DE102021133644A1 - Exhaust system heater - Google Patents

Abstract

An electrical heating device of an exhaust gas system, which can be installed in an exhaust gas line transversely to an exhaust gas flow and through which the exhaust gas to be treated can flow axially, has a disc-shaped, electrically conductive heating element (12) made of metal foam, which is electrically coupled to at least two electrodes (20). , wherein the heating element (12) has an upstream-oriented front face (14) and a downstream-oriented rear face (16) which are in a row in an axial direction (A). The heating element (12) has one or more axial, slot-shaped recesses (22) which define a tortuous current path through the heating element (12) in a plane perpendicular to the axial direction (A). In addition, a stabilizing structure (28) is provided with at least two stabilizing rods (30) running perpendicular to the axial direction (A), each stabilizing rod (30) in its longitudinal direction in a receiving opening (36) running perpendicular to the axial direction (A) in the heating element (12). is recorded.

Description

The invention relates to an electrical heating device for an exhaust system.

Catalytic converters are usually provided in exhaust systems of internal combustion engines in order to reduce emissions. So that a catalytic oxidation can proceed optimally immediately after a cold start, it is known to provide electrical heating devices that heat the catalytic converter to a reaction temperature.

For example, a heating device through which the exhaust gas flows can be used for this purpose, which is arranged upstream of the catalytic converter and which heats the exhaust gas before it flows through the catalytic converter.

If the heating element of the heating device is to be heated both by current flow due to the Joule effect and also to be located in the exhaust gas flow, it must have high electrical resistance and low flow resistance at the same time. These conditions are met, for example, by heating elements made from an open-pored metal foam.

The front face of the heating element is aligned perpendicularly or at an angle, e.g. at an angle of up to 45°, to an exhaust gas flow, so that the exhaust gas to be treated flows through it axially.

Even a relatively thin sheet of metal foam is sufficient as a heating element to achieve the desired heat transfer to the exhaust gas flow. In order to give the heating element sufficient mechanical stability, it is often provided with stabilizing elements.

The object of the invention is to create an electrical heating device with a heating element that is easy to manufacture, light and mechanically stable.

This object is achieved by an electrical heating device of an exhaust gas system, which can be mounted in an exhaust gas line transversely to an exhaust gas flow and through which the exhaust gas to be treated can flow axially. The heating device has a disk-shaped, electrically conductive heating element made of a metal foam, which is electrically coupled to at least two electrodes, the heating element having an upstream-oriented front face and a downstream-oriented rear face that lie one behind the other in an axial direction. The heating element also has one or more axial slot-shaped recesses that define a tortuous current path through the heating element in a plane perpendicular to the axial direction. The heating device has a stabilizing structure with at least two stabilizing bars running perpendicular to the axial direction, each stabilizing bar being received in a receiving opening running perpendicular to the axial direction in the heating element.

The stabilizing rods ensure axial stabilization of the heating element in order to prevent deformation of the heating element perpendicular to the surface of the heating element, ie along the axial direction.

The stabilizing elements also have the task of maintaining the shape of the recesses and thus the predetermined current path through the heating element and of preventing the individual foam webs of the heating element formed by the recesses from touching one another.

It has been found that the use of such a stabilization structure makes it possible to reduce the material thickness, ie the axial expansion, of the heating element while increasing the stability.

Of course, the stabilizing rods should be designed so rigidly that they can withstand the forces acting on them without any significant deformation.

The recess(es) is/are selected in such a way that a current path is created through the heating element, which allows the heating element to be heated uniformly to a desired temperature by current flow. The electrodes are placed at the ends of the current path. The entire flow of current between the connection electrodes therefore always runs through the heating element. The recess(es) specify the width of adjacent foam webs or foam web sections, which defines the electrical resistance of the current path. The two most common geometries are to make multiple parallel cutouts in the foam material from opposite edges of the heating element, creating a meandering current path with multiple parallel foam ridges, or to provide one or two spiral cutouts to form a helically wound current path. The mode of operation is identical in both cases, so that the exact geometry of the current path is not relevant in the context of this application. In the following, therefore, a small-scale geometry is always considered, which has several adjacent recesses, even if the recesses are connected at another point.

