Exhaust heating arrangement

Abstract

The invention relates to an exhaust gas heating arrangement having a heating unit (12), which comprises a housing heating element (28), which comprises a housing (30) and at least one heat conductor (32) extending in the housing and surrounded by an insulating material, wherein the heating unit (12) is wound helically around a longitudinal center axis (L), wherein a radially inner winding end region (46) of the heating unit (12) is offset in the direction of the longitudinal center axis (L) relative to a radially outer winding end region (48) of the heating unit (12).

Description

Technical Field

[0001] The invention relates to an exhaust gas heating arrangement for an exhaust gas system of an internal combustion engine. Background Art

[0002] The increasingly important requirements for the lowest possible pollutant emissions from internal combustion engines in vehicles require special measures that can reduce pollutant emissions, in particular during the start-up phase of the internal combustion engine. Such measures include, in particular, measures for bringing exhaust gas treatment units provided in the exhaust system, such as catalytic converters or particle filters, to operating temperature as quickly as possible so that the catalytic converters or particle filters can already carry out catalytic reactions at relatively low exhaust gas temperatures during the start-up phase.

[0003] An exhaust gas heating unit is known from DE 10 2019 101 679 A1, which can be arranged upstream of an exhaust gas treatment unit in the exhaust gas flow. The exhaust gas heating unit has a housing heating element, which comprises a housing, for example, made of a metal material, and a heat conductor embedded and received in the interior of the housing with an insulating material. By applying a voltage to the connecting end of the heat conductor, the heat conductor is excited and releases heat to the outside through the housing. On the outside of the housing, a heat transfer surface forming portion is provided in the form of a heat transfer element spirally wound around the housing. The heat transfer element increases the surface through which, when the heat conductor is excited, heat can be released to the exhaust gas circulating in such an exhaust gas heating unit.

[0004] DE 10 2019 107 384 A1 discloses an exhaust gas heating element, in which a heat transfer surface forming portion including a corrugated heat transfer element is provided in order to increase the surface available for heat release. The heat transfer element has a plurality of heat transfer element sections which are arranged in succession and are substantially parallel to each other and are connected to each other by corresponding curved sections of the corrugated structure, and the heat transfer element sections are penetrated by the outer cover heating element and are in heat transfer contact with the outer cover of the outer cover heating element. A heating unit constructed with such an exhaust gas heating element can be structured in such a way that the exhaust gas heating element is held between support structures arranged axially on both sides thereof while being spirally wound around a longitudinal center axis, so that a thermal interaction between the exhaust gas flowing therein and the heating unit can be generated substantially over the entire cross section of an exhaust gas guide housing containing such a heating unit. Summary of the invention

[0005] The object of the present invention is to provide an exhaust gas heating arrangement which, in a compact construction, enables an efficient transfer of heat to the exhaust gas flowing around it.

[0006] According to the invention, this object is achieved by an exhaust gas heating arrangement, which has a heating unit, which includes a housing heating element, which includes a housing and at least one heat conductor extending in the housing and surrounded by an insulating material, wherein the heating unit is wound helically around a longitudinal center axis, wherein a radially inner winding end region of the heating unit is offset in the direction of the longitudinal center axis relative to a radially outer winding end region of the heating unit.

[0007] By virtue of the fact that the heating unit of the exhaust gas heating arrangement constructed according to the invention is not arranged helically in a plane that is essentially orthogonal to the longitudinal center axis, but is extended axially, the length of the outer housing heating element available for heat transfer is increased in relation to the cross-sectional area through which the exhaust gas flows, which in turn leads to an improved heat input into the exhaust gas flowing around such a heating unit.

[0008] In order to be able to increase the surface available for heat transfer even further, it is proposed that the heating unit has a heat transfer surface formation which is supported on the outer casing.

[0009] Since, during operation of the exhaust gas heating arrangement according to the invention, heat is provided very quickly in the area of ​​the surface of the outer cover or the heat transfer surface forming portion, even if the temperature of the exhaust gas of the circulating heating unit is still relatively low, an effective reduction in the content of harmful substances contained in the exhaust gas can be achieved even at a very early moment when the internal combustion engine or the configured exhaust system is started, if the heating unit has an outer surface constructed of a catalytically effective material in the area of ​​the outer cover and / or in the area of ​​the heat transfer surface forming portion.

