WO2020217862A1

WO2020217862A1 - Noise reduction structure for exhaust pipes

Info

Publication number: WO2020217862A1
Application number: PCT/JP2020/014391
Authority: WO
Inventors: 森川　修; 森　正; 馬渕　知樹
Original assignee: ニチアス株式会社; トヨタ自動車株式会社
Priority date: 2019-04-26
Filing date: 2020-03-27
Publication date: 2020-10-29
Also published as: JP6831422B2; JP2020180604A

Abstract

Provided is a novel noise reduction structure for exhaust pipes that has sufficient noise reduction performance particularly for low frequency sound of no more than 1 kHz, even when the structure is thin.　The noise reduction structure for exhaust pipes has a mat that: contains inorganic fibers; has an inorganic fiber molded article as the base material therefor; and is arranged between an inner pipe and an outer pipe. The inorganic fiber-containing mat: comprises a prescribed amount of inorganic binder dispersed inside an inorganic fiber molded body comprising an inorganic fiber needle workpiece having a prescribed needle processing hole; and has an inorganic porous membrane having a prescribed ventilation resistance, upon a main surface on one side. The noise reduction structure for exhaust pipes is characterized by having a thickness of 5–30 mm and having the surface upon which the inorganic porous membrane is provided being arranged so as to face the inner pipe.

Description

Sound reduction structure for exhaust pipe

The present invention relates to a sound reduction structure for an exhaust pipe.

In recent years, the harmonization of standards for automobile noise has been examined at the United Nations Economic Commission for Europe (ECE) World Forum for Harmonization of Automotive Standards, and rules regarding vehicle structure have been established and revised.
Regarding noise outside the vehicle, a regulation value is set in the above ECE Rule 51 (ECE R51), and according to Regulation EU No. 540/2014, which sets the regulation value, 72 dB (Phase 1) by July 2016. , 70 dB (Phase 2) by July 2020, 68 dB (Phase 3) by July 2024, and stricter standards will be enforced, and the regulation level of outside noise will be finally set to July 2016. It is required to reduce by 4 dB with respect to the standard, that is, to reduce the sound pressure energy to about 1 / 2.5.

The above requirements are very strict, but on the other hand, the noise of the automobile is not only the noise generated from the drive system engine room such as the engine, motor, and transmission, but also the exhaust noise, wind noise, tire road noise, etc. However, noise reduction measures are required for each of them, but in the evaluation test method adopted in ECE R51, measures for exhaust noise are particularly required.

The above exhaust noise is the exhaust manifold, exhaust manifold direct type catalytic converter, front pipe, underfloor catalytic converter, sub muffler (center muffler), main muffler, tail end pipe, muffler cutter, etc., in which the engine combustion gas is sequentially connected from the engine exhaust section. (For example, see Patent Document 1), but in the evaluation test method adopted in the above ECE R51, the specific gravity of the acceleration noise is higher than that of the conventional measurement method. This is because the exhaust noise accounts for about 1/4 of the total noise level.

In the above evaluation test method, acceleration noise from a speed of 40 km / h is targeted, and in particular, the specific gravity occupied by noise in a relatively low frequency region of 1 kHz or less increases, so countermeasures are urgently needed.

As a noise reduction measure for the exhaust pipe muffler, sound reduction measures have been taken by installing a sound absorbing material, but as the sound absorbing material is installed, the resistance increases (back pressure increases) and the back pressure increases. There is a limit to the thickness of the sound absorbing material to be installed because it is a countermeasure in a limited space under the floor of the vehicle, and it is difficult to take countermeasures against low frequency noise of 1 kHz or less by the conventional technology.

Japanese Unexamined Patent Publication No. 11-81976

In this way, it is difficult to obtain a sufficient noise suppression effect with the sound reduction structure that has been proposed in the past, against the increasingly strict regulation level.

Under such circumstances, the present invention is a novel sound-reducing structure for an exhaust pipe, which has sufficient sound-reducing performance especially for low-frequency sounds of 1 kHz or less even if the thickness is thin, and has excellent heat resistance and heat insulation. Is intended to provide.

As a result of further studies by the present inventors in order to solve the above technical problems, the inorganic fibers arranged between the inner pipe and the outer pipe of the automobile exhaust pipe having a coaxial double cylindrical structure of the inner pipe and the outer pipe A sound-reducing structure for an exhaust pipe having a containing mat, wherein the inorganic fiber-containing mat has an inorganic binder dispersed in a base material made of an inorganic fiber molded body and a base material made of the glass fiber molded body. An inorganic porous film having a ventilation resistance of 1.8 to 2.6 kPa · s / m is provided on one main surface, and the diameter of the base material made of the glass fiber molded body occupies all the needle-processed holes on the surface. It is composed of an inorganic fiber needle processed product having a proportion of 0.05 to 0.70 mm needle processing holes of 80 to 100%, and the inorganic fiber-containing mat is composed of the inorganic fiber molded body when converted into solid content. The inorganic binder 0.5 to 5.0% by mass is dispersed in 95.0 to 99.5% by mass of the base material, and the surface provided with the inorganic porous film is formed on the inner tube. It has been found that the above technical problem can be solved by a sound reduction structure for an exhaust pipe having a thickness of 5 to 30 mm arranged so as to face the surface, and the present invention has been completed based on the present knowledge.

That is, the present invention
(1) A sound reduction structure for an exhaust pipe having an inorganic fiber-containing mat arranged between the inner pipe and the outer pipe of an automobile exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe.
The inorganic fiber-containing mat has an inorganic binder dispersed in a base material made of an inorganic fiber molded body, and has a ventilation resistance of 1.8 to 2 on one side main surface of the base material made of the glass fiber molded body. It has an inorganic porous film of .6 kPa · s / m and has.
The base material made of the glass fiber molded body is made of an inorganic fiber needle processed product in which the ratio of the needle processed holes having a hole diameter of 0.05 to 0.70 mm to all the needle processed holes on the surface is 80 to 100%.
When the inorganic fiber-containing mat is converted into a solid content, 0.5 to 5.0% by mass of the inorganic binder is dispersed in 95.0 to 99.5% by mass of the base material made of the inorganic fiber molded body. A sound-reducing structure for an exhaust pipe, characterized in that the surface provided with the inorganic porous film is arranged so as to face the inner pipe and has a thickness of 5 to 30 mm.
(2) The sound reduction structure for an exhaust pipe according to (1) above, wherein the ventilation resistance of the base material made of the inorganic fiber molded body is 0.7 to 1.5 kPa · s / m.
(3) The sound reduction structure for an exhaust pipe according to (1) above, wherein the inorganic fiber-containing mat is a glass fiber-containing mat.
(4) The sound reduction structure for an exhaust pipe according to (2) above, wherein the inorganic fiber-containing mat is a glass fiber-containing mat.
(5) The sound reduction structure for an exhaust pipe according to any one of (1) to (4) above, wherein the inorganic porous membrane is a bentonite-containing membrane.
Is to provide.

According to the present invention, a base material made of an inorganic fiber molded body having a predetermined thickness exerts sound reduction (sound absorption) characteristics as well as heat resistance and heat insulation, and the sound reduction characteristics include bentonite having a predetermined ventilation resistance. Resonance effect due to film vibration of the film, suppression of sound loss due to small diameter needle processing holes, and vibration attenuation due to increase in binding points between inorganic fibers due to a predetermined amount of inorganic binder (damping effect of sound pressure energy due to vibration of inorganic fibers) Can be further enhanced.
Therefore, according to the present invention, a new sound-reducing structure for an exhaust pipe, which has sufficient sound-reducing performance especially for low-frequency sounds of 1 kHz or less even if the thickness is thin, and has excellent heat resistance and heat insulation. Can be provided.

It is sectional drawing explaining the morphological example of the sound reduction structure for exhaust pipes which concerns on this invention, FIG. 1A is a vertical sectional view in the direction perpendicular to the longitudinal direction of exhaust pipe 1 for vehicles, and FIG. b) is a vertical cross-sectional view taken along the longitudinal direction of the vehicle exhaust pipe 1. It is a figure explaining the manufacturing example of the sound reduction structure for an exhaust pipe which concerns on this invention. It is a figure which shows the sound absorption property evaluation result in an Example and a comparative example of this invention. It is a figure which shows the sound absorption property evaluation result in an Example and a comparative example of this invention. It is a figure for demonstrating the structure of the 4-terminal method sound reduction performance measuring apparatus used for measuring the transmission loss for each frequency.

