JP2012002085A - Structure of exhaust circulation pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure of an exhaust circulation pipe for preventing deposits in an exhaust pipe by improving a heat retaining property of the exhaust pipe.SOLUTION: The exhaust circulation pipe 9 which is connected to an inlet part 24 of a casing 21 in an exhaust emission control device 20, has a double pipe structure configured of an outer pipe 8 and an inner pipe 7 provided in the outer pipe 8 so as to be spaced from the outer pipe 8. The outer pipe 8 includes an outer pipe body 8A having a first flange part 8Fa at an axially intermediate part and is detachable from the casing 21, and a casing side outer pipe 8B projected from a peripheral edge 21d of the inlet part 24 and including in the casing 21 a second flange part 8Fb in a projected end 8Ba. The inner pipe 7 is bonded to the outer pipe body 8A, and has a length so that tip portions of the outer pipe body 8A and the inner pipe 7 reaches, through the insides of the casing side outer pipe 8B, a base end 8Be of the casing side outer pipe 8B when connecting both flange parts 8Fa, 8Fb.

Description

  INDUSTRIAL APPLICABILITY The present invention is suitable for use in an exhaust gas purification apparatus for an internal combustion engine, particularly an exhaust gas purification apparatus that purifies exhaust gas by mixing a reducing agent into exhaust gas flowing through an exhaust passage and supplying the reducing agent to a downstream selective reduction catalyst. This relates to the structure of the exhaust flow pipe.

  An exhaust gas from an internal combustion engine (hereinafter referred to as an engine), particularly a diesel engine, contains particulate matter such as soot that is an air pollutant (hereinafter abbreviated as PM), NOx, and the like. Therefore, a technique is known in which a particulate filter (hereinafter referred to as DPF) for collecting PM is installed in the exhaust passage of the engine so that PM is not released into the atmosphere. . Furthermore, a selective reduction catalyst (hereinafter referred to as SCR catalyst) for removing NOx is installed in the exhaust passage of the engine, and ammonia is supplied to the SCR catalyst as a reducing agent to reduce NOx in the exhaust. An exhaust gas purification device that purifies exhaust gas is used.

  In the exhaust gas purification apparatus using the SCR catalyst, by supplying urea water as a reducing agent into the exhaust gas upstream of the SCR catalyst, ammonia generated by decomposition from the urea water by exhaust heat is supplied to the SCR catalyst. The In the SCR catalyst, a catalytic metal is supported on a honeycomb structure carrier in which a plurality of minute holes parallel to each other in the axial direction are communicated. The ammonia supplied to the SCR catalyst is once adsorbed by the SCR catalyst, and NOx reduction is performed by promoting the denitration reaction between this ammonia and NOx in the exhaust gas by the SCR catalyst.

  In order to efficiently perform such PM collection and NOx reduction, a combination of a DPF and an SCR catalyst used as an exhaust purification device has been proposed in, for example, Patent Document 1. An exhaust purification device described in Patent Document 1 includes an upstream exhaust purification device having a DPF in a first casing, and a downstream exhaust having an SCR catalyst in a second casing disposed downstream of the first casing. It is comprised by the purification | cleaning apparatus, the intermediate pipe which connects a 1st casing and a 2nd casing, and the injection nozzle which injects a reducing agent.

By the way, since the SCR catalyst exhibits a catalytic function by being held at a temperature equal to or higher than the activation temperature, it is necessary to suppress the temperature of the exhaust gas flowing into the SCR catalyst from lowering than the activation temperature. In addition, since urea water injected as a reducing agent is decomposed into ammonia by the heat of the exhaust, it is necessary to suppress the temperature decrease of the exhaust also from this point.
Therefore, for example, as shown in FIG. 4, the casing 51 in which the SCR catalyst is accommodated and the intermediate pipe 49 connected to the casing 51 are each configured as a double pipe, and the inner pipes 47 b and 48 b, the inner casing 51 b, and the outer pipe A structure is known in which heat insulating air layers 47c, 48c and 51c are provided between 47a and 48a and the outer casing 51a, respectively, to reduce the heat radiation from the intermediate pipe 49 and the casing 51 (see, for example, Patent Document 2). ).

