JPH0216010Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention relates to the improvement of a muffler that attenuates the noise contained in the exhaust gas of internal combustion engines such as automobiles, especially for automobiles where the degree of freedom in installing the muffler is small. This invention relates to a tubular silencer that can be easily installed under the floor of a car.

(Prior Art) Internal combustion engines such as automobiles inevitably generate exhaust noise as they operate. Typically, this noise is attenuated via an exhaust system and then emitted to the outside together with the exhaust gas.

By the way, this exhaust noise is roughly divided into two types: "pulsation noise" and "airflow noise."

Pulsating noise is noise that is generated due to fuel explosion in an internal combustion engine, and is emitted intermittently during each exhaust stroke, and is unavoidable during the operation of the internal combustion engine.

Airflow noise refers to turbulence noise, Karman vortex noise, and
Alternatively, it is a general term for so-called secondary fluid noise, such as jet noise that is emitted into the atmosphere from the rear end of an exhaust pipe.

Generally, when the internal combustion engine rotates at low speed, exhaust noise is dominated by pulsating noise in terms of energy, but as the engine rotates at high speed, airflow noise becomes dominant.

To attenuate such noise, extended type,
Various types of silencers are used, such as interference type, resonance type, sound absorption type, etc.

The extended type is one in which exhaust paths are sequentially combined in a narrow space, a wide space, and a narrow space, and the noise is reflected many times between the partition walls in the wide space and is attenuated by interference. In this type, the exhaust gas expands rapidly over a large space, so the exhaust gas pressure, which is emitted as a pulsation, as well as the pulsating noise, is averaged out.

In the interference type, the exhaust path has two branch pipes of different lengths in the middle, and the pulsation phase is made different to try to muffle the noise at the junction of these pipes. In this type, exhaust gas is also averaged when dense and dense areas overlap.

The resonance type introduces noise into a closed space (resonance chamber) and attenuates it through resonance. In this type, the exhaust gas is normally unaffected, but is subjected to cushioning action if the opening of the resonance chamber faces the exhaust gas flow.

The sound-absorbing type usually creates a sealed space around a perforated tube containing a sound-absorbing material such as glass wool, and attenuates the noise that enters through the holes by converting it into heat. In this type, the exhaust gases are not subjected to any action.

The expansion type, interference type, and resonance type mainly muffle low to medium frequency pulsating noise, and the sound absorption type mainly muffles high frequency airflow noise and other high frequency secondary noise generated in the exhaust system. .

Since these muffling mechanisms have a limited range of frequencies in which they work well, mufflers can be used in various combinations to attenuate the noise in a few specific frequency ranges that are prominent from the internal combustion engine in which they are used. It is designed.

By the way, the expansion type muffler is extremely effective for equalizing the exhaust gas pressure, but
On the other hand, especially on the upstream side of the exhaust, when air is blown from a narrow space into a wide space, a Karman vortex is generated, generating secondary noise, so-called airflow noise.

However, this expandable muffler is essential to attenuate the noise and even out the pulsating exhaust gas pressure, and the newly generated noise is further attenuated by the downstream muffling mechanism. There is. For this reason, there is a demand for an expanded noise-muffling structure that suppresses the generation of airflow noise as much as possible.

A conventional silencer constructed with such considerations in mind is, for example, as shown in Fig. 4 (same as Fig. 1 of Japanese Utility Model Application Publication No. 159607/1983, but the numerals have been changed). There is something. In FIG. 4, a shell surrounding the exhaust pipe 1 is formed by an outer cylinder 19 whose both ends are closed with end plates 17 and 18, and the inside of this shell is partitioned by partition plates 20 and 21. is provided with a through hole 22, and the exhaust pipe 1 has a group of small holes 2 that communicate with compartments 23, 24, 25 in the partitioned shell.
6, 27, and 28 are bored, and a closing plate 29 is provided at the portion of the exhaust pipe 1 within the compartment 24. The small hole group 26 and the closing plate 29 are separated by a length l to form a dead-end chamber 30 therebetween.

