Sound reducer

Abstract

Sound reducer (1), comprising - a main tube (10) in the interior of which a flow body (20) is arranged and fixed to the inner wall of the main tube (10) by means of struts (30; 130, 230) and - a ring chamber (40) which is connected to the interior of the main tube (10) via at least one first window (11) and is otherwise closed and surrounds the main tube (10), acting as a resonator chamber, wherein the main tube (10) comprises a first main tube axial section (110) and a second main tube axial section (210) and the flow body (20) comprises a first flow body axial section (120) and a second flow body axial section (220), characterized by that the first main tube axial section (110) together with the axially corresponding first flow body axial section (120) and a first set of struts (130) is formed in one piece as a first sound-reducing axial section (100) and the second main tube axial section (210) together with the axially corresponding second flow body axial section (220) and a second set of struts (230) is formed in one piece as a second sound-reducing axial section (200), wherein each of the two sound-reducing axial sections (100, 200) is manufactured as a separate component.

Description

Field of invention

[0001] The invention relates to a sound reducer comprising - a main pipe, inside of which a flow body is arranged and fixed to the inner wall of the main pipe by means of struts and - a ring chamber, otherwise closed and surrounding the main tube, which is sound-conducting and connected to the interior of the main tube via at least one first window and acts as a resonator chamber, wherein the main tube comprises a first main tube axial section and a second main tube axial section, and the flow body comprises a first flow body axial section and a second flow body axial section. State of the art

[0002] Such a sound reducer is known from GB 678 344 A.

[0003] Resonance-based noise reduction in fluid lines has long been known to those skilled in the art, for example from DE 10 2017 126 125 A1. In a noise reducer based on this principle, a (liquid or gaseous) fluid, in which sound waves propagate, flows through a main pipe. A larger diameter pipe section, usually arranged concentrically, surrounds the main pipe, creating an annular gap between this outer pipe and the inner pipe formed by the main pipe. End walls, tightly connected to the outer wall of the main pipe, are provided at the ends of the outer pipe, forming a closed annular chamber between the main and outer pipes. This annular chamber is connected to the interior of the main pipe, usually via one or more windows, in a fluid-conducting manner, but at least in a sound-conducting manner. For the sake of simplicity, this description refers to an "annular chamber surrounding the main pipe."However, those skilled in the art will understand that this does not imply a limitation to a single resonator chamber that is continuous in the circumferential direction and completely surrounds the main tube. It is entirely possible that the annular chamber only partially surrounds the main tube in the circumferential direction, that the annular chamber is subdivided into several circumferentially adjacent subchambers by internal axial walls, and / or that several axially adjacent annular chambers are provided. In any case, sound propagating in the main tube enters the annular chamber through the window(s) and is reflected multiple times at its walls. With suitable design of the annular chamber and window dimensions, this results in a destructive superposition of the reflected sound waves, i.e., a reduction in sound intensity. Such sound attenuators are also known as Helmholtz resonators.In the embodiment described in the aforementioned publication, the windows are filled with a preferably open-cell foam (this term is used in the present description to mean a foam body). This foam can be passed through by the fluid and, in particular, the sound transported therein, whereby the sound experiences additional damping in the sense of sound reduction through energy dissipation. Sound attenuators operating on the basis of this combined principle of resonance and absorption are marketed by the applicant under the registered trademark Resabtor. ® designated. Different versions of the Resabtor ® -Technology is described in DE 10 2020 100 162 A1 and DE 20 2016 008 580 U1.

[0004] Problems can arise when particularly high-frequency sound components need to be attenuated. It has been shown that higher frequencies are less effectively attenuated with conventional sound attenuators than lower frequencies. This has proven disadvantageous for broadband tuning of the sound attenuators.

[0005] From the aforementioned, generic patent GB 678 344 A, it is known to place a "torpedo"-shaped flow-through body inside the main tube. This leads directly to a significant improvement in noise reduction at higher frequencies. The flow-through body consists of perforated metal with impermeable conical end caps and is arranged centrally along the axis of the main tube, where it is held in position by riveted struts.

