Patent Application
20240121864
The present invention relates to a PTC heating device and a method of manufacturing the same.
The present invention is based on a PTC heating device with a frame in which a heating cell comprising at least one PTC element made of a ceramic material and contact elements to be assigned different polarity are accommodated. The PTC element has contact surfaces formed by metallization. The contact elements are electrically contacted with these contact surfaces.
The present invention relates in particular to such a PTC heating device for thermal management in a motor vehicle. Here, PTC heating devices of the type mentioned introductorily are sometimes operated at voltages higher than 12 V, which imposes special requirements on the electrical safety to be complied with. From this point of view, it is not only necessary to ensure safe electrical insulation to the outside of the parts of the heating cell carrying the power current. Rather, clearances and creepage distances must also be adapted accordingly.
It must be possible to manufacture the PTC heating device in a process-safe manner, wherein particularly economical requirements are imposed on a component in a vehicle with regard to manufacture. It is known to completely or partially surround a heating cell with a hardening compound, for example to replace air present in the frame with a better heat-conducting material.
An in particular electrically insulating compound is sometimes also used to electrically house the PTC heating cell completely or partially with the result that at least the parts carrying the power current are also covered by the electrically insulating compound inside the heating cell.
It is known that the time required to cure the compound can be reduced by heating it, for example by operating the heating cell in the course of manufacturing or by using an oven process. However, current solutions still offer room for streamlining the manufacturing process.
The underlying problem of the present invention is to provide a PTC heating device which provides good electrical safety and can be manufactured economically.
In order to solve this problem, the present invention proposes a PTC heating device with a frame in which a heating cell is arranged. The heating cell comprises a PTC element made of a ceramic material. On opposite sides, usually main side surfaces of the PTC element, a metallization is provided. This is usually produced by sputtering an electrically conductive material onto the ceramic surface of the PTC element. Contact elements, which serve to supply the power current to the PTC element, are applied in an electrically conductive manner against the regularly opposing contact surfaces formed by the metallization. These contact elements can be formed by contact sheets. However, the contact elements can also be formed by other electrically conductive structures, which can consist of one or more materials that do not necessarily have to be electrically conductive in each case. For example, it is known to use expanded metal or a wire mesh as a contact element, the free spaces of which are filled by a good heat-conducting adhesive (EP 3 515 152 A2). With regard to a defined introduction of the power current, defined contact points, which are formed by the contact element and are applied in an electrically conductive manner against the contact surface, are sometimes also preferred.
The frame can be formed from a plastic or a ceramic In any case, a material is usually selected that has very good electrical insulating properties. The frame can have beams surrounding the PTC element only. The frame may be formed in one or more parts. The frame can be formed integrally with the contact element either by itself or by a segment of the frame, in particular by overmolding the contact element with plastic. The frame is usually surmounted on one side by terminal lugs which are electrically conductively connected to the respective contact elements, preferably formed integrally by them.
An electrically insulating compound, which may be formed by silicone, for example, is provided between the inner circumference of the frame and the outer circumference of the heating cell. The compound is cured and thus dimensionally rigid. The compound serves to fix the heating cell within the frame. The compound may be located only between the outer circumference of the PTC element and the inner circumference of the frame. However, it can also be attached to the opposing inner surfaces of the contact elements. The contact elements surmount the main side surfaces of the PTC element provided with the metallization. This results in an edge-side possibly circumferential overhang of the PTC element due to the two contact elements. In order to fix the heating cell, the cured compound is located, in particular, in the gap formed between the overhangs.
An edge formed by the ceramic material of the PTC element is located between the contact surface and the cured compound. This edge may be only partially formed on a longitudinal side of the PTC element, which is usually provided in a cuboid shape. The edge may extend over an entire longitudinal side of the PTC element. The edge is typically formed as a circumferential edge on the main side surface of the PTC element. The edge creates a distance between the outer circumferential surface of the PTC element and the metallization of at least 0.1 mm. The edge spaces apart the conductive path provided on the PTC element for the power current in the form of the contact surfaces from the outer contour of the PTC element. The cured compound provided adjacent to the edge does not directly contact the metallization. These measures increase the electrical safety of the PTC heating device.
According to an implementation of the present invention, not the entire free space provided between the frame and the heating cell is filled with the compound. Rather, the compound is located only at discrete locations on the outer circumference of the heating cell. Discrete dosing of the cured compound may be provided at the outer circumference of the heating cell. This discrete dosing adequately defines the heating cell in the frame. However, dosing also may be done with a view to using as little as possible of the compound used to manufacture the PTC heating device. This not only allows material of the compound to be saved. Rather, the time required for curing the compound in the course of manufacturing the PTC heating device can also be reduced.
