Electric vehicle fluid heater

Abstract

The invention relates to an electric vehicle fluid heater (12) having a heating element (10), wherein the heating element (10) comprises: - a carrier element (14); and - a heat conductor layer (16) arranged on the carrier element (14); - wherein the heat conductor layer (16) has a heat conductor track (20) in a heat conductor layer plane (18), which is bounded in the heat conductor layer plane (18) by at least one insulating interruption (22); - wherein the heat conductor track (20) extends at least between a first connection region (32) and a further connection region (33, 34), in which regions the heat conductor track is each electrically conductively connected to at least one electrical connection conductor (35); - wherein the heat conductor track (20) has a first heat conductor track section (28) that extends at a first distance from the edge of the support element (14) and along this edge; - wherein the heat conductor track (20) has a second heat conductor track section (30) that extends on the support element (14) parallel to the first heat conductor track section (28) and at a second distance from the edge of the support element (14), which is greater than the first distance; - wherein the first heat conductor track section (28) has a first minimum cross-sectional area perpendicular to its direction of extension and the second heat conductor track section (30) has a second minimum cross-sectional area perpendicular to its direction of extension; - wherein the second minimum cross-sectional area is greater than the first minimum cross-sectional area.

Description

[0001] ELECTRIC VEHICLE LIQUID HEATER

[0002] Technical area:

[0003] The present invention relates to an electric vehicle liquid heater.

[0004] Technical background:

[0005] It is known that electric liquid heaters for vehicles can have one or more heating elements. The heating conductor layer has a heating conductor track and connection areas for electrically contacting the heating conductor track. The heat required for heating operation can be generated in the heating conductor tracks of the heating conductor layer by applying a voltage, with the heating conductor layer acting as a sheet resistor. The heating conductor structures have a conductor track width that is as constant as possible on the current path between the connection areas. The goal here is to achieve uniform heat extraction across the length of the heating conductor.

[0006] In the case of high-voltage liquid heaters for vehicles, which are operated, for example, with a voltage greater than or equal to 400 V, and in particular with a voltage greater than or equal to 700 V, e.g. at around 800 V, the development is confronted with the need to generate very high heating outputs of 5 kW, 8 kW, 10 kW or more in the smallest space as efficiently and quickly as possible, while at the same time ensuring a long-lasting and robust product.

[0007] Description of the invention:

[0008] The present invention is based on the object of providing a liquid heater for a vehicle which can meet these requirements even better than known liquid heaters.

[0009] According to various aspects of the invention, an electric liquid heater for use in a vehicle is proposed, which has a heating element. The heating element comprises a carrier element and a heat conductor layer arranged on the carrier element. The heat conductor layer has a heat conductor track in a heat conductor layer plane, which is delimited by at least one insulation interruption in the heat conductor layer plane.

[0010] The heating conductor track extends at least between a first connection region and a further connection region, in each of which the heating conductor track is electrically conductively connected to at least one electrical connection conductor. The heating conductor track has a first heating conductor track section which extends at a first distance from an edge of the carrier element and along this edge. Furthermore, the heating conductor track has a second heating conductor track section which extends on the carrier element parallel to the first heating conductor track section and at a second distance from the edge of the carrier element which is greater than the first distance. In particular, the second heating conductor track section can extend next to and along the first heating conductor section, separated only by the insulation interruption.

[0011] A distance is understood here as the shortest connection between the corresponding side surfaces of the heating conductor track sections facing the edge of the carrier element and the edge between a narrow edge surface and the upper main surface of the carrier element on which the heating conductor track is arranged.

[0012] In the present application, the term “parallel” generally includes not only straight heating conductor track sections, but also partially or completely curved heating conductor track sections.

[0013] The first distance from the edge of the carrier element is preferably relatively small, preferably significantly smaller than the width of the heating conductor track section. Further preferably, there is no further heating conductor track section between the edge and the first heating conductor track section.

[0014] The first heating conductor track section has a first minimum cross-sectional area perpendicular to its direction of extension, and the second heating conductor track section has a second minimum cross-sectional area perpendicular to its direction of extension. The directions of extension can be parallel to one another or identical. The second minimum cross-sectional area is now larger than the first minimum cross-sectional area.

[0015] The cross-sectional area is typically composed of a respective width b of the heating conductor track section and the relevant layer thickness h. In order to vary the cross-sectional area, either the width b or the layer thickness h or both (in particular bxh in the case of a rectangular cross-sectional profile) can be varied. The width is measured in the heating conductor layer plane, and the layer thickness in a direction perpendicular thereto. In a preferred embodiment, the first heating conductor track section has a first minimum width and the second heating conductor track section has a second minimum width, and the second minimum width is greater than the first minimum width. The layer thickness can also be different, but is preferably chosen to be the same.

