JP4239705B2 - Sound absorbing structure - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention particularly relates to a sound absorbing structure that is provided in a vehicle and suppresses vibration of an installation surface and absorbs engine sound or the like to reduce noise.
[0002]
[Prior art]
Conventionally, in a damping material having a laminated structure of a surface layer, a sound insulation layer, and a damping / sound absorbing layer, a feather fray prevention layer is integrated with the damping / sound absorbing layer by needle punching under the damping / sound absorbing layer. A vibration damping material arranged in this manner is known (for example, see Patent Document 1). In this conventional vibration damping material, it is possible to prevent feather fraying without substantially reducing the vibration damping effect by increasing the mixing ratio of low melting point fibers only to the feather fray prevention layer that comes into contact with the floor panel or the like. Make it possible.
[0003]
[Patent Document 1]
JP 7-315101 A
[Problems to be solved by the invention]
By the way, the floor panel of a vehicle is provided with a high-density and high-viscosity sheet material as a damping material, as in the above-described conventional technology. This sheet material serves to attenuate the vibration of the floor panel due to the effect of its weight and viscosity. However, since this sheet material has a high density, there is a problem in terms of weight. In addition, this sheet material mainly plays a role of suppressing vibration of the installation surface such as a floor panel (vibration suppression or sound insulation), and has a function of effectively absorbing sound in the installation space. Absent.
[0005]
Therefore, the present invention can reduce the weight of the base material provided as the vibration damping material, while efficiently ensuring the vibration damping action by the base material, and further has an excellent sound absorbing function for the base material. An object of the present invention is to provide a sound absorbing structure.
[0006]
[Means for Solving the Problems]
The above object, as described in claim 1, the space of the substantially cylindrical shape both ends is open is formed in plural, the opening of one end of the space portion is placed on the installation surface so as to be closed, the viscosity A base material made of material;
A sound-absorbing material covering the opening at the other end of the space,
The side wall of the base material that defines the space portion includes a flange surface at the opening side end of the space portion, and the flange surface is perpendicular to the side wall in a manner that the opening of the space portion remains. This is achieved by a sound-absorbing structure characterized in that it extends in the opening plane.
[0007]
In the present invention, since the base material is formed with a plurality of substantially cylindrical space portions having both ends opened, when the base material is installed on the installation surface, one end opposite to the installation surface is opened. A plurality of space portions are formed. According to the present invention, by forming a through hole (space part) in the base material, the mass of the base part (part on the installation surface side) of the base material that does not greatly contribute to the vibration damping action is reduced. The weight can be reduced, and the vibration damping action by the base material of the viscous material can be efficiently ensured. Further, according to the present invention, the through hole (space part) for weight reduction provided in the base material is covered with the sound absorbing material, so that the base material has an excellent sound absorbing function in addition to the above-described vibration damping action. Can be made. Also, lighter, according to the present invention, thus the side walls of the base defining the spatial portion within the this with a specific flange surface at an end portion on the opening side of the space, the base material (sound-absorbing structure) Thus, the vibration suppressing function can be efficiently ensured.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0009]
FIG. 1 is a perspective view showing an embodiment of a sound absorbing structure according to the present invention. The sound absorbing structure 10 according to the present invention has a plurality of cylindrical spaces 71 (hereinafter referred to as “sound absorbing cells 71”) having both ends opened. The plurality of sound absorbing cells 71 are arranged in a grid pattern, for example, and are preferably arranged vertically and horizontally in a manner adjacent to each other.
[0010]
The structure including the plurality of sound absorbing cells 71 is formed on a base material 80 made of a viscous material having a large internal damping such as rubber (for example, butyl rubber) or asphalt sheet. Specifically, the plurality of sound absorbing cells 71 described above are formed by forming through holes in a base material 80 made of a viscous material and having a predetermined thickness H. Naturally, the size of the base material 80 corresponds to the size of the region where the sound absorbing structure 10 is installed. Naturally, the number of sound absorbing cells 71 is determined according to the installation range of the sound absorbing structure 10. Moreover, the thickness of the base material 80 does not necessarily need to be constant over the entire installation region.
