JP2006348856A - Heat insulation combined gas flow path structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To actualize highly air-tight connection between divided portions of an inner shell only by fastening divided portions of an outer shell of a filter case having a double shell structure, at their outside. <P>SOLUTION: The filter case 13 has the double shell structure consisting of the inner shell 13a and the outer shell 13b. A clearance between the shells 13a, 13b is a return flow path 16 for recirculating part of exhaust gas 9 passing through a particulate filter 12 to the intake side. The filter case 13 is divided into front and rear parts which are detachably fastened to each other via a flange 13c provided at the end of the outer shell 13b. A taper portion 21 is formed at the end of one of the inner shells 13a facing each other with the diameter gradually smaller as tending to the other side. When the flanges 13c are fastened to each other, the taper portion 21 is internally fitted to and pressed against the end of the other inner shell 13a into a taper in-low form with air tightness. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heat insulating and gas passage structure for recirculating a part of exhaust gas that has passed through a particulate filter to the intake side.

  2. Description of the Related Art Conventionally, in an automobile engine or the like, a part of exhaust gas is extracted from the exhaust side and returned to the intake side, and combustion of fuel in the engine is suppressed by the exhaust gas returned to the intake side so that the combustion temperature is increased. So-called exhaust gas recirculation (EGR) is performed in which the generation of NOx (nitrogen oxide) is reduced by lowering.

In general, when this type of exhaust gas recirculation is performed, an EGR pipe is used between an appropriate position of the exhaust passage extending from the exhaust manifold to the exhaust pipe and an appropriate position of the intake passage extending from the intake pipe to the intake manifold. The exhaust gas is connected and recirculated through the EGR pipe. In an engine equipped with a turbocharger, a high-temperature and high-pressure exhaust gas is extracted from the exhaust manifold and recirculated to the inlet of the intake manifold. A high-pressure loop EGR device (refer to Patent Document 1), which extracts a low-temperature and low-pressure exhaust gas from an exhaust pipe downstream from a turbocharger turbine and recirculates it to an intake pipe upstream from the turbocharger compressor. EGR device (refer to Patent Document 2).
JP 2004-270565 A JP 2001-82233 A

  In a high-pressure loop EGR device that extracts high-temperature and high-pressure exhaust gas from the exhaust manifold and recirculates it to the inlet of the intake manifold, a water-cooled EGR cooler is installed in the middle of the EGR pipe to cool the exhaust gas with water. Therefore, if the exhaust gas is cooled with water and recirculated in this way, the temperature of the exhaust gas is reduced and the volume of the exhaust gas is reduced, so that the combustion temperature can be effectively reduced without significantly reducing the output of the engine. Although the generation of NOx can be reduced, there has been a problem that an excessive heat load is applied to the water cooling system, which complicates the water cooling system and increases the size of the radiator and the fan.

  On the other hand, in the low-pressure loop EGR device that extracts low-temperature and low-pressure exhaust gas from the exhaust pipe downstream from the turbocharger turbine and recirculates it to the intake pipe upstream from the turbocharger compressor, the intercooler downstream from the compressor Since a part of the exhaust gas is recirculated after passing through the particulate filter near the outlet of the exhaust pipe so that the inside is not contaminated with soot or the like, a long EGR pipe is required, and the layout of the EGR pipe There was a problem that became difficult.

  Therefore, the present inventor has a double shell structure for the filter case that is interposed in the exhaust pipe and accommodates the particulate filter, and the double pipe structure for the exhaust pipe from the filter case to the turbine of the turbocharger. A return flow path for returning a part of the exhaust gas that has passed through the particulate filter to the upstream side is formed in the outer layer portion of the filter case and the exhaust pipe, and the most upstream portion near the turbine of the return flow path and the turbocharger The invention has been filed as Japanese Patent Application No. 2005-109847, in which an EGR pipe is connected between the compressor inlet and a low pressure loop is formed by the return flow path and the EGR pipe.

  That is, according to the invention of this already-filed application, a part of the exhaust gas that has passed through the particulate filter is folded back to the return flow path, flows through the filter case and the outer layer part of the exhaust pipe, and flows from the most upstream part of the return flow path. The exhaust gas is recirculated to the compressor inlet via the EGR pipe, but the exhaust gas recirculated here is originally low-temperature and low-pressure when passing through the particulate filter in the middle of the exhaust pipe, and has a large surface area. Since it is cooled by heat dissipation while flowing through the filter case exposed to the outside air and the outer layer portion of the exhaust pipe, it is further sent from here to the intercooler and cooled by air to sufficiently reduce the temperature of the exhaust gas, and the EGR cooler It is no longer necessary to cool the exhaust gas with water, etc., and the complexity of the water cooling system and the enlargement of the radiator and fan can be avoided. To become.

