Support unit for supporting a heating conductor of an exhaust gas heater on a support structure

Description

[0001] The present invention relates to a support unit for supporting a heating conductor of an exhaust gas heater on a support structure, to an exhaust gas heater constructed with at least one such support unit, and to a method for producing such a support unit. The invention further relates to an exhaust system constructed with such an exhaust gas heater.

[0002] DE 10 2020 123 376 A1 discloses an exhaust gas heater for an exhaust system of an internal combustion engine, in which a substantially disc-shaped heating conductor with a generally meandering structure is supported on a support structure at a plurality of fastening points. The support structure comprises a support part upstream and downstream of the heating conductor. The two support parts accommodate the heating conductor between them and enclose it radially on the outside. At the fastening points, insulating elements constructed of ceramic material are positioned between each support part and the heating conductor. Firm cohesion is achieved by the support parts, the insulating elements, and the screw bolts penetrating the heating conductor.

[0003] WO 2022 / 24338 A1 discloses an exhaust gas heater in which a honeycomb-shaped heating element is supported on a support structure by means of a plurality of support units according to the preamble of claim 1.

[0004] It is the object of the present invention to provide a support unit for supporting a heating conductor of its exhaust gas heater on a support structure, with which a stable, electrically insulated support of a heating conductor on a support structure is achieved with a structurally simple design.

[0005] According to the invention, this object is achieved by a support unit for supporting a heating conductor of an exhaust gas heater on a support structure according to claim 1. The support unit comprises a support sleeve extending in the direction of a longitudinal axis and surrounding the longitudinal axis, a support pin with a sleeve connection region extending in the support sleeve and an exhaust gas heater connection region protruding beyond the support sleeve, wherein the support pin is coated with insulating material at least in the region of its sleeve connection region and / or the support sleeve is coated with insulating material on an inner surface surrounding the sleeve connection region of the support pin, and wherein the sleeve connection region is held in the support sleeve by frictional engagement.

[0006] A stable force connection between the support sleeve and the support pin is provided by thermal treatment of the support sleeve and / or the support pin before inserting the sleeve connection area into the support sleeve.

[0007] For this purpose, the support sleeve is heated and / or the support pin is cooled before inserting the sleeve connection area into the support sleeve.

[0008] Since, in a support unit constructed according to the invention, the cohesion of the two components establishing a connection between a heating conductor and a support structure, i.e. the support sleeve and the support pin, are held together solely by frictional engagement and thus without the use of additional components and are held together electrically insulated by the insulating material, a simple structure is achieved which is resistant to mechanical, thermal and chemical stresses.

[0009] For a simple and cost-effective design, the support pin can be designed with a substantially cylindrical outer peripheral contour at least in its sleeve connection area, so that in particular the support sleeve can also be provided as a substantially cylindrical and thus easily producible component.

[0010] In an alternative embodiment, the support pin can be designed to taper, preferably conically, at least in its sleeve connection area, preferably in the direction away from the exhaust gas heater connection area, which facilitates the axial insertion of these two components into one another.

[0011] In particular, with this tapered structure of the support pin, the frictional connection can additionally be provided by axially pressing the sleeve connection area into the support sleeve.

[0012] In order to achieve sufficiently strong electrical insulation even against comparatively high electrical currents, while at the same time not compromising the structural strength provided by the frictional connection, the insulating material can have a layer thickness in the range of 0.01 mm to 0.1 mm. Such a thin coating of insulating material also simultaneously achieves a very low thermal mass of the entire support unit.

[0013] If the insulating material is constructed with ceramic material, very good electrical insulation is achieved with equally good thermal and chemical resistance of the insulating material.

[0014] In order to shield the insulating material as efficiently as possible against external influences, in particular exhaust gas flowing through an exhaust system, it is proposed that the insulating material does not protrude axially beyond the support sleeve at at least one axial end of the support sleeve.

