EP0072274A1 - Reactive silencer or sound attenuator for a pulsating gas flow - Google Patents

Abstract

1. A reactive sound attenuator or silencer, i.e. a reflection or sound wave echo attenuator or silencer, for a pulsed flow-rate of gas submitted to mean and high frequencies, namely of about 300 to 8000 Hz, characterized by a system of several identical sets (1, 2, 3, 4, 5, 6, 7, 8) disposed in parallel, connected with at least an inlet collector (34) and/or an exhaust collector (35), each of the sets being composed of a succession of expansion rooms (1, 2, 3) of different dimensions connected by an axial duct (4, 5, 6), each of the rooms having such dimensions that it is accorded for a field of frequency to be attenuated, whereas the joining ducts (4, 5, 6) have a weak cross-section with respect to the one of the rooms, the system of several sets of rooms (1, 2, 3) connected with ducts (4, 5, 6) being carried out in order that the lenghts of the rooms and ducts are determined so that it can be provided an alveolar imbrication of the elements which are staggered the one with respect to the other in order that the rooms reach the level with the ducts of the adjacent sets and inversely, so as to circumscribe said system in the minimal volume.

Description

Technical area.

The present invention relates to a silencer or attenuator of its reactive sound, that is to say with reflection or echo of sound wave, for pulsed flow of gas subjected to medium and high frequencies, namely from approximately 300 to 8000 Hz.

Problem.

Many machines use or process gases by giving them impulses which are almost always in the sound domain and cause nuisance. This is why, it has been brought for a long time to join to these machines silencers or attenuators of sound which it is necessary to make the most effective possible in the attenuation of the sound by altering as little as possible the output of the machine.

This problem is frequently encountered in heat engines and also in compressors.

The invention proposes to solve it although, as we will see, this has been a concern for many technicians for decades. These technicians had to resolve the elimination of medium and high frequencies ranging between 300 and ô 000 Hz.

State of the prior art and drawbacks.

• La première catégorie concerne les silencieux passifs contenant des matières isolantes et absorbantes. - les silencieux actifs ou réactifs à chicane et à chambre ne comportant pas de matières absorbantes.

Existing silencers can be divided into two main categories:

• The first category concerns passive silencers containing insulating and absorbent materials. - active or reactive mufflers with baffles and chambers that do not contain absorbent materials.

So in the mufflers resting on the principle of absorption noise absorption (passive silencer), the gases are supplied by means of tubes which have holes at the periphery through which the sound wave can exit while being distributed uniformly and is damped up to a certain point by absorbent which surrounds these tubes. These absorption mufflers are used in particular as main mufflers to dampen a wide range of noise. However, they have the disadvantage of being bulky because it is necessary to 'give the tubes which have holes a relatively large section to limit the speed of passage of gases to avoid entrainment of absorbent materials which causes pollution gas and deterioration of the muffler.

In addition to these absorption or passive sound absorbers, there are reflection or baffle absorbers that operate on an active principle where the sound waves are reflected by attenuating the posterior waves. We know that to be able to use the principle of these so-called reflection silencers, the acoustic waves must propagate in plane waves. In these silencers, conduits are provided which bring the gases into chambers or reflection spaces from which the gases can escape in order to flow more regularly with a strongly attenuated sound energy. The principle used for the sound absorbers by reflection rests on the fact that the sound is reduced thanks to modifications of section and changes of direction. Due to the varied reactance encountered in each of the elements, there is an attenuation of the sound energy. For large gas flows, the muffler section is such that only low frequencies can be processed.

The principle of these silencers is illustrated in Figures 1 to 6, of the accompanying drawings.

In Figure 1 of these drawings there is shown a chamber of section S, of length 1, which is connected to two conduits of section s. It is recognized that such a chamber can absorb sound waves whose wavelength is in relation to the length 1 and corresponds to a frequency f ₁ . The attenuation efficiency is a function of the expansion ratio, that is to say the ratio of the S / s sections. We immediately understand that it is advantageous to have a relatively small section s to limit the size of the chamber but that, on the other hand, the flow rate of the device is limited.