[0016] The idea underlying these aspects is therefore to deviate from the classic approach of maintaining as constant a cross-sectional area (preferably: width) of the conductor tracks as possible, at least at the outer edge of the carrier element. The targeted reduction of the cross-sectional area (preferably: width) in a section of the conductor track leads to an increase in resistance in this region, which results in a relative increase in local heating power during operation. In other words, at least in those sections of the first heating conductor track section where the cross-sectional area (preferably: width) is relatively reduced, a relatively increased heat generation takes place. It has been discovered that this makes it possible to compensate for a temperature gradient in the carrier element that arises towards the edge during operation with conventional heating elements by increasing the heating power in the corresponding heating conductor track section(s) at the edge.This, in turn, significantly reduces mechanical stresses caused by temperature gradients in the support element material during heating operation, particularly those observed in tests at the edge of the support element. This increases the longevity and durability of the liquid heating system's operating parameters.

[0017] However, a conventional design of heating conductor tracks with a constant cross-sectional area or width of parallel heating conductor track sections from outside to inside can result in an uneven temperature distribution in the heating element or in the carrier element. The reason for this need not only lie in an internal or external arrangement, but also in inhomogeneous heat dissipation across the heating element surface through the heat exchanger, as well as through radii and deflection areas on the heating conductor itself. Outer radii, in particular, for example, the corners at the edge of a regularly rectangular carrier element, which are usually filled with the heating conductor layer, have a lower current density and thus a lower temperature. Inner radii, on the other hand, show a higher current density, which is associated with higher local temperatures.

[0018] The warmer areas of the heating element or support element now expand more than the colder areas. As a result, thermomechanical tensile stresses arise in the colder areas. This results in operational limitations, particularly when a ceramic is used as a support element (as well as an insulator for the heat exchanger directly or indirectly connected to the rear (e.g., via an adhesive layer, etc.). In addition to their good electrical insulation properties, high operating temperatures, and sufficient thermal conductivity, ceramics exhibit brittle fracture behavior with a sometimes pronounced sensitivity to tensile stresses. The maximum permissible tensile stresses are approximately 30% lower than the maximum permissible compressive stresses.This is because tensile stresses, particularly at the edge of a ceramic substrate, can lead to cracking, which can severely impair the functionality of the heating element. Tests show that in various operating scenarios, such tensile stresses can limit performance or general operation, for example, by setting a power limit for the heating element control system, while the electrical components and circuitry alone could easily achieve higher heating outputs without damaging these components.

[0019] Examples of operating conditions in which maximum permissible tensile stresses, which depend on the ceramic material and the carrier material thickness, could be exceeded include high heating output, uneven heat dissipation, partial dry running of the underlying heat exchanger, high heating dynamics over time (e.g. a rapid change in the heating output requirement), air in the coolant circuit, or incomplete venting, etc. Aspects of the invention therefore provide, as described, a targeted adaptation of the cross-sectional area (preferably width) of the heating conductor track(s) towards the edge of the carrier element, which creates an uneven distribution of the heat flux density in the heating element. According to the specific aspects, the outer regions in the conductor cross-section or the corresponding width are narrowed and consequently have a higher heat flux density than the central regions of the heating element.In alternative aspects of the invention, or in addition to the above aspects, it is also conceivable, as described, to vary the layer thickness of the heating conductor layer, e.g. to reduce it towards the edge from heating conductor track section to heating conductor track section.

[0020] According to further alternatives or additional aspects of the invention, the width and / or layer thickness of mutually parallel heating conductor track sections can also be increased, e.g., towards the edge, instead of being reduced. This can occur, for example, if an underlying region of the heat exchanger is less efficiently flowed through, e.g., due to the design of the corresponding fluid chamber for the cooling medium. The locally lower heat transfer would lead to an excessively high local temperature and thus to thermomechanical stresses in the carrier element if the heating element were operated as usual with a constant width of the heating conductor tracks. This can be compensated for by creating a larger width where the cooling efficiency is reduced.If this area is located at one of the edge sections of the support element, a corresponding first heating conductor section can have a greater maximum width than an adjacent, parallel second heating conductor section. This aspect also takes into account the avoidance of excessive tensile stresses.

[0021] Overall, the aspects proposed here significantly reduce the thermomechanical tensile stresses within the heating element. Furthermore, these aspects influence the location of the local tensile stress maxima. The local tensile stress maxima can, in particular, be specifically shifted from an edge region of the heat-absorbing support element to an inner region. In the edge region of the support element, there are generally elevated notch stresses and thus a significantly increased risk of fracture due to the geometric design, in particular sharp edges, and also due to the manufacturing processes, such as the separation of ceramic substrates during the manufacturing process, in which microcracks can occur.The detailed improvements resulting from the proposed aspects can therefore significantly increase the robustness of the heating element in scenarios with inhomogeneous heat flux density distribution in the electric liquid heater.