[0006] A similar noise reducer is known from US 6,332,511 B1. Here, the torpedo-shaped flow-through body is fixed inside the main tube by means of two sets of C-shaped struts, with both sets of struts being welded to the flow-through body, whereas only one is also welded to the inner wall of the main tube, while the other merely rests against it by friction.

[0007] From US patent 2002 / 0121404 A1, a sound attenuator is known with a double-conical main tube and a centrally arranged, also double-conical, flow-through body, wherein the main tube, formed from metal fibers, is concentrically surrounded by a cylindrical annular chamber wall. The annular chamber formed between the main tube and the annular chamber wall is filled with sound-absorbing insulating material. All three elements are divided axially in the middle, thus each consisting of two axial sections. To fix these in their desired relative position to each other, a mounting collar in the form of a (necessarily perforated) disc with axially projecting annular ribs is provided, which serve as a contact surface for the end faces and the adjacent areas of the aforementioned axial sections.

[0008] A similarly axially subdivided sound attenuator is known from DE 198 25 543 A1. It consists of a main tube with windows and an annular chamber surrounding it. The end walls of the annular chamber have central access openings to which the ends of the main tube are firmly connected. The main tube and the annular chamber wall are each subdivided into two axial sections, so that the basic structure of the sound attenuator consists of two assemblies, each of which in turn consists of a main tube and an annular chamber axial section and is joined together axially to assemble the sound attenuator. The interior of the annular chamber is filled with sound-absorbing insulating material.

[0009] From US Patent 6,116,375 A, a resonant sound reducer is known whose basic structure corresponds to that of a simple tube, but the inner wall of the tube is structured by radial and integrally formed axial ring ribs to form a system of resonant chambers.

[0010] From DE 10 2004 049 446 A1, a resonance sound attenuator with an outer tube is known, which has several annular protrusions between an inlet and an outlet. To complete the assembly, a tubular insert with windows, its outer diameter corresponding to the inner diameter of the ports, is provided. This insert forms the main tube in the area of ​​the resonance chambers formed by the protrusions. Task

[0011] The object of the present invention is to provide a generic sound reducer that is technically simpler and more cost-effective to manufacture. Description of the invention

[0012] This problem is solved in conjunction with the features of the preamble of claim 1 by forming the first main tube axial section together with the axially corresponding first flow body axial section and a first set of struts as a first sound attenuator axial section in one piece, and the second main tube axial section together with the axially corresponding second flow body axial section and a second set of struts as a second sound attenuator axial section in one piece, wherein each of the two sound attenuator axial sections is manufactured as a separate component.

[0013] Preferred embodiments of the invention are the subject of the dependent patent claims.

[0014] The invention initially utilizes the prior art-known improvement in noise reduction at higher frequencies achieved by a flow-through element placed inside the main pipe. The mode structure of sound wave propagation has been identified as the cause of this phenomenon. As is known to those skilled in the art, sound propagates in pipes in so-called modes, which can be described by the shape of the resulting standing waves. The cutoff frequencies at which certain higher-frequency modes become active depend strongly on the geometry and dimensions of the pipes. However, it is immediately apparent that at higher frequencies, i.e., shorter wavelengths, a larger number of sometimes very complex modes can arise within a given space. This can be particularly well illustrated by the so-called double-ring mode: here, the sound propagates largely independently in two concentric radial regions of the main pipe.Only the outer radial region comes into contact with the effective structures of conventional sound attenuators. This means that only sound transported in the outer radial region of the tube can penetrate the resonator chamber through the first window(s) and thus be subjected to destructive resonance and, if applicable, additional absorption. Sound transported in the inner radial region of the main tube, on the other hand, experiences practically no interaction with the effective structures of conventional sound attenuators. However, this inner radial region of the main tube is blocked by the "torpedo" design, which is generally known from the prior art. The corresponding double-ring mode is thereby disrupted or cannot "start up" due to the disruptive structure. This results in sound transport exclusively in the outer radial region of the main tube, which interacts with the effective elements of the sound attenuator in the manner described above.In this way, sound can also be effectively reduced at comparatively high frequencies.

[0015] This approach, highly advantageous from a physical standpoint, encounters less technical than economic difficulties in practical implementation. While it is known to insert a flow-through body with outward-facing struts into the main tube and join the free ends of the struts to the inner wall of the main tube, for example by welding, bolting, or riveting, this is complex and therefore expensive. The construction of the sound attenuator becomes even more complicated in cases where, for example, space constraints require the struts to contact the main tube within the axial dimensions of the resonator chamber.

