Catalytic converter

Abstract

To improve insulation performance of an insulating portion in an electric heating-type catalyst device.SOLUTION: A catalyst device 10 includes a case 20 for housing a catalyst carrier 31 as a heating element generating heat by electrification. An end portion 22 of the case 20 is an insulating portion projecting to an upstream side in an exhausting direction with respect to an end face of the catalyst carrier 31. The catalyst device 10 has an outer pipe 50 radially separating from the end portion 22 in a manner of covering the end portion 22 of the case 20. The outer pipe 50 is constituted by a turbine housing 110 for housing a turbine wheel 130 of a supercharger.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a catalytic device having an electrically heated catalyst. [Background technology]

[0002] Electrically heated catalysts are known, in which the catalyst is heated by passing electricity through a heating element. The catalyst is attached in an electrically insulated state to the tubular case that houses the catalyst. In such electrically heated catalysts, if particulate matter contained in the exhaust adheres to the catalyst and causes an electrical short circuit between the catalyst and the case, electricity will also flow through the case. For this reason, the case must be insulating.

[0003] In order to ensure the insulation of the case, for example, the catalytic converter described in Patent Document 1 has insulating portions at the ends of the case. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-84776 A Summary of the Invention [Problem to be solved by the invention]

[0005] Even in a catalytic converter such as that disclosed in Patent Document 1, there is a risk that particulate matter may accumulate in the insulating portion of the case end. Therefore, there is a demand for improving the insulation of the insulating portion of the case end by suppressing the accumulation of particulate matter. [Means for solving the problem]

[0006] A catalytic device for solving the above problem is a catalytic device that is disposed in an exhaust passage of an internal combustion engine equipped with a turbocharger, the catalytic device having a catalyst for purifying exhaust gas, a heating element that generates heat by energizing to heat the catalyst, and a case that is a tube that houses the catalyst and the heating element. The direction in which exhaust gas flows through the exhaust passage is defined as the exhaust direction, and an end of the case on the upstream side of the exhaust direction protrudes upstream in the exhaust direction further than an end of the heating element on the upstream side of the exhaust direction, and is an insulating part that provides electrical insulation. The catalytic device also has an outer tube that covers the end of the case and is radially separated from the end. The outer tube is configured as a turbine housing that houses a turbine wheel of the turbocharger.

[0007] When the temperature of the outer tube becomes lower than the temperature of the end of the case, the particulate matter adhering to the end of the case moves to the inner peripheral surface of the outer tube by thermophoresis, and the accumulation of the particulate matter in the insulating portion is suppressed. When the accumulation of the particulate matter in the insulating portion is suppressed, the insulating property of the insulating portion is improved.

[0008] In this configuration, the outer tube is configured as a turbine housing of a turbocharger. Since the turbine housing has a large heat capacity, the temperature rise is gradual, for example, during a cold start. Therefore, the temperature of the outer tube is promoted to be relatively low compared to the temperature of the end of the case exposed to the exhaust gas. Therefore, the insulation of the insulating part at the end of the case is improved.

[0009] In the above catalytic converter, the outer pipe may entirely comprise the turbine housing. According to this configuration, the heat capacity of the outer tube is larger than when a part of the outer tube is formed by the turbine housing, which further promotes a state in which the temperature of the outer tube is relatively lower than the temperature of the end of the case, thereby further improving the insulation of the insulating part at the end of the case.

[0010] In the above-mentioned catalytic device, the diameter of the end of the turbine wheel on the downstream side in the exhaust direction is set to be an outlet diameter, and the diameter of the tip of the upstream side of the end of the case in the exhaust direction is set to a diameter larger than the outlet diameter, and the shortest distance between the tip and the inner surface of the turbine housing may be set to a distance greater than the shortest distance capable of insulation at the maximum voltage supplied to the heating element.

[0011] With this configuration, the exhaust gas that has passed through the turbine wheel is less likely to flow into the space between the outer pipe and the end of the case, and most of the exhaust gas flows into the case that houses the catalyst. This makes it possible to suppress the decrease in turbine efficiency of the turbocharger that would be caused by the presence of such a space.