  Further, in general, the intermediate pipe 49 is considered to be assembled to the casing 51 in which the SCR catalyst is accommodated, for example, as shown in FIG. 4, the intermediate pipe body 47 and the casing side pipe 48 protruding from the casing 51 side. The intermediate pipe main body 47 and the casing side pipe 48 are connected to each other through flanges provided at respective end portions. That is, by connecting the flange portion 48 f provided at the end portion of the casing side pipe 48 welded in advance to the exhaust inlet 54 of the casing 51 and the flange portion 47 f provided at the end portion of the intermediate pipe body 47. The casing side pipe 48 and the intermediate pipe body 47 are connected.

JP 2008-274878 A JP 2009-85171 A

  By the way, as shown in FIG. 4, when the intermediate pipe main body 47 has a double tube structure, a tapered portion 47t having a diameter expanded at the tip is formed at the tip of the inner tube 47b, and the inner tube 47b is formed at the flange 47f. And the outer tube 47a are in contact with each other. Similarly, when the casing-side pipe 48 also has a double-pipe structure, a tapered portion 48t having an enlarged diameter is formed at the distal end portion of the inner tube 48b, and the inner tube 48b and the outer tube 48a are in contact with each other at the flange portion 48f. It will be in the state.

  When the intermediate pipe main body 47 and the casing side pipe 52 are connected via the flange portions 47f and 48f, the end portion of the inner tube 47b is in contact with and supported by the outer tube 47a at the connecting portion. Although the end portion is in contact with and supported by the outer tube 48a, a valley is formed by both the tapered portions 47t and 48t in the inner periphery of the connecting portion of the inner tubes 47b and 48b, and a heat insulating air layer is not formed in the valley.

  On the other hand, in the intermediate pipe 49, the exhaust gas from which the PM has been removed by the upstream side exhaust gas purification device equipped with the DPF and the urea water as the reducing agent injected into the exhaust gas are mixed and circulated. In the exhaust gas containing urea water as the reducing agent, ammonia is decomposed and generated from the urea water by exhaust heat, and this ammonia is supplied to the SCR catalyst disposed in the casing 51 to reduce NOx. Is called.

  However, in the valley formed at the connection portion between the intermediate pipe main body 47 and the casing side pipe 52, the flow of the exhaust gas is disturbed and a separation vortex is generated. Since this exhaust contains urea water as a reducing agent injected on the upstream side of the intermediate pipe main body 47, when a separation vortex is generated in the flow of the exhaust, mist-like urea captured by the separation vortex Water does not have an adiabatic air layer, and further heat dissipation of exhaust gas is promoted in a valley between connecting portions where there is a flange serving as a heat radiating plate. When the temperature of the exhaust heat decreases, a part of the urea water sprayed into the exhaust adheres to the valleys of the connection portion, and solidified urea accumulates as the water evaporates. For this reason, the amount of ammonia supplied to the SCR catalyst in the casing 51 temporarily decreases, and there is a possibility that the reduction of NOx is reduced.

  Furthermore, the urea deposited in such a low temperature state is rapidly sublimated and generates ammonia when the high temperature exhaust gas flows, and an excessive amount of ammonia is supplied to the SCR catalyst. . As a result, the post-stage oxidation catalyst that is provided on the downstream side of the SCR catalyst and removes excess ammonia cannot be treated, and ammonia may be discharged from the outlet pipe.

  The present invention has been devised in view of such problems, and an object of the present invention is to provide a structure of an exhaust circulation pipe that improves the heat retention of the exhaust pipe and can suppress the generation of deposits in the exhaust pipe. And

  In order to solve the above problems, the structure of the exhaust gas flow pipe according to the present invention is a structure of an exhaust gas flow pipe connected to the inlet portion of the casing of the exhaust gas purification apparatus, and includes an outer pipe and the outer pipe in the outer pipe. An outer tube body which is formed in a double tube structure comprising an inner tube spaced apart from the outer tube, the outer tube having a first flange portion at an axially intermediate portion and detachable from the casing And a casing-side outer pipe that protrudes from the periphery of the inlet portion and has a second flange portion that is coupled to the first flange portion at a protruding end portion. The outer tube main body and the distal end of the inner tube pass through the interior of the casing side outer tube when the two flange portions are combined. That the length is set to reach the proximal end. It is a symptom.

