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(11) | EP 0 396 753 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 158(3) EPC |
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| (54) | SILENCER FOR COMBUSTION EXHAUST GAS |
| (57) A light-weight and durable silencer not causing secondary pollution and exhibiting
a high silencing effect can be obtained by packing or loading a bulky carbon fiber
assembly into the main body of the silencer for a combustion exhaust gas noise and
equipped in its main body (1) with an exhaust gas inlet (2) and an outlet (3). |
(Field of Art)
[0001] The present invention relates to a muffler for exhaust combustion gas noise and particularly to an exhaust muffler to be mounted to internal combustion engines such as automobiles and motorbikes, jet engines, or gas turbines to attenuate exhaust gas noise while allowing the exhaust gas from any such engine to pass therethrough, or an exhaust muffler for boilers or combustors such as those for heating or cooling.
(Background Art)
[0002] If an exhaust combustion gas produced by the combustion of a high-pressure air and fuel in a combustion engine is discharged into the atmosphere, it will expand rapidly and generate a loud noise. This noise is now a subject of discussion as noise pollution. To reduce such exhaust gas noise, a muffler is provided in the exhaust gas passage.
[0003] In conventional mufflers for exhaust combustion gas it has been tried to fill the interior space of a cylindrical body formed of a metallic material such as steel or stainless steel with a sound absorbing material such as glass wool or rock wool. However, a satisfactory noise. , absorbing effect is not obtained unless the filling density is increased. And if the filling density is increased, there occurs lowering of the combustion efficiency due to increase of the back pressure and there also occurs a great increase in weight of the muffler. Further, the filler is deteriorated by the exhaust gas of high temperature and the resulting partial separation and release thereof causes a secondary pollution. To solve this problem, for example in Japanese Patent Laid-Open No.18420/1987 there is disclosed a method which employs a porous sound absorbing material of a desired porosity obtained by heat-melting a fibrous material. Stainless steel fiber is exemplified therein as the fibrous material. However, stainless steel fiber is not satisfactory in point of service life because it is corroded by exhaust gas.
[0004] Further, it is disclosed in Japanese Patent Laid-Open No.75521/1980 that the outer shell of a muffler is constituted using a synthetic resin which exhibits a noise attenuating effect in place of a metallic material. Resins reinforced with fibers such as carbon fibers and glass fibers are exemplified therein. However, synthetic resins involve problems; for example, they are not proof against the high temperature of exhaust gas and the connection thereof with mirror plates is difficult.
[0005] Thus, all of the above conventional means are unsatisfactory in point of reducing the noise which has recently become a serious problem as environmental pollution.
(Disclosure of the Invention)
[0006] It is the object of the present invention to overcome such problems of the conventional sound absorbing materials, namely, secondary pollution caused by separation and release of the sound absorbing materials due to deterioration, corrosive deterioration of the sound absorbing materials, and increase of the back pressure and of weight caused by high filling density, and attain a structure capable of improving the heat resistance of a synthetic resin outer shell whose noise attenuating effect is expected, by combination with a sound absorbing material.
[0007] The present invention relates to a muffler for exhaust combustion gas noise which has a cylindrical body, an inlet pipe and an outlet pipe and in which the interior of the said cylindrical body is filled with bulky, accumulated carbon fibers, or such accumulated carbon fibers are mounted to the cylindrical body interior.
[0008] The cylindrical body, inlet pipe and outlet pipe which constitute the muffler of the present invention may be of known shapes and structures. If desired, the muffler of the invention may be further provided with a partition plate and a conduit, or resonance holes may be formed in the inlet, outlet pipes and the conduit.
[0009] As examples of the shape of the bulky, accumulated carbon fibers to be filled or mounted in the muffler of the present invention there are included mat- and felt-like shapes, fabrics and three-dimensional fabrics.
[0010] It is preferable that the bulky, accumulated carbon fibers used in the present invention have a bulk density in the range of 0.001 to 0.20 g/cm3. The "bulk density" as referred to herein indicates a bulk density of the said accumulated carbon fibers when mounted or filled in the interior of the muffler body. If the bulk density is lower than 0.001 g/cm3, there will not be obtained a satisfactory muffling effect, and if the bulk density is higher than 0.20 g/cm3, the amount of fuel consumed will be increased due to pressure loss although there will be obtained a satisfactory muffling effect. A particularly preferred bulk density range is 0.02 to 0.20 g/cm3.
[0011] As the carbon fibers to be used for obtaining the bulky, accumulated carbon fibers in the present invention there may be used any of rayon-, polyacrylonitrile-, petroleum pitch- and coal pitch-based carbon fibers, but pitch-based carbon fibers are particularly effective. As to the length of the carbon fibers, there may be used any of short, medium and long carbon fibers. These carbon fibers are characteristic in that they are superior in the resistance to heat and to acids and low in thermal conductivity. The term "carbon fibers" as used herein is a generic term for carbon fibers and graphite fibers.
