JP5315861B2 - Car body structure and instrument panel - Google Patents

Description

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

In a vehicle body structure, a technique for absorbing sound entering a vehicle compartment is known. For example, Patent Document 1 discloses a sound absorbing structure in which an acoustic panel is formed by injecting a foamed resin into a gap formed between a base material and a skin disposed on the surface of the base material in an instrument panel. It is disclosed.
JP-A-9-281974

However, the technique using a porous sound absorber such as foamed resin disclosed in Patent Document 1 uses a sound absorbing mechanism based on particle velocity driving, so it is large for low-frequency sound. Since a back air layer is necessary, sound in a relatively low frequency region such as engine noise, wind noise during running, and road noise from tires and road surfaces could not be attenuated. Porous sound-absorbing materials such as resin foams and felts with continuous voids have the maximum sound absorption coefficient when placed at the position where the acoustic particle velocity is maximum and perpendicular to the direction where the velocity is maximum. Become. For this reason, it is necessary to have a space of about λ / 4 of the target frequency behind, and a large air layer (for example, 27 cm at 315 Hz) is required to absorb the low frequency range, and it is actually installed in the vehicle interior. Not right. Therefore, the sound absorption in the low frequency region cannot be absorbed by the porous sound absorption structure with a small back air layer, and the low frequency acoustic energy cannot be dissipated.
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 an instrument panel provided below a windshield, and a sound absorbing structure that is provided in the instrument panel and absorbs sound by driving sound pressure. And the sound absorbing structure includes a plate sound absorber having a diaphragm and an air layer defined by the diaphragm, and a fundamental vibration frequency of elastic vibration of the diaphragm is the diaphragm. It is characterized in that it is in the range of 5% to 65% of the resonance frequency of the spring mass system constituted by the mass and the spring component of the air layer .
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 in the instrument panel is high .

In the vehicle body structure, it is preferable that the sound absorbing structure includes a tube sound absorbing body having a cavity which is a closed portion where one end is closed and an opening which is opened at the other end.
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 above vehicle body structure, it is preferable that the sound absorbing structure includes a Helmholtz sound absorber having a closed space and a tubular member communicating the closed space with the space of the passenger compartment .

In order to solve the above-described problems, an instrument panel employed by the present invention is an instrument panel provided below a windshield in a vehicle, and is an instrument panel base material that forms the base of the instrument panel. And a sound absorbing structure that is provided on the instrument panel base material and absorbs sound by driving sound pressure, and the sound absorbing structure includes a diaphragm and an air layer defined by the diaphragm. A basic sound frequency of elastic vibration of the diaphragm is in a range of 5% to 65% of a resonance frequency of a spring mass system composed of a mass of the diaphragm and a spring component of the air layer. 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, for example, sound such as engine sound coming from the engine compartment or the like, sound that penetrates the instrument panel and enters the vehicle compartment, It is possible to efficiently absorb the low-frequency sound that has passed through the instrument panel and reflects off the windshield.

Hereinafter, the vehicle body structure including the sound absorbing structure will be described.
<First Embodiment>
The present inventors have focused on providing a sound absorbing structure on an instrument panel provided below a windshield in a 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.
In addition, the instrument panel in this embodiment is the whole interior part provided in the downward direction of the windshield in a vehicle, and was attached to the front surface of a driver's seat and a passenger seat.

(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 this 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 110 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 110 and the door 102. The chassis 110 includes a base 111, a front pillar 112 extending upward from the base 111, a center pillar 113, a rear pillar 114, a ceiling 115 supported by the pillars 112, 113, 114, a vehicle interior 105 and a luggage compartment 107. A trunk partition partition wall 117, an instrument panel 200 provided in the vehicle interior 105 in the vehicle 100, a trunk partition partition wall 117 that is divided into the vehicle interior 105 and the luggage compartment 107, and a windshield 118 that is supported by the pillar 112 and the like. And have. The instrument panel 200 is supported by the vehicle body of the vehicle 100 in the passenger compartment 105. The instrument panel 200 is provided below the windshield 118, and is provided at a position relatively close to the engine compartment 106 shown in FIG.

