Electric heating unit for heating an exhaust gas stream

Abstract

The invention relates to an electric heating unit 1 for heating an exhaust gas stream in an exhaust system, in particular of a motor vehicle with an associated exhaust gas flow direction A, comprising an enclosure 2 surrounding the exhaust gas stream and at least one heating assembly 4.1,...,4.8 comprising a heating element 5.1 arranged in the enclosure 2, wherein the heating element 5.1 comprises heating resistance sections 7 and exhaust gas flow passages 6 and wherein a space 9.1,...,9.n is provided between a distal end of the heating assembly 4.1,...,4.8 and an inner wall of the enclosure 2. A special feature is that the space 9.1,...,9.n is essentially shielded by at least one guide body 10.1,...,10.m held on the housing 2 and the guide body 10.1,...,10.m has at least one cover surface 11.1,...,11.1 pointing in the exhaust gas flow direction A.

Description

[0001] The present invention relates to an electric heating unit for heating an exhaust gas flow in an exhaust system, in particular of a motor vehicle with an associated exhaust gas flow direction, comprising a housing enclosing the exhaust gas flow and at least one heating assembly comprising a heating element and arranged in the housing, wherein the heating element comprises heating resistance sections and exhaust gas flow passages and wherein there is a gap between a distal end of the heating assembly and an inner wall of the housing

[0002] The effective operation of an exhaust gas purification system requires a sufficient operating temperature. Therefore, especially for vehicle applications, a warm-up period must be allowed after a cold start. This warm-up period can be shortened by installing an electric heating unit upstream of the exhaust gas purification system. Such an electric heating unit must meet various requirements. On the one hand, it must provide a long service life for a large number of heating cycles; on the other hand, it must be compact and lightweight, enabling energy-efficient operation.

[0003] Known designs of generic electric heating units comprise at least one heating assembly located within an enclosure through which exhaust gas flows. In a preferred embodiment, a heating assembly has a heating element with an internal structure that provides gas-flow passages and heating resistor sections. Such heating elements can be prefabricated as multi-layer continuous material and used to assemble an electric heating unit in predetermined lengths in an enclosure for containing an exhaust gas flow. Reference is made to EP 0 541 585 A1 as an example. Disclosed is a wound arrangement of a sheet stack sequence with alternating smooth and corrugated layers. The winding arrangement adapts to a substantially circular inner contour of the enclosure, with an all-round air gap being provided between the inner wall of the enclosure and the heating element.This measure electrically insulates the heating element, allowing for simplified installation of the electrode structure for power supply. In addition, the resistance-heated area is thermally separated from the cooler interior walls of the enclosure.

[0004] Another example of an electric heating unit with an elongated heating assembly comprising a heating element having heating resistance sections and passages through which gas flows is disclosed in EP 2 802 752 B1. In an axial plane of the housing, the spiral-shaped heating assembly is arranged such that free spaces exist between its adjacent heating element sections. Furthermore, a portion of the exhaust gas flow can pass through a free path created between parts of the inner wall of the housing and the outermost section of the spiral winding of the heating assembly. This results in flow sections in which the exhaust gas is heated to different temperatures. Furthermore, one of the distal ends of the heating assembly is applied to a section of the inner wall of the housing for the current discharge. In this area, there is a reduced heating effect due to the outwardly directed heat flow in the contact area.

[0005] DE 698 04 564 T2 discloses a heating unit which is held in a housing with extensive heat insulation.

[0006] The invention is based on the object of providing an electric heating unit with partially flowing heating elements for heating an exhaust gas flow in an exhaust system, which is easy to install and enables uniform heating of the exhaust gas with high efficiency.

[0007] This object is achieved by an above-mentioned, generic electric heating unit in which the intermediate space is substantially shielded by at least one guide body held on the housing and the guide body has at least one cover surface pointing in the exhaust gas flow direction.

[0008] Advantageous embodiments emerge from the subclaims and the description.

