Electric heating device and method for manufacturing an electric heating device

Abstract

An electric heating device (100, 200, 300) with a tubular metal sheath (110, 210, 310) and an electric heating element (120, 220, 320) which is at least partially coiled and electrically connected to a connecting bolt (130, 230, 330), wherein electrically insulating material (140, 150, 250) is arranged between the electric heating element (120, 220, 320) and the connecting bolt (130, 230, 330) on the one hand and the tubular metal sheath (110, 210, 310) on the other hand, characterized in that the electrically conductive connection of the electric heating element (120, 220, 320) and the connecting bolt (130, 230, 330) is via a section (131, 231, 331) of the connecting bolt (130,230,330) is manufactured, which is placed or inserted on the outside of at least one formed helix (122,222,322) of the helical section of the electric heating element (120,220, 320).

Description

[0001] Electric heating devices for heating objects or media are widely used. Particularly in electric heating devices that operate at low voltages, for example in the automotive sector with the vehicle electrical system of a car, high currents are used during operation.

[0002] Exemplary examples of such electric heating devices are disclosed in DE 10 2009 005 481 B3, US 3 702 387 A, JP 2018 - 41 631 A and DE 10 2019 127 753 A1.

[0003] In many applications, it is desirable for the heated area of ​​the electric heating device to be as precisely defined as possible. To achieve this, connecting studs made of a material with a significantly lower specific resistance than that of the electric heating element, which in many cases is a coiled resistance wire, are typically used. These connecting studs are usually inserted into the coil's inner space at the ends of the electric heating element, creating an electrically conductive connection between the components. However, it has been found that the process reliability of creating this electrically conductive connection is still unsatisfactory, and that excessive heat can still be dissipated at the connecting studs at high currents.

[0004] The object of the invention is therefore to provide an electric heating device that can be manufactured with improved process reliability and to specify a more reliable method for manufacturing such an electric heating device.

[0005] This problem is solved by an electric heating device with the features of claim 1 and a method for manufacturing an electric heating device with the features of claim 8. Advantageous embodiments of the invention are the subject of the respective dependent claims.

[0006] The electric heating device according to the invention, which can in particular be a tubular heating element, has a tubular metal sheath and an electric heating element which is at least partially, preferably also completely, coiled and which is electrically connected to a connecting bolt.

[0007] The electric heating element can, for example, be made from a coiled heating wire, which can be either round or flat. The connecting bolt is typically made of a material with low specific resistance, such as copper or nickel, and typically has a larger cross-sectional area than the heating wire in order to minimize the heat generated by the current flowing through the connecting bolt.

[0008] An electrically insulating material is arranged between the electric heating element and the connecting bolt on the one hand and the tubular metal sheath on the other, particularly in the directions perpendicular to a central axis of the tubular metal sheath, so that a short circuit is avoided.

[0009] It should be noted that this does not preclude the possibility of using the tubular metal sheath as a return conductor; the possibility of such an arrangement is also the reason why, although in most cases there will be two connecting bolts that are electrically connected to the electric heating element at opposite ends, a functional electric heating device can already be created with just one such connecting bolt.

[0010] This electrically insulating material can be, in particular, a magnesium oxide powder or granules, or a ceramic material; the use of molded parts is also possible.

[0011] A key aspect of the invention is that the electrically conductive connection between the electric heating element and the connecting bolt is established via a section of the connecting bolt that is placed on or inserted into the outer surface, in particular the outer surface of a formed section, of at least one formed helix of the helical section of the electric heating element. "Placed on" or "inserted" here means, in particular, that the corresponding section of the connecting bolt is not surrounded in one direction by a section of a helix of the helical section of the electric heating element, which is not the case with inserted or pushed-on arrangements.

[0012] This specific design of the connection geometry allows for a highly reliable electrical connection, particularly with welding monitoring, achieved through welding, preferably resistance welding. This is because the two elements to be welded can be optimally engaged with welding electrodes and are directly accessible. Furthermore, the connection geometry can also accommodate connecting bolts with a larger cross-sectional area than previously possible, thus reducing the heating power required at the connecting bolt.

