JP2004076587A - Exhaust pipe structure of internal combustion engine - Google Patents

Abstract

Provided is an exhaust pipe structure of an internal combustion engine that can suppress generation of exhaust noise while suppressing a change in arrangement of components and an increase in the size of a muffler.
An inner tube is connected to a catalyst case, and the outer tube is entirely separated from the outer surface of the catalyst case, and the outer tube is connected to the catalyst rear end pipe. The tube part 33 is connected. A partition plate 36 for partitioning a space 35 between the outer peripheral surface of the catalyst case 31 and the inner peripheral surface of the outer cylinder portion 33 into an upstream compartment 35a and a downstream compartment 35b is provided in the outer cylinder 33. Is provided. In addition, a resonance opening 37 is provided in the wall surface of the inner tube 25 for communicating a space 26a between the outer peripheral surface of the inner tube 25 and the inner peripheral surface of the outer tube 26 with the space 25a inside the inner tube 25. A resonance pipe is formed downstream of the center of the resonance opening 37 in the space 26a. Further, the upstream compartment 35a is a resonance chamber connected to the resonance pipe.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust pipe structure of an internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an exhaust system of an internal combustion engine is provided with a catalytic converter for purifying exhaust gas discharged from the engine and a muffler for silencing an exhaust sound generated when the exhaust gas flows through the exhaust system. (See, for example, Japanese Patent No. 3078253 and Japanese Utility Model Laid-Open No. 55-135118).
[0003]
Further, in such an exhaust system, the catalyst in the catalytic converter may be warmed up using the heat of the exhaust gas so that the catalyst is quickly activated after the engine is started. In such cases, a double-pipe exhaust pipe is often used upstream of the catalytic converter in the exhaust system for the purpose of keeping the exhaust gas warm.
[0004]
In general, in a vehicle on which the internal combustion engine is mounted, the exhaust system is disposed in a space under the floor of the vehicle. In addition, in the underfloor space, in addition to the components constituting the exhaust system, many components such as a vehicle underbody component and a fuel tank are provided.
[0005]
[Problems to be solved by the invention]
By the way, although the muffler is provided in the exhaust system of the internal combustion engine, this muffler is only for reducing the sound pressure level of the exhaust sound, and the exhaust sound is completely silenced through the muffler. Not in translation.
[0006]
On the other hand, in recent years, demands for quietness during vehicle running and the like have been increasing. If the sound pressure level of the exhaust sound is further reduced to meet such demands, the capacity of the muffler itself must be naturally increased.
[0007]
However, as described above, since there is often no sufficient space below the floor of the vehicle, the increase in the capacity of the muffler is naturally limited. As a result, it is difficult to achieve the above requirement for quietness due to space restrictions.
[0008]
However, even if the arrangement of the various components mounted on the vehicle is fundamentally changed, including the various components provided in the underfloor space, the muffler having a large capacity can be provided. Sometimes it is possible. However, such a design change is a large-scale change, which is disadvantageous in terms of production cost and the like.
[0009]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an exhaust pipe of an internal combustion engine capable of achieving higher quietness without causing a change in the arrangement of components and an increase in the size of a muffler. It is to provide structure.
[0010]
[Means for Solving the Problems]
The means for achieving the above object and the effects thereof will be described below.
The invention according to claim 1 has a double-pipe structure comprising an inner pipe and an outer pipe between an exhaust manifold of an internal combustion engine and a catalytic converter containing a catalyst for purifying exhaust gas from the engine. The gist is that a resonance pipe is formed between the inner pipe and the outer pipe by providing a resonance opening in the pipe wall of the inner pipe.
[0011]
Generally, when the catalytic converter is disposed, for example, in a space under the floor of a vehicle, a double pipe having a double pipe structure including an inner pipe and an outer pipe has a relatively long pipe length between the exhaust manifold and the catalytic converter. It is provided. Thereby, a sufficient length (resonance pipe length) along the axis of the inner pipe from the center of the resonance opening provided in the pipe wall of the inner pipe to the end of the portion having the double pipe structure is provided. can do.
[0012]
Therefore, without increasing the capacity of a muffler generally provided in the exhaust system of the internal combustion engine, low-frequency noise generated when exhaust gas from the internal combustion engine flows through the exhaust system can be eliminated, and the exhaust noise can be reduced. Generation can be further suppressed. Further, since it is not necessary to increase the size of the muffler, the muffler is not visually recognized from the outside, and for example, the appearance of a vehicle or the like can be prevented from being deteriorated.
[0013]
Conventionally, when a catalytic converter is provided in an exhaust system of an internal combustion engine, a double pipe structure is often used between the internal combustion engine and the catalytic converter to keep the exhaust gas warm. The space between the outer peripheral surface of the inner tube and the inner peripheral surface of the outer tube was used exclusively as a heat insulating layer.
[0014]
On the other hand, in the above configuration, the space between the outer peripheral surface of the inner tube and the inner peripheral surface of the outer tube of the double tube structure is used not only as a heat insulating layer but also as a resonance pipe. It becomes. For this reason, it is not necessary to particularly form a space functioning as a resonance pipe, for example, by providing an outer pipe so as to cover a part of the outer peripheral surface of the single exhaust pipe in the exhaust system. Further, even when the exhaust system is provided in, for example, a limited space under the floor of the vehicle, the space under the floor can be effectively utilized.
[0015]
According to a second aspect of the present invention, in the exhaust pipe structure of the internal combustion engine according to the first aspect, an axial position of the resonance opening in the inner pipe, an outer diameter of the inner pipe, and an inner diameter of the outer pipe. The gist of the invention is that the resonance frequency is set in accordance with the resonance frequency of the exhaust pipe and the vibration waveform of air column resonance generated when the exhaust gas flows through the inner pipe constituting the double pipe structure.
[0016]
According to the above configuration, a desired resonance frequency or air column resonance can be silenced with a simple configuration without providing a special device or the like.
