muffler

Abstract

The aim is to enable cost reduction. [Solution] The silencer 10 is a silencer 10 provided in the exhaust path 12. The silencer 10 is formed in the exhaust pipe 30 through which the exhaust gas G flows, and in the node region 36 of the exhaust pipe 30 where at least the node portion 34 of the air column resonance 32 generated in the exhaust path 12 is located, with each opening area being 2.6 mm 2 The silencer 10 comprises a plurality of microholes 40, and an outer wall portion 44 that covers the portion of the exhaust pipe 30 in which the microholes 40 are formed and forms an empty space 42 on the outer circumference of the exhaust pipe 30.

Description

[Technical Field]

[0001] This invention relates to a silencer. [Background technology]

[0002] Patent Document 1 discloses a silencer. This silencer comprises an exhaust pipe having a plurality of communication holes, a shell positioned outside the exhaust pipe, and a sound-absorbing material positioned between the exhaust pipe and the shell. The sound-absorbing material is made of glass wool. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-125711 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, this silencer requires processing costs for filling it with glass wool, as well as the cost of the glass wool material itself, which leads to higher costs.

[0005] This invention has been made in view of the above-mentioned problems, and aims to enable the reduction of the cost of silencers. [Means for solving the problem]

[0006] According to one aspect of the present invention, a silencer provided in the exhaust path is formed in the exhaust pipe through which the exhaust gas flows and in the region of the nodal portion of the exhaust pipe where at least the nodal portion of the air column resonance generated in the exhaust path is located, and each opening area is 2.6 mm 2 The device comprises a plurality of microholes, and an outer wall portion that covers the portion of the exhaust pipe where the microholes are formed and forms a hollow space on the outer circumference of the exhaust pipe. [Effects of the Invention]

[0007] In the above embodiment, the exhaust gas flowing through the exhaust pipe moves back and forth between the inside of the exhaust pipe and the space around its outer circumference via microholes. At this time, friction occurs between the exhaust gas particles and the edges of the microholes, generating frictional heat. As a result, the energy of the air column resonance generated in the exhaust path by the exhaust gas is converted into frictional heat and reduced.

[0008] Thus, since the silencer achieves its sound-dampening effect by attenuating air column resonance through friction between exhaust gas particles and the edges of microholes, it eliminates the processing costs and material costs for filling with glass wool compared to using glass wool for sound dampening. Therefore, it is possible to reduce the cost of the silencer. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is an explanatory diagram used to describe the silencer according to this embodiment. [Figure 2] Figure 2 is an explanatory diagram used to provide a detailed explanation of the silencer. [Figure 3] Figure 3 is a cross-sectional view along the line III-III in Figure 2. [Figure 4] Figure 4 is a magnified view showing the surface of the exhaust pipe. [Figure 5] Figure 5 is a magnified cross-sectional view of the microhole area of ​​the silencer. [Figure 6] Figure 6 shows the formula for calculating the acoustic Reynolds number. [Figure 7] Figure 7 shows the relationship between the opening area of ​​a microhole and the acoustic Reynolds number. [Figure 8] Figure 8 shows the relationship between the opening area of ​​a microhole and its acoustic resistance. [Figure 9] Figure 9 shows the relationship between the open area ratio and the sound pressure level. [Figure 10] Figure 10 shows the relationship between engine speed and sound pressure level. [Figure 11]FIG. 11 is a longitudinal sectional view showing a muffler according to a first modified example. [Figure 12] FIG. 12 is an enlarged view showing the surface of an exhaust pipe according to a second modified example. [Figure 13] FIG. 13 is an enlarged view showing the surface of an exhaust pipe according to a third modified example.

Mode for Carrying Out the Invention

[0010] <Embodiment> Hereinafter, referring to the drawings, a muffler 10 according to an embodiment of the present invention will be described.

[0011] First, referring to FIGS. 1 to 5, the configuration of the muffler 10 will be described.

[0012] FIG. 1 is an explanatory diagram used for explaining the muffler 10, showing the inside of the outer wall portion 44. FIG. 2 is an explanatory diagram used for a detailed explanation of the muffler 10. FIG. 3 is a cross-sectional view taken along the line III-III of FIG. 2. FIG. 4 is an enlarged view showing the surface of the exhaust pipe 30. FIG. 5 is an enlarged cross-sectional view of a part of the micro holes 40 of the muffler 10.

