JP2011085761A - Noise reduction structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a noise reduction structure provided with a sound absorption structure and a sound insulation structure that utilize a porous plate which provides a stable effect in a broader frequency range. <P>SOLUTION: The noise reduction structure 1 is configured with a plurality of vertical belt-like plates 10 arranged in a parallel, and a plurality of horizontal belt-like plates 20 arranged in parallel, in a direction perpendicular to the vertical belt-like plates 10. At intersections of the vertical belt-like plates 10 and the horizontal belt-like plates 20, grating holes 30 are formed. By viscosity of air at the grating holes 30, vibration energy of the air is converted to thermal energy, thereby reducing noise. When the belt-like plates vibrate, two belt-like plates intersecting with each other are rubbed, and the vibration energy is converted to the thermal energy, thereby reducing the vibration energy and suppressing noise caused by the belt-like plates. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a noise reduction structure that effectively absorbs noise.

In recent years, a perforated plate soundproofing that absorbs noise incident on the interior plate by adopting a configuration in which an interior plate having a large number of through holes formed on the entire plate surface is disposed opposite the exterior plate via an air layer. The structure is drawing attention.
For example, Japanese Patent Application Laid-Open No. 2003-50586 (Patent Document 1) discloses a porous soundproof structure formed by opposingly arranging an exterior plate and an interior plate having a large number of through holes. The hole diameter and the hole area ratio are set so as to satisfy a design condition for generating a viscous action in the air flowing through the through hole. According to this porous soundproof structure, the porous soundproof structure is formed by the inner plate having a thickness, a hole diameter, and a hole area ratio that satisfy the design conditions for generating a viscous action on the air. As a result of promoting the conversion of vibration into thermal energy, sufficient sound absorption performance is reliably exhibited over a wide frequency bandwidth.

  Furthermore, Japanese Patent Application Laid-Open No. 2008-46618 (Patent Document 2) discloses a solid sound reduction structure that is installed on the surface of a structure that vibrates and emits noise, and that reduces noise emitted from the surface of the structure to the surroundings. Disclosure. The solid sound reducing structure is provided on the surface of the structure, the surface plate having a gas flow portion that is disposed so as to cover at least a part of the surface of the structure and that can pass in the thickness direction. A wall surface portion that supports the outer peripheral edge of the surface plate portion so that it vibrates integrally with the surface of the structure body, and forms an internal gas chamber between the surface of the structure body and the surface plate portion. And an outer peripheral wall surface portion.

  According to this solid sound reduction structure, the entire surface plate portion vibrates substantially uniformly together with the structure surface. At this time, the acoustic radiation efficiency (vibration-to-sound conversion efficiency) of the surface plate portion is reduced by providing the gas flow portion in the surface plate portion. Thereby, the sound radiated from the vibrating structure can be reduced. In addition, since the inner gas chamber and the outer space are partitioned in the in-plane direction by the outer peripheral wall portion, the sound radiated from the structure surface to the inner gas chamber proceeds in the in-plane direction and enters the outer space. Propagation can be blocked by the outer peripheral wall surface portion, and sound leakage to the external space can be suppressed.

Japanese Patent Laid-Open No. 2003-50586 JP 2008-46618 A

  By the way, in the sound absorbing structure and the solid sound reducing structure using the porous plate as described above, the plate vibration of the porous plate itself may be increased. In particular, when the perforated plate resonates, the sound absorbing performance of the perforated plate may be deteriorated, or noise emission from the perforated plate may be increased, which may increase noise before the countermeasure. The causes of large plate vibrations of the perforated plate include vibration due to the sound pressure of incident sound, vibration due to the sound pressure generated in the back air layer, and vibration due to the structure via the support member.

