JPH10159547A - Exhaust pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To early increase catalytic activity just after an engine is started, subsequently suppress a rise in back pressure and prevent an overrise in an exhaust gas temperature. SOLUTION: When pressure of exhaust gas from an engine is low like just after the engine is started, exhaust gas flow in first and second routes P1 and P2. Exhaust gas flows in only the first route P1 because a valve element 23 remains clogging the downstream end of the second route P2. Because heat insulation is high because this first route P1 is surrounded by the second route P2, lowering of a temperature in exhaust gas flowing in the first route P1 is suppressed as much as possible. When pressure of exhaust gas from the engine is high, exhaust gas flows in the first and second routes P1 and P2 and the valve element 23 opens the downstream end of the second route P2. Thus, a rise back pressure can be suppressed because flowing cross sectional area is increased and an overrise in an exhaust gas temperature can be prevented because exhaust gas flowing in the second route P2 is properly cooled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an exhaust pipe arranged between an engine and a catalyst device.

[0002]

2. Description of the Related Art Heretofore, as an exhaust pipe arranged between an engine and a catalyst device, a double pipe type exhaust pipe has been known for the purpose of increasing the catalytic activity as soon as possible immediately after starting the engine. . As such a double pipe type exhaust pipe, for example, as shown in FIG.
And an inner pipe 106 and an outer pipe 101 arranged to form a gap 107 are known.

According to such a double pipe type exhaust pipe, since the heat insulation of the inner pipe 106 is enhanced by the presence of the air gap 107, the temperature of the high-temperature exhaust gas decreases when flowing through the inner pipe 106. Can be prevented. Therefore, even immediately after the start of the engine, the catalytic activity of the downstream catalytic device can be quickly increased.

[0004]

However, recent exhaust gas regulations require that the catalyst activity be increased very quickly immediately after the start of the engine. For example, the diameter of the inner pipe 106 in the exhaust pipe is reduced. It is considered that the heat capacity is reduced by reducing the thickness and the plate thickness.

[0005] However, when the diameter of the inner pipe 106 is reduced to reduce the plate thickness, it is possible to effectively prevent a decrease in the temperature of exhaust gas flowing inside the inner pipe 106 immediately after the engine is started. Although it can be increased, when the number of revolutions of the engine becomes several thousand revolutions, there is a possibility that the back pressure may adversely affect the engine output, or the exhaust gas temperature may rise too much and adversely affect the catalyst. Further, when the thickness of the inner pipe 106 is reduced, the heat resistance may be reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an exhaust pipe which enhances the catalyst activity immediately after the start of the engine, and thereafter suppresses a rise in back pressure and prevents an exhaust gas temperature from rising too much. Aim.

[0007]

Means for Solving the Problems and Effects of the Invention In order to solve the above-mentioned problems, the present invention relates to an exhaust pipe arranged between an engine and a catalyst device, wherein a first path having high heat insulating property and a heat insulating property are provided. A second path having a low flow rate is provided, so that exhaust gas from the engine flows only through the first path immediately after the engine is started, and thereafter, the second path can also flow.

In such an exhaust pipe, immediately after the start of the engine, the exhaust gas from the engine flows only through the first path having high heat insulation, so that a decrease in the exhaust gas temperature caused by flowing through this path is suppressed. For this reason, the temperature of the exhaust gas that has reached the catalytic device is sufficiently high, and the catalytic activity can be increased at an early stage. Therefore, an effect is obtained that the exhaust gas can be sufficiently cleaned immediately after the start of the engine.

On the other hand, after a while from the start of the engine, the exhaust gas from the engine is discharged by the first heat insulating material.
Not only the route but also the second route having low heat insulation can be circulated. For this reason, the cross-sectional area of the path through which the exhaust gas can flow increases, and an increase in the back pressure of the exhaust gas is suppressed. In addition, since the exhaust gas flowing through the second path having low heat insulation is cooled appropriately,
The catalyst in the catalytic device does not become so hot that it deteriorates thermally. Therefore, after a while after the start of the engine, it is possible to prevent the engine output from being lowered due to the increase in the back pressure and the catalyst from being deteriorated due to the exhaust gas temperature being too high.

