JPH0842335A - Double tube integrated flexible tube - Google Patents

Abstract

PURPOSE:To prevent bellows from being broken owing its high temperature and the temperature of exhaust gas from being lowered owing to the absorption of the heat of the exhaust gas by the bellows or the like having large heat capacity. CONSTITUTION:A flexible tube comprises a bellows 207 capable of being bent, an inner tube 209 consisting of a plurality of thin cylindrical pipes whose inside diameters are gradually increased so as to have a telescopic relationship therebetween and pins 213 for connecting the plurality of cylindrical pipes together so as to be bent. The diameter of the rear end connecting part of the inner pipe of an upstream exhaust pipe is throttled. The inner tube 209 is constructed in such a way that a cylindrical pipe 209a in the upstream exhaust pipe is fitted and fixed, by means of a pin, to the rear end of the inner pipe of the upstream exhaust pipe 200, cylindrical pipes at next positions are sequentially fitted and fixed by means of pins to the outside parts of cylindrical pipes at preceding positions and a final cylindrical pipe 209m in the downstream is fitted and fixed by means of a pin to the inside of the inner pipe 205 of a downstream exhaust pipe 203.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an upstream side exhaust pipe and a downstream side exhaust pipe which are connected to an engine and a catalyst for purifying exhaust gas of the engine, and which are formed in a double structure with an outer pipe and an inner pipe. The present invention relates to a double tube-integrated flexible tube for connecting three-dimensionally so as to be bendable.

[0002]

2. Description of the Related Art In an exhaust system of an automobile, in order to prevent heat of an exhaust pipe including an exhaust manifold from entering an engine room and adversely affecting various devices in the engine room, a part of the exhaust pipe or It is well known in the prior art to use a double pipe as a whole to reduce the surface temperature of the exhaust pipe.

Further, in order to improve the efficiency of exhaust gas purification at the time of cold start of the engine, it is necessary to raise the temperature of the exhaust gas flowing into the catalyst to a temperature at which the catalyst is activated at an early stage. For that purpose, it has been clarified by the study of the present inventor that it is effective to make the inner pipe of the double exhaust pipe thin. That is, by thinning the inner pipe of the double exhaust pipe, its heat capacity is reduced and the inner pipe temperature is raised early. As the temperature of the inner pipe rises, the amount of heat transferred from the exhaust gas to the inner pipe decreases, and the temperature drop of the exhaust gas flowing into the catalyst installed behind the exhaust pipe is suppressed and the catalyst is activated early. Is to be achieved.

Further, in the exhaust system of a vehicle, in order to prevent the vibration of the engine from being transmitted to the muffler and damaging the catalyst and other members housed in the muffler, the exhaust pipe connected to the upstream side of the engine is connected to the upstream exhaust pipe. It is also known to provide a flexible tube for connection with a downstream exhaust pipe connected to the muffler.

In the conventional connecting method using a flexible tube, as shown in FIG. 6, an upstream exhaust pipe 601 and a downstream exhaust pipe 602 are formed by a stainless thin plate (for example, two layers with a thickness of 0.3 mm). Are connected by a bellows 603. Then, in order to prevent the stepping stones or the like from directly hitting the bellows 603, the bellows 603 is covered with an outer blade 604 which is knitted in a tubular shape using a stainless thin wire (for example, a diameter of 0.4 mm). Also,
In order to suppress the temperature rise of the bellows 603 when the exhaust gas becomes high in temperature, an inner blade 605 knitted in a tubular shape using stainless fine wires is provided inside the bellows 603 to form the flexible tube 600.