[0010] In order to maximize the heat transfer surface while utilizing the available volume, it can be arranged, for example, that the heat transfer surface shaped portion has at least one heat transfer element which spirally surrounds the outer cover heating element, or / and the heat transfer surface shaped portion has a plurality of disc-shaped heat transfer elements which are arranged one after another in the longitudinal direction of the outer cover heating element, or / and the heat transfer surface shaped portion has at least one heat transfer element which extends in a corrugated manner along the outer cover heating element and is penetrated by the outer cover heating element in the corresponding heat transfer element section, or / and the heat transfer surface shaped portion has a substantially round, preferably circular outer circumferential contour.

[0011] The heating unit can be arranged in an exhaust guide housing extending longitudinally in the direction of the longitudinal center axis, wherein, in order to interact particularly effectively with the exhaust flow, a radially inner spiral end region of the heating unit is arranged upstream relative to a radially outer spiral end region of the heating unit with respect to the main flow direction of the exhaust gas in the exhaust guide housing.

[0012] Such a design with a radially inner convolution end region arranged in the upstream direction is particularly advantageous for a compact design if the exhaust gas guide housing has a housing region which expands radially in the main flow direction of the exhaust gas and the heating unit is arranged at least partially in the radially expanded housing region.

[0013] An exhaust gas treatment unit, preferably a catalytic converter unit and / or a particle filter unit, which is heated during the start phase by the exhaust gas flow heated by the heating unit can also be arranged downstream of the heating unit.

[0014] In order to be able to utilize the flow conditions prevailing in the interior of the exhaust gas guide housing for an effective interaction between the exhaust gas flow and the heating unit, it is proposed that in at least one, preferably each circumferential region, the radially expanding housing region has an opening angle relative to the longitudinal center axis that is smaller than a heating unit positioning angle relative to the longitudinal center axis of a heating unit positioning line that intersects the longitudinal center axis and at least two, preferably all winding sections of the heating unit in the region of the center of the outer cover heating element in the at least one circumferential region.

[0015] It can preferably further be provided that the exhaust gas treatment unit has an inflow side oriented in the upstream direction and inclined relative to the longitudinal center axis at an exhaust gas treatment unit pitch angle, and that in at least one, preferably each circumferential region, the heating unit pitch angle is smaller than the exhaust gas treatment unit pitch angle.

[0016] It is particularly advantageous not only with regard to the thermal interaction of the exhaust gas flow with a heating unit arranged in the exhaust gas guiding housing but also with regard to a compact design if the heating unit positioning angle is less than or equal to half the sum of the opening angle and the exhaust gas treatment unit positioning angle.

[0017] A very efficient transfer of heat to the exhaust gas flow can be achieved by radially overlapping at least two, preferably all, directly adjacent convolution segments of the heating unit in at least one, preferably each circumferential region, or / and axially overlapping at least two, preferably all, directly adjacent convolution segments of the heating unit in at least one, preferably each circumferential region. Cross-sectional areas in which the exhaust gas flow has essentially no thermal interaction with the heating unit can thus be largely avoided.

[0018] In order to nevertheless avoid excessive throttling of the exhaust gas flow, it is further proposed that in at least one, preferably each circumferential area, at least two, preferably all directly adjacent winding sections of the heating unit do not overlap each other, but are preferably at a distance from each other, in the direction of a heating unit positioning line which intersects the longitudinal center axis and at least two, preferably all winding sections of the heating unit in the area of ​​the center of the outer cover heating element in the at least one circumferential area.

[0019] An interaction of the heating unit with the exhaust gas flow can also be achieved in the central region, ie in the region of the longitudinal center axis, in that the radially inner convolution end region intersects the longitudinal center axis.

[0020] In a particularly simple and realizable design, in particular with regard to integration into an exhaust gas guide housing with housing sections extending radially in the exhaust gas flow direction, it is proposed that in at least one, preferably each circumferential region, at least some of the convolutions of the heating unit, preferably all of the convolutions of the outer cover heating element lie centered on a heating unit positioning line extending in a straight line and intersecting the longitudinal center axis. This results in a substantially conical design of the heating unit.

[0021] In an alternative design, in at least one, preferably each circumferential region, at least a portion of the winding segments of the heating unit, preferably all winding segments, can be located on a heating unit positioning line, for example curved in an arc shape, intersecting the longitudinal center axis with the center of the outer cover heating element.

[0022] In order to be able to accommodate the heating unit stably in the exhaust system or in an exhaust gas guiding housing of the exhaust system, it is further proposed that a support structure for axially supporting the heating unit is provided on at least one, preferably both axial sides of the heating unit.

[0023] The invention furthermore relates to an exhaust gas system for an internal combustion engine, which has at least one exhaust gas heating arrangement according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Next, the present invention will be described in detail with reference to the accompanying drawings.

