Sound insulation structure

Abstract

To reduce noise with a relatively wide frequency range of dominant frequencies while ensuring a function as an air passageway that an opening for communicating interior and exterior of a vehicle compartment has.SOLUTION: A sound insulation structure 10 reduces sound attempting to transmit from exterior 20A of a vehicle compartment 21 in a vehicle to interior 21A of the vehicle compartment 21. The sound insulation structure 10 includes an air passage 11 provided within the vehicle and allowing air to flow in at least either a direction from the exterior 20A toward the interior 21A or a direction from the interior 21A toward the exterior 20A. Additionally, the sound insulation structure 10 comprises a multi-tube structure 12 in which the air passage 11 is provided at an opening 11A opened to the vehicle compartment 21 and also a plurality of cylindrical inner surfaces 12A for communicating the exterior 20A and the interior 21A are arranged in a bundled state.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a sound insulation structure.

Background Art

[0002] Conventionally, in a vehicle such as an automobile, a trim member that is attached inside the vehicle and constitutes the design aspect of the passenger compartment is provided with an opening that communicates the inside and outside of the passenger compartment. This opening is a necessary configuration as a passage for air when, for example, opening and closing the vehicle door, but at the same time it also serves as a path for external noise to enter the passenger compartment. In response to this, a technique has been known in which a configuration for reducing noise transmitted from the outside to the inside of the passenger compartment is provided around the opening provided in the trim member (see, for example, Patent Document 1 below).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional technology described in Patent Document 1 above, noise reduction is achieved by forming an extended muffler on the opposite side of the design surface of the trim member. Here, the extended muffler has a characteristic that it is difficult to reduce sound for a specific frequency of sound (and its harmonics) determined by its specific shape due to resonance phenomena and the like. For this reason, the above conventional technology has a problem that the effect of reducing noise with a relatively wide frequency range of dominant frequencies (for example, road noise generated when the vehicle is running) is limited.

[0005] The present disclosure provides a sound insulation structure that can reduce noise with a relatively wide frequency range of dominant frequencies while ensuring the function as a passage for air in an opening that communicates the inside and outside of the passenger compartment.

Means for Solving the Problems

[0006] According to one aspect of the present disclosure, there is provided a sound insulation structure that reduces sound transmitted from the outside of the passenger compartment to the inside of the passenger compartment in the vehicle interior. This sound insulation structure is provided inside the vehicle and has an air passage through which air can escape in at least one of the directions from the outside to the inside or from the inside to the outside. Further, the sound insulation structure includes a multi-tube structure provided at an opening where the air passage opens into the passenger compartment and having a state in which a plurality of cylindrical inner surfaces communicating the outside and the inside are bundled together.

[0007] According to the above sound insulation structure, noise that attempts to be transmitted from the outside of the passenger compartment to the inside of the passenger compartment through the air passage passes through a plurality of cylindrical inner surfaces that communicate the outside and the inside of the passenger compartment in the multi-tube structure. These cylindrical inner surfaces allow air to escape between the inside and outside of the passenger compartment when air enters their interior, and transmit sound through the vibration of this air. Here, when sound is transmitted inside the cylindrical inner surface, the amount of air moved by the sound pressure of this sound is limited by the cylindrical inner surface. On the other hand, when sound is transmitted outside the cylindrical inner surface (such as inside the passenger compartment), the limitation on the amount of air moved by the sound pressure of this sound is less. As a result, an acoustic impedance (the quotient obtained by dividing the sound pressure of the sound by the volume velocity of the medium (e.g., air) moved by the vibration of this sound) inside the cylindrical inner surface differs from the acoustic impedance outside the cylindrical inner surface. This difference in acoustic impedance causes a so-called "open-end reflection attenuation" (a phenomenon in which, for sound attempting to escape from one end to the other end of the cylindrical inner surface, a part of the sound is reflected to the one-end side near the other end, thereby reducing the sound emitted from the other end). This open-end reflection attenuation does not have the characteristic that it is difficult to reduce sound due to a resonance phenomenon or the like for sound of a specific frequency, such as the attenuation of sound by the extended muffler described above as a conventional technique. Thereby, it is possible to provide a sound insulation structure that can reduce noise with a relatively wide frequency range of dominant frequencies while ensuring the function as a passage for air that the opening communicating the inside and outside of the passenger compartment has.

[0008] In one preferred embodiment, the sound insulation structure reduces sound belonging to a predetermined frequency range. In this sound insulation structure, the opening of each cylindrical inner surface in the multi-cylindrical structure is narrow enough so that when sound belonging to the above frequency range passes through this opening, the wave of this sound can be regarded as a plane wave.

[0009] Open-end reflection attenuation is a phenomenon that occurs under the condition that the sound wave trying to pass through the cylindrical inner surface can be regarded as a plane wave. Here, when the wavelength of the sound wave passing through this opening is too short (the frequency is too high) with respect to the size of the opening of the cylindrical inner surface, for example, both the dense part and the sparse part in the sound wave appear at the opening and this wave cannot be regarded as a plane wave, and there is a possibility that the open-end reflection attenuation will not occur well. On the other hand, according to the above sound insulation structure, by making the openings on each cylindrical inner surface of the multi-cylindrical structure narrow according to the frequency (wavelength) of the sound to be reduced, it is possible to reduce the possibility that the reduction effect due to the open-end reflection attenuation of this sound becomes small.