According to a third aspect of the present invention, in the exhaust pipe structure of the internal combustion engine according to the first or second aspect, the inner pipe constituting the double pipe structure is provided in a catalyst case in which the catalyst is accommodated in the catalytic converter. Outside of the catalyst case, the outer tube constituting the double tube structure is extended, and the outer circumference of the outer circumference of the catalyst case is separated from the outer circumference of the catalyst case. An outer cylinder portion for covering is provided, and the other end of the outer cylinder portion connected to the outer tube is connected to an outer peripheral surface of the catalyst case or an exhaust pipe on the downstream side of the catalyst case. A main point is that a muffler which is a resonance chamber connected to the resonance pipe is formed between the muffler and the outer cylinder portion.
[0017]
In general, a catalytic converter requires a larger amount of catalyst as the displacement of the internal combustion engine increases, so that the size of the catalyst case naturally increases. Also, usually, for example, when an internal combustion engine is mounted on a vehicle and the catalytic converter is arranged in a space under the floor of the vehicle, the portion where the catalytic converter is arranged in the space under the floor is the largest catalyst case between the same platforms. The mounting space is secured in accordance with the catalytic converter having the above. When a catalytic converter having a relatively small catalyst case is disposed in the underfloor space of the vehicle, a space is created around the catalyst case in the underfloor space.
[0018]
In this regard, according to the above configuration, in the case where a vacant portion is formed around the catalyst case in the underfloor space as described above, the outer cylindrical portion is provided in the vacant portion around the catalyst case. It becomes. For this reason, the outer cylinder can be provided without changing the arrangement of the components arranged in the underfloor space of the vehicle.
[0019]
Further, it is possible to suppress the contact between the inner pipe and the outer pipe without providing an intervening material such as a wire mesh between the outer peripheral face of the inner pipe and the inner peripheral face of the outer pipe having a double pipe structure. It becomes possible. Thus, when the exhaust gas flows through the exhaust pipe having the double pipe structure, the heat of the inner pipe having the double pipe structure is not directly transmitted to the outer pipe or transmitted through the inclusion. . Therefore, when the exhaust gas from the internal combustion engine flows through the inner tube, the heat of the exhaust gas is less likely to be transmitted to the inner tube, and the temperature of the exhaust gas can be hardly reduced. As a result, the exhaust gas maintained at a high temperature can flow into the catalyst case, and the temperature of the catalyst in the catalyst case can be appropriately raised. Further, the warm-up property of the catalyst can be improved.
[0020]
According to a fourth aspect of the present invention, in the exhaust pipe structure for an internal combustion engine according to the third aspect, the outer cylinder portion covers the entirety of the catalyst case and is connected to an exhaust pipe immediately downstream of the catalyst case. A partition plate for partitioning the muffler into an upstream compartment and a downstream compartment is provided inside the outer tubular portion, and an exhaust pipe connected to the outer tubular portion and the catalyst case are provided. Means that they are maintained in a state of being separated from each other.
[0021]
According to the above configuration, while the upstream compartment in the space between the outer peripheral surface of the catalyst case and the inner peripheral surface of the outer cylindrical portion has a function as a resonance chamber, the downstream compartment has the inside of the catalyst case. It functions as an expansion chamber that expands the exhaust gas that has passed and flows into the exhaust pipe immediately downstream of the catalyst case. For this reason, the level of the exhaust noise generated when the exhaust gas flows through the exhaust pipe having the double pipe structure can be more suitably suppressed.
[0022]
In addition, since the catalyst case and the exhaust pipe immediately downstream of the catalyst case are not directly connected, the inner pipe and the outer pipe when high-temperature exhaust flows through the exhaust pipe having a double pipe structure are not connected. Even if the inner pipe is displaced relative to the outer pipe due to the thermal expansion, the difference in thermal expansion can be suitably absorbed. In addition, since it is not necessary to provide a special component to absorb the thermal expansion, it is possible to suppress an increase in the number of components of the exhaust system.
[0023]
According to a fifth aspect of the present invention, in the exhaust pipe structure of the internal combustion engine according to the fourth aspect, the catalyst case has a cone portion whose inner diameter gradually decreases toward the downstream in a downstream portion thereof. The gist of the present invention is that the cone portion is provided such that an opening at a downstream end thereof is opposed to an upstream opening of an exhaust pipe connected to the outer cylinder portion.
[0024]
According to the above configuration, the exhaust gas flowing through the inside of the catalyst case is rectified by the cone on the downstream side of the catalyst case to the opening of the exhaust pipe to which the outer cylinder is connected. For this reason, it is possible to suppress an increase in airflow resistance when exhaust gas flowing through the inside of the catalyst case flows into the exhaust pipe to which the outer cylinder portion is connected, and thus suppress a decrease in engine output. can do.
[0025]
According to a sixth aspect of the present invention, in the exhaust pipe structure of the internal combustion engine according to the fourth or fifth aspect, the catalyst case is configured to discharge at least moisture generated inside the catalyst case into the downstream compartment. The gist of the present invention is that a drain hole is provided.
[0026]
In general, after the internal combustion engine is stopped, if the internal combustion engine is left in an environment where the outside air temperature is low, such as at night, the exhaust manifold and the exhaust pipe and the catalyst case, etc., which constitute the double pipe structure, have the same temperature. Rapidly cooled by low outside air. Then, due to the temperature difference between the exhaust manifold and the wall of the exhaust pipe and the catalyst case and the like constituting the double pipe structure and the exhaust remaining in the inside thereof, water vapor and the like in the exhaust are condensed, and water, so-called Condensed water is generated.
[0027]
If the condensed water gradually accumulates in the catalytic converter and the catalyst is immersed in the condensed water for a long time, the components of the catalyst immersed in the condensed water may elute in the condensed water. This causes a reduction in exhaust gas purification performance of the catalyst.
[0028]
In this regard, according to the above configuration, even if condensed water is generated inside the exhaust pipe and the catalyst case that constitute the exhaust manifold and the double pipe structure, the condensed water flows together with the exhaust gas inside the catalyst in the catalyst case. After that, it is quickly discharged to a downstream compartment in the outer cylinder through a drain hole provided in the catalyst case.
[0029]
For this reason, contact between the catalyst and the condensed water for a long time due to accumulation of the condensed water in the catalyst case and elution of the components of the catalyst into the condensed water can be suppressed. Capability reduction can be suppressed.