  Furthermore, since the exhaust gas recirculated to the compressor inlet is cleaner than the atmosphere that has been dust-removed through the particulate filter, the interior of the intercooler downstream of the compressor is contaminated by soot or the like in the exhaust gas. There is no worry, and exhaust gas is recirculated to the inlet of the compressor, which is the lowest pressure in the intake system, so that a sufficient differential pressure between the exhaust side and the intake side is ensured and exhaust gas is satisfactorily Will be recycled.

  At this time, most of the exhaust gas returned from the rear of the particulate filter to the compressor inlet is returned by the return flow path that forms the outer layer portion of the filter case and the exhaust pipe, so that it is close to the turbine of the return flow path. It is only necessary to connect a short EGR pipe between the most upstream part and the inlet of the compressor of the turbocharger, and the overall structure is compact, so that the layout of the EGR pipe is not troublesome.

  On the other hand, from the particulate filter side, the outer periphery is insulated and insulated by the exhaust gas flowing through the return flow path, making it difficult for heat to be taken away by the outside air. Since the temperature is raised, the temperature of the entire particulate filter is efficiently increased, the combustion of the collected particulates is promoted, and the reliable regeneration with little remaining particulates is performed.

  However, since the ash generated by in-cylinder combustion due to the lubricating oil gradually accumulates in the particulate filter, the particulate filter may be cleaned directly by air washing, water washing, etc. It is necessary to adopt a split structure that can be attached to and detached from the filter case so that it can be replaced with a new particulate filter, and it is difficult to apply this split structure to a filter case having a double shell structure as described above. There was a problem.

  That is, when the filter case having a double shell structure is divided and attached or detached, the outer shell (outer shell) divided portion is fastened from the outside so that the inner shell (inner shell) divided portion is also connected. However, it has been difficult to realize a highly airtight connection with respect to the inner shell that cannot perform such direct fastening.

  The present invention has been made in view of the above-described circumstances, and it is possible to realize a highly airtight connection in the inner shell divided portion only by fastening the outer shell divided portion in the double shell structure filter case from the outside. The purpose is to be.

  In the present invention, a filter case holding a particulate filter in the middle of an exhaust pipe has a double shell structure composed of an inner shell and an outer shell, and an exhaust gas passing through the particulate filter is formed between the inner shell and the outer shell. Is a heat insulating combined gas flow path structure that serves as a first return flow path for recirculating a part of the filter case to the intake side, and includes a flange that divides the filter case into front and rear portions and is provided at the end of the outer shell. And a tapered portion that gradually decreases in diameter toward the other side at one end of the inner shells facing each other, and the inner shell is fastened when the flanges are fastened together. The taper part of the shell forms a taper inlay to the end part of the other inner shell, and is configured to be hermetically fitted and press-fitted. It is intended to.

  Thus, in this case, when connecting the filter cases divided in the front and rear directions, if the flanges of the outer shells to be connected are overlapped and fastened, the taper at one end portion of the inner shells facing each other is fastened. The portion is formed into a taper inrow with respect to the end of the other inner shell and is hermetically fitted and press-contacted, and a highly airtight connection is realized with respect to the inner shell that cannot be directly fastened.

  In the present invention, the exhaust pipe upstream of the filter case has a double pipe structure consisting of an inner pipe and an outer pipe, and the gap between the inner pipe and the outer pipe is defined as the first return flow on the particulate filter side. The second return flow path communicates with the road, and the exhaust pipe is divided into front and rear parts so that they can be detachably fastened via a flange provided at the end of the outer pipe, and the inner pipes facing each other A tapered portion that gradually decreases in diameter toward the other side is formed at one end of the other, and when the flanges are fastened, the tapered portion of one inner tube forms a tapered inrow with respect to the end of the other inner tube. Thus, it is also possible to configure such that the inner fitting pressure contact is airtight.

  In this way, when connecting the exhaust pipes divided on the upstream side of the filter case, when the flanges of the outer pipes to be connected are overlapped and fastened, at one end of the inner pipes facing each other, The tapered portion forms a taper in-row with the end of the other inner tube in an airtight manner, so that a highly airtight connection is realized for the inner tube that cannot be directly fastened. .