[0015] To avoid leakage currents, the insulating material can protrude axially beyond the support sleeve at least at one axial end of the support sleeve facing the exhaust gas heater connection area.

[0016] If the support pin and the support sleeve are constructed with metal material, a thermally, mechanically and chemically resistant structure is supported and at the same time the possibility is provided to connect the support pin and the support sleeve to the heating conductor or support structure in a material-locking manner, for example by welding.

[0017] The invention further relates to methods for producing a support unit according to the invention, wherein, for the non-positive connection of the support sleeve to the support pin, the support sleeve is heated and / or the support pin is cooled before the sleeve connection area is inserted into the support sleeve. The present invention thus utilizes the effect that when the support sleeve is heated, it initially expands and, upon subsequent cooling, firmly grips the support pin that has already been inserted into it or is pressed firmly with its inner surface against an outer surface of the support pin to produce a stable frictional connection. A corresponding effect can be achieved by cooling the support pin before insertion into the support sleeve, so that it contracts and, upon the expansion that occurs again during subsequent heating, is pressed with its outer surface against the inner surface of the support sleeve to produce a stable frictional connection.

[0018] It is particularly advantageous if the support sleeve is heated to a temperature above a maximum upper limit temperature occurring on an exhaust gas heater and / or the support pin is cooled to a temperature below a maximum lower limit temperature occurring on an exhaust gas heater. The upper limit temperature is a temperature that is generally not reached or exceeded by an exhaust gas heater integrated into an exhaust system, particularly during operation. Likewise, the lower limit temperature is a temperature that is generally not undercut by an exhaust gas heater integrated into an exhaust system, for example, at very low ambient temperatures.This ensures that after integration of such an exhaust gas heater into an exhaust gas system, external influences do not cause cooling or heating of a support unit which could lead to the non-positive or frictional connection brought about by thermal conditioning being canceled again.

[0019] The invention further relates to an exhaust gas heater for an exhaust system of an internal combustion engine, comprising a support structure and at least one heating conductor carried on the support structure by means of at least one support unit constructed according to the invention.

[0020] For a stable structure, the at least one support unit, preferably with its support sleeve, can be fixed to the support structure in a material-locking manner, preferably by welding, and, preferably with its support pin, can be fixed to the at least one heating conductor in a material-locking manner, preferably by welding.

[0021] The invention further relates to an exhaust system with at least one exhaust gas heater constructed according to the invention.

[0022] The present invention is described in detail below with reference to the accompanying figures. It shows: Fig. 1a section of an exhaust gas heater for an exhaust system of an internal combustion engine; Fig. 2the exhaust gas heater of the Fig. 1 in viewing direction II in Fig. 1 ; Fig. 3 a longitudinal sectional view of a support unit connecting a heating conductor to a support structure of an exhaust gas heater; Fig. 4 one of the Fig. 1 corresponding view of an alternative design of a support unit; Fig. 5 a schematic representation of an exhaust system with an exhaust gas heater.

[0023] Before referring to the Fig. 1-4 The structure of a support unit for supporting a heating conductor on a support structure of an exhaust gas heater is described in detail, first with reference to the Fig. 5 the basic structure of an exhaust system 10 containing such an exhaust gas heater is explained.

[0024] The exhaust system 10 comprises an exhaust gas guide element 12, for example, tubular in design, in which exhaust gas A flows in a main exhaust gas flow direction. An exhaust gas heater 14 arranged in the exhaust gas guide component 12 comprises a plate-like support structure 16, for example, designed as a formed sheet metal part or stamped sheet metal part, which is connected in its outer peripheral region to an inner surface of the exhaust gas guide component 12, for example by material bonding, for example welding. A heating conductor 18, formed for example by cutting out of a flat material, for example with a meandering or spiral-wound structure, is firmly supported on the support structure 12 by a plurality of support units 20. By applying an electrical voltage to the connection ends of the heating conductor 18, the heating conductor is heated to a temperature of, for example, several hundred °C by the electrical current flowing through it.The heat generated in the heating conductor 18 can be transferred to the exhaust gas A flowing through the heating conductor 18 and also through the support structure 16 in the region of flow openings 21 formed therein. The exhaust gas A heated in the region of the exhaust gas heater 14 flows further toward an exhaust gas treatment unit, generally designated 22. This unit can be configured, for example, as a catalyst, such as an oxidation catalyst, SCR catalyst, or the like, or as a particulate filter.

