Electric heating device and method for its manufacture

Abstract

The present invention relates to an electric heating device (2), particularly for a motor vehicle, comprising a housing (20) that is at least partially electrically conductive and has a circumferential groove (36) on its end face, and a sheet metal cover (34) that closes the housing (20) and engages with a circumferential rim (42) in the groove (44), which contains a sealant (74). To increase the sealing of the housing while reliably shielding electrical components housed in the housing, the circumferential rim (42) has a first leg (54) that engages in the groove (44) and a second leg (56) extending from it, which is electrically conductively contacted with one of the boundary walls (48) of the groove (44). In the method for manufacturing the electric heating device (2), the circumferential rim (42) is first inserted into the groove (44), followed by a sealant (74) that seals the groove and hardens within the groove (44).

Description

The present invention relates to an electric heating device and a method for its manufacture. An electric heating device known from DE 20 2020 000 689 U1 is considered to be of the generic type. This prior art discloses an electric heating device with a housing that is at least partially electrically conductive and a cover made of sheet metal, which closes the housing and covers the housing opening. The present invention relates in particular to an electric heating device in which the housing comprises a heating chamber with inlet and outlet openings for a fluid to be heated, a heating element thermally connected to the heating chamber (which can be designed as a thick-film heating element or as a PTC heating element), and an electrical connection in a connection chamber. A partition typically separates the heating chamber from the connection chamber in a fluid-tight manner. In the electrical heating device according to the invention, several PTC heating elements can be accommodated in the housing. Typically, several PTC heating elements are electrically connected in the connection chamber, optionally grouped into heating circuits. For this purpose, a circuit board can be provided in the connection chamber, which assigns different PTC heating elements to different heating circuits. Furthermore, a populated circuit board can be provided in the connection chamber, which is a central component of a control device that controls the heating elements to adjust the power output of the electrical heating device appropriately. The heating system is usually located on one side of the partition wall, and a control system is usually located on the other side. These details are also known from DE 20 2020 000 689 U1. The features mentioned above can also be preferred features of the electrical heating device according to the invention. With certain electric heating devices, especially when the PTC heating element is switched on, a problem arises: interference with other components in the vicinity is caused by electromagnetic waves. These components can include, for example, electronic components or on-board entertainment components in a vehicle. Therefore, it is known to design the housing to be at least partially electrically conductive for shielding purposes. This electrical contact is implemented not only for EMC reasons, but especially for high-voltage safety (grounding). Otherwise, an electrical potential could be present on the cover, which would not be detected by the insulation monitoring system. Specifically, the connection chamber and the control unit located within it are housed in a metallic enclosure.Parts of the housing surrounding or defining the heating chamber can be made of an electrically non-conductive material. Plastic is preferred for weight reduction. The requirements for an electric heating device in a motor vehicle, in particular, include several additional considerations. The electric heating device must not only be as lightweight as possible, but its electrical components must also be reliably protected from the environment. This is especially important for electric heating devices used in electric vehicles, which are typically operated at high voltage. Moisture and / or dirt, which can penetrate, for example, the connection chamber, can impair the desired electrical insulation of individual components. Dirty or moist surfaces can promote the formation of leakage currents. The present invention addresses the problem of providing an electric heating device and a method for its manufacture that enable the best possible sealing of the housing while reliably shielding electrical components contained in the housing. To solve this problem, the present invention provides an electric heating device of the type mentioned above, in which the housing has a circumferential groove on one end face. A circumferential groove in this sense is understood to be a groove that extends around the entire circumference. It is not necessary for the groove to have the same depth over its entire circumference. A sealant is introduced into the groove to seal it completely. The cover has a circumferential rim that engages in the