JP2013185573A - Electric heating catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress electricity from flowing in a case of an electric heating catalyst.SOLUTION: An electric heating catalyst 1 includes: a heating element 3 heated by energization; a case 5 housing the heating element 3; and a mat 4 insulating electricity by being held between the hating element 3 and the case 5 including an outer pipe 51 serving as a partition from outside, and an inner pipe 52 contained inside the outer pipe 51. An upstream side end of the inner pipe 52 is provided at the upstream side from the mat 4. A gap is provided between the outer pipe 51 and the inner pipe 52 at the upstream side end of the inner pipe 52 so that a space between the outer pipe 51 and the inner pipe 52 is opened in an exhaust path. A downstream side end of the inner pipe 52 is provided at a part contacting the mat 4. The outer pipe 51 and the inner pipe 52 are brought into contact with each other at the downstream side end so that a space between the outer pipe 51 and the inner pipe 52 is closed.

Description

  The present invention relates to an electrically heated catalyst.

  As an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine, an electrically heated catalyst (hereinafter also referred to as EHC) in which a catalyst is heated by a heating element that generates heat when energized has been developed. Yes.

  Then, a solid layer sandwiched between mats is provided between a catalyst carrier that generates heat upon energization and a case that accommodates the catalyst carrier, and the solid layer is formed of an insulating member and is located upstream of the mat and A technique of projecting to the downstream side is known (see, for example, Patent Document 1).

  According to this solid layer, even if particulate matter (hereinafter referred to as PM) in the exhaust gas adheres to the mat or the catalyst carrier, it can be suppressed to some extent that electricity passes between the case and the catalyst carrier. However, when PM is deposited on the solid layer, electricity may flow between the catalyst carrier and the case via the PM.

WO2011-121710 gazette

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a technique for suppressing electricity from flowing through the case of an electrically heated catalyst.

In order to achieve the above object, an electrically heated catalyst according to the present invention provides:
A heating element that generates heat when energized;
A case for housing the heating element;
A mat that is sandwiched between the heating element and the case to insulate electricity;
In an electrically heated catalyst comprising:
The case includes an outer tube serving as a partition wall with the outside, and an inner tube provided inside the outer tube,
The upstream end of the inner pipe is provided on the upstream side of the mat,
At the upstream end of the inner pipe, a gap is provided between the outer pipe and the inner pipe so that a space between the outer pipe and the inner pipe opens into the exhaust passage.
The downstream end portion of the inner pipe is provided at a place in contact with the mat,
At the downstream end of the inner tube, the outer tube and the inner tube are in contact so that a space between the outer tube and the inner tube is closed.

  The heating element may be a catalyst carrier or may be provided upstream of the catalyst. The mat is in contact with the heating element and the case, respectively. This mat is also used for fixing the heating element in the case.

The case is composed of a double pipe from a place in contact with the mat to the upstream side of the mat. Exhaust gas does not circulate on the outer peripheral surface side of the outer pipe (outer pipe) of the double pipe. The inner pipe (inner pipe) of the double pipe is provided with a clearance from the outer pipe at the upstream end, and is provided in contact with the outer pipe at the downstream end. For this reason, between the inner pipe of the double pipe and the outer pipe, it leads to the exhaust passage, and the exhaust gas of the internal combustion engine flows in.

  Here, it can be said that the inner pipe protrudes into the flow of exhaust. For this reason, the temperature of the inner pipe is likely to rise due to the heat of the exhaust. Moreover, since gas is present between the inner tube and the outer tube by using a double tube, heat transfer from the inner tube to the outer tube can be suppressed. Furthermore, since the downstream end of the inner tube is in contact with the mat, heat is transmitted from the heating element to the inner tube via the mat. These increase the temperature of the inner tube. For this reason, even if PM adheres to the inner tube, oxidation of PM is promoted. That is, PM can be removed from the inner tube. Therefore, it can suppress that electricity flows between a heat generating body and a case.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that electricity flows into the case of an electrically heated catalyst.

