Heat exchanger, method for manufacturing heat exchanger and electric water heater

Abstract

Disclosed is a heat exchanger (2) for an electric water heater, comprising a heating conductor (4), a heat transfer element (6) and an insulating element (8) arranged between the heating conductor (4) and the heat transfer element (6) for electrically insulating the heating conductor (4) and the heat transfer element (6) from each other, wherein the insulating element (8) is arranged on the heat transfer element (6) by means of a thermally conductive elastic adhesive (10).

Description

Technical Field

[0001] The invention relates to a heat exchanger, a method for manufacturing a heat exchanger and an electric water heater. Background Art

[0002] Heat exchangers are often used to transfer heat from a heating element to a heat-conducting medium. Such heat exchangers are often installed in heaters, in which the heat generated by the heating conductor is transferred to the heat transfer element, which in turn transfers the heat to the medium. The medium used here is, for example, water or a coolant, so that such heaters are also called water heaters and, in the case of electrically operated heating conductors, electric water heaters. A typical field of application for such electric water heaters is in motor vehicles, for example for heating the passenger compartment.

[0003] In order to achieve electrical insulation between the heating conductor and the heat transfer element, especially the medium, an insulating element is usually arranged in the heater. As mentioned above, the insulating element, also called the insulating layer, should have an electrical insulating effect on the one hand and a good thermal conductor on the other hand.

[0004] This means that only a few materials are suitable. These materials are usually plastics or ceramics, but they often exhibit thermal expansion mismatches, i.e. different linear expansions when heated during operation and production, which can cause the insulation to peel off and / or form cracks. Summary of the invention

[0005] It is therefore an object of the present invention to provide a heat exchanger, a method and an electric water heater, whereby the mechanical stresses during operation of the heater can at least be reduced.

[0006] With regard to the heat exchanger, this object is achieved according to the invention by a heat exchanger comprising the features of claim 1. With regard to the method, this object is achieved according to the invention by a method for producing a heat exchanger comprising the features of claim 7. With regard to the electric water heater, this object is achieved according to the invention by an electric water heater having the features of claim 6. Furthermore, within the scope of the present application a motor vehicle or a construction machine or a watercraft is disclosed and claimed, which has an electric water heater according to the invention.

[0007] Preferred embodiments, improvements and variants are subject matter of the dependent claims. The advantages and preferred embodiments listed with respect to the heat exchanger apply, mutatis mutandis, to the method and the electric water heater and vice versa.

[0008] In this context, the term "water heater" is to be understood in a broad sense. The term "water heater" refers to a heater that can be operated using any type of water as a medium, i.e. a coolant (water-glycol mixture) can also be used.

[0009] Specifically, the object is achieved by a heat exchanger for an electric water heater, the heat exchanger having a heating conductor and a heat transfer element. The heating conductor can be, for example, an electric heating conductor. The heat transfer element can be, for example, a metal heat transfer element.

[0010] Furthermore, the heat exchanger has an insulating element which is arranged between the heating conductor and the heat transfer element. This arrangement can also be referred to as a "sandwich" structure. The insulating element serves to electrically insulate the heating conductor and the heat transfer element from one another so that no electrical short circuit occurs between the two components.

[0011] Furthermore, the insulating element is attached to the heat transfer element by means of a thermally conductive elastic adhesive.

[0012] The advantages of this design are that, on the one hand, the thermal conductivity required for the heat exchanger is not impaired by the adhesive, since the adhesive is both thermally conductive and elastic. On the other hand, the elastic properties of the adhesive can compensate for the mechanical stresses between the individual components, in particular between the insulating element and the heat transfer element, which occur during operation and the associated heating of the heat exchanger. In other words, by using an elastic adhesive, the insulating element can be arranged directly on the heat transfer element.

[0013] According to one embodiment, a joint gap is formed between the heat transfer element and the insulating element, and the adhesive is arranged in the joint gap. This does not damage the "sandwich" structure of the heat exchanger (which is considered necessary and has been described above), and can achieve accurate positioning of the adhesive.

[0014] In a further embodiment, the geometrical dimensions of the joint gap are designed based on at least one of the following parameters:

[0015] - Thermal conductivity of the adhesive;

[0016] - thermal expansion of insulating and heat transfer elements;

[0017] - stretchability of the adhesive;

[0018] - operating temperature of the heat exchanger;

[0019] - the continuous operating temperature of the adhesive; and

[0020] - The bonding properties of the adhesive to the material of the insulating element and to the material of the heat transfer element.

