WO1989004915A2

WO1989004915A2 - Automotive exhaust system with resin muffler associated with exhaust gas cooling system

Info

Publication number: WO1989004915A2
Application number: PCT/JP1988/001162
Authority: WO
Inventors: Hideo Yoshikawa; Katsuyoshi Takeuchi; Takashi Ikeda
Original assignee: Yamato Kogyo Company, Limited; Showa Denko Kabushiki Kaisha
Priority date: 1987-11-17
Filing date: 1988-11-17
Publication date: 1989-06-01
Also published as: WO1989004915A3; JPH01134021A

Abstract

An exhaust system employs an exhaust gas temperature controlling system associated with a muffler (10) made of a resin so as to avoid influence of heat of exhaust gas, which otherwise causes shortening of life of the resin muffler (10). The exhaust gas temperature controlling system comprises a heat converting means (11) provided at a location upstream of the muffler (10) for controlling exhaust gas temperature below a predetermined temperature.

Description

S P E C I F I C A T I O N

AUTOMOTIVE EXHAUST SYSTEM WITH RESIN MUFFLER ASSOCIATED WITH EXHAUST GAS COOLING SYSTEM

FIELD OF THE INVENTION

The present invention relates generally to an exhaust system of a vehicle powered by an internal combustion engine, such as automotive vehicles, motor cycles, industrial vehicles, agricultural vehicle and so forth, which includes a muffler made of a resin. More particularly, the invention relates to an exhaust system which can effectively lower a temperature of an exhaust gas introduced into a resin muffler so as to avoid influence of heat on the muffler.

BACKGROUND OF THE INVENTION As is well known, exhaust noise of automotive vehicles is one of problems to be solved in the automotive technologies. In view of noise suppression, various proposals have been made. For example, U. S Patent 4,239,091, issued on December 16, 1980, to Paulo M. Negro, discloses a muffler which encloses rock wool as a noise creating vibration energy absorbing medium. Similar idea has been proposed in U. S. Patent 4,589,516, issued on May 20, 1986, to Takeshi Inoue et al. discloses a muffler with sound insulative lining provided on the inner periphery of the muffler body and supported by means of a resin base which is bonded on the muffler body. Though such prior proposed muffler may achieve certain level of noise suppression. These clearly reduces path area for the exhaust gas to lower discharge efficiency of the exhaust gas. Furthermore, these prior proposed mufflers may not answer the needs for reduction of muffler weight. In order to accomplish both, the co-pending U.

S. Patent Application Serial No. 125,579, filed on November 25, 1987, corresponding European Patent Application of which has been published as European Patent First Publication No. 0 269 116, and assigned to the common assignee to the present invention, has been proposed. In the U. S. Patent Serial No. 125,579 discloses an automotive muffler made of a fiber reinforced synthetic resin. Such resin muffler is effective for elastically absorbing noise creating energy and whereby for suppressing exhaust noise which is caused by pulsatile flow of the exhaust gas.

As is well known, the exhaust gas discharged from exhaust ports of an internal combustion engine has a temperature in a range of 500 °C to 700 °C. The exhaust gas is past through an exhaust gas and introduced into a catalytic converter which may be provided in the exhaust system for purification of exhaust gas by removing NO_x, HC and CO for anti-polution purpose. The catalytic converter is generally composed of a catalyst carrier made of ceramics, metal and so forth, and a catalyst made of metal oxide, such as those disclosed in SAE Technical Paper No. 850131, "Metal Support for Exhaust Gas Catalysts", February 25 - March 1, 1985, U. S. Patent 2,750,283, issued on June 12, 1956, to Donald L. Loveless, U. S. Patent 3,852,063, issued on December 3, 1974, to Itaru Niimi et al., U. S. Patent 4,414 ,023, issued on November 8, 1983, to George Aggen et al. The metal oxide as the catalyst react with high temperature exhaust gas to generate a heat. As a result, the exhaust gas temperature is rised to be in a range of 800 °C to 850 °C in the catalytic converter. In addition, chemical reaction caused between the metal oxide and the exhaust gas generates corrosive ionized gas.

In viewpoint of corrosion resistance, the resin muffler is advantageous in comparison with known metal muffler. However, on the other hand, the problem is encountered in the resin muffler by substantially high temperature of the exhaust gas flowing into the muffler. Namely, as will be normally awared, the synthetic resins has lower heat resistance in comparison with the metals. In particular, the exhaust gas temperature tends to fluctuate in various engine driving conditions. Therefore, the muffler may be subject to relatively wide temperature range of heat. For example, at substantially high engine load condition, the exhaust gas temperature tends to be high. When the resin muffler is repeatedly subject to substantial temperature variation including temporary high temperature, it will cause secular variation in unacceptable short period. Furthermore, when substantially high temperature exhaust gas, whose temperature is higher than the melting point of the resin is introduced into the resin muffler, the resin may be melted down to cause breakage of the muffler. SUMMARY OF THE INVENTION

Therefore, it is a primary object of the present invention to make a muffler made of synthetic resin applicable for an exhaust system.

Another object of the invention is to provide a system for controlling the temperature of an exhaust gas to be introduced into the resin muffler.

In order to accomplish the above-mentioned and other objects, an exhaust system, according to the present invention, employs an exhaust gas temperature controlling system associated with a muffler made of a fiber reinforced resin. The exhaust gas temperature controlling system comprises a heat converting means provided at a location upstream of the muffler for controlling exhaust gas temperature below a predetermined temperature.

