PTC heating element and electric heating device comprising such a

Abstract

PTC heating element (22) for an electric heating device, with frame (44) made of an electrically non-conductive material, which encloses at least one PTC element (30), conductor tracks (38) electrically connected to the PTC element (30) and insulating layers (34) thermally conductive against the opposite main side surface (32) of the PTC element (30), wherein the frame (44) is projected by contact tongues (42) which are electrically conductively connected to the conductor tracks (38) for energizing the PTC element (30) with different polarities, characterized by a film (46) covering the outer surfaces of the insulating layers (34) which, together with the frame (44), is formed by overmolding the PTC element (30), the insulating layers (34) and the conductor tracks (38) with an electrically insulating plastic.

Description

[0001] The present invention relates to a PTC heating element with the features outlined in claim 1. Such a PTC heating element is known from EP 3 334 242 A1.

[0002] The present invention further relates to an electric heating device with at least one PTC heating element arranged in a circulation chamber, comprising a frame that integrates at least one PTC element and the contact tongues supplying current to the PTC element as a single structural unit. The contact tongues project beyond the frame and are electrically connected to conductors of opposite polarity for supplying current to the PTC element. For this purpose, the frame typically incorporates and encloses contact plates, which preferably form the contact tongues as a single unit. The electric heating device according to the invention further comprises a partition separating the circulation chamber from a connection chamber, wherein the contact tongues of the PTC heating element, projecting through the partition, are exposed and electrically connected in the connection chamber.

[0003] An electric heating device of the aforementioned type is known, for example, from EP 2 607 121 A1 or EP 3 334 242 A1.

[0004] In the electric heating device according to EP 2 607 121 A1, several PTC elements are housed in a frame forming the heating element housing. These elements are contacted on opposite main side surfaces by contact plates which are snapped to the frame. At one end, the heating element housing is extended by connection spigots that are integrally formed with the frame and over which Teflon sealing sleeves with a labyrinth seal provided on the outer circumferential surface are fitted. Insulating layers made of a plastic film are applied to the outer surface of the contact plates facing away from the PTC elements.

[0005] Similar PTC heating elements and heating devices of the same type are known from EP 1 253 808 A1 and EP 1 395 098 A1. In this prior art, at least on one side, the contact plate is overmolded together with the insulating layer during the manufacture of the heating element housing, so that only the PTC elements need to be inserted into the opening of the frame and covered on the opposite side by the contact plate and the insulation.

[0006] While such a design represents a simplification in terms of manufacturing compared to the previously described state of the art, the structure remains relatively space-consuming and complex.

[0007] The present invention relates in particular to an electric heating device for a motor vehicle and a PTC heating element of such an electric heating device. Such components have always been designed with weight optimization in mind. Furthermore, due to the high production volumes in the automotive industry, cost-effective manufacturing must be a priority. For electric heating devices with PTC heating elements, designs that enable the best possible and most symmetrical heat dissipation of the heat generated in the PTC element are also preferred. Moreover, especially for motor vehicles that operate at high voltage, i.e., electrically powered vehicles, good insulation of the energized elements of the PTC heating element within the frame is crucial. This is because the PTC heating element in an electrically powered vehicle is typically operated at high voltage.

[0008] The present invention addresses the problem of providing a PTC heating element and an electric heating device with at least one PTC heating element that allows good heat extraction with good insulation of the electrified parts surrounded by the frame.

[0009] To solve this problem, the first aspect of the present invention proposes a PTC heating element having the features of claim 1.

[0010] The PTC heating element has a frame made of an electrically non-conductive material. The frame completely surrounds the PTC element and the insulating layers on either side. Thus, the frame encloses the edges of the insulating layers. The PTC element sits within an opening in the frame. In some cases, the edges of the PTC element may extend into the frame's stiles.

[0011] In the aforementioned prior art according to EP 3 334 242 A1, the plastic material forming the frame surrounds the insulating layers at the edges, so that the insulating layers are completely sealed by the frame. However, the problem there is that a leak can occur between the ceramic insulating layer and the frame member, and between the sealing lip formed by the frame member and the surface of the insulating layer. This allows dirt and moisture to reach the energized elements of the PTC heating element.