[0025] By heating the exhaust gas A, which, for example, has a comparatively low temperature at comparatively low outside temperatures or at the start of operation of an internal combustion engine, it is possible to bring the exhaust gas treatment unit 22, positioned downstream of the exhaust gas heater 14, to the required operating temperature more quickly or to reliably maintain it at such an operating temperature. In particular, it is also possible to heat another gas, for example air, conducted through the exhaust gas guide component 12 at the exhaust gas heater 14 before the internal combustion engine is started up and then to use the heat transferred to this gas for the thermal conditioning of the exhaust gas treatment unit 22 even before the internal combustion engine is started up.

[0026] In the Fig. 1-3 An embodiment of such a support unit 20 used in the exhaust gas heater 14 is shown in detail. The support unit 20 comprises a support sleeve 24 elongated in the direction of a longitudinal axis L. In the illustrated embodiment, the support sleeve 24 has a cylindrical, for example circular, cross-sectional geometry, in particular an inner cross-sectional geometry, and is preferably constructed of metal material.

[0027] A support pin 26 with a sleeve connection area 28 is accommodated in the support sleeve 24. In the illustrated embodiment, the support pin 26 is secured to the heating conductor 18 by an exhaust gas heater connection area 30 protruding beyond the support sleeve 24.

[0028] The support sleeve 24 is in a region between an axial end 32 facing away from the exhaust gas heater connection region 30 and an axial end 42 facing the exhaust gas heater connection region 30, in which the support sleeve 26 has an associated opening 44 in the Fig. 2 , penetrates the plate-like support structure 16 shown, and is fixed to the support structure 14. Both the fixing of the support pin 26 to the heating conductor 18 and the fixing of the support sleeve 24 to the support structure 14 can be achieved by a respective weld 34, 36. Various welding processes, such as laser welding, MAG welding, TIG welding, or the like, can be used for this purpose. In this way, a connection of the support unit 02 to both the heating conductor 18 and the support structure 14 is ensured that is chemically resistant to mechanical and thermal stresses and also to the exhaust gas flowing through the exhaust gas heater 14.

[0029] For electrical insulation of the heating conductor 18 with respect to the support structure 14, which is also constructed of metal material, a coating of insulating material 40 is provided, for example, on an outer surface 38 of the support pin 26 in the sleeve connection area 28 thereof. The insulating material 40 can preferably be constructed of ceramic material and can be applied, for example, in the form of a lacquer coating or vapor deposition with a layer thickness in the range of 0.01 mm to 0.1 mm.

[0030] The insulating material 40 does not protrude beyond the support sleeve 24 at either the axial end 32 facing away from the exhaust heater connection area 30 or the axial end of the support sleeve 24 facing the exhaust heater connection area 42, but rather preferably ends flush with it. At these two axial ends 32, 42 of the support sleeve 24, the insulating material 40 is thus only exposed to the outside with a very small, ring-like end face and can therefore only come into contact with the exhaust gas flowing around the support unit 20 in this area. This additionally protects the insulating material 40 against external influences, in particular the chemically aggressive exhaust gas A.

[0031] Alternatively or in addition to coating the support pin 26 with the insulating material 40, such insulating material could also be applied to an inner surface 46 of the support sleeve 24, for example in the form of a lacquer coating or by vapor deposition or the like.