(1-1-2) Instrument Panel A feature of this embodiment is that a box-shaped plate sound absorber is provided on the instrument panel 200.
FIG. 3 is a view showing the appearance of the instrument panel 200 of the present embodiment provided at the position of the region a shown in FIG. In a space formed inside the instrument panel 200, various switches, an air conditioning unit, audio equipment, and the like are accommodated in addition to instruments such as a speedometer, a fuel gauge, and a distance meter. In addition, the accommodation space formed in the instrument panel 200 and provided with the above-described accommodation is hereinafter referred to as “inside the instrument panel 200”. Specifically, the inside of the instrument panel 200 is a housing space formed between the instrument panel 200 and the engine partition barrier 116.
On the front surface of the instrument panel 200, as shown in FIG. 3, there are provided such instruments and switches, speakers 201 and 202 constituting a part of the audio equipment, a cooling / heating air outlet 203 from which the cooling / heating air blows out, and the like. . A plurality of defroster outlets 204 are provided on the upper surface of the instrument panel 200, and warm air sent from an air conditioning unit 205 described later is blown out from the defroster outlet 204. A glove box 207 is provided in the lower left part of the instrument panel 200, and a vehicle verification, a map, and the like are accommodated in the glove box 207. In the figure, the lid 208 of the glove box 207 is closed. is there.

  FIG. 4 is a diagram schematically showing the inside of the instrument panel 200 and its peripheral structure in the region a shown in FIG. FIG. 4 shows a cross section taken along the cutting line xx of FIG. As shown in the figure, in the instrument panel 200, an air conditioning unit 205, a defroster duct 206, and a plurality of plate sound absorber groups 1 are provided. In addition to what is shown in the figure, the above-described accommodation is accommodated, but the illustration is omitted here. Moreover, the plate sound-absorbing body group 1 and the hole H which were illustrated with the dotted line in the same figure shall not be provided in this embodiment, and this is demonstrated in a modification.

The air conditioning unit 205 functions as a defroster that sends warm air for removing frost on the vehicle exterior side of the windshield 118 and fog on the vehicle interior 105 side, or functions as an air conditioning device that sends air conditioning air to the vehicle interior 105. . Hot air sent from the air conditioning unit 205 as a defroster is blown out from the defroster outlet 204 toward the windshield 118 via the defroster duct 206. On the other hand, the cooling / heating air sent from the air conditioning unit 205 is blown out from the cooling / heating air outlet 203 shown in FIG. 3 via a heating air duct (not shown). A plurality of plate sound absorber groups 1 are provided in the instrument panel 200. Here, FIG. 5 is a diagram illustrating an arrangement mode of the plate sound absorber group 1 when the instrument panel 200 is viewed from the direction of arrow I (upward) shown in FIG. As shown in the figure, a plurality of plate sound absorber groups 1 are provided over a wide range on the upper inner wall in the instrument panel 200. In addition to this, as shown in FIG. 4, in the instrument panel 200, the plate sound absorber group 1 is provided on the defroster duct 206 and the inner wall at other positions.

The plate sound absorber group 1 includes a plurality of plate sound absorbers 10.
FIG. 6 is a plan view showing the structure of the plate sound absorber group 1. As shown in FIG. 2A, the plate sound absorber group 1 provided in the instrument panel 200 is composed of six 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. Each of the plate sound absorbers 10 included in the plate sound absorber group 1 has the same mounting structure. Therefore, here, the mounting structure of the plate sound absorber 10 provided in the plate sound absorber group 1 will be described as an example.
Fig.7 (a) is sectional drawing when the instrument panel 200 is cut | disconnected by 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 in the recess 122 in the direction toward the back of the paper or toward the front of the paper. As shown in the figure, the instrument panel 200 is formed of an instrument panel base material 120 formed of a synthetic resin or the like and a non-woven cloth material having sound pressure permeability. And a surface material 135 covering the surface. A portion of the surface material 135 corresponding to the plate sound absorber 10 serves as a sound pressure transmitting portion 136 that transmits the sound pressure in the instrument panel 200 to the plate sound absorber 10.

  The instrument panel base 120 is provided with a flat plate portion 121 and a rectangular concave portion 122 that is formed to open in the instrument panel 200 by projecting from the flat plate portion 121 to the side opposite to the direction of the surface material 135. And have. In addition, a plurality of pin holes 124 are formed at the bottom of the recess 122, 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 recessed portion 122.

