Electric heating element, electric heating device made therewith, and respective manufacturing process therefor

Abstract

Electric heating element (1) with - a plurality of flow channels (3) extending transversely to a main plane (1") of the heating element (1), open on both sides at the front, through which a fluid can freely flow, - wherein the heating element (1) consists of a plurality of adjacent, mutually electrically insulated layers (2a, b) in the main plane (1") as sections of a continuous heating conductor (2), which can thus form a current path, made of electrically conductive material, - in the cross-section (Q) of the electrical heating conductor (2) transversely to its direction of travel (2'), several of the flow channels (3) are present next to one another, characterized in that - the cross-section (Q) of the heating conductor (2) changes in the perpendicular (10) to the main plane (1") of the heating element (1).

Description

I. Area of ​​application

[0001] The invention relates to an electric heating device, in particular for heating exhaust gases from internal combustion engines to the operating temperature of a catalyst, in particular an SCR catalyst, which is intended to clean the exhaust gases of pollutants, as well as a manufacturing method for such a heating device and its heating element. II. Technical background

[0002] It is known to remove soot particles from the exhaust gases of an internal combustion engine, in particular a diesel engine, by means of an oxidation catalyst by conversion into gaseous CO2, for which, in addition to a sufficient amount of NO2, a sufficiently high reaction temperature of at least 200 °C over a sufficiently long exposure period must be present.

[0003] It is also known to reduce NOx, or nitrogen oxide compounds, from the exhaust gases of an internal combustion engine, particularly a diesel engine, by converting them into nitrogen and water by adding gaseous ammonia to the exhaust gas as a reducing agent. This does not impair the efficiency of the internal combustion engine, but rather enables even more fuel-efficient operation of the internal combustion engine, especially in diesel engines.

[0004] Provided that the reaction temperature is sufficient, a liquid ammonia precursor solution, usually liquid urea, is first converted into gaseous ammonia and isocyanic acid in a thermolysis process. (NH2)2CO → NH3 + HNCO and in a subsequent hydrolysis NH3 + H2O → NH3 + CO2 further ammonia and carbon dioxide are produced. Subsequently, the selective catalytic reduction (= SCR) takes place, namely - either the standard reduction of nitrogen oxides at a reaction temperature above 250 °C 4NO +4 NH3 + O2 → 4 N2 + 6 H2O, - and / or the rapid reduction of nitrogen oxides at a reaction temperature between 170 °C and 300 °C NO + NO2 + 2 NH3 → 2 N2 + 3 H2O.

[0005] However, such reaction temperatures are not yet present in such a catalyst immediately after starting the combustion engine, so that without additional measures, the desired exhaust gas purification does not occur at the beginning of the operating period.

[0006] While this is still acceptable for longer continuous operating times of the combustion engine, the proportion of these initial operating times in hybrid vehicles, which frequently switch between electric drive and drive by the combustion engine, increases significantly in relation to the total operating time of the combustion engine and is no longer acceptable.

[0007] It is therefore already known to electrically heat the exhaust gases before they enter the catalyst or the corresponding catalyst itself during such initial operating times by means of an electrical resistance heater, for example by using a similar honeycomb-shaped carrier body made of a metal foil matrix, as is used as a carrier body for the catalytic coating of a catalyst, in a modified structure as an electrical, disc-shaped heating element, which can be installed transversely in an exhaust system and through which the exhaust gases flow and / or simultaneously acts as a catalyst by means of a coating.

[0008] Since the electrical resistance, and thus the heating, increases with the length of the electrical heating conductor, a relatively long length of the electrical heating conductor is advantageous. On the other hand, since the electrical resistance decreases with increasing conductor cross-section, the use of a very thin metal foil matrix as a heating conductor is advantageous.

[0009] However, the known designs of a so-called heating catalyst, for example according to EP 2836687 B1, are complex to manufacture and adapt to different applications.

[0010] Furthermore, reference is made to documents DE 43 42 652 A1 and DE 10 2019 203 984 A1. III. Description of the inventiona) Technical problem

[0011] It is therefore the object of the invention to provide an electric heating device and in particular its heating element which is suitable for use in an exhaust gas purification system, is simple and cost-effective to manufacture and is easily adaptable to different applications, as well as a corresponding manufacturing method therefor. b) Solution to the task

[0012] This object is achieved by the features of claims 1, 26 and 29. Advantageous embodiments emerge from the subclaims.

[0013] A known, particularly disc-shaped, electric heating element comprises a plurality of flow channels extending transversely to a main plane of the heating element, open at both ends, through which a fluid, particularly a gas, can freely flow, thus forming no dead ends, particularly in the direction of flow. Several of the flow channels are arranged side by side in the cross-section of the electric heating conductor, transverse to its direction of travel.

[0014] The flow channels may be the channels of a honeycomb body, which may be formed from a plurality of layers of a three-dimensionally structured foil of electrically conductive material, in particular a metal foil.