  Further, in the present invention, the outer shell of the filter case is divided into front and rear at a position where nothing is accommodated in front of the particulate filter, and the outer diameter of the divided front shell is smaller than that of the rear outer shell. And a flange is provided radially outward at the rear end of the front outer shell, and a flange is provided radially inward at the front end of the rear outer shell. It is preferable to detachably fasten at a plurality of locations in the circumferential direction, and to be arranged so that each fastening position is drawn inward in the radial direction by narrowing the first return flow path in the radial direction at each fastening position. .

  That is, when a filter case having a double-shell structure is simply divided into front and rear parts and attached or detached, the outer shell is uniformly formed with a larger diameter than the particulate filter inside the filter case, and the divided part is outside the radial direction. Although a fastening structure that connects by fastening flanges facing each other is generally considered, in this case, the outermost diameter of the filter case becomes larger because the flange protrudes larger than the outer peripheral surface of the outer shell, According to such a configuration, the flange does not have to protrude outward from the outer peripheral surface of the rear outer shell holding the particulate filter.

  According to the above-described heat-insulating gas flow path structure of the present invention, various excellent effects as described below can be obtained.

  (I) According to the invention described in claim 1 of the present invention, there is provided a filter case having a double shell structure so as to form a first return flow path for recirculating a part of exhaust gas to the intake side. When the outer shell is divided and attached, it is possible to realize a highly airtight connection at the inner shell divided portion only by fastening the outer shell divided portion from the outside.

  (II) According to the invention described in claim 2 of the present invention, the exhaust pipe having a double-pipe structure for forming a second return flow path for recirculating a part of the exhaust gas to the intake side is provided. When attaching and detaching by dividing, it is possible to realize a highly airtight connection at the divided portion of the inner tube simply by fastening the divided portion of the outer tube from the outside.

  (III) According to the invention described in claim 3 of the present invention, the outer peripheral surface of the rear outer shell holding the particulate filter is set as the outermost diameter, and the overhang of the flange to the outside is avoided. Therefore, the outermost diameter of the filter case can be kept as small as possible, and the mountability to the vehicle can be maintained well.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 to 7 show an example of an embodiment for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a diesel engine equipped with a turbocharger 2, and intake air 4 guided from an air cleaner 3 is an intake pipe 5. And the intake air 4 pressurized by the compressor 2a is sent to the intercooler 6 to be cooled, and the intake air 4 further flows from the intercooler 6 to the intake manifold 7. It is guided and distributed to each cylinder 8 of the diesel engine 1 (the case of in-line 6 cylinders is illustrated in FIG. 1).

  Further, the exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 10, and the exhaust gas 9 that has driven the turbine 2b passes through the exhaust pipe 11. It is designed to be discharged outside the vehicle.

Further, in the middle of the exhaust pipe 11, a catalyst regeneration type particulate filter 12 integrally carrying an oxidation catalyst is provided by being held by a filter case 13. In front of the curate filter 12, when the exhaust air-fuel ratio is lean, NOx in the exhaust gas 9 is oxidized and temporarily stored in the form of nitrate, and unburned HC when the O ₂ concentration in the exhaust gas 9 decreases. A NOx occlusion reduction catalyst 14 having the property of decomposing and releasing NOx and reducing and purifying it through the intervention of CO and CO is disposed.

The exhaust pipe 11 upstream of the filter case 13 is equipped with a fuel addition device 15 (fuel addition means) for adding fuel (HC) as a reducing agent for regenerating the NOx storage reduction catalyst 14. When the O ₂ concentration in the exhaust gas 9 is reduced by the fuel addition by the fuel addition device 15, NOx is decomposed and released by the remaining added fuel to be reduced and purified.

  Further, the filter case 13 has a double shell structure comprising an inner shell 13a and an outer shell 13b, and an exhaust pipe 11 extending from the filter case 13 to the turbine 2b of the turbocharger 2 is formed from an inner pipe 11a and an outer pipe 11b. The particulate filter 12 is formed in the outer layer of the filter case 13 and the exhaust pipe 11 (between the inner shell 13a and the outer shell 13b and between the inner pipe 11a and the outer pipe 11b). Return passages 16 and 17 are formed for returning the exhaust gas 9 having passed through to the upstream side.

  As shown in FIG. 2, the filter case 13 is divided into front and rear at a position where nothing is accommodated on the front side of the particulate filter 12, and the divided outer shell 13b is larger in outer diameter than the rear outer shell 13b. The flange 13c is provided radially outward at the rear end of the front outer shell 13b, and the flange 13c is provided radially inward at the front end of the rear outer shell 13b. Are bolted so as to be detachable at a plurality of locations in the circumferential direction.

