Exhaust purification device for internal combustion engine

Abstract

In an exhaust purification device (EHC) for an internal combustion engine according to the present invention, an electrode terminal (6) is drawn outward in the radial direction, and thus there is no risk that the electrode terminal (6) would be exposed to high-temperature exhaust gas flowing through an exhaust pipe. It is thus possible to suppress increases in the gradient of resistance of the electrode terminal (6) in the axial direction and appropriately disperse current of a metal foil electrode (4) in the axial direction.

Description

Exhaust gas purification device for internal combustion engine

[0001] The present invention relates to an exhaust gas purification device for an internal combustion engine.

[0002] As described in Patent Document 1 below, for example, a conventional exhaust gas purification device for an internal combustion engine has a catalyst carrier whose outer peripheral side is covered with a sealing material made of an insulating material and is press-fitted into a metal catalyst case, and a pair of electrodes are arranged on the outer peripheral side of the catalyst carrier. By energizing the catalyst carrier through the electrodes, the catalyst carrier can be heated, and good exhaust gas purification performance can be exhibited immediately after engine startup.

[0003] However, in the conventional exhaust gas purification device for an internal combustion engine, the electrode terminals are taken out from the axial end portions, and the electrode terminals are exposed to the high-temperature exhaust gas flowing through the exhaust passage. Therefore, there is a risk that the electrode terminals are oxidized by the high-temperature exhaust gas, and the resistance gradient in the axial direction of the exhaust gas purification device increases. As a result, there is still room for improvement in that it is difficult to appropriately disperse the current in the axial direction of the exhaust gas purification device.

[0004] Japanese Unexamined Patent Application Publication No. 2014 - 208994

[0005] In one aspect of the present invention, there is provided a catalyst case for housing a catalyst carrier, a metal foil electrode provided on the outer peripheral side of the catalyst carrier, a mat member that surrounds the outer peripheral side of the catalyst carrier and is press-fitted into the inner peripheral side of the catalyst case together with the catalyst carrier, and holds the metal foil electrode in a pressed state against the catalyst carrier in the catalyst case, and an electrode terminal having one end connected to the metal foil electrode and the other end drawn out radially outward from a circumferential position that does not overlap with the installation region of the metal foil electrode.

[0006] According to the present invention, since the electrode terminal is drawn out radially outward, there is no risk that the electrode terminal is exposed to the high-temperature exhaust gas. As a result, an increase in the resistance gradient in the axial direction of the electrode terminal is suppressed, and appropriate dispersion of the current in the axial direction of the metal foil electrode can be achieved.

[0007] Furthermore, because the electrode terminals are extended radially, the degree of freedom in the position and manner of extension of the electrode terminals is improved, thereby improving the layout flexibility of exhaust gas purification devices in internal combustion engines.

[0008] Furthermore, according to the present invention, since the electrode terminals are drawn out from a circumferential position that does not overlap with the installation area of ​​the metal foil electrode, it is not necessary to remove the catalyst case when drawing out the electrode terminals in the installation area of ​​the metal foil electrode. This makes it possible to suppress the decrease in the pressing state of the mat member that occurs when the catalyst case is removed, and to maintain an appropriate pressing state of the metal foil electrode on the catalyst support. As a result, the contact pressure of the metal foil electrode on the catalyst support is made uniform, and the heating performance of the catalyst support can be improved.

[0009] This is a perspective view of the exhaust gas purification device for an internal combustion engine according to the present invention. This is a cross-sectional view taken along line A-A in Figure 2. This is a cross-sectional view of the exhaust gas purification device for an internal combustion engine showing a first modified example of the exhaust gas purification device for an internal combustion engine according to the present invention. This is a cross-sectional view of the exhaust gas purification device for an internal combustion engine showing a second modified example of the exhaust gas purification device for an internal combustion engine according to the present invention.

[0010] The exhaust gas purification device for an internal combustion engine according to the present invention will be described in detail below with reference to the drawings. Furthermore, in the embodiments described below, an example will be described in which the exhaust gas purification device for an internal combustion engine according to the present invention is applied to an electrically heated catalyst used in an internal combustion engine for automobiles, similar to the conventional invention described above.

