EP2394033B1 - Muffler with helical inserts - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a silencer with at least one gas channel through which a gas flows and the features of the preamble of the independent patent claim 1.

By means of a silencer according to the invention, the flowing gas should be able to pass through as unhindered as possible. However, in the flowing gas propagating sound waves, which are to be understood here as any fast pressure fluctuations of the flowing gas, but should be as damped as possible.

STATE OF THE ART

In addition to silencers, in which sound waves energy is removed by gas friction in porous material and converted into heat, are also known mufflers that absorb sound dynamically. In engineering they are referred to as acoustic absorbers, in physics as dynamic absorbers. These are resonance systems that absorb sound occurring at their natural frequency very well and can dissipate in the sequence. Examples include so-called hole or Helmholtz resonators. It is also part of the measures known in the field of dynamic sound absorbers to build up acoustic resonators with the aid of one or more cross-sectional jumps, ie changes in the diameter of the pipe delimiting a gas duct. As a result, however, the flow resistance for the gas flowing through the muffler gas is drastically increased.

From the DE 196 44 089 A1 a muffler for internal combustion engines having the features of the preamble of independent claim 1 is known. Here, a helical installation is provided in a gas channel through which a gas flows, which gives a helical course to an interior region of the gas channel. The sound is to be reduced at the helical surfaces of the helical installation by reflection and scattering and subsequent absorption in the channel wall of the gas channel and also prevented due to the so-called cut-off effect on its propagation. For absorption in the channel wall of the gas channel, the gas channel is surrounded by an annular channel which communicates via perforations with the gas channel and is arranged in the sound absorption material, such as ceramic wool. A vote on one or more main sound frequencies, ie a particularly high efficiency at these main sound frequencies is not possible in the known muffler.

From the DE 199 32 714 A1 It is known to arrange a helical membrane equipped with anti-sound generating elements in a tubular and air-flow device to actively dampen sound in the tubular device. Active sound attenuation with anti-sound generating elements requires active control of these elements and is correspondingly expensive.

From the DE 10 2004 006 031 A1 a device for reducing pressure pulsations in fluid-carrying piping systems is known. In this case, a throttle body is arranged in a line of the conduit system, which has a helical coil whose screw axis is aligned in the propagation direction of the pressure pulsations in the conduit. The pressure pulsations interact with the helical coil. This may be a passive interaction under elastic shaping of the helical coil. Alternatively, the helical coil can be activated actively. It can also be arranged a plurality of throttle body in the form of helical coils in a fixed distance between the throttle bodies in a row in the respective line. The doctrine of DE 10 2004 006 031 A1 expressly different from that of the DE 199 32 714 A1 not on gas-carrying, but only on liquids leading piping systems.

From the DE 195 33 623 B4 An absorber for absorbing airborne sound is known, in which an acoustic series circuit and an acoustic parallel circuit are coupled together, wherein the acoustic series circuit is a Helmholtz resonator. This Helmholtz resonator consists of a hollow body with an air volume and a cross-sectional constriction as an opening. The parallel circuit is also a resonator, which is realized by a parallel connection of an acoustic suspension - realized by an air volume - with an acoustic mass, which is given by the oscillating air in a neck. The acoustic series circuit and the acoustic parallel circuit are tuned to the same resonant frequency. The known absorber as such is not traversed by a gas, but is provided to form a generally gas-tight wall in a sound-absorbing manner. The temporary entry of gas into the hollow body or air volumes of the known absorber, unlike a gas-flowed muffler, does not lead to any net gas flow that runs through it.

The GB 460,148 A discloses another muffler for internal combustion engines having the features of the preamble of independent claim 1. In this case, embodiments of the known muffler are described, which have a plurality of gas channels, which is divided by the flowing gas. Helical internals may be provided inside the gas channels. The helical internals may have at their ends inlet and outlet areas in which their diameter in the direction of flow of the gas steadily approaches from the inside to the wall of the gas channel and from this. The slope of the helical internals of the known muffler can be variable. The gas channels may also have tapers and extensions of their free cross section along their main extension direction. The multiple gas channels are z. B. are used for the extinguishing superposition of sound waves, which propagate in the flowing gas.