Further, as a conventional connecting method using a flexible tube, in order to further suppress the temperature rise of the bellows, an interlock in which the plate members are formed in an S shape and connected to each other is provided inside the inner blade. The prior art is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-322093. Further, a prior art in which an interlock is provided instead of the inner blade is disclosed in, for example, Japanese Patent Laid-Open No. 4-127832. Furthermore, extend the end of the upstream exhaust pipe and the end of the downstream exhaust pipe into the bellows,
A prior art in which exhaust gas is not directly applied to the bellows by making the respective ends face each other is disclosed in "Exhaust pipe connecting device" of Japanese Utility Model Laid-Open No. 57-31521.

[0007]

However, according to the connection method (FIG. 6) using the flexible tube in which the inner blade is provided in the above-mentioned conventional bellows, the exhaust gas is discharged to the inner blade or the stitches of the inner blade. Since it passes through the gap and contacts the bellows, the heat of the exhaust gas is absorbed by the inner blade and the bellows, which have a large heat capacity, and the exhaust gas temperature drops. There is a problem that exhaust gas may leak from the gap.

Further, according to the above-mentioned method of providing the interlock, although the exhaust gas leaks from the interlock to the bellows side is small, the heat capacity of the interlock itself is large, so that the heat of the exhaust gas is generated in the interlock. There was a problem that the exhaust gas temperature was lowered due to absorption.

According to the conventional method of extending the end portion of the exhaust pipe into the bellows, the exhaust gas does not directly hit the bellows, but the exhaust gas leaks to the bellows side from the gap between the end portions of the exhaust pipes. Therefore, as in the above case, the heat of the exhaust gas is absorbed by the bellows, and the exhaust gas temperature drops.

The present invention has been made in view of the above, and prevents the bellows from being damaged due to a high temperature, and the heat of the exhaust gas is absorbed by the bellows having a large heat capacity, so that the temperature of the exhaust gas is reduced. The purpose is to avoid lowering.

[0011]

In order to achieve the above-mentioned object, the present invention provides a double tube-integrated flexible tube comprising an outer tube and an inner tube thinner than the outer tube. Upstream exhaust pipe connected to the engine, a double pipe formed of an outer pipe and an inner pipe thinner than the outer pipe, and a downstream exhaust pipe connected to the catalyst. In a double tube-integrated flexible tube that flexibly connects with each other, a bellows flexibly connected between the outer tube of the upstream side exhaust pipe and the outer tube of the downstream side exhaust pipe, and a thin wall, The upstream exhaust pipe is provided with an inner tube composed of a plurality of cylindrical pipes whose inner diameters are gradually increased so as to form a nested relationship, and a connecting means for connecting the plurality of inner tubes in a bendable manner. The diameter of the rear end connection of the inner tube of The In'nachubu, among the plurality of cylindrical pipe, fitting, a cylindrical pipe of the upstream side exhaust pipe side to the rear end connecting portion of the inner pipe of the upstream side exhaust pipe
Connect, sequentially, fit and connect the cylindrical pipe at the next position to the outside of the cylindrical pipe at the previous position, and put the last cylindrical pipe on the downstream side inside the inner pipe of the exhaust pipe on the downstream side. It is a structure for fitting and connecting.

According to a second aspect of the present invention, in the double tube-integrated flexible tube, the gap between the last cylindrical pipe on the downstream side and the inner side of the inner pipe of the downstream side exhaust pipe is the outer pipe. The gap is narrower than the gap between the inner pipe and the inner pipe.

Further, in the double tube-integrated flexible tube according to a third aspect, the connecting means is a plurality of pins.

The double tube-integrated flexible tube according to claim 4 comprises a double tube formed of an outer tube and an inner tube thinner than the outer tube, and is connected to the engine in an upstream exhaust pipe. And a double tube formed of an outer tube and an inner tube thinner than the outer tube, wherein the downstream exhaust tube connected to the catalyst is bendably connected to the double tube integrated flexible tube, Between the bellows connected flexibly between the outer pipe of the upstream exhaust pipe and the outer pipe of the downstream exhaust pipe, and between the inner pipe of the upstream exhaust pipe and the inner pipe of the downstream exhaust pipe It is provided with an inner tube that is thin and thin and that is formed by overlapping strip-shaped plate materials and spirally winding them.