[0016] The invention therefore provides that, for the sake of economic feasibility, the functional, radial subdivision of the sound attenuator is abandoned in favor of a functionally counterintuitive, axial subdivision. In particular, the main tube and the flow body are divided into two axial sections, with the corresponding axial sections of the main tube and flow body being formed integrally. A set of struts, also integrally formed with the aforementioned axial sections, serves to connect the axial sections of the main tube and the flow body. Each of the two resulting sound attenuator axial sections can be manufactured cost-effectively, particularly as an injection-molded plastic part.The assembly is carried out by simply, axially connecting the two sound reducer axial sections to form the sound reducer according to the invention, wherein the two main tube axial sections form the main tube and the two flow body sections form the flow body.

[0017] A further development of this idea leads to a particularly advantageous embodiment of the invention, in which the annular chamber is composed of a first annular chamber axial section and a second annular chamber axial section, wherein the first annular chamber axial section is formed as an additional element of the one-piece, first sound-attenuating axial section, and the second annular chamber axial section is formed as an additional element of the one-piece, second sound-attenuating axial section. In other words, the annular chamber is also incorporated into the explained concept of axial two-part construction. In this embodiment, the first sound-attenuating axial section thus consists of the first flow-through body axial section, the first set of struts, the first main tube axial section, and the first annular chamber axial section, with all of these components being formed as a single piece.The same applies to the second sound-reducing axial section. In the aforementioned further development, this consists of the second flow-through body axial section, the second set of struts, the second main tube axial section, and the second annular chamber axial section, with all of these components being formed as a single piece.

[0018] The concept described can be used both for a sound attenuator designed as a pure resonator and for one designed as a resabtor. ® A specially designed sound attenuator is used. As explained earlier, the latter is designed so that at least one first window of the main pipe is filled with a first wall made of preferably open-cell foam. For information on the physical mode of operation, please refer to the explanations in the introductory part of this description.

[0019] In particular, but not exclusively, in connection with a design of the sound attenuator according to the invention as a resabtor ®It is particularly advantageous if the at least one first window of the main tube is designed as a first gap arranged between the two main tube axial sections, extending in particular completely around the circumference of the main tube. Then, as provided in a further development of this approach, the first wall, preferably made of open-cell foam, can be designed as a first hollow foam cylinder bridging the first gap and held between the two main tube axial sections and coaxial to them. In other words, in this embodiment, the sound attenuator according to the invention consists not only of its two sound attenuator axial sections but also includes the aforementioned hollow foam cylinder, which is inserted between the main tube axial sections when the two sound attenuator axial sections are joined together.The gap between the two main tube axial sections, created by the first window, is thus bridged in the axial direction by the hollow foam cylinder inserted during assembly. This construction can also be described as the hollow foam cylinder representing a central section of the main tube in its final assembled state.

[0020] This can be achieved particularly efficiently by holding the first hollow foam cylinder axially on both sides in a positive-locking annular groove formed in the end face of the corresponding main tube axial section facing it. During assembly, the hollow foam cylinder can be pre-inserted into the annular groove of one of the two sound-reducing axial sections, in particular its main tube axial section. The other sound-reducing axial section is then fitted in such a way that the still free end face of the hollow foam cylinder engages in the annular groove of the sound-reducing axial section being fitted, in particular its main tube axial section.

[0021] Instead of a first window that completely surrounds the main pipe, it is of course also conceivable that a plurality of first windows spaced apart in the circumferential direction are provided, which can be filled in an analogous manner by insertable first walls made preferably of open-pore foam.

[0022] To avoid edges that could cause turbulence in the fluid inside the sound attenuator according to the invention, it is advantageously provided that the end faces of the two axial sections of the flow body have corresponding positive locking structures which together form a (at least radially) positive connection between the two axial sections of the flow body and said flow body. These can, for example, be corresponding annular shoulders. In this embodiment, the positive locking structures only provide a radial connection. However, more complex designs are conceivable in which the positive locking structures form a snap-fit ​​connection that also provides axial locking.