[0013] As shown in FIG. 1, the muffler 10 is provided, for example, in a muffler device 14 that constitutes an exhaust path 12 of an automobile, and is a device that reduces the sound output from an engine (not shown) as an internal combustion engine. The muffler 10 constitutes a center muffler disposed between a main muffler 16 provided near the outlet of the exhaust gas G in the exhaust path 12 and a catalyst 18 provided downstream of the engine.

[0014] That is, the muffler device 14 includes a catalyst 18 connected via an exhaust pipe 20 fixed to the engine, a muffler 10 connected to the catalyst 18 via a first pipe 22, and a main muffler 16 connected to the muffler 10 via a second pipe 24.

[0015] The exhaust path 12 for the exhaust gas G is formed in the region from the end of the exhaust pipe 20, through which the exhaust gas G is sent from the engine, to the end of the main muffler 16, which discharges the exhaust gas G. The muffler device 14 removes harmful substances from the exhaust gas G discharged from the engine using a catalyst 18 and silences the exhaust gas with a silencer 10 and a main muffler 16 that constitute the center muffler.

[0016] The silencer 10 primarily suppresses air column resonance occurring in the muffler device 14, thereby improving the noise reduction effect for low-frequency sounds, such as those below 500 Hz. Furthermore, the silencer 10 can suppress booming noises, such as those between 40 Hz and 150 Hz, and airflow noises that occur when the engine is running at low RPMs.

[0017] As shown in Figures 1 and 2, the silencer 10 is provided on the muffler device 14 and in the exhaust path 12. The silencer 10 includes an exhaust pipe 30 (see Figure 2) through which the exhaust gas G flows. The silencer 10 is formed in the nodal region 36 of the exhaust pipe 30 where at least the nodal portion 34 of the air column resonance 32 (see Figure 1) that resonates in the exhaust path 12 is located, and each opening area is 2.6 mm². 2 The silencer 10 is equipped with multiple microholes 40 (see Figure 2), as described below. The silencer 10 also includes an outer wall portion 44 that covers the portion of the exhaust pipe 30 in which the microholes 40 are formed, and forms an empty space 42 on the outer circumference of the exhaust pipe 30.

[0018] To explain in more detail, in the muffler device 14, an air column is formed by the exhaust gas G flowing through the exhaust pipe 20, catalytic converter 18, first pipe 22, silencer 10, second pipe 24, and main muffler 16. The air column is formed in the exhaust path 12 from the end of the exhaust pipe 20 to the end of the main muffler 16. When air column resonance 32 occurs in this air column, a standing wave is formed.

[0019] As shown in Figure 1, the air column resonance 32 can be represented by a sound pressure vibration amplitude waveform 50 indicating the sound pressure of the air column resonance 32, and a particle vibration amplitude waveform 52 indicating the velocity of the particles of the exhaust gas G constituting the air column resonance 32.

[0020] The sound pressure vibration amplitude waveform 50 has an antinode where the amplitude of the sound pressure vibration is maximum and a node 34 where the amplitude of the sound pressure vibration is almost zero.

[0021] In the particle vibration amplitude waveform 52, the particle velocity of the exhaust gas G that forms the air column resonance 32 increases at the location corresponding to the node 34 of the sound pressure vibration amplitude waveform 50. In the particle vibration amplitude waveform 52, antinodes 54 are formed at the location corresponding to the node 34 of the sound pressure vibration amplitude waveform 50.

[0022] The silencer 10 is positioned at a location corresponding to the nodal portion 34 of the air column resonance 32 that occurs in the exhaust path 12 of the muffler device 14.

[0023] (Outer wall) As shown in Figures 2 and 3, the outer wall portion 44 constituting the silencer 10 comprises a cylindrical body 60 that surrounds the exhaust pipe 30, one end surface 64 provided on one end side 62 of the cylindrical body 60, and another end surface 68 provided on the other end side 66 of the cylindrical body 60.