[0015]

The double-tube integrated flexible tube of the present invention (Claim 1) uses a plurality of cylindrical pipes which are thin and whose inner diameter is gradually increased so as to form a nested relationship. , The upstream side exhaust pipe side cylindrical pipe is fitted and connected to the upstream side exhaust pipe inner pipe rear end connection part, and the next position cylindrical pipe is outside the previous position cylindrical pipe. Then, the last cylindrical pipe on the downstream side is fitted and connected to the inside of the inner pipe of the downstream side exhaust pipe to form an inner tube. Therefore, the exhaust gas that has flowed in from the rear end connection portion (upstream exhaust pipe) whose diameter has been narrowed down is the inner tube (exhaust gas) formed by a plurality of cylindrical pipes whose inner diameter increases from the upstream side to the downstream side. Since it is discharged to the exhaust pipe on the downstream side after passing through the passage), the heat capacity of the portion in contact with the exhaust gas becomes small, and for example, when the exhaust gas is low, the wall temperature of the inner tube is raised early,
The temperature drop of exhaust gas is prevented. Further, since the contact between the bellows having a large heat capacity and the exhaust gas is reduced, the temperature drop of the exhaust gas is prevented. Further, when the exhaust gas is at a high temperature, the exhaust gas is suppressed from leaking from the inner tube to the bellows, the temperature of the bellows is prevented from becoming high, and damage can be prevented.

Further, in the double-tube integrated flexible tube of the present invention (claim 2), the gap between the last cylindrical pipe on the downstream side and the inner side of the inner pipe of the downstream side exhaust pipe is Since this is a narrower gap than the gap between the inner pipe and the inner pipe, exhaust gas leakage from the gap between the last cylindrical pipe on the downstream side and the inner pipe is suppressed.

In the double-tube integrated flexible tube of the present invention (claim 3), since the connecting means is a plurality of pins, a cylindrical pipe can be easily connected with a simple structure.

The double tube-integrated flexible tube of the present invention (claim 4) has a thin inner tube formed by overlapping strip-shaped plate materials and spirally winding the inner tube of the upstream exhaust pipe. It is provided between the downstream exhaust pipe and the inner pipe. Therefore,
The exhaust gas flowing in from the upstream side exhaust pipe passes through the inner tube (exhaust passage) and is discharged to the downstream side exhaust pipe, so that the heat capacity of the portion in contact with the exhaust gas becomes small. , The wall temperature of the inner tube is raised early to prevent the temperature of exhaust gas from decreasing. Further, since the contact between the bellows having a large heat capacity and the exhaust gas is reduced, the temperature drop of the exhaust gas is prevented. Further, when the exhaust gas is at a high temperature, the exhaust gas is suppressed from leaking from the inner tube to the bellows, the temperature of the bellows is prevented from becoming high, and damage can be prevented.

[0019]

[Embodiment] Hereinafter, a double-tube integrated type flexible tube according to the present invention will be described as [Embodiment 1], [Embodiment 2],
[Third Embodiment] and [Fourth Embodiment] will be described in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an automobile exhaust system to which the present invention is applied. 100 is an upstream exhaust pipe connected to an engine (not shown), 101 is a downstream side connected to a catalyst (not shown). The exhaust pipe 102 is a flexible tube connecting the upstream exhaust pipe 100 and the downstream exhaust pipe 101.

[Embodiment 1] FIG. 2 is a vertical cross-sectional view of Embodiment 1 of the present invention, in which an upstream exhaust pipe 200 is doubled with an outer pipe 201 and an inner pipe 202, and 203 is Similarly to the upstream side exhaust pipe 200, the downstream side exhaust pipe is doubled by the outer pipe 204 and the inner pipe 205, and 206 is the upstream side exhaust pipe 2.
00 is connected to the downstream side exhaust pipe 203. The flexible tube 206 is a bellows 2 provided between the outer tube 201 and the outer tube 204.
07, outer blade 2 covering the outside of the bellows 207
08, an inner tube 209 and the like provided between the inner pipe 202 of the upstream side exhaust pipe 200 and the inner pipe 205 of the downstream side exhaust pipe 203.

