PTC heating element and an electric heating device

Abstract

PTC heating element (2) with two insulating layers (4) provided on one side with a metallic coating (6) and a PTC element (8) arranged between them, the PTC element (8) being provided on opposite main side faces with a metallization (10) which is electrically conductively connected to the coating (6) of one of the insulating layers (4), wherein the metallization (10) provided on one of the main side faces is assigned only to one potential for energizing the PTC element (8) and the metallization (10) provided on the other of the main side faces is assigned only to the other potential for energizing the PTC element (8), and wherein at least one of the insulating layers (4) forms a contact tongue (12) which projects beyond the PTC element (8), characterized by that the insulating layers (4) are bonded to the PTC element (8) and the coating (6) of the insulating layers (4) directly contacts the metallization (10) of the PTC element (8) in an electrically conductive manner, and that a frame segment (14) is pushed onto the insulating layers (4) which has retaining channels (16) for the contact tongue (12) or for a plug tongue element (30) contacted with the contact tongue (12).

Description

[0001] The present invention relates to a PTC heating element and an electric heating device with such a PTC heating element.

[0002] The present invention relates in particular to a PTC heating element having the features outlined in claim 1.

[0003] Such a PTC heating element is known from EP 0 026 457 A2. The PTC heating element known from this prior art has a plastic frame that is injection-molded and to which aluminum oxide plates are attached on opposite main faces of the PTC heating element. These plates are coated with a layer of ductile solder that is electrically conductive and in contact with the PTC element, which is provided within the frame and is metallized on the main faces opposite the aluminum oxide plates. In the prior art, electrical connection tracks protrude through the frame and are soldered to the ductile solder of the aluminum oxide plate. The continuous metallizations provided on the two main faces of the PTC element are each assigned different polarities. Thus, the power flow must pass through the PTC element in the thickness direction to heat it.

[0004] The aforementioned prior art still leaves room for improvement. The present invention aims in particular to provide an improved PTC heating element for use in motor vehicles with improved heat extraction. In motor vehicles, PTC heating elements of the type mentioned above are used, for example, to heat liquids, to heat components or the vehicle interior, or as finned heaters, where they are heated by the air flowing into the passenger compartment. Such auxiliary heaters are usually located downstream of a vehicle's heat exchanger and do not have coolant-carrying pipes. Contact is made by contact elements of different polarities, which are usually insulated within the frame. The electrically conductive tracks leading to the PTC element are also electrically insulated from one another within a frame, which is typically made of plastic.These design features, which are generally known from the prior art, are also preferred further developments of the electrical heating device according to the invention.

[0005] To solve this problem, the present invention proposes a PTC heating element with the features of claim 1.

[0006] In the PTC heating element according to the invention, a metallization is provided on one of the main side faces, which is assigned to only one potential for energizing the PTC element, whereas the other potential is present on the other main side face and the metallization provided there. To heat the PTC element via the power flow, it is therefore necessary that the power flow through the PTC element in the thickness direction. The largest surface of the PTC element is usually considered the main side face. The PTC elements can be round. In this case, the circular surfaces, which are usually parallel to each other, are the main side faces, but not the circumferential surfaces. Preferably, however, the PTC element is cuboid. Two opposing, parallel main side faces are usually connected to each other by a circumferential rim.The perpendicular boundary surfaces have the same thickness, i.e., height extent. This extent is usually considerably smaller, regularly by a factor of 5 or more, than the smallest dimension (width or length) of the main side surfaces.

[0007] In the PTC heating element according to the invention, the current is supplied via the coating provided on the insulating layer. The insulating layer can be a plastic film or a ceramic layer. The insulating layer can also be formed as a hybrid insulating layer consisting of several individually insulating layers, for example, a combination of at least one ceramic plate with at least one film. The ceramic plate typically has the coating.

[0008] According to the invention, the metallization on the PTC element is contacted via the coating of the insulating layer. The metallized insulating layer is bonded to the PTC element. The two are thus bonded together to form a heating cell. The insulating layer typically has a coating applied across its entire inner surface. The coating or metallization on the PTC element is applied by screen printing or sputtering. The semiconducting material of the PTC is located directly beneath the metallization. Thus, in the present invention, heat is conducted directly from the PTC to the metallization applied to it, and from there to the insulating layer and its coating. The insulating layer forms the heat-emitting outer surface of the PTC heating element according to the invention.