[0024] The cylindrical body 60 has an elliptical cross-section (see Figure 3), and there are sections with a long distance between the cylindrical body 60 and the exhaust pipe 30, as well as sections with a short distance. One end face 64 allows the exhaust pipe 30 to pass through and closes one end 62 of the space 42 formed on the outer circumference of the exhaust pipe 30. The other end face 68 allows the exhaust pipe 30 to pass through and closes the other end 66 of the space 42 formed on the outer circumference of the exhaust pipe 30.

[0025] As a result, an empty space 42 is formed around the outer circumference of the exhaust pipe 30, where no sound-absorbing material such as glass wool is present. This space 42 constitutes an expansion chamber that expands the exhaust path 12.

[0026] (Exhaust pipe) As shown in Figure 2, the exhaust pipe 30 constituting the silencer 10 is made up of a cylindrical pipe. The exhaust pipe 30 protruding from one end 62 of the silencer 10 is connected to the first pipe 22 (see Figure 1). Exhaust gas G is supplied to the exhaust pipe 30 from the first pipe 22. The exhaust pipe 30 protruding from the other end 66 of the silencer 10 is connected to the second pipe 24 (see Figure 1). The exhaust pipe 30 supplies the exhaust gas G to the second pipe 24.

[0027] (Microholes) As shown in Figures 2 and 4, the exhaust pipe 30 has multiple microholes 40 formed in the portion surrounded by the outer wall 44. Multiple microholes 40 are arranged at equal intervals in the circumferential direction S of the exhaust pipe 30 (see Figure 3), and multiple microholes 40 are also arranged at equal intervals in the axial direction J of the exhaust pipe 30 (see Figure 2).

[0028] As shown in Figure 5, the microhole 40 connects the internal space 70 of the exhaust pipe 30 with the space 42 formed on the outer circumference of the exhaust pipe 30. As a result, the exhaust gas G flowing through the exhaust pipe 30 can move back and forth between the internal space 70 and the space 42 within the exhaust pipe 30 via the microhole 40.

[0029] The microholes 40 formed in the exhaust pipe 30 consist of circular holes with a diameter of approximately 1.8 mm. The opening area of ​​the microholes 40 is 2.6 mm². 2 As described below, the opening area is smaller compared to the communication holes that allow the exhaust gas G of the exhaust pipe 30 to flow to the glass wool filled on the outer circumference.

[0030] Here, as the opening area of ​​the microhole 40 decreases, the viscosity of the exhaust gas G passing through it increases. When the viscosity of the exhaust gas G passing through the microhole 40 increases, the acoustic resistance increases (see Figure 8), and the sound-dampening effect improves.

[0031] As shown in Figure 5, friction occurs between the exhaust gas G particles moving through the microhole 40 and the edge 40A of the microhole 40, and frictional heat is generated at the edge 40A of the microhole 40. At this time, the energy of the air column resonance 32 generated in the exhaust path 12 is converted into frictional heat and reduced. As a result, the microhole 40 exhibits a sound-dampening effect.

[0032] Furthermore, the microhole 40 has an opening area of ​​2.6 mm². 2 In the following cases, the noise-reducing effect due to the viscosity generated in the exhaust gas G passing through the micro-holes 40 becomes dominant over the noise-reducing effect when the exhaust path 12 is expanded by the space 42 on the outer circumference of the exhaust pipe 30.

[0033] Furthermore, because the microhole 40 has a small opening area, the frictional heat generated by the exhaust gas G particles and the edge 40A of the microhole 40 becomes large. As a result, the amount of energy reduction in the air column resonance 32 increases for this microhole 40.

[0034] As shown in Figure 4, no protrusions or the like are formed on the circumferential surface of the exhaust pipe 30 in which the microholes 40 are formed. The microholes 40 are circular through-holes that ensure the passage of exhaust gas G toward the radially outward direction 80 (see Figure 4).

[0035] As shown in Figures 1 and 2, the microholes 40 are located in the nodal region 36 where the nodal portion 34 (see Figure 1) of the air column resonance 32 is located. Some of the microholes 40 (see Figure 2) that are arranged in the axial direction J of the exhaust pipe 30 are located at nodal position 34A of the nodal portion 34 calculated by simulation, for example. Specifically, the centers of some of the microholes 40B are located at nodal position 34A.

