Double-Wall Structure

Abstract

A double-wall structure (1), comprising plate-like bodies (2) and (3) disposed oppositely to each other to form an inner room (4) therebetween, peripheral members (5) disposed so that the inner room (4) can be completely or approximately closed, and perforated plates (13) with a large number of holes (8) disposed between the plate-like bodies facing each other. The double-wall structure is characterized in that an air layer (A) is interposed between the perforated plates and the peripheral members. Thus, since the double-wall structure can suppress the deterioration of a sound reduction index for sound with specific frequencies, it can stably develop sound insulation performance for sound with the various frequencies.

Description

FIELD OF ART

The present invention relates to a double-wall structure.

BACKGROUND ART

It has heretofore been proposed to use a double-wall structure as automobile parts such as doors, hood and a trunk lid. For example, a conventional double-wall structure is a hollow box-like structure (bag structure) wherein an air space is formed between plate-like members opposed to each other at a predetermined distance, the air space being closed with side plates. In this conventional double-wall structure, however, when a sound wave of noise containing a sound component of a specific frequency is incident from below on the double-wall structure, there occurs resonance (mainly resonance in a direction parallel to the plate members) in the air space against the sound component. This causes an increase in amplitude of the upper plate-like member as a radiation plane and the resulting increase of a radiation sound deteriorates the sound insulating performance. Further, the conventional double-wall structure in question is characteristic in that in the state of resonance the sound pressure becomes high particularly in the vicinity of the side plates.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a double-wall structure capable of suppressing the deterioration of a sound transmission loss against a sound of a specific frequency and capable of displaying sound insulating performance stably against sounds of various frequencies.

The double-wall structure according to the present invention has the following basic configurations and effects.

In a first aspect of the present invention there is provided a double-wall structure having an air space formed between opposed plate-like members, the air space being closed completely or substantially, wherein a perforated plate having a large number of holes is disposed between the opposed plate-like members and a layer of air is interposed between the perforated plate and a circumferential member of the double-wall structure.

A sound absorbing mechanism is formed by the space between the perforated plate and the circumferential member.

With the sound absorbing mechanism, it is possible to effectively diminish a sound pressure near the circumferential members and suppress the resonance of the whole of the air space. Consequently, the sound pressure of the air space decreases and so does the vibration generating force on the radiation plane side, so that the vibration of the radiation plane decreases and it is possible to improve the sound transmission loss. Moreover, by adjusting the hole diameter, plate thickness and the ratio of holes in the perforated plate, as well as the thickness of the layer of air, it is also possible to obtain a configuration capable of suppressing an arbitrary frequency particularly effectively.

In the above double-wall structure, the perforated plate may be disposed so as to be inclined with respect to the circumferential member.

According to this configuration, it is possible to suppress resonance in every direction within the air space and hence possible to provide a double-wall structure superior in sound insulating performance.

In the above double-wall structure it is preferable that the perforated plate be provided in a plural number and that a layer of air be interposed between the plural perforated plates.

According to this configuration, the resonance in the air space can be suppressed to a greater extent by two layers of air and hence it is possible to provide a double-wall structure superior in sound insulating performance.

In the above double-wall structure, the perforated plate, may be disposed so that an end thereof is in contact with the circumferential member, and in the vicinity of the contacted end a hole may be formed in the circumferential member. Even in the presence of such a hole the air space of the double-wall structure is substantially kept closed.

Consequently, foreign matters such as dust and water getting into the air space can be discharged easily through the aforesaid hole.

It is preferable for the double-wall structure to have a partition member for partitioning the space formed between the perforated plate and the circumferential member.

With such a partition member, the sound insulating performance of the double-wall structure is improved.

In the above double-wall structure it is preferable that a large number of holes be formed in the partition member.

According to this configuration, the sound insulating performance of the double-wall structure is further improved.

