JPH10282965A - Sound absorption device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sound absorption device capable of efficiently absorbing sound even in a narrow installation space, and also absorbing sound of even extremely frequency. SOLUTION: A resonance sound absorption material 1 is provided with an opening introducing sound waves from outside on a volume-type formed wall surface, and a resonance frequency f0 is generated from the sound waves introduced from this opening, and the wall surface is excited by the resonance frequency f0 , and the sound waves are attenuated by this vibrations and change of the vibrations into heat. At this time, this device is provided with porous type sound absorption material 4 on either opening side or counter opening side or on both sides.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound absorbing device for absorbing sound with high efficiency.

[0002]

2. Description of the Related Art For example, a vehicle emits various noises such as an engine noise, a gear noise in a transmission or a differential, a ground contact noise of a tire, and a wind noise of a vehicle body. Particularly in a construction vehicle equipped with a diesel engine, such as a wheel loader, the engine sound during a load operation is maximized. Where the fundamental frequency f of the engine sound
e can be obtained by the following equation 1 for a 4-cycle engine.

[0003]

## EQU1 ## where n is the number of cylinders and N is the engine speed rpm.

[0004] When the wind noise of the fan, the rotation noise of the supercharger, the gear noise inside the engine, the rotation noise of the hydraulic pump for work equipment, and the like are taken into account, the engine noise generates an engine sound over an audible range. It should be noted that the maximum value of the engine combustion sound usually appears as a sound at a frequency four times the fundamental frequency fe for four cycles.

[0005] In such a vehicle, the engine room is sealed to prevent external leakage of engine noise. In some cases, a sound absorbing material is provided on the inner wall surface of the engine room to absorb sound. As the sound absorbing material, it is common to use a porous sound absorbing material that is made of a fibrous, porous, or foamed material and that attenuates the sound due to airflow resistance between fibers, porous material, and air bubbles. Recently, in passenger cars, a resonance type sound absorbing material is fixed on the engine under cover, and the engine sound is converted to vibration energy by the resonance type sound absorbing material and heat energy based on the vibration to attenuate and absorb sound. Be scattered.

[0006]

However, the above conventional sound absorbing device has the following problems. (1) Even if the engine room is closed, the engine sound leaks outside by the engine cooling fan. That is, basically, it is required to reduce the sound in the engine room with higher efficiency.

(2) The porous sound absorbing material is circulating and inexpensive. However, the sound absorption coefficient tends to gradually increase as the frequency Hz increases, as shown in FIG. 11, which is a test result of a urethane product having a thickness of 25 mm, for example.
That is, there is a problem that a low frequency sound absorption coefficient is low.

(3) In the resonance type sound absorbing material, as shown in FIG. 12, an opening 12 for introducing a sound wave 20 from outside is provided on a wall surface 11 formed into a volume shape, and the sound wave 20 introduced from the opening 12 The resonance frequency fo produces a Helmholtz resonator 10 which attenuates a sound wave 20 by vibrating the wall surface 11 by the resonance frequency fo and converting the vibration into heat. Although the Helmholtz resonator 10 has a narrow range, it also resonates and absorbs a sound having a frequency near the resonance frequency fo.

[0009]

[Formula 2] fo ≒ (C / 2π) · ｛S / ｛(L + 0.8 ·
S ^1/2) · V}] ^1/2 where, C is sound velocity, S is the area of the opening 12, L is the length of the opening 12, V is the back of the internal volume of the opening 12.

As is apparent from the above equation (2), the Helmholtz resonator 10 can freely select V based on the opening area S, the opening length L and the internal volume. That is, the resonance frequency f to be absorbed
o can be set freely. That is, the resonance type sound absorbing material includes a plurality of Helmholtz resonators 10 having the same resonance frequency fo and various Helmholtz resonators 10 having different resonance frequencies fo. As a result, the resonance type sound absorbing material exhibits an extremely high sound absorbing effect for each resonance frequency fo. However, such a Helmholtz resonator 10
Has the following problems.

For ease of explanation, a trial engine will be described first. The test engine has the most standard four-cycle, six-cylinder engine with a minimum idle speed of 600 rpm and a maximum idle speed of 2500 rpm. In this case, the fundamental frequency fe is 30 to 125 Hz from the above equation (1). Also, the maximum sound is usually the fundamental frequency fe in a four-cycle engine
Since the sound has a frequency four times higher than that of the sound, the sound has a frequency of 120 to 600 Hz. That is, the loud noise in the sample engine is about 30H
It occurs at z (minimum idle speed) or higher. Further, in order to further facilitate the description, the specifications of the Helmholtz resonator 10 are set to S = 1 cm ² and L = 0.1 cm. And C = 3
4000 cm / s.