[0009] Although adhesive is present between the coating and the metallization, according to the invention, the electrical contact between the coating and the metallization is achieved through direct electrically conductive contact between the coating and the metallization. The coating and the metallization typically have certain roughness peaks that abut each other and partially interlock. Electrical contact between the coating and the metallization is usually established via these contact points. The adhesive is applied in such a way that as many defects and gaps as possible between the PTC element and the metallization applied to it, and between the insulating layer and the coating applied to it, are filled by the adhesive, while at the same time the coating and the metallization are in direct contact with each other.

[0010] To ensure good electrical contact and increase roughness peaks, the PTC element is preferably roughened in the metallization area.

[0011] This creates a PTC element which can have a small layer thickness between the PTC element and the outer surface of the insulation layer, which facilitates heat dissipation from the PTC element.

[0012] The adhesive can be highly thermally conductive. Such an adhesive can fill any remaining gaps within the roughness peaks of the coating and the metallization when they are in direct contact, thereby improving thermal conductivity between the PTC element and the insulating layer, even in the area of ​​the metallization and the coating. To increase the thermal conductivity of the adhesive, it preferably contains a highly thermally conductive filler in the form of thermally conductive particles. The particle size must be selected so that the contact between the roughness peaks of the metallization and the coating is not bridged or impaired by the particles. Thus, the particles are typically very small, depending on the dimensions of the roughness peaks, no larger than 2 to 5 µm. The particles should not exceed 20 µm in size, preferably no larger than 10 µm.Suitable thermally conductive particles include ceramic particles with a thermal conductivity between 20 and 30 W / (m K). These thermally conductive particles are incorporated, for example, into a silicone adhesive. The thermal conductivity of the adhesive (either on its own or as a suspension containing the particles) should be at least 3 W / (m K). The adhesive can be electrically conductive or electrically insulating.

[0013] According to the invention, at least one of the insulating layers forms a contact tongue that projects beyond the PTC element. Preferably, each of the two insulating layers forms corresponding contact tongues. The insulating layers are preferably identical so that identical parts can be used to manufacture the heating cell. According to the invention, a frame segment is slid onto the insulating layers, which has retaining channels for the contact tongue or for a connector tongue element contacted with the contact tongue.

[0014] The contact tongue can be extended at the edge via a frame and provide the external connection of the PTC heating element according to the invention to a power current. The frame typically seals the insulating layers, at least at the edges, so that the medium to be heated cannot reach the current-carrying parts of the heating cell inside the frame. The frame is preferably made of silicone and is preferably connected to the heating cell by overmolding. The contact tongue formed by the insulating layer is usually guided through the frame segment, which is integrated into the frame during overmolding. Accordingly, the frame segment forms a seal at an end face of the heating cell that is projected over by the contact tongues.

[0015] According to an alternative embodiment, the electrical contact of the PTC element on the outside of the frame is achieved by contact tongue elements that are electrically connected to the associated coatings of the insulating layers. These contact tongue elements project beyond the frame at the end. They are preferably formed from stamped sheet metal pieces and preferably bear against the associated insulating layer and the coating provided thereon under preload. The connector tongues can be connected to the coating of the insulating layer, in particular by soldering. However, contact under preload without a corresponding direct connection between the connector tongue element and the associated insulating layer or coating is preferred.Insofar as the following description, which deals with the contacting of the plug tongue elements on the coating of the insulating layer, refers to the insulating layer as such, it is based on the assumption that only the insulating layer, in the form of, for example, a ceramic layer, is suitable to create a support for the separate plug tongue element and that the coating is only sufficiently stable by being applied to the insulating layer.

[0016] For pre-positioning and sealing during overmolding of the frame, a frame segment is preferably provided that forms the retaining channels for the connector tongue elements and is slid onto the insulating layers. Sliding the frame segment onto the insulating layers positions it relative to the heating cell. The frame segment is typically fitted with the connector tongue elements before being slid onto the heating cell. The frame segment preferably has a ventilation opening through which air from inside the heating cell or frame can be displaced during overmolding until the cavity is volumetrically filled and all spaces within the heating cell are filled with the injected plastic. This overmolding bonds the frame segment to the frame and seals it within. The connector tongue element is preferably held in the frame segment by a form-fitting mechanism.For this purpose, the plug tongue element formed by stamping a sheet metal piece usually has a detent projection formed by stamping and bending out of the sheet metal plane, which interacts with a detent opening of the frame segment.