It is possible that the stabilizing structure has the recesses perpendicular to the axial direction completely filled to reduce passage of exhaust gas through the recesses. Such a design is of particular interest if the heating element also develops an exhaust gas cleaning effect. For this purpose, the heating element can be provided with a catalytic coating, for example.

The stabilizing bars preferably run parallel to one another in a plane perpendicular to the axial direction, so that rectilinear stabilizing bars and receiving openings can be used.

In one possible variant, at least one receiving opening is formed by a recess, so that at least one stabilizing bar is arranged in a recess. In this case, the recess also serves as a receiving opening, which simplifies production, since no additional openings have to be cut into the heating element.

In order to fix the stabilizing bar in the recess in a simple manner, the recess and the stabilizing bar can have complementary cross sections, the stabilizing bar then being received in the recess in a form-fitting manner. In particular, any shape that produces an undercut in the axial direction is suitable here, for example a cross section of two triangles that point towards one another with their tips, similar to the side view of a double cone with tips pointing towards one another.

In the case of recesses running in a straight line, a stabilizing rod shaped in this way can be pushed into the recess from the edge of the heating element without the heating element having to be deformed in the process.

Stabilizing bars are preferably arranged in all recesses.

In another variant, at least one receiving opening runs transversely to at least one recess through the metal foam of the heating element.

In this variant, the receiving openings are holes in the foam material of the heating element and are therefore completely surrounded circumferentially by the material of the heating element. They are provided in addition to the recesses.

The receiving openings preferably run in a straight line, extending through a plurality of foam ridges, each of which is spaced from one another by a recess. The recesses thus interrupt the receiving openings.

The receiving openings preferably each extend from an edge section of the heating element to an opposite edge section of the heating element, so that the stabilizing rods can be pushed into the heating element until their ends protrude from the heating element. On the one hand, this enables the stabilizing rods to be easily introduced into the heating element and, on the other hand, the heating element can be easily fixed in a holder via protruding ends of the stabilizing rod for further mechanical stabilization. In the case of a circular heating element, the receiving openings follow, in particular, chords of a circle.

Laser cutting or water jet cutting, for example, can be used to produce the receiving openings in the foam material of the heating element, analogously to the production of the recesses.

The use of exactly two stabilizing rods has proven to be advantageous in terms of production technology and for reasons of weight if the stabilizing rods run transversely to the cutout or cutouts. However, three or more stabilizing bars could also be provided.

The heating element can have at least one projection on an inner side pointing into the recess in an exit region of the receiving opening, in particular a projection surrounding the receiving opening in a ring shape. Alternatively or additionally, the heating element can have a projection on at least one end face along the receiving opening.

If a projection is provided on an end face, the heating element is axially thickened in the area of the receiving openings. Such a projection extends, for example, along the entire receiving opening.

Providing more material in one or more of these areas compensates for the removal of heating element material in the receiving openings themselves to obtain the desired electrical resistance of the foam ridges.

In order to adjust the electrical resistance of the heating element in the area of the receiving openings to the resistance in the area away from the receiving openings and to maintain a uniform heating effect, the volume of the at least one projection, which is assigned to a receiving opening, can correspond to the volume of the receiving opening, for example. If the receiving opening extends transversely to a foam web, the opposite is preferred th mouths of the section of the receiving opening running through this foam web are provided with projections, which together increase the cross-section through which current flows and match it to the cross-section in the foam web remote from the receiving opening. Alternatively, in particular the volume of all the projections together corresponds to the total volume of the receiving openings.

The stabilization structure can comprise at least one stabilization element which has at least one opening through which a stabilization rod protrudes, the stabilization element being arranged in a recess.