[0022] In this case, an electric liquid heater is understood to be a heater in which heat is transferred to a liquid heat transfer medium of a heat transfer circuit flowing through the heater. The heat transfer medium can in particular be a vehicle's liquid coolant, which transports heat within the vehicle and can transfer it at various points. Alternatively, the liquid heater can also be part of a vehicle's heat pump, for example, so that the heat transfer medium can be a coolant in a heat pump, for example. In this case, the coolant may only be in completely liquid form under certain conditions and only temporarily, or perhaps never, and may otherwise be partially or completely gaseous. Nevertheless, this is also understood to be a liquid heater.

[0023] An electric vehicle liquid heater is a liquid heater designed for use in a vehicle. A vehicle is generally understood to include all possible mobile applications, in particular passenger cars, trucks or commercial vehicles, construction machinery, aircraft, and watercraft. This also includes, for example, construction machinery or cranes, as well as trailers such as caravans that can be towed and transported by other vehicles.

[0024] The electric liquid heater preferably has a heating output of at least 5 kW, preferably of at least 7 kW, for example of at least 9 kW. The heating output is in each case preferably less than or equal to 13 kW. The operating voltage at which the vehicle heater is operated, which can be the same as the on-board voltage of an electrically powered vehicle, is greater than or equal to 400 V, preferably greater than or equal to 700 V, for example 800 V, 900 V or 1000 V. The liquid heater has at least one heating element and at least one heating conductor layer. Preferably, the liquid heater has at least two heating conductor layers, particularly preferably at least three heating conductor layers and in each case corresponding heating conductor tracks. The heating conductor layers and heating conductor tracks can be arranged together on a single carrier element, or else on two or three different ones. Preferably, each heating conductor layer orEach heating conductor track is applied to its own separate carrier element.

[0025] The two connection areas can be arranged individually or jointly adjacent to the edge of the carrier element or at a distance from it. The two connection areas can be individually or jointly part of the heating conductor layer, or pads made of another electrically conductive material connected to it. The carrier element can be formed by a flat plate with a plate thickness, preferably rectangular, and thereby have a narrow edge divided into, for example, four straight sections, preferably perpendicular to its two main surfaces, the width or height of which corresponds to the plate thickness. Sections of the edge form corners of the carrier element.

[0026] The heating conductor track can be regarded as the region in which a current flows after an electrical voltage is applied to the existing connection regions. The heating conductor track extends at least from the first electrical connection region to the further electrical connection region. It can also extend beyond this, e.g., over a second to a third connection region. Such a third connection region as well as the first connection region can, for example, be arranged at an actual end of the heating conductor track. The heating conductor track is delimited, in particular, laterally in the plane of the heating conductor track by the insulation interruption, wherein no current flows in the region of the insulation interruption.

[0027] The insulation interruption can, for example, be an area that is free of the heating conductor layer and divides it into heating conductor track sections, which together form a path of the heating conductor track between a first end and a second end, as well as between two, three, or more connection areas. However, the insulation interruption can also comprise material of the heating conductor layer that is electrically insulated from the heating conductor track.

[0028] The connection areas can, for example, be defined or distinguished from the rest of the heating conductor track by the fact that a significantly lower amount of heat is generated in the connection areas during heating operation (compared to a normal heating conductor track section of the same area). Electrical contact can be established in the connection areas with an electrical energy source external to the heating conductor track. The necessary electrical contact can involve contacting processes such as laser welding, soldering, or thermal bonding, etc.

[0029] The heating conductor layer can have an additional coating in the connection areas and / or a greater thickness than other areas to facilitate the contacting process and ensure long-lasting and reliable electrical contact. The additional coating can be a metal, for example, copper. The connection area or end typically leads into the heating conductor track in one or both directions.

[0030] The heating conductor layer can, for example, be formed as a metallization made of a resistance alloy, which represents the corresponding heating resistance. The insulation interruption can be created, for example, by laser ablation in the heating conductor layer or by a screen printing process during application.

[0031] The heating conductor layer plane can refer to one of the two main surfaces of the support element that supports the heating conductor. If the surface of the support element supporting the heating conductor is flat, for example, the heating conductor layer plane is a plane oriented parallel to this main surface of the support element. Even if the surface of the support element supporting the heating conductor is a curved surface, the heating conductor layer plane is always parallel to the main surface (or curved surface) supporting the heating conductor. However, the then curved heating conductor layer plane is defined at each point only by the tangential plane, which can be determined at all points on the heating conductor layer, or the local plane at the respective point.

[0032] A pattern or "layout" formed by the heating conductor track can include one or more non-current-carrying areas located at corresponding reversal points where the heating conductor track turns 180°. These non-current-carrying areas form widened, dead-end-like regions at the end of each insulation break. The widening, which, for example, appears tropical-shaped when viewed from above, serves to prevent local overheating in this area of ​​the heating conductor track. A sharp, pronounced double inner corner would cause very high local current densities, which would lead to significant temperature and thus voltage stresses.