[0015] The heating element consists of several adjacent, electrically insulated layers of a heating conductor made of electrically conductive material arranged along the main plane. In one known design, the heating conductor is twisted in an S-shape along the main plane, forming a kind of two-armed spiral.

[0016] According to one aspect of the invention, such a known heating element is designed such that the cross-section of the heating conductor changes in the transverse direction to the main plane of the heating element, in particular in the direction perpendicular to the main plane. The cross-section can have a larger cross-sectional width at one end, for example, at one end face of the heating disc, than at the other end, i.e., the other end face of the heating disc.

[0017] Since this transverse direction, especially the vertical, is usually the channel direction of the flow channels, the cross-section of the heating conductor decreases in this direction and thus its temperature increases.

[0018] By varying the cross-sectional area in this direction, the temperature gradient of the heating conductor and thus of the entire heating element can be adjusted in this direction, thus facilitating adaptation to different applications.

[0019] This means that when installed in the direction of flow of the combustion gases, the temperature of the heating element increases, which facilitates efficient heating.

[0020] Preferably, this change in cross-section remains the same - at least qualitatively, preferably also quantitatively - over the essential part of the length of the heating conductor, i.e. over more than 50%, better more than 70%, better more than 80%, better more than 90%, in its direction of extension.

[0021] A known heating element as described above can be designed in such a way that the layers of the heating conductor are not only electrically insulated from each other, but also spaced apart from each other.

[0022] If the flow channels in the top view of the main plane of the heating element are arranged in a regular pattern in the heating element and thus also in the heating conductor - e.g. as in a matrix body - this regular pattern can be completed virtually, i.e. notionally, across the distances between the layers of the heating conductor to form a continuous regular pattern, as would be the case, for example, when separating the heating element from a regular pattern such as a matrix body.

[0023] By maintaining the regular pattern in the individual layers of the heating conductor, reproducible and thus defined electrical conditions prevail there - even if the size of the distances is changed to adapt to different applications - which greatly simplifies the control of the heating element with regard to temperature and temperature gradients in the individual spatial directions and also the adaptation to different applications.

[0024] The following explanations concern optional configurations: By arranging the heating conductor in several layers - which form sections of the entire, continuous heating conductor and are therefore connected to one another in particular on one side - along the main plane of the heating element, a length of the heating conductor is achieved which is at least four times, better at least six times, better at least ten times the largest diameter of the heating element, in particular the heating disc, along its main plane or the equivalent diameter in the case of a heating element which is non-circular when viewed from above on the main plane, as is advantageous for efficient, rapid heating.

[0025] If the regular pattern in its complete state comprises a center, such as in the case of a matrix wound spirally around a center, the heating element, and in particular also the heating conductor, should also comprise this center or preferably even be arranged concentrically to this center, since this can ensure that the individual layers of the heating conductor, in particular if they run spirally, each have approximately the same internal structure.

[0026] However, the heating conductor can also run in a meandering or S-shaped manner or in another way along the main plane.

[0027] The individual layers of the heating conductor can be essentially straight or wavy or zigzag-shaped when viewed from the main plane.

[0028] It is therefore preferably sufficient if only a single heating conductor is present along the main plane of the heating element, i.e. at an axial position along the perpendicular to the main plane, which greatly simplifies the construction of a heating device therefrom, since with a single heating element only two electrical connection elements are necessary, each at one of the two ends of the single heating conductor.

[0029] The heating conductor can - viewed from the main plane of the heating element - have a variable width, i.e. cross-sectional width, along its direction of extension, whereby the temperature development in the direction of extension along the heating conductor can be controlled.

[0030] The matrix that forms the flow channels can be designed in different ways: It can be made of different structures, for example of expanded material, in particular expanded metal, of a woven fabric, a nonwoven fabric, a foam or even of several interconnected layers of foils, in particular metal foils, between which the channels are formed, for example by at least one of the layers having a three-dimensional structure or by keeping the layers at a distance from one another in another way and producing flow channels between them.

[0031] The material used must be electrically conductive, and the components, for example the individual threads in a fabric, must be electrically connected to one another, as must the films in a layered matrix body.

[0032] A preferred embodiment is a matrix body in which a three-dimensionally structured film and a smooth film, or at least a less three-dimensionally structured film, alternate in succession. Especially if the highly structured film has a structure that extends in only one direction, for example, the highly structured film is a selected film with parallel wave troughs and wave peaks, the smooth film or less structured film adjacent to the wave peaks creates flow channels that are preferably parallel to one another, thus creating a regular pattern of flow channels along the main plane, such as the end face, of the heating element, or of a blank from which the heating element is cut.

[0033] In order to achieve high electrical conductivity, only some of the contact points and contact areas between the layers, in particular foils, of such a layered matrix are designed to be electrically conductive, in particular soldered.

[0034] When two different foils are used, for example, one with a stronger and one with a weaker structure, the thicknesses of the two foils can be different relative to each other and selected such that, taking into account the respective electrical conductivity of the foil material and the different lengths of the cradle along the two foils, the electrical resistance of the two foils remains the same over a specific length of the heating conductor transverse to the channel direction. This ensures optimal current distribution along the heating conductor and thus also the heating element.

