Catalytic device

Abstract

To provide a catalyst device which enables improvement of a thermophoresis effect.SOLUTION: A catalytic device 10 has: a connection region A1 where an introduction pipe 14 and an outer pipe 30 are connected; a first double pipe region A2 where the introduction pipe 14 and the outer pipe 30 are overlapped separated from each other in a radial direction; a triple pipe region A3 where the introduction pipe 14, the inner pipe 20, and the outer pipe 30 are overlapped separated from each other in the radial direction; and a second double pipe region A4 where the inner pipe 20 and the outer pipe 30 are overlapped separated from each other in the radial direction. The connection region A1, the first double pipe region A2, the triple pipe region A3, and the second double pipe region A4 are arranged in this order from the upstream side toward the downstream side in an exhaust direction. A sealing member 17 having a heat insulating property is sandwiched between the inner pipe 20 and the outer pipe 30 in the second double pipe region A4. A passageway between the introduction pipe 14 and the inner pipe 20 in the triple pipe region A3, a passageway between the introduction pipe 14 and the outer pipe 30 in the first double pipe region A2, and a passageway between the inner pipe 20 and the outer pipe 30 in the triple pipe region A3 are in communication.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a catalytic converter. [Background technology]

[0002] Patent Document 1 describes a catalytic converter arranged in an exhaust passage of an internal combustion engine. The catalytic converter includes a catalyst that is heated by passing current through it, a case that houses the catalyst, and an introduction pipe that introduces exhaust gas from the internal combustion engine into the case.

[0003] In Patent Document 1, the case has a double-pipe structure having an inner pipe that houses a catalyst and an outer pipe that is located on the outer periphery of the inner pipe. When the direction in which exhaust flows from the inlet pipe to the catalyst is defined as the exhaust direction, the upstream end of the outer pipe in the exhaust direction is connected to the outer periphery of the inlet pipe. The downstream end of the outer pipe in the exhaust direction is connected to the outer periphery of the inner pipe.

[0004] In a catalytic converter having such a double-tube case, the inner tube is exposed to the exhaust gas, while the outer tube is exposed to both the exhaust gas and the outside air. This causes the outer tube to be cooler than the inner tube. This causes particulate matter floating between the outer circumferential surface of the inner tube and the inner circumferential surface of the outer tube to be drawn toward the inner circumferential surface of the outer tube by thermophoresis. As a result, the particulate matter is less likely to adhere to the outer circumferential surface of the inner tube. Hereinafter, particulate matter will be referred to as "PM." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2023-058325 A Summary of the Invention [Problem to be solved by the invention]

[0006] The heat of the catalyst is transferred to the inner tube and then to the outer tube at the connection between the inner tube and the outer tube, which may reduce the temperature difference between the inner tube and the outer tube and thus reduce the thermophoretic effect. [Means for solving the problem]

[0007] A catalytic device for solving the above problem includes a catalyst that is heated by passing current through it, a case having an inner pipe that houses the catalyst and an outer pipe that is positioned around the outer periphery of the inner pipe, and an introduction pipe that introduces exhaust gas discharged from an internal combustion engine into the case, wherein, assuming that a direction in which the exhaust flows from the introduction pipe toward the catalyst is an exhaust direction, an upstream end of the inner pipe in the exhaust direction is located upstream of an upstream end face of the catalyst in the exhaust direction, an upstream end of the outer pipe in the exhaust direction is located upstream of the upstream end of the inner pipe in the exhaust direction, a downstream end of the introduction pipe in the exhaust direction is inserted inside the inner pipe, and a connection region where the introduction pipe and the outer pipe are connected and a connection region where the introduction pipe and the outer pipe are connected are provided. a first double pipe region located downstream of a continuous region in the exhaust direction and in which the introduction pipe and the outer pipe overlap with a radial separation; a triple pipe region located downstream of the first double pipe region in the exhaust direction and in which the introduction pipe, the inner pipe, and the outer pipe overlap with a radial separation; and a second double pipe region located downstream of the triple pipe region in the exhaust direction and in which the inner pipe and the outer pipe overlap with a radial separation, wherein a sealing member having thermal insulation properties is sandwiched between the inner pipe and the outer pipe in the second double pipe region, and a passage between the introduction pipe and the inner pipe in the triple pipe region, a passage between the introduction pipe and the outer pipe in the first double pipe region, and a passage between the inner pipe and the outer pipe in the triple pipe region are connected. Effect of the Invention