[0033] According to a special development of the electric liquid heater, the edge is formed by at least one connection side, an opposite end side, and two long sides of the support element. In particular, a rectangular shape can be defined as a result. The rectangular shape includes a square shape. The connection side is defined in that both the first connection region and the further connection region are arranged adjacent to it, with the first heating conductor track section and the second heating conductor track section parallel thereto extending along one of the long sides and / or the end side and / or the side opposite it. If the two connection regions are located in diametrically opposite corners of the main surface of the support element, which is not common practice but is also not excluded, all sides can be regarded as connection sides, long sides, and end sides.

[0034] According to a special development of the electric liquid heater, the first heating conductor track section and the second heating conductor track section are each straight sections. When designing the pattern or "layout", the aim is to cover the available area, i.e. the one main surface of the carrier element, with conductor tracks as efficiently as possible. Since, as described, bends in the conductor tracks by 90° or 180° lead to local variations in the current density at the inner and outer radii of the bends, the number of these bends is chosen to be as small as possible in the design and tends to be located in the outer corners of the main surface. As a result, the straight conductor track sections that are efficient in this respect extend parallel to the nearest edges on the connection, longitudinal or end faces.

[0035] It has been discovered that, in some embodiments of the layout, the largest temperature gradients directed radially from a center of the carrier element meet the corresponding edge in the region of the center of the respective connection, longitudinal, or end sides. The gradients taper off toward the corners. In this respect, aspects of the invention can advantageously be applied to straight first and second (and possibly further) conductor track sections, which extend particularly in the central regions near the edge of the respective connection, longitudinal, or end sides. According to a further development of the electric vehicle liquid heater, a width of the first heating conductor track section is constant over the length of the first heating conductor track section and corresponds to the first minimum width. This corresponds to a particularly simple structure, so that the desired temperature compensation can be easily adjusted.

[0036] According to an alternative development of the electric vehicle liquid heater, the width of the first heating conductor track section varies across the length of the first heating conductor track section. In the case where the edge is formed by at least one connection side, an opposite end face, and two longitudinal sides of the support element, the width of the first heating conductor track section decreases continuously or gradually from a center of the respective side toward a corner of the support element formed by one of the longitudinal sides and the connection side or the end face opposite it.

[0037] According to this embodiment, the local heating output at the edge of the support element can be adjusted even more precisely along the relevant side. The further reduction in width toward the corners leads to increased heating output there. If, for example, comparatively large connection areas are located at or near the relevant corners, which define inherently colder sections, this approach can provide compensation.

[0038] The corners themselves can have the aforementioned bends in the heating conductor track, where the cross-section of the heating conductor track typically increases for geometric reasons. Therefore, the first heating conductor track section and the second heating conductor track section can each extend toward the corner to a location where the minimum first width is reached, with this location being spaced from the corner. The corresponding minimum distance can, for example, be a (minimum) conductor track width plus an (inner) curve radius specified during the layout.

[0039] According to a refinement of the electric vehicle liquid heater according to these alternative developments, when the first heating conductor track section extends along the longitudinal side of the support element, a profile of its width is formed symmetrically along the extension direction. As a result, a maximum width of the heating conductor track section is achieved in a region of the middle of the longitudinal side. This creates a kind of bulbous shape of the first heating conductor track section. Preferably, the maximum width of the first conductor track section is smaller than the second minimum width of the second conductor track section. However, the maximum width may also be equal to or even greater than the second minimum width of the second conductor track section.

[0040] According to a further development of the electric vehicle liquid heater according to one of the above aspects or developments, the heating conductor track extends on the carrier element in a meandering shape with at least two reversal points that are spaced apart from one another in a longitudinal direction of the carrier element. The first heating conductor track section and the second heating conductor track section are defined only in a region lying between the two reversal points along the longitudinal direction. As described, the reversal points are defined by a widening region for rounding inner edges at the 180° bends of the heating conductor tracks to avoid current density peaks. The reversal points therefore occupy a region along the longitudinal direction specified, for example, by the droplet shape.

[0041] The electric vehicle liquid heater according to the above aspects or developments can have a ceramic substrate as the carrier element, preferably comprising Al2O3. In this case, the advantages are particularly clear due to the tensile stress problem.

[0042] In electric vehicle liquid heating, the ceramic substrate can be attached to a metallic heat exchanger.

[0043] According to advantageous embodiments, the first minimum width may be in an interval of 70% to 90% of the second minimum width, preferably in an interval of 75% to 85% of the second minimum width.

[0044] According to particularly advantageous embodiments, the temperature and voltage compensation can be adjusted even more finely by the heating conductor track having a third heating conductor track section, which extends on the carrier element parallel to the first heating conductor track section and to the second heating conductor track section at a third distance from the edge of the carrier element that is greater than the first and second distances, wherein the third heating conductor track section has a third minimum width perpendicular to its direction of extension, wherein the third minimum width is greater than the second minimum width. Thus, in a sense, a radial temperature and voltage compensation profile can be realized.