[0011] (Configuration of the exhaust gas purification device for an internal combustion engine) Figure 1 is a schematic diagram showing the internal structure of the exhaust gas purification device EHC for an internal combustion engine according to this embodiment, and shows a perspective view of the exhaust gas purification device EHC with the catalyst case 1 omitted. Figure 2 shows a cross-sectional view of the exhaust gas purification device EHC for an internal combustion engine according to this embodiment, cut perpendicular to the axis. In the explanation of each figure, the longitudinal direction of the exhaust gas purification device EHC through which the exhaust gas flows is defined as the "axial direction", the direction perpendicular to the longitudinal direction of the exhaust gas purification device EHC is defined as the "radial direction", and the direction around the axial direction of the exhaust gas purification device EHC is defined as the "circumferential direction".

[0012] For example, as shown in Figures 1 and 2, the exhaust gas purification device (EHC) for an internal combustion engine according to this embodiment comprises a cylindrical catalyst case 1, a catalyst carrier 2 housed inside the catalyst case 1, a pair of ceramic electrodes 3 provided in pairs on the outer circumference of the catalyst carrier 2, a pair of metal foil electrodes 4 provided on the outer circumference of the ceramic electrodes 3, a mat member 5 surrounding the outer circumference of the catalyst carrier 2, and a pair of electrode terminals 6, each with one end connected to the pair of metal foil electrodes 4 and the other end extended to the outside of the catalyst case 1.

[0013] The catalyst case 1 is made of a metal material such as stainless steel, and is formed in a hollow cylindrical shape that extends along the direction of exhaust gas flow, and has a catalyst housing space inside in which the catalyst carrier 2 is housed. The upstream end of the catalyst case 1 is connected to an internal combustion engine (not shown), and the downstream end of the catalyst case 1 is connected to a muffler (not shown).

[0014] The catalyst support 2 is formed in a generally cylindrical shape from a porous ceramic having a well-known honeycomb structure. The catalyst support 2 is supported by the catalyst case 1 by being press-fitted into the inner circumference of the catalyst case 1.

[0015] The pair of ceramic electrodes 3 consists of a first ceramic electrode 31 and a second ceramic electrode 32 connected to the outer circumferential surface of the catalyst support 2. The first ceramic electrode 31 and the second ceramic electrode 32 are arranged with a 180° phase difference in the circumferential direction and each extends over a predetermined circumferential region on the outer circumferential surface of the catalyst support 2. Note that this pair of ceramic electrodes 3 is not an essential component of the present invention, as it suppresses heat generation in the metal foil electrodes 4 by gradually reducing the resistance of the pair of metal foil electrodes 4, thereby ensuring good current conduction.

[0016] The pair of metal foil electrodes 4 are composed of a first metal foil electrode 41 and a second metal foil electrode 42, which are formed from metal foil of, for example, about 0.05 mm thickness and have a lower resistance value than the catalyst support 2. In this case, the circumferential widths of the first metal foil electrode 41 and the second metal foil electrode 42 are set to be the same as, or smaller than, the circumferential widths of the first ceramic electrode 31 and the second ceramic electrode 32, respectively.

[0017] Furthermore, the first metal foil electrode 41 and the second metal foil electrode 42 are arranged to straddle the central portion of the circumferential direction of the first ceramic electrode 31 and the second ceramic electrode 32, respectively. In this embodiment, the first metal foil electrode 41 and the second metal foil electrode 42 are positioned approximately in the center of the circumferential region of the first ceramic electrode 31 and the second ceramic electrode 32.

[0018] Furthermore, the first metal foil electrode 41 and the second metal foil electrode 42 are arranged to straddle the axial central portions of the first ceramic electrode 31 and the second ceramic electrode 32, respectively. In this embodiment, the first metal foil electrode 41 and the second metal foil electrode 42 are arranged over almost the entire axial region of the first ceramic electrode 31 and the second ceramic electrode 32.

[0019] Each mat member 5 is formed in a generally cylindrical shape from ceramic wool or alumina wool and includes a first mat member 51 that surrounds the metal foil electrodes 4 (first metal foil electrodes 41 and second metal foil electrodes 42), and a second mat member 52 that is provided radially on the outer circumference of the first mat member 51 and serves as an insulating member that surrounds the electrode terminals 6 (first circumferentially extending portion 612 and second circumferentially extending portion 622, which will be described later).