First, the sound reduction structure for the exhaust pipe according to the present invention will be described.
The sound reduction structure for an exhaust pipe according to the present invention is a sound reduction structure for an exhaust pipe having an inorganic fiber-containing mat arranged between the inner pipe and the outer pipe of an automobile exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe. In the sound structure, the inorganic fiber-containing mat has an inorganic binder dispersed in a base material made of an inorganic fiber molded body, and is ventilated on one side main surface of the base material made of the glass fiber molded body. It has an inorganic porous film having a resistance of 1.8 to 2.6 kPa · s / m, and the base material made of the glass fiber molded body occupies a pore diameter of 0.05 to 0.70 mm in all needle processing holes on the surface. The base material 95.0 to 99 made of the inorganic fiber molded body when the inorganic fiber-containing mat is converted into a solid content and is made of a needle processed product of an inorganic fiber in which the ratio of the needle processing holes in the above is 80 to 100%. The inorganic binder 0.5 to 5.0% by mass was dispersed in 5.5% by mass, and the surface provided with the inorganic porous film was arranged so as to face the inner tube. It is characterized in that it has a thickness of 5 to 30 mm.

The sound reduction structure for an exhaust pipe according to the present invention is formed by arranging an inorganic fiber-containing mat between the inner pipe and the outer pipe of an automobile exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe.

The exhaust pipe for arranging the sound reduction structure according to the present invention is not particularly limited as long as it is a pipe that discharges exhaust gas from an automobile. For example, a type selected from a center muffler, a main muffler, a tail end pipe, a muffler cutter, and the like. The above can be mentioned.

Hereinafter, the sound reduction structure for an exhaust pipe according to the present invention will be described by taking a muffler cutter arranged at the end of an exhaust pipe for an automobile as an example and referring to the drawings as appropriate.
FIG. 1 is a cross-sectional view showing an example of an embodiment of the exhaust pipe sound reduction structure 1 according to the present invention, and FIG. 1 (a) is a vertical cross section in a direction perpendicular to the longitudinal direction of the exhaust pipe sound reduction structure 1. FIG. 1B is a vertical cross-sectional view of the exhaust pipe sound reduction structure 1 along the longitudinal direction.

As shown in FIG. 1, the sound reduction structure 1 for an exhaust pipe has an inner pipe 2.
In the documents of the present application, the inner pipe means an exhaust pipe through which exhaust gas (combustion gas) flows, and the inner pipe is made of a material corresponding to the temperature of the exhaust gas flowing inside, and the purpose is It is preferable to appropriately select from those capable of exhibiting the temperature characteristics and sound absorption characteristics.
As the inner tube, one having heat resistance is preferable, and specific examples thereof include a metal tube and a resin tube made of a heat-resistant resin, and a metal tube is preferable.

As the metal pipe, a stainless steel pipe (SUS pipe) is mainly used from the viewpoint of heat resistance and corrosion resistance, but an aluminum pipe (aluminum pipe) may also be used.

The average thickness of the inner tube is preferably 0.5 to 2.0 mm, more preferably 0.7 to 1.8 mm, and further preferably 0.9 to 1.6 mm. Appropriate.
In this application document, the average thickness of the inner tube means the arithmetic mean value when the thickness at 10 points is measured with a caliper.
Further, the outer diameter of the inner tube is preferably 20 to 90 mm, more appropriately 30 to 80 mm, and even more appropriately 40 to 70 mm.
In this application document, the outer diameter of the inner tube means a value measured by a caliper.

When the average thickness and inner diameter of the inner pipe are within the above range, it becomes easy to control the temperature inside and outside the inner pipe within a suitable range.

The cross-sectional shape of the inner tube is not particularly limited, and may be circular or elliptical as shown in the cross-sectional view in FIG. 1A.
Further, the inner tube may be formed by providing a plurality of holes in the side wall in the longitudinal direction thereof, or may be formed of, for example, punching metal.

As illustrated in FIG. 1, the exhaust pipe sound reduction structure 1 according to the present invention has an outer pipe 3 provided coaxially with the inner pipe 2 on the outer periphery of the inner pipe (exhaust pipe) 2. There is.

In the application documents, the outer pipe means a tubular heat shield plate that can suppress the heat radiated from the exhaust gas flowing inside the exhaust pipe to the vehicle body side, and the vehicle body. It is preferable to appropriately select from a material having heat resistance corresponding to the heat radiated to the side and not causing deterioration or the like, and a metal one is preferable.

As the metal constituting the outer tube, stainless steel (SUS) is mainly used from the viewpoint of heat resistance, corrosion resistance, aesthetics, etc., and aluminum may be used, but the emissivity is low and the aesthetics are high. Therefore, stainless steel is preferable.

The average thickness of the outer tube is preferably 0.5 to 2.0 mm, more preferably 0.7 to 1.8 mm, and further preferably 0.9 to 1.6 mm. Appropriate.
In this application document, the average thickness of the outer tube means the arithmetic mean value when the thickness at 10 points is measured with a caliper.
Further, the outer diameter of the outer tube is preferably 24 to 114 mm, more appropriately 34 to 104 mm, and even more appropriately 44 to 94 mm.
In this application document, the outer diameter of the outer tube means a value measured by a caliper.

When the average thickness and outer diameter of the outer pipe are within the above range, it becomes easy to control the temperature inside and outside the outer pipe within a suitable range.

The cross-sectional shape of the outer tube is not particularly limited, and as shown in FIG. 1A, it may be substantially circular, oval, or the like.

The inner pipe or the outer pipe may be an integrally molded product or a joint product of a divided product.
For example, as shown in FIG. 2, in the sound reduction structure for an exhaust pipe according to the present invention, the outer pipe 3 has an upper heat shield plate 3a in which a tubular object is half-split and a tubular object in half. It may be made of a joint with the lower heat shield plate 3b.
Since the outer pipe 3 is composed of a half-split upper heat shield plate 3a and a half-split lower heat shield plate 3b, the inorganic fiber-containing mat is wound around the inner pipe, and then the upper heat shield is applied to the outer periphery thereof. By interposing the plate 3a and the lower heat shield plate 3b and joining them together, the sound reduction structure for the exhaust pipe according to the present invention can be easily manufactured.

In FIG. 1, the muffler cutter is described as an example, but the coaxial double cylindrical structure composed of the inner pipe and the outer pipe is formed over the entire exhaust pipe for automobiles or in a part other than the muffler cutter. By being formed, the exhaust pipe sound reducing structure according to the present invention may be formed.

As shown in FIG. 1, the sound reduction structure 1 for an exhaust pipe according to the present invention is an inorganic fiber-containing mat arranged between an inner pipe 2 and an outer pipe 3 provided coaxially with the inner pipe 2. It has 4.

In the sound reduction structure for an exhaust pipe according to the present invention, the inorganic fiber-containing mat arranged between the inner pipe and the outer pipe of the exhaust pipe for an automobile having a coaxial double cylindrical structure is based on an inorganic fiber molded body. Is.

As the inorganic fibers constituting the inorganic fiber molded product, those having an average fiber diameter of 5 to 20 μm are preferable, those having an average fiber diameter of 5 to 15 μm are more preferable, and those having an average fiber diameter of 7 to 10 μm are further preferable.
In this application document, the average fiber diameter of the inorganic fiber means an arithmetic mean value when the cross-sectional diameter of 400 points arbitrarily extracted in the cross-sectional observation image by a scanning electron microscope (SEM) is measured.

As the inorganic fibers constituting the inorganic fiber molded product, those having an average fiber length of 20 to 300 mm are preferable, those having an average fiber length of 40 to 200 mm are more preferable, and those having an average fiber length of 60 to 100 mm are further preferable.
In the documents of the present application, the average fiber length of the inorganic fibers means the arithmetic mean value when the fiber lengths of 400 arbitrarily extracted inorganic fibers are measured with a dial thickness gauge manufactured by Peacock.

Examples of the inorganic fiber constituting the inorganic fiber molded body include one or more selected from glass fiber, silica fiber, alumina fiber, silica alumina fiber, rock wool, basalt fiber, zirconia fiber and the like, which are economical and available. Glass fiber is preferable in consideration of ease of use and the like.

By adopting an inorganic fiber molded body as the base material of the inorganic fiber-containing mat, when the exhaust sound propagates through the voids between the inorganic fibers as a coarse and dense wave, friction with the void wall is generated and the sound pressure energy becomes thermal energy. As a result of the conversion, the exhaust noise can be reduced.

In the sound reduction structure for an exhaust pipe according to the present invention, as the inorganic fiber molded body, a needle processed product obtained by needle punching an inorganic fiber is used.
When producing the above-mentioned inorganic fiber molded body, specifically, while adjusting the thickness with a thickness adjusting roller, the inorganic fiber is introduced into the needle punching device, and a large number of needles having barbs (protrusions) are produced at high speed. By reciprocating up and down and entwining (entangled) the inorganic fibers with each other, a felt-like molded body having a porous shape can be obtained.

In the sound-reducing structure for exhaust pipes according to the present invention, the inorganic fiber molded body that is the base material of the inorganic fiber-containing mat has a hole diameter of 0 occupying all the needle-processed holes as the hole diameter of the needle-processed holes averaged in the mat thickness direction. It is composed of inorganic fiber needle processed products with a needle processing hole ratio of 0.05 to 0.70 mm of 80 to 100%, and the ratio of needle processing holes with a hole diameter of 0.05 to 0.70 mm in all needle processing holes is 85. It is preferably composed of a needle-processed product of inorganic fiber having a diameter of about 100%, and a needle-processed product of inorganic fiber having a ratio of needle-processed holes having a hole diameter of 0.05 to 0.70 mm to 90 to 100% of all needle-processed holes. It is more preferable to consist of.