[0011]
The sound absorbing structure 10 of the present embodiment is provided with a sound absorbing material 76. The sound absorbing material 76 is fixed to the upper end 72a (see FIG. 2) of the side wall 72 of each sound absorbing cell 71 by bonding or the like so as to cover one open end of each sound absorbing cell 71. The sound absorbing material 76 is formed from a material having sound absorbing properties, for example, 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, It may be formed from a rubber-based soft material, a porous material, or the like.
[0012]
FIG. 2 is a cross-sectional view showing an installation state of the sound absorbing structure 10 of the present embodiment, corresponding to a cross section taken along the line II of FIG. The sound absorbing structure 10 of the present embodiment is fixed to an installation surface such as a body panel so that an opening at one end of the sound absorbing cell 71 (an opening on the side where the sound absorbing material is provided) faces a sound source (for example, an engine). The The opening surface at the other end of the sound absorbing cell 71 (opening surface on the lower end 72b side) is configured to be along the installation surface, and therefore the opening at the other end of the sound absorbing cell 71 is blocked by the installation surface. The lower end 72b of the side wall 72 of each sound absorbing cell 71 is fixed to the installation surface with an adhesive or the like. 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.
[0013]
Next, with reference to FIG. 3, the vibration damping action by the sound absorbing structure 10 of the present embodiment will be described. 3A and 3B show a cross section of the sound absorbing structure 10 in the installed state when viewed from the same direction as in FIG.
[0014]
The sound absorbing structure 10 according to the present embodiment functions to suppress vibration of the installation surface (that is, the body panel). Specifically, when the body panel is deformed by vibration, the sound absorbing structure 10 (base material 80) is deformed as shown in FIGS. 3 (A) and 3 (B). In this case, the side wall 72 of the base material 80 is deformed in such a manner that the opening of the sound absorbing cell 71 is widened or narrowed. Due to the deformation of the base material 80 made of the viscous material, the vibration of the body panel is attenuated.
[0015]
At this time, the deformation amount (vibration speed) of the base material 80 becomes the largest, particularly on the upper end 72a side (sound absorbing material side) of the side wall 72. That is, the deformation on the side of the upper end 72a of the side wall 72 contributes most to the suppression of the vibration of the body panel. In the present embodiment, since the through hole is formed in the base material 80 so as to correspond to the sound absorbing cell 71 as described above, the bottom surface of the base material 80 is substantially constituted only by the bottom surface of the side wall 72. Yes. Therefore, according to the present embodiment, it is possible to efficiently ensure the vibration suppressing function while reducing the weight of the base material 80 (the sound absorbing structure 10). From this viewpoint, the thickness of the side wall 72 may be set larger toward the upper end 72a. In this case, the cross-sectional area of the sound absorbing cell 71 gradually increases toward the bottom. Alternatively, from the same viewpoint, as shown in FIG. 4, a flange surface 72 c may be formed on the upper end 72 a of the side wall 72 so as to extend perpendicularly to the side wall 72 and into the opening surface. However, the flange surface 72c is set so that the opening width D (vertical and horizontal) of the sound absorbing cell 71 is 20 mm or more.
[0016]
Next, the principle of sound absorption of the sound absorbing structure 10 according to the present invention will be described with reference to FIG. 5A and 5B show a cross section of the sound absorbing structure 10 in the installed state when viewed from the same direction as in FIG.
[0017]
Referring to FIG. 5A, when a sound wave having a wavelength λ is incident on the sound absorbing cell 71 substantially perpendicularly, the incident wave and the reflected wave reflected by the installation surface (that is, the body panel) enter the sound absorbing cell 71. A standing wave is formed by the combination with. On the other hand, even when a sound wave having a wavelength λ is incident on the sound absorbing cell 71 from an oblique direction, the oblique incident angle of the sound wave is limited by each side wall 72 as shown in FIG. A standing wave is formed.
[0018]
This standing wave has an antinode in the sound absorbing cell 71 at a position away from the installation surface by an odd multiple of ¼ of the wavelength λ, and the particle velocity of the sound wave becomes maximum at the antinode. Therefore, if the sound absorbing material 76 is provided at a position where the particle velocity is maximum and the sound wave is passed through the sound absorbing material 76 at the position having the highest particle velocity, the sound wave can be attenuated most efficiently.
