JPH09303143A - Silencer for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a silencing effect in a low rotational speed region of an engine, by providing an energizing means applying a closing directional load to act in a butterfly valve to a prescribed opening from its fully closed condition, in the butterfly valve opening operated by a flow of exhaust gas. SOLUTION: In a low rotational speed region of an engine, valve closing force by a return spring 12 is strong, to hold a butterfly valve 10 in a closed condition, so as to ensure a function as a low frequency resonance chamber of an inner pipe. However, in accordance with the increasing of an engine speed, a dynamic pressure of exhaust gas rises, when the butterfly valve 10 is started to open, a link 17 is turned downward, but until its connecting pin 18 leads to a turn over position A, a compression spring 23 is compressed, its extension force acts in a closing direction of the butterfly valve 10. When the connecting pin 16 passes through the turn over position, the link 17 is turned downward, the butterfly valve 10 is opened.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a silencer for an internal combustion engine.

[0002]

2. Description of the Related Art In a silencer for an internal combustion engine of an automobile,
Conventionally, as shown in FIG. 12, an outer shell 100 of a silencer is partitioned by a partition wall 101 into a plurality of chambers 103 to 105, and an inner pipe 106 or an elbow 107 thereof passing through the partition wall 101 has a dynamic pressure of exhaust gas. A butterfly valve 108 that is opened and closed by an eccentric shaft 109 is eccentrically provided so that the butterfly valve 108 is closed by the biasing load of the return spring 110 when the internal combustion engine with low dynamic pressure of exhaust gas is at low rotation speed or low load. To increase the sound deadening effect (forming a resonance chamber), and when the internal combustion engine with high exhaust gas dynamic pressure is in medium to high rotation or medium to high load, the dynamic pressure is resisted against the return spring 110. There is an exhaust gas actuated variable muffler that opens the butterfly valve 108 (replaces the resonance chamber with the expansion chamber) to lower the back pressure to improve the engine output. In example JP 6-221130).

[0003]

In the above-mentioned conventional technique, the butterfly valve 108 is driven by the biasing load of the return spring 110 in the low rotation or low load region of the internal combustion engine.
However, if the internal combustion engine shifts to the medium to high rotation range or the medium to high load range, the following problems occur.

That is, as the opening of the butterfly valve 108 increases, the angle between the flow direction of the exhaust gas and the pressure receiving surface of the butterfly valve 108 gradually decreases, and the opening actuation force of the butterfly valve 108 due to the exhaust gas decreases. ,
The biasing load of the return spring 110 also gradually increases. Therefore, the butterfly valve 108 does not open to the expected position in the medium to high rotation range or the medium to high load range of the internal combustion engine,
There is a problem that the back pressure cannot be lowered sufficiently when the flow rate of exhaust gas is large.

On the other hand, if the biasing load of the return spring 110 is set to a small value by giving priority to ensuring a sufficient opening of the butterfly valve 108, the butterfly valve 108 will open when the exhaust gas has a small flow rate in the low rotation or low load region. As a result, the low-frequency resonance chamber is not firmly formed and a sufficient silencing effect cannot be obtained, and chattering of the butterfly valve 108 also occurs.

Therefore, in the above conventional technique,
Ensuring a fully closed operation in the low rotation or low load range and ensuring a fully open operation in the medium to high rotation range or medium to high load range are in a conflicting relationship that is difficult to solve, and satisfy the intended purpose in both areas. However, there was a problem that the original merit of the exhaust gas actuated variable muffler could not be fully exerted.

This is mainly due to the structural problem that the butterfly valve opening is tuned with respect to the dynamic pressure of the exhaust gas only by setting the characteristics of the return spring (spring characteristics and initial load setting).

Therefore, the present invention applies a valve closing load in addition to the valve closing load of the return spring in the low rotation or low load region of the internal combustion engine, and exhausts in the medium to high rotation or medium to high load region. It is an object of the present invention to provide a silencer for an internal combustion engine, which solves the above problem by adding a valve opening load in addition to the valve opening load due to the dynamic pressure of gas.

[0009]

In order to solve the above-mentioned problems, a first invention according to a first aspect of the present invention provides a pipe constituting a silencer with a butterfly valve eccentrically with respect to its valve shaft. When the butterfly valve is opened by the exhaust gas flow and urged in the valve closing direction, a load in the valve closing direction is applied to the butterfly valve from the fully closed state of the butterfly valve to a predetermined opening, and the exhaust gas is opened when the opening is higher than that. It is characterized in that a biasing means for assisting the valve opening action by the flow is provided.

