JP3521577B2 - Sound absorbing material - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a sound absorbing material attached to an object to be attached, for example, a hood panel, a roof panel, a floor panel, an engine for a vehicle. The present invention relates to a sound absorbing material attached to an engine cover or the like for suppressing noise from propagating to the outside, a vehicle interior, or the like. 2. Description of the Related Art Conventionally, for example, a sheet-shaped sound absorbing member is provided on a surface of a hood panel (hood) for a vehicle on the engine room side in order to minimize leakage of noise generated from an engine or the like to the outside. Lumber is attached. As this kind of sound absorbing material, non-woven fiber materials such as felt and glass wool are used, and these non-woven fiber materials exhibit a large sound absorbing ability mainly in a high frequency range. As a material exhibiting a sound absorbing ability in a relatively low frequency range, for example, a device having a resonance layer formed of a perforated plate and an air layer is known. [0003] However, according to the existing conventional technology, when there are many noise sources such as an engine room and the generated frequency levels are different, an effective sound absorbing performance can be obtained. There were no cases. That is, various members such as an engine main body, an intake system, and a transmission are arranged in the engine room, and these various members generate noise having various frequency levels.
On the other hand, in the sound absorbing material using the nonwoven fiber material described in the related art, noise in a relatively low frequency region (for example, 2 k
It is difficult to absorb noise (less than 0.5 Hz), and in order to secure the sound absorbing ability in such a low frequency region, the nonwoven fiber must be made thicker or heavier. Further, it is difficult for a sound absorbing material having a resonance layer to absorb noise in a relatively high frequency region (for example, noise of 2 kHz or more). Things are forced. Further, as described above, the sound absorbing material employed to absorb the noise in the engine room is required not only to increase the sound absorbing coefficient but also to be reflected by the sound absorbing material. It is desired to reduce the amount of noise generated as much as possible. However, when the sound absorbing material is constituted by the perforated plate and the resonance layer including the air layer as described above, a part of the noise is reflected by the perforated plate, and as a result, the noise cannot be efficiently absorbed. Was sometimes caused. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a large number of noise sources.
It is an object of the present invention to provide a sound-absorbing material that can efficiently absorb noise of different frequency levels even when the noise is generated. [0006] In order to achieve the above object, according to the first aspect of the present invention, the propagation of noise which is attached to an object to be attached and which is generated inside the object to be attached. A high-frequency region absorbing layer made of a non-woven fiber layer, provided so as to overlap the high-frequency region absorbing layer, comprising a perforated plate and an air layer behind it. Comprising a low frequency region absorption layer, and the high frequency region absorption layer
An air layer is provided between the low-frequency region absorption layer and the high-frequency region absorption layer, and the low-frequency region absorption layer is disposed on the side far from the noise source. The gist is that they did. According to the first aspect of the present invention, the sound absorbing material is attached to the adherend, and the sound absorbing material reduces noise generated inside the adherend. Propagation is suppressed. The sound-absorbing material has a high-frequency region absorption layer made of non-woven fiber and a low-frequency region absorption layer consisting of a perforated plate and an air layer behind it, and the high-frequency region absorption layer mainly absorbs high-frequency noise. Is done. That is, when noise is incident on the high frequency region absorption layer, the energy of the noise is attenuated by viscous resistance and heat conduction of air between the non-woven fibers in the layer. Alternatively, the nonwoven fibers themselves vibrate slightly, and friction occurs between the nonwoven fibers that are in contact with each other. And
These energies are converted into heat of vibration and heat of friction, whereby the energy of the noise is attenuated. Further, noise in the low frequency region can be absorbed mainly by the low frequency region absorbing layer. That is, the noise in the relatively low frequency region that has passed through the high frequency region absorption layer is:
The energy of the noise is attenuated by the resonance action in the low frequency region absorption layer. At this time, for example, if holes having the same diameter are formed at regular intervals in the perforated plate of the low frequency region absorption layer, the resonance frequency f of the noise that can be absorbed can be obtained based on the following equation. [0010] However, in the above equation, “c” is the speed of sound, “a” is the radius of the hole provided in the perforated plate, “B” is the distance between the holes, and “h” is the same.
Is the thickness of the perforated plate, and "d" is the thickness of the air layer. Therefore, according to the present invention, even if there are many noise sources and noises of different frequency levels are generated,
The noise can be absorbed at a high level as a whole, ie in a wide frequency range. Further, in the present invention, the high frequency region absorbing layer is arranged on the side closer to the noise source, and the low frequency region absorbing layer is arranged on the side farther from the noise source. for that reason,
The problem that noise is reflected by the low-frequency region absorbing layer, and as a result, the reflected sound leaks out is solved.