[0012] The present invention provides a remedy by proposing to provide the insulating layer with a film on its outer surface, which typically runs strictly parallel to the main side faces of the PTC element and the insulating layer applied to it. In this way, the PTC element is completely encapsulated by the frame and the film. However, the film is a thin-walled film, so that heat can be dissipated perpendicular to the main side face of the PTC element through the insulating layer and through the film, which typically forms the outer surface of the PTC element, without significant thermal resistance.

[0013] The frame is made of plastic, for example silicone or another heat-resistant and elastic plastic material. The frame and film are formed as a single unit by overmolding the PTC element, the conductive traces, and the insulating layers on the opposing main surfaces of the PTC element with the frame material. This overmolding creates a sealed connection between the conductive parts of the PTC heating element and the frame.

[0014] In this process, the film is also formed on the outer surfaces of the insulating layers. In the solution according to the invention, the insulating layer is preferably made of a ceramic, in particular a ceramic plate, preferably made of aluminum oxide. The relatively brittle and thin ceramic can exhibit cracks, so that with the solution according to the invention, the outer surface of the PTC element is protected from the ingress of dirt or moisture by the film and the frame members surrounding the PTC element, even in the event of a leak in the insulating layer. Furthermore, the problem of leakage at the sealing lip formed by the frame material on the surface of the insulating layer, known from the prior art mentioned above, does not occur.

[0015] The film completely covers the insulating layers on both main side surfaces of the frame. It extends fully into the frame's stiles. The film and the frame are made of the same material.

[0016] The film is thin. It typically has a thickness of no more than 100 µm, preferably no more than 50 µm, and particularly preferably no more than 20 µm. A lower limit for the layer thickness is not generally required. What is essential is that the film is applied to the insulating layer across its entire surface and is sealed to the frame. A minimum film thickness in the range of 5 µm to 10 µm is considered sufficient in any case.

[0017] In the present invention, the two conductor tracks are preferably formed from a stamped sheet metal part, which also forms the contact tongue as a single unit. The contact tongues penetrate the frame and project beyond it on the outside. The remaining length of the contact sheets is located within the frame.

[0018] According to a preferred embodiment of the present invention, the frame members surrounding the insulating layers and the PTC element project beyond the film on both sides in the thickness direction of the PTC heating element. The thickness direction extends perpendicular to the main side surface of the PTC element. In other words, the frame members form a complete enclosure of the insulating layer and the PTC element, thus creating a frame opening against which the film is offset inwards on both sides towards the PTC element. Accordingly, the frame members form the chassis or heating element housing of the PTC heating element. They provide the structural integrity of the PTC heating element. The film is designed solely to achieve the desired seal against the main side surface of the PTC element or the insulating layer. The thinner the film, the better the heat dissipation through the film in the thickness direction of the PTC heating element.Thus, heat extraction from the PTC heating element usually occurs primarily, if not exclusively, via the main side surfaces and not the edge surfaces of the PTC element that connect the two main side surfaces.

[0019] According to a preferred embodiment of the present invention, the film is bonded to the insulating layer. This results in improved heat dissipation compared to the configuration in which the PTC heating element, the insulating layers adhering to both sides of its main side surfaces, and the two films are merely layered. However, such a solution still falls within the scope of claim 1. With a view to achieving the best possible heat dissipation through the main side surfaces of the PTC element, it is further preferably bonded to the insulating layer, for example, by gluing or soldering.

[0020] According to a further preferred embodiment of the present invention, a core made of an electrically insulating material is provided, which is penetrated by the contact tongues and received in the frame. The core can be limited to that part of the frame which is penetrated and projected at right angles by the contact tongues. The core typically consists of a rigid plastic, such as PP, PE, or PA. The core is usually surrounded or overmolded by the soft, elastic plastic, which can be formed as a labyrinth seal in the area of ​​the core.