Under the above conditions, the stepwise transition of the internal volume V at which a resonance frequency fo of 30 Hz or more is obtained is obtained from the above equation (2) at fo = 30 Hz, V ≒ 33 ³ cm ³ (= 33
cm × 33 cm × 33 cm). Similarly, for example, 8
In 0Hz about 17 ³ cm ^3, 120Hz in about 13 ³ c
m ^3, 200 Hz in about 9.3 ³ cm ^3, 300Hz in about 7.1 ³ cm ^3, 400Hz in about 5.9 ³ c
m ^3, 500Hz in about 5.1 ³ cm ^3, the 600Hz about 4.5 ³ cm ^3, 700Hz in about 4.0 ³ c
m ³ , ... The reason why the inner volume V of the Helmholtz resonator 10 is indicated by the cube cubic cm ³ as described above is to make the description easy to understand. The actual Helmholtz resonator 10 has a trapezoidal or rectangular parallelepiped, a so-called perforated plate type shown in FIG.
= H · d ² ). The optimum Helmholtz resonator is determined from these.

That is, the following can be understood from the stepwise transition of the internal volume V. The resonance type sound absorbing material is, for example, 30 to 500 Hz.
About 33 ³ to about 5 to obtain a sound absorbing effect on the degree of sound.
It is that 1 ³ cm ³ is required to have a large number of Helmholtz resonator 10 having a large internal volume V that.
However, in the engine room of the vehicle, there is usually no room or area for installing a resonance type sound absorbing material having a large number of such large Helmholtz resonators 3.
The foremost, in such a narrow space, even in the provision of the Helmholtz resonator 10 which is the large internal volume V (about 33 ³ to about 5.1 ³ cm ^3), the number is only slight. That is, only a part of the resonance frequency fo, which is the extremely low frequency of 30 to 500 Hz, can be absorbed.

That is, in the above-mentioned conventional "passenger car having a resonance type sound absorbing material provided on an engine under cover", sound of about 600 Hz or more can be absorbed, but sound of about 600 Hz or less cannot be basically absorbed. Also 600-700Hz
Even the sound of extent possible sound absorption, this internal volume ^{V (4.5 3 ~4.0 3 cm 3} ) which corresponds also large, it is difficult to arrange a large number also such Helmholtz resonator 10. That is, the sound absorbing effect P1 as shown in FIG. 14 and the high sound absorbing coefficient can be obtained are limited to the range of about 700 to 2 kHz. The upper limit is about 2 kHz mainly because each Helmholtz resonator 10 is made of a resonance type sound absorbing material of the same material, and it is necessary to produce such a small Helmholtz resonator 10. Due to difficulty. In the range of about 700 to 2 kHz, as shown in FIG. 14, an extremely high sound absorption coefficient of 95% can be obtained with the resonance type sound absorbing material.

The present invention has been made in consideration of the above-described problems of the related art, and has as its object to provide a sound absorbing device that can more efficiently absorb sound even in a narrow installation space and can absorb sound of an extremely low frequency.

[0016]

In order to achieve the above object, a sound absorbing device according to the present invention firstly has an opening for introducing a sound wave from outside on a volume-shaped wall,
A resonance frequency is generated by the sound wave introduced from the opening, a wall surface is excited by the resonance frequency, and the resonance type sound absorbing material attenuates the sound wave by the vibration and the vibration is converted into heat. It is characterized by having a porous sound absorbing material on one or both of the opening side and the non-opening side.

According to the first structure, as shown in FIG. 6, the sound absorbing effect P1 (solid line) by the resonance type sound absorbing material and the sound absorbing effect P12 (solid line) obtained by superimposing the sound absorbing effect P2 (solid line) by the porous sound absorbing material. (Dotted line) is obtained. That is, according to the first configuration, sound can be absorbed more efficiently even in a narrow installation space than in the related art.

Secondly, an opening for introducing a sound wave from the outside is provided on a wall surface formed into a volume shape, and a sound wave introduced from the opening generates a resonance frequency. The resonance type sound absorbing material which attenuates the sound wave by converting this vibration into heat and the outer surfaces on the opening side of each other has a separation distance of not less than half a wavelength of the lowest resonance frequency generated by both resonance type sound absorbing materials. It is characterized by being arranged facing each other so as to face each other.