Further, there is a structure in which the sound absorber 10 is attached as shown in FIG. That is, as shown in FIG. 2B, the instrument panel base 120 is not provided with the recess 122, but the instrument panel base 120 having a flat surface is provided with the pin holes 124, so that the plate sound absorber 10 is Protrusively attached. In this case, the surface material 135 is not provided, and a portion of the plate sound absorber 10 that is in contact with the inside (space) of the instrument panel 200 is a sound pressure transmitting portion that transmits the sound pressure inside the instrument panel 200. When the occupant looks inside the instrument panel 200, it is a case of removing or exchanging the equipment accommodated therein, and there are not many such opportunities. Therefore, since it hardly affects the design of the vehicle 100 and does not interfere with the user, such a mounting structure can be adopted.
In the following description, the configuration in the case of adopting the mounting structure shown in FIG. 7A will be described unless otherwise specified. In that case, even when the mounting structure shown in FIG. 7B is adopted, the same configuration as that of the mounting structure shown in FIG. This is because there is only a difference between whether the plate sound absorber 10 is fitted in the recess 122 of the instrument panel base material 120 or whether the plate sound absorber 10 protrudes from the instrument panel base material 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. 7A will be described as an example. As shown in FIG. 7A, the plate sound absorber 10 includes a rectangular casing 11 having an opening 12, a diaphragm 13 that closes the opening 12, and air defined in the casing 11. And a layer 14. 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, whereby the difference between the sound pressure in the instrument panel 200 transmitted to the diaphragm 13 through the sound pressure transmitting portion 136 and the sound pressure on the air layer 14 side (that is, vibration). The diaphragm 13 is driven by the difference in sound pressure before and after the plate 13. 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).
(Equation 1)

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。

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).
(Equation 2)

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.

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, the inventors conducted intensive experiments, and as a result, when 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, the above parameters are satisfied so as to satisfy the following equation (3). I found that I should 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.
(Equation 3)
0.05 ≦ fa / fb ≦ 0.65

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.
(Equation 4)
0.05 ≦ fa / fb ≦ 0.40
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) Effects and Effects of First Embodiment In the plate sound absorber 10 according to the present embodiment, the engine sound coming from the engine compartment 106, the road noise passing through the windshield, etc. in the instrument panel 200, etc. Is transmitted to the diaphragm 13 to vibrate the diaphragm 13. Due to this vibration, sound wave energy in the instrument panel 200 is consumed as mechanical energy to absorb sound, and propagation of sound transmitted through the instrument panel 200 to the passenger compartment 105 is suppressed. For example, by setting the sound absorber 10 to the value of the above parameter, low-frequency sound such as engine sound or road noise from the engine room 105 (sound pressure corresponding to the natural vibration in the instrument panel 200). The sound frequency (band of 160 Hz to 315 Hz) at which the frequency becomes locally high can be efficiently absorbed. As a result, the sound absorption effect is exhibited even for the sound that has been reflected by the windshield 118 among the sound that has passed through the instrument panel 200.
Incidentally, the instrument panel 200 usually has some kind of opening (sound pressure transmission part). Therefore, the plate sound absorber 10 provided in the instrument panel 200 consumes the sound wave energy propagated from the passenger compartment 105 into the instrument panel 200 and absorbs the sound, so that the sound transmitted to the passenger compartment 105 is absorbed. Become. On the other hand, when the inside of the instrument panel 200 is sealed with a sound insulation layer or the like so that the opening (sound pressure transmitting portion) is eliminated, the plate sound absorber 10 provided in the instrument panel 200 The sound transmitted to the instrument panel 200 without passing through the chamber 105 is absorbed. However, in this case as well, the plate sound absorber 10 absorbs the radiated sound transmitted from the engine compartment 106 via the engine partition barrier 116, which contributes to improving the quietness of the passenger compartment 105. That is, the sound pressure-driven sound absorber 10 provided in the instrument panel 200 has different functions and effects depending on whether or not the instrument panel 200 has an opening.

In the present embodiment, the box-shaped plate sound absorber 10 is provided on the instrument panel 200 of the vehicle 100. Sound with a relatively low frequency, such as engine sound, is efficiently absorbed by the sound absorber 10.
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. 8 shows the results of an experiment for examining the noise reduction effect when the plate sound absorber 10 is provided in the instrument panel 200. This graph is a frequency characteristic showing the sound pressure at the driver's seat, where the solid line indicates that there is no sound absorbing structure and the dotted line indicates that there is a sound absorbing structure. As shown in the figure, in the frequency range of 160 to 315 Hz, the noise level was reduced, and a result of absorbing sound at a low frequency where noise was concentrated was obtained. In addition, a decrease in noise level is observed even in a higher frequency range. As a result, in the vehicle body structure in the present embodiment, the plate sound absorber 10 provided in the instrument panel 200 can efficiently absorb, for example, engine sound, road noise, and the like. A feeling can be heightened.

