JPH08189332A - Muffler for internal combustion engine - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a muffler for an internal combustion engine capable of exhibiting optimum silencing effect in all operating regions. [Structure] A first chamber 1 in which an exhaust introduction pipe 4 is opened, a third chamber 3 in which an exhaust outlet pipe 5 is opened, and a second chamber 2 arranged between the first chamber 1 and the third chamber 3, The first chamber 1 and the second chamber 2, and the second chamber 2 and the third chamber 3 of the internal combustion engine muffler including the inner pipe 6 that communicates the first chamber 1 and the third chamber are respectively communicated with each other. The inner pipe 6 is provided with an opening / closing valve 7a which is communicatively connected by a pipe 8 and a second communicating pipe 9 and which is forcibly opened and closed according to the engine operating state, and the outlet of the second communicating pipe 9 is automatically opened by the exhaust gas pressure. An on-off valve 7b is provided.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a muffler for an internal combustion engine, and more particularly to a muffler for an automobile internal combustion engine.

[0002]

2. Description of the Related Art As shown in FIG. 4, a first chamber in which an exhaust introduction pipe is open, a third chamber in which an exhaust discharge pipe is open, and a second chamber arranged between the first and third chambers. Chamber and an inner pipe that communicates the first chamber and the third chamber, the inner pipe is provided with an opening / closing valve that opens and closes in an engine operating state, and the first chamber and the second chamber, the second chamber and the third chamber There is known a muffler for an internal combustion engine, which communicates with each other by a relatively thin inner pipe and makes the second chamber function as an expansion chamber or a resonance chamber in accordance with opening and closing of an on-off valve. (See Japanese Utility Model Laid-Open No. 04-95609)

[0003]

However, in the above-mentioned prior art device, since there is only one on-off valve, only two types of muffling characteristics can be obtained, and the optimum muffling effect is exhibited in all operating regions. There was a problem that I could not do it. The present invention has been made in view of the above problems, and an object thereof is to provide a muffler for an internal combustion engine capable of exhibiting an optimum silencing effect in all operating regions.

[0004]

According to the first aspect of the present invention, the first chamber in which the exhaust introduction pipe is opened, the third chamber in which the exhaust discharge pipe is opened, and the first chamber and the third chamber In a muffler for an internal combustion engine, which includes a second chamber arranged between them and an inner pipe that communicates the first chamber and the third chamber, the exhaust introduction pipe is provided with a communication hole that communicates with the second chamber. , The first chamber and the second chamber, the second chamber and the third chamber, respectively, the first communication pipe, the second
The first pipe and the third chamber are connected to the inner pipe through a communication pipe.
A first on-off valve that opens and closes communication with a chamber is provided, a second on-off valve that opens and closes communication between the first chamber and the second chamber is provided on the first communication pipe, and the first on-off valve and the second on-off valve are provided. A muffler for an internal combustion engine is provided, wherein one of the valves is an on-off valve that is controlled to be opened and closed according to an engine operating state, and the other is an on-off valve that is automatically opened and closed by the pressure of exhaust gas.

According to the second aspect of the present invention, the first chamber in which the exhaust introduction pipe is opened, the third chamber in which the exhaust outlet pipe is opened, and the first chamber arranged between the first chamber and the third chamber 2 rooms and the first
A muffler for an internal combustion engine, comprising an inner pipe that communicates a chamber with a third chamber, wherein a communication hole communicating with the second chamber is provided in the exhaust gas introducing pipe, and the first chamber and the second chamber communicate with each other. A first opening / closing that automatically connects the inner chamber with the inner chamber to communicate with the third chamber by the pressure of exhaust gas. A second opening / closing valve for opening and closing the first communication pipe to control communication between the first chamber and the third chamber according to an engine operating state;
There is provided a muffler for an internal combustion engine, which is provided with a third opening / closing valve that automatically opens and closes the communication between the second chamber and the third chamber with the pressure of exhaust gas in the communication pipe.

[0006]

According to the first aspect of the present invention, first, when the engine speed is small, the first on-off valve is closed and the exhaust gas introduced through the exhaust introduction pipe passes through the communication hole of the exhaust introduction pipe. Enter the 2nd chamber, expand in the 2nd chamber and pass through the 2nd communicating pipe to the 3rd chamber
While entering the chamber and expanding in the third chamber and exiting from the exhaust gas outlet pipe, the first chamber acts as a resonance chamber for the flow flowing from the exhaust gas inlet pipe to the second chamber during this period.