According to the second configuration, as shown in FIG. 8, the resonance type sound absorbing material 1 itself has a sound absorbing effect P of a low frequency or higher.
1 (solid line) and a second sound absorbing effect P3 (solid line) obtained by arranging two resonance-type sound absorbing materials facing each other with a separation distance of half a wavelength or more of the lowest resonance frequency among them and facing each other. Are superimposed to obtain a sound absorbing effect P13 (dotted line). That is, according to the second configuration, compared to the related art, sound can be absorbed more efficiently even in a narrow installation space, and sound of an extremely low frequency can be absorbed.

Third, the sound absorbing devices of the first configuration face each other so that their outer surfaces on the opening side face each other with a separation distance of at least half a wavelength of the lowest resonance frequency generated by both resonance type sound absorbing materials. In addition, it is characterized by being arranged facing.

According to the third configuration, as shown in FIG. 9, the sound absorbing effect P12 (solid line) of the first configuration and 2
The second sound absorbing effect P3 (solid line) obtained by arranging the two resonance type sound absorbing materials facing each other with a separation distance of at least a half wavelength of the lowest resonance frequency and a sound absorbing effect P123 (solid line). (Dotted line) is obtained. That is, according to the third configuration, sound can be absorbed more efficiently even in a narrow installation space and sound of an extremely low frequency can be absorbed as compared with the related art.

[0022]

Embodiments and Examples of the Invention FIGS.
This will be described with reference to FIG. The vehicle on which the embodiment is mounted is the wheel loader. This wheel loader uses the sample engine (4 cycles, 6 cylinders, minimum idle speed 600r).
pm, maximum idle speed 2500 rpm) is installed in the engine room.

As shown in FIG. 1, the resonance type sound absorbing material 1 used in the embodiment is obtained by forming a polypropylene sheet having a thickness of about 1 mm into convex trapezoids of various sizes, and further forming a convex trapezoid on the top surface. The hole 2 (the opening) is punched, and then the counter hole 2
The side can be fixed to the inner wall of the engine room with screws or adhesives.

Here, each of the convex trapezoids forms a Helmholtz resonator 3a, 3b,... (Hereinafter, these Helmholtz resonators 3a, 3b,.
When collectively referred to, it is simply referred to as Helmholtz resonator 3).
However, as described above, the engine room has no space for accommodating a large number of large Helmholtz resonators 3. Therefore, in the resonance type sound absorbing material 1, the Helmholtz resonator 3a having the largest size is as follows. That is, the internal volume V is set to about 4.5 ³ cm ³ , and the opening area S of the hole 2 is set to about 1c.
a Helmholtz resonator 3a which was m ^2. The smaller Helmholtz resonators 3b, 3c,.
The internal volume V is 4.5 ³ cm ³ or less and the opening area S of the hole 2
Is set to 1 cm ² or less. The length L of the opening of each Helmholtz resonator 3 is about 1 mm, which is the sheet thickness. That is, the Helmholtz resonator 3 minimizes the resonance frequency 600 Hz of the Helmholtz resonator 3a, and the Helmholtz resonators 3b, 3c,... Have resonance frequencies fob, foc,.

In the first embodiment, as shown in FIG. 2, in the resonance type sound absorbing material 1, the resonance type sound absorbing material 1 is connected to an inner wall surface 6 of an engine room 5 through a sheet-like porous sound absorbing material 4a.
Attached to. The porous sound absorbing material 4a is made of various materials such as glass wool, felt, urethane foam, and melamine foam (the same applies hereinafter).

In the second embodiment, as shown in FIG. 3, the resonance type sound absorbing material 1 is mounted on the inner wall surface 6 of the engine room 5, and the sheet type porous sound absorbing material is provided on the front side of the resonance type sound absorbing material 1. 4b was attached. In this case, as shown in FIG. 4, the Helmholtz resonator 3 may be exposed from the porous sound absorbing material 4b to the engine room 5 side.

In the third embodiment, as shown in FIG. 5, the resonance type sound absorbing material 1 is mounted on the inner wall surface 6 of the engine room 5 via the sheet-like porous sound absorbing material 4a, and the resonance type sound absorbing material is mounted. 1, a sheet-like porous sound absorbing material 4b was mounted on the front side. Also in this case, the Helmholtz resonator 3 may be exposed from the porous sound absorbing material 4b to the engine room 5 side.