[0009] The starting point of the invention is an electric heating unit that has a housing enclosing the exhaust gas flow. The housing can be tubular with a circular contour. Alternatively, a non-circular cross-section can be used, particularly to adapt to the available installation space or the upstream flow geometry. The electric heating unit is assigned an exhaust gas flow direction, which is determined by averaging the cross-section of the heating unit exposed to the exhaust gas.

[0010] Typically, at least one heating assembly comprising a heating element is provided within the housing. The heating element has an internal structure comprising gas-flow passages and heating resistor sections. This internal structure can be delicate or porous. In particular, designs as honeycomb heaters or as a layered composite with foam layers offering free movement, or in the form of corrugated strips with a sequence of smooth and corrugated layers are conceivable. The heating elements preferably have a longitudinal extension in a direction perpendicular to the exhaust gas flow direction that is greater than their transverse dimensions.

[0011] Along its longitudinal extension in a cross-sectional plane of the housing facing the exhaust gas flow, the heating element of the heating assembly can be arranged in a meandering or spiral shape. For such a curved structure, the heating element is assigned a longitudinal direction in sections, which is determined by averaging along the respective sections. In a preferred design, the heating unit comprises several heating assemblies comprising a parallel arrangement of straight heating elements.

[0012] According to the invention, the arrangement of at least one heating assembly in the housing of an electric heating unit results in an intermediate space extending between an inner wall of the housing and a distal end of the heating assembly. This intermediate space, created by the spacing of the inner wall of the housing and the heating assembly, is substantially shielded by at least one guide body held on the housing. The guide body has at least one cover surface facing in the exhaust gas flow direction. In the present case, a cover surface aligned in this way is understood to be a surface element with an averaged surface normal that is in any case substantially parallel to the exhaust gas flow direction.This measure reduces, and preferably substantially blocks, the passage of exhaust gas between the inner wall of the housing and a distal end of the heating assembly by means of a separate component, the guide body. For this purpose, it is not necessary for the guide body to completely seal the intermediate space in a fluid-tight manner. Instead, an intermediate gap region can be provided around the cover surface facing the exhaust gas flow, particularly for the compensation of thermal stresses. In such a configuration, a dynamic pressure effect resulting from the reduction in flow velocity caused by the cover surface is used to block the exhaust gas flow in this area.

[0013] A guide body according to the invention results in a concentration of the exhaust gas flow on the part of the electric heating unit that is highly heated during operation, i.e. on the central area within the housing in which the arrangement with at least one heating module is located. The exhaust gas is therefore kept away from the cooler inner walls of the housing and the areas where no parts of the heating module are present by a dynamic pressure effect. A self-regulating exhaust gas cushion is formed. Accordingly, a shielded, flow-calmed area exists in the intermediate space, which is essentially blocked by the guide body. If the structure of the guide body is designed for reduced heat transfer, an effective thermal barrier is created against the heated area of ​​the electric heating unit.

[0014] The conducting element is preferably secured to the housing by means of a support element. In a preferred embodiment, the support element is designed as an electrical insulator, so that the conducting element can be set to a predetermined electrical potential independent of the housing. It is conceivable to use the conducting element as a component for supplying power or as an intermediate element for conducting power between serially connected heating assemblies.

[0015] In a further preferred embodiment, the guide body is designed as a hollow part. This advantageously reduces the thermal mass and improves the guide body's function as a temperature barrier between the respective heating assembly and the housing.

[0016] In an advantageous further design, in addition to its flow guidance function for the exhaust gas, the guide body also fulfills the further mechanical function of serving as a support for the heating assembly. For this purpose, the guide body preferably has a mounting arrangement designed for attaching the heating assembly. For this purpose, an embodiment is advantageous for which the mounting arrangement encloses an area of ​​the heating assembly, typically a distal end of the heating assembly. For this purpose, form-fitting components can be provided which simplify the assembly of the electric heating unit. Particularly preferred are embodiments of the mounting arrangement which spatially restrict the contact area with the heating assembly for the lowest possible heat transfer and at the same time provide effective support against the loads during operation, in particular caused by vibrations and the thrust load from the exhaust gas flow.

