion engine and propagating in the exhaust system. Each anti-noise system outputs an
airborne noise propagating in the exhaust system to zero (for noise cancellation) or a preset
threshold (by affecting the noise) by outputting the sound using at least one speaker. A so-called
filtered X least mean square (FxLMS) algorithm may be used which seeks to reduce The
loudspeakers of the anti-noise system are usually in fluid communication with the exhaust
system. In order to achieve a completely destructive interference between the sound waves of the
airborne sound propagating in the exhaust system and the antinoise generated by the speaker,
the sound waves from the speaker consist of the sound waves propagating in the exhaust system
and the amplitude and It must have a relative phase shift of 180 degrees while the frequencies
are matched. Even if the sound wave of the airborne noise propagating in the exhaust system
matches the frequency with the anti-noise sound wave generated by the speaker and there is a
relative phase shift of 180 degrees, the exhaust does not match if the amplitude does not match.
The sound waves of airborne sound propagating in the system are only attenuated. Anti-noise
determines the appropriate frequency and phase of two sinusoidal oscillations 90 degrees apart
from each other and separately for each frequency band of airborne noise propagating in the
exhaust pipe using the FxLMS algorithm and these sinusoids It can be calculated by calculating
the required amplitude of the vibration. For example, each system is known from the following
patent documents 1-18.
[0008]
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The goal of an active sound system may be that the cancellation or influence of the sound be
audible and measurable at least outside the exhaust system. In some cases, it is audible and
measurable even inside the exhaust system that the sound has been canceled or that the sound
has been influenced.
[0009]
Such active sound systems have the disadvantage that they must be fail safe to meet the noise
protection legislation. Therefore, it is often used as a supplement to existing mufflers. However,
the space in the undercarriage of the vehicle is very limited.
[0010]
U.S. Patent No. 4,177,874 U.S. Patent No. 5,229,556 U.S. Patent No. 5,233,137 U.S. Patent No.
5,343,533 U.S. Patent No. 5,336 U.S. Pat. No. 5,432,857 U.S. Pat. No. 5,600,106 U.S. Pat. No.
5,619,020 European Patent No. 0 373 188 European Patent Application Publication No. 0 674
097 Patent EP 0 755 045 European Patent 0 916 817 European Patent 1 055 804 European
Patent No. 1 627 996 German Patent Application Publication No. German Patent No. 10 2006
042 224 German Patent Application Publication No. 10 2008 018 085 German Patent
Application Publication No. 1 0 2009 031 848 Specification
[0011]
Embodiments relate to providing an active noise control system that is particularly compact and
requires only a small space in the undercarriage of a vehicle with an internal combustion engine.
[0012]
An embodiment of a sound generator for an active noise control system for a vehicle with an
internal combustion engine comprises a first casing and at least one electroacoustic transducer.
The first casing has at least one exhaust gas inlet and at least one exhaust gas outlet different
from the at least one exhaust gas inlet.
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The at least one electro-acoustic transducer is configured to generate sound in response to an
electrical control signal and is located internally of the first casing or directly attached to the first
casing. Here, the term "directly" means that no separate pipe is provided to connect the at least
one electro-acoustic transducer to the casing. This does not exclude the provision of gaskets or
distance pieces whose longitudinal extent is less than 40 mm, in particular less than 20 mm and
more particularly less than 5 mm.
[0013]
Thus, at least one electro-acoustic transducer of the sound generator is integrated directly into
the exhaust gas system and uses the components of the exhaust gas system. The first casing is
thereby used both to guide the exhaust gas and to support and / or store the at least one
electroacoustic transducer.
[0014]
According to one embodiment, the at least one electro-acoustic transducer may be completely
surrounded by the first casing. Thereby, the first casing prevents the at least one electroacoustic
transducer from being externally affected, such as moisture or mechanical shock.
[0015]
According to an alternative embodiment, the at least one electro-acoustic transducer is such that,
on the side wall of the first casing, the at least one electro-acoustic transducer covers one or
several holes of the side wall. It can be attached. The at least one hole is provided in front of the
at least one electro-acoustic transducer to allow sound generated by the at least one electroacoustic transducer to enter the first casing . If there is one hole in the side wall of the first
casing, the hole may have a diameter slightly smaller than the diameter of the electroacoustic
transducer. Here, “slightly smaller” means that the diameter of the hole is less than 10%
smaller or less than 5% smaller than the diameter of the electroacoustic transducer covering the
hole.