As a countermeasure against such resonance, Patent Document 2 discloses that a porous plate structure is designed in consideration of resonance, and that a damping material is provided on the porous plate in order to suppress the resonance of the porous plate. Yes.
However, when it is desired to obtain a remarkable effect in a high frequency range (high sound), there is a possibility that it is difficult in terms of weight, cost, etc., such as a support pitch of the porous plate being narrowed or a porous plate being thick. Furthermore, it may be difficult to provide a damping material while maintaining the holes of the perforated plate. By providing the damping material, the light weight and high resistance to sound that are the advantages of the sound absorbing structure / solid sound reducing structure by the perforated plate are possible. There is also the possibility of losing the environmental characteristics.

  Then, an object of this invention is to provide the noise reduction structure provided with the sound absorption structure and solid sound reduction structure which can acquire an effect stably in view of the said problem.

In order to achieve the above-described object, the present invention takes the following technical means.
That is, the noise reduction structure according to the present invention is formed by a plurality of strip plates that intersect in a plane weave in the vertical and horizontal directions, two adjacent vertical strip plates, and two adjacent lateral strip plates. A front plate including a lattice hole to be reduced, and a back plate disposed on the back surface of the front plate and disposed between the front plate via an air layer.

  According to this noise reduction structure, the vibration energy of air propagating noise is converted into thermal energy by the viscous damping action of air in the lattice hole, that is, the air circulation part, and noise can be reduced. In addition, when the belt-like plate itself vibrates, the belt-like plates crossing the plane weave in the vertical and horizontal directions are rubbed together, the vibration energy is converted into heat energy, the vibration energy is reduced, and the resonance vibration is suppressed. That is, it is possible to provide a noise reduction structure including a sound absorption structure / solid sound reduction sound insulation structure that can stably obtain an effect in a wider frequency range without resonating.

Preferably, among the plurality of strip-shaped plates, at least some of the strip-shaped plates may be set so that the natural frequency is higher than the frequency of noise emitted from the noise source.
By doing so, it is possible to realize a noise reduction structure including a sound absorption structure and a solid sound reduction structure that can avoid resonance of the front plate (perforated plate) and can stably obtain an effect in a wider frequency range.

More preferably, the thickness of the longitudinal strip and the lateral strip is different, and the thickness of the strip-shaped plate with the smaller thickness is set to be equal to the side length of the lattice hole. .
According to this, noise reduction with a small lattice hole that can obtain a larger viscous damping effect while maintaining high rigidity, that is, high natural frequency by the thicker strip plate to avoid resonance of the perforated plate (front plate) A structure can be realized.

Further, it is preferable that the overlapping surfaces of the intersecting vertical strip and lateral strip are in full contact with each other.
According to this noise reduction structure, when the strips themselves vibrate, the strips rub against each other over a larger area, and a greater vibration suppressing effect can be obtained. In manufacturing the noise reduction structure, it is preferable that the belt-like plate is made into a plain weave and then pressed from both the upper and lower directions of the belt-like plate or a tensile force is applied to the belt-like plate from both ends of the belt-like plate.

  It is very preferable that the front plate is disposed so as to face the noise source.

  According to the noise reduction structure according to the present invention, noise can be reliably and effectively reduced.

1 is an overall plan view of a noise reduction structure according to an embodiment of the present invention. It is the elements on larger scale of FIG. It is a figure which shows a normal incidence sound absorption coefficient. It is a figure which shows the change of normal incidence sound absorption coefficient with the change of the side length of a grating | lattice hole. It is a figure which shows the relationship between the side length of a lattice hole, and the frequency of the noise absorbed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.
FIG. 1 is a plan view of a noise reduction structure according to an embodiment of the present invention, and FIG. 2 is a partially enlarged view of FIG.

The noise reduction structure according to the present embodiment may be any medium that transmits noise, but in the following, the medium is air. In the following, both the sound absorption structure and the solid sound reduction structure (the structure that reduces the noise emitted from the noise source, especially the noise source that causes contact / collision between the solids) And described as a noise reduction structure.
As shown in FIG. 1, the noise reduction structure 1 includes a plurality of longitudinal strips 10 arranged in parallel and a plurality of transverse sides arranged in parallel in a direction perpendicular to the longitudinal strips 10. The front plate comprised from the strip | belt-shaped board 20 is provided. The vertical belt-like plate 10 and the horizontal belt-like plate 20 are each a strip-like plate body and a thin belt-like plate. In the following description, the longitudinal strip 10 may be simply referred to as the strip 10 and the lateral strip 20 may be simply referred to as the strip 20.