[0017] In a preferred embodiment, the guide body has two cover surfaces spaced apart from one another and running parallel. These are advantageously part of a U-shaped structure and form its legs. The pair of legs is connected to a back element, to which the support element is attached for support on the inner wall of the housing. Furthermore, at the free ends of the legs and thus at the respective cover surfaces, support parts of the mounting arrangement are provided on the front sides, which serve to attach the heating module. The back element can extend over only part of the legs, so that the connection between the legs is tapered compared to their corresponding extension. However, it can also be provided for the back element to be designed essentially flush with the legs, thus improving a uniform current feed across the legs.

[0018] According to the invention, the electrical connection of the respective heating assembly is established via the associated conductive element. The electrical power supply to the conductive element can be established via the respective support element as a whole or via an electrical contact element integrated into it or a separate electrical contact element.

[0019] For a further development of the invention, the guide body is designed such that it serves as a compensating body in the mechanical assembly and, in particular, compensates for temperature-related length variations of the connected heating assembly. For this purpose, the guide body is preferably designed such that it exhibits greater elasticity in a longitudinal direction determined by the extension of the heating assembly than in a direction transverse to the longitudinal direction. For this purpose, a stability-reducing structural element is preferably provided on the cover surface of the guide body. Advantageously, an embossed portion extending transversely to the longitudinal direction of the heating assembly can be applied to the cover surface for this purpose.

[0020] Alternatively or additionally, to provide greater elasticity in the longitudinal direction of the heating assembly, a stability-reducing structural element can also be applied to the back element of the guide body. In addition, in a preferred embodiment, the guide body is mounted on the inner wall of the enclosure in such a way that a lever arm results, which forms a floating bearing for the corresponding heating assembly. For this purpose, the support element on the guide body is arranged transversely offset from the longitudinal axis of the associated heating assembly.

[0021] In a preferred embodiment, the electric heating unit has at least two heating assemblies that are electrically connected in series with one of the guide bodies interposed. These series-connected heating assemblies advantageously form a parallel arrangement, thus the heating assemblies, which are held together with the interposition of the guide body and connected in series with one another, have matching longitudinal directions. The intermediate guide body can in turn be designed as a lever arm for at least one heating assembly. For this purpose, it is provided that the intermediate guide body is designed asymmetrically. A first mounting arrangement has a greater transverse offset from the position of the support element than a second mounting arrangement. Thus, a loose bearing is created for the first mounting arrangement and a fixed bearing is created on the guide body for the second mounting arrangement.For a preferred embodiment with a plurality of heating assemblies running parallel to one another, it is provided for each of the heating assemblies to use a loose bearing on a first guide body at a first distal end and a fixed bearing on a second guide body at a second distal end.

[0022] For a preferred embodiment of the electric heating unit according to the invention, it has at least one heating assembly with a heating element and a coupling part connected to the heating element, which advantageously serves for connection to the conducting body. The heating element has thin-walled connection sections, and the coupling part has receptacles designed to separately enclose each of the connection sections. This results in a power supply to a connection section that is spacious and symmetrical and evenly distributed across all connection sections of a heating element.

[0023] 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. If the heating element has a honeycomb structure, the complementary comb plates can be adapted to engage in a row of honeycomb channels. This facilitates the shearing, holding, and electrical contacting of a continuous material with a honeycomb structure for forming heating elements of the heating assemblies of an electric heating unit according to the invention.

[0024] Exemplary embodiments of the invention are explained below in conjunction with figures. These schematically show the following: Fig. 1: Embodiment of the electric heating unit according to the invention in perspective view, Fig. 2: electric heating unit from Fig. 1 under supervision, Fig. 3: enlarged section of the electric heating unit of Fig. 1, Fig. 4: Partial section from Fig. 3 as a free cut, Fig. 5: perspective view of a heating assembly and Fig. 6: Heating assembly from Fig. 5 in exploded view.

