Muffler and mechanical equipment

Abstract

The invention provides a silencer. The silencer comprises an inner barrel and a first silencing unit. The inner cylinder is provided with a front-back through airflow channel; the first silencing unit comprises a first outer barrel, a porous sound absorption medium and a plurality of partition plates. The first outer cylinder is arranged on the inner cylinder in a sleeving manner, and a sound absorption cavity is defined by the first outer cylinder; the porous sound absorption medium is filled in the sound absorption cavity; and the multiple partition plates are constructed to surround the inner cylinder body and are embedded in the porous sound absorption medium at intervals, so that the porous sound absorption medium is divided into multiple layers, and sound waves are reflected and refracted multiple times through the multiple partition plates when the sound waves are transmitted in the porous sound absorption medium, so that attenuation of sound wave energy is caused.

Description

Technical Field

[0001] The present disclosure relates to the technical field of muffler, and in particular to a muffler and mechanical equipment. Background Art

[0002] With the rapid development of industries and transportation, low-frequency noise pollution has become increasingly prominent, which has had adverse effects on people's living environment, work efficiency and even health. Low-frequency noise has the characteristics of long propagation distance and strong penetration, and traditional high-frequency noise control methods are often difficult to effectively deal with.

[0003] Therefore, low-frequency noise mufflers came into being. This type of muffler is based on acoustic principles and achieves effective attenuation of low-frequency noise through specific structural design and material selection. In the prior art, structures such as Helmholtz resonant cavity and micro-perforated plate can usually be used to achieve the purpose of low-frequency noise reduction. The structure of micro-perforated plate + Helmholtz resonant cavity is complex and difficult to process. In addition, the sound absorption band is narrow and the low-frequency sound absorption effect still needs to be improved. Summary of the invention

[0004] In view of this, the present disclosure provides a muffler and a mechanical device.

[0005] A muffler provided according to the present disclosure includes: an inner cylinder having an airflow passage extending from front to back; a first muffler unit including: a first outer cylinder sleeved on the inner cylinder, the first outer cylinder defining a sound absorbing cavity; a porous sound absorbing medium filled in the sound absorbing cavity; and a plurality of baffles, the plurality of baffles being configured to respectively surround the inner cylinder and be embedded in the porous sound absorbing medium at intervals, so as to divide the porous sound absorbing medium into multiple layers, so that when sound waves propagate in the porous sound absorbing medium, they are reflected and refracted multiple times by the plurality of baffles, thereby causing attenuation of sound wave energy.

[0006] According to an embodiment of the present disclosure, the first outer cylinder further includes a plurality of blocking plates, and the plurality of blocking plates divide the first outer cylinder into a plurality of sound absorbing cavities.

[0007] According to an embodiment of the present disclosure, each partition is fixedly connected to the sealing plate on one side, and a distance is left between each partition and the sealing plate on the other side.

[0008] According to an embodiment of the present disclosure, different numbers of partitions are provided in different sound absorbing cavities.

[0009] According to an embodiment of the present disclosure, the length of the sound absorption cavity along the axial direction of the first outer cylinder is 50-500 mm, and the thickness of the sound absorption cavity from the bottom close to the inner cylinder to the top of the sound absorption cavity is 25 mm-2000 mm.

[0010] According to an embodiment of the present disclosure, the number of partitions is greater than or equal to 2, and the length of the partition is 5 mm to 475 mm.

[0011] According to an embodiment of the present disclosure, a second sound-absorbing unit is also included, and the second sound-absorbing unit includes: a second outer cylinder, which is sleeved on the inner cylinder, and the second outer cylinder defines a sound-absorbing cavity; and a porous sound-absorbing medium, which fills the cavity part of the sound-absorbing cavity.

[0012] According to an embodiment of the present disclosure, a lower baffle and a micro-perforated plate spliced ​​with the lower baffle are further provided on one side of the sound absorption cavity close to the inner cylinder, so that sound waves can enter the sound absorption cavity through the micro-perforated plate.

[0013] According to an embodiment of the present disclosure, the micro-perforated plate protrudes toward the bottom relative to the lower baffle, and a groove is provided at a position of the inner cylinder relative to the micro-perforated plate so that the micro-perforated plate can be embedded in the groove.