In connection with the perforated plate used in the double-wall structure, at least one of its thickness, the hole diameter, the ratio of holes, and the thickness of the layer of air, may be made different between the spaces partitioned by the partition member. In the case where the thickness of the layer of air is not uniform in each of the partitioned spaces, a representative thickness (e.g., an average thickness) of the layer of air may be different between the spaces partitioned by the partition member. In the case where holes are formed in the partition member, at least one of the thickness of the member, the hole diameter and the ratio of the holes may be made different between the spaces partitioned by the partition member.

According to this configuration, the sound absorbing structure composed of the perforated plate and the circumferential member can display sound absorbing performance at a desired frequency and it is possible to provide a double-wall structure having particularly good sound insulating performance.

In the above double-wall structure it is preferable that a vibration damping/isolating member be disposed between the perforated plate and at least one of the opposed plate-like members.

According to this configuration it is possible to further improve the sound insulating performance of the double-wall structure.

In the above double-wall structure, a foil- or film-like member comprised of a single foil or film, or superimposed foils or films may be disposed in place of the perforated plate.

Also in this case, as in the above case, by a sound absorbing mechanism formed by the space (layer of air) between the foil- or film-like member and the circumferential member, it is possible to diminish the sound pressure near the circumferential member and hence possible to suppress resonance of the whole of the air space. Consequently, the sound pressure of the air space decreases and so does the vibration generating power on the radiation plane side, so that the vibration of the radiation plane decreases and it is possible to improve the sound transmission loss. As a result, it is possible to afford a structure superior in sound insulating performance.

In the above double-wall structure it is preferable that a large number of holes be formed in the foil- or film-like member.

According to this configuration it is possible to further improve the sound insulating performance of the double-wall structure.

In a second aspect of the present invention there is provided a double-wall structure having an air space formed between opposed plate-like members, the air space being closed completely or substantially, wherein a porous member is disposed near a circumferential member of the double-wall structure.

According to this configuration, the sound pressure near the circumferential member can be diminished by the porous member and it is possible to suppress resonance of the whole of the air space. Consequently, the sound pressure of the air space decreases and so does the vibration generating power on the radiation plane side, so that the vibration of the radiation plane diminishes. Further, coupled with the sound absorbing effect of the porous member itself, it is possible to improve the sound transmission loss. As a result, it is possible to afford a structure superior in sound insulating performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of embodiment 1-1 of the double-wall structure of the present invention.

FIG. 2 is a schematic diagram of the embodiment 1-1.

FIG. 3 is a schematic diagram of embodiment 1-2.

FIG. 4 is a schematic diagram of embodiment 1-3.

FIG. 5 is a schematic diagram of embodiment 1-4-1.

FIG. 6 is a schematic diagram of embodiment 1-4-2.

FIG. 7 is a schematic diagram of embodiment 2-1.

FIG. 8 is a schematic diagram of embodiment 2-2-1.

FIG. 9 is a schematic diagram of embodiment 2-2-2.

FIG. 10 is a schematic diagram of embodiment 2-3-1.

FIG. 11 is a schematic diagram of embodiment 2-3-2.

FIG. 12 is a schematic diagram of embodiment 2-4.

FIG. 13 is a schematic sectional diagram of embodiment 3-1-1.

FIG. 14 is a schematic sectional diagram of embodiment 3-1-2.

FIG. 15 is a schematic diagram of embodiment 4-1.

FIG. 16 is a schematic diagram of embodiment 5-1.

FIG. 17 is a graph showing a sound transmission suppressing effect of the embodiments 1-1 to 1-3 in comparison with that of a conventional example.

FIG. 18 is a graph showing a sound transmission suppressing effect of the embodiments 2-1, 2-2-1, 2-3-1 and 2-3-2 in comparison with that of a conventional example.

FIG. 19 is a graph showing a sound transmission suppressing effect of the embodiments 4-1 and 5-1 in comparison with that of a conventional example.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described hereinunder with reference to FIGS. 1 to 16.

