Vehicle cabin soundproofing structure

Abstract

To provide a vehicle interior soundproof structure that can improve soundproof performance in a middle frequency band.SOLUTION: A vehicle interior soundproof structure comprises a partition member 12 as a main body that partitions a vehicle interior, a sound absorption layer 14 having a number of voids therein, a non-ventilation layer 30 made of non-ventilation materials and a compressed fiber layer 32A formed primarily of compressed fiber aggregate. Strength of adhesion between the compressed fiber layer 32A and the non-ventilation layer 30 is set lower than strength of adhesion between the non-ventilation layer 30 and the sound absorption layer 14, so that resonance caused by a resonance transmission phenomenon and resonance caused by extension of the sound absorption layer 14 cause antiresonance therebetween (refer to 10A), which can reduce insertion loss in a middle frequency band to improve soundproof performance in the middle-frequency band.SELECTED DRAWING: Figure 14

Description

[Technical field]

[0001] The present invention relates to a vehicle compartment soundproofing structure for suppressing noise from outside a vehicle compartment. [Background technology]

[0002] Conventionally, soundproofing structures are provided in the parts that divide the vehicle compartment so that noise from the outside of the vehicle or the drive unit of the vehicle is not transmitted to the inside of the vehicle compartment. As the soundproofing structure, for example, as in the automobile trim part described in the following Patent Document 1, a structure having the characteristics of a spring mass system (spring mass system), specifically, a structure in which a sound absorbing layer (decoupling layer) as a spring element, a mass element consisting of a non-breathable layer (impermeable barrier layer) and a compressed fiber layer (porous fiber layer) are laminated in order from the panel side to the inside of the panel that is the main part that divides the vehicle compartment, is often seen. Note that the automobile trim part described in Patent Document 1 aims to soundproof a frequency band between a relatively low frequency noise of 50 Hz to 500 Hz and a high frequency noise of more than 2 kHz, and it is disclosed that it is possible to exhibit high sound insulation performance in that frequency band by adjusting the Young's modulus of the porous fiber layer. In addition, the following Patent Document 2 discloses that when priority is given to sound absorption, the thickness of the porous fiber layer with the Young's modulus adjusted is made larger than when priority is given to sound insulation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2013-522094 [Patent Document 2] Special Publication No. 2013-521190 Summary of the Invention [Problem to be solved by the invention]

[0004] In the soundproofing structures having the configurations described in Patent Documents 1 and 2, the barrier layer and the porous fiber layer are firmly bonded to each other, and both of them function as mass elements. As described above, the soundproofing structure described in Patent Document 1 has high sound insulation properties in a relatively high frequency band and a higher frequency band. In such a configuration, a phenomenon that the sound absorbing layer as a spring element transmits relatively low frequency sounds (about 200 Hz to 500 Hz) from the main member that divides the vehicle compartment to the mass layer, that is, a so-called resonance transmission phenomenon (resonance), has conventionally occurred, and deterioration of soundproofing performance in the frequency range of 200 Hz to 630 Hz (hereinafter sometimes referred to as the "mid-frequency band") has become a problem.

[0005] The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a vehicle compartment soundproofing structure that can improve soundproofing performance in the mid-frequency band. [Means for solving the problem]

[0006] In order to solve the above problems, the vehicle compartment soundproofing structure of the present invention comprises: A vehicle cabin soundproofing structure for suppressing noise from outside a vehicle cabin, comprising: A partition member that serves as a main component for partitioning the vehicle compartment; A sound absorbing layer disposed on the indoor side of the partition member and having a large number of voids therein; A non-breathable layer arranged on the indoor side of the sound absorbing layer and made of a non-breathable material; a compressed fiber layer disposed on the indoor side of the non-breathable layer and formed mainly of a compressed fiber aggregate, The bonding strength between the compressed fiber layer and the air-impermeable layer is lower than the bonding strength between the air-impermeable layer and the sound absorbing layer.

[0007] In general, the dashboard, floor, and the like of a vehicle are configured such that soundproofing materials are arranged on the interior side of partition members such as panels that are the main components that partition the vehicle cabin. When considering the soundproofing performance of a vehicle cabin, a spring-mass system model may be used. Specifically, the spring element corresponds to a part arranged on the interior side of a rigid partition member and formed of a low-density material such as uncompressed felt or foam material, and the mass element corresponds to a part formed of a high-density impermeable material provided on the interior side of the spring element, and a spring-mass system model is used. In addition, when the spring-mass system and the rigid part corresponding to the partition member are included, it has the characteristics of a hollow double wall. The soundproofing performance of the vehicle cabin is evaluated, for example, using the insertion loss, which is the difference between the sound pressure level when there is no soundproofing material (spring-mass system) and the sound pressure level when there is a soundproofing material. Generally, the compressed fiber layer is firmly bonded to the non-breathable layer. In such cases, both the non-breathable layer and the compressed fiber layer act as mass elements, causing resonance (resonant transmission phenomenon) in the mid-frequency range and reducing the insertion loss.