It is preferable that a first tapered portion having a diameter expanded at the tip is formed at the tip of the inner tube.
At this time, the rear end side portion of the outer tube main body from the first flange portion is formed to have the same diameter as the casing side outer tube, and the front end side portion of the outer tube main body from the first flange portion is It is preferable that the outer diameter of the casing side outer pipe is smaller than the inner diameter of the casing side outer pipe so as to overlap with the casing side outer pipe.

  Further, the rear end side portion of the outer tube main body from the first flange portion is formed to have the same diameter as the casing side outer tube, and the front end portion of the outer tube main body from the first flange portion is A second taper portion that is gradually spaced from the casing-side outer tube and has a reduced diameter so as to gradually approach the inner tube from the first flange portion side, and a tip that corresponds to the first taper portion of the inner tube It is preferable that a third taper portion whose diameter is increased is formed.

  It is preferable that the exhaust purification device includes a selective reduction catalyst, the exhaust circulation pipe is provided upstream of the exhaust purification device, and supplies exhaust gas mixed with a reducing agent to the selective reduction catalyst.

  According to the structure of the exhaust flow pipe of the present invention, the inner pipe is set to have a length so that the distal end of the inner pipe reaches the base end of the casing-side outer pipe, and also at the joint between the first and second flange portions. It is continuous continuously. For this reason, it is possible to eliminate the generation of a stepped surface such as a valley in the inner pipe at the flange coupling portion, and it is possible to smoothly flow the exhaust into the casing while suppressing the generation of the separation vortex. Thereby, it can suppress that the reducing agent (for example, urea water) sprayed in exhaust_gas | exhaustion adheres and accumulates inside an exhaust-gas distribution pipe.

  Further, in the flange joint portion, each flange portion becomes a heat sink and heat dissipation is promoted. However, according to the structure of the exhaust flow pipe according to the present invention, the flange joint portion also insulates between the inner tube and the outer tube main body. Since an air layer can be formed, heat dissipation can be suppressed. Furthermore, when the 1st taper part is formed in the front-end | tip part of an inner pipe, it can flow in exhaust_gas | exhaustion more smoothly in a casing, without disturbing the flow of exhaust_gas | exhaustion.

  As a result, the turbulence of the airflow is suppressed, and the heat dissipation of the exhaust heat is also suppressed. Therefore, the reducing agent (for example, urea water) sprayed in the exhaust adheres inside the inner pipe of the exhaust circulation pipe and is solid. Therefore, it is possible to further suppress the accumulation due to the conversion, and to stably supply the reducing agent to, for example, the selective reduction catalyst of the exhaust purification device in the casing. In addition, since the reducing agent does not accumulate in the inner pipe, for example, the generation of reducing agent (for example, ammonia) in an amount that cannot be processed by the downstream oxidation catalyst provided downstream of the selective catalytic reduction catalyst is suppressed. Emission to the atmosphere can be suppressed.

Further, when the downstream portion of the outer pipe body is formed so as to overlap with the casing-side outer pipe, the space between the inner pipe and the outer pipe body is also downstream of the first flange portion. Since a heat insulation air layer can be formed in this, heat insulation improves.
Moreover, when the 2nd taper part and the 3rd taper part are formed in the outer pipe | tube main body, since the inclination of piping is accept | permitted at the time of the assembly | attachment of an exhaust flow pipe, an assembly property improves.