First Embodiment

See FIGS. 1 to 6

A double-wall structure of embodiment 1-1 shown schematically in FIGS. 1 and 2 assumes a door as a part of a passenger car. This double-wall structure, indicated at 1, has plate-like members 2 and 3 disposed in parallel with each other and opposed to each other at a predetermined distance. The plate-like members 2 and 3 are each formed in a rectangular shape which is a little longer in one direction and an air space 4 is formed between the two opposed plate-like members 2 and 3. Four side plates (circumferential members) 5 are disposed so as to connect edges of the plate-like members 2 and 3 with one another, whereby the air space 4 is closed substantially. In other words, with the plate-like members 2, 3 as double walls and the side plates 5, the double-wall structure of this embodiment is constituted as a bag structure which encloses the air space 4.

In this embodiment, finely perforated rectangular plates 13 are disposed so as to partition the air space 4. Each of the finely perforated plates 13 is formed with a large number of fine through holes (fine holes 8). In this embodiment 1-1 four finely perforated plates 13 are disposed in a rectangular shape to partition the air space 4 of the double-wall structure 1 into two spaces which are a central space and a circumferential space close to the side plates 5. In other words, the finely perforated plates 13 are disposed in parallel with the side plates 5 respectively while leaving a predetermined spacing with respect to the four side plates 5 and a layer of air A having a thickness corresponding to the above predetermined spacing is interposed between the finely perforated plates 13 and the side plates 5. As the material of the finely perforated plates 13 there may be used, for example, iron, aluminum, resin, fiber-reinforced composite material, or paper.

In connection with the above configuration, a description will now be given about the case where the plate-like member 2 is vibrated under sound pressure by noise from below in FIG. 1. If the noise contains a sound component of a specific frequency, resonance tends to occur in the longitudinal or transverse direction of the air space 4 as a result of vibration of the plate-like member 2. In this resonance mode, the sound pressure becomes high particularly in the vicinity of the side plates 5. However, the high sound pressure near the side plates 5 is reduced effectively by a sound absorbing mechanism which is constituted by the finely perforated plates 13, the side plates 5 and the layer of air A present therebetween. Consequently, a resonance mode becomes difficult to be formed and resonance is suppressed. As a result, the vibration generating power of the upper plate-like member 3 as the radiation plane is deteriorated, so that the amplitude of the radiation plane is decreased and it is possible to diminish a drop of the sound transmission loss.

According to the configuration of embodiment 1-2 (FIG. 3), finely perforated plates 13 are installed near one of the four side plates 5 in the double-wall structure 1. The finely perforated plates 13 are disposed at an incline to the side plate 5 so as to be in a generally V shape in FIG. 3. As a result, layers of air A of a triangular shape are formed between the finely perforated plates 13 and the side plate 5. In this configuration, the layers of air A are located at corners where the sound pressure is high particularly in resonance mode, whereby the sound pressure at the corners can be reduced to a satisfactory extent. Besides, since the finely perforated plates 13 are disposed at an incline to the side plates 5, it is possible to suppress resonance in every direction within the air space 4 and hence possible to improve the sound insulating performance of the double-wall structure 1.

According to the configuration of embodiment 1-3 (FIG. 4), additional finely perforated plates 13 are used in the configuration of embodiment 1-2 (FIG. 3) and plural finely perforated plates 13 are disposed in parallel so that a gap is formed in the thickness direction between both finely perforated plates 13 facing each other. As a result, a layer of air B is interposed between both finely perforated plates 13 facing each other. That is, in this embodiment 1-3, there are formed two layers of air. One is the layer of air A formed between a finely perforated plate 13 and a side plate 5 and the other is the layer of air B formed between a pair of finely perforated plates 13 facing each other.

Consequently, the resonance suppressing effect can be made more outstanding.