[0021] The core creates a certain resistance when the corresponding frame member is inserted into a female connector recess formed by the partition of the electric heating element. This allows the PTC heating element to be inserted into the partition in a sealed manner and held in place. This prevents the fluid to be heated from entering the connection chamber from the circulation chamber.

[0022] Preferably, the PTC heating element has a fluid-permeable, preferably water-permeable, metal structure that defines an electromagnetic shield around the PTC element and the conductor tracks. The fluid-permeable metal structure allows the fluid to be heated to pass directly to the heat-emitting surface of the PTC heating element. Thus, in contrast to the prior art according to DE 10 2012 013 770 A1, the heat generated by the PTC element does not first have to pass through a closed shielding shell to be transferred to the medium. Preferably, the metal structure surrounds the PTC heating element and the conductor tracks as a cage. The metal structure is at ground potential, whereas the two conductor tracks are at the potential of the power current.

[0023] The PTC heating element according to the invention can be used for heating with air or a liquid heat transfer medium, for example, water. The PTC element can be installed in an air heater so that a layer of corrugated fins, which transfers heat to the air, can be placed directly against the metal structure. Any electrical insulation between the electrically conductive components of the PTC heating element, namely the PTC element and the two conductor tracks, can be provided within the shielding. This insulation prevents the medium to be heated from coming into direct contact with the electrically conductive components of the PTC heating element that carry the power current.

[0024] In the circulation chamber, the PTC heating elements of the present invention are exposed, similar to heating fins. The fluid-permeable metal structure surrounds the heat-emitting surface of the PTC heating element at a close distance, creating a flow gap between the shield and the heat-emitting surface. This flow gap exhibits improved heat transfer compared to previously known solutions, as the fluid flow is swirled by the metal structure, leading to improved heat transfer at the interface, i.e., the heat-emitting surface, of the heat-generating PTC heating element. For this purpose, the shield is preferably partially exposed to the heat-emitting surface, which is thermally connected to the PTC element. The distance is typically between 1.0 and 4.0 millimeters.Such a distance allows the flow in the gap to be adjusted in the best possible way with regard to the desired intensive heat transfer between the heat-emitting surface and the medium to be acquired.

[0025] Various metal structures are suitable for achieving the aforementioned effect of turbulence in the fluid being heated, such as metal mesh, metal woven fabric, or expanded metal sheets. Textile structures containing wholly or partially metallic threads, or even incorporating or being formed by textile threads, are also conceivable. The mesh size between individual metallic elements of the fluid-permeable metal structure is determined by the desired shielding effect. However, the mesh size should not be smaller than 1.0 millimeter. While the individual elements of the metal structure can be placed as close together as desired for the required shielding effect, even tightly woven metal structures are fundamentally fluid-permeable. To ensure effective convective heat dissipation, a minimum mesh size should not be undercut.The minimum distance between adjacent fiber or thread elements or expanded metal structures of the metal frame should not be less than 1.0 millimeter. The optimum for achieving good turbulence to generate turbulent flows at the heat-emitting surface of the PTC element, on the one hand, and good flowability for convective heat dissipation, on the other, is achievable with a mesh size between 1.5 and 2.0 millimeters, preferably between 3 and 10 millimeters. Considering stability and, in particular, processability, as well as the desired mesh size, the wire diameter should be between 0.2 and 0.5 millimeters. Such wire diameters are readily woven and available as standard products. In the wavy area, the wire diameter should be selected to be between 0.4 and 1 millimeter.

[0026] According to its second aspect, the present invention provides an electric heating device with the features of claim 9. This device comprises at least one PTC heating element according to any one of claims 1 to 8. As previously discussed, the PTC heating element can be inserted into and / or held in the partition in a sealing manner similar to a male plug connector. For this purpose, the PTC heating element is typically provided, at least in the area of ​​the plug connection, with sealing lips or lamellae that interact sealingly with a female plug connector formed by the partition.