The outer pipes 201 and 204 are formed thick so that they serve as strength members for the entire exhaust pipe. Inner tube 20
Reference numerals 2 and 205 are thinner than the outer tubes 201 and 204, for example, have a plate thickness of 0.5 mm, and are formed of a material such as stainless steel so as to withstand the corrosion due to the high temperature exhaust gas. The inner tube 202 of the upstream exhaust pipe 200 is the flexible tube 20.
It is formed so as to extend from the outer tube 201 with a size corresponding to approximately one third of six. At its tip, a reduced diameter portion 21 with a reduced diameter
0 is formed. Further, the front end of the inner pipe 205 of the downstream side exhaust pipe 203 is also formed to be slightly extended from the outer pipe 204. 211 and 212 are provided between the outer pipe 201 and the inner pipe 202 of the upstream side exhaust pipe 200 and between the outer pipe 204 and the inner pipe 205 of the downstream side exhaust pipe 203, respectively, and are meshes made of a wire made of a heat-resistant metal. Shaped spacer.

The inner tube 209 is composed of the inner tubes 202, 2
As with 05, the outer pipes 201 and 204 are thinner than the outer pipes 201 and 204, for example, the plate thickness is 0.5 mm, and a material such as stainless steel is used to withstand corrosion due to high temperature exhaust gas, and a plurality of cylindrical pipes 209a, 209b ,. , Outer pipe 20
It is formed by connecting 9n. Then, the most upstream cylindrical pipe 209a is fitted to the outside of the reduced diameter portion 210, and then the next cylindrical pipe 209b is fitted to the outside of the cylindrical pipe 209a. Is formed so as to fit outside the cylindrical pipe at the front position, and the most downstream cylindrical pipe 209m fits inside the inner pipe 205 of the downstream side exhaust pipe 203. The cylindrical pipe 2
The gap between 09 m and the inner pipe 205 is equal to the outer pipe 204 and the inner pipe 20.
It is fitted with a gap narrower than the gap with 5. The outer pipe 209n is provided outside the most downstream cylindrical pipe 209m so as to fit inside the outer pipe 204 of the downstream exhaust pipe 203.

A plurality of cylindrical pipes 209a, 209b,
... 209m between each other and the most downstream cylindrical pipe 209
m and the outer pipe 209n are three-dimensionally bendable connected by connecting pins 213 as connecting means at several positions in the circumferential direction. Then, the most upstream cylindrical pipe 209a, the reduced diameter portion 210, and the outer pipe 209n.
And the outer pipe 204 of the downstream exhaust pipe 203 are connected by welding.

The operation of the first embodiment having the above structure will be described. First, the temperature change of the exhaust gas in the upstream exhaust pipe 200 and the downstream exhaust pipe 203 will be described. When the engine is started while the entire exhaust pipe is at room temperature, exhaust gas flows into the inner pipes 202 and 205, and heat is transferred from the exhaust gas to the inner pipes 202 and 205. Inner tube 20
Since the heat capacity of Nos. 2 and 205 is small, the temperature thereof immediately rises, and the temperature difference between the exhaust gas and the inner pipes 202 and 205 becomes small. Therefore, the amount of heat transferred from the exhaust gas to the inner pipes 202 and 205 is reduced, and the exhaust gas temperature is maintained.