[0036] At the nodal position 34A, the particle velocity of the exhaust gas G is high (see Figure 1). Therefore, the particle velocity of the exhaust gas G moving back and forth through the microhole 40 is higher compared to other locations. Consequently, the frictional heat generated between the particles of the exhaust gas G and the edge 40A of the microhole 40 increases. As a result, the decrease in energy of the air column resonance 32 becomes even greater.

[0037] Here, the node position 34A of the node 34 may change depending on the environment. For this reason, multiple microholes 40 are arranged in the node region 36 (see Figure 2), which has a width over the aforementioned node position 34A.

[0038] Furthermore, it is desirable to set the position where the most effective sound reduction effect can be obtained to the node of the sound pressure vibration amplitude waveform 50, that is, the position where the particle vibration amplitude waveform 52 of the exhaust gas G is at its maximum.

[0039] (Sound dampening effect) Next, the sound-dampening effect of the micro-holes 40 will be explained in detail with reference to Figures 6 to 10.

[0040] Figure 6 shows the formula for calculating the acoustic Reynolds number k. Figure 7 shows the relationship between the opening area of ​​the microhole 40 and the acoustic Reynolds number k. Figure 8 shows the relationship between the opening area of ​​the microhole 40 and the acoustic resistance. Figure 9 shows the relationship between the opening ratio and the sound pressure level. Figure 10 shows the relationship between engine speed and sound pressure level. "Engine speed" refers to the number of rotations of the crankshaft per unit time (here, 1 minute) [rpm], and is synonymous with "engine rotational speed," which is the rotational velocity of the crankshaft.

[0041] The acoustic Reynolds number k is known as a proportionality constant that shows the relationship between the diameter of a capillary and the thickness of the viscous boundary layer, and the acoustic Reynolds number k is expressed by the equation shown in Figure 6 (see Sound Absorption Characteristics of Microporous Plates, Mikio Yairi [Kajima Technical Research Institute] and Kimihiro Sakagami [Faculty of Engineering, Kobe University]).

[0042] The range where the acoustic Reynolds number k is from 1 to 10 indicates a transitional region where the inertial force of the fluid changes from being dominant (inertia-dominated) to the region where the flow suppression effect by the viscosity of the fluid becomes dominant (viscosity-dominated).

[0043] Fig. 7 shows the relationship between the aperture area of the micro hole 40 obtained based on the formula in Fig. 6 and the acoustic Reynolds number k.

[0044] Fig. 7 shows that when the acoustic Reynolds number k is 10 or less, the flow transitions from inertia-dominated to viscosity-dominated. The aperture area at which the acoustic Reynolds number k becomes 10 or less is 2.6 mm 2 or less.

[0045] When the aperture area of the micro hole 40 is 2.6 mm 2 or less, for the exhaust gas G as a fluid, the flow suppression effect by viscosity becomes dominant over the inertial force. As a result, when the aperture area of the micro hole 40 of the silencer 10 is 2.6 mm 2 or less, the main silencing function transitions from the extended silencing function of expanding the exhaust path 12 in the middle to the viscous silencing function due to the viscosity of the exhaust gas G passing through the micro hole 40.

[0046] Therefore, the silencer 10 can obtain a silencing effect without increasing the volume of the space 42 on the outer peripheral part of the exhaust pipe 30 or filling the space 42 with glass wool.

[0047] As shown in Fig. 8, for the micro hole 40, the smaller the aperture area, the greater the acoustic resistance and the higher the silencing effect. Therefore, the smaller the aperture area of the micro hole 40, the better, but when it is less than 0.8 mm 2 which corresponds to a circular hole with a diameter of 1 mm, it becomes difficult to drill holes when pressing the exhaust pipe 30. Also, for the micro hole 40, the smaller the aperture area, the narrower the frequency range that can be silenced.

[0048] Therefore, considering the relationship between the silencing effect, workability, and the width of the frequency range that can be silenced, the aperture area of the micro hole 40 is 0.8 mm 2It is desirable that the above be the case.

[0049] The microhole 40 in this embodiment has an opening area of ​​0.8 mm². 2 2.6mm 2 The settings are as follows, and the microhole 40 consists, for example, of a circular through-hole with a diameter of 1.5 mm.