[0019]
FIG. 6 shows a sound absorption coefficient measurement result for the sound absorbing structure 10 according to the present invention. FIG. 6 is a diagram showing the sound absorption rate of the above-described sound absorbing structure 10 when the sound wave is inputted in the direction perpendicular to the opening surface of the sound absorbing cell 71, with the frequency of the inputted sound wave as the horizontal axis. Further, in FIG. 6, as a comparative example, the same measurement result with respect to the sound absorbing structure having the same configuration in which the sound absorbing material 76 is not provided is indicated by a broken line.
[0020]
As shown in FIG. 6, in the present embodiment, a peak appears in the sound absorption rate in a specific frequency band. On the other hand, according to the comparative product, no peak appears in the sound absorption coefficient. The frequency at which the peak of the sound absorption coefficient appears corresponds to the frequency of a sound having a wavelength four times the depth H of the sound absorption cell 71 as described above. Therefore, according to the present embodiment, it can be understood that a high sound absorption effect can be obtained in a specific frequency band. From this viewpoint, the depth H of the sound absorbing cell 71 (the thickness H of the base material 80) is preferably set to 1/4 (or an odd multiple) of the wavelength λ of the sound wave to be absorbed. For example, the depth H (height of the side wall 72) of the sound absorbing cell 71 is set within a range of 10 mm to 30 mm. Further, the opening width D (see FIG. 1) of the sound absorbing cell 71 is set smaller than the wavelength λ of the sound wave in the frequency band to be absorbed in order to regulate the frequency of the sound wave that can enter the sound absorbing cell 71. For example, the opening width D of the sound absorbing cell 71 is set within a range of 40 mm to 60 mm. However, the opening width D of the sound absorbing cell 71 may be different for each sound absorbing cell 71, and may be different in the depth direction and the lateral direction.
[0021]
As described above, according to the present embodiment, in addition to the vibration damping effect due to the viscosity characteristic of the sound absorbing structure 10, the sound absorbing effect due to the cell structure of the sound absorbing structure 10 can be obtained. Noise reduction performance can be improved. Further, according to the present embodiment, by forming the sound absorbing cell 71 on the base material 80 made of a relatively high density viscous material, it is possible to reduce the weight of the sound absorbing structure 10 while ensuring the necessary vibration damping effect. Furthermore, it is possible to obtain the above-described excellent sound absorption effect.
[0022]
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.
[0023]
【The invention's effect】
Since the present invention is as described above, the following effects can be obtained. ADVANTAGE OF THE INVENTION According to this invention, while being able to achieve weight reduction of a base material, the damping effect by the base material of a viscous material can be ensured efficiently. Further, according to the present invention, the base material can have a sound absorbing function.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of a sound absorbing structure according to the present invention.
FIG. 2 is a cross-sectional view showing an installation state of the sound absorbing structure 10 of the present embodiment.
FIG. 3 is an explanatory view of a vibration damping action showing a deformation state of the sound absorbing structure 10 (base material 80) accompanying the deformation of the body panel.
4 is a cross-sectional view of an alternative embodiment of a sound absorbing structure according to the present invention when viewed from the same direction as in FIG.
FIG. 5 is an explanatory diagram of the sound absorption principle of the sound absorbing structure 10 according to the present invention.
FIG. 6 is a diagram showing the results of a sound absorption coefficient measurement test for the sound absorbing structure 10 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Sound absorption structure 71 Sound absorption cell 72 Side wall 76 Sound absorption material 80 Base material

Claims (1)

A plurality of substantially cylindrical space portions having both ends opened, and a base material made of a viscous material installed on an installation surface so that an opening at one end of the space portion is closed;
A sound-absorbing material covering the opening at the other end of the space,
The side wall of the base material that defines the space portion includes a flange surface at the opening side end of the space portion, and the flange surface is perpendicular to the side wall in a manner that the opening of the space portion remains. A sound-absorbing structure characterized in that it extends into the opening surface.

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