FIG. 1A is a schematic cross-sectional view (cross-sectional view taken along the line XX in FIG. 3) showing the structure of the exhaust gas distribution pipe according to the first embodiment of the present invention, and FIG. FIG. 2A is a schematic cross-sectional view (cross-sectional view taken along the line XX in FIG. 3) showing the structure of the exhaust gas distribution pipe according to the second embodiment of the present invention, and FIG. FIG. It is a whole lineblock diagram showing the exhaust gas purification device using the exhaust circulation pipe concerning the 1st and 2nd embodiments of the present invention in the state of arrangement to vehicles. It is typical sectional drawing explaining the conventional subject.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
The structure of the exhaust gas distribution pipe according to the first embodiment of the present invention will be described with reference to FIGS. 1 and 3.
First, the exhaust gas purification apparatus according to the present embodiment will be described with reference to FIG. 3 which is an overall configuration diagram showing the exhaust gas purification apparatus using the exhaust gas distribution pipe according to the present embodiment in an arrangement state on a vehicle. The exhaust purification device of this embodiment is mounted on a truck, and FIG. 3 shows the arrangement of the internal combustion engine 1 and the exhaust purification device 2 in the state of being mounted on the truck. Show. In the following description, the front-rear direction and the left-right direction are defined mainly with respect to the vehicle.

The internal combustion engine 1 is located between the left and right side rails 30a of the ladder frame 30, and is here configured as an in-line 6-cylinder engine. Each cylinder of the internal combustion engine 1 is provided with a fuel injection valve 31. Each fuel injection valve 31 is supplied with pressurized fuel from a common rail 32, and injects fuel into the cylinder of the corresponding cylinder when the valve is opened.
An intake manifold 33 is attached to the intake side of the internal combustion engine 1, and an intake passage 34 connected to the intake manifold 33 is provided with an air cleaner 35, a compressor 36 a of a turbocharger 36, and an intercooler 37 from the upstream side. An exhaust manifold 38 is mounted on the exhaust side of the internal combustion engine 1, and a turbine 36 b of a turbocharger 36 that is coaxially connected to the compressor 36 a is connected to the exhaust manifold 38. An exhaust passage 39 is connected to the turbine 36 b, and the exhaust purification device 2 is provided in the middle of the exhaust passage 39.

  The exhaust passage 39 extends rearward on the lower side of the right side rail 30a. In a general truck, the exhaust passage 39 is extended as far as the rear part of the vehicle body, and each component of the exhaust gas purification device 2 is arranged in series in the middle of the exhaust passage 39. In the truck of this embodiment, the length of the loading platform is increased. Because of this, there is a limit to the space under and under the floor, so the exhaust passage 39 is routed to the right side for side exhaust. Due to the handling of the exhaust passage 39, the exhaust purification device 2 installed in the middle of the exhaust passage 39 is disposed outside the side rail 30a. Details will be described below.

  An upstream exhaust purification device 10 having a cylindrical casing 11 along the front-rear direction is disposed in the middle portion of the exhaust passage 39 so that the exhaust flow is directed in the longitudinal direction of the vehicle (vehicle length direction). Is connected to the lower side of the side rail 30a. A pre-stage oxidation catalyst 12 is disposed on the upstream side inside the casing 11, and a particulate for collecting particulate matter such as soot (Particulate Matter, hereinafter abbreviated as PM) contained in the exhaust gas on the downstream side. A curative filter (Diesel Particulate Filter, hereinafter abbreviated as DPF) 13 is disposed, and an exhaust outlet space 14 called a mixing chamber is formed downstream of the DPF 13.

  An intermediate pipe (exhaust gas distribution pipe) 9 is disposed in the exhaust outflow space 14 of the casing 11 so as to penetrate the casing 11 in the left-right direction. In the exhaust emission control device 2 according to the present embodiment, the upstream end of the intermediate pipe 9 is disposed so as to penetrate the casing 11, and the intermediate pipe 9 is disposed at an exposed portion (insertion portion) of the intermediate pipe 9 into the exhaust outlet space 14. A large number of holes (not shown) for communicating the inside and the outside of the exhaust gas are communicated, and the exhaust outlet space 14 and the intermediate pipe 9 communicate with each other through these holes.