The porous sound-absorbing material 4b in the second and third embodiments has a surface made of, for example, aluminum foil or paint to prevent clogging and breakage of holes in the engine room 5 where there is a lot of dust. Coated.

According to the first to third embodiments, as shown in FIG. 6, the sound absorbing effect P1 of the resonance type sound absorbing material 1 (solid line).
And a sound absorbing effect P12 (dotted line) in which the sound absorbing effect P2 (solid line) of the porous sound absorbing material 3 is superimposed.

In the fourth embodiment, as shown in FIG. 7, two pairs of resonance-type sound absorbing members 1 and 2 are opposed to each other in a space in an engine room 5 with a separation distance D therebetween. The separation distance D is 28 cm or more, and many resonance type sound absorbing materials 1 and 1 are arranged in such a space. In addition, a partition plate is provided in the space to increase the number of opposed sound-absorbing materials 1 and 1 arranged.

According to the fourth embodiment, the following effects can be obtained. In the engine room 5, a large number of engines and related devices having uneven surfaces are accommodated. The surface of the engine cover 5 such as an engine cover or an engine undercover, which is a wall surface of the engine room 5, has various shapes having irregularities. Therefore, there is little room for standing waves (that is, resonance frequencies) to occur in the engine room 5. For example, in the above-mentioned prior art "passenger car having a resonance type sound absorbing material provided on an engine under cover", the resonance type sound absorbing material and the engine oil pan hardly face each other in a parallel plane, and accordingly, the resonance type sound absorbing material is not provided. There is almost no standing wave between the material and the engine oil pan.

However, in the fourth embodiment, the two resonance type sound absorbing members 1, 1 are opposed to each other with a distance D therebetween. Therefore, a standing wave (that is, a second resonance frequency fn) is generated between the resonance type sound absorbing materials 1 and 1 separately from the sound absorption effect P1 due to the resonance frequency fo of each resonance type sound absorbing material 1 and 1. The second resonance frequency fn causes the wall surfaces of the resonance type sound absorbing materials 1 and 1 to resonate, thereby producing a second sound absorbing effect P3 of absorbing the sound having the second resonance frequency fn.

In the fourth embodiment, the distance D between the two resonance type sound absorbing materials 1 and 1 is set to 28 cm or more. The reason is as follows.

The resonance type sound absorbing material 1 in the embodiment can basically absorb a sound of about 600 Hz or more by the Helmholtz resonator 3a. However, this in other words basically means that sound below about 600 Hz cannot be absorbed. Here, the wavelength λ of 600 Hz is about 56.7 cm when the sound speed C is 34000 cm / s.
Therefore, the two resonance type sound absorbing materials 1 and 1 are separated from each other by a distance D (that is,
Wavelength) (D ≧ λ / 2),
The standing wave (that is, the second resonance frequency fn) can be generated even at a wavelength of 600 Hz or less between the two resonance type sound absorbing materials 1 and 1. Here, the half wavelength λ / 2 is about 28 cm, and thus the separation distance D is 28 cm or more.
Specifically, it is as follows.

The engine room 5 in the embodiment has a longest space D with a separation distance of about 170 cm above the engine. Therefore, two resonance-type sound absorbing materials 1 and 1 are arranged at both ends of this space so as to face each other so that the side surfaces of the respective holes 2 face each other with this separation distance D therebetween. That is, the second resonance frequency fn at the separation distance D of 170 cm is 100 Hz (170
cm is a half wavelength), 200 Hz (wavelength 170c
m), 300 Hz (2/3 wavelength of 170 cm), 400
Hz (2/4 wavelength of 170 cm), 500 Hz (170
cm) and these sounds are absorbed by the resonance type sound absorbing materials 1 and 1. Moreover, in the fourth embodiment,
A large number of resonance type sound absorbing materials 1 and 1 are arranged to face each other in a space having a separation distance D in the range of 28 to 170 cm.

Therefore, the above-mentioned second for sound above 100 Hz.
Produces the sound absorbing effect P3. In addition, two resonance type sound absorbing materials 1,
As for 1, as the number increases, the sound absorption volume increases, and as the separation distance D increases, sound of an extremely low frequency (for example, about 30 Hz) can be absorbed. Therefore, the second sound absorbing effect P3 is conceptually as shown in FIGS. It is not necessary to explain that a device having a separation distance D of 28 cm or less may be prepared.