[0008] On the other hand, in the vehicle cabin soundproofing structure of this configuration, the adhesive strength between the compressed fiber layer and the non-air-permeable layer is weaker than that between the non-air-permeable layer and the sound-absorbing layer. In other words, since the non-air-permeable layer and the sound-absorbing layer are relatively firmly bonded to each other, not only resonance due to the resonant transmission phenomenon, which is a characteristic of the hollow double wall described above, occurs between the partition member and the non-air-permeable layer (hereinafter, may be referred to as "air spring resonance"), but also resonance due to the expansion and contraction of the sound-absorbing layer in the thickness direction (hereinafter, may be referred to as "sound-absorbing layer expansion resonance"). The frequency of this sound-absorbing layer expansion resonance is in the low frequency band (315 Hz or less) due to the influence of the relatively small Young's modulus of the sound-absorbing layer. And, due to the existence of the sound-absorbing layer expansion resonance, whose frequency band is close to the resonant frequency of the air spring resonance, anti-resonance occurs in which the phase is reversed between the two resonant frequencies, and the insertion loss in the mid-frequency band can be improved. Furthermore, since the adhesive strength between the compressed fiber layer and the non-air-permeable layer is relatively weak, sound is less likely to be transmitted from the non-air-permeable layer to the compressed fiber layer. In detail, resonance occurs easily between the partition member and the non-breathable layer alone, and the frequency of the resonance shifts to the high frequency range due to the smaller mass layer. This improves the insertion loss in the mid-frequency range, that is, improves the soundproofing performance in the mid-frequency range. Incidentally, if the adhesive strength of the compressed fiber layer to the non-breathable layer is weakened, the soundproofing performance in the high frequency range will be lower than when the adhesive strength of the compressed fiber layer to the non-breathable layer is secured.

[0009] In addition, in the vehicle cabin soundproofing structure of this configuration, "the adhesive strength is weakened" means, for example, that while the non-breathable layer and the sound absorbing layer are entirely bonded, the compressed fiber layer and the non-breathable layer are only partially bonded in the form of dots or lines, or that the amount of adhesive applied is reduced or the type of adhesive is changed, and is not limited to cases where the compressed fiber layer and the non-breathable layer are bonded, but also includes cases where the adhesive strength is zero, that is, where there is no adhesion.

[0010] The "compressed fiber layer" in the vehicle cabin soundproofing structure of this configuration is a fiber aggregate such as felt or glass wool made of natural or synthetic fibers. For example, a so-called compressed felt can be used, which is made by thinly piling up wool fibers, applying heat and alkali to the piled fibers, squeezing and kneading them, and entangling them with each other using only the fulling properties of the wool fibers to form a cloth. It is also possible to use a porous fiber layer with an adjusted Young's modulus as described in the above-mentioned Patent Document 1.

[0011] The "sound absorbing layer" is a so-called silencer, and can be made of a fiber aggregate having many voids or a porous synthetic resin such as urethane foam. The thickness of this sound absorbing layer is preferably 3mm to 60mm. Furthermore, the "non-breathable layer" can be formed in the form of a single layer or multiple layers of film made of polyethylene, polypropylene, polyester, polyamide, ionomer resin, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polystyrene, EVA, EVOH, EMMA, etc.

[0012] In the above-mentioned configuration, the breathable layer may have a weight per unit area of ​​15 gsm or more and 400 gsm or less, desirably 50 gsm or more and 200 gsm or less.

[0013] In the vehicle cabin soundproofing structure having this configuration, the basis weight of the non-air-permeable layer is limited to a relatively small value. The smaller the basis weight of the non-air-permeable layer, the more the resonance frequency (resonance transmission frequency) of the resonance transmission phenomenon shifts to the high frequency side. Therefore, with the vehicle cabin soundproofing structure having this configuration, it is possible to further improve the soundproofing performance in the mid-frequency band (especially, 315 Hz to 500 Hz).

[0014] In the above configuration, the compressed fiber layer may have a mass per unit area of ​​300 gsm or more and 1500 gsm or less, desirably 600 gsm or more and 1000 gsm or less.