The vertical strip 10 and the lateral strip 20 are formed so as to cross each other alternately in a plain weave pattern (in a checkered pattern). When formed like a woven fabric, it becomes a plain weave.
What is characteristic is that a lattice hole 30 is formed at the intersection of the longitudinal strip 10 and the lateral strip 20. The lattice holes 30 are formed by two adjacent vertical strips 10 and two adjacent horizontal strips 20. The lattice hole 30 is a gas circulation part (air circulation part) through which a sound transmission medium such as air circulates as will be described later.

  The material of the belt-like plate 10 and the belt-like plate 20 may be a metal such as steel or aluminum, or plastic or paper, and may be a combination of the same materials or a combination of different materials. Further, the plate thickness or the plate width of the strip plate 10 and the strip plate 20 may be the same or different. Furthermore, the crossing angle between the belt-like plate 10 and the belt-like plate 20 may be other than 90 degrees, and can be changed depending on the shape of the installation location of the noise reduction structure 1 (the shape of the frame material, etc.).

FIG. 2 shows a partial detail view of FIG.
1 and 2, the distance between the vertical strip 10 and the vertical strip 10 and the lateral strip 20 and the lateral strip 20 are shown. The distance (distance between the plates) is described wider than the actual distance. In order to actually obtain a large sound absorption / solid sound reduction effect, it is desirable that the holes be fine, so the distance between the plates is actually shorter and the lattice holes 30 are smaller.

As shown in FIG. 2, the plate thicknesses t (1) and t (2) of the longitudinal and lateral strips 10 are preferably 0.05 mm to 1 mm. When the thickness of the belt-like plates is within this range, the belt-like plates that are overlapped with each other easily come into contact with each other, and attenuation of vibration energy due to friction between the belt-like plates tends to appear.
Furthermore, the open area ratio β is preferably 0.1% to 3%. When the opening ratio β is within this range, a viscous damping action is generated by the air flowing through the lattice holes 30. The aperture ratio β is the ratio of the aperture area of the holes to the total area of the plate provided with the holes.

In addition, the shape of the lattice hole 30 is not a circle but a square as in the prior art. The square is more advantageous than the circle because the surrounding length of the lattice hole 30 becomes longer even if the aperture ratio β is the same, and this is advantageous for the viscous damping action by air.
In summary, the noise reduction structure 1 has a front plate in which a plurality of strip-like plates 10 and 20 are woven into a plain weave. The front plate is provided with a plurality of lattice holes 30 formed by the belt-like plates 10 and 20 for reducing noise, and on the back of the front plate, there is a back plate arranged at a predetermined interval. That is, the back plate, which is one of the constituent members of the noise reduction structure 1, is arranged behind the front plate via the air layer. The noise reduction structure 1 is installed so that the front plate faces the noise source and absorbs noise.

Such a noise reduction structure 1 is installed on the surface of a noise source or in the vicinity thereof, for example, on the engine surface or engine room of an automobile.
When the noise reduction structure 1 is installed on the engine surface for the purpose of preventing noise radiated from the engine (unnecessary and uncomfortable sound waves), the noise reduction structure 1 is caused by the viscous damping action of air in the lattice holes 30. The acoustic radiation efficiency (conversion efficiency from vibration to sound) on the surface is reduced, and engine radiation noise can be reduced. At this time, if the noise reduction structure 1 vibrates (resonates in the worst case) due to the excitation force acting on the noise reduction structure 1 from the engine surface, the noise reduction effect is deteriorated, but the strip plate 10 or the strip plate 20. Even if it tries to vibrate, the two strips that are in contact with each other (intersecting) are rubbed together, and the vibration is suppressed by the frictional damping that converts the vibration energy into thermal energy, so noise can be reduced stably. The effect can be obtained.

