Heating

Abstract

Heating (40) for temperature control of a storage tank for an operating fluid and / or auxiliary fluid (92) of an exhaust aftertreatment system of an internal combustion engine with at least one electrically heated plate-shaped heating element (48, 58), wherein a first side (46) of the at least one plate-shaped heating element (48, 58) is in contact with a contact surface (50) of the heat conductor (42) for electrical contact and heat transfer, and a second side (52) of the at least one plate-shaped heating element (48, 58) pointing away from the heat conductor (42) is electrically connected to a first potential-side busbar (54), wherein the at least one plate-shaped heating element (48,58) and the first potential-side busbar (54) are provided at least partially with an insulating inner overmolding (60) to create a heating module (62), and the heat conductor (42) and the heating module (62) connected thereto are at least partially surrounded by an outer overmolding (90), characterized in that at least one spring element (64, 66, 130) is held by at least two retaining ribs (72, 74, 76, 100) integrally formed on the heat conductor (42) and is supported at least partially on the inner overmolding (60), wherein the at least one spring element (64, 66, 130) is embedded at least partially in the outer overmolding (90).

Description

[0001] The invention relates to a heater for temperature control of a storage tank for an operating fluid and / or auxiliary fluid of an exhaust aftertreatment system of an internal combustion engine, comprising at least one electrically heatable plate-shaped heating element, wherein a first side of the heating element is in contact with a contact surface of the heat conductor for electrical contact and heat transfer, and a second side of the heating element pointing away from the heat conductor is electrically connected to a potential-side busbar, wherein the heating element and the potential-side busbar are at least partially provided with an insulating inner coating to create a heating module, and the heat conductor and the heating module connected thereto are at least partially surrounded by an outer coating. State of the art

[0002] Electrical heating elements with a PTC element are known from DE 38 15 306 A1, a heating device for an operating fluid with a compensating element from DE 10 2012 213 417 A1, and a heat conductor for heating an SCR system from DE 10 2012 204 106 A1. In motor vehicles with internal combustion engines, especially diesel engines, air pollutants such as nitrogen oxides (NOx) must be reduced more and more due to the constantly tightening legal emission limits. A widely used exhaust aftertreatment system is the so-called "SCR" system ("Selective Catalytic Reduction" system). In this system, a liquid reducing agent is pumped from a storage tank to a nozzle in the area of ​​a catalyst integrated into the tubular exhaust stream by means of a pumping module during operation of the internal combustion engine. The reducing agent is typically approximately...A 32.5% urea-water solution, marketed under the trade name AdBlue®, is used. Modern diesel engines achieve up to 96% lower raw NOx emissions than a typical diesel engine from 1990. However, the aqueous urea solution freezes at ambient temperatures of -11°C or below. To ensure the system's dosing capability even below -11°C, electric heaters must be integrated at various points within the SCR system, particularly inside the storage tank.

[0003] A heating system known from the prior art for temperature control of an AdBlue® storage tank comprises, among other things, a one-piece heat distribution body made of die-cast aluminum with several finger-shaped extensions for increasing the surface area, at least one PTC resistor as a heating element, at least one ceramic insulating plate, and a potential-side and a ground-side busbar for power supply. The at least one PTC resistor, the two busbars, and the insulating plate are at least partially surrounded by a pre-molding of a suitable plastic. The heat distribution body has at least one pocket into which a potential-side busbar, including a section of the PTC resistor and an insulating plate, is received.The mechanical positioning of the components within a pocket is achieved by pressing and / or crimping, thereby simultaneously creating a reliable electrical contact between the potential-side busbar and the PTC resistor, as well as a highly thermally conductive connection between the resistor and the heat distribution body. To increase corrosion resistance, the entire assembly, consisting of the heat distribution body, the busbars, the PTC resistor with the insulating plate, including the pre-molding, is at least partially encased in an external overmolding made of plastic.

[0004] One disadvantage is that cracks can form in the insulating plates and PTC resistors during the pressing process, potentially leading to reduced heating performance. During operation, existing cracks can propagate and / or new cracks can develop as a result of such production-related damage. This, combined with a decrease in mechanical clamping force, can cause gaps to form in the press-fit assembly, potentially leading to individual fragments losing electrical contact. Electrical contact can be lost, for example, due to thermal expansion or mechanical vibrations affecting individual PTC resistor fragments. Furthermore, over the lifespan of the heater, there is an increase in electrical contact resistance and a greater tendency for corrosion. This poses a risk of reduced heating performance and / or total failure. Description of the invention

[0005] According to the invention, a heater for temperature control of a storage tank for an operating fluid and / or auxiliary fluid of an exhaust aftertreatment system of an internal combustion engine is proposed, in which at least one spring element is held by at least two retaining ribs integrally formed on the heat conductor body and is supported at least partially on the inner overmolding, wherein the at least one spring element is embedded at least partially in the outer overmolding. Advantages of the invention

