JP5066067B2 - Silencer - Google Patents

Description

  The present invention relates to a silencer.

For example, in a muffler for automobiles, in order to reduce exhaust noise, a control valve that opens and closes at the open end of an inner pipe provided in the muffler shell with exhaust pressure (exhaust gas flow rate) is provided. This is disclosed in Patent Document 1.
JP 2002-89256 A

  The technique described in Patent Document 1 controls a flow path of exhaust gas by a control valve, and the control valve is opened and closed by a single control (ON-OFF control). Conventionally, it was possible to satisfy the user's needs even with mute by ON-OFF control. However, in recent years, further improvement in the muffling performance of the muffler and further reduction in pressure loss have been demanded.

  This is because the demand for quietness in the passenger compartment has become more severe.

  Moreover, it is because the hybrid vehicle which implement | achieves optimal driving | running | working with an engine and a motor has spread in recent years. The hybrid vehicle has a large contribution rate of noise in the muffler because the sound generated during traveling is smaller than the sound generated by the conventional vehicle. Further, in the hybrid vehicle, the engine rotation speed may change abruptly. For this reason, the demand for noise reduction with respect to exhaust noise is stricter than that for conventional vehicles, and even if a muffler for an internal combustion engine, which has not been a problem in the past, is applied to a hybrid vehicle, a sufficient silencing effect can be obtained. I can't.

  In the technique described in Patent Document 1, the control valve opening / closing method is single control (ON-OFF control), which is acoustically ON-OFF control, and the silencing characteristics cannot be finely controlled. Therefore, there is a problem that further improvement of muffler silencing performance and further reduction of pressure loss cannot be realized.

  As a method for solving such a problem, it is conceivable to increase the muffler capacity, but it is difficult to increase the muffler capacity due to the vehicle layout.

  The present invention has been invented in order to solve such problems, and has an object to improve the silencing performance and reduce the pressure loss without increasing the muffler capacity.

According to the first aspect of the present invention, in the silencer, the cylindrical muffler, the inner space of the muffler are divided into the first chamber and the second chamber, and the first hole that communicates the first chamber and the second chamber is provided. A baffle having, an inlet pipe for flowing exhaust gas into the first chamber, an opening provided in the second chamber, and a second hole communicating with the first chamber, and an outlet pipe for discharging the exhaust gas from the muffler; A chamber that is provided in the baffle and controls the opening degree of the first hole according to the amount of exhaust gas flowing into the first chamber, and the chamber that attenuates the sound in the low frequency region, the chamber that attenuates the sound in the middle frequency region, Or a switching means for switching to a chamber for attenuating sound in a high frequency region, and the switching means is rotatably supported and can control the opening degree of the first hole by being displaced toward the second chamber. The control valve is displaced toward the second chamber according to the valve and the amount of exhaust gas flowing into the first chamber. A degree control means and a cylindrical valve provided around the control valve and projecting from the baffle to the second chamber, and at least a portion of the cylindrical opening decreases in a cross section perpendicular to the projecting direction as it projects toward the second chamber. and a case wherein the Rukoto.

Invention according to claim 2, switching means, provided to case, third hole with a first chamber and a second chamber communicating when the control valve is first displacement amount displaced to the second chamber side the provided, by closing the first hole in the control valve, the second chamber and chamber for attenuating sound in the low frequency range, by communicating the first chamber and a second chamber by a third hole, the second The chamber is a chamber for attenuating sound in the middle frequency range.

  According to a third aspect of the present invention, when the case is displaced by the second displacement amount at which the control valve is displaced to the second chamber side relative to the first displacement amount, the first is between the case and the control valve. A communication port that communicates between the chamber and the second chamber is formed, and when the control valve is displaced by the second displacement amount, the switching unit is configured to make the second chamber a chamber that attenuates sound in a high frequency region. To do.

According to a fourth aspect of the present invention, the chamber for attenuating the sound in the low frequency region is a resonator chamber, the chamber for attenuating the sound in the middle frequency region is a resonator chamber and an expansion chamber, and the sound in the high frequency region is The chamber to be attenuated is an expansion chamber.

The invention according to claim 5 is characterized in that the outlet pipe includes a substantially U-shaped curved portion in the second chamber.

The invention according to claim 6 is characterized in that the center of the opening of the outlet pipe is offset from the center of the opening of the case.

