Electric vehicle liquid heater

Abstract

In an electric vehicle liquid heater (12), a heating element (10) comprises a carrier element (14) and a heating conductor layer (16) arranged on the carrier element (14). The heating conductor layer (16) has a heating conductor track (20) in a heating conductor layer plane (18), which is delimited by at least one insulation interruption (22) in the heating conductor layer plane (18). The heating conductor track (20) extends 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).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, and 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. 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. The second minimum cross-sectional area is greater than the first minimum cross-sectional area.

Description

Technical Field:The present invention relates to an electric vehicle liquid heater.Technical Background:It is known that electric liquid heaters for vehicles may include one or more heating elements. The heating conductor layer has a heating conductor track and connection regions 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, wherein the heating conductor layer acts as a sheet resistor. The heating conductor structures have a conductor track width on the current path between the connection regions which is as constant as possible. The aim here is to obtain uniform heat decoupling over the longitudinal extent of the heating conductor.In high-voltage liquid heaters for vehicles which are operated, for example, with a voltage of greater than or equal to 400 V, in particular also with a voltage of greater than or equal to 700 V, for example at approximately 800 V, the development is faced with the fact that very high heating powers of 5 kW, 8 kW, 10 kW or more are generated as efficiently and quickly as possible in the most confined space and at the same time a long-lived and robust product is ensured.Preparation of the Invention:The object of the present invention is to specify a liquid heater for a vehicle which can meet these requirements even better than known liquid heaters.According to various aspects of the invention, an electric liquid heater for use in a vehicle is proposed, which includes a heating element. The heating element comprises a carrier element and a heating conductor layer which is arranged on the carrier element. The heating conductor layer has a heating conductor track in a heating conductor layer plane, which is bounded in the heating conductor layer plane by at least one insulation break.The heating conductor track extends at least between a first connection region and a further connection region, in which the heating conductor track is electrically conductively connected in each case 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 from the first heating conductor section only by the insulation break.A distance is understood here to mean 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.In the present application, the term "parallel" generally includes not only straight heating conductor track sections, but also partially or completely curve-parallel heating conductor track sections.The first distance from the edge of the carrier element is preferably relatively small, preferably significantly smaller than a width of the heating conductor track section. Further preferably, no further heating conductor track section is located between the edge and the first heating conductor track section.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.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 b x h 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 trace portion has a first minimum width and the second heating trace portion has a second minimum width, and the second minimum width is greater than the first minimum width. The layer thickness can likewise be different, but is preferably chosen to be the same.The idea underlying these aspects is therefore to deviate from the classic approach of cross-sectional areas (preferably: widths) of the conductor tracks which are as constant as possible throughout, 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 the resistance in this region, which results in a relative increase in the 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 generation of heat takes place. It has been found that it is thereby possible to compensate for a temperature gradient in the carrier element arising in the direction of the edge during operation with conventional heating elements by an increased heating power in the corresponding heating conductor track section(s) at the edge. As a result, mechanical stresses which arise in the heating operation as a result of temperature gradients in the material of the carrier element, and specifically in particular those which have been established in tests at the edge of the carrier element, can in turn be significantly reduced. This can increase the longevity and durability of the operating parameters of the liquid heater.According to the conventional design of the heating conductor tracks with a constant cross-sectional area or width of mutually parallel heating conductor track sections from the outside to the inside, on the other hand, can result in an uneven temperature distribution in the heating element or in the carrier element. However, the reason does not only need to be located inside or outside in an arrangement, but also in inhomogeneous heat dissipation via the heating element surface through the heat exchanger, and also through radii and deflection regions on