According to the configuration of embodiment 1-4-1 (FIG. 5), a hole 10 is formed in the side plate 5 at a position near ends of the finely perforated plates 13, in addition to the configuration (FIG. 3) of embodiment 1-2 wherein the finely perforated plates 13 are disposed at an incline. Foreign matters such as dust and water getting into the air space 4 can be discharged easily through the hole 10. The hole 10 is formed in the side plate 5 at a position not confronting the layer of air A and therefore the sound absorbing function of the layer of air A is not obstructed. In the construction of embodiment 1-4-1 (FIG. 5), the hole 10 is formed in the side plate 5 in a state in which ends of the finely perforated plates 13 are put in contact with the side plate 5. However, it is not always necessary that the ends of the finely perforated plates 13 be brought into contact with the side plate 5. That is, even in a configuration wherein the ends of the finely perforated plates 13 are spaced apart from the side plate 5, if the hole 10 is formed in the side plate 5 at a position not confronting the finely perforated plates 13, both the sound absorbing function of the layer of air A and the discharge of foreign matters such as dust and water getting into the air space 4 can be made compatible with each other. There may be adopted such a configuration as embodiment 1-4-2 (FIG. 6) wherein finely perforated plates 13 are disposed in a generally W shape and two holes 10 are formed. Thus, the shape of inclination of the finely perforated plates 13 and the number of holes 10 are not limited.

Second Embodiment

See FIGS. 7 to 12

According to the configuration of embodiment 2-1 (FIG. 7), which is a modification of embodiment 1-1 (FIGS. 1 and 2), plural plate-like partition members 9 are provided so as to provide connections between side plates 5 and finely perforated plates 13. With the partition members 9, the layer of air A interposed between the side plates 5 and the finely perforated plates 13 is partitioned in both longitudinal and transverse directions of the double-wall structure 1. It is preferable that the partition members 9 be disposed at positions where a resonance phenomenon occurring in the extending direction of the layer of air between the finely perforated plates 13 and the side plates 5 is difficult to occur at a desired frequency. More specifically, the partition members 9 are disposed at a spacing not coinciding with an integer multiple of a half of the wavelength for the frequency intended to improve the sound insulating performance. As a result, it is possible to enhance the sound absorbing performance of sound absorbing mechanism constituted by the layer of air A between the finely perforated plates 13 and the side plates 5. In this configuration, in order to enhance the sound absorbing performance at a desired frequency, the hole diameter of the fine hole 8 or the ratio of holes, or the thickness of each finely perforated plate 13, may be made different among the spaces partitioned by the partition members 9. The partition members 9 are not always required to be plate-like members. For example, the partition members 9 may each be constituted by a reinforcing foaming agent formed in a lump shape.

The configuration of embodiment 2-2-1 (FIG. 8) corresponds to a combination of embodiment 1-2 (FIG. 3) and embodiment 2-1 (FIG. 7). In this configuration, the thickness (average thickness) of the layer of air A formed between the finely perforated plates 13 and the side plates 5 is made different among the spaces enclosed with the partition members 9. As in embodiment 2-2-2 (FIG. 9), like the foregoing embodiment 1-4-1, a hole 10 may be formed in a side plate 5.

The configuration of embodiment 2-3-1 (FIG. 10) corresponds to a combination of embodiment 1-3 (FIG. 4) and embodiment 2-2-1 (FIG. 8). Partition plates 9 are installed so as to partition each of two layers of air A and B.

According to the configuration of embodiment 2-3-2 (FIG. 11), which is a modification of embodiment 2-1 (FIG. 7), a plurality of finely perforated plates 13 are disposed in the thickness direction and a layer of air B is interposed therebetween.

According to the configuration of embodiment 2-4 (FIG. 12), a large number of fine holes 8 are formed in partition plates 9 of embodiment 2-1 (FIG. 7).

