Exhaust gas aftertreatment device and method for its manufacture

Abstract

Device for the aftertreatment of exhaust gases from an emission source, in particular an internal combustion engine, comprising an exhaust tract through which exhaust gas can flow, comprising at least one catalyst, wherein the catalyst has a ceramic honeycomb body (1, 5, 8, 12, 15) which is provided with a catalytically active surface coating, and an electrically heated heating medium (3, 7, 9), wherein the heating medium (3, 7, 9) is formed by a metallic electrical conductor (3, 7, 9), wherein the honeycomb body (1, 5, 8, 12, 15) has several flow channels through which gas can flow from a gas inlet side (11, 16) to a gas outlet side, wherein the conductor (3, 7, 9) is integrated into the ceramic honeycomb body (1, 5, 8, 12, 15), wherein, viewed in the direction of flow, it faces the gas inlet side (11, 16). is arranged downstream and upstream of the gas outlet side, characterized in thatthat the ceramic honeycomb body (5) is formed from at least two honeycomb bodies designed as disk elements (6), which are arranged one after the other in the direction of flow, wherein each of the disk elements (6) has an integrated conductor (7), wherein the conductors (7) in the disk elements (6) are electrically connected to each other.

Description

Technical area

[0001] The invention relates to a device for the aftertreatment of exhaust gases from an emission source, in particular an internal combustion engine, comprising an exhaust tract through which an exhaust gas can flow, comprising at least one catalyst, wherein the catalyst comprises a ceramic honeycomb body provided with a catalytically active surface coating, and comprising an electrically heatable heating means, wherein the heating means is formed by a metallic electrical conductor, wherein the honeycomb body comprises a plurality of flow channels through which flow can flow from a gas inlet side to a gas outlet side, wherein the conductor is integrated into the ceramic honeycomb body, wherein, viewed in the flow direction, it is arranged downstream of the gas inlet side and upstream of the gas outlet side. Furthermore, the invention relates to a method for producing a honeycomb body State of the art

[0002] To increase the exhaust gas temperature, electric heaters are used in the exhaust system of internal combustion engines to more quickly reach the minimum temperature required for exhaust aftertreatment. This is done to achieve the so-called light-off temperature, at which the catalysts used enable sufficient exhaust aftertreatment, more quickly. This is particularly advantageous during cold starts of the internal combustion engine. In hybrid vehicles, such cold starts can occur with a higher recurrence rate, which is why electric heating is necessary.

[0003] The catalysts used in the exhaust system have either a metallic or ceramic matrix. Auxiliary heaters are typically formed by current-carrying metallic conductors positioned upstream of the corresponding catalysts in the direction of exhaust flow.

[0004] JP H05-:59939A discloses an exhaust emission control device equipped with a honeycomb catalyst held in a converter housing and a heater band. The converter housing has an exhaust gas inlet port connected to an upstream exhaust passage and an exhaust gas outlet port connected to a downstream exhaust passage. The honeycomb catalyst is vertically divided into two parts and consists of an upper support and a lower support. Rectangular vertical holes for inserting the heater band are provided in a line on the upper support and the lower support.

[0005] A particular disadvantage of the prior art devices is that the implementation of electrical heating systems in conjunction with a ceramic catalyst matrix has so far been inadequate. In particular, the heating efficiency and durability of the known systems are not optimal. Description of the invention, task, solution, advantages

[0006] Therefore, the object of the present invention is to provide a device for exhaust gas aftertreatment that has an electric heating source and enables improved heating of the exhaust gas stream and / or the ceramic matrix. Furthermore, a method for producing such a device is provided.

[0007] The object with regard to the device is achieved by a device having the features of claim 1.