Next, when the engine speed slightly increases with the on-off valve closed, the amount of exhaust gas increases and the pressure in the first chamber increases, the second on-off valve is opened, and the exhaust introduction pipe 4 The exhaust gas introduced in (1) enters the first chamber and expands, enters the second chamber through the first communication pipe, expands in the second chamber, enters the third chamber 3 through the second communication pipe, It expands in the third chamber 3 and goes out from the exhaust gas outlet pipe.

When the engine speed further increases, the first
The on-off valve is opened, the exhaust gas flows through the inner pipe having a large diameter, the pressure in the first chamber 1 decreases, and the second on-off valve closes. Therefore, the exhaust gas introduced through the exhaust introduction pipe enters the first chamber and expands, then enters the third chamber through the inner pipe, expands in the third chamber, and exits the exhaust discharge pipe during this period. , The second chamber acts as a resonance chamber for the flow passing through the exhaust gas introducing pipe, and the second chamber acts as a resonance chamber for the expanding flow in the third chamber.

When the engine speed further rises, the pressure in the first chamber 1 rises again and the first on-off valve is opened, and the exhaust gas introduced through the exhaust introduction pipe enters the first chamber and expands. , Through the inner pipe into the third chamber, part of which is the first
From the chamber through the first communication pipe into the second chamber, expand in the second chamber, then through the second communication pipe into the third chamber, expand in the third chamber and exit from the exhaust outlet pipe Go.

According to the second aspect of the present invention, first, when the engine speed is small, the pressure of the exhaust gas passing through the inner pipe is low, so that the first opening / closing valve is closed and the second opening / closing valve is closed. The exhaust gas introduced through the exhaust introduction pipe enters the second chamber through the communication hole of the exhaust introduction pipe, expands in the second chamber, enters the third chamber through the second communication pipe, and expands in the third chamber. Then, the first chamber moves from the exhaust introduction pipe to the second exhaust pipe during this time.
It acts as a resonance chamber for the flow flowing into the chamber.

Next, when the engine speed slightly increases with the second opening / closing valve closed, the amount of exhaust gas increases and the pressure in the first chamber increases, and the first opening / closing valve opens, 3 The on-off valve closes, the exhaust gas introduced through the exhaust introduction pipe enters the first chamber and expands, passes through the inner pipe and enters the third chamber, expands in the third chamber and exits from the exhaust discharge pipe. To go. During this time, the second chamber acts as a resonance chamber for the flow through the exhaust gas introducing pipe.

When the engine speed further increases, the second
The open / close valve is opened, the exhaust gas in the first chamber flows through the first communication pipe, the pressure in the first chamber decreases, the first open / close valve closes, the third open / close valve opens, and exhaust gas is introduced. The exhaust gas introduced by the pipe enters the first chamber and expands, and passes through the first communicating pipe to the second pipe.
It enters the chamber, expands in the second chamber, then enters the third chamber through the second communication pipe, expands in the third chamber 3 and exits from the exhaust outlet pipe 5.

When the engine speed further increases, the pressure in the second chamber rises, both the on-off valve 7 and the on-off valve 12 open, and the exhaust gas introduced through the exhaust gas introducing pipe enters the first chamber. After expanding, enter the third chamber through the inner pipe,
Part of the first chamber through the first communication pipe into the second chamber,
After expanding in the second chamber, it enters the third chamber through the second communicating pipe, expands in the third chamber, and exits from the exhaust outlet pipe.

[0014]

1 (A) to 1 (D) are views for explaining the structure and operation of a first embodiment of a muffler for an internal combustion engine according to the present invention, wherein 1 in FIG. 1 room, 2 is a second room, and 3 is a third room. Reference numeral 4 denotes an exhaust introduction pipe, the upstream end of which is connected to the exhaust port of the engine through an exhaust pipe and an exhaust manifold (not shown), and the downstream end is the first end.
It is open to Chamber 1. Reference numeral 5 denotes an exhaust outlet pipe, the upstream end of which is open to the third chamber 3 and the downstream end of which is open to the atmosphere. Reference numeral 6 denotes an inner pipe, the upstream end of which is open to the first chamber 1, the downstream end of which is open to the third chamber 3, and the first opening / closing valve 7a is arranged substantially in the center. ing.
The first opening / closing valve 7a is a forced opening / closing valve that is opened / closed by a driving unit (not shown) according to a load. In addition, the first chamber 1 and the second chamber 2, and the second chamber 2 and the third chamber 3 are the inner pipe 6 respectively.
The first communication pipe 8 and the second communication pipe 9 which are thinner than each other are connected. An on-off valve 8a is arranged at the outlet of the second communication pipe 9, and the on-off valve 8a is attached to a shaft via a spring (not shown), and is urged toward the end surface of the first communication pipe 8 by the spring. It is an automatic open / close valve that opens automatically when the pressure of exhaust gas rises.

