Catalyst device

Abstract

A catalyst device is provided. The catalyst device includes a catalyst, a heating element, and a housing. A direction in which exhaust gas flows in an exhaust passage is referred to as an exhaust direction. The housing has an end portion on an upstream side in the exhaust direction. The heating element has an end on the upstream side in the exhaust direction. The end portion of the housing is an insulating portion that protrudes more toward the upstream side in the exhaust direction than the end of the heating element and that is electrically insulated. The catalyst device further includes an outer pipe that is radially separated from the end portion of the housing in a manner covering the end portion. The outer pipe is composed of a turbine housing that houses a turbine of a supercharger.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a catalyst device provided with an electrically heated catalyst. BACKGROUND

[0002] An electrically heated catalyst that heats a catalyst by energization to a heating element is known. The catalyst is installed in a tubular housing that houses the catalyst in an electrically insulated state. In such an electrically heated catalyst, if an electrical short occurs between the catalyst and the housing due to the attachment of particulate matter contained in exhaust gas, electric power also flows to the housing. Therefore, the insulating property of the housing is required.

[0003] In order to ensure the insulating property of such a housing, in a catalyst device described in, for example, Japanese Patent Application Publication No. 2016-84776, an end portion of the housing is formed as an insulating portion.

[0004] In the catalyst device disclosed in the above-described publication, particulate matter can also accumulate in the insulating portion of the end portion of the housing. Therefore, it is required to improve the insulating property of the insulating portion of the end portion of the housing by suppressing the accumulation of particulate matter. SUMMARY

[0005] One embodiment of a catalyst device is configured to be arranged in an exhaust passage of an internal combustion engine provided with a supercharger. The catalyst device includes a catalyst configured to purify exhaust gas, a heating element configured to heat the catalyst by energization, and a housing that is a pipe housing the catalyst and the heating element. When a direction in which the exhaust gas flows in the exhaust passage is referred to as an exhaust gas direction, the housing has an end portion on an upstream side in the exhaust gas direction. The heating element has an end on the upstream side in the exhaust gas direction. The end portion of the housing is an insulating portion that protrudes further upstream in the exhaust gas direction than the end of the heating element and is electrically insulated. The catalyst device further includes an outer pipe that is radially separated from the end portion of the housing in a manner of covering the end portion. The outer pipe is constituted by a turbine housing that houses a turbine of the supercharger.

[0006] When the temperature of the outer pipe is relatively lower than the temperature of the end portion of the housing, particulate matter attached to the end portion of the housing moves to an inner peripheral surface of the outer pipe due to thermophoresis. Therefore, the accumulation of particulate matter at the insulating portion can be suppressed. When the accumulation of particulate matter at the insulating portion is suppressed, the insulating property of the insulating portion is improved.

[0007] In this regard, in the structure, such an outer pipe is constituted by a turbine housing of the supercharger. Such a turbine housing is large in heat capacity, so that, for example, at the time of cold start, the temperature rise of the turbine housing becomes slow. Therefore, it is possible to promote a state in which the temperature of the outer pipe is relatively lower than the temperature of the end portion of the housing exposed to the exhaust gas. Therefore, the insulating property of the insulating portion at the end portion of the housing is improved.

[0008] In the above-described catalyst device, it can be that the outer pipe is constituted entirely by the turbine housing.

[0009] According to this structure, the heat capacity of the outer pipe is increased compared to the case where a part of the outer pipe is constituted by the turbine housing. Therefore, it is possible to further promote a state in which the temperature of the outer pipe is relatively lower than the temperature of the end portion of the housing. Therefore, the insulating property of the insulating portion at the end portion of the housing is further improved.

[0010] In the above-described catalyst device, it can be that a diameter of a distal end of the turbine on a downstream side in the exhaust gas direction is set as an outlet diameter, a diameter of a front end portion on an upstream side in the exhaust gas direction of the end portion of the housing is set as a diameter larger than the outlet diameter, and a shortest distance between the front end portion and an inner peripheral surface of the turbine housing is set as a distance equal to or longer than a shortest distance at which insulation is possible at a maximum voltage supplied to the heat generating body.