[0013] According to one embodiment of the invention, the formed helixes are compressed so that they are adapted to a portion of the circumferential line of the section of the connecting bolt that bears against the outside of the formed helix, in particular against the outside of the formed part of the formed helix. "Compressed" here means, in particular, that the internal space of the helix is ​​reduced, and preferably that opposing helix sections bear against each other before the forming process. In advantageous embodiments, the originally convex profile of the outside of a formed part of the formed helix is ​​transformed into a concave profile; it is this concave section of the outside of the formed helix that the section of the connecting bolt is then preferably placed upon or into which the section of the connecting bolt is preferably inserted.

[0014] An adaptation to a part of the circumferential line of the section of the connecting bolt that rests on the outside of the formed helix means that at least locally a surface contact is established between these components.

[0015] In particular, for example, helixes can be deformed such that their originally circular cross-section is transformed into the shape of a double-walled U or a double-walled circular segment, the outer wall of which, facing away from the connecting bolt, essentially follows the original course of the helix, while the inner wall, facing the connecting bolt, is formed by the opposite helix section, which has been pressed in so that it rests against the inside of the outer wall thus formed and is curved in the same direction. It may then be preferred that, in this embodiment, this radius of curvature is selected to correspond to a radius of curvature of the connecting bolt in the section that is attached to or inserted into the deformed helix.

[0016] A further development of this embodiment exists when the portion of the connecting bolt to which the formed coils are adapted is weakened by profiling. In other words, this means that the basic shape of the connecting bolt, which is usually cylindrical and in most cases remains unchanged in the section of the connecting bolt where no contact with the electrical heating element is made, is modified by removing material in the portion of the connecting bolt where contact with the electrical heating element is made. This allows for the use of connecting bolt cross-sections larger than the inner diameter of the coils, even when the minimum distance between the connecting bolt and the tubular metal sheath is determined by the minimum distance between the electrical heating element and the tubular metal sheath, thus reducing the required heating power.

[0017] The cross-section of the connecting bolt can be further optimized if the formed helix is ​​shaped in such a way that it is complementary to the weakening of the connecting bolt caused by the profiling. In other words, the formed helix then complements the profiled section of the connecting bolt, which is attached to or inserted into it, restoring the basic shape of the connecting bolt. This shape can then be cylindrical, in particular, with a diameter corresponding to the outer diameter of the helix, if another part of the circumferential line of the profiled section of the connecting bolt corresponds to the outer circumferential line of an unformed helix of the electrical heating element facing the connecting bolt.

[0018] The electrical and mechanical connection between the connecting bolt and the electrical heating element is preferably achieved by welding the connecting bolt and the electrical heating element together in the area of ​​the formed coil. Resistance welding is particularly suitable as a welding method for this purpose.

[0019] By having the connecting bolt penetrated by a filling opening for the addition of electrically insulating material, it is possible to perform the connection, in particular the welding, of the connecting bolt and the electrical heating element outside the tubular metal casing. The assembly configured in this way can then be inserted into the tubular metal casing, and subsequently filled with the electrically insulating material. This sequence of process steps leads to improved process reliability because verification and, if necessary, adjustment of the electrically conductive connection can still be carried out outside the tubular metal casing.

[0020] The inventive method for manufacturing an electric heating device comprises in particular the steps - Providing a tubular metal sheath, an electrical heating element that is at least partially coiled, and a connecting bolt, - Establishing an electrically conductive connection between the connecting bolt and the electrical heating element, which is at least partially coiled, - Inserting the electrical heating element, which is at least partially coiled, and the connecting bolt into an interior space of the tubular metal sheath, and - Filling the remaining volume inside the tubular metal sheath with an electrically insulating material. It should be noted that these steps preferably, but not necessarily, have to be carried out in the specified sequence. For example, establishing an electrically conductive connection between the connecting bolt and the at least partially coiled electric heating element can also take place only after the at least partially coiled electric heating element and the connecting bolt have been inserted into an interior space of the tubular metal sheath, and the remaining volume inside the tubular metal sheath has been filled with an electrically insulating material, for example, if a press connection is made when the electric heating cartridge is compressed.

[0021] The essential aspect of the invention is that, to produce the electrically conductive connection, at least one coil of the coiled electric heating element is formed, and a section of the connecting bolt is applied to or inserted into an outer surface, in particular the outer surface of a formed section, of at least one formed coil of the coiled section of the electric heating element. This allows simultaneous, direct access to the connecting bolt and the electric heating element, for example, when the section of the connecting bolt that is applied to or inserted into the outer surface of at least one formed coil of the coiled section of the electric heating element is welded to the formed coil.