A silencer having the features of the preamble of independent claim 1 is also known from US Pat. No. 3,746,126 known. Here it is proposed to provide a helical installation in front of or behind a bend in an exhaust pipe of an internal combustion engine.

A silencer having the features of the preamble of independent claim 1, which has a plurality of helical internals, inter alia both in closely spaced Innnenrohrabschnitten as well as in annular spaces between the inner tube sections and an outer tube, is from the FR 804 593 A known.

TASK OF THE INVENTION

The invention has for its object to provide a muffler with the features of the preamble of independent claim 1, which has a high noise attenuation compared with the flow resistance of the gas through the muffler with passive means.

SOLUTION

According to the invention this object is achieved by a silencer having the features of independent claim 1. Preferred embodiments of the new silencer are described in the dependent claims 2 to 12. The dependent claim 13 relates to preferred uses of the new silencer.

DESCRIPTION OF THE INVENTION

In a silencer according to the invention, a Helmholtz resonator is formed in the gas channel, which is excited in the gas channel by means of at least one helical installation in a gas channel through which a gas flows, the installation an inner region of the gas channel spread the gas channel flowing gas. With the help of one or more helical internals in the gas channel, it is possible to form therein a Helmholtz resonator, which is indeed permeable by gas with relatively low flow resistance, but which is able to a considerable extent of energy in the flowing gas Extract propagating sound waves. As a result, these sound waves are strongly attenuated, without greatly throttling the gas flow. This is because it is possible by means of the one or more helical internals to form impedance jumps for the sound waves, without affecting the gas flow to the extent as by an impedance jump, which is achieved (alone) by a change in diameter of the gas channel.

Specifically, in the new muffler for forming a Helmholtz resonator, a cavity in the flow direction of the gas is limited by opposing impedance jumps for the propagating in the gas sound waves. In each such cavity energy is trapped by a continuous sound wave whose wavelength matches the length of the cavity, i. H. to which the Helmholtz resonator is tuned.

In the cavity of the Helmholtz resonator, the gas channel can be free, ie have no helical installation. In the cavity, however, the muffler may also have another helical installation adjacent thereto or other characteristics of the helical installation adjacent thereto. Thus, the opposing impedance jumps for limiting the cavity of the Helmholtz resonator can be set not only by the termination and resumption of helical installation on both sides of the cavity, but also by opposing changes in the pitch and / or diameter of the at least one helical installation.

Specifically, the at least one helical installation, including a wall of the gas channel surrounding it, can have at least two local constrictions or at least one local expansion. A constriction has - acoustically speaking - the effect of an inertial mass whose impedance becomes very high for high frequencies. In particular, the high frequencies are not allowed to pass through such a constriction. Between two such constrictions, a Helmholtz resonator is formed according to the invention. In comparison to a conventional Helmholtz resonator, the helical installation causes a reduced power dissipation of the gas flowing through the constrictions, by passing the gas through the constriction, thus preventing, in particular, turbulent turbulence of the gas behind the constriction. An expansion, on the other hand, acts like a spring, so it is very high-impedance at low frequencies. Here, the helical installation prevents turbulence associated with loss of the gas flowing into the expansion. A Helmholtz resonator can already be formed within such an expansion between its flanks.

The gas channel of the new muffler may have a circular cross-sectional area which is spanned by the at least one helical installation with a two-flighted helix. In the case of a circular cross-sectional area of the gas channel, a single helix for the formation of the helical installation is generally inadequate, since it leaves a passage region for sound waves near its axis, which is virtually uninfluenced by it.

However, if the gas channel has an annular cross-sectional area, it is sufficient if it is spanned by the helical installation with at least one helical coil.

In the new muffler also several gas channels may be provided, to which the flowing gas is divided. In this case, one of these gas passages may have a circular cross-sectional area and another of these gas passages may have an annular cross-sectional area lying around it.

Helmholtz resonators are typically formed by means of helical internals in all of these gas channels of the new silencer.

