JPH09256834A - Noise absorption duct structural body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noise absorption duct structural body applicable to a duct of air-intake/exhaust passage or a duct of an internal combustion engine, and capable of efficiently reducing the noise in the whole frequency range. SOLUTION: The inner diameter of a reference duct 1 is the reference value of an arbitrary sectional shape, and a noise absorption duct having a part of any sectional shape with the inner diameter expanded, in which the center of the section of the expanded part is matched with or not matched with the center of the section of the reference duct 1, and the shape in the longitudinal direction of the expanded part is arbitrary is provided. An expanded duct 2 part having at least one chamber in the expanded duct 2 part is provided by installing a partition in the longitudinal direction or in the sectional direction in the expanded part, noise absorption members 3,4 are arranged in at least one chamber of the expanded duct 2 part, and the outer diameter of the noise absorption duct structural body in the expanded duct 2 part is 1.1-5 times the inner diameter of the reference duct 1, and the overall length of the noise absorption duct structural body is 5-100cm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a duct structure for absorbing sound, and relates to a sound absorbing duct structure having excellent sound absorbing characteristics in the entire frequency range from low frequency to high frequency.

[0002]

2. Description of the Related Art Noise in an intake / exhaust system is caused by air flow noises of a blower, a blower, a high pressure valve, a nozzle, etc., intake / exhaust of an internal combustion engine, a gas generator, combustion of oil or a gas burner. A muffler is used to reduce the noise. These silencers have a structure in which the resistance of the fluid and the duct is made as small as possible, the acoustic energy as a sound source is attenuated as much as possible, and the sound pressure is reduced by using a sound absorbing material and an expansion pipe.

The intake noise of an internal combustion engine uses pulsation due to intake of the engine as a sound source, and is mainly in a low frequency region of 500 Hz or less. At present, sound absorbing structures such as resonators and side branches are mainly installed in order to reduce this intake noise, but as in the above example, this structure only has a frequency attenuation effect due to a specific frequency. Therefore, it is necessary to install a large number of structures in order to absorb a large number of frequencies.

In order to reduce this noise, a large number of small holes are provided in the intake pipe connecting the carburetor and the air cleaner, and a sound absorbing material is attached outside the small holes (Japanese Patent Laid-Open No. 53-53).
No. 148617, Japanese Utility Model Laid-Open No. 55-167562), or a type in which a partition wall for partitioning the internal combustion engine side and the air cleaner element side is arranged, and a throttle hole is provided in the partition wall (Japanese Patent Laid-Open No. 64-53055). There is.

Further, a resonator using a resonator (resonance type silencer) intended to absorb sound of a specific frequency, an air cleaner with a built-in resonator disposed in the center of the element chamber (Japanese Patent Laid-Open No. 62-110722), an internal combustion engine. Resonator with variable resonance frequency (JP-A-55-60444), which changes the volume of the resonance chamber in accordance with the change in the intake pipe pressure, and controls the volume of the resonator in accordance with the change in the intake pressure caused by the change in the engine speed. There is a type (JP-A-2-19644).

Also, a type using a bypass tube for the purpose of damping in the air cleaner case and each duct (JP-A-5-18329), a special resonance duct is connected in communication with the air cleaner case, and resonance damping in a specific frequency range is performed. There is a type (Japanese Patent Laid-Open No. 5-18330).

Further, there is a type (Japanese Patent Laid-Open No. 53-14867) in which a sound absorbing material is installed in the vicinity of the opening end of the one using the sound absorbing material, but it is hardly effective at low frequencies.

[0008]

However, although these structures are effective in absorbing sound of a specific frequency, they cannot be effective in the entire frequency range, and the sound absorbing material type is effective in absorbing noise of a relatively high frequency. However, the sound absorbing effect could not be fully exerted.

In particular, the noise in the intake system of a vehicle is basically a noise in the low frequency region of 500 Hz or less, though it varies depending on the engine speed, and the effect is particularly remarkable over the entire low frequency region. The problem is to obtain a large sound absorbing structure. At the same time, since the space inside the engine room of the vehicle is limited, achieving a high-performance, compact structure is also a serious problem. Another object of the present invention is to obtain a sound-absorbing duct structure applicable to a duct of an internal combustion engine and capable of efficiently reducing noise in the entire frequency range.

[0010]

In order to solve such a problem, the present invention has a portion whose cross-sectional shape does not matter, with the inner diameter of a base duct whose cross-sectional shape does not matter as a reference. , The cross-sectional center of the expanded portion is matched or not matched with the cross-sectional center of the base duct, and in the sound absorbing duct structure including the sound absorbing duct regardless of the shape of the expanded portion in the longitudinal direction, By providing a partition in the internal length direction or cross-sectional direction, the expansion duct section has an expansion duct section having at least one or more chambers, and the expansion duct section is provided with a sound absorbing material in at least one or more chambers. The outer diameter of the sound absorbing duct structure in this expansion duct is 1.1 to 5 times the inner diameter of the base duct, and the total length of the sound absorbing duct structure is 5 to 100 cm.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of a sound absorbing duct structure according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a partially transparent perspective view showing an embodiment of a sound absorbing duct structure according to the present invention. The expansion duct 2 which is the sound absorbing duct in the present embodiment is the base duct 1
A small chamber formed around the sound absorbing member and housing the sound absorbing material 1 and the sound absorbing material 2
Two small chambers are formed, a small chamber for storing the. In this way, the expansion duct 2 is formed by providing at least one small chamber with a partition in the length direction or the cross-sectional direction,
A sound absorbing material is arranged on this. The sound absorbing duct structure 2 has an outer diameter of 1.1 to 5 times the inner diameter of the base duct 1 and a total length of 5 to 100 cm.

