EP3101999A1 - Ptc heating element and electric heater for a motor vehicle comprising such a ptc heating element - Google Patents

Abstract

The present invention relates to a PTC heating element (2) for an electric heating device for a motor vehicle and is intended to specify a PTC heating element (2), which is electrically insulated in an improved manner on the outside, as well as the need for adequate heat transfer from the PTC Element (4) on the heat-emitting surface by the electrical insulating layer (10) is to be taken into account. In order to solve the above problem, the present invention proposes an electrical insulating layer (10) which abuts the outside of at least one of the conductor tracks through which the PTC element (4) is energized and a foil (14) and a foil applied thereto having electrically insulating mass (12) with good thermal conductivity. The electric heater according to the invention, in particular for a motor vehicle, is provided with at least one such PTC heating element (2).

Description

The present invention relates to an electric heating device for a motor vehicle and a PTC heating element as such, which is installed in said electric heating device.

PTC elements have found good acceptance in automotive electric heaters because of 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 on both sides electrically conductively attached to the PTC element printed conductors, which are usually the electrical connection of the PTC element. Such heat-generating elements are applied 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 releases heat to heat-emitting surfaces on both sides.

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

From the EP 1 768 459 A1 For example, an electric heating device for air heating is known, in which the heat-emitting surfaces are formed by corrugated fin layers, which rest on both sides on the PTC element. In the prior art, a plurality of PTC elements are accommodated in a position frame and contacted on both sides with contact plates, which form the generic conductor tracks and serve the electrical connection of the PTC element.

An also generic electric heater is for example from the EP 1 872 986 A1 known. In this prior art, heating fins protrude into a circulation housing, which is of 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 each provided on the outside of the conductor tracks insulation layers are added. As a result, the PTC element and the power supply on both sides of adjacent printed conductors are electrically insulated in the Heizrippe added. Sometimes, however, it is possible, for example, in an operation of the electric heater with the mains voltage of a motor vehicle of 12 volts, only one side to provide insulation and on the other side to contact the PTC element directly to ground. "Mass" can be formed by the outside of a heating rib or by a corrugated fin layer, which bears on one side heat conductive against the one or more PTC elements.

In the from the EP 1 768 458 A1 As is known in the art, the insulating layer is formed by a two-layered structure comprising a polyimide film and a ceramic layer. Especially in high-voltage applications and especially with regard to the operation of the electric heater in an electric vehicle is to ensure a safe electrical insulation of the PTC element and the both sides of this contacting traces. A laminated insulating film for similar purposes describes the EP 2 109 345 A1 ,

The present invention wants to make a contribution to this. The present invention is based on the problem of providing a PTC heating element which is electrically insulated in an improved manner on the outside, 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 ,

To solve the above problem, the present invention provides a PTC heating element having the features of claim 1. This PTC heating element has, as an electrical insulating layer, a combination of a foil and an electrically insulating mass with good thermal conductivity applied thereto. The film is initially prepared together with the mass regularly as a unit and then applied as a prefabricated hybrid film comprising the film and the applied electrically insulating mass on the outside against at least one of the electrical conductor.

In this case, the electrical insulating layer has a layer structure with a usually continuous foil and an applied thereon usually with a constant thickness electrically insulating mass with good thermal conductivity. The film of the invention offers in particular due to the elastic and electrically insulating mass the possibility of bumps, which also small particles such. As dust grains may be to compensate for between the conductor track and a heat-emitting counter surface of an electric heater, in particular in a motor vehicle. Where, however, in conventional insulating films as insulating, which can attract foreign bodies by electrostatic action, the insulation can be penetrated by such bumps on the outside of the PTC element and thus bridged, which has the consequence that the voltage applied to the PTC element just not insulated from the heat emitting surface. This can lead to short circuits within the electric heater and thus to failure. Without a corresponding shutdown, a life-threatening condition may arise.

The electrically insulating mass is preferably a pasty mass, which, although preferably already crosslinked and thus set, so that it is no longer flowable in the true sense. However, the mass can perform certain compensating movements, for example, to escape at positions within the insulating layer with a punctiform pressurization, while receiving the punctiform pressure and to equalize without the insulating effect is lost by the electrical insulating layer. A good thermally conductive material preferably has a thermal conductivity of at least 3 W / (m * K), more preferably of at least 5 W / (m * K). The electrically insulating composition 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 rollers through a bath consisting of the electrically insulating mass. For this purpose, the electrically insulating mass may be mixed with a solvent, whereby the viscosity of the electrically insulating compound is reduced or the wetting of the film can be improved. As an electrically insulating material is usually a plastic compound is used, which sets or cures completely or partially after the coating of the film. Preferably, a crosslinking plastic is used, wherein after the coating of the film can accelerate this accelerated by the addition of heat and / or impingement with an irradiation. For this purpose, the device provided for the production of the insulating layer usually has a heating or irradiation path which passes through the film coated with the mass.