[0008] An embodiment of the invention relates to a device for the aftertreatment of exhaust gases from an emission source, in particular an internal combustion engine, having an exhaust tract through which an exhaust gas can flow, having at least one catalyst, wherein the catalyst has a ceramic honeycomb body provided with a catalytically active surface coating, and having an electrically heatable heating means, wherein the heating means is formed by a metallic electrical conductor, wherein the honeycomb body has a plurality of flow channels through which flow can flow from a gas inlet side to a gas outlet side, wherein the conductor is integrated into the ceramic honeycomb body, wherein, viewed in the flow direction, it is arranged downstream of the gas inlet side and upstream of the gas outlet side, wherein the ceramic honeycomb body is formed from at least two honeycomb bodies designed as disk elements,which are arranged one after the other in the direction of flow, wherein each of the disc elements has an integrated conductor, wherein the conductors in the disc elements are electrically conductively connected to one another.

[0009] Ceramic honeycomb bodies are widely known in the art and are produced, for example, by extrusion, pressing, or casting and subsequently sintered. The honeycomb bodies have a plurality of flow channels through which gas can flow along a main direction from the gas inlet side to the gas outlet side.

[0010] The metallic conductor can be formed, for example, by a metal wire. In addition to different diameters and cross-sections, the material used can also be varied to create a suitable resistance. The heating effect is generated by exploiting the ohmic resistance of the conductor by connecting the conductor to a voltage source outside the honeycomb body and applying a current.

[0011] The arrangement in the flow direction downstream of the gas inlet side and upstream of the gas outlet side is preferred, since this places the conductor within the ceramic honeycomb body. The conductor is therefore not arranged on or upstream of the gas inlet side.

[0012] It is advantageous here if the ceramic honeycomb body is formed from at least two honeycomb bodies designed as disc elements, which are arranged one after the other in the direction of flow, wherein each of the disc elements has an integrated conductor, wherein the conductors in the disc elements are electrically conductively connected to one another.

[0013] The entire honeycomb body can be formed from a plurality of disc elements, each of which has a shorter axial extension than the entire honeycomb body. These disc elements preferably have an identical cell density and channel distribution. In alternative embodiments, different cell densities and channel distributions can also be provided in the individual disc elements.

[0014] Each of the disc elements can have an electrical conductor arranged and fixed in the disc element acting as a honeycomb body according to the principle described above. The individual conductors can be connected to one another via suitable electrical connections to form a common conductor. In this way, a honeycomb body is created which, viewed along its main flow direction, has a heating conductor in several planes parallel to the gas inlet side.

[0015] It is particularly advantageous if the conductor is inserted into recesses in the end face of the gas inlet side and / or the gas outlet side. Recesses can be created, for example, by machining. For example, a groove can be milled into the end face of the gas inlet side of the honeycomb body, into which the conductor is inserted. In this case, the configuration of the groove also determines the conductor's position. Depending on the application, the metallic conductor can also be arranged on the gas outlet side, for example, if heating of downstream areas in the direction of flow is intended.

[0016] It is also advantageous if the conductor is secured in the ceramic honeycomb body by means of locking elements. In addition to the recess(es), locking elements can be provided to secure the conductor in the honeycomb body. This can be achieved, for example, by means of projections and locking lugs. Alternatively, clamping elements can also be provided, which are inserted, for example, into individual flow channels and thereby secure the conductor.

[0017] It is also preferable if a plurality of conductors are integrated into the honeycomb body.

[0018] The conductors can be arranged in a common plane or in different planes, preferably parallel to the gas inlet side. The planes are preferably offset from one another in the axial direction of the honeycomb body.

[0019] Furthermore, it is advantageous if the conductor is arranged in a plane parallel to the end face of the gas inlet side.

[0020] Furthermore, it is advantageous if the conductor is arranged both in a plane parallel to the end face of the gas inlet side and in a direction perpendicular to the end face. The conductor can thus also run in the axial direction of the honeycomb body, i.e., perpendicular to the end face. This allows, for example, one conductor to be used for multiple planes.

[0021] It is also expedient if one or more conductors are arranged in several mutually parallel planes in the honeycomb body.

[0022] The problem with regard to the method is solved by a method having the features of claim 9.

