Patent Application
20210246818
This application claims the benefit of Japanese Patent Application No. 2020-21640 filed on Feb. 12, 2020 with the Japan Patent Office, the entire disclosure of which is incorporated herein by reference.
The present disclosure relates to a muffler.
Japanese Unexamined Patent Application Publication No. 2008-138608 discloses a muffler in an exhaust system of an internal combustion engine for the purpose of noise reduction. The muffler includes an exhaust pipe having several holes.
The muffler described in Japanese Unexamined Patent Application Publication No. 2008-138608 facilitates muffling effect on a sound in a specific frequency by increasing the number of holes on an exhaust pipe or increasing an area of the holes. However, such increase in the number or area of the holes in the exhaust pipe causes reflection of sound waves at the holes within the exhaust pipe. This makes it likely to form nodes in standing waves within the exhaust pipe. As a result, such a muffler may be incapable of achieving the muffling effect on a sound in a specific frequency intended to be dampened.
In one aspect of the present disclosure, it is preferable to provide a muffler capable of muffling effect in a specific frequency while reducing generation of a node of a standing wave.
In one embodiment of the present disclosure, a muffler comprises an exhaust pipe, a shell, and a cover. The exhaust pipe includes communication holes and is configured to allow an exhaust gas to flow through an interior of the exhaust pipe. The shell is disposed outside the communication holes to cover the communication holes. The cover has a tubular shape. The cover is disposed between the exhaust pipe and the shell and at a specific distance from the exhaust pipe. The cover covers at least one of the communication holes.
In the configuration as described above, the cover is placed in a position where a node of a standing wave is to be formed when the communication holes are covered with the shell. This restricts reflection of sound waves in an area where the cover overlaps the communication holes in the exhaust pipe, comparing with a case in which the communication holes are covered with the shell alone. Accordingly, generation of a node of a standing wave is reduced. As a result, the configuration as described above enables muffling effect in a specific frequency while reducing generation of a standing wave with a new frequency.
In one embodiment of the present disclosure, each of the exhaust pipe and the cover may have a cylindrical shape. The exhaust pipe and the cover may have a common central axis. Further, a diameter of the exhaust pipe may be set to not less than 1.8 times larger than a distance between the exhaust pipe and the cover.
By such a configuration, a higher muffling effect can be obtained, comparing with conventional configurations. This is shown in experimental results, which will be described below.
In one embodiment of the present disclosure, both ends of the cover in an axial direction of the exhaust pipe may be fixed to the exhaust pipe.
By such a configuration, misalignment and vibrations of the cover can be limited. This further enhances an inhibiting effect on generation of a node of a standing wave and muffling effect.
In one embodiment of the present disclosure, at least one of the both ends of the cover in the axial direction of the exhaust pipe may be configured as an open end, which includes a gap between the cover and the exhaust pipe.
In the configuration as described above, the gap between the exhaust pipe and the cover is also formed around the open end of the cover, which is open to an outer peripheral surface of the exhaust pipe. In this case, an opening (gap) of the open end of the cover may also serve as one of auxiliary holes, which will be described below. Accordingly, an area available for forming the auxiliary holes is increased in the cover, thereby allowing for facilitation of the muffling effect in the muffler.
In one embodiment of the present disclosure, the cover may include the auxiliary holes disposed in a part facing the outer peripheral surface of the exhaust pipe.
By such a configuration, a flow of the exhaust gas between the cover and the shell can be ensured. Consequently, the exhaust gas is expanded between the cover and the shell, thereby allowing for facilitation of the muffling effect.
In one embodiment of the present disclosure, the muffler may further comprise a sound absorbing material disposed between the exhaust pipe and the cover. The sound absorbing material covers the communication holes.
By such a configuration, the sound absorbing material limits vibrations produced by the exhaust gas, thereby allowing for facilitation of the muffling effect.
An example embodiment of the present disclosure will be described hereinafter by way of example with reference to the accompanying drawings, in which:
An exhaust system 10 shown in
The internal combustion engine 11 to which the exhaust system 10 is applied is not particularly limited, and includes transportation equipment such as automobiles, railways, vessels, and construction machines, and engines used for drivers or generators in power facilities.
The muffler 1 is disposed downstream of the main muffler 13. However, the muffler 1 may be disposed upstream of the main muffler 13. For example, the muffler 1 may be disposed between the catalytic converter 12 and the main muffler 13.
As shown in
The exhaust pipe 2 is a metal pipe allowing exhaust gas G to flow through an interior thereof. As shown in
As shown in
The communication holes 21 are disposed in a part of the straight portion 22 of the exhaust pipe 2 within the shell 3 and provided entirely on a peripheral surface of the straight portion 22. However, the communication holes 21 need not be necessarily provided entirely on the peripheral surface of the exhaust pipe 2.