[0021] For the purposes of this application, the term "thermal conductivity of the adhesive" is understood to mean the overall thermal conductivity of the adhesive. For example, the greater the thermal conductivity of the adhesive, the thicker the joint gap can be designed so that as much adhesive as possible can be introduced into the joint gap and thus achieve mechanical fixing of the components.

[0022] For the purposes of this application, the term "thermal expansion of the insulating element and the heat transfer element" is understood to mean the extent to which these two components expand during operation, ie when heated. The greater the thermal expansion of the components, the greater the elasticity of the adhesive must be in order to compensate for mechanical stresses.

[0023] For the purposes of this application, the term "stretchability of the adhesive" is understood to be the degree of elasticity of the adhesive, so that the adhesive can be selected depending on the mechanical stresses that occur or are expected, and the joint gap can be designed accordingly.

[0024] For the purposes of this application, the term "operating temperature of the heat exchanger" is to be understood as how high the temperature reaches during operation of the heat exchanger. The higher the temperature, the higher the heat resistance of the adhesive must be, or the larger the expected expansion of the components must be, to which the joint gap must be adapted. Typical examples of temperatures are -40 degrees Celsius as the thermal lower limit and the maximum operating temperature of the operating temperature as the thermal upper limit.

[0025] For the purpose of this application, the term "continuous operating temperature of the adhesive" is understood to be the continuous temperature to which the adhesive can be exposed within acceptable tolerances without losing thermal conductivity and elastic properties.

[0026] For the purposes of this application, the term "adhesive properties" is to be understood as meaning that the adhesive must be designed to be able to adhere to different materials, such as ceramics and metals.

[0027] In order to optimize the aforementioned “sandwich” structure, the heat transfer element is arranged on a first side of the insulation element and the heating conductor is arranged on a second side of the insulation element, wherein the first side is opposite to the second side.

[0028] According to one embodiment, the insulating element includes ceramic or is made of ceramic. Specifically, the insulating element can be designed as a ceramic substrate (eg, as a plate-shaped support element), for example, made of Al 2 O 3 The heating element is formed by screen printing a layer of heating conductors on a substrate. Subsequently, an insulating element on which the heating conductors are arranged forms the heating element. The heating conductors can be formed, for example, as metallized structures made of a resistance alloy, which represent the corresponding heating resistors. Iron-nickel alloys or nickel-chromium alloys can be considered. The insulation interruption ensures that long conductor paths are built from the layers that are originally applied flat and then baked, and can be created, for example, by a screen printing process during the application process. The ceramic substrate can be a ceramic support plate. According to aspects of the invention, such an embodiment of the heating element is preferred.

[0029] The heat exchanger can also preferably have a plurality of heating elements. In this case, each individual heating element or the relevant insulating element is arranged on the heat transfer element by an adhesive.

[0030] Furthermore, the heat transfer element may be made of steel or aluminum, preferably aluminum. The heat transfer element may have a deep-drawn base part and a flat cover part in the form of a support plate. The support plate may also be deep-drawn to form a bump as will be described below according to the embodiments. The flat periphery of the base part is connected to the cover part by welding or welding to close the flat fluid cavity formed between the two, through which the coolant or water flows. A turbulator may be used in the fluid cavity, which mixes the fluid flowing through and supports the transfer of heat to the fluid. The fluid may flow into the fluid cavity through the fluid inlet and flow out again through the fluid outlet after being heated.

[0031] According to a specific embodiment, the geometric dimensions of the joint gap, in particular the thickness of the joint gap or the layer thickness of the adhesive arranged therein, can be defined by a plurality of spacers. The spacers can be in the form of glass beads, foil particles in the adhesive, or bumps in the heat transfer element or protrusions on the heat transfer element. In the bonded state, the spacers can be embedded in the (hardened) adhesive or arranged in an area without adhesive. The spacers can form contact surfaces or contact points for the insulating element. When the adhesive is pressed by the insulating element (for example, during production, the insulating element is pressed on the heat transfer element), the spacers can be used as stop points / surfaces for the insulating element, thereby supporting and simplifying the production process. If a separate raised element is formed on the surface of the heat transfer element by locally applying and curing the adhesive before performing the actual application step to form the adhesive layer, the spacers can also be formed by the material of the adhesive itself.

[0032] The height of the spacer may be in the range of 100 μm to 450 μm, preferably between 200 μm and 350 μm. In the example of bumps or protrusions, the height is the distance between the support point of the insulating element (or the first side of the insulating element opposite to the second side on which the heating conductor is arranged) and the surface of the heat transfer element or, depending on the embodiment, the distance to the flat support plate of the heat transfer element forming this surface. In the case of glass beads or foil particles, the height may correspond to their diameter.