[0010] In the above embodiment, it is preferable that each cylindrical inner surface of the multi-cylindrical structure is long enough so that the sound wave propagating inside this cylindrical inner surface can be regarded as a plane wave.

[0011] In this case, the sound wave trying to pass through each cylindrical inner surface of the multi-cylindrical structure reaches the vicinity of the end on the passenger compartment side of the cylindrical inner surface as a plane wave even in random noise, and open-end reflection attenuation occurs there. As a result, it is possible to provide a sound insulation structure in which the possibility that open-end reflection attenuation does not occur due to reasons such as the sound wave reaching the opening of the cylindrical inner surface not being a plane wave is reduced.

Advantages of the Invention

[0012] According to the present disclosure, it is possible to provide a sound insulation structure that can reduce noise with a relatively wide frequency range of dominant frequencies while ensuring the function as an air passage of the opening communicating the inside and outside of the passenger compartment.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0014] Hereinafter, modes for carrying out the present disclosure will be described with reference to the drawings.

[0015] 〈First Embodiment〉 First, the configuration of the sound insulation structure 10 according to the first embodiment will be mainly described with reference to FIGS. 1 to 3. This sound insulation structure 10 is a sound insulation structure of the passenger compartment 21 in the vehicle of the engine vehicle 20, as shown in FIG. 2. The sound insulation structure 10 reduces noise 10A belonging to a predetermined frequency range that is transmitted to the inside 21A of the passenger compartment 21 through the air passage 11 between the body member 20B and the trim member 21B, which is located at a place outside the passenger compartment 21 in the vehicle of the engine vehicle 20.

[0016] In this embodiment, the trim member 21B is an upright deck side trim that forms part of the design surface of the passenger compartment 21 and is erected at a position behind the rear door 20C (see FIG. 1) among the left ends of the dashboard 21C that constitutes the floor of the passenger compartment 21. Further, the body member 20B is provided at a position that covers the trim member 21B from the left side and is a side panel that forms part of the design surface of the motor vehicle 20. Further, as the noise 10A, for example, road noise having a relatively wide frequency range (200 [Hz] to 5000 [Hz]) of dominant frequencies is assumed.

[0017] The sound insulation structure 10 includes an air passage 11 and an opening 11A through which the air passage 11 opens into the passenger compartment 21 from the trim member 21B. A multi-tube structure 12 in which a plurality of cylindrical inner surfaces 12A communicating the air passage 11 outside the passenger compartment 21 to the inside 21A of the passenger compartment 21 are connected in series is provided in the opening 11A. Further, a ventilation duct 11B is provided in a portion of the air passage 11 facing the outside 20D of the motor vehicle 20. With these configurations, the air passage 11 allows air to escape in both directions, i.e., from the outside 20A of the passenger compartment 21 to the inside 21A of the passenger compartment 21 (direction A in FIG. 2) and from the inside 21A to the outside 20A (direction B in FIG. 2).

[0018] As shown in FIG. 3, the multi-tube structure 12 is a structure integrally formed in a shape where a plurality of cylindrical inner surfaces 12A of the same size are bundled in a plurality of rows and a plurality of stages (6 rows and 4 stages in FIG. 3). These cylindrical inner surfaces 12A communicate the outside 20A and the inside 21A of the passenger compartment 21 to ensure the function as an air passage at the opening 11A. That is, the multi-tube structure 12 is provided so as not to impair the function as an air passage of the opening 11A of the air passage 11. Further, the length of each cylindrical inner surface 12A of the multi-tube structure 12 and the cross-sectional area of the opening 12B of each cylindrical inner surface 12A are the same. In the present embodiment, the multi-tube structure 12 is formed into a duct shape by, for example, plastic injection molding. Therefore, hereinafter, the multi-tube structure 12 is also referred to as a "duct shape". Further, each cylindrical inner surface 12A has a cylindrical shape with a cross-sectional area of the opening 12B of about 1.8 [cm 2 .

[0019] In the sound insulation structure 10, the cross-sectional area of the opening 12B of the cylindrical inner surface 12A is set to be narrow enough so that when the noise 10A propagates through the opening 12B in view of the frequency range (wavelength range) of the noise 10A to be reduced, the wave of the noise 10A can be regarded as a plane wave. Specifically, the narrower the cross-sectional area of the opening of the cylindrical inner surface, the more effectively the noise belonging to a higher frequency range can be reduced. For example, when the cross-sectional area of the opening of the cylindrical inner surface is set to about 60 [cm 2 , the noise belonging to the frequency range of about 400 [Hz] or less can be effectively reduced. Further, when the cross-sectional area of the opening of the cylindrical inner surface is set to about 3 [cm 2 , the noise belonging to the frequency range of about 5000 [Hz] or less can be effectively reduced. Further, when the cross-sectional area of the opening of the cylindrical inner surface is set to about 0.8 [cm 2 , the noise belonging to the frequency range of about 6300 [Hz] or less can be effectively reduced. However, it should be noted that if the cross-sectional area of the opening of the cylindrical inner surface is made too narrow, it becomes difficult for air to pass through this opening, and there is a risk that the function as an air passage of the opening of the air passage may be impaired.