[0012] The method for obtaining the bulky, accumulated carbon fibers used in the present invention is not specially limited. There may be used any conventional method; for example, a method in which raw carbon fibers are accumulated and needle-punched, a method in which accumulated pitch fibers obtained by fiberizing and deposition from molten pitch according to a vortex method are rendered infusible and then carbonized, a method in which carbon fibers are subjected to a paper making process, or a method in which those products obtained are further subjected to needle punching. Also employable is a product obtained by impregnating the accumulated carbon fibers with a heat- carbonizable synthetic resin and then heat-treating the thus- impregnated carbon fibers to carbonize the synthetic resin. This product is improved in strength, shape retaining property, deterioration-dissipation preventing property and heat resistance.
[0013] The bulky, accumulated carbon fibers used in the present invention may be a mixture of carbon fibers and organic or inorganic carbon fibers. By using this mixture there can be attained improvement of strength andvshape; retaining property. As employable inorganic fibers there is no special limitation. For example, there may be used boron fibers, silicon carbide fibers, alumina fibers, silicone titanium carbon oxide fibers and amorphous fibers. In the case where organic fibers are used, it is preferable for the improvement of heat resistance that the organic fibers be heat-carbonized after the mixing.
[0014] No special limitation is placed on the method for filling the interior of the cylindrical body with the bulky, accumulated carbon fibers or mounting the latter to the cylindrical body interior. For example, the filling may be done suitably for the interior space of the muffler. As to the mounting method, the bulky, accumulated carbon fibers may be mounted to suitable portions(s), preferably at least one of the inner wall of the cylindrical body, the outer and inner surfaces of a conduit and the surface of a partition plate.
[0015] As the material of the cylindrical body there may be used a conventional metallic material, but the use of a heat-resisting resin is preferred in point of it being light-weight and superior in muffling performance. As to the heat-resisting resin, there is no special limitation. Both thermoplastic and thermosetting resins are employable. Preferably, there is used at least one member selected from the group consisting of epoxy resins, phenolic resins, ? silicone resins, unsaturated polyester resins, diallyl phthalate resins, melamine resins, thermosetting polycarbodiimide resins, and liquid crystal polyesters.
[0016] A heat-resisting resin exhibits a noise absorbing effect particularly in a viscoelastic region not lower than its glass transition point, and a liquid crystal polymer has an extremely high heat deformation temperature, which is not lower than 300°C, and thus superior particularly in heat resistance.
[0017] Various additives may be incorporated in the heat-resisting resin. As to additives, there is no special limitation. For example, there may be used at least one of mica, silicon oxide, talc, aluminum powder, carbon fiber, glass wool and carbon powder.
[0018] The present invention will be described below more concretely with reference to the drawings.
Fig. 1 is a sectional view showing an example of a muffler according to the present invention. Exhaust gass passes through an inlet pipe 2 and a chamber 6 and is discharged through an outlet pipe 3 in accordance with arrows. A cylindrical body 1 is has a cylindrical, elliptic or prismatic shape, and mirror plates 4 with the exhaust gas inlet pipe 2 and outlet pipe 3 connected thereto are connected to both end portions of the cylindrical body 1. The cylindrical body 1 and the mirror plates'4 are obtained by molding using a heat-resisting resin. In Fig. 1, the foregoing bulky, accumulated carbon fibers are mounted as lining 5 to the inner surfaces of the cylindrical body 1 and mirror plates 4, and the chamber 6 defined by the cylindrical body 1 and the inlet, outlet pipes 2, 3 is filled with the bulky, accumulated carbon fibers. As the lining 5 there may be used another heat-resisting material.
In Fig. 2, a partition plate 7 is mounted on one end of the outlet pipe 3 connected to a mirror plate 4 to partition the chamber 6 into compartments 8 and 10, the compartment being filled with the bulky, accumulated carbon fibers and the compartment 10 serving as a free expansion chamber of exhaust gas. Further, a conduit 9 for communication between the compartments 8 and 10 is mounted through the partition plate 7.
Fig. 3 shows a state wherein Fig. 2 the bulky, accumulated carbon fibers are mounted as mountings 11 to both faces of the partition plate 7, the compartments 8 and 10 are filled with the bulky, accumulated carbon fibers, and the same accumulated carbon fibers are mounted as lining 5 to the inner surfaces of the cylindrical body 1 and mirror plates 4.
[0019] The muffler of the present invention exhibits the following functions and effects.
(I) Functions and effects attained by mounting or filing of the bulky, accumulated carbon fibers:
(a) The noise absorbing effects is higher than that of conventional sound absorbing materials such as rock wool.
[0020] Although the reason why the bulky, accumulated carbon fibers exhibit a remarkably superior noise absorbing effect as compared with other sound absorbing materials is not clear, it is presumed to be because the crystal-noncrystal combination of each individual carbon fiber is in conformity with exhaust combustion gas conditions. More particularly, the crystal and noncrystal textures constituting each carbon fiber correspond to a spring having elasticity and a dash pot having viscoelasticity, respectively, functioning as a whole as a viscous damping oscillation system, and this system resonates with the frequency of exhaust combustion gas such as the exhaust gas from an engine. Particularly, the present invention is characteristic in that an outstanding effect is exhibited under the temperature condition of exhaust combustion gas.