In the exhaust pipe according to the present invention, the first path is a path through which exhaust gas from the engine can constantly flow, and the second path is provided so as to surround the first path. When the pressure of the exhaust gas from the engine is low, it may be closed, and when the pressure of the exhaust gas from the engine is high, it may be opened.

In this case, since the first path is surrounded by the second path, the first path has higher heat insulation than the second path. Further, both paths can be configured compactly. Also, when the pressure of the exhaust gas from the engine is low, such as immediately after the start of the engine, the second path is closed, so that the exhaust gas flows only through the first path having high heat insulation. Therefore, as in the case of the first aspect, the exhaust gas reaching the catalytic device has a sufficiently high temperature, the catalytic activity can be increased at an early stage, and the exhaust gas can be sufficiently cleaned immediately after the engine is started.

On the other hand, when the pressure of the exhaust gas from the engine is high, such as when the engine speed is several thousand revolutions, the second path is opened. The second route with low possibility is also distributed. Therefore, similarly to the first aspect, the back pressure of the exhaust gas is suppressed from increasing, and the exhaust gas temperature after flowing through the exhaust pipe is prevented from excessively increasing. As a result, the engine output decreases due to the increase in the back pressure and the catalyst due to high heat. The effect is obtained that the deterioration of can be prevented.

Further, the exhaust pipe of the present invention is provided with a valve in the middle or downstream end of the second passage, and when the pressure of the exhaust gas from the engine is low, the valve connects the second passage with the second passage. When the exhaust gas from the engine is closed and the pressure of the exhaust gas is high, the valve may open the second path. In this case, opening and closing of the second path can be realized with a simple configuration.

Here, as described in claim 4, the valve may be configured to be biased by the biasing member in a direction to close the second path. In this case, when the force exerted by the exhaust gas in the second path on the valve is greater than the urging force of the urging member, the valve opens the second path. Therefore, by appropriately setting the urging force of the urging body, the exhaust gas pressure at which the second path opens and closes can be arbitrarily set.

Further, the exhaust pipe of the present invention is provided so as to form a gap between an outer pipe provided between the engine and the catalyst device and an inner wall of the outer pipe. An inner pipe having a thinner thickness than the outer pipe may be provided, the first path may be an inner pipe, and the second path may be a gap formed between the outer pipe and the inner pipe.

In this case, the inner pipe, which is the first path, is surrounded by the second path, which is an air gap, and has a small heat capacity because it is thin, so that the heat insulation is sufficiently higher than that of the second path. At this time, if the inner diameter of the inner pipe is reduced, the heat capacity is further reduced, so that the heat insulating property is further improved. Also, when the pressure of the exhaust gas from the engine increases, the second path opens, so that the back pressure does not increase even if the diameter of the inner pipe, which is the first path, is small. The effect is obtained that the heat resistance is sufficiently maintained.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. Note that the embodiment of the present invention
It is needless to say that the present invention is not limited to the following embodiments, and can take various forms within the technical scope of the present invention. [First Embodiment] FIG. 1 is a sectional view showing a schematic configuration of an exhaust pipe of a first embodiment, and FIG. 2 is an enlarged view of a main part of FIG. The exhaust pipe 10 of the first embodiment includes an outer pipe 11 and an inner pipe 1.
6, the valve assembly 20 and the like.

The outer pipe 11 has an upstream flange 12 welded to the outer periphery of the upstream end. Outer pipe 1
As shown in FIG. 2, the downstream end of 1 is inserted into a connection pipe 14 welded to the downstream flange 13 and welded. The diameter of the connecting pipe 14 at both ends is substantially the same as the diameter of the outer pipe 11, but the central pipe is formed in a greatly expanded shape near the center.

The inner pipe 16 is provided so as to form a gap 17 with the inner wall of the outer pipe 11 as shown in FIG. 1, and the thickness thereof is set to １ ／ to の of the outer pipe 11. A part of the upstream end of the inner pipe 16 is welded to the outer pipe 11, and the downstream end of FIG.
As shown in (1), it is inserted into the inner terminal pipe 19 and welded. This inner terminal pipe 19 is the outer pipe 11
Spot welded. In this embodiment, the inside of the inner pipe 16 forms the first path P1, and the outer pipe 11
The gap 17 between the inner pipe 16 and the inner pipe 16 forms a second path P2.