  An electromagnetic nozzle 15 is fixed to the upstream end of the intermediate pipe 9 on the side wall surface of the casing 11, and the spray port 15 a of the nozzle 15 projects into the exhaust outlet space 14. The nozzle 15 is configured such that urea water as a reducing agent pumped from a tank (not shown) can be arbitrarily injected into the intermediate pipe 9. Devices such as the fuel injection valve 31 and nozzle 15 of each cylinder of the internal combustion engine 1 and sensors (not shown) are connected to an ECU (electronic control unit) 42, and devices such as the fuel injection valve 31 and the nozzle 15 are connected. Is driven and controlled by the ECU 42 based on detection information from the sensors.

  Exhaust gas that has passed through the pre-stage oxidation catalyst 12 and the DPF 13 in the upstream side exhaust purification device 10 is introduced into the intermediate pipe 9 through outlets such as these holes. The exhaust gas flowing into the intermediate pipe 9 is sprayed with urea water as a reducing agent from the nozzle 15 and mixed with the exhaust gas in the intermediate pipe 9. The downstream end of the intermediate pipe 9 is welded to the outer peripheral surface of a cylindrical cylindrical casing (casing) 21 of the downstream side exhaust purification device 20, and the exhaust gas flowing through the intermediate pipe 9 is downstream of the downstream side exhaust purification device 20. It is introduced in. The downstream side exhaust purification device 20 is disposed on the outside of the right side rail 30a, on the side of the upstream side exhaust purification device 10 with respect to the vehicle length direction so that the exhaust flow faces in the vehicle width direction. It is a T-shaped arrangement visually.

  The downstream side exhaust purification device 20 includes a selective reduction type catalyst (SCR catalyst) 22 that purifies exhaust by reducing NOx contained in the exhaust by supplying ammonia into a cylindrical casing 21 along the vehicle width direction. And a post-stage oxidation catalyst 23 for removing excess ammonia. Further, the downstream side exhaust purification device 20 is provided with an outlet pipe 29 which is a part of the exhaust passage 39, and the outlet pipe 29 is curved to the right and is opened to the side of the vehicle body.

The downstream side exhaust purification device 20 according to the present embodiment includes a selective reduction catalyst (SCR catalyst) 22 that purifies exhaust by reducing NOx contained in exhaust by supplying ammonia, and surplus ammonia in a casing 21. Two post-stage oxidation catalysts 23 are removed in series in the axial direction of the casing 21.
The two SCR catalysts 22 are spaced apart from each other, and an exhaust inlet 24 is provided in the space (first space) S1 between the SCR catalysts 22. The two SCR catalysts 22 are arranged so as to face each other with the inlet 24 interposed therebetween, and a downstream oxidation catalyst 23 is arranged on the downstream side of the SCR catalyst 22. The post-stage oxidation catalyst 23 is set so as to be spaced from each downstream side to the end face of the casing 21, and spaces (second spaces) S <b> 2 are provided at both ends of the casing 21. Each of the second spaces S2 is provided with an exhaust outlet (not shown), and the exhaust that has passed through the SCR catalyst 22 and the post-stage oxidation catalyst 23 passes from the outlet 26 to the atmosphere via the outlet pipe 29. Discharged.

Here, the structure of the intermediate pipe (exhaust gas distribution pipe) according to the present embodiment will be described with reference to FIG. Fig.1 (a) is typical sectional drawing explaining the structure of the intermediate | middle pipe concerning this embodiment, and is XX arrow sectional drawing of FIG. FIG.1 (b) is the elements on larger scale of Fig.1 (a).
As shown in FIG. 1A, the intermediate pipe 9 according to the present embodiment has a space in the casing 21 at the inlet 24 (see FIG. 3) of the casing 21 of the downstream side exhaust purification device 20 provided with the SCR catalyst 22. (First space) The first space is connected to communicate with S1. The intermediate pipe 9 is formed in a double tube structure including an outer tube 8 and an inner tube 7 provided in the outer tube 8 so as to be separated from the outer tube 8.