[0016]
According to one embodiment, the first casing is air-tight to the extent that exhaust gases can
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only enter and exit the casing from the at least one exhaust gas inlet and the at least one exhaust
gas outlet.
[0017]
According to one embodiment, the first casing comprises a chamber, which is in fluid
communication with both the exhaust gas inlet and the exhaust gas outlet, and a sound absorbing
material, in particular a roving glass Filled with fiber (roving fiberglass).
Thereby, the first casing may be a casing of a muffler that functions according to the principle of
absorption, and may be commonly used by the muffler and at least one electro-acoustic
transducer of the sound generator.
[0018]
According to one embodiment, the first casing includes a resonance chamber harmonically tuned
such that destructive interference occurs. Hereby, the first casing can be a casing of a muffler
that functions according to the principle of reflection or destructive interference, and can be
commonly used by the muffler and at least one electro-acoustic transducer of the sound
generator. According to one embodiment, the chamber is a cavity resonator utilizing Helmholtz
resonance. Thereby, the first casing can be a casing of a muffler that functions according to the
principle of destructive interference and can be commonly used by the muffler and at least one
electro-acoustic transducer of the sound generator.
[0019]
According to one embodiment, the sound generator is airtightly connected to the first casing so
as to separate the at least one electro-acoustic transducer from the exhaust gas inlet and the
exhaust gas outlet. It further comprises a flexible membrane. By providing a flexible membrane, it
is possible for the sound waves generated by the at least one electro-acoustic transducer to pass
through the flexible membrane into the first casing while still allowing corrosive exhaust Gas can
be prevented from reaching the at least one electroacoustic transducer. The flexible film can be
made of, for example, a heat resistant silicone or a heat resistant foil made of
polytetrafluoroethylene, an acryloyl group, or polyethylene terephthalate. Furthermore, the
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thermal load on the at least one electro-acoustic transducer is reduced since the at least one
electro-acoustic transducer does not directly contact the hot exhaust gas.
[0020]
According to one embodiment, the at least one electroacoustic transducer comprises an acoustic
diaphragm which forms part of the wall of the first casing. Thereby, the at least one electroacoustic transducer may be, for example, a moving coil speaker. The acoustic diaphragm may be
made of, for example, poly (p-phenylene terephthalamide) (PPTA) known as Kevlar, titanium,
aluminum or other heat resistant material. The acoustic diaphragm and the first casing may be
made of different materials.
[0021]
According to one embodiment, the first casing comprises at least one partition, each of the
partitions defining at least two chambers separated from one another by the at least one
partition, It is connected to the first casing. The first casing further comprises at least one supply
conduit, each of the supply conduits being connected to one of the at least one exhaust gas inlet
and penetrating one of the chambers, It communicates with another chamber. The first casing
further includes at least one exhaust conduit, each of the exhaust conduits being connected to
one of the at least one exhaust gas outlet and penetrating one of the chambers, It communicates
with another chamber. This allows the first casing to be a muffler that functions in accordance
with the principles of reflective or destructive interference. According to an alternative
embodiment, the first casing comprises at least two partitions spaced from one another, each of
the partitions in the first casing so as to define at least three chambers. Connected and adjacent
chambers are separated from one another by one of the partitions. The first casing further
comprises at least one supply conduit, each of the supply conduits being connected to one of the
at least one exhaust gas inlet and penetrating one of the chambers, It communicates with another
chamber. The first casing further includes at least one exhaust conduit, each of the exhaust
conduits being connected to one of the at least one exhaust gas outlet and penetrating one of the
chambers, It communicates with another chamber. This allows the first casing to be a muffler
that functions in accordance with the principles of reflective or destructive interference.