[0006] As a result of the inventive design of the heating element, a reliable electrical contact of the at least one plate-shaped heating resistor is achieved, ideally for the entire service life, and also exhibits high resistance to vibration and corrosion. Furthermore, the pockets previously required on the heat conductor for receiving and securing the heating resistors to the insulating plates are eliminated, which significantly simplifies the mold required for its manufacture due to the elimination of the need for very thin inner cores. In particular, the surface quality of the contact surfaces of the heat conductor, preferably manufactured from aluminum by die casting, is improved by the absence of pockets due to more optimal cooling of the mold at the contact surface of the PTC resistor, thus enabling better electrical and thermal connection of the at least one heating resistor to the heat conductor.The risk of crack initiation in the insulating plates (if present) and / or especially in the plate-shaped (ceramic) heating elements, as occurs during the pressing or crimping of conventional pockets, is also eliminated, thus preventing further contact failures. Furthermore, due to the internal overmolding that covers the busbars on at least one side, ceramic insulating plates are preferably no longer required for the heating element. A technically demanding encapsulation or shielding of the spring before the external overmolding during the injection molding process is no longer necessary due to the special design of the at least one spring element and the retaining ribs. When designing the spring, it is important to ensure that it does not completely lose its preload or contact force due to excessive plastic deformation during overmolding.For safety reasons, the plate-shaped heating resistor(s) are preferably constructed with PTC heating resistors or with heating resistors with a PTC characteristic curve ("Positive Temperature Coefficient").

[0007] In a further development of the inventive concept, the at least one spring element is arranged in a spring support area of ​​the inner overmolding of the heating module, wherein the potential-side busbar and the plate-shaped heating resistor are arranged at least partially between the spring support area of ​​the inner overmolding and the heat conductor.

[0008] This means that the pressure force generated by the spring element primarily acts on the internal molding, in which the potential-carrying busbar, at least in the area of ​​the heating element, and the heating element itself are embedded, at least partially. Consequently, the potential-carrying busbar, together with the heating element, presses against the heat sink with a pressure force or normal force, ensuring reliable electrical contact and optimal thermal connection between the potential-carrying busbar, the heating element, and the heat sink. The ground-side busbar is electrically connected to the heat sink and, together with the potential-side busbar, the heating element, the electrically conductive heat sink, and the vehicle's electrical system, forms a closed circuit for powering the heater. The pressure force or normal force...The preload force runs essentially parallel to the surface normal of the spring support area of ​​the internal overmolding or the contact surface of the heat conductor.

[0009] In a further, advantageous embodiment of the concept underlying the invention, the inner overmolding has at least one recess in the spring support area. This at least one recess ensures the spring element is held in position and the force is distributed during the formation of the outer overmolding. The spring can also be held in position by support on lateral retaining ribs. Optimal force distribution of the spring can also be ensured by a raised section on the inner overmolding, whereby the spring support area can, in principle, be adapted to the spring geometry.

[0010] In a further advantageous embodiment of the solution proposed according to the invention, each retaining rib has two axial supports at its end for the spring element. This largely eliminates changes in the position of the spring element transversely to the retaining ribs, particularly during the production of the external overmolding, or the maximum displacement along the retaining ribs is greatly limited by the supports.

[0011] According to a further development of the heating system, at least one spring element is essentially rectangular. Thus, the circumferential geometry of the spring element corresponds to the typically also rectangular circumferential geometry of the plate-shaped or cuboid heating element, so that the latter is subjected to a spring force acting almost uniformly across its surface and is pressed against the heat conductor largely free from internal mechanical stress peaks. Alternatively, the spring element can also have a triangular, round, or polygonal circumferential geometry.

[0012] In a technically advantageous further development, at least one spring element is designed in a wave-like shape.

[0013] The corrugated design allows for a larger contact area of ​​the spring element with the inner overmolding of the plate-shaped or cuboid heating element. Furthermore, the corrugated surface geometry of the spring element permits more precise adjustment of the contact force or preload exerted by the spring element on the heating element. This also simplifies assembly and allows for the compensation of larger tolerances.

[0014] In a further advantageous embodiment, the at least one spring element has at least two recesses. These at least two preferably round recesses facilitate the assembly of the spring element, particularly under mechanical preload, between the retaining ribs using a suitable tool. Furthermore, the recesses can also have a rectangular, circular, oval, or elliptical circumferential geometry, or a circumferential geometry with at least three corners. When the outer coating is manufactured, the recesses also serve as pressure equalization between the inner and outer sides of the spring, thereby preventing or at least reducing excessive stress on the spring.

[0015] In one design variant, at least one spring element is arc-shaped. This simplifies the manufacturing process of the spring element.