According to the first aspect of the present invention, the opening of the switching means provided in the baffle is controlled according to the flow rate of the exhaust gas flowing into the first chamber, and the second chamber is a chamber that attenuates the sound in the low frequency region. By switching to the chamber for attenuating the sound in the middle frequency region or the chamber for attenuating the sound in the high frequency region, the silencing performance can be improved and the pressure loss can be reduced without increasing the muffler capacity. Further, by providing at least a part of the case so that the opening area of the cross section perpendicular to the protruding direction becomes smaller as it protrudes toward the second chamber side, the control valve can be easily opened and the control valve is closed. Thus, the force of the urging portion acting as described above can be reduced.

  According to the invention described in claim 2, by providing an opening degree control means for displacing the control valve to the second chamber side according to the amount of exhaust gas flowing into the first chamber, and closing the first hole with the control valve, The second chamber is a chamber for attenuating the sound in the low frequency region, and when the control valve is displaced by the first displacement amount, the first chamber and the second chamber are communicated by the third hole provided in the case. By setting the two chambers as chambers for attenuating the sound in the middle frequency region, it is possible to improve the silencing performance in the low frequency region and the middle frequency region.

  According to the third aspect of the present invention, when the control valve is displaced to the second chamber side by the second displacement amount, the communication port is formed between the control valve and the case to thereby form the first chamber and the second chamber. The pressure loss in the high frequency region can be reduced by making the second chamber a chamber that attenuates the sound in the high frequency region.

According to the fourth aspect of the present invention, the chamber for attenuating sound in the low frequency region is a resonator chamber, the chamber for attenuating sound in the middle frequency region is a resonator chamber and an expansion chamber, and the chamber is for reducing sound in the high frequency region. By using as an expansion room, it is possible to attenuate sound in a wide range without increasing the capacity of the muffler.

According to the invention described in claim 5 , by forming a curved portion on the outlet pipe in the second chamber, the outlet pipe can be used as a long tube, and the sound in the low frequency region and the sound in the middle frequency region are attenuated. can do.

According to the sixth aspect of the present invention, the sound in the high frequency region can be reduced by forming the center of the opening of the outlet pipe offset from the center of the opening of the case.

  The configuration of the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of a muffler (silencer) 1 according to the first embodiment. In the present embodiment, a muffler that muffles the sound of exhaust gas discharged from the engine will be described. However, the present invention is not limited to this, and the muffler can be used for a muffler that mutes sound generated by other devices.

  The muffler 1 includes a muffler shell 10, end plates 11 a and 11 b, a baffle 3, an inlet pipe 4, an outlet pipe 5, and a switching unit (switching means) 6.

  The muffler 1 is divided into two chambers by a baffle 3. A chamber into which exhaust gas discharged from the engine flows is referred to as a first chamber 12, and the other chamber is referred to as a second chamber 13. The end plates 11 a and 11 b are provided at the end of the muffler shell 10.

  The baffle 3 includes a first hole 15, and the switching unit 6 is attached so as to cover the first hole 15. By attaching the switching unit 6 to the baffle 3, the rigidity of the baffle 3 can be increased, vibration can be suppressed, and generation of radiated sound from the muffler shell 10 and the end plates 11 a and 11 b can be suppressed. .

  The inlet pipe 4 includes a first opening 16 that communicates with the engine and a second opening 17 provided in the first chamber 12. The inlet pipe 4 is provided through the end plate 11 a that forms the second chamber 13 and the baffle 3. The inlet pipe 4 allows the exhaust gas discharged from the engine to flow into the first chamber 12.

  The outlet pipe 5 includes a third opening 18 provided in the second chamber 13, a fourth opening 19 provided outside the muffler 1, and a substantially U-shaped bent portion 20 in the second chamber 13. And a plurality of second holes 21 that are located in the first chamber 12 and communicate with the space in the first chamber 12 and the outlet pipe 5. The outlet pipe 5 is provided through the baffle 3 and the end plate 11 b that forms the first chamber 12. The third opening 18 is provided with an enlarged diameter from the main body of the outlet pipe 5 to the end. By expanding the diameter of the third opening 18 from the main body of the outlet pipe 5 to the end, it is possible to reduce the contraction loss and the airflow noise. The outlet pipe 5 discharges exhaust gas from the muffler 1 to the outside.

  Although the outlet pipe 5 serves as a long tube by providing the outlet pipe 5 with a substantially U-shaped curved portion 20, the outlet pipe 5 is not limited to a substantially U-shape and may have other shapes. Further, when the function as a long tube is not required, the curved portion 20 may not be provided.