[0025] Fig. Figure 1 shows an embodiment of the electric heating unit 1 according to the invention. It depicts a ring-shaped housing 2 with a power supply 3.1, 3.2, which laterally defines an axially flowing interior area in which parallel heating assemblies 4.1, ..., 4.8 are arranged. The heating assemblies 4.1, ..., 4.8 are connected in series and electrically connected to the power supply 3.1, 3.2.

[0026] Fig. Figure 5 shows an enlarged view of the heating assembly 4.1, which, for the illustrated embodiment, has a heating element 5.1 with a honeycomb structure. The honeycomb channels of the heating element 5.1 form passages 6 through which exhaust gas flows, which are lined by honeycomb walls that act as heating resistor sections 7 when energized. Furthermore, the heating assembly 4.1 has coupling parts 8.1, 8.2 at the distal ends of the heating element 5.1, which are described in more detail in the subsequent embodiments.

[0027] The longitudinal extension of the heating assembly 4.1 is a Fig. 5. For the illustrated embodiment, this is essentially perpendicular to the exhaust gas flow direction A, whereby in the installed position this exhaust gas flow direction A is the surface normal to the paper plane for Fig. 2. This shows a top view of the electric heating unit 1 from Fig. 1, that at the respective distal ends of the heating assemblies 4.1, ..., 4.8 there is a gap 9.1, ..., 9.n to the inner wall of the housing 2. According to the invention, a conducting body 10.1, ..., 10.m is inserted into this gap 9.1, ..., 9.n, which serves to shield it. In this case, from the enlarged section of Fig. 3 that the guide bodies 10.1, ..., 10.m each have at least one cover surface 11.1, ..., 11.1 pointing in the exhaust gas flow direction A. This cover surface 11.1, ..., 11.1 is designed such that an effective flow resistance to the exhaust gas flow is provided and thus the exhaust gas velocity in the intermediate space 9.1, ..., 9.n is reduced to such an extent that the back pressure concentrates the exhaust gas flow on that area of ​​the cross-section within the housing 2 in which the heating assemblies 4.1, ..., 4.8 are arranged.

[0028] Furthermore, in particular Fig. 2 that each guide body 10.1, ..., 10.m is mounted on the housing 2 by a support element 12.1, ..., 12.o. For the preferred embodiment shown, this support element 12.1, ..., 12.o comprises an electrical insulator that provides potential separation from the inner wall of the housing 2. Preferably, the support element 12.1, ..., 12.o represents the only connection between the guide body 10.1, ..., 10.m and the housing 2.

[0029] The Fig. The cutaway view shown in Figure 4, in which the heating assemblies are hidden, illustrates a design in the form of a hollow part composed of sheet metal elements based on the guide bodies 10.1, ..., 10.4 shown. It can be seen that each of the guide bodies 10.1, ..., 10.4 has a U-shaped structure, the legs 13.1, 13.2 of which are formed by two cover surfaces 11.1, 11.2 spaced apart from one another in the exhaust gas flow direction A and arranged parallel. The mechanical connection between the legs 13.1, 13.2 is formed by a back element 14.1, ..., 14.5, wherein at least one of the back elements 14.1, ..., 14.5 is held on the housing 2 on each of the guide bodies 10.1, ..., 10.m by means of an associated support element 12.1, ..., 12.o.

[0030] The selected U-shape of the guide elements 10.1, ..., 10.m results in a hollow structure that minimizes the heat flow from the respective assigned heating assembly 4.1, ..., 4.8 to the enclosure 2. Furthermore, the design with thin-walled sheet metal parts for the guide elements 10.1, ..., 10.m reduces the thermal mass, enabling rapid and energy-efficient heating. This is further improved by the way the respective heating assembly 4.1, ..., 4.8 is attached to the end-mounted guide element 10.1, ..., 10.m, which minimizes the mutual contact surfaces.