[0011] According to this structure, the exhaust gas that has passed through the turbine is difficult to flow into the space between the outer pipe and the end portion of the housing, and most of it flows into the housing that houses the catalyst. Therefore, it is possible to suppress a decrease in the turbine efficiency of the supercharger due to the presence of such a space.

[0012] In the above-described catalyst device, it can be that the turbine housing is constituted by a casting, and the catalyst device includes the turbine housing.

[0013] According to this structure, the turbine housing is formed by a casting, so that the heat capacity of the turbine housing is increased compared to the case where the turbine housing is formed by a plate-shaped metal plate. When the heat capacity of the turbine housing is increased, the temperature of the turbine housing is difficult to rise. Therefore, it is possible to promote a state in which the temperature of the outer pipe is relatively lower than the temperature of the end portion of the housing. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a schematic view of an internal combustion engine provided with a catalyst device according to an embodiment.

[0015] Figure 2 is a cross-sectional view of the catalyst device according to the embodiment.

[0016] Figure 3 is a cross-sectional view of a catalyst device according to a modification of the embodiment. DETAILED DESCRIPTION

[0017] Hereinafter, an embodiment of the catalyst device will be described with reference to Figure 1 and Figure 2 .

[0018] <Internal combustion engine>

[0019] As shown in Figure 1 , the internal combustion engine 90 is provided with a supercharger 100 that supercharges intake air flowing in an intake passage 71 using exhaust gas flowing in an exhaust passage 91. The supercharger 100 has a turbine housing 110 that houses a turbine. Further, the catalyst device 10 is connected downstream of the turbine housing 110. The catalyst device 10 is an electrically heated catalyst device provided with a heating element that generates heat by electric conduction. Note that, in Figure 1 , the direction of exhaust gas, which is the direction of flow of exhaust gas discharged from the internal combustion engine, is indicated by an arrow.

[0020] <Configuration of catalyst device>

[0021] Figure 2 The axis C1 is shown as a straight line along the central axis of the catalyst device 10. Note that, in Figure 2 , the arrow indicating the direction of exhaust gas is also shown as in Figure 1 .

[0022] As shown in Figure 2 , the catalyst device 10 is provided with a catalyst carrier 31 that carries a catalyst for purifying exhaust gas. The catalyst device 10 is provided with a pipe, i.e., a housing 20, that houses the catalyst carrier 31. The catalyst device 10 is provided with a mat 32 that fixes the catalyst carrier 31 to the housing 20. The catalyst device 10 is provided with a pair of electrodes 81 for electrically conducting the catalyst carrier 31.

[0023] Hereinafter, the structure on the upstream side of the direction of exhaust gas will be described with respect to the catalyst device 10. The structure on the downstream side of the direction of exhaust gas can be symmetrical to the structure on the upstream side, or can be a one-layer pipe structure based on the housing 20 that houses the catalyst carrier 31.

[0024] The outer shape of the catalyst carrier 31 is a cylindrical shape with the axis C1 as the central axis. The catalyst carrier 31 is a porous body. As an example, the catalyst carrier 31 is a structure body provided with a honeycomb structure that divides a plurality of passages extending in the direction of exhaust gas.

[0025] As shown in Figure 2As shown, the electrode 81 is connected to the catalyst carrier 31. The current flows to the catalyst carrier 31 by applying a voltage between a pair of the electrodes 81. When the current flows to the catalyst carrier 31, the catalyst carrier 31 generates heat due to the electric resistance of the catalyst carrier 31. That is, the catalyst carrier 31 is a substance that generates heat according to the electric resistance when energized, and is a heating body that generates heat due to the energization. An example of the catalyst carrier 31 is a ceramic made of silicon carbide.

[0026] The mat 32 covers the surface of the catalyst carrier 31 that corresponds to the side surface of the cylinder. The mat 32 is an insulator having a small electric conductivity. An example of the mat 32 is an inorganic fiber having alumina as a main component. The catalyst carrier 31 is covered by the mat 32, whereby the electric power does not flow to the case 20 when the catalyst carrier 31 is energized.