In a particularly preferred embodiment of the new silencer this is designed as a two-circuit resonant absorber, in which in two gas ducts, on which the flowing

Gas is distributed, on the same frequencies of stimulating sound waves tuned Helmholtz resonators are provided, of which the one or more Helmholtz resonators are designed in the one gas channel as an acoustic parallel circuit and the Helmholtz or the resonators in the other gas channel as an acoustic series circuit. Thus, a two-circuit resonant absorber, as he basically already from the DE 195 33 623 B4 is known, for the first time in a gas-flow system application in which the gas flows through the Helmholtz resonators themselves.

In principle, a plurality of Helmholtz resonators can also be formed one behind the other in a gas channel. This is preferred, for example, to attenuate sound waves with a particularly disturbing main sound frequency as completely as possible. In this case, all or at least several of the Helmholtz resonators arranged one behind the other are then to be matched to precisely this main sound frequency. In principle, Helmholtz resonators connected in series can also be tuned to different frequencies, whereby in turn for each frequency a plurality of Helmholtz resonators can be provided.

In addition, it is in principle possible that the at least one helical installation of the new silencer is actively deformable. On the one hand, this active deformability can be used to detune a Helmholtz resonator formed by means of the helical installation. In addition, in the quasistatic range it is possible to vary the impedance jumps occurring at the helical installation. However, active generation of antisound by active dynamic deformation of the helical assembly is also possible to provide an actively sound-attenuating effect in addition to the passive-absorbing function of the Helmholtz resonators.

While it makes sense to limit the cavity of a Helmholtz resonator in the new muffler as sudden as possible to change the impedance for the propagating in the gas flowing sound waves, the sound waves at the ends, especially at the entrance of the new muffler should not reflect unnecessary become. A reflection-poor, soft impedance transition is achieved in the muffler according to the invention in that the helical installation has at least one end of the muffler an inlet or outlet region by its diameter in the flow direction of the gas steadily approaches from the inside to the wall of the gas channel or removed from this. The sound waves thus reach almost completely into the new silencer and are then selectively absorbed there.

Applications for the new silencer are available for all gas-flow pipes, where the gas leads unsteady pressure fluctuations and in particular sound waves. Such tubes exist in internal combustion engines, heaters, such as for the exhaust air of a burner, ventilation systems and the like. In particular, the new muffler can be used advantageously when the sound waves or unsteady pressure fluctuations have a fixed frequency to which the Helmholtz resonator is tunable.

Advantageous developments of the invention will become apparent from the claims, the description and the drawings.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

zeigt einen ersten erfindungsgemäßen Schalldämpfer, bei dem zwei Helmholtz-Resonatoren, die auf gleiche Frequenzen abgestimmt sind, in einem durchströmten Gaskanal ausgebildet sind und dessen Enden für Schallwellen reflexionsarm gestaltet sind.

Fig. 2

zeigt einen erfindungsgemäßen Schalldämpfer, bei dem nur ein Helmholtz-Resonator in einem durchströmten Gaskanal ausgebildet ist. Auch hier sind die Enden des Schalldämpfers für Schallwellen reflexionsarm gestaltet.

Fig. 3

zeigt eine Abwandlung des erfindungsgemäßen Schalldämpfers gemäß Fig. 1, bei der die beiden endseitigen helikalen Einbauten größere Windungszahlen aufweisen als bei der Ausführungsform gemäß Fig. 1.

Fig.4

zeigt eine Abwandlung des erfindungsgemäßen Schalldämpfers gemäß den Fig. 1 und 3, bei der die endseitigen helikalen Einbauten und der zentrale helikale Einbau in den Gaskanal stark unterschiedliche Steigungen aufweisen.

Fig. 5

zeigt eine Abwandlung des erfindungsgemäßen Schalldämpfers gemäß den Fig. 1 und 3, bei der drei Helmholtz-Resonatoren, die auf gleiche Frequenzen abgestimmt sind, hintereinander in dem Gaskanal ausgebildet sind.

Fig. 6

zeigt eine Abwandlung des erfindungsgemäßen Schalldämpfers gemäß den Fig. 1 und 3, bei dem vier Helmholtz- Resonatoren, die auf gleiche Frequenzen abgestimmt sind, hintereinander in dem Gaskanal ausgebildet sind.