[0033] An improvement in this aspect is that the spacer has a supporting point or surface as described above and has at least two different total heights, wherein a first spacer arranged closer to the center of the insulating element has a relatively smaller total height, and a second spacer arranged closer to one of the edges of the insulating element has a relatively larger total height, so that the thickness of the adhesive layer near the edge is greater than the thickness of the adhesive layer near the center.

[0034] This measure eliminates or at least reduces the stringent requirements on the flatness tolerance of the bonding surfaces on the heat exchanger, while increasing process reliability and simplifying production overall. In addition, the smaller thickness of the joint gap in the middle of each insulating element (i.e. away from its outer edge) leads to a more efficient heat transfer and thus to the heat release of the heating element.

[0035] According to an exemplary embodiment, the spacer may be formed as a bump formed in the surface of the heat transfer element as described above. The bump may also be formed by the adhesive itself as described above, for example by applying a bump of adhesive to the surface of the heat transfer element and then curing it, followed by a large-area application of the adhesive to produce the actual adhesive layer, thereby forming the joint gap. Alternatively, the bump may be formed by the heat transfer element itself, for example by deep drawing a corresponding support plate. In this case, the bump may be formed or made integral with the heat transfer element.

[0036] This embodiment has many advantages: On the one hand, the bumps can be formed very accurately using the manufacturing method, so that the local thickness can be set accurately. In addition, the production can be well integrated into the manufacturing process of the heat transfer element, thus saving costs and effort.

[0037] If the aspect of varying (increasing) the layer thickness from the center to the edge of the insulating element with spacers is combined with the concept of bumps, a special advantage results: a locally variable adjustment of the layer thickness, such as an increased thickness in the area close to the edge of the insulating element, can balance or compensate for the shear forces between the bonding surfaces during thermal expansion. In the central area, the thickness of the adhesive (due to the height H of the bumps) is reduced to improve the thermal conductivity. In addition, the bumps themselves can also improve the thermal conductivity when they are in more or less direct contact with the insulating element.

[0038] According to another aspect of the invention, the latter advantage can be utilized. According to this aspect, the first side of the insulating element faces the projection, and the heating conductor is arranged on the opposite second side of the insulating element. In addition, a position can also be defined in the heating conductor, at which the maximum heat release of the heating element during operation, i.e. the maximum or local maximum (peak value), can be determined. In this case, one of the projections can now be placed on the first side at a position opposite to the maximum heat release position on the second side.

[0039] This measure allows for a more even heat distribution, which reduces thermal stresses in the insulating element (ceramic), reduces local heat loads in the heating conductors and transfers heat more efficiently to the heat transfer element.

[0040] Similar aspects relate to further connection of the power switching element to the heat transfer element. The heat exchanger may also include the power switching element, which includes a printed circuit board substrate having a first side and a second side and a power switching element arranged on the second side. The printed circuit board substrate may be arranged on the heat transfer element by means of a thermally conductive elastic adhesive in the same manner as the insulating element. At least one temperature sensor is also arranged at a position on the second side of the printed circuit board substrate. One of the bumps is placed on the first side of the printed circuit board substrate at a position opposite to the position of the temperature sensor.

[0041] This aspect of the invention has the following advantages:

[0042] - an adhesive 10 with a relatively low thermal conductivity can be used, which results in a cost advantage per unit amount of adhesive applied;

[0043] - When the layer thickness increases away from the bump, a larger layer thickness or thickness of the joint gap can be accepted, which leads to an increase in process capability or a larger tolerance window for the layer thickness;

[0044] - the affected electronic components can be replaced with alternative components, e.g. with lower cost or higher performance, which in turn can be achieved through a higher permissible power dissipation;

[0045] -Can increase the service life of electronic components subject to thermal stress;

[0046] -The temperature sensor can be better connected to the point being measured (e.g., a heat exchanger), thus ensuring better measurement accuracy and response time.

[0047] Alternatively or additionally, one (another) bump may also be placed at a (different) position on the first side of the printed circuit board substrate opposite to the position on the second side of the printed circuit board substrate where one of the power switch elements is arranged. The advantages are the same as described above with respect to the maximum heat release position, because the high-voltage power switch element itself is also a considerable heat source during operation, which can be advantageously dissipated by the nearby bump.

[0048] The heat output of the water heater is preferably at least 5 kW, preferably at least 7 kW, for example at least 9 kW. The heating power is preferably less than or equal to 13 kW in each case. The operating voltage when the water heater is operated (which may be equal to the onboard voltage of the electric 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.

[0049] In particular, the object of the method is solved by a method for producing a heat exchanger, wherein the method comprises the following steps:

[0050] - arranging the heating conductor on the insulating element;

[0051] -Provide heat transfer elements;

[0052] - Applying a thermally conductive elastic adhesive on one side of the heat transfer element or on the side of the insulation element on which no heating conductor is arranged.