[0022] It is preferred that the helix is ​​reshaped by placing it in a die and pressing it in with a punch.

[0023] If the connecting bolt is provided with a filling opening that passes through it lengthwise, it is particularly easy to establish the connection between the connecting bolt and the formed helix before insertion into the interior of the tubular metal jacket, so that the connecting bolt and the electrical heating element are inserted as a single assembly, which, without such a filling opening, makes filling the remaining volume of the interior of the tubular metal jacket considerably more difficult.

[0024] In one embodiment of the method, the section of the connecting bolt that rests on the outer surface of at least one formed helix of the helical section of the electric heating element is weakened on the side intended for contact with the formed helix by a profile. This means that the basic shape of the connecting bolt, which is typically cylindrical, is reduced or modified, particularly by material removal, e.g., machining. This can, in particular, reduce the required installation space in the area of ​​the electrically conductive connection between the electric heating element and the connecting bolt via the section of the connecting bolt that rests on or is inserted into the outer surface of at least one formed helix of the helical section of the electric heating element.If material is removed during profiling in such a way that a recess complementary to the formed helix is ​​created in the section of the connecting bolt weakened by the profiling, even an increased installation space requirement can be completely avoided and the cross-section of the connecting bolt maximized.

[0025] The invention is explained in more detail below with reference to figures illustrating exemplary embodiments. These show: Fig. 1a: A first step in forming the coils of a helical heating element in an end-face view, Fig. 1b: a second step in the forming of coils of a helical heating element in an end-face representation, Fig. 1c: the step out Fig. 1b in a perspective view, Fig. 2a: A variant of the first step in forming the coils of a helical heating element in an end-face view, Fig. 2b: a variant of the second step in the forming of coils of a helical heating element in an end-face representation, Fig. 2c: the step out Fig. 2b in a perspective view, Fig. 3a: an open view of one half of a first embodiment of an electric heating device, Fig. 3b: a longitudinal section through one half of the electric heating device made of Fig. 3a, Fig. 4a: an open view of one half of a second embodiment of an electric heating device, Fig. 4b: a longitudinal section through one half of the electric heating device made of Fig. 4a, Fig. 5a: an open view of one half of a third embodiment of an electric heating device, Fig. 5b: a longitudinal section through one half of the electric heating device made of Fig. 5a, and Fig. 5c: the connecting bolt of the electric heating device Fig. 5a.

[0026] First, to better understand the term "reformed helix of the coiled electric heating element", the following should be explained: Fig. Exemplary forming processes are shown in sections 1a to 1c and 2a to 2c. Fig. 1a and 2a each have a die 1 and 2 respectively, into which an electric heating element 10 and 20 respectively is inserted, which in this example initially consists of a resistance wire with flat-band geometry wound along its entire length into coils 11, 21 with an inner coil diameter Wi and an outer coil diameter Wa. The essential difference between the Fig. 1a and Fig. 2a consists in the fact that in the Fig. 1a the geometry of the die recess, in particular its curvature, is adapted to the spiral outer diameter Wa, while in the Fig. 2a the curvature of the die recess is less.

[0027] As the Fig. 1b and Fig. 1c or 2b and Fig. As can be seen from Figure 2c, some of the helixes 11 and 21 are pressed in or compressed with a punch 3 and 4, respectively. The helix sections 11b and 21b are thereby deformed so that they abut the opposing helix sections 11a, 11c and 21a, 21c, respectively, and the originally convex outer surfaces of the deformed helix sections 11b and 21b are transformed into a concave profile. The different curvatures of the recesses in the dies 1 and 2 have such an effect that in the Fig. In the case shown in 1a to 1c, the originally circular helical cross-section is transformed into the shape of a double-walled U, while in the Fig. In the case shown in 2a to 2c, a double-walled circular ring segment is formed. In both cases, the transformed helixes form a structure open in one direction – upwards in the illustrations – which allows for the insertion or attachment of a section of a connecting bolt.

[0028] Preferably, the end face 3a, 4a of the punch, with which the formed helixes are produced, is adapted to the outer contour of the surface of the section of the connecting bolt that comes into contact with the helix during insertion or attachment, so that surface contact can occur. This can, for example, be part of the cylindrical surface of a connecting bolt with a cylindrical basic geometry, but also a surface resulting from the partial or complete profiling of a connecting bolt with such a basic geometry.