  Here, as shown in FIGS. 3 to 5, the flange 13c of the front outer shell 13b is formed to have a long radial dimension so as to narrow the return flow path 16 radially inward at each fastening position. The portion corresponding to each fastening position at the rear end of the outer shell 13b of the outer shell 13b has a shape recessed inward in the radial direction (see particularly FIG. 4), and the flange 13c of the rear outer shell 13b is also fastened to each fastening position. The radial dimension is long so that the return flow path 16 is narrowed radially inward at the position, and each fastening position is arranged to be drawn inward in the radial direction.

  When the flanges 13c of the front and rear outer shells 13b are fastened together, the front end portion folded back radially outward of the rear inner shell 13a, the gasket 13d, and the outer peripheral portion of the separator 20 are sandwiched together. A taper portion 21 that gradually decreases in diameter toward the front side is formed in the vicinity of the outer peripheral portion of the separator 20, and the taper portion 21 is formed between the flanges 13 c. At the time of fastening, a taper inlay is formed with respect to the rear side end portion of the front inner shell 13a so as to make an airtight inner pressure contact.

  In the example shown here, the separator 20 provided with the taper portion 21 in the vicinity of the outer peripheral portion is integrated by fastening together with the front end portion of the rear inner shell 13a, and this rear inner portion is integrated. A tapered portion 21 facing the rear end of the front inner shell 13a is formed separately from the front end of the shell 13a. However, the rear outer shell 13b is a front side of the rear inner shell 13a. If the structural change is made so that the vicinity of the end portion can be supported via a flange 13c (a part where the return flow path 16 is secured), the front end portion itself of the rear inner shell 13a is It is also possible to integrally mold as a tapered portion similar to the tapered portion 21.

  Further, the inner pipe 11a of the exhaust pipe 11 having a double pipe structure extends to a position where it abuts against the front surface of the separator 20, and the NOx occlusion reduction catalyst 14 passes through the air diffusion holes 11e at the tip and the air diffusion holes 20a of the separator 20. On the other hand, the outer pipe 11b of the exhaust pipe 11 is welded to the outer peripheral surface of the inner pipe 11a when the outer pipe 11b of the exhaust pipe 11 penetrates the front end of the inner shell 13a. The return flow path 16 on the filter case 13 side and the return flow path 17 on the exhaust pipe 11 side communicate with each other through a communication hole 11f at the tip of the outer pipe 11b.

  Further, in the present embodiment, the exhaust pipe 11 can also be divided at the entrance side of the filter case 13, and as shown in an enlarged view in FIG. 6, the divided portions of the outer pipe 11 b are at the respective end portions. The flange 11c provided is detachably bolted with the gasket 11d interposed therebetween, while a tapered portion 22 that gradually decreases in diameter toward the rear side is formed at the rear end portion of the front inner tube 11a. When the flanges 11c are fastened to each other, the tapered portion 22 of the front inner tube 11a forms a tapered inlay with the front end portion of the rear inner tube 11a so as to be intimately press-fitted.

  Further, as shown in FIG. 1, the most upstream portion of the return flow path 17 near the turbine 2b and the inlet of the compressor 2a of the turbocharger 2 are connected by a relatively short EGR pipe 18, and the EGR The pipe 18 is equipped with an EGR valve 19 for adjusting the recirculation amount of the exhaust gas 9.

  Here, the connection between the most upstream portion of the return flow path 17 and the EGR pipe 18 is, as shown in an enlarged view in FIG. 7, an opening provided in the outer pipe 11b with a flange 18a provided at the end of the EGR pipe 18. This is done by bolting the seat 11h around the portion 11g via a gasket 11i, and the end of the inner tube 11a is welded to the end of the outer tube 11b to form a bag path. It has become.

  Further, in the example shown in FIGS. 1 and 2, a silencer chamber 23 is formed at the rear stage of the particulate filter 12 in the filter case 13, and as shown in an enlarged view in FIG. 5, a rear portion of the inner shell 13a. A part of the exhaust gas 9 is taken into the return flow path 16 from the communication hole 13 e between the sound deadening chamber 23 and the particulate filter 12.