[0045] It should be noted that the heating conductor track sections provided according to the aspects and developments can be provided only on the connection side, only on the front side, or only on one of the two long sides. Depending on the desired compensation, corresponding heating conductor track sections can also be provided in combination on two, e.g., opposite sides, or three or more of the aforementioned sides, in particular on all sides.

[0046] Furthermore, it can also be provided that two adjacent heating conductor track sections closest to the edge are provided with the same comparatively reduced width. In this case, the width of the respective first semiconductor section is to be compared with the width of a third or possibly fourth section, etc., viewed from the edge, which then constitutes the second heating conductor section within the meaning of this application.

[0047] Short description of the drawings:

[0048] The invention is explained below by way of example with reference to the following figures.

[0049] They show:

[0050] Figure 1 is a plan view of a heating element of an electric liquid heater according to a comparative example;

[0051] Figure 2 shows a section of the heating element shown in Fig. 1;

[0052] Figure 3 is a plan view of a heating element of an electric liquid heater according to a first embodiment;

[0053] Figure 4 shows a section of the heating element shown in Figure 3; Figure 5 shows a plan view of a heating element of an electric liquid heater according to a second embodiment;

[0054] Figure 6 is a section of the heating element shown in Fig. 5;

[0055] Figure 7 shows a cross section through a section of a heating element of a liquid heater according to the first or second embodiment; and

[0056] Figure 8 shows a simplified representation of an electric liquid vehicle heater.

[0057] Detailed description of preferred embodiments:

[0058] In the following description of the drawings, the same reference symbols refer to the same or comparable components.

[0059] 1 and 2 show a plan view of a heating element 10 of an electric liquid heater 12 according to a comparative example, wherein Fig. 2 shows an enlarged section of Fig. 1.

[0060] 3 and 4 show a plan view of a heating element 10 of an electric liquid heater 12 according to a first embodiment, wherein Fig. 4 shows an enlarged section of Fig. 3.

[0061] 5 and 6 show a plan view of a heating element 10 of an electric liquid heater 12 according to a second embodiment, wherein Fig. 6 shows an enlarged section of Fig. 5.

[0062] Figure 7 shows a partial cross-section through the heating element 10 perpendicular to the longitudinal direction or central axis 48, which, however, only represents the first and second exemplary embodiments. The reference numerals are otherwise also compatible with the comparative example.

[0063] The following explanations initially apply jointly to Figures 1 to 6. The heating element 10 comprises a carrier element 14 formed as a ceramic substrate and a heating conductor layer 16 formed thereon. In the illustration, the carrier element 14 is almost completely covered by the heating conductor layer 16. The heating conductor layer 16 has been structured, for example, using a screen printing process, so that it forms a heating conductor track 20 by means of a suitable arrangement of insulation interruptions 22.

[0064] The support element 14 has a rectangular shape with two opposite, longitudinally extending long sides 21, as well as connection and end faces 17, 19, which are perpendicular thereto, ie, extend in the transverse direction and are also opposite one another. A central axis 48 extending in the longitudinal direction forms an axis of symmetry for the support element 14 and a pattern formed by the heating conductor track 20 and the insulated interruptions 22.

[0065] In the specific comparative and exemplary embodiments, the heating conductor track 20 is defined by two end points, which form a first connection region 32 and a third connection region 33. The heating conductor track 20 can be formed from a copper alloy and, without restriction of generality, have a thickness h of, for example, 12 μm. The two connection regions 32, 33 can be formed from the same material or supplemented by an additional material to enable the connection, for example, of a bonding wire or another type of electrical connection conductor 35. Contacting by an electrical connection conductor 35 can also be provided in a second connection region 34 arranged symmetrically in the center of the heating conductor tracks 20. Electrical energy can be supplied to the heating conductor track 20 via the electrical connection conductor 35, which energy is converted into heat in the heating conductor track 20.

[0066] The electrical connection conductors 35 connect the connection areas 32, 33, 34 to a connection electronics that is not shown in the figures. This can be a power board, a control unit that includes power electronics, or the like. Each connection area 32, 33, 34 can be electrically connected to more than one electrical connection conductor 35, whereby the number can differ between the two connection conductors. The connection conductors 35 extend from the connection areas 32, 33, 34 in the direction of the connection side 17, which they thereby define, and beyond the edge of the heating conductor layer 16 running along the connection side 17. As described, these can each be bond wires. The arrangement shown in the figures makes it possible to operate the heating element 10 in at least two different modes. In a first mode, which is intended, for example, for use at a comparatively higher high voltage, e.g.800 V, a high voltage provided by the power board, the control unit, or the power electronics can be applied via the connecting conductors 35 between the first connection area 32 and the third connection area 33. The voltage drops over the entire length of the heating conductor track 20. The heating resistance is correspondingly large, so that a predetermined current flow results. In a second mode, a comparatively lower high voltage, e.g. 400 V, can be provided via the connecting conductors 35 between the second connection area 34 on the one hand and the first connection area 32 and the third connection area 33 on the other. The voltage drops over half the length of the heating conductor track 20. As a result, the heating resistance is halved, so that twice the amount of current flows compared to the first mode.At half the high voltage and twice the current flow, the same heating output is achieved, which is possible with the same heating element design for different vehicle electrical system voltages. The heating output can be adjusted using pulse-width modulation, for example.

