EP3101999B1 - Ptc heating element and electric heater for a motor vehicle comprising such a ptc heating element - Google Patents

Description

The present invention relates to a method for producing a PTC heating element with the preamble features of claim 1. Such a method is over EP 0 057 172 A2 known. A similar procedure is out WO 91/07068 A1 known.

PTC elements have found good acceptance in electrical heating devices for motor vehicles, which is due to the self-regulating properties of PTC elements. A heat-generating element in an electrical heating device usually consists of at least one PTC element and conductive tracks attached to the PTC element in an electrically conductive manner on both sides, which are usually used for the electrical connection of the PTC element. Such heat-generating elements are either directly or with the interposition of an insulating layer against heat-emitting surfaces. The PTC elements are usually installed in such a way that the PTC element gives off heat to heat-emitting surfaces on both sides.

Examples of electrical heating devices with an insulating layer that covers at least one of the conductor tracks on the outside are, for example EP 1 768 459 A1 or the EP 2 637 475 A1

From the EP 1 768 459 A1 an electrical heating device for air heating is known, in which the heat-emitting surfaces are formed by corrugated rib layers that rest on both sides of the PTC element. In the known prior art, several PTC elements are accommodated in a positioning frame and contacted on both sides with contact plates which form the conductor tracks and are used for the electrical connection of the PTC element.

Another electrical heating device is, for example, from EP 1 872 986 A1 known. In this prior art, heating ribs protrude into a circulation housing which is exposed to a fluid to be heated is flowed through. The heating ribs form a U-shaped pocket in which the PTC element and the conductor tracks and insulating layers provided on the outside of the conductor tracks are received. As a result, the PTC element and the conductor tracks lying thereon on both sides for energization are accommodated in the heating rib in an electrically insulating manner. Sometimes, however, it is possible, for example when the electrical heating device is operated with the mains voltage of a motor vehicle of 12 volts, to provide insulation only on one side and to contact the PTC element directly with ground on the other side. "Ground" can be formed by the outside of a heating rib or by a corrugated rib layer, which on one side rests against the PTC element or elements in a heat-conducting manner.

The one from the EP 1 768 458 A1 known prior art, the insulating layer is formed by a two-layer structure which comprises a polyimide film and a ceramic layer. Particularly in the case of high-voltage applications and especially with regard to the operation of the electrical heating device in an electric vehicle, it is important to ensure reliable electrical insulation of the PTC element and the conductor tracks that make contact with it on both sides. A laminated insulating film for the same purposes describes the EP 2 109 345 A1 .

The present invention aims to contribute to this. The present invention is based on the problem of specifying a method for producing a PTC heating element which is electrically insulated on the outside in an improved manner, while also taking into account the need for adequate heat transfer from the PTC element to the heat-emitting surface through the electrical insulating layer Should be taken into account.

To solve the above problem, the present invention specifies a method for producing a PTC heating element having the features of claim 1. This PTC heating element has, as an electrical insulating layer, a combination of a film and an electrically insulating mass with good thermal conductivity applied to it. The film is first prepared together with the mass as a unit and then applied as a prefabricated hybrid film comprising the film and the electrically insulating mass applied to it on the outside against at least one of the electrical conductor tracks.

In this case, the electrical insulating layer has a layer structure with a film that usually runs through it and one that is applied thereon, usually with a constant thickness electrically insulating mass with good thermal conductivity. The insulating layer according to the invention offers, in particular due to the elastic and electrically insulating mass, the possibility of unevenness, which also small particles such. B. grains of dust to balance between the conductor track and a heat-emitting opposite surface of an electrical heating device, in particular in a motor vehicle. Where, on the other hand, with conventional insulating foils as an insulating layer, which can also attract foreign bodies through electrostatic effects, the insulation on the outside of the PTC element can be pierced by such unevenness and thus bridged, with the result that the voltage applied to the PTC element is even is not insulated from the surface emitting heat. This can lead to short circuits within the electrical heating device and thus to failure. A life-threatening condition can arise without an appropriate cut-off device.