[0032] In order to achieve a stable connection between the support sleeve 24 and the support pin 26 without having to use additional means leading to a material connection or a form fit, the support pin 26 in the support unit 20 is held in the support sleeve 24 solely by force connection, i.e. frictional connection. Fig. 1 In the embodiment shown, in which the support sleeve has a substantially cylindrical inner surface 26 and the support pin 26 has a substantially cylindrical outer surface 38, this frictional connection is achieved by thermally treating the support sleeve 24 and / or the support pin 26 before these two components are inserted into one another. For example, the support sleeve 24 can be heated so that it expands and the support pin 26 can initially be inserted into the support sleeve 24 essentially without significant frictional contact with the coating of insulating material 40 already provided on the sleeve connection area 28. During subsequent cooling, the support sleeve 24 contracts and presses its inner surface 26 firmly and essentially uniformly over its entire surface against the outer surface 38 of the support pin 26 or the insulating material 40 provided thereon.This reliably prevents local overloading, particularly of the insulating material 40. To ensure that this force-locking connection is not disrupted during operation of an exhaust system 10 or the exhaust gas heater 14 and the resulting heating of the support unit 20, the support sleeve 24 is preferably heated during this thermal treatment to a temperature that is higher than the maximum temperature that the exhaust gas heater 14 or the heating conductor 18 thereof can reach during operation of the exhaust system 10.

[0033] In an additional or alternative thermal treatment, the support pin 26 can be cooled before being inserted into the support sleeve 24, preferably to a temperature that is below a temperature to which the exhaust gas heater 14 and the support unit 20 provided thereon are maximally exposed. In this case, very low ambient temperatures, which can be in the range of -30°C to -40°C, must be considered below the limit temperatures. After the support pin 26 has cooled in this way, it can be inserted into the support sleeve 24 to the desired extent with the coating of insulating material 40 already provided thereon and subsequently heated back to ambient temperature, so that the subsequent expansion of the support pin 26 presses it firmly and evenly against the inner surface 46 of the support sleeve 24 with the coating of insulating material 40 provided on its outer surface 38.

[0034] In order to ensure with this thermal treatment when connecting the support sleeve 24 to the support pin 26 that a stable cohesion of the support sleeve 24 with the support pin 26 is maintained after the connection has been made, even taking into account the thermal loading of such a support unit 20 that occurs in a vehicle, the support sleeve 24 with its inner dimension and the support pin 26 with its outer dimension are preferably matched to one another in such a way that only after this thermal treatment, i.e. after heating the support sleeve 24 and / or cooling the support pin 26, can the support pin 26 be inserted into the support sleeve 24 with the smallest possible radial play.

[0035] Since, even when connecting the support unit 20 to the heating conductor 18 or the support structure 14, for example by welding, the support unit 20 is not heated to such an extent that the resulting thermally induced deformation, in particular of the support sleeve 24, would significantly impair the frictional connection, there is also no risk that a relative movement leading to an undefined connection state could occur between the support pin 26 and the support sleeve 24 during the production of the welds 34, 36. Even the fact that different materials, in particular metal materials, with different thermal expansion coefficients can be used for the support sleeve 24 and the support pin 26 does not impair the structural strength of the support unit 20 in such a connection brought about by thermal treatment.

[0036] An alternative embodiment of such a support unit 20 is shown in Fig. 2 shown. In this embodiment, the support pin 26 is designed, particularly in its sleeve connection area 28, with a cross-sectional geometry that preferably tapers conically in the direction away from the exhaust gas heater connection area 30. Accordingly, the support sleeve 24 is designed with a cross-sectional area that decreases in the direction from the axial end 42 to the axial end 32. This can be achieved, for example, by inserting a sleeve-like insert part 48 into the support sleeve 24, which is generally designed with a cylindrical cross-sectional geometry. The insert part 48 has a cylindrical structure on its outer circumferential surface 50 that is adapted to the inner cross-sectional geometry of the support sleeve 24, and has an inner surface 56 on its inner side that tapers correspondingly in the axial direction, for example to the conical cross-sectional geometry or conically tapered structure of the support pin 26.For example, this insert part 48 can also be constructed from metal material. In an alternative embodiment, the inner cross-sectional geometry tapering conically in the axial direction can be provided directly on the inner surface 46 of the support sleeve 24. In a further alternative embodiment, the conically tapering structure could also be provided such that a cross-sectional decrease of the support pin 26 is provided in the direction of the exhaust gas heater connection area 30 not surrounded by the support sleeve 24.

