EP1687572A2

EP1687572A2 - Heat exchanger, especially for a heater or air conditioner of a motor vehicle, and method for the production thereof

Info

Publication number: EP1687572A2
Application number: EP04797952A
Authority: EP
Inventors: Hans-Heinrich Angermann; Roland Burk; Herbert Damsohn; Markus Watzlawski; Michael Kohl; Erwan Gogmos
Original assignee: Behr GmbH and Co KG
Current assignee: Mahle Behr GmbH and Co KG
Priority date: 2003-11-20
Filing date: 2004-11-17
Publication date: 2006-08-09
Anticipated expiration: 2024-11-17
Also published as: JP2007511412A; EP1687572B1; WO2005050101A3; WO2005050101A2; DE102004055523A1

Abstract

The invention relates to a heat exchanger (1), particularly for a heater or air conditioner of a motor vehicle, comprising several parallel flat tubes (2) through which a heat transfer medium flows. An electrically operated heating element (4) which is mounted following soldering of the heat exchanger (1) is assigned to at least some of the flat tubes (2) as an additional heating unit. Said heating element (4) is directly or indirectly fixed to the heat exchanger (1) while being formed at least in some areas by at least three different layers that are permanently interconnected across a large area thereof.

Description

BEHR GmbH & Co. KG Mauserstrasse 3, 70469 Stuttgart

Heat exchanger, in particular for a heating or air conditioning system of a motor vehicle, and a method for producing such

The invention relates to a heat exchanger, in particular for a heating or air conditioning system of a motor vehicle, according to the preamble of claim 1.

In the case of low-consumption vehicles, due to the low amount of waste heat, an additional heating output is required to heat the passenger compartment and to quickly remove a fitting (ice or water), particularly on the windshield. For this purpose, it is known to provide additional heating in the form of PTC heating elements, at least on the outer tubes, in the case of heat exchangers which are constructed from flat tubes through which a heat transfer medium flows, which emits heat in the case of heating. The attachment of such PTC heating elements is, however, quite complex.

US 6; 124,570 suggests individual tubes of the heat exchanger through

To replace PTC heating elements, which are held between contact plates, which at the same time create a heat-conducting connection to the adjacent ribs. The disadvantage of this is that the constructive Adapting the heat exchanger to accommodate PTC heating elements as well as the PTC heating elements themselves are very expensive. For this reason, such a combination heat exchanger may be more expensive than a combination of a conventional heat exchanger with a separate PTC heater. The space required for the PTC heating elements and their contacting also significantly deteriorates the power density of the heat exchanger. The replacement of individual tubes of the heat exchanger can also be found in DE 44 36 791 A1 and DE 100 12 320 A1.

Furthermore, it is proposed in DE 198 58 499 A1 to design the flat tubes as multi-chamber profiles and to design at least one of the outer chambers in the form of an insertion groove for an insulated heating wire, the walls of which are then bent together for fastening the heating wire. The heating wire is inserted after the heat exchanger has been soldered. The disadvantage of this is that such a heat exchanger requires special flat tubes and a large part of the electrically introduced heating power goes into the coolant and thus only contributes to the heating of the air to be supplied to the vehicle interior with a delay.

US Pat. No. 6,178,292 B1 discloses a heat exchanger with an electric heater which is arranged within a carrier element and which is pushed between two adjacent fin packs. Here, the carrier element includes a pair of parallel plates, between which an electrical heating element is held and electrically contacted. The electric heater consists of a heating element and an insulation element and has a multilayer structure which is essentially penetrated by a heating current perpendicular to the individual layers. Fastening elements running perpendicular to the support element and heater are provided for fastening. Such a heat exchanger still leaves something to be desired, especially what the Parts variety and number, and thus affects the manufacturing costs of the entire radiator.

It is an object of the invention to provide an improved and less expensive heat exchanger.

This object is achieved by a heat exchanger with the features of claim 1.