the heating conductor itself. Outer radii, in particular e.g. the corners, which are usually filled in a planar manner with the heating conductor layer, at the edge of a carrier element which is regularly formed in a rectangular shape, have a lower current density and thus a lower temperature. Internal radii, on the other hand, show a higher current density, which is associated with higher local temperatures.The warmer regions of the heating element or of the carrier element now expand more in comparison to the colder regions. As a result, thermomechanical tensile stresses are produced in the colder regions. In particular when using a ceramic as a carrier element (and also as an insulator with respect to the heat exchanger adjoining on the rear side directly or indirectly (e.g. via an adhesive layer etc.), this results in restrictions for operation. Ceramics have, in addition to their good electrical insulation properties, their high service temperature and their sufficient heat conducting properties, a brittle fracture behavior with an sometimes pronounced sensitivity to tensile stresses. The amount of maximum permissible tensile stresses is here substantially below the level of the maximum permissible compressive stresses at about 30%. This is because tensile stresses, in particular at the edge of a ceramic substrate, can lead to crack formation, which can seriously impair the functionality of the heating element. Tests show that in various operating scenarios, such tensile stresses can restrict the performance or the general operation, for example by setting a power limit for controlling the heating element, while higher heating powers would be readily achievable by the electrical components and the electrical circuit arrangement per se without these components being damaged.Examples of operating cases in which, for example, maximum permissible tensile stresses dependent on the ceramic material and the thickness of the carrier material could be exceeded may be mentioned, inter alia, a high heating power, an uneven heat dissipation, a partial dry running of the underlying heat exchanger, a heating dynamics (for example a rapid change in the heating power requirement) or air in the coolant circuit or an incomplete venting, etc. considered over time.Aspects of the invention therefore provide, as described, a specific adaptation of the cross-sectional area (preferably: width) of the heating conductor track(s) towards the edge of the carrier element, which generates an unequal distribution of the heat flux density in the heating element. According to the special aspects, the outer regions are narrowed in the conductor cross section or the corresponding width and consequently have a higher heat flux density than the central regions of the heating element. As described, it is also conceivable in principle to vary the layer thickness of the heating conductor layer, e.g. to reduce it from heating conductor track section to heating conductor track section towards the edge.According to further alternatives or additional aspects of the invention, the width and / or the layer thickness of mutually parallel heating conductor track sections can also be increased, for example towards the edge, instead of being reduced. This can be effected, for example, if a lower-lying region of the heat exchanger is flowed through less efficiently, for example on account of the configuration of the corresponding fluid chamber for the cooling medium. The locally lower heat transfer would lead to an excessive local temperature and thus to thermomechanical stresses in the carrier element if the heating element were operated with a constant width of the heating conductor tracks, as is conventional. This can be compensated for by setting a larger width where the cooling efficiency is reduced. If this region is located on one of the edge sections of the carrier element, a corresponding first heating conductor track section can have a greater maximum width than an adjacent, parallel second heating conductor track section. In this aspect too, the avoidance of unacceptably high tensile stresses is consequently taken into account.Overall, the aspects proposed here therefore significantly reduce the thermomechanical tensile stresses within the heating element. Furthermore, these aspects influence the location of the occurrence of the local tensile stress maxima. The local maxima of the tensile stress can be shifted in particular in a targeted manner from an edge region of the carrier element which absorbs the heat into an inner region. In the edge region of the carrier element, because of the geometric configuration, in particular because of sharp edges, and also because of the manufacturing processes in which, for example, by separating ceramic substrates in the manufacturing process in which microcracks can occur, generally increased notch stresses and thus a clearly increased risk of breakage are present. The detail improvements resulting from the proposed aspects can consequently significantly increase the robustness of the heating element in scenarios with inhomogeneous heat flux density distribution in the electric liquid heater.In the present case, an electric liquid heater is understood to mean a heater in which heat is transferred to a liquid heat transfer medium of a heat transfer medium circuit flowing through the heater. The heat transfer medium can be, in particular, liquid coolant of a vehicle, which can transport heat in the vehicle and emit it at various points. Alternatively, the liquid heater