groove such that the rim of the cover is immersed in the sealant all the way around. This results in a completely fluid-tight seal of the cover in the area of ​​the groove. A suitable sealant is, in particular, an adhesive, especially a curing adhesive that remains elastic even after curing. For example, a silicone adhesive can be used. Due to its adhesive properties, the adhesive can help the lid adhere to the housing. However, the adhesive can also simply act as a sealant, preventing the penetration of dirt and / or moisture in the groove area by encasing and bonding the surrounding edge. The lid is preferably made of sheet metal. This wording indicates that the lid material has a wall thickness predetermined by the sheet metal material. The lid is preferably produced by stamping and bending or other forming operations such that a circumferential rim and / or additional contact tabs on the rim project substantially perpendicularly from the otherwise essentially flat covering surface of the lid. The adhesive is preferably applied volumetrically into the groove. It is generally applied after the cover has been joined to the housing, usually by pressing it into place. This also protects the contact points for the electrical connection between the cover and the housing from external influences. The adhesive is preferably applied only to a gap between an inner surface defining the groove and the surrounding edge of the cover. This allows the amount of adhesive required to be kept to a minimum. Corrosion at the contact point is not a concern due to the adhesive seal, ensuring reliable electrical contact between the cover and the housing even over extended periods of use. Furthermore, the connection between the cover and the housing is improved because the cover or contact tab is not only mechanically clamped in the groove, but also secured by the adhesive properties of the partially cured adhesive. The adhesive typically extends vertically along the groove to a free outer end of the lid's rim, which, according to the present invention, is formed by an outwardly bent outer leg projecting outwards from an inner leg of the rim. Depending on the product requirements, the fill level can thus be flexibly varied and adjusted. The surrounding edge has a first leg that engages in the groove and a second leg extending from it. The first leg typically originates from a cover surface; the second leg is connected to the first leg via a bend. The first and second legs are generally arranged in a V-shape relative to each other, with the bend located opposite a groove bottom and usually forming the deepest engagement in the groove. The first leg is usually an inner leg, the second leg is usually an outer leg. The first leg interacts with an inner boundary wall of the groove; the second leg interacts with an outer boundary wall of the groove. The terms "outer" and "inner" preferably refer to the corresponding areas relative to the interior of the housing. The outer leg is therefore typically located further from the interior of the housing than an inner leg of the rim. However, the outer leg and its corresponding outer boundary wall can also be formed by the areas of the groove and rim that are closer to the interior of the housing. In this variant, the inner leg and its corresponding inner boundary wall are located further from the interior of the housing than the outer leg and its outer boundary wall. One leg, preferably the outer leg, makes electrically conductive contact with the corresponding boundary wall of the groove, for which purpose the outer leg is usually applied with preload against the outer boundary wall. This contact point should be covered by the sealant or adhesive to ensure optimal corrosion protection. The inner leg of the edge is located within the groove and is typically supported by the inner boundary wall of the groove. The housing forming the groove is preferably a die-cast part. The circumferential rim according to the present invention has two legs that form a bending region between them. In an unstressed state, the maximum distance between the two legs, preferably the inner surface of the inner leg and the outermost surface of the outer leg, is greater than the width of the groove. One leg, preferably the outer leg, typically projects obliquely outwards and upwards from the curved bending region in the unstressed state. Thus, the circumferential rim preferably has a funnel-shaped geometry that widens outwards in cross-section. This results in the rim being elastically clamped within the groove when it is inserted. Typically, an assembly tool is inserted from above into the bending area and the upward-facing circumferential rim, pressing the bending area and thus the circumferential rim completely into the circumferential groove of the housing. The bending area allows for increased bending, particularly of the outer leg, which usually engages with the inner outer boundary wall via a sharp-edged end section and interlocks against it. This ensures that the cover is securely held to the housing. The elastic preload between the outer and inner legs reinforces this interlocking effect. This elastic preload