According to one aspect of the invention, an exhaust system for an internal combustion engine for a vehicle, comprising: an exhaust gas passage means defining a path for flowing an exhaust gas exhausted from the internal combustion engine therethrough, the exhaust gas passage means including a first and a second section mutually separated from each other; a noise reduction muffler provided between the first and second sections of the exhaust passage means for completing the exhaust gas path for discharging the exhaust gas to the atmosphere, the muffler comprising a hollow muffler body defining an internal space having an inlet connected to the internal combustion engine via the first section of the exhaust gas passage means and an outlet connected to the second section of the exhaust passage means for discharging the exhaust gas therethrough, the muffler body being formed with a synthetic resin which has visco-elastic property for dissipating noise creative energy of exhaust gas at a given operating temperature range and has a known melting point or glass transition point; and a cooling means associated with the exhaust gas passage means for controlling a temperature of the exhaust gas flowing through the internal space of the muffler to a temperature range lower than a predetermined temperature which is set higher than the known melting point or glass transition point of the synthetic resin in a magnitude of approximately 200 °C.

The synthetic resin compound is composed of a heat resistant thermosetting resin, or in the alternative a heat resistant thermoplastic resin. The thermostting resin is further composed of a hardner and a cure-promoting agent. The synthetic resin is also composed of a filler. In case that the synthetic resin is the thermosetting resin, the thermosetting resin is selected among epoxy resin, phenol resin, silicon resin, unsaturated polyester resin, diallyl phthalate resin, melamine resin, thermosetting poly carbodiimide. On the other hand, in case that the synthetic resin is a thermoplastic resin, the thermoplastic resin is selected among polyamide resin, polyester resin, polyphenylene sulfide resin, thermoplastic fluorine containing resin, polysulfon resin, poly phenylene ether resin.

The synthetic resin is preferably the epoxide resin is selected among bisphenol F-type epoxide resin, bisphenol A-type epoxide resin, novolac type epoxide resin. In such case, the hardner may be selected among acid anhydride, aliphatic, aromatic or fatty amine compound and derivative thereof, and imidazole, or mixture thereof. The cure-promoting agent may be selected among 2,4,6-dimethyl amino phenol (DMP-30), dimethyl amino imidazole.

The synthetic resin compound may contain an inorganic material. The inorganic material is selected among mica, silicon oxide, silica (SiO₂), talc, alumina

(Al₂O₃), beryllia (BeO), cesium oxide (CeO₇), magnesia

(MgO), quartz (SiO₂), titania (TiO₂), zirconia (ZrO₂), mullite (3Al₂O₃.2SiO₂), spinel (MgO.Al₂O₃), silicon carbide (Si.C), titanium carbide (TiC), boron carbide (B₄C), tungsten carbide (WC), carbon black (C), boron nitride (BN), silicon nitride (Si₃N), aluminium titanate

(AlTiO₃), mica ceramics (muscobite, sericite), sepiolite, pyrophyllite, steatite (MgO.SiO₂), forsterite

(2MgO.SiO₂), zircon (ZrO₂,SiO₂), cordielite (2MgO.2Al₂O₃.5SiO₂), fiber, flocculent or cloth material, such as glass wool, glass fiber, glass cloth, asbestos cloth, carbon fiber or metal fiber.

The muffler may further comprise a heat-protective layer structure formed on the inner periphery of the muffler body. The heat-protective layer structure may be formed by a material selected among metal, heat resistant resin, ceramics, glass wool, glass fiber, glass cloth, asbestos cloth, carbon fiber, and inorganic material.

The cooling means comprises a heat radiation fin means provided at least on the first section of the exhaust gas passage means. The heat radiation fin means may comprise a plurality of annular disc shaped fin arranged in longitudinal alignment with given intervals, or a plurality of fins extending longitudinally along an axis of the exhaust gas path and arranged with circumferentially spaced apart relationship to each other with given circumferential intervals. In the alternative, the heat radiation fin means may comprise a single fin extending at least on the outer periphery of the first section of the exhaust gas passage means in spiral fashion.

In the further alternative, the cooling means comprises a water jacket formed at least around the first section of the exhaust gas passage means. In addition, the cooling means may also be provided for the muffler.

According to another aspect of the invention, an exhaust system for an internal combustion engine for a vehicle, comprising: an exhaust gas passage means defining a path for flowing an exhaust gas exhausted from the internal combustion engine therethrough, the exhaust gas passage means including a first, second and a third section mutually separated from each other; a catalytic converter disposed between the third and first sections so that it is connected to the internal combustion engine through the third section of the exhaust gas passage means for introducing the exhaust gas therethrough and discharging through the first section; a noise reduction muffler provided between the first and second sections of the exhaust passage means for completing the exhaust gas path for discharging the exhaust gas to the atmosphere, the muffler comprising a hollow muffler body defining an internal space having an inlet connected to the catalytic converter via the first section of the exhaust gas passage means and an outlet connected to the second section of the exhaust passage means for discharging the exhaust gas therethrough, the muffler body being formed with a synthetic resin which has visco-elastic plastisity for dissipating noise creative energy of exhaust gas at a given temperature range and has a known melting point or glass transition point; and a cooling means associated with the exhaust gas passage means for controlling a temperature of the exhaust gas flowing through the internal space of the muffler to a temperature range lower than a predetermined temperature which is set higher than the known melting point or glass transition point of the synthetic resin in a magnitude of approximately 200 ºC.

According to a further aspect of the invention, an exhaust system for an internal combustion engine for a vehicle, comprising: an exhaust gas passage means defining a path for flowing an exhaust gas exhausted from the internal combustion engine therethrough, the exhaust gas passage means including a first and a second section mutually separated from each other, the exhaust gas at an exhaust port of the internal combustion engine having a known temperature; a noise reduction muffler provided between the first and second sections of the exhaust passage means for completing the exhaust gas path for discharging the exhaust gas to the atmosphere, the muffler comprising a hollow muffler body defining an internal space having an inlet connected to the internal combustion engine via the first section of the exhaust gas passage means and an outlet connected to the second section of the exhaust passage means for discharging the exhaust gas therethrough; and a cooling means associated with the exhaust gas passage means .for cooling the exhaust gas flowing through the internal space of the muffler below a predetermined temperature.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the preferred embodiment of the invention, which, however, should not be taken to limit the invention to the specific embodiment but are for explanation and understanding only.