[0025] Figure 1 a perspective view showing a heating unit of an exhaust gas heating arrangement upstream relative to an exhaust gas treatment unit;

[0026] Figure 2 Shown with Figure 1 A longitudinal sectional view of an exhaust gas treatment device of a heating unit and an exhaust gas treatment unit;

[0027] Figure 3 A partial longitudinal section view is shown, which is shown in the schematic diagram Figure 2 The structure of the exhaust gas treatment device;

[0028] Figure 4 Show Figure 2 A detailed view of three convoluted sections of a heating unit of an exhaust gas heating arrangement, which are positioned directly adjacent to one another in the circumferential region;

[0029] Figure 5 Shown corresponding to Figure 4 , which graphically illustrate alternative designs;

[0030] Figure 6 A side view of a heating unit arranged in a straight extension is shown, comprising a housing heating element and a heat transfer surface forming portion of the housing surrounding the heating unit;

[0031] Figure 7 Shown is a device for an internal combustion engine Figure 2 A schematic diagram of an exhaust device with an exhaust heating arrangement. DETAILED DESCRIPTION

[0032] Figure 1 Shown in perspective Figure 2 1 shows an assembly of an exhaust gas treatment unit 10 and a heating unit 12 of an exhaust gas heating arrangement 14. The exhaust gas heating arrangement 14 further comprises an exhaust gas guide housing 16, which comprises a substantially cylindrical housing region 18 for receiving the exhaust gas treatment unit 10 and a housing region 20 adjoining the substantially cylindrical housing region 18 upstream in the main exhaust gas flow direction A and extending radially in the main exhaust gas flow direction A with respect to the longitudinal center axis L. The exhaust gas treatment unit 10, which can be designed as a catalytic converter unit, can have a catalyst component 22 coated with a catalytically active material, which is held in the substantially cylindrical housing region 18 of the exhaust gas guide housing 16 with an intermediate support fiber mat 24 or the like.

[0033] The heating unit 12 is arranged upstream of the exhaust gas treatment unit 10 on the inflow side 26 thereof and has a substantially longitudinally extending housing heating element 28. The housing heating element 28 is formed with a housing 30, which is usually formed of a metallic material, and at least one heat conductor 32 extending in the housing 30. In order to achieve electrical insulation between the heat conductor 32 and the housing 30, the heat conductor 32 is embedded in an electrically insulating material, for example in powder form, in the housing 30. In two connection end regions 34, 36, which are located outside the exhaust gas guide housing 16, the housing heating element 28 can be connected to a power supply 37 (see Figure 7 ), so that by applying a voltage to the two connection end regions 34 , 36 , the heat conductor 32 and, via it, the outer casing 30 are heated.

[0034] A heat transfer surface formation, generally designated 38, is connected to the outer circumference of the housing 30 of the housing heating element 28, which is not integrated into the current flow. The heat transfer surface formation 38 serves to increase the surface available for releasing heat to the exhaust gas of the circulation heating unit 12. An example of a housing heating element 28 surrounded by such a heat transfer surface formation 38 is shown in FIG. Figure 6. In the design example shown, the heat transfer surface forming part has a heat transfer element 40 which is wound in a thread-like manner and extends along the outer cover 30 of the outer cover heating element 28 in its longitudinal direction. With its thread-like winding structure, the heat transfer element 40, which is also made of a metal material, for example, provides two heat transfer surfaces 42, 44 which extend helically in the longitudinal direction of the outer cover heating element 28. The heat transfer element 40 forms an outer circumferential contour which is surrounded and bounded radially outwardly with respect to the heat conductor 32 by the contour line K and is preferably circular.

[0035] It should be noted that the heat transfer surface forming part 38 can also have another structural structure. In this way, the heat transfer surface forming part can, for example, have a plurality of disc-shaped heat transfer surface forming parts, for example, with a circular outer circumferential contour, which are arranged successively in the longitudinal direction of the outer cover heating element 28, and the heat transfer surface forming part is penetrated by the outer cover heating element, for example, in the central area. In another alternative design, the heat transfer surface forming part 38 can have a corrugated (meandering) coiled heat transfer element, which has a plurality of heat transfer element sections arranged substantially parallel to each other in the straight extension of the outer cover heating element. The heat transfer element sections can be penetrated by the outer cover heating element 28 in the central area, for example, between corresponding curved sections that connect adjacent heat transfer element sections to each other.

