JP2007296952A - Sound absorbing material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a sound absorbing material capable of making sound reducing effect and a ventilating property compatible. <P>SOLUTION: The sound absorbing material 10 is provided with straight holes 26 and slanting holes 28 penetrating from an end surface 16 to an end surface 18. The straight holes 26 extend in a vertical direction to the end surface 16, and the slanting holes 28 tilt in an X direction in regard to the end surface 16 by an angle θ. Therefore, the path length of the straight holes 26 and the slanting holes 28 is different, so that sound waves of noise generated in an engine shift in phase by passing through the straight holes 26 and the slanting holes 28, and the level of noise leaking to the outside by mutual interference can be reduced. Since just the tilting angles to the end surface 16 of the straight holes 26 and the slanting hole 28 are made to be different so as to reduce noise, the good ventilating property can be ensured. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sound absorbing material.

  Conventionally, various sound absorbing structures have been proposed in order to prevent the noise generated by the engine from leaking outside the vehicle. Incidentally, a vent (opening) is formed in the engine room in order to cool the engine or the like, and how to reduce engine noise leaking from the vent to the outside becomes a problem.

Patent Document 1 listed below discloses an engine noise reduction device that reduces a noise generated from an engine by providing a concave hole in a sound absorption pipe. According to this configuration, the sound wave that enters the sound absorption tube from the engine is out of phase with the sound wave that enters the recessed hole and the sound wave that does not enter the recessed hole, and the engine noise that has passed through the sound absorption tube is reduced due to mutual interference between sound waves. Has been.
JP-A-10-212973

  However, when the above-described prior art engine noise reduction device is disposed in the vent, since a part of the sound absorbing pipe is closed as a concave hole, the air permeability is lowered and the cooling performance of the engine is lowered. There's a problem.

  In view of the above facts, an object of the present invention is to obtain a sound absorbing material that exhibits predetermined noise reduction performance while ensuring air permeability.

  The sound-absorbing material according to the first aspect of the present invention is a sound-absorbing material having a constant thickness, the first passage penetrating from one surface in the thickness direction to the other surface, and the one surface to the other. The first passage and the second passage having a different path length are parallel to each other and penetrate the surface.

  According to the first aspect of the present invention, since the path lengths of the first passage and the second passage of the sound absorbing material are different, if the sound absorbing material is disposed in the vent portion of the engine room, the sound wave generated from the engine is the first. By passing through the first passage and the second passage, the phases are shifted, and mutual interference occurs. As a result, the engine noise level leaking to the outside is reduced. On the other hand, according to the sound-absorbing material according to the present invention, since there is no special structure for reducing sound waves inside the passages in both the first passage and the second passage, good air permeability for cooling the engine or the like can be secured. . In addition, since the thickness of the sound absorbing material is constant, the degree of freedom of installation is high, and for example, it can be disposed in front of the radiator.

  The sound absorbing material according to a second aspect of the present invention is the sound absorbing material according to the first aspect, wherein the first passage and the second passage are each formed in a straight line and have different inclination angles with respect to the one surface. It is characterized by.

  According to the second aspect of the present invention, the linear first passage and the second passage from one surface of the sound absorbing material to the other surface have different inclination angles with respect to the one surface, so that the path lengths can be different. it can. Therefore, if this sound absorbing material is disposed in the vent portion of the engine room, the sound waves generated from the engine are out of phase by passing through the first passage and the second passage having different path lengths and interfere with each other. As a result, the engine noise level leaking to the outside is reduced. On the other hand, according to the sound absorbing material of the present invention, both the first passage and the second passage are special in order to reduce sound waves inside each passage only by changing the inclination angle with respect to one surface of the straight passage. Since there is no structure, air permeability for cooling the engine or the like can be ensured satisfactorily.

  A sound absorbing material according to a third aspect of the present invention is the sound absorbing material according to the first or second aspect, wherein the first passage and the second passage are alternately arranged in parallel.

  According to the third aspect of the present invention, since the first passages and the second passages are alternately arranged in parallel, the sound wave generated from the engine passes through the first passage and the second passage and the phase thereof is increased. When deviated, mutual interference is more effectively performed.

