JP2010058538A - Car body structure and floor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sound absorbing structure for absorbing sound by consuming sound wave energy as mechanical energy by converting sound wave to vibration, for example, when the frequency of a sound absorbed by the sound absorbing structure is set at a low value, the sound of low frequency such as a road noise is efficiently absorbed. <P>SOLUTION: A vehicle includes a floor 111 serving as a floor of a cabin. A plate sound absorbing structure group 1 for absorbing sound by sound pressure driving is provided on the floor. The plate sound absorbing structure group 1 is constituted of a plurality of plate sound absorbing bodies. In the plate sound absorbing body, sound booming in the cabin is transmitted to a vibration plate through a sound pressure transmission portion and vibrates the vibration plate. The sound wave energy in the cabin is consumed as the mechanical energy by this vibration, and the sound is absorbed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vehicle body structure capable of absorbing noise of a relatively low frequency such as road noise.

In a vehicle body structure, a technique for absorbing sound entering a passenger compartment is known. For example, Patent Document 1 discloses a technique for reducing road noise that has entered a vehicle interior by using the principle of a Helmholtz resonance tube. Patent Document 2 discloses a foot panel including a sound absorbing member and a shock absorbing member made of a material capable of absorbing noise.
JP 2006-142885 A JP 2005-145383 A

  By the way, in the technique described in Patent Document 1, as shown in FIGS. 10 and 11 of Patent Document 1, a result of attenuation is obtained in a relatively high frequency region of 500 Hz or higher. It was not possible to attenuate sound in a relatively low frequency region such as noise. This is because, for example, in the technique described in Patent Document 1, the plate thickness of the resonance member is thin. In addition, since the technique described in Patent Document 2 is a sound absorbing structure using particle velocity, a porous material is disposed at a position where the particle velocity of the sound wave is maximized and perpendicular to the direction in which the velocity is maximized. Sound absorption efficiency is maximized when For this reason, it is necessary to have a space of about λ / 4 of the target frequency behind the room boundary (wall surface). In order to absorb the low sound range, a large air layer (for example, 27 cm in the case of 315 Hz) is required. Must be secured. In this case, it is practically impossible to install the sound absorbing structure inside a member having a small thickness such as a vehicle floor. In other words, a porous sound absorbing structure with a small back air layer cannot absorb low frequencies and cannot dissipate low frequency acoustic energy. As described above, none of the techniques described in Patent Documents 1 and 2 can absorb the sound in the low frequency band.

  The present invention has been made in view of the above-described problems, and an object thereof is to efficiently absorb sound in a low frequency region.

In order to solve the above-described problems, a vehicle body structure employed by the present invention includes a floor and a sound absorbing structure that is provided on the floor and absorbs sound by sound pressure driving.
In the vehicle body structure, it is preferable that the portion driven by the sound pressure driving of the sound absorbing structure is disposed at a portion where the sound pressure on the floor is high.
In the vehicle body structure, the sound absorbing structure is preferably a plate sound absorbing body having a diaphragm and an air layer defined behind the diaphragm.

In the vehicle body structure, the sound absorbing structure is preferably a tube sound absorbing body having a cavity that is a closed portion with one end closed and an opening with the other end opened.
The tube sound absorber preferably has a plurality of the cavities.
The tube sound absorber preferably includes a plurality of the cavities having different lengths.

In the vehicle body structure, the sound absorbing structure is preferably a Helmholtz sound absorber having a closed space and a tubular member that communicates the closed space and the space of the passenger compartment.
In the vehicle body structure, the sound absorbing structure includes a plate sound absorber having a diaphragm and an air layer defined behind the diaphragm, and an opening having a closed end with one end closed and the other end opened. It is desirable that the sound absorber is composed of any combination of a sound absorber having a tube sound absorber having a cavity serving as a portion, a closed space, and a tubular member that communicates the closed space with the outside. .

  In order to solve the above-described problems, the floor employed by the present invention is a floor serving as a floor of a passenger compartment, and includes a sound absorbing structure that is provided on a base of the floor and absorbs sound by sound pressure driving. It is characterized by that.

  According to the present invention, the sound absorbing structure converts sound waves into vibrations, consumes sound wave energy as mechanical energy, and performs sound absorption. For example, when the frequency at which the sound absorbing structure absorbs sound is set to a low value, low frequency sound such as road noise can be efficiently absorbed.

Hereinafter, the vehicle body structure including the sound absorbing structure will be described.
<First Embodiment>
The present inventors paid attention to providing a sound absorbing structure on the floor of the vehicle. In general, at the boundary surface of the passenger compartment, the particle velocity of sound waves does not take a large value, whereas the sound pressure is high and low (so-called sound pressure distribution). Therefore, a sound absorbing structure having a sound absorbing mechanism by sound pressure driving has a structure in which the sound pressure driving sound absorbing structure is provided at a portion of high sound pressure because the sound energy to be absorbed is determined by the product of the sound absorbing efficiency and the sound energy incident thereon. By arranging them preferentially, it is possible to dissipate acoustic energy in the passenger compartment efficiently. In addition, since the sound absorbing structure based on sound pressure driving can be realized without configuring a λ / 4 back air layer, sound absorption near the wall surface is possible, and a large back air layer is also provided for sound in a low frequency region. There is an advantage that it is not necessary.