[0016] In the case of a technically advantageous further development, the at least two retaining ribs of the heat conductor are plastically compressible perpendicular to the contact surface of the heat conductor. This allows, among other things, the defined adjustment of the spring force applied by the spring element, which acts essentially parallel to the surface normal of the contact surface of the heat conductor. This enables force-free assembly of the spring and allows for a very simple design (e.g., rectangular). Furthermore, the plastic deformation of the retaining ribs through upsetting or compression allows for a permanently reliable, and especially vibration-resistant, securing of the spring elements to the heat conductor. Plastic deformation of the retaining ribs of up to 1 mm each is possible.

[0017] Depending on the material properties of the solid metallic heat conductor, deformation paths exceeding 1 mm may be achievable. Furthermore, any dimensional tolerances between the heating element, the potential-carrying busbar, the outer coating, and the heat conductor, and especially its contact surface and varying material roughness, can be more easily compensated for.

[0018] Continuing the inventive concept, at least one ground-side busbar is electrically connected to the heat conductor. This allows the typically highly electrically conductive metallic heat conductor to serve a space-saving dual function: it simultaneously acts as a (ground) return conductor for the current fed into the plate-shaped heating resistor(s) from the vehicle's electrical system via the potential-side busbar.

[0019] Advantageously, the at least two continuous retaining ribs are designed perpendicular to the contact surface of the heat conductor and spaced parallel to each other. This allows the spring element to be clamped between the retaining ribs, if necessary with a sufficiently high mechanical preload to ensure a captive fit, before the external overmolding is applied at the end of the manufacturing process, e.g., using a known injection molding process.

[0020] In the case of a further development of the inventive idea, two longitudinal edges of the at least one spring element run behind two projections of the retaining ribs that point towards each other and run parallel to the contact surface of the heat conductor.

[0021] This ensures reliable mechanical positioning of at least one spring element. The projections can extend over the full length of the retaining ribs or alternatively be formed only in sections.

[0022] The use of different materials results in varying rates of thermal expansion at rising temperatures, leading to stresses. These stresses, and especially design-related stress peaks, can eventually cause cracks or damage in external overmolding, potentially leading to leaks and compromising the protective function for internal components. To minimize stresses in the external overmolding, sharp external edges should be avoided wherever possible, and all overmolded parts should have the largest possible radius. Since sharp edges and / or very small radii are unavoidable in the spring due to its typically thin walls and manufacturing constraints, the spring is slightly recessed into its surroundings. This prevents or at least significantly reduces stresses. Other unavoidable sharp edges and small radii (e.g.,(on a power rail) can be defused, thereby significantly increasing the service life of the heating element and the outer coating.

[0023] According to a favorable embodiment, it is provided that the outer coating is formed with a thermoplastic material, in particular with high-pressure polyethylene.

[0024] This design ensures high chemical resistance of the heating element, which is integrated directly into a storage tank for the temperature control of the operating fluid, such as a urea-water solution, and is permanently exposed to it. Furthermore, the plastic used should not crack even at lower temperatures and should exhibit sufficiently high residual elongation and stress crack resistance at low temperatures. The internal overmolding is also preferably made of a thermoplastic material, preferably PPA (polyphthalamide), which should possess the highest possible mechanical strength.Furthermore, the plasticizing temperature of the plastic used for internal encapsulation should ideally be higher than that of the plastic used for external encapsulation of the heating element. This prevents the internal / pre-injection material from melting and being carried over during the external encapsulation process, thus avoiding undesirable changes in the position of the heating elements, busbars, and spring elements during the formation of the external encapsulation using conventional injection molding processes. Additionally, the thermoplastic materials used for internal and / or external encapsulation can be reinforced with fibers. Furthermore, internal and / or external encapsulation can also be achieved using thermosetting plastics, possibly with integrated fiber reinforcement.

[0025] Further developing the inventive concept, it is provided that the heat conductor is formed integrally with a metallic material, in particular with aluminum or an aluminum alloy. This enables mass production of the heat conductor, which typically has a complex three-dimensional shape, using, for example, a known die-casting process, ensuring dimensionally accurate and cost-effective manufacturing. Furthermore, due to the good thermal conductivity of the metallic material, the heat released by the heating elements can be transferred to the operating or auxiliary material to be heated with excellent energy efficiency and distributed evenly.Furthermore, the ground-carrying busbar can be connected to the heat conductor, which is usually electrically conductive, so that the heat conductor, in addition to its heat distribution function, also has the task of current return of the electric current supplied to the heating resistors via the potential-carrying busbar. Brief description of the drawings

[0026] The invention is described in more detail below with reference to the drawing.

