EP4379199A1 - Heating device for heating a gas flow - Google Patents

Abstract

A heating device (100) for heating a gas flow, in particular an exhaust gas flow of an internal combustion engine, comprises an electrically conductive heating element (102) and a carrier device (104) with at least one electrically insulating carrier element (106) for the electrically conductive heating element. The heating device is characterized in that the electrically conductive heating element (102) is designed as a three-dimensional structure (TPMS), the surface of which is formed at least in sections from triply periodic minimal surfaces, such as gyroid (302) or black diamond structure (BDS). Furthermore, the heating device (100) can consist of two heating segments or two partial bodies arranged one after the other or in parallel, which can be separately electrically controlled in electrical series or parallel connection.

Description

The invention relates to a heating device for heating a gas stream, in particular an exhaust gas stream of an internal combustion engine.

Catalysts are used for exhaust gas aftertreatment in vehicles. Catalysts convert pollutants such as nitrogen oxides into harmless substances and are used to clean the exhaust gases produced by an internal combustion engine, for example a petrol or diesel engine, through the combustion of a fuel. The conversion or transformation rate of the pollutants into non-harmful substances is temperature-dependent for the catalysts used. Pollutant emissions are only converted into non-harmful substances once a minimum temperature has been reached. In order to reduce pollutant emissions, it is therefore necessary to shorten the time until the minimum temperature is reached. Active heating measures are used for this purpose, particularly with a view to future exhaust gas standards (EU7). Active heating measures include, for example, an electrically operated heating system (electric heater). The heating effect of electrical heating systems is based on the law of electrical heat transfer ("Ohmic heating"), i.e. the supply of current to a metallic heating matrix.

Known heating element structures are limited in their geometric design, i.e. in their volume, mass, surface and structure, due to manufacturing processes as well as thermomechanical and structural dynamic considerations.

It is an object of the invention to provide a device with which an improvement in the thermodynamic and structural dynamic properties can be achieved compared to known devices from the prior art and thus a faster reaching of the minimum temperature, for example of a catalyst or a cleaning unit of another type, can be achieved.

This object is achieved by a heating device having the features of claim 1.

The heating device according to the invention for heating a gas flow, in particular an exhaust gas flow of an internal combustion engine, comprises an electrically conductive heating element and a carrier device with at least one electrically insulating carrier element for the electrically conductive heating element. The heating device is characterized in that the electrically conductive heating element is designed as a three-dimensional structure, the surface of which is formed at least in sections from triply periodic minimal surfaces.

The internal combustion engine can be designed as an internal combustion engine, for example as a gasoline engine or diesel engine. The internal combustion engine can also implement other combustion processes, for example a Miller combustion process, or use other fuels, for example synthetic fuels or hydrogen. When such a machine is operated, pollutants are produced. The pollutant concentrations can depend heavily on the operating conditions, for example on the type of fuel, the concentration of the fuel in the fuel-air mixture used, the amount of the fuel-air mixture, the speed of the internal combustion engine and/or the operating temperature of the internal combustion engine.

The exhaust gases produced by the combustion of a fuel in the internal combustion engine form a gas stream, in particular an exhaust gas stream. The exhaust gases are conducted to the outside via an exhaust system connected to the internal combustion engine through an exhaust gas treatment device, i.e. are released into the ambient air of the vehicle. The exhaust gas treatment device can comprise a catalyst, wherein the gas flow is cleaned by a catalytic reaction in the catalyst when the gas flow flows through the catalyst. When the internal combustion engine is cold started, the exhaust gases still have a comparatively low temperature. The catalyst, or a catalyst unit, through which the exhaust gas flows is also comparatively cool, so that a threshold temperature or minimum temperature at which efficient cleaning of the exhaust gas can take place is often not yet reached. This means that the exhaust gases are not completely cleaned. Only with increasing heating of the exhaust gases and the associated heating of the catalyst does the system reach a temperature range in which the desired catalytic reactions take place efficiently.

One measure for improving the cold start behavior of a corresponding exhaust system can be to provide a heating device in front of the catalyst or in front of the exhaust treatment unit, by means of which the incoming exhaust gas is heated. The heating device can comprise a heating element that supplies additional heat to the exhaust gas flow in order to bring the system as quickly as possible into a temperature range in which efficient exhaust gas aftertreatment can take place. However, other areas of application for the heating device are also possible. For example, the heating device can be used to preheat combustion air in an intake tract of an internal combustion engine or, more generally, to heat any gas flow. The heating element can be made of an electrically conductive material, in particular metal, so that the heating element is also electrically conductive. In addition, the heating device can comprise a carrier device that carries the heating element. The carrier device can, for example, hold the heating element in front of the exhaust gas treatment unit in the flow direction of the exhaust gas. The At least one carrier element of the carrier device can be designed in a ring-like manner or have a basic geometry of a circular segment. For example, the at least one carrier element is a ring or a ring section that is applied to one of the end faces of the heating element if it has a circular contour. The carrier element is designed to complement the basic geometry of the heating element. In contrast to the electrically conductive heating element, the at least one carrier element is made of an electrically insulating material, for example of a temperature-resistant plastic and/or of ceramic.