[0022]
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According to one embodiment, the first casing comprises a partition, the partition defining the
first and second chambers separated from one another by the partition. Connected to the casing
of The first casing further comprises at least one supply conduit, each of the supply conduits
being connected to one of the at least one exhaust gas inlet, penetrating the first chamber, the It
communicates with the second chamber. The first casing further includes at least one exhaust
conduit, each of the exhaust conduits being connected to one of the at least one exhaust gas
outlet, penetrating the first chamber, and It communicates with the second chamber. The at least
one electro-acoustic transducer is disposed opposite to the open end of at least one of the supply
conduit and the exhaust conduit. This allows the first casing to be a muffler that functions in
accordance with the principles of reflective or destructive interference.
[0023]
In this document, the expression "at least one electroacoustic transducer is arranged opposite to
the open end of one of the supply and exhaust conduits" is the main direction of sound emission
by the at least one electroacoustic transducer. Is directed to the open end of one of the supply
and exhaust conduits.
[0024]
According to one embodiment, the first casing comprises two partition walls, which define first,
second and third chambers separated from one another by the partition walls. As such, it is
connected to the first casing.
The first casing further comprises at least one supply conduit, each of the supply conduits being
connected to one of the at least one exhaust gas inlet and penetrating the first and second
chambers , In communication with the third chamber. The first casing further includes at least
one exhaust conduit, each of the exhaust conduits being connected to one of the at least one
exhaust gas outlet and penetrating the third and second chambers , In communication with the
first chamber. The at least one electro-acoustic transducer is disposed opposite to the open end
of at least one of the supply conduit and the exhaust conduit.
[0025]
According to one embodiment, the supply conduit and the exhaust conduit each comprise a
portion in which the supply conduit and the exhaust conduit are guided parallel to one another.
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In this part, the exhaust gas can be guided in the same direction or in the opposite direction
through the supply and exhaust conduits.
[0026]
According to one embodiment, the sound generator includes two or more exhaust gas inlets, two
or more exhaust gas outlets, and two or more electroacoustic transducers. One of the electroacoustic transducers is disposed opposite the open end of the supply conduit connected to one of
the exhaust gas inlets, and another one of the electro-acoustic transducers is And disposed
opposite the open end of another supply conduit connected to another one of the exhaust gas
inlets.
[0027]
According to an alternative embodiment, the sound generator includes two or more exhaust gas
inlets, two or more exhaust gas outlets, and two or more electro-acoustic transducers. One of the
electro-acoustic transducers is arranged opposite the open end of the exhaust conduit connected
to one of the exhaust gas outlets and another one of the electro-acoustic transducers is And
disposed opposite the open end of another exhaust conduit connected to another one of the
exhaust gas outlets.
[0028]
According to one embodiment, at least one of the partitions is perforated or all the partitions are
perforated. According to a further embodiment, at least one of the conduits is perforated or all
the conduits are perforated. According to a further embodiment, at least one of the partitions is
unperforated or all of the partitions are non-perforated. According to yet further embodiments, at
least one of the conduits is non-perforated or all of the conduits are non-perforated. Thus, both
some or all of the partitions and some or all of the conduits may be perforated or non-perforated,
and some or all of the partitions may be perforated And some or all of the conduits may be nonperforated, some or all of the partition walls are non-perforated, and some or all of the conduits
May be perforated. It is emphasized that neither the dividing wall nor the conduit need to be
perforated over its entire area. For example, the conduit may be perforated only partially or not
at all. Perforating the dividing wall and / or the conduit may facilitate the provision of Helmholtz
resonance.
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[0029]
According to one embodiment, a sound absorbing material, for example roving glass fibers, is
arranged in at least one of the chambers.
[0030]
According to one embodiment, the sound generator is at least one second casing different from
the first casing, attached to the first casing or stored in the first casing And a supported second
casing, the second casing housing the at least one electro-acoustic transducer.
The second casing may protect the at least one electroacoustic transducer from external
influences such as water or mechanical shock. Use of the second casing may facilitate installation
of the at least one electro-acoustic transducer in the first casing or to the first casing.