[0014] Another aspect of the present disclosure provides a mechanical device comprising the above-mentioned muffler.

[0015] According to the silencer provided by the present disclosure, by filling a porous sound-absorbing medium in the sound-absorbing cavity and embedding a plurality of partitions in the porous sound-absorbing medium, a multi-layer composite meta-material can be formed, so that the propagation path of the sound wave in the porous sound-absorbing medium is changed. These partitions cause the sound waves to need to bypass them to propagate, thereby increasing the path length of the sound waves. The extended propagation path causes the sound waves to spend longer time propagating in the material, thereby exhibiting a lower effective sound speed. The sound waves experience more reflections and refractions between entering and leaving the material, thereby achieving sound energy attenuation at low frequencies. In addition, the combination of the partition and the porous sound-absorbing medium does not require complex processes, has a simple structure, and is easy to process and manufacture. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0017] Figure 1 Schematically shows a three-dimensional cross-sectional view according to an embodiment of the present disclosure;

[0018] Figure 2 Schematically shows an expanded view of a first muffler unit according to an embodiment of the present disclosure;

[0019] Figure 3 Schematically shows a three-dimensional cross-sectional view according to another embodiment of the present disclosure;

[0020] Figure 4 is a schematic diagram of the propagation of sound waves in a porous sound-absorbing medium layer according to an embodiment of the present disclosure;

[0021] Figure 5 is a schematic diagram of the propagation of sound waves after the multi-hole sound absorbing medium layer and the partition are combined according to an embodiment of the present disclosure;

[0022] Figure 6 is an equivalent schematic diagram of a three-layer composite metamaterial according to an embodiment of the present disclosure; and

[0023] Figure 7 This is a diagram showing the sound elimination effect of a multilayer composite metamaterial according to an embodiment of the present disclosure.

[0024] Reference numerals

[0025] 1. Inner cylinder;

[0026] 2. The first muffler unit;

[0027] 21. a first outer cylinder;

[0028] 211, blocking plate;

[0029] 212, lower baffle;

[0030] 213. Micro perforated plate;

[0031] 214, upper top plate;

[0032] 22. Sound absorbing cavity;

[0033] 23. Partition;

[0034] 3. The second muffler unit;

[0035] 31. A second outer cylinder. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0037] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0038] All terms used herein, including technical and scientific terms, have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0039] When using expressions such as "at least one of A, B, and C, etc.", it should generally be interpreted as the meaning of the expression generally understood by those skilled in the art. For example, "a system having at least one of A, B, and C" should include but not be limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc. When using expressions such as "at least one of A, B, or C, etc.", it should generally be interpreted as the meaning of the expression generally understood by those skilled in the art. For example, "a system having at least one of A, B, or C" should include but not be limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.

[0040] It should also be noted that the directional terms mentioned in the embodiments, such as "upper", "lower", "front", "back", "left", "right", etc., are only reference directions of the drawings and are not intended to limit the scope of protection of the present disclosure. Throughout the drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or configurations will be omitted when they may cause confusion in the understanding of the present disclosure.

[0041] Low-frequency noise is one of the pain points in the field of muffler design. The current common solution is to design a complex structure corresponding to low-frequency noise for sound absorption or isolation. Due to the limitations of the application environment, especially the limitations of material thickness and other dimensions, there is currently no good solution on the market for wide-frequency sound absorption within the frequency range of 50-400Hz.

[0042] Acoustic composite metamaterials are special materials that manipulate the propagation characteristics of sound waves through precise structural design. These materials can achieve extraordinary acoustic effects such as negative refraction, sound wave focusing, noise isolation, or acoustic invisibility by controlling the propagation path, speed, frequency selectivity and other characteristics of sound waves. The present disclosure proposes a muffler for low-frequency noise, which combines a porous sound-absorbing medium and multiple partitions into a multi-layer composite metamaterial, in order to solve at least part of the above technical problems.

[0043] Figure 1 A three-dimensional cross-sectional view according to an embodiment of the present disclosure is schematically shown.