[0012] The above catalytic converter may have the turbine housing formed by casting. According to this configuration, since the turbine housing is made of a casting, the thermal capacity of the turbine housing is increased compared to a case where the turbine housing is made of a plate-shaped metal plate. When the thermal capacity of the turbine housing is increased, the temperature of the turbine housing is less likely to increase. Therefore, it is possible to promote a state in which the temperature of the outer tube is relatively low compared to the temperature of the end of the case. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic diagram showing an internal combustion engine equipped with an embodiment of a catalytic device; [Diagram 2] FIG. 2 is a cross-sectional view of the catalytic converter according to the embodiment. [Diagram 3] FIG. 4 is a cross-sectional view of a catalytic converter according to a modified example of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, one embodiment of the catalyst device will be described with reference to FIGS. <About internal combustion engines> As shown in Fig. 1, an internal combustion engine 90 includes a turbocharger 100 that uses exhaust gas flowing through an exhaust passage 91 to supercharge the intake air flowing through an intake passage 71. The turbocharger 100 includes a turbine housing 110 that houses a turbine wheel. A catalytic device 10 is connected downstream of the turbine housing 110. The catalytic device 10 is an electrically heated catalytic device that includes a heating element that generates heat when electricity is applied. Note that in Fig. 1, an arrow indicates the exhaust direction as the flow direction of the exhaust gas discharged from the internal combustion engine.

[0015] <Structure of catalytic converter> In Fig. 2, an axis C1 is shown as a straight line extending along the central axis of the catalytic converter 10. Note that, like Fig. 1, an arrow indicating the exhaust direction is also shown in Fig. 2.

[0016] As shown in Fig. 2, the catalytic device 10 includes a catalyst carrier 31 that supports a catalyst for purifying exhaust gas. The catalytic device 10 includes a case 20 that is a tube that houses the catalyst carrier 31. The catalytic device 10 includes a mat 32 that fixes the catalyst carrier 31 to the housing portion 21 in the case 20. The catalytic device 10 includes a pair of electrodes 81 for passing electricity through the catalyst carrier 31.

[0017] The following describes the configuration of the upstream side in the exhaust direction of the catalytic converter 10. The configuration of the downstream side in the exhaust direction may be symmetrical to the configuration of the upstream side, or may be a single-tube structure with a case 20 that houses the catalyst carrier 31.

[0018] The catalyst carrier 31 has an outer shape of a cylinder 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 having a honeycomb structure in which a plurality of passages extending in the exhaust direction are defined.

[0019] As shown in Fig. 2, electrodes 81 are connected to the catalyst carrier 31. A current flows through the catalyst carrier 31 by applying a voltage between the pair of electrodes 81. When a current flows through the catalyst carrier 31, the catalyst carrier 31 generates heat due to the electrical resistance of the catalyst carrier 31. In other words, the catalyst carrier 31 is a material that generates heat according to the electrical resistance when electricity is passed through it, and is a heating element that generates heat when electricity is passed through it. One example of the catalyst carrier 31 is ceramics made of silicon carbide.

[0020] 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 with low electrical conductivity. An example of the mat 32 is inorganic fiber containing alumina as a main component. Since the catalyst carrier 31 is covered with the mat 32, electricity is prevented from flowing through the case 20 when electricity is applied to the catalyst carrier 31.

[0021] The case 20 is a tube made of a metal material such as stainless steel. The axis C1 coincides with a straight line along the central axis of the case 20. The case 20 includes a housing section 21 and an end section 22 located upstream of the housing section 21 in the exhaust direction. The upstream end surface of the catalyst carrier 31 housed in the case 20 in the exhaust direction is called the catalyst upstream end 31A. The upstream portion of the case 20, which is bounded by the catalyst upstream end 31A, is called the end section 22, and the downstream portion is called the housing section 21. The distance from the axis C1 to the inner peripheral surface of the housing section 21 is called the inner diameter of the housing section 21. The inner diameter of the housing section 21 is constant in the direction in which the axis C1 extends. The end section 22 of the case 20 protrudes upstream of the catalyst upstream end 31A in the exhaust direction. The surface of the end section 22 of the case 20 is covered with an insulator. An insulating layer is formed on the end section 22 by the insulator that covers the entire surface of the end section 22. In this manner, the end 22 of the case 20 is an insulating portion.

[0022] An electrode insertion hole 26 into which an electrode 81 is inserted is opened in the accommodation portion 21 of the case 20. The electrode 81 connected to the catalyst carrier 31 protrudes to the outside of the case 20 via the electrode insertion hole 26. The electrode insertion hole 26 is closed by an electrode holding portion 82. The electrode holding portion 82 fixes the electrode 81 inserted in the electrode insertion hole 26. The electrode holding portion 82 is an insulator with low electrical conductivity. The electrode holding portion 82 supports the electrode 81, thereby preventing electricity from flowing through the case 20.

[0023] The end 22 of the case 20 includes a constant diameter portion 23 located at the end of the case 20 on the upstream side in the exhaust direction, and a reduced diameter portion 24 located between the constant diameter portion 23 and the storage portion 21 and connecting the constant diameter portion 23 and the storage portion 21. The distance from the axis C1 to the inner peripheral 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 in which the axis C1 extends. The inner diameter D of the constant diameter portion 23 is smaller than the inner diameter of the storage portion 21. A tip portion 25 on the upstream side in the exhaust direction of the constant diameter portion 23 is an opening through which exhaust air flows into the case 20.