[0015] In the vehicle compartment soundproofing structure having this configuration, the basis weight of the compressed fiber layer is limited, and sufficient soundproofing performance can be ensured without increasing the thickness of the compressed fiber layer.

[0016] In the above-described configuration, the first region may be configured such that the air-impermeable layer and the compressed fiber layer are not bonded to each other.

[0017] The vehicle cabin soundproofing structure having this configuration can prevent the resonance of the non-breathable layer due to the resonance transmission phenomenon from being transmitted to the compressed fiber layer, and can effectively improve the soundproofing performance in the mid-frequency range. Effect of the Invention

[0018] According to the present invention, it is possible to provide a vehicle cabin soundproofing structure capable of improving soundproofing performance in the mid-frequency band. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a perspective view showing a floor panel of a vehicle in which a vehicle floor structure according to an embodiment of the present invention is used; [Diagram 2] Plan view of the floor panel shown in Figure 1 [Diagram 3] FIG. 3 is a cross-sectional view showing a schematic floor structure in the first area shown in FIG. 2; [Figure 4] FIG. 3 is a cross-sectional view showing a schematic floor structure in the second area shown in FIG. 2 . [Diagram 5] FIG. 1 is a cross-sectional view showing a first verification floor structure; [Figure 6] FIG. 13 is a cross-sectional view showing a second verification floor structure. [Figure 7] FIG. 13 is a cross-sectional view showing a schematic diagram of a floor structure of a comparative example. [Figure 8] Spring-mass system model of the floor structure in Figures 6 and 7 [Figure 9] Figure 5. Spring-mass system model of the floor structure [Figure 10] Graph showing the relationship between frequency and insertion loss for each floor structure [Figure 11]A graph showing the relationship between 1 / 3 octave frequency and acoustic sensitivity in a vehicle floor structure using two test floor structures and a floor structure of a comparison example. [Figure 12] A graph showing the relationship between the overall thickness of the floor structure and the resonant frequency [Figure 13] Figure 6. Spring-mass system model of the floor structure [Figure 14] Graph showing the relationship between frequency and insertion loss for each floor structure [Figure 15] Graph for explaining change in insertion loss when the mass per unit area of ​​the non-breathable layer is changed DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The vehicle compartment soundproofing structure of the present invention is used in the structure of the floor of a vehicle (automobile), which is a vehicle, and the vehicle floor structure 10 will be described below. The vehicle floor structure 10 is composed of a vehicle floor panel 12 shown in Figures 1 and 2, and a floor silencer 14 and a carpet 16, which are stacked on top of the vehicle floor panel 12 and will be described in detail later. The floor panel 12 is a partitioning member that serves as the main partitioning member of the floor surface of the vehicle compartment, which is the vehicle compartment, and is made of metal, for example, and has a generally rectangular shape that is long in the front-to-rear direction of the vehicle in a plan view.

[0021] As shown in FIG. 1 and FIG. 2, the floor panel 12 has a floor tunnel 20 formed in the center of the vehicle width direction, which extends in the vehicle front-rear direction and bulges upward. In addition, the vehicle is provided with reinforcing members (two in this embodiment) extending in the vehicle width direction, and the floor panel 12 also has bulging portions 22, 23 bulging upward in a shape along the reinforcing members so that the two reinforcing members fit together. In addition, the driver's seat and the passenger's seat are arranged above the two bulging portions 22, 23 in the vehicle. In addition, the floor panel 12 has a standing wall portion 24 formed at the rear end, and the rear seat is arranged behind the standing wall portion 24 in the vehicle. In other words, in the floor panel 12, the area Aa in front of the bulging portion 22 on the front side and the area Ab between the standing wall portion 24 and the bulging portion 23 on the rear side correspond to the foot pool portion, which is the foot area of ​​a seated occupant.

[0022] In the vehicle floor structure 10 of this embodiment, a first floor structure 10A, which is the floor structure in the areas Aa, Ab that serve as the foot pools and the area Ac between the two bulging parts 22, 23, and a second floor structure 10B, which is the floor structure in a portion of the floor panel 12 other than the areas Aa, Ab, Ac (area A2 described below), are different structures. Below, the first floor structure 10A shown in Fig. 3 and the second floor structure 10B shown in Fig. 4, and the differences between the first floor structure 10A and the second floor structure 10B will be described in detail.

