JP2006022817A - Sound absorbing material for silencer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sound absorbing material for a silencer capable of maintaining sound absorbing performance for a long period without being deteriorated by heat and spattering fibers. <P>SOLUTION: This sound absorbing material is formed mainly of a crystalline aluminum fibers with an α-aluminum crystallization rate of 5% or less and a mullite crystallization rate of 80% or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sound absorbing material used for a silencer.

In general, an internal combustion engine, for example, an automobile engine or the like, is provided with a silencer in the middle of an exhaust pipe so as to attenuate the noise component generated in the exhaust system.
As a silencer for attenuating a noise component generated in such an exhaust system, there are conventionally various structures, and those having a structure suitable for various conditions such as the size of the engine are adopted. . For example, a silencer that attenuates a high-frequency noise component among the noise components contained in the exhaust is one in which a metal cylinder with a plurality of small holes is covered with a fibrous sound absorbing material. It has been.

  In this type of silencer, the impact pressure accompanying the flow of high-temperature exhaust is concentrated in the small hole of the metal cylinder. Therefore, when glass fiber or the like is used as a sound absorbing material, especially when the exhaust gas temperature rises as in recent years, the glass fiber with low heat resistance melts and shrinks to bead-like, or the fiber strength deteriorates due to hotness. However, it has been a problem that the sound absorption effect is remarkably reduced due to the glass fibers being scattered from the small holes into the outside air due to vibration and pulsation of the exhaust gas.

  As a silencer for solving this problem, Patent Document 1 and Patent Document 2 include a stainless steel wool or wire mesh cushioning material interposed between a metal cylinder having a small hole and a sound absorbing material. Proposed.

  However, these stainless steel wool and wire mesh cushioning materials have a structure in which the pores are continuous in order to attenuate the noise component, so the function of thermally protecting the glass fiber layer is small, and The metal cushion material is easily softened in the hot state, and the effect as the cushion material is extremely low. Therefore, it has been difficult to attenuate noise components over a long period of time.

On the other hand, it has been proposed to improve heat resistance by using silica-alumina ceramic fiber or crystalline alumina fiber as the inorganic sound absorbing material. However, since the silica-alumina ceramic fiber contains nearly 50 mass% of particulate matter called a shot, there is a problem that when the shot moves inside the sound absorbing material due to vibration, a hole is formed in the sound absorbing material. The general-purpose crystalline alumina fiber is a refractory heat insulating material that is conventionally used as a heat insulating material for high-temperature kilns at around 1400 ° C., and is extremely brittle in strength. There is a disadvantage that the sound absorbing effect is remarkably reduced by scattering into the outside air. Furthermore, inorganic fibers are scattered in the atmosphere, which causes air pollution.
Japanese Utility Model Publication No. 61-59819 Japanese Utility Model Publication No. 6-19785

  Therefore, the present invention is intended to provide a sound absorbing material for a silencer that can maintain excellent sound absorbing performance over a long period of time without scattering the sound absorbing material into the outside air through a small hole in a metal cylinder.

  That is, the present invention provides a sound absorbing material for a silencer for an internal combustion engine, in which a sound absorbing material is provided around a metal cylinder having a plurality of small holes, and the outside of the sound absorbing material is covered with a metal shell. A sound-absorbing material for a silencer, characterized by comprising crystalline alumina fibers having a rate of 5% or less and a mullite crystallization rate of 80% or less.

  The present invention also provides one or more kinds of fiber materials selected from an alumina comprising crystalline alumina fibers having an α-alumina crystallization rate of 5% or less and a mullite crystallization rate of 80% or less, and silica-alumina and glass, and others. A sound-absorbing material for a silencer, comprising a composite of an inorganic material and an organic material.

  In the present invention, the silica-alumina-based inorganic fiber includes a crystalline alumina fiber having an alumina content of 85 mass% or less, an α-alumina crystallization rate: 5% or less, and a mullite crystallization rate: 80% or less. In addition, the crystalline alumina fiber contains 10 mass% or less of particulate matter having a diameter of 44 μm or more, and a combination of the crystalline alumina fiber-containing layer and another layer of inorganic fiber material with low heat resistance. Thus, it is advantageous that the crystalline alumina fiber-containing layer has a thickness that does not exceed the heat resistance temperature of the inorganic fiber material having low heat resistance.

The sound absorber for a silencer according to the present invention is attached to the side surface of the inner tube of a metal cylinder, and by using a crystalline alumina fiber with a controlled crystallization rate, it prevents thermal deterioration of the sound absorber due to high-temperature exhaust gas. In addition, since the scattering of inorganic fibers due to vibration and pulsation of exhaust gas can be prevented, stable silencing performance can be maintained over a long period of time.
In addition, in the crystalline alumina fiber, it is possible to prevent deterioration due to vibration inside the crystalline alumina fiber layer by setting the content of the particulate matter having a diameter of 44 μm or more to 10% or less, particularly in the atmosphere. It is possible to provide an excellent silencer for an internal combustion engine in which no fibrous material is scattered.