According to the invention, a heat exchanger, in particular for a heating or air conditioning system of a motor vehicle, with a plurality of flat tubes arranged parallel to one another and through which a heat transfer medium flows, with at least some of the flat tubes being associated with an electrically operated heating element which is attached after the heat exchanger has been soldered, and which is directly or indirectly associated with this is fixed to the heat exchanger, and the heating element is formed at least in regions from at least three different layers which are firmly connected to one another over a large area. The production is preferably carried out by rolling (laminating) stainless steel strip material and an aluminum foil laminated with a polymer layer or by laminating other materials with suitable properties. To simplify the lamination process, one or more layer components can be provided with a self-adhesive layer or a heat-seal adhesive layer, so that production-related adhesive layers can be provided between the actual layers, the adhesive layers also having a function when the heating element is in operation. The heating element is pushed between two adjacent, protruding rib packets. In order to avoid damage to the heating element, the ribs can be rounded on one side, but preferably on both sides, or provided with a chamfer, which facilitates the insertion of the heating element. The heating element can be produced both as a composite and from individual interconnected individual elements. The network must still be separated according to the later connection, unless all individual elements are to be connected in parallel later. The individual elements are to be connected to one another in accordance with the subsequent interconnection.

In this case, the heating element is preferably formed by at least one heating conductor layer, one insulation layer and one heat conducting and protective layer, wherein further layers can also be provided, in particular one or more adhesive layers, which can also be designed as a self-adhesive coating.

The heating conductor layer is preferably formed by a steel, in particular a stainless steel layer, which in particular has a thickness of 0.1 to 0.25 mm and is elastically deformable, so that the heating element rests resiliently on the protruding rib packets when there is a corresponding deformation and is non-positively between them is held.

The insulation layer is preferably formed by a polymer, in particular a polyester layer. However, other, higher temperature-resistant materials such as PEN or polyimides are also possible.

The insulation layer is preferably formed from an insulating film or a lacquer. It preferably has a thickness of 10 μm to 100 μm, in particular 15 μm to 50 μm. Furthermore, a thin special paper, e.g. an adhesive tape or a thin plastic film possible.

According to an advantageous embodiment, an adhesive layer is provided between the heat conductor layer and the insulation layer, which two layers permanently bonded together after lamination. In the case of an adhesive layer that has sufficient insulation and thermal conductivity, the alternative is also possible to replace the polyester insulation layer with the adhesive layer.

The heat conducting and protective layer is preferably formed by a metal layer, in particular an aluminum layer or a layer made of a preferably relatively soft aluminum alloy. The heat conducting and protective layer takes on the function of transferring the heat generated in the heating conductor layer focused onto the corrugated fins, in particular the crests of the corrugated fins, ie. H. to perform a task that the insulation layer could only fulfill to a lesser extent. In addition to the heat-conducting function, this heat-conducting and protective layer also has a protective function, so that the adjacent insulation layer is protected against injuries, for example when the heating elements are introduced. It preferably has a thickness of 20 μm to 200 μm, in particular 50 μm to 100 μm. Here, the heat conducting and protective layer is preferably directly adjacent and arranged in contact with the fin packs of the heat exchanger, so that an optimal heat transfer is possible.

The aluminum layer is. as well as a stainless steel tape that can be used for the heating conductor layer are commercially available as aluminum foil laminated with a self-adhesive film. This makes it possible to create a permanent connection between the aluminum layer and the insulating layer underneath. Here, too, it is conceivable as an alternative to dispense with the polymer or polyester insulating layer mentioned in favor of the adhesive layers, if adequate insulation and heat conduction are ensured by these. As already mentioned, the laminate according to the invention is produced by rolling and can thus be processed further like a sheet. The heating element itself is preferably designed as a heating grid, or a plurality of heating elements are connected to form a heating grid, in particular in such a way that the current is conducted, for example in a meandering manner, t through the heating grid in such a way that the required electrical

Resistance to achieve a desired heating output for a given

Voltage. The heating elements and / or the heating conductor layer can in turn be meandering, for example around the electrical one

To increase resistance for a given layer thickness, individual heating elements running parallel to one another being connected on each side to at least one adjacent heating element via connecting webs.

The heating element is preferably mounted on the end of the air outflow side with respect to the corresponding flat tube and running parallel thereto, the heating element being accommodated at least in regions between the above rib packets. This enables simple, space-saving and inexpensive attachment.

The electrical resistance and thus the heating power can preferably be set by providing recesses in the layer used to generate heat, for example slots produced by punching, e.g. through a expanded metal-like design.