[0023] A floor silencer 14 is laid on the floor panel 12. The floor silencer 14 may be a fiber aggregate having many voids or a porous synthetic resin such as urethane foam. In this embodiment, the floor silencer 14 is a felt made of thermoplastic resin fibers. The floor silencer 14 is disposed on the indoor side of the floor panel 12 as a partition member, and functions as a sound absorbing layer having many voids inside. The above-mentioned foot pool areas Aa and Ab of the floor structure 10 are easily exposed, unlike the parts covered with mass parts such as seats and a center console on the floor structure 10. In order to improve the insertion loss of the foot pool areas Aa and Ab, for example, it is desirable to make the thickness of the floor silencer 14 larger than that of other parts. Therefore, the thickness of the floor silencer 14 is made larger in the parts (first floor structure 10A) corresponding to the above-mentioned foot pool areas Aa and Ab and the area Ac between the two bulging parts 22 and 23 than in other parts. That is, the thickness of the portion 14A of the floor silencer 14 corresponding to the first floor structure 10A is made larger than the thickness of the portion 14B corresponding to the second floor structure 10B. In this embodiment, the thickness of the portion 14A corresponding to the first floor structure 10A is about 20 mm, and the thickness of the portion 14B corresponding to the second floor structure 10B is about 10 mm. The thickness of the floor silencer 14 is preferably 3 mm to 60 mm in order to absorb the sound transmitted from the outside of the floor panel 12.

[0024] The vehicle floor structure 10 of this embodiment is characterized by the difference in the structure of the carpet 16 between the first floor structure 10A and the second floor structure 10B. Therefore, in evaluating the soundproofing performance of the first floor structure 10A and the second floor structure 10B, the thickness of the floor silencer in each structure is treated as being the same, and is shown as the same thickness in Figures 3 and 4.

[0025] A carpet 16 is laid on the upper side of the floor silencer 14. As shown in Figs. 3 and 4, the carpet 16 is formed by laminating an air-impermeable layer 30, a compressed fiber layer 32, and a surface layer 34 in this order from the floor silencer 14 side (the outdoor side). The air-impermeable layer 30 and the compressed fiber layer 32 are bonded together with an adhesive to form an adhesive layer 38. An adhesive layer 36 is formed only partially between the compressed fiber layer 32 and the surface layer 34, as will be described in detail later. The carpet 16 is also bonded to the floor silencer 14 with an adhesive to form an adhesive layer 40.

[0026] The non-breathable layer 30 is a film made of a non-breathable material, and is located on the indoor side of the floor silencer 14, which is a sound absorbing layer, and is intended to mainly insulate sound from the outdoor side. The non-breathable layer 30 may be formed as a single-layer or multi-layer film made of, for example, polyethylene, polypropylene, polyester, polyamide, ionomer resin, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polystyrene, EVA, EVOH, EMMA, etc. The non-breathable layer 30 has a mass per unit area of ​​15 gsm to 400 gsm, preferably 50 gsm to 200 gsm. In this embodiment, the non-breathable layer 30 is a single-layer film made of polyethylene, and has a mass per unit area of ​​100 gsm.

[0027] The compressed fiber layer 32 is laminated on the interior side of the non-breathable layer 30 for the purpose of absorbing and insulating sound. The compressed fiber layer 32 can be, for example, a so-called compressed felt made by felting natural fibers, synthetic fibers, or a mixture of these fibers with binder fibers. The compressed felt is preferably made of recycled fiber materials such as recycled cotton, or other recycled fibers such as polyester, so-called synthetic fiber recycled material. Specifically, the compressed fiber layer 32 can be, for example, a material made by mixing a low-melting point polyester as a binder into a synthetic fiber recycled material, and then heating and forming the accumulated material into a desired mat shape by pressing. It is considered that the thicker the compressed fiber layer 32, the better the soundproofing performance. However, since the vehicle interior space is limited, it is desirable to make the thickness of the compressed fiber layer 32, in other words, the mass per unit area, small. In view of this, the mass per unit area of ​​the compressed fiber layer 32 can be set to 300 gsm or more and 1500 gsm or less, preferably 600 gsm or more and 1000 gsm or less. In this embodiment, the mass per unit area of ​​the compressed fiber layer 32 is set to 800 gsm in both the first floor structure 10A and the second floor structure 10B.

[0028] The compressed fiber layer 32 is different between the first floor structure 10A and the second floor structure 10B. Specifically, the first compressed fiber layer 32A, which is the compressed fiber layer 32 in the first floor structure 10A, is a general compressed felt manufactured by the above-mentioned method, whereas the second compressed fiber layer 32B, which is the compressed fiber layer 32 in the second floor structure 10B, has an adjusted Young's modulus and, as will be described in detail later, has improved soundproofing performance in the high frequency range (1000Hz to 8000Hz).