Each size of the communication holes 21 and an interval therebetween may be changed as appropriate. However, a total open area of the communication holes 21 is large enough for at least one node in a standing wave to be formed in the exhaust pipe 2 within the shell 3 in configurations in which the cover 6 is not provided. It should be noted that a node of a standing wave is formed in the exhaust pipe 2 inside the shell 3, when sound waves are reflected by the communication holes 21 or when a pressure of the exhaust gas G in the exhaust pipe 2 is reduced by the communication holes 21, that is, it is considered equivalent to a state in which the exhaust pipe 2 is in an open state.
A shape of the communication hole 21 is not limited to a perfect circle, but may be other shapes such as an oval or a polygon. Further, the communication hole 21 may be provided with a louver such that a part of a pipe wall of the exhaust pipe 2 is cut and bent outward.
<Shell>
The shell 3 is a metal pipe disposed outside the exhaust pipe 2 to surround an outer peripheral surface of the exhaust pipe 2. The shell 3 has a cylindrical shape. The shell 3 is disposed outside the communication holes 21 in the exhaust pipe 2 so as to fully cover the communication holes 21. An inner diameter of the shell 3 is larger than an outer diameter of the exhaust pipe 2.
The shell 3 incudes a first opening 31 and a second opening 32, each of which has a smaller diameter toward an outer side of the exhaust pipe 2 in an axial direction. Each of the first opening 31 and the second opening 32 is fixed to the outer peripheral surface of the exhaust pipe 2, for example, by welding. The shell 3 surrounds the outer peripheral surface of the exhaust pipe 2, and is positioned to form a space between the shell 3 and the exhaust pipe 2. The first sound absorbing material 4 and the second sound absorbing material 5, which will be described below, are arranged in the space.
<Cover>
The cover 6 is a cylindrical member in contact with the second sound absorbing material 5 from outside in a radial direction of the exhaust pipe 2. The cover 6 is disposed between the exhaust pipe 2 and the shell 3.
The cover 6 has a tubular shape and covers at least one of the communication holes 21. The cover 6 may cover at least part of the communication holes 21. The cover 6 is disposed between the shell 3 and the exhaust pipe 2. The cover 6 is disposed at a distance E, which is specified in advance, from the exhaust pipe 2. The exhaust pipe 2 and the cover 6 each have a cylindrical body and a common central axis. Further, a diameter of the exhaust pipe 2, in particular, a diameter D of the outer peripheral surface of the exhaust pipe 2 located within the shell 3 and covered with the cover 6, is set to not less than 1.8 times as large as the distance E between the outer peripheral surface of the exhaust pipe 2 and an inner peripheral surface of the cover 6.
Here, in a graph shown in
As shown in
The data in examples shown in
The cover 6 includes a first end portion 62 and a second end portion 63, which are fixed to the exhaust pipe 2. The first end portion 62 and the second end portion 63 correspond to both ends of the cover 6 in the axial direction of the exhaust pipe 2. Specifically, the second end portion 63 has a smaller diameter toward a downstream in the direction in which the exhaust gas G flows. An end of the second end portion 63 is fixed to the outer peripheral surface of the exhaust pipe 2 by a fixing portion 64, for example, by welding. The second end portion 63 is an end portion of the cover 6 in the axial direction of the exhaust pipe 2. The second end portion 63 is positioned downstream in the direction in which the exhaust gas G flows.
The first end portion 62 does not taper and is fixed to the outer peripheral surface of the exhaust pipe 2, for example, by a connection member 65. The connection member 65 connects the first end portion 62 with the exhaust pipe 2. The first end portion 62 is the other end portion of the cover 6 in the axial direction of the exhaust pipe 2. The first end portion 62 is positioned upstream in the direction in which the exhaust gas G flows.
The connection member 65 is made of, for example, a metal rod. One end of the connection member 65 is fixed to the exhaust pipe 2, and the other end is fixed to the cover 6, thereby fixing the cover 6 to the exhaust pipe 2. The connection member 65 does not completely seal a gap, which is provided at the first end portion 62, between the cover 6 and the exhaust pipe 2, and partially remains the gap therebetween. Accordingly, the first end portion 62 is configured as an open end, which includes a gap between the exhaust pipe 2 and the cover 6. In other words, the connection member 65 is fixed to the exhaust pipe 2 in a state where the first end portion 62 of the cover 6 is open.