Fig. 7

zeigt eineen Schalldämpfer, bei dem insgesamt sechs Helmholtz- Resonatoren hintereinander in dem Gaskanal ausgebildet sind. Anders als bei den erfindungsgemäßen Schalldämpfern weisen die endseitigen helikalen Einbauten bei dieser Ausführungsform keine Einlauf- bzw. Auslaufbereiche mit geringer Schallreflexion auf.

Fig. 8

zeigt einen erfindungsgemäßen Schalldämpfer, bei dem zwei Helmholtz-Resonatoren durch drei Einschnürungen eines helikalen Einbaus in den Gaskanal samt der Wandung des Gaskanals ausgebildet ist.

Fig. 9

zeigt eine Ausführungsform des erfindungsgemäßen Schalldämpfers, bei dem ein Helmholtz-Resonator durch eine Ausweitung des Querschnitts des Gaskanals samt des darin vorgesehenen helikalen Einbaus ausgebildet ist.

Fig. 10

zeigt einen erfindungsgemäßen Schalldämpfer mit einer Reihenschaltung eines Helmholtz-Resonators gemäß Fig. 8, eines Helmholtz-Resonators gemäß Fig. 9 und eines weiteren Helmholtz-Resonators gemäß Fig. 8, wobei die Einschnürungen und die Aufweitung weniger stark ausgeprägt sind als in den vorangehenden Fig. 8 und 9.

Fig. 11

zeigt einen Schalldämpfer, bei dem das strömende Gas auf zwei Gaskanäle aufgeteilt wird, in denen jeweils ein Helmholtz-Resonator ausgebildet ist, die auf gleiche Resonanzfrequenz abgestimmt sind, von denen aber der eine als akustischer Parallelkreis und der andere als akustischer Serienkreis ausgebildet ist.

Fig. 12

zeigt einen Schalldämpfer, bei der in Abwandlung gegenüber Fig. 11 in dem einen Gaskanal mehrere, aber ebenfalls auf dieselbe Resonanzfrequenz abgestimmte Helmholtz-Resonatoren hintereinander vorgesehen sind.

The invention will be explained in more detail below with reference to preferred embodiments with reference to the accompanying figures and described. In all figures, a silencer is shown in a perspective side view with cut-wall of a gas channel in each case.

Fig. 1

shows a first muffler according to the invention, in which two Helmholtz resonators, which are tuned to the same frequencies, are formed in a flow-through gas channel and the ends are designed for reflection of sound waves.

Fig. 2

shows a silencer according to the invention, in which only a Helmholtz resonator is formed in a gas channel through which flows. Again, the ends of the muffler for sound waves are designed to be low reflection.

Fig. 3

shows a modification of the silencer according to the invention according to Fig. 1 in which the two end-side helical internals have larger numbers of turns than in the embodiment according to FIG Fig. 1 ,

Figure 4

shows a modification of the silencer according to the invention according to the Fig. 1 and 3 , in which the end-side helical internals and the central helical incorporation into the gas channel have very different slopes.

Fig. 5

shows a modification of the silencer according to the invention according to the Fig. 1 and 3 in which three Helmholtz resonators, which are tuned to equal frequencies, are formed one behind the other in the gas channel.

Fig. 6

shows a modification of the silencer according to the invention according to the Fig. 1 and 3 in which four Helmholtz resonators, which are tuned to the same frequencies, are formed one behind the other in the gas channel.

Fig. 7

shows a muffler, in which a total of six Helmholtz resonators are formed one behind the other in the gas channel. Unlike the silencers according to the invention, the end-side helical internals in this embodiment have no inlet or outlet areas with low sound reflection.

Fig. 8

shows a silencer according to the invention, in which two Helmholtz resonators is formed by three constrictions of a helical installation in the gas duct, including the wall of the gas channel.

Fig. 9

shows an embodiment of the muffler according to the invention, in which a Helmholtz resonator is formed by an expansion of the cross section of the gas channel, including the provided therein helical installation.

