Catalytic converter with heating disc

Abstract

Electric heating device (1) in an exhaust system of a motor vehicle, comprising an externally circumferential, in particular round, housing, wherein a heating conductor is arranged in the housing which can be heated by applying an electric current and heats a catalyst (2), characterized in that the heating conductor is designed as a heating disc (3) which emits radiant heat onto a neighboring catalyst (2) and that the width (6) of the heating conductor transverse to the exhaust flow direction (A) is at least five times greater than the depth (7) of the heating conductor in the exhaust flow direction (A).

Description

[0001] The present invention relates to an electric heating device according to the features in the preamble of claim 1.

[0002] A heating device in exhaust systems is used to quickly warm the exhaust aftertreatment components. Common applications include full-flow exhaust gas systems, exhaust gas recirculation, and SCR technology for the hydrolysis of urea-water solutions to ammonia. Typical designs are electrical heating elements made of thin metal strips with small channels for improved heat transfer.

[0003] As the exhaust gas flows over the heating element, convection heats the exhaust gas flowing past it. This heated exhaust gas then transfers its heat to the catalyst downstream in the exhaust gas flow direction, also via convection, so that the catalyst reaches operating temperature more quickly. Such a design variant is known, for example, from DE 10 2015 111 689 B3. However, in this design, the heating element itself is embedded in a porous mineral structure, resulting in increased manufacturing costs.

[0004] Furthermore, a heating disc is known from DE 10 2009 018 182 A1.

[0005] The object of the present invention is to provide an auxiliary heater for a catalyst, which is initially arranged decoupled from the catalyst, meets high thermal and mechanical requirements in the vehicle exhaust system and, in particular, provides particularly rapid heating for a cold start process.

[0006] The aforementioned problem is solved according to the invention in an electric heating device in an exhaust system of a motor vehicle with the features in claim 1.

[0007] Advantageous design variants are described in the dependent claims.

[0008] The electric heating device in the exhaust system of a motor vehicle has an externally surrounding housing. This housing is, in particular, round. A heating element is arranged within the housing, and this element can be heated by applying an electric current. The heating element heats a catalyst. The catalyst is also located within the housing. Specifically, the catalyst is positioned downstream of the heating element in the direction of exhaust flow.

[0009] According to the invention, the heating conductor itself is designed as a heating disc. This is achieved by the heating conductor covering a large portion of the subsequent catalyst in terms of its surface area, particularly its cross-sectional area. This design, according to the invention, ensures that the heat energy generated and emitted by the heating conductor is transferred to the adjacent catalyst in the form of radiant heat.

[0010] Thus, according to the invention, it is achieved that an exhaust gas flow is not even necessary to transfer heat to the catalysts, but rather a large part of the heating power is already achieved through thermal radiation. Therefore, the catalyst can be heated even during the start-up process of the internal combustion engine, i.e., even before any exhaust gas flow occurs. When the exhaust gas flow begins, the catalyst already has a corresponding preheating and can thus reduce exhaust emissions, thereby significantly improving emissions during cold starts.

[0011] To allow exhaust gas flow, including through the heating element, the heating disc itself is perforated. Therefore, the heating disc has holes, recesses, or other perforations to allow exhaust gas to flow through it.

[0012] The heating element is formed by the heating conductor itself. For this purpose, the heating conductor is wound in a meandering or spiral shape, so that a spiral is visible when viewed from a cross-sectional view through the heating device or from a view of the transverse surface of the heating element itself. This meandering or spiral exhibits a coverage of the downstream catalyst of more than 40%, particularly more than 45%, preferably more than 50%, very preferably more than 60%, particularly more than 70%, and very preferably more than 80%, and particularly more than 90%, in its cross-sectional area or outer dimension.

[0013] This means that the heating element covers a cross-sectional area within the aforementioned percentage ranges, in particular a large portion of the cross-sectional area of ​​the catalyst in the direction of exhaust gas disturbance. However, to prevent an increase in back pressure in the exhaust gas flow, the heating element, or rather the individually wound conductor tracks of the heating conductor itself, are perforated. The aforementioned percentage values ​​for the cross-sectional area therefore refer to the external dimensions, not the perforation. The perforations or recesses in the heating conductor itself would theoretically have to be subtracted from this cross-sectional area. With regard to the inventive effect, whereby a large area of ​​the downstream catalyst is covered in such a way that the radiant heat emitted by the heating element is transferred to the downstream catalyst over as large an area as possible and thus also homogeneously, the cross-sectional area of ​​the covering is important. The perforation or...Exclusions can be deducted from this, since the perforation surrounding the edge areas of the heating conductor heat up due to electrical energy and then, in particular, transfer radiant heat to the catalyst.