In order to avoid short circuits or current bridges, in particular between the electrically conductive layers of the laminate, the cut edges are deburred after the punching process. This is preferably done by means of a pulsed voltage which is applied between the current-conducting layers, the voltage preferably being increased from pulse to pulse. In this case, possible connection burrs between the two metal layers burn off as a result of the short-term arc, the surrounding areas not or only because of the shortness of the pulses very limited to be affected by excessive heat. Deburring can also be carried out using an etching process or in some other way.

The deburring can be carried out, for example, directly after the punching, if appropriate also before the lamination, or after the lamination has taken place, followed by punching and subsequent shaping of the heating element.

In particular, the deburred cutting edges are preferably sealed, for example by applying a varnish or an adhesive which hardens after application. However, sealing can also be carried out, for example, in the case of elements of different dimensions which are produced separately and are then firmly connected to one another, the sealing preventing a later short-circuit-forming deformation of the edges, in particular if the layers of the highly electrically conductive layers are small.

A polymer is preferably used for sealing, whereby the thickness of the seal can be adjusted by choosing the viscosity and the application method (e.g. dipping, rolling off, wiping or applying a bead). Sealing is preferably carried out directly after deburring, but can optionally be carried out as the last method step after connecting and shaping the individual heating elements to form a heating grid.

In a further advantageous embodiment, the laminate has the layers indicated above, the heat-conducting and protective aluminum layer being in contact with the corrugated fins, while the non-insulated surface of the heat conductor layer forms the side facing away from the heat exchanger. This results in between the aluminum layer and the corrugated fins on. improved heat transfer, in particular with soft aluminum alloy, so that a certain conformity to the tops of the corrugated ribs is possible.

In a further advantageous embodiment, contact conductors with contact lugs are provided which engage in an electrically conductive manner in the grooves or folds of the heating device and thus contact the heating conductor layer directly. This achieves the advantage that the electrical heating device makes contact from the outside with simple means, ie. H. can be supplied with electrical energy from the electrical system.

In a further advantageous embodiment, the grid-shaped heating device can be secured against falling out by means of an additional adhesive to be applied. In principle, the heating device holds by means of a force-fit connection, ie. H. by pinching the folds into the spaces between the protruding ribs.

In a further advantageous embodiment, the grid-shaped heating device is formed in a meandering manner, i. H. Heating strands arranged in parallel in the form of folds are alternately connected at the ends by wide and narrow webs, so that a

^ connected structure, which is easy to handle during assembly. Individual current paths or heating lines can be interrupted and bridged by PTC elements to protect against overheating. With this design of the heating device, different circuit variants are also possible. In addition, several heating devices can be assigned to a radiator, each covering a part of the end face. These can be switched on or off in succession or at the same time in order to gradate the heating output. Overheating fuses are preferably provided in the current path, which automatically interrupt the current flow when the temperatures are too high. The Overheating fuses are preferably formed by solder connections with a low-melting solder between two contact plates, one of the contact plates being a spring steel that is under prestress. The overheating safeguards can protect the entire heating grid and / or parallel sections of the heating grid against overheating.

The invention is explained in detail below on the basis of exemplary embodiments with variants and with reference to the drawing. The drawing shows:

1 shows a section through a heating element in the stretched state, FIG. 2 shows a section through a built-in heating element,

3 shows a section perpendicular to the normal flow direction of the air, FIG. 4 shows an enlarged representation of a region from FIG. 3 with clarification of the heat transfer, FIG.

5a-5d different views and representations of a heating grid which comprises a plurality of heating elements,

6 shows a perspective illustration of a heat exchanger with an attached additional heater, FIG. 7 shows a section through an installed heating element in the area of an electrical contact, 8a shows a plan view of a heating element according to the second exemplary embodiment, shown in stretched form,

8b is a plan view of the heating conductor layer,

8c is a plan view of the insulation layer and heat conducting and protective layer,

9 shows a section through an overheating fuse,

10 shows a section through an overheating fuse according to a variant,

11a, 11b two variants of heating elements with overheating fuses,

12 shows a section through an alternative contact,

13a-13e embodiments for a heating element for adjusting the electrical resistance,