[0027] It shows: Fig. 1. A perspective and partially cutaway view of a conventional heating system according to the state of the art without external coating, Fig. 2 the heating of Fig. 1 however with external coating, Fig. 3 a perspective and partially cutaway view of the heater according to the invention without an external coating, Fig. 4 the heating of Fig. 3 with external coating, Fig. 5 an enlarged cross-section through the heating system according to the arrows VV from Fig. 3, Fig. 6 an enlarged cross-section through the heating system according to arrows VI-VI of Fig. 4, Fig. 7 a schematic view of the heating system of Fig. 4, Fig. 8 a section through the heating system according to section line VIII - VIII of Fig. 7, Fig. 9 a greatly enlarged view of the circular section IX from the Fig. 8 and Fig. 10, Fig. 11 a partial representation of the heating system similar to the view of Fig. 9 but without external overmolding and a cut only through an internal overmolding (60) with a spring element arc-shaped according to an embodiment variant in an untensioned and in a tensioned state.

[0028] The representation according to the Fig. Figure 1 shows a perspective and partially cutaway view of a conventional heating system without external coating, in accordance with the state of the art. According to [source / reference] Fig. Figure 1 comprises the heater 10, among other components, a multi-fingered thermal conductor 12, on which several corrugated fingers 14 or finger-like extensions are integrally formed to increase the surface area. Furthermore, the thermal conductor 12 has, by way of example, two pockets 16, 18, which serve to receive and attach a heating module 20. The heating module 20 includes, among other components, a plate-shaped heating resistor 22, one side of which rests against the thermal conductor 12 and the side facing away from it is electrically conductively contacted with a potential-carrying busbar 24. A ceramic insulating washer 26 is also positioned, at least partially, on the side of the plate-shaped heating resistor 22 facing away from the thermal conductor 12. Similarly, a concealed plate-shaped heating resistor, connected to the potential-carrying busbar 24, is received in the rear pocket 18, along with an insulating plate that is likewise not visible.

[0029] The heat conductor 12 is also electrically connected to a ground-carrying potential rail (not visible here), so that the plate-shaped heating resistor 22 can be connected to the electrical system of a motor vehicle via the two busbars to supply it with electrical energy. The heat conductor 12 is made of aluminum or an aluminum alloy, and its complex three-dimensional spatial design can be manufactured in a manner suitable for mass production, e.g., using the known die-casting process.

[0030] To secure the individual components of the heating module 20 in relation to one another, to simplify the entire manufacturing process, in particular the injection molding process for applying the external overmolding, and for electrical insulation, the heating module 20 is provided, at least in some areas, with an internal overmolding 28 made of a suitable thermoplastic material. The thermoplastic material should have high mechanical strength, good electrical insulation properties, and preferably a higher melting point than the material used for the external overmolding.

[0031] The heating module 20 is preferably secured within the pockets 16, 18 by crimping or riveting. However, this can lead to the formation of microcracks and cracks in the plate-shaped heating element 22, which enlarge over its service life. As the preload in the crimped assembly of the plate-shaped heating element 22 decreases, thermal movement and the resulting plastic deformation create gaps between individual parts of the heating module 20. Cracks in the plate-shaped heating element 22, together with gaps, can impair the electrical contact between the busbars and the heating element, as well as the thermal coupling between the plate-shaped heating element 22 and the heat conductor. This can potentially lead to an unacceptable reduction in the heating power of the heater 10, or even to its complete failure.

[0032] The representation according to the Fig. 2 shows the heating of Fig. 1, however with an almost all-round external overmolding 30 made of a thermoplastic material, such as high-density polyethylene (HD-PE), which enables permanent direct immersion of the heater 10 in a chemically aggressive medium, such as AdBlue®, for its direct heating or temperature control. Design variants

[0033] The perspective representation according to Fig. Figure 3 shows a perspective view of a heater according to the invention without an external coating.

[0034] A heater 40 according to the invention comprises a multi-fingered heat conductor 42, on which a plurality of corrugated fingers 44 or finger-like extensions are formed. The heat conductor 42 is preferably designed as a one-piece, solid die-cast aluminum part. A first side 46 of a first plate-shaped heating element 48 with a PTC characteristic ideally rests fully against a contact surface 50 of the heat conductor 42. The heat released in the first plate-shaped heating element 48 is transferred to the heat conductor 42 between the first side 46 of the first plate-shaped heating element 48 and the contact surface 50. A second side 52 of the first plate-shaped heating element 48, facing away from the heat conductor 42, rests against a first potential-carrying busbar 54 and is electrically connected to it.The first potential-carrying busbar 54 has an L-shaped cross-sectional geometry, at least in sections, whereas for progressive die manufacturing (pre-punching, coating, and stamping-bending-overmolding), a straight / perpendicular geometry is preferably desired in the area of ​​the first plate-shaped heating element 48. A ground-side busbar 56, on the other hand, is electrically connected to the heat conductor 42 and, together with it, forms an electrical return path for the current supplied to the first plate-shaped heating element 48 via the first potential-carrying busbar 54. Thus, the first plate-shaped heating element 48 can be electrically heated by energizing the two busbars 54 and 56. For this purpose, the two busbars 54 and 56 are connected, for example, to the electrical system of a motor vehicle.The first plate-shaped heating element 48, a further concealed, second plate-shaped heating element 58, and the first potential-carrying busbar 54 are at least partially enclosed by an internal overmolding 60 made of an electrically insulating, preferably thermoplastic material (such as PPA) to create a heating module 62 or a pre-assembly group. The heating module 62 simplifies the assembly of the heating element 40 and the application of the external overmolding.