  Here, the sound deadening chamber 23 is once squeezed and taken in the exhaust gas 9 through the connecting pipe 23b penetrating the separator 23a, then expanded in the chamber and guided to the tail pipe 23c, so that the sound of the exhaust gas 9 is obtained. Energy is attenuated, and pressure loss is increased in the muffler chamber 23, so that smooth return of the exhaust gas 9 to the return flow path 16 is promoted.

  In the figure, 24 is an exhaust brake, 24a is a gasket, 25 is a cushioning material for protecting the outer periphery of the NOx storage reduction catalyst 14 and the particulate filter 12, and 26 is an axis of the NOx storage reduction catalyst 14 and the particulate filter 12. The end plate which restrains the movement of a direction is shown.

  Thus, in the case where the low-pressure loop is configured as described above, the fuel addition by the fuel addition device 15 is stopped and the EGR valve is stopped during the low and medium load operation in which the exhaust temperature decreases and the activity of the NOx storage reduction catalyst 14 decreases. When the EGR pipe 18 is opened by holding 19 in an open state, a part of the exhaust gas 9 that has passed through the particulate filter 12 is folded back to the return flow path 16 from the communication hole 13e behind the inner shell 13a. 13 and the outer layer portion of the exhaust pipe 11, and is recirculated from the most upstream portion of the return flow path 17 to the inlet of the compressor 2 a via the EGR pipe 18.

  At this time, the exhaust gas 9 recirculated to the inlet of the compressor 2a is at a low temperature and low pressure when it passes through the particulate filter 12 in the middle of the exhaust pipe 11, and is exposed to the outside air with a large surface area. And since it is cooled by heat dissipation while flowing through the outer layer portion of the exhaust pipe 11, the temperature of the exhaust gas 9 is sufficiently lowered by being sent to the intercooler 6 and air-cooled from here, using an EGR cooler or the like. It is not necessary to cool the exhaust gas 9 with water, and the complexity of the water cooling system and the enlargement of the radiator and the fan are avoided.

  Further, since the exhaust gas 9 recirculated to the inlet of the compressor 2a is cleaner than the atmosphere that is dust-removed through the particulate filter 12, the intercooler downstream of the compressor 2a due to soot or the like in the exhaust gas 9 6 and the exhaust gas 9 is recirculated to the inlet of the compressor 2a having the lowest pressure in the intake system, so that the differential pressure between the exhaust side and the intake side is sufficient. Therefore, a large amount of exhaust gas 9 is recirculated.

  Further, since the exhaust gas 9 returned from the rear of the particulate filter 12 to the inlet of the compressor 2a is returned by the return flow passages 16 and 17 constituting the outer layer portion of the filter case 13 and the exhaust pipe 11, It is only necessary to connect the most upstream portion of the return flow passages 16 and 17 near the turbine 2b and the inlet of the compressor 2a of the turbocharger 2 with a short EGR pipe 18, so that the overall structure becomes compact and the EGR pipe 18 You will not have to worry about the layout.

  On the other hand, when viewed from the particulate filter 12 side, the outer peripheral portion is insulated and insulated by the exhaust gas 9 flowing through the return flow path 16 so that it is difficult for heat to be taken away by the outside air. Since the temperature of the difficult outer peripheral portion is increased, the entire particulate filter 12 is efficiently heated to promote the combustion of the collected particulates, and the reliable regeneration with little remaining particulates is performed. Become.

  During high load operation where the pressure difference from the exhaust side is difficult to secure because the intake side is supercharged, the EGR valve 19 is closed to stop the recirculation of the exhaust gas 9, while the fuel added by the fuel addition device 15 Addition is executed, and NOx reduction can be effectively achieved by the NOx occlusion reduction catalyst 14 whose activity has increased at a high exhaust temperature during high load operation.

  In this embodiment, when the filter case 13 having a double shell structure composed of the inner shell 13a and the outer shell 13b is divided and detached, the flanges 13c of the outer shells 13b to be connected to each other are overlapped with each other. When fastened, the taper portion 21 formed separately from the front end portion of the rear inner shell 13a forms a taper inrow with respect to the rear end portion of the front inner shell 13a and is intimately press-fitted. Thus, a highly airtight connection is realized with respect to the inner shell 13a that cannot be directly engaged.

  Further, when connecting the exhaust pipe 11 divided on the upstream side of the filter case 13, when the flanges 11c of the outer pipes 11b to be connected are overlapped and fastened, the rear end portion of the front inner pipe 11a is connected. The taper portion 22 of the inner pipe 11a forms a taper in-row with the end portion of the inner tube 11a on the rear side and is hermetically fitted and press-contacted, thereby realizing a highly airtight connection with respect to the inner tube 11a that cannot be directly fastened. Will be.

