JP4453319B2 - Sound absorbing structure - Google Patents

Description

  The present invention relates to a sound absorbing structure that is provided particularly in a vehicle and absorbs engine sound or the like to reduce noise.

Conventionally, a skin layer composed of a dense layer formed of a resin material or a fiber material and a skin layer laminated on the dense layer, and a base material layer formed of a sound absorbing material and laminated on the dense layer of the skin material layer, There is known an automobile interior carpet having a laminated structure made of (for example, see Patent Document 1). In this prior art, the sound insulation is enhanced by placing the base material layer side on the body panel in the trunk room and blocking the sound entering the room from the trunk room.
JP-A-11-99869

  However, in the laminated structure composed of a plurality of layers as described above, the skin material layer is formed of a dense layer, so that sound waves incident from the skin material layer side are easily reflected on the surface of the skin layer and the joint surface of each layer. There is a problem that it is difficult to promote the input of sound waves into the base material layer (sound absorbing layer) below the skin layer. As a result, there is a problem that it is difficult to achieve a high sound absorption rate for the sound in the trunk room (it is difficult to reduce the muffled sound in the trunk room) even if sound insulation against sound entering the room can be secured.

  Accordingly, an object of the present invention is to provide a sound absorbing structure having a high sound absorption coefficient.

In order to solve the above-described problem, according to one aspect of the present invention, a first sound absorbing portion that is in contact with an air layer;
A partition plate having a communication hole;
A second sound absorbing portion that is separated from the air layer by the partition plate and communicates with the air layer through the communication hole of the partition plate and the first sound absorbing portion;
The first sound absorbing part is formed of a material having an acoustic impedance substantially equal to or slightly larger than the acoustic impedance of air, and the second sound absorbing part is made of a material having an acoustic impedance larger than that of the first sound absorbing part. It is characterized by being formed ,
There is provided a sound absorbing structure in which the first sound absorbing portion has an exponential, triangular or semi-oval cross-sectional shape .

In this aspect, the sound wave propagating through the air layer is input into the sound absorbing structure from the first sound absorbing unit in contact with the air layer. At this time, since the first sound absorbing portion is formed of a material having an acoustic impedance substantially the same as or slightly larger than the acoustic impedance of air, most of the sound wave is between the air layer and the first sound absorbing portion. It propagates into the first sound absorbing part without being reflected at the boundary surface. Next, the sound wave propagating in the first sound absorbing portion is taken into the second sound absorbing portion through the communication hole of the partition plate. Since the second sound absorbing part communicates with the air layer only through the communication hole of the partition plate and the first sound absorbing part, the sound wave once taken into the second sound absorbing part is outside the second sound absorbing part. It is difficult to propagate easily. Therefore, according to this aspect, the sound taken into the second sound absorbing portion can be effectively attenuated by a material having an acoustic impedance larger than that of the first sound absorbing portion without being released to the outside. In this aspect, the first sound absorbing portion has an exponential shape, a triangular shape, or a half-oval shape. In this case, smooth propagation of the sound wave in the first sound absorbing part is realized, and it becomes possible to easily take in the sound wave in the second sound absorbing part.

  Further, in this aspect, effectively, the partition plate is formed from a thin plate having a cross section extending toward the bottom side, and the communication hole is a notch formed near the bottom edge of the partition plate. . In this case, the sound wave can be taken into the second sound absorbing portion near the bottom of the second sound absorbing portion.

  Further, in this aspect, effectively, the partition plate is formed from a thin plate having a letter-shaped cross section that widens on the bottom side, and a plurality of the communication holes are formed in the partition plate. In this case, the sound wave propagating in the first sound absorbing portion while being repeatedly reflected by the partition plate can be efficiently taken into the second sound absorbing portion.

  According to the present invention, it is possible to obtain a sound absorbing structure having a high sound absorption coefficient by realizing a structure in which sound waves are easily incident but sound waves are not easily output.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

Figure 1 is a sectional view showing an embodiment of a sound absorbing structure (currently reference example not belonging to the present invention). The sound absorbing structure 10 of the present embodiment has a sheet-like form, and is composed of multiple layers (two layers in this example) of sound absorbing layers 12a and 12b. The sound absorbing structure 10 of this embodiment is mounted such that the basic surfaces of the sound absorbing layers 12a and 12b are along an installation surface (for example, a body panel) around a sound source (for example, an engine). The installation surface of the sound absorbing structure 10 may be the inner surface of the hood panel, the engine panel side surface of the dash panel, the indoor side surface of the roof panel, the indoor side surface of the floor panel, or the like.