In FIG. 1, the expansion duct 2 is formed concentrically and substantially in the same shape as the base duct 1, but the present invention is not particularly limited to this, as will be described later.
That is, the cross-sectional shape of the expansion duct 2 is not limited to the circular shape, and the center of the expansion duct 2 does not have to coincide with the center of the base duct 1.

The noise caused by the air flowing inside the duct is mainly a resonance sound in a low frequency region of 500 Hz or less and a relatively high frequency air flow sound formed therein. It has been difficult for a single sound absorbing structure to absorb sound in a wide frequency range over all frequencies.

In the present invention, in order to reduce this noise,
This is achieved by a special combination of the expansion duct 2 having an expanded inner diameter, a small chamber formed in the expansion duct 2, and sound absorbing materials 3 and 4 installed in the small chamber. The expansion of the inner diameter forms a kind of hollow silencer, which is effective in damping relatively low frequencies, and the sound absorbing material inside is made of a porous material type sound absorbing structure.
Effective in absorbing sound at high frequencies. By partitioning the expansion part into small rooms, it is possible to install sound absorbing materials with different sound absorbing characteristics in each of the partitioned small rooms, and by distributing the frequency components to each of them, as a result, a sound absorbing duct with a wide sound absorbing area. A structure is formed.

The sound absorbing duct portion 2 has a round cross section, a square cross section,
It is necessary to have a portion (hereinafter, referred to as an expansion duct) whose inner diameter is expanded in a basic duct (hereinafter, referred to as a base duct) such as an elliptical cross section. The cross-sectional shape of this expanded portion does not matter. Therefore, various combinations such as a structure having the elliptical expansion duct 2 in the base duct 1 having a circular cross section and a structure having the elliptical expansion duct 2 in the elliptical base duct 1 are effective, but are not particularly limited.

The center of the cross section of the base duct 1 and the center of the cross section of the expansion duct 2 may or may not coincide. Therefore, the extreme arrangement may be such that the outer circumference of the base duct and the outer circumference of the expansion duct are in contact with each other on one side.

The cross-sectional centers of the two base ducts 1 located on both sides of the expansion duct portion may or may not coincide with the cross-sectional center of the other. Further, the cross-sectional centers of the two base ducts 1 and the cross-sectional centers of the cross-sections of the expansion duct portion may be the same, the two cross-sectional centers may be the same, or they may be different from each other. The above-described relationship between the cross-sectional center of the expansion duct 2 and the cross-sectional center of the base duct 1 depends on the space for installing the sound absorbing duct, but does not depend on the target sound absorbing performance at a frequency of 500 Hz or lower. However, in the high frequency region of 1 kHz or higher, the positional relationship between the base duct 1 and the expansion duct 2 affects the sound absorbing performance, and the state where the three cross-section centers are evenly diffused in each of the sound absorbing performances. Is good. In particular, it is preferable that the centers of the cross sections of the two base ducts 1 are separated as much as possible, but there is no limitation.

These positional relationships are largely dependent on the space where the sound absorbing duct is installed. Especially when the sound absorbing duct is installed in the engine room of the vehicle, depending on the shape of the front tire house, the position of the battery, etc. The cross-sectional shape and the center position of the duct change.

The shape of the extension duct 2 in the longitudinal direction does not matter. Therefore, various types such as a columnar shape, a conical shape, a quadrangular pyramid shape, and a shape matching the space of the installation site can be used, but the shape is not particularly limited.

In the hollow silencer, the transmission loss TL can be theoretically calculated by appropriately modeling the silencing element. The theoretical formula is shown in the following formula (1).

TL = 10 log | 1+ {1/2 (m−1 / m) sin ² kL} ² | (1) m: expansion ratio of inner diameter k: wavelength constant k = 2πf / C (f: frequency, C: speed of sound) L: length of expansion section If the expansion ratio of the expansion duct 2 is made larger than this, the amount of attenuation increases, and by increasing the length of the expansion duct section 2,
An attenuation effect in the entire frequency range (particularly in the low frequency range) can be obtained.

However, in the present embodiment, the sound absorbing material is installed inside the cavity type silencer, and the effect of the sound absorbing material cannot be completely expressed by the theoretical formula. Therefore, only the formula (1) can be explained. Absent.

The outer diameter of the expansion duct 2 is preferably 1.1 to 5 times the inner diameter of the base duct 1. The expansion ratio affects the amount of attenuation, and the larger the expansion ratio is, the greater the amount of sound attenuation and the greater the effect. If the expansion ratio is less than 1.1 times, there is almost no damping effect, and the performance of the sound absorbing duct is not satisfied. Further, the structure having the expansion duct 2 having the expansion ratio 5 times or more that of the base duct 1 is out of the actual level in terms of volume. Especially for use in the engine compartment of a vehicle, a structure as small as possible is desirable and it is not possible to use expansion ducts with expansion ratios greater than 5 times.

