Silencer drainage structure

Abstract

The utility model provides a silencer drainage structure which comprises a silencer body, a first drainage through hole is formed in the silencer body, and the first drainage through hole is located at the lowest position of the silencer body. A second drainage through hole is formed in the silencer patch; a second drainage through hole is formed in the silencer patch; the silencer patch is fixed on the outer wall of the silencer body, and the first drainage through hole is wrapped in the silencer patch; a cavity is formed between the outer wall of the silencer body and the silencer patch, and the cavity is filled with silencing filler. The problems that water vapor is condensed and gathered in the silencer, so that a pipeline is blocked, and the silencing effect is poor when condensate water is discharged out of the silencer are solved.

Description

Technical Field

[0001] The utility model relates to the technical field of automobile mufflers, in particular to a muffler drainage structure. Background Art

[0002] As a noise reduction device on the whole vehicle, the muffler spans the chassis of the whole vehicle and connects the engine and the whole vehicle. The muffler is connected to the body or the front and rear axles of the chassis through hooks and hanging ears. It is mainly used to reduce the noise generated when the engine is working. When the car is running, due to the operation of the engine and the emission of exhaust gas, strong noise will be generated, which not only affects the comfort of the driver and passengers, but also may cause interference to the surrounding environment and personnel. The role of the car muffler is to reduce this noise and provide a quieter riding environment for the driver and passengers.

[0003] Specific as Figure 1 As shown, due to the layout of the muffler 5, there is always a local water accumulation structure under the chassis, and the muffler 5 has a similar Figure 1 Such a U-shaped structure with a low middle and high ends, and it is precisely because of the existence of such a U-shaped structure that when working in a low temperature environment, the wall temperature of the exhaust pipe 6 is low, so that the water vapor burned by the engine condenses when passing through the exhaust pipe 6 and gathers in the exhaust pipe 6. Figure 1 At the lowest point of the U-shaped tube shown, as the engine is used at low temperatures for a long time, more and more condensed water accumulates, and under the condition of long-term low temperatures, blockage of the exhaust pipe 6 will inevitably occur.

[0004] A resonance tube and its muffler assembly with Chinese patent publication number CN209724452U, including an inner tube, an outer tube covering the inner tube, and a sound cavity formed between the inner tube and the outer tube, wherein the inner tube is provided with an exhaust inlet, a plurality of first through holes connecting the exhaust inlet and the sound cavity are opened on the side wall of the inner tube, and a plurality of second through holes connecting the sound cavity with the atmosphere are opened on the side wall of the outer tube. The patent adopts a two-layer circular tube set, and the outer tube and the inner tube are perforated on the circumference. Since the outer tube and the inner tube are perforated on the circumference, when a large amount of airflow is discharged, it will be accompanied by noise radiation, affecting the muffler effect. Utility Model Content

[0005] The purpose of the utility model is to provide a muffler drainage structure. One purpose is to solve the problem that water vapor from engine combustion condenses and accumulates in the muffler when passing through the muffler pipeline, causing pipeline blockage; the second purpose is to solve the problem of poor silencer effect when condensed water is discharged from the muffler.

[0006] In order to achieve the above purpose, the technical solution adopted by the utility model is as follows:

[0007] A muffler drainage structure comprises a muffler body, wherein the muffler body is provided with a first drainage through hole, and the first drainage through hole is located at the lowest point of the muffler body;

[0008] A muffler patch, wherein a second drainage through hole is formed on the muffler patch; the muffler patch is fixed on the outer wall of the muffler body, and the first drainage through hole is covered in the muffler patch;

[0009] A cavity is formed between the outer wall of the muffler body and the muffler patch, and the cavity is filled with a muffler filler.

[0010] Furthermore, the sound-absorbing filler is steel wool.

[0011] According to the above technical scheme, the silencer filler of the utility model adopts steel wool to reduce or eliminate the noise generated during exhaust in the muffler. When the high-speed exhaust gas generated by the engine passes through the muffler, they will hit and pass through the steel wool. In this process, the sound wave energy in the exhaust gas will be absorbed and scattered by the steel wool, thereby reducing the intensity and propagation distance of the sound. In addition, steel wool can also help reduce the emission of particulate matter in the exhaust gas, capture and fix some tiny particulate matter, and purify the exhaust quality.