Further, since the exhaust gas passing through the inner pipe is guided from the reduced diameter portion 210 into the inner tube 209,
Do not touch the outer tube with large heat capacity. At this time, the inner tube 209, like the inner tubes 202 and 205,
Since the wall is thin and the heat capacity is small, the temperature of the inner tube 209 immediately rises, and the exhaust gas and the inner tube 209
The temperature difference between Therefore, the amount of heat transfer from the exhaust gas to the inner tube 209 is reduced, and the exhaust gas temperature is maintained. Further, the pressure of the exhaust gas is gradually increased by the inner tube 209 which gradually increases in diameter after increasing in the diameter-reduced portion 210. That is, the upstream side, where the temperature is high, becomes faster and passes through rapidly, so the amount of heat exchange is reduced. Further, since the downstream sides are overlapped with each other, the exhaust gas rarely leaks from the coupling gap of the inner tube 209, and the heat loss of the exhaust gas due to the inner tube 209 is reduced. Therefore, the temperature drop of the exhaust gas is suppressed.

Further, when the vehicle travels at high speed or when traveling uphill, the flow rate of exhaust gas is high and the temperature is high, but similarly, gas leakage from the connecting gap of the inner tube 209 is small, and the exhaust gas generated by the inner tube 209 is small. The heat loss of the gas is reduced. Also, bellows 207
However, since it is not directly exposed to high temperature exhaust gas, it is prevented from being damaged due to high temperature. Inner tube 202, 2
05, the inner tube 209 has a high temperature, but since it is not a strength member forming the exhaust pipe, thermal stress is not concentrated and damaged.

Further, the outer pipe 209n and the outer pipe 204 of the downstream side exhaust pipe 203 are connected by welding, respectively, and the gap between the cylindrical pipe 209m and the inner pipe 205 is narrower than the gap between the outer pipe 204 and the inner pipe 205. Since they are fitted in the gap, the exhaust gas is prevented from entering the gap between the outer pipe 204 and the inner pipe 205, and the outer pipe 201,
The elongation of the inner pipes 202 and 205 due to the temperature difference with 204 is absorbed. In addition, a plurality of cylindrical pipes 209a, 209
b, ... 209m each other, and the most downstream cylindrical pipe 2
The 09m and the outer pipe 209n are three-dimensionally bendable connected by connecting pins 213 as connecting means at several positions in the circumferential direction, so that the vibration of the engine is prevented from being transmitted to the muffler.

[Embodiment 2] FIG. 3 is a partial vertical sectional view of Embodiment 2 of the present invention, showing a connecting portion between a downstream side exhaust pipe 300 and a flexible tube 301. The downstream exhaust pipe 300 includes an outer pipe 302 and an inner pipe 303 as in the first embodiment.
And is double formed. The outer pipe 302 is formed thick so as to be a strength member for the entire exhaust pipe. Inner tube 303
Is thinner than the outer tube 302, for example, a plate thickness of 0.5 mm
Therefore, it is made of a material such as stainless steel so as to withstand the corrosion caused by high temperature exhaust gas. Further, a spacer 304 is provided between the outer pipe 302 and the inner pipe 303, as in the first embodiment. The flexible tube 301 is a bellows 305 provided between an outer pipe (not shown) of the upstream exhaust pipe and an outer pipe 302 of the downstream exhaust pipe 300, and an outer blade 306 covering the outside of the bellows 305. , An inner tube 307 provided between an inner pipe (not shown) of the upstream exhaust pipe and an inner pipe 303 of the downstream exhaust pipe 300.

At the front end of the inner tube 303, the expanded diameter portion 30
8 is formed extending from the outer tube 302. Expanded part 3
Reference numeral 08 denotes an outer pipe 3 which will be described later between the outer pipe 302 and the outer pipe 302.
It is formed with a gap into which 07n can be inserted.