In the present application documents, the hole diameter of the needle-processed hole provided on the surface of the inorganic fiber-containing molded body is determined from the tomographic photograph of the hole measured by an X-ray CT device (Skyscan1272 Micro-CT manufactured by BRUKER). When the pore volume from the front surface (needle entry surface) to the back surface is obtained and approximated to a cylinder having the same height as the front surface to the back surface of the inorganic fiber-containing molded body and having the same volume as the pore volume. Means the diameter of the cylinder.
Further, in the present application documents, the ratio (%) of the needle-machined holes having a hole diameter of 0.05 to 0.70 mm in all the needle-machined holes is as follows when the hole diameters of 100 needle-machined holes are measured by the above method. It means the value calculated by the formula.
Percentage of needle machined holes with a hole diameter of 0.05 to 0.70 mm (%) = (number of needle machined holes with a hole diameter of 0.05 to 0.70 mm / 100) x 100

The ratio of the needle-machined holes having a hole diameter of 0.05 to 0.15 mm to the total needle-machined holes on the surface of the base material made of the inorganic fiber-molded body is, for example, a needle to be attached to a needle punching device used when manufacturing the inorganic fiber-molded body. It can be controlled by adjusting the needle diameter of the needle).

In the sound reduction structure for the exhaust pipe according to the present invention, the ratio of the needle-machined holes having a hole diameter of 0.05 to 0.70 mm to the total needle-machined holes on the surface of the base material made of the inorganic fiber molded body is within the above range. That is, due to the high proportion of small-diameter needle-machined holes on the surface of the inorganic fiber molded body, when used as a base material for an inorganic fiber-containing mat, sound loss due to the needle-machined holes is suppressed and desired sound reduction (sound absorption) is achieved. The effect can be easily exerted.

In order to improve the heat insulating property and the sound insulating property, it is desirable that the thickness (mm) of the inorganic fiber molded product is a length equal to or more than the distance (mm) between the inner pipe and the outer pipe.
The ratio of the thickness of the inorganic fiber molded body to the distance between the inner tube and the outer tube (the width of the gap defined between the inner tube and the outer tube) ((thickness (mm) / inner of the inorganic fiber molded body). The distance (mm)) × 100) between the tube and the outer tube is preferably 100 to 400%, more preferably 100 to 300%, and even more preferably 100 to 200%.
Specifically, the thickness of the inorganic fiber molded product is preferably 5 to 15 mm, more preferably 6 to 12 mm, and even more preferably 8 to 10 mm.
In the documents of the present application, the thickness of the inorganic fiber molded body means the arithmetic average value when the thickness of 10 arbitrarily extracted inorganic fiber molded bodies is measured with a dial thickness gauge manufactured by Peacock Co., Ltd. The distance between the tube and the outer tube also means the value measured by the dial thickness gauge manufactured by Peacock.

In the sound reduction structure for exhaust pipes according to the present invention, the thickness of the inorganic fiber molded body is equal to or greater than the distance between the inner pipe and the outer pipe, so that the inorganic fiber-containing mat based on the inorganic fiber molded body is the inner pipe. Since it is held in a pressed state between the (exhaust pipe) and the outer pipe (cylindrical heat shield plate), it exerts sufficient elasticity (repulsive force) and appropriately suppresses the vibration of the outer pipe. While doing so, it is possible to exhibit desired sound reduction (sound absorption).

In the exhaust pipe down sound structure according to the present invention, the bulk density of the inorganic fiber molded body is preferably 50 ~ 300kg / ^{m 3,} more preferably from 80 ~ 200kg / ^{m 3,} more preferably 100 ~ 160kg / ^{m 3.}
In the application documents, the bulk density of the inorganic fiber molded body is obtained by measuring the thickness of the inorganic fiber molded body cut out to 100 mm × 100 mm with a caliper or the like to determine the volume, and the weight separately measured by an electronic balance is divided by the above volume. It means the value obtained by.

In the sound reduction structure for exhaust pipes according to the present invention, when the thickness and bulk density of the inorganic fiber molded body are within the above ranges, the inorganic fiber-containing mat exhibits desired heat resistance and heat insulating properties, and is reduced for exhaust pipes. It becomes easy to suppress the thermal deterioration of the member on the vehicle body side facing the sound structure, and the internal temperature of the exhaust pipe sound reduction structure can be easily controlled within a certain range.

In the sound reduction structure for exhaust pipes according to the present invention, the ventilation resistance of the inorganic fiber molded body as the base material of the inorganic fiber-containing mat is preferably 0.7 to 1.5 kPa · s / m, preferably 0.8. It is more preferably about 1.5 kPa · s / m, and even more preferably 0.8 to 1.2 kPa · s / m.

In the present application documents, the airflow resistance of the inorganic fiber molded body is based on the breathability A method (Frazier type method) specified in JIS L 1096, and the inorganic fiber molded body to be measured has a thickness of 15 mm and a bulk density of 130 kg /. After adjusting to m ³ , the flow rate of air when air is passed in the direction perpendicular to the main surface at a differential pressure of 0.125 kPa flows through the flow resistance measuring instrument (product name: KES-F8-AP1). , Made by Kato Tech Co., Ltd., and converted to ventilation resistance.

When an inorganic fiber molded body having the above-mentioned ventilation resistance is used, it is possible to easily exhibit excellent heat resistance and heat insulating property while exhibiting desired sound absorption.

In the sound reduction structure for an exhaust pipe according to the present invention, the inorganic fiber-containing mat is formed by dispersing an inorganic binder in a base material made of an inorganic fiber molded body.

Examples of the inorganic binder include one or more selected from viscous minerals such as bentonite, borosilicate glass, colloidal silica, colloidal alumina and the like.

In the sound-reducing structure for exhaust pipes according to the present invention, the inorganic fiber-containing mat has an inorganic binder of 0.5 to 99.5% by mass in a base material of 95.0 to 99.5% by mass of the inorganic fiber molded body when converted into solid content. 5.0% by mass is dispersed, and 1.0 to 3.0% by mass of the inorganic binder is dispersed in 97 to 99% by mass of the base material made of the inorganic fiber molded body. It is more preferable that the inorganic binder 2.0 to 3.0% by mass is dispersed in 97 to 98% by mass of the base material made of the inorganic fiber molded body.

In the sound reduction structure for exhaust pipes according to the present invention, the inorganic fiber-containing mat is formed by dispersing a predetermined amount of an inorganic binder in a base material made of an inorganic fiber molded body, whereby the inorganic fibers constituting the base material are formed. Inorganic binders adhere to the intersections of the fibers to increase the binding points between the fibers and enhance the integrity. Further, when the exhaust sound vibrates (solid-propagates) as a compressional wave and a transverse wave to the inorganic fiber skeleton constituting the inorganic fiber-containing mat, the inorganic fiber constituting the mat is vibrated and deformed around the plurality of binding points. By doing so, mechanical energy attenuation (attenuation of sound pressure energy due to vibration of the inorganic fiber) can be caused, and the sound reduction (sound absorption) characteristic of the inorganic fiber-containing mat can be further enhanced.
The solid-borne sound attenuation effect (mechanical energy attenuation effect) causes friction with the void wall when the exhaust sound propagates through the voids between the inorganic fibers as a coarse and dense wave, and the sound pressure energy is converted into thermal energy. Compared with the attenuation effect of airborne sound, the attenuation effect is high in the low frequency region of 1 kHz or less, and it is considered that the attenuation effect is dominant especially in the range of 300 to 500 Hz.

If the amount of the inorganic binder is too small with respect to the amount of the inorganic fiber molded body (base material amount), the binding point cannot be sufficiently formed, and if the amount of the inorganic binder is too large with respect to the inorganic fiber molded body amount (base material amount), Since the inorganic binder is dispersed so as to fill the entire gap between the inorganic fibers constituting the inorganic fiber molded body and the inorganic fibers are firmly bonded to each other, it is difficult for the inorganic fibers to be attenuated due to vibration.

To disperse the inorganic binder, for example, after impregnating the above-mentioned inorganic fiber molded body with a dispersion liquid containing a desired inorganic binder, the mixture is appropriately squeezed with a felt roller or the like to adjust the impregnation amount or to perform a drying treatment. It can be done by things such as.

In the sound reduction structure for exhaust pipes according to the present invention, the inorganic fiber-containing mat is an inorganic substance having a ventilation resistance of 1.8 to 2.6 kPa · s / m on one main surface of a base material made of an inorganic fiber molded body. It has a porous membrane.

Examples of the inorganic porous membrane include one or more selected from bentonite-containing membranes and the like, and bentonite-containing membranes are preferable.