First, when the engine speed is low, the first opening / closing valve 7a is closed as shown in FIG. 1 (A). Then, the exhaust gas introduced through the exhaust gas introducing pipe 4 becomes 1
It is impossible to enter the third chamber 3 from the chamber 1 through the inner pipe 6, and the pressure of the exhaust gas is small, so that the first communication pipe 8
Since it is not possible to push the second on-off valve 8a open to enter the second chamber 2 from above,
Enters the chamber, expands in the second chamber, enters the third chamber through the second communication pipe 9, expands in the third chamber, and exits from the exhaust outlet pipe 5, while the first chamber 1 introduces exhaust gas. It acts as a resonance chamber for the flow from the tube 4 to the second chamber 2, and two-stage expansion + resonance is performed.

Next, the first on-off valve 7a is kept closed even when the engine speed is slightly increased. Then, the amount of exhaust gas increases and the pressure in the first chamber 1 increases, so that the second opening / closing valve 8a opens as shown in FIG. 1 (B). Therefore, after entering the first chamber introduced by the exhaust introduction pipe 4 and expanding, passing through the first communicating pipe 8 and entering the second chamber 2, expanding in the second chamber 2 and passing through the second communicating pipe 9. It enters the third chamber 3, expands in the third chamber 3 and exits from the exhaust outlet pipe 5, and three-stage expansion is performed.

When the engine speed further increases, the first
The on-off valve 7a is opened, and the exhaust gas flows through the inner pipe 6 having a large diameter, so that the pressure in the first chamber 1 decreases and
As shown in (C), the second opening / closing valve 8a is closed. Therefore, the exhaust gas introduced through the exhaust introduction pipe 4 enters the first chamber 1 and expands, and then passes through the inner pipe 6 to reach the third exhaust gas.
The gas enters the chamber 3, expands in the third chamber 3 and exits from the exhaust gas outlet pipe 5, while the second chamber 2 expands in the third chamber 3 as a resonance chamber for the flow through the exhaust gas inlet pipe 4. It acts as a resonance chamber for the flowing flow, and two-stage expansion + resonance is performed.

When the engine speed further rises, the pressure in the first chamber 1 rises again, so that the second opening / closing valve 8a opens as shown in FIG. 1 (D). Therefore, after the exhaust gas introduced through the exhaust introduction pipe 4 enters the first chamber 1 and expands,
Pass through the inner pipe 6 and enter the third chamber 3, part of which is the first
From the chamber 1 through the first communication pipe 8 into the second chamber 2 and expanding in the second chamber 2, then through the second communication pipe 9 into the third chamber 3 and expanding in the third chamber 3. And goes out from the exhaust outlet pipe 5. Therefore, although three-stage expansion is performed, there is a flow through the inner pipe 6 and a flow through the first communication pipe 8 and the second communication pipe 9, so exhaust resistance is low. As described above, in the first embodiment of the present invention, four kinds of actions can be obtained, and it is possible to more finely correspond to each operation region.

2 (A) to 2 (D) are views for explaining the structure and operation of the second embodiment of the muffler for an internal combustion engine according to the present invention. Compared with the first embodiment, the first chamber 1 And the second
The second on-off valve that opens and closes the communication of the chamber 2 is automatically opened and closed from 8a to 8b that is forcibly opened and closed according to the load.
The first on-off valve that opens and closes the communication between the chamber 1 and the third chamber 3 is changed from 7a that is forcibly opened and closed according to the load to 7b that is automatically opened and closed by the pressure of exhaust gas.