(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. 4, a plurality of plate sound absorber groups 1 are provided in the instrument panel 200, but the positions and number of the plate sound absorber groups 1 are provided in the embodiment. It is not restricted to the aspect described in. In particular, the plate sound absorber 10 is not limited to the inside of the instrument panel 200, but may be any configuration provided in the instrument panel 200.

For example, the plate sound absorber group 1 may be provided on the lid 208 of the glove box 207 shown in FIG. The lid 208 also constitutes a part of the instrument panel base 120.
FIG. 9 is a diagram schematically showing an attachment structure of the plate sound absorber group 1 attached to the lid 208 of the glove box 207. As shown in the figure, a recess 127 is formed in the lid 208 so as to open toward the passenger compartment 105 side. The plate sound absorber group 1 composed of three plate sound absorbers 10 having the same shape as shown in FIG. 6B is fitted in the recess 127. Further, the surface of the plate sound absorber group 1 is covered with the surface material 135. The structure of the plate sound absorber group 1 is substantially the same as that shown in FIG. 7A of the first embodiment, and is attached by fitting a pin (not shown) into the pin hole. In this case, the sound pressure transmitting portion 136 transmits the sound pressure on the passenger compartment 105 side to the plate sound absorber 10. The size of each plate sound absorber 10 here is as follows.
The size of the plate sound absorber 10: height 100 mm × width 100 mm × thickness 10 mm

  Next, FIG. 10 shows the results of an experiment for examining the noise reduction effect when the plate sound absorber group 1 is provided on the lid 208 of the glove box 207 as described above. This graph is a frequency characteristic showing the sound pressure in the passenger seat, with the solid line indicating no sound absorbing structure and the dotted line indicating the presence of a sound absorbing structure. As shown in the figure, also in this case, in the frequency range of 160 to 315 Hz, the noise level was reduced, and a result of absorbing sound at a low frequency where noise was concentrated was obtained.

Further, the plate sound absorber group 1 may be provided at a position other than the glove box 207 on the side of the passenger compartment 105 of the instrument panel 200. For example, you may provide in the position (outer wall) of the lower side in the driver's seat front surface of the instrument panel base material 120 as shown with the dashed-two dotted line in FIG. In FIG. 11, the result of the experiment which investigates the noise reduction effect at the time of providing the board sound-absorbing body 10 in the instrument panel 200 is shown. In this case, each plate sound absorber 10 has a size of height 100 mm × width 100 mm × thickness 20 mm, and the plate sound absorber group 1 is composed of six plate sound absorbers 10 having the same shape. This graph is a frequency characteristic showing the sound pressure at the driver's seat. The solid line indicates that there is no sound absorbing structure and the dotted line indicates that there is a sound absorbing structure. As shown in FIG. 11, in the frequency range of 160 to 315 Hz, the noise level was reduced, and a result of absorbing sound at a low frequency where noise was concentrated was obtained. In addition, a decrease in noise level was observed even in a higher frequency range.
As described above, the expected sound absorbing effect can be obtained not only in the instrument panel 200 but also by providing the plate sound absorber 10 on the vehicle compartment 105 side of the instrument panel 200. From this, it can be said that the provision of the plate sound absorber 200 in the instrument panel 200 contributes to enhancing the quietness in the passenger compartment 105.

(1-3-2)
In the first embodiment described above, a hole H may be provided on the upper surface of the instrument panel 200 at a position closer to the seat than the defroster duct 206 as shown in FIG. By providing the hole H, the sound trapped in the passenger compartment 105 enters the instrument panel 200 using the hole H as an inlet. Since this intruded sound is absorbed by the plate sound absorber 10 in the instrument panel 200, it is possible to expect a sound absorbing effect due to this sound absorption. It is sufficient that the size of the hole H in the width direction is, for example, the same as the size of the defroster duct 206 in the width direction.