[0035] To optimize heat transfer between the two plate-shaped heating elements 48, 58 and the heat conductor 42, two identically constructed, and here exemplarily wave-shaped, spring elements 64, 66 are used. The two spring elements 64, 66 are each positioned in a spring support area 68, 70 of the internal molding 60 and are supported between two rib-like retaining ribs 72, 74, 76, integrally formed on the heat conductor 42 (not continuously visible or marked), and the spring support areas 68, 70 of the internal molding 60. This applies a defined contact force F to the two plate-shaped heating elements 48, 58, as indicated by the two white arrows. Aor preload force is pressed against the heat conductor 42, thus ensuring reliable electrical and thermal contact over the entire service life. The positioning of the spring elements 64, 66 can also be carried out on retaining ribs 72, 74, 76; this is particularly advantageous for avoiding long tolerance chains, because the positioning and the spring support area 64, 66 are thus carried out on the same retaining ribs 72, 74, 76.

[0036] Both spring elements 64, 66 each have, for example, four recesses with an oval or elliptical circumferential geometry, of which only two are designated here with reference numerals 78, 80 for the sake of clarity in the drawing. Furthermore, at least one support is formed at the end, preferably at the bottom, of each retaining rib 72, 74, 76, particularly during the production of the external overmolding 30, 90, for the axial positioning of the spring elements 64, 66. One support 84 of the retaining rib 76 is designated as representative of all the others. Since, for the sake of better graphical representation, the external overmolding 30, 90 of the heater 40 is shown in the Fig. With figure 3 omitted, at least a cavity exists between the spring elements 64, 66 and the internal overmolding 60, of which only one cavity 86 is visible. The internal overmolding 60 combines the two plate-shaped heating resistors 48, 58 and the two busbars 54, 56 into the heating module 62, which can be easily joined to the heat conductor 42 and the spring elements 64, 66 during manufacturing. This largely eliminates the risk of component displacement during the application of the external overmolding, e.g., using a known injection molding process to complete the heating element 40. Furthermore, the internal overmolding 60 ensures potential isolation between the spring elements 64, 66 and the heat conductor 42, thus eliminating the need for additional insulating elements, such as ceramic insulating plates or the like.For special requirements, a ceramic insulating plate can be used for potential isolation instead of the internal overmolding 60. In the example shown, the ground-side busbar 56 is already pre-assembled in the thermal interface material 42.

[0037] The internal overmolding 60 is designed such that the plastic front flowing in during the formation of the external overmolding cannot directly affect the two plate-shaped heating elements 48, 58, and furthermore, positional changes of the busbars 54, 56 and the two plate-shaped heating elements 48, 58 are largely avoided. When designing the internal overmolding 60, care must also be taken to minimize the mechanical stress on the external overmolding caused by any sharp-edged contours of the spring elements 64, 66. For example, the internal overmolding 60 can have a design corresponding to the geometric shape of the spring elements 64, 66 and always cover them with a sufficiently thick layer or "protrude" from them. This largely protects the external overmolding from damage or from localized load peaks or stresses that may arise due to flow or...The creep tendency of thermoplastics under the influence of higher continuous mechanical loads due to temperature fluctuations could lead to an impairment of the integrity of the external overmolding.

[0038] The Fig. 4 shows the heating according to the Fig. 3, however with the applied outer coating.

[0039] The heat conductor 42, the heating module 62, the busbars 54, 56, and the spring elements 64, 66 are at least partially surrounded by an external overmolding 90 made of a high-density polyethylene (HDPE) that is highly resistant to chemicals and, in particular, AdBlue. The spring element 64 is designed such that, during the injection molding process for producing the external overmolding 90 of the heating element 40, it does not significantly deviate from the internal overmolding 60 or any of the retaining ribs ( Fig. 3: 72, 74, 76). Thus, no impermissible (continuous) plastic deformation of the spring element 64 should occur in order to guarantee the contact force FA throughout its service life. Furthermore, the spring element 64 should not cause an impermissible reduction in the wall thickness of the outer overmolding 90 during the injection molding process. The spring element 64 is secured in position by means of the retaining ribs and supports arranged on both sides of it (see Figure 3: 72, 74, 76). Fig. 3) These requirements are optimally met. Alternatively, the spring element 64 can also be thermally joined to the heat conductor 42, e.g., by welding or soldering. However, this approach requires flawless thermal joining of the material used for the spring element 64 with the aluminum or aluminum alloy of the heat conductor 42, whereby several thermal joining processes for connections between stainless steel / steel and aluminum (especially in connection with lightweight construction) are already known in the art.