The surface of the three-dimensional structure of the heating element has characteristics that can be described mathematically as minimal surfaces. A minimal surface describes a surface in three-dimensional space that has a minimal surface area locally for a specified edge curve. Minimal surfaces are characterized by the fact that they are essentially stress-free surfaces. For example, a minimal surface can be constructed using a closed wire or wire ring by pulling the wire ring through a soap solution. The resulting surface of soap solution, which is bordered by the wire ring, has a minimal surface area and represents a minimal surface. If these minimal surfaces repeat in all spatial directions, triply periodic minimal surfaces (TPMS) are created.

According to one embodiment, the electrically conductive heating element can have a substantially circular basic geometry. The basic geometry of the heating element can describe the geometry of a surface of the heating element that a gas flow encounters when entering the heating device. The heating element can have any suitable basic geometry. The basic geometry can be adapted to a geometry of a downstream exhaust gas treatment unit, for example a catalyst. It can prove advantageous if if the heating element and the catalyst have the same or essentially the same basic geometry. Essentially in this context can mean that minor deviations are possible. For example, an essentially circular basic geometry does not have to be exactly circular. A slightly oval-shaped basic geometry can therefore still be described as an essentially circular basic geometry.

According to one embodiment, the three-dimensional structure of the electrically conductive heating element can have a uniform thickness. The heating element is designed as a three-dimensional structure that has a basic geometry. Starting from the two-dimensional basic geometry, the heating element extends in a third spatial direction. The thickness of the heating element can be described by the extension in the third spatial direction. The heating element has a uniform thickness if the extension of the heating element in the third spatial direction is constantly the same over the entire area of the basic geometry. A uniform thickness of the heating element can offer advantages with regard to heating the heating element in that all areas of the heating element can be heated evenly by energizing the heating element according to the current heat law.

According to another embodiment, the three-dimensional structure of the electrically conductive heating element can have a different thickness at least in sections. The thickness of the heating element can vary over the range of the basic geometry of the heating element, i.e. the thickness of the heating element does not have to be constantly the same. The heating element can have a different thickness in some sections or areas than in other sections or areas. As a result, individual sections or areas of the heating element can be heated more or less. For example, areas in the middle of the heating element can have a greater thickness than edge areas of the Heating element, whereby the areas in the middle of the heating element would heat up less when the heating element is energized than the edge areas with a smaller thickness. Areas of the heating element with different thicknesses are, in simplified terms, a series connection of individual resistors. According to the law of an electrical series connection, the current in all individual resistors is the same, whereas the total voltage is the sum of the individual voltages dropped across the individual resistors. According to the formula P=I ² *R, where P is the power, I is the current and R is the resistance, an area with a smaller cross-section leads to a larger individual resistor, across which a greater power is dropped than in an area with a larger cross-section and therefore smaller resistance.

According to a further embodiment, the three-dimensional structure of the electrically conductive heating element can be made of a temperature-resistant material. The material or a substance from which the electrically conductive heating element or the surface of the electrically conductive heating element is made can be a temperature-resistant or heat-resistant and/or corrosion-resistant material, in particular a metallic material, or a temperature-resistant or heat-resistant and/or corrosion-resistant alloy. When such a material or alloy is heated, a thick, stable oxide layer can form that protects the surface of the electrically conductive heating element. The strength can be maintained over a wide temperature range, which makes such materials particularly suitable for high-temperature applications.

According to another embodiment, the three-dimensional structure of the electrically conductive heating element can comprise a plurality of gyroid cells and/or a plurality of black diamond cells. Both a gyroid cell and a black diamond cell form a minimal area. A cell can have a represent the smallest unit of the minimal area. By lining up the multitude of gyroid and/or black diamond cells, i.e. a repetition of the minimal area formed by the gyroid cell or the black diamond cell, a three-dimensional structure can be formed whose surface is made up of minimal areas. Furthermore, the multitude of cells lined up in space can have different wall thicknesses, in particular between 0.05 mm and 3 mm, different cell sizes and/or different cell types. The cell size describes a spatial extension in three dimensions of a cell. A cell can extend between 0.5 mm and 10 mm in each of the three spatial dimensions, in particular independently of one another. In addition to a cube-shaped design of the cell, for example by extending uniformly in all three spatial dimensions, a cell can also be cuboid-shaped. In addition to the cell types of a gyroid and/or a Schwarz-Diamond cell already described, the three-dimensional structure of the electrically conductive heating element can also, alternatively or additionally, have a variety of Schwarz-Primitive (Schwarz P) cells, Schwarz-Hexagonal (Schwarz H) cells, Schwarz crossed layers of parallels (Schwarz CLP) cells, Fischer-Koch S cells, Fischer-Koch CY cells, Schoen I-WP cells, Neovius cells or a combination thereof. In principle, all known minimal surfaces are suitable as the three-dimensional structure of the electrically conductive heating element.