The sound absorbing layer 12a of the sound absorbing structure 10 of the present embodiment realizes an acoustic impedance that smoothly changes between the sound absorbing structure 10 and the air layer, and the acoustic impedance between the air layer and the sound absorbing layer 12b is abrupt. Plays a role in mitigating change. Specifically, the sound absorbing layer 12a in contact with the air layer is formed of a material having a first acoustic impedance that is substantially equal to or slightly larger than the acoustic impedance of the air, and is below the sound absorbing layer 12a (that is, on the installation surface). sound absorbing layer 12b of the contact side) is formed from a material having a first acoustic impedance Z ₁ is greater than the second acoustic impedance Z _2. For example, the acoustic impedance Z ₁ of the sound absorbing layer 12 a may be about 415 [kg / m ² · s], and the acoustic impedance Z ₂ of the sound absorbing layer 12 b is about 1.5 times that of the sound absorbing layer 12 a (about 600 [Kg / m ² · s]).

Here, the acoustic impedance of the material (medium) is defined by the ratio of the particle velocity to the sound pressure. For example, the acoustic impedance Z of the air is Z = ρ · c = 415 [kg / m ² · s] where the sound velocity c = 340 × 10 ³ [mm / s]. Further, the acoustic impedance of the material (medium) can be measured by using a normal incidence sound absorption coefficient measuring device. In this specification, the magnitude relationship between the acoustic impedances is ISO 10534-1 (calculation of sound absorption coefficient and acoustic impedance using an acoustic impedance tube: a method using a standing wave ratio) or ISO 10534-2 (sound absorption coefficient using an acoustic impedance tube). And calculation of acoustic impedance: transfer function method) may be based on values obtained by a measuring method.

  The acoustic impedance of a material depends on the density, wire diameter, porosity, etc. of the material. For this reason, the acoustic impedance of each of the sound absorbing layers 12a and 12b can be adjusted by adjusting the density, wire diameter, porosity, and the like. Therefore, for example, the sound absorbing layer 12b may be embodied as a sound absorbing layer having a higher density and a lower porosity than the sound absorbing layer 12a. At this time, the acoustic impedance of the sound absorbing layer 12b may be adjusted so that an effective sound absorbing action can be exhibited in the frequency band of engine sound, that is, about 800 Hz to 3 kHz.

  The materials of the sound absorbing layers 12a and 12b may be the same material as long as the acoustic impedance magnitude relationship is realized as described above. Specific materials of the sound absorbing layers 12a and 12b include inorganic fibers such as glass wool and rock wool, metal fiber materials such as aluminum fibers, synthetic resin foams such as polystyrene resins and polyethylene resins, urethane and rubber. It may be a soft material of the system, a porous material or the like. The sound absorbing structure 10 is formed by bonding the sound absorbing layers 12a and 12b made of the above-described materials with an adhesive or the like.

Meanwhile, the acoustic impedance of the backing layer 12a is materially different from the acoustic impedance of air (e.g., if the acoustic impedance Z ₁ of the sound absorbing layer 12a is the same as the acoustic impedance Z ₂ of the backing layer 12b), the sound absorbing structure 10 Most of the incident sound waves are reflected at the boundary surface between the sound absorbing layer 12a and the air layer, that is, the surface of the sound absorbing layer 12a due to the acoustic impedance difference between the sound absorbing layer 12a and the air layer. Therefore, in such a configuration, since sound waves incident on the sound absorbing structure 10 cannot be efficiently taken into the sound absorbing layer 12a, effective sound absorption by the sound absorbing structure 10 cannot be realized.