  Hereinafter, the present invention will be described in detail. The sound-absorbing material for a silencer of the present invention is an inorganic fibrous material provided in contact with and around a metal cylinder, and α-alumina crystallization rate: 5% or less and mullite crystallization rate: 80% or less. It is characterized by the use of crystalline alumina fibers. It is also possible to form all of this inorganic fibrous sound absorbing material with crystalline alumina fibers.

  Here, the crystalline alumina fiber is usually produced by spinning a precursor called a precursor at a low temperature and firing at around 1400 ° C. And, when using crystalline alumina fiber as a high-temperature kiln heat insulation material, which is a conventional general application, the suppression of joint opening due to thermal shrinkage during reheating becomes an important issue, so manufacturing The firing conditions are controlled, and generally, α-alumina crystals are precipitated to about 20% or mullite crystallization rate is controlled to be close to 100%.

  However, the crystallization rate in the crystalline alumina fiber and its fiber strength have a negative correlation. Therefore, there is no particular problem if it is used in a stationary state, such as a high-temperature kiln insulation, but the material used for parts used under vibrations such as automobile parts is insufficient in strength and long. It cannot stand the use of time.

  On the other hand, as a sound-absorbing material for automobile exhaust system parts, heat resistance up to 1000 ° C. is sufficient, and rather strength is required. Therefore, in order to maintain the required strength, in the present invention, the α-alumina crystallization rate in the crystalline alumina fiber is set to 5% or less and the mullite crystallization rate is set to 80% or less. It was made to cancel. That is, if the α-alumina crystal is precipitated over 5% or the mullite crystallization rate is over 80%, the fiber strength is deteriorated. This is because when crystalline alumina fibers used in the present invention are produced by firing a precursor, mullite crystals and α-alumina crystals having a small inter-lattice distance are constant in Al-Si spinel structure fibers. This is because precipitation of more than the amount causes deterioration of fiber strength.

  For the reasons described above, the mullite crystallization rate is desirably as small as possible in order to increase the fiber strength. However, when used as a sound absorbing material for automobile exhaust system parts, it may be 80% or less.

  By the way, since crystals other than α-alumina crystals and mullite crystals, for example, crystals such as θ-alumina, γ-alumina, and δ-alumina, are sufficiently used, other than α-alumina crystals and mullite crystals There are no particular restrictions on the crystals of.

  Moreover, when the alumina content is high, the transition from the Al—Si spinel structure to the α-alumina crystal is promoted. In particular, when the alumina content exceeds 80 mass%, the fiber strength is significantly reduced. From this, the alumina content is set to 85 mass% or less, more preferably 60 to 80 mass%.

  Furthermore, it is preferable to regulate the particulate matter content in the crystalline alumina fiber layer. In particular, it is advantageous to suppress the content of particulate matter having an average particle size of 44 μm or more to 10 mass% or less. This is because if the average particle size contains a large amount of particulate matter having a particle size of 44 μm or more, the particulate matter in the sound absorbing material opens a sound absorbing material hole by the vibration of the silencer, as in the case of the silica-alumina ceramic fiber described above. It is necessary to limit the content of the particulate matter having an average particle size of 44 μm or more to 10 mass% or less. In particular, the content of the particulate matter having a diameter of 44 μm or more is preferably 5 mass% or less.

  The above-described crystalline alumina fiber can be obtained by controlling the firing conditions during production by setting the alumina content to 85 mass% or less.

  Further, when the inorganic fibrous sound-absorbing material is used in combination with a crystalline alumina fiber disposed on the metal cylinder side and another inorganic fibrous material having low heat resistance, the crystalline alumina fiber is low in heat resistance. The thickness is set to be equal to or lower than the heat resistant temperature of the inorganic fibrous material.

The inorganic fibrous sound absorbing material made of crystalline alumina fiber is provided in the space between the metal cylinder having a plurality of holes and the metal shell as described above, and the average bulk density thereof is 0.05. It is preferable to be in a range of ˜0.30 g / cm ³ . This is because, the average bulk density, 0.05 g / cm and less than ³ cause problems on durability, whereas, it can not be much expected and silencing effect exceeds 0.30 g / cm ^3. In addition, by providing an inorganic fiber sound-absorbing material in the space with an average compression rate of 1% or more, the inorganic fiber sound-absorbing material can be reliably fixed in the space. It is possible to effectively prevent displacement and powdering.