[0020] Also, the cylindrical inner surface 12A is preferably long enough so that the sound waves transmitted through the cylindrical inner surface 12A can be regarded as plane waves. When the cross-sectional area of the opening 12B is about 1.8 [cm 2 , for example, the length may belong to the range of 1.0 [cm] to 5.0 [cm]. In the present embodiment, the length of the cylindrical inner surface 12A is 3.0 [cm].

[0021] According to the sound insulation structure 10 described above, the noise 10A that tries to be transmitted from the outside 20A of the passenger compartment 21 to the inside 21A of the passenger compartment 21 through the air passage 11 passes through a plurality of cylindrical inner surfaces 12A that communicate the outside 20A and the inside 21A of the passenger compartment 21 in the multi-stage cylinder structure 12. When air enters these cylindrical inner surfaces 12A, they allow air to escape between the inside and outside of the passenger compartment 21 while transmitting sound through the vibration of this air. Here, when sound is transmitted inside the cylindrical inner surface 12A, the amount of air moved by the sound pressure of this sound is limited by the cylindrical inner surface 12A. On the other hand, when sound is transmitted outside the cylindrical inner surface 12A, the limitation on the amount of air moved by the sound pressure of this sound is less. As a result, a difference occurs between the acoustic impedance inside the cylindrical inner surface 12A and the acoustic impedance outside the cylindrical inner surface 12A. This difference in acoustic impedance causes what is called "open-end reflection attenuation". This open-end reflection attenuation does not have the characteristic that it is difficult to reduce sound due to resonance phenomena or the like for sounds of specific frequencies, like the attenuation of sound by the extended muffler described above as a conventional technique. Thereby, it is possible to provide a sound insulation structure 10 that can reduce the noise 10A with a relatively wide frequency range of dominant frequencies while ensuring the function of the opening 11A that communicates the inside and outside of the passenger compartment 21 as a passage for air.

[0022] Note that the sound reflection due to the above-mentioned "difference in acoustic impedance" can occur at two locations, namely, near the end on the vehicle cabin 21 side of each cylindrical inner surface 12A of the multi-cylindrical structure 12 and near the end on the air passage 11 side. (Here, the "nearby" in the present disclosure refers to the region that substantially functions as the end of the cylindrical inner surface, obtained by taking into account the influence such as the so-called "open-end correction".) Therefore, the sound reflected to the air passage 11 side near the end on the vehicle cabin 21 side is partially reflected back to the vehicle cabin 21 side near the end on the air passage 11 side. However, the intensity of the sound reflected back to the vehicle cabin 21 side as described above often becomes negligibly small. Further, the noise 10A attempting to transmit from the outside 20A of the vehicle cabin 21 to the inside 21A of the vehicle cabin 21 through the air passage 11 is reduced by partial reflection near the end on the air passage 11 side, and further reduced by generating open-end reflection attenuation near the end on the vehicle cabin 21 side.

[0023] Further, according to the sound insulation structure 10, with the configuration in which the multi-cylindrical structure 12 has a plurality of cylindrical inner surfaces 12A bundled together, it is possible to secure a large total cross-sectional area of the openings 12B in the entire multi-cylindrical structure 12 while reducing the cross-sectional area of the openings 12B in each individual cylindrical inner surface 12A. As a result, it becomes easier to ensure the function as a passage for air that the opening 11A communicating the inside and outside of the vehicle cabin 21 has.

[0024] Further, according to the sound insulation structure 10, by making the openings 12B in each cylindrical inner surface 12A of the multi-cylindrical structure 12 narrow in accordance with the frequency (wavelength) of the noise 10A to be reduced, it is possible to reduce the possibility that the reduction effect due to the open-end reflection attenuation of this noise 10A becomes small.

[0025] Also, according to the sound insulation structure 10, the waves of the sound (for example, noise 10A) trying to pass through each cylindrical inner surface 12A of the multi-cylindrical structure 12 reach the vicinity of the end (opening 12B) on the passenger compartment 21 side of the cylindrical inner surface 12A as plane waves even in random noise, and opening end reflection attenuation is generated there. Thereby, it is possible to provide the sound insulation structure 10 in which the possibility that the opening end reflection attenuation does not occur due to reasons such as the sound wave reaching the opening 12B of the cylindrical inner surface 12A not being a plane wave is reduced.

[0026] Also, in the sound insulation structure 10, as described above, by narrowing the opening 12B in the cylindrical inner surface 12A according to the frequency (wavelength) of the noise 10A to be reduced, the possibility that the reflection of the noise 10A due to the opening end reflection attenuation becomes small is reduced. For this reason, if a cylindrical inner surface with a relatively large cross-sectional area of the opening is mixed in the plurality of cylindrical inner surfaces of the multi-cylindrical structure, these cylindrical inner surfaces will become paths for sound to escape, and the possibility that the sound reduction effect of the entire multi-cylindrical structure will become small is higher. On the other hand, according to the sound insulation structure 10, by making the cross-sectional areas of the openings 12B in each cylindrical inner surface 12A of the multi-cylindrical structure 12 the same, the cylindrical inner surfaces that serve as paths for sound to escape in the multi-cylindrical structure 12 are eliminated, and the possibility that the reduction effect of the noise 10A of the entire multi-cylindrical structure 12 becomes small can be reduced.