(1-3-3)
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, as shown in FIG. 7, 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 instrument panel base material 120. However, the method of attaching the plate sound absorber 10 is not limited to this. For example, similar to the method of attaching the defroster duct 206 in the first embodiment, the plate sound absorber 10 may be fixed to the instrument panel substrate 120 (including the lid 208) with an adhesive or the like.
In addition, as shown in FIG. 12, 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 surface material 135. In this case, since the air in the instrument panel 200 is transmitted to the plate sound absorber group 1 through the insertion hole 120A, the plurality of insertion holes 120A serve as sound pressure transmitting portions.

(1-3-4)
In 1st Embodiment mentioned above, although the instrument panel base material 120 and the board sound-absorbing body 10 were provided separately, it is not restricted to this. As shown in FIG. 13, a part of the instrument panel base material 120 may be used as the housing of the plate sound absorber 10A. Specifically, a rectangular recess 122A that opens in the instrument panel 200 is formed, and the diaphragm 13 is fixed directly to the opening 12 of the recess 122A. The recess 122A, the diaphragm 13, the recess 122A, and A plate sound absorber 10A is constituted by the air layer 14 defined by the diaphragm 13. In this case, a portion of the surface material 135 corresponding to the diaphragm 13 becomes the sound pressure transmitting portion 136.

(1-3-5)
Moreover, the installation aspect of the board sound-absorbing body 10 is not restricted to what was demonstrated in 1st Embodiment mentioned above. Here, FIG. 14 is a view showing the appearance of another form of the instrument panel 200. As shown in FIG. 14, a speaker SP and two plate sound absorbers 10 are provided on the upper surfaces of the instrument panel 200 near the left and right sides, respectively. FIG. 15 shows a cross section taken along the cutting line yy of FIG. As shown in FIG. 15, the speaker SP and the two plate sound absorbers 10 are housed in the recess 230 of the instrument panel 200, and the opening of the recess 230 is covered with the net N. Even in such a configuration, the plate sound absorber 10 consumes acoustic energy propagating from the passenger compartment 105 and energy of radiated sound emitted from the engine compartment 106 through the engine partition barrier 116. Absorb sound. The mounting structure of the plate sound absorber 10 is the same as that shown in FIG. Here, the configuration in which the plate sound absorber 10 is accommodated in the recess 230 in which the speaker SP is accommodated has been described. However, the sound absorber 10 may be accommodated together in a space in which other devices are accommodated, and is not limited to the net N. Further, the plate sound absorber 10 may be provided so as to face the passenger compartment 105 through the grill, the mesh, or the slit. Also in FIG. 15, the illustration of the accommodations that are confiscated in the instrument panel 200 is omitted.

(1-3-6)
In the embodiment described above, the plurality of 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. Also good. 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 state (mode) in the instrument panel 200 or the vehicle interior), specifically glass or the like. The plate sound absorber group 1 disposed in a recessed space or the like made of a reflective member is provided in the portion where the plate sound absorber group 1 includes the plate sound absorber 10 having a large size and the sound pressure becomes low. The plate sound absorber group 1 to be arranged may include a plate sound absorber 10 having a small size.

(1-3-7)
In the first embodiment described above, the structure of the plate sound absorber 10 includes a rectangular casing 11, a diaphragm 13 that closes the opening 12 of the casing 11, and an air layer defined in 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. 16 shows that the diaphragm 13 (size: 100 mm × 100 mm, thickness: 0.85 mm) is fixed to the 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 of the central part 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 ], the surface density of the peripheral member is 799 [g / m ² ], and the average density of the diaphragm 13 is (1) 783 [g / m ² ]. m ² ], (2) 799 [g / m ² ], (3) 815 [g / m ² ], (4) 831 [g / m ² ], (5) 863 [g / m ² ] This is a simulation result.
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 tube sound absorber is used for the sound absorbing structure provided in the instrument panel 200. 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. 17 is a region a shown in FIG. 2 in the second embodiment, and is a diagram schematically showing the structure in the instrument panel 200 and its peripheral structure. FIG. 17 shows a cross section taken along the cutting line xx of FIG. In the instrument panel 200, a plurality of tube sound absorbers 30 are provided in the depth direction of the drawing. The opening of the pipe sound absorber 30 is arranged from a part of the defroster outlet 204 toward the vehicle interior 105. The hot air sent from the air conditioning unit 205 is blown out from the other part of the defroster outlet 204.