It is assumed that the chamber has a relatively large length 1 to attenuate a relatively small frequency f ₁ .

To widen the bandwidth, one can mount in series (Figures 3 and 4) two chambers, the second chamber having a length 1 ₂ shorter than 1 ₁ so that the frequencies are attenuated according to the spectrum which is shown in the Figure 4 where, as in Figure 2, there is shown on the ordinate the attenuation in dB and on the abscissa, the attenuated frequency. The lower (300 Hz) and upper (5,000 Hz) limits between which the device must be effective have also been shown.

Following the same resonance, we can adopt the basic principle which is represented in FIGS. 5 and 6, by adding a third chamber which has a length 1 ₃ shorter than the length 1 ₂ and which absorbs frequencies f ₃ greater than f ₂ . The damped frequency spectrum is shown in Figure ^- 6 which can be commented on in the same way as what was done for Figure 2.

This theoretical arrangement leads to adopt a bulky construction of the sound damper to obtain the same damping properties as with a shock absorber by absoption, which results in a greater expenditure of materials and therefore makes the dampers more expensive by reflection known so far.

The problem therefore comes down to obtaining the largest possible S / s ratio, the number of chambers of different dimensions in series as large as possible and, however, limiting the pressure losses and the bulk, all this by reducing the price of returns from the device.

This is the aim which the present invention proposes to achieve.

It should be noted that an improvement consists in providing tapered chamber bottoms, as shown in dotted lines in FIG. 1, in order to reduce the pressure losses without however affecting efficiency.

Statement of the invention.

The silencer or sound attenuator of the invention is characterized by a system of several identical assemblies arranged in parallel, connected to at least one intake manifold and / or one exhaust manifold, each of the assemblies being constituted by a succession of expansion chambers of different dimensions connected by an axial duct, each of the chambers having dimensions such as it is granted for a frequency domain to be attenuated while that the connecting conduits have a small cross section relative to the cross section of the chambers.

Said chambers can be prismatic and / or cylindrical and their section depends on the upper frequency limit which can be attenuated while their length depends on the frequency range which can be obtained, it being understood that these latter frequencies are below the upper limit of frequencies to be processed. If they are cylindrical, they are preferably of revolution with frustoconical bottoms adapting to axial tubular conduits.

A very important characteristic of the invention resides in the fact that a system of several sets of chambers connected by conduits is produced, a system in which the lengths of the chambers and of the conduits are determined so that an alveolar nesting can be ensured elements which are offset from each other so that the chambers are placed at the level of the conduits of the adjacent assemblies and vice versa, so that the system occupies the minimum volume.

To practically manufacture these systems, there are two main solutions.

The first consists in making the silencer by sections perpendicular to the axis of the conduits and that said sections are assembled by known means in order to constitute a sound-absorbing block. In this case, the sound-absorbing block can be either prismatic, generally parallelepipedic, or cylindrical.

The second consists in making the silencer by identical plane elements, in the form of composite plates. as each recessed, on their two faces, of the complementary parts of the assemblies connected by conduits, said complementary parts being arranged to adapt exactly to the corresponding parts of the adjacent planar elements to reconstitute the system of sets of chambers and conduits by means of assembly and relative positioning. It is more convenient for the planar elements to have, in hollow, on each of their faces, a half of each assembly constituted by a section of the chambers and conduits along a diametral plane thereof, said elements comprising means of assembly by tie rods ensuring juxtaposition and tightening to thus form a sound-absorbing parallelepiped block.

Preferably, the intake and exhaust manifolds are constituted by boxes respectively covering the inputs and outputs of the sound-absorbing block. To make said boxes in a simple way, an elongated box is provided in the central part of which there is the sound-absorbing block, leaving upstream and downstream two chambers serving as collectors having a relatively large length for processing and damping the low frequencies. .

This elongated box generally serves as a base for the machine producing the sound pulses of gas.

Solution to the problem, advantages and industrial result.