[0053] The step of arranging the heating conductor on the insulating element preferably comprises applying the heating conductor to the insulating element by screen printing.The insulating element with the applied heating conductor then forms the heating element.

[0054] The thermally conductive elastic adhesive is preferably applied to a first side of the insulating element (the side opposite to the heating conductors).

[0055] According to one embodiment of the method, the method further comprises the following steps:

[0056] - defining a joint gap between the heat transfer element and the insulating element, and

[0057] - Arrange adhesive in the joint gap.

[0058] For the purposes of the present application, the term “defined” is understood to mean that the joining gap is achieved, for example, by a defined contact pressure, wherein the two elements are pressed together, for example in a mold provided for this purpose.

[0059] Preferably, the adhesive is applied to the insulating element, in particular to the first side of the insulating element (the side of the insulating element opposite to the heating conductor). For example, the insulating element with the heating conductor arranged thereon is placed in the adhesive device in such a way that the heating conductor faces downwards. Then, the heat transfer element is placed on top and fixed to the frame with screws, and a weight may also be loaded in the middle.

[0060] It is also conceivable that spacers (glass beads in the adhesive, foil particles, bumps in the heat transfer element) may be used as described above to adjust the joint gap.

[0061] For example, if the spacer is a bump, the bump can be manufactured as follows: For example, the surface of the heat transfer element to be joined can be a deep-drawn plate-shaped sheet metal part. The bump is stamped into the sheet metal part by a stamping or punching tool, which has an embossing corresponding to the bump. Alternatively, it is also conceivable to use a process including aluminum casting and CNC post-machining to manufacture the bump.

[0062] With the manufacturing method described, the bumps can be formed very precisely, so that the local thickness can be set precisely. In addition, the production can be well integrated into the manufacturing process of the heat transfer element, thus saving costs and effort. The other advantages are the same as above.

[0063] In a further embodiment, the method further comprises the following steps:

[0064] - The geometry of the joint gap is designed based on at least one of the following parameters:

[0065] - Thermal conductivity of the adhesive;

[0066] - thermal expansion of insulating and heat transfer elements;

[0067] - stretchability of the adhesive;

[0068] - operating temperature of the heat exchanger;

[0069] - the continuous operating temperature of the adhesive; and

[0070] - The bonding properties of the adhesive to the material of the insulating element and to the material of the heat transfer element. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Exemplary embodiments of the present invention will be explained in more detail below with reference to the accompanying drawings. The accompanying drawings show in a partially simplified diagrammatic representation:

[0072] Figure 1 is a schematic cross-sectional view of a heat exchanger according to the present invention;

[0073] Figure 2 is based on Figure 1 A schematic cross-sectional view of a heat transfer element and an insulating element of a heat exchanger or heating element according to an exemplary embodiment with a spacer, showing the overall structure;

[0074] Figure 3 is based on Figure 2 A cross-sectional view of a heat transfer element having bumps formed therein as spacers according to a compatible exemplary embodiment;

[0075] Figure 4 is a perspective view of a heat exchanger without a heating element, wherein a Figure 3 The bump shown;

[0076] Figure 5 yes Figure 4 A plan view of the heating element and power switch components mounted on the heat exchanger. DETAILED DESCRIPTION

[0077] Figure 1 A cross section of a heat exchanger 2 according to the invention for an electric water heater (not shown) is shown. The heat exchanger 2 has a heating conductor 4, of which only a cross section of a plurality of windings is shown.

[0078] Furthermore, the heat exchanger 2 has a heat transfer element 6. An insulating element 8 is arranged between the heating conductor 4 and the heat transfer element 6 for electrically insulating these two components. The insulating element 8 is arranged on the heat transfer element 6 by means of a heat-conducting elastic adhesive 10. Figure 1 In the exemplary embodiment shown, the adhesive 10 is arranged in a joint gap 12 formed between the insulation element 8 and the heat conducting element 6 .

[0079] In addition, from Figure 1 It can be seen that the heat transfer element 6 is arranged on a first side 14 of the insulation element 8 and the heating conductor 4 is arranged on a second side 16 of the insulation element 8 to form the “sandwich” structure already mentioned at the beginning.

[0080] During operation of the heat exchanger 2, the electrical heating conductor 4 is heated and the heat is transferred to the insulating element 8, which is usually designed as a ceramic. Subsequently, the heat is transferred from the insulating element 8 via the thermally conductive adhesive 10 to the heat transfer element 6, which in turn transfers the heat to the medium 18 (for example water, which is only schematically shown in the figure).