  FIG. 18 is a view showing the structure of the pipe sound absorber 30 in which an opening is provided in the defroster outlet 204 of the instrument panel 200. In addition, in order to prevent the figure from becoming complicated, an opening 33 and a resistance member 34 described later are attached only to the pipe 31-1, but the other pipes have the same configuration. Moreover, in the figure, although the code | symbol is not attached | subjected about the pipes 31-2 to 31-11, these are provided in order toward the pipe 31-12 from the pipe 31-1. The pipe sound absorber 30 includes a plurality of pipes 31 (31-1 to 31-12) having different lengths, and these pipes are arranged with the opening 33 facing the defroster outlet 204. These pipes 31 are connected to each other three by one, or are connected to each other by a dedicated member, and are integrally formed. 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 arranged in a line for each of the three connected pipes 31 so that the openings 33 are adjacent to each other. Thereby, the sound pressure transmission part 136 is formed in the instrument panel base material 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 0.5 m, 0.34 m, and 0.2 m are used, and these absorb sound mainly at 170 Hz, 250 Hz, and 425 Hz, respectively. (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. 19 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. 18, the frequency of the coupled vibration between adjacent pipes s is as follows.

L1 (m) L2 (m) Coupled vibration frequency (Hz)
0.5 0.34 202
0.5 0.2 243
0.34 0.2 314
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 of each pipe 31-1 to 31-12 alone (centered at 200, 250, and 315 Hz).

(2-3) Effects and Effects of Second Embodiment As described above, by providing the pipe sound absorber 30 in the instrument panel 200, relatively low frequency noise such as engine sound and road noise is generated by the pipe sound absorber 30. Sound can be absorbed efficiently, and a quiet feeling in the passenger compartment 105 can be enhanced. Moreover, since the opening 33 is accommodated in the instrument panel 200 with the opening 33 facing the defroster outlet 204, the opening 33 of the pipe sound absorber 30 cannot be seen from the occupant, and the design inside the vehicle 100 is impaired. There is no.

(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, as shown in FIGS. 17 and 18, the soot absorber 30 is provided so that the opening portion faces the passenger compartment 105. On the other hand, as shown in FIG. 20, the pipe sound absorber 30 is arranged so that the opening 33 is directed into the instrument panel 200 in the recess 122 of the instrument panel base material 120 shown in FIG. May be accommodated. In this way, since the sound in the instrument panel 200 is absorbed by the tube sound absorber 30, the sound reflected on the windshield 118 among the sound transmitted through the instrument panel 200 can be efficiently absorbed. .

21A, the opening 33 of the tube sound absorber 30 is provided inside the speaker net N of the speakers 201 and 202 so as to open around the diaphragm D. Also good. In this case, the plurality of pipes 31A of the soot absorber 30 are arranged so as not to interfere with the speaker structure. FIG. 6B is a view of the speakers 201 and 202 of FIG. 6A viewed from the direction of arrow III, and the opening 33 of the pipe 31A faces the vehicle interior 105 side in the speakers 201 and 202. It extends linearly in the direction within the instrument panel 200. In this case, the shape of the pipe sound absorber 30 is not limited to that described above, and if it interferes with the contents in the instrument panel 200, the pipe is bent as appropriate so that the pipe does not interfere with the pipe. 31A may be extended.
Similarly, the pipe sound absorber 30 may be provided inside the cooling / heating air outlet 203 (not shown) so that the opening 33 of the pipe faces the passenger compartment side from the cooling / heating air outlet 203.
According to these configurations, the opening 33 of the soot absorber 30 can be made inconspicuous.

(2-4-2)
In the second embodiment described above, one end portion of the soot sound absorber 30 is an opening portion 33 and the other end portion is a closed portion 32, which is a so-called closed tube. However, the shape of the pipe 31 is not limited thereto. . For example, both ends of each pipe 31 may be opened to form an opening 32 and an opening 33 (so-called an open tube), or the closed tube and the open tube 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 as the sound absorbing structure provided in the instrument panel 200. 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. 22 is a cross-sectional view of the instrument panel 200 according to the third embodiment (the instrument panel 200 is provided with the Helmholtz sound absorber 40) cut along the cutting line bb in FIG.
The Helmholtz sound absorber 40 used in the present embodiment is inserted into a rectangular parallelepiped housing 41 having a space formed therein, and an insertion hole 42 formed on the inside of the instrument panel 200 of the housing 41. And a tubular member 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 the insertion hole 120G formed in the instrument panel base material 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 instrument panel 200 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 inside of the instrument panel 200, 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.
In this manner, by providing the Helmholtz sound absorber 40 in the instrument panel 200, noise with a relatively low frequency such as engine sound is efficiently absorbed by the Helmholtz sound absorber 40.