[0044] According to the muffler provided by the present disclosure, Figure 1As shown, it includes an inner cylinder 1 and a first sound-absorbing unit 2. The inner cylinder 1 includes an air inlet, an air outlet, and an air flow channel that passes through the front and back. The first sound-absorbing unit 2 includes a first outer cylinder 21, a plurality of baffles 23, and a porous sound-absorbing medium. Among them, the first outer cylinder 21 is sleeved on the inner cylinder 1, and the first outer cylinder 21 defines a sound-absorbing cavity 22. The porous sound-absorbing medium is filled in the sound-absorbing cavity 22. The plurality of baffles 23 are configured to surround the inner cylinder 1 and are embedded in the porous sound-absorbing medium at intervals, so as to divide the porous sound-absorbing medium into multiple layers, so that when the sound wave propagates in the porous sound-absorbing medium, it is reflected and refracted multiple times by the plurality of baffles 23, thereby causing the attenuation of the sound wave energy.

[0045] In such an embodiment, by filling the sound absorbing cavity 22 with a porous sound absorbing medium and embedding a plurality of partitions 23 in the porous sound absorbing medium, a multilayer composite metamaterial can be formed, so that the propagation path of the sound wave in the porous sound absorbing medium is changed. These partitions 23 cause the sound waves to bypass them for propagation, thereby increasing the path length of the sound waves. The extended propagation path causes the sound waves to take longer to propagate in the material, thereby exhibiting a lower effective sound speed. The sound waves experience more reflections and refractions between entering and leaving the material, thereby achieving sound energy attenuation at low frequencies. In addition, the combination of the partition 23 and the porous sound absorbing medium does not require complex processes, has a simple structure, and is easy to process and manufacture.

[0046] According to the embodiments of the present disclosure, Figure 1 As shown, the cross section of the inner cylinder 1 can be circular, but the present disclosure is not limited thereto, and can also be elliptical, rectangular, racetrack-shaped, etc. The inner cylinder 1 is usually made of metal materials, such as cast iron, stainless steel, and the like.

[0047] Figure 2 The expanded view of the first muffler unit according to the embodiment of the present disclosure is schematically shown.

[0048] According to the embodiments of the present disclosure, Figure 2 As shown, an upper top plate 214 is also provided on the top of the sound absorbing cavity 22. A lower baffle 212 and a micro-perforated plate 213 spliced ​​with the lower baffle 212 are also provided on the side of the sound absorbing cavity 22 close to the inner cylinder 1, so that sound waves can enter the sound absorbing cavity 22 through the micro-perforated plate 213.

[0049] In such an embodiment, the lower baffle 212 blocks the incoming sound waves, so that the sound waves only enter the sound absorbing cavity 22 from the micro-perforated plate 213, thereby further increasing the propagation path of the sound waves and preventing the porous sound absorbing medium from falling.

[0050] In an exemplary embodiment, the micro-perforated plate 213 may be a perforated aluminum plate with a diameter of 2 mm and a perforation rate of 10%.

[0051] According to an embodiment of the present disclosure, the micro-perforated plate 213 protrudes toward the bottom relative to the lower baffle 212, and a groove is provided at a position of the inner cylinder 1 relative to the micro-perforated plate 213 so that the micro-perforated plate 213 can be embedded in the groove.

[0052] In an illustrative embodiment, a corresponding ventilation opening may be provided at a position of the inner cylinder 1 corresponding to the position in contact with the micro-perforated plate 213 , so as to form a channel for the transmission of sound waves with the micro-perforated plate 213 .

[0053] According to an embodiment of the present disclosure, the length of the sound absorption cavity 22 along the axial direction of the first outer cylinder 21 is 50-500 mm, and the thickness of the sound absorption cavity 22 from the bottom close to the inner cylinder 1 to the top of the sound absorption cavity 22 is 25 mm-2000 mm.

[0054] like Figure 2 As shown, the axial length of the sound absorbing cavity 22 along the first outer cylinder 21 is the distance between the two blocking plates 211 , and the thickness of the sound absorbing cavity 22 is the distance between the upper top plate 214 and the lower baffle plate 212 .

[0055] Figure 3 A three-dimensional cross-sectional view according to another embodiment of the present disclosure is schematically shown.

[0056] According to the embodiments of the present disclosure, Figure 3 As shown, the first outer cylinder 21 further includes a plurality of blocking plates 211 , and the plurality of blocking plates 211 divide the first outer cylinder 21 into a plurality of sound absorbing cavities 22 .