[0020] The second mat member 52 does not hold the metal foil electrodes 4 (first metal foil electrodes 41 and second metal foil electrodes 42) in a pressed state against the catalyst carrier 2, but rather protects the electrode terminals 6 (first circumferentially extending portion 612 and second circumferentially extending portion 622, described later) which are arranged to bypass the circumferential direction of the catalyst carrier 2, and is not an essential component of the present invention. Alternatively, as an alternative to the second mat member 52, an insulating treatment such as providing an insulating member or insulating coating on the inner circumference side of the catalyst case 1 may be applied between the catalyst case 1 and the electrode terminals 6 (first circumferentially extending portion 612 and second circumferentially extending portion 622, described later).

[0021] The electrode terminal 6, like the metal foil electrode 4, is composed of a pair of first electrode terminals 61 and second electrode terminals 62 formed from a metal foil of, for example, about 0.05 mm in thickness. The first electrode terminal 61 and second electrode terminal 62 integrally include a first carrier-side connecting portion 611 and a second carrier-side connecting portion 621 extending in the radial direction, a first circumferentially extending portion 612 and a second circumferentially extending portion 622 that bend in the circumferential direction relative to the first carrier-side connecting portion 611 and the second carrier-side connecting portion 621, and a first terminal-side connecting portion 613 and a second terminal-side connecting portion 623 that bend in the radial direction relative to the first circumferentially extending portion 612 and the second circumferentially extending portion 622.

[0022] The first carrier-side connecting portion 611 and the second carrier-side connecting portion 621 extend along the radial direction of the catalyst carrier 2, penetrate the first mat member 51, with one end connected to the catalyst carrier 2 via the first metal foil electrode 41 and the second metal foil electrode 42 inside the first mat member 51, and the other end connected to one end of the first circumferentially extending portion 612 and the second circumferentially extending portion 622 outside the first mat member 51. The axial widths of the first carrier-side connecting portion 611 and the second carrier-side connecting portion 621 are set to be smaller than the axial widths of the first metal foil electrode 41 and the second metal foil electrode 42, respectively.

[0023] Furthermore, the first carrier-side connection portion 611 and the second carrier-side connection portion 621 are arranged to straddle the central portion of the circumferential direction of the first metal foil electrode 41 and the second metal foil electrode 42, respectively. In this embodiment, the first carrier-side connection portion 611 and the second carrier-side connection portion 621 are connected to approximately the central position of the circumferential region of the first metal foil electrode 41 and the second metal foil electrode 42.

[0024] Furthermore, the first carrier-side connection portion 611 and the second carrier-side connection portion 621 are arranged to straddle the axial central portions of the first metal foil electrode 41 and the second metal foil electrode 42, respectively. In this embodiment, the first carrier-side connection portion 611 and the second carrier-side connection portion 621 are arranged over approximately the central position in the axial region of the first metal foil electrode 41 and the second metal foil electrode 42.

[0025] The first circumferentially extending portion 612 and the second circumferentially extending portion 622 extend circumferentially between the first mat member 51 and the second mat member 52. That is, one end of the first circumferentially extending portion 612 and the second circumferentially extending portion 622 in the longitudinal direction is connected to the first carrier-side connection portion 611 and the second carrier-side connection portion 621, and the other end extends along the circumferential direction of the catalyst carrier 2 to the second circumferential region X2, excluding the first circumferential region X1, which is the installation area of ​​the first carrier-side connection portion 611 and the second carrier-side connection portion 621. In this embodiment, the first circumferentially extending portion 612 and the second circumferentially extending portion 622 extend over approximately 90° in the circumferential direction, and the exit positions of the first terminal-side connection portion 613 and the second terminal-side connection portion 623 are shifted by approximately 90° with respect to the first carrier-side connection portion 611 and the second carrier-side connection portion 621.