[0027] The case 20 is a pipe formed of a metal material such as stainless steel. The axis line CI coincides with a straight line along the central axis of the case 20. The case 20 has the housing portion 21 and the end portion 22 located on the upstream side of the exhaust gas direction with respect to the housing portion 21. In the catalyst carrier 31 housed in the case 20, the end surface on the upstream side of the exhaust gas direction is referred to as the catalyst upstream end 31A. The portion on the upstream side of the case 20 with the catalyst upstream end 31A as a boundary is provided as the end portion 22, and the portion on the downstream side is provided as the housing portion 21. The distance from the axis line CI to the inner peripheral surface of the housing portion 21 is referred to as the inner diameter of the housing portion 21. The inner diameter of the housing portion 21 is constant in the direction in which the axis line CI extends. The end portion 22 of the case 20 protrudes toward the upstream side of the exhaust gas direction than the catalyst upstream end 31A. The end portion 22 of the case 20 is covered with a surface by an insulator. An insulating layer is formed on the end portion 22 by the insulator that covers the entire surface of the end portion 22. In this way, the end portion 22 of the case 20 corresponds to an insulating portion.

[0028] The electrode insertion hole 26 into which the electrode 81 is inserted is opened in the housing portion 21 of the case 20. The electrode 81 connected to the catalyst carrier 31 protrudes outside the case 20 via the electrode insertion hole 26. The electrode insertion hole 26 is occluded by the electrode holding portion 82. The electrode holding portion 82 fixes the electrode 81 inserted into the electrode insertion hole 26. The electrode holding portion 82 is an insulator having a small electric conductivity. The electrode holding portion 82 supports the electrode 81, whereby the electric power is prevented from flowing to the case 20.

[0029] The end 22 of the housing 20 includes: a constant-diameter portion 23 located upstream of the housing 20 in the exhaust direction; and a reduced-diameter portion 24 located between the constant-diameter portion 23 and the receiving portion 21, connecting the constant-diameter portion 23 and the receiving portion 21. The distance from the axis C1 to the inner circumferential surface of the constant-diameter portion 23 is defined as the inner diameter D of the constant-diameter portion 23. The inner diameter D of the constant-diameter portion 23 is constant in the direction extending from the axis C1. The inner diameter D of the constant-diameter portion 23 is smaller than the inner diameter of the receiving portion 21. In the constant-diameter portion 23, the upstream end 25 in the exhaust direction becomes an opening for exhaust gas to flow into the housing 20.

[0030] Regarding the reduced diameter portion 24 at end 22, the tube gradually tapers in such a way that the distance to the axis C1 decreases as it moves upstream in the exhaust direction. That is, the inner diameter of the inner circumferential surface 22B of the reduced diameter portion 24 decreases as it moves upstream in the exhaust direction.

[0031] The catalyst unit 10 has an outer tube 50 that covers the end 22 of the housing 20 and is radially separated from the end 22. The outer tube 50 is composed of a connecting pipe 120 and an enlarged diameter portion 114 of the turbine housing 110.

[0032] The connecting pipe 120 is formed of a metal material such as stainless steel. In the connecting pipe 120, the downstream end 122, located downstream in the exhaust direction, engages with the outer peripheral surface 22A of the reduced diameter portion 24. The inner peripheral surface 120B of the connecting pipe 120 covers the reduced diameter portion 24 of the end 22 and is radially separated from that end 22. In the connecting pipe 120, a flange 126 is provided at the upstream end in the exhaust direction.