In contrast, in the present embodiment, as described above, the sound absorbing layer 12a constituting the air layer and the boundary surface in the installed state, the first substantially equal to or slightly acoustic impedance of air greater acoustic impedance Z ₁ (That is, the continuity of the acoustic impedance of the air layer and the sound absorbing layer 12a is maintained). For this reason, most of the sound waves incident on the sound absorbing structure 10 reach the sound absorbing layer 12b without being reflected by the surface of the sound absorbing layer 12a. Further, a part of the sound wave reaching the sound absorbing layer 12b is caused by an acoustic impedance difference between the sound absorbing layer 12a and the sound absorbing layer 12b on the boundary surface between the sound absorbing layer 12a and the sound absorbing layer 12b, that is, the upper surface of the sound absorbing layer 12b. Can reflect. However, in this embodiment, since the discontinuity of the acoustic impedance between the sound absorbing layer 12a and the sound absorbing layer 12b is relatively small, such a reflection component can be minimized, and for such a reflection component, In the process of reaching the air layer, the sound absorbing layer 12a is given a damping action. Furthermore, since the sound absorbing layer 12a is interposed between the air layer and the sound absorbing layer 12b, the sound wave can be taken into the sound absorbing layer 12b more efficiently than when no sound absorbing layer 12b is interposed. Therefore, according to the present embodiment, it is possible to effectively impart a high attenuation action by the sound absorbing layer 12b to the sound wave incident on the sound absorbing structure 10. As a result, the sound absorbing structure 10 of the present embodiment has a high sound absorption rate.

  In this embodiment, the sound absorbing structure 10 is composed of two sound absorbing layers 12a and 12b. However, sound waves are efficiently transmitted from the air layer to the inside of the sound absorbing structure 10 (finally, the lowermost layer). The sound absorbing structure 10 is composed of three or more sound absorbing layers so that it can be captured, and the acoustic impedance of the three or more sound absorbing layers is gradually increased in the direction from the air layer toward the lowest sound absorbing layer. You may change smoothly so that it may increase.

  Next, a second embodiment of the sound absorbing structure 10 according to the present invention will be described with reference to FIGS. FIG. 2 is a cross-sectional view of the sound absorbing structure 10 of this embodiment. The sound absorbing structure 10 of the present embodiment includes a thin partition plate 72 inside the sound absorbing layer. The partition plate 72 of the present embodiment has an exponential (exponential curve type) (or hemispherical) cross section as shown in FIG. As shown in FIG. 3A, the partition plate 72 may have a shape obtained by rotating an exponential section around the central axis Z, or as shown in FIG. It may have a constant equal section in the vertical direction of the paper. However, the partition plate 72 may have a triangular or dimple (half-egg) cross-sectional shape having a vertex on the upper side. The partition plate 72 may be formed of a thin plate such as an aluminum plate or a steel plate, or may be formed of a hard resin such as a polypropylene resin.

The sound absorbing layer of the sound absorbing structure 10 of the present embodiment is partitioned into a first sound absorbing portion 14a and a second sound absorbing portion 14b by a partition plate 72. The first sound absorbing part 14a is defined on the outside of the partition plate 72 of the exponential type, similar to the embodiment described above, the first substantially equal to or slightly acoustic impedance of air greater acoustic impedance Z ₁ It is formed from the material which has. The second sound absorbing portion 14b is defined inside the exponential partition plate 72 and is made of a material having a _second acoustic impedance Z2 larger than the _first acoustic impedance Z1, as in the above-described embodiment. It is formed. In addition, the description regarding the material and acoustic impedance of each sound absorption part 14a, 14b of a present Example is the same as that of each description regarding each sound absorption layer 12a, 12b of the above-mentioned Example.

  The partition plate 72 is formed with a communication hole 74 that allows the first sound absorbing portion 14a and the second sound absorbing portion 14b to communicate with each other. As shown in FIGS. 2 and 3, the communication hole 74 may be a notch formed in the vicinity of the bottom edge of the partition plate 72. As shown in FIG. 3 (A), the communication holes 74 may be formed at a plurality of locations at predetermined intervals along the circumferential direction of the bottom edge of the partition plate 72. Similarly, as shown in FIG. 3 (B). A plurality of locations may be formed at predetermined intervals along the longitudinal direction of the bottom edge of the partition plate 72.

  As shown in FIG. 2, the sound absorbing structure 10 of the present embodiment is fixed to a body panel or the like with clips, screws, or the like so that the outer surface of the exponential partition plate 72 faces the sound source, for example. Is done. In this case, the inner surface of the exponential partition plate 72 faces the body panel (installation surface). However, the present invention does not specify the installation method, the installation location, and the installation mode (for example, the direction of the sound absorption structure 10 within the installation surface) of the sound absorption structure 10. For example, the installation location of the sound absorbing structure 10 may be a hood panel, a fender cover, a dash panel, a roof panel, a floor panel, or the like.