is generated and maintained particularly in the bending area. The bending area can be reinforced by embossing the sheet metal, thereby increasing its strength and thus the preload force holding the rim in the groove.The embossing is distributed circumferentially, preferably directly next to a hook formed by the two legs and / or within such a hook. It is understood that the aforementioned preload is preferably counteracted by the inner leg and its support against the inner boundary wall of the groove. This wall typically extends in the vertical direction of the groove. While the outer boundary wall usually has a horizontally flat inner surface, against which the outermost end section slides when the circumferential edge is inserted into the groove, the inner boundary wall can be thinner in its upper region than in its lower region, with a certain sloping surface between the two regions. This design facilitates the insertion of the circumferential groove under preload and increases the interlocking at the end of the assembly movement by narrowing the groove on the one hand and by creating a thickened inner wall that offers increased resistance to the elastic tension of the circumferential edge in the groove. To reduce the mechanical stress on the housing, a preferred embodiment of the present invention proposes to provide the circumferential edge of the groove only in sections on the outer boundary wall. Accordingly, elastic interlocking occurs only in sections, thus reducing the mechanical stress on the walls of the housing that define the groove. Additionally, the housing can incorporate webs extending through the groove, which are provided in sections and connect the outer boundary wall of the groove to the inner boundary wall, thus improving the groove's strength. These webs allow for a relatively thin-walled design of the groove's boundary walls despite the elastic tension of the circumferential edge within the groove, as the webs brace and stiffen the groove transversely. The webs typically project vertically above the groove's base by an amount that is at least 40 percent, preferably at least 50 percent, of the groove's height. The groove's height is determined by the distance between the groove's base and the groove's shallowest boundary wall. The groove's boundary walls can have the same height on both the inner and outer sides.With a view to improved electrical contact and sealing, as well as a compact design of the present invention, it is preferable to make the outer boundary wall higher than the inner boundary wall. The cover is preferably designed to rest against the inner boundary wall. Furthermore, this design allows the cover surface, which essentially covers the housing, to be positioned no higher than the upper edge of the outer boundary wall. The outer boundary wall can extend beyond the cover surface, thus enabling the electric heating device to be supported by its end face of the outer leg during transport after manufacturing. Consequently, the electric heating device does not need to be supported by the relatively thin-walled cover surface during transport. The cover preferably rests on top of the inner boundary wall. At the level of the webs penetrating the groove, the circumferential edge preferably has an inner leg truncated at the top and terminates there. Thus, at the level of the webs, there is no outer leg interacting with the outer boundary wall, resulting in mechanical relief of the outer boundary wall. The leg truncated at the level of, or possibly slightly above, the aforementioned inclined surface, can terminate at the inner boundary wall. The leg truncated at the level of, or possibly slightly above, the web it spans can be wider in the direction of the groove. A leg truncated at the top can also project beyond two webs positioned at a distance from each other. According to the inventive method, the circumferential edge is first inserted into the groove, and only then is the sealant, for example in the form of an adhesive, introduced, usually in liquid form, preferably metered, to seal the circumferential edge in the groove. Metering is typically volumetric, ensuring that the sealant does not overflow the boundaries of the groove. The lid resting on the inner boundary wall also prevents the sealant from unwantedly penetrating into the interior of the housing. The amount of adhesive is preferably adjusted so that it does not fill the entire groove, but a smaller volume of a gap that is formed between the outer wall of the groove and the inner leg. Further details and advantages of the present invention will become apparent from the following description of an exemplary embodiment in conjunction with the drawing. In this drawing: Fig. 1 shows a perspective exploded view of an exemplary embodiment of an electric heating device; Fig. 2 shows a longitudinal sectional view of a heating device using the example of a PTC heating device; Fig. 3 shows a perspective top view of a cover mounted on the housing; Fig. 4 shows a perspective cross-sectional view of the groove and the edge of the cover for the example according to Fig. 3; and Fig. 5 shows an enlarged cross-sectional view of the