[0030]
According to a seventh aspect of the present invention, in the exhaust pipe structure of the internal combustion engine according to the sixth aspect, the lower surface of the exhaust pipe connected to the outer cylinder is lower than the lower surface of the catalyst in the catalytic converter in the direction of gravity. The drainage hole is provided further below the lower surface of the exhaust pipe connected to the outer cylinder in the direction of gravity.
[0031]
According to the above configuration, the condensed water generated in the inside of the catalyst case and the like is discharged into the downstream compartment inside the outer cylinder without being accumulated so as to contact the catalyst inside the catalyst case. Further, the condensed water discharged into the downstream compartment is discharged into the exhaust pipe to which the outer cylinder is connected before contacting the catalyst in the catalyst case.
[0032]
For this reason, the contact between the catalyst and the condensed water for a long time due to the accumulation of the condensed water in the catalyst case can be reliably suppressed.
According to an eighth aspect of the present invention, in the exhaust pipe structure for an internal combustion engine according to the seventh aspect, an exhaust pipe connected to the outer cylinder has an upstream end inserted into the outer cylinder. The gist is that a portion of the exhaust pipe inserted into the outer cylinder portion is formed in such a manner that the diameter thereof is increased toward the upstream side.
[0033]
According to the above configuration, the condensed water discharged from the inside of the catalyst case to the downstream compartment in the outer cylinder portion is drawn by the exhaust gas when the exhaust gas flows through the exhaust system. The air flows upward from below on the inner peripheral surface of the portion of the exhaust pipe to which the outer tube is connected in the exhaust tube. For this reason, the condensed water in the downstream compartment can be easily discharged to the inside of the exhaust pipe to which the outer cylindrical portion is connected by using the flow of the exhaust gas.
[0034]
According to a ninth aspect of the present invention, in the exhaust pipe structure for an internal combustion engine according to the eighth aspect, the exhaust pipe connected to the outer cylinder has an axis lower than an axis of the outer cylinder in the direction of gravity. The gist is that they are connected so as to be positioned.
[0035]
According to the above configuration, the distance between the lower surface of the inner circumference of the outer cylinder and the lower surface of the inner circumference of the exhaust pipe to which the outer cylinder is connected can be reduced. For this reason, it is possible to reduce the amount of the condensed water that accumulates in the downstream compartment in the outer cylinder.
[0036]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment in which the present invention is embodied in an exhaust pipe structure of a vehicle-mounted internal combustion engine will be described with reference to FIGS.
[0037]
As shown in FIG. 1, an exhaust system 20 is connected to a cylinder head 11 of the internal combustion engine 10 so as to communicate with an exhaust port 12 thereof.
The exhaust system 20 includes an exhaust manifold 21, a front pipe 22, a center pipe 23, and a tail pipe (not shown) in order from the internal combustion engine 10 side. The exhaust manifold 21, the front pipe 22, the center pipe 23, and the tail pipe are connected to each other by bolts (not shown) at flanges 24 provided at their ends. Most of the exhaust system 20 is provided in the underfloor space 16 below the floor 15 of the vehicle.
[0038]
The front pipe 22 has an inner pipe 25 and an outer pipe 26 between the upstream end in the flow direction of the exhaust gas from the internal combustion engine 10, that is, from the end on the exhaust manifold 21 side to a position slightly downstream from the center in the axial direction. And a double-pipe portion 27 that forms a double-pipe structure.
[0039]
The double pipe section 27 is provided with a thermal expansion absorbing mechanism 28 for absorbing relative displacement of the inner pipe 25 with respect to the outer pipe 26 due to thermal expansion. As the thermal expansion absorbing mechanism 28, a known configuration including, for example, a bellows tube 29 can be adopted.
[0040]
Further, the front pipe 22 is provided with a catalytic converter 30 connected to the double pipe portion 27 and for purifying exhaust gas from the internal combustion engine 10. The catalytic converter 30 includes a NOx storage-reduction catalyst 32a and a seal mat 32b that covers an outer peripheral surface of the NOx storage-reduction catalyst 32a inside the catalyst case 31. Here, in the NOx storage reduction catalyst 32a, for example, potassium (K) and a noble metal such as platinum (Pt) are supported on a ceramic carrier. The carrier may be made of metal. In this case, the metal carrier may be directly held in the catalyst case 31 without providing the seal mat 32b.
[0041]
At least one of the center pipe 23 and the tail pipe is provided with a muffler (main muffler) (not shown) for lowering the exhaust sound level of exhaust flowing through the exhaust system 20.
[0042]
In the present embodiment, as shown in FIG. 1, the inner tube 25 of the double tube portion 27 is connected to the catalyst case 31 of the catalytic converter 30, while the outer tube 26 of the double tube portion 27 is connected to the same. The outer tube 26 is connected to an outer cylindrical portion 33 covering the whole of the catalyst case 31 in a state of being extended to the downstream side and separated from the outer peripheral surface of the catalyst case 31. In the present embodiment, a metal case, for example, an iron case is used as the catalyst case 31, and the thickness thereof is set to be in a range of 0.3 mm or more and 0.8 mm or less.
[0043]
The other end of the outer tube portion 33 on the side connected to the outer tube 26 of the double tube portion 27 is connected to a catalyst rear end pipe 34 immediately downstream of the catalyst case 31. The catalyst rear end pipe 34 has its axis m1 located below the axis m2 of the outer cylinder 33 in the direction of gravity, and the upstream end 34a is inserted into the outer cylinder 33 while the outer cylinder 34 is inserted. 33.
[0044]
Further, in the space 35 between the outer peripheral surface of the catalyst case 31 and the inner peripheral surface of the outer cylindrical portion 33, the same space 35 is provided inside the outer cylindrical portion 33 and the upstream partitioned chamber 35a and the downstream partitioned portion. An annular partition plate 36 for partitioning into the chamber 35b is provided. The partition plate 36 is fixed by, for example, welding or caulking while being in contact with both the outer peripheral surface of the catalyst case 31 and the inner peripheral surface of the outer cylindrical portion 33.
[0045]
In the present embodiment, the catalyst case 31 and the catalyst rear end pipe 34 are kept apart from each other, and the catalyst case 31 and the catalyst rear end pipe 34 are not connected.