[0008] According to the present invention, the temperature difference between the inner tube and the outer tube is increased, so that the thermophoretic effect can be increased. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing an internal combustion engine, an exhaust passage, and a catalytic converter. [Diagram 2] FIG. 2 is a cross-sectional view of the catalytic converter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, one embodiment of the catalyst device will be described with reference to Figs. FIG 1 shows an internal combustion engine 90 of a vehicle, an exhaust passage 91 connected to the internal combustion engine 90, and a catalytic converter 10 arranged in the exhaust passage 91. The internal combustion engine 90 in this embodiment is a gasoline engine. Exhaust gas discharged from the internal combustion engine 90 flows through the exhaust passage 91. The catalytic converter 10 purifies the exhaust gas. The catalytic converter 10 is an electrically heated catalytic converter in which a catalyst is heated by passing electricity through it.

[0011] <Catalyst device configuration> 2, the catalytic converter 10 includes a catalyst 11, a pair of electrodes 12 for passing electricity through the catalyst 11, a case 13 for housing the catalyst 11, and an introduction pipe 14 for introducing exhaust gas from the internal combustion engine 90 into the case 13. In the following description, the direction in which exhaust gas flows from the introduction pipe 14 toward the catalyst 11 is referred to as the exhaust direction.

[0012] The catalyst 11 of this embodiment is cylindrical. Although not shown, the catalyst 11 has a catalyst carrier and a catalyst body supported on the catalyst carrier. The catalyst carrier is a porous body. The catalyst carrier has, for example, a honeycomb structure in which a plurality of passages extending in the axial direction of the catalyst 11 are partitioned. The catalyst carrier is made of a material that becomes electrically resistant and generates heat when electricity is applied. The catalyst carrier of this embodiment is made of silicon carbide. The catalyst body of this embodiment is a three-way catalyst. The catalyst body may be an oxidation catalyst, a selective reduction catalyst, or the like.

[0013] The pair of electrodes 12 are attached to the outer peripheral surface of the catalyst 11. In this embodiment, the pair of electrodes 12 are arranged at positions shifted by 180 degrees in the circumferential direction of the catalyst 11. A pair of leads 15 extend from the pair of electrodes 12. A current flows in the catalyst 11 by applying a voltage between the pair of electrodes 12. When a current flows in the catalyst 11, the catalyst 11 generates heat due to the electrical resistance of the catalyst 11.

[0014] The case 13 has a double-pipe structure having an inner pipe 20 and an outer pipe 30 located on the outer periphery of the inner pipe 20. The inner pipe 20 and the outer pipe 30 are each made of metal. In this embodiment, the inner pipe 20 and the outer pipe 30 are each made of stainless steel. The inner pipe 20 accommodates a catalyst 11. The axial direction of the inner pipe 20 and the axial direction of the catalyst 11 are aligned.

[0015] A mat 16 is disposed between the outer peripheral surface of the catalyst 11 and the inner peripheral surface of the inner pipe 20. The mat 16 is sandwiched between the catalyst 11 and the inner pipe 20 in a compressed state. The catalyst 11 is held in the inner pipe 20 by the restoring force of the compressed mat 16. The mat 16 is made of an insulating material. Therefore, the mat 16 has insulating properties. The mat 16 of this embodiment is made of inorganic fibers containing alumina as a main component. This prevents current from flowing through the inner pipe 20 via the mat 16 when current flows through the catalyst 11.

[0016] The mat 16 of this embodiment is annular. The mat 16 is arranged over the entire circumference of the catalyst 11 and the inner pipe 20 in the circumferential direction. Two insertion holes 16a are formed in the mat 16. The two insertion holes 16a are arranged at positions shifted by 180 degrees in the circumferential direction of the mat 16.

[0017] The inner pipe 20 has a housing portion 21 located on the outer periphery of the catalyst 11, and an upstream portion 22 located upstream in the exhaust direction from the upstream end face of the catalyst 11 in the exhaust direction. Hereinafter, the upstream end face of the catalyst 11 in the exhaust direction is referred to as the "upstream end face 11a". Two insertion holes 21a are formed in the housing portion 21. The two insertion holes 21a are arranged at positions shifted by 180 degrees in the circumferential direction of the inner pipe 20. An insulating portion (not shown) is provided on the inner peripheral surface and the outer peripheral surface of the upstream portion 22 of the inner pipe 20. The insulating portion is formed by applying an insulating material to the inner peripheral surface and the outer peripheral surface of the upstream portion 22 of the inner pipe 20. The insulating material in this embodiment is glass.

