JP2006207378A - Noise reduction device for exhaust system and exhaust system having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively reduce sound radiation while suppressing a cost. <P>SOLUTION: In this noise reduction device 10A, exhaust from a driving source flows from one end side to the other end side of an inner pipe 11, an outer pipe 12 is disposed outside the inner pipe 11 so that both pipe ends of the outer pipe 12 are closed to surround an outer circumference of the inner pipe 11 through a space S, and a part surrounded by the outer pipe 12 forms double-pipe structure constituted of the outer pipe 12 and the inner pipe 11. A lot of small holes 13 are formed in a pipe wall of the inner pipe 11 of a part of a range of a longitudinal direction of the double pipe structure so that the small holes communicates between the inside and the outside of the inner pipe 11, and a length L of a part with no small hole is set to be 300mm or less. The noise reduction device 10A is arranged inside the muffler interposed in an exhaust passage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is equipped with an exhaust system that exhausts exhaust generated in a power source such as an engine or compressor of an automobile or a fuel cell stack of a fuel cell automobile into the atmosphere, thereby reducing noise caused by the exhaust. The present invention relates to a noise reduction device for an exhaust system to be reduced, and an exhaust system including the device.

Conventionally, an exhaust system of an automobile engine as shown in FIG. 11 is known as an example of such an exhaust system. In the figure, 1 is an exhaust tube, 2 is an exhaust manifold that collects exhaust exhausted from each cylinder of an engine (not shown) and connects it to the exhaust tube 1, and 3 is a harmful substance in the exhaust (for example, CO, HC, NOx) Etc.) are converted into harmless substances (for example, CO ₂ , H ₂ O, NO _2, etc.) by catalytic reaction, 4 is a pre-muffler that roughly reduces noise caused by exhaust, and 5 is an appropriate value for the noise. This is a rear muffler (main muffler).

  The exhaust manifold 2 to the rear muffler 5 are sequentially connected by the exhaust tube 1. In the figure, 6 is a flexible tube. This flexibly connects the exhaust tube 1 connected to the exhaust manifold 2 and the exhaust tube 1 connected to the catalytic converter 3. In general, a portion upstream of the pre-muffler 4 of the exhaust tube 1, that is, a portion on the engine side is called a front tube 1A, and a portion downstream of the pre-muffler 4, that is, the rear muffler 5 side is connected to the center tube 1B. is called.

  By the way, in recent years, in such an exhaust system, there is a tendency to increase the diameter of the exhaust tube 1 in order to reduce the back pressure, or to increase the volume of the pre-muffler 4 and the rear muffler 5 in order to increase the silence volume. As a result, the muffler cross-sectional area is increasing.

  However, when the diameter of the exhaust tube 1 is increased in this way, the pressure loss is reduced and the pulsation pressure generated from the engine is less likely to be attenuated, so that radiated sound is likely to be generated from a part of the exhaust system due to the pulsation. End up.

  On the other hand, when the size of the pre-muffler 4 and the rear muffler 5 is increased in order to increase the muffled volume, the cross-sectional shape of each of the mufflers 4 and 5 must be flattened due to limitations due to the vehicle layout, etc. As a result, radiated sound tends to be generated from the muffler surface. In particular, since the rear muffler 5 is usually larger than the pre-muffler 4, it can be said that generation of radiated sound is more likely to occur.

In order to reduce such radiated sound, in recent years, measures to improve the muffling efficiency by changing the rigidity of the muffler (for example, refer to Patent Document 1 and Patent Document 2), and sound absorption made of glass wool or the like in the pre-muffler. Measures have been taken to improve the noise reduction level of the entire exhaust system by filling the material (see, for example, Patent Document 3).
JP 2002-21594 A Japanese Unexamined Patent Publication No. 2000-213328 (pages 2 and 3 and FIG. 1) JP-A-9-49415

  However, in the techniques described in Patent Document 1 and Patent Document 2, a noise reduction level difference is produced depending on the exhaust system, and it is difficult to standardize the rear muffler 5, so the rigidity of the rear muffler 5 must be appropriately changed for each exhaust system. There is a problem that increases costs.