[0040] Due to the cavity-free design of the outer coating 90, good and rapid heat transfer is ensured between the first plate-shaped heating element 48, the first potential-carrying busbar 54, the inner coating 60, the spring element 64, and the outer coating 90 to the outside, up to the operating fluid and / or auxiliary fluid 92 surrounding the heating element 40. Sufficiently large gaps between the spring element 64 and the inner coating 60, as well as the recesses provided in the spring element 64 as needed (see especially the figure), ensure the cavity-free design of the outer coating 90. Fig. 3) The plastic used for the internal overmolding 60 should have good electrical insulating properties combined with high mechanical stiffness and preferably a higher melting point than the plastic used for the external overmolding 90. This prevents material carryover caused by melting of the internal overmolding 60 during the application of the external overmolding 90.

[0041] It is important that the contact force F built up by the spring element 64 AThe spring element 64 is embedded in the outer coating 90 without damage or impermissible plastic deformation, due in part to the special geometric shape and design of the spring element 64 and its installation position, which ensures that the spring acts permanently on the first plate-shaped heating element 48. Despite the almost complete embedding of the spring element 64 in the outer coating 90, its elastic spring action is not unduly or impermissibly impaired due to the inherent elasticity of the outer coating 90. The preceding explanations regarding the structural design of the spring element 64 apply accordingly to all other spring elements of the heating element 40 that are not shown and / or not fully visible.

[0042] The presentation of Fig. 5 is an enlarged cross-section through the heating system according to the arrows VV in Fig. 3 can be seen.

[0043] The first potential-carrying busbar 54 and the first plate-shaped heating element 48 of the heater 40 are at least partially enclosed by the internal overmolding 60 and form the heating module 62. Due to the spring action of the spring element 64, the internal overmolding 60, the first potential-carrying busbar 54, and the first plate-shaped heating element 48 are pressed against the surface by the contact force F. AThe first plate-shaped heating element 48 is pressed perpendicularly against the contact surface 50 of the heat conductor 42, thus providing excellent thermal coupling to the heat conductor 42, which acts as a good heat sink. The first plate-shaped heating element 48 is powered via the first potential-carrying busbar 54, which is connected to the second side 52 of the first plate-shaped heating element 48, and the ground-side busbar 56, which is electrically connected to the heat conductor 42.

[0044] The Fig. Figure 6 shows an enlarged cross-section through the heater according to arrows VI-VI in Fig. 4.

[0045] As a result of the pressure force F emanating from the spring element 64 A- which acts on the contact surface 50 of the heat conductor 42 essentially parallel to a surface normal of the heat conductor 42 - the first potential-carrying busbar 54, which is at least partially provided with the internal overmolding 60, and the first plate-shaped heating resistor 48 are pressed against the contact surface 50 of the heat conductor 42, resulting in excellent electrical and thermal coupling of the first plate-shaped heating resistor 48 to the heat conductor 42. The ground-side busbar 56 is conductively connected to the heat conductor 42, so that the current can be supplied to the first plate-shaped heating resistor 48 via the busbars 54 and 56.

[0046] In contrast to the representation of Fig. In section 5, the outer overmolding 90 is almost completely formed on the heat conductor 42 of the inner overmolding 60 and other individual parts of the heater 40. The partially existing cavity between the spring element 64 and the inner overmolding 60 is completely or almost completely filled with the plastic of the outer overmolding 90. This significantly reduces the stresses on the spring element 64 during the overmolding process and simultaneously ensures good heat transfer to the second side 52 of the first plate-shaped heating element 48. Due to this good heat transfer, the first plate-shaped heating element 48 also transfers heat energy to the second side 52, thus providing greater heating power.

[0047] In the Fig. Figure 7 is a schematic view of the heating system of Fig. 4 shown.

[0048] The heat conductor of the heater 40, concealed here, with the three fingers 44 visible here, is completely enclosed by the outer overmolding 90. Between the fingers 44 are the two overmolded spring elements 64, not visible here, along with all other overmolded components.

[0049] The illustration of Fig. 8 is a section through the heater according to section line VIII - VIII of Fig. 7 can be seen.

[0050] The heat conductor 42 of the heater 40 has a plurality of outwardly directed fingers 44 or finger-shaped extensions and, including the heating module 62 with the two plate-shaped heating resistors 48, 58, is completely enclosed by the outer coating 90 for corrosion protection. Preferably, the internal parts, such as the heat conductor 42 of the heater 40, are not provided with the outer coating 90 only within electrical and mechanical interfaces, thus ensuring complete enclosure from the tank interior after installation of the heater 40.