[0033] The turbine housing 110 is formed by a casting made of a metal material such as cast iron or an aluminum alloy. The turbine housing 110 has a turbine housing portion 112 that houses the turbine 130. Also, the turbine housing 110 has a cylindrical exhaust gas outflow portion 118 through which exhaust gas that has passed through the turbine 130 flows. The central axis of this exhaust gas outflow portion 118 is the same as the axis line Cl. Also, the inner diameter of the exhaust gas outflow portion 118 is constant in the direction in which the axis line Cl extends. If the diameter of the outlet end of the turbine 130 on the downstream side in the exhaust gas direction is referred to as the outlet diameter Dt, then the inner diameter of the exhaust gas outflow portion 118 is slightly larger than the outlet diameter Dt. In the exhaust gas outflow portion 118, the opening 119 on the downstream side in the exhaust gas direction is located upstream of the front end 25 of the end portion 22. Also, the turbine housing 110 has a diameter expansion portion 114. The diameter expansion portion 114 is formed on the downstream side in the exhaust gas direction with respect to the opening 119 of the exhaust gas outflow portion 118. The inner diameter of this diameter expansion portion 114 is larger than the inner diameter of the exhaust gas outflow portion 118. Also, the inner peripheral surface 112B of the diameter expansion portion 114 covers the end portion 22 and is separated in the radial direction with respect to the end portion 22. In the diameter expansion portion 114, a flange 116 is provided on the downstream side in the exhaust gas direction. By connecting the flange 116 of the diameter expansion portion 114 and the flange 126 of the connection pipe 120, the end on the downstream side in the exhaust gas direction in the turbine housing 110 is fixed to the housing 20.

[0034] The above inner diameter D, which is the diameter of the front end 25 of the end portion 22, is set to be larger than the outlet diameter Dt of the turbine 130. Also, the shortest distance L between the front end 25 and the inner peripheral surface 112B of the turbine housing 110 is set to be a distance that is equal to or greater than the shortest distance La at which insulation is possible at the maximum voltage supplied to the catalyst carrier 31. Note that in the present embodiment, the positional relationship between the front end 25 and the inner peripheral surface 112B is set so that the shortest distance L becomes the shortest distance La at which insulation is possible.

[0035] <Effects>

[0036] The effects of the present embodiment will be described.

[0037] (1) If the temperature of the outer pipe 50 is relatively lower than the temperature of the end portion 22 of the housing 20, then the particle-like substance (hereinafter referred to as PM) that adheres to the outer peripheral surface 22A of the end portion 22 of the housing 20 moves to the inner peripheral surface of the outer pipe 50 by thermophoresis. Therefore, the accumulation of PM at the end portion 22, which is the insulating portion, can be suppressed. If the accumulation of PM at the insulating portion can be suppressed, then the insulating property of the insulating portion improves.

[0038] In this regard, in the present embodiment, a portion of such an outer pipe 50 is constituted by the turbine housing 110 of the supercharger 100. Such a turbine housing 110 has a large heat capacity, and thus, when, for example, cold start is performed, the temperature of the turbine housing 110 becomes slow to rise. Thus, a state in which the temperature of the outer pipe 50 is relatively lower than the temperature of the end portion 22 of the housing 20 exposed to exhaust gas can be promoted. Thus, the insulating property of the insulating portion at the end portion 22 of the housing 20 is improved.

[0039] (2) The above inner diameter D of the diameter of the front end 25 of the end portion 22 is set to be larger than the outlet diameter Dt of the turbine 130. Also, the shortest distance L between the front end 25 and the inner peripheral surface 112B of the turbine housing 110 is set to be the shortest distance La at which insulation is possible at the maximum voltage supplied to the catalyst carrier 31. By having such a configuration, exhaust gas that has passed through the turbine 130 is difficult to flow into the space S (refer to FIG. 1) between the outer pipe 50 and the end portion 22 of the housing 20. Thus, most of the exhaust gas that has passed through the turbine 130 flows into the housing 20. Thus, a decrease in the turbine efficiency of the supercharger 100 due to the presence of such a space S can be suppressed. Figure 2 ) Thus, most of the exhaust gas that has passed through the turbine 130 flows into the housing 20. Thus, a decrease in the turbine efficiency of the supercharger 100 due to the presence of such a space S can be suppressed.

[0040] (3) In the present embodiment, the turbine housing 110 is formed of a casting, and thus, compared to a case in which the turbine housing 110 is formed of a plate-shaped metal plate, the volume of the turbine housing 110 is increased. Thus, the heat capacity of the turbine housing 110 is increased. When the heat capacity of the turbine housing 110 is increased, the temperature of this turbine housing 110 is difficult to rise. On the other hand, the end portion 22 of the housing 20 is exposed to exhaust gas, and thus, the temperature of this end portion 22 is easy to rise. In this way, while the temperature of the end portion 22 of the housing 20 is easy to rise, the temperature of the turbine housing 110 is difficult to rise. Thus, a state in which the temperature of the outer pipe 50 is relatively lower than the temperature of the end portion 22 of the housing 20 can be promoted.