[0057] According to the embodiments of the present disclosure, Figure 3 As shown, different numbers of partitions 23 are provided in different sound absorbing chambers.

[0058] For example, Figure 3 As shown, two sound absorbing cavities 22 may be provided in the first outer cylinder 21, and a blocking plate 211 is provided between the two sound absorbing cavities 22 to form two complementary and interfering sound absorbing cavities 22. The present disclosure is not limited thereto, and three, four or more sound absorbing cavities may also be provided, and each sound absorbing cavity 22 may be provided with different lengths along the axial direction.

[0059] In such an embodiment, by providing a plurality of sound absorbing cavities 22, and providing a sound absorbing medium and a plurality of partitions 23 in each sound absorbing cavity 22, each sound absorbing cavity 22 can absorb different frequency bands of low-frequency noise, thereby increasing the sound absorption frequency range of the low-frequency noise and improving the overall sound absorption effect of the muffler.

[0060] According to the embodiments of the present disclosure, Figure 3 As shown, each partition plate 23 is fixedly connected to the blocking plate 211 on one side and is spaced apart from the blocking plate 211 on the other side.

[0061] According to the embodiment of the present disclosure, Figure 2 As shown, multiple partitions 23 can be connected to the sealing plate 211 on the same side, but the present disclosure is not limited to this. Multiple partitions 23 can also be connected to the sealing plates 211 on different sides in a staggered manner and be spaced a certain distance from the sealing plates 211 on the other side to form a maze-like sound wave transmission channel to increase the transmission path of the sound waves.

[0062] According to an embodiment of the present disclosure, the number of the partitions 23 is greater than or equal to 2, and the length of the partitions 23 is 5 mm to 475 mm.

[0063] The length of the partition plate 23 is the length extending from the one side blocking plate 211 to the other side blocking plate 211 .

[0064] In an illustrative embodiment, the partition 23, the upper top plate 214, the lower baffle plate 212 and the sealing plate 211 are preferably 5 mm thick steel plates, and the partition 23 and the sealing plate 211 can be connected by welding, but the present disclosure is not limited thereto.

[0065] In such an embodiment, since the 5 mm thick steel plate has a high density and elastic modulus, it has the characteristics of low absorption and high reflection for sound wave propagation, so that it is difficult for the sound wave to cause significant vibration of the material when propagating therein, thereby maintaining a high reflectivity.

[0066] According to the embodiments of the present disclosure, Figure 3 As shown, the muffler also includes a second muffler unit 3, which includes a second outer cylinder 31 and a porous sound absorbing medium. The second outer cylinder 31 is sleeved on the inner cylinder 1, and the second outer cylinder 31 defines a sound absorbing cavity 22. The porous sound absorbing medium fills the cavity part of the sound absorbing cavity 22.

[0067] In such an embodiment, by only providing a porous sound absorbing medium in the sound absorbing cavity of the second sound absorption unit 3, a better absorption effect can be achieved for high-frequency and medium-frequency noise.

[0068] According to the embodiment of the present disclosure, the number, spacing, length of the partitions 23 and the axial length of the sound absorbing cavity 22 are optimized and determined by a numerical method.

[0069] In such an embodiment, the multilayer meta-composite material optimized by numerical methods can manipulate sound waves within a wider frequency range with higher flexibility and precision, thereby meeting the requirements for improving the acoustic performance of the muffler.

[0070] According to an embodiment of the present disclosure, the propagation characteristics of acoustic waves in multilayer composite metamaterials may be analyzed by using a transfer matrix method.

[0071] Figure 4 It is a schematic diagram of the propagation of sound waves in a porous sound-absorbing medium layer according to an embodiment of the present disclosure.

[0072] According to the embodiments of the present disclosure, Figure 4 As shown, for a single-layer porous sound-absorbing medium, the relationship between the sound pressure of the sound wave and the particle velocity can be expressed by the transfer matrix, see formula (1):

[0073] (1)

[0074] in, is the sound pressure before the sound wave propagates in the i-th layer, is the particle velocity before the sound wave propagates in the i-th layer, is the sound pressure after the sound wave propagates in the i-th layer, is the particle velocity after the sound wave propagates in the i-th layer, is the propagation matrix of the i-th layer, see formula (2)

[0075] (2)

[0076] in, is the thickness of the porous sound-absorbing medium in the i-th layer, is the wave number of the sound wave in the i-th layer, is the equivalent density of the porous sound-absorbing medium in the i-th layer, is the speed of sound wave in the i-th layer.