[0027] Further details and advantages of the present invention will become apparent from the following description of exemplary embodiments in conjunction with the drawing. The drawing shows: Fig. 1 a perspective side view of an embodiment of an electric heating device; Fig. 2 a perspective side view of the embodiment according to Fig. 1 after connecting the PTC heating elements; Fig. 3 a perspective side view of parts of a PTC heating element; Fig. 4 a partially broken perspective side view of the PTC heating element; Fig. 5 a perspective cross-sectional view of the PTC heating element; Fig. 6 a perspective, partially cut-away side view of a second embodiment of a PTC heating element; Fig. 7 the detail VII according to Fig. 6 in enlarged view and Fig. 8 a sectional view along line VIII-VIII according to Fig. 6.

[0028] Fig. Figure 1 shows a perspective top view of a housing, designated by reference numeral 2, of an electric heating device designed as a water heater. The housing 2 has a housing tray element 4 made of plastic. The housing 2 forms an inlet nozzle 6 and an outlet nozzle 8, which are formed integrally with the housing tray element 4. The nozzles 6 and 8 are designed as hose connection nozzles and form an inlet opening 10 and an outlet opening 12, respectively, to a circulation chamber designated by reference numeral 14.

[0029] The circulation chamber 14 is separated from a connection chamber 18 by a plastic partition 16 and sealed against it. The partition 16 forms female plug-in receptacles 20 for PTC heating elements 22, which are inserted into the female plug-in receptacles 20 in a sealing manner and supported on a base 24 of the housing tray element 4.

[0030] The Fig. 3, Fig. 4 to Fig. Figure 5 illustrates details of the PTC heating element 22, which in this case comprises only a PTC element 30, the insulating layer 34 of which is covered on its opposing main side surfaces 32. The insulating layer 34 is, in this case, a ceramic plate made of aluminum oxide. However, it can also be applied as a coating to the PTC element 30 or be implemented as a combination of a coating with a single- or multi-layer insulating layer. The PTC element 30 is designed as a plate with a width B and a length L that are at least 10 times greater than the thickness D, which corresponds to the distance between the two main side surfaces 32.Extending essentially in the direction of length L, sheet metal strips 38 are provided on opposing end faces 36. These strips are bonded to the PTC element 30 and electrically connected to a surface metallization of the PTC element 30, which can be applied as a layer by means of PVD or CVD. Each sheet metal strip 38 consists of a relatively narrow contact rib 40 and a contact tongue 42 that widens in the direction of width B relative to the contact rib 40.

[0031] The contact bridges 40 form the conductive paths to the PTC element 30 and are electrically connected to the metallization of the PTC element 30. The sheet metal strip 38 is designed so that it does not extend beyond the main side surfaces 32 of the PTC element 30 at any point. As the Fig. 4 and Fig. As can be seen in Figure 5, the insulating layers 34 project laterally beyond the PTC element 30. Accordingly, the insulating layers 34 have a base area that is larger than the base area of ​​the main side surfaces 32 of the PTC element 30. Consequently, the outer edges of the insulating layers 34 accommodate the contact bridge 40 between them on both sides (see Figure 5). Fig. 5) The insulating layer 34 is bonded to the PTC element 30. The insulating layer 34 rests directly on the PTC element. Thus, one of the insulating layers 34 directly contacts the corresponding main side surface 32 of the PTC element 30.

[0032] Alternatively, according to the invention, the sheet metal strip 38 can be applied wholly or partially as a contact plate to the main side surface 32. However, with regard to good heat dissipation perpendicular to the main side surface 32, the variant discussed in connection with the exemplary embodiment is preferable.

[0033] The sheet metal strip 38 is predominantly enclosed within a frame 44 made of an insulating material, which surrounds the PTC element 30 on all four sides. The frame 44 has four frame members 45 for this purpose. This frame 44 completely encloses the circumferential edges of the insulating layers 34. The contact webs 40 are also sealed within the material forming the frame 44. The frame 44 is formed by overmolding with an elastomeric material, in particular silicone.

[0034] In the finished PTC heating element 22, only the contact tongues 42 protrude beyond the frame 44 on one end face. All other functional parts of the PTC heating element 22, which serve for heat generation and current conduction, are enclosed within the frame 44.