The electrically insulating mass is preferably a pasty mass that is preferably already crosslinked and thus set, so that it is no longer flowable in the actual sense. The mass can, however, perform certain compensatory movements, for example in order to evade positions within the insulating layer with a punctual application of pressure, while absorbing and equalizing the punctual pressure without the insulating effect being lost by the electrical insulating layer. A mass with good thermal conductivity preferably has a thermal conductivity of at least 3 W / (m * K), particularly preferably of at least 5 W / (m * K). The electrically insulating mass can be applied to the film with a technology that is used in the production of adhesive tapes and in which the film is passed through a bath consisting of the electrically insulating mass via rollers. For this purpose, the electrically insulating mass can be mixed with a solvent, as a result of which the viscosity of the electrically insulating mass is reduced or the wetting of the film can be improved. A plastic compound is usually used as the electrically insulating compound, which sets or hardens completely or partially after the film has been coated. A crosslinking plastic is preferably used, and after the film has been coated, it can also cure more rapidly by adding heat and / or applying irradiation. The device provided for producing the insulating layer usually has a heating or irradiation path through which the film coated with the compound runs.

An electrical insulating layer initially prepared in this way is then applied against the outside of the at least one, preferably both, conductor tracks of the PTC element. This conductor track can be formed by a metal sheet or in a printed layer.

In addition to the aforementioned coating of the film from a system of rollers and the electrically insulating mass in a molten bath, this can also be applied to the film by printing or spraying, with a doctor blade being preferred in the case of printing.

The mass preferably comprises a silicone mass as the liquid phase. The liquid phase is preferably formed by an addition-crosslinking 2-component silicone that hardens at room temperature and hardens under heat. The mass has a viscosity at 25 ° C of between 100 and 200 Pa s. With a view to good flowability, the 2-component silicone is usually mixed with benzine or Tuluol as a thinner to achieve a viscosity in a range of between 4 and 15, preferably between 5 and 8 Pa s. In the crosslinked state, the component of the mass forming the liquid phase should have a Shore A hardness of about 10-40. A solid which increases the thermal conductivity but is electrically insulating is usually added to this liquid phase.

The mass is preferably selected so that there are good wetting properties in relation to the particles with good thermal conductivity. The particles can additionally be treated with an adhesive before the particles are added to the pasty mass in order to disperse them evenly therein. The mass can for example be a silicone mass or at least predominantly comprise silicone mass.

With a view to the electrical insulating properties of the insulating layer, this filler component is usually formed by electrically insulating particles with good thermal conductivity, with particles made of aluminum oxide being preferred, especially particles diluted with gas or water, which due to their morphology are relatively dense within the liquid phase let pack and the flow properties of the filled insulating mass do not deteriorate so much as particles of other morphology. The filler content of the particles with good thermal conductivity within the liquid phase is at least 50% by volume, particularly preferably between 85% and 95% by volume. Such a volume fraction of filler within the mass improves the thermal conductivity due to the good thermal conductivity of the particles, but does not hinder the flow of the pasty mass and thus the molten application of the mass to the film.

According to a preferred development, the insulating layer consists of the film and the electrically insulating mass, wherein the electrically insulating mass itself can have several phases, namely, for example, the filler component and the liquid phase. The further development entails that the design of the insulating layer is formed solely from the film and the electrically insulating mass, the film also being designed to be self-adhesive on the side facing away from the mass and accordingly being provided with an adhesive layer. This adhesive layer is usually provided on the prefabricated insulating layer. It is applied to one side of the film after or before the electrically insulating compound has been applied to the opposite surface of the film.

Due to the self-regulating properties of PTC elements, the layer thickness should be limited. Thus, according to a preferred development of the present invention, it is proposed to form the electrically insulating layer with a thickness of not more than 250 μm.

The insulating layer has a layer thickness of between 100 and 300 μm, preferably between 150 μm and 250 μm. These thickness dimensions result in sufficient electrical safety, ie reliable external insulation of the PTC element through the electrical insulating layer with sufficient absolute heat dissipation through the electrical insulating layer, which is favorable for effective operation of the PTC element with a view to the self-regulating properties of the PTC element . Practical tests have shown that, in particular with a compound filled with electrically insulating filler particles, in particular applied to a polyimide layer, on the one hand, with a layer thickness of 250 µm, the insulating layer has an overall specific electrical breakdown strength of 20 kV / mm, a specific volume resistance of 1.9 * 10 ¹⁵ Ohm / cm and a tracking resistance of CTI> 600 can be achieved. The electrical insulating layer is preferably temperature-resistant in a temperature range from -40 ° C to 260 ° C.