[0046]
Further, in the present embodiment, the catalyst case 31 has a rear cone portion 31a whose inner diameter gradually decreases toward the downstream in a portion downstream of the NOx storage reduction catalyst 32a. The rear-side cone portion 31a is provided such that an opening 31b at a downstream end thereof is opposed to an upstream-side opening 34b in the catalyst rear end pipe 34.
[0047]
In the present embodiment, the upstream end 34 a of the portion of the catalyst rear end pipe 34 inserted into the downstream compartment 35 b inside the outer cylinder 33 is connected to the outer cylinder 33 and the catalyst rear end pipe. It is formed in such a manner that the diameter increases as it goes from the connection portion to the upstream opening 34b. Specifically, the upstream end 34a of the catalyst rear end pipe 34 is formed in a flared shape such that the outer peripheral surface of the upstream opening 34b substantially contacts the lower part of the inner peripheral surface of the outer cylindrical portion 33. I have.
[0048]
In this embodiment, the space between the outer peripheral surface of the inner tube 25 and the inner peripheral surface of the outer tube 26 and the inner space of the inner tube 25 Opening 37 is formed so as to communicate with the space 25a. Thereby, a resonance pipe is formed between the center of the resonance opening 37 in the axial direction of the inner tube 25 in the space 26a and the connection portion between the outer tube 26 and the outer tube portion 33. The upstream-side compartment 35a in the outer cylindrical portion 33 connected to the outer cylinder 33 is a muffler which is a resonance chamber.
[0049]
Further, in the present embodiment, the position of the resonance opening 37 in the axial direction of the inner tube 25, specifically, the center of the resonance opening 37 in the axial direction of the inner tube 25, causes the outer tube 26 and the outer cylinder 33 to move from the center. The distance L1 to the connection part is set according to the resonance frequency of the double pipe part 27 and the vibration waveform of the air column resonance in the double pipe part 27. Further, the outer diameter of the inner tube 25 and the inner diameter of the outer tube 26 of the double tube portion 27, more specifically, from the center of the resonance opening 37 in the axial direction of the inner tube 25, The cross-sectional area of the space 26a in a plane perpendicular to the axis up to the connection portion is set in advance according to the resonance frequency.
[0050]
In the present embodiment, the inner pipe 25 and the outer pipe 26 of the double pipe section 27 are provided so as not to abut on each other downstream of the flange 24 connected to the exhaust manifold 21. Further, in the space 26a of the double pipe portion 27, for example, a wire mesh provided so as to be in contact with both surfaces so as to keep the distance between the outer peripheral surface of the inner tube 25 and the inner peripheral surface of the outer tube 26 constant. No contact member is provided. That is, the inner pipe 25 and the outer pipe 26 of the double pipe section 27 are not in contact with each other by the flange 24 on the exhaust manifold 21 side and the partition plate 36 provided in the space 35 of the outer pipe section 33. It is only supported.
[0051]
Further, as shown in FIG. 2, in the present embodiment, the catalyst case 31 includes a space 25a in the inner tube 25 of the double tube portion 27 (see FIG. 1), the inside of the catalyst case 31 itself, and the like. A drain hole 38 is provided for discharging generated moisture, that is, condensed water, into the space 35 of the outer cylindrical portion 33.
[0052]
Specifically, the drain hole 38 is formed on the lower surface of the rear-side cone portion 31a of the catalyst case 31, and the condensed water flowing into the catalyst case 31 is formed by the water formed in the rear-side cone portion 31a. It is discharged into the downstream-side compartment 35b of the outer cylindrical portion 33 through the hole 38.
[0053]
Further, the drain hole 38, the NOx occlusion reduction type catalyst 32a, and the catalyst rear end pipe 34 have the following relationship in a state where the internal combustion engine 10 and the exhaust system 20 are respectively disposed at the use positions. It is provided to have.
[0054]
That is, as shown in FIG. 2, the lower surface of the catalyst rear end pipe 34 in the general portion downstream of the connection portion with the outer cylinder portion 33 is lower than the lower surface of the NOx storage reduction type catalyst 32a in the catalyst case 31. Is also provided so as to be located below in the direction of gravity. The drain hole 38 is provided such that the lower portion thereof is located further below the lower surface of the general portion of the catalyst rear end pipe 34 in the direction of gravity. Thereby, the height of the lower surface of the NOx storage reduction catalyst 32a with respect to the horizontal road surface 40, the height of the lower surface of the general portion of the catalyst rear end pipe 34, and the height of the lower portion of the drain hole 38 are H1, H2, H3, respectively. Then, H1>H2> H3.
[0055]
As described in detail above, according to the exhaust pipe structure of the internal combustion engine according to this embodiment, the following excellent effects can be obtained.
(1) In the present embodiment, the inner tube 25 of the double tube portion 27 and the catalyst case 31 are separated from the outer tube 26 and the outer surface of the catalyst case 31 of the catalytic converter 30 in a state of being separated from the outer surface of the catalyst case 31. It covers the entirety and is connected to an outer cylinder 33 connected to the catalyst rear end pipe 34. Further, in a space 35 between the outer peripheral surface of the catalyst case 31 and the inner peripheral surface of the outer cylindrical portion 33, both surfaces of the outer peripheral surface of the catalyst case 31 and the inner peripheral surface of the outer cylindrical portion 33 are in contact with each other. A partition plate 36 is provided for partitioning the space 35 into an upstream compartment 35a and a downstream compartment 35b. In addition, a resonance opening 37 that communicates a space 26a between the outer peripheral surface of the inner tube 25 and the inner peripheral surface of the outer tube 26 and the space 25a inside the inner tube 25 is formed in the tube wall of the inner tube 25. Provided.
[0056]
Thereby, the upstream-side compartment 35a between the outer peripheral surface of the catalyst case 31 and the inner peripheral surface of the outer cylinder portion 33, the outer peripheral surface of the inner tube 25 in the double tube portion 27, and the inner peripheral surface of the outer tube 26 Is in communication with the space 26a. Then, while the upstream-side partitioned chamber 35a has a function as a resonance chamber, a portion downstream of the resonance opening 37 in the space 26a has a function as a resonance pipe. Further, a portion of the space 26a upstream of the resonance opening 37 has a function as a side branch type muffler. Here, since the double pipe portion 27 has a certain length, the resonance opening 37 in the axial direction of the inner pipe 25 which is sufficient to suppress low frequency noise included in the exhaust sound from the exhaust system 20. (Resonance pipe length) L1 from the center of the above to the connecting portion between the outer tube 26 and the outer tube portion 33 can be easily secured.