In the present embodiment, the first sound absorbing portion 14a is defined between adjacent outer surfaces of the exponential partition plate 72 as described above. For this reason, the first sound absorbing portion 14a similarly has an exponential cross section, and has a cross sectional area that gradually decreases from the opening side toward the bottom as seen in the incident direction of the sound wave. . Further, in the present embodiment, as in the above-described embodiment, the first sound absorbing portion 14a constituting the interface with the air layer has a first acoustic impedance that is approximately equal to or slightly larger than the acoustic impedance of the air. Z ₁ is included. For this reason, most of the sound waves incident on the sound absorbing structure 10 reach the bottom of the first sound absorbing portion 14a while being reflected on the outer surface of the partition plate 72 without being reflected on the surface of the sound absorbing layer 12a. become. Therefore, according to the present embodiment, the sound wave incident on the sound absorbing structure 10 can be guided to the bottom of the first sound absorbing portion 14a, and during that time, the damping action by the first sound absorbing portion 14a can be given. .

  Furthermore, in the present embodiment, the communication hole 74 of the partition plate 72 is located near the bottom of the first sound absorbing portion 14a. Accordingly, a part of the sound wave reaching the bottom of the first sound absorbing portion 14 a is reflected on the body panel surface, which is the installation surface of the sound absorbing structure 10, or the outer surface of the partition plate 72, and then the communication hole 74 of the partition plate 72. Is taken into the second sound absorbing portion 14b (see the arrow in FIG. 2). The sound wave input into the second sound absorbing portion 14b is the first sound absorbing portion 14a from the second sound absorbing portion 14b because the second sound absorbing portion 14b is substantially closed by the inner surface of the partition plate 72. Alternatively, it is practically hardly output again to the external space. Thus, according to the present embodiment, the sound wave incident on the sound absorbing structure 10 can be efficiently taken into the second sound absorbing portion 14b having a high sound absorbing action. In addition, since the sound once taken into the second sound absorbing portion 14b is difficult to be output to the outside, the energy of the sound wave incident on the sound absorbing structure 10 is effectively used in the second sound absorbing portion 14b having a high sound absorbing action. Can be attenuated. As a result, the sound absorbing structure 10 of the present embodiment has a high sound absorption rate.

  As an example for realizing the sound absorbing action as described above, as shown in FIG. 2, when the overall height H1 of the sound absorbing structure 10 is designed to be 30 to 50 mm, the height h1 and the width of the communication hole 74 are designed. Is set to about 5 to 10 mm. In addition, the separation width D2 (that is, the width D2 of the bottom of the first sound absorbing portion 14a) between adjacent bottom edges of the exponential partition plate 72 is set to about 20 mm, and the first sound absorbing portion 14a The opening width D1 is set to about 50 mm.

  In this embodiment, the sound absorbing layer 14a having a constant acoustic impedance is interposed between the air layer and the sound absorbing layer 14b. However, the sound wave can be more efficiently taken into the communication hole 74 from the air layer. So that the acoustic impedance of the sound absorbing layer 14a is gradually increased downward (for example, the sound absorbing layer 14a is composed of a plurality of sound absorbing layers), and the sound absorbing layer via the sound absorbing layer 14a is formed from the air layer. The continuity of the acoustic impedance up to 14b may be further smoothed.

  Next, a third embodiment of the sound absorbing structure 10 according to the present invention will be described with reference to FIG. FIG. 4 is a cross-sectional view of the sound absorbing structure 10 of this embodiment. The sound absorbing structure 10 of the present embodiment is different from the second embodiment described above only in the configuration of the partition plate 72 and the communication hole 74 formed in the partition plate 72. Only the configuration different from that of the second embodiment will be described below.

  In this embodiment, the partition plate 72 has a cross-sectional shape in which substantially triangular waveforms continue. However, the partition plate 72 may have a cross-sectional shape in which an exponential or dimple (half-egg) waveform continues. In the present embodiment as well, the sound absorbing layer of the sound absorbing structure 10 is divided into the first sound absorbing portion 14a and the second sound absorbing portion 14b by the partition plate 72.

  The communication hole 74 is formed on the side surface of the partition plate 72 having a triangular cross section. At this time, the communication holes 74 may be formed at a plurality of positions in the depth direction at predetermined intervals on the side surface of the partition plate 72, and along the longitudinal direction of the partition plate 72 (that is, the direction perpendicular to the drawing sheet). A plurality of locations may be formed at predetermined intervals.