In the drawings:

Fig. 1 is a fragmentary illustration of the first embodiment of an exhaust system according to the present invention, in which a muffler made of a fiber reinforced resin is employed;

Fig. 2 is an enlarged section of a resin muffler employed in the shown embodiment of the exhaust system of Fig. 1; Fig. 3 is an enlarged partial perspective view of an exhaust pipe which is employed in the first embodiment of the exhaust system of Fig. 1;

Fig. 4 is a fragmentary illustration of the second embodiment of an exhaust system according to the present invention, in which the resin muffler is employed;

Fig. 5 is a section taken along line V - V of Fig. 4;

Fig. 6 is a fragmentary illustration of the third embodiment of an exhaust system according to the present invention, in which the resin muffler is employed ;

Fig. 7 is a fragmentary illustration of a modification of the third embodiment of an exhaust system of Fig. 6; Fig. 8 is a partially sectioned side elevation of an exhaust pipe constituting part of the fourth embodiment of an exhaust system;

Fig. 9 is a section of a cooling device associated with an exhaust pipe and constituting the fifth embodiment of an exhaust system;

Fig. 10 is a section taken along line X - X of Fig. 9;

Fig. 11 is a graph showing relationship between an engine revolution speed and an exhaust gas temperature at the inlet of the resin muffler; and

Fig. 12 is a graph showing relationship between the engine revolution speed and a noise level. DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, particularly to Fig. 1, an exhaust system is generally associated with an internal combustion engine 1 which has an exhaust manifold 3 with a branch passages 2 connected to exhaust ports (not shown) of respective engine cylinders. In the shown construction, the exhaust manifold 3 is directly connected to a muffler 10 via an exhaust pipe

4. An exhaust gas exhausted from the engine cylinders is fed through the exhaust pipe 4 and introduced into the muffler 10. The exhaust gas introduced into the muffler 10 is lowered the pressure and absorbed pulsating energy to be discharge through a discharge pipe 6 as a steady flow.

Fig. 2 shows one of a typical and the simpliest construction of an muffler. The muffler 10 comprises a muffler body 5 in a hollow cylindrical or hollow box-shaped configuration. The muffler body 5 is formed of a heat-resistant synthetic resin or its composite, material of which will be discussed later. Both axial ends of the muffler body 10 are closed by mirror plates 7 and 8. Through the mirror plate 7, the exhaust pipe 4 which connects an exhaust port (not shown) of an automotive internal combustion engine to the muffler 5, is inserted. On the other hand, a discharge pipe 6 for discharging an exhaust gas to the atmosphere is inserted through the mirror plate 8.

The muffler body 5 has much greater cross-section than the exhaust pipe 4. Therefore, the exhaust gas introduced into the internal space of the muffler body 5 via the exhaust pipe 4 is decelerated and cause decrease of pressure thereof. Similarly, the discharge pipe 6 has smaller cross-sectional path area than the muffler body 5 to limit the exhaust gas flow rate. With such construction, the pulsating magnitude of the exhaust gas to be discharged through the., discharge pipe can be structurally reduced.

The muffler body 5 has a inner periphery coated by a heat protective layer structure 9. Typically, the heat protective layer structure is formed of ceramics, stainless steel, aluminium, copper, or a heat resistant resin, such as ceramics, glass wool, glass fiber, glass cloth, asbestos cloth, carbon fiber and so forth.

In order to accomplish absorption of noise creative pulsatile vibration, the muffler body 5 employed in the shown embodiment, is formed of a heat-resistant synthetic resin having a visco-elastic property in a predetermined temperature range. In the visco-elastic temperature range, the motion of the molecular chain segment of the material resin comes to be appropriate to dissipate noise creative pulsating energy as heat energy. In the shown embodiment, the epoxy resin which is specifically developed to replace metal as a material of the muffler, is used as a material for forming the muffler body 5. Such epoxy resin brings about noise reduction by absorbing noise creative energy and, more specifically, reduces the gas stream noise in the muffler and the jet stream noise at the outlet of the discharge pipe. Epoxy resin containing at least two epoxy in a single molecule, is selected. Bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, novolac epoxide resin and so forth are considered as typical epoxide resins to be used for forming the preferred embodiment of the resin muffler.