  In addition, the technique described in Patent Document 3 has a problem that not only the cost is increased by using many sound absorbing materials, but also the sound absorbing performance is deteriorated due to scattering of the sound absorbing materials, and environmental problems are caused.

  In the first place, sound absorbing materials are considered to be water-condensed and fixed due to condensed water, which leads to deterioration in sound-absorbing properties, low recyclability, and disadvantages from recent social trends. It is a material that wants to avoid (use as much as possible).

  Accordingly, the present invention has been made to solve the above-described problem, and includes a noise reduction device for an exhaust system that can effectively reduce radiated sound while suppressing cost, and the noise reduction device. It aims to provide an exhaust system.

  The noise reduction device for an exhaust system of the invention of claim 1 surrounds the outer periphery of the inner pipe through a space outside the inner pipe through which exhaust from the power source flows from one end side to the other end side. In this way, the outer tube whose both tube ends are closed is arranged, and the portion surrounded by the outer tube is made into a double tube structure by the outer tube and the inner tube, and the length direction of the double tube structure A large number of small holes communicating with the inside and outside of the inner tube are formed in the tube wall of the inner tube in a part of the range, and the length of the portion where the small hole is not formed is set to 300 mm or less.

  A second aspect of the present invention is the noise reduction device for an exhaust system according to the first aspect, wherein the pipe diameter is reduced to a part of the length direction of the outer pipe of the double pipe structure as compared with other parts. A reduced diameter portion is provided.

  An exhaust system according to a third aspect of the invention is characterized in that the noise reduction device for an exhaust system according to the first or second aspect is disposed inside a muffler interposed in an exhaust passage.

  The noise reduction device according to the first aspect of the present invention has a simple configuration in which an outer tube is provided outside the inner tube to form a double tube structure, and a small hole is formed in a part of the tube wall of the inner tube. Since the device only extends in the tube axis direction, the device can be miniaturized and is not subject to layout restrictions on surrounding components. Therefore, it can be easily disposed, for example, in the middle of the exhaust pipe or in the muffler while reducing the cost. Further, since only a small hole is provided in the tube wall of the inner tube through which the exhaust flows, the airflow noise and the pressure loss level do not deteriorate. In addition, for example, it is possible to reduce the radiated sound simply by mounting the device in the muffler, so that the main part of the muffler can be standardized, leading to a significant cost reduction.

  Further, the portion where the small holes are not formed is a space necessary for resonance, but the length is set to 300 mm or less, so that it is generated based on the pulsation of the power source while being small. Generation of noise can be effectively suppressed. Incidentally, the peak level of radiated sound generation can be reduced by 5 to 10 dB or more. Moreover, not only the radiated sound but also the effect of reducing the discharge sound and airflow sound in the middle to high frequency range can be exhibited. For example, it is possible to attenuate high-frequency components of discharge noise of 500 Hz or higher, so that when equipped in a muffler, it is possible to reduce the middle to high-frequency silencing structure in the muffler, and to reduce the size of the muffler It can also contribute to the transformation. Note that if there are many high-frequency components in the radiated sound due to entanglement with the center frequency of the radiated sound to be reduced, it is preferable to set the length of the portion where the small holes are not formed short, and longer if there are many low-frequency components. It is preferable to set.

  According to the second aspect of the present invention, since the reduced diameter portion in which the tube diameter is reduced compared to the other portions is provided in a part in the length direction of the outer tube of the double tube structure, the ratio of the reduced diameter (the reduction ratio) ) Is increased, the frequency to be attenuated can be tuned to the lower frequency side.

  According to the invention of claim 3, since the noise reduction device is arranged inside the muffler interposed in the exhaust passage, the layout can be easily performed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a noise reduction device 10A according to a first embodiment of the present invention. In FIG. 1, the thickness of the outer tube is not shown.

  In this noise reduction device 10 </ b> A, both ends of the pipes are disposed so as to surround the outer periphery of the inner pipe 11 outside the inner pipe 11 through which exhaust from the power source flows as indicated by an arrow A from one end side to the other end side. The outer tube 12 is closed, and the portion surrounded by the outer tube 12 has a double tube structure composed of the outer tube 12 and the inner tube 11. The outer tube 12 has a cylindrical peripheral wall 12 c and both end walls 12 a and 12 b, and a space S having a predetermined size is secured between the outer tube 12 and the inner tube 11.