Fig. 10

shows a silencer according to the invention with a series circuit of a Helmholtz resonator according to Fig. 8 , a Helmholtz resonator according to Fig. 9 and another Helmholtz resonator according to Fig. 8 , wherein the constrictions and the expansion are less pronounced than in the preceding Fig. 8 and 9 ,

Fig. 11

shows a muffler, in which the flowing gas is divided into two gas channels, in each of which a Helmholtz resonator is formed, which are tuned to the same resonant frequency, but one of which is designed as an acoustic parallel circuit and the other as an acoustic series circuit.

Fig. 12

shows a muffler, when compared to Fig. 11 in which one gas channel several, but also tuned to the same resonant frequency Helmholtz resonators are provided one behind the other.

DESCRIPTION OF THE FIGURES

An in Fig. 1 sketched muffler 1 has in a tube 2 with a wall 3 three helical internals 4, 5 and 6. In this case, the helical installation 5 lies between the end-side helical internals 4 and 6 and has a same free distance 7 in the direction of the tube axis 8 of the tube 2 for each of these. Each of the helical internals 4-6 consists of a twinned helix 9 twisted around the tube axis 8. At the ends of the muffler, the diameter of the double-flighted helix 9 of the end helical internals 4 and 6 steadily increases from zero to the diameter of the tube 2. Wherever the two-start helix 9 has the diameter of the tube 2, it is firmly mounted on the wall 3. As a result, the distances 7 are fixed. The double-flighted helices 9 impart a helical course to an inner region 10 of a gas channel 11 leading through the tube 2 and bounded by the wall 3 thereof. In this case, each of the double-flighted helices 9 delimits two helically extending part inner regions 12 of the gas channel 8 from one another. For a gas flow along the tube axis 8 through the gas channel 11 mean the helical internals 4-6, although an increase in the flow resistance. However, this increase in the flow resistance is relatively small. For spreading in the flowing gas Sound waves mean that the helical internals 4-6, however, a strong variation of the impedance. This variation is continuous at the ends of the muffler 1 due to the continuously changing diameters of the double-flighted helices. However, where the helical internals 4-6 abruptly terminate, ie on both sides of both distances 7, impedance jumps occur. In this way, two Helmholtz resonators 13 are formed in the muffler 1, the cavities or cavities 14 correspond to the free pipe cross section along the distances 7. Both Helmholtz resonators 13 are tuned by the same distances 7 to the same frequencies, which is a main sound frequency, which occurs in the gas flowing through the gas channel 11 gas. Sound waves with this main sound frequency is deprived of energy by the Helmholtz resonators 13, which is ultimately converted into heat. This is done in comparison to the efficiency of the sound attenuation only minimal impairment of the gas flow, ie with minimal flow resistance for the flowing gas.

The embodiment of the muffler 1 according to Fig. 2 differs from the one according to Fig. 1 in that only one Helmholtz resonator 13 is formed, in which no additional helical installation between the helical internals 4 and 6 is provided. In addition, the geometric relationships in the helical internals 4 and 6 are different than in Fig. 1 in that their numbers of turns are greater and the end-side inlet or outlet areas in which the diameter of the double-flighted helices 9 continuously widens from zero to the diameter of the tube 2 are stretched longer. The frequency to which the respective muffler 1 is tuned depends essentially on the length of the cavity 14 of its Helmholtz resonators 13, ie on the distance 7. This length must be adjusted so that waves standing here with the wavelength of the can train interesting main sound frequency. That is, it depends not only on the geometric distance 7 but also on the speed of sound propagation within the gas channel 10 and thus on the gas guided therefrom and its state.

The muffler 1 according to Fig. 3 is again essentially the same Fig. 1 , ie there is again an additional helical installation 5 available. However, the geometric data of the muffler 1 are opposite Fig. 1 varied.