[0035] The term “equal electrical resistance” preferably means that the greater electrical resistance of one of the two films is not more than 20%, better not more than 10%, better not more than 5% above the smaller electrical resistance of the other film.

[0036] With regard to the direction of the layers of, for example, foil, fabric, or expanded metal, relative to the direction of the heating conductor, these layers should either be aligned in the direction of the heating conductor or at an acute angle to it, covering the majority of the surface of these layers, i.e., at least 50%, preferably at least 70%. Preferably, the existing acute angle—which, as explained, can also be zero—is the same along the entire length of the heating conductor, with a tolerance of + / -10%.

[0037] The matrix forming the flow channels, especially the matrix foils, can also be catalytically coated, allowing the heating element to simultaneously serve as a catalyst. Preferably, the catalytic coating should also be made of an electrically conductive material.

[0038] To mechanically stabilize the heating element, the layers of the heating conductor can be kept at a distance from each other by spacers, which must then of course act as an electrical insulator between the layers.

[0039] For the same purpose, positioning pins can be fixed in the heating element with a force-locking or form-locking mechanism. These pins can then be held in position both axially, i.e., perpendicular to the main plane of the heating element, and along the main plane of the heating element within a heating device. However, this alters the electrically conductive structure of the heating element due to an irregularity, which can be disadvantageous.

[0040] To improve the temperature transfer from the heated matrix to the gases rushing through it, the individual layers of the matrix can be of different lengths across the main plane of the heating element, particularly in the channel direction. For example, if two films with different textures form the matrix, one of them can be longer than the other, particularly the more textured layer. The overhang of a longer layer relative to a shorter layer should preferably always be on the same side relative to the main plane of the heating element.

[0041] In order to be suitable for applications in the exhaust system of an internal combustion engine, the material of the heating element, in particular the heating conductor, should be a high-temperature resistant material with a melting point of at least 400 C, better at least 600 C, better at least 800 C, better at least 1000 C, better at least 1100 C, better at least 1200 C.

[0042] With regard to an electric heating device comprising an electric heating element and additionally an electric connection element at each end of the electric heating element, the existing object is achieved in that the electric heating element is designed as described above.

[0043] Preferably, the electrical connection element is transversely connected or soldered to the respective end of the heating element, in particular the heating conductor, in order to damage the internal structure of the heating conductor as little as possible.

[0044] If the heating element was cut out of a blank in the form of a matrix with a surrounding jacket tube, the matrix being electrically connected to the jacket tube, the sections of the jacket tube attached to the ends of the heating conductor, which are located on the outside in the radial direction, are preferably left and used as electrical connection elements.

[0045] This section of the casing tube can have a varying width in the circumferential direction when viewed from the outside, depending on the desired electrical resistance and the desired current distribution in this direction.

[0046] Likewise, this section could have a varying thickness in the circumferential direction for the same reason in order to be able to adjust the electrical parameters of the electrical connection element.

[0047] Preferably, the electrical connection elements are arranged only on the radial outer side of the heating element, in particular the heating disc, at the respective end of the heating conductor, but in the case of a regular structure with a center, an electrical connection element could also be arranged in the center thereof, which, however, makes the power supply more difficult due to the prevailing ambient temperature.

[0048] If spacers or positioning pins are present in the heating element, they are held in position relative to each other and / or to a surrounding housing of the heating device by means of a supporting structure to which they are attached. The supporting structure preferably consists of struts that are as narrow as possible when viewed from the main plane of the heating element, in particular struts arranged in a star shape, in order to minimize the flow resistance caused by the heating device.

[0049] With regard to a method for producing an electric heating element, the latter should be designed overall as described above.

[0050] Then, the existing problem is solved in that the heating element is separated, in particular cut out or separated by means of another separation method, from a matrix which comprises a plurality of flow channels running alongside one another, in particular arranged regularly alongside one another.

[0051] The separation process also creates the individual, spaced-apart layers of the heating conductor by appropriately positioning the joints. The joints naturally extend from the front to the rear end face of the usually disc-shaped matrix.

[0052] The joints are placed in such a way that the heating conductor along the main plane of the heating element is at least four times as long, preferably at least six times as long as the largest diameter of the heating element, in particular the heating disc.

[0053] The layers of the heating conductor thus produced are then, if possible, no longer displaced or even bent along the main plane of the heating element or transversely thereto, but are left in their original position and fixed as far as possible, for example by means of the aforementioned positioning pins and / or spacers and their fixation relative to, for example, a housing of the heating device.

[0054] Preferably, when separating the heating element from the particularly regular matrix, the blank, the procedure can be such that the cross section of the heating conductor produced changes in the direction perpendicular to the main plane of the heating element, i.e. for example in the channel direction, i.e. at one end, one end face of the heating disc, it has a larger cross-sectional width than at the other end, the other end face of the heating disc.