  Here, if the cross-sectional area of the outer tube 12 is too large, the influence of resonance in the cross-sectional direction appears. Therefore, in the case of a circular cross section (which may be an equivalent cross section), the diameter is preferably 100 mm or less. In the case of an elliptical cross section, it is preferable that the length of the major axis is 100 mm or less. However, if the cross section of the outer tube 12 is made too small, there is a possibility that a sufficient silence level cannot be obtained.

  Further, in this noise reduction device 10A, a large number of small holes 13 communicating the inside and outside of the inner tube 11 are formed on the tube wall of the inner tube 11 in a predetermined range on the upstream end side in the length direction of the portion having the double tube structure. The length L (the distance from the end of the portion where the small hole 13 is formed to the downstream end wall 12b) which is formed as a group and does not form the small holes 13 is 300 mm or less. Is set.

  Further, a drain hole 12e for draining condensed water is formed in the bottom of the outer tube 12 with a size that does not adversely affect acoustics. In addition, although it is desirable that the group of small holes 13 formed in the tube wall of the inner tube 11 has a large aperture ratio so that sound waves can easily enter and exit, if the aperture ratio is 30% or more, sufficient silencing The effect can be expected. Since the small hole 13 is clogged with impurities when the hole diameter is small, in the case of an internal combustion engine, the diameter is desirably about 3 mm (Φ3). Further, in the case of clean exhaust such as a fuel cell vehicle, it is preferable that the hole diameter of the small hole 13 is 1 mm to 2 mm (Φ1 to Φ2) effective in silencing.

  These small holes 13 can be easily opened by pressing or the like in the tube wall itself of the inner tube 11. Alternatively, the small hole 13 may be formed by pressing at the stage of a flat plate, and the inner tube 11 may be configured later by winding it into a pipe shape. Further, only the range in which the small holes 13 are provided may be formed of a foam metal pipe or a sintered metal pipe having a large aperture ratio.

  If only a large number of small holes 13 are provided in the tube wall of the inner tube 11 in this manner, the flow of exhaust gas in the inner tube 11 is not particularly affected, and deterioration of airflow noise and pressure loss can be prevented.

[Second Embodiment]
FIG. 2 is a cross-sectional view schematically showing a schematic configuration of a noise reduction device 10B according to the second embodiment of the present invention. In FIG. 2, the thickness of the outer tube is not shown.

  Most of the parts are the same as the noise reduction device 10A of the first embodiment. However, in this noise reduction device 10B, the upstream end in the length direction of the outer pipe 12 constituting the double pipe structure is a different feature point. On the side, a reduced diameter portion 12E is provided in which the tube diameter is smaller than other portions (downstream portions). That is, the outer tube 12 is configured as a stepped tube having a reduced diameter portion 12E and an enlarged diameter portion 12F.

  The reduced diameter portion 12E covers a portion where the small hole 13 is formed. In this case, the diameter reduction ratio, that is, the aperture ratio is a parameter that determines the acoustic performance (described later). Since the other configuration is exactly the same as the noise reduction device 10A of the first embodiment, the same components are denoted by the same reference numerals and description thereof is omitted.

  Since the noise reduction devices 10A and 10B having the above-described configuration are provided with a small hole 13 in a part of the inner tube 11 and a resonance cavity (space S) formed by the outer tube 12 outside thereof, When resonance occurs in the devices 10 </ b> A and 10 </ b> B, sound waves can be converted into thermal energy and attenuated by the resistance of the small holes 13. In addition, since the length of the resonance space S is set to 300 mm or less, it is possible to effectively suppress the generation of noise based on the pulsation of the power source while being small. Incidentally, the peak level of radiated sound generation can be reduced by 5 to 10 dB or more (described later). Further, not only the radiated sound but also the effect of reducing the discharge sound and the airflow sound in the middle to high frequency range can be exhibited. For example, the high frequency component of the discharge noise of 500 to 3000 Hz can be attenuated (described later). If the radiated sound has many high-frequency components in relation to the center frequency of the radiated sound to be reduced, the length L of the portion where the small holes 13 are not formed may be set short, and if there are many low-frequency components. You can set it longer.