As shown in FIG. 1B, the outer tube 8 includes an outer tube body 8 </ b> A configured to be detachable from the casing 21, and a casing side fixed to the casing 21 so as to protrude from the peripheral edge 21 d of the inlet portion 24. It consists of an outer tube 8B.
The casing side outer pipe 8B is formed in a cylindrical shape having the same diameter in the axial direction, and protrudes from the peripheral edge 21d of the inlet portion 24 of the casing 21 so as to communicate with the first space S1 in the casing 21. In 8Ba, a flange portion (second flange portion) 8Fb is fixed to the outer periphery of the casing-side outer tube 8B by circumferential welding or the like.

  In the outer tube main body 8A, a flange portion (first flange portion) 8Fa is fixed to the outer space of the outer tube main body 8A by circumferential welding or the like at a portion (axial intermediate portion) separated from the tip portion by a predetermined distance in the axial direction. ing. The outer tube main body 8A is assembled by coupling its flange portion 8Fa to the flange portion 8Fb of the casing side outer tube 8B. Further, the outer tube main body 8A has a distal end portion 8Aa that passes through the inside of the casing side outer tube 8B when the two flange portions 8Fa and 8Fb are joined together, that is, the base end 8Be of the casing side outer tube 8B, that is, the cylindrical casing 21. It is set to a length that reaches the peripheral edge 21d of the inlet portion 24. Accordingly, the predetermined distance, which is the position where the flange portion 8Fa of the outer pipe main body 8A is disposed, corresponds to the axial length of the casing side outer pipe 8B.

  Further, the outer pipe main body 8A is formed in a cylindrical shape having the same diameter as that of the casing side outer pipe 8B up to the upstream side (upstream exhaust purification device side) portion of the first flange portion 8Fa. The portion downstream of the flange portion 8Fa (on the cylindrical casing 21 side) has a cylindrical shape having an outer diameter smaller than the inner diameter of the casing side outer tube 8B by an insertion clearance so as to be able to overlap with the casing side outer tube 8B. Is formed. A tapered portion 8t having a diameter reduced toward the downstream side is formed between the upstream portion and the downstream portion having different diameters in the inner portion of the first flange portion 8Fa of the outer tube main body 8A. ing.

On the other hand, the inner tube 7 is coupled to the outer tube main body 8A at a distance from the inner peripheral surface of the outer tube main body 8A through a plurality of bushes B disposed between the inner tube 7A and the outer tube main body 8A. Similarly to the outer tube main body 8A, the inner tube 7 also has a length that the distal end portion 7a reaches the base end 8Be of the casing side outer tube 8B through the inside of the casing side outer tube 8B when the flange portions 8Fa and 8Fb are coupled. Is set to Further, the inner tube 7, until the vicinity of the tip portion 7a is formed in a cylindrical shape having a constant inner diameter, the distal end portion 7a, a first tapered portion 7t ₁ which is enlarged toward the tip is formed, the The downstream end of the first taper is in contact with and supported by the outer tube main body 8A.

Since the intermediate pipe (exhaust gas distribution pipe) 9 according to the present embodiment is configured as described above, the exhaust gas circulates as follows.
First, the exhaust gas that has passed through the upstream oxidation catalyst 12 and the DPF 13 in the upstream side exhaust purification device 10 is introduced into the intermediate pipe 9 through an outlet such as a hole, and the exhaust gas flowing into the intermediate pipe 9 from the nozzle 15 Urea water as a reducing agent is injected (see FIG. 3). The injected urea water (reducing agent) is diffused into the exhaust gas in the intermediate pipe 9, mixed with the exhaust gas, decomposed by exhaust heat to produce ammonia (reducing agent), and the SCR in the downstream side exhaust purification device 20. By supplying ammonia as a reducing agent to the catalyst 22, NOx in the exhaust gas is reduced.

  At this time, according to the structure of the intermediate pipe 9 according to the present embodiment, the inner tube 7 is set in length so that the distal end portion 7a reaches the base end 8Be of the casing-side outer tube 8B. The joints of the second flange portions 8Fa and 8Fb are also continuous continuously. For this reason, it is possible to eliminate the generation of a stepped surface such as a valley in the inner pipe 7 in the flange coupling portion, and it is possible to smoothly flow the exhaust into the cylindrical casing 21 while suppressing the generation of the separation vortex. Furthermore, since the first tapered portion T1 is formed in the inner pipe 7 toward the inlet portion 24 of the cylindrical casing 21, the exhaust can be caused to flow into the cylindrical casing 21 more smoothly.