  Therefore, according to the above-described embodiment, when the filter case 13 having a double shell structure is formed and detached to form the return flow path 16 for recirculating a part of the exhaust gas 9 to the intake side, the outer shell is removed. A return flow path for recirculating a part of the exhaust gas 9 to the intake side can be realized by fastening the divided portion 13b from the outside to achieve a highly airtight connection in the divided portion of the inner shell 13a. Even when the exhaust pipe 11 having a double-pipe structure is divided and attached to form 17, a highly airtight connection in the divided part of the inner pipe 11 a is realized simply by fastening the divided part of the outer pipe 11 b from the outside. can do.

  Further, when the filter case 13 having a double shell structure is simply divided into front and rear parts and attached or detached, the outer shell 13b is uniformly formed with a larger diameter than the particulate filter 12 inside the filter case 13 and the divided part. Is generally considered to be connected by fastening the flanges 13c outward in the radial direction. In this case, the flange 13c protrudes larger than the outer peripheral surface of the outer shell 13b, and the outermost diameter of the filter case 13 is increased. On the other hand, if the outer shell 13b fastening structure as described in the present embodiment is adopted, the outer peripheral surface of the rear outer shell 13b holding the particulate filter 12 is the outermost diameter. Since it is possible to avoid overhanging the flange 13c to the outside, the filter case can be It is possible to maintain good mountability to the vehicle diameter enjoyed minimized.

  It should be noted that the heat insulating and gas passage structure of the present invention is not limited to the above-described embodiments, and it is needless to say that various modifications can be made without departing from the scope of the present invention.

It is the schematic which shows an example of the form which implements this invention. It is sectional drawing which expands and shows the principal part of FIG. It is sectional drawing of the III-III arrow of FIG. It is sectional drawing of the IV-IV arrow of FIG. It is sectional drawing of the VV arrow of FIG. It is sectional drawing which expands and shows the structure of the division | segmentation part of an exhaust pipe. It is sectional drawing which shows the connection structure of a 2nd return flow path and an EGR pipe.

Explanation of symbols

9 exhaust gas 11 exhaust pipe 11a inner pipe 11b outer pipe 11c flange 12 particulate filter 13 filter case 13a inner shell 13b outer shell 13c flange 14 NOx occlusion reduction catalyst 16 first return flow path 17 second return flow path 18 EGR pipe 21 Tapered part 22 Tapered part

Claims (3)

  The filter case holding the particulate filter in the middle of the exhaust pipe has a double shell structure consisting of an inner shell and an outer shell, and the gap between the inner shell and outer shell is part of the exhaust gas that has passed through the particulate filter. A heat insulating and gas flow path structure that serves as a first return flow path for recirculation to the intake side. The filter case is divided into front and rear parts, and is detachable via a flange provided at the end of the outer shell. A tapered portion that is configured to be fastened and that gradually decreases in diameter toward the other side at either end of the inner shells facing each other, and the tapered portion of one inner shell when the flanges are fastened together Is configured to be intimately press-fitted in a hermetic manner by forming a tapered inrow against the end of the other inner shell. Use gas channel structure.   The exhaust pipe upstream of the filter case has a double pipe structure consisting of an inner pipe and an outer pipe, and a gap between the inner pipe and the outer pipe is communicated with the first return flow path on the particulate filter side. A return flow path is constructed so that the exhaust pipe is divided into front and rear parts and can be detachably fastened through a flange provided at the end of the outer pipe, and either one of the inner pipes facing each other A taper part that gradually decreases in diameter toward the other side is formed in the part, and when the flanges are fastened together, the taper part of one inner pipe forms a taper inlay with the end part of the other inner pipe, and the inner fitting pressure contact is airtight The heat insulation combined use gas channel structure according to claim 1 constituted so that it may do.   The outer shell of the filter case is divided forward and backward at a position where nothing is accommodated on the front side of the particulate filter, and the divided outer shell is configured to have an outer diameter smaller than that of the rear outer shell. A flange is provided radially outward at the rear end of the outer shell, and a flange is provided radially inward at the front end of the rear outer shell. The flanges of both outer shells can be attached and detached at multiple locations in the circumferential direction. The first return flow path is narrowed in the radial direction at each fastening position, and the fastening positions are arranged so as to be drawn inward in the radial direction. A heat-insulating gas flow path structure as described in 1.

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