According to a second aspect of the present invention, a pipe constituting a silencer is provided with a butterfly valve eccentrically with respect to its valve shaft so as to be opened by an exhaust gas flow and urged in a valve closing direction. In this case, a turnover mechanism for assisting the opening and closing of the butterfly valve is provided.

According to a third aspect of the present invention, the above-mentioned urging means or turnover mechanism is provided inside a silencer. According to a fourth aspect of the present invention, the biasing means or the turnover mechanism is provided outside the silencer.

According to a fifth aspect of the present invention, the pipe is an inner pipe, an outlet pipe or an inlet pipe.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described based on an embodiment shown in FIGS. 1 to 4 show a first embodiment in which a biasing means composed of a turnover mechanism is provided in a silencer.

FIG. 1 shows a sectional view of the silencer as a whole.
Is the outer shell of the silencer, and the inside thereof is partitioned into a plurality of chambers 3, 4, 5 by the partition wall 2 as in the conventional case, and these are communicated with each other by inner pipes 6, 7. Reference numeral 8 indicates an inlet pipe, and 9 indicates an outlet pipe.

A casing 1 having a butterfly valve 10 built in at the downstream end of an inner pipe 6 which connects the chambers 3 and 5 with each other.
1 is arranged. A return spring 12 is provided on one side wall of the casing 11, and a turnover mechanism 13 as an urging means is provided on the other side wall. The casing 11 incorporating the butterfly valve 10, the return spring 12 and the turnover mechanism 13 will be described in detail with reference to FIGS.

As shown in FIGS. 2 and 3, the casing 11 is formed of a rectangular metal frame as viewed in the exhaust gas flow direction, and its upstream side 11a is hermetically connected to the downstream end of the inner pipe 6. It is like this. A valve shaft 14 is rotatably provided in the casing 11 so as to penetrate therethrough in the transverse direction. Further, the butterfly valve 10 is fixedly mounted in the casing 11 at a position eccentric from the center of the casing 11, and the dynamic pressure receiving area of the exhaust gas flowing in the casing 11 is located above the valve shaft 14. The side 10a has a small amount and the lower side 10b has a large amount so that the valve is opened as shown in FIG. 3 by the dynamic pressure of the exhaust gas flowing in the direction of arrow a.

The butterfly valve 10 is formed in a rectangular shape when viewed from the exhaust gas flow direction, and when the valve is closed, its outer periphery is close to the inner surface of the casing 11 to prevent the exhaust gas from leaking. Furthermore, butterfly valve 1
A locking piece 10c formed by bending at the tip of the lower side 10b of 0.
Are integrally formed, and when this is closed as shown in FIG.
The stopper 11b formed integrally with the casing 11 is in contact with the stopper 11b, and the valve closing position is regulated by the contact so that the butterfly valve 10 does not bite into the casing 11 when the valve is closed, and the locking piece A cushioning member 15 such as a wire mesh is fixed to the inside of 10c to prevent a tapping sound from being generated when the valve is closed.

One end of the valve shaft 14 has a casing 11
The spring receiver 16 is fixed to the tip of the one side wall 11c. Also, the protruding valve shaft 1
A return spring 12 is wound around the outer periphery of the spring 4, and one end 12a of the return spring 12 is attached to the spring receiver 1
6 and the other end is locked to a spring hooking portion 11d formed on the casing 11, and the butterfly valve 10 is always biased in the closing direction by the restoring force of the return spring 12.

Next, the turnover mechanism 13 will be described in detail. A link 17 is provided on the outside of the other side wall 11e of the casing 11 so as to be fixed to the protruding portion of the valve shaft 14, and rotates around the valve shaft 14 in synchronization with the opening / closing operation of the butterfly valve 10. It is designed to move.
A rod 19 is provided at the tip of the link 17 by a connecting pin 18.
Is rotatably connected, and its rod 19 is arranged in a direction opposite to the valve shaft 14 side.

A first retainer 20 is provided on the rod 19 on the side of the connecting pin 18 by being inserted and fixed to the rod 19 (not fixed to a support plate 11f described later). In addition, a support plate 11 formed integrally with the casing 11
A second retainer 21 is rotatably provided on the f by a rotation pin 22, and the rod 1 is attached to the second retainer 21.
The tip of 9 is slidably penetrated, and the rod 19 is slidably supported by the second retainer 21.