can also be part of a heat pump of a vehicle, for example, so that the heat transfer medium can be a refrigerant of a heat pump, for example. In this case, it may be that the refrigerant is present only under certain conditions and only temporarily or perhaps never in completely liquid form and otherwise is also partially or completely gaseous. Nevertheless, this is also understood to mean a liquid heating system.The vehicle electric liquid heater is a liquid heater provided for a vehicle. A vehicle is to be understood as meaning in principle all possible mobile applications, in particular passenger cars, trucks or commercial vehicles, construction machines, aircraft and watercraft. This also includes, for example, construction machines or cranes and trailers such as residences that can be towed and transported by other vehicles.The electrical liquid heater preferably has a heating power of at least 5 kW, preferably of at least 7 kW, for example of at least 9 kW. The heating power is preferably less than or equal to 13 kW each. The operating voltage with which the vehicle heating system is operated, which may be equal to the on-board voltage of an electrically driven 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 heating system has at least one heating element and at least one heating conductor layer. The liquid heater preferably has at least two heating conductor layers, particularly preferably at least three heating conductor layers and respective corresponding heating conductor tracks. The heating conductor layers and heating conductor tracks can be arranged jointly on a single carrier element, or else on two or three different ones.Preferably, each heating conductor layer or each heating conductor track is applied to its own, separate carrier element.The two connection regions can be arranged individually or jointly adjacent to the edge of the carrier element or at a distance from the latter. The two connection regions can be individually or jointly part of the heating conductor layer, or pads made of another electrically conductive material connected thereto. The carrier element can be formed by a flat plate with a plate thickness, preferably in rectangular form, and in this case have a narrow edge which is divided into, for example, four straight sections, preferably perpendicularly to its two main surfaces and the width or height of which corresponds to the plate thickness. Portions of the rim form corners of the support member.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. via a second connection region to a third connection region. Such a third and the first connection region can be arranged, for example, at an actual end of the heating conductor track. The heating conductor track is bounded in particular laterally in the plane of the heating conductor track by the insulation break, wherein no current flows in the region of the insulation break.The insulation break can be, for example, a region which is free of the heating conductor layer and divides the latter into heating conductor track sections which together form a path of the heating conductor track between a first end and a second end and between two, three or more connection regions. The insulation break can, however, also comprise material of the heating conductor layer which is electrically insulated from the heating conductor track.The connection regions can be defined, for example, or differ from the rest of the heating conductor track in that a substantially smaller amount of heat is generated in the connection regions during heating operation (compared to a normal heating conductor track section of equal size). In the connection regions, electrical contacting with an electrical energy source external to the heating conductor track can be realized. The electrical contacting necessary for this purpose can comprise contacting methods such as laser welding, soldering or thermal bonding, etc.The heating conductor layer can have an additional coating and / or a thickness increased in comparison to other regions in the connection regions in order to promote the contacting method and a long-lived and reliable electrical contacting. The additional coating may be a metal and may comprise copper, for example. The connection region or the end usually opens into the heating conductor track in one direction or in two directions.The heating conductor layer can be formed, for example, as a metallization made of a resistor alloy, which represents the corresponding heating resistor. The insulation break can be produced, for example, by laser ablation in the heating conductor layer or can already be produced during application by means of a screen printing process.The heating conductor layer plane can denote one of the two main surfaces of the carrier element which carries the heating conductor. If the surface of the carrier element carrying the heating conductor is planar, the heating conductor layer plane is, for example, a plane which is oriented parallel to this main surface of the carrier element. Even if the surface of the carrier element carrying the heating conductor is a curved surface, the heating conductor layer plane is everywhere parallel to the main surface (or curved surface) carrying the heating conductor. However, the then curved heating conductor layer plane in each point is only still defined by the tangential plane or local plane in the respective point that can be determined in all points of the heating conductor layer.A pattern or "layout" formed by the heating conductor track can be one or more regions through which current does not flow at corresponding reversal points at which the heating conductor track turns by 180°. These regions through which current does not flow form widened dead-end regions at the end of a respective insulation interruption. The tropical widening, e.g. viewed in plan view, serves to avoid local overheating in this region of the heating conductor track. A sharp, pronounced double inner corner would in each case cause very high local current densities, which would lead to marked temperature and thus voltage loads.According to a special development of the electric liquid heating, the edge is formed at least by a connection side, an opposite end side and two longitudinal sides of the carrier element. In particular, a rectangular shape can thereby be defined. 