  A sound absorbing material according to a fourth aspect of the present invention is the sound absorbing material according to any one of the first to third aspects, wherein when the wavelength of the sound wave to be reduced is λ, the first passage and the second The path length difference of the passage is (1/2 + n) × λ (n is a natural number).

  According to the fourth aspect of the present invention, if the path length difference between the first passage and the second passage is (1/2 + n) × λ (n is a natural number) corresponding to the wavelength λ of the engine noise to be reduced. When the sound wave having the wavelength λ passes through the first path and the second path, the phase is shifted by a half wavelength to become an opposite phase, and the noise level can be most effectively reduced.

  As described above, since the sound absorbing material according to the first aspect of the present invention includes the first passage and the second passage having different thicknesses and the sound absorbing material having a constant thickness, it passes through the first passage and the second passage. The noise level can be reduced by the mutual interference of the sound waves. In addition, since there is no special structure inside the first passage and the second passage in order to reduce the noise level, good air permeability is ensured. That is, both noise reduction performance and air permeability can be ensured satisfactorily. Moreover, since the sound absorbing material has a constant thickness, the degree of freedom of installation is high. For example, it can be installed in front of a radiator in an engine room.

  In the sound absorbing material according to the second aspect of the present invention, the path length is differentiated only by changing the inclination angle with respect to one surface of the linear first passage and the second passage. Therefore, the noise level can be reduced by the mutual interference of the sound waves that have passed through the first passage and the second passage. In addition, since there is no special structure inside the first passage and the second passage in order to reduce the noise level, good air permeability is ensured. That is, both noise reduction performance and air permeability can be ensured satisfactorily. Further, the path length of the passage can be easily changed by simply changing the inclination angle.

  In the sound-absorbing material according to the third aspect of the present invention, since the first passage and the second passage are alternately arranged, the sound waves whose phases are shifted effectively interfere with each other, and the noise reduction performance is further improved. Can do.

  Since the sound-absorbing material according to the fourth aspect of the present invention is (1/2 + n) × λ (n is a natural number) of the wavelength λ of noise for which the path length difference between the first passage and the second passage is to be reduced, the wavelength When the sound wave of λ passes through the first passage and the second passage, the phase is different by half wavelength, and the noise level of the sound reduction target can be most effectively reduced.

  Hereinafter, an embodiment of a sound absorbing material according to the present invention will be described with reference to FIGS.

  As shown in FIG. 2A, the sound absorbing material 10 is disposed in an opening portion in front of the radiator 14 disposed in front of the engine 12 in the engine room.

  As shown in FIG. 1, the sound-absorbing material 10 has a rectangular shape, and an opening 20 penetrating from the end face 16 to the end face 18 is divided by a partition wall 22 and partition walls 24A and 24B, so that a straight hole 26 and a slant The hole 28 is formed.

  The partition wall 22 divides the opening 20 in the horizontal direction (arrow Y direction in FIG. 1, hereinafter referred to as Y direction), and is provided between the end faces 30 and 32 in the horizontal direction constituting the opening 20 at regular intervals. It is what. Thus, the opening 20 is divided into small openings 20A to 20J.

  On the other hand, the partition wall 24A divides the small openings 20A, 20C, 20E, 20G, and 20I in the vertical direction (arrow X direction in FIG. 1, hereinafter referred to as X direction), and is perpendicular to the end face 16 (arrow in FIG. 1). Z direction (hereinafter referred to as Z direction), and arranged in parallel at a constant interval between the X direction end faces 34A, 36A constituting the small openings 20A, 20C, 20E, 20G, 20I. is there.

  In addition, the partition wall 24B divides the small openings 20B, 20D, 20F, 20H, and 20J in the X direction, and the small openings 20B, 20D, 20F, 20H, and 20J have an angle θ in the X direction with respect to the end face 16. It is inclined by (θ ≠ 90 °) (see FIG. 3B) and is arranged in parallel with a certain interval between the X direction end faces 34B, 36B.

  Note that the end surfaces 34A and 36A of the portion facing the partition wall 24A are formed parallel to the partition wall 24A (Z direction), and the end surfaces 34B and 36B of the portion facing the partition wall 24B are parallel to the partition wall 24B (to the end surface 16). And inclined in the X direction by an angle θ).

  Therefore, in the small openings 20A, 20C, 20E, 20G, and 20I, a portion surrounded by the partition wall 22 (end surface 30) and the partition wall 24A (end surfaces 34A, 36A) becomes the straight hole 26 (see FIG. 3A).