[0023] An embodiment of the invention relates to a method for producing a ceramic honeycomb body with a metallic electrical conductor according to one of the preceding claims, wherein the following manufacturing steps are carried out: - Producing a ceramic honeycomb body, for example by molding, pressing or casting the ceramic powder or granules, - pressing the metallic conductor into the ceramic honeycomb body, and - Sintering of the honeycomb body with the pressed-in metallic conductor.

[0024] The conductor is pressed into the not-yet-sintered honeycomb body, known as the green body. At this stage, the ceramic does not yet possess the strength that is achieved after the sintering process. By pressing the conductor into the honeycomb body and subsequently sintering it, a precise and durable fit of the conductor is achieved within the ceramic honeycomb body. For example, the conductor can be placed in the desired shape on the end face of the gas inlet side and then pressed flat into the honeycomb body.

[0025] An additional processing step can also be characterized by the pre-forming of an axial recess, whereby a recess for inserting the metallic conductor into the ceramic honeycomb body is created with the aid of suitable mechanical processing.

[0026] Furthermore, it is advantageous if the metallic conductor is pressed into the end face of the honeycomb body from its gas inlet side toward the gas outlet side. This places the heating conductor at the beginning of the honeycomb body, viewed in the direction of flow, essentially heating the flowing exhaust gas before it passes through the honeycomb body. This promotes faster heating of the exhaust gas.

[0027] Furthermore, it is expedient if the metallic conductor follows a defined path, particularly in a spiral or meandering pattern. It is particularly advantageous if the conductor is distributed as evenly as possible across the cross-section of the honeycomb body to ensure the most homogeneous heating of the exhaust gas.

[0028] Improved heating can be achieved through uneven distribution, for example, in the case of non-homogeneous flow through the honeycomb body. Non-homogeneous flow can be caused, for example, by deflections in the exhaust gas flow path, which can lead to uneven distribution of the exhaust gas concentration and also to different flow velocities across the cross-section of the honeycomb body.

[0029] It is also advantageous if a plurality of metallic conductors are pressed into the end face of the honeycomb body.

[0030] Advantageous further developments of the present invention are described in the subclaims and in the following description of the figures. Short description of the drawings

[0031] The invention is explained in detail below using exemplary embodiments with reference to the drawings. In the drawings: Fig. 1 a schematic view of the arrangement of a conductor on the end face of a honeycomb body, Fig. 2 a sectional view through a honeycomb body formed from several disc elements, Fig. 3 a sectional view through a honeycomb body with a pressed-in conductor near the end face of the gas inlet side, Fig. 4 a view of a ceramic honeycomb body with a heating disc in front, and Fig. 5 a sectional view through a honeycomb body with a milled groove for receiving the conductor. Preferred embodiment of the invention

[0032] The Fig. Figure 1 shows a top view of the end face of a honeycomb body 1. Visible are the flow channels 2, which in the example shown have a rectangular cross-section, and also a conductor 3, which runs corrugated along the end face of the honeycomb body 1. Furthermore, a contacting option 4 is shown, which serves to electrically contact the conductor 3.

[0033] It can be seen that the conductor 3 intersects the flow channels 2 and thus covers a certain portion of the flow cross-section of the channels 2.

[0034] Fig. Figure 2 shows a honeycomb body 5 formed from several disc elements 6. Each of the disc elements 6 has a conductor 7. The conductors 7 are electrically connected between the disc elements 6. Thus, the conductors 7 form a common conductor that extends through the entire honeycomb body 5. By stacking the disc elements 6, multiple levels are essentially created within the honeycomb body 5, in which the flowing exhaust gas is heated.

[0035] Fig. 3 shows a section through a honeycomb body 8. The walls 10 indicate the flow channels which extend from the gas inlet side 11 through the honeycomb body 8. The reference numeral 9 designates the electrical conductor which is analogous to the one shown in Fig. 1 is arranged distributed over the cross-section of the honeycomb body 8. It can be seen in particular that the conductor 9 is arranged in the immediate vicinity of the end face 11 of the honeycomb body 8.