[0027] In addition, the present inventor conducted a control experiment (hereinafter, also simply referred to as the "control experiment") to verify the effect of reducing the noise 10A transmitted from the outside 20A of the passenger compartment 21 to the inside 21A of the passenger compartment 21 by the sound insulation structure 10. In this control experiment, the noise inside the passenger compartment with respect to the random noise generated outside the vehicle was measured. The experimental results of this control experiment are shown in FIG. 4.

[0028] In the graph of FIG. 4, the vertical axis represents the sound pressure level, and its unit is [dB]. Also, the horizontal axis of the graph in FIG. 4 is the 1 / 3 octave band frequency from 100 [Hz] to 6300 [Hz].

[0029] In FIG. 4, the "object" is the engine vehicle 20 (see FIG. 2) to which the sound insulation structure 10 is applied in the passenger compartment 21. Also, the "control" is an engine vehicle having exactly the same configuration as the object, except that it does not have a configuration corresponding to the multi-cylinder structure 12 (see FIG. 2) provided in the opening 11A of the trim member 21B. Therefore, in the present disclosure, the object is also referred to as "with duct shape", and the control is also referred to as "without duct shape".

[0030] According to the above experimental results, for the control (without duct shape), for the object (with duct shape), an effect of noise reduction was observed in the continuous frequency range of 125 [Hz] to 800 [Hz]. Also, in the object (with duct shape), an effect of noise reduction was also observed at each frequency from 2000 [Hz] to 6300 [Hz]. Here, in an engine vehicle, generally, the dominant frequency of the road noise generated during its running is said to be 200 [Hz] to 5000 [Hz], and similarly, the dominant frequency of the wind noise is said to be 400 [Hz] to 6300 [Hz]. From this, it can be said that the sound insulation structure 10 according to the first embodiment has an effect of reducing the road noise and (a part of) the wind noise during the running of the engine vehicle 20.

[0031] <Second Embodiment> Subsequently, the configuration of the sound insulation structure 30 according to the second embodiment will be described with reference to FIGS. 5 to 7. As shown in FIG. 5, this sound insulation structure 30 is a sound insulation structure for the passenger compartment 41 in the hybrid vehicle 40. The sound insulation structure 30 reduces various noises 30A (see FIG. 6) that tend to be transmitted from the space 40A (described later) outside the passenger compartment 41 to the inside 41A of the passenger compartment 41 in the hybrid vehicle 40. This noise 30A belongs to, for example, the frequency range of 200 [Hz] to 5000 [Hz].

[0032] The hybrid vehicle 40 is provided with seat seats arranged in three rows in the front-rear direction inside the passenger compartment 41. Hereinafter, among the seat seats arranged in three rows, the seat seat in the foremost row is also referred to as the "front seat 41B". Also, the seat seat in the second row from the front is also referred to as the "rear seat 41C". Also, the seat seat in the last row is also referred to as the "auxiliary seat 41D".

[0033] In the hybrid vehicle 40, an instrument panel 40B is disposed at a position in front of the front seat 41B. The instrument panel 40B constitutes the design surface on the front side of the passenger compartment 41 together with various components (for example, refer to the operation panel 40C shown in FIG. 5) attached to the instrument panel 40B. For this reason, the space 40A surrounded by the instrument panel 40B and the above various components becomes a space outside the passenger compartment 41 inside the hybrid vehicle 40.

[0034] The hybrid vehicle 40 is provided with two air conditioning units 40D and 40E. The air conditioning unit 40D is disposed in the space 40A described above. The air conditioning unit 40E is disposed at a position behind the auxiliary seat 41D and outside the passenger compartment 41 inside the hybrid vehicle 40.

[0035] A plurality of ducts (for example, refer to the defroster duct 31 and the duct 51 shown in FIG. 5) are connected to the air conditioning unit 40D. The defroster duct 31 extends toward a defroster air outlet 31A provided through the instrument panel 40B in the vertical direction and communicates with the defroster air outlet 31A. In the present embodiment, as shown in FIG. 6, the defroster air outlet 31A is a slit-shaped opening extending in the left-right direction of the passenger compartment 41.

[0036] As shown in FIG. 5, the duct 51 extends rearward along the floor of the passenger compartment 41 and opens into the passenger compartment 41 at the opening 51A at its tip. In the present embodiment, the opening 51A opens rearward at a position below the front seat 41B.

[0037] The air conditioning unit 40D adjusts the temperature of the air in the space 40A according to the operating state of the operation panel 40C. Further, the air conditioning unit 40D allows the temperature-adjusted air to escape into the interior 41A of the passenger compartment 41 through one or more of the plurality of ducts according to the operating state of the operation panel 40C. When the air escapes into the interior 41A of the passenger compartment 41 through the defroster duct 31, this air is blown out from the defroster air outlet 31A toward the upper windshield glass 41E. When the air escapes into the interior 41A of the passenger compartment 41 through the duct 51, this air is blown out from the opening 51A toward the foot area of the rear seat 41C.

