JPH08146967A - Low frequency sound absorbing material - Google Patents

Abstract

PURPOSE: To obtain characteristics excellent in decreasing low frequencies, to reduce a cost and to effectively utilize the space in an engine room by laminating a sound absorbing material layer, rubber-like spacing layer and back layer successively from a sound incident surface. CONSTITUTION: This sound absorbing material is composed by laminating the sound absorbing material layer 1, the rubber-like spacing layer 2 and the back layer 3 successively from the sound incident surface. The fiber base materials for constituting the sound absorbing material layer 1 and the back layer 3 are preferably fiber assemblies consisting essentially of synthetic fibers. The air permeation rate of the sound absorbing material layer 1 is in a range of 1/5 to 1/100 as compared with the air permeation rate of the back layer 3. The air permeability of the sound absorbing material layer 1 is in a range of 0.01 to 1cc/cm<2> sec and the air permeability of the back layer 3 is in a range of 1 to 10cc/cm<2> sec. Vulcanized rubber having IRHD hardness within a range of 10 to 90 points and a surface density within a range of 0.1 to 10kg/m<2> is preferably used as the spacing layer 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a low frequency sound absorbing material for reducing intake noise of an internal combustion engine.
The present invention relates to a low frequency sound absorbing material having excellent characteristics for reducing low frequencies in the range of 00 to 300 Hz.

[0002]

2. Description of the Related Art Generally, in an intake system of a reciprocating internal combustion engine, air is blown into a combustion chamber intermittently by opening and closing an intake valve, which causes pulsation of intake air and causes noise. ing. A resonator called a resonator is installed to reduce this noise. FIG. 2 is a schematic diagram showing a basic configuration of a conventionally known resonator. As shown in FIG. 2, the conventional resonator is mounted in the middle of the intake duct 4 and communicates with the inner intake passage of the intake duct 4 and a resonance chamber 6 communicating with the other end of the communication part 5.
It consists of and.

The conventional resonator is based on the general name of a Helmholtz type resonator, and its sound absorbing mechanism is such that when a sound wave having a resonance frequency enters a cavity in the system as shown in FIG. It vibrates violently, and the sound energy is lost due to the friction loss with the side wall, and the sound is absorbed. The resonance frequency is represented by the following equation (1), and the maximum sound absorption coefficient is obtained at that frequency.

[0004]

[Equation 1] Here, f is the resonance frequency, C is the speed of sound, D is the inner diameter of the communication portion, t is the length of the communication portion, and V is the internal volume of the resonance chamber. On the other hand, there is also known a method of using a sound absorbing material such as felt, urethane and a fibrous body in order to reduce noise.

[0005]

However, the conventional resonators have the drawback that they are effective only for very narrow frequencies and cannot exhibit sufficient sound absorbing performance. Therefore, when the noise generated by the pulsation of intake air appears at a plurality of frequencies, a resonator has to be installed for each of them. Further, although the resonator is practically installed so as to exert an effect on low-frequency noise in the range of 100 to 300 Hz, the inner volume of the resonance chamber increases as the frequency becomes lower, and the engine room is occupied. The ratio will increase. further,
Increasing the internal volume brings about high rigidity of the intake duct, which is also a factor of increasing weight and increasing cost.

On the other hand, the conventional method of using a sound absorbing material such as felt, urethane and fibrous body is effective for noise of 500 Hz or more, but for low frequency noise in the range of 100 to 300 Hz. There was a drawback that a sufficient effect could not be obtained.

Therefore, the present invention has been made in view of the above circumstances, and has a structure in which a sound absorbing material layer, a rubber-like intermaterial layer, and a back layer are laminated in this order from the sound incident surface.
By developing a low-frequency sound absorbing material with excellent characteristics for reducing low frequencies in the range of 00 Hz, we aim to replace conventional resonators, reduce costs, and effectively use space in the engine room. To aim.

[0008]

SUMMARY OF THE INVENTION The above objects of the present invention are as follows.
This has been achieved by a low-frequency sound absorbing material, characterized in that a sound absorbing material layer, a rubber-like interlayer material layer, and a back layer are laminated in this order from the sound incident surface.