[0026] The first terminal-side connection portion 613 and the second terminal-side connection portion 623 extend along the radial direction of the catalyst carrier 2, penetrate the second mat member 52, with one end connected to the first circumferentially extending portion 612 and the second circumferentially extending portion 622 inside the catalyst case 1, and the other end drawn out to the outside of the catalyst case 1 and connected to the first terminal member 71 and the second terminal member 72 inside the electrode box 7 attached to the outer circumference of the catalyst case 1. The first terminal-side connection portion 613 and the second terminal-side connection portion 623 are drawn out to the outside of the catalyst case 1 through a notch portion 10 that is cut out of the catalyst case 1 corresponding to the opening 70 of the electrode box 7 facing the outside of the catalyst case 1.

[0027] (Effects of this embodiment) With the above configuration, the exhaust gas purification device EHC for an internal combustion engine according to this embodiment has electrode terminals 6 (first terminal side connection part 613 and second terminal side connection part 623) that are drawn out radially outward, so there is no risk of the electrode terminals 6 (first terminal side connection part 613 and second terminal side connection part 623) being exposed to high-temperature exhaust gas flowing through an exhaust pipe (not shown). As a result, the increase in the resistance gradient in the axial direction of the electrode terminals 6 is suppressed, and appropriate distribution of current in the axial direction of the metal foil electrodes 4 (first metal foil electrode 41 and second metal foil electrode 42) can be achieved.

[0028] Furthermore, in this embodiment, since the electrode terminals 6 are extended radially, the degree of freedom in the extension position and manner of the electrode terminals 6 is improved, thereby improving the layout flexibility of the exhaust gas purification device (EHC) in an internal combustion engine.

[0029] Furthermore, in this embodiment, the electrode terminals 6 (first carrier-side connection portion 611 and second carrier-side connection portion 621) are extended from a second circumferential region X2 that does not overlap with the installation region (first circumferential region X1) of the metal foil electrodes 4 (first metal foil electrode 41 and second metal foil electrode 42). As a result, in the installation region (first circumferential region X1) of the metal foil electrodes 4 (first metal foil electrode 41 and second metal foil electrode 42), it is no longer necessary to remove (cut out) the catalyst case 1 when extending the electrode terminals 6 (first carrier-side connection portion 611 and second carrier-side connection portion 621). This makes it possible to suppress the decrease in pressing force of the mat member 5 that occurs when the catalyst case 1 is removed, and to maintain an appropriate pressing state of the metal foil electrodes 4 (first metal foil electrode 41 and second metal foil electrode 42) against the catalyst carrier 2. As a result, the contact pressure of the metal foil electrodes 4 (first metal foil electrode 41 and second metal foil electrode 42) with respect to the catalyst support 2 is made uniform, and the heating performance of the catalyst support 2 can be improved.

[0030] Furthermore, in this embodiment, ceramic electrodes 3 (first ceramic electrode 31 and second ceramic electrode 32) with a lower resistance value than the catalyst support 2 are provided between the catalyst support 2 and the metal foil electrodes 4 (first metal foil electrode 41 and second metal foil electrode 42), making it possible to reduce the resistance gap between the catalyst support 2 and the metal foil electrodes 4 (first metal foil electrode 41 and second metal foil electrode 42). As a result, heat generation of the metal foil electrodes 4 (first metal foil electrode 41 and second metal foil electrode 42) is suppressed, and a good current supply to the catalyst support 2 can be ensured.

[0031] Furthermore, in this embodiment, the metal foil electrodes 4 (first metal foil electrode 41 and second metal foil electrode 42) are arranged to straddle the circumferential central portion of the ceramic electrodes 3 (first ceramic electrode 31 and second ceramic electrode 32). This allows for good current distribution in the circumferential direction of the ceramic electrodes 3 (first ceramic electrode 31 and second ceramic electrode 32).

[0032] Furthermore, in this embodiment, the metal foil electrodes 4 (first metal foil electrode 41 and second metal foil electrode 42) are arranged to straddle the axial center of the ceramic electrodes 3 (first ceramic electrode 31 and second ceramic electrode 32). This allows for good current distribution in the axial direction of the ceramic electrodes 3 (first ceramic electrode 31 and second ceramic electrode 32).

[0033] Furthermore, in this embodiment, the electrode terminals 6 (first carrier-side connection portion 611 and second carrier-side connection portion 621) are arranged to straddle the circumferential central portion of the metal foil electrode 4 (first metal foil electrode 41 and second metal foil electrode 42). This allows for good current distribution in the circumferential direction of the metal foil electrode 4 (first metal foil electrode 41 and second metal foil electrode 42).

