Patent Application
20160061081
This application claims priority under 35 USC 119 from Japanese Patent Application No. 2014-177982 filed Sep. 2, 2014, the disclosure of which is incorporated by reference herein.
1. Technical Field
The present invention relates to a catalytic converter apparatus that is provided at an exhaust pipe of an internal combustion engine.
2. Related Art
Japanese Patent Application Laid-Open (JP-A) No. 2013-185573 discloses an electrically heated catalytic structure in which an inner pipe, in a shape that tapers to the upstream side of an exhaust gas flow direction, is provided at an outer pipe that accommodates a heat generating body (a catalyst substrate). In this electrically heated catalytic structure, an insulating layer is provided at the surface of the inner pipe.
In the electrically heated catalytic structure described above, the insulating layer may be formed by, for example, a material of the insulating layer being coated onto the surface of the inner pipe and fired. However, because the insulating layer at the surface of the inner pipe contracts in the firing process, cracks may form in the insulating layer at a distal end portion of the inner pipe. To describe this in more detail, an upstream side end portion of the inner pipe in a simply cut state has sharp corners, and it is likely that cracks form in the insulating layer starting from these corners.
In consideration of the situation described above, the present invention provides a catalytic converter apparatus that may suppress the formation of cracks in an insulating layer at an axial direction end portion of an inner pipe.
A catalytic converter apparatus according to a first aspect of the present invention includes: a catalyst substrate that supports a catalyst for cleaning exhaust gas exhausted from an internal combustion engine, the catalyst substrate being heated by electrification; a case formed in a tubular shape, the catalyst substrate being accommodated inside the case and the case being attached to an exhaust pipe; an outer pipe provided at the case, the outer pipe being disposed at least at an upstream side of an exhaust gas flow direction relative to the catalyst substrate; an inner pipe provided at the case inside the outer pipe, an axial direction end portion of the inner pipe being formed in a tapered shape and a distal end face of the axial direction end portion being formed in a curved surface shape; and an insulating layer provided at least at an inner side face and the axial direction end portion of the inner pipe.
According to the first aspect of the present invention, the catalyst substrate is accommodated inside the tubular case that is attached to the exhaust pipe, and the catalyst substrate inside the case is heated by electrification. As a result, exhaust gas exhausted from the internal combustion engine is cleaned. The outer pipe and the inner pipe are provided in the case. The outer pipe is disposed at least at the upstream side of the exhaust gas flow direction relative to the catalyst substrate. The axial direction end portion of the inner pipe is formed in the tapered shape at the inside of the outer pipe. The distal end face of the axial direction end portion of the inner pipe is formed in the curved surface shape. Because the insulating layer is provided at least at the inner side face and the axial direction end portion of the inner pipe, insulation between the catalyst substrate and the inner pipe may be maintained. In this structure, the distal end face of the axial direction end portion of the inner pipe is formed in the curved surface shape. Thus, sharp corners at the distal end face of the inner pipe are removed. Therefore, the formation of cracks in the insulating layer at the distal end face of the inner pipe may be suppressed. More specifically, the insulating layer is formed by, for example, a material of the insulating layer being coated onto at least the inner side face and axial direction end portion of the inner pipe and fired. At this time, because sharp corners at the distal end face of the inner pipe are removed, cracking of the insulating layer starting from sharp corners due to contraction of the insulating layer during firing may not occur, as a result of which the formation of cracks in the insulating layer at the distal end face of the inner pipe may be suppressed.
In a catalytic converter apparatus according to a second aspect of the present invention, in the first aspect, if a radius of curvature of the distal end face of the axial direction end portion is represented by R, chamfer machining is applied such that R≧0.5 mm.
According to the second aspect of the present invention, if the radius of curvature of the distal end face of the axial direction end portion of the inner pipe is represented by R, chamfering machining is applied such that R≧0.5 mm. Thus, the distal end face of the axial direction end portion of the inner pipe is formed to a smoother curved surface shape. Hence, the formation of cracks in the insulating layer at the distal end face of the axial direction end portion of the inner pipe may be more reliably suppressed.
In a catalytic converter apparatus according to a third aspect of the present invention, in the first aspect, a thickness of the insulating layer is set to at least 100 μm and at most 200 μm.