For this variant, i.e. the variant with a stabilizing element lying in the recess and running along it, the following applies: since several recesses are normally provided in order to be able to produce a highly tortuous current path, there are usually several stabilizing elements, in particular 3 to 10 stabilizing elements. In particular, a stabilizing element is used in all recesses that lie along the course of the stabilizing bar.

The shape of the stabilizing elements can be adapted to the projections on the inside of the recesses, so that they can be inserted into the respective recess with a positive fit.

In the simplest embodiment, the stabilizing element is an annular spacer whose outer diameter is less than or equal to the axial thickness of the heating element.

However, there is preferably at least one stabilizing element which has an opening for each stabilizing bar, so that increased stability is also achieved in the direction perpendicular to the longitudinal extension of the stabilizing bars.

At least one stabilizing element can be a stabilizing plate. A plane of the stabilizing plate is in particular aligned parallel to the axial direction.

Of course, the stabilizing structure should be electrically isolated from the heating element.

The stabilizing rods can consist of a ceramic, but also of a metal. In the latter case, the electrical insulation is used, for example, an insulating coating or a cover made of an insulating textile fabric.

The stabilizing element(s) can also consist of a coated metal, but a ceramic is preferably used here for reasons of weight.

• - 1 eine schematische Draufsicht einer erfindungsgemäßen Heizvorrichtung in einer ersten Variante;
• - 2 eine schematische Explosionsdarstellung eines Heizelements einer erfindungsgemäßen elektrischen Heizvorrichtung;
• - 3 eine schematische Draufsicht einer erfindungsgemäßen Heizvorrichtung in einer zweiten Variante;
• - 4 eine schematische Draufsicht des Heizelements der Heizvorrichtung aus 1;
• - 5 und 6 einen vergrößerten Ausschnitt des Heizelements aus 4;
• - 7 und 8 verschiedene Varianten eines Stabilisierungselements der Heizvorrichtung aus 1;
• - 9 eine schematische Darstellung eines Heizelements mit einer daran montierten Stabilisierungsstruktur einer erfindungsgemäßen Heizvorrichtung;
• - 10 eine schematische Draufsicht einer erfindungsgemäßen Heizvorrichtung in einer dritten Variante;
• - 11 eine schematische Schnittansicht der Heizvorrichtung aus 10 entlang der Linie XI-XI;
• - 12 eine schematische Schnittansicht der Heizvorrichtung aus 10 entlang der Linie XII-XII;
• - 13 eine schematische Draufsicht einer erfindungsgemäßen Heizvorrichtung in einer vierten Variante;
• - 14 eine schematische Draufsicht einer erfindungsgemäßen Heizvorrichtung in einer fünften Variante;
• - 15 eine schematische Schnittansicht der Heizvorrichtung aus 14 entlang der Linie XV-XV;
• - 16 eine schematische Draufsicht des Heizelements der Heizvorrichtung aus 14;
• - 17 eine schematische Schnittansicht des Heizelements aus 16 entlang der Linie XVII-XVII; und
• - 18 eine schematische Darstellung eines Schrittes der Fertigung der Heizvorrichtung aus 14.

The invention is described in more detail below using several exemplary embodiments with reference to the attached figures. In the figures show:

• - 1 a schematic plan view of a heating device according to the invention in a first variant;
• - 2 a schematic exploded view of a heating element of an electrical heating device according to the invention;
• - 3 a schematic plan view of a heating device according to the invention in a second variant;
• - 4 Figure 12 shows a schematic top view of the heating element of the heating device 1 ;
• - 5 and 6 an enlarged section of the heating element 4 ;
• - 7 and 8th different variants of a stabilizing element of the heating device 1 ;
• - 9 a schematic representation of a heating element with a stabilization structure mounted thereon of a heating device according to the invention;
• - 10 a schematic plan view of a heating device according to the invention in a third variant;
• - 11 a schematic sectional view of the heating device 10 along line XI-XI;
• - 12 a schematic sectional view of the heating device 10 along line XII-XII;
• - 13 a schematic plan view of a heating device according to the invention in a fourth variant;
• - 14 a schematic plan view of a heating device according to the invention in a fifth variant;
• - 15 a schematic sectional view of the heating device 14 along line XV-XV;
• - 16 Figure 12 shows a schematic top view of the heating element of the heating device 14 ;
• - 17 a schematic sectional view of the heating element 16 along line XVII-XVII; and
• - 18 a schematic representation of a step in the manufacture of the heating device 14 .

