JPH0510306B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sound absorbing material used in an exhaust silencing device for an internal combustion engine.

Conventionally, sound absorbing materials used in exhaust silencers for internal combustion engines include glass wool, porous ceramic bodies, porous metal bodies, and the like. However, if these materials are used as sound absorbing materials as they are, when an internal combustion engine is operated, tar, which is the combustion residue of fuel such as gasoline, will adhere to the surface and cause clogging in a relatively short period of time. This often resulted in a decline in sound absorption performance, increased noise, and adversely affected the fuel efficiency of internal combustion engines. In addition, when a porous metal material is used as a sound absorbing material, the temperature of the exhaust gas inside the silencer is as high as 400 to 800℃, and the exhaust gas contains corrosive sulfur oxides and nitrogen oxides. Unless a special heat-resistant alloy is used, corrosion deterioration due to high-temperature oxidation will be significant, resulting in clogging due to the fuel combustion residue and its corrosion products, and the skeleton of the porous metal body will corrode and disappear. It was inevitable that the material would become useless as a sound absorbing material. In addition, since the basic characteristic of porous metal bodies is that the pore diameter is relatively large, there are disadvantages in that there are no metal porous bodies that have good sound absorption performance.

Conventional sound absorbing materials, no matter what material they are made of, have the major drawbacks mentioned above.
Improvement was desired.

Therefore, the inventors of this application have developed a sound absorbing material by oxidatively decomposing the combustion residue of the fuel, inhibiting the polymerization of the combustion residue, and further neutralizing or saponifying the polymer of the combustion residue. We have conducted various investigations focusing on the ability to prevent clogging and corrosion, and as a result, we have developed a material that uses one or more materials selected from low-temperature oxidation catalysts, solid acid catalysts, reducing agents, and alkaline agents. We were able to previously propose several types of sound absorbing materials that are held in porous metal bodies using a binder.

However, all of the above sound absorbing materials exhibit maximum sound absorption coefficients in a relatively high frequency range (0.6 to 1.0 kHz), and in lower frequency ranges (0.2 to 0.5 kHz), sound absorption gradually decreases as the frequency increases. Although the sound absorption rate increased, it was difficult to expect a large sound absorption effect. On the other hand, since internal combustion engines generate noise in a low frequency range, the sound absorbing material used in the exhaust silencing device is desired to have a maximum sound absorption coefficient in the low frequency range of about 0.2 to 0.5 kHz.

This invention was made in view of the above circumstances.

In other words, this invention is characterized in that the surface of a porous material is coated with a layer or porous film made of particles having a specific surface area of 5 to 100 m ² /g, and according to this, the sound absorption coefficient is increased. The maximum value exists in the frequency range of noise generated from internal combustion engines,
Moreover, its maximum value is equivalent to that of the above-mentioned sound absorbing material.

In this invention, the adhesion of fuel combustion residues such as soot and tar to the sound-absorbing material is not a particular issue, but in order to maintain high sound-absorbing properties over a long period of time, it is necessary to prevent clogging due to the adhesion of combustion residues. It is desirable to consider problems such as corrosion of porous metal bodies.

From this point of view, desirable porous materials that can be used in the present invention include commercially available general-purpose materials such as foamed metals, sintered metals, metal fibers, and inorganic fiber-reinforced metals, and these materials include Ni, Cu, Al, Ni−Cr, Fe−Cr, Fe−Ni−
Alloy materials such as Cr and Fe-Cr-Al are suitable.
As other porous materials, glass-based materials such as Ganaswool or ceramic-based materials can be used, and the porosity thereof is preferably 40 to 95%. This is because if the porosity is less than 40%, sufficient sound absorption properties cannot be obtained even if the surface is covered with a porous layer, and if the porosity is more than 95%, the material becomes brittle. Among these, metal-based materials are particularly desirable in consideration of vibration resistance and impact resistance. In addition, materials for coating the surface of the porous materials listed above include low-temperature oxidation catalysts that oxidize and burn fuel combustion residues at low temperatures, and materials that prevent oxidative polymerization (polymerization) of combustion residues attached to the surface. It is desirable to use a solid acid catalyst that reduces the molecular weight of the components and vaporizes them, as well as a reducing agent or alkaline agent that neutralizes or saponifies the combustion residue to prevent oxidative polymerization. As low-temperature oxidation catalysts, MnO ₂ , CuO, NiO, CoO,
Co ₈ O ₄ , Cr ₂ O ₃ , Fe ₂ O ₈ , Ag ₂ O, ZnO, PbO and other metal oxides, MnFe ₂ O ₄ , NiCr ₂ O ₄ ,
MnCr ₂ O ₄ , CuCr ₂ O ₄ and other composite metal oxides,
Single noble metals such as Pt, Pd, Rh, Ru, Ag and others can be used. Furthermore, as the solid acid catalyst, natural zeolite, synthetic zeolite, activated clay, acid clay, silica zirconia, silica magnesia, activated alumina, silica alumina, vanadium pentoxide, alumina boria, and other solid acid catalysts can be used. Furthermore, as a reducing agent, silver powder, sodium sulfite, metal powder, carbon powder, sulfite, ferrous salt, tin salt, stannous nitrate, stannous sulfate, oxalate, and other reducing agents are used. be able to. Furthermore, as alkaline agents, potassium silicate, sodium aluminate, sodium silicate, lithium silicate, sodium carbonate, alkali metal oxides, alkali metal silicates, hydroxides, basic oxides and other alkaline agents may be used. can be used.