[0029] The surface layer 34 is not particularly limited, and various materials such as Dior surface, velour surface, plain surface, tufted carpet surface, etc. can be used. In this embodiment, Dior surface is used, and the weight per unit area is 350gsm. This surface layer 34 is the same in both the first floor structure 10A and the second floor structure 10B.

[0030] The adhesive layers 36, 38, 40 may be formed from a liquid adhesive or a solid adhesive such as a film or tape. The adhesive layer 38 between the compressed fiber layer 32 and the skin layer 34 is bonded in the same manner in both the first floor structure 10A and the second floor structure 10B. The adhesive layer 38 is not essential and may be non-adhesive.

[0031] On the other hand, the adhesive layer 36 between the non-breathable layer 30 and the compressed fiber layer 32 has different adhesive strengths in the first floor structure 10A and the second floor structure 10B. Specifically, in the second floor structure 10B, an adhesive layer 36 is formed between the non-breathable layer 30 and the second compressed fiber layer 32B, whereas in the first floor structure 10A, the non-breathable layer 30 and the first compressed fiber layer 32A are not bonded. In other words, the adhesive strength between the non-breathable layer 30 and the first compressed fiber layer 32A in the first floor structure 10A is set to 0. However, the non-breathable layer 30 and the first compressed fiber layer 32A in the first floor structure 10A are not limited to being non-adhesive. For example, the adhesive layer 36 is fully bonded in that area as shown in Fig. 12, while the adhesive layer 102 is partially bonded in dots or lines as shown in the floor structure 100 in Fig. 5, so that the adhesive strength between the non-breathable layer 30 and the first compressed fiber layer 32A in the first floor structure 10A is reduced. When the non-breathable layer 30 and the first compressed fiber layer 32A in the first floor structure 10A are bonded in this way, the method of reducing the adhesive strength is not particularly limited, and for example, the amount of liquid adhesive applied can be reduced compared to the adhesive layer 36, or a different type of adhesive can be used.

[0032] The first floor structure 10A is structured such that the bonding strength between the first compressed fiber layer 32A and the non-breathable layer 30 is lower than the bonding strength between the non-breathable layer 30 and the floor silencer 14, which is a sound absorbing layer. In other words, this first floor structure 10A is the vehicle compartment soundproofing structure of the present invention. In this embodiment, the first compressed fiber layer 32A and the non-breathable layer 30 are not bonded to each other, but the present invention is not limited thereto, and it is sufficient that the bonding strength between the first compressed fiber layer 32A and the non-breathable layer 30 is lower than the bonding strength between the non-breathable layer 30 and the floor silencer 14 by the above-mentioned method.

[0033] As described above, in the vehicle floor structure 10, the regions Aa, Ab, and Ac are defined as the first region A1, which is a region where the adhesive strength between the non-air-permeable layer 30 and the compressed fiber layer 32 is relatively low, and the other regions except the regions Aa, Ab, and Ac are defined as the second region A2, which is a region where the adhesive strength between the non-air-permeable layer 30 and the compressed fiber layer 32 is relatively high. In the following, the soundproofing performance in each of the first region A1 and the second region A2 will be described. First, in order to explain the difference in soundproofing performance due to the difference in adhesive strength between the non-air-permeable layer 30 and the compressed fiber layer 32, a structure in which the carpet 16 and the floor silencer 14 are not bonded, in other words, a structure in which the non-air-permeable layer 30 and the floor silencer 14 are not bonded, will be described. Specifically, as shown in Fig. 5, a first verification floor structure 100 in which the non-air-permeable layer 30 and the floor silencer 14 are not bonded and the adhesive strength between the non-air-permeable layer 30 and the first compressed fiber layer 32A is relatively low, and as shown in Fig. 6, a second verification floor structure 120 in which the non-air-permeable layer 30 and the floor silencer 14 are not bonded and the adhesive strength between the non-air-permeable layer 30 and the second compressed fiber layer 32B is relatively high will be used for explanation. Furthermore, as a comparative example, a conventional vehicle floor structure 140 will also be used. Below, before explaining the difference in sound insulation performance due to the difference in adhesive strength between the non-air-permeable layer 30 and the compressed fiber layer 32, a schematic structure of the vehicle floor structure 140 of the comparative example will be explained with reference to Fig. 7.