[0031] From a summary of the Fig. 3 and Fig. 5 shows that, for a preferred embodiment, the heating assembly 4.1 is attached to the end faces of the cover surfaces 11.1, 11.2 on the guide body 10.1 via the coupling part 8.1, which is designed as a sheet metal part. In this area, there are laterally arranged projections that serve as a mounting arrangement 15.1, 15.2, 15.3 and are described in more detail in Fig. 4. Additionally, the fastening can be improved after an initial assembly step by means of a material-to-material joining technique, such as soldering or welding, particularly laser welding. This is particularly advantageous if, for a preferred embodiment, the heating assembly 4.1 is electrically connected to the guide body 10.1.

[0032] For the preferred embodiment shown, at least some of the guide bodies 10.1, ..., 10.m are designed such that a change in the length of the connected heating assembly 4.1, ..., 4.8 is possible under thermal load. This is explained below with reference to the Fig. 4 shown view of the guide element 10.2, which, as in Fig. 2, two heating assemblies 4.2, 4.3 are assigned. The first heating assembly 4.2 is attached to a first mounting arrangement 15.2 and the second heating assembly 4.3 is attached to a second mounting arrangement 15.3 on the guide body 10.2. Between the first mounting arrangement 15.2 and the associated support element 12.2 of the guide body 10.2 on the housing 2, there are regions of the cover surfaces 11.3, 11.4 with stability-weakening structural elements 16.1, 16.2 in the form of a notch, which result in the heating assembly 4.2 having greater elasticity for a change in length of the guide body 10.2 in the longitudinal direction L than in a direction transverse to the longitudinal direction L. Thus, a floating bearing is applied to the first mounting arrangement 15.2 for the first heating assembly 4.2, the increased elasticity of which is additionally provided by an asymmetrical arrangement of the support element 12.2 assigned to the guide body 10.2. It is evident that this is also required for the second mounting arrangement 15.3 of the second heating assembly 4.3 is essentially centrally located, so that in comparison there is a more rigid fastening and thus a fixed bearing.

[0033] If the Fig. Considering the overall diagram shown in Figure 1, it can be seen that for each heating assembly 4.1, ..., 4.8 of the parallel arrangement, there is a floating bearing at one distal end and a fixed bearing at the opposite distal end. The guide bodies 10.1, 10.5, which are connected to the power supplies 3.1, 3.2 and are held by only one distal end of the heating assemblies 4.1, 4.8, represent fixed bearings, while all other guide bodies 10.m are designed as asymmetrically mounted lever arms with a floating or fixed bearing.

[0034] For a further development of the invention, which is Fig. 5 and Fig. As shown in Figure 6, each of the heating assemblies 4.1, ..., 4.8 has a coupling part 8.1, 8.2 for contacting connection sections 17.1, ..., 17.4 on an electrical connection area 18.1, 18.2 of the heating element 5.1. A coupling part 8.1 with a two-part construction is shown. The coupling part 8.1 has two complementary comb plates 19.1, 19.2 with interlocking prongs 20.1, ..., 20.5 and recesses 21.1, ..., 21.5. When the comb plates 19.1, 19.2 are assembled, as shown in Fig. 5, a uniform gap between the end faces of a corresponding pairing of prongs 20.1, ..., 20.5 and recess 21.1, ..., 21.5, so that an arrangement of receptacles 22.1, ..., 22.4 for the thin-walled connection sections 17.1, ..., 17.4 on the heating element 5.1 is provided.

[0035] For the present embodiment with a honeycomb-shaped heating element 5.1, as shown in Fig. 6, the thin-walled connecting sections 17.1, ..., 17.4 are formed by shearing off the honeycomb structure parallel to the exhaust gas flow direction A and perpendicular to the longitudinal direction L, which divides a transverse row arrangement of the passages 6. The honeycomb webs thus exposed at the distal end of the heating element 5.1 form thin-walled connecting sections 17.1, ..., 17.4, which are each mutually supported by the honeycomb webs and form an arrangement of parallel sheet metal extensions with a fixed transverse spacing extending in a transverse direction Q perpendicular to the exhaust gas flow direction A and perpendicular to the longitudinal direction L. The prongs 20.1, ..., 20.5 and the recesses 21.1, ..., 21.5 on the comb plates 19.1, 19.2 are adapted to this transverse distance, so that the above-mentioned receptacles 22.1, ..., 22.4 are aligned with this after the coupling part 8.1, 8.2 has been assembled.