[0050] Furthermore, the silencer 10 has an opening ratio of 1.4% or less, which is the sum of the opening areas of all microholes 40 formed in the exhaust pipe 30 relative to the surface area of ​​the exhaust pipe 30 covered by the outer wall portion 44.

[0051] (First measurement test) Figure 9 shows the sound pressure level measurements taken near the outlet when the opening ratio of the microholes 40 formed in the exhaust pipe 30 was set to 0.5%, 0.8%, 1.3%, and 1.8%. The measurements were performed with an engine speed of 2800 rpm as the representative point.

[0052] In the diagram, the first level 100 is an opening area of ​​3.0 mm in the exhaust pipe 30. 2 The first comparative example shows the sound pressure level measured in which a hole is formed and the space 42 on the outer circumference of the exhaust pipe 30 functions as an expansion chamber. The second level 102 in the figure is when the exhaust pipe 30 has an opening area of ​​3.0 mm². 2 The sound pressure level measured in the second comparative example, in which a hole is formed and glass wool is filled in the space 42 on the outer circumference of the exhaust pipe 30, is shown.

[0053] It can be seen that when the perforation ratio of the silencer 10 is 1.4% or less, the sound-dampening effect is higher than that of the first and second comparative examples. Furthermore, the sound-dampening effect of the silencer 10 increases as the perforation ratio decreases.

[0054] (Second measurement test) Figure 10 shows the measurement results of the sound pressure level near the outlet as a function of engine speed, when the opening ratio of the microholes 40 formed in the exhaust pipe 30 was set to 0.5%, 0.8%, 1.3%, and 1.8%. The resonance frequency of the air column resonance 32 that occurs in the exhaust path 12 of the muffler device 14 used in the measurement is 70 Hz at an engine speed of 2800 [rpm].

[0055] Figure 10 shows the relationship between engine speed and sound pressure level for the first test specimen 110, in which the opening ratio of the microholes 40 formed in the exhaust pipe 30 was 0.5%, and the second test specimen 112, in which the opening ratio was 0.8%. Figure 10 also shows the relationship between engine speed and sound pressure level for the third test specimen 114, in which the opening ratio was 1.3%, and the fourth test specimen 116, in which the opening ratio was 1.8%.

[0056] In this figure, at the first rotational speed 120, which is the engine speed at 2800 [rpm] where air column resonance 32 occurs, the sound pressure level near the outlet decreases in the order of first test sample 110, second test sample 112, third test sample 114, and fourth test sample 116.

[0057] However, at the second rotational speed of 122, which corresponds to an engine speed of 3500 rpm, the sound pressure level near the outlet decreases in the order of fourth test sample 116, first test sample 110, second test sample 112, and third test sample 114. Thus, at the second rotational speed of 122, a reversal occurs in which the sound pressure level of the fourth test sample 116, with an open area ratio of 0.5%, is the highest.

[0058] Therefore, in order to obtain a stable noise reduction effect as the engine speed increases, it is desirable that the opening ratio of the micro-holes 40 be 0.8% or higher.

[0059] In this embodiment, the porosity ratio, which is the sum of the opening areas of all microholes 40 formed in the exhaust pipe 30 relative to the surface area of ​​the exhaust pipe 30 covered by the outer wall portion 44, is set to be 0.8% or more and 1.4% or less.

[0060] (Mechanism of Action and Effects) According to the above embodiments, the following effects are achieved.

[0061] The silencer 10 of this embodiment is a silencer 10 provided in the exhaust path 12. The silencer 10 is formed in the exhaust pipe 30 through which the exhaust gas G flows, and in the nodal region 36 of the exhaust pipe 30 where at least the nodal portion 34 of the air column resonance 32 generated in the exhaust path 12 is located, with each opening area being 2.6 mm². 2 The silencer 10 comprises a plurality of microholes 40, and an outer wall portion 44 that covers the portion of the exhaust pipe 30 in which the microholes 40 are formed and forms an empty space 42 on the outer circumference of the exhaust pipe 30.

[0062] In this configuration, the exhaust gas G flowing through the exhaust pipe 30 moves back and forth between the inside of the exhaust pipe 30 and the space 42 on the outer periphery of the exhaust pipe 30 via the microholes 40. At this time, friction occurs between the particles of the exhaust gas G and the edge 40A of the microholes 40, generating frictional heat. As a result, the energy of the air column resonance 32 generated in the exhaust path 12 by the exhaust gas G is converted into frictional heat and reduced.