  Further, the noise reduction devices 10A and 10B are provided with an outer tube 12 outside the inner tube 11 to form a double tube structure, and only a small hole 13 is formed in a part of the tube wall of the inner tube 11. Therefore, the device can be miniaturized and is not subject to layout restrictions on surrounding parts. Therefore, for example, it can be easily disposed in the middle of the exhaust pipe or in the muffler while suppressing the cost.

“Embodiment in which noise reduction device is placed in exhaust system muffler”
Below, the example in the case of equip | installing the noise reduction device 10A, 10B of the said embodiment in the exhaust system muffler is demonstrated. The exhaust system given here as an example is the exhaust system of the automobile engine shown in FIG. 11, and this exhaust system includes two mufflers, a pre-muffler 4 and a rear muffler 5 connected by an exhaust tube 1. The noise reduction devices 10A and 10B can be arranged inside these mufflers 4 and 5. In the drawings referred to below, the case where the noise reduction device 10A of the first embodiment is disposed is illustrated, but the noise reduction device 10B of the second embodiment may be replaced.

  3 to 6 show examples when the noise reduction devices 10A and 10B are installed in the pre-muffler 4. FIG.

  In the pre-muffler 4A of FIG. 3, an exhaust flow pipe 21 is provided in the center of the drum-shaped muffler main body 22 through both end walls 22a and 22b of the muffler main body 22, and the exhaust flow pipe 21 in the muffler main body 22 is provided. A large number of small holes 23 are formed in a predetermined range on the downstream side of the wall, and the noise reduction devices 10 </ b> A and 10 </ b> B are disposed in an upstream portion of the exhaust flow pipe 21 in the muffler body 22. In this case, the exhaust flow pipe 21 itself corresponds to the inner pipe 11.

  In addition to the configuration of the pre-muffler 4A shown in FIG. 3, a sound absorbing material 25 is filled in the inner space of the muffler main body 22 in the pre-muffler 4B shown in FIG.

  In addition to the configuration of the pre-muffler 4A shown in FIG. 3, the pre-muffler 4C shown in FIG. 5 is provided with a partition wall 24 that partitions the upstream side and the downstream side inside the muffler main body 22 and reduces noise in the upstream chamber 26A. The devices 10A and 10B are positioned, and a portion where a large number of small holes 23 are formed on the downstream side of the exhaust flow pipe 21 is positioned in the downstream chamber 26B. In addition, a large number of small holes 27 are newly formed on the exhaust flow pipe 21 at a position upstream of the noise reduction devices 10A and 10B in the upstream chamber 26A.

  In the pre-muffler 4D of FIG. 6, in addition to the configuration of the pre-muffler 4C of FIG. 5, the sound absorbing material 25 is filled in the downstream chamber 26B.

  7 and 8 show examples when the rear muffler 5 is equipped with noise reduction devices 10A and 10B.

  In the rear muffler 5A of FIG. 7, three pipes are arranged in a drum-like muffler main body 55 in parallel to the axial direction. The first pipe is an inlet pipe 51 into which exhaust gas is introduced, the second pipe is an outlet pipe 52 through which exhaust gas is led out, and the third pipe is a relay pipe 53.

  The interior space of the muffler body 55 is divided into three chambers in the axial direction by the first and second partition walls 56 and 57, that is, the upstream first chamber 58, the intermediate second chamber 59, and the downstream side. The inlet pipe 51 has a distal end penetrating from the one end wall 55a side of the muffler main body 55 through the end wall 55a and the two partition walls 56 and 57, to the third chamber 60. It is inserted into the chamber 60.

  The outlet pipe 52 is inserted into the first chamber 58 from the other end wall 55 b side of the muffler main body 55 through the end wall 55 b and the second and first partition walls 57 and 58. In addition, the relay pipe 53 is disposed so as to penetrate the first and second partition walls 56 and 57, thereby communicating the first chamber 58 and the third chamber 60 across the second chamber 59. Yes.