[0036] To achieve the best possible mechanical contact between the walls of the gap-shaped receptacles 22.1, ..., 22.4 and the thin-walled connecting sections 17.1, ..., 17.4, the prongs 20.1, ..., 20.5 and the corresponding complementary recesses 21.1, ..., 21.5 are slightly trapezoidal in shape when viewed from above. Accordingly, when the comb plates 19.1, 19.2 are assembled, the end faces of the prongs 20.1, ..., 20.5 and the recess 21.1, ..., 21.5 successively converge until the desired flat contact with the thin-walled connecting sections 17.1, ..., 17.4 is achieved. Further equalization of the electrical contact resistance is achieved by an additional assembly step, carried out after the coupling part 8.1, 8.2 has been attached, using a material-to-material connection. Soldering or welding, particularly laser welding, is preferred for this purpose.

[0037] In Fig.Figure 5 shows a design in which the coupling part 8.1, 8.2 is located at the respective distal end of the heating element 5.1. Consequently, the honeycomb structure of the heating element 5.1 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 19.1, 19.2 are first placed on a honeycomb strip in the form of endless material by means of a prong engagement in a transverse row of honeycomb openings at a predetermined longitudinal position. The complementary design of the comb plates 19.1, 19.2 creates a stabilizing, mutual support of the honeycomb webs, allowing a subsequent shearing step of the endless honeycomb strip to be carried out more easily. For an alternative design not shown in detail, the shearing is offset towards the end face 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.

[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 assembly 5.1 Heating element 6 exhaust gas flow passage 7 Heating resistance section 8.1, 8.2 Coupling part 9.1, ..., 9.n space 10.1, ..., 10.m guide body 11.1, ..., 11.1 Cover area 12.1, ..., 12.o Support element 13.1, 13.2 Legs 14.1, ..., 14.5 back element 15.1, 15.2, 15.3 Bracket arrangement 16.1, 16.2 stability-weakening structural element 17.1, ..., 17.4 Connection section 18.1, 18.2 electrical connection area 19.1, 19.2 Comb plate 20.1, ...,20.5 prongs 21.1, ..., 21.5 Recess 22.1, ..., 22.4 Recording A Exhaust gas flow direction L longitudinal direction Q transverse direction