The extension tact 2 preferably has a length of 5 to 100 cm. The length of the expansion duct 2 also affects the amount of attenuation, and the longer it is, the greater the attenuation effect in the low frequency range is,
Greatly effective at high frequencies. Extension duct 2 has a length of 5c
A sound absorbing duct of m or less has a small sound deadening effect even if the expansion ratio is increased, and it is difficult to form a small chamber therein. Further, the structure having the expansion duct having a length of 100 cm or more is out of the actual level in terms of volume. Especially for use in the engine compartment of a vehicle, a structure that is as small as possible is desirable, and the extension duct 2 having a length of 100 cm or more cannot be used.

It is necessary to provide a partition in the expansion duct section and divide the expansion section into small chambers. This division may be in the longitudinal direction of the base duct or in the cross-sectional direction.

When the resonance antinodes for each frequency are continuous in the tube, the small chamber is divided in the longitudinal direction as shown in FIG.
It is effective for the sound absorbing effect to install the sound absorbing material therein by tuning the characteristics of the sound absorbing material to the continuous antinode frequency.

When the antinodes of resonance for each frequency are dispersed in the tube, the small chamber is divided in the cross-sectional direction as shown in FIG.
It is possible to effectively provide a sound absorbing effect by installing the sound absorbing material in the shape of a round slice at the position of the antinode of each resonance.

As the number of small chambers increases, it becomes possible to exert effects on various frequencies, but the space for installing the sound absorbing material decreases, which makes it impossible to increase the sound absorbing force. Therefore, it is desirable that the number of small chambers is at most four, but the number is not particularly limited.

The volume of each small chamber and the contact area with the air flow can be changed according to the demand for sound absorbing performance at a target frequency. For example, if the purpose is to reduce four frequencies, the importance may differ, but in that case, the sound absorption performance can be changed by allocating more volume and contact area to the sound absorbing material of that frequency. Becomes

It is necessary to install a sound absorbing material, which is a fiber assembly, in at least one or more small chambers. Further, increasing the volume of the small chamber is effective in improving the sound absorbing performance.
At this time, the volume may be made larger than the thickness of the sound absorbing material.
With this configuration, the effect of the sound absorbing material and the effect of the volume are combined, so that the sound absorbing performance can be efficiently improved.

When a complete chamber cannot be formed, a sound absorbing effect can be obtained to some extent by installing a sound absorbing material whose frequency is set without dividing the inside of the expansion duct 2 by a partition.
No particular limitation is imposed.

The sound absorbing material installed inside the expansion duct preferably has an average diameter in the range of 0.1 to 60 μm. The performance of the sound absorbing material depends on the average fiber diameter of the fiber assembly constituting the sound absorbing material, and the smaller the fiber diameter, the higher the sound absorbing performance. However, fine fibers are not common, and the rigidity of the fibers themselves is low, so it is difficult to arrange them in the air flow in the duct. When the rigidity of the fiber is small, it is difficult to impart sublime, which is one of the performances of the sound absorbing material, and the binding force of the fiber itself is small, so that the fiber easily comes out of the sound absorbing material in the air flow. From the above, fibers of 0.1 μm or less cannot be used. On the other hand, if the fiber is thick, the sound absorbing performance is deteriorated. Therefore, if the fiber having a thickness of 60 μm or more is used, the sound absorbing performance cannot be satisfied.

The fibers constituting the sound absorbing material may be short fibers having a length of 5 cm or less, or long fibers having a length longer than that. Since the sound absorbing performance does not depend on the length of the constituent fibers, there is almost no need to specify the fiber length to secure the sound absorbing performance. However, when manufacturing the sound absorbing material or considering the rigidity of the sound absorbing material itself, the mechanical strength of the sound absorbing material is influenced by the fiber length, so it is meaningful to specify these. When the fiber is molded into the sound absorbing material, it is important that the fiber length is in the range of 3 to 10 cm, but it is not particularly limited. A fiber having a fiber length of 3 cm or less has a too short fiber length, and thus it is difficult to form a sound absorbing material. In addition, it is difficult to uniformly disperse fibers having a size of 10 cm or more to form a sound absorbing material with a general manufacturing apparatus. Therefore, there is a high possibility that a part of the fibrous body becomes a one-sided sound absorbing material in the sound absorbing material, and it is difficult to always maintain a constant performance.

The surface density of the sound absorbing material is 50 to 4000 g / m ²
Is preferably within the range. This is because the performance as the sound absorbing structure cannot be secured at 50 g / m ² or less. In the area of 4000 g / m ² or more, the weight and the cost associated therewith exceed the performance and are not effective, but the ventilation volume of the sound absorbing material itself decreases as the surface density increases. , The wall is made of sound absorbing material, and the damping effect is the same as that of duct only.

The fiber aggregate constituting the sound absorbing material may be in the form of woven fabric or non-woven fabric. This is because the sound absorbing performance does not depend on the form of the fiber aggregate. However, since the form of the fiber assembly is strongly dependent on ensuring the sublime and ensuring the mechanical strength of the sound absorbing material, it is necessary to determine the form of the sound absorbing material in consideration of the environment around which the sound absorbing material is installed. is there. At this time, a non-woven fabric form is desirable when sublime is emphasized, and a woven fabric form is desirable when mechanical strength is emphasized, but is not particularly limited.