  As shown in FIG. 3A, the straight hole 26 is a hole extending in the Z direction from the opening 26 </ b> A formed in the end surface 16 toward the opening 26 </ b> B formed in the end surface 18. The path length L1 of the straight hole 26 is the same as the distance in the Z direction from the end face 16 to the end face 18 (thickness t of the sound absorbing material 10) (L1 = t).

  On the other hand, in the small openings 20B, 20D, 20F, 20H, and 20J, the portion surrounded by the partition wall 22 (end surface 32) and the partition wall 24B (end surfaces 34B and 36B) becomes the oblique hole 28 (see FIG. 3B). .

  As shown in FIG. 3B, the oblique hole 28 is inclined by an angle θ in the X direction with respect to the end surface 16 from the opening 28 </ b> A formed on the end surface 16 toward the opening 28 </ b> B formed on the end surface 18. It is a linear hole part. Therefore, the path length L2 of the oblique hole 28 is t / sin θ (L2 = t / sin θ). The shapes of the openings 28A and 28B are the same as the openings 26A and 26B.

  As described above, the straight holes 26 and the oblique holes 28 are respectively formed continuously in the vertical direction (the X direction in FIG. 1) in the small openings 20A to 20J. The rows in which the holes 28 are arranged are formed so as to alternate in the Y direction.

  When the sound absorbing material 10 configured in this manner is disposed in front of the radiator 14 in the engine room of the vehicle, as shown in FIG. 2A, the X direction is the upper direction, the Y direction is the vehicle width direction, Arranged so that the Z direction is the front direction. That is, it arrange | positions so that the end surface 16 of the sound-absorbing body 10 may become the engine 12 side.

(Operation and effect of this embodiment)
Next, the operation and effect of this embodiment will be described.

  Sound waves of noise generated from the engine 12 pass through the radiator 14 and reach the end surface 16 of the sound absorbing material 10. The sound wave enters the straight hole 26 and the oblique hole 28 from the openings 26A and 28A formed in the end face 16, and exits from the openings 26B and 28B formed in the end face 18. Here, the path length difference dL between the path length L1 of the straight hole 26 and the path length L2 of the oblique hole 28 is dL = L2−L1 = t / sin θ−t (see FIG. 4). The phase of the sound wave that has escaped from the hole 28 is shifted by the path length difference dL. Therefore, the sound waves that have passed through the straight hole 26 and the oblique hole 28 interfere with each other, and the engine noise level that leaks to the outside can be reduced. In particular, since the straight holes 26 and the oblique holes 28 are alternately arranged in the Y direction, sound waves that have passed through the adjacent straight holes 26 and the oblique holes 28 can effectively interfere to reduce the sound pressure. it can.

  The sound waves transmitted through the straight hole 26 and the oblique hole 28 are most preferably in the opposite phase from the viewpoint of noise reduction effect. Therefore, when the wavelength of the noise to be reduced is λ, the path length difference dL between the straight hole 26 and the oblique hole needs to satisfy the relational expression dL = (1/2 + n) × λ (n is a natural number). Here, since dL = L2−L1 = t / sin θ−t, by changing the thickness t of the sound absorbing material 10 and the inclination angle θ of the inclined hole 28 (partition wall 24B) so as to satisfy the above relational expression, Noise of the targeted wavelength (frequency) can be effectively reduced.

Here, the influence of the thickness t and the inclination angle θ of the sound absorbing material 10 on the noise reduction performance was calculated. First, let f be the frequency to be reduced most in engine noise, and V be the speed of sound.
λ = V / f
Therefore, the phase difference dθ is
dθ = dL / (V / f) × 2π = 2π (t / sin θ−t) (V / f)
It becomes.

  Here, from the formula of trigonometric function 1/2 × (sin (α + β) + sin (α−β)) = sin α · cos β, if the phase difference is 2β, the level of the original sine wave is cos β times.

Therefore, the transmitted sound level is
cos (dθ / 2) = cosπ (t / sinθ−t) / (V / f)
When this is displayed in decibels,
Reduction amount = 20 × log (cosπ (t / sin θ−t) / (V / f))
It becomes.