[0067] On both sides of the second connection region 34 or the central axis 48, the conductor track 20 extends in a partially meandering or spiral shape up to the respective end point, the first connection region 32 and the third connection region 33. The elongated rectangular shape of the carrier element 14 and the subdivision of the layout into two symmetrical sub-regions along the central axis 48 enables an elongated pattern with long straight sections.

[0068] The limited space nevertheless makes it necessary for the heating conductor tracks 20 to reverse by 180° at two locations designated as reversal points 60, 62. The two reversal points 60, 62 are arranged approximately centrally in the transverse direction to the left and right of the central axis 48 in the two divided layouts. In the longitudinal direction, the first reversal point 60 is adjacent to the end face 19 and the second reversal point 62 is adjacent to the connection side 17. The two reversal points 60, 62 define a distance between them in the longitudinal direction. The reversal points 60, 62 each form, as described, a section of the insulation interruption 22 which, in plan view, widens in a droplet shape towards the end face 19 or the connection side 17, i.e. they cover an area with a length in the longitudinal direction which leaves the distance between them.The two reversal points 60 and 62 result in less space being available for the longitudinally passing sections of the heating conductor track 20, viewed in the transverse direction. This is taken into account in various ways in the examples.

[0069] A first conductor track section 28 extends along the edge of the carrier element 14 on one of the two longitudinal sides 21 thereof. A narrow piece of the main surface of the carrier element 14 is exposed, ie, the first conductor track section 28 has a preferably constant and very small distance b r from the edge of the support element 14. The distance b shown in Fig. 7 r from the edge of the carrier element 14 can be 0.5 mm. However, the first conductor track section 28 can also be flush with the surface of the edge of the carrier element 14, so that the distance b r zero mm. The distance b rcan also vary along the longitudinal direction. These specifications also apply analogously to conductor track sections on the connection side and the front side that are not specifically described.

[0070] A second heating conductor section 30 extends directly next to and parallel to the first heating conductor section 28, also in the longitudinal direction parallel to the central axis 48, only interrupted by the insulating interruption 22. The insulating interruption 22 can have a width bj S0 of 0.2 mm, which thus determines the distance between the second heating conductor section 30 and the first heating conductor section 28. The second heating conductor section 30 therefore has a distance from the edge of the same long side 21 that is greater than the corresponding distance of the first heating conductor section 28.

[0071] A third heating conductor track section 36 extends directly adjacent to and parallel to the second heating conductor track section 30 (and to the first heating conductor track section 28), also longitudinally parallel to the central axis 48, interrupted only by the insulation interruption 22. A fourth heating conductor track section 38, a fifth heating conductor track section 40, and a sixth heating conductor track section 42—in this order, viewed from the edge on the long side 21—adjoin the third heating conductor track section 36. The six heating conductor track sections 28 to 42 considered here are each straight sections. In the present examples, they extend at least between a connection-side end C of the front-side reversal point 60, viewed in the longitudinal direction, and the front-side end D of the connection-side reversal point 62, viewed in the longitudinal direction.However, depending on the heating conductor section, they can also extend between the respective bending points A at the front end and the respective bending points B at the connection end.

[0072] The first heating conductor track section 28 has a constant width bi in the examples shown in Figures 1 to 4. The second heating conductor track section 30 has a constant width b2 in the examples shown therein. The third heating conductor track section 36 has a constant width b3 in the examples shown in Figures 1 to 4. The fourth heating conductor track section 38 has a constant width b4 in the examples shown in Figures 1 to 4. The fifth heating conductor track section 40 has a constant width bs in the examples shown in Figures 1 to 4. The sixth heating conductor track section 42 has a constant width be in the examples shown in Figures 1 to 4.

[0073] In the comparative example shown in Figs. 1 and 2, the width of the heating conductor track is almost constant throughout. Except for curved sections and the sections of the heating conductor track immediately adjacent to the reversal points. This means that the following applies to the widths of the heating conductor track sections: b1 = b2 = b3 = b4 = b5 = b6.

[0074] A usual error tolerance depending on the manufacturing process must be taken into account.

[0075] 3 and 4, the width bi of the first heating conductor track section 28 is selected to be smaller than the width b2 of the second heating conductor track section 30. In particular, the following applies: bi < b2 = b3 = b4 = b5 < b6. In the present examples of Figures 1 to 6, the minimum heating conductor track width b can preferably be greater than or equal to 1.5 mm and less than or equal to 7 mm. A minimum heating conductor track width b between 2.5 mm and 6 mm inclusive is particularly preferred. For example, in the comparative example, bi = b2 = bs = b4 = bs = be = 4.5 mm. In comparison, in the first exemplary embodiment, bi = 3.75 mm, b2 = ba = b4 = bs = 4.5 mm and be = 4.8 mm.