The fibers constituting the fiber assembly may be natural fibers or synthetic fibers. Here, the thickness of the fiber, the unit length of the fiber, the distribution of the fibrous body, etc. can all be specified, and the same fiber can always be produced, and a synthetic fiber capable of producing a uniform density distribution is particularly effective as a sound absorbing material. . Further, in view of the advantages such as the recycling of the sound absorbing material, simultaneous integral moldability, and the ability to maintain the shape, the polyester fiber capable of blending fibers having different softening points is particularly effective. At this time, the polyester fiber has an average diameter of 10 to 40 μm produced by the melt spinning method.
Are preferred. Melt-spun polyester fibers are the most common and economical. With this method, it is difficult to manufacture a fiber having a thickness of 10 μm or less, and a thickness of 40 μm is required to secure the sound absorbing performance depending on the surface area of the fiber.
The following is effective.

Polypropylene fibers can be used to produce ultrafine fibers, and the use of the fibers is effective for improving sound absorbing performance. At this time, it is effective that the average diameter of the fibers is in the range of 1 to 15 μm. 1μ in this fiber construction method
It is difficult to manufacture a film having a thickness of m or less, and it is required to have a thickness of 15 μm or less for economical manufacturing. In terms of sound absorption performance, polypropylene fibers manufactured by the melt blown method are effective because it is easy to manufacture ultrafine fibers, but on the contrary, it is difficult to manufacture thick fibers. The polyester fiber manufactured in 1. becomes effective.

Since the rigidity of the sound absorbing material itself cannot be obtained from the ultrafine fibers, it is possible to mix two fibers of polypropylene fiber and polyester fiber as a sound absorbing material having both sound absorbing performance and rigidity. Very effective.

As the fibers other than the above, synthetic fibers such as nylon, polyacrylonitrile, polyacetate, polyethylene, linear polyester and polyamide can be used, but the fibers are not particularly limited.

When molding the sound absorbing material, it is effective that fibers having different softening points at 20 ° C. are mixed in the fibrous body. The reason for blending fibers having different softening points of at least 20 ° C. is to enable heating and press molding to produce a product while maintaining the shape of the fiber assembly. When the difference in the softening point becomes smaller than this, depending on the difference in the softening point, in the temperature range in which only some of the fibers are softened, the softening fiber is used as a binder,
It becomes impossible to give a shape to the fiber assembly. That is, it is considered that the whole fibrous body is softened and melted, which is not suitable.

It is also effective to form a fibrous body into a fibrous aggregate by using a method such as needle punching. This makes it possible to fabricate a nonwoven fabric with only one kind of fibers having the same softening point, and it is possible to form a sound absorbing material without using relatively expensive fibers having different softening points.

The number of layers constituting the laminate is at least 2
More layers are needed. This is because the existence of the layers having different densities has succeeded in imparting sound absorbing performance to a low frequency region which could not be realized conventionally. Further, in the laminated body, the lower the high frequency region is, the easier it is to set the higher-density layer on the side of the base duct on which sound enters. In a realistic range of number of layers,
A four-layer structure is suitable, but a multilayer body of any other combination can achieve the object of the invention but is not particularly limited.
Actually, a laminate having four or more layers has a performance of 4 as a sound absorbing material.
Since it is not much different from a layered product, it is not an efficient sound absorbing material considering the cost of stacking.

In order to obtain a sound absorbing material having a high sound absorbing performance in a low frequency region of 500 Hz or less, the density of the high density layer of the laminate should be in the range of 0.1 to 1.0 g / cm ³ . The other layers are 0.1 g / cm ³ or less, and the sound absorbing performance can be tuned by this density difference.

When it is necessary to set the sound absorbing performance at a low frequency, or when it is necessary to enhance the sound absorbing performance, a back air layer is formed on the back surface of the sound absorbing material in the small chamber to obtain a high effect. I don't.

Further, the use of the sound absorbing material in the air layer behind the low frequency sound absorbing material is effective in improving the sound absorption coefficient. Among these, a structure in which a sound absorbing material is attached to the back side of the laminate and a back air layer is secured behind the sound absorbing material is particularly effective for improving sound absorbing performance.

Tuning of the sound absorption frequency will be described here. This laminated structure forms a mass-spring system having one degree of freedom or multiple degrees of freedom in which a high density layer is a mass part and a low density layer which is another layer is a spring part. For example, a laminated body formed of two layers, a high-density layer and a low-density layer, forms a one-degree-of-freedom mass-spring system in which the high-density layer is regarded as one part by weight to attenuate sound energy. . The four-layer structure (FIG. 4) has a mass-spring system with two degrees of freedom in which two high-density layers are parts by weight, and a multilayer body having more than two layers has a mass-spring system with a degree of freedom in the number of high-density layers. , Attenuate the energy of sound.

The natural angular frequencies (resonance vibration frequencies) ω ₁ and ω ₂ of the two-degree-of-freedom mass-spring system are determined from the following equation (2) according to the spring constant of the low density layer and the mass of the high density layer. It Therefore, basically, the low frequency one of the natural angular frequencies of the vibration system composed of this laminated structure is 500 Hz.
It is necessary to set each parameter as follows.

The natural angular frequency (resonance vibration frequency) ω of the mass-spring system having one degree of freedom is determined by the following equation (3) according to the spring constant of the low density layer and the mass of the high density layer. Therefore,
Basically, it is necessary to set each parameter so that the low frequency one of the natural angular frequencies of the vibration system constituted by this laminated structure is 500 Hz or less. The model is shown in FIG.