The same reference symbols designate identical or essentially identical components and parts. For reasons of clarity, not all identical components are always provided with reference numbers.

1 shows an electric heating device 10 of an exhaust system of a vehicle, not shown in detail, in a first variant.

The heating device 10 includes an electric heating element 12 made of an open-pore metal foam. The opposite faces 14, 16 of the disk are spaced apart in an axial direction A by a height h of the heating element 12 (see Fig 2 ). The heating element 12 is disc-shaped, ie its diameter is greater than its axial height h.

The heater 10 is intended to be placed in an exhaust pipe of a vehicle's exhaust system, e.g.

It is possible to provide the heating element 12 with an exhaust gas cleaning coating, for example a catalytically active coating.

When installed in an exhaust gas line, the heating element 12 is arranged transversely to the exhaust gas flow, so that the exhaust gas flows through the end faces 14, 16. The heating device 10, including an indicated holder 18, which surrounds the heating element 12 circumferentially, essentially fills the cross section of the exhaust gas pipe.

The heating element 12 is electrically conductively connected to two electrodes 20 which are arranged on the holder 18 and are connected to electrical connecting lines, not shown, so that current can be conducted through the heating element 12 . If the exhaust gas flows through the heating element 12 while current is flowing through it and is being heated thereby, it gives off heat to the exhaust gas and heats it up. The current flow through the heating device 10 follows a predetermined current path from one of the electrodes 20 through the heating element 12 to the other electrode 20.

The current path through the heating element 12 is defined by cutouts 22 in the metal foam, which specify the path of the electric current through the heating element 12 .

The recesses 22 are slot-shaped and parallel here, with the heating element 12 being completely severed axially at the recesses 22 but not being completely interrupted radially at any point. A continuous connection remains on mutually opposite edge sections, so that the heating element 12 is a one-piece component with a meander structure. In this example, there is therefore a meandering current path through the heating element 12.

Of course, the cutouts 22 in the heating element 12 could also be selected in a different form, so that a spirally wound current path results, for example (not shown).

Foam webs 24 are formed between adjacent recesses 22 , through which the electric current flows through the heating element 12 . The cross-sectional area of these foam webs 24 determines, among other things, the electrical resistance of the heating element 12.

In this example, the metal foam of the heating element 12 is compressed around the circumference in an edge region 26 in order to reduce the electrical resistance there and thus the heating.

The heating element 12 is mechanically stabilized by a stabilization structure 28 . The stabilizing structure 28 comprises stabilizing rods 30 and stabilizing elements 32, which in this variant are stabilizing plates 33 (see in detail 2 ).

In this example, exactly two stabilizing rods 30 and one stabilizing plate 33 are provided for each of the recesses 22 .

Each of the stabilizing plates 33 has an opening 34 for each of the stabilizing rods 30, and thus has exactly two openings 34 here (see also 7 and 8th ).

A receiving opening 36 is formed in the heating element 12 for each of the stabilizing rods 30 , which opening extends in a plane parallel to the end faces 14 , 16 and perpendicular to the axial direction A and runs through the metal foam of the heating element 12 . Here, the receiving openings 36 run as chords of a circle from one edge section 37 to an opposite edge section 37 of the heating element 12.

The receiving openings 36 are made, for example, by laser cutting or water jet cut as through-openings through the metal foam of the heating element 12 produced.

The receiving openings 36 are each interrupted in the recesses 22 .

The stabilizing plates 33 are inserted into the recesses 22 in such a way that their surface runs parallel to the axial direction A and the openings 34 in the exit regions 38 of the receiving openings 36 are aligned with the receiving openings 36 on the inner sides 40 of the recess 22 pointing towards the recess 22 (see also 9 ).