The inner tube 307 comprises a plurality of cylindrical pipes and an outer pipe, as in the first embodiment.
Like the inner pipe 303, it is thinner than the outer pipe 302, for example, has a plate thickness of 0.5 mm, and is formed of a material such as stainless steel so as to withstand the corrosion due to high-temperature exhaust gas. Further, the most downstream cylindrical pipe 307m is the expanded diameter portion 20 of the inner pipe 303.
8 is fitted from the inside. The inner tube 307 has an outer pipe 30 on the outer side of the most downstream cylindrical pipe 307 m.
2 and the outer diameter 308 of the outer pipe 307 to be inserted
n is provided.

The plurality of units, and the most downstream cylindrical pipe 307m and outer pipe 307n are three-dimensionally bendable by connecting pins 309 as connecting means at several positions in the circumferential direction. The outer pipe 307n and the outer pipe 302 are connected by welding.

The operation of the second embodiment having the above structure will be described. The enlarged diameter portion 308 formed at the front end of the inner tube 302 of the
The outer pipe 307n forming the inner tube 307 is inserted between the outer pipe 302 and the outer pipe 302, and the expanded diameter portion 30
Since the most downstream cylindrical pipe 307m is fitted inside 8, the exhaust gas leakage from the outer pipe 302, the outer pipe 307n, the expanded diameter portion 308, and the gaps between the most downstream cylindrical pipe 307m is further prevented. To be done. The operation in other configurations is the same as that of the first embodiment.

[Third Embodiment] FIG. 4 is a partial vertical sectional view of a third embodiment of the present invention, showing a connecting portion between a downstream side exhaust pipe 400 and a flexible tube 401. The downstream exhaust pipe 400 is the same as in the first and second embodiments.
It is double formed with 03. The outer pipe 302 is formed thick so as to be a strength member for the entire exhaust pipe. Inner tube 4
03 is thinner than the outer tube 402, for example, a plate thickness of 0.5 m
It is the same as that of the first embodiment in that it is formed of a material such as stainless steel so as to withstand the corrosion due to the high temperature exhaust gas and is slightly extended from the outer pipe 402. Further, a spacer 40 is provided between the outer pipe 402 and the inner pipe 403.
4 is provided as in the first embodiment. The flexible tube 401 is a bellows 405 provided between an outer pipe (not shown) of the upstream side exhaust pipe and an outer pipe 402 of the downstream side exhaust pipe 400, and its bellows 405.
Is formed by an outer blade 406 covering the outer side of the inner pipe 407, an inner tube 407 provided between an inner pipe (not shown) of the upstream exhaust pipe and an inner pipe 403 of the downstream exhaust pipe 400, and the like.

The inner tube 407 is composed of a plurality of cylindrical pipes having an S-shaped cross section, an outer pipe having a J-shaped cross section folded back inward, and a most downstream cylindrical pipe.
Similarly to the outer tube 402, the outer tube 402 is thinner than the outer tube 402, for example, has a plate thickness of 0.5 mm, and is made of a material such as stainless steel so as to withstand the corrosion caused by the high temperature exhaust gas. The outer pipe 407n is fitted and welded inside the outer pipe 402 of the downstream exhaust pipe 400. Outer pipe 407n
The most downstream cylindrical pipe 407m is fitted inside the, and the fitting portion 407p is fitted to the inner pipe 403. The cylindrical pipes are connected by a curved portion 407r, and the most downstream cylindrical pipe 407m and the S-shaped cylindrical pipe 407k are connected by a curved portion 407q.

The plurality of cylindrical pipes, and the most downstream cylindrical pipe 407m and the outer pipe 407n are three-dimensionally bendable by connecting pins 408 as connecting means at several positions in the circumferential direction. .

The operation of the third embodiment having the above configuration will be described. The fitting portion 407p is fitted to the inner pipe 403, and the most downstream cylindrical pipe 407m and the S-shaped cylindrical pipe 407k are curved portions 407q, and the plurality of cylindrical pipes are curved portions 407r. The exhaust gas leaks from the gaps are further prevented because they are connected by. The operation in other configurations is the same as in the first and second embodiments.

