JPH03105014A - Heat insulating exhaust muffler - Google Patents

Abstract

PURPOSE:To reduce the thermal influence to the environment by forming a heat insulating member installed into the space formed between the inner cylinder and the outer cylinder of a muffler, by laminating fine glass fiber sheets and radiation reflecting films onto a ceramic felt layer. CONSTITUTION:Exhaust gas is introduced into a muffler body from a muffler inlet 11, and transferred in succession into an expansion chamber 19 through a communication pipe 15 and into a intermediate expansion chamber 18 through a multihole plate 13, and finally discharged into the atmosphere through a communication pipe 16. As the result, the expansion and contraction are repeated, and the exhaust noise is attenuated. Further, a heat insulating member 3 is installed into the space between an inner cylinder 1 consisting of a multihole plate and an outer cylinder 2, and the irradiated noise of the muffler body which is discharged to the outside environment is reduced. In this case, the heat insulating member 3 is formed by alternately laminating fine glass fiber sheets 33 consisting of glass fibers and thin plate-shaped radiating reflecting foils 34 onto the outer periphery of a ceramics felt layer 32.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application 3 The present invention relates to an exhaust muffler for internal combustion engines such as motorcycles and passenger cars.

[Prior Art] Mufflers (silencers) are installed in the exhaust gas systems of internal combustion engines such as motorcycles and passenger cars, except in special cases such as speed competitions. The main purpose of this muffler is to reduce exhaust noise, and therefore a mechanism is provided inside the muffler to obtain a silencing effect.On the other hand, depending on the operating conditions, the exhaust gas temperature may exceed 500°C.
To exceed this, it is necessary to take measures such as ensuring the durability of the casing, ensuring the safety of surrounding equipment as the casing heats up, and preventing burns. A sound-absorbing structure is adopted.
This I! In the conventional muffler, as shown in Fig. 4, the 7r thermal layer is provided with a fiber diameter of 5 to 20 mm in the space between the inner cylinder 1 and the outer cylinder 2.
Glass wool 41 made of μm glass fiber is filled, and an alkali-free glass (E glass) cloth 42 is placed on the inner surface of the glass reel to prevent the glass wool from flying off.
is located.

However, such glass wool and glass cloth alone are by far insufficiently effective, and in the case of motorcycles, the temperature on the outside surface of the muffler rises, often causing problems such as burns to the driver or passenger. There is. In addition, the temperature of the E-glass cloth and the glass wool itself becomes high, and the thermal insulation properties are greatly reduced due to scattering or melting and fixation due to deterioration of the materials, causing problems in terms of not only the thermal insulation properties but also the durability.

Therefore, as a method to improve the insulation property, it is possible to create a vacuum in the insulation part like a thermos flask, but due to assembly and manufacturing problems and safety problems when the motorcycle falls over, it is not possible.
Practical implementation is difficult and has not been achieved.

On the other hand, a heat insulating material consisting of a multilayer structure of aluminum foil and inorganic fibers was presented in "Heat Transfer Engineering Materials" (Japan Society of Mechanical Engineers, revised 3rd edition, published September 21, 1980, pp. 268). ing. That is, the combination of aluminum foil and glass fiber provides the heat insulation performance as shown in Table 1.

Since this lIIr thermal material uses vacuum in combination, it has the above-mentioned problem and cannot be put to practical use as a heat insulating material for mufflers as it is.

On the other hand, it is possible to use the same structure in an atmospheric pressure atmosphere, but if the temperature of the exhaust gas is 600℃, it will be cold.Radiation shield material: Aluminum foil, thickness: 0.051 mm. Number of 10 sheets Inorganic fiber material: Glass fiber II Thickness: 0.51 mm Multilayer density: 0.26 g/cm3,,
H Size: 6.35 1111I1 Degree of Vacuum: Below Tommug《Characteristics》Average conductivity: 0.000347 Kcal/m/h/'C may be exceeded, so the heat resistance of glass fiber, aluminum foil, etc. Furthermore, there is the problem of glass fiber deterioration and scattering due to high temperature exhaust gas and vibration. [Problem M to be solved by the present invention] As mentioned above, the conventional Ur thermal structure cannot obtain sufficient performance unless it is thick enough, and it also lacks sufficient heat resistance and durability. I can't find anything.

Further, even though structures with excellent heat insulation properties are known, none have been found to be satisfactory as heat insulation materials for exhaust mufflers for internal combustion engines in terms of heat resistance, durability, and safety.

The purpose of the present invention is to improve the heat insulation properties, use a thin heat insulating material with the same thickness as before, lower the outer surface temperature of the muffler, prevent burns, fires, etc., and enable long-term use. However, our objective is to provide a highly reliable heat-insulating exhaust muffler that does not deteriorate its heat-insulating performance.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems.