14a-14c a top view and side sections of a heating grid formed from individual elements with a series connection of two heating elements connected in parallel to adjust the electrical resistance,

15a-15c sections through a heating element after punching, when applying a voltage source and after sealing, 16a, 16b sections through a heating element, in which the lamination takes place after punching, and

17a, 17b sections through a heating element processed by etching,

18 shows a section through a heating element with a folded-over composite in the end regions, FIG. 19 shows a plan view of a heat exchanger with a heating element, the heating element being fixed to the heat exchanger with the aid of a holding element,

20 is a perspective view of the heat exchanger with heating element and holding element of FIG. 19,

21 is a perspective view of the holding element of FIGS. 19 and 20, FIGS. 22a-22h show various examples of the application of a current band, and

23a-23c, three different ^'Examples with two views of the positioning of an overheating fuse.

A heat exchanger 1 for a motor vehicle air conditioning system, in particular for a low-consumption vehicle, with a plurality of flat tubes 2 arranged parallel to one another and through which a heat transfer medium flows, and between the flat tubes 2 arranged fin packages 3 has electrically operated heating elements 4 as additional heating, which can be switched on if required , Here are a plurality of individual heating elements 4 after soldering from the air outflow side of the heat exchanger in each case inserted between adjacent, protruding fin packs 3, each heating element 4 being U-shaped for this purpose. In the present exemplary embodiment, each row of flat tubes 2 is equipped with a heating element 4, but any other variant is also possible, for example that only every second or third row of flat tubes is provided with a heating element, as shown in FIGS. 9 and 10.

The heating elements 4, the structure of which is illustrated in FIG. 1, have a heating conductor layer 5, formed by a stainless steel layer, an adhesive layer 6, formed by an adhesive coating of the subsequent insulation layer 7, which is formed from a polyester film, and an adjoining layer Thermally conductive and protective layer 8, which is formed by an aluminum layer. In the present case, the planar composite of the individual layers is produced by means of lamination, which is why the heating element 4 can also be referred to as a laminate. After the lamination, a stamping and bending process is provided, during which the heating elements 4 are formed, whereby they have an essentially U-shaped cross section, so that the flanks bear against the protruding rib packs 3 in the installed state. However, the cut can also be on. other than by punching, for example using a laser.

In the present case, the heating conductor layer 5 has a thickness of approximately 0.15 mm, the thickness of the heating conductor layer 5 being selected such that the total electrical resistance at the applied voltage U (generally 13 V) and the selected electrical circuit of the individual heating elements Desired heating output (P = U ² / R) results. For manufacturing reasons, the electrical circuit and the heat conductor layer are, for example, by means of Recesses selected or designed so that the desired total resistance results in thicknesses from 0.1 to 0.25 mm.

The insulation layer 7 has a thickness of approximately 25 μm, so that reliable insulation, but also good heat transfer, is ensured. The heat conducting and protective layer 8 has a thickness of approximately 100 μm, which does not cause any problems in terms of forming technology and is also sufficient with regard to the protective function.

In order to protect the heating elements 4, in particular the heat-conducting and protective layer 8 and the insulation layer 7, when inserting them, 3 insertion bevels are provided on the protruding rib packs (see FIG. 2). These insertion bevels can be applied, for example, by a shaping process before soldering the radiator block or also afterwards, for which purpose, for example, a special shaping tool is inserted between the respective fin packs 3 in the direction of insertion of the heating elements 4, so that the corners of the individual fin packs 3 are deformed and thereby beveled ,

Due to the use of stainless steel, the heating element 4 has a certain spring force when deformed, which is used to keep the heating elements 4 between the rib packs 3 in the largest possible area (non-positive connection). Here, the heating conductor layer 5 is arranged on the inside and the heat conducting and protective layer 8 on the outside. Figures 3 and 4 show a section through the ribs of the protruding rib packs 3 and a heating element 4 perpendicular to the flow direction of the air. In Fig. 4, the heat flow through the insulation layer 7 and the heat focusing in the heat conducting and protective layer 8 is illustrated by arrows. Depending on the electric resistance-board voltage and desired electrical heating power can not ^¬ shown manner are connected by parallel and / or series circuit via connecting webs the individual heating elements 4 in here. A pulse width modulation method is used for power control, but there are also others

Power control procedure possible.