[0050]

[Equation 1]

A = (k1 + k2) / m1, b = k2 / m
1, c = k2 / m2 ω _1,2 : natural angular frequency m1: mass of high-density layer 1 m2: mass of high-density layer k1: spring constant of low-density layer k2: spring constant of low-density layer 2

[0052]

[Equation 2]

M1: mass of the high-density layer 1 k1: spring constant of the low-density layer 1 However, in the above equations (2) and (3), the laminated sound absorbing material is not a complete two-degree-of-freedom mass-spring damping system. I can't explain it completely. Another object of the present invention is to obtain a sound absorbing material that is particularly effective in the low frequency range. However, in a complete two-degree-of-freedom mass-spring damping system, sound absorbing performance is obtained only at two natural angular frequencies. Often, it is not really suitable for use. Therefore, the structure of the present embodiment is essential in order to absorb sound in a wide frequency range without deteriorating the peculiar sound absorbing performance. Therefore, the above equation cannot accurately represent the performance of the present embodiment, but the performance can be tuned by referring to this equation.

From the above, in order to tune the sound absorption performance in the low frequency range, the following specifications are made with reference to the above equation.

In order to set the natural angular frequency to a low frequency (about 200 Hz), the mass (area density) of the high density layer may be increased. However, it is not possible to increase the thickness in view of the space, and conversely, if it is made too thin, ventilation is lost, so it is advisable to mold the surface density to 0.4 to ² kg / m ² and the thickness to 1 to 6 mm. Area density 1.2 kg / m ² , thickness 3 mm
Is more suitable but not limited.

In order to set a frequency having a low natural angular frequency to a lower frequency, it is effective to reduce the spring constant of the low density layer on the surface where sound does not enter. Therefore, in view of the space, if the low-density layer has the same surface density, it is preferable to form the thickness 2-3 times. A surface density of 0.4 kg / m ² and a thickness of 10 m in a low-density layer sandwiched between high-density layers
m, other low-density layer has an areal density of 1.2 kg / m ² , thickness of 30
It is suitable to use mm material, but not limited to.

In order to prevent the installed sound absorbing material from flowing due to the gas flow in the duct, it is effective to attach a cylindrical inner tube having an opening ratio of 30 to 90% having a cross section equivalent to that of the base duct to the expansion duct portion. Is. The inner pipe is located inside the expansion duct and is connected to two base ducts.
The sound absorbing material is filled in the space between the base duct and the expansion duct. Since the aperture ratio of the inner tube depends on the sound absorbing performance, it is desirable that the aperture ratio be as high as possible. However, if the aperture ratio is too high, it becomes difficult to install the sound absorbing material. Therefore, if the opening ratio is less than 30%, the amount of sound attenuation is small, which is unsuitable. The shape of the hole of the opening is not particularly limited. Therefore, a round shape, a square shape, etc. are sufficient and satisfy the performance.

Considering the performance of the sound-absorbing duct and the installation conditions of the sound-absorbing material, the optimum opening ratio of the inner tube is in the range of 50 to 80%, but it is not particularly limited. Further, instead of a tubular structure, a structure like a restraining rod may be installed, but the structure is not particularly limited.

In order to prevent the fibers from falling out of the sound absorbing material installed in the expansion duct, the inner surface of the inner surface of the fiber assembly or the fiber assembly is covered with an average fiber length of 1 to 100 cm and an average diameter of 1 to 30 μm. It is effective to install a non-woven skin made of synthetic fiber having an areal density of 20 to 200 g / m ² .
The constituent fibers may be short fibers of 10 cm or less or long fibers. These fibers are formed into a cloth-like non-woven fabric or a woven fabric. In the case of a non-woven fabric, the needle punching method or the manufacturing method in which a part of the cloth is heat-sealed to increase the rigidity of the cloth and the ventilation. It is effective and secure. Further, it is particularly effective to use only 10 cm or more long fibers as the constituent fibers because the rigidity of the cloth can be further improved, but the present invention is not limited thereto.

It is particularly effective to install at least one sound absorbing duct structure of the present embodiment in the intake side duct partitioned by the air cleaner of the intake duct of the internal combustion engine for vehicles, or in the engine side duct. . This sound-absorbing duct structure can be installed anywhere in the duct without narrowing the flow path and increasing ventilation resistance, and can efficiently absorb the intake sound generated by the intake air of the engine. Furthermore, high sound absorption characteristics can be obtained not only in the low frequency region but also in the medium and high frequency regions, and the noise can be reduced very effectively.

Further, it is possible to remove a part or all of the resonator and the side branch installed in the intake system for this purpose. This is very effective because it secures space in the engine and is cost effective to remove the accessory parts.

As a result of installing the sound absorbing duct structure of the present embodiment on the blower duct of the house or in the air duct for the intake system for the vehicle, it has a high sound deadening characteristic not only in the low frequency region but also in the medium and high frequency regions. It was confirmed that an excellent sound absorbing duct structure was obtained.

Examples of the present invention, conventional examples, comparative examples, and
This will be described with reference examples and test examples.

[Embodiment 1] FIG. 3 shows the structure of the sound absorbing duct of Embodiment 1. Expansion duct part is 20 cm in length and the expansion ratio is twice that of the base duct with a circular cross section (diameter 5 cm)
The cross-sectional center of the base duct and the cross-sectional center of the expansion duct section are aligned, and a partition plate is provided in the expanded duct section in the longitudinal direction so that the two chambers have the same volume. The sound absorbing materials 5 and 6 set to 200 Hz and 300 Hz are arranged in the two rooms, and the sound absorbing materials 5 and 6 set to 200 Hz and 300 Hz are installed so as to be scissored in the expansion portion by the tubular inner tube having the same cross section as the base duct and the opening ratio of 80%. Then, a cylindrical sound absorbing duct structure 1 (sound absorbing duct shape A) having a double expansion ratio from the base duct was produced.