In this muffler, the exhaust gas that has traveled through the exhaust pipe 1 from the left in the drawing travels straight through the dead-end chamber 30, returns and is subjected to the cushioning action, and then passes through the small hole group 26 into the section of the outer cylinder. 23, enters the compartment 24 through the through hole 22, and then contracts while entering the exhaust pipe 1 through the small hole group 27 and flows down the exhaust pipe 1. At this time, when the exhaust gas flows from the small hole group 26 to the compartment 23 and from the small hole group 27 to the exhaust pipe 1, a Karman vortex is generated and airflow noise is generated. After being subjected to the cushioning action, the gas flows out from the small hole group 26 into the compartment 23, so that the exhaust gas pressure is averaged out to some extent, and the generation of airflow noise is prevented accordingly. Further, from the small hole group 26, the section 2
3, passage through the through hole 22, and contraction from the section 23 to the small hole group 27, etc., the exhaust gas pressure is gradually averaged, and when it is discharged into the atmosphere from the pipe end, it almost reaches the average pressure. The airflow noise caused by the jet from the tube end is significantly reduced.

On the other hand, the pulsating noise generated by the internal combustion engine is
3 and the section 24, the noise is subjected to interference and attenuated by repeated reflections, and further enters the section 25, which has a resonance effect matching the frequency of this noise, from the small hole group 28, and is attenuated by the resonance effect.

(Problem to be solved by the invention) This conventional silencer expands, contracts,
It is configured to apply effects such as cushioning and resonance to the exhaust gas to equalize the exhaust gas pressure and attenuate exhaust noise, but it is not suitable for mounting under the floor of a car to cover the exhaust pipe with a large diameter shell. It was inconvenient. That is, the ground clearance under the floor of an automobile is not high, and the propeller shaft, brake hydraulic pipe, suspension mechanism, reinforcing structure, etc. are installed, so it is not possible to freely select the location where the silencer is installed. Even if the shell is formed flat, it is still difficult to select the mounting location.

Furthermore, since the muffler is designed to prevent an increase in back pressure, in order to attenuate pulsating noise,
It wasn't necessarily a good thing.

In addition to the main muffler, a front muffler and a rear muffler are usually used as mufflers, and these are connected in series to each other in the middle of the exhaust pipe. Since it has a considerably larger cross-sectional area compared to other models, there are restrictions on where it can be installed under the floor of a car, which is narrow and has little flexibility in installation.

Furthermore, because a silencer has the property that its ability to attenuate low-frequency components of noise changes depending on where it is installed, it is not always possible to obtain a good noise reduction effect even if the silencer is installed in a place where it can be installed under the floor. figure,
Therefore, in many cases, the original performance of the silencer could not be fully demonstrated.

In order to avoid this inconvenience, it has been considered to construct the silencer into a tubular shape by attaching an outer pipe that is slightly thicker than the exhaust pipe to the exhaust pipe instead of using a shell that is significantly thicker than the exhaust pipe (for example, 56−29223
However, such conventional tubular silencers only exhibit a limited silencing effect among various silencing effects such as expansion, contraction, sound absorption, and resonance, or they do not reduce the exhaust gas pressure. Since the exhaust gas cannot be averaged sufficiently within the muffler, there is a drawback that the airflow noise due to the jet stream becomes significant at the end of the pipe where the exhaust gas is released into the atmosphere, and the current situation is that it is not always possible to obtain a sufficient silencing effect. be.

The present invention eliminates the drawbacks of the conventional structure as described above, eliminates the need for a muffler with a significantly thick pipe body, improves installation ease, and muffles noise in a wide frequency range by distributing various sound muffling mechanisms in a well-balanced manner. Moreover, the present invention provides a muffler that sufficiently averages the exhaust gas pressure and significantly reduces the generation of air flow noise at the tube end.

(Means for solving the problem) The tubular silencer of the present invention has an inner pipe 1 and an outer pipe 2 having a larger diameter fitted together, and both ends and the middle part of the outer pipe 2 are squeezed. The outer tube 2 is partially tightly fixed to the outer peripheral surface of the inner tube 1, and the inner and outer tubes 1,
2, a plurality of cylindrical spaces 5 and 6 having no openings communicating with the atmosphere are formed, and a large number of small holes are bored in the inner tube 1 in the portions within these spaces 5 and 6. A plurality of small hole groups are provided, and a plurality of small hole groups are provided between the first small hole group and the second small hole group on the most upstream side with respect to the exhaust gas flow, and between the third small hole group and the fourth small hole group on the third side. th fourth
A plurality of closing plates 3 and 4 are provided in the inner tube 1 to close the cross section of the inner tube 1 between the small hole group and the downstream closing plate with respect to the exhaust gas flow. The lengths l ₁ , l ₂ ,
The above problem has been solved by providing a tubular muffler in which a plurality of dead-end chambers 14, 15, and 16 having resonance and cushioning effects with different l ₃ values are obtained.