[0036] The connection between the housing heating element 28 and the heat transfer surface shaped part 38 can be established, for example, by manufacturing the heat transfer surface shaped part 38 with a shape memory material. For example, an opening in the central region of the heat transfer surface shaped part, through which the housing heating element 28 is to pass, can be provided by cold forming in such a way that it has a slightly larger diameter than the housing heating element 28. After the housing heating element 28 has been inserted into such an opening, the heat transfer surface shaped part 38, which is constructed with a shape memory material, can be shrunk again by heating, thereby achieving a high clamping force for the housing heating element and thus a fixed and permanent connection, without the need to produce, for example, a material-locking connection.

[0037] Figure 1 and 2 It is clear that the heating unit, together with the housing heating element 28 and the heat transfer surface shaped portion 38 surrounding it, is arranged in a spirally wound manner around the longitudinal center axis L, so that along the spiral structure of the housing heating element 28 surrounded by the heat transfer surface shaped portion 38, the radial distance relative to the longitudinal center axis L increases. The heating unit 12 is further configured such that in the spirally wound structure, the radially inner winding end region 46 is axially offset from the radially outer winding end region 48 in the direction of the longitudinal center axis L. In this case, Figure 2It can be seen that the axial offset is selected such that the radially inner convolution end region 46 is offset with respect to the radially outer convolution end region 48 in the upstream direction, ie opposite to the exhaust gas main flow direction A, and is therefore positioned at a greater distance from the inflow side 26 of the exhaust gas treatment unit 10 .

[0038] By means of the substantially conical design of the heating unit 12, it is possible to achieve a heating unit 12 for an internal combustion engine 52 or a heating unit 12 constructed therefrom and in Figure 7 . On the one hand, it can be seen that the heating unit 12 with its axially extending, spiral structure is positioned in such a way that it is positioned at least partially in a housing region 20 which is radially widened and, for example, also designed in a conical or circular conical structure. Thus, a compact design is ensured, wherein, for example, the exhaust gas flowing in through the exhaust gas duct 54 in the main exhaust gas flow direction A is guided in a defined manner in the direction of the radially further extending inflow side 26 of the exhaust gas treatment unit 10 while circulating around the heating unit 12. Thus, a thermal interaction of the heating unit 12 with the exhaust gas flow guided to the exhaust gas treatment unit 10, which will be explained in detail below, is also ensured. In this case, for the sake of efficient use of the available structural space, it can also be provided, for example, that the last winding section of the spiral structure of the heating unit 12, which also has the radially outer winding end region 48, is positioned substantially completely in the substantially cylindrical housing region 18 of the exhaust gas guide housing 16, so that also in the radially outermost region of the exhaust gas treatment unit 10, a thermal interaction of the heating unit 12 with the exhaust gas flow upstream of the exhaust gas treatment unit 10 can be ensured.

[0039] Furthermore, the helically wound, axially extending structure of the heating unit 12 results in that the total length of the housing heating element 28 surrounded by the heat transfer surface formation 38 can be significantly increased compared to a helical structure that is essentially in one plane, i.e., does not extend axially. As a result, the surface available for heat transfer to the exhaust gas of the housing 30 and the heat transfer surface formation 38 is increased, which contributes to more effective heating of the exhaust gas flow to the exhaust gas treatment unit 10.

[0040] refer to Figures 3 to 5 Next, the structural design aspects of the exhaust gas heating arrangement 14 constructed according to the invention are explained.

[0041] Figure 3 In a plane containing the longitudinal center axis L, forming a circumferential region of the exhaust gas heating arrangement 14 or the heating unit 12, three mutually adjacent convolution sections 56, 58, 60 of the heating unit 12 are shown, wherein Figure 3The convolution section 60 located at the top and at the furthest distance relative to the longitudinal center axis L provides the radially outer convolution end region 48 and the convolution section 56 shown at the bottom and therefore closest relative to the longitudinal center axis L provides the radially inner convolution end region 46. In each of the convolution sections 56, 58, 60, the center Z of the housing heating element 28, for example defined by the heat conductor 32 or its center point, is located on a heating unit positioning line H, which extends linearly from the radial inner side to the radial outer side at a heating unit positioning angle b with respect to the longitudinal center axis L and therefore also the main flow direction A of the exhaust gas. The convolution sections 56, 58, 60 of the heating unit 12 arranged in this way are held or axially supported between two support structures 62, 64 arranged axially on both sides thereof. In order to enable the exhaust gas to pass through, these support structures 62, 64 can be designed in a grid-like or cross-like manner and be fixed to the exhaust gas guide housing 16 in their radially outer regions.