First, when the engine speed is low, the second opening / closing valve 8b is closed as shown in FIG. 2 (A). Then, the exhaust gas introduced through the exhaust introduction pipe 4 is 1
It is also impossible to enter the second chamber 2 from the chamber 1 through the first communication pipe 8, and the pressure of the exhaust gas is small, so the inner pipe 6
Since it is not possible to push open the first opening / closing valve 7b to enter the third chamber 3, the second chamber enters the second chamber through the communication hole 4a and expands in the second chamber, and the third chamber passes through the second communication pipe 9. The first chamber 1 acts as a resonance chamber for the flow flowing from the exhaust introduction pipe 4 to the second chamber 2 and expands in the third chamber and then exits from the exhaust outlet pipe. Is performed.

Next, the second on-off valve 8b is kept closed even when the engine speed is slightly increased. Then, the amount of exhaust gas increases and the pressure in the first chamber 1 increases, so that the first opening / closing valve 7b opens as shown in FIG. 2 (B). Therefore, it enters and expands in the first chamber introduced by the exhaust introduction pipe 4, and enters the third chamber 3 through the inner pipe 6,
While expanding in the third chamber 3 and exiting from the exhaust lead-out pipe 5, during this time, the second chamber is a resonance chamber for the flow through the exhaust lead-in pipe 4,
Alternatively, it acts as a resonance chamber for the flow expanding in the third chamber, and two-stage expansion + resonance is performed. However, since the combination of the expanding chamber and the resonating chamber is different, the frequency at which the silencing effect is exerted is different from that shown in FIG. 2 (A).

When the number of revolutions increases a little, the second
The on-off valve 8b is opened. Then, since the exhaust gas can flow through the first communication pipe 8, the pressure in the first chamber 1 is lowered and the first opening / closing valve 7 is opened as shown in FIG.
b is closed by the biasing force of the spring. Therefore, the exhaust gas introduced through the exhaust introduction pipe 4 enters the first chamber and expands, enters the second chamber 2 through the first communication pipe 8, and enters the second chamber 2.
After expanding in the chamber 2, it enters the third chamber 3 through the second communicating pipe 9, expands in the third chamber 3 and exits from the exhaust outlet pipe 5.
Dan expansion is performed.

When the engine speed further increases, the pressure in the first chamber 1 rises again, so that the second opening / closing valve 8b opens as shown in FIG. 2 (D). Therefore, after the exhaust gas introduced through the exhaust introduction pipe 4 enters the first chamber 1 and expands,
In addition to entering the third chamber 3 through the inner pipe 6, expanding in the third chamber 3 and exiting from the exhaust outlet pipe 5,
The first chamber 1 passes through the first communication pipe 8 to enter the second chamber 2, expands in the second chamber 2, and then passes through the second communication pipe 9 to reach the third chamber 2.
Enters, expands in the third chamber 3 and exits from the exhaust outlet pipe 5. Therefore, although three-stage expansion is performed, there is a flow through the inner pipe 6 and a flow through the first communication pipe 8 and the second communication pipe 9, so exhaust resistance is low. As described above, also in the second embodiment, four kinds of actions can be obtained as in the first embodiment.

FIGS. 3A to 3D are views for explaining the structure and operation of a third embodiment of the muffler for an internal combustion engine according to the present invention, which is a second communicating pipe as compared with the second embodiment. A third opening / closing valve 9a for opening / closing the communication of 9 is provided so as to move together with a first opening / closing valve 7b for opening / closing the communication of the inner pipe 6. The first on-off valve 7b is integrally biased by a spring in the direction in which the first on-off valve 7b closes the communication of the inner pipe 6.

First, when the engine speed is low, the second opening / closing valve 8b is closed as shown in FIG. 3 (A). Then, the exhaust gas introduced through the exhaust introduction pipe 4 is 1
It is also impossible to enter the second chamber 2 from the chamber 1 through the first communication pipe 8, and the pressure of the exhaust gas is small, so the inner pipe 6
It is also impossible to push the first on-off valve 7b open to enter the third chamber 3. Therefore, the exhaust gas enters the second chamber through the communication hole 4a and expands in the second chamber. And the first on-off valve 7
On the contrary, since the third opening / closing valve 9a is opened by closing b, the third opening / closing valve 9a passes through the second communication pipe 9 to enter the third chamber,
While expanding in the chamber and exiting from the exhaust outlet pipe 5, the first chamber 1 acts as a resonance chamber for the flow flowing from the exhaust inlet pipe 4 to the second chamber 2 during this period, and two-stage expansion + resonance is performed.