[Fourth Embodiment] FIG. 5 is a perspective view showing a part of a fourth embodiment of the present invention, showing a modification of the inner tube.

In this embodiment, connected to the engine,
An upstream exhaust pipe that is double formed by an outer pipe and an inner pipe, a downstream exhaust pipe that is connected to a catalyst and that is double formed by an outer pipe and an inner pipe, and an outer pipe of an upstream exhaust pipe The bellows provided between the downstream side exhaust pipe and the outer pipe, the outer blade covering the outside of the bellows, and the like are the same as those in the first embodiment, and are not shown.

The inner tube 500 of this embodiment is thinner than the outer tube, for example, has a plate thickness of 0.5 mm, and has a strip-shaped plate material 5 such as stainless steel which is resistant to corrosion by high-temperature exhaust gas.
01 is spirally wound so as to overlap each other. Therefore, the inner tube 500 is formed with a thin end portion 502 having the strip plate member 501 on the inner side and a thick end portion 503 having the outer side on the outer side.

The thin end portion 5 of the inner tube 500
02 is fitted to the reduced diameter portion from the outside and the thick end portion 503 is fitted to the inner pipe of the downstream side exhaust pipe from the inside, but it is omitted in the figure.

The operation of the above structure will be described. In the fourth embodiment, since the inner tube 500 is formed by spirally winding one strip-shaped plate member 501, the number of parts is small, the weight can be reduced, and the manufacturing cost can be reduced. Further, since the inner tube 500 is thin and has a small heat capacity, its temperature immediately rises and the temperature difference between the exhaust gas and the inner tube 500 becomes small. Therefore,
The amount of heat transferred from the exhaust gas to the inner tube 500 is reduced, and the exhaust gas temperature is maintained. Further, since the pressure of the exhaust gas rises at the reduced diameter portion and is gradually decreased by the inner tube 500 that gradually expands, the exhaust gas rarely leaks from the connecting gap of the inner tube 500, and the inner tube 500 is less likely to leak. The heat loss of the exhaust gas due to is reduced. Therefore, the temperature drop of the exhaust gas is suppressed. The operation in other configurations is the same as that of the first embodiment.

[0043]

As described above, according to the double tube-integrated flexible tube of the present invention (claim 1), heat is transferred from the exhaust gas flowing in the inner tube of the exhaust tube to the inner tube and the inner tube. . Since the inner tube and the inner tube are thin, the temperature thereof rises immediately, the heat loss of the exhaust gas is reduced, and the temperature decrease of the exhaust gas can be suppressed. Therefore,
Early activation of the catalyst connected to the downstream exhaust pipe can be achieved. Further, since the exhaust gas that has passed through the inner pipe is gradually reduced by the inner tube that gradually expands in diameter, it is possible to prevent the exhaust gas from leaking from the connection gap of the inner tubes. Therefore, even when the flow rate of exhaust gas is high and the temperature is high during high-speed traveling or uphill traveling, it is possible to prevent the bellows from being damaged due to high temperature due to exhaust gas.

Further, in the flexible tube integrated with a double pipe of the present invention (claim 2), the gap between the last cylindrical pipe on the downstream side and the inner side of the inner pipe of the downstream side exhaust pipe is Since it is a narrower gap than the gap between the inner pipe and the inner pipe, exhaust gas leakage from the gap between the last cylindrical pipe on the downstream side and the inner pipe is suppressed.

Further, in the double tube-integrated flexible tube of the present invention (claim 3), since the connecting means is a plurality of pins, it is possible to easily connect the cylindrical pipes with a simple structure. .

