JPS6215735B2 - - 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 so-called porous materials in the form of fibers, foams, particles, etc., such as glass wool, porous ceramics, and porous metals. However, if these materials are used as sound-absorbing materials as they are, when an internal combustion engine is operated, soot, which is the combustion residue of fuel such as gasoline, will infiltrate the surface and the inside of the porous material and become visible within a relatively short period of time. As a result of clogging, sound absorption performance deteriorates, resulting in an unavoidable problem of intensifying noise and adversely affecting the fuel efficiency of the internal combustion engine.

The inventors conducted various studies to find out why soot adheres to the surface of sound-absorbing materials.
It was found that the main cause was water (steam) produced by the combustion of gasoline or a tar-like substance that was the combustion residue. In other words, the soot discharged from the engine exhaust port is a moderate particle with an average particle size of several hundred Å, but the adhesion force (surface energy ) becomes large, so that it is tightly adhered to the entire surface and inside of the sound absorbing material. Therefore, it has been found that in order to prevent soot from adhering, it is sufficient to coat the surface of the sound absorbing material with a substance having low surface energy to prevent it from adhering to the surface and from entering into the interior. Therefore, the inventors used various substances with low surface energy to coat the surface of sound-absorbing materials and actually used them as exhaust silencing devices for internal combustion engines. It was discovered that the surface temperature of the sound absorbing material inside the device was between 150 and 500 degrees Celsius, causing it to decompose and lose its low surface energy properties. Next, we conducted a similar study after dispersing and adhering an inorganic solid lubricant such as graphite or molybdenum disulfide to the surface of the sound absorbing material, and found that the surface temperature also increased, causing it to decompose or increase the surface energy. As a result, soot adheres to the
In addition, because some of the materials adhered to the surface, they caused clogging, significantly impeding the sound-dampening performance, and creating new defects.

The present invention provides a new sound absorbing material that can be used in an exhaust silencing device for an internal combustion engine, does not suffer from any of the above-mentioned disadvantages, and can significantly suppress the soot adhesion that conventional sound absorbing materials have. In other words, the inventors discovered that graphite fluoride, a compound of fluorine and carbon, was adhered and dispersed on the surface of a sound-absorbing substrate, and was used in an exhaust silencer for internal combustion engines due to its low surface energy. We have found that the adhesion of soot can be significantly suppressed in cases where this is the case, and we have already proposed sound-absorbing materials that utilize this technology. The present invention also relates to a sound absorbing material using fluorinated graphite, and the surface fluorinated graphite layer is grown by fluorinating the surface of carbon fiber used as a base material. In other words, in the sound absorbing material of the present invention, the graphite fluoride layer and the base material are essentially integrated, so there is little possibility of peeling, etc., and there is no need for work such as painting the graphite fluoride, so it is easy to manufacture. It is possible.

Hereinafter, the present invention will be explained in detail with reference to Examples.

Example As shown in an enlarged schematic diagram in FIG. 1a, a commercially available carbon fiber was treated with hot hydrochloric acid to activate its surface. 1 is one carbon fiber, and 2 is activated unevenness. This was heat-treated in a fluorine gas atmosphere (600° C., 1 hour) to fluorine the carbon fiber surface, resulting in a structure as shown in the enlarged cross-sectional view shown in FIG. 1b. 3 is a fluorinated film. Note that the fluorine gas used was generated by electrolysis of fluorine acid. Using the sound absorbing material of the present invention produced in this way and bonded with an inorganic binder,
We investigated the sound absorption coefficient, soot adhesion, and the accompanying deterioration of sound-absorbing performance over time by comparing it with a conventional sound-absorbing material made of porous ceramic material.

Figure 2 shows the normal incidence sound absorption coefficient measured under the same conditions by the in-pipe method (JISA1405). Curve A is the characteristic of the sound absorbing material of the present invention, and curve B is the characteristic of the conventional sound absorbing material made of porous ceramic material.
From FIG. 2, it can be seen that the sound absorbing material of the present invention has a higher sound absorption coefficient and better characteristics than the conventional sound absorbing material.