The present invention therefore provides an electrical insulating layer which has very good thermal conductivity, so that the PTC element can be operated with good efficiency, which can also be easily prepared and manufactured by the meter and thus easily processed and furthermore high temperature resistance Has. Since the film serves as a carrier for the insulating mass within the electrical insulating layer, the electrical insulation and the good thermal conductivity are mainly brought about by the insulating mass, this can also be provided on both sides of a thinner film. In such a case, it is only necessary to ensure that the film within the electrically insulating layer has good heat resistance. Furthermore, mechanical properties such as good tear resistance and the like are desired. The thinner the film is chosen within the electrical insulating layer, the less attention must be paid to good thermal conductivity of the film itself.

The liquid phase of the electrically insulating mass, i.e. H. the liquid phase of the suspension, which may contain particles of good thermal conductivity, is formed from a cold-curing 2-component compound. The liquid phase preferably consists solely of such a 2-component mass. Such a cold-hardening mass usually hardens in a few minutes when heated to not more than 80 ° C. H. off in 2 to 8 minutes. Higher temperatures do not have to be used to achieve hardening of the mass.

In a preferred development, the conductor track usually consists of a stamped contact sheet, which also forms the connection lugs for the electrical connection of the heat-generating layer. The heat-generating layer is the PTC element with the conductor tracks lying on it or directly connected to it and the insulating layer provided on the outside. The at least one PTC element and the contact plates that are usually directly adjacent to it can be provided as a preassembled unit in a frame that holds these elements of the heat-generating element together to form a preassembled unit, as shown, for example, in FIG EP 1 921 896 or. EP 2 637 475 is described. The pasty mass is applied to this preassembled unit so that the outer surface of the contact plate is provided with the insulating layer. If a wedge element is used to brace the heat-generating element in a U-shaped pocket and, if necessary, is movably guided and held on the frame, as shown in FIG EP 1 921 896 A1 is known, there is usually a sliding layer on this side between the electrical insulating layer, over which the wedge element can slide in an improved manner when the heat-generating element is braced in the pocket. Such a layer can be formed, for example, by a sheet metal strip which is provided between the wedge element and the mass.

With its independent claim 15, the present invention proposes a heating device in particular for a motor vehicle with heat-emitting surfaces. These heat-emitting surfaces can be outer surfaces of a radiator element provided with corrugated ribs or else opposing inner surfaces of an essentially U-shaped pocket of a liquid heater.

The electrical heating device proposed with its secondary aspect is in particular a heating device for high-voltage applications in a motor vehicle. The heating device is operated with a voltage of up to 800 volts.

Fig. 1

eine perspektivische Seitenansicht eines nach einem ersten Ausführungsbeispiel hergestellten PTC-Heizelementes einer ersten elektrischen Heizvorrichtung;

Fig. 2

eine perspektivische Seitenansicht der ersten elektrischen Heizvorrichtung;

Fig. 3

eine perspektivische Seitenansicht eines nach einem zweiten Ausführungsbeispiel hergestellten PTC-Heizelementes für eine zweite elektrische Heizvorrichtung und

Fig. 4

eine perspektivische Seitenansicht der zweiten elektrischen Heizvorrichtung.

Further details and advantages of the present invention emerge from the following description of exemplary embodiments in conjunction with the drawing. In this show:

Fig. 1

a perspective side view of a PTC heating element produced according to a first embodiment of a first electrical heating device;

Fig. 2

a perspective side view of the first electric heater;

Fig. 3

a perspective side view of a PTC heating element produced according to a second embodiment for a second electrical heating device and

Fig. 4

a perspective side view of the second electric heater.

This in Fig. 1 The PTC heating element shown and identified by the reference numeral 2 comprises several PTC elements 4 provided one behind the other in the longitudinal direction of the PTC heating element 2, which are located between two conductor tracks 6 lying on opposite sides of the PTC elements 4, in the present case in the form of contact sheets which are connected to an end face of the PTC element 4 for the formation of contact tongues 8 beyond the actual heat-generating element are extended. This heat-generating element of the PTC heating element 2 comprises In addition to the aforementioned components, an insulating layer 10, which rests on both sides of the conductor tracks 6 and covers the heat-generating element of the PTC heating element 2 on the outside. The electrical insulating layer 10 consists of an electrically insulating compound 12 which adheres to a film 14 made of polyimide. The electrical insulating layer 10 has previously been prepared by applying the electrically insulating compound 12 to the film 14 and then placed on the respective conductor track 6. The cutting of the electrical insulating layer 10 is selected in the width direction so that it protrudes slightly beyond the PTC elements 4. A circumferential positioning frame 16 is provided between the opposing edges of the electrical insulating layer 10. This frame is a positioning frame 16 which has webs provided one behind the other in the longitudinal direction of the PTC heating element 2, which ensure a predetermined distance between the PTC elements 4 lying one behind the other. In the area in Fig. 1 this web corresponds to the gap S.