  The switching unit 6 will be described with reference to FIG. FIG. 2 is a schematic diagram of the switching unit 6. FIG. 2A is a schematic cross-sectional view of the switching unit 6. FIG.2 (b) is the schematic of the AA cross section of Fig.2 (a). The switching unit 6 includes a control valve 30, a case 31, and an urging unit (opening control means) 32. The switching unit 6 is configured to change the second chamber 13 according to the flow rate of the exhaust gas flowing into the first chamber 12 into a chamber for attenuating sound in a low frequency region, a chamber for attenuating sound in a middle frequency region, or a high frequency region. Switch to a room that attenuates sound. Thereby, without increasing the muffler capacity, the sound deadening performance can be improved and the pressure loss can be reduced.

  The control valve 30 is rotatably supported by the hinge mechanism 33, and is provided so that the first hole 15 of the baffle 3 can be opened and closed. The control valve 30 is urged in a direction to close the first hole 15 of the baffle 3 by an urging portion 32 such as a coil spring, for example, according to the difference between the urging force of the urging portion 32 and the pressure in the first chamber 12. Then, the first hole 15 of the baffle 3 is opened and closed to control the flow of exhaust gas.

  The case 31 is formed in a cylindrical shape. The case 31 covers the periphery of the control valve 30, and one fifth opening 34 of the case 31 contacts the baffle 3 on the second chamber 13 side and is attached to the baffle 3. That is, the case 31 is provided so as to protrude from the baffle 3 into the second chamber 13. The other sixth opening 35 of the case 31 is provided in the second chamber 13.

  The case 31 includes a plurality of third holes 36 in the vicinity of the baffle 3. The third hole 36 provided in the case 31 is a second position that is a position displaced by a first predetermined opening (first displacement amount) from the first position where the control valve 30 closes the first hole 15 of the baffle 3. The first chamber 12 and the second chamber 13 are communicated with each other. In addition, the shape of a hole can be made into various shapes, such as a round hole, an ellipse, a square, and a slit. In FIG. 2A, the state in which the control valve 30 rotates further to the second chamber 13 side than the second position, and the control valve 30 is located closer to the second chamber 13 side than the third hole 36 is shown by a one-dot chain line. It shows with.

  A part of the case 31 is provided in accordance with the shape of the control valve 30, and no gap is generated between the control valve 30 and the case 31 when the control valve 30 rotates from the first position to the second position. A shape or a shape with a small gap is generated. As a part of the case 31 protrudes into the second chamber 13, the opening area of the cross section in the direction perpendicular to the protruding direction becomes smaller. Thereby, it is possible to easily open the control valve 30 due to the pressure increase in the first chamber 12 and to reduce the turbulence of the airflow.

  In addition, when the control valve 30 is easy to open and there is little airflow turbulence, the length that the case 31 protrudes into the second chamber 13 can be shortened.

  By adopting a shape that does not cause a gap between the case 31 and the control valve 30 or a shape that has a small gap, the exhaust gas is prevented from flowing into the second chamber 13 from the gap between the case 31 and the control valve 30. When the two chambers 13 act as a resonator chamber, the sound can be effectively silenced.

  When a gap is generated between the case 31 and the control valve 30, when the control valve 30 is rotated to the second position, the exhaust gas is discharged from the gap generated between the control valve 30 and the case 31 into the second chamber. 13 flows. However, the flow rate of the exhaust gas flowing into the second chamber 13 from this gap is very small. Therefore, the influence on the silencing performance of the second chamber 13 is small.

  Further, when the control valve 30 is rotated from the first position to the third position, which is a position displaced by the second predetermined opening (second displacement amount), the communication port 37 is provided between the case 31 and the control valve 30. Case 31 is formed to occur. When the communication port 37 is generated between the case 31 and the control valve 30, the exhaust gas mainly flows from the first chamber 12 to the second chamber 13 through the communication port 37. The second predetermined opening is an opening larger than the first predetermined opening. In FIG. 2B, a state in which the control valve 30 is rotated further toward the second chamber than the third position is indicated by a two-dot chain line. The size (area) of the communication port 37 varies depending on the opening degree of the control valve 30.

  The case 31 and the outlet pipe 5 are the center of the sixth opening 35 of the case 31 and the center of the third opening 18 of the outlet pipe 5 when viewed from the direction in which the case 31 protrudes into the second chamber 13. It is desirable to provide at a position away from each other. That is, the center of the sixth opening 35 of the case 31 is preferably offset from the center of the third opening 18 of the outlet pipe 5. Thereby, when the control valve 30 is opened and the second chamber 13 functions as an expansion chamber, it is possible to suppress the exhaust gas passing through the switching unit 6 from flowing into the outlet pipe 5 without being sufficiently expanded. .