[0034] Furthermore, in this embodiment, a second mat member 52 is provided on the outer circumference of the first mat member 51, between the catalyst case 1 and the electrode terminals 6 (first circumferentially extending portion 612 and second circumferentially extending portion 622), acting as an insulating member. This ensures good insulation of the metal foil electrodes 4 (first metal foil electrode 41 and second metal foil electrode 42).

[0035] The present invention is not limited to the configurations illustrated in the above embodiments, and can be freely modified according to the specifications of the internal combustion engine to which the exhaust gas purification device EHC is applied, without departing from the technical spirit of the present invention, for example, by changing the way the electrode terminals 6 (first carrier-side connection part 611 and second carrier-side connection part 621) are drawn out, as shown in the following modified examples, to match the layout of the exhaust gas purification device EHC in the internal combustion engine.

[0036] (First Modified Example) Figure 3 shows a cross-sectional view of an exhaust gas purification device EHC for an internal combustion engine, representing a first modified example of the exhaust gas purification device for an internal combustion engine according to the present invention.

[0037] For example, as shown in Figure 3, the electrode terminal 6 may be configured such that the first circumferentially extending portion 612 and the second circumferentially extending portion 622 extend over approximately 45° in the circumferential direction, and the pulling-out positions of the first terminal-side connecting portion 613 and the second terminal-side connecting portion 623 are shifted by approximately 45° relative to the first carrier-side connecting portion 611 and the second carrier-side connecting portion 621, so that the first terminal-side connecting portion 613 and the second terminal-side connecting portion 623 are pulled out at an angle.

[0038] (Second Modification) Figure 4 shows a cross-sectional view of an exhaust gas purification device EHC for an internal combustion engine, representing a second modification of the exhaust gas purification device for an internal combustion engine according to the present invention.

[0039] The configuration in which the first terminal-side connection portion 613 and the second terminal-side connection portion 623 are drawn out together from a predetermined location (one location) in the circumferential direction is not limited to this configuration. For example, as shown in Figure 4, the electrode box 7 may be divided into a first electrode box 701 and a second electrode box 702, each independently in the circumferential direction, and the first terminal-side connection portion 613 and the second terminal-side connection portion 623 may be drawn out from different circumferential positions. In this case, there is an advantage in that the first circumferential extension portion 612 and the second circumferential extension portion 622 can be shortened while maintaining the same circumferential length of the first circumferential extension portion 612 and the second circumferential extension portion 622.

Claims

1. An exhaust gas purification device for an internal combustion engine, comprising: a catalyst case for housing a catalyst carrier; a metal foil electrode provided on the outer circumference of the catalyst carrier; a mat member surrounding the outer circumference of the catalyst carrier and pressed into the inner circumference of the catalyst case together with the catalyst carrier, holding the metal foil electrode in a pressed state against the catalyst carrier within the catalyst case; and an electrode terminal, one end of which is connected to the metal foil electrode and the other end of which is drawn radially outward from a circumferential position that does not overlap with the installation area of ​​the metal foil electrode.

2. An exhaust gas purification device for an internal combustion engine according to claim 1, wherein a ceramic electrode with a lower resistance value than the catalyst carrier is provided between the catalyst carrier and the metal foil electrode.

3. An exhaust gas purification device for an internal combustion engine according to claim 2, wherein the metal foil electrode is arranged to straddle the circumferential central portion of the ceramic electrode.

4. An exhaust gas purification device for an internal combustion engine according to claim 2, wherein the circumferential width of the metal foil electrode is set to be equal to or smaller than the circumferential width of the ceramic electrode.

5. An exhaust gas purification device for an internal combustion engine according to claim 2, wherein the metal foil electrode is arranged to straddle the axial central portion of the ceramic electrode.

6. An exhaust gas purification device for an internal combustion engine according to claim 2, wherein the electrode terminal is arranged to straddle the circumferential central portion of the metal foil electrode.

7. An exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 6, wherein an insulating member is provided between the catalyst case and the electrode terminals on the outer circumference side of the mat member.

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