[0017] With a view to ensuring reliable electrical contact, which is not impaired by the injected plastic used to form the frame (usually silicone), a preferred embodiment of the present invention proposes to design the connector tongue element with a contacting projection and an adjacent abutment. The contacting projection is in direct electrical contact with the coating of the insulating layer. The contacting projection can be provided with a certain roughness or applied contact points that allow for point contact between the insulating layer and the coating. The abutment rests against the opposite insulating layer and accordingly presses the contacting projection against its associated insulating layer.The support of the abutment on the opposite insulating layer is preferably achieved by means of an intermediate contact rib made of an insulating material. The contact rib is preferably formed by the frame segment, which extends between the insulating layers in one direction essentially parallel to the longitudinal extent of the connector tongue element. Thus, while the connector tongue element is supported on the opposite insulating layer, it is electrically isolated from the polarity of the opposite insulating layer by the insulating contact rib.

[0018] While previously the connection was described as a connection provided by the insulating layer to which contact tongues are attached, preferably metallic contact tongues, according to an alternative embodiment the insulating layer itself can also form the corresponding contact tongue. For this purpose, the insulating layer is extended beyond the outer enclosing of the insulating material that typically surrounds both insulating layers and the PTC element. Only the relatively short, narrow segment projecting from a base surface of the insulating layer forms a contact tongue that extends beyond the edge of the PTC element, the edge being formed by an insulating material, for example in the form of an insulating bead of adhesive, which completely seals the PTC element and can form a frame as defined in the invention.

[0019] According to its secondary aspect, the present invention proposes an electric heating device, particularly for a motor vehicle, with several PTC heating elements of the type discussed above. The outer surface of the insulating layer facing away from the PTC element forms a free surface for heat transfer to the medium to be heated. This outer surface is exposed within the housing. The outer surface, as well as the sealing strip that completely seals the PTC element and the insulating layers, can be designed according to EP 3 334 244 A1 and / or inserted into the electric heating device and electrically connected in the manner described therein. Alternatively, the outer surface of the insulating layer can also be in at least partial thermally conductive contact with a radiator onto which the medium to be heated flows. Such a configuration is preferably used in an air heater.The heat emitted by the PTC element is thus thermally transferred through the insulating layer to individual heating fins of the radiator element. There, the generated heat is dissipated convectively via the radiator element. While in the first configuration the heat transfer occurs directly from the outer surface of the insulating layer to the medium being heated, in the second configuration the main heat dissipation occurs between the surface of the radiator element and the medium being heated, typically a gas, preferably air.

[0020] The electric heating device can be a high-voltage heating device. In this case, the current-carrying elements of the electric heating device are sealed and insulated from the medium. This sealing is typically achieved by the frame and the insulating layers. The contact tongues, which extend beyond these, are also sealed and extend into a connection chamber, where each individual PTC element is electrically connected to a controller and / or power supply. This connection chamber is usually part of the electric heating device and may contain control components that actuate the PTC elements of the electric heating device. The connection chamber typically houses at least one circuit board for the electrical connection of the various contact tongues.The printed circuit board can also simply group the various contact tongues of the PTC elements into one or more heating circuits of different PTC heating elements. The connection chamber is usually separated from the circulation chamber by a partition. The partition preferably has a female connector for each PTC heating element, into which the PTC heating element is inserted in a fluid-tight manner. For this purpose, the frame typically forms a sealing structure, usually located at the level of the frame segment, which receives internal support from the frame segment, typically made of a resin component.

[0021] Further details and advantages of the present invention will become apparent from the following description in conjunction with the drawing. The drawing shows: Fig. 1 a perspective side view of components of a first embodiment of a PTC heating element; Fig. 2 a view according to Fig. 1 after applying the next layer of insulation; Fig. 3 a view according to in Fig. 1 and Fig. 2 after completion of the frame; Fig. 4 a perspective side view in exploded view of a second embodiment; Fig. 5 a perspective front view of the second embodiment. Fig. 6 a longitudinal sectional view of the upper part of the embodiment according to Fig. 4 and Fig. 7 a plug tongue element of the second embodiment according to the Fig. 4 and Fig. 6.

[0022] The PTC heating element, designated by reference numeral 2 in the figures, has a lower insulating layer 4 provided with a coating 6, onto which a PTC element 8 is bonded. The PTC element 8 has a metallization 10 that covers the entire surface of opposite main faces of the PTC element 8. This metallization 10 is directly electrically connected to the coating 6 of the insulating layer 4. This connection is achieved through contact between the roughness peaks of the coating 6 and the metallization 10.