To the epoxide resin, hardner, cure-promoting agent and filler are added. As a hardner, acid anhydride, such as anhydride methyl nagic acid (MNA) , aliphatic, aromatic or fatty amine compound, such as triethylene tetramine, metaphnylene diamine, epomate and so forth and derivative thereof, imidazole, such as 2-ethyl-4-methyl imidazole, are preferred. As a filler,, one or more inorganic material, such as mica, silicon oxide, boron nitride, talc is selected. Also in case of epoxy resin, the cure-promoting agent is selected among 2,4,6-dimethyl amino phenol (DMP-30), amino imidazole. The synthetic resin further composed of an inorganic material which is selected among mica, silicon oxide, silica (SiO₂), talc, alumina (Al₂O₃), beryllia (BeO), cesium oxide (CeO₇), magnesia (MgO), quartz (SiO₂), titania (TiO₂), zirconia (ZrO₂), mullite (3Al₂O₃.2SiO₂), spinel (MgO.Al₂O₃), silicon carbide (Si.C), titanium carbide (TiC), boron carbide (B₄C), tungsten carbide (WC) , carbon black (C), boron nitride (BN), silicon nitride (Si₃N), aluminium titanate (AlTiO₃), mica ceramics (muscobite, sericite), sepiolite, pyrophyllite, steatite (MgO.SiO₂), forsterite (2MgO.SiO₂), zircon (ZrO₂,SiO₂), cordielite (2MgO.2Al₂O₃.5SiO₂), fiber, flocculent or cloth material, such as glass wool, glass fiber, glass cloth, asbestos cloth, and carbon fiber. Though the shown embodiment specifically uses epoxy resin for forming the muffler body, any resin materials which have characteristics of visco-elastic property depending upon the temperature of operation can be used for forming the muffler body 5. For example, any of the thermosetting resin selected among phenol resin, silicon resin, unsaturated polyester resin, diallyl phthalate resin, melamine resin, thermosetting poly carbodiimide, can be materials for forming the muffler body. On the other hand, the thermoplastic resin selected among polyamide resin, polyester resin, polyphenylene sulfide resin, thermoplastic fluorine containing resin, polysulfon resin, poly phnylene ether resin can also be used for forming the muffler body. In preparation, the hardner is, at first, added to the base material of epoxide resin. Therefore, cure-promoting agent is added to the mixture of the base material of epoxide resin and the hardner. Then, the inorganic filler is added. The mixture is then formed into the desired configuration by utilizing a molding dies. Bable removable is then performed by vaccum furnace and thereafter perform heat treatment. Temperature for heat treatment may be variable depending upon the hardner to be used. For example, when acid anhydride is used as the hardner, heat treatment is performed at about 120 °C for 2 hours and further heated for curing at a temperature about 200 °C for 4 to 8 hours. In the alternative, when fatty amine is used as the hardner, heat treatment is performed at a temperature 30 to 50 ° for 2 to 3 hours and further heated at about 100 °C for 4 hours for curing. In both case, the formed resin is cooled after curing.

The amount of inorganic material is variable depending upon the kind and particle size of the inorganic material to use. However, the maximum proportion of the inorganic material may be 600 parts by weight for 100 parts by weight of epoxide resin.

The muffler body 5 may be reinforced by a reinforcement core which is made of glass cloth, asbestos cloth, carbon fiber and so forth. For the reinforcement core, the material having high heat resistance at high temperature will be suitable to use. Such reinforce core is molded with the synthetic resin so that all of the surface thereof may be covered by the resin for preventing polution.

Detailed construction of the resin muffler set forth above, variations of material composition for forming muffler, variation of muffler constructions and so forth have been disclosed in the foregoing European Patent First Publication No. 0 269 116 which has been assigned to the common assignees to the present invention. The disclosure of the European Patent First, Publication will be herein incorporated by reference for the sake of disclosure. As seen from Figs. 1 and 3, the exhaust pipe 4 is formed with a plurality of radially and circumferentially extending cooling fins 11. As particularly shown in Fig. 3, each of the individual cooling fins 11 is thin annular disc configuration. The cooling fins 11 are formed integrally with the exhaust pipe 4, or, in the alternative separately formed and attached on the outer periphery of the exhaust pipe. Interval of the fins 11 and the outer diameter thereof may be determined according to required cooling efficiency in view of possible highest exhaust gas temperature.

As shown in Fig. 1, the cooling fins 11 may also be provided for the muffler body 5 for cooling the muffler body per se. Furthermore, the cooling fins 11 may be provided for the discharge pipe 6, if desired. However, it should be noted that the fins provided in the muffler body and the discharge pipe may not be essential for the subject matter of the invention.

The fins 11 extending from the outer periphery of the exhaust pipe 4 is effectively for performing heat conversion and thus for cooling the exhaust pipe. Therefore, the exhaust gas passing through the exhaust pipe can be cooled to a temperature below a given temperature which may be set at a temperature lower than a melting point of the synthetic resin. Since the cooling system set forth above is effective for satisfactorily lower the temperature of the exhaust gas, the resin muffler can be applied for exhaust system without a fear for influence of exhaust gas heat. Though the shown embodiment employs the cooling fins independently of each other, it may be possible to provide single fin arranged in spiral fashion.

Figs. 4 and 5 show the second embodiment of the exhaust system, according to the invention. In this embodiment, the cooling fins 12 are radially and longitudinally extended on the outer periphery of the exhaust pipe 4. As will be seen from Fig. 5, the cooling fins 12 are arranged on the outer periphery of the exhaust pipe 4 in circumferentially spaced apart relationship with a given circumferential intervals.

As seen from Fig. 4, the fins 12 may also be formed on the outer peripheries of the muffler body 5 and the discharge pipe 6 if necessary. Again, it should be appreciated that the fins on the muffler body and the discharge pipe are not essential for the present invention.

In either of the first and second embodiments illustrated in Figs. 1 through 5, the cooling fins 11 and 12 are preferably formed of a heat conductive material, such as steel, aluminium, aluminium alloy and so forth .

Fig. 6 shows the third embodiment of the exhaust system which has a catalytic converter 13. The cooling system employed in this embodiment is substantially the same as that illustrated in the first embodiment set forth above. Therefore, the same components with the same construction and same function will be represented by the same reference numerals for avoiding unnecessary confusion and for clear understanding of the context.