It is a figure which shows schematic structure of the electrically heated catalyst which concerns on an Example. It is the figure which showed the electric heating type catalyst in case a connection part is provided in the upstream rather than the mat | matte. The relationship between the distance from the position where the spatial distance between the outer tube and the inner tube is 8 mm and the temperature is shown.

  Hereinafter, specific embodiments of the electrically heated catalyst according to the present invention will be described with reference to the drawings. The following embodiments can be combined as appropriate.

<Example 1>
FIG. 1 is a diagram illustrating a schematic configuration of an electrically heated catalyst 1 (hereinafter referred to as EHC 1) according to the present embodiment. The EHC 1 according to the present embodiment is provided in the exhaust pipe 2 of the internal combustion engine mounted on the vehicle. The internal combustion engine may be a diesel engine or a gasoline engine. It can also be used in a vehicle that employs a hybrid system equipped with an electric motor.

  The EHC 1 shown in FIG. 1 is a cross-sectional view of the EHC 1 cut in the longitudinal direction along the central axis A of the EHC 1. Since the shape of EHC 1 is line symmetric with respect to the central axis A, only the upper part is shown in FIG. Further, the shape of the downstream side of the EHC 1 may be symmetrical with the shape of the upstream side, or may be the same shape as the conventional one, and is not shown. Further, the arrow B in FIG. 1 indicates the flow direction of the exhaust gas.

  The EHC 1 according to the present embodiment includes a cylindrical catalyst carrier 3 centering on a central axis A. A catalyst carrier 3, a mat 4, and a case 5 are provided in this order from the central axis A side.

The catalyst carrier 3 is made of a material that generates electrical resistance and generates heat when energized. For example, SiC is used as the material of the catalyst carrier 3. The catalyst carrier 3 has a plurality of passages extending in the exhaust gas flow direction B (which may be the direction of the central axis A) and having a cross section perpendicular to the exhaust gas flow direction forming a honeycomb shape. Exhaust gas flows through this passage. The outer shape of the catalyst carrier 3 is, for example, a cylindrical shape centered on the central axis A of the exhaust pipe 2. In addition, the cross-sectional shape of the catalyst carrier 3 having a cross section orthogonal to the central axis A may be, for example, an ellipse or a polygon. The central axis A is a central axis common to the exhaust pipe 2, the catalyst carrier 3, and the case 5. In this embodiment, the catalyst carrier 3 corresponds to the heating element in the present invention. The present embodiment can be similarly applied to a heating element provided with a heating element upstream of the catalyst.

  A catalyst is supported on the catalyst carrier 3. Examples of the catalyst include an oxidation catalyst, a three-way catalyst, an occlusion reduction type NOx catalyst, and a selective reduction type NOx catalyst. A pair of electrodes (not shown) are connected to the catalyst carrier 3, and the catalyst carrier 3 is energized by applying a voltage between the electrodes. The catalyst carrier 3 generates heat due to the electrical resistance of the catalyst carrier 3.

  The mat 4 is made of an electrical insulator, such as a ceramic fiber mainly composed of alumina. The mat 4 is wound around the outer peripheral surface of the catalyst carrier 3. Since the mat 4 covers the outer peripheral surface of the catalyst carrier 3 (a curved surface parallel to the central axis A), electricity is prevented from flowing to the case 5 when the catalyst carrier 3 is energized.

  The outer diameter of the mat 4 when the mat 4 is wound around the catalyst carrier 3 is larger than the inner diameter of the case 5. For this reason, when the mat 4 is accommodated in the case 5, the mat 4 is compressed, so that the catalyst carrier 3 is fixed in the case 5 by the repulsive force of the mat 4.