According to the third aspect of the present invention, the thickness of the insulating layer is specified to be at least 100 μm and at most 200 μm. Thus, because the thickness of the insulating layer is suitably specified, the formation of cracks in the insulating layer at the distal end face of the axial direction end portion of the inner pipe may be suppressed. For example, if the thickness of the insulating layer is thinner than 100 μm, cracking of the insulating layer may be caused by contraction of the insulating layer during firing, and if the thickness of the insulating layer is more than 200 μm, it is difficult to form the insulating layer with a more uniform thickness.
In a catalytic converter apparatus according to a fourth aspect of the present invention, in the first aspect, the axial direction end portion is an upstream end portion that is arranged toward the upstream side of the exhaust gas flow direction.
According to the fourth aspect of the present invention, the axial direction end portion of the inner pipe is the upstream end portion that is arranged toward the upstream side of the exhaust gas flow direction. Thus, the formation of cracks in the insulating layer that is provided at the upstream end portion of the inner pipe may be suppressed.
Exemplary Embodiments of the present invention will be described in detail based on the following figures, wherein:
As shown in
The catalyst substrate 14 is formed of, for example, silicon carbide. A catalyst (platinum, palladium, rhodium or the like) is adhered to surfaces of the catalyst substrate 14 and supported thereat.
The catalyst features an action that cleans substances (hydrocarbons and the like) from the exhaust gas flowing in the exhaust pipe 10.
Two electrodes 16A and 16B are adhered to the catalyst substrate 14, and two terminals 18A and 18B are connected to the electrodes 16A and 16B, respectively. The catalyst substrate 14 is heated by electricity from the terminals 18A and 18B being passed through the electrodes 16A and 16B to the catalyst substrate 14. The catalyst supported at the surfaces of the catalyst substrate 14 is raised in temperature by this heating. Therefore, the catalyst exhibits the cleaning action more effectively. In other words, the catalytic converter apparatus 12 structures an electrically heated catalyst (EHC) in which the catalyst substrate 14 is heated by electrification.
The catalyst substrate 14 is retained in a state of being accommodated inside a tubular case 28, with a retention mat 26 that is disposed at an outer periphery of the catalyst substrate 14 therebetween. The retention mat 26 is formed in a cloth shape with insulativity and a predetermined resilience. The retention mat 26 is formed of, for example, an alumina mat, a resin mat, ceramic wool, an INTERAM mat, mullite or the like. When the catalyst substrate 14 is electrified, flows of current to the case 28 are suppressed by the retention mat 26.
The case 28 is provided with an accommodation tube 30 in a circular tube shape and an upstream side decreasing diameter portion 32. The accommodation tube 30 has a constant diameter from the upstream side to the downstream side thereof. The upstream side decreasing diameter portion 32 continues toward the upstream side from the upstream end of the accommodation tube 30 and serves as an inner pipe whose diameter is decreased in steps. That is, the upstream side decreasing diameter portion 32 is structured so as to form a shape that tapers toward the upstream side. In the example shown in
The case 28 is provided with an upstream side conical member 20 and a connecting member 22 between the accommodation tube 30 and the upstream side exhaust pipe 10A. The upstream side conical member 20 and the connecting member 22 are disposed in this order from the upstream side of the exhaust gas flow direction. The outer pipe of the present invention is structured by the upstream side conical member 20 and the connecting member 22. The upstream side conical member 20 includes a fixed tube 20A and a fixed tube 20B. The fixed tube 20A is fixed to the outer side of the upstream side exhaust pipe 10A by welding or the like over the whole circumference thereof. The fixed tube 20B is fixed to the inner side of the connecting member 22 by welding or the like over the whole circumference thereof The fixed tube 20B has a larger diameter than the fixed tube 20A. A truncated cone portion 20C connects between the fixed tube 20A and the fixed tube 20B. The diameter of the truncated cone portion 20C progressively increases from the fixed tube 20A toward the fixed tube 20B. At the inner side of the fixed tube 20A, the upstream side exhaust pipe 10A projects to the downstream side at the inner side of the truncated cone portion 20C, structuring a projection portion 10B.
The upstream side decreasing diameter portion 32 is disposed at the upstream side relative to the catalyst substrate 14 and at the downstream side relative to the truncated cone portion 20C. The upstream side decreasing diameter portion 32 is disposed inside the upstream side conical member 20 and connecting member 22 that serve as the outer pipe. Thus, two truncated cone-shaped members (the truncated cone portion 20C and the upstream side decreasing diameter portion 32) that increase in diameter from the upstream side toward the downstream side are provided successively in the exhaust gas flow direction.