The valve assembly 20 has a second path P2
Is provided at the downstream end. The valve assembly 20 mainly includes a valve body support member 21 and a valve body (valve) 2.
3. It is composed of a coil spring 25. The valve body support member 21 has a pipe portion 21a inserted into a space formed by the outer pipe 11 and the inner terminal pipe 19, and gradually expands in diameter from the pipe portion 21a backward (to the right in FIG. 2). A tapered portion 21b extended to
A pair of stays 2 provided at the rear end of the tapered portion 21b
1c (only one is shown in FIG. 2). A wire mesh 22 is fixed to the inner peripheral surface of the tapered portion 21b.

The valve body 23 is swingably supported via a shaft 24 between a pair of stays 21c. This valve 23
Has a substantially frusto-conical convex portion 23a projecting forward, and the outer peripheral surface of the convex portion 23a is formed in a shape that overlaps with the wire mesh 22 fixed to the tapered portion 21b of the valve body support member 21. . When the outer peripheral surface of the convex portion 23a of the valve body 23 overlaps with the wire mesh 22, the space formed by the outer pipe 11 and the inner terminal pipe 19 (that is, the downstream end of the second path P2) is closed. In addition,
When the valve element 23 closes the downstream end of the second path P2, the wire mesh 22 functions as a cushioning material, thereby preventing occurrence of a tapping sound.

The coil spring 25 is inserted through the shaft 24. One arm of the coil spring 25 is fixed to the valve body support member 21, and the other arm presses the valve body 23.
Accordingly, the valve element 23 is urged by the coil spring 25 in a clockwise direction in FIG. 2, that is, in a direction to close the downstream end of the second path P2.

Next, the operation of the exhaust pipe 10 of this embodiment will be described. First, the case where the pressure of the exhaust gas from the engine is low, such as immediately after the start of the engine, will be described. At this time, the exhaust gas flows into the first path P1 and the second path P2 as shown by the solid arrow and the dotted arrow in FIG. 1, but since the pressure of the exhaust gas from the engine is low, the valve body 2
3 keeps the downstream end of the second path P2 closed. That is, since the urging force of the coil spring 25 on the valve body 23 in the closing direction is greater than the force of the exhaust gas in the second path P2 on the valve body 23 in the opening direction, the valve body 23 remains closed. Therefore, the exhaust gas flows only through the first path P1.

Here, the inner pipe 16, which is the first path P1, is surrounded by the second path P2. For this reason, the heat insulation of the 1st path | route P1 is high, and the fall of the exhaust gas which circulates here is suppressed from falling. Also, the inner pipe 16
Is smaller than the cross-sectional area of the entire exhaust pipe 10, and the plate thickness is smaller than that of the outer pipe 11, so that the first path P1 has a small heat capacity. Therefore, the exhaust gas flowing through the first path P1 has less heat taken by the inner pipe 16 and the like,
Also in this respect, a decrease in the temperature of the exhaust gas can be suppressed.

Therefore, when the pressure of the exhaust gas is low, for example, immediately after the start of the engine, the exhaust gas
The gas flows into the catalyst device only through the path P1. At this time, the temperature of the exhaust gas is reduced as much as possible, so that the temperature of the catalyst device becomes very high (about 350 ° C.) very quickly, and the catalytic activity is enhanced. As a result, the catalyst functions sufficiently immediately after the engine is started, and the exhaust gas is sufficiently purified.

Next, a case where the pressure of exhaust gas from the engine is high, for example, when the accelerator pedal is depressed to increase the engine speed, will be described. At this time, the exhaust gas flows into the first path P1 and the second path P2 as shown by solid arrows and dotted arrows in FIG.
Since the pressure of the exhaust gas is high, the valve element 23 opens the downstream end of the second path P2 (see a two-dot chain line in FIG. 2). That is, the exhaust gas in the second path P2 exerts a greater force in the opening direction on the valve body 23 than the biasing force in the closing direction exerted on the valve body 23 by the coil spring 25, so that the valve body 23 swings in the opening direction. You do it. Therefore, the exhaust gas flows not only in the first path P1 but also in the second path P2.