Next, the above-mentioned sound absorbing material of the present invention is made into a cylindrical shape using a protective material (metal mesh), and an exhaust silencer is constructed as shown in the cross-sectional view of FIG.
1.800cc), and after driving approximately 10,000 km, the noise reduction performance was measured according to JISD1616 and compared with the initial value before the actual driving. In addition, tests similar to those described above were also conducted on a conventional sound absorbing material made of porous ceramic material molded into a cylindrical shape. In FIG. 3, 4 is a housing constituting the exhaust silencer, 5 is an exhaust gas inlet pipe, 6 is an exhaust gas passage, 7 is the sound absorbing material of the present invention, 8 is a protection material for the sound absorbing material,
9 is an air layer on the back side of the sound absorbing material, and 10 is an exhaust gas exit device. Figure 4 shows the frequency characteristics of the silencing performance. Curves C and C' are the initial and actual characteristics when using the sound absorbing material of the present invention, respectively, and curves D and D' are the initial and after actual running characteristics, respectively, when using the sound absorbing material made of a conventional ceramic porous body. These are the characteristics after actual driving. As can be seen from Figure 4, the sound absorbing material of the present invention not only has good initial sound damping performance, but also has almost no decline in initial performance after 10,000 km of actual driving.
The sound-absorbing material made of porous ceramic material had significantly reduced sound-dampening performance in all frequency bands after actual driving. In addition, after measuring the silencing performance, both sound absorbing materials were taken out and visually observed, and it was found that the sound absorbing material of the present invention was almost as clean as the initial stage, and the excellent soot of the fluorinated layer on the surface of the carbon fiber was found. While the adhesion inhibiting effect was demonstrated, the ceramic porous material had a large amount of graphite soot adhering to the entire surface, causing severe clogging.

Furthermore, when the surface of the sound absorbing material of the present invention was analyzed by X-ray diffraction etc., a thin film of so-called fluorinated graphite (carbon fluoride) was formed on the surface of each carbon fiber due to fluorination. I found out. In other words, the good soot adhesion prevention effect of the sound absorbing material of the present invention is due to the low surface energy property of this fumed graphite, and it is also possible to prevent liquid fuels such as water (steam) and tar, which are the main causes of soot adhesion. It is thought that this makes it difficult for the combustion residue to adhere to the surface of the sound-absorbing material, so that soot either does not adhere, or even if it does, it is easily blown away by the flow of exhaust gas.

By the way, various kinds of carbon fibers are commercially available to be used as the base material of the sound absorbing material of the present invention, and any of them may be used. However, since the strength of carbon fibers alone is low, the carbon fibers used in the examples are It is necessary to harden it with a binder or use a protective material. Further, the method for combining the surface of the carbon fiber with fluorine may be a method other than those in the examples, and it can be combined with fluorine relatively easily.

The sound absorbing material of the present invention is intended to be used in an exhaust silencing device for an internal combustion engine, but depending on how it is used, it may also be used as a sound absorbing material in other equipment such as combustion equipment.

As explained above, the sound absorbing material of the present invention, in which the surface of the carbon fiber base material is coated with a fluorinated film, has good sound damping performance and is an exhaust muffling device for an internal combustion engine. When used as a sound-absorbing material, it is possible to prevent deterioration of sound-damping performance caused by clogging with soot and maintain the initial good sound-damping performance. Therefore, since it has high performance and long life, it can be widely used in exhaust silencing devices for internal combustion engines such as automobiles.

[Brief explanation of the drawing]

FIG. 1 is an enlarged view showing the structure of a sound absorbing material according to an embodiment of the present invention, FIGS. 2 and 4 are characteristic diagrams showing the performance of the sound absorbing material of the present invention, and FIG. 3 is a diagram showing the characteristics of the sound absorbing material of the present invention. It is a sectional view showing an example of application. 1 is carbon fiber, 2 is surface unevenness, 3 is fumed graphite film, 4 is casing, 5 is inlet pipe, 6 is exhaust gas passage, 7 is sound absorbing material, 8 is protective material, 9 is rear air layer,
10 is an outlet pipe. The same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A sound absorbing material for an exhaust silencer for an internal combustion engine, characterized in that a carbon fiber whose surface is fluorinated is used as a base material.