[0037] Also in the Fig. 2 In the embodiment shown, the insulating material 40 can be applied to the outer surface 38 of the support pin 26, for example, by applying a lacquer coating or by vapor deposition or the like. Fig. 2 that at the axial end 42 of the support sleeve 24, the insulating material 40 protrudes axially and extends into the area of ​​the exhaust gas heater connection area 30 which is not surrounded by the support sleeve 24 and is designed, for example, with a substantially cylindrical outer circumferential structure. In this way, reliable protection can also be achieved against creepage currents between the exhaust gas heater connection area 30 and the axial end 42 of the support sleeve 24. In order to prevent the occurrence of creepage currents between the support pin 26 and the carrier structure 14 at the axial end 32 of the support sleeve 24, at which, in the illustrated embodiment, the support pin 26 ends with its sleeve connection area 28 substantially flush with the support sleeve 24, the support pin 26 can also protrude axially beyond the support sleeve 24 in the area of ​​the axial end 32 and can be coated with the insulating material 40 on the section protruding beyond the support sleeve 24.It should be noted that such a structure is of course also used in . Fig. 1 can be realized in the embodiment shown.

[0038] For the secure connection of the support pin 26, which is tapered at least in its sleeve connection area 28, to the support sleeve 24, the support pin 26 can be pressed axially into the support sleeve 24 upon axial insertion thereof, so that a frictional connection or force connection leading to self-locking is created. This also creates a uniform surface pressure on the coating of insulating material 40 surrounding the support pin 26, in particular in its sleeve connection area 28. Alternatively or additionally, according to the principles of the present invention, the force connection can also be achieved in this embodiment of a support unit 20 by the previously described with reference to the embodiment of the Fig. 1described thermal treatment of the support sleeve 24 and / or the support pin 26.

[0039] With the construction of a support unit according to the invention, a mechanically stable connection of a heating conductor of an exhaust gas heater to a support structure is achieved with a structurally simple design and a small number of components. At the same time, reliable electrical insulation between the heating conductor and the support structure is ensured, whereby the material and / or the layer thickness of the coating with insulating material can be selected, adapted to the respective dimensions and the electrical currents against which electrical insulation is required. At the same time, this coating of electrically insulating material bears the load, particularly when it is made of a comparatively poor thermal conductor, such as, for example,Ceramic material, contributes to thermal insulation of the heating conductor, so that the heat generated therein is essentially not transferred to the support structure, but primarily to the gas or exhaust gas flowing around the heating conductor. Since the insulating material applied in the form of a coating is essentially completely shielded from the chemically aggressive exhaust gas by the support sleeve surrounding the support pin, there is no risk of such chemical influences, possibly supported by thermal stress, damaging the insulating material over the operating life of an exhaust gas heater and the risk of a short circuit occurring between the support sleeve and the support pin accommodated in it. This is also helped by the fact that the frictional connection generated between the support sleeve and the support pin subjects the insulating material to an essentially constant contact pressure that is evenly distributed over its surface.The penetration of corrosive media into the space between the support pin and the support sleeve, in which the insulating material is essentially arranged, is thus equally reliably prevented.