Further, in the flange coupling portion, each flange portion 8Fa, 8Fb becomes a heat sink and heat dissipation is promoted, but also in the flange coupling portion, a heat insulating air layer is formed between the inner tube 7 and the outer tube main body 8A. Therefore, heat radiation from the flange coupling portion can also be suppressed.
As described above, according to the structure of the intermediate pipe 9 according to the present embodiment, the turbulence of the airflow is suppressed and the heat dissipation of the exhaust heat is also suppressed. The sprayed urea water (reducing agent) adheres to the SCR catalyst which can suppress deposition due to solidification and stably arrange the reducing agent in the casing 21 of the downstream side exhaust purification device 20. Can be supplied. And since urea water does not accumulate in the inner pipe 7, it is equipped in the downstream of the SCR catalyst 22, and generation | occurrence | production of ammonia as a reducing agent of the quantity which cannot be processed with the post-stage oxidation catalyst 23 which removes surplus ammonia (reducing agent) It is possible to suppress ammonia from being discharged from the outlet pipe 29 into the atmosphere.

[Second Embodiment]
Next, the structure of the intermediate pipe (exhaust gas distribution pipe) according to the second embodiment of the present invention will be described with reference to FIG. The same members as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and redundant descriptions are omitted. Fig.2 (a) is typical sectional drawing explaining the structure of the intermediate | middle pipe concerning this embodiment, and is XX arrow sectional drawing of FIG. FIG. 2B is a partially enlarged view of FIG.

As shown in FIG. 2, the structure of the intermediate pipe 9 according to the present embodiment is configured in the same manner as that of the first embodiment except for the portion related to the outer tube main body 8A ′.
The outer tube main body 8A 'according to the present embodiment is formed in a cylindrical shape having the same diameter as the casing side outer tube 8B up to the upstream side (upstream exhaust purification device side) portion of the first flange portion 8Fa. A second taper portion 8t ₂ is formed on the downstream side (casing 21 side) portion of the first flange portion 8Fa of 8A ′ and on the upstream side of the protruding end portion 8Ba of the casing side outer tube 8B. Yes. The second taper portion 8t ₂ is formed to have a diameter reduced from the first flange portion 8Fa side so as to gradually move away from the casing side outer tube 8B and gradually approach the inner tube 7.

The downstream side of the second taper portion 8t ₂ of the outer tube main body 8A ′ is formed in a cylindrical shape having a constant inner diameter without being separated from the inner tube 7, and is coupled to the inner tube 7. The outer tube main body 8A ′ has a distal end portion 8Aa ′ coupled to a portion corresponding to the first tapered portion 7t ₁ of the inner tube 7 without being separated from the first tapered portion 7t _1, and a third diameter expanded at the distal end. A tapered portion 8t ₃ is formed, and a downstream end portion of the first tapered portion 7t ₁ of the inner tube 7 is brought into contact with a downstream end portion of the third tapered portion 8t ₃ .

  Since the intermediate pipe (exhaust gas distribution pipe) 9 according to the present embodiment is configured as described above, in addition to the effects of the structure of the intermediate pipe 9 shown in the first embodiment, the integrally formed outer pipe main body 8A. When inserting the 'and the inner pipe 7 into the casing side outer pipe 8B, the pipe can be inserted while being inclined, so that the assemblability is improved.

[Others]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  For example, in the above-described embodiment, two SCR catalysts 22 and two post-stage oxidation catalysts 23 are arranged in series in the axial direction inside the casing 21 of the downstream side exhaust purification device, and the two SCR catalysts 22 are connected to each other. The exhaust space 24 is provided in the first space S1 and an intermediate pipe is connected to the space S1. However, the present invention is not limited to this. A structure in which an SCR catalyst and a post-stage oxidation catalyst are arranged in series from one end inside the casing, an exhaust inlet is provided at one end of the casing, an exhaust outlet is provided at the other end, and an intermediate pipe is connected to the exhaust inlet It can also be.