According to a further embodiment, the electrically conductive heating element can be traversed by the gas flow. The gas flow penetrates into the three-dimensional structure of the heating element on one side, an inlet side of the heating element, penetrates the heating element in the flow direction of the gas flow and exits completely from the heating element on another side, an outlet side of the heating element. The gas flow can be deflected in its flow direction within the heating element. The deflection or a Turbulence of the gas flow can be caused by designing the three-dimensional structure of the heating element.

According to another embodiment, the electrically conductive heating element can have at least two heating segments, which are separated from one another in sections by a gap that is open on one side in particular. The heating segments are formed from a three-dimensional structure, the surface of which is formed at least in sections from triply periodic minimal surfaces. The gas flow can preferably flow through the heating segments themselves. The gas flow can flow both through the at least one gap and through the heating segments themselves. This means that not the entire gas flow flows through the at least one gap during operation, but also through the heating segments. For this purpose, the heating segments can have channels, the walls of which enable efficient transfer of heat from the conductive material of the heating element to the gas.

According to a further embodiment, the electrically conductive heating element can comprise at least two partial bodies which are arranged in such a way that the gas flow can flow through the at least two partial bodies one after the other or in parallel. The at least two partial bodies can have an identical basic geometry, for example a substantially circular basic geometry. Each of the at least two partial bodies has a three-dimensional structure, the surface of which is formed at least in sections from triply periodic minimal surfaces. The at least two partial bodies are made of electrically conductive material and are each electrically connected to electrodes, so that when energized by means of a control device, a potential difference can be formed between the electrodes in order to heat each of the at least two partial bodies.

A sequential arrangement of the at least two partial bodies can be advantageous. The at least two partial bodies can be arranged in an axial direction that essentially corresponds to a flow direction of the gas flow, so that the gas flow first flows through the first partial body before the gas flow enters and flows through the second partial body. An outer contour of the first partial body and an outer contour of the second partial body can be identical and completely overlap. By arranging the at least two partial bodies in this way, the flow direction of the gas flow flowing through the at least two partial bodies can be influenced, for example to generate targeted turbulence in the gas flow, which can be advantageous for heating a catalyst arranged downstream.

The at least two partial bodies can also be arranged in parallel. In such an arrangement, part of the gas flow can flow through a first partial body and another part of the gas flow can flow through a second partial body. The partial bodies arranged in parallel can be arranged in the same plane or arranged parallel but spatially offset.

In such an embodiment, the at least two partial bodies of the electrically conductive heating element can be electrically controlled separately from one another by means of a control device. The at least two partial bodies can be electrically controlled in such a way that each partial body forms its own heating element. This makes it possible to heat the at least two partial bodies differently.

In such an embodiment, the at least two partial bodies of the electrically conductive heating element can be electrically connected by means of a series connection or a parallel connection. If the at least two electrically conductive partial bodies are electrically connected in series, an electrical output of the first partial body is directly connected to an electrical input of the second A single current path is formed, which first leads through the first partial body and then through the second partial body. By connecting at least two partial bodies in series in this way, an electrical resistance of the heating element and thus a heating power for the heating element can be set.

If the at least two partial bodies are electrically connected in parallel, the electrical inputs of the at least two partial bodies and the electrical outputs of the at least two partial bodies are electrically connected to one another. At least two current paths are formed, with the first current path leading through the first partial body and the second current path leading through the second partial body. The current path is therefore split.

According to a further embodiment, the at least one carrier element can cover an edge region of the electrically conductive heating element at least in sections. The at least one carrier element can be connected to the heating element in a form-fitting manner. For example, the carrier device can comprise a first carrier element and a second carrier element, each of which surrounds at least part of the circumference of the heating element and/or each of which covers at least part of an edge region of at least one end face of the heating element. It is possible, for example, for the first carrier element and the second carrier element to be ring-shaped and each to cover an outer edge region of the two end faces. Carrier elements of the same or different construction or dimensions can be combined to form a carrier device suitable for the respective application. Cost savings in terms of production and assembly result when the first and second carrier elements are identical parts.

According to another embodiment, the at least one carrier element can have at least two openings through which the electrically conductive heating element can be electrically contacted. For the purpose of supplying the heating element with electrical energy, the at least one carrier element can have a first and a second opening through which the heating element can be electrically contacted. Corresponding connections or electrodes are connected to a control device for operating the heating device. In embodiments with several carrier elements, each of the carrier elements can have (partial) openings. The (partial) openings can be designed to hold the connections or electrodes.

According to a further embodiment, the electrically conductive heating element can be electrically connected to at least two electrodes, wherein an electrical potential difference can be formed between the at least two electrodes by means of a control device. By applying an external voltage to the at least two electrodes, an electrical potential difference builds up between the electrodes, so that an electrical current flows. The electrically conductive heating element represents an electrical resistance, which leads to heating of the heating element. The control device can be used to control the current flow between the electrodes and thus the heating of the heating element. The greater this current flow, the greater the heating of the electrically conductive heating element and the faster a catalyst unit arranged downstream of the heating element can heat up.