[0009]

Next, the operation of the present invention will be described. FIG. 1 shows the basic structure of the low frequency sound absorbing material of the present invention. In the sound absorbing material of the present invention, the sound absorbing peak frequency substantially matches the logical value of the membrane resonance expressed by the following equation (2). Therefore, the sound absorbing mechanism of the sound absorbing material of the present invention is the sound absorbing material layer 1 and the rubber-like interstitial material layer. It is considered that 2 and 1 form an integrated film and absorb sound by its resonance.

[0010]

[Equation 2] Where f is the resonance frequency, C is the speed of sound, ρ is the air density, and M is
Is the areal density of the film and L is the thickness of the back layer.

Each layer will be described in more detail below.

Sound Absorbing Material Layer 1 In the present invention, the fiber base material forming the sound absorbing material layer 1 is preferably a fiber assembly containing synthetic fibers as a main component. Although the fineness of the synthetic fiber is not particularly specified, the fineness should be small in order to improve the sound absorbing performance. This is because the sound absorption by the fibrous body is absorbed by the sound energy being converted into thermal energy by vibrating the fiber.

In the case of ultrafine fibers, the number of fibers per unit volume increases, so that the sound absorbing performance also improves.
In the melt blown manufacturing method in which molten resin is extruded by applying pressure from pores to form fibers, ultrafine fibers at a level of several microns can be obtained, and a fiber body having high sound absorbing performance can be obtained. In addition, the ventilation volume of the sound absorbing material layer 1 is 1% greater than that of the back layer 3.
In the range of / 5 to 1/100, and when the sound absorbing material layer 1 is a high density layer having an air permeability of 0.01 to 1 cc / cm ² sec, reduction of a low frequency of 200 Hz or less, in particular. Is effective for.

Interstitial material layer 2 In the present invention, the interstitial material layer 2 has an IRHD hardness of 10-9.
Vulcanized rubber in the range of 0 points is preferable. The rubber type can be appropriately selected and used from known rubbers, and may be natural rubber or synthetic rubber. Moreover, the compounding is also arbitrary.

There is a correlation between the surface density (Kg / m ² ) of rubber and the sound absorption peak frequency, and the sound absorption peak frequency shifts to the lower frequency side as the surface density increases. Therefore, the sound absorbing performance can be exhibited at an arbitrary frequency by selecting the optimum surface density of rubber. In order to exhibit the sound absorbing performance in the range of 100 to 300 Hz which is the main set frequency of the resonator, it is preferable to use a vulcanized rubber having an area density of 0.1 to 10 kg / m ² . Also, the interstitial layer 2
When a rigid body such as a polyethylene plate is used as
No rubber-like effect.

Back Layer 3 In the present invention, the fiber base material forming the back layer 3 is preferably a fiber assembly mainly composed of synthetic fibers similar to the sound absorbing material layer 1. Contrary to the case of the sound absorbing material layer 1, a low density layer having an air permeability of 1 to 10 cc / cm ² sec is preferable.

In the present invention, the use of the laminated sound absorbing material in the space on the internal combustion engine side or the space on the air intake side partitioned by the air filter element in the air cleaner of the vehicle, or on both sides of the space reduces noise in the low frequency range. It is especially effective in reducing. This makes it possible to remove a part or all of the resonator and the resonance duct attached to the air cleaner, so that it is possible to secure the space in the engine and reduce the cost for removing accessory parts.

[0018]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited thereto.

In the experiment, a normal incidence sound absorption coefficient measuring apparatus as shown in FIG. 3 was used. This device emits sound from a speaker 7 installed on one wall surface, and after being absorbed by a test body 9, a reflected sound is detected by a microphone 8. The sound absorption coefficient of the test body 7 can be obtained from the output component and the reflection component. Note that L indicates the thickness of the back air layer provided behind the test body by the piston 10.

The function of a conventional resonator can be reproduced by using an acrylic plate having a hole of φ10 mm as the perforated plate 9 and forming a back air layer. In this case, the diameter of the hole of the acrylic plate corresponds to the inside D of the communicating portion, the plate thickness of the acrylic plate corresponds to the length t of the communicating portion, and the volume of the back air layer corresponds to the internal volume V of the resonance chamber. In the case of the laminated sound absorbing material of the present invention, the thickness was unified to 47 mm, and the measurement was performed without taking the back air layer.