In the exhaust heat insulating muffler of the present invention, a heat insulating material is loaded in a required space between an inner cylinder that is provided in the exhaust passage of an internal combustion engine and that forms an exhaust gas flow path and an outer cylinder that forms the outer shape of the muffler. The material is characterized in that multiple layers of fine glass fiber sheets made of glass fiber and thin radiation reflective foils are alternately laminated on the outer periphery of the ceramic felt layer. In a preferred form of the exhaust heat insulating muffler of the present invention, the single layer thickness of the fine glass fiber sheet is 0.2 mm.
This is the above, and the number of laminated layers with the first radiation reflective foil is three or more.

Further, more preferably, the ceramic felt is
Fibers made of glass or ceramics with a heat resistance temperature of 500°C or higher are shaped into felt, and the thermal resistance [=(thickness)/'(thermal conductivity)] is 0.02rrl'-h"・°C
/kcal or more is used.

In a further preferred embodiment of the present invention, a glass cloth made of quartz glass is arranged on the inner peripheral side of the ceramic felt to prevent the ceramic felt and the fine glass fiber sheet from scattering. Furthermore, in another preferred embodiment of the exhaust heat insulating muffler of the present invention, the radiation reflective foil is... This metal foil has a thickness of 0.1 μ or less and a surface emissivity of 0.2 or less.

The average fiber diameter of the fine glass fibers is preferably 3 μIn or less, since the thinner the fibers, the more convenient it is to obtain heat insulation properties.

The reason why the ceramic felt layer is placed inside the heat insulating material made by laminating multiple layers of fine glass fiber sheets and reflective foil is to maintain the temperature of the fine glass fibers below the allowable heat resistance temperature.

In addition, the natural resistance of the ceramic felt layer (thickness)/(
Thermal conductivity〉0.02rr+'-hr-'C/
The reason for setting it above kcal is that it is preferable to prevent the temperature of the fine glass fiber seam 1 from exceeding 500°C even when the maximum exhaust gas temperature of a motorcycle is 650°C.

Rather than increasing the thickness of the single layer of Fine Glass Fiber Sea I, the thickness of the single layer should be made thinner to reduce the number of layers with reflective material within the same overall thickness. It is preferable to increase the number in order to improve insulation. As a concrete value,
The thickness of the single layer of fine glass fiber is preferably 1 mm or less.

On the other hand, if the thickness is thinner than 0.2 mm, the density of the fine glass fiber sheet tends to become uneven, and direct radiant heat transfer occurs between the reflective foils, and sometimes contact between the reflective foils occurs, resulting in an increase in conductivity. This is not desirable because it invites

It is preferable that the number of laminated layers of the fine glass fiber sheet and the reflective foil is three or more each, since this is effective in obtaining heat insulating properties.

The reason why a glass cloth made of quartz glass is placed inside the ceramic felt is to prevent the ceramic felt from being torn and blown away by the dynamic pressure of exhaust gas and engine vibration. This is because it is preferable as a material that does not deteriorate due to vibration or the dynamic pressure of exhaust gas, such as tearing or losing elasticity, and can effectively prevent the wear and tear of ceramic felt.

The thickness of the radiation reflective foil is preferably thin as long as it has durability, and if it is 0.1101 or less, a material with no problems in terms of durability can be obtained. In addition, the reason why the emissivity of the reflective foil is set to 02 or less is that materials with low emissivity usually have high reflectance, so by setting the emissivity to 02 or less, heat transfer due to radiation is suppressed and a sufficient heat insulation effect is achieved. This is because easily available materials such as metal foil can be used and are preferred.