[0023] The shape of the flow body can further contribute to avoiding turbulence. This preferably has a streamlined profile in longitudinal section along the longitudinal axis of the main tube. Advantageously, it extends at least over the axial length of the resonator chamber. This ensures that any double-ring mode that might form in front of or behind the sound attenuator is at least partially suppressed or destroyed over the entire length of the sound attenuator, so that the entire length of the sound attenuator can be effectively utilized.

[0024] The internal structure of the flow-through body is irrelevant for the acoustic effect described in detail above. Nevertheless, it is preferred that the flow-through body be hollow. This contributes to material and weight savings. Furthermore, it is a prerequisite for a further development of the invention, in which the flow-through body has at least one second window through which its interior, acting as an additional resonance chamber, is sound-conducting and connected to the interior of the main tube. In other words, the flow-through body is used as an additional resonator, in addition to its mode-disturbance function as described above. The sound transported between the flow-through body and the wall of the main tube can therefore penetrate both radially outward, namely through the first window into the annular chamber, and radially inward, namely through the second window into the interior of the flow-through body.In both chambers, sound reflections occur which, as explained, lead to a destructive superposition of sound waves from selected frequency ranges when appropriately designed and dimensioned. In particular, due to the typically different dimensions of the annular chamber and the inner surface of the flow-through body, resonators can be created that are optimized for attenuating different frequency ranges. The sound reduction potential of the sound attenuator according to the invention is therefore further increased.

[0025] The resonance chamber provided by the flow-through body in the aforementioned further development of the invention can be used as a pure resonator. However, its use as a resonator is also possible. ® possible. For this purpose, at least one second window is filled with a second wall made of preferably open-cell foam. Regarding the resulting resabtor ®The effect is explained above in the context of the (outer) annular chamber.

[0026] In an axially divided design of the flow body, it can be further provided for practical implementation that the at least one second window is designed as a second gap arranged between the two axial sections of the flow body and extending completely around the circumference of the flow body. In this embodiment, the two axial sections of the flow body do not contact each other directly, but are separated by a gap. This gap can, in the aforementioned design, act as a receptacle. ®The second wall is bridged by a second hollow foam cylinder. In other words, this embodiment provides that the second wall, preferably made of open-cell foam, is designed as a second hollow foam cylinder bridging the second gap and held coaxially between the two axial sections of the flow body. To fix it between the two axial sections, it can be axially secured on both sides by a positive locking mechanism in an annular groove formed in the end face of the corresponding axial section of the flow body facing it. Regarding the resulting assembly method, reference can be made analogously to the above explanations in the context of the first hollow foam cylinder.

[0027] Of course, it is also conceivable here that instead of a second window completely encircling the flow body, a plurality of second windows spaced apart in the circumferential direction are provided, which may be filled by preferably pluggable second walls made of preferably open-pore foam.

[0028] The two axial sections of the annular chamber preferably contact each other directly and are advantageously connected axially along a common contact line, particularly by a material bond, preferably by welding. Due to the one-piece construction of the sound-reducing axial sections, such a radially external and therefore easily accessible connection line is sufficient to fix the relative alignment of the two main tube axial sections and the two flow-through body axial sections. Furthermore, no window is provided in the annular chamber that could interrupt the connection line between its two axial sections. A direct connection between the two axial sections of the annular chamber is therefore, from several perspectives, the ideal approach for joining the sound-reducing axial sections.

[0029] It is conceivable that both annular chamber axial sections are essentially symmetrical. However, this can pose problems for the formation of a reliable and durable weld, particularly in the case of a thin-walled design. Therefore, in a preferred embodiment of the invention, the first annular chamber axial section comprises a first annular chamber end wall, and the second annular chamber axial section comprises a second annular chamber end wall as well as an annular chamber shell adjoining the latter and extending axially to the first annular chamber end wall, wherein the radially outer edge of the first annular chamber end wall and the free axial edge of the annular chamber shell have contact structures on which said contact line is formed.In this embodiment, the entire annular chamber shell is assigned to the second annular chamber axial section, while the first annular chamber axial section is essentially reduced to the first annular chamber end wall. The contact line between the two annular chamber axial sections thus runs along the outer edge of the first annular chamber end wall, or along the axial edge of the annular chamber shell. This "corner" area is particularly easily accessible for a welding device. Furthermore, this area is stable in several directions, so that even high manufacturing tolerances do not impede the formation of a secure and tight joint.