[0081] The present invention is not limited to the above exemplary embodiments. On the contrary, those skilled in the art may also derive other variations of the present invention therefrom without departing from the subject matter of the present invention. In particular, all individual features described in conjunction with the exemplary embodiments may also be combined with each other in other ways without departing from the subject matter of the present invention.

[0082] Figure 2 The schematic diagram in shows a further development of the exemplary embodiment described above. For simplicity, only the insulating element 8 of the heating element and the heat transfer element 6 of the heat exchanger 2 are shown, wherein a joint gap 12 to which the adhesive 10 is applied extends between the insulating element 8 and the heat transfer element 6. For example, Figure 2 Omitted Figure 1 The heating conductor 4 or the medium 18 in the ... Figure 2 The joining gap 12 is adjusted by means of spacers (glass beads in the adhesive, foil particles, bumps in the heat transfer element 6 or protrusions on the heat transfer element 6) which are shown very schematically in FIG. In principle, according to an exemplary embodiment, these spacers can have the same height. However, in Figure 2 In the exemplary embodiment of FIG. 1 , spacers 20 , 22 of different heights are provided.

[0083] In order to produce a not too thick joint gap, narrow tolerances for the uniformity of the bonding surfaces on the heat exchanger are required in order to provide sufficient process reliability (uniform and large-area distribution of the adhesive between the surfaces). In practice, however, due to possibly different expansion coefficients, the maximum length difference between the insulating element 8 and the heat transfer element 6 occurs at the edge of the bonding area when the temperature changes, while the center is actually the starting point for the mutual displacement. Therefore, the basic idea of ​​the present exemplary embodiment is to make the joint gap thicker near the edge of the heating element or the insulating element 8, while the joint gap in the center is relatively thin.

[0084] Figure 2 It is shown that the spacers 22 on the outside (i.e. closer to the edge of the insulating element 8) have a greater height than the spacers 20 on the inside (i.e. closer to the center). This increases the thickness of the adhesive layer 10 exactly at those critical points where the difference in thermal expansion length is large and therefore the layer will be subjected to the greatest stress. This measure eliminates or at least reduces the strict requirements on the flatness tolerance of the bonding surface on the heat exchanger, while increasing process reliability and simplifying production overall. It is worth noting that the height H of the support points or support surfaces 25 of the spacers can be produced very accurately. As Figure 2 As shown in the slightly exaggerated figure, the deflection of the overlying heating element is quite acceptable. In addition, the smaller thickness of the joint gap 12 in the center of the corresponding insulating element 8 leads to more efficient heat transfer and thus heat release of the heating element.

[0085] According to an exemplary embodiment of the method of the present invention, the thickness can also be adjusted by:

[0086] the adhesive comprises fillers (e.g. glass beads) having a defined size and shape distribution, wherein the fillers act as mechanical spacers when the adhesive 10 is pressed between adjacent surfaces of the insulating element 8 and the heat conducting element 6;

[0087] - the means for pressing the adhesive 10 have a geometric stop on the outside, acting as a mechanical spacer;

[0088] - the means for pressing the adhesive 10 exerts a defined force distribution, which ultimately results in the adhesive 10 having a defined layer thickness; or

[0089] - Before pressing, auxiliary means (eg doctor blade / screen printing) are used to bring the adhesive 10 to a defined layer thickness and the adhesive 10 no longer undergoes geometric changes during the subsequent pressing process.

[0090] However, if Figure 3 As shown, a particularly advantageous exemplary embodiment provides that the surface of the heat transfer element 6 to be joined is provided with a plurality of projections 24 as spacers 20 or 22, such as Figure 2. The bumps 24 are integrally formed with the heat transfer element 6. When the adhesive 10 is pressed, the opposite surface of the insulating element 8 of the heating element can now rest against these bumps (equivalent to a form fit). Therefore, the raised surface of the bump 24 serves as an impact surface or contact surface 25 for the surface of the insulating element 8. In the case where very small particles or beads are present in the adhesive (for example, ceramics with a diameter of, for example, 60 μm, etc.), these particles or beads remain between the bearing surface of the spacer and the first side (i.e., the back side) of the insulating element in the final pressed state (it can be said to be "sandwiched") and do not come out of the narrow gap. Subsequently, the thickness of the adhesive layer will increase accordingly by a small amount. In this regard, the bump height H determines the measure of the layer thickness of the adhesive 10. Figure 3 Only the side of the heat transfer element 6 is shown; the insulating element 8 not shown in the figure is Figure 3 The right side of the second embodiment approaches and is pressed on when adhesive 10 is applied therebetween.