Next, the second on-off valve 8b is kept closed even when the engine speed is slightly increased. Then, since the amount of exhaust gas increases and the pressure in the first chamber 1 increases, the first opening / closing valve 7b opens and the third opening / closing valve 9a closes, as shown in FIG. 3 (B). To do. Therefore, the gas enters the first chamber introduced by the exhaust introduction pipe 4 and expands, enters the third chamber 3 through the inner pipe 6, expands in the third chamber 3 and exits from the exhaust discharge pipe 5. During this time, the second chamber acts as a resonance chamber for the flow passing through the exhaust introduction pipe 4, and the second stage expansion +
Resonance occurs. However, since the combination of the expanding chamber and the resonating chamber is different, the frequency at which the silencing effect is exerted is different from that shown in FIG. 3 (A).

When the engine speed increases a little more,
The second opening / closing valve 8b is opened. Then, since the exhaust gas can flow through the first communication pipe 8, the pressure in the first chamber 1 is lowered and the first opening / closing valve 7b is urged by the spring as shown in FIG. 3 (C). Closed by the third, conversely
The on-off valve 9a opens. Therefore, the exhaust gas introduced through the exhaust introduction pipe 4 enters the first chamber and expands, passes through the first communication pipe 8 and enters the second chamber 2, expands in the second chamber 2, and then expands into the second communication pipe. It enters into the third chamber 3 through 9, and expands in the third chamber 3 and exits from the exhaust gas outlet pipe 5, and three-stage expansion is performed.

As the engine speed further increases, the pressure in the second chamber 2 also increases, so the pressure in the first chamber 1 and the pressure in the second chamber 2 increase.
As shown in (D) of FIG. 3, the pressure of the spring + the urging force of the spring are balanced, and the first opening / closing valve 7b and the third opening / closing valve 9 are
a stays in the valve opening position. Therefore, the exhaust gas introduced through the exhaust introduction pipe 4 enters the first chamber 1 and expands, and then enters the third chamber 3 through the inner pipe 6,
A portion of the first chamber 1 passes through the first communication pipe 8 to enter the second chamber 2, expands in the second chamber 2, and then passes through the second communication pipe 9 into the third chamber 3, It expands in 3 chambers 3 and goes out from the exhaust outlet pipe 5. Therefore, although three-stage expansion is performed, since the passage that passes through the inner pipe 6 and the passage that passes through the first communication pipe 8 and the second communication pipe 9 are open, the exhaust resistance is small.

FIGS. 4A and 4B are views for explaining the structure and operation of the conventional muffler, which are different from those of the embodiment of the present invention shown in FIGS. No communication hole 4a is provided in the inner pipe 6, and the opening / closing valve is an automatic opening / closing valve indicated by 7 or a forced opening / closing valve at approximately the center of the inner pipe 6.
The first communication pipe 8 is not provided with an opening / closing valve but is provided individually.

As shown in FIG. 4A, when the on-off valve 7 is closed, the flow of the inner pipe 6 is blocked, so that the exhaust gas entering the first chamber 1 from the exhaust introduction pipe 4 is blocked. The gas expands in the first chamber 1, then enters the second chamber 2 through the first communication pipe 8 and expands in the second chamber 2, and then enters the third chamber 3 through the second communication pipe 9. After being expanded, the gas is discharged into the atmosphere through the exhaust outlet pipe 5 and expanded in three stages. As shown in FIG. 4B, when the on-off valve 7 is open, the exhaust gas entering the first chamber 1 from the exhaust introduction pipe 4 is the first exhaust gas.
After expanding in the chamber 1, through the inner pipe 6 and into the third chamber 3, through the first communication pipe 8, into the second chamber 2, and after expanding in the second chamber 2, the third chamber 3 After entering and expanding in the third chamber 3, it is released into the atmosphere through the exhaust outlet pipe 5, so three-stage expansion is performed. Since the passage that passes through the inner pipe 6 and the passage that passes through the first communication pipe 8 and the second communication pipe 9 are open, the exhaust resistance is small.

As described above, each of the embodiments of the present invention can obtain four types of muffling characteristics, whereas in the prior art, the two types shown in FIGS. 4A and 4B are used. It is difficult to finely adapt to each operating condition because only the muffling characteristics of the above can be obtained.