[0029] The one in the Fig. 3a and Fig. The section shown in Figure 3b of an electric heating device 100 represents the left half of the electric heating device 100; it can be symmetrically extended to form the complete electric heating device 100. The same applies to the electric heating devices 200 and 300 discussed below.

[0030] One can see a tubular metal sheath 110, inside of which is an electric heating element 120, coiled along its entire length in this example, with coils 121 and shaped coils 122, which are, for example, formed by the Fig. The forming process shown in Figures 1a to 1c may have been produced. The electrical heating element 120 is connected via a connecting bolt 130, the section 131 of which is placed on the outside of formed sections 122a of several formed coils 122 or inserted into the interior of the double-walled U-shaped sections created during the forming of the coils 122 and is preferably welded to them. It is immediately clear that such an arrangement results in excellent electrical contact between these components, firstly because there is a large surface contact area, and secondly because, for example, during resistance welding, the welding electrodes can be brought into contact with both components very easily, so that welding can be carried out simply and in a monitored manner.

[0031] Both the electric heating element 120 and the connecting bolt 130 are electrically insulated from the tubular metal sheath 110 by an electrically insulating, highly thermally conductive material 140, e.g. magnesium oxide powder or granules.

[0032] At the end face, the tubular metal casing 110 is closed off with a plug 150 through which the connecting bolt 130 is passed.

[0033] The in the Fig. 4a and Fig. The electrical heating device 200 shown in section 4b, with tubular metal jacket 210, electric heating element 220 with coils 221 and formed coils 222, connecting bolt 230 with section 231, electrically insulating material 240 and plug 250, is essentially constructed the same way, which is why reference can be made to the above description with appropriately adapted reference numerals for details of the construction.

[0034] However, the reshaped helixes 222 are as in the Fig. The components shown in Figures 2a to 2c have the geometry of a double-walled circular ring segment and, as is immediately apparent, allow the use of a connecting bolt 230, which has a significantly larger cross-section than the connecting bolt 130. As shown in Fig. 4b visibly it is possible that the sections of the formed helixes 222 facing the tubular metal sheath 210 have a reduced distance to the tubular metal sheath 222, which can also help to maximize the cross-section of the connecting bolt 230 and thus keep the heat production in this area as low as possible.

[0035] The in the Fig. 5a and Fig. The electrical heating device 300 shown in section 5b, with tubular metal jacket 310, electric heating element 320 with coils 321 and formed coils 322, connecting bolt 330 with section 331, electrically insulating material 340 and plug 350, is essentially constructed the same way, which is why reference can be made to the above description with appropriately adapted reference numerals for details of the construction.

[0036] The reshaped helixes 322 are again as in the Fig. Figures 1a to 1c show that the components were produced and accordingly have the geometry of a double-walled U. The use of a connecting bolt 330, with the largest possible cross-section at a given minimum distance to the tubular metal shell 310, is made possible here by a special design of the connecting bolt 330, which is shown in Fig. 5c is shown in detail.

[0037] As the Fig. As illustrated in Figure 5c, section 331, which is attached to or inserted into the interior of the double-walled U-shape of the formed helixes 322, is profiled. Material has been removed from the cylindrical basic geometry still present in section 332 of the connecting bolt 330 by machining, such that the formed helixes 322 complement section 331 of the connecting bolt 330 again to its basic shape. In other words, section 331 of the connecting bolt 330 has been given a U-profile that exactly matches the U-profile shown in Figure 5c. Fig. As shown in 1b, it has been weakened. Accordingly, the geometry of the remaining bridge 331a and at least the end face 3a of the punch 3 also correspond to each other.

[0038] Furthermore, the connecting bolt 330 is penetrated by a filling opening 333 to facilitate the filling of the interior of the tubular metal jacket 310 with the electrically insulating material 340 during the manufacture of the electric heating device 300. Reference symbol list 1.2 Die 3.4 stamps 3a,4a Front 10, 20, 120, 220, 320 electric heating element 11.21 Wendel Sections 11a, 11b, 11c Sections 21a, 21b, 21c 100, 200, 300 electric heating device 110, 210, 310 tubular metal casing 120, 220, 320 electric heating element 121,221,321 Wendel 122,222,322 transformed helix 130, 230, 330 Connecting bolts Sections 131, 231, 331, 332 140, 240, 340 electrically insulating material 150, 250, 350 plugs 331a Steg 333 Filling opening Wi helix inner diameter Wa turning outer diameter