[0036] Fig. 4 shows a ceramic honeycomb body 12. A heating disk 13 is positioned in front of the honeycomb body 12 and is connected to the honeycomb body 12 by connecting elements 14. The heating disk 13 is preferably also a ceramic honeycomb body, which has a conductor similar to the previously described figures.

[0037] Fig. Figure 5 shows a section through a honeycomb body 15. Recesses 17 are shown on its gas inlet side 16, which are incorporated into the finished, i.e., sintered, honeycomb body. These can be created, for example, by a machining process. The individual recesses 17 can form a continuous groove in a plan view of the gas inlet side 16, into which the conductor is inserted.

[0038] The examples of the Fig. 1 to 5 are not restrictive in nature and serve to clarify the inventive concept.

Claims

[1] Device for the aftertreatment of exhaust gases from an emission source, in particular an internal combustion engine, with an exhaust tract through which an exhaust gas can flow, with at least one catalyst, wherein the catalyst has a ceramic honeycomb body (1, 5, 8, 12, 15) which is provided with a catalytically active surface coating, and with an electrically heatable heating means (3, 7, 9), wherein the heating means (3, 7, 9) is formed by a metallic electrical conductor (3, 7, 9), wherein the honeycomb body (1, 5, 8, 12, 15) has a plurality of flow channels through which flow can pass from a gas inlet side (11, 16) to a gas outlet side, wherein the conductor (3, 7, 9) is integrated into the ceramic honeycomb body (1, 5, 8, 12, 15), wherein, viewed in the flow direction, it is located opposite the gas inlet side (11, 16) is arranged downstream and upstream of the gas outlet side, characterized byin that the ceramic honeycomb body (5) is formed from at least two honeycomb bodies designed as disc elements (6), which are arranged one after the other in the direction of flow, wherein each of the disc elements (6) has an integrated conductor (7), wherein the conductors (7) in the disc elements (6) are electrically conductively connected to one another. [2] Device according to claim 1, characterized by that the conductor is inserted into recesses (17) in the end face of the gas inlet side (16) and / or the gas outlet side. [3] Device according to claim 2, characterized by that the conductor is fixed in the ceramic honeycomb body by means of locking elements. [4] Device according to one of the preceding claims, characterized by that a plurality of conductors are integrated into the honeycomb body. [5] Device according to one of the preceding claims, characterized bythat the conductor (3, 7, 9) is arranged in a plane parallel to the end face of the gas inlet side (11, 16). [6] Device according to one of the preceding claims, characterized by that the conductor is arranged both in a plane parallel to the end face of the gas inlet side and in a direction transverse to the end face. [7] Device according to one of the preceding claims, characterized by that one or more conductors (7) are arranged in several mutually parallel planes in the honeycomb body (5). [8] Method for producing a ceramic honeycomb body (1, 5, 6, 8, 12, 15) with a device for aftertreating exhaust gases from an emission source according to one of the preceding claims, characterized by that the following manufacturing steps are carried out: - producing a ceramic honeycomb body (1, 5, 6, 8, 12, 15), for example by molding, pressing or casting the ceramic powder or granules, - pressing the metallic conductor (3, 7, 9) into the ceramic honeycomb body (1, 5, 6, 8, 12, 15), and - Sintering the honeycomb body (1, 5, 6, 8, 12, 15) with the pressed-in metallic conductor (3, 7, 9). [9] Method according to claim 8, characterized by that the metallic conductor (3, 7, 9) is pressed into the end face of the honeycomb body (1, 5, 6, 8, 12, 15) from its gas inlet side (11, 16) in the direction of the gas outlet side. [10] Method according to one of claims 8 or 9, characterized by that the metallic conductor (3, 7, 9) follows a defined course, being arranged in a spiral or meandering manner. [11] Method according to one of claims 8 to 10, characterized bythat a plurality of metallic conductors are pressed into the end face of the honeycomb body.

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