[0032]

According to the present invention, four types of silencing characteristics can be obtained, and silencing can be performed more effectively according to each operating condition. Even if all the valves are forced control valves, the same effect can be obtained by causing them to operate in the same manner as the automatic valve.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a first embodiment of a muffler according to the present invention, (A) shows a case where both a first on-off valve and a second on-off valve are in a closed state, and (B) shows a first example. The first open / close valve is in the closed state, the second open / close valve is in the open state, (C) is the first open / close valve in the open state, and the second open / close valve is in the closed state. 1
The case where both the on-off valve and the second on-off valve are open is shown.

2A and 2B are views showing the structure of a second embodiment of the muffler according to the present invention, in which FIG. 2A is a case where both the first on-off valve and the second on-off valve are closed, and FIG. 1 open / close valve is open, 2nd
When the open / close valve is in the closed state, (C) is the case where the first open / close valve is in the closed state, and the second open / close valve is in the open state, and (D) is both the first open / close valve and the second open / close valve. The case where the valve is open is shown.

FIG. 3 is a diagram showing the structure of a third embodiment of the muffler according to the present invention, in which (A) shows the first open / close valve and the second open / close valve in the closed state, and the third open / close valve in the open state. In the case (B), the first opening / closing valve is in the open state, and the second opening / closing valve and the third opening / closing valve are in the closed state, and (C) is the first opening / closing valve in the closed state, the second opening / closing valve. And (D) shows the case where all of the first opening / closing valve, the second opening / closing valve, and the third opening / closing valve are in the open state.

FIG. 4 is a diagram showing a structure of a conventional muffler,
(A) shows the case where the on-off valve is in the closed state, and (B) shows the case where the on-off valve is in the open state.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st chamber 2 ... 2nd chamber 3 ... 3rd chamber 4 ... Exhaust introduction pipe 4a ... Communication hole 5 ... Exhaust introduction pipe 6 ... Inner pipe 7a ... 1st opening / closing valve (forced opening / closing valve: 1st Example) 7b ... 1st opening / closing valve (automatic opening / closing valve: 2nd Example, 3rd Example) 8 ... 1st communicating pipe 8a ... 2nd opening / closing valve (Automatic opening / closing valve: 1st Example) 8b ... 2nd opening / closing valve (forced) Open / close valve: second embodiment, third embodiment 9 ... Second communication pipe 9a ... Third open / close valve (automatic open / close valve: third embodiment)

Claims (2)

[Claims] 1. A first chamber in which an exhaust introduction pipe opens, a third chamber in which an exhaust discharge pipe opens, a second chamber arranged between the first chamber and the third chamber, and the first chamber. In an internal combustion engine muffler including an inner pipe that communicates with the third chamber, a communication hole that communicates with the second chamber is provided in the exhaust introduction pipe, and the first chamber, the second chamber, and the second chamber 3rd chamber, 1st
A first opening / closing valve that opens and closes the communication between the first chamber and the third chamber is provided in the inner pipe, and the first chamber and the second chamber are provided in the first communication pipe. A second opening / closing valve for opening / closing the communication is provided, and one of the first opening / closing valve and the second opening / closing valve is an opening / closing valve whose opening / closing is controlled according to the engine operating state, and the other is automatically controlled by the pressure of exhaust gas. A muffler for an internal combustion engine, which is an on-off valve that opens and closes. 2. A first chamber in which an exhaust introduction pipe opens, a third chamber in which an exhaust discharge pipe opens, a second chamber arranged between the first chamber and the third chamber, and the first chamber. In an internal combustion engine muffler including an inner pipe that communicates between the first chamber and the third chamber, a communication hole that communicates with the second chamber is provided in the exhaust introduction pipe, and the first communication pipe connects the first chamber and the second chamber. A first opening / closing valve for communicating the second chamber and the third chamber with a second communication pipe and automatically opening and closing the communication between the first chamber and the third chamber with the inner pipe by the pressure of exhaust gas. A second opening / closing valve for opening / closing the first communication pipe to control communication between the first chamber and the third chamber according to an engine operating state; and providing the second communication pipe with the second chamber and the second chamber. A muffler for an internal combustion engine, comprising a third opening / closing valve that automatically opens and closes communication with the three chambers by the pressure of exhaust gas.