The sound material set inside the sound absorbing duct and set to 200 Hz is made of polypropylene (hereinafter abbreviated as PP) having an average fiber diameter of 3 to 5 μm and has an overall surface density of 800.
It is a sound absorbing material of g / m ² and has a density of 0.5 on the side where sound enters.
It has a high density layer of g / cm ³ , 2 mm and a density of 0.
It is a laminated sound absorbing material having a two-layer structure and having a weight of 05 g / cm ³ and about 20 mm.

The sound material set at 300 Hz is 20 g of a sound absorbing material having an overall surface density of 800 g / m ² which is made of polypropylene (hereinafter abbreviated as PP) having an average fiber diameter of 3 to 5 μm. 0.4g / c for those who
Has a high-density layer of m ³ and 2.5 mm, and has a density of 0.0 on the back surface.
It is a laminated sound absorbing material having a two-layer structure having 5 g / cm ³ and about 20 mm.

[Second Embodiment] FIG. 4 shows the structure of a sound absorbing duct according to a second embodiment. A partition plate in the lengthwise direction of the expanded portion is provided so that the volume becomes 1: 2, a sound absorbing material 7 set to 200 Hz is installed in a large volume room, and a sound absorbing material set to 300 Hz is set in a small volume room. Sound absorbing duct structure 2 was produced in exactly the same manner as sound absorbing duct structure 1 except that 8 was installed (sound absorbing duct shape B).

[Third Embodiment] FIG. 5 shows the structure of a sound absorbing duct according to a third embodiment. A sound absorbing material set to 300 Hz is made of polyester having an average fiber diameter of 10 to 20 μm (hereinafter PE
Abbreviated as T. ) Composed of a total areal density of 1000 g / m
The sound absorbing material 9 of No. ^{2 and} the sound absorbing material 10 set to 400 Hz are also made of PET having an average fiber diameter of 10 to 20 μm and having an overall surface density of 1000 g / m ² (Structure C). Sound absorbing duct structure 3 was produced in exactly the same manner as.

[Embodiment 4] FIG. 6 shows the structure of a sound absorbing duct of Embodiment 4. Sound absorbing material 1 with a partition plate installed in the cross-sectional direction of the expanded part and set to 300 Hz and 400 Hz
Sound absorbing duct structure 4 was produced in exactly the same manner as sound absorbing duct structure 1 except that (1) and (12) (sound absorbing duct shape D) were used.

[Fifth Embodiment] FIG. 7 shows the structure of a sound absorbing duct according to a fifth embodiment. A partition plate in the cross-sectional direction was installed in the expanded portion, and a sound absorbing material 13 set to 200 Hz and a sound absorbing material 14 set to 300 Hz were arranged therein (sound absorbing duct shape E). A sound absorbing duct structure 5 was produced in the same manner as the sound absorbing duct structure 2 except for the above.

[Sixth Embodiment] FIG. 8 shows the structure of a sound absorbing duct according to a sixth embodiment. A partition plate in the lengthwise direction is provided in the expanded portion, three chambers are provided so that the volume of the expanded portion becomes one-third, and sound absorbing materials 15, 16, and 17 set to 200 Hz, 300 Hz, and 400 Hz are used (sound absorbing material). An adsorption duct structure 6 was produced in exactly the same manner as the sound absorption duct structure 1 except for the duct shape F). Further, the sound material set to 400 Hz is a polypropylene having an average fiber diameter of 3 to 5 μm (hereinafter P
Abbreviated as P. The total areal density of 800 g / m ²
The sound absorbing material is 20 g, and the density of 0.2
It has a high density layer of g / cm ³ , 5 mm and a density of 0.
It is a laminated sound absorbing material having a two-layer structure and having a weight of 05 g / cm ³ and about 20 mm.

[Seventh Embodiment] FIG. 9 shows the structure of a sound absorbing duct according to a seventh embodiment. The partition plate was installed in the cross-sectional direction, and the sound absorbing materials 18, 19, 20 of 200 Hz, 300 Hz, and 400 Hz were arranged therein. A sound absorbing duct structure 7 (sound absorbing duct shape G) was manufactured in the same manner as the sound absorbing duct structure 6 except for the above.

[Embodiment 8] FIG. 10 shows the structure of a sound absorbing duct of Embodiment 8. A partition plate in the lengthwise direction is provided in the expanded part, and four chambers are provided so that the expanded part volume becomes 1/4, and 200 Hz, 250 Hz, 300 Hz and 4
A sound absorbing duct structure 8 was manufactured in exactly the same manner as the sound absorbing duct structure 1 except that the sound absorbing materials 21, 22, 23 and 24 set to 00 Hz were used (sound absorbing duct shape H). Also,
The sound material set to 250 Hz is 20 g of a sound absorbing material having an overall surface density of 800 g / m ² which is made of polypropylene (hereinafter, abbreviated as PP) having an average fiber diameter of 3 to 5 μm, and has a density of 0 when the sound enters. A laminated sound absorbing material having a two-layer structure having a high density layer of 0.45 g / cm ³ and 2 mm and a density of 0.05 / cm ³ and about 20 mm on the back surface.