An upstream end portion 32D, which is an axial direction end portion of the upstream side decreasing diameter portion 32, is disposed at the downstream side relative to a downstream end portion 10C of the upstream side exhaust pipe 10A (the projection portion 10B). Thus, the upstream side exhaust pipe 10A and the upstream side decreasing diameter portion 32 do not overlap (coincide) in the exhaust gas flow direction (the direction of arrow F1). A reservoir region 36 is structured between the upstream side conical member 20 and connecting member 22 and the upstream side decreasing diameter portion 32. As described below, the reservoir region 36 is a region in which condensed water (liquid water) that is condensed from moisture in the exhaust gas accumulates.
An inner diameter of the upstream end portion 32D of the upstream side decreasing diameter portion 32 is larger than an inner diameter of the downstream end portion 10C of the upstream side exhaust pipe 10A.
A glass coating layer 40 that serves as an insulating layer is applied to a range reaching from an inner periphery face of the accommodation tube 30 of the case 28 over an inner periphery face (an inner side face) of the upstream side decreasing diameter portion 32 to the outer periphery face of the upstream side decreasing diameter portion 32 (substantially the whole surface of the upstream side decreasing diameter portion 32). In the present exemplary embodiment, the glass coating layer 40 contains an inorganic substance such as a glass material or the like. The glass coating layer 40 is formed of a material that has a lower thermal conductivity than the case 28 and is formed with a predetermined porosity. The glass coating layer 40 is electrically insulative. Although the glass coating layer 40 is provided in the present exemplary embodiment, an insulating layer formed of an alternative material such as a ceramic or the like may be provided instead.
As shown in
In the present exemplary embodiment, after the material of the glass coating layer has been coated onto the range reaching from the inner periphery face of the accommodation tube 30 over the inner periphery face of the upstream side decreasing diameter portion 32 to the outer periphery face of the upstream side decreasing diameter portion 32, the glass coating layer 40 is formed by firing of the materials. At this time, because sharp corners have been removed at the distal end face 33 of the upstream end portion 32D of the upstream side decreasing diameter portion 32, the formation of cracks in the glass coating layer 40 starting from sharp corners, due to contraction of the glass coating layer 40 during the firing, is suppressed.
The thickness of the glass coating layer 40 is preferably set to at least 100 μm and at most 200 μm, and is more preferably set to to at least 120 μm and at most 180 μm. When the thickness of the glass coating layer 40 is set in a suitable range, the formation of cracks in the glass coating layer 40 at the distal end face 33 of the upstream end portion 32D of the upstream side decreasing diameter portion 32 may be more effectively suppressed. For example, if the thickness of the glass coating layer is thinner than 100 μm, cracks in the glass coating layer at the distal end face of the upstream end portion may be caused by the contraction of the glass coating layer during firing. In addition, it may not be possible to assure satisfactory electrical insulation. If the thickness of the glass coating layer is more than 200 μm, it is difficult to form the glass coating layer with a more uniform thickness.
In the catalytic converter apparatus 12, moisture is included in the exhaust gas. The moisture may condense and form water droplets inside the exhaust pipe 10 at the upstream side relative to the catalytic converter apparatus 12. In the catalytic converter apparatus 12 according to the present exemplary embodiment, the upstream side exhaust pipe 10A and the upstream side decreasing diameter portion 32 do not overlap in the exhaust gas flow direction. Therefore, water condensing from the exhaust gas passes between the upstream side exhaust pipe 10A and the upstream side decreasing diameter portion 32 and accumulates in the reservoir region 36 that is between the upstream side conical member 20 and connecting member 22 and the upstream side decreasing diameter portion 32. Thus, adherence of condensed water to the catalyst substrate 14 is suppressed. Therefore, short circuits between the electrodes 16A and 16B caused by condensed water are suppressed. Therefore, electric current amounts in the catalyst substrate 14 are assured and the catalyst substrate 14 is effectively raised in temperature.