In other words, contrary to the configuration of the present invention, when the low frequency region absorption layer is arranged on the side closer to the noise source, the perforated plate of the low frequency region absorption layer before absorbing the high frequency region noise. Some of the noise is reflected. However, according to the configuration of the present invention, the above-mentioned disadvantages are solved, and efficient sound absorption characteristics can be obtained. In addition, an air layer is provided between the high frequency region absorption layer and the low frequency region absorption layer. In this case, by providing the air layer, the frequency level of the noise absorbed by the high frequency region absorption layer shifts to the low frequency side. Therefore, it is possible to more effectively absorb noise having a desired frequency level. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A first embodiment of the present invention will be described below with reference to FIGS. In the present embodiment, noise generated from the engine or the like is prevented from leaking to the outside on the surface of the hood panel (bonnet) P as a body to be attached to the vehicle on the engine room side (lower side in the figure). Sound absorbing material 1 is attached. In FIG. 1, this sound absorbing material 1 has a sheet shape as a whole, and a felt layer 2 as a high frequency region absorbing layer.
And a resonance layer 3 as a low frequency region absorption layer provided so as to overlap the felt layer 2.
The felt layer 2 is arranged on the side closer to the noise source (the lower side in the figure), and the resonance layer 3 is located on the side farther from the noise source (the upper side in the figure).
Placed in An air layer 4 having a predetermined width (10 mm in the present embodiment) is provided between the felt layer 2 and the resonance layer 3. The felt layer 2 is composed of, for example, a relatively thick non-woven fiber layer made of coarse hair (thickness = about 10 m).
m). The resonance layer 3 has a large number of holes 5 at regular intervals and the same diameter.
It is composed of a perforated plate having a and an air space 6 provided behind the plate. In the present embodiment, the perforated plate 5 is formed of, for example, PP (polypropylene), the thickness of the perforated plate 5 is 0.5 mm, the interval between the holes 5a is 4 mm, and
The diameter of the hole 5a is 0.5 mm. Air layer 6
Is 10 mm in width. The sound absorbing material 1 is attached to the hood panel P by attaching a clip (not shown) at a peripheral portion thereof. Next, the function and effect of the sound absorbing material 1 in the present embodiment will be described. In the present embodiment, the sound absorbing material 1 attached to the hood panel P can suppress noise generated in the engine room from the hood panel P from propagating to the outside. That is, noise in a relatively high frequency range can be mainly absorbed by the felt layer 2. At this time, when noise is incident on the felt layer 2, the viscous resistance and heat conduction of air between the non-woven fibers in the layer 2 cause
The energy of the noise is reduced. Alternatively, the nonwoven fibers themselves vibrate slightly, and friction occurs between the nonwoven fibers that are in contact with each other. Then, those energies are converted into vibration heat and friction heat, whereby the energy of the noise is attenuated. On the other hand, the air layer 4 provided behind the felt layer 2 makes the felt layer 2
, The sound absorption characteristic is shifted to the lower frequency side. The noise in the relatively low frequency range that has passed through the felt layer 2 and the air layer 4 is transmitted to the perforated plate 5 and the air layer 6.
Can be mainly absorbed by the resonance layer 3 made of That is, the noise passing through the holes 5a of the perforated plate 5 is attenuated by the resonance action. As described above, in the present embodiment, the sound absorbing material 1 is constituted by the felt layer 2 and the resonance layer 3 including the perforated plate 5 and the air layer 6. As a result, good sound absorption performance can be exhibited in a wide frequency range. In such a case, it is not necessary to make the felt layer 2 thick or heavy, and it is possible to reduce the weight of the entire sound absorbing material 1. In particular, various members such as an engine body, an intake system, and a transmission are arranged in the engine room, and these various members may generate noise having various frequency levels. However, according to the sound absorbing material 1 of the present embodiment, as described above, it is possible to exhibit a high level of sound absorbing characteristics even with noise having various frequency levels. In this embodiment, the felt layer 2 is arranged on the side closer to the noise source, and the resonance layer 3 is arranged on the side farther from the noise source. Therefore, it is possible to avoid a situation in which noise is reflected by the perforated plate 5 of the resonance layer 3 and as a result, the reflected sound leaks outside. That is, contrary to the present embodiment, when the resonance layer 3 is arranged on the side closer to the noise source (the lower side in the figure), the perforated plate 5 of the resonance layer 3 before absorbing the noise in the high frequency region. As a result, noise is reflected, and this reflected sound leaks out from the opening below the engine room. However, according to the configuration of the present embodiment,