The conductor tracks 6 are delimited on the inside by the positioning frame 16. Only the insulating layer 10 rests on the outside of the positioning frame 16. At this point, the insulating layer 10 is firmly and fluid-tightly connected to the position frame 16, for example glued or connected to the position frame 16 by injection molding, namely during the injection molding production of the position frame 16 from a heat-resistant plastic. This plastic can be silicone, for example.

In any case, care must be taken that, in the exemplary embodiment shown, the electrical insulating layer 10 is connected to the edges of the positioning frame 16 in such a way that no moisture or dirt can get into the interior of the positioning frame 16.

In the installation situation shown, the electrical insulating layer 10 has the film 14 on its outside, whereas the electrically insulating compound 12 is located between the film 14 and the conductor track 6.

In Fig. 2 a side view of an electrical heating device 20 is shown, in which a plurality of PTC heating elements 2 are installed as heat-generating layers. Corrugated rib elements 22 are provided adjacent to the PTC heating elements 2, which bear against the outside of the electrical insulating layer 10 and conduct heat with the PTC heating elements 2 are connected in order to initially absorb the heat generated in the heat-generating element by conduction and to give it off to the air passed transversely through a frame made of plastic, identified by reference numeral 24. For this purpose, the PTC elements 2 and the corrugated rib elements 22 are inserted as layers in the frame 24 and held in a pretensioned manner with respect to one another with a spring.

This two-part plastic frame 24 in the present case is connected to a control housing 26 in which the contact tongues 8 are electrically connected to a control device. Connectors for the power current 28 and the control current 30 are exposed on the control housing 26. In the plug of the power current 28, two poles are exposed for energizing the electrical heating device 20 with a plus and a minus phase. Furthermore, the control housing 26 is surmounted by a connecting pin 32, with which the control device is connected to ground.

Depending on the control signals of the control current, the control device provided in the control housing 26 is switched in such a way that all or individual PTC heating elements 2 connected together to form heating circuits are supplied with power current 28. The heat generated in the interior of the PTC heating element 2 is conducted by conduction through the conductor track 6 and transversely to its areal extension through the electrical insulating layer 10 and conducted away to the corrugated rib elements 22.

The Fig. 3 shows a PTC heating element 2 produced according to a second exemplary embodiment. The same components are compared with the exemplary embodiment according to FIG Fig. 1 provided with the same reference numerals.

In this exemplary embodiment, too, the present single PTC element 4 rests on opposing conductor tracks 6, which in the present case are formed by metallic contact plates. The contact tongues 8 are formed in one piece through these metal sheets 6 by punching them out. This heat-generating element of the PTC heating element 2 is wrapped in a hybrid film consisting of the film 14 and the electrically insulating mass 12. The film 14 forms the outside of the PTC heating element 2. The PTC element 4 and the contact plates 6 cut to the same dimensions are located at a distance from a bottom of a U-shaped area 40, which is caused by the impact of the heat-generating element in the electrical insulating layer 10 is formed. Furthermore, the electrical insulating layer 10 projects beyond the PTC element 4 and the Contact plates 6 also on the outside. In the finished product, the free space formed all around the PTC element 4 and the contact plates 6 can be filled with an insulating compound in order to eliminate or at least reduce air and creepage distances between the contact plates 6 of different polarity. The casting compound used in this case can have the same material as the electrically insulating compound which forms the corresponding layer of the electrical insulating layer 10 identified by reference numeral 12.

The Fig. 4 shows a second embodiment of an electrical heating device 20. This electrical heating device 20 has a self-contained housing 50 with two connecting pieces 52, via which a circulation chamber formed in the housing 50 is accessible. The inlets and outlets to the circulation chamber formed by the connecting pieces 52 serve to supply and discharge a liquid medium which is to be heated in the electrical heating device 20.

