Electric heating unit for heating exhaust gas in an exhaust system

Abstract

The invention relates to an electric heating unit 1 for heating exhaust gas in an exhaust system, in particular of a motor vehicle, with a heating element 4.1,...,4.8, to which a longitudinal direction L is assigned, wherein the heating element 4.1,...,4.8 comprises heating resistance sections 6 and exhaust gas flow passages 5 and has an electrical connection area 7.1, 7.2, which comprises at least two thin-walled connection sections 13.1,...,13.4 spaced apart from each other transversely to the longitudinal direction L, each of which is electrically connected to a heating resistance section 6 and is supported against each other by the structure of the heating element 4.1,...,4.8. A special feature is that for electrical contacting of the connection sections 13.1,...,13.4 in the connection area 7.1, 7.2 a coupling part 8.1, 8.2 with receptacles 12.1,...,12.4 for the connection sections 13.1,...,13.4 is provided, wherein each connection section 13.1,...,13.4 is separately enclosed in an associated receptacle 12.1,...,12.4.

Description

[0001] The invention relates to an electric heating unit for heating exhaust gas in an exhaust system, in particular of a motor vehicle, having a heating element to which a longitudinal direction is assigned, wherein the heating element comprises heating resistance sections and passages through which exhaust gas flows and has an electrical connection region which comprises at least two thin-walled connection sections spaced apart from one another transversely to the longitudinal direction, which are each electrically connected to a heating resistance section and are supported against one another by the structure of the heating element.

[0002] For efficient purification of exhaust gases from an internal combustion engine, the exhaust gas must be sufficiently heated. Since the necessary temperature is not yet present immediately after the engine starts, a known measure for faster exhaust gas tempering is to install a separate electric heating unit upstream of the actual exhaust gas purification system.

[0003] For an electric heating unit for heating an exhaust gas stream, reference is made to EP 3 320 196 B1 as an example. Disclosed is an arrangement comprising a tubular housing and elongated electric heating elements extending from the inner wall of the tube. Each heating element comprises a stacked arrangement with a layer sequence of structured metallic foils and smooth layers in between, thus providing gas-flow passages surrounded by heating resistor sections.

[0004] DE 19512097 A1 also discloses an electrically heated catalytic converter. A special feature here is that the heater is designed as a single piece with a large surface area and numerous electrical connection points.

[0005] JPH 06-11 838 U apparently describes an electrically heated catalyst, in which a meander-shaped heating coil is inserted into a pipe cross-section.

[0006] For the electrical contacting or connection of two heating elements, EP 3 320 196 B1 proposes pressing the honeycomb-shaped heating elements together at their distal ends to create connection sections. The connection sections of two adjacent heating elements, compacted in this way, are penetrated and mechanically connected to one another by a rod element used for the holder and electrical supply line. A disadvantage of this design is that when the distal end of a multi-layer heating element is compressed, the outer layers represent a longer path than the inner layers, so that the current flows primarily via the inner layers. Furthermore, it cannot be completely ruled out that, instead of an extensive surface area, the adjacent compacted layers have point contact points that lead to a highly localized heat development when energized.The resulting thermoelectric voltages increase the risk of failure of the electrical heating unit.

[0007] Generic electric heating units are required to have a particularly long service life, which, for use in the exhaust system of a motor vehicle, corresponds at least to the entire service life of the vehicle. Therefore, special attention is paid to the electrical connection area of ​​the heating elements in the electric heating unit, which is subject to high thermal and mechanical stress. The state of the art described above does not meet these requirements.

[0008] To hold band-shaped, one-piece heating elements of an electric heating unit, DE 10 2019 123 486 A1 proposes merging the positive and negative electrical connections of the band-shaped heating elements in a multi-part coupling part. Holding jaws are used, which are clamped against each other with a screw bolt and interposed electrical insulators. Each individual heating band is energized only from one lateral side, while the opposite lateral side is in contact with an electrically insulating holding jaw. Electrical contact by clamping in a vice-like arrangement cannot simply be applied to the electrical connection of a heating element through which exhaust gas flows, which consists of several thin-walled layers and whose distal end is not sufficiently compression-resistant.

[0009] The invention is based on the object of providing an electric heating unit with a long service life, which comprises an electrically contacted heating element with gas-flow passages and heating resistance sections.