In particular, in the present exemplary embodiment, the upstream side decreasing diameter portion 32 projects integrally from the accommodation tube 30 and there is no joint between the upstream side decreasing diameter portion 32 and the accommodation tube 30. Therefore, water that has accumulated in the reservoir region 36 does not ingress through a joint between the upstream side decreasing diameter portion 32 and the accommodation tube 30 to the side thereof at which the catalyst substrate 14 is disposed.
Further, in the catalytic converter apparatus 12 according to the present exemplary embodiment, the inner diameter of the upstream end portion 32D of the upstream side decreasing diameter portion 32 is larger than the inner diameter of the downstream end portion 10C of the upstream side exhaust pipe 10A. Thus, although carbon is included in the exhaust gas, when, for example, the engine is starting at low temperature or the like, flows into the reservoir region 36 of the carbon in the exhaust gas that flows through the upstream side exhaust pipe 10A are suppressed. As a result, adherences of carbon to the outer periphery face of the upstream side decreasing diameter portion 32 are suppressed and short circuits between the electrodes 16A and 16B caused by carbon are suppressed. Therefore, electric current amounts in the catalyst substrate 14 are assured and the catalyst substrate 14 is effectively raised in temperature.
In the catalytic converter apparatus 12 according to the present exemplary embodiment, the diameter of the upstream side decreasing diameter portion 32 decreases toward the upstream side. Therefore, eddies form in the exhaust gas flowing at the inner side of the upstream side decreasing diameter portion 32, and the upstream side decreasing diameter portion 32 more easily absorbs heat from the exhaust gas. Thus, the temperature of the upstream side decreasing diameter portion 32 may be raised more easily, and combustion of carbon adhering to the upstream side decreasing diameter portion 32 may be promoted.
Now, operation of the catalytic converter apparatus 12 according to the present exemplary embodiment is described.
As shown in
In the catalytic converter apparatus 12, the catalyst substrate 14 is electrified by the terminals 18A and 18B and the electrodes 16A and 16B, and the catalyst substrate 14 is heated. Thus, the catalyst supported by the catalyst substrate 14 is raised in temperature and may exhibit the cleaning action more effectively. For example, if the temperature of the exhaust gas is low, just after starting of the engine or the like, because the catalyst substrate 14 is already electrified and heated, the cleaning performance of the catalyst may be assured in an initial period when the engine starts.
The glass coating layer 40 is applied in the range reaching from the inner periphery face of the accommodation tube 30 of the case 28 over the inner periphery face of the upstream side decreasing diameter portion 32 to the outer periphery face of the upstream side decreasing diameter portion 32 (substantially the whole surface of the upstream side decreasing diameter portion 32). Thus, insulation of the case 28 (the accommodation tube 30 and the upstream side decreasing diameter portion 32) is improved. Therefore, current leakages to the case 28 (the accommodation tube 30 and the upstream side decreasing diameter portion 32) when the catalyst substrate 14 is electrified are suppressed. As a result, electric current amounts in the catalyst substrate 14 may be assured and the catalyst substrate 14 may be raised in temperature effectively.
As shown in
In the present exemplary embodiment, after the material of the glass coating layer has been coated onto the range reaching from the inner periphery face of the accommodation tube 30 over the inner periphery face of the upstream side decreasing diameter portion 32 to the outer periphery face of the upstream side decreasing diameter portion 32, the glass coating layer 40 is formed by firing of the materials. At this time, because the distal end face 33 of the upstream end portion 32D of the upstream side decreasing diameter portion 32 has been formed to the curved surface shape (machined to curved chamfers) and sharp corners of the distal end face 33 have been removed, cracking of the glass coating layer 40 starting from sharp corners, due to contraction of the glass coating layer 40 during the firing, is suppressed. Therefore, the formation of cracks in the glass coating layer 40 at the distal end face 33 of the upstream end portion 32D of the upstream side decreasing diameter portion 32 may be suppressed as a result.
To describe this in more detail, the upstream end portion of the upstream side decreasing diameter portion, in a simply cut state, has sharp corners at the distal end face thereof Thus, because the glass coating layer contracts during firing, cracks may form in the glass coating layer starting from these corners. When cracks form in the glass coating layer, regions that may not insulate are produced and, because of short circuits, it may not be possible to assure electric current amounts in the catalyst substrate. In contrast, in the present exemplary embodiment, because the distal end face 33 of the upstream end portion 32D of the upstream side decreasing diameter portion 32 is formed in the curved surface shape (machined to curved chamfers), even when the glass coating layer 40 at the distal end face 33 of the upstream end portion 32D contracts during firing, the formation of cracks in the glass coating layer 40 may be suppressed.