[0042] The inclination of the heating unit positioning line H, which is represented by the heating unit positioning angle b and which also essentially represents the cone angle of the conical structure of the heating unit 12, is also selected in consideration of the winding pitch of the heating unit 12 so that the winding sections 56, 58, 60 adjacent to each other in one or each circumferential region around the longitudinal center axis L overlap in the radial direction and in the axial direction. The overlap is considered in this case with respect to the outer circumferential contour of the winding sections of the heating unit 12, which is represented by the contour line K, and which is defined in the illustrated design example by the outer circumferential contour of the heat transfer surface forming part 38 and therefore has an essentially circular outer circumferential contour in the illustrated design example. As a result, a radial overlap U is generated between the winding sections 56, 58, 60 that are directly adjacent to each other. r , and produces an axial overlap U of the convoluted sections 56, 58, 60 that are directly adjacent to each other a Furthermore, the convoluted sections 56, 58, 60 are positioned such that in one or each circumferential region, the centers Z on the heating unit positioning line H are at such a distance from one another in the direction of the heating unit positioning line H that the individual convoluted sections 56, 58, 60 do not overlap one another, but are advantageously at a distance b from one another.

[0043] Taking into account the flow guidance in the exhaust gas guide housing 16, the heating unit positioning angle b is selected relative to the longitudinal center axis L such that it is greater than the opening angle a of the radially widening housing region 20 of the exhaust gas guide housing 12. Furthermore, the heating unit positioning angle b is selected such that it is smaller than the exhaust gas treatment unit positioning angle c of the inflow side 26 of the exhaust gas treatment unit 10. In this case, the exhaust gas treatment unit positioning angle c can be 90° in the case of a substantially flat inflow side 26.

[0044] It has proven to be advantageous if the heating unit positioning angle b lies approximately centrally between the exhaust gas treatment unit positioning angle c and the aperture angle a of the radially widened housing region 20 or is smaller, so that the heating unit positioning angle b is less than or equal to half the sum of the exhaust gas treatment unit positioning angle c and the aperture angle a of the radially widened housing region 20. It should be noted that for this angle, in designs deviating from a substantially rotationally symmetrical design, an average angle or angles that are comparable to one another in a defined region in the direction of the longitudinal center axis L and in the circumferential direction can be considered in each case.

[0045] Such a conical structure ensures that the exhaust gas flow, with increasing distance from the longitudinal center axis L, has a flow direction that deviates from the main flow direction A of the exhaust gas and is oriented radially outwards in a manner such that a thermal interaction between the exhaust gas and the heating unit 12 that is as effective as possible is achieved. It is important here that an effective overlap U is generated with the exhaust gas flow that deviates radially outwards from the main flow direction A of the exhaust gas or with respect to the positioning of the convolution sections 56, 58, 60 that overlap one another. eff , the overlap is significantly greater than the radial overlap U r Or also greater than the axial overlap U a . Thus, in each swirl section around which the exhaust gas flow circulates, an effective thermal interaction of the exhaust gas flow with both the housing heating element 28 and the surface area of ​​the heat transfer surface shaped portion 38 which is positioned in the corresponding swirl section or in the corresponding circumferential area is ensured. Nevertheless, the distance d existing between the individual swirl sections ensures that no excessive flow obstruction or excessively large flow resistance occurs for the exhaust gas flow through the heating unit 12. Good durability of the heating unit 12 constructed in this way is also achieved by avoiding mutual contact between the swirl sections 56, 58, 60 directly adjacent to each other due to the distance d. However, it is avoided as much as possible that there are regions in which the exhaust gas flow essentially has no thermal interaction with any swirl section.

[0046] It should be noted here that the effective overlap U eff The angle is determined essentially by the heating unit positioning angle b. The smaller this angle is, the more pointed the conical structure of the heating unit 12 is and the smaller the angle between the heating unit positioning line H and the flow direction S of the exhaust gas flow in the region further radially away from the longitudinal center axis L. A distance d that is as small as possible also contributes to a large effective overlap U eff .

[0047] Different variants of the heating unit 12 are Figure 5 It can be seen in the diagram. Figure 5, the radially inner convolution end region and also the convolution section 56 providing the radially inner convolution end region 46 are positioned further radially inwards, so that they intersect the longitudinal center axis L, for example, in the region of the center Z of the housing heating element 28. This ensures that, also in the central region, there is no cross section through which the exhaust gas can flow without thermal interaction with the heating unit 12.

[0048] Figure 5 To illustrate further, again with regard to the circumferential region, the center Z of the housing heating element 28 in the respective convoluted sections 56, 58 does not necessarily have to lie on a straight-running heating unit positioning line H, but can also lie, for example, on a curved, preferably arcuately curved heating unit positioning line H', which is, for example, Figure 5 The exhaust gas flow can be convexly or concavely arched as shown in FIG. It should be emphasized that the positioning of the center Z on such a curved heating unit positioning line H' is of course simulated (formed) in the overall structure of the heating unit 12 when more than two winding sections are considered, because of course a straight line can always be drawn through two winding sections.