In addition, since the inner tube only needs to be provided separately from the outer tube, the bush is not essential. For example, if the pipe length is short, the end portions of the inner tube and the outer tube may only be coupled, and a ring or the like may be interposed instead of the bush.
Further, the inner tube may not be formed first tapered portion 7t ₁ is, in this case, it is possible to form a heat insulating air layer to the periphery of the cylindrical casing, thereby improving the heat insulating properties.

  Further, in the above embodiment, the exhaust circulation pipe (intermediate pipe) 9 is provided on the upstream side of the casing 21 and the exhaust gas flows into the casing 21, so that the casing-side outer pipe 8B on the downstream side of the outer pipe main body 8A. The side inserted into the front end side is the front end side, and the upstream side of the outer tube main body 8A is the rear end side. On the other hand, the exhaust gas distribution pipe may be provided on the downstream side of the casing 21 for the outflow of exhaust gas. In this case, the configuration is the reverse of the above-described embodiment, and the upstream side of the outer pipe body is the casing side. The side inserted into the outer tube is the front end side, and the downstream side of the outer tube main body is the rear end side.

1 Internal combustion engine
2 Exhaust purification device 7 Inner pipe 7t ₁ First taper part 8 Outer pipe 8A, 8A 'Outer pipe body 8B Casing side outer pipe 8t ₂ Second taper part 8t ₃ Third taper part 9 Intermediate pipe (exhaust flow pipe)
10 Upstream exhaust purification device 12 Pre-stage oxidation catalyst 13 DPF (diesel particulate filter)
14 Exhaust outflow space 15 Nozzle 20 Downstream exhaust purification device 21 Cylindrical casing (casing)
22 SCR catalyst (selective reduction catalyst)
23 Subsequent oxidation catalyst 24 Entrance

Claims (5)

An exhaust flow pipe structure connected to the inlet of the casing of the exhaust purification device,
Formed in a double tube structure comprising an outer tube, and an inner tube provided in the outer tube at a distance from the outer tube,
The outer tube has a first flange portion at an axially intermediate portion, and an outer tube main body detachable from the casing;
A casing-side outer pipe that protrudes from the periphery of the inlet portion in the casing and has a second flange portion that is coupled to the first flange portion at a protruding end portion;
The inner pipe is provided in combination with the outer pipe main body in the outer pipe main body,
The length is set so that the outer tube main body and the distal end of the inner tube reach the base end of the casing side outer tube through the inside of the casing side outer tube when the two flange portions are joined. A feature of the exhaust flow pipe structure. The exhaust pipe structure according to claim 1, wherein a first taper portion having a diameter enlarged at the tip is formed at a tip of the inner tube. The rear end side portion of the outer pipe body from the first flange portion is formed to have the same diameter as the casing side outer pipe,
The tip side portion of the outer tube main body is formed to have an outer diameter smaller than the inner diameter of the casing side outer tube by an insertion clearance so as to overlap with the casing side outer tube. The exhaust flow pipe structure according to claim 2, wherein the exhaust flow pipe structure is provided. The rear end side portion of the outer pipe body from the first flange portion is formed to have the same diameter as the casing side outer pipe,
A second end portion of the outer tube main body that is more distal than the first flange portion is gradually separated from the casing side outer tube and gradually reduced in diameter so as to gradually approach the inner tube from the first flange portion side. 3. The structure of an exhaust gas flow pipe according to claim 2, wherein a tapered portion and a third tapered portion having a diameter expanded at the tip so as to correspond to the first tapered portion of the inner tube are formed. The exhaust purification device includes a selective reduction catalyst,
5. The exhaust gas distribution pipe according to claim 1, wherein the exhaust gas distribution pipe is provided upstream of the exhaust gas purification device, and supplies exhaust gas mixed with a reducing agent to the selective catalytic reduction catalyst. Exhaust flow pipe structure.

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