As will be seen from Fig. 6, the cooling fins 11 are provided for the exhaust pipe 4 in a range between the catalytic converter 13 and the muffler 5. As will be appreciated, the catalyst in the catalytic converter is generally active in relatively high temperature range for effectively removing NO_x, HC and CO from the exhaust gas. Therefore, it is not desirable to provide cooling fins for the exhaust gas upstream of the catalytic converter 13. As is well known, the chemical reaction caused in the catalytic converter generates heat to rise the exhaust gas temperature so that the exhaust gas temperature at the outlet of the catalytic converter becomes higher than that at the inlet thereof. For instance, generally, the exhaust gas temperature at the exhaust port of the engine is normally in a range of 500°C to 700 °C and the temperature is rised to 800 °C to 850 °C in the catalytic converter. Therefore, in the shown construction, higher heat conversion efficiency is required in comparison with that in the first embodiment. In addition, though the required cooling efficiency is higher in the shown embodiment than the first embodiment, the length of the exhaust pipe 4 for which the cooling fins 11 can be provided, is limited. Therefore, in order to obtain satisfactory cooling efficiency, the longitudinal interval of the fins 11 may be reduced to provide the fins with higher density.

Fig. 7 shows a. modification of the aforementioned third embodiment of the exhaust system. The shown embodiment introduces water cooling technologies for obtaining higher cooling efficiency for the exhaust gas. In this embodiment, the portion of the exhaust pipe 4 located downstream of the catalytic converter 13 and upstream of the muffler 5 is surrounded by a cooling water jacket 14. The cooling water jacket 14 may be of generally cylindrical construction with closed ends. The cooling water jacket 14 is coaxially arranged with respect to the exhaust pipe 4 to form a cross-sectionally annular shaped cooling water chamber therewithin. The cooling water chamber is communicated with a cooling water source via an inlet pipe 16 to introduce the cooling water and via a outlet pipe 15 to recirculate the cooling water to the cooling water source.

Preferably, the cooling water is an engine coolant normally circulating within a engine cooling circuit. Because the engine coolant is pressurized by the engine driven water pump and cooled by a radiator, such coolant may be conveniently used for cooling the exhaust gas. Furthermore, if desired, it may be possible to use any fluid, such as oil and so forth as cooling medium in place of water.

Instead of forming the annular water jacket as shown in Fig. 7, it may be possible to provide a water tube 17 helically wound around the exhaust pipe to form the fourth embodiment of the exhaust system according to the invention, as shown in Fig. 8. The water tube 17 may be connected to the cooling water source for recirculating the cooling water. This may provide satisfactorily and equivalent cooling effect to the embodiment of Fig. 7. This embodiment may be advantageous in view of avoiding substantial increase of the weight .

Fig. 9 shows fifth embodiment of the exhaust system. Similarly to the foregoing embodiment of Fig. 7, this embodiment employs water cooling technologies for effectively cooling the exhaust gas. In this embodiment, a heat exchanger 18 is provided for the exhaust pipe 4 downstream of the catalytic converter and upstream of the muffler. The heat exchanger 18 comprises a housing 21. The exhaust pipe 4 is separated into four branch pipes 22a, 22b, 22c and 22d within the housing 21 for providing greater surface area to contact with the cooling water, as particularly shown in Fig. 10. The internal space of the housing 21 is communicated with the cooling water source via inlet pipe 19 and outlet pipe 20.

Since such construction of heat exchanger 18 may have substantially high exhaust gas cooling efficiency, it may be possible to make the heat exchanger small so that substantial weight gain may not be occurred by introduction of this in the exhaust system.

In general, the muffler device made of the synthetic resin set forth above changes states from glassy state to visco-elastic state wherein motion of the segment of the resin comes relaxed to dissipate noise creating energy when temperature rises in the vicinity of a glass transition temperature (T ). The resin maintains visco-elasticity suitable for absorbing the noise creating energy for translating into heat energy. When the temperature further rises across the glass transition temperature, state of the resin becomes rubber state.

As set forth above, absorption of the noise creative energy becomes optimal in the visco-elastic range in the temperature range intermediate of the glassy range and rubbery range. For instance, while the resin temperature is in a range of +50 ºC of the thermal deformation temperature or glass transition temperature, across which the characteristics of the resin changed between visco-elastic range and glassy range. The temperature range set forth above is preferred for effectively reducing the noise creative energy. As will be appreciated, since heat resistant resin has lower heat transmission coefficient in comparison with that of the steel plate or stainless steel. Therefore, temperature gradient in the peripheral wall of the muffler body between outside and inside is high. Namely, at least a portion of the muffler body wall may fall within the visco-elastic temperature range for exhibiting optimal energy absorption characteristics by matching the temperature with the glassy transition temperature.

Therefore, as long as the resin muffler is protected from the heat, it will exhibit good noise suppressing performance without requiring any additional noise or sound insulative materials. Furthermore, since the resin muffler is lighter in weight, employment of the resin muffler will assist for reducing weight of the vehicular body construction for better fuel economy. Furthermore, since the resin has generally higher corrosion resistance, the resin muffler will be advantageous in viewpoint of corrosion in comparison with the conventional metal muffler.

In order to demonstrate the advantages of the exhaust systems with the exhaust gas cooling system for controlling exhaust gas temperature, experiments have been performed. In the experiments, an internal combustion engine which is water cooled, 4-cylinder gasoline engine (E15S engine available from Nissan Motor Company, Limited), was used. In the implementation of the present invention, a water jacket as shown in Fig. 7 was provided for the exhaust pipe. The length of the water jacket was about one meter. By the water jacket, the exhaust gas passing through the exhaust gas was cooled. The exhaust gas temperatures at various point in the exhaust pipe and noise level were measured during experiments. The results of experiments are shown in Figs. 11 and 12.