[Example] Figures 1 to 3 are explanatory views of an example of the heat insulating exhaust muffler according to the present invention. Exhaust gas is introduced into the muffler from the muffler inlet 11 in FIG. 1 through an exhaust pipe (not shown), further through the communication vibrator 15, into the expansion chamber 19, further through the perforated plate 13, into the intermediate expansion chamber 18, and then through the communication pipe. 16 and is finally released into the atmosphere. Exhaust noise is attenuated by repeating these processes, ie, contraction when flowing into the communication vibe, and expansion when being discharged to the h5 bladder. In addition, in order to prevent radiated sound emitted to the outer circumference of the muffler, the inner cylinder 1 is made of a perforated plate, and a heat material 3 (described later) is installed in the space formed between the inner cylinder 1 and the outer cylinder 2. The temperature of the exhaust gas introduced is between 300 and 650 in normal operation.
℃, and unless some countermeasure is taken, the outer cylinder 2
The temperature of the engine also rises to the same level as the exhaust gas temperature. In the actual example manufactured as a prototype for testing, the inner cylinder 1 is made of a stainless steel perforated plate with a wall thickness of 1.2 mm, an outer diameter of 92 mm, a circular hole diameter of 3 mm, and a circular hole pitch of 6 u. As shown in Fig. 3, silica glass fibers with an average fiber diameter of 10 μm are placed in a twill weave with a thickness of 0.3 mm and excellent tensile strength in the space formed between the aluminum alloy outer cylinder 2 with a diameter of 114 and 4 u. Formed silica cloth and packing density 1
60ko/m3, J'Jsa2. Cerami-socks felt made of On+m alumina silicate short fibers, and the outer periphery is coated with a fiber diameter of 0.8 μm, a packing density of 115 kg/m, and a thickness of 1 layer of 0.8 μm. The heat insulating structure is made by laminating 10 layers of 7mm glass fiber sheets and 14μm thick aluminum foil alternately, and one more layer of glass fiber sheet 1 on the outermost periphery. In addition, in the 3rd composition explanatory drawing, the glass fiber sheet is omitted into four layers due to restrictions on illustration.

Here, the fiber diameter of the glass fiber is preferably thinner from the viewpoint of heat, and in the above example, a fine glass fiber of 0.8 μm was used. As a result, the thermal conductivity of the glass fiber alone is 0.0% when the fiber diameter is 13 μm used in a conventional muffler. 06kcal/m
/hr/”C, approximately 172 0.035kca
The tail was improved to l/m/hr/℃. Further, from the viewpoint of heat insulation, it is preferable that the thickness of the single layer of the glass fiber sheet be as thin as possible, and the number of laminated layers be increased within the allowable thickness of the entire heat insulating material.

On the other hand, as described above, the minimum value of the single layer thickness is preferably as thin as possible, but from the viewpoint of glass fiber filling, it is preferably 0.2 mm or more. 0.1~. 0.15mm
In the results of prototype evaluation in the + range, it was observed that due to the non-uniformity of the packing density, the aluminum foil came into contact with the aluminum foil in some areas, resulting in an increase in the overall thermal conductivity. Therefore, in the above example, the single layer thickness was set to 0.7 mm, and a total of 11 layers were laminated. As for the number of laminated layers, the higher the thermal properties, but since the Ur thermal properties and the number of laminated layers are not linearly proportional, the practical range is 3 or more layers, more preferably 5 or more layers. 0.8
In actual measurements using μm fine glass fiber,
Thermal conductivity for one layer is 0.035 kcal/m/h
r/'C, 0.025kcal in 3 layers
/n+/hr/ ”C, 0.021kcal/ in 5 layers
m/hr/℃, 0.020kcal/m/h in 10 layers
r/°C, and the effectiveness of 3 layers and 5 layers has been confirmed. In the above example, the fiberglass sheet as a whole is 11 mm, taking full advantage of the allowable insulation thickness.
Laminated layers. Further, the ceramic felt is
Glass fiber seam 1 located on the outer circumference side
・It is arranged to lower the temperature and ensure durability. In other words, from the perspective of the heat resistance of the material, the laminate of glass fiber and aluminum foil, which is a major element of the present invention, is better, but the heat resistance of this glass fiber sheet is Since the temperature is 500°C, which is lower than the maximum temperature of exhaust gas, ceramic felt with high heat resistance is placed inside the glass fiber sheet.
The temperature of the fiber sheet is lowered to below its heat-resistant temperature.

Therefore, this ceramic felt layer is required to have heat resistance, and it is desirable that it be thin and have as low thermal conductivity as possible. As a material that is relatively easily available at present, the above-mentioned alumina ceramic felt (thermal conductivity 0
．． 06kcal/m/hr/'C) was used. Here, when testing the ceramic surface with a thickness of 0.5 mm (thermal resistance value -0.008) and with the other configurations being exactly the same, when the exhaust gas temperature is 660°C, the temperature of the glass fiber sheet is Since it was observed that the temperature exceeds 500°C, in the above example, glass fiber
The thickness of the ceramic felt was set to 2u (thermal resistance value -0.033 >
And so.

The quartz glass fiber cloth has excellent elasticity and durability at the exhaust gas temperature level, and prevents the fibers of the ceramic felt and glass fiber sheet placed around its outer periphery from being blown away by the exhaust gas. has a role to play.

Therefore, a relatively dense knitting method is preferable. In addition, in the exhaust heat insulating muffler of the present invention, since the heat insulation performance of the heat material is greatly improved, the inner member, that is, the quartz glass fiber cloth in this embodiment is more effective than in the conventional embodiment. It becomes high temperature. Therefore, the internal measurement member is required to have heat resistance, and the conventional alkali-free glass cloth cannot be used due to its durability.