The individual heating elements 4 are connected according to the first embodiment, as can be seen from Figures 5a to 5d, by means of connecting webs 11 and auxiliary connecting webs 12, so that the heating elements

4 can also be referred to as heating strands of a heating grid 13 ^" , consisting of a plurality of heating elements 4, connecting webs 11 and auxiliary connecting webs 12. Here, FIG. 5a shows a perspective view of the heating grid 13, FIG. 5b shows an enlarged section, wherein the Direction of insertion, as is also shown in FIGS. 5a and 5c, by an arrow,

5c a section corresponding to FIG. 5b through two heating elements 4 and FIG. 5d a top view of the heating conductor layer 5 of the heating grid 13. As can be seen in particular from FIG. 5a, the arrangement of the heating elements 4 and connecting webs 11 is meandering, whereby on the a connecting web 11 opposite side to increase the strength of the heating grid 13, an auxiliary connecting web 12 is provided, which is cut during or after installation.

In order to optimally arrange the heat-generating areas of the heating elements 4 in the area of the fin packs 3 and to bring the contact pressure of the flanks of the U-shaped heating elements to the fin packs to an optimum value, punched-out areas, which in the present case are circular, are in the heating conductor layer 5 in provided adjacent to the flat tubes 2 area. Instead of circular punch-outs, punch-outs or recesses extending in the longitudinal direction of the heating elements can also be provided. The flanks of the heating elements can also have recesses, as shown in FIGS. 13a and 13b using two further exemplary embodiments. According to the exemplary embodiment shown in FIG. 13 a, the heating element, in this case made of stainless steel 1.4301, itself has a meandering structure, as a result of which the resistance of the individual heating element is increased. According to the exemplary embodiment shown in FIG. 13b, which is preferred, the current flow and thus the heat development is conducted less through the bottom of the U-shaped holding element, so that less heat is introduced into the coolant. A polyester-laminated aluminum foil is applied to the heating element.

According to a further exemplary embodiment, not shown in the drawing, a planed and appropriately formed expanded metal structure is provided, in which a special cut of the metal strip material and simultaneous stretching result in diamond-shaped meshes with corresponding webs for the power line. By choosing the mesh parameters, the electrical resistance can be set within wide limits.

FIGS. 13c to 13e show how the path of the current flow can be extended by the arrangement of punched-out areas, for example FIG. 13c shows a high electrical resistance, FIG. 13d shows a medium electrical resistance and FIG. 13e shows a relatively low electrical resistance.

To protect against overheating, a gap 21 is provided in the circuit, which gap is bridged by means of a fuse element (in particular a fuse, not shown) which interrupts the circuit ^" when a predetermined limit temperature is exceeded. According to a variant of the first exemplary embodiment, a temperature-resistant adhesive is provided on the heat exchanger 1 to additionally secure the heating elements 4.

FIG. 6 shows a heat exchanger 1 with a mounted and electrically contacted additional heater, which is formed by heating elements 4 arranged in a meandering manner. For the electrical contacting, contact tabs 31 are provided for a plug contact of a radiator-side plug, not detailed, on a narrow side of the heat exchanger 1. The four contact lugs 31 present in the present example are formed in one piece with contact conductors 32 which have contact lugs 33 for contact with the heating elements 4. At least two contact conductors 32 are preferably provided, one of which is designed as a ground rail 32a, which also has a plurality of contact tabs 33 in the presence of several heating grids. The ground contact conductor 32a has an additional electrically conductive connection 34 as equipotential bonding to the heat exchanger block. 7 shows a section through the contact point of contact lug 33 and heating element 4. Here, the dimensions of contact lug 33 are matched to the free space in the U-shaped area of heating elements 4. This contact lug 33 can have spring elements (not shown) to ensure reliable contact.