Third Embodiment

See FIGS. 13 and 14

FIG. 13 is a sectional view of a double-wall structure 1 according to embodiment 3-1-1. As shown in FIG. 13, there is a case where a finely perforated plate 13 cannot contact the plate-like member 2 on the vibration generating side and the plate-like member 3 on the opposite side in a completely airtight manner and certain slits are formed. The absence of such slits is preferred, so in this embodiment a vibration damping/isolating member 16 formed of, for example, rubber or urethane is installed in each of the portions corresponding to the slits. As a result, it is possible to enhance the sound absorbing performance of sound absorbing mechanism. As shown in embodiment 3-1-2 (FIG. 14), the vibration damping/isolating member 16 may be disposed between the finely perforated plate 13 and only one of the two plate-like members 2 and 3. If the above slits are fine slits, the vibration damping/isolating member 16 may be omitted and it is possible to let the slits themselves exhibit a sound absorption function.

Fourth Embodiment

See FIG. 15

In embodiment 4-1 (FIG. 15), the finely perforated plates 13 used in embodiment 2-2-1 (FIG. 8) are each substituted for a superimposed foil- or film-like members 14. In this embodiment 4-1, a large number of fine holes 8 are formed in the foil- or film-like members 14 in order to improve the sound absorbing performance, provided the fine holes 8 may be omitted. A single such foil- or film-like member may be used without using such foils- or films in a superimposed form.

Fifth Embodiment

See FIG. 16

In the configuration of embodiment 5-1 (FIG. 16), two porous members 15,15 are disposed near side plates 5 in the double-wall structure 1. As the material of the porous members 15 there may be used not only glass wool or felt but also, for example, PET fiber, polyurethane or open-cell foamed material. In this embodiment 5-1 the porous members 5 are formed in a triangular shape and are disposed at two corners on one side of the air space 4 so as to contact the side plates 5. The shape and layout of the porous members 15 are not limited those described above. In this configuration, sound is absorbed particularly at positions (near the side plates 5, especially at and near the corners of the air space 4) where the sound pressure is high in resonance, whereby the sound pressure in resonance of the entire air space 4 can be reduced and it is possible to improve the sound transmission loss.

The following experiment was conducted to check the effectiveness of the above embodiments. First, the double-wall structures 1 having the configurations of embodiments 1-1 to 1-3, 2-1, 2-2-1, 2-3-1, 2-3-2, 4-1 and 5-1 were each positioned between a sound source chamber and a sound receiving chamber in a reverberant chamber comprising both such chambers. Then, on the basis of JIS A 1416 (ISO 140-3, 140-1), a certain noise was generated from one side of the double-wall structures 1 and sound pressures were measured on both sides of the double-wall structures 1 with use of noise meters to determine a sound transmission loss.

Experiment Results (see FIGS. 17 to 19)

The results of the experiment are shown in FIGS. 17 to 19. In the graphs of these figures there are also shown the results of an experiment conducted for a conventional structure. As shown in the graph of FIG. 17 it is seen that in the configurations of embodiments 1-1 to 1-3, in comparison with the conventional example, the formation of a resonance mode is suppressed by the finely perforated plates 13, whereby the sound transmission loss is improved and so is the sound insulating performance. It is seen that also in the configurations (FIG. 18) of embodiments 2-1, 2-2-1, 2-3-1 and 2-3-2 and the configurations (FIG. 19) of embodiments 4-1 and 5-1 the sound transmission loss is improved and so is the sound insulating performance by the resonance mode suppressing function of the finely perforated plates 13 and the porous members 15.

Although preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the above embodiments, but the invention may be practiced in various modified forms.

For example, the double-wall structure of the present invention is applicable not only to the doors of a passenger car but also to, for example, the hood and trunk lid. As to the shape of the plate-like members 2 and 3, it goes without saying that no limitation is made to the rectangular shape described above, but that various changes may be made in accordance with the shape of a part required.