[0055] The cutting out can be done by laser cutting, water jet cutting, plasma cutting or another suitable cutting process, but other cutting processes than cutting processes can also be used.

[0056] With regard to a method for producing an electrical heating device which comprises an electrical heating element, for example as described above, the existing object is achieved in that the electrical connection elements at the ends of the heating conductor are clamped, welded or soldered to the latter, but preferably the heating conductor is not pierced or drilled but the fastening is carried out only on the outer surfaces of the heating conductor.

[0057] If the electrical heating device is cut out of a matrix with a circumferentially surrounding jacket tube, against which it is fixed, in particular electrically conductively fixed, the jacket tube is also cut through once or several times, but those sections of the jacket tube of the heating conductor cut out of the matrix in the beginning and end area are left on the matrix and thus the heating conductor and used as electrical connection elements.

[0058] Furthermore, the jacket tube is preferably cut at an acute angle to the tangential device when viewed from the front, so that the thickness of this section of the jacket tube changes in the circumferential direction.

[0059] The two connecting elements, in particular jacket pipe sections and / or positioned pins and / or spacers, are fixed relative to a housing of the heating device, in particular by means of a supporting structure running parallel to the main plane and made of support struts that are as thin as possible.

[0060] Care must be taken to ensure that the supporting structure does not cause electrical short circuits between different layers of the heating element. Therefore, the supporting structure is preferably made of an electrically insulating material, particularly a high-temperature-resistant ceramic material. The spacers and / or positioning pins can also be relevant components of the supporting structure.

[0061] A significant advantage of the invention is that - the material of the heating element, in particular the heating conductor and / or - the shape of the heating conductor viewed from the main plane and / or - the circumferential contour of the heating element and / or - the width of the heating conductor along its direction of extension and / or - the quantitative and qualitative change in the cross-sectional width of the heating conductor perpendicular to the main plane of the heating element, in particular in the channel direction and / or - when using foils or expanded metal, the thickness of the foils and / or - when using fabric, the thickness of the fibers and / or - the manufacturing process can be selected so that when the heating element is supplied with a current and / or voltage specified in its operation - a predetermined temperature gradient and / or absolute temperatures are reached at defined points along the main plane perpendicular to the main plane and / or - in the directions of the main plane, in particular in the radial direction of the heating element, a predetermined temperature gradient and / or absolute temperatures are achieved at defined points along the main plane. c) Examples of implementation

[0062] Embodiments according to the invention are described in more detail below by way of example. They show: Fig. 1a: a wound honeycomb body, Fig. 1b: a heating element, supplemented on one side to form a heating device, Fig. 2: an enlarged section of a peripheral area of ​​the Fig. 1b, supplemented by a housing of the heating device, Fig. 3a: a section through the heating device 50 along the line IIIa-IIIa in Fig. 1b, Fig. 3b: a side view of the heating disc 1 supplemented to form a heating device, Fig. 4: a heating element 1 made of a layered honeycomb body which is rectangular when viewed in the channel direction.

[0063] Fig. 1a shows a front view of a blank 22 from which the heating element 1 according to Fig. 1b can be produced cost-effectively: The front view of the disc-shaped blank 22 in Fig. 1a shows that it consists of a spirally wound matrix 20, the so-called honeycomb body, and a surrounding jacket tube 21 with a round inner and outer cross-section.

[0064] Such a known matrix 20 can be produced by winding a corrugated strip-shaped metal foil 5.1 and a smooth strip-shaped metal foil 5.2 placed thereon together around a center Z, three-dimensionally a straight line in the axial direction 10, as a spiral with a winding direction 20', in this case clockwise, up to a size such that the wound matrix 20 just fits into the casing tube 21, which prevents the subsequent separation of the spiral winding.

[0065] Since the wave troughs and wave crests in the corrugated film strip 5.1 run in the direction of the winding axis 10 across the width of the film strip from one side edge to the other side edge, usually in the direction of the winding axis 1' of the wound matrix 20, the two adjacent films 5.1, 5.2 in the wound matrix 20 create continuous channels 3 that run from one end face to the other, are open on both sides and thus freely flowable, the channel direction 3' of which usually coincides with the direction of the winding axis 10 and thus the perpendicular to the main plane 1" of the disc-shaped matrix or cylindrical matrix 20.

[0066] As especially in Fig. 2, this creates a regular pattern M of channels 3 across the front side of the matrix 20.

[0067] Such channels 3 could also be created if the smooth foil 5.2 were omitted and only the regularly corrugated foil 5.2 were wound spirally as a single layer, but then in a much less regular pattern and with differently sized channel cross-sections.

[0068] As a rule, the two foils 5.1, 5.2 are also fixed to each other at the mutual contact points, for example by soldering, preferably on all layers S1, S2 of the wound matrix 20 formed in the radial direction by these only two foil strips 5.1, 5.2, and also the outermost layer S1 opposite the jacket tube 21.