(Function) In the tubular muffler of the present invention constructed as described above, the exhaust gas pulsatingly fed into the muffler through the inner pipe 1 first flows into the most upstream chamber 14 which has a cushioning effect. After the pressure is regulated to some extent by the cushioning action, the first small hole group 8 on the most upstream side is passed through the first small hole group 8 between the inner tube 1 and the outer tube 2 due to the cushioning effect. After flowing into the space 5 and being subjected to the cushioning action, it passes through the second small hole group 9 on the downstream side and returns to the inner tube 1 again. Furthermore, the exhaust gas repeats this cushioning action and passes through the small holes, and is then discharged from the exhaust pipe.

During this time, the exhaust gas pressure is not only averaged by expansion and contraction as it passes through the small holes, but also gradually averaged by the cushioning action in each of the multiple dead-end chambers 14, 15, and 16. When the gas is discharged, the gas pressure is approximately equalized, and the generation of air flow noise due to the jet flow at the end of the pipe is greatly reduced.

In particular, when the exhaust gas passing through the tubular muffler of the present invention passes through a group of small holes that communicate between the inside and outside of the inner pipe 1, the dead-end chamber 1 has a cushioning effect.
The pulsation is always regulated to a certain extent by the cushioning action of each of the cushions 4, 15, and 16 before passing through the small hole group, so secondary noise accompanying the airflow vortex inside the muffler, that is, airflow noise is generated. can be prevented as much as possible.

On the other hand, pulsating noise is handled by a plurality of dead-end chambers 14, 15, 16 each having different lengths l ₁ , l ₂ , l ₃ that act as resonators, and different frequency bands are generated by resonance. At the same time, the noise is attenuated by interference due to repeated reflections of the noise in the plurality of cylindrical spaces 5 and 6 between the inner and outer tubes 1 and 2. In this way, the dead-end chambers 14, 15 are equipped with different silencing mechanisms of resonance action and interference due to reflection, and act as a plurality of resonators each having a different resonance frequency.
16, it is possible to attenuate noise in a wide frequency band.

(Example) Hereinafter, the present invention will be explained in more detail with reference to drawings showing examples.

FIG. 1 is a schematic sectional view showing an embodiment of the present invention. This muffler consists of a small-diameter inner tube 1, a larger-diameter outer tube 2, and an inner tube 1, which are concentrically combined with each other.
It consists of closing plates 3 and 4 that close the cross section in the middle of the.

Both ends and two intermediate portions of the outer tube 2 are drawn to a small diameter and brought into close contact with the outer circumferential surface of the inner tube 1. Therefore, between the inner circumferential surface of the outer tube 2 and the outer circumferential surface of the inner tube 1, from the front side (upstream side of the exhaust flow, left side in the drawing), there are first spaces 5 each having a cylindrical shape and not communicating with the atmosphere. , a second space 6, and a third space 7 are formed.

A first small hole group 8 having a large number of small holes is provided at the front end of the portion of the inner tube 1 facing the first space 5, and a similar second small hole group 9 is provided in the intermediate portion. A first closing plate 3 is provided in the inner tube 1 slightly in front of the second small hole group 9 to close the cross section of the inner tube 1.

Further, a similar third small hole group 10 is formed at the front end of the portion of the inner tube 1 facing the second space 6, and a similar fourth small hole group 11 is formed at the rear end. A second closing plate 4 is provided in the inner tube 1 slightly in front of the fourth small hole group 11 to close the inner tube 1.

Furthermore, the portion of the inner tube 1 facing the third space 7 is provided with a large number of small holes 12, 12 over almost its entire length.
At the same time, a sound absorbing material 13 is installed in the third space 7.
is filled with.

In the silencer constructed in this manner, the exhaust gas sent from the left side of FIG. 3
The dead-end chamber 14 inside the inner pipe 1 between the two acts as a resonator against pulsating noise, and at the same time has a cushioning effect against exhaust gas,
The pressure of the exhaust gas pulsating from the left side of FIG. 1 is regulated to equalize the flow as much as possible.