The present invention is not limited to the configuration of the third embodiment described above, and various measures are possible.
The mounting structure of the Helmholtz sound absorber 40 is not limited to the configuration of the third embodiment described above, and various correspondences are possible. Further, the housing 41 of the Helmholtz sound absorber 40 may be integrally formed with the instrument panel base material 120. Moreover, you may provide in the compartment 105 side (outside of the lid | cover 208 or the instrument panel 200) of the instrument panel base material 120 similarly to the modification of 1st Embodiment.
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 configured such that its length can be freely changed. FIG. 23 is a view showing an example of the configuration of the tubular member 43 of this aspect, (a) is a cross-sectional view of the tubular member 43 when viewed in the same direction as FIG. 23, and (b) shows the tubular member 43. It is the figure seen from the arrow line of (a).
As shown in the figure, the tubular member 43 includes an inner tube 43a and an outer tube 43b. The inner tube 43a is a tubular member, and a groove constituting a male screw is provided on the outer peripheral surface thereof. The inner tube 43a is inserted into an insertion hole 120G formed in the instrument base 120 and fixed to the instrument panel base 120 in the same manner as in FIG. The outer tube 43b is a tubular member having an inner diameter larger than that of the inner tube 43a, and a groove constituting a female screw is provided on the inner peripheral surface thereof. The tubular member 43 is configured by screwing the inner tube 43a into the outer tube 43b, and the overall length of the tubular member 43, that is, the length L of the opening 45, depends on the degree of screwing of the outer tube 43b with respect to the inner tube 43a. Determined. As shown in FIG. 5B, the outer circumference of the outer tube 43b is a hexagonal column, and the user can freely change the length L of the opening 45 by adjusting the screwing condition using a tool such as a spanner. it can. As described above, since the resonance frequency f0 of the Helmholtz sound absorber 40 is determined by the length of the tubular member 43, the user can adjust the resonance frequency f0 as needed at any time.
In order to change the length of the tubular member 43, the inner tube 43a and the outer tube 43b constitute screw members. However, the inner member 43a and the outer tube 43b may be constituted by three or more screw members, or may have a bellows shape. A scissors may be used, and various configurations that allow the tubular member 43 to expand and contract can be used. Further, the outer periphery of the outer tube 43b may not be a hexagonal column shape, but is preferably processed so that the user can easily adjust the length of the tubular member 43.

  Further, the adjustment of the length of the tubular member 43 may be automated. In this case, an automatic adjustment mechanism that adjusts the length of the tubular member 43, such as a microphone, a frequency analysis device, a controller, and a drive device, is provided. In the automatic adjustment mechanism, sound is picked up by a microphone, and a frequency analysis device analyzes a signal representing the picked-up sound to identify a particularly noisy frequency. 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 corresponding to the length to a drive device composed of a solenoid or the like. The drive device adjusts the length of the tubular member 43 of the Helmholtz sound absorber 40 according to the drive signal, so that the sound absorption characteristic of a frequency with particularly high noise is improved. Note that the controller may perform feedback control when driving according to the length of the tubular member 43.

<Fourth embodiment>
Next, a fourth embodiment according to the present invention will be described. A feature of the present embodiment is that a plate sound absorber and a tube sound absorber are used for the sound absorbing structure provided in the instrument panel 200. 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. 24 is a diagram illustrating a configuration of an instrument panel 200 according to the fourth embodiment. In the instrument panel 200, the plate sound absorber 10 is provided in the recess 122 of the instrument panel base material 120, and the interior of the instrument panel 200 is such that the opening 33 faces the vehicle interior 105 from the defroster outlet 204. The pipe sound absorber 30 is provided.
Thus, by providing the plate sound absorber 10 and the tube sound absorber 30 in the instrument panel 200, as described in the first embodiment and the second embodiment, the plate sound absorber 10 and the tube sound absorber 30 can, for example, Engine noise, road noise, and the like can be absorbed efficiently, and a quiet feeling in the passenger compartment 105 can be enhanced.
In addition, by using the two types of plate sound absorbers 10 and 30, the sound absorption efficiency can be improved as compared to 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.