[0069] The aim is to produce a heating element 1 for an electrical resistance heater from such a blank 22, wherein the electrically contracting, electrically conductive foils 5.1, 5.2 are to form the heating conductor 2 of the heating element 1, which, however, is to be considerably longer than, for example, the diameter of the blank 22 in order to achieve a high heating output.

[0070] For this purpose - when viewed from the front according to Fig. 1b - two parting lines T - shown here in black - are introduced into the blank 22, starting, for example, at the outer circumference at a slight angle to the tangential direction, first through the casing tube 21 and then spirally continuing inwards through the coil 20, from two opposite sides of the cross-section, which in this case is circular, and with the same shape of the two parting lines, which can be produced, for example, by laser cutting or water jet cutting.

[0071] Near the center Z, these two separating joints T again end on sides that are preferably opposite one another with respect to the center Z. The heating element 1 produced in this way then consists of a heating conductor 2 in the form of a two-armed spiral, the two spiral arms 8, 9 of which are connected to one another at the center Z and merge into one another, thus forming a double spiral whose outer ends are approximately opposite one another with respect to the center Z. However, the latter is not a condition for the implementation of the invention, but only arises when the two separating joints T introduced are approximately identical and offset by a rotation angle of 180° with respect to the center Z.

[0072] The heating conductor 2 forming the heating element 1 thus extends from its one end 2.1 on one side of the circumference spirally inwards along one spiral arm, e.g. 8 to the center Z and from there along the second spiral arm 9 again spirally outwards to its other end 2.2 on the opposite side of the circumference and thus has a length which corresponds to several times, approximately five to ten times, the diameter of the matrix 10.

[0073] Since, for stability reasons, the matrix 20 is usually still surrounded by the cladding tube 21 when the separating joints T are introduced, the cladding tube 21 is also severed - especially when separating cuts are made in the radial direction.

[0074] Preferably, the - matching - winding direction 8', 9' of the two spiral arms 8, 9 is selected in such a way - which is determined by the position and shape of the joints T - that this winding direction 8', 9' coincides with the winding direction 20' of the layers S1 and S2 in the original matrix 20 in the circumferential direction, but not with regard to the orientation to the tangential direction: Instead, as in Fig. 2 - the parting line T - which is preferably always the same width along its length - and thus its lateral edges are more inclined to the tangential direction than the direction of the two films 5.1, 5.2, so that they lie at an acute angle α to each other.

[0075] Fig. 2 also shows that the heating conductor 2, which is present in several layers 2a, 2b electrically separated from one another by the distance A due to the separating joints T, but which nevertheless result in a common continuous heating conductor 2, comprises several flow channels 3 next to one another in the radial direction in the transverse direction along the main plane 1" - which is perpendicular to the winding axis 1' and usually represents the largest extension plane of the heating disc.

[0076] Due to the angle α, the current conducted through the heating conductor 2 cannot flow along, for example, only the smooth foils 5.2, because each of the foils 5.1, 5.2 ends at one of the separating joints T and must change there at the latest from this ending foil strip to an electrically connected adjacent foil strip, which causes a good current distribution in the transverse direction of the heating conductor 2 and thus its uniform heating.

[0077] Fig. 2 further shows that the regular pattern M in the form of channels 3 and the foil strips 5.1, 5.2 delimiting these within the individual layers 2a, 2b of the heating conductor 2 could be virtually continued and completed across the parting line T, which is due to the fact that the heating element 1 was produced from a regular pattern in the form of the wound matrix 20 that originally ran across the end face.

[0078] There Fig. 2 shows a finished heating device 50, this is preferably also surrounded circumferentially by a housing 53, to which on the one hand the supporting structure 52 is fastened, and which on the other hand is electrically insulated from the electrical connection elements 51.1, 51.2, although these connection elements can certainly pass through the housing 53.

[0079] Fig. Figure 3a shows a radial section along the line IIIa - IIIa of the Fig. 1b, that the parting lines T can become wider from one end face to the other, whereby the increase in width can be controlled in many parting processes.

[0080] For better clarity, Fig. 3a only the smooth foil 5.2 and the corrugated foil 5.1 are shown for the outermost two layers 2a, 2b of the heating conductor 2.

[0081] Due to the separating joints T becoming wider in the axial direction 10, the cross-sectional width QB increases - in a conversely analogous manner - from one end Q1 on one end face to the other end Q2 on the other end face of the cross-section Q, which means that when current flows through the heating conductor 2 in the main direction of extension, its cross-section is heated more strongly at the end Q2 with the smaller cross-sectional width than at the other end Q1.

[0082] This can be used advantageously when fluid passing through the channels 3, such as the exhaust gas of an internal combustion engine, is to be heated by selecting the side with the less heated heating conductor 2, i.e. the side with the larger cross-sectional width QB, as the inflow side.