[0031]
According to one embodiment, the sound generator further comprises at least one second casing
different from the first casing. The second casing houses the at least one electroacoustic
transducer. The at least one electro-acoustic transducer comprises an acoustic diaphragm. The
acoustic diaphragm is sealed to the second casing. Thus, the second casing and the acoustic
diaphragm define the internal space of the electroacoustic transducer. This internal space acts as
an air suspension for the acoustic diaphragm. Thereby, the at least one electroacoustic
transducer can be, for example, a moving coil speaker with a separate casing. The acoustic
diaphragm may be made of, for example, poly (p-phenylene terephthalamide) (PPTA) known as
Kevlar, titanium, aluminum or other heat resistant material. The acoustic diaphragm and the first
casing and / or the second casing may be made of different materials.
[0032]
According to one embodiment, the first casing and / or the second casing consist of metal, in
particular stainless steel. In one embodiment, a gasket is provided between the first casing and
the second casing.
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[0033]
In one embodiment, the electro-acoustic transducer is a moving coil speaker. According to an
alternative embodiment, the electro-acoustic transducer is different from a moving coil speaker.
[0034]
According to one embodiment, the first casing is removably attached to the second casing, for
example by using screws. According to an alternative embodiment, the first casing is irremovably
mounted to the second casing, for example by welding.
[0035]
Embodiments of the active noise control system include the sound generator described above
and a control unit. The control unit is configured to generate an electrical control signal and to
provide the electrical control signal to the electro-acoustic transducer of the sound generator.
This electrical control signal is suitable for driving the electroacoustic transducer of the sound
generator in such a way that the exhaust sound waves guided in the exhaust gas system of the
vehicle are partially, particularly completely, counteracted. It is.
[0036]
Embodiments of the vehicle include a combustion engine and an active noise control system as
described above. The exhaust gas inlet of the sound generator of the active noise control system
is connected to the combustion engine, and the exhaust gas outlet of the sound generator of the
active noise control system is connected to the tail pipe. Exhaust gases flowing from the
combustion engine to the tail pipe are guided through the exhaust gas inlet and exhaust gas
outlet of the sound generator casing of the active noise control system before reaching the tail
pipe. Of course, the vehicle comprises further components, such as the car body and the wheels,
but these components are not relevant to the claimed invention. Therefore, the description is
omitted.
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[0037]
The above and other advantageous features of the present invention will become more apparent
from the following detailed description of representative embodiments of the present invention,
taken in conjunction with the accompanying drawings. It is noted that not all possible
embodiments of the present invention will necessarily exhibit all or any one of the advantages
identified herein.
[0038]
Further features of the present invention will be apparent from the following description of
representative embodiments and the drawings associated with the claims. The present invention
is not limited to the form of the exemplary embodiment described below, but is defined by the
scope of the appended claims. In particular, the individual features in the embodiments of the
present invention can be realized in different numbers and combinations from the examples
given below. In the following description of representative embodiments of the invention,
reference is made to the accompanying drawings.
[0039]
FIG. 1A shows a schematic cross-sectional view of a sound generator for an active noise control
system according to a first embodiment. FIG. 1B shows a schematic cross-sectional view of a
sound generator for an active noise control system according to a second embodiment. FIG. 1C
shows a schematic cross-sectional view of a sound generator for an active noise control system
according to a third embodiment. FIG. 2 shows a schematic cross-sectional view of an
electroacoustic transducer that may be used in the sound generator of FIG. 1A, FIG. 1B or FIG. 1C.
FIG. 3 shows a block diagram of an active noise control system using the sound generator of FIG.
1A, FIG. 1B or FIG. 1C. FIG. 4 schematically illustrates a vehicle using the active noise control
system of FIG.
[0040]
In the exemplary embodiments described below, components that are similar in function and
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structure are denoted as much as possible by similar reference numerals. Thus, to understand the
features of the individual components of a particular embodiment, reference should be made to
the other embodiments and the general description of the invention.
[0041]
For the sake of clarity, the drawings show only those elements, components and functions that
are necessary for an understanding of the present invention. However, embodiments of the
present invention are not limited to the elements, components, and functions described, but may
be other elements, components, and elements that may be necessary for their particular
application or range of functions. It may also include features.
[0042]
A schematic cross-sectional view of a sound generator for an active noise control system
according to a first embodiment is shown in FIG. 1A.
[0043]
The sound generator, generally designated 1, comprises a generally cylindrical stainless steel
casing 10.