In order to fix the heating cell, compound is usually introduced into the frame on opposite sides between the heating cell and the frame. The compound is usually introduced at the frame, which is still open on one side. In other words, the frame or a segment of the frame is usually closed on one side, for example by attaching and connecting one of the contact elements to the frame. This side forms the lower side of the frame or frame segment during assembly. In the following, the term “frame” is also used as a synonym for “frame segment.” The PTC element is then inserted into the frame or frame segment that is open at the top.
In the process, the contact surface is applied to the contact element in an electrically conductive manner. Then, dosing of the compound into the gap between the PTC element and the frame is carried out. Dosing may be carried out such that there is no protrusion of the compound onto the main side surface of the PTC element. Appropriate volumetric dosing ensures that the compound remains within the gap and also does not protrude outward beyond the frame. However, the compound is usually introduced up to the level of the contact surface not yet occupied by a contact element. When the other contact element is subsequently placed on the PTC element, this can result in a slight displacement of the compound, as a result of which the compound is also dispensed against both inner surfaces of the contact elements and, if necessary, slightly compressed in the area of the overhang. In this way, the other contact element is regularly fixed against the PTC element and the frame through the compound.
For this fixing, it is only desired that the further contact element, which is applied later, in any case surmounts the compound with an overhang. The contact element can otherwise be adapted to the dimensions of the contact surface and accordingly be made smaller than usual. It is usual for the PTC element to be surmounted by the contact elements on its entire outer circumference. The contact element applied later can also be joined beforehand with another segment of the frame to form a preassembled unit, for example by overmolding a plastic forming the segment around the contact element.
The PTC heating device is usually part of an electrical heating device of a motor vehicle. This heating device has a heater housing with inlet and outlet openings for a medium to be heated. The housing accommodates at least one, usually more, PTC heating devices. These are coupled in a heat-conducting manner to the medium to be heated. The medium to be heated may be a liquid or gaseous medium.
In the case of a gaseous medium, there are usually insulating layers on the outside of the respective contact elements, against which corrugated fin layers abut on the outside. Usually, the electrical heating device comprises several layers of corrugated fins and PTC heating devices. This layering is usually fixed in a frame-shaped heater housing under the pretension of a spring; cf. EP 2 298 582 B1 and its U.S. counterpart 8,729,433, both incorporated herein by reference.
For installation in the electrical heating device, the PTC heating device of the type introductorily mentioned can also be arranged in a metallic housing which forms a kind of pocket into which the PTC heating device is inserted (cf. EP 3 101 364 A1 and its U.S. counterpart 10,098,183, both incorporated herein by reference). Here, too, an insulating layer is usually abutted to the outer surfaces of the contact elements so that there is no direct electrical contact between the elements of the PTC heating device carrying the power current and the housing. The housing is surmounted by the terminal lugs. The housing may also have a sealing collar which serves as a sealing plug-in contact in a partition wall of the electrical heating device, which separates a circulation chamber carrying the medium to be heated from a connection chamber of the electrical heating device, in which the terminal lugs of the PTC heating device are connected to the power current to be supplied. The connection chamber usually also accommodates a control system for the electrical heating device.
The present invention offers a plurality of advantages. By reducing the total amount of compound used, not only is material saved. Rather, the time required for curing the compound is also reduced. By reducing the volume of cured compound used and discretely dosing compound at predetermined points, overhang of compound is prevented. In particular, the compound is prevented from spreading to areas of the contact surface during manufacture, contaminating it and preventing the introduction of the power current onto the PTC element over as large an area as possible. In particular, a circumferential edge prevents contact of the compound with the contact surface and also prevents edge flashovers of the power current.
Further details and advantages of the present invention will be apparent from the following description of an embodiment in conjunction with the drawing. Therein:
The housing lower part 4 is trough-shaped and encloses a heating chamber 8 and forms inlet and outlet nozzles 10 which communicate with the heating chamber 8. These inlet and outlet nozzles 10 are integrally formed with the housing lower part 4 by injection molding. A plurality of PTC heating devices 12 are shown between the housing upper part 6 and the housing lower part 4.
As
The PTC heating devices 12 are held in plug-in contact in accommodations 28 provided for this purpose of a partition wall 30 of the housing upper part 6 and are electrically connected and controlled in a connection chamber 29 of a control system 31. Details of this configuration are described in EP 3 334 242 A1 and its U.S. counterpart 10,760,822, both of which originate from the applicant and both of which are incorporated by reference.
The top view according to
In the course of manufacture, the frame 22 with the lower contact element 16.1 is first produced by overmolding this contact element with a plastic forming the frame 22. In the arrangement shown in
Further manufacturing steps may follow in which additional components are added to the PTC heating device 12, which have been described with reference to
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 125 637.5 | Oct 2022 | DE | national |