[0063] Thus, the silencer 10 achieves its sound-dampening effect by attenuating the air column resonance 32 through friction between the exhaust gas G particles and the edge 40A of the microhole 40. For this reason, compared to the case where sound dampening is performed using glass wool provided on the outer circumference of the exhaust pipe 30, the silencer 10 eliminates the processing costs and material costs for filling with glass wool. Therefore, it is possible to reduce the cost of the silencer 10.

[0064] Furthermore, the microholes 40 are formed in the nodal region 36 of the exhaust pipe 30 where the nodal portion 34 of the column resonance 32 that resonates in the exhaust path 12 is located. The particle velocity of the exhaust gas G that forms the column resonance 32 is higher in the nodal region 36 of the exhaust pipe 30 where the nodal portion 34 of the column resonance 32 is located.

[0065] As a result, the amount of frictional heat generated by the particles of exhaust gas G and the edge 40A of the microhole 40 increases, which further increases the reduction in the energy of the air column resonance 32 and enhances the sound-dampening effect of the microhole 40.

[0066] Thus, since the silencer 10 can achieve a sound-dampening effect without using glass wool, it is possible to reduce the diameter and shorten the length compared to the case where it is necessary to secure a filling space for a predetermined amount of glass wool around the outer circumference of the exhaust pipe 30.

[0067] Furthermore, since the silencer 10 can achieve a sound-dampening effect without using glass wool, it can be used even in environments where the heat resistance temperature of glass wool exceeds the limit.

[0068] Furthermore, since the silencer 10 does not require glass wool, it is lighter than when glass wool is used, and allows for smoother discharge of exhaust gas G. In addition, because the silencer 10 does not use glass wool, measures to prevent scattering due to glass wool deterioration are unnecessary, and recycling is easier as there is no need to separate the glass wool during recycling.

[0069] In the silencer 10 of this embodiment, the opening area is 0.8 mm 2 That's all.

[0070] According to this configuration, the opening area of ​​the microhole 40 is 0.8 mm². 2 2.6mm 2 As a result, it becomes possible to obtain a sound-dampening effect while maintaining ease of processing.

[0071] In the silencer 10 of this embodiment, the porosity ratio, which is the sum of the opening areas of the multiple microholes 40 relative to the surface area of ​​the exhaust pipe 30 covered by the outer wall portion 44, is 1.4% or less.

[0072] With this configuration, the silencer 10 has an opening ratio of 1.4% or less for the microholes 40, which makes it possible to improve the sound-dampening effect compared to when using glass wool for sound dampening.

[0073] In the silencer 10 of this embodiment, the opening ratio is 0.8% or more.

[0074] With this configuration, the porosity of the microholes 40 will be between 0.8% and 1.4%.

[0075] Therefore, the silencer 10 can achieve a stable noise reduction effect regardless of the engine speed, for example, compared to the case where the opening ratio of the microholes 40 is less than 0.8%.

[0076] In the silencer 10 of this embodiment, the microholes 40 formed in the exhaust pipe 30 are through holes that ensure the passage of exhaust gas G toward the radially outward direction 80.

[0077] With this configuration, the micro-holes 40 can enhance the sound-dampening effect compared to the case where the flow of exhaust gas G toward the radially outward 80 is obstructed.

[0078] The silencer 10 in this embodiment constitutes a center muffler positioned between the main muffler 16, which is located near the outlet of the exhaust gas G in the exhaust path 12, and the catalytic converter 18, which is located downstream of the engine.

[0079] In this configuration, the exhaust gas G emitted from the engine as an internal combustion engine has harmful substances removed by the catalyst 18, and then is silenced by the center muffler, which is part of the silencer 10, and the main muffler 16, which is located near the outlet of the exhaust path 12.

[0080] In this embodiment, the case where the cross-sectional shape of the outer wall portion 44 of the silencer 10 is elliptical was used as an example for explanation, but the shape of the outer wall portion 44 of the silencer 10 is not limited to this shape. The outer wall portion 44 of the silencer 10 will have the same effects as in the embodiment even if it has the shape shown in the following modified example.