In the present application, the inorganic porous membrane means a membrane containing an inorganic porous substance such as bentonite as an inorganic binder.
Bentonite contains montmorillonite as the main component and silicate minerals such as quartz, α-Christovalite, and opal as subcomponents, silicate minerals such as pebbles, mica, and zeolite, and carbonate minerals such as calcite, dolomite, and gypsham. It is a weakly alkaline clay mineral that can contain sulfide minerals such as sulphate minerals and pyrite.

The inorganic porous membrane preferably contains an inorganic binder in an amount of 85 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 95.0 to 100% by mass.

In the sound reduction structure for an exhaust pipe according to the present invention, the thickness of the inorganic porous membrane is preferably 10 to 1,000 μm, more preferably 100 to 1,000 μm, and more preferably 200 to 500 μm. More preferred.

In the sound reduction structure for exhaust pipes according to the present invention, the thickness of the inorganic porous membrane means the arithmetic mean value when the cross section of the inorganic fiber-containing mat is observed at 50 points with a microscope.

In the sound reduction structure for exhaust pipes according to the present invention, the aperture ratio of the inorganic porous membrane is preferably 0.01 to 2.00%, more preferably 0.01 to 1.00%. , 0.01 to 0.50%, more preferably.
Further, in the sound reduction structure for an exhaust pipe according to the present invention, the opening diameter of the inorganic porous membrane is preferably 0.1 to 400.0 μm, more preferably 0.1 to 100.0 μm. It is more preferably 0.1 to 10.0 μm.

In the sound reduction structure for exhaust pipes according to the present invention, the pore size of the inorganic porous membrane was obtained when the surface of the inorganic porous membrane was observed with an SEM (JEOL Ltd., JSF-6300A). The observation range of 100 μm × 100 μm in the SEM image was subjected to image analysis processing and black-and-white binarization processing, and the area of the black portion was approximately calculated as the pore (gap) area excluding the detection particle area represented by white. It means the arithmetic average value at any 50 points of the pore opening ratio calculated by (total area of pores between inorganic binder particles / area of inorganic porous film) × 100.

Further, in the present application documents, the opening diameter of the inorganic porous film is black and white by performing image analysis processing on the observation range of 100 μm × 100 μm in the obtained SEM image when the surface of the inorganic porous film is observed by the above SEM. After digitizing and determining the area of each of the 50 holes displayed in black formed between the detection particles represented in white, a circle having the same area as each hole area. It means the arithmetic mean value when the diameter is individually calculated as the pore diameter between the aggregated inorganic binder particles.

The inorganic porous film exhibits the same degree of flexibility as the inorganic fiber molded body, especially within the above-mentioned film thickness range, and serves as a constituent film of the inorganic fiber-containing mat between the inner and outer pipes of the exhaust pipe for automobiles. Even when it is bent and arranged, it can be easily arranged while being integrally deformed with the inorganic fiber molded body.

In the sound reduction structure for exhaust pipes according to the present invention, the ventilation resistance of the inorganic porous membrane provided on the main surface of the base material made of the inorganic fiber molded body is 1.8 to 2.6 kPa · s / m. It is preferably 1.8 to 2.5 kPa · s / m, and more preferably 1.8 to 2.3 kPa · s / m.

In the present application documents, the aeration resistance of the inorganic porous membrane is adjusted so that the inorganic fiber molded body coated with the inorganic binder has a thickness of 15 mm and a bulk density of 130 kg / m ^3, and then the aeration specified in JIS L1096. Based on the property A method (Frazier type method), the flow resistance of the air flow rate when air is passed from the coated surface side in the direction perpendicular to the main surface of the inorganic fiber molded body at a differential pressure of 0.125 kPa. It means the one measured by a measuring instrument (manufactured by Kato Tech Co., Ltd., product name: KES-F8-AP1) and converted into airflow resistance.

In the sound-reducing structure for an exhaust pipe according to the present invention, the inorganic porous film can be formed by aggregating and fixing the solid content when the inorganic binder-containing liquid is applied to the inorganic fiber molded body to form the film. Yes, the air permeability can be exhibited by the gaps formed between the fine particles constituting the membrane.
The ventilation resistance of the inorganic porous membrane can be easily controlled by adjusting the concentration of the inorganic binder contained in the inorganic binder-containing liquid or the like.

The sound reduction structure for an exhaust pipe according to the present invention can further improve the sound reduction characteristics by the resonance effect (resonance effect) due to the membrane vibration of the inorganic porous membrane having the above-mentioned predetermined ventilation resistance.

Inorganic fiber-containing mats with an inorganic porous film on one side are considered to have Helmfortz-type film vibration (resonance) characteristics, and Masaru Koyasu (Theory of Sound Insulation / Absorption Materials and Composite Materials, Journal of the Japan Society for Composite Materials, No. Based on the report of Vol. 2, No. 4 (1976)), the maximum value (structural resonance frequency) f ₀ of the resonance frequency of the sound absorption performance of the inorganic fiber-containing mat according to the present invention can also be expressed by the following equation (1). Conceivable.

(However, f ₀ : structural resonance frequency (Hz)
c: Speed of sound (m / s)
p: Pore opening ratio of the inorganic porous membrane t: Thickness of the inorganic porous membrane (m)
d: Opening diameter (m) of the inorganic fiber-containing mat
L: Thickness of mat containing inorganic fiber (m)
Is. )

Then, with respect to the opening diameter d of the inorganic fiber-containing mat, a case where both the inorganic fiber molded body and the inorganic porous film constituting the inorganic fiber-containing mat had an open portion was examined diligently. As a result, the inorganic fiber-containing mat was examined. It was found experimentally that the opening diameter d of the above can be approximated by the following equation (2).

d = -0.6892T _r + T _r0 (2)
(However, d: Opening diameter (m) of the inorganic fiber-containing mat
_Tr : Ventilation resistance of inorganic porous membrane (kPa · s / m)
_Tr0 : Ventilation resistance of inorganic fiber molded product (kPa · s / m)
Is. )

By substituting the above equation (2) into the above equation (1) and rearranging it, the following equation (3) is derived.

(However, f ₀ : structural resonance frequency (Hz)
c: Speed of sound (m / s)
p: Pore opening ratio of the inorganic porous membrane t: Thickness of the inorganic porous membrane (m)
_Tr : Ventilation resistance of inorganic porous membrane (kPa · s / m)
_Tr0 : Ventilation resistance of inorganic fiber molded product (kPa · s / m)
L: Thickness of mat containing inorganic fiber (m)
Is. )

From the above equation (3), along with the sound velocity c, the pore size p of the inorganic porous membrane, the thickness t of the inorganic porous membrane, the ventilation resistance _Tr0 of the inorganic fiber molded body, and the thickness L of the inorganic fiber-containing mat are constant values. It can be seen that the structural resonance frequency f ₀ , which is the maximum value of the resonance frequency of the inorganic fiber-containing mat, can be arbitrarily specified by controlling the ventilation resistance _Tr of the inorganic porous membrane.
Therefore, in the sound reduction structure for the exhaust pipe according to the present invention, the structural resonance frequency f ₀ of the inorganic fiber-containing mat is set to a frequency of 1 kHz or less by controlling the ventilation resistance _Tr of the inorganic porous membrane within a predetermined range. It is considered that the sound absorption characteristic (sound reduction characteristic) in the low frequency region of 1 kHz or less can be effectively improved by controlling.

An inorganic fiber-containing mat provided with an inorganic porous film on one side main surface can be produced by applying an inorganic binder-containing liquid to one side main surface of an inorganic fiber molded body in which an inorganic binder is dispersed inside.
Examples of the inorganic binder-containing liquid include an aqueous solution containing an inorganic binder. The concentration of the inorganic binder in the inorganic binder-containing liquid is preferably 0.5 to 5.0% by mass.
The method of applying the inorganic binder-containing liquid is not particularly limited, and examples thereof include spray coating, brush coating, and roller coating.

In the sound reduction structure for an exhaust pipe according to the present invention, the thickness of the inorganic fiber-containing mat is 5 to 30 mm, preferably 5 to 20 mm, and more preferably 5 to 10 mm.

In the application documents, the thickness of the inorganic fiber-containing mat means the arithmetic mean value when the thicknesses of 10 arbitrarily extracted inorganic fiber-containing mats are measured with a dial thickness gauge manufactured by Peacock.

According to the sound reduction structure for an exhaust pipe according to the present invention, even if the thickness is thin, it is possible to have sufficient sound reduction performance especially for low frequency sound of 1 kHz or less and to exhibit excellent heat resistance and heat insulation. it can.

In the sound reduction structure for the exhaust pipe according to the present invention, the inorganic fiber-containing mat is arranged so that the surface provided with the inorganic porous membrane faces the inner pipe, and the surface provided with the inorganic porous membrane in this way. Is arranged so as to face the inner tube, so that the sound absorption characteristics in the low frequency region of 1 kHz or less can be effectively improved.