[0041] (4) The turbine housing 110 is utilized to constitute the outer pipe 50. Thus, compared to a case in which the entire outer pipe 50 is constituted by the above connection pipe 120 without utilizing the turbine housing 110, the catalyst device 10 can be suppressed from being large-sized.

[0042] <Modification Example>

[0043] The above embodiments can be modified as follows. The embodiments and the following modification examples can be implemented in combination with each other within a range in which they are not technically contradictory.

[0044] • The outer pipe 50 of the above embodiments is constituted by the connection pipe 120 and the turbine housing 110. In addition, the entire outer pipe 50 can also be constituted by the turbine housing 110.

[0045] Figure 3 One way in which this modification example is shown. As this Figure 3As shown, the catalyst device 10 of the modification example does not have the connection pipe 120 described above. Also, the downstream end 117 of the end of the expansion portion 114 of the turbine housing 110 located downstream in the exhaust direction is joined to the outer peripheral surface 22A of the reduced diameter portion 24.

[0046] According to this modification example, the heat capacity of the outer pipe 50 increases compared to the case where the outer pipe 50 is constituted by the turbine housing 110. Therefore, the state in which the temperature of the outer pipe 50 is relatively lowered than the temperature of the end portion 22 of the housing 20 is further promoted. Therefore, the insulating property of the insulating portion at the end portion 22 of the housing 20 is further improved. Note that in this modification example, the downstream end 117 can also be joined to the outer peripheral surface of the housing accommodation portion 21 of the housing 20.

[0047] • In the above-described embodiment, the downstream end 122 of the connection pipe 120 can be joined to the outer peripheral surface of the housing accommodation portion 21 of the housing 20.

[0048] • In the above-described embodiment, the housing 20 having the reduced diameter portion 24 is exemplified. The housing 20 is not limited to the structure having the reduced diameter portion. For example, the inner diameter of the end portion of the housing 20 can be constant in the direction extending along the axis of the center axis of the catalyst device.

[0049] • In the above-described embodiment, the housing 20 having the constant diameter portion 23 is exemplified. The housing 20 is not limited to the structure having the constant diameter portion. That is, as the end portion 22 of the housing 20, the constant diameter portion can be omitted, or can be tapered in such a manner that the distance to the center axis of the catalyst device is shorter as it goes further upstream in the exhaust direction.

Claims

1. A catalyst device configured to be disposed in an exhaust passage of an internal combustion engine provided with a supercharger, wherein the catalyst device is provided with: a catalyst configured to purify exhaust gas; a heating element configured to heat by electric conduction to thereby heat the catalyst; and a housing that houses the catalyst and the heating element, when a direction in which exhaust gas flows in the exhaust passage is referred to as an exhaust gas direction, the housing has an end portion on an upstream side in the exhaust gas direction, the heating element has an end on the upstream side in the exhaust gas direction, the end portion of the housing is an insulating portion that protrudes more toward the upstream side in the exhaust gas direction than the end of the heating element and is electrically insulated, the catalyst device is further provided with an outer tube that is radially separated from the end portion of the housing in a manner covering the end portion, the outer tube is entirely composed of a turbine housing that houses a turbine of the supercharger.

2. The catalyst device according to claim 1, wherein the end portion of the housing includes a front end on the upstream side in the exhaust gas direction, when a diameter of an outlet on a downstream side in the exhaust gas direction of the turbine is referred to as an outlet diameter, a diameter of the front end of the end portion is set to be larger than the outlet diameter, a shortest distance between the front end and an inner peripheral surface of the turbine housing is set to be a distance that is longer than a shortest distance at which the heating element can be insulated at a maximum voltage supplied to the heating element.

3. The catalyst device according to claim 1, wherein the turbine housing is composed of a casting, and the catalyst device includes the turbine housing.

Images