For an experiments, the resin muffler having the construction as shown in Fig. 12 was prepared. As a material for forming the heat-protective layer structure 40, a stainless steel of 0.15 mm thick was used. The heat-protective layer structure 40 was formed into a cylindrical configuration with 200 mm of internal diameter (ℓ) and 300 mm of overall length (L). As a base material for forming the muffler body, a thermosetting resin, i.e. bisphenol F diglycidyl ether

(Epikoto-807) was selected. For bisphenol F diglycidyl ether, a harder, i.e. methyl nagic anhydride (Kaya-hard

MCD: available from Nippon Kayaku K.K.), a cure-promoting agent, i.e. a mixture of 2-ethyl-4methylimidazole (2E4MZ: available from Shikoku Kasei K.K.) and sericite, were added to form a material resin. The material resin was prepared to have the following composition:

bisphenol F diglycidyl ether 100g methyl nagic anhydride 90g

2-ethyl-4methylimidazole 2g sericite 50g

The material resin was impregnated to a glass cloth coated by aminosilane (tradename: available from Nippon Unica K.K.). The glass cloth used in the experiment was of 0.1 mm thick. The material resin impregnated glass cloth was heated at 80 ºC for 2 hours for presolidification and thus formed into an epoxy preimpregnation. In the prepared epoxy preimpregnation, content of epoxy resin was 53%.

Around the outer circumference of the metallic heat-protective layer structure, 12 pieces of epoxy preimpregnations were fitted. Hot press, at 2 kg/cm ², 120 ºC, was performed for the epoxy preimpreganations fitted on the metal layer structure for 12 hours. By this, the muffler body was formed. The peripheral wall thickness of the formed muffler body was 2 mm thick. For this muffler body, the mirror plates made of copper were attached to both axial ends. The exhaust pipe and discharge pipes are inserted through the associated mirror plates. The muffler produced in the process and materials set forth above will be hereafter referred to as "samples 4 to 6". In Fig. 11, line (1) represents variation of the exhaust gas temperature at the exhaust port at an engine output of 30 PS (horse power), and line (2) represents variation of the exhaust gas temperature at the exhaust port at an engine output of 20 PS. Line (3) represents the exhaust temperature variation at the inlet of the conventional metal muffler connected to the engine via the exhaust pipe having no exhaust gas cooling system, at the engine output of 30 PS, and line

(4) represents the exhaust temperature variation at the inlet of the conventional metal muffler connected to the engine via the exhaust pipe having no exhaust gas cooling system, at the engine output of 20 PS. Line

(5) represents the exhaust temperature variation at the inlet of the conventional metal muffler connected to the engine via the exhaust pipe with the water jacket type exhaust gas cooling system, at the engine output of 30 PS. Line (6) represents the exhaust gas temperature variation at the outlet of the conventional metal muffler connected to the engine via the exhaust pipe having no exhaust gas cooling system, at the engine output of 20 PS. Lines (7) and (8) represent the exhaust gas temperature variation at the inlet and outlet of the .conventional metal muffler connected to the engine via the exhaust pipe with exhaust gas cooling system, at the engine output of 20 PS. Lines (9) and (10) represent the exhaust gas temperature variation at the inlet of the conventional metal muffler with fin type cooling system, respectively at 30 PS and 20 PS.

As will be seen herefrom, the lines (5), (7),

(8), (9) and (10) show much lower exhaust gas temperature in comparison with lines (3), (4) and (6) when the temperatures between the corresponding engine output power conditions are compared.

In Fig. 12, the lines (3), (4), (5), (7), (9) and (10) show variation of noise level at the same condition to the above. Line (11) represents variation of noise level when the resin muffler is employed in place of the metal muffler, and the water jacket type, cooling system is used. Lines (3A) , (5A) and (7A) represents variation of pressure difference between inlet and outlet of the metal muffler in the condition of lines (3), (5) and (7). As will be seen herefrom, the resin muffler can exhibit better noise suppressing effect at any engine revolution speed range.

Further experiments were performed with respect to various mufflers of various materials. Experiments were performed at the engine output of 30 PS at the engine revolution speed of 3000 rpm. The condition, material and resultant noise levels are shown in the following table 1.

In the table given hereabove, the noise levels of the samples 1 through 13 are shown in noise reduction versus the noise level of the sample 1 as the standard conventional exhaust system construction.

Further experiments were performed for checking noise suppression performance depending upon orientations of the cooling fins. The experiments were performed by providing the cooling fins at various orientations, i.e. at the exhaust pipe, at the muffler body and at the discharge pipe. The resultant data are shown in the following table 2.

Similarly to the foregoing table 1, the noise level of the samples 15 to 21 are shown as noise reduction level versus the noise level of the sample 1 as the standard conventional exhaust system.

As will be appreciated from the results of various experiments, the combination of the synthetic resin muffler associated with the cooling system exhibits the best results of noise reduction among all. However, the results of experiments set forth above also exhibits certain level of noise suppression effect for metal mufflers. This noise reduction is considered to be caused by increasing of density by of the exhaust gas lowering of the its gas temperature before and/or after introduction into the muffler. Particularly for the muffler made of aluminium, the noise reduction as associated with the cooling system is substantial. In case of aluminium as the material of the muffler, it has been considered as not applicable material for forming the muffler because of low heat resistance. Therefore, the cooling system for cooling exhaust gas to enable use of the resin muffler also enables use of metals which are considered not appropriate for insufficient heat resistance. Therefore, the invention will be applicable for metal muffler made of iron, copper, aluminium and so forth, which are regarded as not appropriate material for forming the muffler for low heat resistance.

While the present invention has been disclosed in terms of the preferred embodiment in order to facilitate better understanding of the invention, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments which can be embodied without departing from the principle of the invention set out in the appended claims.