Further, in the double tube-integrated flexible tube of the present invention (claim 4), an inner tube which is thin and spirally wound by overlapping strip-shaped plate members is used as an inner pipe of the upstream side exhaust pipe. It is provided between the downstream exhaust pipe and the inner pipe. Therefore,
The exhaust gas flowing in from the upstream side exhaust pipe passes through the inner tube (exhaust passage) and is discharged to the downstream side exhaust pipe, so that the heat capacity of the portion in contact with the exhaust gas becomes small. , The wall temperature of the inner tube is raised early to prevent the temperature of exhaust gas from decreasing. Further, since the contact between the bellows having a large heat capacity and the exhaust gas is reduced, the temperature drop of the exhaust gas is prevented. Further, when the exhaust gas has a high temperature, the exhaust gas is suppressed from leaking from the inner tube to the bellows, and the temperature of the bellows is prevented from becoming high. Furthermore, since the inner tube is formed by spirally winding a single strip-shaped plate material, the number of parts is small, the weight can be reduced, and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an automobile exhaust system to which the present invention is applied.

FIG. 2 is a vertical sectional view of the first embodiment of the present invention.

FIG. 3 is a partial vertical sectional view of a second embodiment of the present invention.

FIG. 4 is a partial vertical cross-sectional view of Embodiment 3 of the present invention.

FIG. 5 is a perspective view showing a part of a fourth embodiment of the present invention.

FIG. 6 is a vertical sectional view of a conventional example.

[Explanation of symbols]

100,200,601 Upstream exhaust pipe 101,203,300,400,602 Downstream exhaust pipe 201,204,302,402 Outer pipe 202,205,303,403 Inner pipe 209,307,407,500 Inner tube 209a , 209m, 307m, 407m Pipe 209n, 307n, 407n Outer pipe 213, 309, 408 Connecting pin 501 Strip plate material

Claims (4)

[Claims] 1. An upstream exhaust pipe, which is composed of an outer pipe and an inner pipe thinner than the outer pipe, is connected to an engine, an outer pipe, and an inner pipe thinner than the outer pipe. A double-tube-integrated flexible tube comprising a double pipe formed by the above, and flexibly connecting the downstream exhaust pipe connected to the catalyst to the outer pipe of the upstream exhaust pipe and the outer pipe of the downstream exhaust pipe. A bellows that is freely bendable connected to the pipe, thin,
The upstream exhaust pipe is provided with an inner tube composed of a plurality of cylindrical pipes whose inner diameters are gradually increased so as to form a nested relationship, and a connecting means for connecting the plurality of inner tubes in a bendable manner. The diameter of the rear end connection portion of the inner pipe of the inner tube is reduced, and the inner tube has a cylindrical pipe on the upstream exhaust pipe side of the inner pipe of the upstream exhaust pipe among the plurality of cylindrical pipes. Fit and connect to the rear end connection part, then sequentially fit and connect the cylindrical pipe at the next position to the outside of the cylindrical pipe at the front position, and the last cylindrical pipe on the downstream side to the downstream side. A double-tube integrated flexible tube characterized in that it is fitted and connected to the inside of the inner tube of the exhaust pipe. 2. The gap between the last cylindrical pipe on the downstream side and the inner side of the inner pipe of the downstream side exhaust pipe is narrower than the gap between the outer pipe and the inner pipe. The double-tube integrated flexible tube according to claim 1. 3. The double-tube integrated flexible tube according to claim 1, wherein the connecting means is a plurality of pins. 4. An upstream exhaust pipe connected to the engine, which comprises a double pipe formed of an outer pipe and an inner pipe thinner than the outer pipe, an outer pipe, and an inner pipe thinner than the outer pipe. A double-tube-integrated flexible tube comprising a double pipe formed by the above, and flexibly connecting the downstream exhaust pipe connected to the catalyst to the outer pipe of the upstream exhaust pipe and the outer pipe of the downstream exhaust pipe. The bellows, which is connected to the pipe in a freely bendable manner, is provided between the inner pipe of the upstream side exhaust pipe and the inner pipe of the downstream side exhaust pipe, and is thin and overlaps the strip-shaped plate material. A double-tube integrated type flexible tube, which is provided with an inner tube that is spirally wound.