[0049] With such a positioning of the centers of the individual convoluted sections 56, 58 on the curved heating unit positioning line H', the envelope of the entire heating unit 12, which is defined by the outer circumferential contour or contour line K of the heat transfer surface forming part 38, also lies on a line with a corresponding convex or concave extension with respect to the circumferential area. Figure 3 and 4 The explained positioning can be considered, for example, in the radially inner region, ie where such a heating unit positioning line H' intersects the longitudinal center axis L, but also with reference to the average positioning angle of such a curved heating unit positioning line H'.

[0050] Furthermore, it should be pointed out that for reasons of symmetry, preferably substantially identical structures can be provided along the longitudinal center axis L over the entire circumference, ie approximately the same course of the heating unit positioning lines H and H′.

[0051] The exhaust gas heating arrangement 14 designed according to the invention, which has a heating unit 12 designed in a spirally and axially extending structure wound upstream of the exhaust gas treatment unit 10, ensures that the exhaust gas flowing to the exhaust gas treatment unit 10 is effectively heated, especially during the starting phase of the internal combustion engine 52, and that this heat is then also introduced into the exhaust gas treatment unit or its catalytically active material. As a result, the time period during which the exhaust gas treatment unit 10 is not hot enough to carry out the catalytic reaction to be achieved therein during the starting phase of the operation of the internal combustion engine 52 can be significantly shortened.

[0052] The efficiency of the exhaust gas heating arrangement 14 or the heating unit 12 can be further improved by injecting hydrocarbons, that is, for example, the fuel used in the internal combustion engine 52, into the heating unit 12. This can be achieved, for example, by using a nozzle positioned upstream of the heating unit 12 and at Figure 3 68 shown in FIG. 1 . During the heating operation of the heating unit 12, the hydrocarbons incident thereon are converted due to the temperature prevailing there, thereby releasing additional reaction heat, which can be transferred to the exhaust gas treatment unit 10 located downstream via the exhaust gas flow. In particular, when the internal combustion engine 52 is a diesel internal combustion engine and the exhaust gas treatment unit 10 has an SCR catalytic converter and / or a diesel particle filter, these system regions can be brought to operating temperature very quickly. This effect can also be achieved by operating the internal combustion engine 52 in such a way that, due to a defined ignition angle adjustment, part of the fuel is not burned therein, but is ejected unburned and is therefore transferred to the heating unit 12 with the exhaust gas flow.

[0053] In order to achieve a further reduction in the pollutant emissions, in particular during the start-up phase of the operation of the internal combustion engine 52, the heating unit 12 can be provided with a surface comprising a catalytically active material 70 in the region of the outer surface of the housing 30 and / or on the heat transfer surface shaped portion 38. Since, when the housing heating element 28 is activated, this catalytically active material 70 can be heated very quickly and thus brought to the temperature required for carrying out the catalytic reaction, a catalytic conversion and thus a reduction in the pollutant content in the exhaust gas is achieved in this way already upstream of the exhaust gas treatment unit 10.

[0054] If the exhaust gas treatment unit 10 has a three-way catalytic converter in an internal combustion engine 52 designed as a gasoline engine, the catalytically active material can be provided, for example, by a coating with platinum and / or palladium and / or rhodium. If the internal combustion engine 52 is a diesel engine and the exhaust gas treatment unit is a diesel oxidation catalyst accordingly, the catalytically active material can be provided, for example, by a coating with platinum and / or palladium. When use as a NOx storage catalyst is provided in an internal combustion engine 52 designed as a diesel engine, a corresponding coating can also be provided, wherein, for example, a compound containing barium can be provided as a storage component.

[0055] If the exhaust gas treatment unit 10 has an SCR catalyst and is arranged on the internal combustion engine 52 configured as a diesel engine, the catalytically active material can be a hydrolysis catalyst, which realizes the preparation of the urea / water solution to be carried out upstream of the SCR catalyst. For example, a coating can be provided for this purpose, which is constructed with titanium dioxide, zirconium dioxide and / or aluminum oxide. In the interaction with the exhaust gas treatment unit 10 with an SCR catalyst, the catalytically active material 70 can also be constructed with Fe zeolite, Cu zeolite or vanadium oxide (for example vanadium pentoxide). In particular, in the case of a coating comprising such an oxide, it is also possible to provide the catalytically active material as a mixed oxide coating.