[0038] A duct 61 for allowing the air temperature-adjusted by the air conditioning unit 40E to escape into the interior 41A of the passenger compartment 41 is connected to the air conditioning unit 40E. This duct 61 extends upward from the air conditioning unit 40E to reach the ceiling of the passenger compartment 41 and further extends forward along this ceiling. Further, a plurality of openings 61A that open into the passenger compartment 41 in a downward-facing state are provided in the portion of the duct 61 along the ceiling of the passenger compartment 41. In the present embodiment, the openings 61A of the duct 61 are provided one by one in the portion of the duct 61 located above the rear seat 41C and in the portion located above the spare seat 41D as well.

[0039] Also, in the hybrid vehicle 40, a casing 40F having a storage space 40H inside is disposed at a location under the rear seat 41C. This storage space 40H is a space that is separated from the passenger compartment 41 by the casing 40F and is outside the passenger compartment 41 inside the hybrid vehicle 40.

[0040] The casing 40F extends forward from the storage space 40H and has an air passage 71 that opens into the passenger compartment 41 at the opening 71A at its front end. Also, inside the storage space 40H, a battery assembly 40G that supplies driving power for the hybrid vehicle 40 is stored. In this embodiment, the battery assembly 40G includes a cooling fan (not shown) that cools the heat generated during its charging and discharging. This cooling fan cools the above-mentioned heat generation by introducing the air in the passenger compartment 41 into the storage space 40H through the air passage 71.

[0041] The sound insulation structure 30 includes the above-described defroster duct 31, a defroster air outlet 31A, and a multi-tube structure 32 provided by being fitted into the defroster air outlet 31A. The defroster duct 31 functions as an air passage through which air escapes from the space 40A outside the passenger compartment 41 toward the inside 41A of the passenger compartment 41. The defroster air outlet 31A functions as an opening through which the defroster duct 31 opens into the passenger compartment 41.

[0042] As shown in FIGS. 6 and 7, the multi-tube structure 32 is a structure integrally formed in a shape in which a plurality (for example, 10 in this embodiment) of cylindrical inner surfaces 32A of the same size are bundled in a row. These cylindrical inner surfaces 32A communicate the space 40A outside the passenger compartment 41 and the inside 41A of the passenger compartment 41 to ensure the function as an air passage at the defroster air outlet 31A. That is, the multi-tube structure 32 is provided so as not to impair the function as an air passage that the defroster air outlet 31A of the defroster duct 31 has. Further, in each cylindrical inner surface 32A of the multi-tube structure 32, the length and the cross-sectional area of the opening 32B are the same. In this embodiment, the multi-tube structure 32 is formed, for example, by plastic injection molding. Further, the cross-sectional area of the opening 32B of each cylindrical inner surface 32A is set to be narrow enough so that when noise 30A (see FIG. 6) belonging to the frequency range of 200 [Hz] to 5000 [Hz] is transmitted through the opening 32B, the wave of this noise 30A can be regarded as a plane wave. Further, each cylindrical inner surface 32A is made long enough so that the wave of the sound transmitted through the cylindrical inner surface 32A can be regarded as a plane wave. Specifically, each cylindrical inner surface 32A has a rectangular cylindrical shape with a length of 4.0 [cm] and a cross-sectional area of the opening 32B of about 3 [cm 2 .

[0043] According to the sound insulation structure 30 described above, the noise 30A (see FIG. 6) that tries to be transmitted from the space 40A outside the passenger compartment 41 through the defroster duct 31 to the inside 41A of the passenger compartment 41 passes through a plurality of cylindrical inner surfaces 32A that communicate the space 40A (outside the passenger compartment 41) and the inside 41A of the passenger compartment 41 in the multi-cylindrical structure 32. When air enters these cylindrical inner surfaces 32A, while allowing air to escape between the inside and outside of the passenger compartment 41, sound is transmitted by the vibration of this air. Here, when sound is transmitted inside the cylindrical inner surface 32A, the amount of air moved by the sound pressure of this sound is limited by the cylindrical inner surface 32A. On the other hand, when sound is transmitted outside the cylindrical inner surface 32A, the limitation on the amount of air moved by the sound pressure of this sound is less. As a result, an acoustic impedance difference occurs between the acoustic impedance inside the cylindrical inner surface 32A and the acoustic impedance outside the cylindrical inner surface 32A. This difference in acoustic impedance causes what is called "open-end reflection attenuation". This open-end reflection attenuation does not have the characteristic that, like the extended muffler described above as a conventional technique, it becomes difficult to reduce sound due to resonance phenomena for sounds of specific frequencies. Thereby, while ensuring the function as an air passage of the defroster air outlet 31A that communicates the inside and outside of the passenger compartment 41, it is possible to provide a sound insulation structure 10 capable of reducing the noise 30A even when the dominant frequency of the noise 30A extends over a relatively wide frequency range.

[0044] Further, according to the sound insulation structure 30, with the configuration in which the multi-cylindrical structure 32 has a plurality of cylindrical inner surfaces 32A bundled together, it is possible to ensure a large total cross-sectional area of the openings 32B in the entire multi-cylindrical structure 32 while reducing the cross-sectional area of the openings 32B in each individual cylindrical inner surface 32A. Thereby, it becomes easier to ensure the function as an air passage of the defroster air outlet 31A that communicates the inside and outside of the passenger compartment 41.