[0023] As can be seen, the insulating layer 4 forms a contact tongue 12 that projects beyond the PTC element 8. The contact tongue 12 of the first embodiment is shaped like a tongue and can therefore be used as the female contact element of a plug connector. The contact tongue 12 has a rectangular cross-section and a cylindrical shape. The contact tongue 12 is formed from the material of the insulating layer 4 and has the electrically conductive coating 6 on its inwardly facing surface.

[0024] In Fig. 2. A further insulating layer 4 is placed on the PTC element 8. This further insulating layer 4 is designed like the lower insulating layer 4. Both insulating layers are identically shaped. Thus, the contact tongues 12 lie on opposite edges of the PTC heating element in the width direction and are separated from each other by the thickness of the PTC element by the metallization of the PTC element 8 with the insulations 10 on both surfaces and the coatings 6.

[0025] The Fig. Figure 2 further illustrates a frame segment 14, which forms retaining channels 16 for the contact tongues 12. The contact tongues 12 are sealed against the retaining channel. For this purpose, a separate sealing element 18 can be inserted into the respective retaining channel 16 together with the contact tongues. The frame segment 14 also has a degassing opening 20, through which air can escape from the interior of the frame being manufactured, and thus from the injection mold, during overmolding of the heating cell formed by the PTC element 8 and the two insulating layers 4. During injection molding, the frame segment 14 seals the injection mold in the direction of the contact tongues 12 and their free ends.

[0026] The frame produced by overmolding is in Fig. Figure 3 is shown and labelled with reference numeral 22. The frame 22 has, in this case, nozzles 24 of the frame segment 14, which define the retaining channels 16, and surrounding labyrinth seals 26, which are inserted in a sealing manner into the through-openings of a partition wall of an electrical heating device to separate a circulation chamber, in which the PTC heating element is essentially exposed, from a connection chamber, in which the free ends of the contact tongues 12 for electrical connection are exposed. This creates a fluid-tight seal directly through the frame 22.

[0027] The Fig. 4 shows together with the Fig. Figures 5 to 7 show an alternative embodiment. Identical components are identified with the same reference numerals as in the previously discussed embodiment.

[0028] In Fig. In Figure 4, only the insulating layers together with the frame 22 are recognizable as essential parts of the PTC heating element 2. The PTC element is arranged within the frame 22. As in the first embodiment, the insulating layers 4 consist of ceramic plates, in particular aluminum oxide plates, provided with the coating 6. However, the insulating layers 4 of the second embodiment do not have contact tongues formed by the insulating layers. Instead, separate connector tongue elements 30 are provided, which are formed by punching and bending a sheet metal material. The connector tongue elements 30 have an end section that is formed by the original sheet metal without deformation and forms a female connector tongue for plug-in contact within the connection chamber. A locking projection 32 extends from this straight section, which is formed from the sheet metal material by punching and bending and – as Fig. Figure 6 illustrates - engages in a locking opening 33 of the frame segment 14 to connect the plug tongue element 30 to the frame segment 14.

[0029] The Fig. As illustrated in Figure 5, the coating 6 extends beyond the base of the PTC element 8 to form a contact tongue 12 that remains within the frame 22. This contact tongue 12 is somewhat wider than the associated connector tongue element 30, but significantly narrower than the insulating layer 4. The connector tongue element 30 is in electrically conductive contact with this contact tongue 12.

[0030] As the Fig. 6 and Fig. As illustrated in Figure 7, the connector tongue element has a U-shaped contact projection 34 extending from the sheet metal plane towards the associated insulating layer 4, which makes electrical contact with the contact tongue 12 at a point or along a line. The free end of the connector tongue element 30 is formed by a support 36, which rests against a contact rib 38 formed by the frame segment 14 and located between the two insulating layers 4. The contact rib 38 is supported on one side against the insulating layer 4 opposite the one associated with the connector tongue element 30. Opposite the flat contact surface of the contact rib 38 against the insulating layer 4, the support 36 rests against the contact rib 38. Accordingly, the contact projection 34 is crimped against the coating 6 of the insulating layer 4 associated with this connector tongue element 30.This design ensures reliable contact even when the heating cell is overmolded together with the connector tongue elements 30. The plastic, which expands during curing and forms the frame 22, cannot impair the electrical contact between the connector tongue element 30 and the associated insulating layer.

[0031] Fig. Figure 7 illustrates point-like needle-shaped protrusions on the bearing surface of the abutment 36, which penetrate into the support web 38 during assembly and thus ensure improved fastening between the two elements.