In this example, the silica glass fiber cloth was strengthened with an inorganic binder. As for the aluminum foil, it is preferable that it be thinner from the viewpoint of the thickness of the heat insulating structure, but in this example, the thickness was set to 14 μm from the viewpoints of strength, durability, and handling.

Further, from the viewpoint of reducing radiant heat transfer, it is preferable that the surface has a low emissivity and a high reflectance. In general, surfaces with low emissivity have low absorption of natural rays and reflect heat rays well.
As mentioned above, the thermal conductivity of the laminate when shiny aluminum foil (emissivity 0.04) is used is 0.04. 020kca
l/m/hr/ ``C, whereas 600'
C'''C'' When using oxidized aluminum foil (emissivity: 018), it is approximately 10%, and when using copper foil (emissivity: 0.55), which is oxidized at 600°C, it is approximately 30%. An increase in thermal conductivity (decreased lgr ripeness) was observed.Therefore, in the above example, the aluminum foil was arranged with the shiny side facing inside.

Furthermore, in this example, the 17i thermal structure is compressed in advance and fixed using an organic adhesive, and after being installed in the space formed between the inner cylinder and the outer cylinder, the thermal structure is The organic adhesive was blown off and fixed by heating. High-temperature combustion gas was passed through the adiabatic exhaust muffler made of the above-mentioned 11 layers of glass fiber sheets, which is an embodiment of the present invention, and the temperature of the outer cylinder surface was measured, and the results shown in Table 2 were obtained. .

Furthermore, as a comparative example, similar measurements were made for an exhaust muffler made of E glass cloth shown in Fig. 4 and a single layer of glass fiber with a fiber diameter of 13 μm, which was conventionally adopted instead of the Ur thermal structure of the present invention. The results are also shown in Table 2.

In addition, the outside air condition is approximately 25℃ using a commercially available electric fan.
Forced air cooling was performed in the atmosphere. As a result, even if the exhaust gas temperature reaches 650°C, the outer cylinder surface temperature can be kept below 80°C.

Table 2 [Effects of the Invention] As explained above, in the present invention, the outer surface of the muffler is It is possible to lower the temperature and prevent dangers such as heat damage to surrounding equipment, burns, and fire.

Furthermore, by using the insulating exhaust muffler of the present invention, exhaust noise can be reduced to the same level as before, and sufficient insulation efficiency can be achieved.

[Brief explanation of drawings]

Figures 1 to 3 are schematic structural explanatory diagrams showing one embodiment of an exhaust muffler according to the present invention, Figure 2 is a cross-sectional structural diagram taken along A-^' of Figure 2, and Figure 3 is an adiabatic exhaust muffler. FIG. FIG. 4 is an enlarged sectional view for explaining the heat insulating structure of the muffler, which was adopted as a conventional muffler. In the figure, 1 is an inner cylinder, 2 is an outer cylinder, 3 is definitely a structure, 11 is a muffler inlet, 15, 17. 19 is the muffler expansion chamber, 13
15 and 16 are perforated plates, 15 and 16 are muffler communication tubes, 31 is quartz glass cloth, 32 is ceramic felt, 33 is a glass fiber sheet, 34 is a radiation reflective foil, 42 is E glass cloth, and 41 is a glass fiber layer.

Claims (5)

[Claims] (1) In a muffler that is provided in an exhaust passage of an internal combustion engine and that is filled with a heat insulating material in a required space between an inner cylinder that forms an exhaust gas flow path and an outer cylinder that forms an outer shape of the muffler, the heat insulating material A heat insulating exhaust muffler characterized in that a plurality of layers of fine glass fiber sheets made of glass fiber and thin radiation reflective foil are alternately laminated on the outer periphery of a ceramic felt layer. (2) The heat insulating exhaust muffler according to claim 1, wherein the thickness of a single layer of the fine glass fiber sheet is 0.2 mm or more, and the number of laminated layers with the radiation reflective foil is three or more. (3) The ceramic felt has a heat resistance temperature of 500°C.
The above glass or ceramic fibers are molded into a felt shape, and its thermal resistance R value [=(thickness)/(thermal conductivity)] is 0.02m^2・hr・℃/k
Claim 1 or 2 which has a property of greater than or equal to cal.
The insulated exhaust muffler described in . (4) The heat insulation according to claim 1, 2 or 3, wherein a glass cloth made of quartz glass is further arranged on the inner peripheral side of the ceramic felt to prevent the ceramic felt and the fine glass fiber sheet from scattering. exhaust muffler. (5) The heat insulating exhaust muffler according to any one of claims 1 to 4, wherein the radiation reflecting foil is a metal foil having a thickness of 0.1 mm or less and a surface emissivity of 0.2 or less.