Instead of a plug contact, another contact can also be provided, for example spring tongues, screws or rivets. Likewise, welding, soldering or gluing can also be provided for electrical contacting of the heating grid with the power supply, contact elements, in particular contact plates, being able to be formed in one piece with the heating grid or separately therefrom. An example of an alternative contacting in another exemplary embodiment is shown in FIG. 12. A corresponding material selection for the contact tabs and / or coating, for example tinning, silvering, improves the conductivity and thus the contact. The contact tabs can also be attached to the contact conductor, for example by means of a soldered connection, welded connection or crimped or riveted connection. The contact conductor can also form a structural unit with elements for fastening to the heat exchanger, for which Ciipse can be provided, for example. For this purpose, all contact conductors can be encapsulated by a plastic part, not shown, which holds the individual contact conductors in their relative position, includes clip elements and at the same time forms the housing of a plug.

8a shows the second exemplary embodiment according to which a plurality of individually designed heating elements 4 are correspondingly connected to one another. Here, a double-T-shaped stainless steel heating plate is provided as the heating conductor layer 5 (see FIG. 8b), which has a plurality of circular punched-outs which are arranged along the longitudinal axis. A rectangular punched or cut insulating and protective film, which consists of an insulating layer and a heat conducting and protective layer, is laminated onto this heating circuit board. As a result of the shape of the heating plate, flags 41 are provided, which can be used to form connection areas according to FIG. 12 or connecting webs of heating elements 4 connected in parallel or to form an overheating protection 42, as shown in FIGS. 9 and 10. The provision of overheating fuses 42 is particularly useful when no air flows over the heat exchanger 1, no water or water mixture flows through the flat tubes 2, in particular when there is no water in the heat exchanger 1 (radiator) and a very high electrical heating output is required. The overheating fuse 42 is in the present case formed by a thermally triggering fuse, the two lugs 41 of adjacent heating elements 4 being soldered to one another by means of a soft solder or a eutectic solder. For this the heating elements 4 are deformed elastically, so that in the event of overheating and an associated loosening of the solder connection, the heating elements 4 deform back again and the tabs 41 come out of contact, as a result of which the circuit is interrupted. By choosing the solder, the self-heating due to the current density and the thermal connection to the heating bridge, the limit temperature at which the circuit is interrupted can be determined, in the present case this is around 150 ° C. During operation, an equilibrium temperature is established at the soldering point, at which the heat loss generated and the heat dissipated to the air flowing past and the heating element are in equilibrium. If it is no longer possible to give off sufficient heat to the air flowing past, the temperature at the soldering point rises and when the limit temperature is exceeded, the soldering connection is released, ie the overheating fuse 42 responds, so that the electrical auxiliary heating is automatically stopped as a result of the interruption in the circuit , so that overheating of the heating elements 4 or other elements arranged in the area of the heat exchanger 1 or the subsequent air ducts can be avoided.

FIGS. 11 a and 11 b show how the triggering temperature of the overheating fuse 42 can be set to the desired value by varying the conductive cross section in the area of the solder joint. The other connections serve in particular the fixed connection of the individual heating elements 4, so that a heating grid is formed from the individual heating elements 4, corresponding to that of the first exemplary embodiment, but with a parallel connection of two heating elements. Such a coherent heating grid is easier to assemble, since individual heating elements do not have to be positioned and contacted. Furthermore, parallel connections and series connections of heating elements can be implemented in a simple manner. The connection to the electrical contact element can, as shown above or as shown in FIG. 12, be made via soldering points 51, which can simultaneously serve as overheating protection devices.

According to a further exemplary embodiment, the insulation layer 7 is already provided by a self-adhesive coating of an aluminum foil, which forms the heat conducting and protective layer 8.

According to a further exemplary embodiment, for which reference is again made to FIGS. 1 and 2, a heating element 4 is formed by a current supply layer 5 (first electrode), formed by a steel heating grid, an adhesive layer 6, formed by an adhesive coating of the subsequent polymers -PTC layer 7, which is formed from a polymer PTC material with a defined specific resistance, and an adjoining mass, heat conducting and protective layer 8, which is formed by an aluminum layer (second electrode). The production takes place according to the first embodiment. In contrast to the previous exemplary embodiments, the layer which is the most distant from the fin packs 3 is used only to a limited extent for heat generation, but rather for power supply and distribution, so that the current flows uniformly through the adhesive layer 6 and in particular the polymer PTC layer 7, which serves for heat generation , flows and is discharged via the heat conducting and protective layer 8 (second electrode). In this case, the adhesive layers must also be sufficiently electrically conductive, which can be achieved, for example, by admixing conductive carbon black or other electrically conductive particles. Other adhesive bonding techniques between the metal layers and the polymer PTC layer are also conceivable. Due to the PTC resistance behavior (positive temperature coefficient) of the polymer PTC layer 7, the heating grid 13 thus formed has sufficient intrinsic safety so that no overheating protection is required. In principle, the construction of all of the previous exemplary embodiments is possible, but the electrical contacting must be adapted to the different conductance behavior. The heat exchanger 1 is preferably at the ground potential, as in all of the previous exemplary embodiments.