The realization of the invention allows a great efficiency of the silencers since the S / s ratio is important and that the disadvantage of a small section s is avoided by arranging in parallel a large number of sets equivalent. The diameter of the elementary silencers is calculated to allow propagation in plane waves up to high frequencies, 8000 Hz for example. It is possible to extend this limit at high frequencies by using elementary silencers of smaller diameters.

The nesting of the different chambers and conduits has made it possible to considerably reduce the overall dimensions. It should be noted that all of the conduits and chambers have the same length whatever the flow rate to pass since this flow rate can vary by multiplying the number of attached sets. In practice, mufflers are obtained which are two to ten times shorter, for the same efficiency, than the device simply applying the theoretical principle.

As the passive silencer principle is not used by the presence of absorbent products, higher passage speeds can be adopted in the assemblies without the risk of entraining this absorbent material. This improves the longevity of the silencer and the purity of the gas leaving the device.

It should be noted that this device makes it possible to process high frequencies since it is possible to reduce the length of the chambers in a simple manner. Finally, the cost price is considerably reduced, above all, as we have seen if the device is integrated into the base of the device.

The invention will be better understood with the aid of the description below which gives some nonlimiting examples of practical embodiment and which are illustrated by the accompanying drawings.

Brief description of the figures.

• La figure 1 est une vue schématique d'une chambre d'un silencieux actif ou à réflexion.
• La figure 2 est un graphique montrant comment le son est atténué par le dispositif de la figure 1.
• La figure 3 représente schématiquement un silencieux actif à deux chambres en série traitant des fréquences différentes.
• La figure 4 est un graphique montrant l'évolution de l'atténuation du son du silencieux schématisé à la figure 3.
• La figure 5 est une troisième version du silencieux à trois chambres successives pour traiter trois zones de fréquences f_l, f₂, f₃, les chambres ayant des longueurs allant en diminuant l, 12, 1₃.
• La figure 6 est le graphique représentant l'atténuation du son relative au dispositif schématisé à la figure 5.
• La figure 7 est une vue en perspective d'un bloc amortisseur parallélépipèdique avec une coupe médiane représentant la répartition imbriquée de façon alvéolaire des différents conduits et chambres.
• La figure 8 est une coupe transversale verticale d'un élément en forme de plaques longitudinales.
• La figure 9 est une coupe suivant un plan longitudinal, d'un élément transversal susceptible de réaliser le bloc amortisseur de la figure 7 suivant une autre version.
• La figure 10 est une vue en élévation d'un élément transversal, similaire à celui de la figure 9, destiné à constituer un bloc amortisseur cylindrique à section circulaire.
• La figure 11 est une vue éclatée d'un caisson allongé servant de socle à la machine produisant les pulsations sonores de gaz, et contenant le bloc amortisseur de son de l'invention.
• La figure 12 est une vue de profil du caisson de la figure 11 qui est alors assemblé. Description de quelques modes de réalisation.

In these drawings:

• Figure 1 is a schematic view of a chamber of an active silencer or reflection.
• Figure 2 is a graph showing how the sound is attenuated by the device in Figure 1.
• FIG. 3 schematically represents an active silencer with two chambers in series processing different frequencies.
• FIG. 4 is a graph showing the evolution of the attenuation of the sound of the silencer shown diagrammatically in FIG. 3.
• FIG. 5 is a third version of the silencer with three successive chambers for treating three zones of frequencies f _l , f ₂ , f ₃ , the chambers having lengths decreasing l, 12, 1 ₃ .
• FIG. 6 is the graph representing the attenuation of the sound relating to the device shown diagrammatically in FIG. 5.
• FIG. 7 is a perspective view of a parallelepipedal damping block with a median section representing the nested cellular distribution of the various conduits and chambers.
• Figure 8 is a vertical cross section of an element in the form of longitudinal plates.
• Figure 9 is a section along a longitudinal plane, of a transverse element capable of producing the damper block of Figure 7 according to another version.
• FIG. 10 is an elevation view of a transverse element, similar to that of FIG. 9, intended to constitute a cylindrical damping block with circular section.
• FIG. 11 is an exploded view of an elongated box serving as a base for the machine producing the sound pulsations of gas, and containing the sound-absorbing block of the invention.
• Figure 12 is a side view of the box of Figure 11 which is then assembled. Description of some embodiments.