[0034] The vehicle floor structure 140 of the comparative example is composed of a floor silencer 142 and a carpet 144, similar to the vehicle floor structure 10 of this embodiment. The floor silencer 142 is similar to the floor silencer 14 of this embodiment. The carpet 144 is composed of, in order from the lower layer side (floor silencer 142 side), a backing layer (non-breathable layer) 150 made of polyethylene, a compressed fiber layer 152 made of compressed felt, and a surface layer 154 which is a Deloitte surface layer, and adhesive layers 156, 158 are formed between each layer by adhesive, so that the layers are firmly bonded to each other. In other words, it is similar to the second verification floor structure 120 shown in FIG. 6.

[0035] However, the backing layer 150 of the carpet 144 has a larger mass per unit area of ​​600 gsm than the non-breathable layer 30 in this embodiment. Also, the compressed fiber layer 152 is made of compressed felt like the first compressed fiber layer 32A in this embodiment, but has a smaller mass per unit area of ​​300 gsm than the compressed fiber layer 32 in this embodiment.

[0036] The soundproofing performance of each of the first verification floor structure 100, the second verification floor structure 120, and the floor structure of the comparative example 140 was evaluated by performing an actual vehicle experiment using a taste piece and performing a trial calculation using simulation software. When performing this simulation, a spring-mass system model shown in Fig. 8 and Fig. 9 was used. In detail, the second verification floor structure 120 and the floor structure of the comparative example 140 are shown in Fig. 8, and the first verification floor structure 100 is shown in Fig. 9. In addition, the evaluation of the soundproofing performance this time was performed on a structure excluding the skin layer 34. The evaluation of the soundproofing performance of each floor structure was performed using the insertion loss, which is the difference between the sound pressure level when there is no soundproofing material (spring-mass system) and the sound pressure level when there is a soundproofing material.

[0037] In the spring-mass system model, the spring element is a part that is arranged on the indoor side of the rigid floor panel 12 and is made of a low-density material such as uncompressed felt or foam material, and in both structures, corresponds to the floor silencer 14, 142. The mass element is a part that is arranged on the indoor side of the spring element and is made of a high-density impermeable material. That is, in the second verification floor structure 120, the second compressed fiber layer 32B is firmly adhered to the non-breathable layer 30 by the adhesive layer 36, and the non-breathable layer 30 and the second compressed fiber layer 32B correspond to the mass element. The floor structure 140 of the comparative example is also similar to the second verification floor structure 120, and the backing layer 150 and the compressed fiber layer 152, which are non-breathable layers, correspond to the mass element.

[0038] As shown in FIG. 10, when comparing the insertion loss of the floor structure 140 of the comparative example with the insertion loss of the second verification floor structure 120, the second verification floor structure 120 exhibits higher soundproofing performance in the high frequency band (1000 Hz to 8000 Hz) than the floor structure 140 of the comparative example due to the function of the second compressed fiber layer 32B with an adjusted Young's modulus. On the other hand, these floor structures have a hollow double-wall characteristic when including the spring mass system and the floor panel 12, which is a rigid part, and a phenomenon called a resonance transmission phenomenon (resonance) occurs between the floor panel 12 and the mass element, in which a relatively low frequency sound (about 200 Hz to 500 Hz) is transmitted to the mass layer. As a result, as shown in FIG. 10, the insertion loss decreases in that frequency band (hereinafter sometimes referred to as the "mid-frequency band"). Incidentally, the resonance transmission frequency f, which is the frequency at which this resonance transmission phenomenon occurs, can be calculated by Equation 1. In the formula 1, m1 represents the weight per unit area of ​​the floor panel 12, m2 represents the weight per unit area of ​​the mass element, E represents the Young's modulus of the spring element (air), and d represents the thickness of the spring element. Incidentally, in this floor structure 1020, 140, the resonance transmission frequency is 469 Hz, and it can be seen from Fig. 10 that the insertion loss is the lowest.

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[0039] On the other hand, in the first verification floor structure 100, the adhesion between the non-air-permeable layer 30 and the first compressed fiber layer 32A is weaker (close to non-adhesion) than that of the second verification floor structure 120, and as shown in the conceptual diagram of FIG. 9, the vibration of the non-air-permeable layer 30 is less likely to be transmitted to the first compressed fiber layer 32A. In addition, since it can be considered that almost only the non-air-permeable layer 30 corresponds to the mass element, the weight of the mass element is small, and when the resonance frequency is calculated by the formula 1, it shifts to the high frequency side from the resonance transmission frequency of the second verification floor structure 120 and the floor structure 140 of the comparative example described above. Incidentally, in the first verification floor structure 100, the resonance frequency is 1389 Hz. As a result, as shown in FIG. 10, the insertion loss decreases in the high frequency band (1000 Hz to 3000 Hz), but the resonance transmission phenomenon is suppressed in the medium frequency band, and the decrease in the insertion loss can be suppressed. In other words, compared to the second verification floor structure 120, the first verification floor structure 100 has reduced soundproofing performance in the high frequency band, but is able to suppress the reduction in soundproofing performance in the mid-frequency band.