<Modification>
In addition, although the various aspects which provide a sound-absorbing body in the instrument panel 200 were demonstrated in 1st-4th embodiment mentioned above, the installation aspect of a sound-absorbing body is not restricted to what was described above. For example, the case where it attaches to the housing | casing etc. of the various apparatuses accommodated in the instrument panel 200 is included.

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 showing typically the chassis of vehicles. It is the figure which showed the external appearance of the instrument panel. It is a figure which shows the structure of the instrument panel which concerns on 1st Embodiment. It is the figure which showed the arrangement | positioning aspect of the board sound-absorbing body group when an instrument panel is seen from upper direction. 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 a noise reduction effect. It is the figure which represented typically the attachment structure of the board sound-absorbing body group provided in the glove box which concerns on a modification (1-3-1). It is a figure which shows the result of the experiment which investigates the noise reduction effect which concerns on a modification (1-3-1). It is a figure which shows the result of the experiment which investigates another noise reduction effect which concerns on a modification (1-3-1). It is a figure which shows the structure which concerns on a modification (1-3-3). It is a figure which shows the structure which concerns on a modification (1-3-4). It is the figure which showed the external appearance of the instrument panel which concerns on a modification (1-3-5). It is a figure which shows the structure of the instrument panel which concerns on a modification (1-3-5). It is the figure which showed the simulation result by the modification (1-3-7). It is a figure which shows the structure of the instrument panel which concerns on 2nd Embodiment. It is a figure which shows the structure of the soot sound-absorbing body 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 a figure which shows another structure which concerns on a modification (2-4-1). It is sectional drawing similar to Fig.7 (a) in 3rd Embodiment. It is a figure explaining the structure of the tubular member which concerns on the modification of 3rd Embodiment. It is a figure which shows the structure of the instrument panel which concerns on 4th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Plate sound-absorbing body group, 10 ... Plate sound-absorbing body, 11, 41 ... Housing | casing, 12 ... Opening part, 120 ... Instrument panel base material, 13 ... Diaphragm, 135 ... Surface material, 136 ... Sound pressure transmission part, DESCRIPTION OF SYMBOLS 14 ... Air layer, 200 ... Instrument panel, 201, 202 ... Speaker, 203 ... Air-conditioning / air outlet, 204 ... Defroster outlet, 205 ... Air-conditioning unit, 206 ... Defroster duct, 207 ... Glove box, 208 ... Lid, 30 ... Tube sound absorber, 31-1 to 31-12 ... pipe, 32 ... closed portion, 33 ... opening, 34 ... resistance material, 40 ... Helmholtz sound absorber, 43 ... tubular member, 44 ... sealed space.

Claims (7)

An instrument panel provided below the windshield,
A sound-absorbing structure that is provided in the instrument panel and absorbs sound by driving sound pressure ;
The sound absorbing structure is
Including a plate sound absorber having a diaphragm and an air layer defined by the diaphragm;
A fundamental vibration frequency of elastic vibration of the diaphragm is in a range of 5% to 65% of a resonance frequency of a spring mass system constituted by a mass of the diaphragm and a spring component of the air layer. Car body structure. The vehicle body structure according to claim 1,
The vehicle body structure is characterized in that the portion driven by the sound pressure drive of the sound absorbing structure is disposed at a portion of the instrument panel where the sound pressure is high. In the vehicle body structure 請 Motomeko 1 or 2,
The sound-absorbing structure includes 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. In the vehicle body structure 請 Motomeko 3 wherein,
The tube sound absorber has a plurality of the cavities. In the vehicle body structure 請 Motomeko 3 wherein,
The tube sound absorber includes a plurality of the cavities having different lengths. In the vehicle body structure according to any one of 請 Motomeko 1 5,
The sound-absorbing structure includes 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. A instrument panel provided below the windshield in the vehicle both,
An instrument panel base material that forms the base of the instrument panel;
A sound-absorbing structure that is provided on the instrument panel base material and absorbs sound by driving sound pressure ;
The sound absorbing structure is
Including a plate sound absorber having a diaphragm and an air layer defined by the diaphragm;
A fundamental vibration frequency of elastic vibration of the diaphragm is in a range of 5% to 65% of a resonance frequency of a spring mass system constituted by a mass of the diaphragm and a spring component of the air layer. instrument panel.

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