[0012] Furthermore, the sound-absorbing filler is made of a hydrophilic material.

[0013] According to the above technical solution, the sound-absorbing filler is made of hydrophilic material which can better absorb and scatter sound waves. When the sound waves encounter the hydrophilic material, the energy of the sound waves will be more easily converted into heat or other forms of energy, thereby reducing the transmission of sound. At the same time, the hydrophilic material has the ability to absorb and retain moisture, which means that in a humid or moist environment, the sound-absorbing filler can absorb and retain moisture, thereby preventing moisture from accumulating inside the muffler and maintaining the stability of the performance of the muffler. At the same time, it will also more effectively prevent the propagation of sound, thereby enhancing the sound-absorbing effect.

[0014] Furthermore, the sound-absorbing filler is fiber felt.

[0015] According to the above technical solution, the muffler filler is fiber felt, which is usually soft and plastic and can be easily processed into a shape and size suitable for the muffler. At the same time, the installation of fiber felt is relatively simple and can be fixed inside the muffler by filling or pasting. Fiber felt has a high sound absorption performance and can effectively absorb and reduce the noise in the muffler body. When sound waves encounter fiber felt, they will rub and collide with the fibers, causing sound energy to be converted into heat energy, thereby reducing the transmission of sound. In addition, fiber felt usually has excellent thermal stability and can withstand high temperature environments without losing its sound absorption performance, which helps to maintain the stability of the performance of the muffler and extend its service life.

[0016] Furthermore, the first drainage through hole is a single-hole structure or a multi-hole structure.

[0017] According to the above technical solution, multiple first drainage holes are provided in the muffler body, which can ensure that moisture and exhaust gas can be smoothly discharged from the inside of the muffler body, which can not only prevent moisture from damaging the sound-absorbing material, but also maintain the stability of the performance of the muffler and extend its service life. In addition, the design of multiple first drainage holes can also improve the drainage efficiency, ensuring that the muffler body can effectively discharge moisture and exhaust gas under different working conditions.

[0018] Furthermore, the second drainage through hole is a single-hole structure or a multi-hole structure.

[0019] According to the above technical solution, by opening a plurality of second drainage holes on the muffler patch, when the exhaust gas containing moisture enters the cavity, the second drainage holes can effectively drain the moisture and prevent the moisture from accumulating in the cavity; if too much moisture or impurities accumulate in the cavity, it may cause the channel of the muffler to be blocked. The accumulation of moisture may change the acoustic characteristics of the cavity, reduce the sound elimination effect, and even cause internal corrosion; the provision of a plurality of second drainage holes can help reduce the risk of such blockage, keep the cavity unobstructed, reduce performance fluctuations caused by moisture and impurities, and improve the overall reliability of the muffler.

[0020] Furthermore, the muffler patch is welded and fixed on the outer wall of the muffler body.

[0021] According to the above technical solution, the overall structural strength of the muffler body can be increased by welding the muffler patch to the outer wall of the muffler body. Welding connection is a strong connection method that can provide higher strength and rigidity, allowing the muffler to withstand external loads and vibrations and improve the stability of the connection.

[0022] Furthermore, a flange structure is formed around the muffler patch, and the flange structure is fitted with the outer wall of the muffler body.

[0023] According to the above technical solution, the flange structure formed around the muffler patch can better fit with the outer wall of the muffler body, making it easier for the two to be fixed to each other.

[0024] Furthermore, the muffler patch is connected to the flange structure in a smooth transition.

[0025] According to the above technical solution, by adopting a smooth transition connection between the muffler patch and the flange structure, stress can be dispersed, the structural strength can be improved, and thus the stability of the connection can be improved.

[0026] Furthermore, a middle portion of the muffler patch bulges in a direction away from the muffler body to form the cavity.