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, wherein the first heating conductor track section and the second heating conductor track section parallel thereto extend along one of the longitudinal sides and / or the end side and / or the side opposite thereto. If the two connection regions are located in diametrically opposite corners of the main surface of the carrier element, which is not common practice but is also not excluded, then all sides can be regarded as desired as a connection end, longitudinal end and end side.According to a special development of the electric liquid heating, the first heating conductor track section and the second heating conductor track section are straight sections. When configuring the pattern or "layout", there is a tendency to cover the available surface, i.e. the one main surface of the carrier element, with conductor tracks as efficiently as possible. Since, as described, bends of the conductor tracks by 90° or 180° lead to local variations of the current density at the inner and outer radii of the bends, these are selected as small as possible in number in the design and tend to lie in the outer corners of the main surface. As a result, the rectilinear conductor track sections which are efficient in this respect extend therebetween parallel to the respectively closest edges on the connection, longitudinal or end sides.It has been found that in some embodiments of the layout, the largest gradients of temperature directed radially from a center of the carrier element meet the corresponding edge in each case in the region of the center of the respective connection, longitudinal or end sides. The gradients flatten out towards the corners. In this respect, aspects of the invention can be advantageously applied precisely to straight first and second (and optionally further) conductor track sections which extend in particular in the central regions close to the edge of the respective connection, longitudinal or end sides.According to a further development of the electric vehicle liquid heating system, 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 construction, so that the desired temperature compensation can easily be set.According to an alternative development of the electric vehicle liquid heating system, the width of the first heating conductor track section varies over the length of the first heating conductor track section. In the case that the edge is formed at least by a connection side, an opposite end side and two longitudinal sides of the carrier element, the width of the first heating conductor track section decreases continuously or stepwise as viewed from a center of the relevant side in the direction of a corner of the carrier element formed by one of the longitudinal sides and the connection side or the end side opposite thereto.According to this embodiment, the local heating power at the edge of the carrier element can be set even more precisely along the relevant side. The further decrease in the width toward the corners leads to an increased heating power there. If, for example, comparatively large-area connection regions are located at or near the relevant corners, which define inherently colder sections, this approach can provide compensation.The corners themselves can have the named bends of the heating conductor track, where the cross section of the heating conductor track generally increases for geometric reasons. Therefore, the first heating trace portion and the second heating trace portion may each extend towards the corner to a location where the minimum first width is reached, which location is spaced from the corner. The corresponding minimum distance can be, for example, a (minimum) conductor track width plus an (inner) curve radius defined during the layout.According to a refinement of the electric vehicle liquid heating according to these alternative refinements, if the first heating conductor track section extends along the longitudinal side of the carrier element, a profile of its width is configured symmetrically along the direction of extent. As a result, a maximum width of the heating conductor track section is achieved in a region of the center of the longitudinal side. This produces a kind of bulge-like 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.