  A metal is used as the material of the case 5, and for example, a stainless steel material can be used. The case 5 includes an outer tube 51 serving as a partition wall with the outside, and an inner tube 52 extending from the outer tube 51 into the exhaust. The inner tube 52 is provided closer to the central axis A than the outer tube 51. For this reason, in the case 5 where the inner tube 52 is provided, the inner tube 52 and the outer tube 51 form a double tube. A downstream end portion (referred to as a connection portion 53) of the inner tube 52 is connected to the outer tube 51. The connecting portion 53 is located at a location where the case 5 and the mat 4 are in contact. That is, the connection portion 53 is provided on the outer peripheral surface of the mat 4. The inner pipe 52 extends from the connecting portion 53 toward the upstream side of the exhaust pipe 2 along the outer peripheral surface of the mat 4 on the central axis A side than the outer pipe 51. Further, the upstream end portion of the inner pipe 52 is located upstream of the mat 4. Then, on the upstream side of the upstream end portion of the mat 4, the inner tube 52 extends toward the central axis A side and the upstream side of the exhaust gas while the inner diameter (which may be a passage cross-sectional area) gradually decreases. That is, the inner diameter of the inner pipe 52 is lower than the inner diameter of the downstream side upstream of the mat 4.

  The outer tube 51 includes an inlet portion 511, an inclined portion 512, and a cylindrical portion 513 in order from the upstream side. The inclined portion 512 is inclined with respect to the central axis A so that the inner diameter increases toward the downstream side. An upstream end portion of the inclined portion 512 is connected to the inlet portion 511. A flange is formed at the upstream end of the inlet 511 of the case 5, and is connected to the exhaust pipe 2 by the flange. The inlet portion 511 is open, and the exhaust gas flows into the case 5 through the inlet portion 511. Further, the downstream end portion of the inclined portion 512 of the case 5 is connected to the upstream end portion of the cylindrical portion 513.

  The cylindrical portion 513 of the case 5 is formed in a tubular shape centered on the central axis A, and has a curved surface parallel to the central axis A. The upstream end portion of the inner pipe 52 is located upstream of the connecting portion between the inclined portion 512 and the cylindrical portion 513 and downstream of the connecting portion between the inclined portion 512 and the inlet portion 511. A gap through which exhaust gas flows is provided at the upstream end of the inner pipe 52 and the inclined portion 512. Further, the downstream end portion of the inner pipe 52 is located on the downstream side of the connection portion between the inclined portion 512 and the cylindrical portion 513.

  Further, a cylindrical introduction portion 514 extending parallel to the central axis A toward the downstream side is connected to a connection portion between the inlet portion 511 of the case 5 and the inclined portion 512 of the case 5. The inner diameter of the introduction portion 514 is smaller than the inner diameter of the upstream end portion of the inner tube 52. For this reason, the exhaust gas flowing downstream from the introduction portion 514 hardly flows between the outer tube 51 and the inner tube 52. In the present embodiment, the introduction unit 514 is not always necessary.

  As described above, in this embodiment, the passage cross-sectional area of the inner pipe 52 and the inclined portion 512 is larger toward the downstream side. Here, as shown in FIG. 1, the angle of the inner tube 52 and the inclined portion 512 with respect to the central axis A may not be constant, but may be constant.

  In this embodiment, the inner peripheral surface of the inner tube 52 is covered with an insulating layer 521. The insulating layer 521 is formed by applying an insulator such as ceramic. The insulating layer 521 is formed on the inner peripheral surface of the inner tube 52, but may also be formed on the outer peripheral surface of the inner tube 52. In addition, in the case 5, the insulating layer 521 may also be formed at a portion in contact with the mat 4. Here, since the exhaust gas hardly flows in the portion of the case 5 that is in contact with the mat 4, there is no possibility of PM adhering, so there is no need to provide the insulating layer 521. However, an insulating layer 521 may be provided on the surface of the case 5 even at a place where the mat 4 is provided in order to prevent short circuit more reliably. Further, the insulating layer 521 may be slightly included in the range where the mat 4 is provided.