[0014] The heating disc or the coiled heating conductor forming the heating disc is itself made of a wire mesh, expanded metal, or perforated sheet metal. In particular, the heating conductor is perforated. According to the invention, the heating conductor is thus coiled to form a disc or a disc-shaped body.

[0015] This heating element is preferably supported by the catalyst itself, which follows the heating element in the exhaust gas flow direction. The support is preferably electrically insulated. However, the support can also be thermally conductive. Thus, in addition to heat radiation, heat conduction can also occur from the heating element to the catalyst.

[0016] A support catalyst can also be positioned upstream of the heating disc in the exhaust gas flow direction. In particular, the support catalyst is also preheated by thermal radiation, especially during cold starts, which further contributes to a reduction in emissions, particularly during cold starts. The initial exhaust gas flow during a cold start thus first encounters the support catalyst, which has already been preheated by thermal radiation, allowing pollutants to be converted within the support catalyst itself. However, the support catalyst also serves, in particular, to compensate for vibrations and / or thermal expansion during subsequent operation, thereby ensuring the longevity of the entire arrangement according to the invention.

[0017] Two or more heating elements can also be mechanically arranged and electrically connected in parallel. This can improve the heating performance.

[0018] It is also possible to position the heating disc between two catalytic converters. The "between" refers to the direction of exhaust gas flow. A gap can remain so that the heating disc is not in direct contact with the converters. In particular, this allows the radiant heat to be transferred to both upstream and downstream catalytic converters when the heating disc is activated.

[0019] When the exhaust gas flows, the upstream catalyst is also heated by radiant heat. This heat is then transferred to the downstream catalyst via convection as the exhaust gas passes over the heating disc.

[0020] In another particularly preferred embodiment, the heating disc is designed as a coiled heating conductor. The heating conductor strand itself is formed as a finned sheet with a curved cross-section. The individual coiled strands overlap radially. Due to the fact that each individual strand is curved in a wave-like cross-section, an axial opening is created despite the radial overlap. This ensures that the largest possible area is covered as a transverse span, so that the downstream catalyst is covered to the greatest extent possible, especially when radiation is emitted. At the same time, however, it allows exhaust gas to flow through the heating disc itself without the heating conductor strand being perforated.

[0021] Further advantages, features, properties, and aspects of the present invention are the subject of the following description. Preferred embodiments are illustrated in the figures. These serve to facilitate understanding of the invention. They show: Fig. 1 an arrangement of an electric heating device according to the invention, Fig. 2 a longitudinal section view; Fig. 3 a top view, Fig. 4 and Fig. 5 a heating disc in the form of a coiled heating conductor with radial overlap.

[0022] In the figures, the same reference symbols are used for identical or similar components, even if a repeated description is omitted for the sake of simplicity.

[0023] Fig. Figure 1 shows an arrangement of an electric heating device 1 according to the invention. For this purpose, a catalyst 2 with a heating disc 3 positioned upstream in the exhaust gas flow direction A is arranged in a housing, in particular a round housing 4. Electrical connections 5 can be provided on the housing 4 so that the heating disc 3 arranged in the housing 4 can be supplied with current.

[0024] Fig. Figure 2 shows a longitudinal section view. In the housing 4, the catalyst 2 is located downstream of the heating disc 3 in the exhaust gas flow direction A. The heating disc 3 itself is disc-shaped and has a meandering or spirally wound heating conductor.

[0025] The heating disc 3 extends over a large cross-sectional area of ​​the downstream catalyst 2. This is further illustrated in Fig. Figure 3 shows that the heating disc 3 itself is formed from a perforated sheet metal strip and is wound in a spiral or meandering pattern. The cross-sectional area of ​​the outer dimensions of the sheet metal strip covers more than 40%, in particular more than 45%, more than 50%, and in this case more than 70% of the cross-sectional area of ​​the catalyst 2 behind it. The heating element of the heating disc 3 is perforated between its outer dimensions. This perforation is not subtracted from the percentage of the area covered. Thus, exhaust gas can also pass through the perforated heating element 5. At the same time, however, the area behind it is covered due to the outer dimensions of the heating disc 3, so that the radiant heat emitted by the heating disc 3 covers a large proportion of the area of ​​the catalyst behind it. Any supports for the heating disc on the catalyst itself are not shown in detail.However, these are present to achieve mechanical stability against the flowing exhaust gas, and at the same time to compensate for thermal expansions and / or vibrations.