[0057]
For this reason, even if the capacity of the muffler (main muffler) provided in the exhaust system 20 is not increased, the low frequency noise can be eliminated, and the generation of exhaust noise can be further suppressed. Further, since it is not necessary to increase the size of the muffler, the muffler is not visually recognized from the outside, so that the appearance of the vehicle can be prevented from being deteriorated.
[0058]
Conventionally, when a catalytic converter is provided in an exhaust system of an internal combustion engine, a double pipe is often used between the internal combustion engine and the catalytic converter to keep the exhaust gas warm. The space between the outer peripheral surface of the inner tube and the inner peripheral surface of the outer tube was only used exclusively as a heat insulating layer.
[0059]
On the other hand, in the present embodiment, the space 26a between the outer peripheral surface of the inner tube 25 and the inner peripheral surface of the outer tube 26 in the double tube portion 27 is not only used as a heat insulating layer, but also serves to reduce exhaust noise. It will also be used as a resonance pipe that keeps the level low. For this reason, for example, a space that functions as a resonance pipe is provided by newly providing an outer pipe so as to partially cover the outer peripheral surface of a single exhaust pipe section such as the center pipe 23 or the tail pipe of the exhaust system 20. Need not be formed specially. Further, the underfloor space 16 of the vehicle, in which a large number of components are provided as well as the exhaust system 20, can be effectively utilized.
[0060]
Further, in general, a catalytic converter requires a larger amount of catalyst as the displacement of the internal combustion engine increases, so that a large catalytic converter is naturally used. Usually, when the catalytic converter provided in the exhaust system of the vehicle-mounted internal combustion engine is arranged in the space under the floor of the vehicle, the portion where the catalytic converter is arranged in the space under the floor is the largest catalyst case between the same platforms. The mounting space is secured in accordance with the catalytic converter.
[0061]
As a result, when a catalytic converter having a relatively small catalyst case is disposed in the underfloor space of the vehicle, a space is created around the catalyst case. If the outer cylindrical portion 33 of the present embodiment is provided in a vacant portion around the catalyst case, the outer cylindrical portion 33 can be provided without changing the arrangement of the components arranged in the underfloor space of the vehicle. it can.
[0062]
(2) In the present embodiment, the distance L1 from the center of the resonance opening 37 in the axial direction of the inner tube 25 to the connection between the outer tube 26 and the outer tube 33 is determined by the resonance frequency in the double tube 27. , And the exhaust gas flow through the inner tube 25 of the double tube portion 27. Further, from the outer diameter of the inner tube 25 and the inner diameter of the outer tube 26 of the double tube portion 27, that is, from the center of the resonance opening 37 in the axial direction of the inner tube 25 to the connection portion between the outer tube 26 and the outer tube portion 33. The cross-sectional area of the space 26a between the outer peripheral surface of the inner tube 25 and the inner peripheral surface of the outer tube 26 in a plane orthogonal to the axis of the double pipe 27 between It is set according to.
[0063]
Thus, by setting the position of the resonance opening 37 in the axial direction of the inner tube 25, and the outer diameter of the inner tube 25 and the inner diameter of the outer tube 26, respectively, the catalyst case 31 and the outer cylindrical portion 33 having the same size are provided. The sound of a different frequency can be extinguished by using. Further, by setting the axial position of the resonance opening 37 in the inner tube 25 in accordance with the vibration waveform of the columnar resonance generated in the double tube portion 27, the columnar resonance can also be appropriately silenced. it can. In addition, a desired resonance frequency and air column resonance can be silenced with a simple configuration without providing a special device or the like.
[0064]
The closer the position of the resonance opening 37 in the axial direction of the inner tube 25 to the exhaust manifold 21, that is, from the center of the resonance opening 37 in the axial direction of the inner tube 25, The resonance frequency becomes lower as the distance L1 to the connection portion with the tube portion 33 increases. Also, the difference between the inner diameter of the outer tube 26 and the outer diameter of the inner tube 25, that is, the distance between the outer circumferential surface of the inner tube 25 and the inner circumferential surface of the outer tube 26 on a plane orthogonal to the axis of the double tube portion 27. The resonance frequency increases as the cross-sectional area increases.
[0065]
(3) In the present embodiment, the inner pipe 25 and the outer pipe 26 of the double pipe section 27 are provided so as not to abut on each other downstream of the flange 24 connected to the exhaust manifold 21. Further, in the space 26a of the double pipe portion 27, there is no intervening material such as a wire mesh which is in contact with both the outer peripheral surface of the inner tube 25 and the inner peripheral surface of the outer tube 26.
[0066]
Accordingly, when the exhaust gas is flowing through the double pipe portion 27, the heat of the inner pipe 25 is not directly transmitted to the outer pipe 26 or transmitted through the contact member. Therefore, when the exhaust gas flows through the inner pipe 25, the heat of the exhaust gas is less likely to be transmitted to the inner pipe 25, and the temperature of the exhaust gas can be made more difficult to lower.
[0067]
As a result, the exhaust gas flows from the inside of the inner tube 25 into the inside of the catalyst case 31 and passes through the inside of the NOx occlusion-reduction type catalyst 32a while the temperature thereof is maintained at a high temperature. The temperature of the NOx storage reduction catalyst 32a can be improved while the temperature of the NOx storage catalyst 32a can be appropriately increased.
[0068]
(4) In the present embodiment, the catalyst case 31 and the catalyst rear end pipe 34 are provided so as to be kept apart from each other. As a result, the downstream compartment 35b in the space 35 between the outer peripheral surface of the catalyst case 31 and the inner peripheral surface of the outer cylindrical portion 33 passes through the inside of the catalyst case 31 and flows into the inside of the catalyst rear end pipe 34. This serves as an expansion chamber for expanding the exhaust gas. For this reason, the level of the exhaust noise generated when the exhaust gas flows through the inside of the double pipe portion 27 can be more suitably suppressed.