[0091] Figure 3 A cross-sectional view of a heat transfer element 6 is shown, which comprises a fluid cavity 32 formed thereby, in which a medium 18 or fluid (eg water) flows, and turbulators 26 arranged therein for mixing the medium 18 and for enhancing heat transfer.

[0092] The manufacturing can be carried out as follows: For example, the surface of the heat transfer element 6 to be joined can be a deep-drawn plate-shaped sheet metal part. The bump 24 is embossed onto the sheet metal part in a stamping or punching tool, which has an embossing corresponding to the bump 24. Alternatively, it is also conceivable to use a process including aluminum casting and post-processing by CNC machine tools to manufacture the bump 24. In the present exemplary embodiment, the total height H of the bump can be 0.32 mm, the diameter of the contact surface 25 can be 1 mm, and the total diameter of the bump (including the side) can be 2.31 mm.

[0093] Back to Figure 2 , the inclination of the surfaces that engage with each other can be adjusted by specially setting the height H of the bump 24. This allows the above-mentioned local variable adjustment of the layer thickness, such as increasing the thickness in the area close to the edge 30 of the insulating element 8 to compensate for shear during thermal expansion between the engaging surfaces. In the central area, the thickness of the adhesive 10 (due to the height H of the bump) is designed to be smaller to increase thermal conduction. The bump 24 can also be formed very accurately using the manufacturing process, so that the local thickness can be set accurately. In addition, the production can be well integrated into the manufacturing process of the heat exchanger 2, which saves costs and workload.

[0094] exist Figure 4, a perspective view of a heat exchanger 2 without a heating element or heat transfer element 6 is shown, wherein the viewing direction is directed toward a substantially flat support plate 60 of the heat transfer element 6, which support plate 60 forms a surface for engagement with the insulating element 8 of the heating element. In this exemplary embodiment, a total of three heating elements (i.e., three insulating elements 8) are added, as well as a printed circuit board (not shown) providing power switching elements for operating the heating elements.

[0095] In the support plate 60 of the heat transfer element 6, a plurality of projections 24 are arranged as spacers 20 or 22 distributed on its surface as described. The position of its first side 14 is also shown in dashed lines when one of the three insulation elements 8 is joined to the heat transfer element 6. It can be seen that the first projections 24 or spacers 20 (here two per heating element) are close to the center of the first side 14, while the second projections 24 or spacers 22 (here four per heating element) are close to its edges 30. The two edges 30 at the longitudinal ends of the insulation element are relevant here, because shearing has a greater effect in the longer longitudinal range than in the transverse direction.

[0096] In addition to the fluid chamber 32, Figure 4 Also shown are connections 34 for fluid inlet or outlet, and a plurality of through holes formed in the support plate 60 for feed-through of electrical conductor tracks from a control module (not shown) to a power switching component (not shown).

[0097] Figure 4 The exemplary embodiments of the present invention also illustrate another independent aspect of the present invention, which can be independent of Figure 2 The basic idea of ​​the exemplary embodiment of Figure 4 The bumps 24 (25) in FIG. 1 are only considered as examples. The contour lines ( Figure 4 The outline corresponds to the power switch component 45 to be attached, which is designed as a printed circuit board substrate 46, on which a power switch element 47 (only schematically shown) is arranged for operating the heating element 9 (see Figure 5 The power switch component 45 comprises, for example, a FR4 substrate or the like as a printed circuit board substrate 46, which, like the heating element 9, is bonded to a substantially flat support plate 60 of the heat transfer element 6 and, like the support plate 60, dissipates the heat generated by the power switch element 47 during operation to the medium flowing through the fluid cavity 32 via the thermally conductive adhesive 10 and the heat transfer element 6.

[0098] In the aspect considered here, the basic idea is to place the bumps 24 (25) that are in direct contact with the printed circuit board substrate or the insulating element below the areas corresponding to the maximum heat release of the joined electronic components (in the exemplary embodiment, the heating element 9 or the power switching component 45). As a result, the local thermal connection or heat dissipation effect in these areas is better than in their surrounding areas. For example, in the case of the power switching component 45, this area corresponds exactly to the power switching element 47 (power MOSFET or IGBT). However, the heating element is more or less completely covered by the heating conductor, so the local differences in heat release are smaller here, but depending on the structure, thermal peaks may also occur here, which can be effectively reduced by appropriate positioning of the bumps.