[0018] The upstream portion 22 includes the upstream end portion of the inner pipe 20 in the exhaust direction. Hereinafter, the upstream end portion of the inner pipe 20 in the exhaust direction is referred to as the "upstream end portion 22a." As described above, the upstream portion 22 is a portion located upstream of the upstream end face 11a of the catalyst 11 in the exhaust direction. Therefore, the upstream end portion 22a is located upstream of the upstream end face 11a of the catalyst 11 in the exhaust direction. The upstream end portion 22a of the inner pipe 20 in this embodiment is a reduced diameter portion whose inner diameter decreases from the downstream side to the upstream side in the exhaust direction.

[0019] The outer pipe 30 overlaps with the inner pipe 20 while being radially separated from each other. The outer peripheral surface of the outer pipe 30 is exposed to the outside air. The outer pipe 30 has a storage section 31 located on the outer periphery of the catalyst 11, and an upstream portion 32 located upstream of the upstream end face 11a of the catalyst 11 in the exhaust direction.

[0020] Two insertion holes 31a are formed in the housing 31. The two insertion holes 31a are arranged at positions shifted by 180 degrees in the circumferential direction of the outer pipe 30. The upstream portion 32 includes an upstream end of the outer pipe 30 in the exhaust direction. Hereinafter, the upstream end of the outer pipe 30 in the exhaust direction is referred to as the "upstream end 32a." The upstream end 32a of the outer pipe 30 is located upstream of the upstream end 22a of the inner pipe 20 in the exhaust direction.

[0021] The upstream portion 32 of the outer pipe 30 of this embodiment is composed of a first portion 321, a second portion 322, a third portion 323, and a fourth portion 324. The first portion 321 has an inner diameter that increases from the downstream side to the upstream side in the exhaust direction. The second portion 322 is located upstream of the first portion 321 in the exhaust direction. The second portion 322 extends along the axial direction of the outer pipe 30. The third portion 323 is located upstream of the second portion 322 in the exhaust direction. The third portion 323 has an inner diameter that decreases from the downstream side to the upstream side in the exhaust direction. The third portion 323 extends parallel to the upstream end portion 22a of the inner pipe 20. The fourth portion 324 is located upstream of the third portion 323 in the exhaust direction. The fourth portion 324 extends along the radial direction of the outer pipe 30. In this embodiment, the thickness of the outer pipe 30 at the first portion 321 is the same as the thickness of the outer pipe 30 at the storage portion 31. The thickness of the outer pipe 30 at each of the second to fourth portions 322 to 324 is thicker than the thickness of the outer pipe 30 at the first portion 321.

[0022] The introduction pipe 14 is made of metal. The introduction pipe 14 of this embodiment is made of stainless steel. The downstream end of the introduction pipe 14 in the exhaust direction is inserted inside the inner pipe 20. Hereinafter, the downstream end of the introduction pipe 14 in the exhaust direction is referred to as the "downstream end 14a". The downstream end 14a of the introduction pipe 14 overlaps with the upstream end 22a of the inner pipe 20 while being radially separated from it. In this embodiment, the downstream end 14a of the introduction pipe 14 is an expanded diameter portion whose inner diameter expands from the upstream side to the downstream side in the exhaust direction. The downstream end 14a of the introduction pipe 14 extends parallel to the upstream end 22a of the inner pipe 20.

[0023] The upstream end 32a of the outer pipe 30 is joined to the outer peripheral surface of the introduction pipe 14. In this embodiment, the upstream end 32a of the outer pipe 30 is welded to the outer peripheral surface of the introduction pipe 14. As described above, the upstream end 32a of the outer pipe 30 is located upstream of the upstream end 22a of the inner pipe 20 in the exhaust direction. Therefore, the joint position between the outer pipe 30 and the introduction pipe 14 is located upstream of the upstream end 22a of the inner pipe 20 in the exhaust direction.