[0051] The Fig. Figure 9 illustrates a greatly enlarged view of the circular section IX from the Fig. 8 with external coating.

[0052] The first side 46 of the first plate-shaped heating element 48 of the heater 40 rests against the flat contact surface 50 of the heat conductor 42 to create thermal coupling with the lowest possible thermal resistance. The second side 52 of the first plate-shaped heating element 48, facing away from this, is in electrically conductive contact with the first potential-carrying busbar 54, which is itself at least partially surrounded by the internal overmolding 60 or the pre-molding. The ground-side busbar 56 is at least partially electrically connected to the heat conductor 42. The first plate-shaped heating element 48, including the partially formed internal overmolding 60, is pressed against the corrugated or sinusoidally corrugated spring element 64 by the contact force F. A pressed against the contact surface 50 of the heat conductor 42.

[0053] For this purpose, the spring element 64 is arranged or clamped between the retaining rib 76 and a second, opposing retaining rib 100, with two parallel longitudinal edges 102, 104 of the spring element 64 bearing against projections 106, 108 formed on the retaining ribs 76, 100. The two retaining ribs 76, 100 run parallel to each other and are perpendicular or almost perpendicular (due to necessary draft angles in the injection molding process) to the contact surface 50 of the heat conductor 42. To enable a simple symmetrical design of the spring element 64, the draft angle can be compensated for by appropriate design of the internal overmolding 60. The two projections 106, 108, integrally formed on the retaining ribs 76, 100 and having an approximately rectangular cross-sectional geometry, preferably run parallel to the contact surface 50 of the heat conductor 42 or at least parallel to recesses 110, 112 respectively.to the contact surface of the spring element 64 with internal overmolding 60 and extend continuously over the entire length of the retaining ribs 76, 100 (perpendicular to the plane of the drawing).

[0054] Due to the corrugated or sinusoidally wave-like design of the spring element 64, it rests relatively extensively in recesses 110, 112 of the inner overmolding 60 in the spring bearing area. To further optimize the positioning of the spring element 64 during the formation of the outer overmolding 90 or the final overmolding, two trough-like recesses 110, 112, running parallel to each other, are formed in the inner overmolding 60 as an example, in which a wave trough 114, 116 of the spring element 64 rests at least partially. In contrast, three wave crests 120, 122, 124 of the spring element 64 are embedded in or enclosed by the outer overmolding 90. The spring element 64 can alternatively or additionally center itself on the projections 106 and 108. The cavity 86 between the spring element 64 and the inner injection molding (cf. Fig. 3) is completely or almost completely filled by the external overmolding 90, thereby reducing the loads on the spring element 64 when the external overmolding 90 is applied and improving heat dissipation towards the spring element 64.

[0055] The Fig. 10 and Fig. 11 - which will be referred to later in the description - show a partial representation of the electric heating system similar to the view of Fig. 9 with a cut only through the internal overmolding 60 with a spring element 130 in an arc-shaped state according to a design variant in an untensioned and in a tensioned state.

[0056] The external coating of the heater 40 is both in the Fig. 10 as well as in the Fig. 11 is not yet shown in Figure 11 for the sake of clarity. In contrast to the spring elements described in detail above, in this embodiment, a spring element 130 has a slightly arcuate, rather than a wave-like, shape, with the spring element 130 having an approximately annular sector-shaped cross-sectional geometry. In the Fig. In the unstressed state of the spring element 130, its longitudinal edges 132, 134 lie behind the projections 106, 108 of the retaining ribs 76, 100 of the heat conductor 42. The first plate-shaped heating resistor 48 is located between the contact surface 50 of the heat conductor 42 and the first potential-carrying busbar 54, whereby, due to the in Fig. 10 still untensioned spring element 130 no contact force F A attacks the first plate-shaped heating resistor 48.

[0057] To establish high-quality thermal and electrical contact between the first potential-carrying busbar 54, the first plate-shaped heating element 48, and the contact surface 50, the retaining ribs 76, 100 are plastically compressed perpendicular to the contact surface 50 by applying the mechanical force F until the Fig. The condition shown in Figure 11 is reached, in which the distance 136 between the spring support area 68 of the internal overmolding 60 and the longitudinal edges 132, 134 has been reduced by up to 1 mm. This increases the (initial) radius R1 of the arcuately curved spring element 130 to a (final) radius R2, so that the contact force F is now Aat the inner overmolding 60 of the first potential-carrying busbar 54. This presses the first plate-shaped heating element 48 against the contact surface 50 of the heat conductor 42, creating an extremely durable and robust thermal and electrical connection via the first potential-carrying busbar 54 and the inner overmolding 60. It is also possible to provide the straight spring support area 68 with a raised section or a convex shape (contrary to the one described in Fig. (10, spring element crowning), which also allows a straight spring element 130 to be used and only given a radius by deformation after reducing the distance 136. This makes it possible, for example, to design the spring element 130 very simply as a plate geometry.