[0040] In other words, as a vehicle floor structure, a first verification floor structure 100 that suppresses deterioration in soundproofing performance in the mid-frequency band is adopted in the first region A1 where the thickness of the floor silencer 14 is relatively large and excellent at absorbing sound in the high-frequency band, and a second verification floor structure 120 that has excellent soundproofing performance in the high-frequency band is adopted in the second region A2 where the thickness of the floor silencer 14 is relatively small, thereby making it possible to improve the soundproofing performance of the entire interior of the vehicle.

[0041] Fig. 11 shows the acoustic sensitivity near the head of a passenger seated in the rear seat of a vehicle. The solid line is for a vehicle floor structure that uses the above-mentioned first verification floor structure 100 and second verification floor structure 120 in combination, and the dotted line is for a case in which the comparative floor structure 140 is used on the entire surface of the floor panel 12. As can be seen from Fig. 11, it was confirmed that the vehicle floor structure that uses the first verification floor structure 100 and second verification floor structure 120 in combination has improved soundproofing performance in a wide frequency band from 250 Hz to 2000 Hz, compared to the comparative floor structure 140.

[0042] Moreover, Fig. 12 shows the relationship between the thickness of the entire floor structure and the resonant frequency when the mass per unit area (basis weight) of the non-ventilated layer is changed in the first verification floor structure 100. As can be seen from Fig. 12, the smaller the basis weight of the non-ventilated layer, the more the resonant frequency shifts to the high frequency side (upper side in Fig. 12), regardless of the thickness of the floor silencer, etc. In other words, the higher the frequency shift, the smaller the effect on the mid-frequency band can be, and therefore the less the deterioration of soundproofing performance in the mid-frequency band can be suppressed. Therefore, in the first verification floor structure 100, that is, in the first floor structure 10A, it is considered desirable to reduce the basis weight of the non-ventilated layer.

[0043] Next, the effect of bonding the non-ventilation layer 30 and the floor silencer 14 in each of the first floor structure 10A and the second floor structure 10B will be described. First, the second floor structure 10B will be compared with the second verification floor structure 120. The second floor structure 10B is considered to correspond to a spring-mass system model as shown in FIG. 13. That is, similar to the second verification floor structure 120 shown in FIG. 8, not only does resonance 210 (hereinafter sometimes referred to as "air spring resonance 210") occur due to the resonance transmission phenomenon, which is a characteristic of the hollow double wall, but also resonance 212 (hereinafter sometimes referred to as "sound absorbing layer expansion and contraction resonance 212") of the mass element (non-ventilation layer 30) occurs due to the expansion and contraction of the floor silencer 14 in the thickness direction.

[0044] The resonance frequency v of the sound absorbing layer expansion and contraction resonance 212 can be calculated by the following formula 2. In the formula 2, t represents the thickness of the floor silencer 14 which is a compressed felt, E represents the Young's modulus of the compressed felt (floor silencer 14), and ρ represents the density of air. In this embodiment, the resonance frequency is 196 Hz.

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[0045] The solid line in Fig. 14 is for the second verification floor structure 120, and the line connecting the rectangles in Fig. 14 is for the second floor structure 10B in this embodiment. The above-mentioned sound absorbing layer expansion and contraction resonance 212 exists in a frequency band close to the resonance frequency of the air spring resonance 210, and an anti-resonance occurs between these two resonance frequencies in which the phase is reversed. As a result, as shown in Fig. 14, the insertion loss is improved in the frequency band of 250Hz to 500Hz, and the soundproofing performance is improved.

[0046] Next, the effect of the first floor structure 10A will be described. The line connecting the triangles in FIG. 14 is the insertion loss of the first floor structure 10A. The line connecting the circles in FIG. 14 is also for a floor structure in which the non-breathable layer and the floor silencer are not bonded, as in the first verification floor structure 100. Furthermore, this floor structure is a structure in which the non-breathable layer 30 and the first compressed fiber layer 32A are not bonded, that is, the floor structure in this case has almost the same (more precisely, better) soundproofing performance as the first verification floor structure 10A. Since this floor structure is a modified version of the first verification floor structure 100, it will be called the modified floor structure. In these first floor structure 10A and the modified floor structure, as in the first verification floor structure 100, the resonant frequency of the air spring resonance is shifted to the high frequency side, making it possible to suppress the deterioration of soundproofing performance in the mid-frequency band compared to the floor structure 140 of the comparative example. Furthermore, the first floor structure 10A also experiences anti-resonance between the resonance frequency of the air spring resonance 210 and the resonance frequency of the sound absorbing layer amplitude resonance 212. As shown in Fig. 14, the first floor structure 10A has been confirmed to have improved insertion loss over a wide frequency range from mid to high frequencies (315 Hz or higher) compared to the floor structure that is the modified example, due to the synergistic effect of these factors. The same tendency was also confirmed in trial calculations using simulation software.