Claims

[1] Electric heating unit (1) for heating an exhaust gas flow in an exhaust system, in particular of a motor vehicle with an associated exhaust gas flow direction (A), comprising a housing (2) enclosing the exhaust gas flow and at least one heating assembly (4.1,...,4.8) comprising a heating element (5.1) and arranged in the housing (2), wherein the heating element (5.1) comprises heating resistor sections (7) and passages (6) through which exhaust gas flows, and wherein an intermediate space (9.1,...,9.n) is present between a distal end of the heating assembly (4.1,...,4.8) and an inner wall of the housing (2), wherein the intermediate space (9.1,...,9.n) is substantially shielded by at least one guide body (10.1,...,10.m) held on the housing (2), and the guide body (10.1,...,10.m) has at least one in the exhaust gas flow direction (A) facing cover surface (11.1,...,11.I) characterized by that the heating assembly (4.1,...,4.8) is electrically connected to the guide body (10.1,...,10.m). [2] Electric heating unit according to claim 1, characterized by that the guide body (10.1,...,10.m) is supported on the housing (2) by means of an electrical insulator. [3] Electric heating unit according to one of the preceding claims, characterized by that the guide body (10.1,...,10.m) is designed as a hollow part. [4] Electric heating unit according to one of the preceding claims, characterized by that the guide body (10.1,...,10.m) is designed as a sheet metal component. [5] Electric heating unit according to one of the preceding claims, characterized by that the guide body (10.1,...,10.m) has a support arrangement (15.1, 15.2, 15.3) on which the heating assembly (4.1,...,4.8) is supported. [6] Electric heating unit according to claim 5, characterized by that the mounting arrangement (15.1, 15.2, 15.3) encloses an area of ​​the heating assembly (4.1,...,4.8) for support by means of a receptacle. [7] Electric heating unit according to one of claims 5 or 6, characterized by that the guide body (10.1,...,10.m) is held on the housing (2) by means of a support element (12.1,...,12.o) and has a U-shaped structure, wherein a back element (14.1,...14.5) adjoining the support element (12.1,...,12.o) creates a connection between legs (13.1, 13.2) of the U-shaped structure having cover surfaces (11.1,...,11.1), and support elements of the holding arrangement (15.1, 15.2, 15.3) are provided at the free ends of the legs (13.1, 13.2). [8] Electric heating unit according to one of the preceding claims, characterized by that the guide body (10.1,...,10.m) is designed such that it has a higher elasticity in a longitudinal direction (L) predetermined by the extension of the heating assembly (4.1,...,4.8) than in a direction transverse to the longitudinal direction (L). [9] Electric heating unit according to claim 8, characterized byin that, in order to provide the higher elasticity, the part of the guide body (10.1,...,10.m) forming the cover surface (11.1,...,11.1) has at least one stability-weakening structural element (16.1, 16.2). [10] Electric heating unit according to claim 9, characterized by that the stability-weakening structural element (16.1, 16.2) is an embossing running transversely to the longitudinal direction (L) of the heating assembly (4.1,...,4.8). [11] Electric heating unit according to one of claims 8 to 10, characterized by that in order to provide the higher elasticity, a back element (14.1,...,14.5) of the guide body (10.1,...,10.m) has a stability-weakening structural element. [12] Electric heating unit according to one of claims 8 to 11, characterized by that the support of the guide body (10.1,...10.m) is arranged transversely offset from the housing (2) to a longitudinal axis of the heating assembly (4.1,...,4.8). [13] Electric heating unit according to one of the preceding claims, characterized by that the heating unit (1) has at least two heating assemblies (4.2, 4.7) which are electrically connected in series with the guide body (10.1,...,10.m) interposed and are connected to separate mounting arrangements (15.1, 15.2, 15.3) on the intermediate guide body (10.1,...,10.m). [14] Electric heating unit according to claim 13, characterized by that the heating assemblies (4.1,...,4.8) have matching longitudinal directions (L). [15] Electric heating unit according to one of claims 13 or 14, characterized by that the separate mounting arrangements (15.1, 15.2, 15.3) on the intermediate guide body (10.1,...,10.m) have a different transverse offset for supporting the guide body (10.1,...10.m), for example a support element (12.1,...,12.o) of the guide body (10.1,...,10.m), in order to create a loose bearing and a fixed bearing. [16] Electric heating unit according to claim 15, characterized by that at least one heating assembly (4.1,...,4.8) is assigned a floating bearing on a first guide body (10.1,...,10.m) at a first distal end and a fixed bearing on a second guide body (10.1,...,10.m) at a second distal end. [17] Electric heating unit according to one of the preceding claims, characterized by that the heating unit (1) has a plurality of heating assemblies (4.1,...,4.8) which are arranged in the cross-section of the heating unit (1) facing the exhaust gas flow, and that all intermediate spaces (9.1,...,9.n) between the heating assemblies (4.1,...,4.8) and the housing (2) are each substantially shielded by a guide body (10.1,...,10.m). [18] Electric heating unit according to one of the preceding claims, characterized by that the heating assembly (4.1,...,4.8) has a heating element (5.1) with a honeycomb structure. [19] Electric heating unit according to one of the preceding claims, characterized by that the heating assembly (4.1,...,4.8) has a coupling part (8.1, 8.2), wherein the coupling part (8.1, 8.2) is designed for connecting the heating assembly (4.1,...,4.8) to the guide body (10.1,...,10.m).

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