An exhaust gas inlet 11 connected to the supply duct 3 and an exhaust gas outlet 12 connected
to the exhaust duct 4 are provided on the bottom of the casing 10. The supply duct 3 may be
fluidly connected to the vehicle's combustion engine and the exhaust duct 4 may be fluidly
connected to the tail pipe. A perforated partition 15 made of stainless steel is connected to the
casing 10 so as to define two chambers A, B inside the casing 10. The chambers A and B are
separated from each other by the partition wall 15. The supply duct 3 connected to the exhaust
gas inlet 11 extends as a non-perforated supply conduit 17 inside the casing 10 and the exhaust
duct 4 connected to the exhaust gas outlet 12 is a non-perforated exhaust conduit inside the
casing 10 Extends as 18. Inside the casing 10, the supply conduit 17 and the exhaust conduit 18
are arranged in parallel. The exhaust gas flowing through the supply conduit 17 is directed in the
opposite direction to the exhaust gas flowing through the exhaust conduit 18. Both the supply
conduit 17 and the exhaust conduit 18 penetrate the chamber A adjacent to the exhaust gas inlet
11 and the exhaust gas outlet 12 and are separated from the exhaust gas inlet 11 and the
exhaust gas outlet 12 by the dividing wall 15 It communicates with B. The sound supplied to the
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chamber B of the casing 10 together with the exhaust gas via the supply conduit 17 enters the
chamber A via the holes of the dividing wall 15. The holes in the dividing wall 15 and the
dimensions of the chamber A are chosen such that a destructive interference of sound occurs in
the chamber A. A movable coil speaker 20 used as an electroacoustic transducer is mounted on
the bottom of the casing 10 opposite to the exhaust gas inlet 11 and the exhaust gas outlet 12
via the mount 13 inside the casing 10. An acoustic diaphragm made of poly (p-phenylene
terephthalamide) is placed towards the open end of the supply conduit 17 and the exhaust
conduit 18. Thereby, the main direction of sound emission of the speaker 20 is directed to the
open end of the supply conduit 17 and the exhaust conduit 18. The speaker 20 generates a
sound in response to the electrical control signal. In order to separate the speaker 20 from the
supply conduit 17 and the exhaust conduit 18 and the exhaust gas inlet 11 and the exhaust gas
outlet 12, the flexible membrane 14 made of heat resistant silicone comprises the open end of
the speaker 20 and the supply conduit 17 and the exhaust conduit 18 And is connected to the
casing 10. In a first embodiment, the electroacoustic transducer is completely housed within the
casing 10 of the sound generator and does not have a separate casing.
[0044]
Hereinafter, a second embodiment of the sound generator 1 'will be described with reference to
FIG. 1B. FIG. 1B shows a schematic cross-sectional view of the sound generator 1 '.
[0045]
The sound generator, generally designated 1 ', comprises a (first) generally cubic casing 10'
consisting of a zinc coated tin plate. An exhaust gas inlet 11 connected to the supply duct 3 and
an exhaust gas outlet 12 connected to the exhaust duct 4 are provided on opposite sides of the
casing 10 '. The casing 10 is spaced from one another such that two parallel non-perforated
partitions 15, 15 'of zinc coated tin plate define three chambers A, B', C inside the casing 10 '.