[0047] Next, in the second floor structure 10B, the insertion loss was compared when the weight distribution between the non-breathable layer and the compressed fiber layer was changed without changing the weight of the entire mass element. In detail, in addition to the second floor structure 10B with a compressed fiber layer of 800 gsm and a non-breathable layer of 100 gsm, Comparative Example 1 with a compressed fiber layer of 850 gsm and a non-breathable layer of 50 gsm, Comparative Example 2 with a compressed fiber layer of 700 gsm and a non-breathable layer of 200 gsm, Comparative Example 3 with a compressed fiber layer of 500 gsm and a non-breathable layer of 400 gsm, and Comparative Example 4 with a compressed fiber layer of 300 gsm and a non-breathable layer of 600 gsm were set, and the insertion loss of each was calculated using simulation software. As shown in FIG. 15, it was confirmed that the smaller the basis weight of the non-breathable layer, the lower the insertion loss in the high frequency band (1000 Hz or more), but the insertion loss in the mid-frequency band (315 Hz to 630 Hz) was improved, and the soundproofing performance in the mid-frequency band was improved. As a result, in the second floor structure 10B, it is desirable for the mass per unit area of ​​the non-breathable layer to be 50 gsm or more and 200 gsm or less. In other words, it was confirmed that it is desirable for the non-breathable layer to have a small basis weight not only in the first floor structure 10A but also in the second floor structure 10B.

[0048] <Other embodiments> The present invention is not limited to the above-described embodiment, and can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art. For example, the following embodiments are also included within the technical scope of the present invention. (1) In the above embodiment, the skin layer is provided on the interior side of the compressed fiber layer, but the skin layer is not essential. For example, if there is a component that constitutes the design surface of the vehicle compartment, it is sufficient that the sound absorbing layer, the air impermeable layer, and the compressed fiber layer are laminated between the component and the partition member. (2) In the above embodiment, the vehicle compartment soundproofing structure of the present invention is used in the floor structure of the vehicle, but is not limited thereto. The vehicle compartment soundproofing structure of the present invention may also be used in the wall of the vehicle, the boundary with the engine room, etc. (3) Furthermore, the vehicle compartment soundproofing structure of the present invention is not limited to being provided in vehicles, but can be applied to various types of vehicles. [Explanation of symbols]

[0049] Reference Signs List 10: vehicle floor structure, 10A: first floor structure (vehicle compartment soundproofing structure), 10B: second floor structure, 12: floor panel (compartment member), 14: floor silencer (sound absorbing layer), 16: carpet, 30: non-breathable layer, 32: compressed fiber layer, 40: adhesive layer

Claims

1. A vehicle cabin soundproofing structure for suppressing noise from outside a vehicle cabin, comprising: A partition member that serves as a main component for partitioning the vehicle compartment; A sound absorbing layer disposed on the indoor side of the partition member and having a large number of voids therein; A non-breathable layer arranged on the indoor side of the sound absorbing layer and made of a non-breathable material; a compressed fiber layer disposed on the indoor side of the non-breathable layer and formed mainly of a compressed fiber aggregate, 2. A soundproofing structure for a vehicle compartment, wherein the bonding strength between said compressed fiber layer and said non-permeable layer is lower than the bonding strength between said non-permeable layer and said sound absorbing layer.

2. 2. The vehicle cabin soundproofing structure according to claim 1, wherein the non-breathable layer has a mass per unit area of ​​15 gsm or more and 400 gsm or less, preferably 50 gsm or more and 200 gsm or less.

3. 3. The vehicle cabin soundproofing structure according to claim 1 or 2, wherein the compressed fiber layer has a mass per unit area of ​​300 gsm or more and 1500 gsm or less, preferably 600 gsm or more and 1000 gsm or less.

4. 4. The vehicle compartment soundproofing structure according to claim 1, wherein the compressed fiber layer and the non-breathable layer are not bonded to each other.

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