[0024] The catalytic converter 10 has a connection region A1, a first double pipe region A2, a triple pipe region A3, and a second double pipe region A4. The connection region A1 is a region where the inlet pipe 14 and the outer pipe 30 are connected. The first double pipe region A2 is located downstream of the connection region A1 in the exhaust direction. The first double pipe region A2 is a region where the inlet pipe 14 and the outer pipe 30 overlap with each other while being separated in the radial direction. The triple pipe region A3 is located downstream of the first double pipe region A2 in the exhaust direction. The triple pipe region A3 is a region where the inlet pipe 14, the inner pipe 20, and the outer pipe 30 overlap with each other while being separated in the radial direction. The second double pipe region A4 is located downstream of the triple pipe region A3 in the exhaust direction. The second double pipe region A4 is a region where the inner pipe 20 and the outer pipe 30 overlap with each other while being separated in the radial direction.

[0025] In the second double-pipe region A4, a sealing member 17 is sandwiched between the outer peripheral surface of the inner pipe 20 and the inner peripheral surface of the outer pipe 30. The sealing member 17 is sandwiched between the inner pipe 20 and the outer pipe 30 in a compressed state. The inner pipe 20 is held in the outer pipe 30 by the restoring force of the compressed sealing member 17. The sealing member 17 is made of an insulating material. The sealing member 17 is made of a heat-insulating material. Therefore, the sealing member 17 has insulating and heat-insulating properties. The sealing member 17 of this embodiment is made of inorganic fibers mainly composed of alumina. That is, the material of the sealing member 17 of this embodiment is the same as the material of the mat 16.

[0026] In this embodiment, the sealing member 17 is disposed downstream of the upstream end face 11a of the catalyst 11 in the second double pipe region A4 in the exhaust direction. More specifically, the sealing member 17 is sandwiched between the accommodation portion 21 of the inner pipe 20 and the accommodation portion 31 of the outer pipe 30. The passage between the accommodation portion 21 of the inner pipe 20 and the accommodation portion 31 of the outer pipe 30 is sealed by the sealing member 17. The sealing member 17 is not sandwiched between the upstream portion 22 of the inner pipe 20 and the upstream portion 32 of the outer pipe 30. The passage between the upstream portion 22 of the inner pipe 20 and the upstream portion 32 of the outer pipe 30 is not sealed by the sealing member 17.

[0027] The sealing member 17 in this embodiment is annular. The sealing member 17 is disposed over the entire circumferential circumference of the inner pipe 20 and the outer pipe 30. Two insertion holes 17a are formed in the sealing member 17. The two insertion holes 17a are disposed at positions offset from each other by 180 degrees in the circumferential direction of the sealing member 17.

[0028] The insertion hole 16a of the mat 16, the insertion hole 21a of the inner tube 20, the insertion hole 17a of the sealing member 17, and the insertion hole 31a of the outer tube 30 overlap in the radial direction. A pair of terminal holders 18 are fixed to the outer tube 30. The terminal holder 18 holds a terminal (not shown). The terminal holder 18 is cylindrical. The terminal holder 18 is welded to the outer circumferential surface of the outer tube 30 so as to surround the insertion hole 31a of the outer tube 30. The lead 15 is drawn out to the outside of the case 13 through the insertion holes 16a, 21a, 17a, and 31a. The lead 15 is away from the surface that defines the insertion hole 21a in the inner tube 20 and the surface that defines the insertion hole 31a in the outer tube 30. This prevents current from flowing through the lead 15 to the inner tube 20 and the outer tube 30. The tip of the lead 15 is welded to a terminal inside the terminal holder 18 .

[0029] No sealing member 17 is sandwiched between the inlet pipe 14 and the inner pipe 20 in the triple pipe region A3, between the inlet pipe 14 and the outer pipe 30 in the first double pipe region A2, and between the inner pipe 20 and the outer pipe 30 in the triple pipe region A3. Therefore, the passage between the inlet pipe 14 and the inner pipe 20 in the triple pipe region A3, the passage between the inlet pipe 14 and the outer pipe 30 in the first double pipe region A2, and the passage between the inner pipe 20 and the outer pipe 30 in the triple pipe region A3 are connected. The passage between the inlet pipe 14 and the inner pipe 20 in the triple pipe region A3, the passage between the inlet pipe 14 and the outer pipe 30 in the first double pipe region A2, and the passage between the inner pipe 20 and the outer pipe 30 in the triple pipe region A3 form a labyrinth structure.