According to the present invention, a base material made of an inorganic fiber molded body having a predetermined thickness exerts sound absorption (sound reduction) characteristics as well as heat resistance and heat insulation, and the sound reduction characteristics are exhibited by an inorganic porous body having a predetermined ventilation resistance. Resonance effect due to film vibration of the quality film, suppression of sound loss due to small diameter needle processing holes, and vibration damping due to increase in binding points between inorganic fibers due to a predetermined amount of inorganic binder (damping effect of sound pressure energy due to vibration of inorganic fibers) ) Can be further enhanced.
Therefore, according to the present invention, a new sound-reducing structure for an exhaust pipe, which has sufficient sound-reducing performance especially for low-frequency sounds of 1 kHz or less even if the thickness is thin, and has excellent heat resistance and heat insulation. Can be provided.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following examples.

(Example 1)
(1) Manufacturing process of glass fiber molded body While adjusting the thickness with a thickness adjusting roller, glass fibers having an average fiber diameter of 10 μm and an average fiber length of 100 mm are introduced into a needle punching device, and a large number of needles having barbs (protrusions) (protrusions). By reciprocating (needle diameter 0.58 mm) up and down at high speed and entwining (interlacing) the glass fibers with each other, a felt-like glass fiber molded body having a porous shape (thickness 6 mm, bulk density 100 kg / m) ^3. The ratio of needle-machined holes with a hole diameter of 0.05 to 0.70 mm to the total needle-machined holes on the surface (95%) was obtained.
Further, when a plurality of the above-mentioned glass fiber molded bodies were laminated and pressurized, and the ventilation resistance was measured at a thickness of 15 mm and a bulk density of 130 kg / m ³ , it was 1.0 kPa · s / m.
(2) Impregnation Step of Inorganic Binder The glass fiber molded body having a thickness of 6 mm is impregnated with an aqueous dispersion having a bentonite content of 2.5% by mass and squeezed with a felt roller to convert the impregnation amount into solid content. After adjusting to 2.5% by mass, it was dried and impregnated with bentonite inside, and dispersed in an inorganic binder-containing glass fiber molded body (content ratio of glass fiber molded body 97.5% by mass, bentonite). Content ratio of 2.5% by mass) was obtained.
(3) Step of Forming Bentonite-Containing Film Next, an aqueous dispersion having a bentonite concentration of 10% by mass is roller-coated on one side of the main surface of the inorganic binder-containing glass fiber molded body obtained in (2), and the coated surface is coated. A bentonite-containing film (thickness 0.2 mm, pore size 0.5%, aeration resistance 2.) was formed on the inner main surface of the glass fiber molded body by winding it in a cylindrical shape with the inner peripheral surface side as the inner peripheral surface side and then drying it. A glass fiber-containing mat (thickness 10 mm, inner diameter 40 mm, outer diameter 60 mm) having a cylindrical shape as a whole was obtained, forming 3 kPa · s / m and a bentonite content of 100% by mass).

(4) Filling Process of Glass Fiber-Containing Mat As shown in FIG. 1, the inner pipe (exhaust pipe) 2 is a SUS pipe in the shape of a punching metal having a plurality of openings provided on the entire side wall in the longitudinal direction. (Inner diameter 38 mm, outer diameter 40 mm) was prepared, and a SUS pipe (inner diameter 60 mm, outer diameter 62 mm) was prepared as the outer pipe (heat shield plate on the cylinder) 3.
When the inner pipe 2 and the outer pipe 3 are arranged coaxially, a gap having a width of 10 mm is formed between them.
As shown in FIG. 1, by inserting the glass fiber-containing mat obtained in Example 1 into the gap between the inner tube 2 and the outer tube 3, the inner tube and the outer tube have a coaxial double cylindrical structure. A sound reduction structure 1 for an exhaust pipe in which a mat material was arranged between the inner pipe and the outer pipe was produced.
When the glass fiber-containing mat was inserted into the gap between the inner tube 2 and the outer tube 3, the surface provided with the bentonite-containing film was arranged so as to face the inner tube.

(Sound absorption evaluation)
The sound absorption characteristics of the exhaust pipe sound reduction structure 1 were measured by the method shown in FIG.
That is, as shown in FIG. 5, tubular bodies T ₁ and T ₂ having an inner diameter equal to the inner diameter of the inner pipe 2 are arranged coaxially with the inner pipe 2 at both ends of the exhaust pipe sound reduction structure 1. At the same time, two condenser microphones M on the sound incident side A and B / sound transmission side C and D were arranged on the tubular bodies T ₁ and T ₂ . In this state, when the speaker (Fostex Co. 103E) S was placed at the end of the tubular body T _1, was generated random noise toward the exhaust pipe down sound structure 1 of the inner tube 2, the exhaust The sound pressure level between the condenser microphones M and M arranged before and after the sound reduction structure 1 for pipes is measured by the four-terminal method, and the difference from the separately measured sound pressure level before inserting the mat material is the transmission loss for each frequency. Asked as.
The transmission loss at frequencies of 800 Hz to 2000 Hz is shown in FIG.

From FIG. 3, the sound-reducing structure 1 for an exhaust pipe obtained in Example 1 has bentonite on the surface of a base material made of a glass fiber molded body having a predetermined needle-processed hole in which a predetermined amount of an inorganic binder is dispersed therein. It can be seen that the material containing the film is excellent in heat resistance and heat insulating property, and is excellent in transmission loss (volume reduction) especially in the low frequency region around 800 Hz to 1.25 kHz even if the thickness is thin. ..

As for the sound reduction characteristic, the bentnite-containing film provided on the surface of the glass fiber molded body causes a spring effect having a Helmfortz type film vibration (resonance) characteristic, and particularly vibration damping in the low frequency range of 800 Hz to 1.25 kHz. It is probable that it was caused by the larger size.

(Comparative Example 1)
(1) Manufacturing process of glass fiber molded body While adjusting the thickness with a thickness adjusting roller, glass fibers having an average fiber diameter of 10 μm and an average fiber length of 100 mm are introduced into a needle punching device, and a large number of needles having barbs (protrusions) (protrusions). By reciprocating (needle diameter 0.85 mm) up and down at high speed and entwining (entangled) the glass fibers with each other, a felt-like glass fiber molded body having a porous shape (thickness 6 mm, bulk density 100 kg /) m ^3, to obtain a ratio of 20% or less) of needled hole of all needled holes occupying the pore diameter 0.05 ~ 0.70 mm at the surface.
Further, when a plurality of the above glass fiber molded bodies were laminated, pressed, and the ventilation resistance was measured at a thickness of 15 mm and a bulk density of 130 kg / m ³ , it was 0.3 kPa · s / m.
(2) Impregnation Step of Inorganic Binder The glass fiber molded body having a thickness of 6 mm is impregnated with an aqueous dispersion having a bentonite content of 5.0% by mass and squeezed with a felt roller to convert the impregnation amount into solid content. After adjusting to 5.0% by mass, the glass is wound into a cylindrical shape so that the cross-sectional diameter is 60 mm, and then dried, and the inside is impregnated with bentonite and dispersed to form a cylindrical shape. An inorganic binder-containing glass fiber molded body having a thickness of 10 mm was obtained.
(3) Filling Step of Inorganic Binder-Containing Glass Fiber Molded Body In (4) of Example 1, instead of the glass fiber-containing mat, the inorganic binder-containing glass fiber molded body obtained in the above (3) is used as the inner tube 2 and the outer tube. By inserting it into the gap with the pipe 3, a sound-reducing structure for a comparative exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe and a mat material arranged between the inner pipe and the outer pipe was produced. ..

(Sound absorption evaluation)
In the sound absorption evaluation described in Example 1, the sound absorption was evaluated in the same manner as in Example 1 except that the comparison exhaust pipe sound reduction structure was used instead of the exhaust pipe sound reduction structure 1.
The transmission loss at frequencies of 800 Hz to 2000 Hz is shown in FIG.

From FIG. 3, it can be seen that the inorganic binder-containing glass fiber molded body obtained in Comparative Example 1 is inferior in sound reduction performance particularly in the low frequency region because it does not have a bentonite-containing film on the surface.