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

In addition to the aforementioned coating of the film from a system of rolls and in a molten bath of the electrically insulating composition, it may also be applied to the film by printing or spraying, in which case doctoring is preferred in the case of printing.

The composition preferably comprises as liquid phase usually a silicone composition. The liquid phase is preferably formed by an addition-crosslinking 2-component silicone which cures at room temperature and cures under pressure under heat. The mass has a viscosity at 25 ° C of between 100 and 200 Pa s. In view of a good fluidity, the 2-component silicone is usually mixed with gasoline or toluene as a diluent to obtain a viscosity at 25 ° C in a range of between 4 and 15, preferably between 5 and 8 Pa s. When crosslinked, the liquid phase constituent of the composition should have a hardness of Shore A of about 10-40. This liquid phase is usually admixed with a heat conductivity increasing but electrically insulating solid.

The mass is preferably selected so that good wetting properties to the particles with good thermal conductivity exist. The particles may additionally be treated with an adhesive before the particles are added to the pasty mass in order to disperse them uniformly. The mass may be, for example, a silicone composition or at least predominantly comprise silicone composition.

In view of the electrical insulating properties of the insulating layer of this filler fraction is usually formed by electrically insulating particles with good thermal conductivity, with particles of alumina are preferred, especially gas or water-diluted particles, which are due to their morphology relatively close within the liquid phase and do not degrade the flow properties of the filled insulating mass as 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, more preferably between 85% by volume and 95% by volume. Such a volume fraction on 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 foil and the electrically insulating mass, wherein the electrically insulating mass itself can have several phases, namely, for example, the filler fraction and the liquid phase. The development brings with it that the design of the insulating layer is formed solely of the film and the electrically insulating material, wherein the film on the side facing away from the mass may be additionally formed self-adhesive and may accordingly be provided with an adhesive layer. This adhesive layer is usually provided on the prefabricated insulating layer. It is applied to the film on one side after or before the electrically insulating mass 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 embodiment, the present invention proposes 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 .mu.m, preferably between 150 .mu.m and 250 .mu.m. By this thickness dimensions results in a sufficient electrical safety, ie reliable outside insulation of the PTC element by the electrical insulating layer with a sufficient absolute heat dissipation through the electrical insulating layer, which is favorable in view of the self-regulating properties of the PTC element for effective operation of the same , Practical experiments have shown that, in particular with a composition filled with electrically insulating filler particles, in particular applied to a polyimide layer on the one hand at a layer thickness of 250 μm of the insulating layer, a specific electrical breakdown strength of 20 kV / mm, a volume resistivity of 1.9 * 10 ¹⁵ ohms / cm and a tracking resistance of CTI> 600 can be achieved. In this case, the electrical insulating layer is preferably temperature-resistant in a temperature range of -40 ° C to 260 ° C.

With the present invention, therefore, an electrical insulating layer is given, which has a very good thermal conductivity, so that the PTC element can be operated with good efficiency, which is also easy to prepare and produce by the meter and thus easy to process and furthermore a 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, however, is mainly caused by the insulating mass, this can also be provided on both sides of a thinner selected film. In such a case, care must be taken only for good heat resistance of the film within the electrically insulating layer. Furthermore, mechanical properties such as good tear resistance and the like are desired. The thinner the film is selected within the electrical insulating layer, the less must be paid to a good thermal conductivity of the film itself.

The liquid phase of the electrically insulating mass, d. H. the liquid phase of the suspension, which possibly absorbs particles of good thermal conductivity, is formed from a cold-curing 2-component material. Preferably, the liquid phase alone consists of such a 2-component composition. Such a cold curing compound usually cures at a heating of not more than 80 ° C in a few minutes, d. H. in 2 to 8 minutes. Higher temperatures do not have to be expended to achieve a hardening of the mass.