The muffler 1 according to Fig. 4 differs from those according to the Fig. 1 and 3 again by its geometric dimensions. While so far all two-stringed Helices 9 in the helical internals 4 to 6 had the same slope, here in the helical installation 5 a strongly deviating upward slope is provided. In this way, a further Helmholtz resonator 15 may be formed, the cavity of which extends along the helical partial inner regions 12 in the region of the helical installation 5. In principle, the formation of such a further Helmholtz resonator 15 is conceivable in all helical installations 4-6. However, the attenuation within the helical internals 4-6 at a smaller pitch of the double-flighted helices 9 for the formation of an effective resonator is quickly too large. In the case of the end-side helical internals 4 and 6 shown so far, the function as a Helmholtz resonator is also hindered by the outgoing diameter of the double-flighted helices 9, because this means a flowing impedance transition and no impedance jump. A flowing impedance transition does not reflect sound waves in the gas within the gas channel 11 and is therefore unsuitable for limiting the cavity of a Helmholtz resonator. In the case of the silencer 1, this flowing transition serves specifically to allow the sound waves initially to enter the silencer 1 unhindered, in order then to absorb them there.

The muffler 1 according to Fig. 5 shows again in all helical internals 4-6 equal slopes of the double-flighted helices 9. However, two helical internals 5 are now provided between the end-side helical internals 4 and 6. Also between these helical internals 5 is the same distance 7 as before to the helical internals 4 and 6. Accordingly, three Helmholtz resonators 13 are formed here. Depending on the configuration of the helical internals 5, additional Helmholtz resonators 15 (not shown here) may in principle also be formed in their regions.

The muffler 1 according to Fig. 6 has yet another central helical installation 5, so that a total of four Helmholtz resonators 13 are formed between the helical internals 4-6. In addition, here the pitch of the double-flighted helices 9 of the helical internals 5 is significantly smaller than in the case of the double-flighted helices 9 of the end-side helical internals 4 and 6.

Fig. 7 shows a muffler 1, in which on the one hand by means of a total of five central helical internals 5 between the end-side helical internals 4 and 6 six Helmholtz resonators over the free distances 7 are formed, and in the other end of the helical internals 4 and 6 abrupt, ie with full diameter of its double-flighted Helices 9 end. In this way, an impedance jump is formed at the ends of the muffler 1. Accordingly, an additional Helmholtz resonator 15 can also be formed here within each helical installation 4-6.

Fig. 8 outlined a muffler 1, in the tube 2 only a single helical installation 4 is provided. This helical installation 4 runs at both ends of the muffler 1 with the tube axis 8 steadily decreasing diameter of its double-flighted helix 9 in order to form reflection-free transitions there. To form two Helmholtz resonators 16, the helical installation 4 and the tube 2 have three common constrictions 17. The constrictions act acoustically like sluggish masses whose impedance becomes very high for high frequencies, so that the high-frequency sound waves are reflected between them.

In the silencer 1 according to Fig. 9 have the tube 2 and the helical installation 4 instead of the constrictions 17 according to Fig. 8 an expansion 19 for forming a Helmholtz resonator 18 between the flanks 20 on. The whole expansion 19 also acts like a spring.

In the embodiment of the muffler 1 according to Fig. 10 are constrictions 17 according to Fig. 8 and the expansion 19 according to Fig. 9 combined to form various Helmholtz resonators 16 and 18.

With the mufflers 1 according to the FIGS. 11 and 12 that will basically come from the DE 195 33 623 B4 known principle of a dual-circuit resonant absorber with an acoustic series circuit and an acoustic parallel circuit applied to a muffler for a flowing gas. For this purpose, the gas is divided into two gas channels 21 and 22, wherein the gas channel 21 is an annular channel which extends between the tube 2 and an inner tube 23, while the gas channel 22 extends through the inner tube 23. The inner regions 24 and 25 of the gas channels 21 and 22 are here each formed by helical internals 26 and 27 to screw flights. In this case, only the helical internals 27 in the inner tube 23 are necessarily double-flighted helices9. The helical internals 6 in the annular gas channel 21 may also be single helices, as shown here. With the helical internals 26 and 27, Helmholtz resonators 28 and 29 are formed in both gas channels 21 and 22, but here the order of helical internals 26 and 27 and their free distances between the gas channels 21 and 22 is reversed. D. h., At the ends of the gas channel 21 are helical internals and at the ends of the gas channel 22 are free spaces. The acoustic parallel circuit forms the gas channel 22, which has the end-side free spaces. These form acoustic springs, while the helical internals 26 and 27 correspond to acoustic masses. In the two-band resonator absorbers outlined, a particularly high absorption power is achieved at the main sound frequency, to which the individual Helmholtz resonators 28 and 29 are tuned. The two embodiments of the muffler according to the FIGS. 11 and 12 differ by the geometric structure of the helical internals 26 and 27th