(Comparative Example 2)
(1) Manufacturing process of glass fiber molded body While adjusting the thickness with a thickness adjusting roller, glass fibers having an average fiber diameter of 10 μm and an average fiber length of 100 mm are introduced into a needle punching device, and a large number of needles having barbs (protrusions) (protrusions). By reciprocating (needle diameter 0.58 mm) up and down at high speed and entwining (interlacing) the glass fibers with each other, a felt-like glass fiber molded body having a porous shape (thickness 6 mm, bulk density 100 kg / m) ^3. The ratio of needle-machined holes with a hole diameter of 0.05 to 0.70 mm to the total needle-machined holes on the surface (95%) was obtained.
Further, when a plurality of the above-mentioned glass fiber molded bodies were laminated and pressurized, and the ventilation resistance was measured at a thickness of 15 mm and a bulk density of 130 kg / m ³ , it was 1.0 kPa · s / m.
(2) Impregnation Step of Inorganic Binder The glass fiber molded body having a thickness of 6 mm is impregnated with an aqueous dispersion having a bentonite content of 2.5% by mass and squeezed with a felt roller to convert the impregnation amount into solid content. After adjusting to 2.5% by mass, it was dried and impregnated with bentonite inside, and dispersed in an inorganic binder-containing glass fiber molded body (content ratio of glass fiber molded body 97.5% by mass, bentonite). Content ratio of 2.5% by mass) was obtained.
(3) Step of Forming Bentonite-Containing Film Next, an aqueous dispersion having a bentonite concentration of 8.5% by mass was roller-coated on one side of the main surface of the inorganic binder-containing glass fiber molded product obtained in (2). By winding the coated surface in a cylindrical shape on the inner peripheral surface side and then drying it, a bentonite-containing film (thickness 0.2 mm, pore opening rate 0.7%, ventilation resistance) is applied to the inner main surface of the glass fiber molded body. A glass fiber-containing mat (thickness 10 mm, inner diameter 40 mm, outer diameter 60 mm) having a cylindrical shape as a whole was obtained, which formed 1.5 kPa · s / m and a bentonite content of 100% by mass).
(4) Filling Step of Glass Fiber-Containing Mat Using the glass fiber-containing mat obtained in (3) above, the glass fiber-containing mat is combined with the inner tube 2 and the outer tube 3 in the same manner as in Example 1 (4). By inserting it into the gap, a sound reduction structure 1 for an exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe and having a mat material arranged between the inner pipe and the outer pipe was produced.
When the glass fiber-containing mat was inserted into the gap between the inner tube 2 and the outer tube 3, the surface provided with the bentonite-containing film was arranged so as to face the inner tube.

(Comparative Example 3)
(1) Manufacturing process of glass fiber molded body While adjusting the thickness with a thickness adjusting roller, glass fibers having an average fiber diameter of 10 μm and an average fiber length of 100 mm are introduced into a needle punching device, and a large number of needles having barbs (protrusions) (protrusions). By reciprocating (needle diameter 0.58 mm) up and down at high speed and entwining (interlacing) the glass fibers with each other, a felt-like glass fiber molded body having a porous shape (thickness 6 mm, bulk density 100 kg / m) ^3. The ratio of needle-machined holes with a hole diameter of 0.05 to 0.70 mm to the total needle-machined holes on the surface (95%) was obtained.
Further, when a plurality of the above-mentioned glass fiber molded bodies were laminated and pressurized, and the ventilation resistance was measured at a thickness of 15 mm and a bulk density of 130 kg / m ³ , it was 1.0 kPa · s / m.
(2) Impregnation Step of Inorganic Binder The glass fiber molded body having a thickness of 6 mm is impregnated with an aqueous dispersion having a bentonite content of 2.5% by mass and squeezed with a felt roller to convert the impregnation amount into solid content. After adjusting to 2.5% by mass, it was dried and impregnated with bentonite inside, and dispersed in an inorganic binder-containing glass fiber molded body (content ratio of glass fiber molded body 97.5% by mass, bentonite). Content ratio of 2.5% by mass) was obtained.
(3) Step of Forming Bentonite-Containing Film Next, an aqueous dispersion having a bentonite concentration of 9% by mass is roller-coated on one side of the main surface of the inorganic binder-containing glass fiber molded body obtained in (2), and the coated surface is coated. A bentonite-containing film (thickness 0.2 mm, pore size 0.6%, ventilation resistance 1.) was formed on the inner main surface of the glass fiber molded body by winding it in a cylindrical shape with the inner peripheral surface side and then drying it. A glass fiber-containing mat (thickness 10 mm, inner diameter 40 mm, outer diameter 60 mm) having a cylindrical shape as a whole was obtained, forming 75 kPa · s / m and having a bentonite content of 100% by mass).
(4) Filling Step of Glass Fiber-Containing Mat Using the glass fiber-containing mat obtained in (3) above, the glass fiber-containing mat is combined with the inner tube 2 and the outer tube 3 in the same manner as in Example 1 (4). By inserting it into the gap, a sound reduction structure 1 for an exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe and having a mat material arranged between the inner pipe and the outer pipe was produced.
When the glass fiber-containing mat was inserted into the gap between the inner tube 2 and the outer tube 3, the surface provided with the bentonite-containing film was arranged so as to face the inner tube.

(Example 2)
(1) Manufacturing process of glass fiber molded body While adjusting the thickness with a thickness adjusting roller, glass fibers having an average fiber diameter of 10 μm and an average fiber length of 100 mm are introduced into a needle punching device, and a large number of needles having barbs (protrusions) (protrusions). By reciprocating (needle diameter 0.58 mm) up and down at high speed and entwining (interlacing) the glass fibers with each other, a felt-like glass fiber molded body having a porous shape (thickness 6 mm, bulk density 100 kg /) m ³ , the ratio of needle-machined holes having a hole diameter of 0.05 to 0.70 mm to all needle-machined holes on the surface (95%) was obtained.
Further, when a plurality of the above-mentioned glass fiber molded bodies were laminated and pressurized, and the ventilation resistance was measured at a thickness of 15 mm and a bulk density of 130 kg / m ³ , it was 1.0 kPa · s / m.
(2) Impregnation step of inorganic binder The glass fiber molded body having a thickness of 6 mm is impregnated with an aqueous dispersion having a bentonite content of 2.5% by mass and squeezed with a felt roller to convert the impregnation amount into solid content. After adjusting to 2.5% by mass, it was dried and impregnated with bentonite inside, and dispersed in an inorganic binder-containing glass fiber molded body (content ratio of glass fiber molded body 97.5% by mass, bentonite). Content ratio of 2.5% by mass) was obtained.
(3) Step of Forming Bentonite-Containing Film Next, an aqueous dispersion having a bentonite concentration of 9.5% by mass was roller-coated on one side of the main surface of the inorganic binder-containing glass fiber molded product obtained in (2). By winding the coated surface in a cylindrical shape on the inner peripheral surface side and then drying it, a bentonite-containing film (thickness 0.17 mm, pore opening rate 0.55%, ventilation resistance) is applied to the inner main surface of the glass fiber molded body. A glass fiber-containing mat (thickness 10 mm, inner diameter 40 mm, outer diameter 60 mm) having a cylindrical shape as a whole was obtained, forming 1.83 kPa · s / m and bentonite content (100% by mass).
(4) Filling Step of Glass Fiber-Containing Mat Using the glass fiber-containing mat obtained in (3) above, the glass fiber-containing mat is combined with the inner tube 2 and the outer tube 3 in the same manner as in Example 1 (4). By inserting it into the gap, a sound reduction structure 1 for an exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe and having a mat material arranged between the inner pipe and the outer pipe was produced.
When the glass fiber-containing mat was inserted into the gap between the inner tube 2 and the outer tube 3, the surface provided with the bentonite-containing film was arranged so as to face the inner tube.

(Example 3)
(1) Manufacturing process of glass fiber molded body While adjusting the thickness with a thickness adjusting roller, glass fibers having an average fiber diameter of 10 μm and an average fiber length of 100 mm are introduced into a needle punching device, and a large number of needles having barbs (protrusions) (protrusions). By reciprocating (needle diameter 0.58 mm) up and down at high speed and entwining (interlacing) the glass fibers with each other, a felt-like glass fiber molded body having a porous shape (thickness 6 mm, bulk density 100 kg / m) ^3. The ratio of needle-machined holes with a hole diameter of 0.05 to 0.70 mm to the total needle-machined holes on the surface (95%) was obtained.
Further, when a plurality of the above-mentioned glass fiber molded bodies were laminated and pressurized, and the ventilation resistance was measured at a thickness of 15 mm and a bulk density of 130 kg / m ³ , it was 1.0 kPa · s / m.
(2) Impregnation Step of Inorganic Binder The glass fiber molded body having a thickness of 6 mm is impregnated with an aqueous dispersion having a bentonite content of 2.5% by mass and squeezed with a felt roller to convert the impregnation amount into solid content. After adjusting to 2.5% by mass, it was dried and impregnated with bentonite inside, and dispersed in an inorganic binder-containing glass fiber molded body (content ratio of glass fiber molded body 97.5% by mass, bentonite). Content ratio of 2.5% by mass) was obtained.
(3) Step of Forming Bentonite-Containing Film Next, an aqueous dispersion having a bentonite concentration of 10% by mass is roller-coated on one side of the main surface of the inorganic binder-containing glass fiber molded body obtained in (2), and the coated surface is coated. A bentonite-containing film (thickness 0.18 mm, pore size 0.55%, ventilation resistance 1.) was formed on the inner main surface of the glass fiber molded body by winding it in a cylindrical shape with the inner peripheral surface side and then drying it. A glass fiber-containing mat (thickness 10 mm, inner diameter 40 mm, outer diameter 60 mm) having a cylindrical shape as a whole was obtained, which formed 9 kPa · s / m and a bentonite content of 100% by mass).
(4) Filling Step of Glass Fiber-Containing Mat Using the glass fiber-containing mat obtained in (3) above, the glass fiber-containing mat is combined with the inner tube 2 and the outer tube 3 in the same manner as in Example 1 (4). By inserting it into the gap, a sound reduction structure 1 for an exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe and having a mat material arranged between the inner pipe and the outer pipe was produced.
When the glass fiber-containing mat was inserted into the gap between the inner tube 2 and the outer tube 3, the surface provided with the bentonite-containing film was arranged so as to face the inner tube.