[0081] <Variation> Next, a modified example of this embodiment will be described with reference to Figures 11 to 13.

[0082] <First Torture> Figure 11 is a longitudinal cross-sectional view showing a silencer 200 according to the first modified example.

[0083] In the first modified example, the silencer 200 has a circular cross-sectional shape for the cylindrical body 60 that constitutes the outer wall portion 44 of the silencer 200. Furthermore, the distance from the cylindrical body 60 of the outer wall portion 44 to the exhaust pipe 30 surrounded by the outer wall portion 44 is approximately constant around the entire circumference, and this silencer 200 also functions in the same way as the silencer 10 of the embodiment.

[0084] Furthermore, although the above-described embodiment used a silencer 10 in which circular micro-holes 40 are formed in the exhaust pipe 30 as an example, the shape of the micro-holes 40 is not limited to this shape. Even if the micro-holes 40 have the shape shown in the following modified example, the same or equivalent parts as in the embodiment will produce the same effects and advantages.

[0085] <Second variation> Figure 12 is an enlarged view showing the surface of the exhaust pipe 30 according to the second modified example, showing the state in which the outer wall portion 44 of the silencer 210 has been removed.

[0086] The microholes 212 formed in the exhaust pipe 30 are elongated holes that are long in the axial direction J of the exhaust pipe 30. The arrangement of the microholes 212 is the same as in the embodiment. Also, the opening area of ​​each microhole 212 is the same as in the embodiment.

[0087] <Third variation> Figure 13 is an enlarged view showing the surface of the exhaust pipe 30 according to the third modified example, showing the state in which the outer wall portion 44 of the silencer 220 has been removed.

[0088] The microholes 222 formed in the exhaust pipe 30 are composed of louver holes formed by cutting and bending a portion of the exhaust pipe 30 radially outward 80, and open in the axial direction J of the exhaust pipe 30.

[0089] Specifically, the microhole 222 extends from the edge of the opening 224 of the exhaust pipe 30 and includes a roof portion 226 that reaches the radially outer side 80 of the opening 224. The exhaust gas G discharged from the opening 224 of the exhaust pipe 30 has its flow radially outward 80 obstructed by the roof portion 226 and is also guided axially J by the roof portion 226.

[0090] The arrangement of the microholes 222 is the same as in the embodiment. Furthermore, the opening area of ​​each microhole 222 is equivalent to that in the embodiment.

[0091] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

[0092] Furthermore, the aforementioned silencers 10, 200, 210, and 220 may also be used in piping other than that used in automobiles, such as factory piping. [Explanation of Symbols]

[0093] 10, 200, 210, 220 Silencer 12 Exhaust path 14. Muffler device 16 Main muffler 18 Catalyst 32 Air column resonance 34 Nodes 34A Node position The area of ​​Section 36 40, 212, 222 microholes 40B Microhole 42 Space 44. Outer wall portion 80 radial direction outward

Claims

1. A silencer installed in the exhaust path, The exhaust pipe through which exhaust gases pass, At least in the region of the exhaust pipe node where the nodal portion of the air column resonance generated in the exhaust path is located, each opening has an area of ​​2.6 mm ２ The following are multiple microholes, An outer wall portion that covers the portion of the exhaust pipe in which the microholes are formed and forms a hollow space on the outer circumference of the exhaust pipe, Equipped with, Silencer.

2. A silencer according to claim 1, The aforementioned opening area is 0.8 mm ２ That's all. Silencer.

3. A silencer according to claim 2, The porosity ratio, which is the sum of the opening areas of the multiple microholes relative to the surface area of ​​the exhaust pipe covered by the outer wall, is 1.4% or less. Silencer.

4. A silencer according to claim 3, The aforementioned porosity is 0.8% or more. Silencer.

5. A silencer according to claim 4, The microholes formed in the exhaust pipe are composed of through holes that ensure the passage of exhaust gas radially outward. Silencer.

6. A silencer according to any one of claims 1 to 5, In the aforementioned exhaust path, a center muffler is positioned between the main muffler located near the exhaust gas outlet and the catalyst located downstream of the internal combustion engine. Silencer.

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