[0026] Furthermore, in comparison of Fig. 3 to Fig. 2 to recognize that the width 6 of the heating conductor of the heating disc 3, which is measured perpendicular to the exhaust gas flow direction A, is at least five times greater than that in Fig. 2 shown depth 7 of the heating conductor, where the depth 7 is measured in exhaust gas flow direction A.

[0027] Fig. Figure 4 shows a perspective view of a heating device 1.

[0028] Fig. Figure 5 shows a longitudinal section view along the section line BB. Fig. 4 on the same heating device 1.

[0029] Here too, a catalyst 2 is arranged in a housing 4. The catalyst 2 is located downstream of the heating disc 3 in the exhaust gas flow direction A. The heating disc 3 is a spirally or meanderingly wound heating conductor 8, which is connected to a power source via electrical connections 5 (not shown) located outside the housing 4.

[0030] In the Fig.Figure 5 shows the cross-sectional view of each turn of the heating conductor 8. These are individual lamellae, each exhibiting an S-shaped, Z-shaped, or wave-like profile in its own cross-section. Thus, the individual turns of the heating conductor 8 overlap radially. In the axial direction, the exhaust gas can pass through the heating disc 3 in the direction of exhaust gas flow A, as indicated by the dashed line. For this purpose, the individual turns, which overlap radially, are spaced apart axially, creating an opening 9 for the exhaust gas to pass through. In this way, the heating disc 3 provides the largest possible coverage of the cross-section of the housing 4 and the transverse contact surface of the catalyst 2. The radiated heat from the heating disc 3 thus covers the largest possible area.Due to the individual cross-section of each turn of the heating conductor 8, which is essentially rigid, a good current flow and thus heating of the heating conductor 8 for heat emission via thermal radiation is achieved. The individual turns can be coupled to each other (not shown in detail), for example, supported against each other, so that even in the event of exhaust gas flow, deformation of the individual turns relative to each other is prevented. Reference symbol: 1 Heating device 2 catalyst 3 Heating disc 4 cases 5 electrical connection 6 Width 7 Depth 8 heating conductors 9 Opening A Exhaust gas flow direction

Claims

[1] Electric heating device (1) in an exhaust system of a motor vehicle, comprising an outer circumferential, in particular round, housing, wherein a heating conductor is arranged in the housing which can be heated by applying an electric current and heats a catalyst (2), characterized by , that the heating conductor is designed as a heating disc (3) which emits radiant heat onto a neighboring catalyst (2) and that the width (6) of the heating conductor perpendicular to the exhaust gas flow direction (A) is at least five times greater than the depth (7) of the heating conductor in the exhaust gas flow direction (A). [2] Electric heating device (1) according to claim 1, characterized by , that the heating disc (3) is perforated. [3] Electric heating device (1) according to claim 1 or 2, characterized by , that the heating disc (3) is formed by a meander. [4] Electric heating device (1) according to any one of the preceding claims, characterized by that the heating disc (3) covers at least 40% of the cross-sectional area of ​​the catalyst (2), in particular more than 45%, preferably more than 50%, particularly preferably more than 60%, most preferably more than 80%. [5] Electric heating device (1) according to any one of the preceding claims, characterized by , that the heating disc (3) is made of a wire mesh, expanded metal or perforated sheet metal. [6] Electric heating device (1) according to any one of the preceding claims, characterized by , that the heating disc (3) is catalytically coated. [7] Electric heating device (1) according to any one of the preceding claims, characterized by , that the heating disc (3) is supported on the catalyst (2). [8] Electric heating device (1) according to any one of the preceding claims, characterized by , that the catalyst (2) is located upstream or downstream of the heating disc (3) in the direction of exhaust gas flow. [9] Electric heating device (1) according to any one of the preceding claims, characterized by , that the heating disc (3) is arranged in the exhaust gas flow direction between two catalysts (2). [10] Electric heating device (1) according to any one of the preceding claims, characterized by that two or more heating discs (3) are arranged in parallel and electrically connected. [11] Electric heating device (1) according to any one of the preceding claims, characterized by , that the heating disc (3) is formed by a spirally wound heating conductor (8), wherein the individual windings overlap in the radial direction and are spaced apart from each other in the axial direction, such that exhaust gas can flow through the heating disc (3).

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