(Example 4)
(1) Manufacturing process of glass fiber molded body While adjusting the thickness with a thickness adjusting roller, glass fibers having an average fiber diameter of 10 μm and an average fiber length of 100 mm are introduced into a needle punching device, and a large number of needles having barbs (protrusions) (protrusions). By reciprocating (needle diameter 0.58 mm) up and down at high speed and entwining (interlacing) the glass fibers with each other, a felt-like glass fiber molded body having a porous shape (thickness 6 mm, bulk density 100 kg / m) ^3. The ratio of needle-machined holes with a hole diameter of 0.05 to 0.70 mm to the total needle-machined holes on the surface (95%) was obtained.
Further, when a plurality of the above-mentioned glass fiber molded bodies were laminated and pressurized, and the ventilation resistance was measured at a thickness of 15 mm and a bulk density of 130 kg / m ³ , it was 1.0 kPa · s / m.
(2) Impregnation Step of Inorganic Binder The glass fiber molded body having a thickness of 6 mm is impregnated with an aqueous dispersion having a bentonite content of 2.5% by mass and squeezed with a felt roller to convert the impregnation amount into solid content. After adjusting to 2.5% by mass, it was dried and impregnated with bentonite inside, and dispersed in an inorganic binder-containing glass fiber molded body (content ratio of glass fiber molded body 97.5% by mass, bentonite). Content ratio of 2.5% by mass) was obtained.
(3) Step of Forming Bentonite-Containing Film Next, an aqueous dispersion having a bentonite concentration of 10% by mass is roller-coated on one side of the main surface of the inorganic binder-containing glass fiber molded body obtained in (2), and the coated surface is coated. A bentonite-containing film (thickness 0.19 mm, pore size 0.55%, ventilation resistance 2.) was formed on the inner main surface of the glass fiber molded body by winding it in a cylindrical shape with the inner peripheral surface side and then drying it. A glass fiber-containing mat (thickness 10 mm, inner diameter 40 mm, outer diameter 60 mm) having a cylindrical shape as a whole was obtained, which formed 05 kPa · s / m and had a bentonite content of 100% by mass).
(4) Filling Step of Glass Fiber-Containing Mat Using the glass fiber-containing mat obtained in (3) above, the glass fiber-containing mat is combined with the inner tube 2 and the outer tube 3 in the same manner as in Example 1 (4). By inserting it into the gap, a sound reduction structure 1 for an exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe and having a mat material arranged between the inner pipe and the outer pipe was produced.
When the glass fiber-containing mat was inserted into the gap between the inner tube 2 and the outer tube 3, the surface provided with the bentonite-containing film was arranged so as to face the inner tube.

(Example 5)
(1) Manufacturing process of glass fiber molded body While adjusting the thickness with a thickness adjusting roller, glass fibers having an average fiber diameter of 10 μm and an average fiber length of 100 mm are introduced into a needle punching device, and a large number of needles having barbs (protrusions) (protrusions). By reciprocating (needle diameter 0.58 mm) up and down at high speed and entwining (interlacing) the glass fibers with each other, a felt-like glass fiber molded body having a porous shape (thickness 6 mm, bulk density 100 kg / m) ^3. The ratio of needle-machined holes with a hole diameter of 0.05 to 0.70 mm to the total needle-machined holes on the surface (95%) was obtained.
Further, when a plurality of the above-mentioned glass fiber molded bodies were laminated and pressurized, and the ventilation resistance was measured at a thickness of 15 mm and a bulk density of 130 kg / m ³ , it was 1.0 kPa · s / m.
(2) Impregnation Step of Inorganic Binder The glass fiber molded body having a thickness of 6 mm is impregnated with an aqueous dispersion having a bentonite content of 2.5% by mass and squeezed with a felt roller to convert the impregnation amount into solid content. After adjusting to 2.5% by mass, it was dried and impregnated with bentonite inside, and dispersed in an inorganic binder-containing glass fiber molded body (content ratio of glass fiber molded body 97.5% by mass, bentonite). Content ratio of 2.5% by mass) was obtained.
(3) Step of Forming Bentonite-Containing Film Next, an aqueous dispersion having a bentonite concentration of 10% by mass is roller-coated on one side of the main surface of the inorganic binder-containing glass fiber molded body obtained in (2), and the coated surface is coated. A bentonite-containing film (thickness 0.18 mm, pore opening rate 0.5%, airflow resistance 2.) was formed on the inner main surface of the glass fiber molded body by winding the glass fiber molded body in a cylindrical shape and then drying it. A glass fiber-containing mat (thickness 10 mm, inner diameter 40 mm, outer diameter 60 mm) having a cylindrical shape as a whole was obtained, which formed 1 kPa · s / m and a bentonite content of 100% by mass).
(4) Filling Step of Glass Fiber-Containing Mat Using the glass fiber-containing mat obtained in (3) above, the glass fiber-containing mat is combined with the inner tube 2 and the outer tube 3 in the same manner as in Example 1 (4). By inserting it into the gap, a sound reduction structure 1 for an exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe and having a mat material arranged between the inner pipe and the outer pipe was produced.
When the glass fiber-containing mat was inserted into the gap between the inner tube 2 and the outer tube 3, the surface provided with the bentonite-containing film was arranged so as to face the inner tube.

(Comparative Example 4)
(1) Fabrication process of glass fiber molded body While adjusting the thickness with a thickness adjusting roller, glass fibers having an average fiber diameter of 10 μm and an average fiber length of 100 mm are introduced into a needle punching device, and a large number of needles having barbs (protrusions) (protrusions). By reciprocating (needle diameter 0.58 mm) up and down at high speed and entwining (interlacing) the glass fibers with each other, a felt-like glass fiber molded body having a porous shape (thickness 6 mm, bulk density 100 kg / m) ^3. The ratio of needle-machined holes with a hole diameter of 0.05 to 0.70 mm to the total needle-machined holes on the surface (95%) was obtained.
Further, when a plurality of the above-mentioned glass fiber molded bodies were laminated and pressurized, and the ventilation resistance was measured at a thickness of 15 mm and a bulk density of 130 kg / m ³ , it was 1.0 kPa · s / m.
(2) Impregnation Step of Inorganic Binder The glass fiber molded body having a thickness of 6 mm is impregnated with an aqueous dispersion having a bentonite content of 2.5% by mass and squeezed with a felt roller to convert the impregnation amount into solid content. After adjusting to 2.5% by mass, it was dried and impregnated with bentonite inside, and dispersed in an inorganic binder-containing glass fiber molded body (content ratio of glass fiber molded body 97.5% by mass, bentonite). Content ratio of 2.5% by mass) was obtained.
(3) Step of Forming Bentonite-Containing Film Next, an aqueous dispersion having a bentonite concentration of 5.0% by mass was roller-coated on one side of the main surface of the inorganic binder-containing glass fiber molded product obtained in (2). A bentonite-containing film (thickness 0.2 mm, pore opening rate 2.5%, ventilation resistance) is applied to the inner main surface of the glass fiber molded body by winding it in a cylindrical shape with the coated surface on the inner peripheral surface side and then drying it. A glass fiber-containing mat (thickness 10 mm, inner diameter 40 mm, outer diameter 60 mm) having a cylindrical shape as a whole was obtained with 1.2 kPa · s / m and a bentonite content of 100% by mass).
(4) Filling Step of Glass Fiber-Containing Mat Using the glass fiber-containing mat obtained in (3) above, the glass fiber-containing mat is combined with the inner tube 2 and the outer tube 3 in the same manner as in Example 1 (4). By inserting it into the gap, a sound reduction structure 1 for an exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe and having a mat material arranged between the inner pipe and the outer pipe was produced.
When the glass fiber-containing mat was inserted into the gap between the inner tube 2 and the outer tube 3, the surface provided with the bentonite-containing film was arranged so as to face the inner tube.