(1-1) Configuration (1-1-1) Vehicle FIG. 1 is a perspective view showing a four-door sedan type vehicle 100 according to the first embodiment of the present invention. In the vehicle 100, a bonnet 101, four doors 102 serving as entrances and exits of the vehicle 100, and a trunk door 103 are attached to a chassis serving as a base of a vehicle body structure so as to be opened and closed.
FIG. 2 is a diagram schematically showing the inside of the chassis and the door 102. The chassis includes a floor 111, a front pillar 112, a center pillar 113, a rear pillar 114 extending upward from the floor 111 or a base portion formed on the floor 111, and a ceiling 115 supported by the pillars 112, 113, 114. The engine partition wall 116 that divides the interior of the vehicle 100 into a vehicle compartment 105 and an engine chamber 106 and the trunk partition wall 117 that divides the vehicle 100 into a vehicle compartment 105 and a cargo compartment 107 are provided.

(1-1-2) Floor A feature of the present embodiment is that a box-shaped plate sound absorber is provided on the floor 111. The floor 111 is a part belonging to the floor of the vehicle body, and includes a toe board, a heel kick, a console, and the like under a seat on which an occupant sits. The toe board is a floor portion provided in front of a toe of an occupant seated in the front seat. The heel kick is a floor portion provided behind the heel of the passenger seated in the rear seat. A console is a floor part located in the centerline part of a vehicle body.
FIG. 3A is a view of the portion a in the figure as seen from the obliquely rear side with the passenger seat side floor 111 shown in FIG. 2 as the center. FIG. 3B is a diagram when the rear seat shown in FIG. 2 is viewed from the front seat (driver seat, front passenger seat). The board sound absorber group 1 is provided on the toe board, heel kick, under the seat, and console of the floor 111, respectively. The plate sound absorber group 1 is composed of a plurality of plate sound absorbers 10. FIG. 4 is a plan view showing the structure of the plate sound absorber group 1 provided on the toe board in FIG. As shown in the figure, the plate sound absorber group 1 is composed of three plate sound absorbers 10 having the same shape. The size of each plate sound absorber 10 is as follows.
The size of the plate sound absorber 10: height 100 mm × width 100 mm × thickness 10 mm

Next, the mounting structure of the plate sound absorber 10 will be described with reference to FIG.
FIG. 5 is a cross-sectional view of the toe board 200 taken along the cutting line bb in FIG. In the figure, only one plate sound absorber 10 is shown, but in reality, three plate sound absorbers 10 are arranged side by side in the direction toward the back of the page or toward the front of the page. The floor carpet 130 is a floor material that partitions the vehicle compartment and the space below the vehicle compartment, and is formed of a non-woven cloth material having sound pressure permeability. In the floor carpet 130, a portion corresponding to the plate sound absorber 10 serves as a sound pressure transmitting portion 136 that transmits the sound pressure on the vehicle interior 105 side to the plate sound absorber 10.

  A plurality of pin holes 124 are formed in the vehicle body 120, and a retaining portion 125 having a reduced diameter is formed at the opening of the pin hole 124. A barrel-shaped pin 15 protruding from the bottom of the plate sound absorber 10 is inserted into the pin hole 124. By fitting the pin 15 into the pin hole 124, the reduced diameter portion of the pin 15 is locked to the retaining portion 125, and the plate sound absorber 10 is fixed to the vehicle body 120. Thereby, the board sound absorber 10 is installed between the floor carpet 130 and the vehicle body 120.

(1-1-3) Plate Sound Absorber Next, the structure of the plate sound absorber 10 will be described. Since each plate sound absorber 10 has the same configuration, here, the structure of the plate sound absorber 10 shown in FIG. 5 will be described as an example. As shown in FIG. 5, the plate sound absorber 10 includes a rectangular casing 11 having an opening 12, a diaphragm 13 that closes the opening 12, and an air layer 14 defined in the casing 11. Are provided. The casing 11 is formed of a synthetic resin material (for example, ABS resin), and the diaphragm 13 is formed in a sheet shape by a polymer compound (for example, an olefin-based copolymer with an inorganic filler). In the present invention, the diaphragm 13 may be formed of an elastic material in a film shape.

  The plate sound absorber 10 is set to the conditions described later, so that the difference between the sound pressure on the passenger compartment 105 side transmitted to the diaphragm 13 through the sound pressure transmitting portion 136 and the sound pressure on the air layer 14 side (that is, the diaphragm 13). The diaphragm 13 is driven by the difference in sound pressure before and after. Thereby, the energy of the sound wave reaching the plate sound absorber 10 is consumed by the vibration of the diaphragm 13 and the sound is absorbed. That is, the plate sound absorber 10 exhibits a sound absorbing effect due to vibration excited by sound pressure driving.

(1-1-4) Setting Conditions for Plate Sound Absorber Here, setting conditions for the plate sound absorber 10 will be described.
In general, for a sound absorbing structure that absorbs sound by a plate-like or membrane-like vibrator and an air layer, the frequency to be attenuated depends on the resonance frequency of the spring mass system due to the mass component (mass component) of the vibrator and the spring component of the air layer. Is set. The density of air is ρ ₀ [kg / m ³ ], the speed of sound is c ₀ [m / s], the density of the vibrating body is ρ [kg / m ³ ], the thickness of the vibrating body is t [m], When the thickness is L [m], the resonance frequency of the spring mass system is expressed by the equation (1).

  In the case of the plate / membrane vibration type sound absorbing structure, when the vibrating body has elasticity and elastically vibrates, the property of a bending system due to elastic vibration is added. In the field of architectural acoustics, the shape of the vibrating body is rectangular, the length of one side is a [m], the length of the other side is b [m], the Young's modulus of the vibrating body is E [Pa], and the Poisson of the vibrating body When the ratio is σ [−] and p and q are positive integers, the resonance frequency of the plate / membrane vibration type sound absorbing structure is obtained by the following formula 2, and the obtained resonance frequency is used for acoustic design. (In the case of peripheral support).