Claims

1. An exhaust system for an internal combustion engine for a vehicle, comprising: an exhaust gas passage means defining a path for flowing an exhaust gas exhausted from said internal combustion engine therethrough, said exhaust gas passage means including a first and a second section mutually separated from each other; a noise reduction muffler provided between said first and second sections of said exhaust passage means for completing the exhaust gas path for discharging the exhaust gas to the atmosphere, said muffler comprising a hollow muffler body defining an internal space having an inlet connected to said internal combustion engine via said first section of said exhaust gas passage means and an outlet connected to said second section of said exhaust passage means for discharging the exhaust gas therethrough, said muffler body being formed with a synthetic resin which has visco-elastic property for dissipating noise creative energy of exhaust gas at a given operating temperature range and has a known melting point or glass transition point; and a cooling means associated with said exhaust gas passage means for controlling a temperature of said exhaust gas flowing through said internal space of said muffler to a temperature range lower than a predetermined temperature which is set higher than the known melting point or glass transition point of the synthetic resin in a magnitude of approximately 200 °C.

2. An exhaust system as set forth in claim 1, wherein said synthetic resin compound is composed of a heat resistant thermosetting resin.

3. An exhaust system as set forth in claim 1, wherein said cooling means controls the temperature of the exhaudt gas in such a manner that the temperature of said resin is maintained in atemperature range +50 °C of the thermal deformation temperature or glass transition temperature.

4. An exhaust system as set forth in claim 1, wherein said synthetic resin is composed of a heat resistant thermoplastic resin.

5. An exhaust system as set forth in claim 1, wherein said synthetic resin compound is selected among a thermosetting resin and a thermoplastic resin, and further composed of a filler.

6. An exhaust system as set forth in claim 2, wherein said thermosetting resin is selected among epoxy resin, phenol resin, silicon resin, unsaturated polyester resin, diallyl phthalate resin, melamine resin, thermosetting poly carbodiimide.

7. An exhaust system as set forth in claim 3, wherein said thermoplastic resin is selected among polyamide resin, polyester resin, polyphenylene sulfide resin, thermoplastic fluorine containing resin, polysulfon resin, poly phenylene ether resin.

8. An exhaust system as set forth in claim 6, wherein said epoxide resin is selected among bisphenol F-type epoxide resin, bisphenol A-type epoxide resin, novolac type epoxide resin.

9. An exhaust system as set forth in claim 5, wherein said filler material is selected among mica, silicon oxide, silica (SiO₂), talc, alumina (Al₂O₃), beryllia (BeO), cesium oxide (CeO₇), magnesia (MgO), quartz (SiO₂), titania (TiO₂), zirconia (ZrO₂), mullite (3Al₂O₃.2SiO₂), spinel (MgO.Al₂O₃), silicon carbide (Si.C), titanium carbide (TiC), boron carbide (B₄C), tungsten carbide (WC), carbon black (C), boron nitride (BN), silicon nitride (Si₃N), aluminium titanate (AlTiO₃), mica ceramics (muscobite, sericite), sepiolite, pyrophyllite, steatite (MgO.SiO₂), forsterite (2MgO.SiO₂), zircon (ZrO₂,SiO₂), cordielite (2MgO.2Al₂O₃.5SiO₂), fiber, flocculent or cloth material, such as glass wool, glass fiber, glass cloth, asbestos cloth, carbon fiber.

10. An exhaust system as set forth in claim 1, wherein said muffler further comprises a heat-protective layer structure formed on the inner periphery of said muffler body.

11. An exhaust system as set forth in claim 10, wherein said heat-protective layer structure is formed by a material selected among metal, heat resistantive resin, ceramics, glass wool, glass fiber, glass cloth, asbestos cloth, carbon fiber, and inorganic material.

12. An exhaust system as set forth in claim 1, wherein said cooling means comprises a heat radiation fin means provided at least on said first section of said exhaust gas passage means.

13. An exhaust system as set forth in claim 12, wherein said heat radiation fin means comprises a plurality of annular disc shaped fin arranged in longitudinal alignment with given intervals.

14. An exhaust system as set forth in claim 13, wherein said heat radiation fin means comprises a plurality of fins extending longitudinally along an axis of said exhaust gas path and arranged with circumferentially spaced apart relationship to each other with given circumferential intervals.

15. An exhaust system as set forth in claim 12, wherein said heat radiation fin means comprises a single fin extending at least on the outer periphery of said first section of said exhaust gas passage means in spiral fashion.

16. An exhaust system as set forth in claim 1, wherein said cooling means comprises a water jacket formed at least around said first section of said exhaust gas passage means.

17. An exhaust system as set forth in claim 1 wherein said cooling means is also provided for said muffler.

18. An exhaust system as set forth in claim 1, which is applicable for an automotive internal combustion engine.

19. An exhaust system for an internal combustion engine for a vehicle, comprising: an exhaust gas passage means defining a path for flowing an exhaust gas exhausted from said internal combustion engine therethrough, said exhaust gas passage means including a first, second and a third section mutually separated from each other; a catalytic converter disposed between said third and first sections so that it is connected to said internal combustion engine through said third section of said exhaust gas passage means for introducing the exhaust gas therethrough and discharging through said first section; a noise reduction muffler provided between said first and second sections of said exhaust passage means for completing the exhaust gas path for discharging the exhaust gas to the atmosphere, said muffler comprising a hollow muffler body defining an internal space having an inlet connected to said catalytic converter via said first section of said exhaust gas passage means and an outlet connected to said second section of said exhaust passage means for discharging the exhaust gas therethrough, said muffler body being formed with a synthetic resin which has visco-elastic property for dissipating noise creative energy of exhaust gas at a given temperature range and has a known melting point or glass transition; and a cooling means associated with said exhaust gas passage means for controlling a temperature of said, exhaust gas flowing through said internal space of said muffler to a temperature range lower than a predetermined temperature which is set higher than the known melting point or glass transition point of the synthetic resin in a magnitude of approximately 200 °C.

20. An exhaust system as set forth in claim 19, wherein said synthetic resin compound is composed of a heat resistant thermosetting resin.