  Further, the noise reduction structure 1 may be installed in the engine room (including the engine surface) for the purpose of absorbing and reducing noise generated in the engine room. The noise that propagates through the engine room and reaches the noise reduction structure 1 passes through the lattice holes 30, but the vibration energy of the noise is converted into heat energy by the viscous damping action of air in the lattice holes 30. , Expresses sound absorption effect.

By appropriately selecting the material of the belt-like plate, it is possible to realize a structure for reducing noise while having light weight and high environmental resistance. In particular, it is not necessary to use a damping material or the like, and the noise reduction structure 1 according to the present embodiment can be formed from a single material.
In addition, it was difficult to make a fine hole with the conventional perforated plate. That is, when punching a hole, in order to realize a hole size of 0.1 mm to 0.5 mm (details will be described later) as in this embodiment, a punching tool with a very small diameter is required. The strength is remarkably lowered and punching is impossible. However, in the noise reduction structure 1 according to the present embodiment, the minimum lattice holes 30 of 0.1 mm to 0.5 mm can be easily formed, and sound absorption performance or sound insulation performance can be ensured. it can.

In order to compare the sound absorption structure by the conventional perforated plate and the noise reduction structure 1 according to the present embodiment, each normal incident sound absorption coefficient was evaluated.
The specifications of the perforated plate of the conventional structure are steel, a round plate having a diameter of 88 mm, a thickness of 0.5 mm, a hole diameter of 1.5 mm, and a hole area ratio β of 0.4%. The thickness is 10 mm. This specification is designed to obtain the maximum effect at 800 Hz.

In the broken line of FIG. 3, the result (measurement result of the perforated plate having a conventional structure) of the normal incident sound absorption coefficient using an acoustic tube is shown. The deterioration of the sound absorption coefficient due to the excitation of the porous plate by the incident sound wave and excitation of the resonance of the porous plate is seen centering on 650 to 700 Hz.
On the other hand, regarding the specifications of the noise reduction structure 1 according to the present embodiment, the strips 10 and 20 have a thickness of 0.5 mm, and the side lengths D (1) and D (2) of the square lattice holes 30 are 1. .3 mm and the aperture ratio β is 0.4%. For example, the noise reduction structure 1 is manufactured by knitting a strip-like plate, which is a steel plate having a width of 19.7 mm and a plate thickness of 0.5 mm, at 90 degrees and knitting at intervals of 1.3 mm. The air layer behind is the same, and the design frequency is also 800 Hz.

  The solid line in FIG. 3 shows the result of the normal incidence sound absorption coefficient of the noise reduction structure 1 according to the present embodiment (result predicted by theoretical analysis). As is clear from this result, since the resonance of the plate can be suppressed by the effect of frictional damping in the belt-like plate, an effective sound absorbing performance as designed can be obtained.

In order to design a specification that increases the sound absorption performance of the noise reduction structure 1, the normal incident sound absorption coefficient when the side lengths D (1) and D (2) are changed in various ways was predicted by theoretical analysis.
In FIG. 4, the thicknesses t (1) and t (2) of the strips 10 and 20 are both 0.1 mm and the design frequency is 500 Hz (the strips 10 and 10 are designed so that the maximum sound absorption coefficient is obtained at 500 Hz). 20 shows the normal incidence sound absorption coefficient when 20 plate widths L (1) and L (2) and the thickness of the air layer behind are designed. As is apparent from this figure, the peak at 500 Hz becomes dull as the side length increases. That is, as the side length is smaller, a higher sound absorption rate can be stably obtained in a wider frequency band.

  FIG. 5 shows details of changes in the sound absorption characteristics accompanying changes in the side length. FIG. 5 is an arrangement of frequency band widths (in the range of 1000 Hz or less) having a sound absorption coefficient of 0.3, 0.5, 0.6, 0.7, 0.8, 0.9 or more. From this figure, it can be seen that the reduction of the bandwidth is remarkable from the side length of around 0.5 mm. That is, by setting the side length to 0.5 mm or less, a high sound absorption coefficient can be stably obtained in a wider frequency band.