groove and the edge of the cover for the example according to Figs. 3 and 4. Fig. 1 shows an embodiment of an electric heating device 2 with a multi-part heater housing comprising a lower housing part 4 made of plastic and an upper housing part 6 formed in one piece from metal by means of die casting. The lower housing part 4 is trough-shaped and encloses a heating chamber 8, forming inlet and outlet ports 10 that communicate with the heating chamber 8. These inlet and outlet ports 10 are molded as a single piece with the lower housing part 4 by injection molding. Several heating elements 12 are shown between the upper housing part 6 and the lower housing part 4. As illustrated in Fig. 2, these heating devices 12 each have at least one PTC element 14, against which contact elements 16.1; 16.2 bear, forming contact tongues 18 that project beyond a metallic housing 20. The PTC element 14 is received in a frame 22 and between the contact elements 16.1; 16.2. Insulating layers 26 are provided between the metallic housing 20 and a heating cell 24 formed by the two contact elements 16.1; 16.2 and the PTC element 14. The heating devices 12 are held by plug-in connections in a designated receptacle 28 of a partition 30 of the upper housing part 6 and are electrically connected in a connection chamber 32, which accommodates a control unit 34 controlling the heating devices 12, the essential component of which is a printed circuit board 36. Details of this embodiment are described in EP 3 334 242 A1, which originates from the applicant. The upper housing part 6 is sealed and electrically connected to a cover 38, the cover surface 40 of which covers the connection chamber 32 and is essentially flat. The upper housing part 6 thus exemplarily forms the housing according to claim 1 and is hereinafter referred to simply as housing 6. As illustrated in Figures 3, 4 to 5, the cover 38 has a circumferential rim 42 that engages in a circumferential groove 44 of the housing 6. The groove 44 is bounded internally by an inner boundary wall 46 and externally by an outer boundary wall 48 of the housing 6 and has a groove base 50 provided between them, which is partially penetrated by webs 52 in the circumferential direction of the groove 44. The circumferential rim 42 has an inner leg 54 that extends substantially parallel to the inner boundary wall 46, and an outer leg 56 that is directed obliquely outwards and away from the groove base 50 by bending the sheet metal material forming the cover 38. At the level of the webs 52, the circumferential edge 42 ends with an inner leg stub 58. As shown in Figs. 4 and 5, the inner boundary wall 46 has a slightly stepped profile with a widened lower area 62, an upper area 64 above it of lesser thickness, and an intermediate inclined surface 66, which is located in the area of ​​the free end 60 and between the webs 52 associated with the leg stub 58, so that sealant subsequently introduced into the groove 44 can also reach between the inner leg 54 and the inner boundary wall 46 and act as a seal there. A bending area of ​​the circumferential rim 62, designated by reference numeral 68, is arranged vertically at a distance from the base of the groove 50, allowing the circumferential rim 42 to move freely and elastically within the bending area 68. Reference numeral 69 designates an embossing applied externally to the bending area 68, which stiffens the inner leg 54 relative to the outer leg 56. This provides sufficient clamping force to secure the cover 38 in the groove 44. In the end position shown in Fig. 4, the front tip, or optionally a slightly rounded end (made by stamping), of an outermost end section 70 of the outer leg 56 engages with the outer boundary wall 48, thus securing the end position of the circumferential rim 42 and therefore the cover 38 relative to the housing 6. As Figures 4 and 5 illustrate, the inner boundary wall 46 is less high than the outer boundary wall 58. The joined cover 38 shown in Figures 4 and 5 rests with its supporting section, marked with reference numeral 72, on the free end of the inner boundary wall 64. The cover surface 40 is lower overall than the upper free end of the outer boundary wall 48. During assembly, the circumferential rim 42 of the cover 38 is positioned over the groove 44. A tool (not shown) engages the bending area 68 of the circumferential rim 42 and presses the cover 38 into the groove 44. This further bends the bending area 68, while the outer leg 56, which is initially prepared with an excess width relative to the groove 44, projects outwards beyond it, elastically rests against the inner boundary wall 46, and slides along it. As the insertion movement progresses, with the inner leg 54 bearing against the inner boundary wall 46, the outer convex curvature of the bending area 68 meets the inclined surface 66, further increasing the elastic tension of the circumferential rim 42. The insertion movement or pressing process is completed when the cover 38 with its resting section 72 is placed against the inner boundary wall 46. A sealant, for example an adhesive, is then applied volumetrically and circumferentially to the circumferential groove 