The stabilizing bars 30 are guided through the receiving openings 36 and the openings 34 of all stabilizing plates 32 .

The stabilizing rods 30 are so long here that they protrude completely through the heating element 12 and are mechanically fixed in the holder 18 for additional mechanical stability in a manner that is not shown in detail.

The stabilizing rods 30 are arranged here in a straight line and parallel to one another.

The stabilizing structure 28, that is to say here both the stabilizing rods 30 and the stabilizing plates 33, are electrically insulated from the heating element 12. This is done, for example, by the choice of material, for example an electrically insulating ceramic, or by an electrically insulating coating or, for example, an electrically insulating fabric cover. In particular, this allows the use of metal rods for the stabilizing rods 30.

By using the stabilization structure 28, the height h of the heating element 12 can be reduced, in this example to approximately 15 mm. For this purpose, stabilizing rods 30 with a diameter of about 2 to 3 mm have proven to be sufficient.

The 7 and 8th show possible shapes for the stabilizing plates 33. At the discretion of the person skilled in the art, the shape can be freely selected, with the stabilizing plate 33 on the one hand having the smallest possible area in order to keep the weight low, but on the other hand its dimensions and shape should be selected in such a way that that they reliably electrically insulate the foam webs 24 of the heating element 12 that are adjacent in the recesses 22 from one another. In this respect, the trapezoidal structure according to 8th slightly lighter than that of 7 .

As in 1 is indicated, the shape of the stabilizing plates 33 can be adapted to the resulting shape of the recess 22 and lie in the respective recess 22 with a positive fit.

In this way, the stabilizing rods 32 can fulfill a further function, namely an at least partial sealing of the recesses 22 against the passage of exhaust gas.

With reference to the 4 until 6 In a first variant, the recesses 22 have a projection 42 on the exit areas 38 (mouths) of the receiving openings 36 into the recesses 22 on each foam web 24 on at least one inner side 40, here on both opposite inner sides 40. The projection 42 forms, so to speak, a radial thickening of the respective foam web 24 of the heating element 12.

As in 5 is illustrated, in this example the volume V ₁ of all projections 42 together is approximately equal to the volume V ₂ of the receiving openings 36, so that the volume of metal foam missing in the receiving opening 36 is compensated for by the projections 42 and thus the electrical resistance of the foam webs 24 and so that the heating effect of the heating element 12 is not changed by the receiving opening 36.

3 shows a second variant to achieve this balance. Here the recesses 22 are designed as slits of uniform width, while the axial thickness of the foam webs 24 of at least one of the end faces 14, 16 along the receiving openings 36 is increased in a projection 44 in each case to such an extent that the volume compensation described results.

Both variants could also be combined, with the total volume of the projections 42, 44 being selected such that the total volume of the receiving openings 36 is compensated, or the volume per foam web 24.

The 10 until 13 show a third and a fourth variant of a heating device 10.

In contrast to the variants just described, the stabilization structure 28 here comprises a total of exactly three stabilization rods 30, and instead of the stabilization plates 33, stabilization rings 46 are used as stabilization elements 32 (see 13 ) and/or a rod-shaped stabilizer 48 (see 10 ) arranged in the recesses 22.

The stabilizing rings 46 have a relatively small diameter, which corresponds here approximately to the axial height h of the heating element 12, and each have only a single opening 34 (see also 12 ).

Stabilizing elements 32 can be present for each of the stabilizing rods 30 in each recess 22, but stabilizing elements 32 can also be placed only at selected locations, such as FIG 10 and 13 imply.

in the in 10 In the third variant shown, in addition to some stabilizing rings 46, there is also a single rod-shaped stabilizer 48 which is inserted into one of the recesses 22 and which is essentially the same length as the recess 22. Analogously to the stabilizing plates 33 described above, the stabilizer 48 has for each the stabilizing rods 30 have their own opening 34, so here it has three openings 34, through which one of the stabilizing rods 30 protrudes.

in the in 13 Fourth variant shown are only stabilizing rings 46, so neither stabilizing plates 33 nor stabilizers 48, are used in the recesses 22.