Concatenate to '. A supply duct 3 connected to the exhaust gas inlet 11 extends as a supply
conduit 17 inside the casing 10 'and an exhaust duct 4 connected to the exhaust gas outlet 12 as
an exhaust conduit 18 inside the casing 10'. Inside the casing 10 ', the supply conduit 17 and the
exhaust conduit 18 are arranged parallel in part D. The exhaust gas flowing through the supply
conduit 17 is directed in the same direction as the exhaust gas flowing through the exhaust
conduit 18, but the supply conduit 17 and the exhaust conduit 18 are offset. The supply conduit
17 penetrates the chamber A adjacent to the exhaust gas inlet 11 and the central chamber B ′
and communicates with the chamber C adjacent to the exhaust gas outlet 12. The supply
conduits 17 are perforated in the area across the chambers A and B '. The exhaust conduit 18
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14
penetrates the chamber C adjacent to the exhaust gas outlet 12 and the central chamber B ′ and
communicates with the chamber A adjacent to the exhaust gas inlet 11. Exhaust conduit 18 is
perforated in the area across chambers C and B '. The holes of the supply conduit 17 and the
exhaust conduit 18 and the dimensions of the chambers A, B 'and C are chosen such that
Helmholtz resonance is achieved. A moving coil speaker 20 used as an electroacoustic transducer
is mounted on the wall of the casing 10 opposite to the exhaust gas inlet 11 and the open end of
the supply conduit 17. At the position of the moving coil speaker 20, a hole is made in the wall of
the casing 10. The diameter of the hole of this casing is the same as the diameter of the
diaphragm of the movable coil speaker 20. The diaphragm of the moving coil speaker 20 is made
of titanium, and thus is made of a material different from the wall of the casing 10. The
diaphragm covers the hole in the wall of the casing 10. A (second) speaker casing 5 consisting of
a zinc coated tin plate and housing the loudspeaker 20 is airtightly welded to the casing 10 'and
additionally seals the holes of the casing 10'. The diaphragm of the movable coil speaker 20 is
sealed with respect to the speaker casing 5.
Thus, the speaker casing 5 and the diaphragm define a closed internal space of the movable coil
speaker 20.
[0046]
Hereinafter, a third embodiment of the sound generator 1 ′ ′ will be described with reference
to FIG. 1C. FIG. 1C shows a schematic cross-sectional view of the sound generator 1 ′ ′.
[0047]
The sound generator, generally indicated by reference numeral 1 & quot ;, comprises a generally
cylindrical stainless steel casing 10 & quot ;. Two exhaust gas inlets 11, 11 ', each connected to a
supply duct, and two exhaust gas outlets 12, 12', each connected to an exhaust duct, are
provided on opposite sides of the casing 10 '' . Two parallel perforated partitions 15, 15 'made of
stainless steel are spaced apart from one another so as to define three chambers A, B', C inside
the casing 10 ''. Connected to Each supply duct connected to the exhaust gas inlet 11, 11
'extends as a supply conduit 17, 17' respectively inside the casing 10 '' and each exhaust duct
connected to the exhaust gas outlet 12, 12 'is a casing It extends as an exhaust line 18, 18
'respectively inside 10' '. The supply conduits 17, 17 'are bent so as to be arranged parallel in
part E inside the casing 10' '. The exhaust gases flowing through the supply conduits 17, 17 'are
directed in the opposite direction in part E. The supply conduit 17 penetrates the chamber A
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15
adjacent to the exhaust gas inlet 11 and the central chamber B 'and communicates with the
chamber C adjacent to the other exhaust gas inlet 11'. The supply conduit 17 ′ penetrates the
chamber C adjacent to the exhaust gas inlet 11 ′ and the central chamber B ′ and
communicates with the chamber A adjacent to the other exhaust gas inlet 11. The supply
conduits 17, 17 'are perforated in the area transverse to the central chamber B'. The nonperforated exhaust conduits 18, 18 'merely exit the chambers A and C, respectively, without
intersecting the chamber B'. Roving glass fiber is accommodated as a sound absorbing material in
the central chamber B '. Two moving coil speakers 20, 20 ', used as electroacoustic transducers,
are mounted on opposite walls of the casing 10. A hole is drilled in the wall of the casing 10 at
the location of each moving coil speaker 20, 20 '. The diameter of the holes of these casings is
10% larger than the diameter of each diaphragm of the moving coil speakers 20, 20 '. The
diaphragm of each moving coil speaker 20 is made of aluminum and thus is made of a material
different from the wall of the casing 10. The diaphragm of each speaker covers most of one of
the holes in the wall of the casing 10. The acoustic diaphragm of one speaker 20 is placed
towards the open end of the supply conduit 17 ′ and the acoustic diaphragm of the other
speaker 20 ′ is placed towards the open end of the supply conduit 17.
The flexible membrane 14, 14 ′ made of polytetrafluoroethylene separates the loudspeaker 20,
20 ′ from the corrosive exhaust gas by the loudspeaker 20, 20 ′ and the supply conduits 17,
17 ′ and the exhaust conduit 18, It is connected to casing 10 '' between the open end of 18 '.
The acoustic diaphragms of the speakers 20, 20 'hermetically seal the holes of the casing 10' '.