44 between the inner leg 54 and the inner boundary wall 46. The adhesive is designated by reference numeral 74 in Fig. 4. The fill level of the adhesive 74 is above the inclined surface 66. In the embodiment shown here, the adhesive 74 extends within the groove 44 approximately to the supporting section 72. The present invention requires a certain groove depth. Due to the sealant 74 completely or partially filling the groove 44, an extended creepage distance results. During manufacturing or storage, the completed electric heating device 2 can be placed on the outer boundary wall 48, as this wall extends beyond the cover 38. This prevents the circumferential edge 42 from moving relative to the groove 44, which could impair the bond between the circumferential edge 42 and the sealant 74, and thus the seal. Furthermore, the supporting section 72 rests on the inner boundary wall 46. These webs 52 are distributed circumferentially, providing support for the cover 38 around the groove 44. This also protects the bond with the sealant 74 and increases the seal.The outer legs 56 lie between the inner leg stubs 58 in the circumferential direction, section by section, against the outer boundary wall 48 and thus interlock. The elastic tension of the circumferential edge 42 in the groove 44 secures the connection between the cover 38 and the housing 6. Reference symbol list 2 Heating device 4 Lower housing part 6 Upper housing part 8 Heating chamber 10 Inlet and outlet nozzles 12 Heating elements 14 PTC element 16 Contact element 16.1 Lower contact element 16.2 Upper contact element 18 Contact tongue 20 Housing 22 Frame 24 Heating cell 26 Insulation layer 28 Receptacle 30 Partition 32 Connection chamber 34 Control unit 36 ​​Circuit board 38 Cover 40 Cover surface 42 Circumferential edge 44 Groove 46 Inner boundary wall 48 Outer boundary wall 50 Groove base 52 Web 54 Inner leg 56 Outer leg 58 Inner leg stub 60 Free end 62 Lower area 64 Upper area 66 Slanted surface 68 Bending area 70 Outermost end area 72 Contact section 74 Adhesive / Sealant QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature DE 20 2020 000 689 U1 [0001, 0005] EP 3 334 242 A1

[0033]

Claims

Electric heating device (2), in particular for a motor vehicle, with a housing (6) that is at least partially electrically conductive, on the end face of which a circumferential groove (44) is provided, and a cover (38) made of sheet metal, which closes the housing (6) and engages with a circumferential edge (42) in the groove (44) which contains a sealing agent (74), characterized in that the circumferential edge (42) has a first leg (54) engaging in the groove (44) and a second leg (56) extending from it bent over. Electric heating device (2) according to claim 1, characterized in that at least one of the legs (54, 56) is electrically conductively contacted with a boundary wall (48) of the groove (44). Electric heating device (2) according to claim 1 or 2, characterized in that at least one of the legs (56) is interlocked with at least one of the associated boundary walls (48), preferably an outer leg (56) with an outer boundary wall (48). Electric heating device (2) according to one of the preceding claims, characterized in that at least one of the legs (56) is applied under elastic preload to at least one of the associated boundary walls (48), preferably an outer leg (56) is applied under elastic preload to an outer boundary wall (48). Electric heating device (2) according to claim 4, characterized in that the preload is counteracted by supporting one leg (54) against one of the boundary walls (48), preferably an inner leg (54) against an inner boundary wall (46) of the groove (44). Electric heating device (2) according to one of the preceding claims, characterized in that the circumferential edge (42) only partially abuts one of the boundary walls (48), preferably the outer boundary wall (48). Electric heating device (2) according to one of the preceding claims, characterized in that the housing (6) forms webs (52) penetrating the groove (44) and that the circumferential edge (42) terminates at the level of the webs (52) with an inner leg stub (58). Electric heating device (2) according to one of the preceding claims, characterized in that the outer boundary wall (48) projects beyond the inner boundary wall (46) and that the cover (38) rests on the inner boundary wall (46). Electric heating device (2) according to one of the preceding claims, characterized in that a cover surface (40) covering the housing (6) projects beyond a section (72) of the cover (38) resting on the inner boundary wall (46). Method for manufacturing an electric heating device (2) with a housing (6) that is at least partially electrically conductive, on the end face of which a circumferential groove (44) is provided, and a cover (38) made of sheet metal, which closes the housing (6) and engages in the groove (44) with a circumferential edge (42), characterized in that the circumferential edge (42) is inserted into the groove (44) and then a sealing sealant (74) is inserted into the groove (44), which hardens in the groove (44).

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