PTC heating device

Abstract

PTC heating device with a PTC element (22) and a frame element (14) forming a recess (20) circumferentially enclosing the PTC element (22), which is covered on both sides with electrically insulating plates (2) which cooperate with the frame element (14) to seal the PTC element (22) in the recess (20), characterized in that the insulating plates (2) are each provided with a metallization (4) which is electrically conductively connected to the PTC element (22) and electrically conductively connected to an associated contact surface (24) provided on the outer surface of the electrically insulating plate (2) for the electrical connection of the PTC heating device.

Description

[0001] The present invention relates to a PTC heating device with a PTC element and a frame element which forms a recess surrounding the PTC element, which is covered on both sides with electrically insulating plates which cooperate with the frame element to seal the PTC element in the recess.

[0002] Such a PTC heating device is known from EP 1 921 896 A1.

[0003] In both the previously known PTC heating device and the present invention, the frame element is typically made of an electrically insulating plastic material. The frame element is also referred to as the positioning frame. It completely surrounds the PTC element. The PTC element is slightly thicker than the frame element, so that the main side surface of the PTC element projects beyond the frame element. The main side surfaces of the PTC element are those surfaces of the regularly cuboidal PTC element through which heat is extracted from the PTC element and which are at least five times larger than the other surfaces, i.e., the surface(s) extending in the circumferential direction. In the present invention, the electrical contact between the PTC element and the power current is made at these main side surfaces.

[0004] The PTC element is sealed within the recess of the frame element. The opposing electrically insulating plates are accordingly connected to the frame element in such a way that the recess is encapsulated from the environment.

[0005] In the above-mentioned state of the art, the PTC element is energized via contact plates that extend laterally beyond the frame element and form connecting tabs for the plug-in connection of the PTC heating element. Particular attention must be paid to ensuring adequate sealing at this point to prevent moisture or the fluid to be heated from penetrating the recess from the outside. This is not always easy when extending the contact tabs from the frame element.

[0006] In PTC heating devices of the type mentioned above, it is further preferable to extract the heat symmetrically from both main side surfaces of the PTC heating element. The PTC heating device of the present invention is intended for use in a motor vehicle, similar to the PTC heating device known from the prior art. Scalable production processes are required in this application. The PTC heating device should be manufactured with consistently reliable quality.

[0007] The present invention addresses the problem of providing a PTC heating device of the type mentioned above which allows a reliable electrical connection of the PTC element with reliable sealing of the PTC element in the recess.

[0008] To solve this problem, the present invention proposes a PTC heating device with the features of claim 1. This differs from the previously described solution in that the insulating plate is provided with a metallization that is electrically conductive against the PTC element and is electrically conductively connected to an associated contact surface provided on the outer surface of the electrically insulating plate for the electrical connection of the PTC heating device.

[0009] In the present invention, the electrical connection of the PTC element to the power supply is made via contact surfaces provided on the outer surface of the electrically insulating plate. The electrically insulating plate accordingly carries the corresponding contact surfaces. These contact surfaces are applied to and connected to the electrically insulating plate as electrically conductive segments. The electrically insulating plate has sufficient inherent rigidity, such that, for example, direct bonding of the insulating plate to the frame element results in a substantially rigid frame element in which the PTC element is completely surrounded by the frame element and rigidly covered by the insulating plates on the opposing main side surfaces.

[0010] These insulating plates are in direct electrical contact with the PTC element. For this purpose, the electrically insulating plates are coated with a metallization that is in direct electrical contact with the PTC element. This contact can be achieved using an electrically conductive adhesive. Alternatively, a non-conductive adhesive can be used. In the latter case, the metallization on the insulating plate and / or any existing metallization on the PTC element is designed with a certain degree of roughness to facilitate current coupling into the semiconductor PTC element. This roughness allows peaks to penetrate the adhesive layer and establish electrical contact on the opposite side. A non-conductive adhesive is preferable, as it typically bonds the insulating plate to the frame element and thus forms part of the electrically insulating enclosure.Alternatively, an electrically insulating adhesive can be applied to the outer circumference of the recess and bonded to the electrically insulating plate, whereas within this perimeter insulating bond an electrically conductive adhesive can be provided, which electrically connects the PTC element to the metallization of the electrically insulating plate.

[0011] It is understood that this metallization does not usually extend to the edge of the electrically insulating plate. The situation is different at the point where the contact surface is provided. This contact surface can be located around the perimeter of the electrically insulating surface. Preferably, however, the contact surface is located on one of the main surfaces of the electrically insulating plate. Preferably, only the contact surface is an area in electrical contact with the PTC element. The usual enclosure formed by the frame element and the electrically insulating plates is electrically insulating.