Here, since the exhaust gas flows not only in the first path P1 but also in the second path P2, the flow cross-sectional area increases as compared with the case where only the first path P1 flows. For this reason, an increase in back pressure can be suppressed. Further, since the second path P2 has lower heat insulation than the first path P1, the exhaust gas flowing therethrough is cooled appropriately and reaches the catalyst device.

Therefore, when the exhaust gas pressure is high, such as when the number of revolutions of the engine is several thousand, the effect of preventing a decrease in engine output due to an increase in back pressure and deterioration of the catalyst due to high heat can be obtained. Can be [Second Embodiment] FIG. 3 is a sectional view showing a schematic configuration of an exhaust pipe according to a second embodiment, and FIG. 4 is an enlarged view of a main part of FIG. The exhaust pipe 30 of the second embodiment includes an outer pipe 31, an inner pipe 3
6. It is composed of an annular valve body (valve) 43 and the like.

The outer pipe 31 has an upstream flange 32 welded to the outer periphery of the upstream end. Outer pipe 3
As shown in FIG. 4, the downstream end of 1 is inserted into a connection pipe 34 welded to the downstream flange 33 and welded. The connecting pipe 34 has two funnel-shaped pipes 3.
By welding 4a and 34b, the vicinity of the center is formed in a greatly swelled shape. An annular fixing member 38 is fixed to the inner wall of the connecting pipe 34. The annular fixing member 38 has a cylindrical portion 38a through which the inner pipe 36 can be inserted, and a plurality of small holes 38b.

The inner pipe 36 is provided so as to form a gap 37 with the inner wall of the outer pipe 31 as shown in FIG. 3, and the thickness thereof is set to １ ／ to の of the outer pipe 31. A part of the upstream end of the inner pipe 36 is welded to the outer pipe 31, and the downstream end of the inner pipe 36 is shown in FIG.
It is a free end as shown in FIG. In the present embodiment, the inside of the inner pipe 36 forms the first path P1, and the gap 37 between the outer pipe 31 and the inner pipe 36 is the second path P2.
To form

The annular fixing member 38 of the inner pipe 36
An annular wire mesh 36a is fixed to a portion penetrating through the tubular portion 38a of the inner pipe 36. The inner pipe 36 is slidably supported by the tubular portion 38a of the annular fixing member 38 via the annular wire mesh 36a. ing.

An annular valve element 43 is disposed in the inner pipe 36 in front of the annular fixing member 38 (on the left side in FIG. 4). This annular valve element 43 is
6 and is freely slidable along the outer circumference of the inner pipe 36. A coil spring 45 is provided between the annular valve body 43 and the annular fixing member 38, and the coil spring 45 urges the annular valve body 43 forward. For this reason, the outer peripheral tapered surface 43a of the annular valve body 43 is pressed against the wire mesh 46 fixed to the inner wall of the connection pipe 34 by the coil spring 45, and closes the downstream end of the second path P2.

Next, the operation of the exhaust pipe 30 of this embodiment will be described. First, when the pressure of the exhaust gas from the engine is low, such as immediately after the start of the engine, the urging force in the closing direction exerted on the annular valve body 43 by the coil spring 45 depends on the exhaust gas in the second path P2. , The annular valve element 43 remains closed. Therefore, the exhaust gas flows only through the first path P1 (see the solid arrow in FIG. 3).

Here, the inner pipe 36, which is the first path P1, is surrounded by the second path P2, and its cross-sectional area is smaller than the cross-sectional area of the entire exhaust pipe 30, and the plate thickness is smaller than that of the outer pipe 31. Since the first path P1 has a small heat capacity because of its small thickness, the temperature of the exhaust gas flowing through the first path P1 is suppressed as much as possible. Therefore, the temperature of the catalyst device becomes very high (about 350 ° C.) very early, the catalytic activity is enhanced, and the exhaust gas is sufficiently purified immediately after the engine is started.