[0045] Further, according to the sound insulation structure 30, by making the openings 32B in each cylindrical inner surface 32A of the multi-cylindrical structure 32 narrow in accordance with the frequency (wavelength) of the noise 30A to be attenuated, it is possible to reduce the possibility that the reduction effect due to the open-end reflection attenuation of this noise 30A becomes small.

[0046] Further, according to the sound insulation structure 30, by making the cross-sectional areas of the openings 32B in the respective cylindrical inner surfaces 32A of the multi-tube structure 32 the same, it is possible to eliminate a cylindrical inner surface where reflection of the noise 30A hardly occurs in the multi-tube structure 32, and reduce the possibility that the noise reduction effect of the entire multi-tube structure 32 on the noise 30A becomes small.

[0047] Also, according to the sound insulation structure 30, it is possible to reduce the possibility that the opening-end reflection attenuation does not occur due to reasons such as the sound wave reaching the opening 32B in each cylindrical inner surface 32A of the multi-tube structure 32 not being a plane wave.

[0048] <Third Embodiment> Subsequently, the configuration of the sound insulation structure 50 according to the third embodiment will be described with reference to FIGS. 5 and 8. As shown in FIG. 5, this sound insulation structure 50 is a sound insulation structure of the passenger compartment 41 that is provided separately from the above-described sound insulation structure 30 inside the vehicle of the above-described hybrid vehicle 40.

[0049] The sound insulation structure 50 includes the above-described duct 51, an opening 51A, and a multi-tube structure 52 provided by being fitted into the opening 51A. The duct 51 functions as an air passage through which air escapes from the space 40A outside the passenger compartment 41 toward the inside 41A of the passenger compartment 41. The multi-tube structure 52 is provided in a state of protruding in the direction in which air escapes from the duct 51 (rearward in FIG. 5) with respect to the opening 51A of the duct 51.

[0050] As shown in FIG. 8, the multi-tube structure 52 is a structure integrally formed by molding a shape in which a plurality of types of cylindrical inner surfaces are bundled. In other words, in the multi-tube structure 52, each cylindrical inner surface is integrated in a state where a plurality are connected. The multi-tube structure 52 may be formed, for example, by plastic injection molding.

[0051] Each cylindrical inner surface of the multi-cylindrical structure 52 communicates the space 40A outside the passenger compartment 41 and the inside 41A of the passenger compartment 41, thereby ensuring the function as an air passage at the opening 51A of the duct 51 (see FIG. 5). That is, the multi-cylindrical structure 52 is provided so as not to impair the function as an air passage that the opening 51A of the duct 51 has.

[0052] In the present embodiment, the multi-cylindrical structure 52 is a structure in which eight types of cylindrical inner surfaces 52A, 52C, 52E, 52G, 52J, 52L, 52N, and 52Q having the same length (for example, 3.0 [cm]) are arranged without gaps, and a teardrop-shaped row overlaps in four stages. Here, the opening 52B of the cylindrical inner surface 52A has a teardrop shape with a round bottom. Also, the opening 52D of the cylindrical inner surface 52C has a shape obtained by vertically dividing the teardrop shape with a round bottom into two. Also, the opening 52F of the cylindrical inner surface 52E has a teardrop shape with a flat bottom. Also, the opening 52H of the cylindrical inner surface 52G has a shape obtained by horizontally dividing the design of the "warp angle" into two. Also, the opening 52K of the cylindrical inner surface 52J has a shape obtained by cutting out the corner of the design of the "warp angle". Also, the opening 52M of the cylindrical inner surface 52L has a substantially right triangle shape. Also, the opening 52P of the cylindrical inner surface 52N has a substantially equilateral triangle shape. Also, the opening 52R of the cylindrical inner surface 52Q has a substantially right triangle shape. Each of the openings 52B, 52D, 52F, 52H, 52K, 52M, 52P, and 52R has a different cross-sectional area.

[0053] According to the above-described sound insulation structure 50, noise that attempts to be transmitted from the space 40A outside the passenger compartment 41 to the inside 41A of the passenger compartment 41 through the duct 51 passes through a plurality of cylindrical inner surfaces 52A, 52C, 52E, 52G, 52J, 52L, 52N, 52Q that communicate the space 40A (outside the passenger compartment 41) and the inside 41A of the passenger compartment 41 in the multi-tube structure 52. When air enters these cylindrical inner surfaces, while allowing air to escape between the inside and outside of the passenger compartment 41, sound is transmitted by the vibration of this air. Here, when sound is transmitted inside the cylindrical inner surface, the amount of air moved by the sound pressure of this sound is limited by the cylindrical inner surface. On the other hand, when sound is transmitted outside the cylindrical inner surface, the limitation on the amount of air moved by the sound pressure of this sound is less. As a result, an acoustic impedance difference occurs between the acoustic impedance inside each cylindrical inner surface and the acoustic impedance outside each cylindrical inner surface. This difference in acoustic impedance generates what is called "open-end reflection attenuation". This open-end reflection attenuation does not have the characteristic that, like the extended muffler described above as a conventional technique, it becomes difficult to reduce sound due to resonance phenomena for sounds of specific frequencies. Thereby, while ensuring the function as a passage for air that the opening 51A of the duct 51 communicating the inside and outside of the passenger compartment 41 has, it is possible to provide a sound insulation structure 50 capable of reducing noise even when the dominant frequency of the noise extends over a relatively wide frequency range.