The direction and degree of the sound pressure mode which causes resonance differ depending on various circumstances such as the shape of the double-wall structure 1 and a positional relation thereof to a noise source. Therefore, the direction, thickness and the number of the finely perforated plates 13, as well as the number, diameter, shape and ratio of the fine holes 8, may be determined suitably taking the above circumstances into account. That is, where and how many the finely perforated plates 13 and the porous members 15 are to be provided may be determined optimally in consideration of a resonance mode within the air space 4 of the double-wall structure 1 caused by a presumed noise. The fine holes 8 formed in the finely perforated plates 13, partition members 9 and foil- or film-like members 14 in the above plural embodiments may be increased in diameter into holes of a size not regarded as “fine” holes. In case of applying the double-wall structure 1 to the doors of a passenger car, it is presumed that various devices and reinforcing members are disposed in the air space 4, therefore, the finely perforated plates 13 and the porous members 15 may be disposed at sidestepped positions.

It is optional whether the finely perforated plates 13 and the porous members 15 are to be disposed for all or a part of the side plates 5. For example, in the case of the finely perforated plates 13 used in embodiment 1-2 (FIG. 3), the layer of air A is interposed between them and only one of the four side plates 5, the finely perforated plates 13 may be disposed so as to surround the whole circumference of the air space 4.

Although in the above plural embodiments the finely perforated plates 13 and the partition plates 9 are installed perpendicularly to the plate-like members 2 and 3, no limitation is made thereto. The finely perforated plates 13 and the partition members 9 may be installed at an incline to the plate-like members 2 and 3.

As to the application of the above embodiments, no limitation is made to the case where the embodiments are applied each independently, but plural such embodiments may be applied in combination.

Claims

1. A double-wall structure comprising:

a pair of plate-like members disposed in opposition to each other to form an air space therebetween;

a circumferential member disposed in such a manner that the said air space is closed completely or substantially; and

a perforated plate disposed between the said opposed plate-like members in a direction intersecting the plate-like members, the said perforated plate having a multitude of holes,

wherein a layer of air is interposed between the said perforated plate and the said circumferential member.

2. A double-wall structure according to claim 1, wherein the said perforated plate is disposed at an incline to the said circumferential member.

3. A double-wall structure according to claim 1, wherein the said perforated plate is provided in a plural number and a layer of air is interposed between the plural perforated plates.

4. A double-wall structure according to claim 2, wherein the said perforated plate is provided in a plural number and a layer of air is interposed between the plural perforated plates.

5. A double-wall structure according to claim 2, wherein the said perforated plate is disposed so that an end thereof is in contact with the said circumferential member, and in the vicinity of the contacted end a hole is formed in the said circumferential member.

6. A double-wall structure according to claim 1, further comprising a partition member for partitioning the space between the said perforated plate and the said circumferential member.

7. A double-wall structure according to claim 6, wherein a multitude of holes are formed in the said partition member.

8. A double-wall structure according to claim 6, wherein at least one of a thickness of the said perforated plate, a thickness of the said partition member, a diameter or a ratio of the said holes formed in the said perforated plate or the said partition member, and a thickness of the layer of air interposed between the said perforated plate and the said circumferential member, is made different between the spaces partitioned by the said partition member.

9. A double-wall structure according to claim 1, wherein a vibration damping/isolating member is disposed between the said perforated plate and at least one of the said opposed plate-like members.

10. A double-wall structure according to any of claim 1, wherein a foil- or film-like member comprised of a single foil or film, or superimposed foils or films is disposed in place of the said perforated plate.

11. A double-wall structure according to claim 10, wherein a multitude of holes are formed in the said foil- or film-like member(s).

12. A double-wall structure comprising:

a pair of plate-like members disposed in opposition to each other to form an air space therebetween;

a circumferential member disposed in such a manner that the said air space is closed completely or substantially; and

a porous member disposed in the vicinity of the said circumferential member.

13. A double-wall structure according to claim 4, wherein the said perforated plate is disposed so that an end thereof is in contact with the said circumferential member, and in the vicinity of the contacted end a hole is formed in the said circumferential member.

14. A double-wall structure according to claim 7, wherein at least one of a thickness of the said perforated plate, a thickness of the said partition member, a diameter or a ratio of the said holes formed in the said perforated plate or the said partition member, and a thickness of the layer of air interposed between the said perforated plate and the said circumferential member, is made different between the spaces partitioned by the said partition member.