The inconvenience as described above is solved, and efficient sound absorption characteristics can be obtained. In addition, in the present embodiment, the air layer 4 is provided between the felt layer 2 and the resonance layer 3 to shift the sound absorption characteristics obtained by the felt layer 2 to a lower frequency side. As a result, the frequency level (about 2 kHz)
In the vicinity frequency region), good sound absorption characteristics can be obtained. Further, in the sound absorbing material 1 of the present embodiment, the nonwoven fiber layer is constituted by the felt layer 2. Therefore, the sound absorbing material can be formed relatively inexpensively, and the cost can be reduced. Here, in order to confirm this effect, the following experiment was conducted. That is, a sample of the sound absorbing material 1 having the configuration shown in FIG. 1 was prepared, and the frequency thereof was changed, and the normal incidence sound absorbing coefficient was measured. The result is shown in FIG. According to the sample of the sound absorbing material 1 of the present embodiment, as shown by the solid line in FIG. 2, it can be seen that the effect of absorbing noise as a whole is high. More specifically, the felt layer 2 and the air layer 4 absorb sound mainly in a high-frequency region having a frequency of 2 kHz or more (broken line in the figure). At this time, the sound absorption characteristic (broken line in the figure) is shifted to a lower frequency side than when the felt layer 2 is used alone because the air layer 4 is provided behind the felt layer 2. In addition, the resonance layer 3 mainly absorbs a sound whose frequency is around 2 kHz or lower than that frequency (two-dot chain line in the figure). From the above, the sound absorbing material 1 can efficiently absorb low frequency level noise which may be noisy for a driver or a person outside, and as a whole the sound absorbing material 1 has a wide range of frequency levels. And excellent sound absorbing performance can be exhibited. (Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIGS.
However, in the present embodiment, the description of the same parts as those in the first embodiment will be omitted, and different points will be mainly described below. That is, the main difference between the sound absorbing material 11 of the present embodiment and the sound absorbing material 1 of the second embodiment (see FIG. 1) is as follows. 4 is removed, and a resonance layer 12 as a low frequency region absorption layer is provided so as to be in contact with the felt layer 2. In this case, the perforated plate 13 of the resonance layer 12 is arranged so as to be in contact with the felt layer 2 (the perforated plate 13 is equivalent to the perforated plate 5 in FIG. 1), and is located between the perforated plate 13 and the hood panel P. Is provided with an air layer 14 having a width of about 20 mm. However, in the above configuration, similarly to the first embodiment, the felt layer 2 is provided on the noise incident side (the side close to the noise generation source). With respect to the sound absorbing material 11 having the above-described structure, the following experiment was conducted in the same manner as in the first embodiment in order to confirm the operation and effect. That is, a sample of the above-described sound absorbing material 11 was prepared, and the frequency of the sample was changed, and the normal incidence sound absorbing coefficient was measured. The result is shown in FIG. As shown in the figure, the sound absorbing material 11 of the present embodiment can obtain good sound absorbing characteristics in a high frequency region. Further, it is possible to reliably absorb low-frequency level noise (noise having a frequency of less than 2 kHz in a relatively low frequency range) which is perceived by a driver or a person outside to be noisy. In the present embodiment, the thickness of the air layer 14 forming the resonance layer 12 is twice the thickness of the same air layer in the first embodiment. Therefore, the resonance frequency in the resonance layer 12 decreases, and the sound absorption characteristics of the resonance layer 12 are shifted to a lower frequency side than in the first embodiment. Also, in the present embodiment, similarly to the first embodiment, the felt layer 2 is provided on the noise incident side (sound source side), and the resonance layer 12 is provided behind the felt layer 2. Therefore, the inconvenience of noise being reflected by the perforated plate 5 can be eliminated, and excellent sound absorbing performance can be exhibited. (Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIGS.
However, in the present embodiment, the description of the same parts as those of the above-described embodiments will be omitted, and mainly different points will be described below. That is, the main difference between the sound absorbing material 21 of the present embodiment and the sound absorbing material of each of the above embodiments is as follows. In the sound absorbing material 21 of FIG. The resonance layer 22 is provided as the
Inside, two perforated plates 23 and 24 are arranged (perforated plates 23 and 24 are equivalent to perforated plate 5 in FIG. 1). The air layers 25 and 26 constituting the resonance layer 22 are provided in two layers (both have a thickness of 10 mm). However, also in the configuration of the present embodiment, the felt layer 2 is provided on the noise incident side similarly to the above-described embodiments. The same experiment as in each of the above embodiments was performed on the sound absorbing material 21 having the above configuration, and the experimental results are shown in FIG. As shown in FIG.
Thus, good sound absorption characteristics in a high frequency region can be obtained. In addition, a low-frequency level noise (frequency of 2 kHz) which may be noisy for a driver or a person outside.