[0076] Due to the comparatively reduced width of the first heating conductor track section 28, the heating resistance is increased locally there, so that a comparatively greater heating power is achieved than in the second to fifth heating conductor sections 30 to 40. In the sixth heating conductor track section 42, the width bs is even increased again compared to the fifth heating conductor track section 40 which is closer to the edge.

[0077] 5 and 6, the widths bi to bs of the heating conductor track sections 28 to 42 in the region CD are selected as in the first embodiment shown in Figures 3 and 4. Outside the region CD, for example in the regions AC or DB, the width of the first heating conductor track section 28 is continuously reduced in the direction of the corners or in the direction of the end face 19 or the connection side 17. In Fig. 6, the width bi" designates the overall minimum width of the first heating conductor track section 28. In the second embodiment, it is approximately 3 mm and is reached at a point where the inner curve radius for a 90° bend begins on the first heating conductor track section 28. The following therefore applies here: bi" < bi' < bi < b2 .

[0078] Due to the decrease in the width of the first heating conductor section 28 toward the end face 19 or the connection side 17, the parallel extensions of the second and third heating conductor sections 30, 36 each bend toward the associated longitudinal side 21. Their width b2 and bs, respectively, remain constant. This allows the fourth and fifth heating conductor sections 38 and 40 to have a greater width adjacent to the reversal points 60, 62. Returning to the first embodiment of Figures 3 and 4, it is also shown, by way of example, for the connection side 17 that a width Ci of an outer heating conductor section is selected to be smaller than a width C2 of an adjacent, parallel-extending and further inward heating conductor section:

[0079] C1 < c2.

[0080] It should be noted that the above statements regarding heating conductor track sections assigned to one long side 21 or the connection side are equally applicable to corresponding heating conductor track sections assigned to the end side or the other long side. On the other hand, a combination of the comparative example, the first exemplary embodiment, and / or the second exemplary embodiment is also conceivable here. For example, the bulbous shape of the first heating conductor track section of the second exemplary embodiment can only be applied to the long sides, but not to the end or connection side, where the widths corresponding to the comparative example then apply. Alternatively, the dimensions Ci and c2 of the first exemplary embodiment can be applied to the end or connection side.Furthermore, the heating conductor track sections are not limited to the boundaries A, B, C or D shown in the figures, but can also be defined in a variety of other ways.

[0081] Figure 8 shows a simplified representation of an electric liquid heater 12 for a vehicle. The electric vehicle heater 12 shown in Figure 8 comprises, in addition to the electric heating element 10, a liquid heat exchanger 44, on which the electric heating element 10 is arranged according to the exemplary embodiments and to which the heat generated by the heating element 10 during heating operation is transferred, as well as a control unit 46 for controlling the electric heating element 10. For this purpose, the control unit 46 is connected to the electric heating element 10 via electrical connecting lines 50. Further components of the electric vehicle heater 12 not shown in Figure 8, which are not explicitly shown in Figure 8 for the sake of simplicity, are well known to those skilled in the art and are supplemented by them to ensure the functionality of the electric vehicle heater 12.The features of the invention disclosed in the above description, in the drawings and in the claims may be essential for the realization of the invention both individually and in any combination.

[0082] List of reference symbols

[0083] 10 Heating element

[0084] 12 electric liquid heaters

[0085] 14 support element

[0086] 16 Heating conductor layer

[0087] 17 Connection side

[0088] 18 Heating conductor layer level

[0089] 19 long sides

[0090] 20 heating conductor track

[0091] 21 Front side (opposite the connection side)

[0092] 22 Insulation break

[0093] 28 first heating conductor section

[0094] 30 second heating conductor section

[0095] 32 first connection area

[0096] 33 third connection area

[0097] 34 second connection area

[0098] 35 electrical connecting conductor

[0099] 36 third heating conductor section

[0100] 38 fourth heating conductor section

[0101] 39 recess

[0102] 40 fifth heating conductor section

[0103] 42 sixth heating conductor section

[0104] 44 heat exchangers

[0105] 46 Control unit

[0106] 48 Central axis

[0107] 50 electrical connection cables

[0108] 60 connection-side reversal point

[0109] 62 frontal reversal point

[0110] A, B, C, D Section boundaries bi, b2, ba, b4, bs, be Widths of the first to sixth heating conductor sections (longitudinal side) bi, bi', bi“ Variable width of the first heating conductor section (longitudinal side)

[0111] Ci, C2 Widths of the first and second heating conductor sections (front and / or connection side) h Layer thickness