[0012] The frame element can be made of plastic or an electrically insulating ceramic. The frame element can have one or more recesses. Each recess can accommodate one or more PTC elements. As explained above regarding the use of an electrically insulating adhesive in the edge region of the insulating plates, it is understood that the metallization is not intended to cover the entire surface of the opposing inner surfaces of the electrically insulating plates. Rather, the metallization is typically limited to the area that is in direct contact with the PTC element or against which the PTC element is in direct or indirect electrical contact.

[0013] With a view to a simple, effective, and large-area connection, a preferred embodiment of the present invention proposes that the contact surface be provided on an outer main side face of the electrically insulating plate. The contact surface is typically located near an edge of the electrically insulating plate. The contact surface can have a metallization applied to the outside of the electrically insulating plate, forming a continuous contact surface on the outer main side face of the corresponding electrically insulating plate. This contact surface is preferably electrically connected to the metallization via at least one through-hole. The through-hole extends through the electrically insulating plate.Typically, an electrically conductive material passes through a hole that is cut into the electrically insulating plate and connects the metallization provided inside with the contact surface provided outside.

[0014] As mentioned previously, the electrically insulating plate is preferably made of ceramic. This plate is usually flat and only a few millimeters thick.

[0015] Preferably, a highly thermally and electrically conductive layer is provided between the PTC element and the metallization, sealed between the electrically insulating plates. The aforementioned electrically conductive adhesive can form such an electrically conductive layer. Alternatively or additionally, the electrical layer can also be formed from a graphite or copper foil or plate. Good thermal conductivity as well as good electrical conductivity are essential. A material should be used that allows the penetration of surface roughness peaks, particularly on the surface of the PTC element, into the electrically conductive layer, thus creating a planar contact between the metallization of the electrically insulating layer and the PTC element. The electrically conductive layer is not a printed circuit board in the sense of the aforementioned prior art.It merely facilitates the electrical contact between the metallization on the PTC element and the surface of the PTC element at right angles to the main side face. Thus, the electrically conductive layer is typically located only where the PTC element is positioned opposite the electrically insulating layer. Preferably, the electrically conductive layer is approximately the size of the main side face of the PTC element.

[0016] In a manner known per se, the PTC heating element can be designed for plug-in connection to accommodate a specific power current. For this purpose, contact plates are proposed, each electrically connected to its corresponding contact surface and projecting beyond the associated electrically insulating plate on one side. These contact plates can be completely surrounded by an electrically insulating collar that encircles the contact surfaces and is positioned at their level. Typically, the collar extends only a short distance along the electrically insulating plates and is located at one edge of each plate. The collar can be formed by overmolding the contact plates and the electrically insulating layers after they have been positioned against the frame element, with the PTC element being inserted, and then bonded to this unit.The collar can also be formed by two shell elements that completely encircle the electrically insulating plates and may, for example, be bonded to them. The collar typically has contact plate receptacles in which the contact plates are held so that their contact surfaces rest against the outer surface of the electrically insulating plates.

[0017] Further details and advantages of the present invention will become apparent from the following description of an exemplary embodiment in conjunction with the drawing. The drawing shows: Fig. 1. A perspective exploded view of the essential parts of the PTC heating device; Fig. 2 the exemplary embodiment according to Fig. 1 after joining the electrically insulating plates and Fig. 3 a perspective side view of the completed embodiment together with the contact surfaces.

[0018] In Fig. Reference numeral 2 provides two ceramic plates as examples of electrically insulating plates. These plates have a metallization 4 on opposite inner surfaces, spaced apart from the longitudinal edges of the ceramic plate 2 (marked by reference numeral 6) and a lower edge 8, and extending to an upper edge 10. This creates an electrically non-conductive U-shaped strip 12 on opposite inner surfaces of the respective ceramic plates 2. A ceramic frame element, marked by reference numeral 14, has longitudinal bars 16 and a lower transverse bar 18, the width of which is matched to the width of the U-shaped strip 12. The frame element 14 is made of aluminum oxide. The frame element 14 forms a recess 20 in which a PTC element 22 can be received with a small transverse clearance. (See exploded view according to...) Fig. 1. This PTC element 22 is located below the frame element 14.

[0019] At the in Fig. On the upper ceramic plate 2, a contact surface 24 is visible on the outside, which is electrically conductive and in contact with the metallization 4 of the inner main side surface of the ceramic plate 2. How Fig. As can be seen in Figure 2, which shows the completed heating cell consisting of the two ceramic plates 2, the frame element 14, and the PTC element 22, this contact surface 24 is connected to the metallization 2 on the inner main side surface via vias 26. Applying a metallization results in a continuous rectangular contact surface 24 on the outer main side surface, which is electrically connected to the metallization 4 by electrical conductors 26 extending in the thickness direction of the ceramic plate 2.

