ELECTRIC HEATING DEVICE FOR MOBILE APPLICATIONS

Abstract

An electrical heating device for mobile applications, includes a substrate and a heat-conducting layer formed on the substrate. The heat-conducting layer has at least one heat-conducting track that is arranged on the substrate, and the heat-conducting track is structured such that a multiplicity of track sections, separated from one another by insulating gaps, is formed. The heat-conducting track has at least one deflection section at which the heat-conducting track is deflected and which is arranged between a first and a second track section, wherein the first and the second track section have a smaller curvature in comparison with the deflection section. The heat-conducting track in the first track section or in the deflection section branches into at least two branch tracks separated from one another by one or more branch insulating gaps. The branch tracks meet up again in the second track section or in the deflection section.

Claims

1. Electrical heating device for mobile applications, having: a substrate and a heat-conducting layer formed on the substrate, wherein the heat-conducting layer has at least one heat-conducting track that is arranged on the substrate, wherein the heat-conducting track is structured such that a multiplicity of track sections, separated from one another by insulating gaps, is formed, wherein the heat-conducting track has at least one deflection section at which the heat-conducting track is deflected and which is arranged between a first and a second track section, wherein the first and the second track section have a smaller curvature in comparison with the deflection section, in particular are designed so as to be at least substantially straight, wherein the heat-conducting track in the first track section or in the deflection section branches into at least two branch tracks separated from one another by one or more branch insulating gaps, wherein the branch tracks meet up again in the second track section or in the deflection section.

2. Electrical heating device according to claim 1, wherein the first and second track section run at least sectionally parallel to one another and/or in that the deflection section brings about a deflection by at least approximately 180.

3. Electrical heating device according to claim 1, wherein an inner branch track is designed so as to be narrower with respect to an outer branch track, at least on average and/or at least sectionally, preferably completely.

4. Electrical heating device according to claim 1, wherein the branch tracks extend over at most 70%, preferably at most 30%, more preferably at most 15% and/or at least 5%, preferably at least 10%, of the first and/or second track section.

5. Electrical heating device according to claim 1, wherein the heat-conducting track in the first track section or in the deflection section branches into at least three branch tracks that are separated from one another by branch insulating gaps, the branch tracks meeting up again in the second track section or in the deflection section.

6. Electrical heating device according to claim 1, wherein the branch tracks are arranged at the same height with respect to a surface of the substrate and/or have an identical thickness perpendicular to the surface of the substrate.

7. Electrical heating device according to claim 1, wherein a distance between adjacent track sections having mutually opposing current flow directions is designed so as to be locally widened in the region of the reversal section and/or in that the at least one heat-conducting track extends on the substrate in a bifilar pattern.

8. Electrical heating device according to claim 1, wherein the heat-conducting track has at least two or at least three deflection sections.

9. Electrical heating device according to claim 1, wherein the heat-conducting layer covers at least 80% of the substrate surface, preferably at least 85% of the substrate surface and/or wherein an electrically insulating material is arranged in the insulating gaps and/or the heat-conducting track is designed such that in each case two track sections with an identically oriented current flow direction run adjacent and parallel to one another at least over a predominant proportion of its length and/or the heat-conducting track is designed such that it runs straight over a predominant proportion of its length, and/or wherein at least one further layer, in particular an insulating layer, is formed on the heat-conducting layer.

10. Electrical heating device according to claim 1, wherein the electrical heating device is a motor vehicle heating device.

11. Vehicle, in particular motor vehicle, comprising an electrical heating device according to claim 1.

12. Use of an electrical heating device according to claim 1, in a motor vehicle.

Description

[0031] The disclosure is described below with reference to exemplary embodiments that are explained in more detail with reference to the drawings. In the figures:

[0032] FIG. 1 shows a schematic sectional view of an electrical heating device according to the disclosure;

[0033] FIG. 2 shows a section of a heat-conducting layer according to a comparative example;

[0034] FIG. 3 shows a section analogous to FIG. 2, according to an exemplary embodiment according to the disclosure; and

[0035] FIG. 4 shows a section analogous to FIGS. 2 and 3 according to a further exemplary embodiment.

[0036] In the following description, the same reference signs are used for identical and functionally identical parts.

[0037] FIG. 1 shows a schematic section of a heating device according to the disclosure. Said heating device comprises a substrate 10, an electrically insulating layer 11 arranged (directly) on the substrate 10, a heat-conducting layer 12 arranged (directly) on the electrically insulating layer 11, and an insulating layer 13 arranged (directly) on the heat-conducting layer 12. The electrically insulating layer 11 and the insulating layer 13 are merely optional. The electrically insulating layer 11 is provided in particular when the substrate 10 is formed from a conductive material, for example metal.