[0030] As described above, in this embodiment, in the second double pipe region A4, the sealing member 17 is not sandwiched between the upstream portion 22 of the inner pipe 20 and the upstream portion 32 of the outer pipe 30. Therefore, the passage between the inner pipe 20 and the outer pipe 30 in the triple pipe region A3 communicates with the passage between the upstream portion 22 of the inner pipe 20 and the upstream portion 32 of the outer pipe 30 in the second double pipe region A4.

[0031] <Exhaust flow> The flow of exhaust gas in the catalytic converter 10 will now be described. The exhaust gas that flows into the case 13 from the inlet pipe 14 passes through the catalyst 11. At this time, part of the exhaust gas that flows into the case 13 from the inlet pipe 14 collides with the upstream end face 11a of the catalyst 11 and flows from the downstream side to the upstream side in the exhaust direction. In other words, part of the exhaust gas that flows into the case 13 collides with the upstream end face 11a of the catalyst 11 and flows back.

[0032] The backflowing exhaust gas flows into the passage between the inlet pipe 14 and the inner pipe 20 in the triple pipe region A3. The exhaust gas that has passed through the passage between the inlet pipe 14 and the inner pipe 20 in the triple pipe region A3 flows into the passage between the inlet pipe 14 and the outer pipe 30 in the first double pipe region A2. The exhaust gas that has flowed into the passage between the inlet pipe 14 and the outer pipe 30 in the first double pipe region A2 collides with the outer pipe 30, thereby changing the flow direction from the upstream side to the downstream side in the exhaust direction. A part of the exhaust gas that has changed the flow direction flows into the passage between the inner pipe 20 and the outer pipe 30 in the triple pipe region A3. In this embodiment, the exhaust gas that has passed through the passage between the inner pipe 20 and the outer pipe 30 in the triple pipe region A3 flows into the passage between the upstream part 22 of the inner pipe 20 and the upstream part 32 of the outer pipe 30 in the second double pipe region A4.

[0033] In this way, both the inner and outer circumferential surfaces of the inner pipe 20 are exposed to the exhaust gas. On the other hand, the inner circumferential surface of the outer pipe 30 is exposed to the exhaust gas, but the outer circumferential surface is exposed to the outside air. Therefore, the outer pipe 30 has a lower temperature than the inner pipe 20. As a result, PM floating between the outer circumferential surface of the inner pipe 20 and the inner circumferential surface of the outer pipe 30 is attracted to the inner circumferential surface of the outer pipe 30 by thermophoresis. As a result, PM is less likely to adhere to the outer circumferential surface of the inner pipe 20.

[0034] <Actions and Effects of the Present Embodiment> The operation and effects of this embodiment will be described. (1) Since the sealing member 17 having thermal insulation properties is sandwiched between the inner pipe 20 and the outer pipe 30, heat is not easily transferred from the inner pipe 20 to the outer pipe 30. This increases the temperature difference between the inner pipe 20 and the outer pipe 30. In addition, since the first double pipe region A2 and the triple pipe region A3 form a labyrinth structure, exhaust gas is not easily allowed to flow between the inner pipe 20 and the outer pipe 30. This also increases the temperature difference between the inner pipe 20 and the outer pipe 30. The increase in the temperature difference between the inner pipe 20 and the outer pipe 30 can increase the thermophoresis effect. Therefore, the amount of PM adhering to the outer peripheral surface of the inner pipe 20 decreases. As a result, an electrical short circuit between the catalyst 11 and the case 13 via the PM is less likely to occur, improving the insulation of the case 13.

[0035] (2) The sealing member 17 is disposed in the second double pipe region A4. This increases the space through which PM moves by thermophoresis, compared to when the sealing member 17 is also disposed between the inner pipe 20 and the outer pipe 30 in the triple pipe region A3. In addition, the amount of material for the sealing member 17 can be reduced, thereby reducing the cost of the catalytic converter 10.

[0036] (3) As a configuration for improving the insulation of the case 13, for example, it is possible to increase the area of ​​the insulating portion provided in the upstream portion 22 by lengthening the upstream portion 22 of the inner pipe 20 in the axial direction of the inner pipe 20. However, in this case, the case 13 becomes larger in the axial direction of the inner pipe 20, which reduces the mountability of the catalytic converter 10 on a vehicle.

[0037] In contrast, in this embodiment, the amount of PM adhering to the outer circumferential surface of the inner pipe 20 is reduced by increasing the thermophoresis effect, thereby improving the insulation of the case 13. In this case, it is not necessary to increase the length of the upstream portion 22 of the inner pipe 20 in the axial direction of the inner pipe 20, so the case 13 can be made smaller in size in the axial direction of the inner pipe 20. This improves the mountability of the catalytic converter 10 on a vehicle.