[0027] According to the above technical scheme, the formation of a cavity can enhance the sound elimination effect, that is, the cavity can utilize the principle of sound wave resonance to generate a larger acoustic impedance within a specific frequency range, thereby reducing the transmission of sound waves; when the sound wave enters the cavity, it will interact with the air molecules in the cavity, so that part of the sound energy is converted into heat energy or other forms of energy, thereby reducing the intensity of the sound; it can also broaden the sound elimination frequency band of the silencer, which enables the silencer to more effectively reduce noise of different frequencies and improve the overall sound elimination effect.

[0028] Beneficial effects of the utility model:

[0029] The utility model installs the muffler patch on the muffler body, and at the same time opens a first drainage through hole on the muffler body and a second drainage through hole on the muffler patch, so that the water vapor of the engine combustion can enter the cavity through the first drainage through hole, and utilizes the principle of sound wave resonance, so that the cavity generates a larger acoustic impedance within a specific frequency range, thereby reducing the transmission of sound waves and the intensity of sound, and finally the water vapor of the engine combustion is discharged from the cavity through the second drainage through hole, so as to achieve the purpose of discharging the water vapor of the engine combustion, and avoid the water vapor condensation and accumulation in the muffler to cause pipeline blockage;

[0030] The prior art uses a double-layer perforated sleeve filled with silencer cotton to achieve the purpose of silencer. It can basically only be designed as a tubular structure and can only be arranged on the pipeline. Moreover, the structure adopts the form of evenly distributed through holes on the circumference of the outer tube. During use, condensed water is usually discharged from the through holes at the bottom of the outer tube due to gravity, and the through holes at the top of the outer tube form redundancy, which increases the radiated noise, affects its acoustic performance, and reduces the silencer effect. Compared with the prior art, the utility model adopts the method of installing a silencer patch at the lowest point of the silencer body, and then opening a second drainage through hole on the silencer patch, which can ensure that the influence of the drainage function of the silencer on the silencer effect is minimized, which not only meets the drainage function but also maintains the silencer effect, and has a compact structure and strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural schematic diagram of a muffler drainage structure in the prior art;

[0032] Figure 2 It is a structural schematic diagram of the drainage structure of the muffler in one direction of the utility model;

[0033] Figure 3 It is a structural schematic diagram of the drainage structure of the muffler in another direction of the utility model;

[0034] Figure 4 It is a schematic diagram of the structure of the muffler body of the muffler drainage structure in the utility model;

[0035] Figure 5 It is a cross-sectional schematic diagram of the drainage structure of the muffler in the utility model.

[0036] 1-muffler body; 11-first drainage hole; 2-muffler patch; 21-second drainage hole; 22-flange structure; 3-cavity; 4-muffler filler. DETAILED DESCRIPTION

[0037] The following will describe the implementation of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific implementations, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, not for limiting the scope of protection of the present invention.

[0038] It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and thus the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed at will, and the component layout may also be more complicated.

[0039] It should be noted that the outer tube of the cited prior art covers the inner tube, adopts a double-layer perforated sleeve and is filled with sound-absorbing cotton to achieve the purpose of sound absorption. It can basically only be designed as a tubular structure and can only be arranged on the pipeline. Moreover, the structure adopts the form of evenly distributed through holes on the circumference of the outer tube; and during use, condensed water is usually discharged from the through holes at the bottom of the outer tube due to gravity, while the through holes at the top of the outer tube form redundancy, which increases the radiated noise, affects its acoustic performance, and reduces the sound absorption effect.

[0040] like Figures 2 to 5As shown, this embodiment provides a muffler drainage structure, including a muffler body 1 and a muffler patch 2, the muffler body 1 is provided with a first drainage through hole 11, and the first drainage through hole 11 is located at the lowest point of the muffler body 1; the muffler patch 2 is fixed on the outer wall of the muffler body 1 and covers the first drainage through hole 11, the muffler patch 2 is provided with a second drainage through hole 21, and the first drainage through hole 11 is enclosed in the muffler patch 2; wherein, the diameter, number and distribution shape of the first drainage through hole 11 and the second drainage through hole 21 are also set according to the specific processing environment of the vehicle.

[0041] In this embodiment, the muffler patch 2 is welded and fixed to the outer wall of the muffler body 1. By welding and fixing the muffler patch 2 to the outer wall of the muffler body 1, the overall structural strength of the muffler body 1 can be increased. Welding connection is a strong connection method that can provide higher strength and rigidity, so that the device can withstand larger external loads and vibrations and improve the stability of the connection.