  Next, the operation of the embodiment of the present invention will be described.

  When exhaust gas is not discharged from the engine, the exhaust gas does not flow into the first chamber 12. At this time, the control valve 30 is in the first position by the urging force of the urging portion 32 and closes the first hole 15 of the baffle 3.

  When exhaust gas is discharged from the engine, the exhaust gas flows into the first chamber 12. When the flow rate of the exhaust gas flowing into the first chamber 12 is small, the exhaust gas flowing into the first chamber 12 is discharged to the outside of the muffler 1 from the second hole 21 provided in the outlet pipe 5. When the flow rate of the exhaust gas flowing into the first chamber 12 is smaller than the flow rate of the exhaust gas that can be discharged from the second hole 21 provided in the outlet pipe 5, the pressure in the first chamber 12 does not increase so much. Therefore, in the control valve 30, the urging force of the urging portion 32 is superior to the force acting on the control valve 30 due to the pressure in the first chamber 12, and the control valve 30 is maintained in the first position, and the first hole 15 of the baffle 3. Is blocked.

  In this state, the second chamber 13 communicates with the first chamber 12 via the second hole 21 of the outlet pipe 5, and sound propagates to the second chamber 13 via the outlet pipe 5. The second chamber 13 acts as a resonator chamber, and the pipe conductivity from the second hole 21 of the outlet pipe 5 to the third opening 18, that is, the length from the second hole 21 of the outlet pipe 5 to the third opening 18. Thus, the attenuation frequency is determined. In the present embodiment, the control valve 30 is set to the first position by setting the length of the pipe from the second hole 21 to the third opening 18 of the outlet pipe 5 according to the capacity of the second chamber 13 and the like. In this case, the second chamber 13 acts as a resonator chamber for attenuating sound in the low frequency region.

  When the flow rate of the exhaust gas flowing into the first chamber 12 increases, the flow rate of the exhaust gas flowing into the first chamber 12 becomes larger than the flow rate of the exhaust gas that can be discharged from the second hole 21 of the outlet pipe 5. The pressure in chamber 12 increases. And if the force which acts on the control valve 30 by the pressure of the 1st chamber 12 becomes larger than the force of the biasing part 32 which urges | biases the control valve 30, the control valve 30 will rotate to the 2nd chamber 13 side. When the control valve 30 rotates and the control valve 30 reaches the second position, the second chamber 13 communicates with the first chamber 12 through the third hole 36 of the case 31 and passes through the third hole 36 of the case 31. Thus, the exhaust gas flows from the first chamber 12 into the second chamber 13.

  In this state, the second chamber 13 functions as a resonator chamber and an expansion chamber. The second chamber 13 has a damping characteristic in which the conductivity of the outlet pipe 5 and the conductivity of the third hole 36 of the case 31 are combined. In the second chamber 13, the sound in the middle frequency region that is higher than the sound in the frequency region that can be attenuated in the first position is attenuated as compared with the case where the control valve 30 is in the first position.

  When the control valve 30 is in the first position and the second position, sound propagates from the second hole 21 of the outlet pipe 5 to the second chamber 13. By providing the curved portion 20 of the outlet pipe 5 in the second chamber 13, the outlet pipe 5 acts as a long tube. Therefore, even when the entire length of the muffler 1 is shortened, the sound in the low frequency region to the medium frequency region can be attenuated.

  If the outlet pipe 5 is a long tube, the resonance of the long tube may appear at the frequency that is the order component of the discharge sound. However, by providing the second hole 21 in the outlet pipe 5, the resonance frequency appears. Can be suppressed.

  When the gas flowing into the first chamber 12 further increases, the flow rate of the gas flowing into the first chamber 12 is larger than the flow rate of the exhaust gas that can be discharged from the second hole 21 of the outlet pipe 5 and the third hole 36 of the case 31. The flow rate increases and the pressure in the first chamber 12 further increases. Then, the control valve 30 is further rotated to the second chamber 13 side and becomes the third position.