Reference numeral 23 is a spring for urging in the extension direction, that is, a compression spring.
It is fitted around the outer periphery of the rod and is interposed between the retainers 20 and 21 in a compressed state. The rod 19 is constantly urged toward the side where the valve shaft 14 is located by a predetermined urging load in the extending direction. are doing.

2 to 4, the valve shaft 14, the link 17, the connecting pin 18, the rod 19 and the second
The relationship of the retainer 22 is that the connecting pin 18 of the link 17 and the rod 19 is in the fully closed state of the butterfly valve 10.
Is positioned above a line A (hereinafter, a position on this line is referred to as a turnover position) connecting the respective centers of the valve shaft 14 and the rotation pin 22 of the second retainer 22. When the link 10 is slightly opened, the link 17 is set so that the connecting pin 18 is located below the turnover position, and the compression spring 23 extends from the fully closed position to the fully open position of the butterfly valve 10. It is compression interposed so that the load in the extension direction acts.

Next, the operation of the first embodiment will be described. In a low engine speed or low load region where the dynamic pressure of exhaust gas is small, the valve closing force of the return spring 12 is stronger than the valve opening force of the butterfly valve 10 due to the dynamic pressure of the exhaust gas, and the butterfly valve 10 is shown in FIG. Is kept closed. At this time, the link 17 is in the state shown in FIG. 2, and the valve closing force is additionally applied to the butterfly valve 10 via the link 17 by the extension force of the compression spring 23. That is, in FIG. 4, assuming that the pressing force of the compression spring 23 is F ₁ and the distance between the valve shaft 18 and the connecting pin 18 is L ₁ , the butterfly valve 10 is compressed by the compression spring 23.
The valve closing force acting on the valve is F ₁ × L ₁ . In this way, the closed state of the butterfly valve 10 is secured by both springs 12 and 23, and the function of the inner pipe 6 as a low frequency resonance chamber is secured.

Further, as described above, in the low engine speed or low load region of the engine, the closing force of the butterfly valve 10 is increased by both springs 12 and 23, so that chattering of the butterfly valve is prevented.

Next, as the engine speed increases, the dynamic pressure of the exhaust gas increases, and the valve opening force acting on the pressure receiving surface of the butterfly valve 10 is stronger than the valve closing force of the return spring 12 and the turnover mechanism 13. Then, the butterfly valve 10 starts to open, and accordingly, the link 17 rotates downward in FIGS. 2 and 4. The compression spring 23 is compressed until the connecting pin 18 of the link 17 reaches the turnover position A, and the extension force acts in the closing direction of the butterfly valve 10.

When the butterfly valve 10 further rotates in the opening direction and the connecting pin 18 passes the turnover position,
The compression direction force of the compression spring 23 due to the link 17 is released, and the compression spring 23
The link 17 is pushed and rotated downward by the extension force, and the opening direction force by the compression spring 23 acts on the butterfly valve 10. Therefore, in the butterfly valve 10, the valve opening force by the compression spring 23 is added in addition to the valve opening force by the dynamic pressure of the exhaust gas with respect to the valve closing force of the return spring 12. The valve opening force by the compression spring 23 is as shown in FIG.
If the pressing force is F ₂ and the distance between the valve shaft 18 and the connecting pin 18 in the figure is L ₂ , then F ₂ × L ₂ .

Therefore, as the opening of the butterfly valve 10 increases, the angle of the pressure receiving surface of the butterfly valve 10 with respect to the flow direction of the exhaust gas gradually decreases, and the valve opening force of the exhaust gas decreases, while the return spring 12 closes. Even if the valve force increases, the valve opening force by the exhaust gas is assisted by the addition of the valve opening force by the compression spring 23 to facilitate the valve opening. Therefore, in the engine ~
Butterfly valve 1 at high rpm or medium to high load range
0 can be easily opened to an opening degree commensurate with the dynamic pressure of the exhaust gas, and the inner pipe 6 can be replaced with an expansion chamber capable of sufficiently reducing the back pressure.

Next, a second embodiment shown in FIGS. 5 to 9 will be described. This embodiment is an embodiment in which a turnover mechanism, which is a biasing means, is provided outside the muffler.