[0083] In the right area of ​​the Fig. 3a further shows the possibility of selecting the two foil strips 5.1, 5.2, from which the original matrix 20 was wound, with axially different widths, but of having them start at the same axial position on one end face, preferably the later inflow side of the fluid to be heated.

[0084] As a result, the smooth foil 5.2 projecting on the other side, for example, further increases the area at which heat can be transferred from the foil 5.2, i.e. the heating conductor 2, to the fluid flowing over it, without significantly increasing the flow resistance.

[0085] Since the heating conductor 2 must be equipped with a connecting element 51.1, 51.2 at its ends 2.1, 2.2, which are usually opposite one another with respect to the end face, for supplying current, in particular into all foil layers of its cross section Q, the separating joint T is preferably also led through the surrounding jacket tube 21 and the part of the jacket tube 21 which is adjacent to the respective outer end 2.1, 2.2 of the heating conductor 2 and is usually already electrically connected to it, in particular soldered, is left as it is, since it only needs to be connected with a threaded bolt welded on from the outside, for example, as in Fig. 1b shown below or another fastening option for attaching a power supply must be provided in order to create a connection element 51.1, 51.2.

[0086] In addition, this offers the possibility of controlling the increase in thickness in the circumferential direction of the piece left on the current conductor 2 by means of an oblique separating cut through the jacket tube 21 - that is, when viewed from the front, not tangentially and not radially, but at an angle in between - and also the width of section 21.1 or 21.2 of the jacket tube 21, viewed in the side view of the heating disc, can be controlled when producing the separating joint.

[0087] This allows the current density to be determined and controlled in the individual areas of the remaining jacket pipe section, e.g. 21.1, into the foil layers of the heating conductor 2.

[0088] Fig. 4 shows, viewed in the channel direction 3', i.e. from the front side, a solution how a heating element 1 can be produced from a layered matrix 20 - in which corrugated foil 5.1 and smooth foil 5.2 are stacked on top of each other in individual foil pieces of a flat shape and then accommodated in a rectangular cladding tube 21: Then, the separating joints T can be introduced into the matrix from the two side surfaces, which each adjoin the end surface and in which the foil pieces end, in order to produce a current conductor 2 which then runs back and forth in a zigzag shape along the end surface in layers 2a to 2z.

[0089] In this case, the corresponding section 21.1, 21.2 of the jacket tube 21 of the original blank - in this case having a rectangular cross-section - is left at one of the two ends of the current conductor 2 due to the electrically conductive connection to the foils 5.1, 5.2 already present there and can be used for the production of a connecting element 51.1, 51.2.

[0090] While in the upper area of ​​the Fig. 4 as the 1st variant the separating joints T are shown arranged parallel to the direction of the planes in which the metal foils 5.1, 5.2 are located, in the lower area as the 2nd variant they are shown arranged obliquely to this at an acute angle α in order to effect, as described above, a frequent change of the current flow from one foil to an adjacent layer S1, S2 and foil 5.1, 5.2 and thus a good current distribution. LIST OF REFERENCE SYMBOLS 1 heating element, heating disc 1.1, 1.2 End 1' axial direction, vertical direction 1'' main level 2 heating conductors, current conductors 2.1, 2.2 End 2a, 2b layers 2' Direction of travel 3 flow channel 3' channel direction 4 Distance 5, 5.1, 5.2 Slide 6 spacers 7 Positioning pin 8 spiral arm 8' spiral direction 9 spiral arm 9' spiral direction 10 perpendiculars 11, 12 direction 20 Matrix 20' winding direction 21 jacket pipe 22 blank 50 heating device 51.1, 51.2 connecting element 52 supporting structure 52a, b supporting strut 53 housings α angle A distance d thickness S1, S2 layer Q cross-section Q.1, Q.2 End cross section QB cross-sectional width, width M pattern T-joint Z center

Claims

[1] Electric heating element (1) with - a plurality of flow channels (3) extending transversely to a main plane (1") of the heating element (1), open on both sides at the front, through which a fluid can freely flow, - wherein the heating element (1) consists of a plurality of adjacent, mutually electrically insulated layers (2a, b) in the main plane (1") as sections of a continuous heating conductor (2), which can thus form a current path, made of electrically conductive material, - in the cross-section (Q) of the electrical heating conductor (2) transverse to its direction of travel (2'), several of the flow channels (3) are present next to one another, characterized by , that - the cross-section (Q) of the heating conductor (2) changes in the perpendicular (10) to the main plane (1") of the heating element (1). [2] Heating element according to claim 1, characterized by , that - the cross-section (Q) of the heating conductor (2) in the vertical (10) has a larger cross-sectional width (QB) at one end (Q.1) of the cross-section (Q) than at the other end (Q.2). [3] Heating element according to one of the preceding claims, characterized by , that - the qualitative change in the cross-section (Q) of the heating conductor (2) in the channel direction (3') is the same over the direction of extension of the heating conductor (2), in particular over the entire direction of extension of the heating conductor (2). [4] Electric heating element (1) according to one of the preceding claims, characterized by , that - the layers (2a, 2b) of the heating conductor (2) are spaced apart from each other, - the flow channels (3) in the heating element (1) and thus in the heating conductor (2) are arranged in a regular pattern (M), which can be virtually completed over the distances (4) between the layers (2a, 2b) of the heating conductor (2), - since in particular the heating element (1) is part of a matrix (20) with such a continuous regular pattern of the flow channels (3), in particular running parallel to one another. [5] Heating element according to one of the preceding claims, characterized by , that - the layers (2a, 2b) of the heating conductor (2) are spaced from each other by at least 0.5 mm, preferably at least 1 mm, preferably at least 2 mm, preferably at least 3 mm, preferably at least 4 mm, preferably at least 5 mm, - the length of the heating conductor (2) is at least 4 times, better at least 6 times, better at least 10 times, the largest diameter of the heating element (1) along its main plane (1") or the equivalent diameter in the case of a non-circular circumferential contour of the heating element (1) in its main plane (1"), wherein the equivalent diameter is the square root of the cross-sectional area divided by 3.