[0038] The electrical heating device according to FIG. 1 is designed to heat a fluid in a vehicle. In this case, the fluid may be formed in particular by air to be heated or by a fluid in a fluid circuit of the vehicle. The electrical heating device is in this case in particular designed as a high-voltage heater for operation with an operating voltage in the range between 150 volts and 900 volts, in particular in the range between 200 volts and 600 volts. However, a design of for example up to more than 1000 volts is also possible.

[0039] The substrate 10 is in particular at the same time designed as a heat exchanger for transferring released heating power to the fluid to be heated. In particular, an underside (not shown) may be provided with a plurality of heat-exchange ribs and/or channels via which the fluid to be heated is guided. The substrate 10 may preferably (inexpensively from a production point of view) be formed from a metal material with a high heat transfer coefficient, in particular from aluminium or an aluminium alloy. It is also however possible in principle to manufacture the substrate 10 from an electrically insulating material with high thermal conductivity, such as in particular from a corresponding ceramic.

[0040] The electrically insulating layer 11 preferably has a high thermal conductivity. The electrically insulating layer 11 is furthermore preferably formed from aluminium oxide. The electrically insulating layer 11 may furthermore be deposited on the substrate 10 in a thermal spraying method. In particular in the event that the substrate is formed from aluminium or an aluminium alloy, the electrically insulating layer 11 may also be formed for example by targeted oxidation of the surface of the substrate 10. The electrically insulating layer 11 is designed to electrically insulate the substrate 10 from the heat-conducting layer 12 (but at the same time also to allow a good transfer of heat to the material of the substrate 10).

[0041] The heat-conducting layer 12 is preferably deposited on the substrate 10 (or on the insulating layer 11). The heat-conducting layer 12 may be formed from a metal material (in particular from a nickel-chromium alloy). The heat-conducting layer 11 is preferably deposited in a thermal spraying method. As an alternative, it is also however possible, for example, to deposit the heat-conducting layer 11 in a printing or casting method.

[0042] The heat-conducting layer 12 is structured such that at least one heat-conducting track is formed, this being designed to release resistive heat when an electric voltage is applied between its opposing ends. In principle, the heat-conducting track may be structured as described in WO 2013/186106 A1 (apart from the branch tracks in the region of the deflection sections, which will be described in more detail below).

[0043] In an edge region of the electrical heating device, there may be provided connections for connecting the heat-conducting tracks to an electric power supply. Such connections may be arranged above an edge of the substrate 10 (for example adjacent to one another) so as to be electrically insulated from one another. In this case, a first connection may be designed to make electrical contact with the heat-conducting track and apply a first electrical potential, and a second connection may be designed to make electrical contact with the heat-conducting track and apply a different second potential. A desired potential difference is thus able to be applied to the heat-conducting track via the two connections.

[0044] FIG. 2 shows a cutout of a comparative example for a structure of the heat-conducting layer 12. In general, this heat-conducting layer may be structured such that it extends on the substrate 10 in a bifilar pattern.

[0045] The heat-conducting layer has a heat-conducting track 14 that comprises a multiplicity of track sections 15a, 15b, 15c and 15d formed adjacent to one another. The track sections 15a to 15d are separated from one another by insulating gaps 16 and thus electrically insulated from one another. The insulating gaps may preferably be formed by virtue of the fact that the heat-conducting layer 12 is initially deposited over the area of the substrate 10 and the material of the heat-conducting layer 12 is then removed in a targeted manner in the region of the insulating gaps, in particular through laser processing. FIG. 2 schematically illustrates preferred current flow directions in the heat-conducting track 14 using arrows.

[0046] The insulating gaps 16 preferably have an (at least substantially) constant width (over their longitudinal extent). This achieves a situation whereby the track sections 15a to 15d of the heat-conducting track 14 are able to cover a large area of the surface of the substrate, such that the available area is able to be utilized as optimally as possible to form track sections that provide heating power.

[0047] The track sections 15a and 15b or 15c and 15d (which run straight) are connected to one another via deflection sections 17a and 17b. The heat-conducting track 14 (in a main plane) is deflected by (at least substantially) 180 degrees in the deflection section 17a, such that the conductor track sections 15a, 15b (with opposing current flow direction) run adjacent and parallel to one another, separated only by an insulating gap 16.

[0048] In the comparative example according to FIG. 2, a region 19 with a comparatively high current flow occurs in the reversal section 17a, since the flowing electric current predominantly seeks the path of least electrical resistance (or the shortest path). Such an inhomogeneous current distribution through the cross section of the heat-conducting track 14 leads to strong local heating in the region 19 through which electric current flows to a greater extent, such that the risk of hotspots exists there, which hotspots may negatively influence the lifetime of the electrical heating device due to strong heating. In the comparative example according to FIG. 2, maximum temperatures of 254 C. may arise in this case.