For this purpose, several U-shaped projections protrude into the circulation chamber, each of the U-shaped recesses, which open in the direction of a housing cover 54 identified by reference numeral 54, and with at least one PTC heating element 2 according to FIG Fig. 3 is provided. The U-shaped recesses are usually formed by heating ribs made of a material with good thermal conductivity, for example aluminum. The PTC heating elements 2 either lie directly on opposite inner surfaces of the heating ribs and are thus cast in a thermally conductive manner or else are pressed into them by a wedge element, as is the case EP 1 872 986 A1 of the present applicant describes. Also in Fig. 4 The embodiment shown has a control housing 26 with plugs 28, 30 for the power current 28 and the control current 30, which is fed to the electrical heating device 20 with the plus and minus poles. Furthermore, a ground connection 32 is also formed.

List of reference symbols

2

PTC heating element

4th

PTC element

6th

Track

8th

Contact tongue

10

electrical insulating layer

12th

electrically insulating mass

14th

foil

16

Position frame

20th

Electric heating element

22nd

Corrugated fin element

24

frame

26th

Control housing

28

Plug / power current

30th

Connector / control current

32

Ground connection

40

U-shaped area

50

casing

52

Connection piece

54

Housing cover

S.

gap

Claims (15)

1. A method of manufacturing a PTC heating element (2) having at least one PTC element (4) which is in electrically conducting contact with inner surfaces of electrical conductor tracks (6), at least one of the conductor tracks (6) being provided on its outer surface with an electrically insulating layer which includes a film (14) and an electrically insulating substance (12) with good thermal conductivity applied thereto, characterized in that initially the film (14) is prepared as an integral unit with the electrically insulating substance (12) and then placed on the outside of at least one of the electrical conductor tracks (6) as a prefabricated hybrid film comprising the film (14) and the electrically insulating substance (12) applied thereto.
2. The method of manufacturing a PTC heating element (2) according to claim 1, characterized in that the substance (2) is filled with particles having good thermal conductivity and has a thermal conductivity of at least 3 W/mK.
3. The method of manufacturing a PTC heating element (2) according to claim 2, characterized in that the volume ratio of the particles having good thermal conductivity is between 85 % and 95 %.
4. The method of manufacturing a PTC heating element (2) according to claim 2 or 3, characterized in that the particles having good thermal conductivity is formed of alumina.
5. The method of manufacturing a PTC heating element (2) according to any one of the preceding claims, characterized in that the electrically insulating substance (12) is formed of a silicone substance.
6. The method of manufacturing a PTC heating element (2) according to any one of the preceding claims, characterized in that the insulating layer is composed of the film (14) and the electrically insulating substance (12).
7. The method of manufacturing a PTC heating element (2) according to any one of the preceding claims, characterized in that the electrically insulating substance (12) is self-adhesive and is adhesively placed on the film (14).
8. The method of manufacturing a PTC heating element (2) according to any one of the preceding claims, characterized in that the film (14) is a polyimide film.
9. The method of manufacturing a PTC heating element (2) according to any one of the preceding claims, characterized in that the electrically insulating substance (12) has a layer thickness of between 100 and 300 µm, preferably between 150 and 250 µm.
10. The method of manufacturing a PTC heating element (2) according to any one of the preceding claims, characterized in that the electrically insulating layer (10) has a thickness of not more than 250 µm.
11. The method of manufacturing a PTC heating element (2) according to any one of the preceding claims, characterised in that the electrically insulating layer (10) has a dielectric strength of at least 3 kV DC at a thickness of 250 µm.
12. The method of manufacturing a PTC heating element (2) according to any one of the preceding claims, characterised in that the electrically insulating layer (10) has a disruptive strength of >20 kV/mm in a temperature range from -40 °C to +260 °C.
13. The method of manufacturing a PTC heating element (2) according to any one of the preceding claims, characterized in that the electrically insulating layer (10) is thermally stable up to 260 °C.
14. The method of manufacturing a PTC heating element (2) according to any one of the preceding claims, characterized in that the liquid phase of the electrically insulating substance (12) is formed of a cold-setting two-component substance.
15. Electrical heating device, in particular for a motor vehicle, having heat-emitting surfaces, characterized by a PTC heating element (2) produced according to one of Claims 1 to 14, its at least one electrically insulating layer being in heat-conductive contact with the heat-emitting surfaces.

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