Referring to Figure 7, we recognize the different assemblies composed of a large chamber (1), a medium chamber (2) and a small chamber (3), these chambers being connected by conduits (4 ), (5), (6) and preceded by intake (7) and exhaust (8) ducts.

The chamber (1) has a length 1 ₁ ; the chamber (2) has a length 1 ₂ ; the chamber (3) has a length 1 ₃ .

The sections of these rooms are identical.

The ends of these chambers are connected to the conduits (4), (5), (6) by frustoconical parts such as (9) which improve the flow of gases and therefore the efficiency. These rooms are therefore identical.

Still in FIG. 7, other assemblies 1a to 8a have been shown which are staggered relative to the assembly (1) to (b) in order to achieve a rigorous nesting of the various assemblies. Note in particular that the conduit ( ¹ 4) has the same length as the chamber (la) while the conduit (5a) has the same length as the chamber (1) and the conduit (5) has the same length as the chamber (2a), that the conduit (6a) has the same length as the chamber (2) and that the chambers (3a) and (3) have the same length. The conduits (7) and (7a), in the same way as the conduits (8) and (8a) have different lengths to make up for the offset between the two assemblies.

The other assemblies are arranged in the same way as the assemblies (1) to (8), on the one hand and (la) to (8a), on the other hand.

In a first version, the damping block (10) is parallelepipedic and is composed of planar elements (11) (Figure 8) which have in hollow on each of their faces a half of each set (1) to (8) and a half of each set (la) to (8a), these sets of chambers (1), (2), (3), (la), (2a), (3a) and conduits (4), (5), (6), (7), (8), (5a), (6a), (7a) and (8a) being cut along a diametrical plane.

These sets cut in hollow on the face (12), as just described above, are also cut in hollow on the face (13) but staggered staggered, as shown in FIG. 8, to gain maximum space.

The elements (11) also include positioning means (not shown) to each other and assembly which are generally threaded rods with nuts which pass through the notches (14), (15), (16 ), (17).

There are shown elements (11) which advantageously came from foundry. One can however imagine similar elements produced by stamping which then gives the chambers (1) to (3), (la) to (3a) and to the conduits (4) to (8) and (5a) to (8a) polygonal sections, preferably hexagonal like the cells of a honeycomb.

We have seen that the damping block (10) was parallelepiped. We can also achieve a similar result by constituting the block (10) by elements (18) which are placed transversely by performing a slicing of the block (10) as indicated by the joint planes (19) to ( 30). In this regard, and by way of simplification, FIG. 7 has brought together the two embodiments, one with elements (11) arranged longitudinally along the joint planes such as (31) and (32), and the other by transverse elements such as (18) with joint planes (19) to (30). In the latter case, longitudinal tie rods are used.

With this latter embodiment by transverse elements (18), it is also possible to use elements (181) (FIG. 10) which then have a circular section by staggered distribution of the sets of chambers and ducts as it is clearly represented in this same FIG. 10 .

Other embodiments can be imagined without departing from the scope of the invention. This would be, for example, of an embodiment by elements such as (18) with polygonal, oval section, etc.

Nevertheless, it is convenient to produce a parallelepiped damping block (10), particularly in the embodiment which will now be described and illustrated in FIGS. 11 and 12.

In this embodiment, the damping block (10) is placed in the central part of an elongated box (33) leaving, upstream, an intake manifold (34) and, downstream, an exhaust manifold (35). The collector (35) is moreover a chamber having a relatively large length for processing the low frequencies which are not processed in the damping block (10).