In such an embodiment, the at least two electrodes can be arranged in an insulating manner against the at least one carrier element. The at least one carrier element is made of electrically insulating material, wherein the at least one carrier element is arranged in a housing. The housing can be made of metal, for example. The at least two electrodes extend both through the housing and through the at least one carrier element in order to energize the heating element or supply it with electrical energy. The electrodes are also connected to the control device, with which can control a current flow and thus the energization of the heating element. In order to enable the current flow from the control device to the electrodes and through the heating element, the at least two electrodes are arranged in an insulating manner both against the housing and against the at least one carrier element.

The present invention further relates to an exhaust gas treatment device with an inlet and an outlet and with at least one exhaust gas treatment unit for treating an exhaust gas flow, in particular with a catalyst unit, wherein a heating device according to at least one of the embodiments described above is arranged between the inlet and the exhaust gas treatment unit, in particular directly in the flow direction of the exhaust gas upstream of the exhaust gas treatment unit. The exhaust gas treatment device can have a one-piece housing component that accommodates the exhaust gas treatment unit and the heating device. Alternatively, the housing section of the heating device forms part of a housing of the exhaust gas treatment device, in particular wherein an inlet of the exhaust gas treatment device is connected to a component of the housing section.

The present invention also relates to an exhaust system of an internal combustion engine with an exhaust gas treatment device according to at least one of the embodiments described above.

The present invention also relates to a vehicle having an internal combustion engine connected to an exhaust system as described above.

Fig. 1

zeigt eine perspektivische Darstellung einer Ausführungsform der Heizeinrichtung,

Fig. 2A

zeigt eine schematische Darstellung einer Ausführungsform des Heizelements,

Fig. 2B

zeigt eine schematische Darstellung einer weiteren Ausführungsform des Heizelements,

Fig. 3A

zeigt eine perspektivische Darstellung einer Ausführungsform des Heizelements mit dreifach periodischen Minimalflächen,

Fig. 3B

zeigt eine perspektivische Darstellung einer Gyroid-Zelle,

Fig. 3C

zeigt eine perspektivische Darstellung einer weiteren Ausführungsform des Heizelements mit dreifach periodischen Minimalflächen,

Fig. 3D

zeigt eine perspektivische Darstellung einer Schwarz-Diamond Zelle,

Fig. 4A

zeigt eine schematische Darstellung einer Ausführungsform einer elektrischen Ansteuerung des Heizelements,

Fig. 4B

zeigt eine schematische Darstellung einer Ausführungsform einer elektrischen Ansteuerung des Heizelements mit zwei Teilkörpern, als Reihenschaltung ausgebildet,

Fig. 4C

zeigt eine schematische Darstellung einer weiteren Ausführungsform einer elektrischen Ansteuerung des Heizelements mit zwei Teilkörpern, als Parallelschaltung ausgebildet,

Fig. 5

zeigt eine perspektivische Darstellung einer Abgasbehandlungseinrichtung.

The invention is explained below purely by way of example using advantageous embodiments with reference to the accompanying drawings.

Fig.1

shows a perspective view of an embodiment of the heating device,

Fig. 2A

shows a schematic representation of an embodiment of the heating element,

Fig. 2B

shows a schematic representation of another embodiment of the heating element,

Fig. 3A

shows a perspective view of an embodiment of the heating element with triply periodic minimal surfaces,

Fig. 3B

shows a perspective view of a gyroid cell,

Fig. 3C

shows a perspective view of another embodiment of the heating element with triply periodic minimal surfaces,

Fig.3D

shows a perspective view of a black diamond cell,

Fig. 4A

shows a schematic representation of an embodiment of an electrical control of the heating element,

Fig. 4B

shows a schematic representation of an embodiment of an electrical control of the heating element with two partial bodies, designed as a series connection,

Fig. 4C

shows a schematic representation of another embodiment of an electrical control of the heating element with two partial bodies, designed as a parallel circuit,

Fig.5

shows a perspective view of an exhaust gas treatment device.

Heating elements in the automotive sector can consist of explicitly (constructively) generated geometries or of stochastic foam structures. The manufacturing process for such heating elements can be based on a joining and assembly technique for sheet metal, foam or 3D printing.

The effectiveness of a heating element, for example a heating disk, can depend on how much energy can be transferred in the form of heat to a downstream substrate, for example a catalyst substrate. The surface of the heating element and the flow situation within a structure of the heating element can be decisive for the heat transfer from the heating element to the substrate.

Operating profiles and thus operating times and/or operating requirements for a heating element can be highly dynamic. A low thermal mass, large heat-transfer surfaces and the generation of highly turbulent flow forms should be represented as best as possible by a heating element in order to meet a dynamic requirement profile. However, due to geometric limitations, known heating elements cannot represent all the desired properties.

The heating device according to the invention represents an optimization and further development of known electrical heating systems. In particular, the heating device described herein leads to an optimization of a heating element or a Heating disc or a heating matrix, i.e. a core part of an electrical heating system. This optimization can be achieved by means of a mathematically implicit geometry formulation of a surface of the heating element.