[0020] For the assembly of the in the Fig. 1 and Fig. In the heating cell shown in Figure 2, an electrically non-conductive adhesive is typically applied to the U-shaped strip 12. An electrically conductive adhesive is applied to the metallization 4 or the opposite main side surface of the PTC element 22. Alternatively or additionally, a highly conductive layer can be arranged between the inner main side surface of the ceramic plate 2 and the PTC element 22. This electrically conductive layer can be a copper or graphite plate or foil. Its primary function is to facilitate the planar electrical contact from the relatively rigid ceramic plate 2 to the main side surface of the PTC element 22. The main function of the electrically conductive layer is to accommodate and even out any point contacts caused by surface roughness, particularly in the area of ​​the PTC element 22, thus ensuring planar contact between the metallization 4 and the PTC element 22.

[0021] How Fig. 1 mediated, an upper crossbeam 28 is wider than the lower crossbeam 18 and accordingly provides a support for the contact surface 24.

[0022] The Fig. Figure 3 shows the completed embodiment. This has two contact plates 30 that lie flat against the contact surface 24 and are accordingly sized to the width of the contact surface (see Figure 3). Fig. 2) are provided. Free-cut contact tongues are formed at opposite edges by the contact plate 30, which essentially project beyond the PTC heating element as an extension of the longitudinal beams 16. The upper area of ​​the ceramic plates 2, corresponding approximately to the width of the upper transverse beam 28, is surrounded by a collar 34, which completely encloses the electrically insulating plates 2 and the frame element 14, thereby enclosing and sealing the contact surfaces 24 and the adjacent area of ​​the contact plates 30, so that a medium flowing towards the ceramic plates 2 and to be heated cannot reach the contact plates 30 or the contact surfaces 24. The collar 34 limits the exposed surfaces of the contact plates 30 intended for plug-in contact to the contact tongues 32.The collar 34 can be made of a soft elastic material, making it suitable for sealing the PTC heating element in a partition wall that separates a heating chamber, in which the ceramic plates 2 are exposed for heat dissipation, from a connection chamber in which the contact tongues 32 are plugged in (see EP 3 334 242 A1). The collar can also be adapted for attaching soft elastic seals or be formed in one piece with an elastomeric seal.

[0023] The in Fig.The embodiment shown in Figure 3 represents the completed PTC heating device. The medium to be heated flows directly over the outer surfaces of the ceramic plate 2 and is heated, in particular, via the outer main side surfaces of the ceramic plate. The collar 34 lies outside the area where the PTC element 22 is electrically and thermally connected to the ceramic plate 2. This ensures good heat extraction from the heat generated by the PTC element 22. This results in good efficiency, especially since the PTC element 22 is connected to the ceramic plate 2 either directly or via a highly thermally conductive layer.

[0024] In the illustrated embodiment, electrical contact between the contact surface 24 and the metallization 2 is achieved through the vias 26. Additionally or alternatively, a corner contact can be implemented, via which the contact surface 24 is electrically connected to the metallization 4 provided on the opposite main side surface. This corner contact extends over the upper end face 10 of the ceramic plate 4. Reference symbol list 2 ceramic plates 4 Metallization 6 Longitudinal edge 8 lower wheel 10 top edge 12 U-shaped strips 14 frame element 16 Longitudinal beam 18 crossbeam 20 Exclusion 22 PTC elements 24 contact surfaces 26 Through-hole plating 28 upper crossbeam 30 contact plates 32 Contact tongue 34 collars

Claims

[1] PTC heating device comprising a PTC element (22) and a frame element (14) forming a recess (20) encompassing the PTC element (22), which is covered on both sides with electrically insulating plates (2) that cooperate with the frame element (14) to seal the PTC element (22) in the recess (20), characterized by , that the insulating plates (2) are each provided with a metallization (4) which is electrically conductively connected to the PTC element (22) and electrically conductively connected to an associated contact surface (24) provided on the outer surface of the electrically insulating plate (2) for the electrical connection of the PTC heating device. [2] PTC heating device according to claim 1, characterized by , that the contact surface (24) is provided on an outer main side surface of the electrically insulating plate (2). [3] PTC heating device according to claim 1 or 2, characterized by, that the contact surface (24) is electrically connected to the metallization (4) on an outer main side surface of the electrically insulating plate (2) via at least one through-hole (26). [4] PTC heating device according to one of the preceding claims characterized by that the electrically insulating plates (2) are flat. [5] PTC heating device according to one of the preceding claims characterized by , that the electrically insulating plates (2) are made of a ceramic. [6] PTC heating device according to one of the preceding claims characterized by , that a highly thermally and electrically conductive layer is provided between the PTC elements (2) and the metallization (4), which is sealed between the electrically insulating plates (2). [7] PTC heating device according to one of the preceding claims characterized by, contact plates (30) which are each electrically connected to the associated contact surface (24) and extend beyond the associated electrically insulating plate (2) on one side. [8] PTC heating device according to one of the preceding claims characterized by , an electrically insulating collar (34) that surrounds the electrically insulating plates (2) and the frame element (14) at the level of the contact surfaces (24) and to which the contact plates (30) are connected.

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