In a preferred embodiment, the conductor track is regularly made of a stamped contact plate, which also forms the terminal lugs for electrical connection of the heat-generating layer. In this case, the heat-generating layer is the PTC element with the conductor tracks adjacent thereto or thus directly connected thereto and the insulating layer provided on the outside. The at least one PTC element and the contact plates usually directly adjacent thereto may be provided as a preassembled unit in a frame which holds these elements of the heat-generating element together to form a preassembled unit, as for example in US Pat EP 1 921 896 respectively. 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 for clamping the heat-generating element in a U-shaped pocket is used and optionally movably guided and held on the frame, as shown in EP 1 921 896 A1 is known, is located on this side between the electrical insulating layer usually a sliding layer on which the wedge element during the distortion of the heat generating element in the pocket can slide past in an improved manner. Such a layer may for example be formed by a sheet metal strip which is provided between the wedge element and the mass.

With its independent claim 14, the present invention proposes a heating device, in particular for a motor vehicle with heat-emitting surfaces. These heat-emitting surfaces may be outer surfaces of a corrugated finned radiator element or opposite inner surfaces of a substantially U-shaped pocket of a fluid heater.

The proposed with their sidelined electrical heating device is in particular a heater for high voltage applications in a motor vehicle. The heater is operated with a voltage up to 800 volts.

Fig. 1

eine perspektivische Seitenansicht eines PTC-Heizelementes für ein erstes Ausführungsbeispiel einer ersten elektrischen Heizvorrichtung;

Fig. 2

eine perspektivische Seitenansicht der ersten elektrischen Heizvorrichtung;

Fig. 3

eine perspektivische Seitenansicht eines zweiten Ausführungsbeispiels eines 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 will become apparent from the following description of embodiments in conjunction with the drawings. In this show:

Fig. 1

a side perspective view of a PTC heating element for a first embodiment of a first electric heater;

Fig. 2

a side perspective view of the first electric heater;

Fig. 3

a side perspective view of a second embodiment of a PTC heating element for a second electric heater and

Fig. 4

a perspective side view of the second electric heater.

This in Fig. 1 shown embodiment of a marked with reference numeral 2 PTC heating element comprises a plurality in the longitudinal direction of the PTC heating element 2 consecutively provided PTC elements 4, the present between two each on opposite sides of the PTC elements 4 adjacent to these tracks 6 in the form of contact plates, the on a front side of the PTC element 4 are extended to form contact tongues 8 on the actual heat generating element out, rest. 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 the heat-generating element of the PTC heating element 2 on the outside respectively covered. The electrical insulating layer 10 consists of an electrically insulating mass 12, which adheres to a film 14 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 blank of the electrical insulating layer 10 is selected in the width direction so that it slightly projects beyond the PTC elements 4. Between the opposite edges of the electrical insulating layer 10, a circumferential position frame 16 is provided. 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 and which ensure a predetermined spacing between successive PTC elements 4. In the partially graphically taken away area in Fig. 1 this bridge corresponds to the gap S.

The conductor tracks 6 are bounded on the inside by the positioning frame 16. Only the insulating layer 10 rests on the outside of the position 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 by injection molding with the position frame 16, in the injection-molding of the position frame 16 of a heat-resistant Kunstsoff. This plastic may be for example silicone.

In any case, care must be taken that, in the 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 reach the interior of the positioning frame 16.

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

In Fig. 2 Fig. 3 is a side view of an electric heater 20 in which a plurality of PTC heating elements 2 are incorporated as heat-generating layers. Adjacent to the PTC heating elements 2 respectively corrugated rib elements 22 are provided, which abut against the outside of the electrical insulating layer 10 and heat-conducting with the PTC heating elements 2 are connected to receive the heat generated in the heat-generating element first by conduction and deliver to the transversely through a marked with reference numeral 24 frame made of plastic air. For this purpose, the PTC elements 2 and the corrugated rib elements 22 are inserted as layers in the frame 24 and held biased against each other with a spring.

This present two-part plastic frame 24 is connected to a control housing 26, in which the contact tongues 8 are electrically connected to a control device. On the control housing 26 are plug for the power current 28 and the control current 30 free. In the plug of the power current 28 are two poles for the energization of the electric heater 20 with a plus and a minus phase free. 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 so that all or individual PTC heating elements 2 interconnected to heating circuits are supplied with power current 28. The heat generated in the interior of the PTC heating element 2 is passed through the conductor track 6 and transversely to its areal extent by the electrical insulating layer 10 and derived to the corrugated rib elements 22.