[0056] Such a coating can be applied, for example, by first applying a so-called washcoat (intermediate layer) with a relatively high Al content, for example FeCr alloy 1.4767 with an Al content of about 5%, to the surface to be coated of the outer shell 30 and / or the heat transfer surface shaped part 38, wherein the surface to be coated can also be subjected to a heat treatment. With this washcoat, a coating of a porous oxide ceramic is achieved, which, due to its porous structure, provides a large inner surface, onto which the coating comprising the catalytically active material 70 can then be applied, for example, by dipping.

[0057] In the previously detailed description of the heating unit 12, the structure or positioning of the convolution sections respectively adjacent to each other was explained in relation to the outer circumferential contour of the heat transfer surface forming part 38. This also relates in particular to the axially and radially overlapping structure of the convolution sections 56, 58, 60 directly adjacent to each other. In particular, such a structure including the heat transfer surface forming part 38 is particularly advantageous for providing a surface that is as large as possible for transferring heat to the exhaust gas flow. Nevertheless, it should be pointed out that the helically wound and axially extended structure of the heating unit 12 including the axially and radially overlapping convolution sections can in principle also be realized in the following case, that is, the structure only has an outer shell heating element 28, but does not have a heat transfer surface forming part arranged on the outer shell 30. The relationship of the axially and radially overlapping convolution sections directly adjacent to each other can then be formed in relation to the outer circumferential contour of the outer shell 30.

Claims

1. An exhaust gas heating arrangement having a heating unit (12), the heating unit comprising a housing heating element (28), the housing heating element comprising a housing (30) and at least one heat conductor (32) extending in the housing and surrounded by an insulating material, wherein: The heating unit (12) is spirally wound around a longitudinal center axis (L), wherein a radially inner winding end region (46) of the heating unit (12) is offset relative to a radially outer winding end region (48) of the heating unit (12) in the direction of the longitudinal center axis (L), and in at least one circumferential region, at least two directly adjacent winding sections (56, 58, 60) of the heating unit (12) radially overlap with each other.

2. The exhaust gas heating arrangement according to claim 1, characterized in that: The heating unit (12) has a heat transfer surface forming portion (38) supported on the outer cover (30).

3. The exhaust gas heating arrangement according to claim 2, characterized in that: The heating unit (12) has an outer surface in the region of the outer casing (30) and / or in the region of the heat transfer surface shaping (38) which is formed with a catalytically active material (70).

4. The exhaust gas heating arrangement according to claim 2 or 3, characterized in that: The heat transfer surface forming portion (38) has at least one heat transfer element (40) which surrounds the outer cover heating element (28) in a spirally wound manner, or / and the heat transfer surface forming portion (38) has a plurality of disc-shaped heat transfer elements which are arranged successively along the longitudinal direction of the outer cover heating element, or / and the heat transfer surface forming portion (38) has at least one heat transfer element which extends in a corrugated manner along the outer cover heating element (28) and is penetrated by the outer cover heating element in a corresponding heat transfer element section.

5. The exhaust gas heating arrangement according to claim 2 or 3, characterized in that: The heat transfer surface forming portion (38) has a circular outer peripheral contour.

6. The exhaust gas heating arrangement according to claim 5, characterized in that: The heat transfer surface forming portion (38) has a circular outer peripheral contour.

7. The exhaust gas heating arrangement according to any one of claims 1 to 3, characterized in that The heating unit (12) is arranged in an exhaust guide housing (16) extending longitudinally in the direction of a longitudinal center axis (L), and a radially inner spiral end region (46) of the heating unit (12) is arranged upstream relative to a radially outer spiral end region (48) of the heating unit (12) with respect to a main flow direction (A) of the exhaust gas in the exhaust guide housing (16).

8. The exhaust gas heating arrangement according to claim 7, characterized in that: The exhaust gas guide housing (16) has a housing region (20) which expands radially along a main flow direction (A) of the exhaust gas, and the heating unit (12) is at least partially arranged in the radially expanded housing region (20), or / and the exhaust gas treatment unit (10) is arranged downstream of the heating unit (12).

9. The exhaust gas heating arrangement according to claim 8, characterized in that: The exhaust gas treatment unit (10) comprises a catalytic converter unit and / or a particle filter unit.

10. The exhaust gas heating arrangement according to claim 8, characterized in that: In at least one circumferential region, an opening angle (a) of a radially expanding housing region (20) relative to a longitudinal center axis (L) is smaller than a heating unit positioning angle (b) of a heating unit positioning line (H) intersecting the longitudinal center axis (L) and at least two winding sections (56, 58, 60) of the heating unit (12) in the region of a center (Z) of the outer cover heating element (28) relative to the longitudinal center axis (L) in the at least one circumferential region.