[0024] The reduced diameter section 24 of the end 22 is gradually tapered so that the distance to the axis C1 becomes shorter the further upstream in the exhaust direction. That is, the inner diameter of the inner circumferential surface 22B of the reduced diameter section 24 is smaller the further upstream in the exhaust direction.

[0025] The catalytic converter 10 has an outer pipe 50 that is radially spaced from the end 22 of the case 20 and covers the end 22. The outer pipe 50 is composed of a connecting pipe 120 and an expanded diameter portion 114 of the turbine housing 110.

[0026] The connecting pipe 120 is made of a metal material such as stainless steel. A downstream end 122 located at the end of the connecting pipe 120 on the downstream side in the exhaust direction is joined to an outer peripheral surface 22A of the reduced diameter portion 24. An inner peripheral surface 120B of the connecting pipe 120 is separated from the end 22 in the radial direction so as to cover the reduced diameter portion 24 of the end 22. A flange 126 is provided at the end of the connecting pipe 120 on the upstream side in the exhaust direction.

[0027] The turbine housing 110 is formed of a casting made of a metal material such as cast iron or an aluminum alloy. The turbine housing 110 has a wheel storage section 112 that stores the turbine wheel 130. The turbine housing 110 also has a cylindrical exhaust outlet section 118 through which the exhaust that has passed through the turbine wheel 130 flows. The central axis of the exhaust outlet section 118 is the same as the axis C1. The inner diameter of the exhaust outlet section 118 is constant in the direction in which the axis C1 extends. If the diameter of the end of the turbine wheel 130 on the downstream side in the exhaust direction is the outlet diameter Dt, the inner diameter of the exhaust outlet section 118 is slightly larger than the outlet diameter Dt. An opening 119 on the downstream side in the exhaust direction of the exhaust outlet section 118 is located upstream in the exhaust direction from the tip 25 of the end section 22. The turbine housing 110 also has an expanded diameter section 114. The expanded diameter section 114 is formed downstream in the exhaust direction with respect to the opening 119 of the exhaust outlet section 118. The inner diameter of this expanded diameter portion 114 is larger than the inner diameter of the exhaust outflow portion 118. The inner circumferential surface 112B of the expanded diameter portion 114 is radially separated from the end portion 22 so as to cover the end portion 22. A flange 116 is provided at the downstream end of the expanded diameter portion 114 in the exhaust direction. The flange 116 of the expanded diameter portion 114 and a flange 126 of the connecting pipe 120 are connected, so that the downstream end of the turbine housing 110 in the exhaust direction is fixed to the case 20.

[0028] The inner diameter D, which is the diameter of the tip portion 25 of the end portion 22, is set to be larger than the outlet diameter Dt of the turbine wheel 130. In addition, the shortest distance L between the tip portion 25 and the inner circumferential surface 112B of the turbine housing 110 is set to be equal to or greater than the shortest distance Lα at which insulation is possible at the maximum voltage supplied to the catalyst carrier 31. In this embodiment, the positional relationship between the tip portion 25 and the inner circumferential surface 112B is set so that the shortest distance L becomes the shortest distance Lα at which insulation is possible.

[0029] <Action and Effects> The operation and effects of this embodiment will be described. (1) When the temperature of the outer tube 50 becomes relatively low compared to the temperature of the end 22 of the case 20, particulate matter (hereinafter referred to as PM) attached to the outer peripheral surface 22A of the end 22 of the case 20 moves to the inner peripheral surface of the outer tube 50 by thermophoresis. This suppresses the accumulation of PM at the end 22, which is an insulating part. When the accumulation of PM at the insulating part is suppressed, the insulating property of the insulating part is improved.

[0030] In this regard, in this embodiment, a part of the outer pipe 50 is configured as the turbine housing 110 of the turbocharger 100. Since the turbine housing 110 has a large heat capacity, the temperature rise is gradual, for example, during a cold start. Therefore, the temperature of the outer pipe 50 is promoted to be relatively lower than the temperature of the end 22 of the case 20 exposed to the exhaust gas. Therefore, the insulation of the insulating part at the end 22 of the case 20 is improved.

[0031] (2) The inner diameter D, which is the diameter of the tip 25 of the end 22, is larger than the outlet diameter Dt of the turbine wheel 130. In addition, the shortest distance L between the tip 25 and the inner circumferential surface 112B of the turbine housing 110 is set to be the shortest distance Lα that allows insulation at the maximum voltage supplied to the catalyst carrier 31. With this structure, the exhaust gas that has passed through the turbine wheel 130 is less likely to flow into the space S (see FIG. 2) between the outer pipe 50 and the end 22 of the case 20, and most of it flows into the case 20. Therefore, it is possible to suppress a decrease in turbine efficiency of the turbocharger 100 caused by the presence of such a space S.