[0038] (4) As a configuration for increasing the temperature difference between the inner pipe 20 and the outer pipe 30, for example, it is conceivable to cool the outer pipe 30 by forming a cooling flow passage through which cooling water flows inside the outer pipe 30. However, in this case, the structure of the outer pipe 30 becomes complicated and the outer pipe 30 becomes large in the radial direction. In contrast, in this embodiment, the sealing member 17 and the labyrinth structure increase the temperature difference between the inner pipe 20 and the outer pipe 30. Therefore, it is possible to avoid the structure of the outer pipe 30 becoming complicated and the outer pipe 30 becoming large in the radial direction due to the formation of a cooling flow passage.

[0039] (5) The downstream end 14a of the introduction pipe 14 is an expanded diameter section whose inner diameter expands from the upstream side to the downstream side in the exhaust direction. As a result, exhaust gas that flows back due to collision with the catalyst 11 is more likely to collide with the downstream end 14a of the introduction pipe 14, so that the exhaust gas is less likely to flow between the introduction pipe 14 and the inner pipe 20. Therefore, the exhaust gas is less likely to flow between the inner pipe 20 and the outer pipe 30, so that the temperature difference between the inner pipe 20 and the outer pipe 30 is greater, and the thermophoresis effect is further enhanced. If the flow rate of the exhaust gas is high, the PM is more likely to be carried to the vicinity of the sealing member 17 by the flow of the exhaust gas. In this embodiment, since the downstream end 14a of the introduction pipe 14 is an expanded diameter section, the flow rate of the exhaust gas is reduced because the flow cross-sectional area at the outlet of the introduction pipe 14 is increased. Therefore, since the PM is less likely to be carried to the vicinity of the sealing member 17, it is possible to buy time for the PM to move by thermophoresis. As described above, by further increasing the thermophoretic effect and increasing the time for the PM to move by thermophoresis, adhesion of the PM to the outer circumferential surface of the inner pipe 20 can be effectively suppressed.

[0040] (6) The sealing member 17 is disposed downstream in the exhaust direction from the upstream end face 11a of the catalyst 11. This makes it possible to increase the space in which PM moves by thermophoresis, compared to a case in which the sealing member 17 is disposed upstream in the exhaust direction from the upstream end face 11a of the catalyst 11. Also, it is possible to increase the space in which an insulating portion can be formed on the outer circumferential surface of the inner pipe 20.

[0041] (7) The sealing member 17 is made of inorganic fibers mainly composed of alumina. Therefore, the sealing member 17 has heat insulating properties and electrical insulation properties. Therefore, heat is not easily transferred from the inner pipe 20 to the outer pipe 30, and the inner pipe 20 and the outer pipe 30 can be electrically insulated from each other.

[0042] (8) The material of the sealing member 17 is the same as the material of the mat 16. Therefore, the material of the mat 16 can be used for the sealing member 17 as well. (9) The upstream end 22a of the inner pipe 20 is a tapered section whose inner diameter tapers from downstream to upstream in the exhaust direction. This makes it easier for the exhaust gas that flows into the passage between the inlet pipe 14 and the inner pipe 20 in the triple pipe region A3 to collide with the upstream end 22a of the inner pipe 20, making it more difficult for the exhaust gas to flow into the passage between the inlet pipe 14 and the outer pipe 30. This makes it more difficult for the exhaust gas to flow between the inner pipe 20 and the outer pipe 30, which increases the temperature difference between the inner pipe 20 and the outer pipe 30, thereby further enhancing the thermophoresis effect.

[0043] (10) The thickness of the outer pipe 30 at each of the second to fourth portions 322-324 of the upstream portion 32 of the outer pipe 30 is greater than the thickness of the outer pipe 30 at the first portion 321 of the upstream portion 32 and the storage portion 31. This increases the heat capacity of the outer pipe 30, making it difficult for the outer pipe 30 to be heated by exhaust air. Therefore, the temperature difference between the inner pipe 20 and the outer pipe 30 becomes larger, and the thermophoresis effect can be further increased.