Claims

[1] Electric heating device (100, 200, 300) with a tubular metal casing (110, 210, 310) and an electric heating element (120, 220, 320) which is coiled at least in sections and is electrically conductively connected to a connecting bolt (130, 230, 330), wherein electrically insulating material (140, 150, 250) is arranged between the electric heating element (120, 220, 320) and the connecting bolt (130, 230, 330) on the one hand and the tubular metal casing (110, 210, 310) on the other hand, characterized by that the electrically conductive connection of the electrical heating element (120,220,320) and the connecting bolt (130,230,330) is established via a section (131,231,331) of the connecting bolt (130,230,330) which is placed or inserted on the outside of at least one formed coil (122,222,322) of the coiled section of the electrical heating element (120,220, 320). [2] Electric heating device (100,200,300) according to claim 1, characterized bythat the formed coils (122,222,322) are compressed in such a way that they are adapted to a part of the circumferential line of the section (131,231,331) of the connecting bolt (130,230,330) which bears against the outside of the formed coil (122,222,322). [3] Electric heating device (100,200,300) according to claim 2, characterized by that the part of the connecting bolt (130,230,330) to which the formed coils (122,222,322) are adapted is weakened by profiling. [4] Electric heating device (100,200,300) according to claim 3, characterized by that the formed helix (122,222,322) is formed in such a way that it is complementary to the weakening of the connecting bolt (130,230,330) by the profiling. [5] Electric heating device (100,200,300) according to claim 3 or 4, characterized bythat a part of the circumferential line of the part of the connecting bolt (130,230,330) weakened by profiling corresponds to the outer circumferential line facing the connecting bolt (130,230,330) of an unformed coil (121,221,321) of the electric heating element (120,220,320). [6] Electric heating device (100, 200, 300) according to one of claims 1 to 5, characterized by that the connecting bolt (130,230,330) and the electric heating element (120,220,320) are welded together in the area of ​​the formed coil (121, 221,321). [7] Electric heating device (100,200,300) according to one of claims 1 to 6, characterized by that the connecting bolt (130,230,330) is penetrated by a filling opening (333) for sprinkling electrically insulating material (140,240,340). [8] Method for producing an electric heating device (100,200,300) comprising the steps - providing a tubular metal casing (110, 210, 310), an at least partially coiled electrical heating element (120, 220, 320) and a connecting bolt (130, 230, 330), - establishing an electrically conductive connection between the connecting bolt (130, 230, 330) and the at least partially coiled electrical heating element (120, 220, 320), - introducing the at least partially coiled electrical heating element (120, 220, 320) and the connecting bolt (130, 230, 330) into an interior of the tubular metal casing (110, 210, 310), and - filling the remaining volume inside the tubular metal casing (110, 210, 310) with an electrically insulating material (140, 240, 340), characterized byin that, to produce the electrically conductive connection, at least one coil of the coiled electrical heating element (120,220,320) is deformed and a section (131,231,331) of the connecting bolt (130,230,330) is applied to an outer side of at least one deformed coil (122,222,322) of the coiled section of the electrical heating element (120,220,320). [9] Method according to claim 8, characterized by that the section (131,231,331) of the connecting bolt (130,230,330) which is applied to the outside of at least one formed coil (122,222,322) of the coiled section of the electrical heating element (120,220,320) is welded to the formed coil (122,222,322). [10] Method according to claim 8 or 9, characterized by that the coil is formed by placing it in a die (1,2) and pressing it in with a punch (3,4). [11] Method according to one of claims 8 to 10, characterized bythat the connecting bolt (130,230,330) is provided with a filling opening (333) extending lengthwise through it. [12] Method according to one of claims 8 to 11, characterized by that the section (131,231,331) of the connecting bolt (130,230,330) which is applied to an outer side of at least one formed coil (122,222,322) of the coiled section of the electrical heating element (120,220,320) is weakened by a profiling on its side intended to bear against the formed coil (122,222,322). [13] Method according to claim 12, characterized by that during the profiling material is removed in such a way that a recess complementary to the formed helix (122,222,322) is created in the section (131,231,331) of the connecting bolt (130,230,330) weakened by the profiling.

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