[0069]
(5) In the present embodiment, in the catalyst case 31, in a portion downstream of the NOx storage reduction catalyst 32 a, the inner diameter gradually decreases toward the downstream, and the opening 31 b at the tip thereof is connected to the catalyst rear end pipe 34. Is provided with a rear-side cone portion 31a facing the upstream opening 34b.
[0070]
As a result, the exhaust gas flowing in the catalyst case 31 is rectified by the rear cone 31a to the opening 34b of the catalyst rear end pipe 34. For this reason, it is possible to suppress an increase in the ventilation resistance when the exhaust gas flowing through the inside of the catalyst case 31 flows into the inside of the catalyst rear end pipe 34, and it is possible to suppress a decrease in the engine output.
[0071]
(6) In the present embodiment, the catalyst case 31 is provided with the space 25a in the inner tube 25 of the double tube portion 27 and the moisture generated in the catalyst case 31 itself in the downstream section chamber 35b in the outer tube portion 33. A drain hole 38 is provided for discharging water into the inside.
[0072]
Generally, when the internal combustion engine 10 is left in an environment where the outside air temperature is low, such as at night, after the operation of the internal combustion engine 10 is stopped, the exhaust manifold 21, the double pipe section 27, and the catalyst case 31 have a low temperature. Rapidly cooled by outside air. Then, due to the temperature difference between the exhaust manifold 21, the double pipe portion 27, and the wall surface of the catalyst case 31 and the exhaust gas remaining in the inside thereof, water vapor and the like in the exhaust gas are condensed, and water, that is, so-called condensed water is formed. appear.
[0073]
When the condensed water gradually accumulates in the catalytic converter 30 and the NOx storage reduction catalyst 32a is immersed in the condensed water for a long time, the portion of the NOx storage reduction catalyst 32a that is immersed in the condensed water may be used. Components (eg, potassium (K), etc.) may elute in condensed water. Such elution of the components of the NOx storage reduction catalyst 32a into the condensed water is a factor that causes a reduction in the exhaust gas purification performance of the NOx storage reduction catalyst 32a.
[0074]
On the other hand, in the present embodiment, even if the condensed water is generated, the condensed water passes through the inside of the NOx storage reduction catalyst 32a in the catalyst case 31 together with the exhaust gas. The fuel is rapidly discharged to the downstream compartment 35b between the outer peripheral surface of the catalyst case 31 and the inner peripheral surface of the outer cylindrical portion 33 via the inner surface 38.
[0075]
For this reason, contact between the NOx storage reduction catalyst 32a and the condensed water for a long time due to accumulation of the condensed water in the catalyst case 31 and elution of the components of the NOx storage reduction catalyst 32a into the condensed water are suppressed. As a result, it is possible to suppress a reduction in the exhaust gas purifying ability of the catalytic converter 30.
[0076]
(7) In the present embodiment, the drain hole 38, the NOx storage-reduction catalyst 32a, and the catalyst rear end pipe 34 are disposed on the road surface 40 in a state where the exhaust system 20 is located at the use position. The height H1 of the lower surface of the catalyst rear end pipe 34> the height H2 of the lower surface of the general portion of the catalyst rear end pipe 34> the height H3 of the lower part of the drain hole 38 is provided.
[0077]
As a result, the condensed water generated inside the exhaust manifold 21, the double pipe portion 27, and the catalyst case 31 does not accumulate in the inside of the catalyst case 31 so as to contact the NOx storage reduction catalyst 32 a, and the outer periphery of the catalyst case 31 It is discharged to the downstream compartment 35b between the surface and the inner peripheral surface of the outer cylindrical portion 33. The condensed water discharged into the downstream compartment 35b flows into the catalyst rear end pipe 34 before coming into contact with the NOx storage reduction catalyst 32a.
[0078]
For this reason, contact for a long time between the NOx storage-reduction type catalyst 32a and the condensed water due to the accumulation of the condensed water in the catalyst case 31 can be suppressed.
(8) In the present embodiment, the outer cylindrical portion 33 and the catalyst rear end pipe 34 are connected to each other, and the upstream end 34 a of the catalyst rear end pipe 34 is connected to the outer peripheral surface of the catalyst case 31 and the inner peripheral surface of the outer cylindrical portion 33. Are connected in a state of being inserted into the downstream-side compartment 35b. The upstream end 34a of the catalyst rear end pipe 34 inserted into the downstream compartment 35b in the outer cylindrical portion 33 is formed in a flared shape whose diameter increases toward the opening 34b.
[0079]
As a result, the condensed water discharged from the inside of the catalyst case 31 into the downstream compartment 35b between the outer peripheral surface of the catalyst case 31 and the inner peripheral surface of the outer cylindrical portion 33 flows into the downstream compartment 35b. Flows on the inner peripheral surface of the upstream end 34a of the catalyst rear end pipe 34 from the opening 34b to the downstream in a form of being pulled by the exhaust gas flowing through. For this reason, the condensed water in the downstream-side compartment 35b of the outer cylindrical portion 33 can easily flow out into the catalyst rear end pipe 34 by using the flow of the exhaust gas.
[0080]
(9) In the present embodiment, the outer cylinder 33 and the catalyst rear end pipe 34 are connected such that the axis m1 of the catalyst rear end pipe 34 is located below the axis m2 of the outer cylinder 33 in the direction of gravity. are doing. Thereby, the distance L2 (see FIG. 1) between the inner lower surface of the outer cylinder portion 33 and the inner lower surface of the catalyst rear end pipe 34 can be reduced. Therefore, the amount of the condensed water that accumulates in the downstream compartment 35b between the outer peripheral surface of the catalyst case 31 and the inner peripheral surface of the outer cylindrical portion 33 can be reduced.
[0081]
(10) In the present embodiment, the catalyst case 31 of the catalytic converter 30 is a metal case, and the thickness of the catalyst case 31 is set to fall within a range of 0.3 mm or more and 0.8 mm or less.
[0082]
As described above, the entirety of the catalyst case 31 of the catalytic converter 30 is covered by the outer cylindrical portion 33, so that the space 35 between the outer peripheral surface of the catalyst case 31 and the inner peripheral surface of the outer cylindrical portion 33 is formed. It becomes to have a function as a heat insulating layer, and it becomes difficult for the heat of the catalyst case 31 to be transmitted to the outer cylinder portion 33.