[0030] The struts connecting the flow-through body to the main tube preferably run at an axial angle, with the struts of the first set and the struts of the second set converging radially from the outside to the inside. This angled arrangement of the struts provides axial stabilization of the flow-through body relative to the main tube compared to purely radially oriented struts. Furthermore, this specific angle ensures that the struts can be attached axially outside the first window (in the main tube) and, despite their angle, do not extend further axially outwards, thereby minimizing the overall axial length of the sound attenuator according to the invention.

[0031] Further details and advantages of the invention will become apparent from the following specific description and the drawings. Brief description of the drawings

[0032] They show: Fig. 1: A perspective, axially parallel sectioned view of a sound attenuator according to the invention, Fig. 2: A perspective view of the first axial section of the sound attenuator of Fig. 1 as well as Fig. 3: A perspective view of the second axial section of the sound attenuator of Fig. 1. Description of preferred embodiments

[0033] Identical reference symbols in the figures indicate identical or analogous elements.

[0034] Fig. Figure 1 shows a perspective, axially parallel section of a sound attenuator 1 according to the invention in its assembled state and connected to a connecting pipe 2. In the illustrated embodiment, the sound attenuator 1 is composed of three elements, namely a first sound attenuator axial section 100, which is Fig. 2 shown separately, a second sound-reducing axial section 200, which is in Fig. 3 is shown separately, and a foam hollow cylinder 300, which is in the in Fig. The assembly shown in Figure 1 is inserted between the first and second axial sections 100, 200 of the sound attenuator. Functionally, the sound attenuator 1 comprises a main tube 10 and a flow-through body 20, which is coaxially fixed inside the main tube 10 by means of struts 30. In the illustrated embodiment, the flow-through body 20 is depicted as an ellipsoid of revolution for illustrative purposes; in practical embodiments, it may be advantageous to use special streamlined designs that also take into account a predominant flow direction of the fluid flowing through the main tube 10. The profile of the struts 30 can also have a shape optimized for low flow resistance.

[0035] In the central region of the main tube 10, a first window 11 is arranged, completely encircling the main tube 10. In the illustrated embodiment, this window is filled by the foam hollow cylinder 300 mentioned above. Radially outside the first window 11, the main tube 10 is surrounded by an annular chamber 40, which extends between a first annular chamber end wall 41 and a second annular chamber end wall 42 and is bounded radially outwards by an annular chamber shell 43. The main tube 10 interacts with the annular chamber 40 via the first window 11 in a generally known manner as a sound-reducing resonator, with the foam hollow cylinder 300 providing an additional sound-reducing absorption effect. The flow element arranged inside the main tube 10 prevents the formation of higher sound propagation modes, which could circumvent this sound-reducing effect.

[0036] With the exception of the foam hollow cylinder, which is designed as a single, continuous component, all functional elements of the sound attenuator 1 according to the invention are assembled as components consisting of two axial sections, wherein the corresponding axial sections of the individual elements are formed as two in the Fig. 2 and Fig. 3 separately depicted, one-piece sound-reducing axial sections 100, 200 are formed. The main tube 10 is composed of the first main tube axial section 110, which is assigned to the first sound-reducing axial section 100, and the second main tube axial section 210, which is assigned to the second sound-reducing axial section 200. The flow-through body 20 is composed of the first flow-through body axial section 120, which is assigned to the first sound-reducing axial section 100, and the second flow-through body axial section 220, which is assigned to the second sound-reducing axial section 200. Similarly, the set of struts 30 is divided into a first set of struts 130, which is assigned to the first sound-reducing axial section 100, and a second set of struts 230, which is assigned to the second sound-reducing axial section 200.The annular chamber 40 is composed of a first annular chamber axial section 140, associated with the first sound-reducing axial section 100, and a second annular chamber axial section 240, associated with the second sound-reducing axial section 200. While the first-mentioned elements are essentially symmetrically subdivided, this is not the case for the illustrated embodiment of the annular chamber 40. Here, the first annular chamber axial section 140 essentially comprises only the first annular chamber end wall 41, whereas the second annular chamber axial section 240 comprises not only the second annular chamber end wall 42 but also the annular chamber shell 43.