With implicitly generated structures, a reduction of the thermal mass of the heating element can be achieved while simultaneously increasing a heat transfer surface and/or improving an increase of turbulent flows in the heat transfer area of the heating element.

Fig.1 shows a perspective view of an embodiment of the heating device 100 according to the invention. The heating device 100 comprises an electrically conductive heating element 102 and a carrier device 104.

In this embodiment, the electrically conductive heating element 102 is designed as a heating disk, wherein the heating disk has a circular basic geometry with respect to a flow axis A. In principle, both the basic geometry, or an outer contour, of the heating element 102, and an axial thickness of the heating element 102 can be freely selected and can be adapted to the respective requirements.

The carrier device 104 carries or holds the electrically conductive heating element 102. The carrier device 104 is also circular in shape according to this embodiment of the heating element 102. The carrier device 104 is basically adapted to the geometry of the outer contour of the heating element 102 and comprises at least one carrier element 106. The carrier element 106 is arranged in an electrically insulating manner between a housing part 103 and the heating element 102 on an end face of the heating element 102. The embodiment of the heating device 100 in Fig.1 has two separate support elements 106, 108, which are formed from circular segments, adapted to the geometry of the outer contour of the heating disc and each on one end face of the heating element 102 are arranged in an electrically insulating manner between the heating element 102 and the housing part 103. The carrier elements 106, 108 are essentially covered by the housing part 103. In addition, the carrier elements 106, 108 surround the heating element 102 almost completely in the circumferential direction. Gaps are only provided in the area of the connections, which are designed as electrodes 110. Deviating from the exemplary embodiment shown, the at least one carrier element 106, 108 can cover an edge area of the electrically conductive heating element 102 at least in sections.

By almost completely enclosing the heating element 102 by the carrier elements 106, 108, with gaps only being provided in the area of the electrodes 110, the electrically conductive heating element 102 is also insulated in the radial direction with respect to the flow axis A. In order to achieve good electrical insulation, the carrier elements 106, 108 are made of electrically insulating material, for example corundum, glass ceramic, mica and/or another ceramic material.

In the area of the electrodes 110, at least one of the carrier elements 106, 108 or both carrier elements 106, 108 have openings through which the electrically conductive heating element 102 can be electrically contacted by means of the electrodes 110. The electrodes 110 can be passed through the openings and are arranged in an electrically insulating manner with respect to the carrier elements 106, 108. Furthermore, the electrodes 110 are electrically connected to the heating element 102. The heating element 102 can be electrically controlled and energized via the electrodes 110 by means of a control device (not shown). By applying a potential difference between the two electrodes 110, a current flow is formed between the two electrodes 110, whereby the heating element 102 heats up due to its electrical resistance (resistance heating). It is fundamentally possible to energize the heating element 102 with a surface formed from triply periodic minimal surfaces.

The heating element 102 is designed as a three-dimensional structure such that the heating element 102 or the three-dimensional structure of the heating element 102 can be flowed through by a gas flow 112, in particular by an exhaust gas flow of an internal combustion engine. The gas flow 112 enters the heating element 102 on an inlet side 114, flows through the three-dimensional structure of the heating element 102 essentially in a flow direction parallel to the flow axis A and exits the heating element 102 again on an outlet side 116. The gas flow 112 is in Fig.1 indicated schematically by two arrows.

Fig. 2A shows a schematic representation of an embodiment of the heating element 102, wherein the heating element 102 has a circular basic geometry. The heating element 102 is at least partially, in particular completely, formed from an electrically conductive material and/or is at least partially coated with such a material. The heating element 102 has parallel gaps 204 which separate individual heating segments 202 from one another in sections. The gaps 204 are alternately open on one side. In Fig. 2A the lateral openings of the column 204 are shown alternately on a right edge 206 and on a left edge 208 with respect to an axis of symmetry B of the heating element 102. In figurative terms, this creates a meandering or serpentine structure of the heating element 102. The heating segments 202 do not represent an impenetrable flow resistance, but have a plurality of fine channels (not shown) through which the gas flow 112 (see Fig.1 ) can flow. The gas flow 112 can also flow through the gap 204 of the heating element 102. By suitable contacting by means of at least two electrodes (see Fig.1 ), a current can flow through the meandering structure of the heating element 102, and the heating element 102 can heat up.

Fig. 2B shows a schematic representation of another embodiment of the heating element 102. As an alternative to the Fig. 2A shown embodiment of a Heating element 102 with a meandering structure, the heating element 102 can also have a three-dimensional structure which has at least in sections a plurality of fine channels 210 through which the gas stream 112 can flow. In Fig. 2B the channels 210 are shown schematically greatly enlarged. The basic geometry of the heating element 102 or the heating matrix in this embodiment is also (as in the embodiment of Fig. 2A ) is circular. However, the shape of the basic geometry of the heating element 102 can be designed as desired. The Fig. 2B The alternative embodiment of the heating element 102 shown can be heated by suitable contacting, for example by two or more spaced-apart large-area electrodes on an outer surface of the heating element 102, and by current supply.