[Ninth Embodiment] FIG. 11 shows the structure of a sound absorbing duct according to a ninth embodiment. The partition plate is installed in the cross-sectional direction, and 200Hz, 250Hz, 300Hz and 400H
A sound absorbing duct structure 9 (sound absorbing duct shape I) was manufactured in exactly the same manner as the sound absorbing duct structure 8 except that the sound absorbing materials 25, 26, 27 and 28 set to z were arranged.

[Comparative Example 1] A sound absorbing duct structure was produced in exactly the same manner as the sound absorbing duct structure 1, except that the expansion duct had an expansion ratio of 1.05 times that of the base duct having a circular cross section.

[Comparative Example 2] A sound absorbing duct structure was manufactured in exactly the same manner as the sound absorbing duct structure 1, except that the expansion duct had an expansion ratio of 1.05 times that of the base duct having a circular cross section. Since it was not a realistic size, it interferes with other parts in the engine room when actually installing it in the vehicle,
Could not be installed.

[Comparative Example 3] A sound absorbing duct structure was manufactured in exactly the same manner as the sound absorbing duct structure 1 except that the length of the expanded duct was 2 cm.

[Comparative Example 4] The extension duct length is 120c.
The sound absorbing duct structure was manufactured in exactly the same manner as the sound absorbing duct structure 1 except that m was used, but it did not have a realistic size, so it interfered with other parts in the engine room when actually installed in the vehicle. , Could not be installed.

Comparative Example 5 The average diameter of the fibers constituting the sound absorbing material was set to 0.05 μm, but the fibers had no rigidity and the sound absorbing material was blown off during the experiment and could not be installed until the end.

[Comparative Example 6] Although PET having an average diameter of fibers constituting the sound absorbing material was 65 μm, the frequency of the sound absorbing material could not be set to 500 Hz or less.

Comparative Example 7 The surface density of the sound absorbing material was 25 g / m.
² and was, but could not frequency setting of the sound absorbing material to 500Hz or less.

[Comparative Example 8] The surface density of the sound absorbing material was 4200 g.
A sound absorbing duct structure was produced in exactly the same manner as the sound absorbing duct structure 1 except that the sound absorbing duct structure was set to / m ² .

[Comparative Example 9] A sound absorbing duct structure was prepared in exactly the same manner as the sound absorbing duct structure 1 except that a cylindrical duct having a cross-section equivalent to that of the base duct and having an opening rate of 20% was installed on the side surface of the inner tube of the sound absorbing material. Was produced.

[Comparative Example 10] A sound absorbing duct structure was prepared in exactly the same manner as the sound absorbing duct structure 1 except that a cylindrical duct having a cross-section equivalent to that of the base duct and having an opening ratio of 95% was installed on the side surface of the inner pipe of the sound absorbing material. However, the sound absorbing material was blown off during the measurement, and the sound absorbing duct structure could not be maintained.

[Comparative Example 11] A skin made of a nonwoven fabric made of PET fiber having an average fiber length of 20 cm and an average fiber diameter of about 20 μm and having an areal density of 10 g / m ^{2 was provided on} the side surface of the inner tube of the sound absorbing material. The skin and the sound absorbing material were blown off, and the sound absorbing duct structure could not be maintained.

[Comparative Example 12] A sound absorbing duct structure except that a skin made of a nonwoven fabric having a surface density of 210 g / m ² made of PET fibers having an average fiber length of 20 cm and an average fiber diameter of about 20 μm was provided on the side surface of the inner tube of the sound absorbing material. A sound absorbing duct structure was produced in exactly the same manner as in 1.

Reference Example 1 The sound absorbing duct structure of Example 1 was connected to the outside air duct of the air cleaner chamber of the vehicle, the engine was started, and the sound pressure level for each frequency was measured.
It was confirmed that the sound absorption effect was almost the same as the result of acoustic excitation.

Reference Example 2 The sound absorbing duct structures of Example 1, Example 9 and Example 24 were connected to the engine side duct of the air cleaner chamber of the vehicle, the engine was started, and the sound pressure level for each frequency was measured. However, it was confirmed that the sound absorbing material did not come off and the sound absorbing effect was almost the same as the result of the acoustic vibration.

[Reference Example 3] When the sound absorbing structure of Example 1 was used in an air duct with a blower in a house, it was confirmed that there was a sound deadening effect almost equivalent to the result of acoustic vibration without obstructing ventilation. It was

[Prior Art Example 1] A resonator set at 200 Hz was installed in the intake duct.

(Test Example) The following experiments were carried out on the sound absorbing duct structures obtained in the above-mentioned examples, conventional examples and comparative examples.

Test Example 1 The base duct 32 of the air cleaner 30 of the intake system system of a 4-cylinder engine in which the sound absorbing duct structure 31 obtained by the method of each of the above-mentioned examples and the comparative example is installed in a semi-anechoic chamber. And attached as shown in FIG. About this system
The insertion loss (IL) measurement, which is the difference between the sound pressure on the intake manifold 30 side connected to the engine and the sound pressure on the intake side, was measured. At this time, IL was measured by a reverse arrangement method in which a vibration source was used as a speaker and vibration was applied from the suction side. The sound pressure level difference at that time was measured for each frequency in dB, and a low frequency of 500 Hz or less, a medium frequency of 500 to 1 kHz, and 1 kHz were measured.
Table 1 shows the averages in the above high frequency region.