The thickness of the glass coating layer 40 is set to at least 100 μm and at most 200 μm. Thus, because the glass coating layer 40 has a suitable thickness, the formation of cracks in the glass coating layer 40 at the distal end face 33 of the upstream end portion 32D of the upstream side decreasing diameter portion 32 may be suppressed. That is, because the distal end face 33 of the upstream end portion 32D of the upstream side decreasing diameter portion 32 is formed in the curved surface shape (the rounded surface shape), the thickness of the glass coating layer 40 may be formed to a substantially uniform thickness. For example, if there is a sharp corner at the upstream end portion of an upstream side decreasing diameter portion, the thickness of a glass coating layer may be thinner in the vicinity of the corner. If, for example, the thickness of a glass coating layer is thinner than 100 μm, cracks may form in the glass coating layer in the vicinity of the distal end face of an upstream end portion, due to contraction of the glass coating layer during firing, in addition to which it may not be possible to assure satisfactory electrical insulation. Further, if the thickness of a glass coating layer is thicker than 200 μm, it is difficult to form the glass coating layer with a more uniform thickness. In contrast, in the present exemplary embodiment, because the thickness of the glass coating layer 40 is set to least 100 μm and at most 200 μm, the thickness of the glass coating layer 40 may be made substantially uniform at the distal end face 33 of the upstream end portion 32D of the upstream side decreasing diameter portion 32. Thus, the formation of cracks in the glass coating layer 40 may be more effectively suppressed.
As shown in
In the present exemplary embodiment, after the material of the glass coating layer has been coated onto a range reaching over an inner periphery face and an outer periphery face of the upstream side decreasing diameter portion 52, the glass coating layer 40 is formed by firing of the materials. At this time, because the two locations of the distal end face 53 of the upstream end portion 52A of the upstream side decreasing diameter portion 52 are formed as the curved chamfer portions 53A and 53B that have been machined to curved surface shapes in the side sectional view and sharp corners of the distal end face 53 have been removed, cracking of the glass coating layer 40 starting from sharp corners, due to contraction of the glass coating layer 40 during the firing, is suppressed. Therefore, the formation of cracks in the glass coating layer 40 at the distal end face 53 of the upstream end portion 52A of the upstream side decreasing diameter portion 52 may be suppressed.
As shown in
Then, as illustrated in
In the present exemplary embodiment, after the material of the glass coating layer has been coated onto a range reaching over an inner periphery face and an outer periphery face of the upstream side decreasing diameter portion 62, the glass coating layer 40 is formed by firing of the materials. At this time, the distal end face 63 of the upstream end portion 62A of the upstream side decreasing diameter portion 62 has been formed into a smooth curved surface shape by the straight chamfer machining followed by the curved chamfer machining. Thus, sharp corners of the distal end face 63 of the upstream end portion 62A of the upstream side decreasing diameter portion 62 are removed. Therefore, cracking of the glass coating layer 40 starting from sharp corners, due to contraction of the glass coating layer 40 during the firing, is suppressed. As a result, the formation of cracks in the glass coating layer 40 at the distal end face 63 of the upstream end portion 62A of the upstream side decreasing diameter portion 62 may be suppressed.
As shown in
In
As can be seen from
Note that the shape of the distal end face of the upstream end portion of an upstream side decreasing diameter portion is not limited by the first to third exemplary embodiments but may be modified to an alternative shape provided it is formed as a curved surface shape.
In the first to third exemplary embodiments, examples are illustrated in which the insulating layer is provided at the distal end face of the upstream end portion of an upstream side decreasing diameter portion that structures an inner pipe of a case, but the present invention is not limited by the first to third exemplary embodiments. For example, the present invention may also be applied to a case in which an insulating layer is provided at a distal end face of an axial direction end portion (a downstream end portion) of a downstream side decreasing diameter portion that is disposed at the downstream side of a catalyst substrate inside a case and structures an inner pipe of the case. The present invention may further be applied to a case in which insulating layers are provided at distal end faces of both an upstream side decreasing diameter portion and a downstream side decreasing diameter portion.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-177982 | Sep 2014 | JP | national |