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 meandering form with at least two reversal points which are spaced apart from one another in a longitudinal direction of the carrier element. In this case, the first heating conductor track section and the second heating conductor track section are fixed along the longitudinal direction only in a region lying between the two reversal points. As described, the reversal points are defined by a widening region for rounding inner edges at the 180° bends of the heating conductor tracks in order to avoid current density peaks. The reversal points thus occupy an area along the longitudinal direction specified, for example, by the drop shape.The electric vehicle liquid heater according to the above aspects or refinements can have a ceramic substrate as a carrier element, preferably comprising Al 2 O 3. In this case, the advantages due to the tensile stress problem are particularly clear.In the vehicular electric liquid heater, the ceramic substrate may be fixed to a metallic heat exchanger.According to advantageous exemplary embodiments, the first minimum width can lie 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.According to particularly advantageous exemplary embodiments, the temperature and voltage compensation can be set even more finely in that the heating conductor track has 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 which is greater than the first and the second distance, 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. A radial temperature and voltage compensation profile can thus be realized in a certain way.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 end side or only on one of the two longitudinal sides. Depending on the desired compensation, corresponding heating conductor track sections can also be provided in combination on two, for example, mutually opposite or three or more of the mentioned sides, in particular on all sides.Furthermore, it can also be provided that two adjacent heating conductor track sections lying closest to the edge are equipped with the same comparatively reduced width. In this case, the width of the relevant first semiconductor section is to be compared with a width of a third or possibly also fourth etc. section, as viewed from the edge, which is then the second heating conductor section in the sense of this application.Brief Description of the Drawings:The invention is explained in the following by way of example with reference to the following figures.The following are shown: FIG. 1 is a plan view of a heating element of an electric liquid heater according to a comparative example; FIG. 2 shows a detail of the heating element shown in FIG. 1 ; FIG. 3 shows a plan view of a heating element of an electric liquid heater according to a first exemplary embodiment; FIG. 4 shows a detail of the heating element shown in FIG. 3 ; FIG. 5 shows a plan view of a heating element of an electric liquid heater according to a second exemplary embodiment; FIG. 6 shows a detail of the heating element shown in FIG. 5 ; FIG. 7 is a cross-sectional view of a portion of a heating element of a liquid heater according to the first or second embodiment; and FIG. 8 is a simplified representation of an electric liquid vehicle heating system.Detailed Description of Preferred Embodiments:In the following description of the drawings, like reference numerals designate like or comparable components.FIGS. 1 and 2 show a plan view of a heating element 10 of an electric liquid heater 12 according to a comparative example, FIG. 2 showing an enlarged detail from FIG. 1.FIGS. 3 and 4 show a plan view of a heating element 10 of an electric liquid heater 12 according to a first exemplary embodiment, FIG. 4 showing an enlarged detail from FIG. 3.FIGS. 5 and 6 show a plan view of a heating element 10 of an electric liquid heater 12 according to a second exemplary embodiment, FIG. 6 showing an enlarged detail from FIG. 5.FIG. 7 shows a detail cross section through the heating element 10 perpendicular to the longitudinal direction or central axis 48, which however represents only the first and second exemplary embodiments. The reference numerals are otherwise also compatible with the comparative example.The following explanations apply first of all to FIGS. 1 to 6 together.The heating element 10 comprises a carrier element 14 designed as a ceramic substrate and a heating conductor layer 16 formed thereon. The heating conductor layer 16 has been structured, for example, in a screen printing method, so that it forms a heating conductor track 20 by means of a suitable arrangement of insulation interruptions 22.The carrier element 14 has a rectangular shape with two opposite longitudinal sides 21 extending in the longitudinal direction and also in each case connection and end sides 17, 19 extending perpendicularly thereto, i.e. in the transverse direction and likewise opposite one another.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 have a thickness h of, for example, 12 μm without limiting generality. The two connection regions 32, 33 can be formed from the same material or supplemented by an additional material in order to enable the connection of, for example, a bonding wire or another type of electrical connection conductor 35. In a second connection region 34 arranged symmetrically in the middle of the heating conductor tracks 20, the contacting by an electrical connection conductor 35 can likewise be provided. The electrical connecting conductors 35 can supply the heating conductor track 20 with electrical energy, which is converted into heat in the heating conductor track 20.The electrical connection conductors 35 connect the connection regions 32, 33, 34 to connection electronics, which is not illustrated in the figures. This can be a power board, a control device that comprises power electronics or the like. Each connection region 32, 33, 34 can be electrically conductively connected to more than one electrical