[0032] (3) In this embodiment, the turbine housing 110 is formed of a casting, and therefore the volume of the turbine housing 110 is larger than when the turbine housing 110 is formed of a plate-shaped sheet metal. Therefore, the heat capacity of the turbine housing 110 increases. When the heat capacity of the turbine housing 110 increases, the temperature of the turbine housing 110 is less likely to increase. On the other hand, the end 22 of the case 20 is exposed to exhaust gas, and therefore the temperature is more likely to increase. In this way, while the temperature of the end 22 of the case 20 is more likely to increase, the temperature of the turbine housing 110 is less likely to increase. Therefore, it is possible to promote a state in which the temperature of the outer tube 50 is relatively lower than the temperature of the end 22 of the case 20.

[0033] (4) The outer pipe 50 is configured by utilizing the turbine housing 110. Therefore, compared to a case in which the entire outer pipe 50 is configured by the connecting pipe 120 without utilizing the turbine housing 110, it is possible to prevent the catalytic converter 10 from becoming large.

[0034] <Example of change> The above-described embodiments can be modified as follows: Each embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0035] In the above embodiment, the outer pipe 50 is composed of the connecting pipe 120 and the turbine housing 110. Alternatively, the outer pipe 50 may be composed of the turbine housing 110 in its entirety. One embodiment of this modified example is shown in Figure 3. As shown in Figure 3, the catalytic converter 10 of the modified example does not include the connecting pipe 120. A downstream end 117 located at the end downstream in the exhaust direction of the expanded diameter portion 114 of the turbine housing 110 is joined to the outer circumferential surface 22A of the reduced diameter portion 24.

[0036] According to this modification, the heat capacity of the outer pipe 50 is larger than when a part of the outer pipe 50 is configured by the turbine housing 110. This further promotes a state in which the temperature of the outer pipe 50 is relatively lower than the temperature of the end 22 of the case 20. This further improves the insulation of the insulating part at the end 22 of the case 20. Note that in this modification, the downstream end 117 may be joined to the outer circumferential surface of the accommodation portion 21 of the case 20.

[0037] In the above embodiment, the downstream end 122 of the connecting pipe 120 may be joined to the outer circumferential surface of the housing portion 21 of the case 20 . In the above embodiment, the case 20 is provided with the reduced diameter portion 24. The case 20 is not limited to having a reduced diameter portion. For example, the inner diameter of the end portion of the case 20 may be constant in the direction in which the axis line along the central axis of the catalytic converter extends.

[0038] In the above embodiment, the case 20 including the constant diameter portion 23 is exemplified. The case 20 is not limited to having a constant diameter portion. In other words, the constant diameter portion may be omitted from the end 22 of the case 20, and the tube may be gradually tapered so that the distance to the central axis of the catalytic converter becomes shorter toward the upstream side in the exhaust direction. [Explanation of symbols]

[0039] 10...Catalyst device 20…Case 21…Storage section 22...End 22A…Outer surface 23... Equal diameter part 24...Reduced diameter part 25...Tip 26...Electrode insertion hole 31...Catalyst carrier 32…Matt 50...Outer tube 81...Electrode 90…Internal combustion engine 91…Exhaust passage 100…Turbocharger 110...Turbine housing 112…Wheel storage area 112B…Inner peripheral surface 114…Enlarged diameter part 118…Exhaust outlet 119...Aperture 120…Connecting pipe 120B…Inner peripheral surface 130…Turbine wheel

Claims

1. A catalytic converter device that is disposed in an exhaust passage of an internal combustion engine equipped with a turbocharger, the catalytic converter comprising: a catalyst that purifies exhaust gas; a heating element that generates heat by energizing the catalyst to heat the catalyst; and a case that is a tube that houses the catalyst and the heating element, a direction in which exhaust gas flows through the exhaust passage is defined as an exhaust direction, and an end portion of the case on an upstream side in the exhaust direction protrudes upstream in the exhaust direction further than an end portion of the heating element on the upstream side in the exhaust direction, and serves as an insulating portion that provides electrical insulation; an outer tube that covers an end of the case and is radially spaced from the end, The entire outer tube is configured as a turbine housing that houses the turbine wheel of the turbocharger. Catalytic device.

2. a diameter of an end of the turbine wheel on the downstream side in the exhaust direction is defined as an outlet diameter, and a diameter of a tip end portion of the case on the upstream side in the exhaust direction is set to a diameter larger than the outlet diameter, The shortest distance between the tip portion and the inner peripheral surface of the turbine housing is set to be equal to or greater than the shortest distance that allows insulation at the maximum voltage supplied to the heating element.

2. The catalytic converter of claim 1.

3. The turbine housing is formed by casting.

2. The catalytic converter of claim 1.

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