[0042] like Figure 5 As shown, a flange structure 22 is formed around the muffler patch 2, and the flange structure 22 fits with the outer wall of the muffler body 1. The flange structure 22 formed around the muffler patch 2 can better fit with the outer wall of the muffler body 1, so that the two are conveniently fixed to each other; wherein, the muffler patch 2 is smoothly connected to the flange structure 22, and the form of smoothly connecting the muffler patch 2 to the flange structure 22 can disperse stress, improve structural strength, and thus improve the stability of the connection.

[0043] like Figure 2 , Figure 3 and Figure 5 As shown, the middle portion of the muffler patch 2 bulges away from the muffler body 1 to form a cavity 3 .

[0044] According to the above technical solution, the formation of cavity 3 can enhance the sound elimination effect, that is, cavity 3 can utilize the principle of sound wave resonance to generate a larger acoustic impedance within a specific frequency range, thereby reducing the transmission of sound waves; when the sound wave enters cavity 3, it will interact with the air molecules in the cavity, so that part of the sound energy is converted into heat energy or other forms of energy, thereby reducing the intensity of the sound; it can also broaden the sound elimination frequency band of the silencer, which enables the silencer to more effectively reduce noise of different frequencies and improve the overall sound elimination effect.

[0045] In this embodiment, by installing the muffler patch 2 on the muffler body 1, and at the same time opening a first drainage hole 11 on the muffler body 1 and a second drainage hole 21 on the muffler patch 2, the water vapor generated by the engine combustion can enter the cavity 3 through the first drainage hole 11. By utilizing the principle of sound wave resonance, the cavity 3 generates a larger acoustic impedance within a specific frequency range, thereby reducing the transmission of sound waves and lowering the intensity of the sound. Finally, the water vapor generated by the engine combustion is discharged from the cavity 3 through the second drainage hole 21, so as to achieve the purpose of discharging the water vapor generated by the engine combustion and avoid the condensation of water vapor and accumulation in the muffler body 1, which may cause pipeline blockage.

[0046] In this embodiment, the cavity 3 is filled with a sound-absorbing filler 4 .

[0047] As an exemplary embodiment, the silencer filler 4 is steel wool; the silencer filler 4 uses steel wool to reduce or eliminate the noise generated during exhaust in the muffler body 1. When the high-speed exhaust gases generated by the engine pass through the muffler body 1, they will hit and pass through the steel wool. During this process, the sound wave energy in the exhaust gas will be absorbed and scattered by the steel wool, thereby reducing the intensity and propagation distance of the sound; in addition, steel wool can also help reduce the emission of particulate matter in the exhaust gas, capture and fix some tiny particulate matter, and purify the exhaust quality.

[0048] As an exemplary embodiment, the sound-absorbing filler 4 is made of a hydrophilic material (or a resistive sound-absorbing material); materials made of hydrophilic materials can better absorb and scatter sound waves. When sound waves encounter hydrophilic materials, the energy of the sound waves can be more easily converted into heat energy or other forms of energy, thereby reducing the transmission of sound; at the same time, hydrophilic materials have the ability to absorb and retain moisture, which means that in a humid or wet environment, the sound-absorbing filler 4 can absorb and retain moisture, thereby preventing moisture from accumulating inside the muffler, maintaining the stability of the performance of the muffler, and at the same time more effectively preventing the propagation of sound, thereby enhancing the sound-absorbing effect.

[0049] Further, as an exemplary embodiment, the sound-absorbing filler 4 is a fiber felt; the fiber felt is generally soft and plastic, and can be easily processed into a shape and size suitable for installation in the cavity 3; at the same time, the installation of the fiber felt is also relatively simple, and it can be fixed inside the cavity 3 by filling or pasting; the fiber felt has a high degree of sound absorption performance, and can effectively absorb and reduce the noise in the muffler body 1. When the sound wave encounters the fiber felt, the sound wave will rub and collide with the fiber, causing the sound energy to be converted into heat energy, thereby reducing the transmission of sound, and the fiber felt generally has excellent thermal stability, and can withstand high temperature environments without losing its sound absorption performance, which helps to maintain the performance stability of the muffler and extend its service life.