そして、本実施形態においては、上記数式から１６０〜３１５Ｈｚバンド（１/３オク
ターブ中心周波数）を吸音するよう、以下のようにパラメータが設定される。
空気の密度ρ_０ ；１．２２５[ｋｇ／ｍ^３]
音速ｃ_０ ；３４０[ｍ／ｓ]
振動体の密度ρ ；９４０[ｋｇ／ｍ^３]
振動体の厚さｔ ；０．００１７[ｍ]
空気層の厚さＬ ；０．０１[ｍ]
筐体の長さａ ；０．１[ｍ]
筐体の長さｂ ；０．１[ｍ]
振動体のヤング率Ｅ ；０．６４[ＧＰａ]
ポアソン比σ ；０．４
モード次数 ；ｐ＝ｑ＝１

In this embodiment, parameters are set as follows so as to absorb the 160 to 315 Hz band (1/3 octave center frequency) from the above formula.
Air density ρ ₀ ; 1.225 [kg / m ³ ]
Speed of sound c ₀ ; 340 [m / s]
Density of vibrating body ρ: 940 [kg / m ³ ]
Thickness t of vibrating body; 0.0017 [m]
Air layer thickness L: 0.01 [m]
Case length a: 0.1 [m]
Case length b: 0.1 [m]
Young's modulus E of the vibrator: 0.64 [GPa]
Poisson's ratio σ: 0.4
Mode order; p = q = 1

On the other hand, in the above formula 2, the term of the spring mass system (ρ ₀ c ₀ ² / ρtL) and the term of the bending system (the term added in series after the term of the spring mass system) are added. For this reason, the resonance frequency obtained by the above equation is higher than the resonance frequency of the spring mass system, and it may be difficult to set the frequency at which the sound absorption peak is low.

In such a sound absorber, the relationship between the resonance frequency of the spring mass system and the resonance frequency of the bending system due to elastic vibration due to the elasticity of the plate has not been fully elucidated, and a plate that exhibits high sound absorption in the low frequency range. The actual situation is that the structure of the sound absorber is not established.
Therefore, as a result of intensive experiments, the inventors have determined that the above equation 3 is satisfied so that the value of the fundamental vibration frequency of the bending system is fa and the value of the resonance frequency of the spring mass system is fb. It turns out that the parameters should be set. As a result, the fundamental vibration of the bending system is coupled with the spring component of the air layer behind, and a vibration having a large amplitude is excited in the band between the resonance frequency of the spring mass system and the fundamental frequency of the bending system (the bending system). The resonance frequency fa <sound absorption peak frequency f <spring mass system fundamental frequency fb), and the sound absorption rate increases.

このように、上記した数３，４の条件を満足するように各種パラメータを設定することにより、吸音のピークとなる周波数を低くした吸音体が構成できる。 Furthermore, when the following equation 4 is set, the frequency of the sound absorption peak is sufficiently smaller than the resonance frequency of the spring mass system. In this case, it has also been found that the fundamental frequency of the bending system is sufficiently smaller than the resonance frequency of the spring mass system due to the low-order elastic vibration mode and is suitable as a sound absorbing structure that absorbs sound having a frequency of 300 [Hz] or less.

In this way, by setting various parameters so as to satisfy the above-described conditions of Equations 3 and 4, it is possible to configure a sound absorber that reduces the frequency at which sound absorption peaks.

(1-2) Action and Effect of First Embodiment In the plate sound absorber 10 according to the present embodiment, the sound accumulated in the passenger compartment 105 is transmitted to the diaphragm 13 through the sound pressure transmitting portion 136, and the diaphragm 13 Vibrate. Due to this vibration, sound wave energy in the passenger compartment 105 is consumed as mechanical energy to absorb sound. For example, by setting the sound absorber 10 to the numerical value of the above parameter, a low-frequency sound such as road noise (a frequency at which the sound pressure corresponding to the natural vibration in the passenger compartment 105 is locally increased). (500 Hz or less)) can be efficiently absorbed.

In the present embodiment, a box-shaped plate sound absorber 10 is provided on a floor 111 of a vehicle 100. Road noise having a relatively low frequency such as tire noise is efficiently absorbed by the plate sound absorber 10 provided on the floor 111.
Here, the relatively low frequency refers to the frequency of the fundamental vibration (about 80 Hz in a normal passenger compartment) which is the lowest frequency among the natural vibrations in the passenger compartment, and the passenger compartment can be regarded as a diffuse sound field. A frequency band between a frequency band (a band of about 500 Hz or more in a normal passenger compartment) and a frequency that can be regarded as having discrete modes in the passenger compartment.

  FIG. 6 shows the results of an experiment for examining the noise reduction effect when the plate sound absorber 10 is provided on the floor 111. FIG. 6 (a) examined the noise reduction effect at the driver's seat when one plate acoustic body 10 of 300mm in length, 300mm in width, and 30mm in depth was installed on the floor below the driver's seat and passenger seat. It is a result. As shown in FIG. 6A, in this case, in the driver's seat, the noise level is reduced in the frequency range of 80 to 400 Hz, and the effect of absorbing sound at a low frequency where noise (road noise or the like) is concentrated is obtained. was gotten. FIG. 6B shows the noise reduction effect in the front passenger seat when two sound absorbers 10 each having a length of 160 mm, a width of 160 mm, and a depth of 20 mm are installed on the toe board of the driver seat and the passenger seat. It is a result. As shown in FIG. 6B, in this case, the noise level is reduced at a frequency of 315 Hz in the passenger seat. FIG. 6C shows the noise reduction effect in the right rear seat when six plate absorbers 10 each having a length of 100 mm, a width of 100 mm, and a depth of 20 mm are installed on both sides of the rear console of the rear seat. It is a result. As shown in FIG. 6C, in this case, in the right rear seat, the noise level was reduced in the frequency range of 200 to 630 Hz. As a result, in the vehicle body structure according to the present embodiment, the plate sound absorber 10 provided on the floor 111 can efficiently absorb, for example, road noise and the like, and the quietness in the passenger compartment 105 can be enhanced. .