[0077] Figure 5 It is a schematic diagram of the propagation of sound waves after the porous sound-absorbing medium layer and the partition are combined according to an embodiment of the present disclosure.

[0078] like Figure 5 As shown, since a partition 23 is provided in the porous sound absorbing medium to form a composite meta-material, the calculation of its equivalent density is referred to formula (3).

[0079] (3)

[0080] in, is the equivalent density, is the dynamic density, For the calculation of , see formula (4).

[0081] (4)

[0082] in, is the mass addition coefficient for infinite frequency time, is the static flow resistance, is the porosity, and are the characteristic viscosity and thermal penetration length, is the dynamic viscosity of air, is the thermal conductivity, is the static air pressure, is the specific heat at constant pressure, is the specific heat ratio, is the air density, is an imaginary unit, is the circular frequency.

[0083] The area ratio of the steel plate is calculated by referring to formula (5).

[0084] (5)

[0085] in, is the length of the i-th partition 23, It is the length of the sound absorbing cavity 22 along the axial direction of the first outer cylinder 21.

[0086] Substituting formula (3) into formula (2) yields the transfer matrix of the porous sound absorbing medium + partition 23.

[0087] For a multilayer composite metamaterial with multiple partitions 23 and porous sound absorbing media, the transfer matrices of each layer can be multiplied in sequence to obtain the total transfer matrix. Assuming there are N layers of material, the transfer matrix of each layer is , , … Total transfer matrix for,

[0088] = (6)

[0089] Surface acoustic impedance of multilayer composite metamaterials It can be expressed as:

[0090] (7)

[0091] in, (1,1) is the total transfer matrix The element in row 1 and column 1 of (1,1) is the total transfer matrix The element in the 2nd row and 1st column of . According to the above formula, the propagation and absorption effect of sound waves in multilayer composite metamaterials can be analyzed.

[0092] Figure 6 is an equivalent schematic diagram of a three-layer composite metamaterial according to an embodiment of the present disclosure.

[0093] like Figure 6As shown, the three partitions can divide the porous sound absorbing material into a three-layer structure of equivalent layer 1, equivalent layer 2 and equivalent layer 3. The surface acoustic impedance of the multi-layer composite metamaterial It can be determined by the above formula. Pi is the input sound pressure, Pr is the output sound pressure, and by comparing the difference between Pi and Pr, the sound absorption effect of the multilayer composite metamaterial can be reflected.

[0094] When the materials of the porous sound absorbing medium and the partition 23 are determined, the parameters that determine the surface acoustic impedance Zs are the wall thickness t, the axial length w of the sound absorbing cavity 22, the thickness l of the partition 23, and the length l of the partition 23. , the spacing of the partition 23 , and the thickness H of the porous medium. Considering factors such as rigid wall and support strength, t and l are limited. H is limited by space and is generally a fixed value. Therefore, the surface acoustic impedance of the multilayer composite metamaterial is related to the thickness of the porous sound-absorbing medium in each layer. , the length of each layer of partition 23 and the axial length of the sound absorbing cavity 22 Therefore, by adjusting the parameters , and , the target acoustic impedance value can be obtained. The acoustic impedance value can be used to estimate the sound absorption coefficient of the multilayer composite metamaterial.

[0095] In order to achieve the optimal sound absorption effect of multilayer composite metamaterials within the target frequency range, numerical optimization methods can be used to , and Make optimizations.

[0096] Specifically, the frequency range of the target noise can be determined first, and then the fixed parameters such as the material of the partition 23 and the porous sound-absorbing medium, the wall thickness t, the thickness l of the partition 23, and the thickness H of the porous medium can be defined, and then the evaluation index of the sound absorption effect can be defined, such as the sound absorption coefficient or the surface acoustic impedance matching. The above acoustic model is used to describe the propagation and absorption effect of the combination of the rigid plug plate and the sound-absorbing material on the sound wave. The input parameters of the model are set to , and . Select appropriate numerical optimization algorithms, such as gradient descent method, genetic algorithm, particle swarm optimization, etc., to optimize the above parameters. Use the sound absorption effect as an evaluation index, reflecting the average or maximum sound absorption effect in the entire frequency range. Use the selected optimization algorithm to iteratively optimize the model. In each iteration, update the , and The final output is the optimized , and .