Further, a dead-end chamber 15 rearward of the second small hole group 9 in the first space 5, the third small hole group 10, and the second closing plate 4
Similar to the chamber 14, exhaust gas does not flow through the dead-end chamber 16 between the chambers 16 and 16.Like the chamber 14, each chamber 15-16 acts as a resonator to attenuate noise, and at the same time acts as a resonator for exhaust gas. It also acts as a cushion chamber to further reduce the difference in height of the pulsating exhaust gas pressure.

If a resonator of length l _x with the end closed is installed on the side of the discharge flow path, the frequency _x of the noise attenuated by this resonator is _x = c/4l _x (c: sound speed), so the blockage By appropriately varying the lengths of the chambers 14, 15, 16 depending on the positions of the plates 3, 4 and the small hole groups 8, 9, 10, it is possible to attenuate noise of various frequencies.

Figure 2 shows dead-end chamber 1 in the structure of Figure 1.
This shows the resonance effect of 4, 15, 16, and the first
For parts equivalent to the constituent parts in the diagram, the corresponding symbol is a.
It is shown with .

Next, with reference to FIG. 2, the silencing effect and pressure regulating effect of the silencer shown in FIG. 1 will be explained.

Pulsating noise sent into the inner tubes 1, 1a from the left side of the drawing flows into the first spaces 5, 5a through the first small hole groups 8, 8a, but at this time, this noise
As a result of being repeatedly reflected within the first spaces 5, 5a, in addition to receiving a silencing effect due to interference, the chambers 14, 14a have a length of l ₁ and act as resonators, so the frequency _{is 1} (=c/4l ₁ ). noise is attenuated. on the other hand,
Before the exhaust gas passes through the first small hole group 8, 8a, the flowing gas pressure is somewhat averaged by the cushioning action of the chambers 14, 14a, so that the exhaust gas passes through the first small hole group 8, 8a. The vortices generated during this process are relaxed, and the generation of secondary noise, that is, airflow noise, is prevented as much as possible. The gas pressure is further averaged by passing through the first small hole group 8, 8a.

The pulsating noise that has flowed into the first spaces 5, 5a flows into the inner pipes 1, 1a again through the second small hole group 9, 9a provided at the rear of the first closing plate 3. In addition to the silencing effect due to interference caused by reflection, this noise also has a frequency of 2 due to the chambers 15 and 15a having length l _{2 .}
(=c/4l ₂ ) of noise is attenuated.

On the other hand, the exhaust gas pressure is
After being averaged by the cushioning action, the light passes through the second small hole group 9, 9a and is further averaged. The vortex flow when passing through the second small hole group 9, 9a is further relaxed, and the generation of airflow noise is further reduced.

The pulsating noise that has circulated inside the inner tubes 1 and 1a then passes through the third small hole group 10 and 10a to the second spaces 6 and 6.
a, returns to the inner tubes 1, 1a through the fourth small hole group 11, 11a again, but _at this time as well, in addition to attenuating this noise due to interference caused by reflection, Room 1
6 and 16a attenuate the noise of frequency ₃ (=c4l ₃ ).

On the other hand, the exhaust gas pressure is further equalized as described above, and the generation of airflow noise is almost prevented.

Inner pipes 1, 1a through the fourth small hole group 11, 11a
The pulsating noise that returns to the muffler is directly discharged into the atmosphere from the rear end opening of the inner tubes 1, 1a, but the high frequency noise based on the airflow noise generated inside this muffler is caused by the large number of small holes 12, 12a. The sound is attenuated when it passes through a section that is drilled and surrounded by sound-absorbing material.

Therefore, when the exhaust gas is released into the atmosphere from the rear end openings of the inner pipes 1 and 1a, pulsation noise and airflow noise are well suppressed over all frequencies, and the exhaust noise is emitted to the surroundings. No more spreading.

On the other hand, the exhaust gas pressure is also sufficiently averaged, so when the exhaust gas is discharged into the atmosphere from the rear end of the exhaust pipe, the generation of new airflow noise due to the jet flow is also significantly reduced compared to before. .

In particular, internal combustion engines often generate noise in a specific frequency range depending on their displacement, normal rotational speed, etc., but as mentioned above, the length of each dead-end chamber 14, 15, 16 that acts as a resonator By changing the , the frequency of the noise to be attenuated can be easily changed, making it easy to obtain the best muffler for the internal combustion engine. In this case, if the lengths l ₁ to _{l 3} of the chambers 14 to 16 are varied stepwise, noises of different frequencies ₁ to ₃ can be attenuated, as shown in FIG. 3.

