The present invention relates to a method for producing a PTC heating element with a PTC element and contact surfaces for electrically contacting the PTC element. In PTC heating elements, as are known, for example, from EP 1 253 808 A1 or EP 1 395 098 A1, respectively, an electrical conductor track typically abuts against oppositely disposed main side surfaces of the PTC element. The conductor track is commonly formed from a contact plate which is connected to a position frame, for example, sealed into the position frame.
Especially with high-voltage applications in electric vehicles, it is necessary to electrically insulate the outer side of the contact plate. For this purpose, it is known from the aforementioned prior art to apply an insulation layer on the outer side of the contact plate.
PTC elements have self-regulating properties. With increasing heating, the power consumption decreases since the electrical resistance of the PTC element increases. It has therefore always been aspired to obtain good heat extraction from the PTC element. Furthermore, with PTC heating elements for the automotive industry, cost-effective production needs to be ensured. The configuration of the PTC heating element must be scalable and reliably producible within predetermined tolerance limits also in large numbers.
The present invention is based on the problem of specifying a method for producing a PTC heating element in which the PTC element is at its face side surfaces reliably electrically contacted to contact surfaces.
For solving the problem, a method having the features of claim 1 is suggested with the present invention.
In the method according to the invention, the contact plates are connected to one another by way of electrically insulating bridge elements while leaving a seat free for the PTC element. It goes without saying that several bridge elements can be used to form several seats. These bridge elements are typically provided spaced apart from each other along elongate contact plates. One or more PTC elements can be provided in each seat.
In the procedure according to the invention, the PTC element is inserted into the seat and between the contact plates. The contact plates are there so far apart from each other that the seat is dimensioned sufficiently large such that the PTC element can be inserted into the seat without being influenced by the contact plates. Only then is each contact plate deformed for obtaining a contact projection abutting against the face side surface of the PTC element.
The contact projection can be shaped during the deformation. In a pre-processing step for the sheet metal strip, the contact projection can alternatively already be shaped typically by way of punching, but not yet be deformed in the direction toward the PTC element for abutting thereagainst. It is conceivable to provide the contact plates with elongate slots through which the contact projections are cut free as strips at a boundary layer to the PTC element. During the subsequent deformation, these thin bars are deformed in the direction toward the PTC element and abutted against a face side surface of the PTC element to provide a sound electrical contact between the PTC element and the respective contact plate.
In the aforementioned embodiment, in which a contact spring bar is typically shaped on the contact plate by the preceding punching operation, the deformation of the contact spring bar for its abutment against the PTC element is preferably performed by a conically widening tool, such as a pin, which is introduced into a slot between the contact spring bar and the remainder of the material of the contact plate for deforming the contact spring bar in the direction toward the PTC element. Several pins are typically provided on a tool for deforming the contact spring bars in this manner and at the same time are introduced into the corresponding slots. This achieves a deformation of the contact spring bars in a cost-effective and reliable manner. For example, the tool can be lowered in a force-controlled manner to ensure that the contact spring bars rest with a predetermined contact pressure on the face side surface of the PTC element. When simultaneously deforming contact spring bars of different contact plates, it is additionally ensured that the PTC element is contacted identically on oppositely disposed face side surfaces.
For deforming the contact projections, the contact plates are preferably received in a tool which abuts against the outer surface of the contact plates. As a result, the forces needed for the deformation are supported so that the deformation arises on the side of the contact plates that is to be contacted with the PTC element, but not on the oppositely disposed free outer sides of the contact plates. In addition, the deformation of the contact spring bars becomes controllable, since the force possibly monitored for deforming the contact spring projections results exclusively in a deformation in the direction toward the PTC element.
According to a preferred embodiment of the present invention, the contact plates are overmolded after the deformation. An insulation layer is preferably applied to the PTC element prior to overmolding. Following this application of the insulation layer, the PTC element is typically on its main side surfaces respectively provided with an insulation layer which can be a ceramic insulation layer. The insulation layer is formed, for example, by an aluminum oxide plate. The insulation layer is preferably glued in a thermally well conductive manner onto the PTC element.
When the contact plates are overmolded, the insulation layer is sealed at the edge with plastic material. However, the largest area of the insulation layer is there left exposed, so that the completed PTC heating element with the overmolding on its outer side is substantially defined by the outer surface of the insulation layer, via which heat generated by the PTC element is given off at a high heat density.
When the contact plates are overmolded, the bridge element or bridge elements is/are usually also overmolded. They can in turn be individually connected to the contact plates by overmolding. However, the contact plates can also be plugged into seats of the bridge elements and thus connected thereto.