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

Also in this embodiment, the present only PTC element 4 is applied to opposite conductor tracks 6, which in the present case are formed by metallic contact plates. By free punching 6, the contact tongues 8 are integrally formed by these metal sheets. 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. In this case, the PTC element 4 and cut to the same dimension contact plates 6 at a distance from a bottom of a U-shaped portion 40, which by the turning 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 thereby all around the PTC element 4 and the contact plates 6 can be filled with an insulating mass in order to eliminate or at least reduce air and creepage distances between the contact plates 6 of different polarity. The molding compound used in this case may be identical to the material of the electrically insulating mass, which forms the corresponding position of the electrical insulating layer 10 marked with reference numeral 12.

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

For this purpose, a plurality of U-shaped projections protrude into the circulation chamber, wherein each of the U-shaped recesses opening 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. 3 is provided. The U-shaped recesses are usually formed by heating ribs made of a good thermal conductivity material, such as aluminum. The PTC heating elements 2 are either directly on opposite inner surfaces of the heating ribs and are thus thermally conductive potted or pressed by a wedge element in it, like this EP 1 872 986 A1 the present applicant describes. Also in Fig. 4 embodiment shown has a control housing 26 with plugs 28, 30 for the power current 28 and the control current 30, which is fed there with plus and minus pole of the electric heater 20. Furthermore, a ground terminal 32 is formed.

LIST OF REFERENCE NUMBERS

2

PTC heating element

4

PTC element

6

conductor path

8th

contact tongue

10

electrical insulating layer

12

electrically insulating mass

14

foil

16

position frame

20

Electric heating element

22

Corrugated fins element

24

frame

26

control housing

28

Plug / power current

30

Plug / flow control

32

ground connection

40

U-shaped area

50

casing

52

spigot

54

housing cover

S

gap

Claims (15)

PTC heating element (2) with at least one PTC element (4) whose electrical conductor tracks (6) are provided on at least one outer surface with an electrical insulating layer (10) which is electrically conductive with its inner surface with the PTC element (4) are contacted and of which at least one is provided on its outer surface with an electrical insulating layer,
characterized,
in that the electrical insulating layer (10) has a foil (14) and an electrically insulating mass (12) with good thermal conductivity applied thereto. PTC heating element (2) according to claim 1, characterized in that the mass (2) with particles of good thermal conductivity of between 1 - 5 W / mK, preferably at least 3 W / mK is filled. PTC heating element (2) according to claim 2, characterized in that the proportion of particles with good thermal conductivity between 85 vol .-% and 95 vol .-%. PTC heating element (2) according to claim 2 or 3, characterized in that the particles of good thermal conductivity are formed from aluminum oxide. PTC heating element (2) according to one of the preceding claims, characterized in that the insulating mass (12) is formed by a silicone compound. PTC heating element (2) according to one of the preceding claims, characterized in that the insulating layer consists of the film (14) and the electrically insulating mass (12). PTC heating element (2) according to one of the preceding claims, characterized in that the electrically insulating compound (12) is self-adhesive and adheres to the film (14). PTC heating element (2) according to one of the preceding claims, characterized in that the film (14) is a polyimide film. PTC heating element (2) according to one of the preceding claims, characterized in that the electrically insulating compound (12) has a layer thickness of between 100 and 300 microns, preferably between 150 and 250 microns. PTC heating element (2) according to one of the preceding claims, characterized in that the electrical insulating layer (10) has a thickness of not more than 250 microns. PTC heating element (2) according to one of the preceding claims, characterized in that the electrical insulating layer (10) at a thickness of 250 microns has an electrical breakdown strength of at least 3 kV DC. PTC heating element (2) according to one of the preceding claims, characterized in that the electrical insulating layer (10) in a temperature range of -40 ° C to +260 ° C has a specific dielectric strength of> 20 kV / mm. PTC heating element (2) according to one of the preceding claims, characterized in that the electrical insulating layer (10) is temperature-resistant up to 260 ° C. PTC heating element (2) according to one of the preceding claims, characterized in that the liquid phase of the electrically insulating mass (12) is formed from a cold-curing 2-component mass. Electric heating device, in particular for a motor vehicle with heat-emitting surfaces, characterized by a PTC element (4) according to one of claims 1 to 13, which bears thermally conductively on the heat-emitting surfaces with the interposition of the at least one electrical insulating layer.

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