Claims

Claims 1. An electric vehicle liquid heater (12) with a heating element (10), the heating element (10) comprising: a carrier element (14); and a heating conductor layer (16) arranged on the carrier element (14); the heating conductor layer (16) having, in a heating conductor layer plane (18), a heating conductor track (20) which is delimited in the heating conductor layer plane (18) by at least one insulation interruption (22); the heating conductor track (20) extending at least between a first connection region (32) and a further connection region (33, 34), in each of which the heating conductor track is electrically conductively connected to at least one electrical connection conductor (35);wherein the heating conductor track (20) has a first heating conductor track section (28) which extends at a first distance from the edge of the carrier element (14) and along this edge, wherein the heating conductor track (20) has a second heating conductor track section (30) which extends on the carrier element (14) parallel to the first heating conductor track section (28) and at a second distance from the edge of the carrier element (14) which is greater than the first distance; wherein the first heating conductor track section (28) has a first minimum cross-sectional area perpendicular to its direction of extension and the second heating conductor track section (30) has a second minimum cross-sectional area perpendicular to its direction of extension, wherein the second minimum cross-sectional area is greater than the first minimum cross-sectional area.

2. Electric vehicle liquid heater (12) according to claim 1, wherein the first minimum cross-sectional area is formed by a first minimum width (bi) perpendicular to the direction of extension of the first heating conductor track section (28), the second minimum cross-sectional area is formed by a second minimum width (b2) perpendicular to the direction of extension of the second heating conductor track section (30), and the second minimum width (b2) is greater than the first minimum width (bi), wherein a layer thickness (h) of the first and second heating conductor track sections (28, 30) is preferably equal to one another.

3. Electric vehicle liquid heater (12) according to claim 1 or 2, wherein the edge is formed by at least one connection side (17), an opposite end side (19) and two longitudinal sides (21) of the carrier element (14), wherein the connection side is defined in that both the first connection region (32) and the further connection region (33, 34) are arranged adjacent to it, wherein the first heating conductor track section (28) and the second heating conductor track section (30) parallel thereto extend along one of the longitudinal sides (21) and / or the connection side (17) and / or the end side (19) opposite it.

4. Electric vehicle liquid heater (12) according to one of claims 1 to 3, wherein the first heating conductor track section (28) and the second heating conductor track section (30) are each straight sections.

5. The electric vehicle liquid heater (12) according to any one of claims 1 to 4, wherein a width of the first heating conductor track section (28) is constant over the length of the first heating conductor track section (28) and corresponds to the first minimum width.

6. Electric vehicle liquid heater (12) according to one of claims 1 to 4, wherein a width of the first heating conductor track section (28) varies over the length of the first heating conductor track section (28), wherein in the case that the edge is formed by at least one connection side (17), an opposite end side (19) and two longitudinal sides (21) of the carrier element (14), the width of the first heating conductor track section (28) decreases continuously or stepwise from a center of the respective side in the direction of a corner of the carrier element (14) formed by one of the longitudinal sides (21) and the connection side (17) or the end side (19) opposite it.

7. The electric vehicle liquid heater (12) of claim 6, wherein the first heating conductor track section (28) and the second heating conductor track section (30) each extend toward the corner to a location at which the minimum first width (bi") is reached, said location being spaced from the corner.

8. The electric vehicle liquid heater (12) according to claim 6 or 7, wherein, when the first heating conductor track section (28) extends along the longitudinal side (21) of the support element (14), a profile of its width is formed symmetrically along the extension direction, so that a maximum width of the first heating conductor track section (28) is achieved in a region of the center of the longitudinal side (21); wherein preferably the maximum width of the first conductor track section is smaller than the second minimum width of the second conductor track section.

9. Electric vehicle liquid heater (12) according to one of claims 1 to 8, wherein the heating conductor track extends on the carrier element in a meandering form with at least two reversal points (60, 62) which are spaced apart from one another in a longitudinal direction of the carrier element (14), wherein the first heating conductor track section (28) and the second heating conductor track section (30) are fixed only in a region lying between the two reversal points (60, 62) along the longitudinal direction.

10. Electric vehicle liquid heater (12) according to one of the preceding claims, wherein the carrier element (14) is a ceramic substrate, preferably comprising Al2O3.

11. The electric vehicle liquid heater (12) of claim 10, wherein the ceramic substrate is attached to a metallic heat exchanger (44).

12. Electric vehicle liquid heater (12) according to one of the preceding claims, as far as dependent on claim 2, wherein the first minimum width (b1) lies in an interval of 70% to 90% of the second minimum width (b2), preferably in an interval of 75% to 85% of the second minimum width (b2).

13. Electric vehicle liquid heater (12) according to one of the preceding claims, as far as dependent on claim 2, wherein the heating conductor track (20) has a third heating conductor track section (36, 38, 40, 42) which extends on the carrier element (14) parallel to the first heating conductor track section (28) and to the second heating conductor track section (30) at a third distance from the edge of the carrier element (14) which is greater than the first and the second distance; wherein the third heating conductor track section (36, 38, 40, 42) has a third minimum width (ba) perpendicular to its direction of extension, wherein the third minimum width (ba) is greater than the first minimum width (bi).

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