[0058] The spring element 130 enables simplified assembly and easy tolerance compensation. Furthermore, during assembly, the spring element 130 can be additionally pressed against the internal overmolding 60 by axially compressing the retaining ribs, thus enabling force-free assembly of the spring element 130.

[0059] Furthermore, the required contact force F can be achieved by upsetting or compressing the retaining ribs 76, 100. A more precisely, without risking damage to the first plate-shaped heating element 48 or other components. Furthermore, the minimum contact force F acting on the connection between the first plate-shaped heating element 48, the first potential-carrying busbar 54, the internal overmolding 60, and the heat-conducting element 42 can be adjusted by means of plastic deformation of the retaining ribs 76, 100, or by compression of the retaining ribs 76, 100 with the spring element 130. Aor preload force is increased. This further optimizes the process stability and reproducibility during the formation of the external overmolding of the heater 40, thereby avoiding in particular changes in position of the first plate-shaped heating resistor 48 and the first potential-carrying busbar 54 including the internal overmolding 60 and the spring element 130 in relation to the heat conductor 42.

[0060] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, within the scope specified by the claims, a multitude of modifications are possible that fall within the bounds of what is considered skilled in the art.

Claims

[1] Heater (40) for temperature control of a storage tank for an operating fluid and / or auxiliary fluid (92) of an exhaust aftertreatment system of an internal combustion engine with at least one electrically heatable plate-shaped heating element (48, 58), wherein a first side (46) of the at least one plate-shaped heating element (48, 58) is in contact with a contact surface (50) of the heat conductor (42) for electrical contact and heat transfer, and a second side (52) of the at least one plate-shaped heating element (48, 58) pointing away from the heat conductor (42) is electrically connected to a first potential-side busbar (54), wherein the at least one plate-shaped heating element (48,58) and the first potential-side busbar (54) are provided at least partially with an insulating inner overmolding (60) to create a heating module (62) and the heat conductor (42) and the heating module (62) connected thereto are at least partially surrounded by an outer overmolding (90), , characterized by , that at least one spring element (64, 66, 130) is held by at least two retaining ribs (72, 74, 76, 100) integrally formed on the heat conductor (42) and is supported at least partially on the inner overmolding (60), wherein the at least one spring element (64, 66, 130) is embedded at least partially in the outer overmolding (90). [2] Heating (40) according to claim 1, characterized by, that the at least one spring element (64, 66, 130) is arranged in a spring support area (68, 70) of the inner overmolding (60) of the heating module (62), wherein the potential-side busbar (54) and the plate-shaped heating resistor (48, 58) are arranged at least partially between the spring support area (68, 70) of the inner overmolding (60) and the heat conductor (42). [3] Heating (40) according to claim 2, characterized by , that the internal overmolding (60) in the spring support area (68, 70) has at least one recess (110, 112). [4] Heating (40) according to any one of the preceding claims, characterized by , that each retaining rib (72, 74, 76, 100) has two end-side axial supports (82, 84) for the spring element. [5] Heating (40) according to any one of the preceding claims, characterized by , that the at least one spring element (64, 66, 130) is essentially rectangular in shape. [6] Heating (40) according to any one of claims 1 to 5, characterized by , that the at least one spring element (64, 66) is shaped in a wave-like form. [7] Heating according to claim 6, characterized by , that the at least one spring element (64, 66) has at least two recesses (78, 80). [8] Heating (40) according to any one of claims 1 to 5, characterized by , that the at least one spring element (130) is arc-shaped. [9] Heating (40) according to any one of the preceding claims, characterized by , that the at least two retaining ribs (72, 74, 76, 100) of the heat conductor (42) are plastically compressible perpendicular to the contact surface of the heat conductor (42). [10] Heating (40) according to any one of the preceding claims, characterized by , that at least one ground-side busbar (56) is electrically connected to the heat conductor (42). [11] Heating (40) according to any one of the preceding claims, characterized by, that the at least two continuous retaining ribs (72, 74, 76, 100) are formed perpendicular to the contact surface of the heat conductor (42) and parallel to each other. [12] Heating (40) according to claim 11, characterized by , that two longitudinal edges (102, 104) of the at least one spring element (64, 66, 130) run behind two projections (106, 108) of the retaining ribs (72, 74, 76, 100) which point towards each other and run parallel to the contact surface (50) of the heat conductor (42). [13] Heating (40) according to any one of the preceding claims, characterized by , that the external overmolding (90) is formed with a thermoplastic material, in particular with high-pressure polyethylene. [14] Heating (40) according to any one of the preceding claims, characterized by , that the heat conductor (42) is formed in one piece with a metallic material, in particular with aluminium or with an aluminium alloy.

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