14. [6] Heating element according to one of the preceding claims, characterized by that for a regular pattern with a center (Z) - the heating element (1), in particular the heating conductor (2), includes the center (Z), - in particular is arranged concentrically around the center (Z). [7] Heating element according to one of the preceding claims, characterized by that there is only one heating conductor (2) along a main plane (1") of the heating element (1). [8] Heating element according to one of the preceding claims, characterized by that the heating conductor (2) has a variable width (QB) viewed in its direction of extension on the main plane (1") of the heating element (1). [9] Heating element according to one of the preceding claims, characterized by that the matrix (20) consists of - a fabric, particularly an open-pored fabric or fleece or foam made of electrically conductive material or - electrically conductive expanded metal or - several successive layers (S1, S2) in one of the directions (11, 12) of the main plane (1") made of electrically conductive foils (5) which are in electrical contact with one another, in particular soldered to one another, and which may also have partial openings, - in particular at least one of the layers (S1, S2) consists of a three-dimensional, in particular strongly, structured film (5.1), the three-dimensional structuring of which extends in particular transversely to the main plane (1") and together with an adjacent film (5.2) forms the flow channels (3). [10] Heating element according to one of the preceding claims, characterized by that all contact areas between the layers (S1, S2), in particular foils (5), are electrically conductive, in particular soldered. [11] Heating element according to one of the preceding claims, characterized by , that - the adjacent film (5.2) is a smooth film (5.2) or at least a less structured film (5.2), - the two foils (5.1, 5.2) have a thickness relative to each other such that, taking into account the respective electrical conductivity of the foil (5.1, 5.2) and the longer path of the more strongly structured foil (5.1) than the less strongly structured foil (5.2) transversely to the channel direction (3'), the electrical resistance of the two foils (5.1, 5.2) is the same, - at least the larger electrical resistance is not more than 20%, preferably not more than 10%, preferably not more than 5% above the smaller electrical resistance. [12] Heating element according to one of the preceding claims, characterized by , that - the layers (S1, S2) of foils (5) or fabric or expanded metal are mostly located in the direction (2') of the heating conductor (2) or at an acute angle thereto, - mostly along the entire heating conductor (2) at the same acute angle or without an angle to it, - in particular over more than 50%, better more than 70%, better more than 80% of the cross-sectional area of ​​the heating element (1). [13] Heating element according to one of the preceding claims, characterized by that the matrix (20), in particular the films (5) of the matrix (20), are catalytically coated, in particular with an electrically conductive material. [14] Heating element according to one of the preceding claims, characterized by that the layers (2a, 2b) of the heating conductor (2) - are kept at a distance (4) from each other by electrically insulating spacers (6) and / or - are held in position by positioning pins (7) fastened in the heating conductor (2) in a force-fitting or form-fitting manner. [15] Heating element according to one of the preceding claims, characterized bythat the layers (2a, 2b) of the heating conductor (2) in the plan view of the main plane (1") of the heating element (1) - meandering or - spiral or - are arranged in an S-shape. [16] Heating element according to one of claims 1 to 14 characterized by , that the layers (2a, 2b) of the heating conductor (2) in the top view of the main plane (1") of the heating element (1) - essentially rectilinear or - wavy or - zigzag-shaped get lost. [17] Heating element according to one of the preceding claims, characterized by , that - the layers (S1, S2) of the matrix (20) are of different lengths in the channel direction (3'), - in particular the more structured layer is longer, - in particular the longer layer always has the overhang on the same side with respect to the main plane (1") of the heating element (1) compared to the shorter layer. [18] Heating element according to one of the preceding claims, characterized by that the material of the heating element (1), in particular of the heating conductor (2), is a high-temperature-resistant material with a melting point of at least 400°C, better at least 600°C, better at least 800°C, better at least 1000°C, better at least 1100°C, better at least 1200°C. [19] Heating element according to one of the preceding claims, characterized by that the material of the heating element (1), in particular of the heating conductor (2), is a material whose specific resistance changes only slightly with increasing temperature, in particular by less than 5%, better by less than 1% above 100°C. [20] Electric heating device (50) with - an electric heating element (1), - one electrical connection element (51, 52) at each of the two ends (1.1, 1.2) of the heating element (1), characterized bythat the electrical heating element (1) is designed according to one of the preceding claims. [21] Electric heating device according to claim 20, characterized by that the electrical connection element (51.1, 51.2) is crimped or soldered to the respective end (1.1, 1.2) of the heating