(1-3) Modified Example of First Embodiment The present invention is not limited to the configuration of the first embodiment described above, and various correspondences are possible.
(1-3-1)
In the first embodiment described above, as shown in FIG. 3, the sound absorber group 1 is provided at the toe board, heel kick, under the seat, and console (rear console, front console) position. Is not limited to this. In short, the plate sound absorber 10 may be provided on the floor 111. That is, in the first embodiment, the sound absorber is not provided in a portion that is stepped on by the occupant's feet, but the plate sound absorber group 1 may be provided in such a portion as long as it has sufficient strength. Since the toe board, the heel kick, the under-seat, and the console are parts with high sound pressure, the sound absorbing effect can be increased by providing the sound absorbing body group 1 at these places as described above.
Further, in the first embodiment described above, one sound absorber group 1 is provided below the toe board and the seat on each floor 111 of the driver seat and the passenger seat, but the number of the sound absorber groups 1 is as follows. Not limited to this. For example, the floor 111 below the driver's seat and the floor 111 below the passenger seat are provided with one plate sound absorber group 1 as in the first embodiment, and two plate sound absorber groups 1 are provided on each toe board. Two or more may be provided.

(1-3-2)
In the first embodiment described above, as shown in FIG. 5, the plate sound absorber 10 is attached by fitting the pin 15 of the plate sound absorber 10 into the pin hole 124 of the vehicle body 120. The attachment method 10 is not limited to this. For example, the plate sound absorber 10 may be fixed to the vehicle body 120 with an adhesive or the like.

(1-3-3)
In the first embodiment described above, as shown in FIG. 5, the surface on which the diaphragm 13 is provided in the plate sound absorber 10 is covered with the floor carpet 130, but this is not a limitation. As shown in FIG. 7A, a flat plate portion 121 </ b> A having a plurality of insertion holes 120 </ b> A may be provided between the plate sound absorber 10 and the floor carpet 130. In this case, since the air in the passenger compartment 105 is transmitted to the plate sound absorber group 1 through the insertion hole 120A, the plurality of insertion holes 120A serve as sound pressure transmission portions. Further, as shown in FIG. 7B, the plate sound absorber 10 may be attached to the floor carpet 130. In this case, the plate sound absorber 10 may be attached to the floor carpet 130 via the spacer 121B so that a space is generated between the surface of the plate sound absorber 10 on which the diaphragm 13 is provided and the floor carpet 130. The spacer 121B is fixed at the outer edge portion of the diaphragm 13 or the outer edge portion of the casing 11 forming the opening 12 so that one end thereof does not hinder the vibration of the diaphragm 13 of the plate sound absorber 10, and the other end. May be fixed to the vehicle body side of the floor carpet 130. In this case, as shown in the figure, the air in the passenger compartment 105 is the sound pressure transmitting portion 136 at the portion of the floor carpet 130 that faces the diaphragm 13.
Moreover, in 1st Embodiment mentioned above, although the vehicle body 120 and the board sound-absorbing body 10 were provided separately, it is not restricted to this. As shown in FIG. 8, a part of the vehicle body 120 may be used as the housing of the plate sound absorber 10A. Specifically, a rectangular recess 122A that opens to the vehicle interior 105 side is formed in the vehicle body 120, and the diaphragm 13 is directly fixed to the opening 12 of the recess 122A. The recess 122A, the diaphragm 13, and the recess The plate sound absorber 10 </ b> A is configured by 122 </ b> A and the air layer 14 defined by the diaphragm 13. In this case, the portion corresponding to the diaphragm 13 in the floor carpet 130 becomes the sound pressure transmitting portion 136.

(1-3-4)
In the first embodiment described above, the three plate sound absorbers 10 included in each plate sound absorber group 1 have the same shape, but these plate sound absorbers 10 have different shapes. It may be. Since the resonance frequency of the plate sound absorber 10 varies depending on the dimensions of the casing 11 of the plate sound absorber 10, the range of frequencies to be absorbed can be expanded, and sound absorption can be performed more reliably.
Each plate sound absorber group 1 may include a plate sound absorber 10 having a resonance frequency suitable for the sound pressure at the provided position. In this case, the part where the sound pressure increases (the part where the sound pressure increases (becomes the antinode of the sound pressure) corresponding to the natural vibration mode (mode) in the passenger compartment), specifically, a reflective member such as glass. The plate sound absorber group 1 disposed in the configured concave space etc.) is provided with a plate sound absorber 10 having a large size and the sound absorber group 1 is disposed at a portion where the sound pressure is lowered. The group 1 may be provided with a plate sound absorber 10 having a small size.