[0010] This object is achieved by a generic heating unit as mentioned above, in which a coupling part with receptacles for the connection sections is provided for the electrical contact of the connection sections in the connection area, wherein each connection section is enclosed separately in an associated receptacle.

[0011] Advantageous embodiments emerge from the subclaims and the description.

[0012] The invention is based on an electric heating unit for heating exhaust gas, which is positioned in an exhaust system. The electric heating unit has at least one heating element with an elongated extension and a longitudinal direction. In the installed position, this longitudinal direction runs essentially perpendicular to the average exhaust gas flow direction.

[0013] Within the heating element, exhaust gas flows through passages, so that at least a portion of the exhaust gas is guided through the body of the heating element. In addition, the heating element comprises heating resistor sections and an electrical connection area having at least two thin-walled connection sections spaced apart from one another transversely to the longitudinal direction. Each of the connection sections is at least indirectly electrically connected to one or more heating resistor sections of the heating element. To improve mechanical stability, adjacent connection sections are mutually supported by the structure of the heating element.

[0014] One possible design of a heating element of this type is a honeycomb body, with the honeycomb channels forming the gas-flow passages of the heating element and running essentially parallel to the main flow direction of the exhaust gas. The walls of the honeycomb channels form the heating resistor sections of the heating element. Furthermore, at least a portion of the honeycomb walls in the electrical connection area also serves as a connection area. The honeycomb dimension at the electrical connection area determines the transverse spacing between adjacent connection sections. In addition, the honeycomb geometry provides mutual support for adjacent connection sections.

[0015] Further designs of this generic electric heating unit are possible. An alternative design uses a layer sequence with flat heating resistor sections, spaced from each other by intermediate layers with gas-flow passages. Foamed materials with free flow paths are considered as possible intermediate layers. The use of corrugated layers between flat heating resistor sections is also possible.

[0016] Generic electric heating units have thin-walled connection sections that occupy a fixed distance transversely to the longitudinal direction of the heating element. In this case, a thin-walled connection section is understood to be a structure whose transverse extent perpendicular to the longitudinal direction is smaller than the entire heating element. Flat connection sections in the form of sheet metal layers are preferred, with sheet thicknesses of less than 1.5 mm and especially less than 1 mm being particularly preferred for thin-walled connection sections.

[0017] For the electric heating unit according to the invention, a coupling part with receptacles for the connection sections is provided for the electrical contact at its connection area. Each connection section of the heating element is enclosed separately in a corresponding receptacle of the coupling part. This results in a structural adaptation to the specified geometry of the connection area on the heating element with the thin-walled connection sections spaced from one another transversely to the longitudinal direction. This ensures that the electrical contact of the heating element is made as flat as possible, at various coupling points and thus distributed across the cross-section of the heating element, so that the current feed is distributed evenly across all connection sections of a heating element and the current supply to a connection section is thus arranged generously and preferably symmetrically.This means that even wide heating elements can be supplied with current without any problems, without the risk that outer layers receive less current than inner ones.

[0018] Preferably, the coupling part has receptacles for the connection sections, which are designed so that each connection section of the heating element rests against the wall of the respective receptacle on at least two opposite side surfaces. This enables advantageous power supply on both sides, thus increasing the contact area and thus reducing the contact resistance.

[0019] Particularly preferred is a design of the receptacle on the coupling part in the form of a through-opening with a substantially closed border. "Substantially" means that designs in which the through-opening is designed in multiple parts are also included. An electrical contact extending in the longitudinal direction of the heating element between the essential parts of the inner wall of the through-opening and the surface areas of the enclosed connection section facing these parts is advantageous. The planar current supply reduces thermal stresses resulting from temperature gradients and simultaneously mechanically stabilizes the connection area in the receptacle.Furthermore, the receptacles provided according to the invention on the coupling part for the separate enclosure of the connection sections are preferably adapted to their arrangement on the heating element, so that no excessive mechanical stresses leading to deformation occur at the distal end of the heating element during the holder.