[0099] exist Figure 4 In the exemplary embodiment shown, the position of the bump 24 (25) corresponds to the position of the temperature sensor 38 on the power switch component 45. Figure 5 The situation shown is relatively visible. Figure 5 1 shows a plan view of three heating elements 9 and a power switch component 45 in a state of being mounted on a support plate 60 of a heat exchanger 2. In this exemplary embodiment, the heating element 9 is designed as a ceramic substrate (as a carrier element), for example made of Al 2 O 3 The long heating conductor 4 is made with a screen-printed heating conductor layer. The heating conductor layer is designed as a metallized structure made of a resistance alloy and provides a corresponding heating resistance. The insulation interruption ensures the structuring of the long heating conductor 4.

[0100] The power switching component 45 has a printed circuit board substrate 46, which has a first side 54 facing the heat transfer element 6 and an opposite second side and a plurality of power switching elements 47, which are formed on the second side of the printed circuit board substrate, for example IGBTs or power MOSFETs, with which the heating element 9 can be operated under PWM control. For this purpose, the corresponding connection pads of the heating conductor 4 or the connection points on the heating conductor 4 are connected to the power switching elements on the power switching component 45 by means of a bonding connection structure 50.

[0101] The power switch component 45 also has a temperature sensor 38 arranged on the second side of the printed circuit board substrate 46, which can detect the temperature for the purpose of controlling the heating operation. In the exemplary embodiment, their position on the second side 55 of the power switch component 45 or the printed circuit board substrate 46 is in each case relatively close to the fluid inlet and fluid outlet on the rear side of the support plate 25 (see Figure 4 A connection piece 34 in the fluid inlet) is provided so that temperature values ​​representing the temperature of the fluid at the fluid inlet and the fluid outlet can be detected, so that the current heating of the fluid can be determined.

[0102] The power switch component 45 is connected to the corresponding connection structures arranged on the three lead frames 48 (stamping grid) by means of further bonding connection structures 51, which are assigned to the corresponding heating elements 9. The bonding connection structures 51 include wires for power supply (high voltage range, for example 60V or higher, preferably 400V or higher, further preferably 800V or higher, for example 900V or 1000V), wires for controlling the power switch element 47 and wires for communicating with the temperature sensor. The lead frame 48 is arranged in the through hole 36 of the support plate 60.

[0103] Figure 5 The temperature sensor 38 in the power switch assembly 45 is assigned to the back side of the power switch assembly 45. Figure 4 The temperature sensor 38 is preferably arranged in the first and second side 54 and 55 of the embodiment of the present invention, and is preferably arranged in the second side 55 of the embodiment of the present invention. The temperature sensor 38 is preferably arranged in the first and second side 54 and 55 of the embodiment of the present invention, and is preferably arranged in the second side ...4 and 55 of the embodiment of the present invention. However, here, the temperature sensor 38 is not related to heat release, but rather to efficient heat supply through the protrusion 24 (25), because the temperature sensor 38 is intended to detect the temperature as accurately as possible, especially at the fluid outlet.

[0104] This aspect of the invention has the following advantages:

[0105] - an adhesive 10 with a relatively low thermal conductivity can be used, which results in a cost advantage per unit amount of adhesive applied;

[0106] - When the layer thickness increases away from the bump, a larger layer thickness or thickness of the joint gap can be accepted, which leads to an increase in process capability or a larger tolerance window for the layer thickness;

[0107] - the affected electronic components can be replaced with alternative components, e.g. with lower cost or higher performance, which in turn can be achieved through a higher permissible power dissipation;

[0108] -Can increase the service life of electronic components subject to thermal stress;

[0109] -The temperature sensor can be better connected to the point being measured (e.g., a heat exchanger), thus ensuring better measurement accuracy and response time.

[0110] Reference numerals list

[0111] 2Heat exchanger

[0112] 4 Heating conductor

[0113] 6Heat transfer element

[0114] 8 Insulation elements

[0115] 9 Heating Elements

[0116] 10 Thermally Conductive Elastic Adhesive

[0117] 12 Joint gap

[0118] 14 First side of the insulation element

[0119] 16 Second side of the insulating element

[0120] 18 Medium

[0121] 20 spacer (inside)

[0122] 22 spacer (outer)

[0123] 24 bumps (as spacers)

[0124] 25 Contact surface

[0125] 26 Turbulator

[0126] 30 Edge of insulating element

[0127] 32 Fluid chamber

[0128] 34 Connector, fluid inlet or fluid outlet

[0129] 36 Through Holes

[0130] 38 Temperature Sensor

[0131] 45 Power switch components

[0132] 46 PCB Substrate

[0133] 47 Power switching element

[0134] 48 lead frame (stamping grid)

[0135] 50 Combined connection structure

[0136] 51 Combined connection structure

[0137] 54 first side (printed circuit board substrate)

[0138] 55 second side (printed circuit board substrate)

[0139] 60 Support plate for heat transfer element

Claims

1. A heat exchanger (2) for an electric water heater, include: - a heating conductor (4); - a heat transfer element (6); and an insulating element (8) arranged between the heating conductor (4) and the heat transfer element (6) for electrically insulating the heating conductor (4) and the heat transfer element (6) from each other; Therein, the insulating element (8) is arranged on the heat transfer element (6) by means of a heat-conducting elastic adhesive (10).