  In the present embodiment, the sound wave incident on the sound absorbing structure 10 is not reflected on the surface of the sound absorbing layer 12a, and is repeatedly reflected on the outer surface of the partition plate 72, as in the second embodiment. It progresses to the bottom part of the part 14a. In the present embodiment, a plurality of communication holes 74 are formed on the side surface of the partition plate 72 as described above. Accordingly, the sound wave is taken into the second sound absorbing portion 14 b through the communication hole 74 in the process of repeated reflection from the outer surface of the partition plate 72. In particular, in the present embodiment, since a plurality of communication holes 74 are formed on the side surface of the partition plate 72, there is a possibility that sound waves may enter the communication holes 74 a plurality of times until reaching the bottom of the first sound absorbing portion 14a. Get higher. Therefore, even when the sound wave is reflected at the boundary surface between the first sound absorbing part 14a and the second sound absorbing part 14b due to the difference in acoustic impedance, the frequency of incidence of the sound wave into the communication hole 74 increases. Input of sound waves into the second sound absorbing portion 14b is promoted such that sound waves are taken into the second sound absorbing portion 14b when entering the next communication hole 74.

  As described above, according to the present embodiment, the sound wave incident on the sound absorbing structure 10 can be efficiently taken into the second sound absorbing portion 14b having a high sound absorbing action, and the sound wave incident on the sound absorbing structure 10 is obtained. Can be effectively attenuated in the second sound absorbing portion 14b having a high sound absorbing action. As a result, the sound absorbing structure 10 of the present embodiment has a high sound absorption rate.

  As an example for realizing the sound absorbing action as described above, as shown in FIG. 4, when the overall height H2 of the sound absorbing structure 10 is designed to be 20 to 30 mm, the width W of the communication hole 74 is about It is set to about 5 mm. Moreover, the width D3 and the opening width D4 of the bottom part of the 1st sound absorption part 14a are set to about 50 mm.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, in the second embodiment described above, the communication hole 74 may be formed not only near the bottom edge of the partition plate 72 but also on the side surface of the partition plate 72 as in the third embodiment.

  In the second and third embodiments described above, the partition plate 72 is completely embedded in the sound absorbing layer of the sound absorbing structure 10, but as shown in FIG. 5, a part of the partition plate 72 is sound absorbing. The structure exposed from the layer may be sufficient. Even in this case, similarly to the second and third embodiments described above, the sound wave is easily taken into the second sound absorbing portion 14b, and the once picked up sound wave is emitted from the second sound absorbing portion 14b. Difficult structures can be realized.

  Furthermore, in the second and third embodiments described above, the sound absorbing material provided in the first sound absorbing portion 14a can be omitted, that is, the first sound absorbing portion 14a can be an air layer. Even in this case, similarly to the second and third embodiments described above, the sound wave is easily taken into the second sound absorbing portion 14b, and the once picked up sound wave is emitted from the second sound absorbing portion 14b. A difficult structure is realized, and effective sound absorption can be realized by the second sound absorbing portion 14b having a high damping action.

It is sectional drawing which shows 1st Example of the sound-absorbing structure by this invention. It is sectional drawing which shows 2nd Example of the sound-absorbing structure by this invention. It is a perspective view which shows the partition plate 72 of the sound-absorbing structure of 2nd Example. It is sectional drawing which shows 3rd Example of the sound-absorbing structure by this invention. It is sectional drawing which shows the alternative Example of the sound-absorbing structure by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Sound absorption structure 12a Sound absorption layer 12b Sound absorption layer 14a 1st sound absorption part 14b 2nd sound absorption part 72 Partition plate 74 Communication hole

Claims (3)

A first sound absorbing part in contact with the air layer;
A partition plate having a communication hole;
A second sound absorbing portion that is separated from the air layer by the partition plate and communicates with the air layer through the communication hole of the partition plate and the first sound absorbing portion;
The first sound absorbing part is formed of a material having an acoustic impedance substantially equal to or slightly larger than the acoustic impedance of air, and the second sound absorbing part is made of a material having an acoustic impedance larger than that of the first sound absorbing part. It is characterized by being formed,
The first sound absorbing part, exponential shape, having a triangular cross-sectional shape or semi-oval, sound absorbing structure. The partition plate is formed of a thin plate-shaped section of the spread at the bottom side, the communication hole is a notch formed near the bottom edge of the partition plate, the sound absorbing structure of the mounting serial to claim 1 . The partition plate is formed of a thin plate-shaped section of the spread at the bottom side, the communication hole is formed in plural on the partition plate, the sound absorbing structure of the mounting serial to claim 1.

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