[0054] Here, regarding open-end reflection attenuation, it is known that if another article comes into contact with or is integrated with the opening edge of the cylindrical inner surface that generates this open-end reflection attenuation, the sound reduction effect becomes small. In contrast, according to the sound insulation structure 50, the multi-tube structure 52 that reflects noise by open-end reflection attenuation is provided in a state of protruding from the opening 51A of the duct 51. Therefore, according to the sound insulation structure 50, it is possible to suppress a decrease in the sound reduction effect due to the duct 51 coming into contact with or being integrated with the opening edges of the respective cylindrical inner surfaces 52A, 52C, 52E, 52G, 52J, 52L, 52N, 52Q in the multi-tube structure 52.

[0055] Also, according to the sound insulation structure 50, with the configuration in which the multi-tube structure 52 has a plurality of cylindrical inner surfaces bundled together, it is possible to ensure a large total cross-sectional area of the openings in the entire multi-tube structure 52 while reducing the cross-sectional area of the openings on each individual cylindrical inner surface. As a result, it becomes easier to ensure the function as an air passage of the opening 51A of the duct 51 that communicates the inside and outside of the passenger compartment 41.

[0056] <Fourth Embodiment> Subsequently, the configuration of the sound insulation structure 60 according to the fourth embodiment will be mainly described with reference to FIG. 5. This sound insulation structure 60 is a sound insulation structure for the passenger compartment 41 that is provided separately from the above-described sound insulation structures 30 and 50 inside the vehicle of the above-described hybrid vehicle 40.

[0057] The sound insulation structure 60 includes the above-described duct 61, an opening 61A, and a multi-tube structure 52 provided by being fitted into the opening 61A. The duct 61 functions as an air passage through which air escapes from the air conditioner unit 40E disposed outside the passenger compartment 41 toward the inside 41A of the passenger compartment 41. The multi-tube structure 52 is provided one by one for each of the openings 61A of the duct 61. Each multi-tube structure 52 is provided in a state of protruding in the direction in which air escapes from the duct 61 (downward in FIG. 5) with respect to the opening 61A.

[0058] Note that the multi-tube structure 52 included in the sound insulation structure 60 is a part having the same configuration as the multi-tube structure 52 included in the sound insulation structure 50. Therefore, specific descriptions of the configuration and the resulting operational effects of the multi-tube structure 52 included in the sound insulation structure 60 are omitted.

[0059] According to the sound insulation structure 60 described above, the noise that tries to be transmitted from the air conditioner unit 40E disposed outside the passenger compartment 41 to the inside 41A of the passenger compartment 41 through the duct 61 passes through a plurality of cylindrical inner surfaces 52A, 52C, 52E, 52G, 52J, 52L, 52N, 52Q that communicate the air conditioner unit 40E (outside the passenger compartment 41) and the inside 41A of the passenger compartment 41 in the multi-tube structure 52. When air enters these cylindrical inner surfaces, while allowing air to escape between the inside and outside of the passenger compartment 41, the vibration of this air transmits sound. Here, when sound is transmitted inside the cylindrical inner surface, the amount of air moved by the sound pressure of this sound is limited by the cylindrical inner surface. On the other hand, when sound is transmitted outside the cylindrical inner surface, the limitation on the amount of air moved by the sound pressure of this sound is less. As a result, an acoustic impedance difference occurs between the acoustic impedance inside each cylindrical inner surface and the acoustic impedance outside each cylindrical inner surface. This difference in acoustic impedance generates what is called "open-end reflection attenuation". This open-end reflection attenuation does not have the characteristic that it is difficult to reduce sound due to resonance phenomena or the like for sounds of specific frequencies, like the extended muffler described above as a conventional technique. Thereby, while ensuring the function as a passage for air that the opening 61A of the duct 61 communicating the inside and outside of the passenger compartment 41 has, it is possible to provide a sound insulation structure 60 capable of reducing noise even when the dominant frequency of the noise extends over a relatively wide frequency range.

[0060] <Fifth Embodiment> Subsequently, the configuration of the sound insulation structure 70 according to the fifth embodiment will be mainly described with reference to FIG. 5. This sound insulation structure 70 is a sound insulation structure for the passenger compartment 41, which is provided separately from any of the above-described sound insulation structures 30, 50, and 60 inside the above-described hybrid vehicle 40.

[0061] The sound insulation structure 70 includes the air passage 71 described above, the opening 71A, and the multi-tube structure 52 provided to be fitted into the opening 71A. In the air passage 71, air escapes from the inside 41A of the passenger compartment 41 toward the storage space 40H which is outside the passenger compartment 41. The multi-tube structure 52 is provided so as not to protrude toward the inside 41A of the passenger compartment 41 with respect to the opening 71A.

[0062] Note that the multi-tube structure 52 included in the sound insulation structure 70 is a part having the same configuration as the multi-tube structure 52 included in the sound insulation structure 50. Therefore, specific descriptions of the configuration and the resulting effects of the multi-tube structure 52 included in the sound insulation structure 70 are omitted.