[0032] The Fig. 4 and Fig. Figure 5 further illustrates a labyrinth seal 26, which fully surrounds the entire frame segment 14 and thus seals the frame 22 as a whole in a female plug-in socket of the partition wall. Reference symbol list 2 PTC heating elements 4 layers of insulation 6 coating 8 PTC elements 10 Metallization 12 Contact tongue 14 frame segment 16 Holding channel 18 Sealing element 20 Degassing opening 22 frames 24 stubs 26 Labyrinth seal 30 plug tongue element 32 Rastvorsprung 33 Locking opening 34 Contacting protrusion 36 abutments 38 jetty 40 glue

Claims

[1] PTC heating element (2) comprising two insulating layers (4) provided on one side with a metallic coating (6) and a PTC element (8) arranged between them, the PTC element (8) being provided on opposite main side faces with a metallization (10) which is electrically conductively connected to the coating (6) of one of the insulating layers (4), wherein the metallization (10) provided on one of the main side faces is assigned only to one potential for energizing the PTC element (8) and the metallization (10) provided on the other of the main side faces is assigned only to the other potential for energizing the PTC element (8), and wherein at least one of the insulating layers (4) forms a contact tongue (12) which projects beyond the PTC element (8), characterized by , that the insulating layers (4) are bonded to the PTC element (8) and the coating (6) of the insulating layers (4) directly contacts the metallization (10) of the PTC element (8) in an electrically conductive manner, and that a frame segment (14) is pushed onto the insulating layers (4) which has retaining channels (16) for the contact tongue (12) or for a plug tongue element (30) contacted with the contact tongue (12). [2] PTC heating element (2) according to claim 1, characterized by , that the contact tongue (12) is sealed by passing through a frame (22) which seals the insulating layers (4) at the edge. [3] PTC heating element (2) according to claim 1, characterized by , that the contact tongue (12) ends within a frame (22) which seals the insulating layers (4) at the edge and is contacted with a plug tongue element (30) which extends beyond the frame (22) at its end. [4] PTC heating element (2) according to claim 3, characterized by, that the plug tongue element (30) is under preload against the associated insulating layer (4). [5] PTC heating element (2) according to claim 3 or 4, characterized by , that the plug tongue element (30) is positively locked in the frame segment (14). [6] PTC heating element (2) according to one of claims 3 to 5, characterized by , that the plug tongue element (30) is formed by a stamped sheet metal piece which forms a contact projection (34) abutting the associated coating (6) of the insulating layer (4) and adjacent to it a buttress (36) abutting the opposite insulating layer (4) with an intermediate contact web (38) of the frame segment (14). [7] PTC heating element (2) according to any one of the preceding claims, characterized by , that the coating (6) and the metallization (10) of the PTC element (8) are bonded with a highly thermally conductive adhesive (40). [8] PTC heating element (2) according to claim 7, characterized by, that an adhesive containing a filler (40) is provided between the coating (6) and the metallization (10) and that the filler has a maximum particle size of 20 µm, preferably of 10 µm. [9] PTC heating element (2) according to any one of claims 2 to 8, characterized by , that the frame segment (14) is sealed into the frame (22) by overmolding. [10] PTC heating element (2) according to any one of the preceding claims, characterized by , that the metallization (10) and / or the coating (6) and / or the adhesive is applied by means of a screen printing process and / or by means of sputtering. [11] PTC heating element (2) according to any of the preceding claims, characterized by , that the PTC element (8) is roughened in the area of ​​metallization (10). [12] An electric heating device, in particular for a motor vehicle, comprising a housing defining inlet and outlet openings, in which several PTC heating elements (2) are arranged, each having two insulating layers (4) provided on one side with a metallic coating (6) and a PTC element (8) arranged between them, wherein the PTC element (8) is provided on opposite main side surfaces with a metallization (10) which is electrically conductively connected to the coating (6) of one of the insulating layers (4), wherein the metallization (10) provided on one of the main side surfaces is assigned only to one potential for energizing the PTC element (8) and the metallization (10) provided on the other of the main side surfaces is assigned only to the other potential for energizing the PTC element (8),wherein the insulating layers (4) are bonded to the PTC element (8) and the coating (6) of the insulating layers (4) directly contacts the metallization (10) of the PTC element (8) in an electrically conductive manner, and wherein an outer surface facing away from the PTC element (8) is exposed as a free surface for transferring heat to the medium to be heated in the housing or is at least partially in thermally conductive contact with a radiator element upon which the medium to be heated flows.

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