The results of these tests are shown in Table 1.

[0094]

[Table 1]

From Table 1, the various sound-absorbing structures produced in the examples are lower in frequency (500 Hz or less), medium frequency (500 to 1 kHz), and higher frequency (1 kHz) than the conventional examples.
It has been confirmed that the sound absorbing duct structure exhibits excellent sound absorbing characteristics in the above range (3), has a small space, and has excellent mountability as compared with a conventional resonator or the like.

Further, the comparative example prepared with the specifications out of the specified range of the present invention cannot be the sound absorption performance in the low / middle frequency region which is particularly required (as a judgment criterion, there is no noise reduction performance of 10 dB in this region. In addition, it was confirmed that they could not be satisfied in terms of space (things that could not fit in the actual engine room of the vehicle were not acceptable).

[0097]

As described in detail above, the sound absorbing duct structure of the present invention is effective in reducing the noise mainly due to the airflow flowing in the duct in the entire frequency range. This is very effective as a structure that improves the sound absorbing performance in the low frequency region in a limited space. It is suitable as a sound absorbing structure not only for construction but also for automobiles where space is not enough.

[Brief description of drawings]

FIG. 1 is a partially transparent perspective view showing an embodiment of a sound absorbing duct structure according to the present invention.

FIG. 2 is a schematic view of a laminated sound absorbing material according to the present invention.

FIG. 3 is a structural schematic diagram of a sound absorbing duct shape A according to the present invention.

FIG. 4 is a structural schematic view of a sound absorbing duct shape B according to the present invention.

FIG. 5 is a structural schematic diagram of a sound absorbing duct shape C according to the present invention.

FIG. 6 is a structural schematic diagram of a sound absorbing duct shape D according to the present invention.

FIG. 7 is a structural schematic view of a sound absorbing duct shape E according to the present invention.

FIG. 8 is a structural schematic view of a sound absorbing duct shape F according to the present invention.

FIG. 9 is a structural schematic view of a sound absorbing duct shape G according to the present invention.

FIG. 10 is a structural schematic view of a sound absorbing duct shape H according to the present invention.

FIG. 11 is a structural schematic view of a sound absorbing duct shape I according to the present invention.

FIG. 12 is a view in which the sound absorbing duct structure according to the present invention is installed in an intake system.

[Explanation of symbols]

1,32 base duct 2 expansion duct 3 sound absorbing material 1 4 sound absorbing material 2 5,7,13,15,18,21,25 200Hz
Sound absorbing material set 6,8,9,11,14,16,19,22,26
Sound absorbing material set at 300 Hz 10, 12, 17, 20, 23, 27 Sound absorbing material set at 400 Hz 24, 28 Sound absorbing material set at 250 Hz 29 Intake manifold 30 Air cleaner 31 Sound absorbing duct structure

Claims (7)

[Claims] 1. A cross-sectional center of the base duct is used as a reference, and an inner diameter of the duct is expanded. The expanded duct has a cross-sectional center that matches the cross-sectional center of the base duct. Or, in a sound-absorbing duct structure provided with a sound-absorbing duct that does not match and has any shape in the lengthwise direction of the expanded part, by providing a partition in the lengthwise direction inside the expanded part or in the cross-sectional direction. An expansion duct part having at least one or more chambers in the expansion duct part, wherein the expansion duct part is provided with a sound absorbing material in at least one or more chambers, and the outer diameter of the sound absorbing duct structure in the expansion duct part Is 1.1 to 5 times as large as the inner diameter of the base duct, and the total length of the sound absorbing duct structure is 5 to 100 cm. 2. The sound absorbing material installed inside the chamber is a woven or non-woven fabric mainly composed of short fibers having an average diameter of 0.1 to 60 μm or long fibers and having an areal density of 50 to 4000 g / m ^2. The sound-absorbing duct structure according to claim 1, wherein the sound-absorbing materials formed in each chamber are the same or different. 3. The fibers constituting the sound absorbing material have an average diameter of 1
0-40 μm polyester fiber or 0.1-average diameter
The sound absorbing duct structure according to claim 1, wherein the sound absorbing duct structure is a polypropylene fiber having a thickness of 10 μm or a mixture thereof. 4. The sound absorbing material is at least two layers, and at least one of the layers constituting the laminate is a high density layer having a density of 0.1 to 1 g / cm ³ , and the high density layer. In a multi-degree-of-freedom vibration system with one or more degrees of freedom in which the layers are mass parts and the other layers are spring parts, the primary resonance vibration frequency is 5
The sound absorbing duct structure according to claim 1, wherein the sound absorbing duct structure can be variably set to 00 Hz or less. 5. The expansion duct portion has a cylindrical inner tube having a cross section equivalent to that of the base duct and having an opening ratio of 30% or more and less than 90%. 4. The sound absorbing duct structure according to 4. 6. The outer surface of the sound-absorbing material, which has a fiber length of 1 to 100 cm and an average diameter of 1 to 30 μm and is made of a nonwoven fabric having a surface density of 20 to 200 g / m ² , is provided on the side surface or the entire surface of the sound absorbing material. The sound absorbing duct structure according to any one of claims 1 to 5. 7. The sound absorbing duct according to claim 1, wherein at least one is installed in an intake side duct or an engine side duct partitioned by an air cleaner of an intake duct of an internal combustion engine of a vehicle. Structure.