PTC heating element and electric heating device for an automotive vehicle comprising such a PTC heating element

Abstract

A PTC heating element is provided that includes including a PTC heating element strip conductors via which the PTC element is powered and at least one of which is insulated on an outer surface with an electrical insulation layer. In order to provide improved insulation while maintaining adequate heat transfer from the PTC element to the heat-emitting surface through the electrical insulation layer, the electrical insulation layer comprises a film and an electrically insulating mass of good thermal conductivity applied to the film. Also provided is an electric heating device for an automotive vehicle that is provided with at least one PTC heating element of such a type.

Claims

1. A PTC heating element comprising: at least one PTC element, electrical strip conductors each having an inner surface in electrical contact with the PTC element, and an electrical insulation layer placed on an outer surface of at least one of the electrical strip conductors, wherein the electrical insulation layer comprises a film and an electrically insulating mass of good thermal conductivity applied to the film, wherein the electrically insulating mass is a paste-like mass applied to the film as a coating, which electrically insulating mass has a layer thickness of between 100 and 300 m, wherein the electrically insulating mass is cross-linked, and wherein the electrically insulating mass contacts the outer surface of the at least one of the electrical strip conductors.

2. A PTC heating element according to claim 1, wherein the electrically insulating mass is filled with particles of good thermal conductivity of between 1-5 W/mK.

3. A PTC heating element according to claim 2, wherein the proportion of the particles of good thermal conductivity in the electrically insulating mass is between 85 vol. % and 95 vol. %.

4. A PTC heating element according to claim 3, wherein the particles of good thermal conductivity are made from aluminum oxide.

5. A PTC heating element according to claim 1, wherein the electrically insulating mass is formed by a silicone mass.

6. A PTC heating element according to claim 1, wherein the insulation layer consists of the film (14) and the electrically insulating mass.

7. A PTC heating element according to claim 1, wherein the electrically insulating mass is self-adhesive and adheres to the film.

8. A PTC heating element according to claim 1, wherein the film is a polyimide film.

9. A PTC heating element according to claim 1, wherein the electrical insulation layer has a thickness of not more than 250 m.

10. A PTC heating element according to claim 1, wherein the electrical insulation layer has a dielectric strength of at least 3 kV DC at a thickness of 250 m.

11. A PTC heating element according, to claim 1, wherein the electrical insulation layer has a specific dielectric strength of >20 kV/mm in a temperature range of 40 C. to +260 C.

12. A PTC heating element according to claim 1, wherein the electrical insulation layer is temperature-stable up to 260 C.

13. A PTC heating element according to claim 1, wherein a liquid phase of the electrically insulating mass is formed from a cold-curing 2-component mass.

14. A PTC heating element comprising: at least one PTC element, electrical strip conductors each having an inner surface in electrical contact with the PTC element, and an electrical insulation layer provided on an outer surface of at least one of the electrical strip conductors, wherein the electrical insulation layer comprises a film and an electrically insulating mass of good thermal conductivity applied to the film, wherein the mass is filled with particles of good thermal conductivity of between 1-5 W/mK, wherein the proportion of the particles of good thermal conductivity is between 85 vol. % and 95 vol. %, and wherein the electrically insulating mass has a layer thickness of between 100 and 300 m.

15. A PTC heating element according to claim 14, wherein the insulation layer consists of the film and the electrically insulating mass.

16. A PTC heating element comprising: at least one PTC element, electrical strip conductors each having an inner surface in electrical contact with the PTC element, and an electrical insulation layer placed on an outer surface of at least one of the electrical strip conductors, wherein the electrical insulation layer comprises a film and an electrically insulating mass of good thermal conductivity applied to the film, wherein the electrical insulation layer has a dielectric strength of at least 3 kV DC at a thickness of 250 m, wherein the electrical insulation layer has a specific dielectric strength of >20 kV/mm in a temperature range of 40 C. to +260 C., wherein the electrical insulation layer is temperature-stable up to 260 C., wherein the electrically insulating mass is formed by a cross-linked plastic applied to the film as a coating in a paste-like form, which electrically insulating mass has a layer thickness of between 100 and 300 m, and wherein the coating of the electrically insulating mass is set after being applied to the film and contacted against the outer surface of the at least one of the electrical strip conductors.

17. An electric heating device for an automotive vehicle, comprising: heat-emitting surfaces, and a PTC heating element comprising, at least one PTC element, electrical strip conductors each having an inner surface in electrical contact with the PTC element, and an electrical insulation layer provided on an outer surface of at least one of the electrical strip conductors, wherein the electrical insulation layer comprises a film and an electrically insulating mass of good thermal conductivity applied to the film, and wherein the PTC heating element lies in a heat-conducting manner against the heat-emitting surfaces with interposition of the least one electrical insulation layer therebetween.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details and advantages of the present invention become apparent from the following description of embodiments in combination with the drawing, in which:

(2) FIG. 1 is a perspective side view of a PTC heating element for a first embodiment of a first electric heating device;

(3) FIG. 2 is a perspective side view of the first electric heating device;

(4) FIG. 3 is a perspective side view of a second embodiment of a PTC heating element for a second electric heating device;

(5) FIG. 4 is a perspective side view of the second electric heating device.