Claims

1. A support unit for supporting a heating conductor of an exhaust gas heater on a carrier structure, comprising a supporting sleeve (24) extending in the direction of a longitudinal axis (L) and surrounding the longitudinal axis (L), a supporting pin (26) having a sleeve connecting area (28) extending in the supporting sleeve (24) and an exhaust gas heater connecting area (30) projecting beyond the supporting sleeve (24), wherein the supporting pin (26), at least in the area of its sleeve connecting area (28), and / or the supporting sleeve (24), on an inner surface (46) surrounding the sleeve connecting area (28) of the supporting pin (26), is coated with insulating material (40), and wherein the sleeve connecting area (28) is held in the supporting sleeve (24) by a force fit, characterized in that the force fit is provided by thermal treatment of the supporting sleeve (24) and / or of the supporting pin (26) before insertion of the sleeve connecting area (28) into the supporting sleeve (24), wherein the supporting sleeve (24) is heated and / or the supporting pin (26) is cooled before insertion of the sleeve connecting area (28) into the supporting sleeve (24).

2. The support unit as claimed in claim 1, characterized in that the supporting pin (26) is formed with a substantially cylindrical outer circumferential contour, at least in its sleeve connecting area (28).

3. The support unit as claimed in claim 1, characterized in that the supporting pin (26), at least in its sleeve connecting area (28), is designed to taper, preferably conically, preferably in the direction away from the exhaust gas heater connecting area (30).

4. The support unit as claimed in one of claims 1-3, characterized in that the force fit is provided by axially pressing the sleeve connecting area (28) into the supporting sleeve (24).

5. The support unit as claimed in one of claims 1-4, characterized in that the insulating material (40) has a layer thickness in the range from 0.01 mm to 0.1 mm.

6. The support unit as claimed in one of claims 1-5, characterized in that the insulating material (40) is formed with ceramic material.

7. The support unit as claimed in one of claims 1-6, characterized in that the insulating material (40) does not project axially beyond the supporting sleeve (24) at at least one axial end (32, 42) of the supporting sleeve (24).

8. The support unit as claimed in one of claims 1-7, characterized in that the insulating material (40) projects axially beyond the supporting sleeve (24), at least at an axial end (42) of the supporting sleeve (24) that faces the exhaust gas heater connecting area (30).

9. The support unit as claimed in one of claims 1-8, characterized in that the supporting pin (26) and the supporting sleeve (24) are made with metallic material.

10. A method for producing a support unit (20) for supporting a conductor of an exhaust gas heater on a carrier structure , wherein the support unit (20) comprises a supporting sleeve (24) extending in the direction of a longitudinal axis (L) and surrounding the longitudinal axis (L), a supporting pin (26) having a sleeve connecting area (28) extending in the supporting sleeve (24) and an exhaust gas heater connecting area (30) projecting beyond the supporting sleeve (24), wherein the supporting pin (26), at least in the area of its sleeve connecting area (28), and / or the supporting sleeve (24), on an inner surface (46) surrounding the sleeve connecting area (28) of the supporting pin (26), is coated with insulating material (40), and wherein the sleeve connecting area (28) is held in the supporting sleeve (24) by a force fit, wherein, for the force-fitting connection of the supporting sleeve (24) to the supporting pin (26), the supporting sleeve (24) is heated and / or the supporting pin (26) is cooled before the insertion of the sleeve connecting area (28) into the supporting sleeve (24).

11. The method as claimed in claim 10, characterized in that the supporting sleeve (24) is heated to a temperature above an upper limiting temperature that occurs at most on an exhaust gas heater (14) and / or the supporting pin (26) is cooled to a temperature below a lower limiting temperature that occurs at most on an exhaust gas heater (14).

12. An exhaust gas heater for an exhaust gas system of an internal combustion engine, comprising a carrier structure (14) and at least one heating conductor (18) carried on the carrier structure (14) by means of at least one support unit (20) as claimed in one of claims 1-9.

13. The exhaust gas heater as claimed in claim 12, characterized in that the at least one support unit (20) is fastened to the carrier structure (14), preferably by its supporting sleeve (24), by material bonding, preferably by welding, and is preferably fastened to the at least one heating conductor (18) by its supporting pin (26), by material bonding, preferably by welding.

14. An exhaust gas system for an internal combustion engine, comprising at least one exhaust gas heater (14) as claimed in claim 12 or 13.