[0063] According to the above-described sound insulation structure 70, the noise generated by the cooling fan of the battery assembly 40G stored in the storage space 40H which is outside the passenger compartment 41 passes through the plurality of cylindrical inner surfaces 52A, 52C, 52E, 52G, 52J, 52L, 52N, 52Q that communicate the storage space 40H and the inside 41A of the passenger compartment 41 in the multi-tube structure 52. When air enters these cylindrical inner surfaces, while allowing air to escape between the inside and outside of the passenger compartment 41, the vibration of this air transmits sound. Here, when sound is transmitted inside the cylindrical inner surface, the amount of air moved by the sound pressure of this sound is limited by the cylindrical inner surface. On the other hand, when sound is transmitted outside the cylindrical inner surface, the limitation on the amount of air moved by the sound pressure of this sound is less. Thereby, an acoustic impedance difference occurs between the acoustic impedance inside each cylindrical inner surface and the acoustic impedance outside each cylindrical inner surface. This difference in acoustic impedance causes so-called "open-end reflection attenuation". This open-end reflection attenuation does not have the characteristic that it is difficult to reduce sound due to resonance phenomena or the like for sounds of specific frequencies, like the extended muffler described as a conventional technique. Thereby, it is possible to provide the sound insulation structure 70 capable of reducing noise even when the dominant frequency of the noise extends over a relatively wide frequency range while ensuring the function as an air passage of the opening 71A that communicates the inside and outside of the passenger compartment 41.

[0064] The above-described embodiments for implementing the present disclosure have been described by the first to fifth embodiments described above. However, it is obvious to those skilled in the art that various substitutions, modifications, and changes can be made without departing from the purpose of the present disclosure. That is, the embodiments for implementing the present disclosure can include all substitutions, modifications, and changes that do not depart from the spirit and purpose of the claims attached to this specification. For example, as embodiments for implementing the present disclosure, various embodiments as follows can be implemented.

[0065] (1) The vehicles to which the sound insulation structure of the present disclosure is applicable are not limited to the above-described engine vehicle 20 (see FIG. 2) and hybrid vehicle 40 (see FIG. 5). That is, the sound insulation structure of the present disclosure can be applied to any type of vehicle having a passenger compartment, such as an electric vehicle, a railway vehicle, a towed vehicle, and the like.

[0066] (2) In the present disclosure, the multi-cylinder structure is not limited to a structure integrally formed by plastic injection molding of a shape in which a plurality of types of cylindrical inner surfaces are bundled. That is, the multi-cylinder structure of the present disclosure can be made by a manufacturing method appropriately selected, such as extrusion molding or assembly of a plurality of parts. Further, the multi-cylinder structure of the present disclosure can be made from appropriately selected raw materials, such as paper or metal.

Explanation of Reference Numerals

[0067] 10 Sound insulation structure 10A Noise 11 Air passage 11A Opening 11B Vent duct 12 Multi-cylinder structure 12A Cylindrical inner surface 12B Opening 20 Engine vehicle 20A Exterior 20B Body member 20C Rear door 20D Outside the vehicle 21 Passenger compartment 21A Inside 21B Trim member 21C Deck board 30 Sound insulation structure 30A Noise 31 Defroster duct (air passage) 31A Defroster air outlet (opening) 32 Multi-tube structure 32A Cylindrical inner surface 32B Opening 40 Hybrid vehicle 40A Space (external) 40B Instrument panel 40C Operation panel 40D Air conditioner unit 40E Air conditioner unit 40F Casing 40G Battery assembly 40H Storage space (external) 41 Passenger compartment 41A Inside 41B Front seat 41C Rear seat 41D Spare seat 41E Windshield glass 50 Sound insulation structure 51 Duct (air passage) 51A Opening 52 Multi-tube structure 52A Cylindrical inner surface 52B Opening 52C Cylindrical inner surface 52D Opening 52E Cylindrical inner surface 52F Opening 52G Cylindrical inner surface 52H Opening 52J Cylindrical inner surface 52K Opening 52L Cylindrical inner surface 52M Opening 52N Cylindrical inner surface 52P Opening 52Q Cylindrical inner surface 52R Opening 60 Sound insulation structure 61 Duct (air passage) 61A Opening 70 Sound insulation structure 71 Air passage 71A Opening

Claims

1. A sound insulation structure for reducing the sound that tries to be transmitted from the outside of the passenger compartment to the inside of the passenger compartment inside the vehicle, An air passage provided inside the vehicle and allowing air to escape in at least one of the directions from the outside to the inside or from the inside to the outside, A multi-tube structure provided at an opening where the air passage opens into the passenger compartment and having a state in which a plurality of cylindrical inner surfaces communicating the outside and the inside are bundled, Comprising, Sound insulation structure.

2. The sound insulation structure according to claim 1, Reducing the sound belonging to a predetermined frequency range, The opening of each cylindrical inner surface in the multi-tube structure is narrow enough so that when the sound belonging to the frequency range passes through the opening, the wave of this sound can be regarded as a plane wave, Sound insulation structure.

3. The sound insulation structure according to claim 2, Each cylindrical inner surface of the multi-tube structure is long enough so that the wave of the sound transmitted through the cylindrical inner surface can be regarded as a plane wave, Sound insulation structure.

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