[0050] Compared with the prior art, the muffler filler 4 used in the utility model is steel wool or fiber felt, etc., to replace the traditional muffler cotton. Although the muffler cotton has a good muffler effect, it is also very easy to be discharged from the second drainage hole 21 on the muffler patch 2 with the airflow, thereby losing its effect. In one embodiment of the present patent, the muffler filler 4 of the utility model is filled with steel wool, and the steel wool has the effect of being completely shaped and not easy to be blown out. In another embodiment of the present patent, the muffler filler 4 is filled with fiber felt with very good hydrophilicity. After the hot air discharged from the engine encounters the hydrophilic fiber felt that is not easy to blow away, it will condense very quickly, and under the combined action of capillary phenomenon and water surface tension, it will be very easy to adsorb and condense the engine combustion water vapor, and guide the condensed water to be discharged from the second drainage hole 21 of the muffler patch 2, so as to achieve a good barrier effect on airflow noise while having a water diversion effect. Since materials such as steel wool or fiber felt that are not easily blown away by the airflow are used, the sizes of the first drainage hole 11 and the second drainage hole 21 on the muffler body 1 and the muffler patch 2 will be designed towards a structure that is more conducive to drainage (for example, increasing the diameters of the first drainage hole 11 and the second drainage hole 21, increasing the number of perforations, adopting a different perforation layout, etc.).

[0051] During use, if the first drainage hole 11 is not set low enough, the water may not be completely discharged, which will cause water accumulation inside the muffler body 1. The accumulated water will not only cause pipe blockage, but may also cause corrosion of metal parts inside the muffler, thereby affecting its performance and life. Figure 2 As shown, the first drainage hole 11 is located at the lowest point of the muffler body 1. It should be noted that, compared with the prior art, the first drainage hole 11 can not only be opened at the lowest point of the muffler body 1, but also can be opened at the lowest point of the muffler pipeline or the muffler shell, and the utility model does not limit it), and the scope of application is wider. The first drainage hole 11 is located at the lowest point of the muffler body 1; that is, the muffler patch 2 is usually installed at a position where condensed water easily accumulates on the muffler body 1, and the second drainage hole 21 opened in the muffler patch 2 is mainly used to discharge condensed water. The radiation noise of the sound wave passing through the second drainage hole 21 is relatively small, which can ensure that the influence of the drainage function of the muffler on the muffler effect is minimized, which not only satisfies the drainage function but also maintains the muffler effect.

[0052] The first drainage hole 11 is located at the lowest point of the muffler body 1, and uses gravity to ensure that the water vapor and other impurities from the engine combustion can flow out naturally, avoiding the occurrence of water accumulation problems, so that the water vapor and impurities flow to the lowest point along the inner wall of the muffler body 1 and are discharged through the first drainage hole 11 and the second drainage hole 21, reducing the risk of corrosion and damage to the muffler body 1 and extending the service life of the device. In one embodiment, as a preferred embodiment, as Figure 4 As shown, the first drainage through hole 11 is a single-hole structure or a multi-hole structure, and its arrangement is also designed according to the structure of the specific muffler body 1. The specific number, diameter, and perforation arrangement position and arrangement shape are not limited. The muffler patch 2 is also arranged at the position of the muffler body 1 where water is most likely to accumulate, and one or more muffler patches 2 can be arranged; the shape of the muffler patch 2 is specifically designed according to the needs, and in actual applications, it can be installed in the pipe, shell and other positions of the muffler body 1 according to the specific situation. The structure of the muffler patch 2 is not limited to square, circular and other shapes, so as to achieve covering the first drainage through hole 11; the width, height, etc. of the muffler patch 2 are not specifically specified, so as to achieve drainage and noise blocking as the ultimate goal.

[0053] According to the above technical solution, a plurality of first drainage holes 11 are provided in the muffler body 1, which can ensure that moisture and exhaust gas can be smoothly discharged from the inside of the muffler body 1, which can not only prevent moisture from damaging the sound-absorbing material, but also maintain the performance of the muffler stable and extend its service life. In addition, the design of the plurality of first drainage holes 11 can also improve the drainage efficiency, ensuring that the muffler body 1 can effectively discharge moisture and exhaust gas under different working conditions.