The basic geometry and in particular a surface of the basic geometry of the heating element 102 can be described by any triply periodic minimal surface (TPMS). For example, the three-dimensional structure of the electrically conductive heating element 102 can have a plurality of gyroid cells and/or a plurality of black diamond cells, as described below with reference to Fig. 3A to 3D The three-dimensional structure of the heating element 102, formed from triply periodic minimal surfaces, can have advantages over known structures of heating elements 102. For example, the electrically conductive heating element 102 according to the invention can have advantageous properties with regard to deformation and energy absorption. In addition, the density, surface and rigidity of the three-dimensional structure of the heating element 102 can be suitably determined depending on the application. Very good resistance to fatigue as well as efficient use of materials and thus cost potential and/or high permeability, for example of a gas flow 112, in comparison to known surface structures of heating elements 102 can also be possible by designing the surface of the three-dimensional structure of the heating element 102 from triply periodic minimal surfaces.

Fig. 3A and 3C show perspective representations of embodiments of the heating element 102 with triply periodic minimal surfaces. Triply periodic minimal surfaces are surface structures known from nature (for example soap films). Minimal surfaces have an average curvature of 0 at every point. Furthermore, minimal surfaces can be formulated implicitly. There are various formulations for TPMS structures. The TPMS structures described below represent only a part of suitable TPMS structures and are to be understood as examples.

The TPMS structure of the electrically conductive heating element 102 is made of an electrically conductive and thermally stable material, for example of a temperature-resistant material, in particular of a metallic material. The surface, or at least sections thereof, of the heating element 102 can be formed from any suitable or any suitable combination of triply periodic minimal surfaces. A gyriod cell 302 (see Fig. 3B ) represents a suitable TPMS structure.

The three-dimensional structure of the heating element 102 of Fig. 3A is formed from a plurality of gyroid cells 302. A perspective view of a single gyroid cell 302 is shown in Fig. 3B shown. The gyroid cell 302 has a three-dimensional structure 304 with a wall thickness 310 that separates a space into two oppositely congruent labyrinths of channels 210. The heating element 102 has a meandering structure (see Fig. 2A ), but may also have any other suitable structure, for example a circular structure without gap 204 as in Fig. 2B The surface of the three-dimensional structure 304 of the heating element 102 has a plurality of triply periodic minimal surfaces. The three-dimensional structure 304 formed from a plurality of gyroid cells 302 can have a uniform thickness or a different thickness, at least in sections.

In general, TPMS structures can be described by an addition of trigonometric functions. The gyroid cell 302 can, for example, be approximated by the following implicit equation: $$\cos \left(x\right)\sin \left(y\right)+\cos \left(y\right)\sin \left(z\right)+\cos \left(z\right)\sin \left(x\right)=0.$$

The gyroid cell 302 is particularly advantageous because it is relatively easy to manufacture using 3D printing. The design of the channels 210 of the gyroid cell 302 can also influence the flow direction of a gas flow 112 flowing through the cell and, for example, lead to turbulence in the gas flow 112, which can have a positive effect on the heat transfer from the heating element 102 to the gas flow 112 and/or from the gas flow 112 to an exhaust gas treatment unit arranged downstream of the heating element 102.

Fig. 3C shows a perspective view of another embodiment of the heating element 102 with triply periodic minimal surfaces. The triply periodic minimal surfaces are formed in this embodiment by a plurality of black diamond cells 306. A perspective view of a black diamond cell 306 is shown in Fig.3D The black diamond cell 306 has a three-dimensional structure 308 with wall thickness 310, which comprises two intertwined congruent labyrinths of channels 210, each of which has the shape of an inflated tubular version of a diamond structure. The heating element 102 comprises heating segments 202 and gaps 204, which form a meandering basic geometry of the heating element 102. Other suitable basic geometries are also possible for the heating element 102, whose three-dimensional structure 308 is formed from black diamond cells 306. The three-dimensional structure 308 formed from a plurality of black diamond cells 306 can have a uniform thickness or a different thickness, at least in sections.

The Schwarz-Diamond cell 306 can, for example, be described by the following angular function: $$\sin \left(x\right)\sin \left(y\right)\sin \left(z\right)+\sin \left(x\right)\cos \left(y\right)\cos \left(z\right)+\cos \left(x\right)\sin \left(y\right)\cos \left(z\right)+\cos \left(x\right)\cos \left(y\right)\sin \left(z\right)=0.$$

Black diamond cells 306 are characterized by a relatively large surface area compared to other minimal surfaces with the same volume. This can promote the heating of a gas stream 112 that flows through a heating element 102 whose structure is formed from black diamond cells 306.