The above-mentioned materials are effective in suppressing the adhesion of soot and tar, and particles other than these can be used in the present invention if the adhesion of combustion residue is not taken into consideration.

In addition, the layer or porous film made of particles that covers the surface of the porous material may be formed by painting, plating, vapor deposition, or any other film forming method, and is limited to specific methods. It's not a thing.

Next, typical embodiments of the invention will be described.

〔Example〕

Using TiO ₂ -MgO ceramic with a porosity of 45%, colloidal silica particles are applied to the surface to form a particle layer, and then fired at 350°C to obtain a specific surface area of 45 m ² /g and thickness. The particle layer was approximately 2 mm thick.

In addition, using the same method, specific surface area of 5 m ² /g and
Two sound absorbing materials having a particle layer of 100 m ² /g on the surface were obtained.

The sound-absorbing properties of the three types of sound-absorbing materials thus obtained were compared with those of a sound-absorbing material composed only of porous bodies made of metal. Figure 1 shows the jurisdictional law (JIS
A1405) shows the normal incidence sound absorption coefficients of the former four, measured under the same conditions. Curve A has a coated particle layer with a specific surface area of 5 m ² /g, curve B
has a coated particle layer with a specific surface area of 45 m ² /g,
Curve C shows the characteristics of the porous body having a coated particle layer with a specific surface area of 100 m ² /g, and curve D shows the characteristics of only the porous body having no coated particle layer. From this figure, the specific surface area is 5~
It can be seen that the sound absorbing material having a coated particle layer of 100 m ² /g has better low frequency characteristics than the sound absorbing material having no coated particle layer. That is, the specific surface area is 5~
For those having a coated particle layer of 100 m ² /g, the maximum value of the sound absorption coefficient exists at a frequency of 0.2 to 0.5 kHz, and this value is also sufficient for practical use. In this way, the reason why the maximum sound absorption coefficient shifts to the lower frequency side by providing a coated particle layer is because the porous material increases its porosity by holding the coated particle layer. be. Therefore, it is obvious that equivalent results can be obtained even if the coated particle layer is formed of other granules listed above. Further, the same applies when the surface of a porous material is coated with a porous film by a method such as plating or vapor deposition. In addition, the specific surface area of the coated particle layer or porous film is 5 to 100.
By increasing or decreasing it between m ² /g, the frequency at which the sound absorption coefficient shows a maximum value can be varied.
That is, by changing the thickness of the coated particle layer and the material constituting it, a sound absorbing material exhibiting the best sound absorbing characteristics at any given frequency can be obtained.

As is clear from the above explanation, the surface of the sound absorbing material of the present invention is coated with a layer or porous film made of particles having a specific surface area of 5 to 100 m ² /g, so that it absorbs low frequency waves generated from internal combustion engines. Shows excellent sound absorption properties against noise.

[Brief explanation of the drawing]

The drawing is a sound absorption characteristic diagram comparing the performance of the sound absorbing material according to the present invention and a conventional product.

Claims (1)

[Claims] 1 Specific surface area on the surface of porous material 5 to 100 m ² /g
1. A sound absorbing material for an internal combustion engine, characterized in that the material is coated with a layer or a porous film made of particles having the following properties.