The box (33) is closed at both ends by U irons (37) and (38) which serve as feet for the assembly and whose upper wings (39) and (40) contribute to the fixing of a cover ( 41) which comprises a blocking element (42) of the block (10). It is also blocked by an angle iron (43) fixed to the bottom of the gutter (36). This gutter, decoupled from the box (33) by a viscoelastic product, serves as a double wall to reduce the acoustic radiation.

The admission of gases into the chamber (34) is through the hole (44) while the exhaust from the chamber (35) is through the exhaust tube (45) which also largely penetrates into overhang inside the exhaust collecting chamber (35). The gas path is also materialized by all the arrows in Figure 12.

There is a valve plug or an access hole (46) which can be plugged with a plate (not shown) which is fixed by the studs (47). Crossbars (48), (49), (50) are also provided which support the mechanics.

The box (33) is therefore massive and its inertia is considerably increased by the weight of the apparatus which rests on it. This contributes to the improvement of sound absorption.

Claims (10)

1. Silent or attenuator of its reactive sound, that is to say with reflection or echo of sound wave, for pulsed flow of gas subjected to medium and high frequencies, of approximately 300 to 8000 Hz, characterized by a system of several identical assemblies (1), (2), (3), (4), ((5), (6), (7), (8) arranged in parallel, connected to at least one intake manifold (34) and / or an exhaust manifold (35), each of the assemblies being constituted by a succession of expansion chambers (1), (2), (3) of different dimensions connected by an axial duct (4), (5), (6), each of the chambers (1), (2), (3) having dimensions such as it is granted for a frequency domain to be attenuated while the connecting conduits (4), (5 ), (6) have a small section compared to the section of the chambers, the system of several sets of chambers (1), (2), (3) connected by conduits (4), (5), (6) being designed so that the lengths of the chambers and conduits are determined so that one can Use a cellular nesting of elements which are offset from one another so that the chambers are placed at the level of the conduits of the adjacent assemblies and vice versa, in order to circumscribe said system in the minimum volume. 2. Silent, as defined in claim 1, characterized in that the chambers (1), (2), (3) are prismatic and that their section depends on the upper limit of frequencies capable of being attenuated , while their length depends on the domain of frequencies likely to be attenuated, it being understood that these latter frequencies are below the upper limit of frequencies to be processed. 3. Silencer, as defined in claim 1, characterized in that the chambers (1), (2), (3) are cylindrical, of revolution, with tapered bottoms (9) adapting to axial conduits tubular (4), (5), (6). 4. Silencer, as defined in the preceding claims, characterized in that it is produced by sections (18) perpendicular to the axis of the conduits (4), (5), (6) and that said sections are assembled by known means in order to constitute a sound damping block (10). 5. Silent, as defined in claim 4, characterized in that the sound-absorbing block (la) is prismatic, generally parallelepipedic. 6. Silencer, as defined in claim 4, characterized in that the sound-absorbing block (la) is cylindrical. 7. silencer, as defined in any one of claims 1 to 3, characterized in that it is produced by identical plane elements (11), in the form of plates each having a hollow, on their two faces (12 ), (13), complementary parts of the assemblies connected by conduits (4), (5), (6), said complementary parts being arranged to adapt exactly to the corresponding parts of the planar elements adjacent to reconstruct the system of sets of chambers and conduits by means of assembly and relative positioning. 8. Silencer, as defined in claim 7, characterized in that the flat elements comprise, in hollow, on each of their faces (12), (13) one half of each assembly constituted by a section of the chambers (1 ), (2), (3) and conduits (4), (5), (6) along a diametral plane thereof, said elements (11) comprising means of assembly by tie rods ensuring the juxtaposition and the tightening to thereby constitute a sound-absorbing parallelepiped block. 9. Muffler, as defined in claim 7, characterized in that there is an elongated box (33) in the central part of which there is the sound damping block (10), leaving two upstream and downstream chambers (34), (35) serving as collectors having a relatively large length For processing and damping low frequencies. 10. Silent, such as defined in claim 9, characterized in that the elongated box (33) serves as a base for the machine producing the sound pulses of gas.

Images