Fig. 4A shows a schematic representation of an embodiment of an electrical control of the heating element 102. The electrically conductive heating element 102 is electrically connected to a first electrode 406 and a second electrode 408. Both the first electrode 406 and the second electrode 408 are electrically connected to a control device 404 via an electrical line 402. By means of the control device 404, an electrical voltage can be applied to the first electrode 406 and to the second electrode 408 in such a way that a potential difference (voltage difference) is formed between the first electrode 406 and the second electrode 408. For example, the first electrode 406 is subjected to a positive voltage potential and the second electrode 408 to a negative voltage potential, or vice versa. The electrically conductive heating element 102 arranged between the first electrode 406 and the second electrode 408 has an electrical resistance. By applying two different voltage potentials to the first electrode 406 and to the second electrode 408, a current flow is created between the first electrode 406 and the second electrode 408, whereby the heating element 102 heats up due to the electrical resistance of the heating element 102 according to the current heat law (Ohmic heating).

Fig. 4B shows a schematic representation of an embodiment of an electrical control of the heating element 102 with two partial bodies 410, wherein the electrical control is designed as a series circuit. According to the embodiment in Fig. 4A the electrically conductive heating element 102 is electrically connected to a first electrode 406 and a second electrode 408. Both the first electrode 406 and the second electrode 408 are electrically connected to a control device 404 via an electrical line 402. By means of the control device 404, an electrical voltage can be applied to the first electrode 406 and to the second electrode 408 in such a way that a potential difference (voltage difference) is formed between the first electrode 406 and the second electrode 408. For example, the first electrode 406 is subjected to a positive voltage potential and the second electrode 408 to a negative voltage potential, or vice versa. The electrically conductive heating element 102 arranged between the first electrode 406 and the second electrode 408 comprises two electrically conductive partial bodies 410 which are electrically conductively connected to one another.

The two partial bodies 410 can - spatially speaking - be arranged in the direction of the flow axis A (see Fig.1 ) spaced apart from one another, i.e. one after the other, or spaced apart from one another in the direction of the axis of symmetry B, i.e. above or below one another, so that the two partial bodies 410 can be flowed through by a gas flow 112. The two partial bodies 410 are electrically connected in series (series connection), so that the electrical resistance of the respective partial bodies 410 adds up to a total resistance of the heating element 102. By applying two different voltage potentials to the first electrode 406 and to the second electrode 408, a current flow is created between the first electrode 406 and the second electrode 408, as a result of which each partial body 410 heats up due to the electrical resistance of the partial bodies 410 and as a result the heating element 102 also heats up according to the current heat law (ohmic heating). It is also possible to connect the - at least - two partial bodies 410 of the Heating elements 102 can be electrically controlled separately by means of a control device 404.

Fig. 4C shows a schematic representation of another embodiment of an electrical control of the heating element 102 with two partial bodies 410, wherein the electrical control is designed as a parallel circuit. According to the embodiment in Fig. 4B The heating element 102 is formed from two electrically conductive parts 410. The parts 410 can - spatially speaking - be arranged in the direction of the flow axis A (see Fig.1 ) spaced apart from one another, i.e. one after the other, or spaced apart from one another in the direction of the axis of symmetry B, i.e. one above or one below the other, so that the two partial bodies 410 can be flowed through by a gas stream 112. The two partial bodies 410 are electrically connected in parallel (parallel connection).

Each of the two partial bodies 410 is electrically connected to a first electrode 406 and a second electrode 408. The heating element 102 thus comprises four electrodes 406, 408, two first electrodes 406 and two second electrodes 408 for each partial body 410. Both the first electrode 406 and the second electrode 408 are electrically connected to a control device 404 via an electrical line 402. By means of the control device 404, an electrical voltage can be applied to the first electrode 406 and the second electrode 408 in such a way that a potential difference (voltage difference) is formed between the first electrode 406 of a partial body 410 and the second electrode 408 of a partial body 410, which results in a current flow between the first electrode 406 and the second electrode 408. For example, the first electrode 406 is subjected to a positive voltage potential and the second electrode 408 to a negative voltage potential, or vice versa. By applying two different voltage potentials to the first electrode 406 and the second electrode 408, a current flow is created between the each first electrode 406 and the respective second electrode 408, whereby each partial body 410 heats up due to the electrical resistance of the partial bodies 410 and thus the heating element 102 also heats up according to the current heat law (ohmic heating). It is also possible to electrically control the - at least - two partial bodies 410 of the heating element 102 separately from one another by means of a control device 404.

The surface of an electrically conductive heating element 102, which is formed from triply periodic minimal surfaces, at least in sections, can be further optimized according to the criteria of surface, resistance, counterpressure and strength. The potential of the heating device 100 according to the invention can be determined using measuring technology for temperature - thermography and thermocouples - and measuring technology for pressure.

Fig.5 shows a perspective view of an exhaust gas treatment device 500 with an inlet 506 and an outlet 508. The exhaust gas treatment device 500 comprises a heating device 100 and a catalyst unit 502 (shown in dashed lines). The heating device 100 and the catalyst unit 502 are held in a housing 504, wherein the catalyst unit 502 is reliably fixed in the housing 504 by at least one bearing mat (not shown). The heating device 100 comprises two electrodes 110 which are electrically connected to a heating element 102. The heating element 102 can be designed according to one of the embodiments described herein. The electrodes 110 are arranged in an electrically insulating manner against the housing 504, wherein the electrodes 110 extend through the housing 504 and contact the heating element 102 in an electrically conductive manner. A control device (not shown) can be connected to the electrodes 110 in order to form a potential difference between the electrodes 110. The catalyst unit 502 is arranged directly adjacent to the heating device 100 in the axial direction of a flow axis A.