[0083]
Further, since the entirety of the catalyst case 31 is covered with the outer cylindrical portion 33, the thickness of the catalyst case 31 can be reduced, and the heat capacity of the catalyst case 31 itself can be reduced. it can. If the thickness of the catalyst case 31 is set in the range of 0.3 mm or more and 0.8 mm or less, the heat capacity of the catalyst case 31 itself is reduced and the heat insulating layer is formed, so that the inside of the catalyst case 31 is formed. The heat of the inflowing exhaust gas is not easily transmitted to the catalyst case 31, and the warm-up property of the NOx storage reduction catalyst 32a can be further improved.
[0084]
When the thickness of the catalyst case 31 is less than 0.3 mm, the catalyst case 31 is rusted by the condensed water generated in the space 25 a in the inner tube 25 of the double tube portion 27 and inside the catalyst case 31. And a hole may be formed in the catalyst case 31. On the other hand, when the thickness of the catalyst case 31 is larger than 0.8 mm, since the heat capacity of the catalyst case 31 itself is not so reduced, the effect of improving the warm-up property of the NOx storage reduction catalyst 32a is reduced by half.
[0085]
The above embodiment can be appropriately modified as follows, for example.
In the above embodiment, the thickness of the catalyst case 31 of the catalytic converter 30 is not limited to 0.3 mm or more and 0.8 mm or less. The catalyst case 31 is not limited to a metal case, and may be formed of a material other than metal.
[0086]
In the above embodiment, the height H1 of the lower surface of the NOx storage reduction catalyst 32a with respect to the road surface 40, the height H2 of the lower surface of the general portion of the catalyst rear end pipe 34, and the height H3 of the lower portion of the drain hole 38 are H1. The drain hole 38, the NOx storage reduction catalyst 32a, and the catalyst rear end pipe 34 may be provided so that> H2 = H3 or H1> H3 ≧ H2. The point is that the height H1 of the lower surface of the NOx storage reduction catalyst 32a with respect to the road surface 40 is larger than the height H2 of the lower surface of the general portion of the catalyst rear end pipe 34 and the height H3 of the lower portion of the drain hole 38. Any configuration may be used as long as the drain hole 38, the NOx storage reduction catalyst 32a, and the catalyst rear end pipe 34 are provided.
[0087]
In the above embodiment, the position where the drain hole 38 of the catalyst case 31 is provided may not necessarily be the rear cone portion 31a. The drain hole 38 may be provided, for example, downstream of the NOx storage-reduction catalyst 32a in the large-diameter portion 31c (see FIG. 2) corresponding to the NOx storage-reduction catalyst 32a of the catalyst case 31.
[0088]
In the above embodiment, the example of the NOx storage reduction type catalyst 32a supporting potassium (K) is shown. However, in the present invention, a component other than the potassium (K) that can be eluted in the condensed water is supported. The present invention can be similarly applied to an exhaust system including the NOx storage reduction catalyst 32a.
[0089]
Further, the present invention can be similarly applied to an exhaust system including the NOx occlusion reduction type catalyst 32a in which components that cannot be eluted in the condensed water are carried. In this case, a configuration in which the drain hole 38 of the catalyst case 31 is omitted may be adopted.
[0090]
In the above embodiment, for example, when the opening 34b of the catalyst rear end pipe 34 is formed so as to have an inside diameter substantially the same as the inside diameter of the large diameter portion 31c of the catalyst case 31, the rear of the catalyst case 31 is used. The side cone part 31a may be omitted.
[0091]
In the above embodiment, the rear catalyst pipe 34 is connected to the outer cylinder 33 so that the axis m1 of the rear catalyst pipe 34 is positioned lower than the axis m2 of the outer cylinder 33 in the direction of gravity. Is not limited. The position at which the catalyst rear end pipe 34 is connected to the outer cylinder portion 33 is such that the height H1 of the lower surface of the NOx storage reduction catalyst 32a with respect to the road surface 40 is equal to the height H2 of the lower surface of the general portion of the catalyst rear end pipe 34 and Any value is possible within a range in which the relationship of being larger than the height H3 of the lower part of the drain hole 38 is established.
[0092]
In the above-described embodiment, the upstream end 34a of the catalyst rear end pipe 34 is provided such that its inner diameter changes in a curve in the axial direction of the catalyst rear end pipe 34. The portion 34a may be provided, for example, such that its inner diameter changes linearly in the axial direction of the catalyst rear end pipe 34.
[0093]
In the above embodiment, the catalyst rear end pipe 34 is inserted into the outer cylindrical portion 33 at the tip of the end 34 a without inserting the upstream end 34 a into the downstream compartment 35 b of the outer cylindrical portion 33. May be connected.
[0094]
In the above embodiment, for example, when the components of the NOx storage reduction catalyst 32a that are supported on the carrier cannot be eluted into the condensed water, or when the lower part of the rear cone 31a of the catalyst case 31 is directed downstream. In the case where there is a down slope, the catalyst case 31 and the catalyst rear end pipe 34 may be connected. In the latter case, the drain hole 38 may be omitted. In any of the former and latter cases, the upstream end 34a of the catalyst rear end pipe 34 may not be formed in a flare shape.
[0095]
In the above embodiment, for example, at least one of the inner pipe 25 and the outer pipe 26 is deformed at a part in the axial direction of the double pipe section 27 so that the inner pipe 25 and the outer pipe 26 come into contact with each other. Is also good. In addition, in a space 26a between the outer peripheral surface of the inner tube 25 and the inner peripheral surface of the outer tube 26 at a part in the axial direction of the double tube portion 27, an inclusion (for example, a wire mesh or the like) that comes into contact with the both surfaces. May be provided. In the case where any one of these configurations is adopted, from the viewpoint of heat insulation of the exhaust, the contact position between the inner tube 25 and the outer tube 26 in the axial direction of the double tube portion 27 and the position where the contact member is provided. Is preferably set as far upstream as possible from the resonance opening 37 of the inner tube 25.