  In addition, a large number of small holes 61 are provided on the pipe wall of the inlet pipe 51 to communicate the inner space of the inlet pipe 51 with the second chamber 59, and the inner wall of the relay pipe 53 is also formed on the pipe wall of the relay pipe 53. A large number of small holes 62 that allow the space to communicate with the second chamber 59 are provided. The noise reduction devices 10 </ b> A and 10 </ b> B are disposed on the inlet pipe 51 so as to straddle the first chamber 58 and the second chamber 59. In this case, the inlet pipe 51 corresponds to the inner pipe 11.

  In the rear muffler 5B of FIG. 8, three pipes are arranged in a drum-like muffler body 75 in parallel to the axial direction. The first pipe is an inlet pipe 71 into which exhaust is introduced, the second pipe is an outlet pipe 72 from which exhaust is led out, and the third pipe is a relay pipe 73.

  The inner space of the muffler main body 75 is divided into three chambers in the axial direction by the first and second partition walls 76 and 77, that is, the upstream first chamber 78, the intermediate second chamber 79, and the downstream side. The inlet pipe 71 has a distal end penetrating from the one end wall 75a side of the muffler main body 75 through the end wall 75a and the two partition walls 76 and 77 to the third chamber 80. It is inserted into the chamber 80.

  The outlet pipe 72 is inserted into the second chamber 79 from the other end wall 75 b side of the muffler body 75 through the end wall 75 b and the second partition wall 77. In addition, the relay pipe 73 is disposed so as to penetrate the first and second partition walls 76 and 77, and thus communicates the first chamber 78 and the third chamber 70 across the second chamber 79. However, the first chamber 78 is closed and there is no air flow.

  In addition, a large number of small holes 81 are provided on the pipe wall of the inlet pipe 71 to communicate the inner space of the inlet pipe 71 with the first chamber 78, and the inner wall of the relay pipe 73 is also formed on the pipe wall of the relay pipe 73. A large number of small holes 82 that allow the space to communicate with the second chamber 79 are provided. The first chamber 78 is filled with a sound absorbing material 85. The noise reduction devices 10 </ b> A and 10 </ b> B are disposed on the inlet pipe 71 so as to be located in the second chamber 79. In this case, the inlet pipe 71 corresponds to the inner pipe 11.

  As described above, since the noise reduction devices 10A and 1B according to the embodiment of the present invention are devices that extend in the tube axis direction and are small in size, the rear muffler 5 (5A) is also included in the pre-muffler 4 (4A to 4D). 5B), the pipe in the muffler can be used as the inner pipe 11 and can be arranged freely and easily.

  By the way, it is a high frequency region component of 500 Hz to 3000 Hz among the frequency components of the radiated sound that is particularly problematic regarding the radiated sound of the exhaust system of the automobile engine. These frequency band components are considered to appear greatly when the engine speed is 500 to 2000 rpm. FIG. 9 shows the result of evaluating the difference in the radiated sound level when the noise reduction device according to the embodiment of the present invention is equipped and when not equipped with the actual radiated sound machine. When this device is not equipped, a large radiated sound protrudes when the engine speed is in the range of 500 to 2000 rpm. However, when this device is equipped, it can be seen that a significant noise reduction effect can be obtained particularly within that range. . For example, if the noise reduction device of the present embodiment is used, the peak level of radiated sound generation can be reduced by about 7 dB to 15 dB.

  As described above, the noise reduction devices 10A and 10B are used in an exhaust system of an automobile engine, so that when exhaust generated in the engine is circulated through the exhaust tube 1, high-frequency components due to pulsation of the exhaust, that is, radiation. The frequency component of 500 to 3000 Hz that is the source of sound can be attenuated by resonating in the outer tube 12. For this reason, the radiated sound from the mufflers 4 and 5 can be reduced.

  In addition, when applying the noise reduction device of the present invention to an exhaust system of an automobile or the like, the muffler tends to flatten as the restrictions on the underfloor layout become more severe in the future. The problem of sound is increasing. Among these, a technology capable of reducing the radiated sound by standardizing the muffler and mounting a small noise reduction device becomes important. Even in the case of a flat muffler structure, the noise reduction device of the present invention can be mounted in the flat muffler, and the generation of radiated sound due to flattening can also be suppressed.