2. The heat exchanger (2) according to claim 1, in, A joint gap (12) is formed between the heat transfer element (6) and the insulation element (8), and the adhesive (10) is arranged in the joint gap (12).

3. The heat exchanger (2) according to claim 2, in, The geometry of the joint gap (12), in particular its thickness or the layer thickness of the adhesive (10) arranged therein, is defined by a plurality of spacers (20, 22).

4. The heat exchanger (2) according to claim 3, in, The spacers (20, 22) have contact points or faces (25) and have at least two different overall heights (H), wherein a first spacer (20) arranged closer to the center of the insulating element (8) has a relatively lower overall height (H) and a second spacer (22) arranged closer to one of the edges (30) of the insulating element (8) has a relatively higher overall height (H), so that the layer thickness of the adhesive (10) closer to the edge (30) is greater than the layer thickness of the adhesive (10) closer to the center.

5. The heat exchanger (2) according to claim 3 or 4, in, The spacers (20, 22) are in the form of bumps (24) formed in the surface of the heat transfer element (6).

6. The heat exchanger (2) according to claim 5, in, A first side (14) of the insulating element (8) faces the projection (24), and the heating conductor (4) is arranged on an opposite second side (16) of the insulating element (8); wherein a position is defined in the heating conductor (4) at which a maximum heat release can be detected during operation, One of the projections (24) is placed at a position on the first side opposite to a position of maximum heat release on the second side.

7. The heat exchanger (2) according to claim 5 or 6, Also included is a power switch component (45), the power switch component (45) comprising a printed circuit board substrate (46) having a first side (54) and a second side (55), the printed circuit board substrate (46) being arranged on the heat transfer element (6) by means of a thermally conductive elastic adhesive (10) in the same manner as the insulating element (8); in, At least one power switching element (47) or at least one temperature sensor (38) is arranged at a position on the second side (55) of the printed circuit board substrate (46); One of the bumps (24) is placed on the first side (54) of the printed circuit board substrate at a position opposite to the position of the temperature sensor (38) or the power switch element (47).

8. Heat exchanger (2) according to any one of the preceding claims, in, The geometrical dimensions of the joint gap (12) are designed based on at least one of the following parameters: - thermal conductivity of the adhesive (10); - thermal expansion of the insulating element (8) and the heat transfer element (6); - the stretchability of the adhesive (10); - the operating temperature of the heat exchanger (2); - the continuous operating temperature of the adhesive (10); and - The adhesive properties of the adhesive (10) to the material of the insulating element (8) and to the material of the heat transfer element (6).

9. Heat exchanger (2) according to any one of the preceding claims, in, The heat transfer element (6) is arranged on a first side (14) of the insulating element (8), and the heating conductor (4) is arranged on a second side (16) of the insulating element (8), wherein the first side (14) is opposite to the second side (16).

10. Heat exchanger (2) according to any one of the preceding claims, in, The insulating element (8) comprises ceramic or is made of ceramic.

11. An electric water heater comprising a heat exchanger (2) according to any one of the preceding claims.

12. A method for producing a heat exchanger (2), in particular a heat exchanger according to one of the preceding claims, said method The following steps are involved: - arranging the heating conductor (4) on the insulating element (8); - providing a heat transfer element (6); - applying a thermally conductive elastic adhesive (10) on one side of the heat transfer element (6) or on the side of the insulating element (8) on which the heating conductor (4) is not arranged; - The heat transfer element (6) is arranged to the insulating element (8) and bonded to the insulating element (8) by means of the applied adhesive (10).

13. The method according to claim 12, further comprising: The following steps are involved: - a joint gap (12) is defined between the heat transfer element (6) and the insulating element (8), and - Arranging adhesive (10) in the joint gap (12).

14. The method according to claim 13, further comprising: The following steps are involved: The geometrical dimensions of the joint gap (12) are designed based on at least one of the following parameters: - thermal conductivity of the adhesive (10); - thermal expansion of the insulating element (8) and the heat transfer element (6); - the stretchability of the adhesive (10); - the operating temperature of the heat exchanger (2); - the continuous operating temperature of the adhesive (10); and - The adhesive properties of the adhesive (10) to the material of the insulating element (8) and to the material of the heat transfer element (6).

15. A motor vehicle, engineering machinery or ship, comprising the electric water heater according to claim 11.

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