(1-3-5)
In the first embodiment described above, as shown in FIG. 5, the diaphragm 13 of the plate sound absorber 10 is provided on the surface of the plate sound absorber 10 on the vehicle interior 105 side, but the present invention is not limited to this. For example, the diaphragm 13 may be provided on a surface outside the vehicle, which is a facing surface of the plate sound absorber 10 on the vehicle interior 105 side. According to this configuration, it is possible to absorb sound entering from outside the vehicle. Or the diaphragm 13 may be provided in the surface by the side of the vehicle interior 105 of the board sound-absorbing body 10, and the surface of the vehicle outer side, respectively. According to this configuration, it is possible to absorb both the sound that stays in the passenger compartment 105 and the sound that enters from outside the vehicle. In short, it is only necessary that the diaphragm 13, which is a part driven by the sound pressure drive of the plate sound absorber 10, be disposed at a part where the sound pressure on the floor 111 is high.

(1-3-6)
In the first embodiment described above, the air layer 14 is formed in the casing 11 of the plate sound absorber 10. However, in order to improve the sound absorption characteristics of the diaphragm 13, an open cell foam resin such as polyurethane foam is used. May fill the housing 11 with a cotton-like fiber such as felt or polyester wool.
In the first embodiment described above, the structure of the plate sound absorber 10 is defined in the rectangular casing 11, the diaphragm 13 that closes the opening 12 of the casing 11, and the casing 11. However, the shape of the housing according to the present invention is not limited to a rectangular shape, and may be a circular shape or a polygonal shape. In any case, it is desirable that a concentrated mass for changing the vibration condition with respect to the diaphragm 13 is provided in the central portion of the diaphragm 13.

As described above, the plate sound absorber 10 has a sound absorbing mechanism formed of a spring mass system and a bending system. Here, the inventors conducted an experiment of the sound absorption coefficient at the resonance frequency when the surface density of the diaphragm 13 was changed.
FIG. 9 shows that a diaphragm 13 (size: 100 mm × 100 mm, thickness: 0.85 mm) is fixed to a casing 11 having a vertical and horizontal size of 100 mm × 100 mm and a thickness of 10 mm. It is the figure which showed the simulation result of the normal incidence sound absorption coefficient of the board sound-absorbing body 10 at the time of changing the surface density of a part (a magnitude | size is 20 mm x 20 mm, thickness 0.85mm). The simulation method is based on JIS A 1405-2 (measurement of sound absorption coefficient and impedance by an acoustic tube—Part 2: transfer function method), and the sound field of the acoustic room in which the plate sound absorber 10 is arranged is a finite element method. The sound absorption characteristics were calculated from the transfer function.

Specifically, the surface density at the center is (1) 399.5 [g / m ² ], (2) 799 [g / m
² ], (3) 1199 [g / m ² ], (4) 1598 [g / m ² ], (5) 2297 [g / m ² ], and the surface density of the peripheral member is 799 [g / m ² ]. And the average density of diaphragm 13 is (1) 7
83 [g / m ² ], (2) 799 [g / m ² ], (3) 815 [g / m ² ], (4) 831 [g
/ M ² ], (5) Simulation results when 863 [g / m ² ].
Looking at the simulation results, the sound absorption rate is high between 300 and 500 [Hz] and in the vicinity of 700 [Hz].
The high sound absorption coefficient near 700 [Hz] is due to resonance of the spring mass system formed by the mass of the diaphragm 13 and the spring component of the air layer 14. In the plate sound absorber 10, sound is absorbed with the sound absorption coefficient at the resonance frequency of the spring mass system as a peak, and even if the surface density of the central portion is increased, the mass of the entire diaphragm 13 does not change greatly. It can be seen that the resonance frequency does not change significantly.
The reason why the sound absorption coefficient is high between 300 and 500 [Hz] is due to the resonance of the bending system formed by the bending vibration of the diaphragm 13. In the plate sound absorber 10, the sound absorption coefficient at the resonance frequency of the bending system appears as a peak on the low frequency side, and only the resonance frequency of the bending system decreases as the surface density at the center increases. I understand.

In general, the resonance frequency of the bending system is determined by an equation of motion that governs elastic vibration of the diaphragm 13 and is inversely proportional to the density (surface density) of the diaphragm 13. The resonance frequency is greatly influenced by the density of the antinodes of natural vibration (when the amplitude is a maximum value). For this reason, in the simulation described above, the region that becomes the antinode of the 1 × 1 eigenmode is formed at different surface densities in the central portion, so that the resonance frequency of the bending system is changed.
Thus, the simulation results show that when the surface density of the central part is made larger than the surface density of the peripheral part, the peak of the sound absorption coefficient on the low frequency side of the frequency that becomes the peak of sound absorption moves further to the low frequency side. Represents. Therefore, it is shown that by changing the surface density of the central portion, a part of the frequency at which the sound absorption is peaked can be moved (shifted) further to the low sound region side or the high sound region side.
In the plate sound absorber 10 described above, the frequency of the sound absorption sound can be changed (shifted) simply by changing the surface density of the central portion. Therefore, the diaphragm 13 is made of the same material as the plate sound absorber 10 as a whole. Compared with the case where the sound absorbing sound is changed by increasing the mass of the plate sound absorber 10 as a whole, the sound to be absorbed can be reduced without greatly changing the mass of the plate sound absorber 10 as a whole.
In this way, changes in the noise characteristics in the passenger compartment due to changes in the sound absorption capacity in the passenger compartment and cargo compartment (number of people and luggage, changes in shape, etc.) and changes in generated noise (changes in tires, changes in road surface conditions, etc.) It can correspond to.
Furthermore, the sound absorption coefficient peak value may be increased by filling the air layer 14 of the plate sound absorber 10 with a porous sound absorbing material (for example, cotton-like fibers such as foamed resin, felt, polyester wool). .