Two stainless steel speaker casings 5, 5 'are removably attached to the casing 10' '. Each of the
speaker casings 5, 5 'houses one of the speakers 20, 20'. Each speaker casing 5, 5 ', together
with the diaphragm of the respective speaker, defines the internal space of each moving coil
speaker 20, 20'.
[0048]
A schematic cross-sectional view of a moving coil speaker used as an electro-acoustic transducer
in the sound generator of FIG. 1A, FIG. 1B or FIG. 1C above is shown in FIG.
[0049]
The loudspeaker, generally designated 20, comprises a sheet metal basket 21 holding a
permanent magnet 22.
The basket 21 has a frusto-conical overall shape. The basket 21 holds the acoustic diaphragm 23
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through an edge 24 made of flexible plastic. In order to ensure sufficient resistance to heat and
corrosion, titanium is used for the diaphragm 23 and heat resistant silicone is used for the edge
24. The diaphragm 23 has a truncated cone-like overall shape. The dust cap 28 and the bobbin
25 are fixed to the top surface of the truncated cone formed by the vibrating plate 23. The end of
the bobbin 25 remote from the diaphragm 23 is disposed in an annular gap provided in the
permanent magnet 22 and holds the voice coil 26. As a result, this coil 26 is located in the
constant magnetic field generated by the permanent magnet 22. Note that the width of the
annular gap in the drawing is greatly exaggerated. The bobbin 25 is centered by the centering
spider 27 with respect to the annular gap. The centering spider 27 consists of a spring radially
extended between the bobbin 25 and the basket 21. In the illustrated embodiment, the basket
21, the edge 24, the diaphragm 23, the dust cap 28, the bobbin 25 and the permanent magnet
22 are rotationally symmetric with the same axis of symmetry. When an electrical control signal
is applied to the voice coil 26, the bobbin 25 moves with the diaphragm 23, whereby a Lorentz
force generates a sound.
[0050]
FIG. 3 shows a block diagram of an active noise control system using the sound generator of FIG.
1A, FIG. 1B or FIG. 1C and the moving coil speaker of FIG. In the following, we focus only on the
special features of the active noise control system. An active noise control system, generally
designated 9, is used to actively annihilate or influence the sound waves in the exhaust system of
a vehicle powered by an internal combustion engine. The exhaust gas inlet 11 of the casing of
the sound generator 1 is connected to the exhaust gas outlet of the internal combustion engine 6
via a supply duct 3. The exhaust gas outlet 12 of the casing of the sound generator 1 is
connected to the tail pipe 91 via the exhaust duct 4. The active noise control system 9 includes a
control unit 90, which is electrically connected to an engine control unit 61 of the internal
combustion engine 6 via a CAN bus in order to transmit and receive control signals or
measurement signals. The control device 61 is further electrically connected to the error
microphone 7 located in the duct 4 of the exhaust system and the speaker 20 of the sound
generator 1.
[0051]
As a function of the operating state of internal combustion engine 6 acquired by engine control
unit 61 of internal combustion engine 6, control unit 90 at least partially extinguish the airborne
noise guided in supply duct 3 and exhaust duct 4 An electrical control signal sent to the speaker
20 to generate a sound is calculated. The electrical control signal can be adjusted by using the
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signal output by the error microphone 7 so that airborne noise is emitted at a reduced sound
pressure in the tail pipe 91 of the exhaust system.
[0052]
FIG. 4 schematically shows a vehicle 8 using the active noise control system 9 of FIG. 3 described
above. The active noise control system is mounted on the lower structure of the vehicle 6. In
addition to other features, the vehicle 8 includes a combustion engine 6 and an exhaust duct 4
terminating in a tail pipe 91.
[0053]
Of course, said sound generator may also act as a sound absorber, depending on the control
signal used for said at least one electro-acoustic transducer.
[0054]
Although the present invention has been described in terms of several representative
embodiments, it is evident that many alternatives, modifications and variations will be apparent
to those skilled in the art.
Accordingly, the representative embodiments of the invention described herein are exemplary
and not in any way limiting. Various changes may be made without departing from the spirit and
scope of the invention as defined in the following claims.
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