  The results of calculating the effect of the noise reduction level by changing the thickness t of the sound-absorbing material 10 and the angle θ of the partition wall 24B (oblique hole 28) as parameters based on this relational expression are shown in FIGS. . Thus, by changing the thickness t of the sound absorbing material 10 and the inclination angle θ of the oblique hole 28, the frequency having the greatest effect of reducing the sound pressure can be changed. Qualitatively, the frequency with the highest reduction effect is reduced by increasing the thickness t of the sound absorbing material 10, and the frequency with the highest reduction effect is increased when the inclination angle θ of the inclined hole 28 is increased. Therefore, by changing the thickness t of the sound absorbing material 10 and the inclination angle θ of the partition wall 24B (the oblique hole 28), it is possible to effectively reduce the sound pressure of a desired frequency to be reduced.

  The sound absorbing material 10 has different path lengths by making the straight holes 26 and the inclined holes 28 have different inclination angles with respect to the end face 16, that is, impedes air permeability inside the straight holes 26 and the inclined holes 28. Since nothing is arranged, the air permeability of the straight hole 26 and the oblique hole 28 is good. Therefore, it is possible to ensure good leakage of engine noise to the outside and good air permeability for cooling the engine.

  Further, since the sound absorbing material 10 is a rectangular body having a constant thickness t, the degree of freedom of arrangement is high, and the sound absorbing material 10 can be arranged in a limited space such as in front of the radiator 14 in the engine room.

[Supplementary explanation of the embodiment]
In the first embodiment described above, the sound absorbing material 10 is disposed in front of the radiator 14 in the engine room. However, the present invention is not limited to this. For example, as shown in FIG. In the case of a vehicle body having no under cover below the engine 12 and having an opening below the engine, the sound absorbing material 10 can be disposed in the opening to effectively reduce engine noise that leaks outside the vehicle, and to provide air permeability. Can be secured satisfactorily.

  In the present embodiment, the straight hole 26 and the oblique hole 28 are combined. However, the present invention is not limited to this as long as the path length is different. Both of them may be oblique holes with different inclination angles with respect to the end face 16. Moreover, since the path length may be different, the hole is not limited to a straight line.

  Furthermore, although the arrangement direction of the straight holes 26 and the oblique holes 28 is also the X direction in the present embodiment, it may be the Y direction. Moreover, it is not essential to arrange the holes of the same type in a row. That is, a configuration in which the straight holes 26 and the oblique holes 28 are alternately arranged in the X direction and the Y direction may be employed.

It is a partially cutaway perspective view of the sound absorbing material according to the present embodiment. (A) is an explanatory view of the arrangement state of the sound absorbing material according to this embodiment, and (B) is an explanatory view of the arrangement state of the sound absorbing material according to other embodiments. (A) is longitudinal section explanatory drawing of the straight hole of the sound-absorbing material which concerns on this embodiment, (B) is longitudinal section explanatory drawing of the oblique hole of the sound-absorbing material which concerns on this embodiment. FIG. 5 is an explanatory diagram of a relationship between a path length and an angle θ of the sound absorbing material according to the present embodiment. It is a sound pressure reduction effect prediction figure of the sound-absorbing material which concerns on this embodiment. It is a sound pressure reduction effect prediction figure of the sound-absorbing material which concerns on this embodiment. It is a sound pressure reduction effect prediction figure of the sound-absorbing material which concerns on this embodiment.

Explanation of symbols

10 Sound absorbing material 16 End face (one face)
18 End face (the other face)
20 Straight hole (1st passage)
22 Oblique hole (second passage)
L1 Path length of straight hole L2 Path length of oblique hole

Claims (4)

A sound absorbing material with a constant thickness,
A first passage penetrating from one surface in the thickness direction to the other surface;
A second passage penetrating from the one surface to the other surface and having a different path length from the first passage;
A sound-absorbing material characterized in that   The sound absorbing material according to claim 1, wherein the first passage and the second passage are each formed in a straight line, and have different inclination angles with respect to the one surface.   The sound absorbing material according to claim 1 or 2, wherein the first passage and the second passage are alternately arranged in parallel.   The path length difference between the first passage and the second passage is (1/2 + n) × λ (n is a natural number), where λ is the wavelength of the sound wave to be reduced. 4. The sound absorbing material according to any one of 3 above.

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