The 14 until 18 show a fifth variant of a heating device 10.

Here, the recesses 22 are also used at the same time as receiving openings 36 so that the heating element 12 does not have any additional receiving openings 36 . Analogous to the in 10 With the stabilizer 48 shown, the stabilizing rods 30 are each pushed into one of the recesses 22 from the edge of the heating element 12 (see also 18 ).

A separate stabilizing rod 30 is provided for each recess 22 here.

The cross section of the recesses 22 and that of the stabilizing rods 30 is chosen to be complementary, so that the stabilizing rods 30 are arranged in a form-fitting manner in the recesses 22 and close the recesses 22 against the passage of exhaust gas.

As the 15 and 17 show, a double-conical cross-section that remains constant along the recess 22 with cone tips facing each other is selected, which forms an undercut on the end faces 14, 16 that holds the stabilizing rod 30 in the recess 22. Of course, other suitable cross-sectional shapes can also be used.

In this variant, the stabilizing structure 28 consists only of the stabilizing rods 30.

The stabilizing rods 30 are each selected here to be as long as the recesses 22 .

All of the features of the individual variants can be freely interchanged or combined with one another at the discretion of the person skilled in the art.

Claims (10)

Electrical heating device of an exhaust gas system, which can be mounted in an exhaust pipe transversely to an exhaust gas flow and through which the exhaust gas to be treated can flow axially, with a disk-shaped, electrically conductive heating element (12) made of a metal foam, which is electrically coupled to at least two electrodes (20), wherein the heating element (12) has an upstream-oriented front end face (14) and a downstream-oriented rear end face (16) which lie one behind the other in an axial direction (A), and the heating element (12) has one or more axial, slot-shaped recesses (22 ) defining a tortuous current path through the heating element (12) in a plane perpendicular to the axial direction (A), and having a stabilizing structure (28) having at least two stabilizing bars (30) perpendicular to the axial direction (A), each stabilizing bar ( 30) is received in its longitudinal direction (I) in a receiving opening (36) running perpendicularly to the axial direction (A) in the heating element (12). heating device after claim 1 , wherein at least one receiving opening (36) is formed by a recess (22), so that at least one stabilizing rod (30) is arranged in a recess (22). heating device after claim 1 wherein at least one receiving opening (36) runs transversely to at least one recess (22) through the metal foam of the heating element (12). heating device after claim 3 wherein the receiving openings (36) extend from an edge portion (37) of the heating element (12) to an opposite edge portion (37) of the heating element (12). heating device after claim 3 or 4 , wherein the heating element (12) has at least one projection (42) on an inner side (40) pointing into the recess (22) in an outlet region (38) of the receiving opening (36), in particular a projection (42) annularly surrounding the receiving opening (36) 42), and/or the heating element (12) has a projection (44) on at least one end face (14, 16) along the receiving opening (36). heating device after claim 5 , wherein the volume (V ₁ ) of the at least one projection (42) which is associated with a receiving opening (36), corresponds to the volume (V ₂ ) of the receiving opening (36) and/or that the volume (V ₁ ) of all projections (42) together corresponds to the total volume (V ₂ ) of the receiving openings (36). Heating device according to one of the preceding claims, wherein the stabilizing structure (28) comprises at least one stabilizing element (32) which has at least one opening (34) through which a stabilizing rod (30) protrudes, the stabilizing element (32) being located in a recess (22 ) is arranged. heating device after claim 7 , wherein at least one stabilizing element (32) is present, which has an opening (34) for each stabilizing rod (30). heating device after claim 7 or 8th , wherein at least one stabilizing element (32) is a stabilizing plate (33). Heating device according to one of the preceding claims, in which the stabilizing structure (28) is electrically insulated from the heating element (12).

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