<Second Embodiment>
Next, a second embodiment according to the present invention will be described. The feature of this embodiment is that a pipe sound absorber is used for the sound absorbing structure provided on the floor 111. In addition, the same code | symbol shall be attached | subjected to the component same as 1st Embodiment mentioned above, and the description shall be abbreviate | omitted.
(2-1) Configuration FIG. 10 is a diagram illustrating a configuration of the floor 111 according to the second embodiment. In the floor 111 under the seat, the pipe sound absorber 30 is provided in the recess 122 of the vehicle body 120.

The structure of the tube sound absorber used in this embodiment will be described.
FIG. 11 is a view showing the structure of the tube sound absorber 30. The tube sound absorber 30 is accommodated in the recess 122 of the vehicle body 120. The pipe sound absorber 30 is integrally formed by arranging a plurality of pipes 31 (31-1 to 31-9) having different lengths in a vertical row and mutually connected or mutually connected by a dedicated member. Yes. Each pipe 31 is composed of a linear rigid pipe having a circular cross section made of a synthetic resin or the like having a predetermined thickness (for example, about 2 mm) and a predetermined inner diameter (for example, a diameter of 60 mm). One end of each pipe 31 is closed to become a closed portion 32, and the other end is opened to become an opening portion 33. The positions of the openings 33 are aligned in a line by the pipes 31 so that the openings 33 are adjacent to each other. Even when the door 102 is closed, the opening 33 of each pipe 31 communicates with the passenger compartment 105 side through a space between the floor 111 and the door 102. As a result, the sound pressure transmitting portion 136 is formed in the vehicle body 120.

The length in each pipe 31 corresponds to a quarter wavelength of the center frequency of the sound wave absorbed by the single cavity of the pipe 31.
Here, three types of pipes having a cavity length L (= pipe length) of 0.85 m, 0.68 m, and 0.53 m are used, and these are 100 Hz, 125 Hz, and 160 Hz (that is, 1 / Sound absorption centering on (3 octave band pitch) (sound speed = 340 m / s).
The neck portion (opening 33 or the vicinity thereof) of the opening 33 of each pipe 31 is blocked by a flow resistance material (material having flow resistance) 34 having sound pressure permeability such as glass wool, cloth, gauze and the like. .

(2-2) Operation Principle of Tube Sound Absorber Next, the sound absorption principle of the tube sound absorber 30 will be described.
FIG. 12 shows two adjacent pipes 31-j and 31-k in the pipe sound absorber 30 shown in FIG. The lengths of the cavities of the pipes 31-j and 31-k are L1 and L2. Sound waves in the passenger compartment 105 are incident on the openings 33-j and 33-k into the cavity, reflected by the closed portions 32-j and 32-k at the other ends, and the openings 33-j and 33-k. Is again released into the room. At this time, while the sound waves having the wavelengths λ1, λ2 (L1 = λ1 / 4, L2 = λ2 / 4) corresponding to four times the cavity lengths L1, L2 create standing waves S1, S2, Energy is consumed by the friction on the inner wall surface of the cavity and the viscous action between the air particles at the openings 33-j and 33-k, and sound absorption is performed around the wavelengths λ1 and λ2. For example, if L1 = 1.35 m and L2 = 0.53 m, then λ1 = 5.4 m and λ2 = 2.12 m, and the center frequencies f1 and f2 of the sound waves absorbed by f1 = 63 Hz and f2 = 160 Hz.

  On the other hand, the sound waves reflected by the blocking portions 32-j and 32-k and emitted from the openings 33-j and 33-k are diffracted by the openings 33-j and 33-k and radiate energy. Part of the energy is incident into the cavity from the openings 33-k and 33-j of the other pipes 31-k and 31-j adjacent to each other. In this way, coupled vibration is generated between the adjacent pipes 31-j and 31-k, and energy is transferred. During this coupled vibration, energy is consumed and sound is absorbed by friction on the inner wall surface of the cavity and viscous action between the air particles at the openings 33-j and 33-k. This coupled vibration can be regarded as a both-end closed tube mode in which the pipes 31-j and 31-k are regarded as a series of pipes, and sound absorption is performed around a wavelength λ3 determined as L1 + L2 = λ3 / 2. For example, when L1 = 1.35 m and L2 = 0.53 m, λ3 = 3.76 m, and the center frequency f3 of the sound wave absorbed by the coupled vibration is f3 = 90 Hz. In the case of the arrangement of FIG. 11, the frequency of the coupled vibration between adjacent pipes is as follows.

L1 (m) L2 (m) Coupled vibration frequency (Hz)
0.85 0.68 111
0.85 0.53 123
0.68 0.53 140
According to this, the sound absorption force is obtained on the average in the range of about 100 to 160 Hz together with the sound absorption (100, 125, 160 Hz is the center) of each pipe 31-1 to 31-9 alone.

(2-3) Actions and Effects of Second Embodiment As described above, by providing the pipe sound absorber 30 on the floor 111, road noise such as tire noise is efficiently absorbed by the pipe sound absorber 30. This can increase the quietness in the passenger compartment 105. Further, when the door 102 is closed, the opening 33 of the pipe sound absorber 30 cannot be seen, so that the design inside the vehicle 100 is not impaired.

(2-4) Modified Examples of Second Embodiment The present invention is not limited to the configuration of the second embodiment described above, and various correspondences are possible.
(2-4-1)
In the second embodiment described above, the pipe sound absorber 30 is configured by the pipe 31 formed in advance, but the pipe 31 may be formed only when the door 102 is closed. FIG. 13 is a diagram showing the floor 111 when this configuration is adopted. As shown in FIG. 13A, a hollow portion 34 extending in the front-rear direction of the vehicle 100 is provided in a portion called a side sill (hereinafter referred to as a side sill 118) of the floor 111. FIG. 13B shows the side sill 118 viewed from the direction of arrow I in FIG. 13A when the door 102 is closed. As shown in FIG. 13B, when the door 102 is closed, the pipe 31 is formed by the hollow portion 34 and the lower end of the door 102. The cross-sectional shape of the cavity 34 may be circular as shown in the figure, or may be other shapes.