Example 1 A polypropylene fiber having an air permeability of 0.04 cc / cm ² sec and a thickness of 10 mm manufactured by a melt blown method was used for the sound absorbing material layer 1, and an interfacial density of 4.0 Kg / m ² was used for the interstitial material layer ^2. And thickness 2
A sound absorbing material was prepared by laminating a natural rubber (IRHD hardness: 50) of mm and a polypropylene fiber of 1 d or less having an air permeability of ² cc / cm ² sec in the back layer 3.

Example 2 As the interstitial layer 2, an areal density of 1.0 Kg / m ² and a thickness of 0.5 mm
A sound absorbing material was produced in exactly the same manner as in Example 1 except that the natural rubber (IRHD hardness: 50) was used.

Example 3 A sound absorbing material was prepared in the same manner as in Example 1 except that natural rubber (IRHD hardness 50) having an areal density of 2.0 Kg / m ² and a thickness of 1 mm was used as the interstitial layer 2. did.

Example 4 As the interstitial layer 2, S having an areal density of 8.6 Kg / m ² and a thickness of 4 mm.
A sound absorbing material was prepared in exactly the same manner as in Example 1 except that BR (IRHD hardness 62) was used.

Example 5 As the interstitial layer 2, N having an area density of 2.4 Kg / m ² and a thickness of 2 mm was used.
A sound absorbing material was produced in exactly the same manner as in Example 1 except that BR (IRHD hardness 70) was used.

Example 6 E having an area density of 2.4 Kg / m ² and a thickness of 2 mm was used as the interstitial material layer 2.
A sound absorbing material was prepared in exactly the same manner as in Example 1 except that PDM (IRHD hardness 73) was used.

Example 7 Sound absorbing material layer 1 having air permeability of ² cc / cm ² sec and thickness of 10 mm
A sound absorbing material was prepared in exactly the same manner as in Example 1 except that the polypropylene fiber was used.

Example 8 As the sound absorbing material layer 1, the air permeability was 10 cc / cm ² sec and the thickness was 10 m.
A sound absorbing material was prepared in exactly the same manner as in Example 1 except that the polyester fiber of m and the polyester fiber having the air permeability of 10 cc / cm ² sec were used as the back layer 3.

Comparative Example 1 A sound absorbing material was prepared in exactly the same manner as in Example 1 except that a polyethylene plate having an areal density of 1.9 Kg / m ² and a thickness of 2 mm was used as the interlayer layer 2.

Comparative Example 2 A sound absorbing material was prepared in exactly the same manner as in Example 1 except that a polyethylene plate having an areal density of 4.6 Kg / m ² and a thickness of 5 mm was used as the interlayer layer 2.

Reference Example 1 A sound absorbing material was prepared in exactly the same manner as in Example 1 except that the interlayer layer 2 was not used.

Reference Example 2 A sound absorbing material was prepared by laminating 47 mm of polypropylene fibers having an air permeability of ² cc / cm ² sec at 1 d or less.

Conventional Example 1 A resonator having a thickness of 70 mm was used as a perforated plate, and the depth L of the back air layer was set to 30 mm to reproduce the resonator.

Conventional Example 2 A resonator was reproduced by using a 40 mm-thick acrylic plate as a perforated plate and setting the depth L of the back air layer to 30 mm.

Conventional Example 3 A sound absorbing material was prepared by laminating 47 mm of polyester fibers having an air permeability of 10 cc / cm ² sec.

For each of the examples, comparative examples, reference examples and conventional examples, the normal incident sound absorption coefficient at 50 to 1600 Hz was measured using the apparatus shown in FIG. 4 to 18 and Table 1 show the measurement results of each Example, Comparative Example, Reference Example and Conventional Example.

[0037]

[Table 1]

4 to 11 and Table 1, the sound absorption peak of the embodiment constructed according to the present invention is in the low frequency region in the range of 100 to 300 Hz as in the resonators of Conventional Examples 1 and 2. I understand. 12 to 13 and Table 1, the comparative example constructed under the conditions deviating from the present invention does not change the sound absorbing performance as compared with the reference example, and the effect of the present invention cannot be obtained.

[0039]

As described above, since the low frequency sound absorbing material of the present invention can exhibit the sound absorbing performance in the low frequency range of 100 to 300 Hz, it can replace the conventional resonator. ) It becomes possible to remove part or all of the resonator and resonance duct attached to the air cleaner,
The space in the engine room can be effectively utilized, and 2) it becomes possible to remove part or all of the resonator and resonance duct attached to the air cleaner,
There are practical effects such as the cost reduction of removing accessory parts.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a low frequency sound absorbing material of the present invention.