That is, according to the fourth embodiment, as shown in FIG. 8, the resonance type sound absorbing material 1 itself has a sound absorbing effect P1 (solid line) of about 600 Hz or more, and the two resonance type sound absorbing materials 1, 1
Are arranged facing each other with a separation distance D equal to or more than half a wavelength of the lowest resonance frequency fa.
Absorption effect P13 superimposed on sound absorption effect P3 (solid line)
(Dotted line) is obtained.

In the fifth embodiment, the sound absorbing devices of the first to third embodiments are arranged facing each other as in the fourth embodiment. By doing so, as shown in FIG. 9, the sound absorbing effect P12 (solid line) of the first to third embodiments and the resonance type sound absorbing materials 1, 1
, A second sound absorbing effect P3 (solid line) superimposed on the second sound absorbing effect P3 (dotted line) is obtained.

The above embodiments can be applied not only to the engine room 5 but also to the driver's seat. In particular, the fourth and fifth embodiments can be applied outside the wheel loader. For example, as shown in FIG. 10, a driver's cab and an engine room are individually arranged on the front and rear frames, and the front and rear frames are bent by pin connection. In a so-called arched wheel loader, the outside of the outer wall between the driver's cab and the engine room is provided. The fourth and fifth embodiments may be applied to the facing surface. In this manner, when the vehicle is not arched, the resonance type sound absorbing materials 1 and 1 face each other, a second resonance frequency fn is generated, and the sound is absorbed. That is, the absolute amount of sound is reduced even if it is slight, and the surrounding noise is reduced accordingly. It is not necessary to explain that it may be arranged inside or outside the building.

Further, the Helmholtz resonator 3 in the resonance type sound absorbing material 1 is not limited to a convex trapezoid as in the above embodiment, but may be a cubic, a rectangular parallelepiped, a perforated plate type as shown in FIG. I do not care.

[Brief description of the drawings]

FIG. 1 is a partially sectional perspective view of a resonance type sound absorbing material used in an example.

FIG. 2 is a side sectional view of the first embodiment.

FIG. 3 is a side sectional view of a second embodiment.

FIG. 4 is a side sectional view of another example of the second embodiment.

FIG. 5 is a side sectional view of a third embodiment.

FIG. 6 is a characteristic graph of the first to third embodiments.

FIG. 7 is a side sectional view of an engine room according to a fourth embodiment.

FIG. 8 is a characteristic graph of the fourth embodiment.

FIG. 9 is a characteristic graph of the fifth embodiment.

FIG. 10 is a perspective view of an arched wheel loader on which the third or fourth embodiment is mounted.

FIG. 11 is a characteristic graph of a porous sound absorbing material.

FIG. 12 is a sectional view of a Helmholtz resonator.

FIG. 13 is a sectional view of another Helmholtz resonator.

FIG. 14 is a characteristic graph of a Helmholtz resonator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Resonance type sound absorbing material, 2 ... Opening (hole), 3 ... Helmholtz resonator, 4 ... Porous type sound absorbing material, 5 ... Engine room, 6
... engine room outer wall, fo ... resonance frequency, fn ... second
Resonance frequency.

Claims (3)

[Claims] An opening for introducing a sound wave from the outside is provided on a wall surface formed into a volume shape, and a resonance frequency is generated by the sound wave introduced from the opening, and the wall surface is excited by the resonance frequency. A resonance type sound absorbing material that attenuates sound waves by converting this vibration into heat, wherein the sound absorbing device has a porous type sound absorbing material on one or both of an opening side and a non-opening side of the resonance type sound absorbing material. . 2. An opening for introducing a sound wave from the outside is provided on a wall surface formed into a volume shape, and a resonance frequency is generated by the sound wave introduced from the opening, and the wall surface is excited by the resonance frequency. The resonance type sound absorbing material which attenuates the sound wave by converting this vibration into heat is opposed to each other with the outer surfaces on the opening side of each other having a separation distance of at least half a wavelength of the lowest resonance frequency generated by both resonance type sound absorbing materials. A sound absorbing device characterized by being arranged to face each other. 3. The sound absorbing device according to claim 1, wherein the outer surfaces on the opening side of each other face each other with a separation distance of at least a half wavelength of the lowest resonance frequency generated by both resonance type sound absorbing materials,
A sound absorbing device characterized by being arranged oppositely.