DETAILED DESCRIPTION

(6) The embodiment shown in FIG. 1 of a PTC heating element marked with reference numeral 2 comprises a plurality of PTC elements 4 which are provided one after the other in longitudinal direction of the PTC heating element 2, which lie between two strip conductors 6 respectively lying at opposite sides of the PTC elements 4 against said elements, in the present case in the form of contact sheets which are extended at a front side of the PTC element 4 for the formation of contact zones 8 beyond the heat-generating element proper. In addition to the above-mentioned components, this heat-generating element of the PTC heating element 2 comprises an insulation layer 10 which adjoins the strip conductors 6 at both sides and respectively covers the heat-generating element of the PTC heating element 2 on the outside. The electrical insulation layer 10 consists of an electrically insulating mass 12 which adheres to a film 14 of polyimide. The electrical insulation layer 10 has previously been prepared by applying the electrically insulating mass 12 to the film 14 and has then been placed on the respective strip conductor 6. The blank of the electrical insulation layer 10 is here chosen in width direction such that it slightly projects beyond the PTC elements 4. A surrounding positioning frame 16 is provided between the opposing edges of the electrical insulation layer 10. This frame is a positioning frame 16 which in longitudinal direction of the PTC heating element 2 comprises webs which are disposed one after the other and guarantee a predetermined distance between PTC elements 4 arranged one after the other. In the area in FIG. 1 which has partly been removed in the drawing, this web corresponds to the gap S.

(7) The strip conductors 6 are confined on the inside by the positioning frame 16. It is just the insulation layer 10 that is positioned on the positioning frame 16 on the outside. At this place the insulating layer 10 is firmly connected in a fluid-tight manner to the positioning frame 16, e.g. glued or connected by overmolding to the positioning frame 16, namely during the injection-molding manufacture of the positioning frame 16 from a heat-resistant plastic. This plastic may e.g. be silicone.

(8) At any rate it must be ensured that in the illustrated embodiment the electrical insulation layer 10 is respectively connected to the edges of the positioning frame 16 in such a manner that no moisture or dirt can pass into the interior of the positioning frame 16.

(9) In the illustrated installation situation the electrical insulation layer 10 is provided on its outside with the film 14, whereas the electrically insulating mass 12 is located between the film 14 and the strip conductor 6.

(10) FIG. 2 is a side view of an electric heating device 20 in which plural PTC heating elements 2 are installed as heat-generating layers. In the vicinity of the PTC heating elements 2, corrugated rib elements 22 are respectively provided that adjoin the outside of the electrical insulation layer 10 and are connected in a heat-conducting manner to the PTC heating elements 2 to receive the heat generated in the heat-generating element, first by way of heat conduction, and to deliver it to the air passed transversely through a frame of plastic, which is marked with reference numeral 24. To this end the PTC elements 2 and the corrugated rib elements 22 are inserted as layers into the frame 24 and held with a spring in a pre-tensioned state relative to one another.

(11) This plastic frame 24, which is here bipartite, 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, plugs for the power current 28 and the control current 30 are exposed. In the plug of the power current 28, two poles for powering the electric heating device 20 with a plus and a minus phase are exposed. Furthermore, a connection pin 32 with which the control device is grounded projects over the control housing 26.

(12) Depending on the control signals of the control current, the control device provided in the control housing 26 is wired such that all or individual ones of the PTC heating elements 2 which are connected together to form heating circuits are supplied with power current 28. The heat generated thereby in the interior of the PTC heating element 2 is passed by conduction through the strip conductor 6 and in a direction transverse to its area-like extension through the electrical insulation layer 10 and is delivered to the corrugated rib elements 22.

(13) FIG. 3 shows a second embodiment of a PTC heating element 2. Like components are provided with like reference numerals by comparison with the embodiment according to FIG. 1.

(14) In this embodiment, too, the PTC element 4, which is here the only one, lies against opposite strip conductors 6 which are here formed by metallic contact sheets. By way of free punching the contact tongues 8 are integrally formed by way of these metal sheets 6. This heat-generating element of the PTC heating element 2 is folded in 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 sheets 6 which are cut to the same dimension are positioned at a distance from a bottom of a U-shaped portion 40, which is formed by the folding in of the heat-generating element in the electrical insulation layer 10. Furthermore, the electrical insulation layer 10 projects over the PTC element 4 and the contact sheets 6 also on the outside. In the finished product, the free space formed thereby over the whole circumference around the PTC element 4 and the contact sheets 6 can be filled with an insulating mass to eliminate or at least reduce air gaps and creep distances between the contact sheets 6 of different polarity. The casting mass used in this process may be of the same material as the electrically insulating mass which forms the corresponding layer, marked with reference numeral 12, of the electrical insulation layer 10.

(15) FIG. 4 shows a second embodiment of an electric heating device 20. This electric heating device 20 has a self-contained housing 50 with two connection nozzles 52 through which a circulation chamber formed in the housing 50 is accessible. The inlets and outlets formed by the connection nozzles 52 with respect to the circulation chamber serve the supply, and discharge, respectively, of a liquid medium which is to be heated in the electric heating device 20.

(16) To this end several U-shaped projections project into the circulation chamber, wherein each of the U-shaped recesses opening towards a housing lid 54 marked with reference numeral 54 is provided with at least one PTC heating element 2 according to FIG. 3. The U-shaped recesses are normally formed by heating ribs of a material of good thermal conductivity, e.g. aluminum. The PTC heating elements 2 lie either directly against opposing inner surfaces of the heating ribs and are thus cast in a heat-conducting manner or, however, are pressed therein by a wedge element, as described in EP 1 872 986 A1 of the present applicant. The embodiment shown in FIG. 4 also has a control housing 26 with plugs 28, 30 for the power current 28 and the control current 30 which is there supplied with plus and minus pole to the electric heating device 20. Furthermore, a ground connection 32 is also formed.