(2-4-2)
In the second embodiment described above, one end of the pipe sound absorber 30 is an opening 33 and the other end is a so-called closed pipe, but the shape of the pipe 31 is not limited thereto. .
For example, both ends of each pipe 31 may be opened to form a pipe that forms an opening 33 (so-called open pipe), or the closed pipe and the open pipe may be mixed and arranged.

<Third Embodiment>
Next, a third embodiment according to the present invention will be described. The feature of this embodiment is that a Helmholtz sound absorber is used for the sound absorbing structure provided on the floor 111. In addition, the same code | symbol shall be attached | subjected to the component same as 1st Embodiment mentioned above, and the description shall be abbreviate | omitted.

FIG. 14 is a cross-sectional view when the floor 111 according to the third embodiment (the Helmholtz sound absorber 40 is provided on the floor 111) is cut along a cutting line bb in FIG.
The Helmholtz sound absorber 40 used in the present embodiment includes a rectangular parallelepiped casing 41 having a space formed therein, and a tubular member inserted into an insertion hole 42 drilled on the casing 105 side of the casing 41. 43. A sealed space 44 is defined inside the casing 41, and an opening 45 that connects the sealed space 44 and the vehicle interior 105 is formed inside the tubular member 43. The tubular member 43 is also inserted into an insertion hole 120G formed in the vehicle body 120.
The housing | casing 41 is formed in the rectangular parallelepiped shape, for example with FRP (fiber reinforced plastic). For the tubular member 43, for example, a pipe made of vinyl chloride can be used, and the inner surface is roughened so that friction with air is likely to occur. The Helmholtz sound absorber 40 acts to attenuate sound generated in the passenger compartment 105 by the air in the sealed space 44, which is a small-sized cavity, acting as a spring.
At this time, since the small opening 45 provided in the sealed space 44 communicates with the passenger compartment 105, a one-mass system spring / mass model is formed using the mass of air in the opening 45 as a mass. At the resonance frequency of this system, the air mass in the opening 45 is vibrated by the sound pressure in the passenger compartment 105, and the sound energy is converted into thermal energy by the friction between the peripheral wall of the opening 45 and the air mass. The That is, the sound is attenuated.

Now, the length of the opening 45 is L, the cross-sectional area of the opening 45 is S, the volume of the sealed space 44 is V, the speed of sound is C, and the effective length of the opening 45 is Le (Le≈L + 0.8 · S ^1/2 ). Then, the resonance frequency f0 of the Helmholtz sound absorber 40 is f0 = 1 / 2π (C ² S / Le · V) ^1/2 .
From this equation, the resonance frequency f0 can be adjusted by changing the cross-sectional area S or the effective length Le of the opening 45, that is, the inner diameter d or the length L of the tubular member 43, thereby reducing sound of different frequencies. I understand that I can do it.
Thus, by providing the Helmholtz sound absorber 40 on the floor 111, road noise with a relatively low frequency such as tire sound is efficiently absorbed by the Helmholtz sound absorber 40.

Note that the mounting configuration of the Helmholtz sound absorber 40 is not limited to the configuration of the above-described third embodiment, and various correspondences are possible. Further, the housing 41 of the Helmholtz sound absorber 40 may be integrally formed with the vehicle body 120.
Further, the shape of the housing 41 of the Helmholtz sound absorber 40 is not limited to a rectangular parallelepiped, and may be other shapes such as a columnar shape.

  Moreover, the tubular member 43 may be comprised so that length can be changed. Fig.15 (a) is sectional drawing which shows an example of the tubular member which can change length. FIG.15 (b) is the figure which looked at this tubular member from the arrow line of Fig.15 (a). As shown in the figure, the inner tube 43a is tubular, and a groove constituting a male screw is provided on the outer peripheral surface. As described above, the inner tube 43a is inserted into the insertion hole 42 formed on the casing 41 side of the casing 41 and the insertion hole 120G formed in the vehicle body 120, and is prevented from rotating by these. It is fixed with. The outer tube 43b is tubular, and a groove constituting a female screw is provided on the inner peripheral surface. The tubular member 43 is configured by screwing the inner tube 43a into the outer tube 43b. The user adjusts the length of the tubular member 43, that is, the length L of the opening 45 by adjusting the degree of screwing of the outer tube 43 b using an appropriate tool. Thereby, the resonance frequency f0 of the Helmholtz sound absorber 40 is determined. Note that the configuration for changing the length of the tubular member 43 is not limited to such a configuration including two screw members, and may include three or more screw members. Moreover, it is not necessary to use a screw, and for example, it may be constituted by a bellows-like tube.

  Moreover, it is good also as a structure provided with the automatic adjustment mechanism so that the length of the tubular member 43 may be adjusted automatically instead of adjusting manually. In this case, the automatic adjustment mechanism includes, for example, a microphone, a frequency analysis device, a controller, and a drive device, and the microphone converts the sound of the space in the passenger compartment into a signal. To determine the noise frequency. Then, the controller calculates the length of the tubular member 43 of the Helmholtz sound absorber 40 according to the specified frequency, and outputs a drive signal according to the calculated length to a drive device such as a solenoid to drive the drive device. Let By driving the drive device in this manner, the length of the tubular member 43 of the Helmholtz sound absorber 40 is adjusted. Note that the controller may perform feedback control when determining the drive signal corresponding to the length.