In FIG. 5, 1 is an outer shell of a silencer, 2 is a partition wall, 3, 4 and 5 are chambers, 6 and 7 are inner pipes that connect the chambers as shown in the figure, 8 is an inlet pipe, and 9 is It is an outlet pipe.

The inner pipe 6 is the same as the inner pipe 6 in the first embodiment. An elbow pipe 30 is connected to the downstream side of the inner pipe 6, and the downstream side portion 30a thereof is one side wall 31 of the silencer. It is placed close to and parallel to. At the downstream end of the downstream side portion 30a, a casing 33 containing a butterfly valve 32 is connected and arranged. A mounting base 35 is fixed to one side of the casing 33. The casing 33 is inserted into the container through the mounting hole 34 formed in the side wall 31, and the mounting base 35 is attached to the side wall 3.
1, the casing 33 is fixedly attached to the casing 1.

The valve shaft 36 of the butterfly valve 32.
Is projected to the outside of the device and is provided with a return spring 37. Further, a turnover mechanism 38 as a biasing means is provided between the mounting base 35 and the valve shaft 36 outside the device.
Is provided.

The casing 33 containing the butterfly valve 32, the return spring 37 and the turnover mechanism 38 will be described in detail with reference to FIGS. 6 to 9. The casing 33 is formed to have a cross-sectional shape as shown in FIG. 7, and a substantially oval exhaust flow passage 33a is formed in the casing 33 so as to penetrate in the front-back direction of the paper surface of FIG. 8 (the vertical direction in FIG. 6). The upstream side of the elbow-shaped pipe 30 communicates airtightly.

A valve shaft 36 is eccentrically provided in the casing 33 and rotatably pierced in the transverse direction. A butterfly valve 32 is provided in the exhaust flow passage 33a.
Is eccentrically fixed to the valve shaft 36, and the pipe 30
When the exhaust gas flows into the exhaust flow passage 33a from, the dynamic pressure of the exhaust gas causes the butterfly valve 32 to rotate and open with the valve shaft 36.

The mounting base 35 is fixedly mounted on the valve receiving portion 33b which is integrally formed with the casing 33 and supports the valve shaft 36. The mounting base 35 causes the casing 33 to be attached to the side wall 31 as described above. Mounted.

A return spring 37 is wound around the outer circumference of a portion 36a of the valve shaft 36 which projects to the outside, and one end 37a of the return spring 37 is locked by a hook 40 of the mounting base 35, and the other end 37b of the valve shaft 36 is The butterfly valve 32 is locked to the shaft 36 side and is constantly biased in the closing direction by a predetermined biasing force of the return spring 37.

Next, the turnover mechanism 38 is shown in FIG.
This will be described in detail with reference to FIGS. A lever 42 is fixed to the valve shaft 36a protruding to the outside, and a rod 44 is rotatably connected to a tip end portion of the valve shaft 36a by a first connecting pin 43. In addition, a bell crank-shaped link 45 is provided on the outer surface side of the mounting base 35 so as to be rotatable around a support shaft 46, and a spring support shaft 47 is projectingly provided at a bent tip portion 45a thereof. There is. The spring support shaft 47 serves as a first spring locking point. The other end of the rod 44 connected to the connecting pin 43 is rotatably connected to the bent portion of the link 45 by a second connecting pin 49. In addition, the lever 42
A spring locking pin 48 is formed in the middle portion of the. The pin 48 is the second spring locking point. A spring that urges in the contracting direction, that is, a tension spring 50 is installed between the spring support shaft 47 and the spring locking pin 48, and always pulls the lever 42 and the link 45 so as to draw each other.

The relationship between each member of the turnover mechanism 38 and the fulcrum is as shown in FIG. 8 when the butterfly valve 32 is fully closed.
Is located below a line B (hereinafter, a position on this line is referred to as a turnover position) connecting the second spring locking point 48 and the support shaft 46 of the link 45, and is in a fully opened state from a predetermined opening of the butterfly valve 32. Up to this point, the link 45 is set to rotate so that the first spring locking point 47 is located above the turnover position.

Next, the operation of the second embodiment will be described. In a low engine speed or low load range where the dynamic pressure of exhaust gas is small, the valve closing force of the return spring 37 is stronger than the valve opening force of the butterfly valve 32 due to the dynamic pressure of the exhaust gas, and the butterfly valve 32 closes. The valve state is maintained.