(Comparative Example 5)
(1) Manufacturing process of glass fiber molded body While adjusting the thickness with a thickness adjusting roller, glass fibers having an average fiber diameter of 10 μm and an average fiber length of 100 mm are introduced into a needle punching device, and a large number of needles having barbs (protrusions) (protrusions). By reciprocating (needle diameter 0.58 mm) up and down at high speed and entwining (interlacing) the glass fibers with each other, a felt-like glass fiber molded body having a porous shape (thickness 6 mm, bulk density 100 kg / m) ^3. The ratio of needle-machined holes with a hole diameter of 0.05 to 0.70 mm to the total needle-machined holes on the surface (95%) was obtained.
Further, when a plurality of the above-mentioned glass fiber molded bodies were laminated and pressurized, and the ventilation resistance was measured at a thickness of 15 mm and a bulk density of 130 kg / m ³ , it was 1.0 kPa · s / m.
(2) Impregnation Step of Inorganic Binder The glass fiber molded body having a thickness of 6 mm is impregnated with an aqueous dispersion having a bentonite content of 2.5% by mass and squeezed with a felt roller to convert the impregnation amount into solid content. After adjusting to 2.5% by mass, it was dried and impregnated with bentonite inside, and dispersed in an inorganic binder-containing glass fiber molded body (content ratio of glass fiber molded body 97.5% by mass, bentonite). Content ratio of 2.5% by mass) was obtained.
(3) Step of Forming Bentonite-Containing Film Next, an aqueous dispersion having a bentonite concentration of 7.5% by mass was roller-coated on one side of the main surface of the inorganic binder-containing glass fiber molded product obtained in (2). By winding the coated surface in a cylindrical shape on the inner peripheral surface side and then drying it, a bentonite-containing film (thickness 0.2 mm, pore opening rate 2.1%, ventilation resistance) is applied to the inner main surface of the glass fiber molded body. A glass fiber-containing mat (thickness 10 mm, inner diameter 40 mm, outer diameter 60 mm) having a cylindrical shape as a whole was obtained, forming 1.4 kPa · s / m and having a bentonite content of 100% by mass).
(4) Filling Step of Glass Fiber-Containing Mat Using the glass fiber-containing mat obtained in (3) above, the glass fiber-containing mat is combined with the inner tube 2 and the outer tube 3 in the same manner as in Example 1 (4). By inserting it into the gap, a sound reduction structure 1 for an exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe and having a mat material arranged between the inner pipe and the outer pipe was produced.
When the glass fiber-containing mat was inserted into the gap between the inner tube 2 and the outer tube 3, the surface provided with the bentonite-containing film was arranged so as to face the inner tube.

(Comparative Example 6)
(1) Manufacturing process of glass fiber molded body While adjusting the thickness with a thickness adjusting roller, glass fibers having an average fiber diameter of 10 μm and an average fiber length of 100 mm are introduced into a needle punching device, and a large number of needles having barbs (protrusions) (protrusions). By reciprocating (needle diameter 0.58 mm) up and down at high speed and entwining (interlacing) the glass fibers with each other, a felt-like glass fiber molded body having a porous shape (thickness 6 mm, bulk density 100 kg / m) ^3. The ratio of needle-machined holes with a hole diameter of 0.05 to 0.70 mm to the total needle-machined holes on the surface (95%) was obtained.
Further, when the above-mentioned glass fiber molded products were laminated and pressurized, and the ventilation resistance was measured at a thickness of 15 mm and a bulk density of 130 kg / m ³ , it was 1.0 kPa · s / m.
(2) Impregnation Step of Inorganic Binder The glass fiber molded body having a thickness of 6 mm is impregnated with an aqueous dispersion having a bentonite content of 2.5% by mass and squeezed with a felt roller to convert the impregnation amount into solid content. After adjusting to 2.5% by mass, it was dried and impregnated with bentonite inside, and dispersed in an inorganic binder-containing glass fiber molded body (content ratio of glass fiber molded body 97.5% by mass, bentonite). Content ratio of 2.5% by mass) was obtained.
(3) Step of Forming Bentonite-Containing Film Next, an aqueous dispersion having a bentonite concentration of 12.5% by mass was roller-coated on one side of the main surface of the inorganic binder-containing glass fiber molded product obtained in (2). By winding the coated surface in a cylindrical shape on the inner peripheral surface side and then drying it, a bentonite-containing film (thickness 0.2 mm, pore opening rate 0.005%, ventilation resistance) is formed on the inner main surface of the glass fiber molded body. A glass fiber-containing mat (thickness 10 mm, inner diameter 40 mm, outer diameter 60 mm) having a cylindrical shape as a whole was obtained, forming 2.7 kPa · s / m and a bentonite content of 100% by mass).
(4) Filling Step of Glass Fiber-Containing Mat Using the glass fiber-containing mat obtained in (3) above, the glass fiber-containing mat is combined with the inner tube 2 and the outer tube 3 in the same manner as in Example 1 (4). By inserting it into the gap, a sound reduction structure 1 for an exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe and having a mat material arranged between the inner pipe and the outer pipe was produced.
When the glass fiber-containing mat was inserted into the gap between the inner tube 2 and the outer tube 3, the surface provided with the bentonite-containing film was arranged so as to face the inner tube.

(Sound absorption evaluation)
In the sound absorption evaluation described in Example 1, the sound reduction structure 1 for exhaust pipes obtained in any of Examples 2 to 5 (ventilation resistance is 1.83 kPa · s / m (Example 2), respectively). A glass fiber-containing mat having a bentonite-containing film of 1.9 kPa · s / m (Example 3), 2.05 kPa · s / m (Example 4), and 2.1 kPa · s / m (Example 5). The sound absorption property was measured in the same manner as in Example 1 except that the above was used.
Then, the OA value (dB sum) of the transmission loss between 800 Hz and 1.25 kHz in Examples 1 to 5 was determined.
The OA value (dB sum) of the transmission loss of the glass fiber-containing mats constituting the sound-reducing structure 1 for each exhaust pipe, which were measured by the above methods, is the ventilation resistance of the bentonite-containing film provided on the surface of each glass fiber-containing mat. The result of plotting against is shown in FIG.
Further, in the sound absorption evaluation described in Example 1, the sound reduction structure 1 for the exhaust pipe (ventilation resistance is 1.5 kPa · s / m, respectively) obtained in any of Comparative Examples 2 to 6 (Comparative Example). 2) 1.75 kPa · s / m (Comparative Example 3), 1.2 kPa · s / m (Comparative Example 4), 1.4 kPa · s / m (Comparative Example 5) and 2.7 kPa · s / m (Comparative Example 5). The sound absorption property was measured in the same manner as in Example 1 except that the glass fiber-containing mat having a bentonite-containing film (comparative example 6) was used, and the transmission loss OA between 800 Hz and 1.25 kHz was used. The values (dB sum) were calculated respectively.
The OA value (dB sum) of the transmission loss of the glass fiber-containing mats constituting the sound-reducing structure 1 for each exhaust pipe, which were measured by the above methods, is the ventilation resistance of the bentonite-containing film provided on the surface of each glass fiber-containing mat. The result of plotting against is shown in FIG.

By comparing the transmission losses of the examples and comparative examples shown in FIG. 4, the transmission loss (sound reduction characteristic) is particularly high when the ventilation resistance of the bentonite-containing membrane is 1.8 to 2.6 kPa · s / m. It turns out to be excellent.

According to the present invention, it is possible to provide a novel sound-reducing structure for an exhaust pipe, which has sufficient sound-reducing performance especially for low-frequency sound of 1 kHz or less even if the thickness is thin, and has excellent heat resistance and heat insulation. Can be done.

1 Sound reduction structure for exhaust pipe 2 Inner pipe (exhaust pipe)
3 Outer pipe (cylindrical heat shield)
3a Upper heat shield 3b Lower heat shield 4 Glass fiber-containing mat

Claims

A sound reduction structure for an exhaust pipe having an inorganic fiber-containing mat arranged between the inner pipe and the outer pipe of an automobile exhaust pipe having a coaxial double cylindrical structure of an inner pipe and an outer pipe.
The inorganic fiber-containing mat has an inorganic binder dispersed in a base material made of an inorganic fiber molded body, and has a ventilation resistance of 1.8 to 2 on one side main surface of the base material made of the glass fiber molded body. It has an inorganic porous film of .6 kPa · s / m and has.
The base material made of the glass fiber molded body is made of an inorganic fiber needle processed product in which the ratio of the needle processed holes having a hole diameter of 0.05 to 0.70 mm to all the needle processed holes on the surface is 80 to 100%.
When the inorganic fiber-containing mat is converted into a solid content, 0.5 to 5.0% by mass of the inorganic binder is dispersed in 95.0 to 99.5% by mass of the base material made of the inorganic fiber molded body. The sound-reducing structure for an exhaust pipe is characterized in that the surface provided with the inorganic porous film is arranged so as to face the inner pipe and has a thickness of 5 to 30 mm.
The sound reduction structure for an exhaust pipe according to claim 1, wherein the ventilation resistance of the base material made of the inorganic fiber molded body is 0.7 to 1.5 kPa · s / m.
The sound reduction structure for an exhaust pipe according to claim 1, wherein the inorganic fiber-containing mat is a glass fiber-containing mat.
The sound reduction structure for an exhaust pipe according to claim 2, wherein the inorganic fiber-containing mat is a glass fiber-containing mat.
The sound reduction structure for an exhaust pipe according to any one of claims 1 to 4, wherein the inorganic porous membrane is a bentonite-containing membrane.