[0020] In a particularly preferred embodiment of the invention, the coupling part is constructed in multiple parts. At least two comb plates are provided, which are designed to complement one another. A first comb plate has at least one prong, and a second comb plate has a recess that is designed to complement the prong. When the comb plates are assembled, a substantially uniform gap forms between the end faces of the recess and the prong, which serves as a receptacle for an individual connection section of the heating element. In the assembled state, the prong engages between the spaced-apart connection sections and contacts them on their mutually facing sides. The recess engages over the prong and contacts the connection sections from the other side, i.e. on their sides facing away from each other. A coupling part that can be assembled in this way with precisely fitting comb plates facilitates assembly.

[0021] A preferred design of the comb plates of a coupling part provides for the complementary prongs and recesses to taper in the same direction, approximately trapezoidally, so that the prong tapers in width toward its free end and the recess tapers complementarily toward its base. This reduces the gap when the two comb plates are fitted together, making it easy to clamp a thin-walled connection section of the heating element across the entire surface. Thickness variations in the contact area of ​​the connection section between two workpieces can also be compensated for in this way.

[0022] For a further preferred embodiment of the invention, webs are provided on the heating element which run essentially transversely to the longitudinal direction and support the connecting sections at a predetermined transverse distance. The coupling part is flat and, at least in the region of the receptacles for the connecting sections, has an extension in the longitudinal direction which is smaller than the transverse distance predetermined by the webs. The webs are particularly preferably arranged in such a way that a heating element with a honeycomb structure is created which comprises exhaust gas flow passages pointing in the exhaust gas flow direction. For such an embodiment, as a further development, the coupling part can have comb plates whose prong dimensions and prong spacing are adapted to the honeycomb structure of the heating element such that, for the electrical contacting and holding, a prong engagement in the exhaust gas flow passages, i.e.the break in the honeycomb structure is possible.

[0023] If the tines are slightly conical and designed according to the honeycomb structure, it is possible to form the coupling part with a single comb that engages in the honeycomb channels of the honeycomb structure and is held in place by friction.

[0024] However, a preferred alternative design provides two complementary comb plates whose recess and prong dimensions are adapted to the honeycomb structure of the heating element, allowing engagement from both sides. A section of the honeycomb wall of the honeycomb-shaped heating element is enclosed in the gap area between the complementary prongs and recesses. This then forms the respective connection section of the heating element.

[0025] For one embodiment of the invention, the coupling part is attached to the heating element at a predetermined distance from its distal end. This means that the current is not introduced directly into the heating element at the front end; instead, there is a non-energized projection on the heating element, which serves as a cooling element and thus evens out the temperature in the electrical connection area.

[0026] In an alternative design, the coupling part forms the distal end of the heating element. Particularly when using a honeycomb structure as the heating element, a coupling part engaging with this structure can be attached to a continuous material in a first manufacturing step. In a subsequent manufacturing step, the continuous material is sheared off against a wall surface of the coupling part. This reliably prevents excessive shear forces on the delicate honeycomb structure during shearing.

[0027] In an advantageous embodiment, after the connection sections have been enclosed in the corresponding receptacles on the coupling part, a material connection is created, particularly by soldering or welding, especially laser welding. This further reduces the electrical contact resistance and also improves the mechanical bond for the holder.

[0028] Exemplary embodiments of the invention are explained below in conjunction with figures. These schematically show the following: Fig. 1: an embodiment of the electric heating unit in perspective view, Fig. 2: a heating element of the electric heating unit for the Fig. 1 illustrated embodiment and Fig. 3: a partially assembled heating element in exploded view.

[0029] Fig. Figure 1 shows an embodiment of the electric heating unit 1 according to the invention in a simplified schematic representation. It shows a tubular housing 2 with the connections of a power supply 3.1, 3.2. The exhaust gas flows axially through the electric heating unit 1, with the exhaust gas flowing partly around and partly through a plurality of heating elements 4.1, ..., 4.8.

[0030] Fig. Figure 2 shows an enlarged view of a single heating element 4.1. This has a honeycomb structure. It can be seen that each honeycomb channel forms a passage 5 through which exhaust gas flows, which is aligned essentially parallel to the average exhaust gas flow direction A. The walls of each of the passages 5 through which exhaust gas flows form a heating resistance section 6 of the heating element 4.1.