[0096]
In the above embodiment, instead of providing the partitioning plate 36 in the space 35 of the outer cylindrical portion 33, for example, the outer cylindrical portion 33 is applied to the entire circumference of the outer circumferential surface of the large diameter portion 31c of the catalyst case 31. The space 35 inside the outer cylindrical portion 33 may be divided into an upstream compartment 35a and a downstream compartment 35b.
[0097]
In addition, for example, when the lower surface of the rear cone portion 31a of the catalyst case 31 is provided so as to have a downward slope toward the downstream, the downstream end of the outer cylindrical portion 33 is, for example, large in the catalyst case 31. The catalyst case 31 and the catalyst rear end pipe 34 may be connected to the outer peripheral surface such as the diameter portion 31c. In this case, the upstream end 34a of the catalyst rear end pipe 34 may not be formed in a flare shape, and the water drain hole 38 of the catalyst case 31 may be omitted. Good.
[0098]
In the above embodiment, the partition plate 36 in the space 35 of the outer cylinder 33 is provided so as to be slidable only on one of the inner peripheral surface of the outer cylinder 33 and the outer peripheral surface of the catalyst case 31. At the same time, the configuration may be such that the thermal expansion absorbing mechanism 28 is omitted. Even in this case, since the catalyst case 31 and the catalyst rear end pipe 34 are provided apart from each other, the high-temperature exhaust gas flows through the inside of the double pipe portion 27, so that the inner pipe 25 and the outer pipe 26 are formed. Is thermally expanded, and even if the inner pipe 25 is displaced relative to the outer pipe 26, the difference in thermal expansion can be suitably absorbed. In addition, since it is not necessary to provide a special component for absorbing the thermal expansion, an increase in the number of components of the exhaust system 20 can be suppressed.
[0099]
In the above-described embodiment, the example of the exhaust system 20 including the catalytic converter 30 accommodating the NOx storage reduction catalyst 32a has been described. However, the present invention relates to a catalytic converter accommodating, for example, a three-way catalyst or a diesel oxidation catalyst. The present invention can be similarly applied to an exhaust system including
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a configuration of a front pipe to which an embodiment of the present invention is applied and a periphery thereof.
FIG. 2 is an enlarged sectional view showing a part of the front pipe according to the embodiment;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Cylinder head, 12 ... Exhaust port, 15 ... Floor, 16 ... Underfloor space, 20 ... Exhaust system, 21 ... Exhaust manifold, 22 ... Front pipe, 23 ... Center pipe, 24 ... Flange, 25 ... Inner pipe , 25a ... space, 26 ... outer tube, 26a ... space, 27 ... double tube portion, 28 ... thermal expansion absorption mechanism, 29 ... bellows tube, 30 ... catalyst converter, 31 ... catalyst case, 31a ... rear side cone portion, 31b ... opening, 31c ... large diameter part, 32a ... NOx storage reduction type catalyst, 32b ... seal mat, 33 ... outer cylinder part, 34 ... catalyst rear end pipe, 34a ... end part, 34b ... opening, 35 ... space, 35a ... Upstream compartment, 35b Downstream compartment, 36 Partition plate, 37 Resonance opening, 38 Drain hole, 40 Road surface.

Claims (9)

A double pipe structure consisting of an inner pipe and an outer pipe is provided between the exhaust manifold of the internal combustion engine and the catalytic converter containing a catalyst that purifies exhaust gas from the engine. An exhaust pipe structure for an internal combustion engine, wherein a resonance pipe is formed between the inner pipe and the outer pipe by providing the openings. The axial position of the resonance opening in the inner pipe and the outer diameter of the inner pipe and the inner diameter of the outer pipe are the resonance frequency of the exhaust pipe, and the inner pipe in which the exhaust forms the double pipe structure. The exhaust pipe structure of an internal combustion engine according to claim 1, wherein the exhaust pipe structure is set in accordance with a vibration waveform of an air column resonance generated when flowing through the inside of the internal combustion engine. The inner tube constituting the double tube structure is connected to a catalyst case containing the catalyst in the catalytic converter, and an outer tube constituting the double tube structure extends outside the catalyst case. An outer cylinder portion is provided to cover the entire outer periphery of the catalyst case in a state separated from the outer peripheral surface of the catalyst case, and the other end of the outer cylinder portion on the side connected to the outer tube is provided. A muffler, which is a resonance chamber connected to the outer peripheral surface of the catalyst case or an exhaust pipe on the downstream side of the catalyst case and connected to the resonance pipe between the catalyst case and the outer cylinder portion, The exhaust pipe structure of an internal combustion engine according to claim 1 or 2. The outer cylinder portion covers the entirety of the catalyst case and is connected to an exhaust pipe immediately downstream of the catalyst case. Inside the outer cylinder portion, the muffler is connected to the upstream compartment and the downstream side. 4. The exhaust pipe structure for an internal combustion engine according to claim 3, wherein a partition plate for partitioning the exhaust pipe into the partition chamber is provided, and the exhaust pipe connected to the outer cylindrical portion and the catalyst case are maintained apart from each other. . The catalyst case has a cone part whose inner diameter gradually decreases toward the downstream in a downstream part thereof, and the cone part has an exhaust pipe whose opening at the downstream end is connected to the outer cylinder part. The exhaust pipe structure for an internal combustion engine according to claim 4, wherein the exhaust pipe structure is provided so as to face the upstream opening in (1). The exhaust pipe structure for an internal combustion engine according to claim 4 or 5, wherein the catalyst case is provided with a drain hole for discharging at least moisture generated inside the catalyst case into the downstream compartment. The lower surface of the exhaust pipe connected to the outer cylinder portion is provided below the lower surface of the catalyst in the catalytic converter in the direction of gravity, and the drain hole is located between the lower surface of the exhaust pipe connected to the outer cylinder portion. 7. The exhaust pipe structure for an internal combustion engine according to claim 6, further comprising: The exhaust pipe connected to the outer cylinder is connected with its upstream end inserted into the outer cylinder, and is inserted into the outer cylinder in the exhaust pipe. The exhaust pipe structure for an internal combustion engine according to claim 7, wherein the portion is formed so as to increase in diameter toward an upstream side thereof. The exhaust pipe structure for an internal combustion engine according to claim 8, wherein the exhaust pipe connected to the outer cylinder is connected such that an axis thereof is located below the axis of the outer cylinder in the direction of gravity.

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