11. The exhaust gas heating arrangement according to claim 10, characterized in that: In each circumferential region, the opening angle (a) of the radially expanding shell region (20) relative to the longitudinal center axis (L) is smaller than the heating unit positioning angle (b) of a heating unit positioning line (H) intersecting the longitudinal center axis (L) and all winding sections (56, 58, 60) of the heating unit (12) in the region of the center (Z) of the outer cover heating element (28) relative to the longitudinal center axis (L).

12. The exhaust gas heating arrangement according to claim 10, characterized in that: The exhaust gas treatment unit (10) has an inflow side (26) oriented in an upstream direction and inclined at an exhaust gas treatment unit positioning angle (c) relative to a longitudinal center axis (L), and in at least one circumferential region, the heating unit positioning angle (b) is smaller than the exhaust gas treatment unit positioning angle (c).

13. The exhaust gas heating arrangement according to claim 12, characterized in that: In each circumferential region, the heating unit positioning angle (b) is smaller than the exhaust gas treatment unit positioning angle (c).

14. The exhaust gas heating arrangement according to claim 12, characterized in that: The heating unit positioning angle (b) is less than or equal to half of the sum of the opening angle (a) and the exhaust treatment unit positioning angle.

15. The exhaust gas heating arrangement according to any one of claims 1 to 3, characterized in that In each circumferential region, all directly adjacent winding sections (56, 58, 60) of the heating unit (12) radially overlap each other, or / and in at least one circumferential region, at least two directly adjacent winding sections (56, 58, 60) of the heating unit (12) axially overlap each other.

16. The exhaust gas heating arrangement according to any one of claims 1 to 3, characterized in that In each circumferential region, all directly adjacent convolution segments (56, 58, 60) of the heating unit (12) overlap axially.

17. The exhaust gas heating arrangement according to any one of claims 1 to 3, characterized in that In at least one circumferential region, at least two directly adjacent convoluted sections (56, 58, 60) of the heating unit (12) do not overlap each other in the direction of a heating unit positioning line (H) extending in a straight line intersecting the longitudinal center axis (L) and the at least two convoluted sections (56, 58, 60) of the heating unit (12) in the region of the center (Z) of the housing heating element (28) in the at least one circumferential region.

18. The exhaust gas heating arrangement according to claim 17, characterized in that In each circumferential region, all directly adjacent convoluted sections (56, 58, 60) of the heating unit (12) do not overlap and have a distance (d) from each other in the direction of a heating unit positioning line (H) extending in a straight line intersecting the longitudinal center axis (L) and all convoluted sections (56, 58, 60) of the heating unit (12) in the region of the center (Z) of the housing heating element (28).

19. The exhaust gas heating arrangement according to any one of claims 1 to 3, characterized in that The radially inner convoluted end region (46) intersects the longitudinal center axis (L).

20. The exhaust gas heating arrangement according to any one of claims 1 to 3, characterized in that In at least one circumferential region, all convolution sections (56, 58, 60) of the heating unit (12) are located with the center (Z) of the outer cover heating element (28) on a straight heating unit positioning line (H) intersecting the longitudinal center axis (L).

21. The exhaust gas heating arrangement according to claim 20, characterized in that In each circumferential region, all convoluted sections (56, 58, 60) of the heating unit (12) are located with the center (Z) of the outer cover heating element (28) on a straight heating unit positioning line (H) intersecting the longitudinal center axis (L).

22. The exhaust gas heating arrangement according to any one of claims 1 to 3, characterized in that: In at least one circumferential region, at least a portion of the convoluted section of the heating unit (12) is located with the center (Z) of the outer cover heating element (28) on a heating unit positioning line intersecting the longitudinal center axis (L).

23. The exhaust gas heating arrangement according to claim 22, characterized in that In each circumferential region, all convoluted sections of the heating unit (12) are located with the center (Z) of the outer cover heating element (28) on an arcuately curved heating unit positioning line intersecting the longitudinal center axis (L).

24. The exhaust gas heating arrangement according to any one of claims 1 to 3, characterized in that A support structure (62, 64) for axially supporting the heating unit (12) is provided on at least one axial side of the heating unit (12).

25. The exhaust gas heating arrangement according to claim 24, characterized in that Support structures (62, 64) for axially supporting the heating unit (12) are arranged on two axial sides of the heating unit (12). 26 . An exhaust system for an internal combustion engine, comprising at least one exhaust gas heating arrangement ( 14 ) according to claim 1 .

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