[0049] The problem of the formation of undesired hotspots is solved or at least alleviated through the formation of the heat-conducting layer 12 according to FIG. 3 (which illustrates an embodiment of the electrical heating device according to the disclosure in more detail). The heat-conducting layer 12 according to FIG. 3 may in particular be designed like the heat-conducting layer 12 according to FIG. 2 (according to the comparative example), with the following differences, which are explained in more detail. Upstream of the deflection section 17a, a first track section 15a branches off, such that the electric current flows over two paths that are insulated from one another (by branch insulating gaps). As a result, the current distribution is effectively moderated in comparison. A region 19 with an increased current density may still occur. However, this region 19 is far less pronounced than in the comparative example according to FIG. 2. Overall, the track section 15a thus branches into two branch sections 21a, 21b. These branch sections 21a, 21b meet up at the end of the deflection section 17a in the embodiment according to FIG. 3. With the same structure, apart from the branch sections, as in the comparative example according to FIG. 2, a considerably lower maximum temperature of just 226 C. occurs.

[0050] FIG. 4 shows a cutout of a further embodiment of the electrical heating device according to the disclosure. In contrast to the embodiment according to FIG. 3, the first track section 15a in this case branches into three branch sections 21a, 21b and 21c (separated by branch insulating gaps 20a, 20b). The current distribution is thereby able to be made even more even. In addition, in the embodiment according to FIG. 4, it is provided for the branch sections 21a to 21c to meet up again only at a distance with respect to an end of the deflection section 17a. The start and the end of the branch sections 21a to 21c thus lie adjacent to one another (in relation to the current direction). In principle, this may also be the case in the embodiment according to FIG. 3.

[0051] It is preferable (as illustrated schematically in FIGS. 3 and 4) for the inner branch section 21a or the two inner branch sections 21a and 21b (according to FIG. 4) to be designed so as to be narrower than the outer (outermost) branch section 21b or 21c (at least on average). As a result, a comparatively high proportion of the current is forced onto the branch sections lying further outward or the branch section lying further outward, which further counteracts the formation of a hotspot in the region 19.

[0052] As illustrated schematically in FIG. 1, at least one further insulating layer 13, which covers the upper side of the heat-conducting layer 12, facing away from the substrate 10, may be formed on the heat-conducting layer 12 or on the correspondingly structured heat-conducting tracks 14. The further insulating layer 13 is preferably in particular designed such that it also fills the insulating gaps 16, 20 between the track sections 15a to 15d. Particularly good insulation of the track sections 15a to 15d from one another is thereby ensured. The further insulating layer 13 may for example be deposited on the structured heat-conducting track 14 following the structuring of the heat-conducting layer 12. The deposition may in this case preferably be performed for example using a thermal spraying method, a casting method or the like. In particular, the further insulating layer 13 may be formed for example by aluminium oxide, so as to achieve good electrical insulation and at the same time good thermal conductivity.

[0053] One or more further layers is/are additionally preferably applied to the further insulating layer 13. It may in particular be advantageous to form at least an additional sensor layer for monitoring the function of the electrical heating device.

[0054] A distance between adjacent track sections in the region of the deflection section 17a may be designed so as to be (locally) widened, such that the deflection of the heat-conducting track 14 encloses for example a (substantially) drop-shaped or match-head-shaped region 22. In the embodiment that is specifically illustrated, the enclosed region 22 is electrically conductively connected to one of the track sections, namely the track section 15b (that is to say no gap in the heat-conducting layer is formed with respect to this conductor 15b). However, it is also possible for example to completely separate the enclosed region 22 from the inner track sections by way of an insulating gap. By virtue of the local widening of the distance between the inner track sections in the region of the deflection section 17a, an excessive length difference between current paths on the outer edge of the inner track sections and current paths on the inner edge of the inner track sections is avoided, such that an excessive concentration of the current flow on the inner side at the deflection sections is further prevented. Through synergistic interaction with the branch sections that are provided, local heating is thereby effectively able to be avoided.

[0055] It is pointed out at this juncture that all of the parts described above, considered individually and in any combination, in particular the details illustrated in the drawings, are comprised in the disclosure. Amendments thereto are familiar to those skilled in the art.

REFERENCE SIGNS

[0056] 10 substrate [0057] 11 electrically insulating layer [0058] 12 heat-conducting layer [0059] 13 insulating layer [0060] 14 heat-conducting track [0061] 15a track section [0062] 15b track section [0063] 15c track section [0064] 15d track section [0065] 16 insulating gap [0066] 17a deflection section [0067] 17b deflection section [0068] 19 region [0069] 20 branch insulating gap [0070] 20a branch insulating gap [0071] 20b branch insulating gap [0072] 21a branch section [0073] 21b branch section [0074] 21c branch section [0075] 22 region