  In the electrically heated catalyst 1 configured as described above, the temperature on the upstream side of the inner pipe 52 is likely to rise due to the heat of the exhaust. Moreover, since gas exists between the inner tube 52 and the outer tube 51 by using the case 5 as a double tube, it is possible to suppress heat from moving from the inner tube 52 to the outer tube 51. Further, since the downstream end of the inner pipe 52 is in contact with the mat 4, heat is transferred from the catalyst carrier 3 to the inner pipe 52 through the mat 4. Moreover, since the distance between the outer tube 51 and the inner tube 52 becomes longer as it approaches the upstream end of the inner tube 52, it is possible to suppress heat from moving from the inner tube 52 to the outer tube 51. As a result, the temperature of the inner pipe 52 increases. For this reason, even if PM adheres to the inner tube 52, oxidation of PM is promoted. That is, PM can be removed from the inner tube 52. Therefore, it is possible to suppress electricity from flowing between the catalyst carrier 3 and the case 5.

  Here, for comparison, FIG. 2 shows the EHC 1 when the connecting portion 53 is provided on the upstream side of the mat 4. That is, FIG. 2 is a diagram showing the EHC 1 when the connecting portion 53 is provided on the upstream side of the mat 4. FIG. 6 is a diagram comparing the temperatures of the respective locations from L1 to L8 of the inner pipe 52 of the EHC 1 (FIG. 1) according to the present embodiment and the temperatures of the respective locations from L1 to L6 of the inner pipe 52 of FIG. It becomes like 3.

  FIG. 3 shows the relationship between the distance from the position where the spatial distance between the outer tube 51 and the inner tube 52 is 8 mm and the temperature. The solid line is the case shown in FIG. 1, and the alternate long and short dash line is the case shown in FIG. That is, in FIGS. 1 and 2, the spatial distance between the outer tube 51 and the inner tube 52 is 8 mm at the position L3. The distance shown in FIG. 3 becomes smaller toward the downstream side of the exhaust flow. On the upstream side of L3, the distance between the outer tube 51 and the inner tube 52 is maintained at 8 mm or more.

  As shown in FIG. 3, the temperature shown in FIG. 1 as a whole is higher than that shown in FIG. Further, as the heat comes closer to the connection portion 53, the outer tube 51 is deprived of heat, so the temperature decreases. The degree of the decrease in temperature is shown in FIG. 2 than in the case shown in FIG. The case is larger.

  Here, in the case shown in FIG. 1, since the connecting portion 53 is in contact with the mat 4, a part of the inner peripheral surface of the inner tube 52 is in contact with the mat 4. Since heat is transmitted from the catalyst carrier 3 to the mat 4, the inner pipe 52 can receive this heat by contacting the inner pipe 52. For this reason, the temperature of the inner pipe 52 can be kept high. On the other hand, in the case shown in FIG. 2, since the inner pipe 52 is not in contact with the mat 4 because it is not in contact with the connecting portion 53 mat 4, the inner pipe 52 is not easily subjected to heat from the mat 4. For this reason, the temperature of the inner pipe 52 tends to be low.

Thus, according to EHC1 which concerns on a present Example, since the temperature of the inner pipe | tube 52 can be maintained high, oxidation of PM adhering to the inner pipe | tube 52 can be accelerated | stimulated. Thereby, it can suppress that electricity flows between catalyst carrier 3 and case 5 via PM.

1 Electric heating catalyst (EHC)
2 exhaust pipe 3 catalyst carrier 4 mat 5 case 51 outer pipe 52 inner pipe 53 connection part 511 inlet part 512 inclined part 513 cylindrical part 514 introduction part 521 insulating layer

Claims (1)

A heating element that generates heat when energized;
A case for housing the heating element;
A mat that is sandwiched between the heating element and the case to insulate electricity;
In an electrically heated catalyst comprising:
The case includes an outer tube serving as a partition wall with the outside, and an inner tube provided inside the outer tube,
The upstream end of the inner pipe is provided on the upstream side of the mat,
At the upstream end of the inner pipe, a gap is provided between the outer pipe and the inner pipe so that a space between the outer pipe and the inner pipe opens into the exhaust passage.
The downstream end portion of the inner pipe is provided at a place in contact with the mat,
An electrically heated catalyst in which the outer tube and the inner tube are in contact with each other so that a space between the outer tube and the inner tube is closed at a downstream end portion of the inner tube.

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