(b) The weight of the muffler can be reduced because the accumulated carbon fibers are in a bulky form such as the form of felt or mat.
(c) Fuel economy is not deteriorated because the back pressure at the outlet of an engine or a combustor is not increased.
(d) There is no fear of the bulky, accumulated carbon fibers being partially deteriorated by exhaust gas and dissipated to the exterior, so a secondary pollution is not likely to occur.
(II) Functions and effects attained by forming the cylindrical body using a heat-resisting resin.
(e) Because of superior resistance to acids and to heat, the life of the cylindrical body is longer than that of a metallic muffler.
(f) Reduction of weight can be attained as compared with a metallic muffler.
(g) Noise attenuating effect is higher than that of a metallic muffler.
(h) A particularly outstanding noise absorbing effect is exhibited in viscoelastic region not lower than the glass transition point of the heat-resisting resin.
(III) Synergistic functions and effects attained by forming the cylindrical body using a heat-resisting resin and mounting the bulky, accumulated carbon fibers to the inner surface thereof:
(I) It is possible to provide a very light-weight muffler.
(j) It is possible to provide a muffler of long life.
(k) It is possible to provide a muffler which exhibits a high noise muffling effect.
Run 1
[0022] The kinds of mufflers were produced as working examples by mounting ceramic paper as lining 5 to the inner surface of a cylindrical body 1 having such a sectional structure as shown in Fig. 1 and formed using a heat-resisting resin (a phenolic resin) and filling a chamber 6 in the cylindrical body 1 with a petroleum pitch-based carbon fiber felt at different bulk densities. Also produced were a muffler not filled with any filler and a muffler filled with rock wool as comparative examples. These mufflers were tested for noise muffling effects. They were each to a 1.5L, 4- cylinder, water-cooled, 4-cycle, gasoline engine and the exhaust noise from the outlet pipe of each muffler was measured by an ordinary sound level meter (JIS-C1052) using a noise measureing microphone. The microphone was disposed at a distance of 50 cm in 45° direction outwards from the outlet pipe and at the same height as the outlet pipe. Fig. 4 shows the relation between the engine speed (rpm) and a total noise level (db(A)) observed at a constant engine output of 15 kw.
[0023] In Fig. 4, ① shows the result obtained using the muffler not filled with any filler; 0, ③ and ④ show the results obtained using the mufflers filled with the bulky, accumulated carbon fibers at bulk densities of 0.035, 0.53 and 0.070 (g/cm3), respectively; and ⑤ shows the results obtained using the muffler filled with 0.15 g/cm of rock wool.
Run 2
[0024] The following mufflers were tested for noise muffing effect in the same manner as in Run 1 using an FFT (fast fourier transformation) analyzer:
the same muffler as ④ in Run 1 filled with the bulky, accumulated carbon fibers at a bulk density of 0.07 g/cm3
② a muffler filled with 0.15 g/cm3 of rock wool
③ a muffler not filled with any filler
[0025] The ese mufflers were each subjected to frequency analysis to check the relation between frequency and noise level. The results are as shown in Fig. 5.
[0026] It is apparent that the muffler 1 which is a working example of the present invention is low in noise level and superior in noise muffling effect as compared with the conventional examples ② and ③.
Run 3
[0027] A carbon felt 11 (10 mm thick) was mounted three rolls in thickness of 30 mm (tatal weight: 265 g) to the inner surface of cylindrical body 1 having such a sectional structure as shown in Fig. 6 and formed of a liquid crystal polyester "XYDAR" (trade name, a product of Amoco Performance Products, Inc., U.S.A.) reinforced with glass fibers.
[0028] This muffler was mounted to a 1.5L, 4-cylinder, 4- cycle, gasoline engine and the relation between the engine speed (rpm) and a total noise level (db(A)) was checked in the same manner as in Run 1 at a constant engine output of 22 kw. The results are as shown in Fig. 7.
Run 4
[0029] A muffler was produced and test was conducted in the same manner as in Run 3 except that the cylindrical body 1 was replaced by a cylindrical body formed of a liquid crystal polyester "XYDAR" (trade name, a product of Amoco Performance Products, Inc., U.S.A.). The results are as shown in Fig. 7.
[0030] Also, this muffler was checked for noise muffling effect using an FFT analyzer in the same manner as in Run 2. The results are as shown in Fig. 7.
Run 5
[0031] As a comparative example there was produced a muffler having a cylindrical outer shell made of steel in place of the one made of the liquid crystal polyester in Run 4. This muffler was subjected to the same tests as in Run 4 with nothing filled or mounted therein.
(Brief Description of the Drawings)
[0033]
Figs. 1 to 3 and are sectional views each showing an example of a muffler according to the present invention;
Figs. 4 and 7 are graphs showing measurements results obtained using an ordinary sound level meter (JIS-C-1052); and
Figs. 5 and 8 are graphs showing the results of FFT analysis of various mufflers.