The overmolding of the contact plates is preferably performed using elastic plastic material, for example TPE, elastomer or duromer. One of the bridge elements, which can be formed from a hard plastic component such as polyamide, can there be provided with a sealing collar having a lamellar seal to form the PTC element as a plug-in heating element which can be inserted in a sealing manner into a plug element seat of a partition wall which separates a circulation chamber, through which the fluid to be heated flows, from a connection chamber, in which contact lugs of the PTC heating element for the electrical connection are exposed. The plastic material sealing the contact surface is preferably selected to have wetting properties to the surface of the insulation layer.
Further preferably, the contact plates are extended on one side beyond one of the bridge elements for forming said contact lugs. An electrical connection element for the PTC heating element is thus formed in a known manner by the respective contact plates.
Further details and advantages of the present invention shall become apparent from the following description of an embodiment in combination with the drawing. Therein, the figures show different phases within the framework of the production of a PTC heating element, where
In the illustration according to
The bridge elements 12, 14 each form spacers 18 which protrude into a seat 20 formed between the two sheet metal strips 2a, 2b and the bridge elements 12, 14. A PTC element 22 to be inserted into the seat 20 and provided in
The intermediate product shown in
On its inner surface, the insulation layer 26 can be provided with electrically well conductive adhesive. It can be completely or partially filled with highly thermally conductive particles in order to improve thermal conductivity of the adhesive. The PTC element 22 is placed onto the surface of the insulation layer 26 thus prepared (
Thereafter, conical pins 30 engage in the longitudinal slots 6. For this purpose, they each have an idealized circular extension 32 which can be seen in
Thereafter, the pins 30 are withdrawn. The housing 36 is removed from the tool 24. Finally, the further insulation layer 28 is placed onto the PTC element 22 in order to create an intermediate product in which the oppositely disposed main side surfaces of the PCT [sic] element 22 are each covered by one of the insulation layers 26, 28. This intermediate product is shown in
The intermediate product shown in
This plastic material can be TPE, silicone, a duromer or an elastomer. Good wetting of the insulation layers 26, 28 by the respective plastic material is of particular importance. The plastic material is overmolded while omitting substantially the main side surfaces of the insulation layer 26, 28 The overmolded plastic material then results in a plastic frame which substantially leaves free the main side surfaces of the insulation layers 26, 28 and forms a window 40 in which the insulation layers 26, 28 are exposed. However, the circumferential edges of the insulation layers 26, 28 are sealed by the material of the plastic frame and a seal of the insulation layers 26, 28 against the plastic frame 38 arises accordingly. As illustrated in
The sealing beads 46 are provided circumferentially surrounding the plastic material of the upper bridge element 12. As a result, the contact force within the female plug element seat is improved.
The product according to the invention is characterized in that the PTC element 22 is reliably contacted with its oppositely disposed face side surfaces 34. The contact surfaces 10 of the sheet metal strips 2a, 2b are there not only in abutment against the PTC element 22 in a press-fit manner. Instead, an elastic deformation is impressed upon the contact spring bar 8 by the lateral spacing between the convex contact surface 10 and the extension 32 receiving the pin 30, with which any possible settling and/or thermal expansion within the PTC heating element 42 during operation can be compensated. The heat-generating cell with the two current-carrying sheet metal strips 2a, 2b connected to different polarities and the PTC heating element 22 are sealed fully circumferentially by the plastic frame 38, since the plastic frame 38 only leaves the insulation layers 26, 28 free.
The bridge elements 12, 14 can also be in a plugged connection with the sheet metal strips 2a, 2b. The attachment between the bridge elements 12, 14 and the sheet metal strips 2a, 2b can be effected, for example, by welding or gluing. Also, positive-fit connections are conceivable. In addition, the bridge elements 12, 14 can each be of a multipart design, where the multiple parts of a single bridge element can be joined together enclosing the sheet metal strips 2a, 2b. The sheet metal strips 2a, 2b in this joining are preferably locked in a positive-fit manner within the bridge element or bridge elements.
Furthermore, it is conceivable to provide several seats 20 one behind the other in the direction of extension of the sheet metal strips 2a, 2b. For this purpose, the sheet metal strips are each provided with several bridge elements in the longitudinal direction, where a seat is provided between each of the adjacent bridge elements.
The PTC heating element 42 illustrated is suitable as a PTC heating element in a fluid heater. Due to the plastic frame 38, there is no risk that the fluid to be heated reaches the PTC element. In this case, the sealing bead 46 is sealingly received in a partition wall, and the lower bridge element 14 protruding beyond the plastic frame 38 can be received in a receptacle recessed at the bottom of the circulation chamber. As a result, the PTC heating element 42 can be held in a predetermined arrangement and orientation within a fluid heater, as is known in principle from EP 2 607 121 B1, EP 2 440 004 B1 or EP 1 921 896 from the applicant.
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10 2017 208 253 | May 2017 | DE | national |
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