[0097] Figure 7 This is a diagram showing the sound elimination effect of a multilayer composite metamaterial according to an embodiment of the present disclosure.

[0098] like Figure 7 As shown, the composite meta-structure material composed of a porous sound-absorbing medium and a plurality of partitions 23 can improve the broadband sound transmission loss below 400 Hz, and the corresponding low-frequency lower limit of 70 Hz can also be reduced by 15 dB. It has a good noise reduction effect and covers a wide low-frequency range.

[0099] The present disclosure also provides a mechanical device, which uses the above-mentioned muffler. For example, it can be installed on the inlet and outlet of the mechanical device to directly process the noise of the airflow entering and exiting the device, thereby reducing noise emissions. The present disclosure is not limited to this.

[0100] The embodiments of the present disclosure are described above. However, these embodiments are only for the purpose of illustration and are not intended to limit the scope of the present disclosure. Although the embodiments are described above separately, this does not mean that the measures in the various embodiments cannot be used in combination to advantage. The scope of the present disclosure is defined by the attached claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A muffler, characterized in that: include: The inner cylinder (1) is provided with an air flow passage extending from front to back; The first muffler unit (2) comprises: A first outer cylinder (21) is sleeved on the inner cylinder (1), wherein the first outer cylinder (21) defines a sound absorbing cavity (22); A porous sound absorbing medium filled in the sound absorbing cavity (22); A plurality of baffles (23), wherein the plurality of baffles (23) are configured to respectively surround the inner cylinder (1) and be embedded in the porous sound absorbing medium at intervals, so as to divide the porous sound absorbing medium into multiple layers, so that when sound waves propagate through the porous sound absorbing medium, they are reflected and refracted multiple times by the plurality of baffles (23), thereby causing attenuation of sound wave energy.

2. The muffler according to claim 1, characterized in that: The first outer cylinder (21) further comprises a plurality of blocking plates (211), wherein the plurality of blocking plates (211) divide the first outer cylinder (21) into a plurality of sound absorbing cavities (22).

3. The muffler according to claim 2, characterized in that: Each of the partition plates (23) is fixedly connected to the blocking plate (211) on one side, and a distance is left between each of the partition plates (23) and the blocking plate (211) on the other side.

4. The muffler according to claim 3, characterized in that: Different sound absorption cavities (22) are provided with different numbers of partitions (23).

5. The muffler according to any one of claims 1 to 4, characterized in that: The length of the sound absorbing cavity (22) along the axial direction of the first outer cylinder (21) is 50-500 mm, and the thickness of the sound absorbing cavity (22) from the bottom close to the inner cylinder to the top of the sound absorbing cavity is 25-2000 mm.

6. The muffler according to any one of claims 1 to 4, characterized in that: The number of the partitions (23) is greater than or equal to 2, and the length of the partitions (23) is 5 mm to 475 mm.

7. The muffler according to any one of claims 1 to 4, characterized in that: It also includes a second sound-absorbing unit (3), wherein the second sound-absorbing unit (3) includes: A second outer cylinder (31) sleeved on the inner cylinder (1), wherein the second outer cylinder (31) defines the sound absorbing cavity (22); A porous sound absorbing medium is filled in the hollow portion of the sound absorbing cavity (22).

8. The muffler according to any one of claims 1 to 4, characterized in that: A lower baffle (212) and a micro-perforated plate (213) spliced ​​with the lower baffle are also provided on a side of the sound absorbing cavity (22) close to the inner cylinder (1), so that sound waves can enter the sound absorbing cavity (22) through the micro-perforated plate (213).

9. The muffler according to claim 8, characterized in that The micro-perforated plate (213) protrudes toward the bottom relative to the lower baffle (212), and a groove is provided at a position of the inner cylinder (1) opposite to the micro-perforated plate (213) so that the micro-perforated plate (213) can be embedded in the groove.

10. A mechanical device, characterized in that: Including the muffler as described in any one of claims 1 to 9.

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