[0044] (11) The outer pipe 30 has the accommodation section 31 and the upstream section 32. This increases the heat capacity of the outer pipe 30 compared to when the outer pipe 30 has only the upstream section 32, making the outer pipe 30 less likely to be heated by exhaust air. This increases the temperature difference between the inner pipe 20 and the outer pipe 30, thereby further enhancing the thermophoresis effect.

[0045] <Example of change> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0046] The internal combustion engine 90 is not limited to a gasoline engine. The internal combustion engine 90 may be, for example, a diesel engine or a hydrogen engine. The catalytic converter 10 may further include a catalyst other than the catalyst 11 of the above embodiment. In other words, the catalytic converter 10 may include a plurality of catalysts including the electrically heated catalyst 11. The additional catalyst may be an exhaust purification member in which the catalyst body is not supported on a catalyst carrier, such as a filter that collects particulate matter in the exhaust gas.

[0047] The method of joining the outer pipe 30 and the introduction pipe 14 is not limited to welding. The outer pipe 30 and the introduction pipe 14 may be joined by, for example, adhesion with an adhesive or by crimping. The upstream end 22a of the inner pipe 20 does not have to be a reduced diameter portion.

[0048] The outer tube 30 does not have to have the receiving portion 31 . The shape of the upstream portion 32 of the outer pipe 30 may be changed as appropriate. The downstream end 14a of the introduction pipe 14 does not have to be an expanded diameter portion.

[0049] The sealing member 17 may also be disposed upstream of the upstream end face 11a of the catalyst 11 in the exhaust direction in the second double-pipe region A4. The material of the mat 16 is not limited to inorganic fibers mainly composed of alumina.

[0050] The material of the sealing member 17 is not limited to inorganic fibers containing alumina as the main component. The material of the sealing member 17 may be different from the material of the mat 16 . The sealing member 17 does not have to be annular. The sealing member 17 may be, for example, in a sheet shape. In this case, the sealing member 17 is wrapped around the outer circumferential surface of the inner tube 20 over the entire circumference of the inner tube 20. [Explanation of symbols]

[0051] 10...catalyst device, 11...catalyst, 11a...upstream end face, 13...case, 14...inlet pipe, 14a...downstream end, 17...sealing member, 20...inner pipe, 22a...upstream end, 30...outer pipe, 32a...upstream end, 90...internal combustion engine, A1...connection region, A2...first double pipe region, A3...triple pipe region, A4...second double pipe region

Claims

1. A catalyst that is heated by passing electricity through it; a case having an inner tube that houses the catalyst and an outer tube that is positioned around the inner tube; an introduction pipe that introduces exhaust gas discharged from an internal combustion engine into the case; A catalytic converter comprising: The direction in which the exhaust gas flows from the inlet pipe toward the catalyst is defined as an exhaust direction, an upstream end of the inner pipe in the exhaust direction is located upstream of an upstream end face of the catalyst in the exhaust direction, an upstream end of the outer pipe in the exhaust direction is located upstream of an upstream end of the inner pipe in the exhaust direction, a downstream end of the introduction pipe in the exhaust direction is inserted into the inner pipe, a connection region where the introduction pipe and the outer pipe are connected; a first double pipe region located downstream of the connection region in the exhaust direction, in which the introduction pipe and the outer pipe overlap with each other while being spaced apart from each other in the radial direction; a triple pipe region located downstream of the first double pipe region in the exhaust direction, in which the introduction pipe, the inner pipe, and the outer pipe overlap each other while being separated from each other in the radial direction; a second double pipe region located downstream of the triple pipe region in the exhaust direction, in which the inner pipe and the outer pipe overlap each other while being spaced apart from each other in the radial direction; having a sealing member having thermal insulation properties is sandwiched between the inner pipe and the outer pipe in the second double pipe region, A catalytic converter device characterized in that the passage between the inlet pipe and the inner pipe in the triple pipe region, the passage between the inlet pipe and the outer pipe in the first double pipe region, and the passage between the inner pipe and the outer pipe in the triple pipe region are connected to each other.

2. 2. The catalytic converter according to claim 1, wherein the end of the inlet pipe on the downstream side in the exhaust direction is a diameter increasing section whose inner diameter increases from the upstream side to the downstream side in the exhaust direction.

3. 2. The catalyst device according to claim 1, wherein the sealing member is disposed downstream in the exhaust direction from an upstream end face of the catalyst in the exhaust direction.

4. 2. The catalytic converter according to claim 1, wherein the sealing member is made of inorganic fibers containing alumina as a main component.

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