connection conductor 35, wherein the number can differ between the two connection conductors. The connection conductors 35 extend from the connection regions 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 on the connection side 17. As described, these may each be bonding 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 provided, for example, for use at a comparatively higher high-voltage voltage, for example 800 V, a high voltage provided by the powerboard, the control device, or the power electronics can be applied via the connection conductors 35 between the first connection region 32 and the third connection region 33. In this case, the voltage falls over the full length of the heating conductor track 20. The heating resistor is correspondingly large, resulting in a predetermined current flow. In a second mode, a comparatively lower high voltage, for example 400 V, can be provided via the connection conductors 35 between the second connection region 34 on the one hand and in each case the first connection region 32 and the third connection region 33 on the other hand. The voltage falls in each case over half the length of the heating conductor track 20. As a result, the heating resistor is halved, so that twice the amount of current flows in comparison with the first mode. At half the high-voltage voltage and double the current flow, this results in the same heating power that is made possible with the same structure of the heating element for different vehicle electrical system voltages in vehicles. The setting of the heating power can be operated, for example, in pulse width modulated fashion.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 as far as the respective end point, the first connection region 32 and the third connection region 33.The limited space nevertheless requires that the heating conductor tracks 20 complete a 180° reversal at two points designated as reversal points 60, 62. The two reversal points 60, 62 are arranged approximately centrally in the transverse direction in the two divided layouts to the left and right of the central axis 48. In the longitudinal direction, the first reversal point 60 is arranged adjacent to the end side 19 and the second reversal point 62 is arranged 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, as described, each form a portion of the insulation break 22 which, in plan view, widens drop-like toward the end side 19 or toward the connection side 17, i.e. they cover a region having a length in the longitudinal direction which leaves the spacing between them. The two reversal points 60, 62 result in less space being available for the sections of the heating conductor track 20 passing in the longitudinal direction, as viewed in the transverse direction. In the examples, this is taken into account in various ways.A first conductor track section 28 extends along the edge of the carrier element 14 on one of the two longitudinal sides 21 thereof. In this case, a narrow piece of the main surface of the carrier element 14 is arranged exposed, i.e. the first conductor track section 28 has a preferably constant and very small distance b r from the edge of the carrier element 14. However, the first conductor track section 28 can also terminate flush with the surface of the edge of the carrier element 14, so that the distance b r is zero mm. The distance b r can also vary along the longitudinal direction. These explanations also apply analogously to conductor track sections on the connection side and the end side, which sections are not described separately.A second heating conductor track section 30 extends directly next to and parallel to the first heating conductor track section 28, likewise in the longitudinal direction parallel to the central axis 48, only interrupted by the insulation interruption 22, The insulation interruption 22 can have a width b iso of 0.2 mm, which thus determines the distance between the second heating conductor track section 30 and the first heating conductor track section 28. The second heating conductor track section 30 therefore has a distance from the edge of the same longitudinal side 21 which is greater than the corresponding distance of the first heating conductor track section 28.A third heating conductor track section 36 extends directly next to and parallel to the second heating conductor track section 30 (and to the first heating conductor track section 28), likewise in the longitudinal direction parallel to the central axis 48, only interrupted by the insulation interruption 22, In the same way, a fourth heating conductor track section 38, a fifth heating conductor track section 40 and a sixth heating conductor track section 42 adjoin one another-viewed in this sequence from the edge on the longitudinal side 21.The six heating conductor track sections 28 to 42 considered here are straight sections in each case. In the present examples, they extend at least between a terminal-side end C, viewed in the longitudinal direction, of the end-side reversal point 60 and the end-side end D, viewed in the longitudinal direction, of the terminal-side reversal point 62, but they can also extend-depending on the heating conductor strip section-between the respective bending points A at the end-side end and the respective bending points B at the terminal-side end.In the examples shown in FIGS. 1 to 4, the first heating conductor track section 28 has a constant width b 1. In the examples shown, the second heating conductor track section 30 has a constant width b 2. there. The third