  In addition, the inorganic fibrous sound-absorbing material is composed of one or more fiber materials selected from alumina composed of the crystalline alumina fiber, silica-alumina containing the crystalline alumina fiber, and glass. What consists of a composite material with an inorganic material and an organic material is suitable. That is, fiber materials made of alumina, silica-alumina, or glass are the most common fiber materials that satisfy the above-described conditions such as density, and are inexpensive. A fiber material having an average fiber diameter of 1.5 to 20 μm and an average fiber length of 5 mm or more is particularly advantageous.

  As the metal cylinder, for example, SUS409, which is made of stainless steel having a thickness of 1.0 mm and an inner diameter of φ60 mm, and punched holes having a diameter of φ3 mm and a pitch of 6 mm are used. Further, as the metal shell, for example, a pipe-like object having a thickness of 1.5 mm, a clam shell-like object, or the like is used. Further, as the material of the metal shell, an aluminum plated steel plate or the like is advantageously used in addition to the stainless steel plate.

Hereinafter, an embodiment in which the sound absorbing material of the present invention is attached to a silencer will be described.
Inorganic fiber sound absorption of various specifications shown below around a metal cylinder in which a plurality of holes with a diameter of 5 mm are provided on the outer peripheral surface of a cylinder made of SUS304 having a thickness of 0.6 mm and an outer diameter of 60 mm at an opening ratio of 20%. A silencer was produced by providing a material and covering the inorganic fibrous sound absorbing material with a metal shell made of an aluminum-plated steel plate (SACD80) having a thickness of 0.6 mm.

(1) As an inorganic fibrous sound-absorbing material of Example 1, particles having alumina: 80 mass% and silica: 20 mass%, α-alumina crystallization rate: 0%, mullite crystallization rate: 70%, 44 μm or more A crystalline alumina fiber having a mass content of 5 mass% was provided at a thickness of 40 mm and a filling bulk density of 0.25 g / cm ³ .
(2) As an inorganic fibrous sound-absorbing material of Example 2, E glass fiber was provided at a thickness of 20 mm and a filling bulk density of 0.15 g / cm ³ , and the same crystalline material as in Example 1 was provided on the side surface of the metal cylinder. Alumina fibers were provided with a thickness of 20 mm.

(3) As an inorganic fibrous sound-absorbing material of Comparative Example 1, glass fibers having an average fiber diameter of 9 μm, a filling bulk density of 0.15 g / cm ³ and a thickness of 35 mm are used, and the metal is used to prevent scattering of the sound-absorbing material. Stainless steel wool (SUS304) was provided on the side surface of the cylinder at a thickness of 5 mm and a filling bulk density of 0.56 g / cm ³ .
(4) As Comparative Example 2, a crystalline alumina fiber having an α-alumina crystallization rate of 5% and a mullite crystallization rate of 95% having the same configuration as in Example 1 was used.

  Each silencer thus obtained was connected to the exhaust pipe of a 2-cylinder 6-cylinder gasoline engine, and when this engine was operated at 4000 rpm, the noise from the exhaust pipe was Measurements were taken at a position 1 m behind. Next, actual vehicle traveling under the same conditions was performed for 30000 km, noise from the exhaust pipe after the traveling was measured in the same manner as described above, and the weight loss ratio of the sound absorbing material after actual vehicle traveling was also investigated. These measurement results are shown in Table 1.

As a result, in Examples 1 and 2 suitable for the present invention, the exhaust noise value after running was lower than that of the sound absorbing material of the comparative example, and almost no weight reduction was observed. That is, it was found that the sound absorbing material can be prevented from thermal deterioration and the inorganic fibers are not scattered, so that the sound deadening performance can be maintained for a long time.

Claims (5)

A sound-absorbing material for a silencer, comprising a crystalline alumina fiber having an α-alumina crystallization rate of 5% or less and a mullite crystallization rate of 80% or less. α-alumina crystallization rate: 5% or less and mullite crystallization rate: 80% or less of alumina composed of crystalline alumina fiber, one or more fiber materials selected from silica-alumina and glass, and other inorganic materials and organic materials A sound-absorbing material for a silencer, comprising a composite material. The silica-alumina contains crystalline alumina fibers having an alumina content of 85 mass% or less, an α-alumina crystallization rate: 5% or less, and a mullite crystallization rate: 80% or less. Or the sound-absorbing material for silencers of 2. The sound absorbing material for a silencer according to any one of claims 1 to 3, wherein a particulate matter having a diameter of 44 µm or more contained in the crystalline alumina fiber is 10 mass% or less. Combining the crystalline alumina fiber-containing layer with another inorganic fiber material layer with low heat resistance so that the thickness of the crystalline alumina fiber-containing layer does not exceed the heat resistance temperature of the inorganic fiber material with low heat resistance The sound-absorbing material for a silencer according to any one of claims 1 to 4, wherein the sound-absorbing material has a sufficient thickness.