Subsequently, when the pressure of the exhaust gas from the engine is high, for example, when the rotation speed of the engine is increased by depressing the accelerator, the biasing force of the coil spring 45 acting on the annular valve body 43 in the closing direction is used. Also, since the force in the opening direction exerted by the exhaust gas in the second path P2 on the annular valve element 43 is larger, the annular valve element 43 opens the downstream end of the second path P2 (see a two-dot chain line in FIG. 3). . Therefore, the exhaust gas flows not only in the first path P1 but also in the second path P2 (see the solid arrow and the dotted arrow in FIG. 3). After passing through the gap between the outer peripheral tapered surface 43a of the annular valve element 43 and the wire mesh 46, the exhaust gas flowing through the second path P2 is
Is discharged to the outside through a plurality of small holes 38b.

At this time, the flow cross-sectional area is increased as compared with the case where only the first path P1 is circulated, so that the rise of the back pressure is suppressed, and the second path P2 has a more adiabatic property than the first path P1. Since the exhaust gas flowing through the exhaust gas is low, the exhaust gas flowing through the exhaust gas is cooled appropriately to reach the catalytic device. Therefore, the effect of preventing a decrease in engine output due to an increase in back pressure and deterioration of the catalyst due to high heat can be obtained.

In this embodiment, for example, when the temperature of the inner pipe 36 becomes higher than that of the outer pipe 31, the inner pipe 36 slides on the cylindrical portion 38a of the annular fixing member 38 due to thermal expansion. That is, the inner pipe 36
Expands independently of the outer pipe 31. Therefore, even when the degrees of expansion of the two pipes 31 and 36 are different, there is no possibility that cracks or the like will occur in the exhaust pipe 30.

In each of the above embodiments, the valve (valve 2
3. Although the annular valve element 43) is provided at the downstream end of the second path P2, it may be provided in the middle of the second path P2. However, the effect of keeping the temperature of the first path P1 by the exhaust gas existing in the second path P2 when the pressure of the exhaust gas is low is higher in the former than in the latter, so the former is preferable.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an exhaust pipe according to a first embodiment.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a cross-sectional view illustrating a schematic configuration of an exhaust pipe according to a second embodiment.

FIG. 4 is an enlarged view of a main part of FIG. 3;

FIG. 5 is a cross-sectional view illustrating a schematic configuration of a conventional exhaust pipe.

[Explanation of symbols]

10 ... exhaust pipe, 11 ... outer pipe, 14 ...
・ Connection pipe, 16 ・ ・ ・ Inner pipe, 17 ・ ・ ・ Void, 19 ・ ・ ・ Inner terminal pipe, 20 ・ ・ ・ Valve assembly, 21 ・ ・ ・ Valve support member, 22 ・ ・ ・ Wire mesh, 23 ・..Valve elements, 24 ... shafts, 25 ...
Coil spring, 30 exhaust pipe, 31 outer pipe, 34 connecting pipe, 36 inner pipe, 37 void, 38 annular fixing member, 43
..Annular valve element, 45 ... coil spring, P1 ... first
Path, P2... Second path.

Claims (5)

[Claims] 1. An exhaust pipe disposed between an engine and a catalyst device, comprising: a first path having high heat insulation; and a second path having low heat insulation. An exhaust pipe wherein only the first path is circulated, and thereafter the second path is also circulated. 2. The first path is a path through which exhaust gas from the engine can constantly flow, and the second path is provided so as to surround the first path, and is closed when the pressure of the exhaust gas from the engine is low. 2. The exhaust pipe according to claim 1, wherein the exhaust pipe is opened when the pressure of the exhaust gas from the engine is high. 3. The method according to claim 1, wherein the second path is closed when the pressure of the exhaust gas from the engine is low, and is opened when the pressure of the exhaust gas from the engine is high. The exhaust pipe according to claim 1, further comprising a valve that operates. 4. The exhaust pipe according to claim 3, wherein the valve is urged by an urging body in a direction to close the second path. 5. An outer pipe provided between an engine and a catalyst device, and an inner pipe provided so as to form a gap with an inner wall of the outer pipe, the inner pipe being thinner than the outer pipe. The exhaust pipe according to any one of claims 1 to 4, wherein the exhaust pipe is an inner pipe, and the second path is a gap formed between the outer pipe and the inner pipe.