[0037] The radially outer edge of the first annular chamber end wall 41, together with the free axial edge of the annular chamber shell 43, forms a joining zone in which the two sound-attenuating axial sections 100, 200 can preferably be joined by a material bond or, in the assembled state, as shown in Fig. The two sound-reducing axial sections 100 and 200 are joined as shown in Figure 1. The joining can preferably be achieved by welding, or optionally by bonding, in the form of a circumferential, annular weld or bond seam. For the rotationally correct alignment of the two sound-reducing axial sections 100 and 200, corresponding positive locking elements are provided in the joining zone. In the illustrated embodiment, these elements are designed as axial grooves 141 on the first sound-reducing axial section 100 and corresponding axial webs 241 on the second sound-reducing axial section 200.

[0038] The mutually facing edges of the main tube axial sections 110, 210 each have an associated annular groove 111, 211 in which the foam hollow cylinder is positively locked in place.

[0039] To make the hollow flow body 20 largely sealed against the fluid flowing around it during operation, a radially effective positive fit is provided between the two axial sections 120, 220 of the flow body. Thus, the opposing edges of the axial sections 120, 220 have corresponding annular shoulders 121, 221, which, in the assembled state, as shown in Fig. 1. They are recognizable and overlap each other. These can be carriers of additional sealing materials, for example an O-ring.

[0040] The dashed lines are used to indicate Fig.Figure 1 indicates a possible further development of the invention. In this embodiment, the axial sections 120, 220 of the flow body do not contact each other directly. Instead, a second window 21 is provided, completely encircling the flow body 20, which may optionally be filled by a further hollow foam cylinder (not shown). In such an embodiment, the interior of the hollow flow body 20 can also be designed as an additional resonator chamber, by means of which sound at frequencies that are not affected, or only insufficiently affected, by the sound-absorbing effect in the outer annular chamber 40 can be reduced.

[0041] Of course, the embodiments discussed in the detailed description and shown in the figures represent only illustrative examples of the present invention. A wide range of variations is available to those skilled in the art in light of the disclosure herein. In particular, the choice of material for the sound attenuator 1 according to the invention can be adapted to the requirements of the individual case. For high-temperature applications, a metallic material is recommended. In contrast, for applications in lower temperature ranges, cost-effective injection-molded plastic solutions can be used. A typical application area of ​​the invention is noise reduction in exhaust pipes or air supply lines of motor vehicles, in refrigerant lines of air conditioning systems, or in other lines through which liquid or gaseous fluids flow. Reference symbol list 1 sound reducer 2 connecting pipe 10 Main pipe 11 windows in 10 / first window 20 flow bodies 21 windows in 20 / second window 30 strut 40 ring chamber 41 first annular chamber end wall 42 second annular chamber end wall 43 Ring chamber mantle 100 first sound attenuator axial section 110 first main pipe axial section 111 Ring groove of 110 120 first axial section of the flow body 121 ring heel of 120 130 strut 140 first annular chamber axial section 141 Radial web 200 second sound attenuator axial section 210 second main pipe axial section 211 Ring groove of 210 220 second flow body axial section 221 ring heel of 220 230 strut 240 second annular chamber axial section 241 Radial groove 300 foam hollow cylinders