Noise in a relatively low-frequency range of less than about 1 GHz). In addition, in the present embodiment, similarly to the above embodiments, the felt layer 2 is provided on the noise incident side, and the resonance layer 22 is provided behind the felt layer 2. Therefore, the inconvenience of noise being reflected by the perforated plate 5 can be eliminated, and excellent sound absorbing performance can be exhibited. (Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIGS.
However, in the present embodiment, the description of the same parts as those in the first to third embodiments will be omitted, and different points will be mainly described below. That is, the main difference between the sound absorbing material 31 of the present embodiment and the sound absorbing material of each of the above embodiments is that, in the sound absorbing material 31 of FIG. 7, the low frequency region absorbing layer is in contact with the felt layer 2. The resonance layer 32 is provided as the
Inside, two perforated plates 33 and 34 are arranged. In these perforated plates 33, 34, the lower perforated plate 33 has the same configuration as the perforated plate 5 in FIG. 1, while the upper perforated plate 34 has a hole interval of 6 mm. I have. Behind the perforated plates 33 and 34, the respective thicknesses are 20
Air layers 35 and 36 of 10 mm and 10 mm are provided in two layers. However, also in the configuration of the present embodiment, the felt layer 2 is provided on the noise incident side similarly to the above-described embodiments. The same experiment as in each of the above embodiments was performed on the sound absorbing material 31 having the above configuration, and the results of the experiment are shown in FIG. As shown in FIG.
Thus, good sound absorption characteristics in a high frequency region can be obtained. In addition, a low-frequency level noise (frequency of 2 kHz) which may be noisy for a driver or a person outside.
Noise in a relatively low-frequency range of less than about 1 GHz). In addition, in the present embodiment, similarly to the above embodiments, the felt layer 2 is provided on the noise incident side (sound source side), and the resonance layer 32 is provided behind the felt layer 2. Therefore, the inconvenience of noise being reflected by the perforated plate 5 can be eliminated, and excellent sound absorbing performance can be exhibited. The present invention is not limited to the above embodiments, and may be configured as follows, for example. (1) In each of the above embodiments, the high-frequency region absorbing layer made of non-woven fiber is constituted by the felt layer 2, but instead or together with the high-frequency region absorbing layer, a glass wool layer or a urethane home layer is used. A layer may be constituted. (2) The arrangement state of the perforated plate and the air layer in the resonance layer and the intervals and sizes of the holes formed in the perforated plate in the above embodiments are merely examples, and the above-described configuration is adopted. However, the present invention is not limited to this. They can be set arbitrarily for noise having a desired frequency level. (3) In each of the above-described embodiments, the sound absorbing material is attached to the hood panel P in the engine room. However, in addition to the above, the roof panel, the wheel house, the floor panel, the engine engine cover, etc. In addition to the various types of adherends, they may be attached to other locations for absorbing noise. As described in detail above, according to the sound absorbing material of the present invention, even if there are many noise sources and noises of different frequency levels are generated, the noises are efficiently absorbed. It has an excellent effect that it can be performed. [0039]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view schematically showing a sound absorbing material according to a first embodiment. FIG. 2 is an actual measurement graph illustrating the operation and effect of the sound absorbing material of the first embodiment. FIG. 3 is a sectional view schematically showing a sound absorbing material according to a second embodiment. FIG. 4 is an actual measurement graph for explaining the operation and effect of the sound absorbing material of the second embodiment. FIG. 5 is a sectional view schematically showing a sound absorbing material according to a third embodiment. FIG. 6 is an actual measurement graph illustrating the operation and effect of the sound absorbing material of the third embodiment. FIG. 7 is a sectional view schematically showing a sound absorbing material according to a fourth embodiment. FIG. 8 is an actual measurement graph illustrating the operation and effect of the sound absorbing material of the fourth embodiment. [Description of Signs] 1, 11, 21, 31: Sound absorbing material, 2: Felt layer as high frequency region absorbing layer, 3, 12, 22, 32: Resonant layer as low frequency region absorbing layer, 4: Air layer , 5,13,
23, 24 ... perforated plate, 6, 14, 25, 26, 35, 3
6 ... air layer, P ... hood panel as an adherend.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-79018 (JP, A) JP-A-52-55702 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G10K 11/16 B60R 13/08 E04B 1/86

Claims (1)

(57) [Claim 1] A sound absorbing material attached to an attached body for suppressing propagation of noise generated inside the attached body, comprising a non-woven fiber A high-frequency region absorbing layer comprising a layer, a low-frequency region absorbing layer comprising a perforated plate and an air layer behind the perforated plate, provided so as to overlap the high-frequency region absorbing layer; and Absorption layer and the low frequency region absorption
An air layer is provided between the storage layer and the absorption layer, and the high-frequency region absorption layer is arranged on the side closer to the noise source, and the low-frequency region absorption layer is arranged on the side farther from the noise source. And sound absorbing material.