In addition, the tubular silencer of the present invention is not limited to the number of embodiments described above, and a plurality of components may be combined as appropriate to achieve the best performance for the internal combustion engine to which the silencer is installed. It can be configured as follows. However, in either case, it consists of an inner tube 1 and an outer tube 2 that have a double structure with a space interposed between them, and a closing plate is provided between a plurality of small hole groups provided in the inner tube 1. It may be necessary to provide a part in the space between the inner and outer tubes or in the inner tube 1 which acts as a resonator and a cushion chamber.

Moreover, it can be widely applied not only to automobile silencers but also to other devices having internal combustion engines.

(Effects of the invention) (1) The tubular silencer of the present invention eliminates the extremely thick pipe body, and fits the inner pipe and the outer pipe, which is slightly thicker than the inner pipe, with a space in between. Since both ends and the middle part are squeezed and brought into close contact with the inner tube, the overall structure is slim and easy to bend.

(2) Therefore, when installing under the floor of a car, for example, it can be installed while avoiding obstructive parts, increasing the degree of freedom in installation.

(3) Pressure regulation and noise reduction, in which the outer tube can be made long so as to fit over almost the entire length of the inner tube, and the elongated silencing portion performs compression, contraction, cushioning, reflective interference, and resonance effects. Since the structure can be created, there is greater freedom in choosing the length of the dead-end chamber and resonance chamber.

(4) Therefore, this length can be used to create a sound-dampening structure with good sound-damping effect.

(5) Since the structure has a well-balanced arrangement of expansion type and resonance type mufflers, and also allows easy attachment of a sound absorbing type muffler if necessary, noise in a wide frequency range can be efficiently muffled.

(6) In order to first muffle the sound with a cushion at the most upstream part of the exhaust flow, the exhaust gas pressure is first lowered to make it difficult to generate secondary high-frequency airflow noise when it passes through the small hole.

(7) The exhaust gas pressure can be sufficiently averaged within the muffler, and the generation of airflow noise at the rear end opening of the exhaust pipe can be significantly reduced.

[Brief explanation of the drawing]

Fig. 1 is a schematic sectional view showing an embodiment of the tubular muffler of the present invention, Fig. 2 is a schematic sectional view showing a muffler equivalent to the muffler in Fig. 1, and Fig. 3 is a schematic sectional view showing an example of the muffler in Fig. A diagram showing the state of noise attenuation in the resonator part of the silencer,
FIG. 4 is a longitudinal sectional view illustrating a conventional muffler. 1... Inner tube, 2... Outer tube, 3, 4... Closure plate, 5
...First space, 6... Second space, 7... Third space, 8... First small hole group, 9... Second small hole group, 10
...3rd small hole group, 11...4th small hole group, 12...
Small hole, 13... Sound absorbing material, 14, 15, 16...
Chamber, 17, 18... End plate, 19... Outer cylinder, 20,
21... Partition plate, 22... Through hole, 23, 24, 25
...Division, 26, 27, 28...Small hole group, 29...
...Blocking board, 30... Dead-end room.

Claims (1)

[Scope of utility model registration request] By fitting one inner tube 1 and an outer tube 2 with a larger diameter, and squeezing both ends and the middle part of the outer tube 2, the outer tube 2 is partially tightly fixed to the outer circumferential surface of the inner tube 1. At the same time, a plurality of cylindrical spaces 5 and 6 having no openings communicating with the atmosphere are formed between the inner and outer tubes 1 and 2, and the inner tube 1 is , a plurality of small hole groups each having a large number of small holes are provided, and a plurality of small hole groups are provided between the first small hole group and the second small hole group on the most upstream side with respect to the exhaust gas flow, and between the third small hole group and the second small hole group. A plurality of plugging plates 3 and 4 are provided in the inner pipe 1 to close the cross section of the inner pipe 1 between the third small hole group and the fourth fourth small hole group, and are arranged on the upstream side with respect to the exhaust gas flow. Lengths l 1 and l are provided between the non-porous inner tube portion between a group of small holes and the blocking plate on the downstream side, and between the closed end of the outer tube 2 located on the downstream side of the group of small holes, _respectively . A tubular muffler having a plurality of dead-end chambers ₁₄ , ₁₅ , 16 having mutually different resonance and cushioning effects.