Further, the cover 6 includes auxiliary holes 61, which are disposed in a part facing the outer peripheral surface of the exhaust pipe 2. Each of the auxiliary holes 61 penetrates the cover 6 such that a space on a side where the exhaust pipe 2 is disposed is communicated with a space on a side where the shell 3 is disposed.
The communication holes 21 are not formed in a part of the outer peripheral surface of the exhaust pipe 2, to which the second end portion 63 is fixed. The communication holes 21 are formed in the exhaust pipe 2 only upstream from the most upstream part of the second end portion 63, that is, only in a more upstream side than a part defined by a dotted line in
<Sound Absorbing Material>
The first sound absorbing material 4 is disposed between the exhaust pipe 2 and the shell 3 to cover some of the communication holes 21.
Specifically, the first sound absorbing material 4 is disposed in an area nearby the first opening 31 of the shell 3, on the straight portion 22 of the exhaust pipe 2. In other words, the first sound absorbing material 4 is disposed so as to circumferentially surround an upstream part of the straight portion 22 of the exhaust pipe 2. The first sound absorbing material 4 is in contact with some of the communication holes 21 positioned upstream.
The first sound absorbing material 4 and the second sound absorbing material 5, which is described below, fills a space between the exhaust pipe 2 and the shell 3. Thus, no empty space between the exhaust pipe 2 and the shell 3 remains. Further, the first sound absorbing material 4 is disposed so as to reach an inner peripheral surface of the shell 3 from the outer peripheral surface of the exhaust pipe 2 in the radial direction of the exhaust pipe 2.
As a material of the first sound absorbing material 4, inorganic fibers such as glass fibers, may be used, for example. In some embodiments, an inorganic fiber assembly such as glass wool, an inorganic fabric, an inorganic knitting, a nonwoven inorganic fabric, or a structural body of inorganic fabrics partially bonded with a binder may be used as the first sound absorbing material 4.
The second sound absorbing material 5 fills a space between the cover 6 and the exhaust pipe 2. The second sound absorbing material 5 has a greater ventilation resistance than the first sound absorbing material 4. For example, the second sound absorbing material 5 contains a material with a higher density than the first sound absorbing material 4 and/or with a greater ventilation resistance than the first sound absorbing material 4. The first sound absorbing material 4 also fills a space between the cover 6 and the shell 3. Accordingly, in the present embodiments, the first sound absorbing material 4 is disposed outside the second sound absorbing material 5 in the radial direction of the exhaust pipe 2.
However, the first sound absorbing material 4 and the second sound absorbing material 5 may be interchanged in position, that is, replaced with each other. The first sound absorbing material 4 may be same as the second sound absorbing material 5, or no sound absorbing material may be provided inside the cover 6.
In an upstream area of the muffler 1, the first sound absorbing material 4 alone is disposed in the radial direction of the exhaust pipe 2. In an area where the cover 6 is disposed in the muffler 1, the second sound absorbing material 5 and the first sound absorbing material 4 are formed in a two-layered structure in the radial direction of the exhaust pipe 2.
All communication holes 21 in the exhaust pipe 2 are covered with either the first sound absorbing material 4 or the second sound absorbing material 5.
As shown in
The standing wave W1 has a waveform in a first mode in which both ends of the exhaust pipe 2 are nodes. A node of a standing wave is formed in a portion where pressure decreases significantly. For example, the node is formed in a part where an end portion of the exhaust pipe 2 is radially enlarged, or where the exhaust pipe 2 is open. Further, a node of the standing wave is formed in an area where the total open area of the communication holes 21 in the exhaust pipe 2 is relatively large with respect to, for example, a cross-sectional area of a flow passage of the exhaust pipe 2. In this area, a sound pressure within the exhaust pipe 2 is decreased or the sound waves are reflected by the communication holes 21, and thus a node of the standing wave is formed.
On the other hand, if the communication holes 21 in the exhaust pipe 2 where the standing wave W1 is generated are covered with the first sound absorbing material 4 alone without the cover 6, the exhaust gas G is discharged from the communication holes 21. This causes decrease in the sound pressure within the exhaust pipe 2 or leads to reflection of the sound waves, thereby to generate two standing waves W2 and W3 within the exhaust pipe 2, instead of the standing wave W1. A node S shown in
In the embodiments described above, the following effects can be obtained.
(1a) In one embodiment of the present disclosure, the muffler 1 comprises the exhaust pipe 2, the shell 3, and the cover 6. The exhaust pipe 2 includes the communication holes 21 and is configured to allow the exhaust gas G to flow through the interior of the exhaust pipe 2. The shell 3 is disposed outside the communication holes 21 to cover the communication holes 21. The cover 6 is tubular and covers at least one of the communication holes 21. The cover 6 is disposed between the exhaust pipe 2 and the shell 3 at a distance, which is specified in advance, from the exhaust pipe 2.