[0035] How in particular the Fig. 4 and Fig. As can be seen in Figure 5, the frame 44 forms a single film 46 which is arranged parallel to the insulating layer 34 and is bonded to it in a material-bonded manner. On both main side surfaces, the insulating layers 34 provided there are each completely covered by the film 46. Each film 46 extends completely into the frame 44. The film 46 has a thickness, i.e., its extent perpendicular to the main side surface 32, of no more than 50 µm, preferably no more than 20 µm.

[0036] How in particular Fig. Figure 5 illustrates that the PTC element 30, the insulating layer 34, and the film 46 are located behind a frame opening, marked with reference numeral 48 and formed by the frame 44. The frame 44, i.e., the frame members 45, are accordingly thicker than the sum of the thicknesses of the PTC element 30, the two insulating layers 34, and the two layers of the film 46.

[0037] In the present case, there is almost no overlap of the frame 44 with the main side surfaces 32 of the PTC element 30, so that the latter is covered by the film 46 and the insulating layer 34 in the frame openings 46 to approximately 100% of its main side surfaces 32.

[0038] The frame 44 forms a sealing collar 50, which is provided with sealing lips 52 arranged conically towards the free end of the contact tongues 42. In this case, three of these sealing lips 52 are arranged one behind the other in the longitudinal direction of the contact tongue 42, forming a labyrinth seal. The sealing collar 50, made of a soft, elastic plastic, is injection-molded around a core 54 made of an electrically insulating plastic. This core 54 has openings (not shown) for the passage of the widened sections of the sheet metal strips 38 and serves for the pre-assembly of the sheet metal strips 38. This core 54 increases the pressing force of the sealing collar 50 when it is inserted into the female connector receptacles 20.

[0039] The sealing collar 50 is limited on the underside by a circumferential annular stop 56, which, after the insertion of the PTC heating element 22 into the female plug-in element receptacle 44, abuts a sealing bead formed by the partition wall 16.

[0040] The Fig. Figure 2 illustrates the electrical connection of the PTC heating elements 22. For the electrical connection, 18 metal sheets are provided in the connection chamber as busbars 60, 62, 64. These busbars have contact projections 66 formed by stamping and bending, which bear against the contact tongues 42 under elastic preload and make contact with them. The contact projections 66 extend into receiving openings 68, which are recessed in the metal strips of the busbars 60, 62, 64. Similarly, connection tongues marked with reference numeral 70 are connected and are contacted with a populated circuit board, which is housed in a control enclosure 72. The busbar 62 is connected directly via the terminal 70, whereas the busbars 60, 64 are terminated via a power transistor 74, which is contacted with stamped leads 76 that are electrically connected to the corresponding terminals 70.

[0041] The control housing 72 has a connector housing 78 for the power current and a connector housing 80 for connecting cables for the control signals.

[0042] The Fig. 6, Fig. 7 to Fig. Figure 8 shows an alternative embodiment of a PTC heating element. Identical components are designated with the same reference numerals as in the previously discussed embodiment. This embodiment has a frame 44, which also forms a sealing collar 50 integrally molded onto it. This collar can be inserted into the housing 2 in a sealing manner as described in DE 10 2016 224 296 A3. As can be seen, the plastic material defining the outer surfaces of the frame 44 is injection-molded around a retaining frame 82 during the injection molding of the frame 44. This retaining frame 82 surrounds a flat metal structure 84 at its edges, which forms an electromagnetic shield. The retaining frame 82 is first connected to the metal structure 84 and placed into the injection mold as an insert. The retaining frame 82 forms the inner circumference of the cavity for the formation of the frame 44.

[0043] The contact tongues 42 are formed in this case by elongated sheet metal strips 38, which bear against the end face of the PTC element 39 and are energized. The main heat-dissipating side surface 32 of the PTC element 30 is covered on the outside with the insulating system 34 and the film 46, which are sealed into the material of the heating element housing 2 at the edges.