<Fourth embodiment>
Next, a fourth embodiment according to the present invention will be described. The feature of this embodiment is that a plate sound absorber and a tube sound absorber are used for the sound absorbing structure provided on the floor 111. In addition, the same code | symbol shall be attached | subjected to the component same as 1st Embodiment mentioned above, and the description shall be abbreviate | omitted.

FIG. 16 is a diagram illustrating a configuration of the floor 111 according to the fourth embodiment. In the floor 111, the vehicle body 120 under the seat is provided with the plate sound absorber 10 and the pipe sound absorber 30.
In this way, by providing the plate sound absorber 10 and the tube sound absorber 30 on the floor 111, as described in the first embodiment and the second embodiment, the plate sound absorber 10 and the tube sound absorber 30 can provide road noise, for example. Etc. can be efficiently absorbed, and a quiet feeling in the passenger compartment 105 can be enhanced.
Moreover, by using the two types of sound absorbers 10 and 30, the sound absorption efficiency can be improved as compared with the above embodiments.
The combination of the sound absorbers is not limited to the fourth embodiment, and may be a combination of the plate sound absorber 10, the tube sound absorber 30 and the Helmholtz sound absorber 40, the tube sound absorber 30 and the Helmholtz sound absorber 40.

1 is a perspective view showing a four-door sedan type vehicle according to a first embodiment of the present invention. It is a figure which shows typically the chassis of a vehicle, and the inner side of a door. It is a figure for demonstrating the setting position of a board sound-absorbing body group. It is a top view which shows the structure of a board sound-absorbing body group. It is sectional drawing which shows the attachment structure of a board sound-absorbing body. It is a figure which shows the result of the experiment which investigates the noise reduction effect in a driver's seat. It is a figure which shows the result of the experiment which investigates the noise reduction effect in a passenger seat. It is a figure which shows the result of the experiment which investigates the noise reduction effect in a right rear seat. It is a figure which shows the structure which concerns on a modification (1-3-3). It is a figure which shows another structure which concerns on a modification (1-3-3). It is the figure which showed the simulation result by the modification (1-3-6). It is a figure which shows the structure of the floor which concerns on 2nd Embodiment. It is a figure which shows the structure of the pipe | tube sound absorber which concerns on 2nd Embodiment. It is a schematic diagram which shows the principle of the said pipe | tube sound absorber. It is a figure which shows the structure which concerns on a modification (2-4-1). It is sectional drawing similar to FIG. 5 in 3rd Embodiment. It is a figure which shows an example of the tubular member which can change length. It is a figure which shows the structure of the floor which concerns on 4th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Plate sound absorber group 10, 10A ... Plate sound absorber, 100 ... Vehicle, 101 ... Bonnet, 102 ... Door, 103 ... Trunk door, 105 ... Car compartment, 106 ... Engine compartment, 107 ... Cargo compartment, 11 ... Housing Body, 111 ... Floor, 112 ... Front pillar, 113 ... Center pillar, 114 ... Rear pillar, 115 ... Ceiling, 116 ... Engine partition wall, 117 ... Trunk partition wall, 118 ... Side sill, 12 ... Opening, 120 ... Vehicle body, 120A , 120G ... insertion hole, 121 ... flat plate portion, 122 ... concave portion, 124 ... pin hole, 125 ... retaining portion, 13 ... diaphragm, 130 ... floor carpet, 136 ... sound pressure transmitting portion, 14 ... air layer, 15 ... pin , 200 ... Toe board, 30 ... Pipe sound absorber, 31 ... Pipe, 32 ... Blocking part, 33 ... Opening part, 34 ... Cavity part, 40 ... Helmholtz sound absorber, 41 Housing, 42 ... insertion holes, 43 ... tubular member, 44 ... closed space, 45 ... opening.

Claims (9)

The floor,
A vehicle body structure comprising: a sound absorbing structure provided on the floor for absorbing sound by driving sound pressure. The vehicle body structure according to claim 1,
The vehicle body structure characterized in that the portion driven by the sound pressure drive of the sound absorbing structure is disposed at a portion of the floor where the sound pressure is high. The vehicle body structure according to claim 1 or 2,
The sound absorbing structure includes a diaphragm,
A vehicle body structure characterized by a plate sound absorber having an air layer defined behind the diaphragm. The vehicle body structure according to claim 1 or 2,
The sound-absorbing structure is a pipe sound-absorbing body having a cavity that is a closed portion with one end closed and an opening with the other end opened. The vehicle body structure according to claim 4,
The tube sound absorber has a plurality of the cavities. The vehicle body structure according to claim 4,
The tube sound absorber includes a plurality of the cavities having different lengths. The vehicle body structure according to claim 1 or 2,
The sound-absorbing structure is a Helmholtz sound-absorbing body having a closed space and a tubular member that communicates the closed space with the space of the passenger compartment. The vehicle body structure according to claim 1 or 2,
The sound absorbing structure is
A plate sound absorber having a diaphragm and an air layer defined behind the diaphragm;
A tube sound absorber having a cavity that is a closed portion with one end closed and an opening with the other end opened;
A Helmholtz sound absorber having a closed space, and a tubular member communicating the closed space with the outside,
A vehicle body structure characterized by comprising a combination of any of the sound absorbers. It is the floor that becomes the floor of the passenger compartment,
A floor comprising a sound absorbing structure that is provided on a base of the floor and absorbs sound by driving sound pressure.

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