In the configuration as described above, the cover 6 is placed in a position where a node of the standing wave is formed. This restricts reflection of the sound waves in an area where the cover 6 overlaps the communication holes 21 in the exhaust pipe 2, thereby reducing generation of a node of the standing wave, comparing with a case in which the communication holes 21 are covered with the shell 3 alone. As a result, the configuration as described above enables the muffling effect in a specific frequency while reducing generation of a standing wave with a new frequency.
In
In
In the graphs shown in
As shown in
That is, from the above-described measurement results shown in
(1b) In one embodiment of the present disclosure, each of the exhaust pipe 2 and the cover 6 has a cylindrical shape and a common central axis. Further, the diameter of the exhaust pipe 2 is set to not less than 1.8 times as large as a distance between the exhaust pipe 2 and the cover 6.
By such a configuration, a higher muffling effect can be achieved, comparing with the conventional configurations.
(1c) In one embodiment of the present disclosure, both ends of the cover 6 in the axial direction of the exhaust pipe 2 may be fixed to the exhaust pipe 2.
By such a configuration, misalignment and vibrations of the cover 6 can be limited. This further enhances an inhibiting effect on generation of a node of a standing wave and increases the muffling effect.
(1d) In one embodiment of the present disclosure, at least one of the both ends of the cover 6 in the axial direction of the exhaust pipe 2 is configured as an open end, which includes the gap between the cover 6 and the exhaust pipe 2.
In the configuration as described above, the gap between the exhaust pipe 2 and the cover 6 is formed around the open end of the cover 6, which is open to an outer peripheral surface of the exhaust pipe 2. In this case, an opening (gap) of the open end of the cover 6 may also serve as one of the auxiliary holes 61. Accordingly, an area available for forming the auxiliary holes 61 is increased in the cover 6, thereby allowing for facilitation of the muffling effect in the muffler 1.
(1e) In one embodiment of the present disclosure, the cover 6 includes the auxiliary holes 61 disposed in a part facing the outer peripheral surface of the exhaust pipe 2.
By such a configuration, a flow of the exhaust gas G between the cover 6 and the shell 3 can be ensured. Consequently, the exhaust gas G is expanded between the cover 6 and the shell 3, thereby allowing for facilitation of the muffling effect.
(1f) In one embodiment of the present disclosure, the muffler 1 further comprises the second sound absorbing material 5 disposed between the exhaust pipe 2 and the cover 6. The second sound absorbing material 5 covers the communication holes 21.
By such a configuration, the second sound absorbing material 5 limits vibrations produced by the exhaust gas G, thereby allowing for facilitation of the muffling effect. Further, when ventilation resistance of the second sound absorbing material 5 is greater than that of the first sound absorbing material 4, it is likely to reliably generate the standing wave W4, instead of the standing waves W2 and W3, owing to the second sound absorbing material 5.
Embodiments of the present disclosure have been described hereinabove. Nevertheless, the present disclosure is not limited to the aforementioned embodiments. The present disclosure can be embodied in various forms.
(2a) In the muffler 1 in the embodiment as described above, the first end portion 62, which is one end of the cover 6, is defined to be open; however, the first end portion 62 is not limited to such configuration. For example, as shown in
(2b) The muffler 1 in the embodiment as described above is configured such that one end of the cover 6 is defined as an open end; however, both ends of the cover 6 may be defined as open ends.
(2c) The muffler 1 in the embodiment as described above comprises the first sound absorbing material 4, the second sound absorbing material 5, the auxiliary holes 61, and the connection member 65; however, they need not be included in a muffler. If the muffler does not include the connection member 65, the cover 6 may be fixed to the exhaust pipe 2 by only one end, i.e., only the second end portion 63, or a partial or an entire portion of the cover 6 may be fixed to the exhaust pipe 2 via the second sound absorbing material 5.
(2d) In the muffler 1 in the embodiment as described above, an upstream and a downstream may be exchanged. In other words, an upstream end and a downstream end of the muffler 1 may be reversed.
(2e) Functions of one component in the aforementioned embodiments may be distributed to two or more components. Functions of two or more components may be integrated and achieved by one component. At least a part of the configurations of the aforementioned embodiments may be replaced with known configurations having the same functions. A part of the configurations of the aforementioned embodiments may be omitted. At least a part of the configurations of aforementioned embodiments may be added to or replaced with other configurations of another one of the aforementioned embodiments. Any and all modes that are encompassed in the technical ideas identified by the languages in the claims are embodiments of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-021640 | Feb 2020 | JP | national |