A gas flow 112, in particular an exhaust gas flow, flowing into the housing 504 through the inlet 506 in the axial direction of the flow axis A is heated by the heating device 100 so that the catalyst unit 502 reaches its operating temperature as quickly as possible. The heating device 100 is arranged between the inlet 506 and the catalyst unit 502, in particular directly in the flow direction of the exhaust gas along the flow axis A in front of the catalyst unit 502.

In order to be able to represent complex surface structures using TPMS structures, the triply periodic minimal surfaces of the electrically conductive heating element 102 can be produced by a 3D printing process; in particular, TPMS structures are mainly produced by 3D printing processes due to their complex structures.

The use of TPMS structures in heating elements 102 can offer potential in the areas of thermal heating behavior, heat transfer - surface area - and weight with regard to regulatory emission standards, for example EU7.

List of reference symbols

100

Heating device

102

Heating element

103

Housing part

104

Carrier device

106

Support element

108

Support element

110

electrode

112

Gas flow

114

Inlet side

116

Exhaust side

202

Heating segment

204

gap

206

right edge

208

left edge

210

channel

302

Gyroid cell

304

three-dimensional structure

306

Black Diamond Cell

308

three-dimensional structure

310

Wall thickness

402

electrical line

404

Control device

406

first electrode

408

second electrode

410

Partial body

500

Exhaust gas treatment device

502

Catalyst unit

504

Housing

506

inlet

508

Outlet

A

Flow axis

B

Axis of symmetry

Claims (15)

Heating device (100) for heating a gas flow (112), in particular an exhaust gas flow of an internal combustion engine, comprising an electrically conductive heating element (102); and a carrier device (104) with at least one electrically insulating carrier element (106) for the electrically conductive heating element (102), characterized,
that the electrically conductive heating element (102) is designed as a three-dimensional structure (304, 308) whose surface is formed at least in sections from triply periodic minimal surfaces. Heating device (100) according to claim 1,
characterized,
that the electrically conductive heating element (102) has a substantially circular basic geometry. Heating device (100) according to at least one of the preceding claims,
characterized,
that the three-dimensional structure (304, 308) of the electrically conductive heating element (102) has a uniform thickness. Heating device (100) according to at least one of claims 1 or 2,
characterized,
that the three-dimensional structure (304, 308) of the electrically conductive heating element (102) has a different thickness at least in sections. Heating device (100) according to at least one of the preceding claims,
characterized,
that the three-dimensional structure (304, 308) of the electrically conductive heating element (102) is made of a temperature-resistant material. Heating device (100) according to at least one of the preceding claims,
characterized,
that the three-dimensional structure (304, 308) of the electrically conductive heating element (102) has a plurality of gyroid cells (302) and/or a plurality of black diamond cells (306). Heating device (100) according to at least one of the preceding claims,
characterized,
that the electrically conductive heating element (102) can be flowed through by the gas stream (112). Heating device (100) according to at least one of the preceding claims,
characterized,
that the electrically conductive heating element (102) has at least two heating segments (202) which are partially separated from one another by a gap (204) which is in particular open on one side. Heating device (100) according to at least one of the preceding claims,
characterized, that the electrically conductive heating element (102) comprises at least two partial bodies (410) which are arranged such that the gas flow (112) can flow through the at least two partial bodies (410) one after the other or in parallel, and/or that the at least two partial bodies (410) of the electrically conductive heating element (102) can be electrically controlled separately from one another by means of a control device (404). Heating device (100) according to claim 9,
characterized,
that the at least two partial bodies (410) of the electrically conductive heating element (102) are electrically connected by means of a series connection or a parallel connection. Heating device (100) according to at least one of the preceding claims,
characterized, that the at least one carrier element (106) covers at least partially an edge region of the electrically conductive heating element (102), and/or that the at least one carrier element (106) has at least two openings through which the electrically conductive heating element (102) can be electrically contacted. Heating device (100) according to at least one of the preceding claims,
characterized, that the electrically conductive heating element (102) is electrically connected to at least two electrodes (110), wherein an electrical potential difference can be formed between the at least two electrodes (110) by means of a control device (404), and/or that the at least two electrodes (110) are arranged in an insulating manner against the at least one carrier element (106). Exhaust gas treatment device (500) with an inlet (506) and an outlet (508) and with at least one exhaust gas treatment unit for Treatment of an exhaust gas flow, in particular with a catalyst unit (502), wherein a heating device (100) according to at least one of the preceding claims is arranged between the inlet (506) and the exhaust gas treatment unit, in particular directly in the flow direction of the exhaust gas upstream of the exhaust gas treatment unit. Exhaust system of an internal combustion engine with an exhaust gas treatment device (500) according to claim 13. Vehicle having an internal combustion engine connected to an exhaust system according to claim 14.

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