Claims

[1] Sound reducer (1) comprising - a main tube (10) in the interior of which a flow body (20) is arranged and fixed to the inner wall of the main tube (10) by means of struts (30; 130, 230) and - a ring chamber (40) which is connected to the interior of the main tube (10) via at least one first window (11) and is otherwise closed and surrounds the main tube (10), acting as a resonator chamber, wherein the main tube (10) comprises a first main tube axial section (110) and a second main tube axial section (210) and the flow body (20) comprises a first flow body axial section (120) and a second flow body axial section (220), characterized by , that the first main tube axial section (110) together with the axially corresponding first flow body axial section (120) and a first set of struts (130) is formed in one piece as a first sound-reducing axial section (100) and the second main tube axial section (210) together with the axially corresponding second flow body axial section (220) and a second set of struts (230) is formed in one piece as a second sound-reducing axial section (200), wherein each of the two sound-reducing axial sections (100, 200) is manufactured as a separate component. [2] Sound reducer (1) according to claim 1, characterized by , that the annular chamber (40) is composed of a first annular chamber axial section (140) and a second annular chamber axial section (240), wherein the first annular chamber axial section (140) is designed as an additional element of the one-piece, first sound-reducing axial section (100) and the second annular chamber axial section (240) is designed as an additional element of the one-piece, second sound-reducing axial section (200). [3] Sound reducer (1) according to any of the preceding claims, characterized by , that each sound-reducing axial section (100, 200) is designed as a one-piece plastic injection-molded part. [4] Sound reducer (1) according to any of the preceding claims, characterized by , that at least one first window (11) of the main tube (10) is filled with a first wall of foam. [5] Sound reducer (1) according to any of the preceding claims, characterized by, that the at least one first window (11) of the main tube (10) is formed as a first gap arranged between the two main tube axial sections (110, 210), in particular extending completely over the circumference of the main tube (10). [6] Sound reducer (1) according to claims 4 and 5, characterized by , that the first wall of foam is formed as a first foam hollow cylinder (300) bridging the first gap, held between the two main tube axial sections (110, 210) and coaxial to them. [7] Sound reducer (1) according to claim 6, characterized by , that the first foam hollow cylinder (300) is held axially on both sides in a positive locking manner in an annular groove (111, 211) which is formed in the end face of the corresponding main tube axial section (110, 210) facing it. [8] Sound reducer (1) according to one of the preceding, characterized by, that the end faces of the two flow body axial sections (120, 220) have corresponding positive locking structures which together form a positive locking connection of the two flow body axial sections (120, 220) to said flow body (20). [9] Sound reducer (1) according to any of the preceding claims, characterized by , that the flow body (20) has a streamlined profile in longitudinal section along the longitudinal axis of the main tube (10). [10] Sound reducer (1) according to any one of the preceding claims, characterized by that the flow body (20) extends at least over the axial length of the annular chamber (40). [11] Sound reducer (1) according to any of the preceding claims, characterized by , that the flow body (20) is hollow. [12] Sound reducer (1) according to claim 11, characterized by, that the flow body (20) has at least a second window (21) through which its interior, acting as an additional resonance chamber, is sound-conductingly connected to the interior of the main tube (10). [13] Sound reducer (1) according to claim 12, characterized by , that at least one second window (21) is filled with a second wall of foam. [14] Sound reducer (1) according to one of claims 12 to 13, characterized by , that at least one second window (21) is formed as a second gap arranged between the two flow body axial sections (120, 220) and extending completely over the circumference of the flow body (20). [15] Sound reducer (1) according to claims 13 and 14, characterized by , that the second wall made of foam is designed as a second foam hollow cylinder bridging the second gap, held between the two flow body axial sections (120, 220) and coaxial to them. [16] Sound reducer (1) according to claim 15, characterized by , that the second foam hollow cylinder is axially held in a positive-locking manner on both sides in an annular groove which is formed in the end face of the corresponding flow body axial section (120, 220) facing it. [17] Sound reducer (1) according to claim 2 or any one of claims 3 to 16, insofar as related to claim 2, characterized by that the two ring chamber axial sections (140, 240) directly contact each other and are axially firmly connected to each other along a common contact line, in particular by a material bond, preferably by welding. [18] Sound reducer (1) according to claim 17, characterized by, that the first annular chamber axial section (140) comprises a first annular chamber end wall (41) and the second annular chamber axial section (240) comprises a second annular chamber end wall (42) and an annular chamber mantle (43) attached to this and extending axially to the first annular chamber end wall (41), wherein the radially outer edge of the first annular chamber end wall (41) and the free axial edge of the annular chamber mantle (43) have contact structures on which said contact line is formed. [19] Sound reducer (1) according to any of the preceding claims, characterized by , that the struts (30; 130, 230) run obliquely in the axial direction, with the struts of the first set of struts (130) and the struts of the second set of struts (230) converging towards each other from radially outside to radially inside.

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