  On the other hand, the number of lattice holes necessary to obtain the sound absorption performance of FIG. 4 increases as the side length decreases. For example, when the side length of the lattice hole is 0.1 mm, the pitch of the lattice hole (that is, the width of the strip plate) is 0.5 mm, and when the side length of the lattice hole is 0.2 mm, the pitch of the lattice hole (that is, the width of the strip plate). ) Is 1.8 mm. In consideration of manufacturing dimensional accuracy and cost, it is difficult to make the side length smaller than 0.1 mm. Therefore, in order to stably obtain a higher sound absorption coefficient in a wider frequency band, it is desirable that the side length of the lattice hole is 0.1 mm to 0.5 mm in combination with the above-described knowledge.

  Although the above exemplifies the study on one design frequency and plate thickness, the inventors have found that the same tendency is observed for other plate thicknesses and design frequencies.

As Example 3, the case where the thickness t (1) of the vertical strip is different from the thickness t (2) of the horizontal strip is illustrated.
For example, t (1) is 1 mm and t (2) is 0.2 mm. If the material of the longitudinal and lateral strips is the same, the natural frequency of the noise reduction structure 1 is determined by the thickness t (1) (thicker) of the longitudinal strip, and the material is steel. When the size of the noise reduction structure 1 is 80 mm square, it is 833 Hz based on the theory in the case of both-end fixed support. In addition, when the belt-like plate is made into a plain weave, the lateral belt-like plate (thin side) is provided with a bent portion of approximately 90 degrees, and the lattice holes 30 having a side length of 0.2 mm are provided by weaving while reversing the bending direction. be able to.

On the other hand, in order to obtain an equivalent natural frequency with a conventional perforated plate (single plate of 80 mm square), a plate thickness of 0.6 mm is required from the theoretical value in the case of peripheral fixed support. With this plate thickness, it is impossible in terms of processing technology and cost to stably provide a hole (0.2 mm) smaller than the plate thickness.
As is apparent from the above, by adopting the noise reduction structure 1 according to the present invention, it is possible to achieve both the avoidance of resonance of the noise reduction structure 1 and a small hole for obtaining a large noise reduction effect. it can.

  As described above, according to the noise reduction structure according to this embodiment, the vibration energy of air is converted into heat energy by the viscous action of air in the lattice holes, and noise can be reliably reduced. When the belt-like plate vibrates, the belt-like plates intersecting each other in the vertical and horizontal directions are rubbed with each other, vibration energy is converted into heat energy, vibration energy is reduced, and vibration is suppressed. In this way, it is possible to stably obtain a soundproofing effect in a wider frequency range (from low to high) without resonant vibration.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Noise reduction structure 10 Vertical strip | belt-shaped board 20 Horizontal strip | belt-shaped board 30 Lattice hole

Claims (5)

A front plate comprising a plurality of belt-like plates vertically and horizontally intersecting in a plain weave form, two adjacent vertical belt-like plates and two adjacent horizontal belt-like plates and a lattice hole for reducing noise;
A back plate located on the back of the front plate and disposed between the front plate with an air layer;
A noise reduction structure comprising:   The noise reduction structure according to claim 1, wherein a natural frequency of at least some of the plurality of strip-shaped plates is higher than a frequency of noise emitted from the noise source. The thickness of the vertical strip and the lateral strip is different,
3. The noise reduction structure according to claim 1, wherein the thickness of the strip-shaped plate having the smaller plate thickness is equal to the side length of the lattice hole.   The noise reduction structure according to any one of claims 1 to 3, wherein the overlapping surfaces of the intersecting vertical strip and lateral strip are in full contact with each other.   The noise reduction structure according to claim 1, wherein the front plate is disposed so as to face a noise source.

Images