element (1). [22] Electric heating device according to one of claims 20 to 21, characterized by that the electrical connection element (51.1, 51.2) is part of a casing tube (21) originally surrounding the matrix (20) circumferentially. [23] Electric heating device according to one of claims 20 to 22, characterized by , that - the electrical connection element (51.1, 51.2) is arranged on the radial outer side of the respective end (2.1, 2.2) of the heating conductor (2) and - has a varying width in the circumferential direction when viewed from the outside and / or - has a varying thickness in the channel direction (3'). [24] Electric heating device according to one of claims 20 to 23, characterized by , that - the spacers (6) in the intervals (4) and / or the positioning pins (7) in the heating conductor (2) are fastened on at least one of the end faces of the heating element (1) to a supporting structure (52) which runs in particular parallel to the main plane (1") of the heating element (1), said supporting structure consisting in particular of supporting struts (52a, b), - the supporting structure (52) is electrically insulated from the heating element (1) if it is made of an electrically conductive material. [25] Electric heating device according to claim 24, characterized by that the supporting structure (52) has a star shape when viewed in the channel direction (3'). [26] Method for producing an electric heating element (1) according to one of the preceding claims 1 to 19, characterized by , that - the heating element (1) is separated, in particular cut out, from a matrix (20) having a plurality of flow channels (3) running side by side, by creating a parting line (T) which passes from one end face of the matrix (20) to the other and produces the heating conductor (2), - wherein, in the plan view of the main plane (1"), the separating joint (T) is placed such that the heating conductor (2) along the main plane (1") is at least four times as long, better at least six times, better at least ten times as long as the largest diameter or the equivalent diameter of the heating element (1). [27] Method according to claim 26 characterized bythat the heating element (1) is separated from the matrix (20) in such a way that the cross-section (Q) of the heating conductor (2) changes in the perpendicular (10) to the main plane (1"), in particular in the channel direction (3'), in particular in the channel direction (3') at one end (Q.1) has a larger cross-sectional width (QB) than at the other end (Q.2). [28] Method according to one of claims 26 to 27, characterized by that the heating element (1) is cut out by means of laser cutting, water jet cutting or plasma cutting or punching or nipping. [29] A method for manufacturing an electric heating device (50) according to any one of claims 20 to 25, characterized by that the electrical connection elements (51.1, 51.2) are clamped, welded or soldered to the ends of the heating conductor (2). [30] Method according to claim 29, characterized bythat the electrical heating device (50) is separated, in particular cut out, from a matrix (20) with a circumferentially surrounding jacket tube (21), relative to which it is fixed, in particular soldered, by severing the jacket tube (21) and retaining only those sections of the jacket tube (21) of the heating conductor (2) separated from the matrix (20) in the start and end region. [31] Method according to one of the preceding method claims 29 to 30, characterized by that the jacket pipe (21) is severed at an acute angle to the tangential direction. [32] Method according to one of the preceding method claims 29 to 31, characterized by , that - the two connecting elements (51.1, 51.2), in particular remaining jacket pipe sections, are fixed against each other transversely to the channel direction (3'), i.e. across the cross section (Q) of the heating element (1), by means of a supporting structure (52), and / or - Positioning pins (7) in the heating conductor (2) and / or spacers (6) in the intervals (4) between the layers (2a, 2b) of the heating conductor (2) are fixed against each other, either individually or jointly, via a supporting structure (52). [33] Method according to one of the preceding method claims 29 to 32, characterized by , that - the material of the heating element (1), in particular of the heating conductor (2) and / or - the shape of the heating conductor (2) viewed from the top of the main plane (1") and / or - the circumferential contour of the heating element (1) and / or - the width of the heating conductor (2) along its direction of extension and / or - the quantitative and qualitative change in the cross-sectional width (QB) of the heating conductor (2) perpendicular (10) to the main plane (1") of the heating element (1), in particular in the channel direction (3') and / or - when using foils (5) or expanded metal, the thickness of the foils (5) and / or - when using fabric, the thickness of the fibers and / or - the manufacturing process be selected so that when the heating element (1) is supplied with current at a predetermined level and / or voltage - in the perpendicular (10) to the main plane (1") a predetermined temperature gradient and / or absolute temperatures are achieved at predetermined positions in the vertical direction (1') and / or - in the directions of the main plane (1"), in particular in the radial direction of the heating element (1), a predetermined temperature gradient and / or absolute temperatures are achieved at predetermined radial positions.

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