[0031] The longitudinal extension of the heating element 4.1 is Fig. 2, which corresponds to the transverse direction Q. Furthermore, it can be seen that at the distal ends of the heating element 4.1 there is an electrical connection area 7.1, 7.2, which serves for electrical contact and support. For this purpose, a coupling part 8.1, 8.2 is provided, the detailed structure of which can be seen in the exploded view of Fig. 3 is evident.

[0032] Shown in Fig. 3 a two-part coupling part 8.1. The coupling part 8.1 has two complementary comb plates 9.1, 9.2 with interlocking prongs 10.1, ..., 10.5 and recesses 11.1, ..., 11.5. When the comb plates 9.1, 9.2 are assembled, as shown in Fig. 2, a uniform gap between the end faces of a corresponding pairing of prongs 10.1, ..., 10.5 and recess 11.1, ..., 11.5, so that an arrangement of receptacles 12.1, ..., 12.4 for thin-walled connection sections 13.1, ..., 13.4 is provided on the heating element 4.1.

[0033] For the present embodiment with a honeycomb-shaped heating element 4.1, as shown in Fig. 3, the thin-walled connecting sections 13.1, ..., 13.4 are separated by a shearing action parallel to the exhaust gas flow direction A and perpendicular to the longitudinal direction L, which divides a transverse row arrangement of the passages 5. The honeycomb webs thus exposed at the distal end of the heating element 4.1 form thin-walled connecting sections 13.1, ..., 13.4, which are mutually supported by the structure of the heating element 4.1, namely the remaining honeycombs. They represent an arrangement with parallel sheet metal extensions that have a fixed transverse spacing extending perpendicular to the exhaust gas flow direction A and perpendicular to the longitudinal direction L. The prongs 10.1, ..., 10.5 and the recesses 11.1, ..., 11.5 on the comb plates 9.1, 9.2 are adapted to this transverse distance, so that the receptacles 12.1, ..., 12.4 are aligned after the coupling part 8.1, 8.2 has been assembled.

[0034] To achieve the best possible mechanical contact between the walls of the gap-shaped receptacles 12.1, ..., 12.4 and the thin-walled connecting sections 13.1, ..., 13.4, the prongs 10.1, ..., 10.5 and the corresponding complementary recesses 11.1, ..., 11.5 taper in the same direction when viewed from above, in a slightly trapezoidal shape here. Accordingly, when the comb plates 9.1, 9.2 are assembled, the end faces of the prongs 10.1, ..., 10.5 and the recess 11.1, ..., 11.5 successively converge until the desired flat contact with the thin-walled connecting sections 13.1, ..., 13.4 is achieved. Further homogenization of the electrical contact resistance is achieved by an additional assembly step, carried out after the attachment of coupling part 8.1, using a material-to-material connection. Soldering or welding, particularly laser welding, is preferred for this purpose.

[0035] In Fig. Figure 2 shows a design for which the coupling part 8.1, 8.2 is located at the respective distal end of the heating element 4.1. Thus, the honeycomb structure of the heating element 4.1 is flush with the end face of the coupling part 8.1, 8.2. This design has the advantage that, for assembly, the two comb plates 9.1, 9.2 are first placed on a continuous honeycomb strip by engaging their prongs in a transverse row of honeycomb openings at a predetermined longitudinal position. The complementary design of the comb plates 9.1, 9.2 creates a stabilizing, mutual support of the honeycomb webs, allowing a subsequent shearing step of a continuous honeycomb strip to be carried out more easily.

[0036] For an alternative design not shown in detail, the shearing in the longitudinal direction L is offset from the front side of the coupling part 8.1, 8.2, so that an extension of the honeycomb band, which acts as a cooling element during operation of the electric heating unit 1, remains.

[0037] From the overall presentation of Fig. 1 shows that each coupling part 8.1, 8.2 is at least indirectly mounted on the housing 2. For the power supply, an electrical contact section 14.1, ..., 14.4 is provided on the coupling parts 8.1, 8.2, which is complementary to a housing-side mounting not shown in detail.