  When the control valve 30 is in the third position, a communication port 37 is formed between the control valve 30 and the case 31, and the exhaust gas flows into the second chamber 13 from the first chamber 12 mainly through the communication port 37. The flow of the exhaust gas flowing out from the first chamber 12 is more dominant than the flow flowing out from the second hole 21 of the outlet pipe 5 from the first chamber 12 through the switching unit 6 to the second chamber 13. Thus, the second chamber 13 acts as an expansion chamber. The second chamber 13 attenuates the sound in a high frequency region higher than the frequency region that can be attenuated in the second position, as compared with the case where the control valve 30 is in the second position.

  Here, discharge sound and pressure loss when the present embodiment is not used and when the present embodiment is used will be described with reference to FIG. As an example of the case where this embodiment is not used, the opening of the control valve is not switched according to the flow rate of the exhaust gas, but is switched by ON-OFF (opening / closing). In FIG. 3, when the muffler 1 of this embodiment is used, it shows with a continuous line, and when not using the muffler 1 of this embodiment, it shows with a broken line. FIG. 3A is a diagram showing the relationship between the engine rotation speed and the discharge sound. FIG. 3B shows the relationship between the engine speed and the pressure loss. In FIG. 3B, the control valve 30 is in the second position at point a, and the first chamber 12 and the second chamber 13 communicate with each other through the third hole 36 of the case 31. Further, at the point b, the control valve 30 is in the third position, a communication port 37 is formed between the control valve 30 and the case 31, and the first chamber 12 and the second chamber 13 are communicated via the communication port 37.

  When the muffler 1 of the present embodiment is used, the muffler of the present embodiment is used in a low frequency region (A region in FIG. 3) where the engine speed is low or an intermediate frequency region (B region in FIG. 3). The discharge sound is reduced as compared with the case where 1 is not used. Further, pressure loss is reduced in a high frequency region (C region in FIG. 3) where the engine speed is high.

  The effect of the embodiment of the present invention will be described.

  A switching unit 6 is provided in the baffle 3 that partitions the muffler 1 into a first chamber 12 and a second chamber 13, and the second chamber 13 is made a resonator chamber, a resonator chamber, and an expansion chamber according to the flow rate of exhaust gas discharged from the engine. Or switch to show the three functions of the expansion room. Thereby, it is possible to mute a wide frequency range in the second chamber 13 and to reduce the muffler capacity. In particular, in the high frequency region, the number of exhaust gas expansions and contractions can be reduced, and pressure loss can be reduced.

  By providing the switching unit 6 in the baffle 3, the structure of the muffler 1 can be simplified. Moreover, the rigidity of the baffle 3 can be raised and the vibration of the baffle 3 can be suppressed. Therefore, the radiated sound generated from the muffler 1 can be suppressed. By attaching the switching unit 6 to one baffle 3, the weight of the muffler 1 can be reduced, and the cost can be reduced. In addition, the manufacturing process can be reduced.

  By attaching the switching unit 6 to the baffle 3 having a relatively large area, the degree of freedom of design is improved. For example, the large switching unit 6 can be used for the muffler 1, and the pressure loss in the high frequency region can be reduced. it can.

  The opening degree of the control valve 30 is controlled according to the flow rate of the exhaust gas, and when the flow rate of the exhaust gas is small, the second chamber 13 is closed by closing the first hole 15 of the baffle 3 with the control valve 30. By acting as a chamber, the sound in the low frequency region can be attenuated. Further, when the flow rate of the exhaust gas increases, the first valve 12 and the second chamber 13 are communicated with each other by the third hole 36 of the case 31 by rotating the control valve 30 to the second position. Can act as a resonator chamber and an expansion chamber to attenuate sound in the middle frequency range. Further, when the flow rate of the exhaust gas is increased, the communication valve 37 is formed between the control valve 30 and the case 31 by rotating the control valve 30 to the third position, so that the second chamber 13 is expanded. The sound in the high frequency region can be attenuated.

  By attaching the switching unit 6 to the baffle 3, the area of the control valve 30, that is, the first hole 15 of the baffle 3, can be increased. For example, when a coil spring is used for the urging unit 32, the spring constant can be reduced. In addition, the flow rate of the exhaust gas passing through the first hole 15 of the baffle 3 can be controlled. Therefore, the vibration of the control valve 30 caused by the exhaust gas pulsation can be suppressed, and the generation of sound can be suppressed.

  The urging unit 32 urges the control valve 30 in a direction to close the first hole 15 of the baffle 3, and according to the pressure of the exhaust gas in the first chamber 12, that is, the pressure of the exhaust gas flowing into the first chamber 12. Then, the control valve 30 is rotated to the second chamber 13. Thereby, the control valve 30 can be rotated or held at a predetermined position without using an actuator, and the cost can be reduced.