21. An exhaust system as set forth in claim 19, wherein said synthetic resin is composed of a heat resistant thermoplastic resin.

22. An exhaust system as set forth in claim 19, wherein said synthetic resin compound is selected among a thermosetting resin and a thermoplastic resin, and further composed of a filler.

23. An exhaust system as set forth in claim 20, wherein said thermosetting resin is selected among epoxy resin, phenol resin, silicon resin, unsaturated polyester resin, diallyl phthalate resin, melamine resin, thermosetting poly carbodiimide.

24. An exhaust system as set forth in claim 21, wherein said thermoplastic resin is selected among polyamide resin, polyester resin, polyphenylene sulfide resin, thermoplastic fluorine containing resin, polysulfon resin, poly phenylene ether resin.

25. An exhaust system as set forth in claim 23, wherein said epoxide resin is selected among bisphenol F-type epoxide resin, bisphenol A-type epoxide resin, novolac type epoxide resin.

26. An exhaust system as set forth in claim 22, wherein said filler is selected among mica, silicon oxide, boron nitride, talc, alumina (Al₂O₃), beryllia (BeO), cesium oxide (CeO₇), magnesia (MgO), quartz (SiO₂), titania (TiO₂), zirconia (ZrO₂), mullite (3Al₂O₃.2SiO₂), spinel (MgO.Al₂O₃), silicon carbide (Si.C), titanium carbide (TiC), boron carbide (B,C), tungsten carbide (WC) , carbon black (C), boron nitride (BN), silicon nitride (Si₃N), aluminium titanate (AlTiO₃), mica ceramics (muscobite, sericite), sepiolite, pyrophyllite, steatite (MgO.SiO₂), forsterite (2MgO.SiO₂), zircon (ZrO₂,SiO₂), cordielite (2MgO.2Al₂O₃.5SiO₂), fiber, flocculent or cloth material, such as glass wool, glass fiber, glass cloth, asbestos cloth, carbon fiber.

27. An exhaust system as set forth in claim 19, wherein said muffler further comprises a heat-protective layer structure formed on the inner periphery of said muffler body.

28. An exhaust system as set forth in claim 27, wherein said heat-protective layer structure is formed by a material selected among metal, heat resistantive resin, ceramics, glass wool, glass fiber, glass cloth, asbestos cloth, carbon fiber, and inorganic material.

29. An exhaust system as set forth in claim 19, wherein said cooling means comprises a heat radiation fin means provided at least on said first section of said exhaust gas passage means.

30. An exhaust system as set forth in claim 29, wherein said heat radiation fin means comprises a plurality of annular disc shaped fin arranged in longitudinal alignment with given intervals.

31. An exhaust system as set forth in claim 29, wherein said heat radiation fin means comprises a plurality of fins extending longitudinally along an axis of said exhaust gas path and arranged with circumferentially spaced apart relationship to each other with given circumferential intervals.

32. An exhaust system as set forth in claim 29, wherein said heat radiation fin means comprises a single fin extending at least on the outer periphery of said first section of said exhaust gas passage means in spiral fashion.

33. An exhaust system as set forth in claim 19, wherein said cooling means comprises a water jacket formed at least around said first section of said exhaust gas passage means.

34. An exhaust system as set forth in claim 19, which is applicable for an automotive internal combustion engine.

35. An exhaust system for an internal combustion engine for a vehicle, comprising: an exhaust gas passage means defining a path for flowing an exhaust gas exhausted from said internal combustion engine therethrough, said exhaust gas passage means including a first and a second section mutually separated from each other, said exhaust gas at an exhaust port of said internal combustion engine having a known temperature; a noise reduction muffler provided between said first and second sections of said exhaust passage means for completing the exhaust gas path for discharging the exhaust gas to the atmosphere, said muffler comprising a hollow muffler body defining an internal space having an inlet connected to said internal combustion engine via said first section of said exhaust gas passage means and an outlet connected to said second section of said exhaust passage means for discharging the exhaust gas therethrough; and a cooling means associated with said exhaust gas passage means for cooling a temperature of said exhaust gas flowing through said internal space of said muffler below a predetermined temperature.

36. An exhaust system as set forth in claim 35, wherein said muffler is made of a synthetic resin compound is composed of a heat resistant thermosetting resin.

37. An exhaust system as set forth in claim 35, wherein said synthetic resin is composed of a heat resistant thermoplastic resin.

38. An exhaust system as set forth in claim 35, wherein said muffler is made of metal having a critical temperature lower than said known exhaust gas temperature.

39. An exhaust system as set forth in claim 38, wherein said muffler is made of light metal.

40. An exhaust system as set forth in claim 39, wherein said light metal is an aluminium.

41. An exhaust system as set forth in claim 38, wherein said metal is selected from iron and copper.

42. An exhaust system as set forth in claim 35, wherein said cooling means comprises a heat radiation fin means provided at least on said first section of said exhaust gas passage means.

43. An exhaust system as set forth in claim 42, wherein said heat radiation fin means comprises a plurality of annular disc shaped fin arranged in longitudinal alignment with given intervals.

44. An exhaust system as set forth in claim 42, wherein said heat radiation fin means comprises a plurality of fins extending longitudinally along an axis of said exhaust gas path and arranged with circumferentially spaced apart relationship to each other with given circumferential intervals.

45. An exhaust system as set forth in claim 42, wherein said heat radiation fin means comprises a single fin extending at least on the outer periphery of said first section of said exhaust gas passage means in spiral fashion.

46. An exhaust system as set forth in claim 35, wherein said cooling means comprises a water jacket formed at least around said first section of said exhaust gas passage means.

47. An exhaust system as set forth in claim 35, wherein said cooling means is also provided for said muffler.

48. An exhaust system as set forth in claim 35, which is applicable for an automotive internal combustion engine.