[Change in center frequency due to changes in the warp ratio of the warped part]
FIG. 10 shows the results of examining how the center frequency of resonance changes by changing the diameter reduction ratio (diaphragm ratio) of the diameter reduction portion 12E in the noise reduction device 10B of the second embodiment. ing. As for the drawing ratio, when the sectional area of the reduced diameter portion 12E is S1, and the sectional area of the enlarged diameter portion 12F is S2,
Aperture ratio = (1−S1 / S2) × 100 [%]
Define in.

  As can be seen from this figure, the higher the aperture ratio, that is, the smaller the diameter of the reduced diameter portion 12E, the greater the rate of movement of the resonating center frequency to the lower band side. In this way, by adjusting the degree of diameter reduction, the resonance center frequency region can be moved to cope with low frequencies.

[Other Embodiments]
Although specific embodiments to which the present invention is applied have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made.

  For example, in the above embodiment, the case where the noise reduction devices 10A and 10B are provided in the mufflers 4 and 5 has been described as an example. However, the noise reduction devices 10A and 10B of the present invention are provided at arbitrary positions on the exhaust pipe. can do.

  In the above embodiment, the case where both the inner tube 11 and the outer tube 12 of the noise reduction devices 10A and 10B are circular is mainly described. However, the inner tube 11 and the outer tube 12 have an oval or rectangular cross section. Polygon may be used. Moreover, the cross-sectional shapes of the inner tube 11 and the outer tube 12 may be different.

  Further, the number of the noise reduction devices 10A and 10B attached may be appropriately selected according to the radiation sound attenuation level.

It is sectional drawing which shows schematic structure of the noise reduction device of 1st Embodiment of this invention. It is sectional drawing which shows schematic structure of the noise reduction device of 2nd Embodiment of this invention. It is sectional drawing which shows the 1st example of the pre-muffler which has arrange | positioned the noise reduction device of embodiment of this invention inside. It is sectional drawing which shows the 2nd example of the pre-muffler which has arrange | positioned the noise reduction device of embodiment of this invention inside. It is sectional drawing which shows the 3rd example of the pre-muffler which has arrange | positioned the noise reduction device of embodiment of this invention inside. It is sectional drawing which shows the 4th example of the pre-muffler which has arrange | positioned the noise reduction device of embodiment of this invention inside. It is sectional drawing which shows the 1st example of the rear muffler which has arrange | positioned the noise reduction device of embodiment of this invention inside. It is sectional drawing which shows the 2nd example of the rear muffler which has arrange | positioned the noise reduction device of embodiment of this invention inside. It is a characteristic comparison figure which shows the difference in the level of a radiated sound with and without the noise reduction device of embodiment of this invention. It is a characteristic view of the noise reduction device of 2nd Embodiment of this invention. It is a perspective view which shows the general structure of the exhaust system of the conventional motor vehicle engine.

Explanation of symbols

4, 4A, 4B, 4C, 4D ... Pre-muffler 5, 5A, 5B ... Rear muffler 10A, 10B ... Noise reduction device 11 ... Inner tube 12 ... Outer tube 13 ... Small hole

Claims (3)

The ends of both pipes are disposed outside the inner pipe (11) through which the exhaust from the power source flows from one end side to the other end side so as to surround the outer periphery of the inner pipe (11) through the space (S). The closed outer pipe (12) is disposed, and the portion surrounded by the outer pipe (12) is formed into a double pipe structure of the outer pipe (12) and the inner pipe (11). A large number of small holes (13) communicating the inside and outside of the inner tube (11) are formed in the tube wall of the inner tube (11) in a partial range in the longitudinal direction of the tube structure, and the small holes (13) are formed. Noise reduction device for exhaust system (10A, 10B), characterized in that the length (L) of the part not to be set is set to 300 mm or less. A noise reduction device for an exhaust system according to claim 1,
Noise reduction for an exhaust system, characterized in that a reduced diameter portion (12E) having a reduced diameter compared to other portions is provided in a part of the length of the outer tube (12) of the double tube structure. Device (10B). The exhaust system noise reduction device (10A, 10B) according to claim 1 or 2 is disposed inside a muffler (4, 4A, 4B, 4C, 4D, 5, 5A, 5B) interposed in the exhaust passage. Exhaust system characterized by

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