LIST OF REFERENCE NUMBERS

1

silencer

2

pipe

3

wall

4

helical installation

5

helical installation

6

helical installation

7

distance

8th

pipe axis

9

double-flighted helix

10

Interior of the gas channel 11

11

gas channel

12

divisions

13

Helmholtz resonator

14

cavity

15

Helmholtz resonator

16

Helmholtz resonator

17

constriction

18

Helmholtz resonator

19

widening

20

flank

21

gas channel

22

gas channel

23

inner tube

24

Interior of the gas channel 11 without the inner region of the inner tube 23rd

25

Inner region of the inner tube 23

26

helical installation

27

helical installation

28

Helmholtz resonator

29

Helmholtz resonator

Claims (13)

1. Sound absorber (1) for sound waves propagating in a flowing gas, comprising at least one gas channel (11, 21, 22) through which a gas flows and in which a helical fixture (4-6, 26, 27) is provided which gives an interior (10, 24, 25) of the gas channel (11) a helical course, characterized in that by means of at least one helical fixture (4-6, 26, 27) a Helmholtz resonator (13, 15, 16, 18, 28, 29) is formed in the gas channel (11) which comprises a cavity (14) delimited, in the flow direction of the gas, by opposite impedance steps for the sound waves propagating in the gas, and which is excited by the sound waves propagating in the flowing gas such that energy of a passing sound wave whose wave lengths fits to the length of the cavity is captured, and that the helical fixture (4), at at least one end of the sound absorber (1), comprises an intake or discharge area in which its diameter in the flow direction of the gas continuously approaches the wall (3) of the gas channel (11) from the interior or gets away from it.
2. Sound absorber (1) according to claim 1, characterized in that the opposite impedance steps are provided by opposite changes of the pitch and/or of the diameter of the at least one helical fixture (4-6, 26, 27).
3. Sound absorber (1) according to claim 2, characterized in that the at least one helical fixture (4) including a wall (3) of the gas channel (11) enclosing it comprises at least one local contraction (17) or expansion (19).
4. Sound absorber (1) according to claim 1, characterized in that no helical fixture is arranged in the cavity (14).
5. Sound absorber (1) according to at least one of the preceding claims, characterized in that the gas channel (11, 12) comprises a circular cross-sectional area which is spanned by the at least one helical fixture (4-6, 27) by means of a double helix (9).
6. Sound absorber (1) according to at least one of the preceding claims 1 to 5, characterized in that the gas channel (21) comprises a ring-shaped cross-sectional area which is spanned by the helical fixture (27) by means of at least one helix.
7. Sound absorber (1) according to at least one of the preceding claims, characterized in that several gas channels (21, 22) are provided, over which the flowing gas is distributed.
8. Sound absorber (1) according to claim 7, characterized in that in all gas channel (21, 22) Helmholtz resonators (28, 29) are formed by means of helical fixtures (26, 27).
9. Sound absorber (1) according to claim 8, characterized in that in all gas channels (21, 22) Helmholtz resonators (28, 29) tuned to a same frequency of the exciting sound waves are provided at least one of which being designed as an acoustic parallel circuit and one as an acoustic series circuit.
10. Sound absorber (1) according to at least one of the preceding claims, characterized in that in the gas channel (11, 21, 22) several Helmholtz resonators (13, 15, 16, 18, 28, 29) are provided one behind the other.
11. Sound absorber (1) according to claim 10, characterized in that the several Helmholtz resonators (13, 15, 16, 18, 28, 29) are all tuned to a single main sound frequency or a few discrete main sound frequencies.
12. Sound absorber (1) according to at least one of the preceding claims, characterized in that the at least one helical fixture (4-6, 26, 27) is actively deformable, particularly due to the integration of functional materials.
13. Tube (2) with gas flowing there through, particularly in a combustion engine, a heating or a ventilation system, comprising a sound absorber (1) according to any of the claims 1 to 12.

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