At this time, the lever 42, the rod 44, and the link 45 are in the state shown in FIG. 8, and the butterfly valve 32 is moved through the lever 42 by the pulling force of the tension spring 50.
The valve closing force additionally acts on.

As described above, the closed state of the butterfly valve 32 is secured by both springs 37 and 50, and the function of the inner pipe 6 as a low frequency resonance chamber is secured.
Further, the closing force of both springs 37.50 becomes strong, and the chattering of the butterfly valve 32 is prevented.

Next, as the engine speed increases, the dynamic pressure of the exhaust gas rises and the valve opening force acting on the pressure receiving surface of the butterfly valve 32 is stronger than the valve closing force of the return spring 37 and the turnover mechanism 38. Then, the butterfly valve 32 starts to open, and accordingly, the lever 42 rotates clockwise in FIG. This rotation causes the rod 44
The link 45 rotates clockwise in FIG.
When rotated to the chain line in FIG. 8, the first spring locking point 47 is located on the turnover position B. Up to the turnover position B, the tension spring 50 acts as a valve closing force.

Next, when the dynamic pressure of the exhaust gas is further increased, the lever 42 and the link 45 are further rotated clockwise in FIG. 8, and the first spring locking point 47 exceeds the turnover position B upward. The tension force of the tension spring 50 assists the butterfly valve 32 in the opening direction against the return spring force, and the valve closing force decreases as the opening degree of the butterfly valve 32 increases.

That is, as shown in FIG. 9, the rotation moment of the return spring 37 in the valve closing direction is Mb, the rotation moment generated by the tension spring 50 on the lever 42 is Mc, and the tension spring 50 is generated on the link 45. When the rotational moment is Md, the actually obtained rotational moment in the opening direction of the butterfly valve 32 is Ma, and this Ma is smaller than the rotational moment Mb due to only the return spring 37. The above rotational moments are accurately curved lines, but are shown as approximate straight lines for easy understanding.

Therefore, the opening operation of the butterfly valve 32 by the dynamic pressure of the exhaust gas is facilitated in the medium to high rotation range or the medium to high load range of the engine, and the butterfly valve 3
2 opens to an opening degree commensurate with the dynamic pressure of the exhaust gas, and the inner pipe 6 can be replaced with an expansion chamber capable of sufficiently reducing the back pressure.

Next, a third embodiment of the present invention shown in FIG. 10 will be described. In the third embodiment, the muffler is provided with two outlet pipes 9 and 9a.
A casing 11 having a butterfly valve 10 in the embodiment, a return spring 12, and a turnover mechanism 13 are provided on the outside projection of one outlet pipe 9a. In the figure, the same reference numerals as those in the first embodiment are the same members and portions as those in the first embodiment.

Also in the third embodiment, the same operation and effect as those of the first embodiment are exhibited, and in addition, by having the two outlet pipes 9 and 9a, the high rotation speed of the engine,
When the load is high, the back pressure is further reduced, and the turnover mechanism 13 is outside the silencer, so that the influence of deterioration due to a high ambient temperature is reduced.

In the third embodiment, the turnover mechanism 3 in the second embodiment is used as the turnover mechanism.
8 may be used. Next, a fourth embodiment of the present invention shown in FIG. 11 will be described.

In the fourth embodiment, the inlet pipe 8 of the silencer is branched and opened into the chamber 5, and the branch pipe 8a is
It is provided with a casing 11 containing the butterfly valve 10 in the first embodiment, a return spring 12, and a turnover mechanism 13. In the figure, the first
The same reference numerals as those in the embodiment are the same members and portions as those in the first embodiment.

Also in the fourth embodiment, the same operation and effect as those of the first embodiment are exhibited. In the fourth embodiment, the turnover mechanism 38 in the second embodiment may be used as the turnover mechanism.

The turnover mechanism may be constructed as follows. When the butterfly valve moves in the closing direction, the compression spring 23 shown in the first embodiment and the tension spring 50 shown in the second embodiment are
It may be used in combination with a damper so that the valve does not move slowly and sits abruptly. For example, in the first embodiment, a rod-shaped absorber may be arranged in the spring instead of the rod 19 to form a suspension strut.