  As the case 31 attached to the baffle 3 protrudes into the second chamber 13, the control valve 30 is reduced without reducing the urging force by the urging portion 32 by reducing the opening area of the cross section perpendicular to the protruding direction. Can be easily rotated to the second chamber 13 side. Moreover, air current turbulence can be suppressed.

  By providing the curved portion 20 of the outlet pipe 5 in the second chamber 13, the outlet pipe 5 can be used as a long tube, and the sound in the low frequency region and the sound in the middle frequency region can be attenuated.

  The center of the third opening 18 of the outlet pipe 5 is offset from the center of the sixth opening 35 of the case 31 so that the second chamber 13 does not expand sufficiently when acting as an expansion chamber. It is possible to suppress the exhaust gas from being discharged from the outlet pipe 5.

  It goes without saying that the present invention is not limited to the above-described embodiments, and includes various modifications and improvements that can be made within the scope of the technical idea.

It is a schematic block diagram of the muffler in embodiment of this invention. It is a schematic block diagram of the switch part of embodiment of this invention. It is a figure which shows the relationship between an engine speed at the time of using embodiment of this invention, and a discharge sound or pressure loss.

Explanation of symbols

1 Muffler 3 Baffle 4 Inlet pipe 5 Outlet pipe 6 Switching section (switching means)
12 1st chamber 13 2nd chamber 15 1st hole 18 3rd opening part 20 Curved part 21 2nd hole 30 Control valve 31 Case 32 Energizing part (opening control means)
36 3rd hole 37 Communication port

Claims (6)

A tubular muffler (1);
The inner space of the muffler (1) is divided into a first chamber (12) and a second chamber (13), and a first hole (15) communicating the first chamber (12) and the second chamber (13). Baffle (3) having
An inlet pipe (4) for flowing exhaust gas into the first chamber (12);
An outlet pipe having an opening (18) provided in the second chamber (13) and a second hole (21) communicating with the first chamber (12) and discharging the exhaust gas from the muffler (1) (5) and
The opening of the first hole (15) is controlled according to the amount of exhaust gas that is provided in the baffle (3) and flows into the first chamber (12), and the second chamber (13) is placed in a low frequency region. Switching means (6) for switching to a room for attenuating sound, a room for attenuating sound in the middle frequency range, or a room for attenuating sound in the high frequency range , and
The switching means (6)
A control valve (30) that is rotatably supported and capable of controlling the opening degree of the first hole (15) by being displaced toward the second chamber (13);
Opening degree control means (32) for displacing the control valve (30) toward the second chamber (13) according to the amount of exhaust gas flowing into the first chamber (12);
Provided around the control valve (30), protrudes from the baffle (3) to the second chamber (13), and at least a part thereof is perpendicular to the protruding direction as it protrudes toward the second chamber (13). muffler, wherein Rukoto opening area of a cross section and a small becomes cylindrical case (31). Said switching means (6) is provided before Symbol casing (31), said control valve (30) is the first chamber when the first displacement amount displaced into the second chamber (13) side (12) A third hole (36 ) communicating with the second chamber (13);
By closing the first hole (15) with the control valve (30), the second chamber (13) is a chamber for attenuating sound in the low frequency region,
By connecting the first chamber (12) and the second chamber (13) through the third hole (36), the second chamber (13) is a chamber for attenuating the sound in the middle frequency range. The muffler according to claim 1. When the case (31) is displaced by a second displacement amount, which is a position where the control valve (30) is displaced toward the second chamber (13) with respect to the first displacement amount, the case (31) A communication port (37) for communicating the first chamber (12) and the second chamber (13) is formed between the control valve (30),
The switching means (6) is characterized in that when the control valve (30) is displaced by the second displacement amount, the second chamber (13) is a chamber for attenuating sound in the high frequency region. The silencer according to claim 2. The chamber for attenuating the sound in the low frequency region is a resonator chamber,
  The chamber for attenuating the sound in the middle frequency range is a resonator chamber and an expansion chamber,
  The silencer according to any one of claims 1 to 3, wherein the chamber for attenuating sound in the high frequency region is an expansion chamber. The silencer according to any one of claims 1 to 4, wherein the outlet pipe (5) comprises a substantially U-shaped bend (20) in the second chamber (13). The center of the opening (18) of the outlet pipe (5) is offset from the center of the opening (35) of the case (31). Silencer.

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