[0038] The invention has been described using an exemplary embodiment. Without departing from the scope of protection defined by the applicable claims, numerous further embodiments for implementing the inventive concept will become apparent to those skilled in the art without the need for further explanation within the scope of these statements. List of reference symbols 1 electric heater 2 Enclosure 3.1, 3.2 Power supply 4.1, ..., 4.8 Heating element 5 Passage 6 Heating resistance section 7.1, 7.2 electrical connection area 8.1, 8.2 Coupling part 9.1, 9.2 Comb plate 10.1, ..., 10.5 prongs 11.1, ..., 11.5 Recess 12.1, ..., 12.4 Recording 13.1, ..., 13.4 Connection section 14.1, ..., 14.4 electrical contact section A Exhaust gas flow direction L longitudinal direction Q transverse direction

Claims

[1] Electric heating unit (1) for heating exhaust gas in an exhaust system, in particular of a motor vehicle, with a heating element (4.1,...,4.8) to which a longitudinal direction (L) is assigned, wherein the heating element (4.1,...,4.8) comprises heating resistance sections (6) and passages (5) through which exhaust gas flows and has an electrical connection area (7.1, 7.2) which comprises at least two thin-walled connection sections (13.1,...,13.4) spaced from one another transversely to the longitudinal direction (L), which are each electrically connected to a heating resistance section (6) and are supported against one another by the structure of the heating element (4.1,...,4.8), characterized bythat for the electrical contacting of the connection sections (13.1,...,13.4) in the connection area (7.1, 7.2) a coupling part (8.1, 8.2) with receptacles (12.1,...,12.4) for the connection sections (13.1,...,13.4) is provided, wherein each connection section (13.1,...,13.4) is enclosed separately in an associated receptacle (12.1,...,12.4). [2] Electric heating unit according to claim 1, characterized by that each connecting section (13.1,...,13.4) rests on at least two opposite side surfaces against a wall of the respective associated receptacle (12.1,...,12.4). [3] Electric heating unit according to claim 1 or 2, characterized by that each receptacle (12.1,...,12.4) on the coupling part (8.1, 8.2) is designed as a through opening with a substantially closed border. [4] Electric heating unit according to one of the preceding claims, characterized byin that the coupling part (8.1, 8.2) comprises at least two comb plates (9.1, 9.2), wherein a first comb plate (9.1) provides at least one prong (10.1,...,10.5) and the second comb plate (9.2) provides a recess (11.1,...11.5) complementary to the prong (10.1,...,10.5), so that in the assembled state of the two comb plates (9.1, 9.2) between end faces of the recess (11.1,...11.5) and of the prong (10.1,...,10.5) there is a substantially uniform gap which forms the receptacle (12.1,...,12.4) for a connecting section (13.1,...,13.4). [5] Electric heating unit according to claim 4, characterized by that the prong (10.1,...,10.5) and the recess (11.1,...,11.5) taper in the same direction, approximately trapezoidal in shape. [6] Electric heating unit according to claim 5, characterized bythat part of the structure of the heating elements (4.1,...,4.8) are webs which run essentially transversely to the longitudinal direction (L) and which support the connecting sections (13.1,...,13.4) against one another with a predetermined transverse distance, and the receptacle (12.1,...,12.4) has an extension in the longitudinal direction (L) which is smaller than the transverse distance between two adjacent webs. [7] Electric heating unit according to one of the preceding claims, characterized by that the heating element (4.1,...,4.8) has a honeycomb structure with honeycomb channels, wherein the honeycomb channels form the exhaust gas flow passages (5) pointing in the exhaust gas flow direction (A). [8] Electric heating unit according to one of the preceding claims, characterized by that the coupling part (8.1, 8.2) is arranged at a distance from a distal end of the heating element (4.1,...,4.8). [9] Electric heating unit according to one of claims 1 to 7, characterized bythat the coupling part (8.1, 8.2) forms the distal end of the heating element (4.1,...,4.8). [10] Electric heating unit according to one of the preceding claims, characterized by that the coupling part (8.1, 8.2) is soldered or welded, in particular laser welded, to the heating element (4.1,...,4.8). [11] Electric heating unit according to one of the preceding claims, characterized by that the coupling part (8.1, 8.2) has electrical contact sections (14.1,...,14.4) in its opposite end regions, to which it is at least indirectly connected to a power supply (3.1, 3.2) of the heating unit (1). [12] Electric heating unit according to one of the preceding claims, characterized by that the heating element (4.1,...,4.8) is supported by means of the coupling part (8.1, 8.2) relative to a housing (2) of the heating unit (1).

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