heating conductor track section 36 has a constant width b 3. in each case in the examples shown in FIGS. 1 to 4. In the examples shown in FIGS. 1 to 4, the fourth heating conductor track section 38 has a constant width b 4. In the examples shown in FIGS. 1 to 4, the fifth heating conductor track section 40 has a constant width b 5. In the examples shown in FIGS. 1 to 4, the sixth heating conductor track section 42 has a constant width b 6.In the comparative example shown in FIGS. 1 and 2, a width of the heating conductor track is almost continuously constant. The recesses are bent sections as well as the sections of the heating conductor track directly adjacent to the reversal points. This means that the following applies to the widths of the heating conductor track sections:A usual fault tolerance dependent on the production process must be taken into account in this case.In the first exemplary embodiment shown in FIGS. 3 and 4, the width b 1 of the first heating conductor track section 28 is selected to be smaller than the width b 2 of the second heating conductor track section 30.In the present examples of FIGS. 1 to 6, the minimum heating conductor track width b may 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 of between 2.5 mm and 6 mm inclusive is particularly preferred. For example, in Comparative Example b, 1= b may be 2= b may be 3= b may be 4= b may be 5= b may be 6= 4,5 mm. In comparison, in the first embodiment, b may be 1= 3,75 mm, b may be 2= b may be 3= b may be 4= b may be 5= 4,5 mm, and b may be 6= 4,8 mm.The heating resistor is locally increased there by the comparatively reduced width of the first heating conductor track section 28, 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 b 6 is increased even once again in comparison with the fifth heating conductor track section 40 closer to the edge.In the second exemplary embodiment shown in FIGS. 5 and 6, the widths b 1 to b 6 of the heating conductor track sections 28 to 42 are selected in the region C-D as in the first exemplary embodiment shown in FIGS. 3 and 4. Outside the region C-D, for example in the regions A-C or D-B, on the other hand, 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. The width b 1" in FIG. 6 denotes the overall minimum width of the first heating conductor track section 28, which in the second exemplary embodiment is approximately 3 mm and is reached at a point where the inner curve radius for a 90-bend attaches to the first heating conductor track section 28. The following applies here:As a result of the reduction in the width of the first heating conductor track section 28 in the direction of the end side 19 or the connection side 17, the parallel continuations of the second and of the third heating conductor track section 30, 36 bend away in each case towards the associated longitudinal side 21. Their widths b 2 and b 3 remain constant. This allows the fourth and fifth heater trace portions 38 and 40 to have a greater width adjacent the turning points 60, 62.Returning to the first exemplary embodiment of FIGS. 3 and 4, it is also shown by way of example for the connection side 17 that a width c 1 of an outer heating conductor track section is selected to be smaller than a width c 2 of an adjacent, parallel extending and further inner heating conductor track section:It should be noted that the above explanations with respect to heating conductor track sections which are assigned to one longitudinal side 21 or to the connection side can be applied in the same way analogously to corresponding heating conductor track sections which are assigned to the end side or to the other longitudinal side. On the other hand, however, a combination of the comparative example, the first exemplary embodiment and / or the second exemplary embodiment is also conceivable here. For example, the bulge-like shape of the first heating conductor track section of the second exemplary embodiment can be applied only to the longitudinal sides, but not to the front side or connection side, where the widths according to the comparative example are then used. Alternatively, the dimensions c 1 and c 2 of the first exemplary embodiment can be used on the front or connection side. Furthermore, the heating conductor track sections are not limited to the limits A, B, C or D shown in the figures, but can also be defined in a wide variety of other ways.FIG. 8 shows a simplified illustration of an electric liquid heater 12 for a vehicle. The electric vehicle heater 12 illustrated in FIG. 8 comprises, in addition to the electric heating element 10, a liquid heat exchanger 44, on which the electric heating element 10 according to the exemplary embodiments is arranged and to which the heat generated during heating operation is transmitted from the heating element 10, and a control unit 46 for actuating the electric heating element 10. Further components of the electric vehicle heating system 12 not shown in FIG. 8, which are not explicitly shown in FIG. 8 for the sake of simplicity, are well known to the person skilled in the art and are supplemented by the electric vehicle heating system 12 in order to ensure the functionality of the electric vehicle heating system 12.The features of the invention disclosed in the above description, in the drawings and in the claims can be essential for the realization of the invention both individually and in any combination.List of reference characters10 Heating element 12 Electrical liquid heater 14 Carrier element 16 Heating conductor layer 17 Connection side 