[0054] As a preferred embodiment, Figure 5 As shown, the second drainage through hole 21 is a single-hole structure or a multi-hole structure. If too much water or impurities accumulate in the cavity 3, the passage of the muffler may be blocked. The accumulation of water may change the acoustic characteristics of the cavity 3, reduce the muffler effect, and even cause internal corrosion. By opening a plurality of second drainage through holes 21 on the muffler patch 2, when the exhaust gas containing water enters the cavity 3, the second drainage through holes 21 can effectively remove the water and prevent the water from accumulating in the cavity 3, thereby reducing the risk of such blockage, keeping the cavity 3 unobstructed, reducing the performance fluctuation caused by water and impurities, and improving the overall reliability of the muffler.

[0055] In some embodiments, the apertures of the first drainage hole 11 and the second drainage hole 21 may also be increased to increase the contact area between the silencer filler 4 and the airflow in the silencer body 1, thereby accelerating the discharge of condensed water and avoiding the accumulation of condensed water, thereby avoiding pipeline blockage.

[0056] Compared with the prior art, the muffler filler 4 of the utility model uses steel wool or fiber felt to replace the traditional muffler cotton. After the hot air flow discharged from the engine encounters the steel wool or hydrophilic fiber felt, it will condense very quickly, and under the combined action of capillary phenomenon and water surface tension, it will be very easy to adsorb and condense the engine combustion water vapor, and guide the condensed water to be discharged from the second drainage hole 21 of the muffler patch 2, so as to achieve a good barrier effect on the airflow noise while having a water diversion effect. Moreover, materials such as steel wool or fiber felt are not easily blown away by the airflow, and the size of the first drainage hole 11 and the second drainage hole 21 on the muffler body 1 and the muffler patch 2 will be designed towards a structure that is more conducive to drainage; at the same time, the muffler patch 2 is installed at the lowest position of the muffler body 1, and then the second drainage hole 21 is opened on the muffler patch 2, which can ensure that the influence of the drainage function of the muffler on the muffler effect is minimized, which not only meets the drainage function but also maintains the muffler effect, and has a compact structure and strong practicality.

[0057] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or modification made by a person skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. A muffler drainage structure, characterized in that: include: A muffler body (1), wherein a first drainage through hole (11) is provided on the muffler body (1), and the first drainage through hole (11) is located at the lowest point of the muffler body (1); A muffler patch (2), wherein a second drainage through hole (21) is provided on the muffler patch (2); the muffler patch (2) is fixed on the outer wall of the muffler body (1), and the first drainage through hole (11) is covered in the muffler patch (2); A cavity (3) is formed between the outer wall of the muffler body (1) and the muffler patch (2), and the cavity (3) is filled with a muffler filler (4).

2. The muffler drainage structure according to claim 1, characterized in that: The sound-absorbing filler (4) is steel wool.

3. The muffler drainage structure according to claim 1, characterized in that: The sound-absorbing filler (4) is made of a hydrophilic material.

4. The muffler drainage structure according to claim 3, characterized in that: The sound-absorbing filler (4) is fiber felt.

5. The muffler drainage structure according to claim 1, characterized in that: The first drainage through hole (11) is a single-hole structure or a multi-hole structure.

6. The muffler drainage structure according to claim 1, characterized in that: The second drainage through hole (21) is a single-hole structure or a multi-hole structure.

7. The muffler drainage structure according to any one of claims 1 to 6, characterized in that: The muffler patch (2) is welded and fixed on the outer wall of the muffler body (1).

8. The muffler drainage structure according to claim 1, characterized in that: The muffler patch (2) is formed with a flange structure (22) around its periphery, and the flange structure (22) is fitted with the outer wall of the muffler body (1).

9. The muffler drainage structure according to claim 8, characterized in that: The muffler patch (2) is connected to the flange structure (22) in a smooth transition.

10. The muffler drainage structure according to claim 1, characterized in that: The middle portion of the muffler patch (2) bulges in a direction away from the muffler body (1) to form the cavity (3).

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