FIG. 2 is a schematic diagram showing a basic configuration of a conventional intake noise reduction device (resonator) for an internal combustion engine.

FIG. 3 is a schematic diagram of a normal incidence sound absorption coefficient measuring apparatus used for confirming the effect of the present invention.

4 is a measurement result obtained by measuring a normal incidence sound absorption coefficient of Example 1 using the apparatus shown in FIG.

5 is a measurement result obtained by measuring a normal incidence sound absorption coefficient of Example 2 by using the apparatus shown in FIG. 3. FIG.

6 is a measurement result obtained by measuring a normal incidence sound absorption coefficient of Example 3 using the apparatus shown in FIG. 3. FIG.

FIG. 7 is a measurement result obtained by measuring a normal incidence sound absorption coefficient of Example 4 using the apparatus shown in FIG.

8 is a measurement result obtained by measuring a normal incidence sound absorption coefficient by using the apparatus shown in FIG. 3 for Example 5. FIG.

9 is a measurement result obtained by measuring a normal incidence sound absorption coefficient of Example 6 using the apparatus shown in FIG.

10 is a measurement result obtained by measuring the normal incident sound absorption coefficient of Example 7 using the apparatus shown in FIG. 3. FIG.

11 is a measurement result obtained by measuring the normal incident sound absorption coefficient of Example 8 using the apparatus shown in FIG. 3. FIG.

12 is a measurement result obtained by measuring the normal incidence sound absorption coefficient of Comparative Example 1 using the apparatus shown in FIG.

13 is a measurement result obtained by measuring a normal incidence sound absorption coefficient of Comparative Example 2 using the apparatus shown in FIG. 3. FIG.

14 is a measurement result obtained by measuring a normal incident sound absorption coefficient using the apparatus shown in FIG. 3 for Reference Example 1. FIG.

15 is a measurement result obtained by measuring a normal incidence sound absorption coefficient by using the device shown in FIG. 3 for Reference Example 2. FIG.

16 is a measurement result obtained by measuring a normal incidence sound absorption coefficient using the apparatus shown in FIG. 3 for Conventional Example 1. FIG.

FIG. 17 is a measurement result obtained by measuring the normal incident sound absorption coefficient of the conventional example 2 using the apparatus shown in FIG. 3.

FIG. 18 is a measurement result obtained by measuring a normal incidence sound absorption coefficient of Conventional Example 3 using the apparatus shown in FIG. 3.

Claims (8)

[Claims] 1. A low-frequency sound-absorbing material comprising a sound-absorbing material layer, a rubber-like interlayer material layer, and a back layer laminated in this order from the sound incident surface. 2. The rubber-like interstitial material layer has IRHD hardness (JIS
In K6253) in the range of 10 to 90 points, the surface density of 0.1 to 10 low-frequency sound absorption material according to claim 1, characterized in that it consists of vulcanized rubber in the range of Kg / m ^2. 3. A sound absorbing material layer and a back layer are made of a fiber aggregate, and the fiber aggregate has a polyester or polypropylene fiber having a softening point substantially equal to each other, or a polyester or polypropylene fiber having a softening point different by at least 20 ° C. or more. The low-frequency sound absorbing material according to claim 1 or 2, wherein the sound absorbing material is for low frequencies. 4. The low frequency according to claim 1, wherein the sound absorbing material layer and the back layer are made of a fiber aggregate and are mainly composed of a synthetic fiber having a thickness of 0.1 to 60 μm. Sound absorbing material. 5. The sound absorbing material layer and the back layer are a high density layer and a low density layer, respectively, and the sound absorbing material layer has a ventilation amount in the range of 1/5 to 1/100 as compared with the back layer. 5. The low frequency sound absorbing material according to claim 1. 6. The sound absorbing material layer has an air permeability of 0.01 to 1 cc / cm.
It is in the range of ² sec and the air permeability of the back layer is 1 to 10 cc / cm.
The low frequency sound absorbing material according to claim 1, wherein the sound absorbing material has a range of ² sec. 7. The sound absorbing material for low frequencies according to claim 1, wherein the laminated sound absorbing material is used in a vehicle. 8. The laminated sound absorbing material is used inside an air cleaner system of a vehicle.
Sound absorbing material for low frequencies described.