Further, as the both springs 23 and 50, non-linear springs (conical type etc.) may be used. As a result, the amount of bending with respect to the load can be changed non-linearly, and the range of setting and tuning can be expanded.
Further, although both the springs 23 and 50 are coil springs, other biasing members such as a torsion bar and a leaf spring may be used instead.

Further, the range of movement of the link and the lever ratio in the above embodiment may be adjustable by an adjusting bolt, or the initial load of the spring may be adjustable. As a result, one general-purpose unit can support multiple vehicle types.

Further, the shape of the butterfly valve and the casing 11 in each of the above embodiments is not limited to the rectangular shape, and may be any shape, and the mounting position of the turnover mechanism with respect to the casing may be set arbitrarily. .

[0054]

As described above, according to the present invention, the valve closing force of the butterfly valve is increased in the low engine speed or low load range of the engine, and the exhaust gas is exhausted in the medium to high speed range or the medium to high load range. Since the urging means for adding the valve opening force that assists the valve opening action due to the dynamic pressure of the gas is provided, the butterfly valve is fully closed in the low engine speed or low load range to ensure that the inner pipe has a low frequency. You can make full use of the function of the resonance chamber and enhance the sound deadening effect.
In the medium to high rotation range or the medium to high load range of the engine, the butterfly valve can be opened to a sufficient opening degree to sufficiently reduce the back pressure and increase the engine output.

Therefore, the original merit of the exhaust gas actuated variable muffler can be more remarkably realized. In addition, chattering of the butterfly valve can be prevented by adding the biasing means.

Further, by using the turnover mechanism as the urging means, the direction and amount of the urging load can be easily set by changing the lever ratio of the spring or the link which constitutes the turnover mechanism. It can be easily adapted to the characteristics of each engine and vehicle.

The biasing means or the turnover mechanism constituting the biasing means may be provided inside or outside the muffler. However, if it is provided inside the muffler, it can be protected from flying stones and dust. If it is provided outside, the influence of deterioration due to high ambient temperature can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic plan sectional view of a silencer showing a first embodiment of the present invention in which a turnover mechanism is incorporated.

2 is a perspective view showing a butterfly valve and a turnover mechanism in FIG. 1, showing a valve closed state. FIG.

FIG. 3 is a perspective view showing a state in which the valve is opened from the state of FIG.

FIG. 4 is a side view illustrating a turnover mechanism in FIG.

FIG. 5 is a schematic plan sectional view of a silencer showing a second embodiment of the present invention in which a turnover mechanism is packaged.

FIG. 6 is a plan view of a main part in FIG.

FIG. 7 is a sectional view taken along line XX in FIG. 6;

FIG. 8 is a left side view of FIG.

9 is a characteristic diagram showing the rotational moment of each member in the embodiment of FIG.

FIG. 10 is a schematic plan sectional view of a silencer showing a third embodiment in which a turnover mechanism is attached to an outlet pipe.

FIG. 11 is a schematic plan sectional view of a silencer showing a fourth embodiment in which a turnover mechanism is attached to an inlet pipe.

FIG. 12 is a plan sectional view showing a conventional technique.

[Explanation of symbols]

6 ... Inner pipe 10, 32 ... Butterfly valve 12, 37 ... Return spring 14, 36 ... Valve shaft 13, 38 ... Turnover mechanism

Claims (5)

[Claims] 1. A butterfly valve in a pipe constituting a silencer, which is eccentrically provided with respect to its valve shaft, is operated to open by an exhaust gas flow, and is biased in a valve closing direction. To a predetermined opening degree, the butterfly valve is provided with a biasing means for applying a closing direction load to the butterfly valve, and at a further opening degree, a biasing means for assisting the valve opening operation by the exhaust gas flow is provided. . 2. A butterfly valve is eccentrically provided with respect to a valve shaft of a pipe that constitutes a silencer, is opened by an exhaust gas flow, and is urged in a valve closing direction to assist opening and closing of the butterfly valve. A silencer for an internal combustion engine, which is provided with a turnover mechanism that operates. 3. A silencer for an internal combustion engine according to claim 1, wherein the biasing means or the turnover mechanism is provided inside the silencer. 4. The silencer for an internal combustion engine according to claim 1 or 2, further comprising a biasing means or a turnover mechanism provided outside the silencer. 5. A silencer for an internal combustion engine, wherein the pipe according to any one of claims 1 to 4 is an inner pipe, an outlet pipe or an inlet pipe.