[0044] The sealing collar 50 is penetrated by a contact plate 86, which is made of sheet metal by stamping and bending and forms a contact section 88 projecting on both sides towards the metal structure 84, which is electrically connected to the metal structure 84. By connecting a shielding connection lug 90 formed by the contact plate 86, it is possible to electrically connect the metal structure 84, provided on a main side surface 32, to a shielding pool.

[0045] The in the Fig. 6, Fig. 7 to Fig.The embodiment shown in Figure 8 has two identically designed contact sections 88, each of which is connected to the respective metal structure 84 provided there as a flat metal mesh on the opposite main side surfaces 32, and of which only the upper contact section 88 is shown. Reference symbol list 2 cases 4 Housing tray element 6 inlet nozzles 8 outlet nozzles 10 Entrance opening 12 Outlet opening 14 Circulation chamber 16 Partition wall 18 Connection chamber 20 female plug-in element holders 22 PTC heating element 24 floor 30 PTC elements 32 Main page area 34 Insulation layer 36 Front surface 38 strips of sheet metal 40 contact bridge 42 Contact tongue 44 frames 45 frame rail 46 Film 48 Frame opening 50 sealing collars 52 Sealing lip 54 core 56 stops 60 busbar 62 busbar 64 busbar 66 contact advantage 68 Inlet opening 70 Connecting tongue 72 Control housings 74 Power transistor 76 supply lines 78 Connector housings Power current 80 connector housings control signals 82 mounting frames 84 Metal structure 86 contact elements 88 Contact point 90 Shielding connection tab B Width of the PTC element L Length of the PTC element D Thickness of the PTC element

Claims

[1] PTC heating element (22) for an electric heating device, with frame (44) made of an electrically non-conductive material, which encloses at least one PTC element (30), conductor tracks (38) electrically connected to the PTC element (30) and insulating layers (34) thermally conductive against the opposite main side surface (32) of the PTC element (30), wherein the frame (44) is projected by contact tongues (42) which are electrically connected to the conductor tracks (38) for energizing the PTC element (30) with different polarities, characterized by a film (46) covering the outer surfaces of the insulating layers (34), which together with the frame (44) is formed by overmolding the PTC element (30), the insulating layers (34) and the conductor tracks (38) with an electrically insulating plastic. [2] PCT heating element (22) according to claim 1, characterized by , that the frame (44) and the film (46) are designed as a structural unit. [3] PTC heating element (22) according to one of the preceding claims, characterized by , that the frame (44) has frame members (45) that completely surround the insulating layer (42) and the PTC element (30) and extend outwards beyond the film (46) on both sides in the thickness direction of the PTC heating element (30). [4] PTC heating element (22) according to one of the preceding claims, characterized by that the frame (44) and the film (46) are made of a soft elastic plastic, in particular silicone. [5] PTC heating element (22) according to one of the preceding claims, characterized by , that the film (46) is bonded to the insulating layer (42) in a materially bonded manner. [6] PTC heating element (22) according to one of the preceding claims, characterized by a core (54) made of an electrically insulating material, which is penetrated by the contact tongues (42) and is received in the frame (44). [7] PTC heating element (22) according to one of the preceding claims, characterized byan electromagnetic shield formed from a fluid-permeable metal structure (84) that surrounds the PTC element (30) and the conductor track (40). [8] PTC heating element (22) according to claim 7, characterized by at least one electrically conductive shielding connection tab (90) connected to the shielding, which extends parallel to the contact tongues (42) and protrudes above the shielding. [9] Electric heating device with at least one PTC heating element (22) arranged in a circulation chamber (14) with a frame (44) which integrates at least one PTC element (30) and contact tongues (42) supplying current to the PTC element (30) as a structural unit and is overlaid by contact tongues (42) electrically connected to the PTC element (30), and with a partition (16) which separates the circulation chamber (14) from a connection chamber (18) in which the contact tongues (42) of the PTC element (22) projecting through the partition (16) are exposed and electrically connected, characterized by , that the PTC heating element (22) is designed according to one of claims 1 to 8. [10] Electric heating device according to claim 9, characterized by , that the PTC heating element (22) is inserted into the partition wall (16) in a sealing manner.

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