18 Heating conductor layer plane 19 Longitudinal sides 20 Heating conductor track 21 End side (opposite the connection side) 22 Insulation break 28 First heating conductor track section 30 Second heating conductor track section 32 First connection region 33 Third connection region 34 Second connection region 35 Electrical connection conductor 36 Third heating conductor track section 38 Fourth heating conductor track section 39 Cutout 40 Fifth heating conductor track section 42 Sixth heating conductor track section 44 Heat exchanger 46 Control device 48 Central axis 50 Electrical connection line 60 Connection-side reversal point 62 End-side reversal point A, B, C, D Section boundaries b 1, b 2, b 3, b 4, b 5, b 6 widths of the first to sixth heating conductor track sections (longitudinal side) b 1, b 1', b 1'' variable width of the first heating conductor track section (longitudinal side) c 1, c 2 widths of the first and second heating conductor track sections (front side and / or connection side) h layer thickness

Claims

An electric vehicle liquid heater (12) having a heating element (10), wherein the heating element (10) comprises: - a carrier element (14); and - a heating conductor layer (16) which is arranged on the carrier element (14); - wherein the heating conductor layer (16) has a heating conductor track (20) in a heating conductor layer plane (18), which is bounded in the heating conductor layer plane (18) by at least one insulation break (22); - wherein the heating conductor track (20) extends at least between a first connection region (32) and a further connection region (33, 34), in which the heating conductor track is electrically conductively connected in each case to at least one electric 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.The vehicle electric liquid heater (12) according to claim 1, wherein the first minimum cross-sectional area is formed by a first minimum width (b 1) perpendicular to the extending direction of the first heater trace portion (28), the second minimum cross-sectional area is formed by a second minimum width (b 2) perpendicular to the extending direction of the second heater trace portion (30), and the second minimum width (b 2) is larger than the first minimum width (b 1) wherein a layer thickness (h) of the first and second heater trace portions (28, 30) is preferably equal to each other.Electric vehicle liquid heater (12) according to claim 1 or 2, wherein the edge is formed at least by a 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 thereto, 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 thereto.The vehicle electric liquid heater (12) according to any one of claims 1 to 3, wherein the first heater trace portion (28) and the second heater trace portion (30) are straight portions, respectively.The vehicle electric liquid heater (12) of any of claims 1 to 4, wherein a width of the first heater trace portion (28) is constant along the length of the first heater trace portion (28) and corresponds to the first minimum width.The electric vehicle liquid heater (12) according to any one of claims 1 to 4, wherein a width of the first heating conductor track portion (28) varies over the length of the first heating conductor track portion (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 support member (14), the width of the first heating conductor track portion (28) decreases continuously or stepwise as viewed from a center of the side in question towards a corner of the support member (14) formed by one of the longitudinal sides (21) and the connection side (17) or the end side (19) opposite thereto.The vehicle electric liquid heater (12) of claim 6, wherein the first heater trace portion (28) and the second heater trace portion (30) each extend toward the corner to a location at which the minimum first width (b 1'') is reached, which location is spaced from the corner.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 carrier element (14), a profile of its width is formed symmetrically along the extension direction, such 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.The electric vehicle liquid heater (12) according to any one of claims 1 to 8, wherein the heating conductor track extends on the support element in meandering form with at least two turning points (60, 62) spaced apart from each other in a longitudinal direction of the support element (14), wherein the first heating conductor track portion (28) and the second heating conductor track portion (30) are fixed along the longitudinal direction only in a region lying between the two turning points (60, 62).The electric vehicle liquid heater (12) according to any of the preceding claims, wherein the support element (14) is a ceramic substrate, preferably comprising Al 2 O 3.The vehicle electrical liquid heater (12) of claim 10, wherein the ceramic substrate is attached to a metallic heat exchanger (44).The electric vehicle liquid heater (12) according to any one of the preceding claims, when dependent on claim 2, wherein the first minimum width (b 1) is in an interval of 70% to 90% of the second minimum width (b 2) preferably in an interval of 75% to 85% of the second minimum width (b 2).The electric vehicle liquid heater (12) according to any one of the preceding claims, insofar as it relates back to 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 (b 3) perpendicular to its direction of extension, wherein the third minimum width (b 3) is greater than the first minimum width (b 1).

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