FIGS. 14a to 14c show a heating grid formed from individual elements with a series connection of two heating elements connected in parallel in order to adapt the electrical resistance. In this case, solder joints are provided at the transitions between the individual heating elements as fuses (overheating fuse 42), in principle a single fuse would suffice. For electrical contacting, contact plates are provided at the ends, represented by "+" and the earth symbol in FIG. 14c. Any other interconnections, e.g. the interconnection of all heating elements 4 in series or the parallel connection of all heating elements 4, are possible.

To remove burrs, which inevitably arise when stamping the circuit boards and possibly lead to unwanted electrical connections between the two electrically conductive layers, the

Heating elements after punching before or after forming and

Connecting to a heating grille deburred, for which - with reference to the first exemplary embodiment and FIGS. 15a to 15c - a pulsed voltage which increases over time is applied between the heating conductor layer 5 and the heat conducting and protective layer 8, so that at

If a sufficiently high voltage is reached, arcs form at the critical points between the two layers and the burrs burn off (oxidize and / or evaporate) as a result of the heat generated in the process. Since the pulses are limited in time, the

Heat development and heat input, especially in the temperature-sensitive intermediate polymer layer are limited so that it is not damaged. The burning process can ensure a minimum distance between the electrically conductive layers.

In order to ensure the minimum distance in the long term, also with regard to possible damage, the deburred cutting edges are sealed after deburring (see Fig. 15c). For this purpose, the cut edges are provided with an insulating polymer (seal 61), which hardens after application.

The individual heating elements are then formed and connected to form a heating grid.

Deburring and sealing can also be the last steps after forming.

The previously described method for deburring and sealing can be used in all of the previously described exemplary embodiments, it also being possible to deburr individual elements that have already been punched before laminating.

According to a variant shown in FIG. 16 a, in which the heating conductor layer is only laminated with the other layers after the stamping process, the insulation layer and the heat conducting and protective layer protrude at least in regions over the heating conductor layer, so that a short circuit due to the protruding insulation layer is excluded.

However, the heating conductor layer is above the insulation layer and the heat conducting and formed according to the insulation layer

Protective layer over, so the distance between the two conductive Layers are not sufficient to safely avoid a short circuit. In this case, a seal 61 is preferably provided, as shown in FIG. 16b.

In FIGS. 17a and 17b, after lamination, there is a free etching of an area (surrounded by a dashed line in FIG. 17a), in which later a separation takes place by means of punching, as shown in FIG. 17b. In this case, only one of the electrically highly conductive layers, in the present case the heat conductor layer, is removed in a relatively small and limited area, the insulation layer remaining undamaged. The width of the area is dimensioned in such a way that it can be ensured that the stamped cut runs in this area and, after the cut has been made, a short circuit is reliably ruled out due to a burr between the two highly electrically conductive layers due to the stamping.

In Fig. 18, a heating element 4 consisting of a steel element (heat-conducting element 8) and a composite sealed thereon (heating-conductor layer 5 and insulation layer 7) is provided. In order to prevent a short circuit, the end regions 71 of the composite are folded over, the insulation layer 7 being located on the outside, as a result of which the heating conductor layer 5, which is on ground, is covered in these end regions 71.

The individual heating elements 4 can be fixed to the heat exchanger 1 by means of adhesive, according to a further exemplary embodiment shown in FIGS. 19 to 21, a plastic holding element 81 is provided for fixing the heating elements 4 to the heat exchanger 1, which is pushed over the heat exchanger 1 and the fixing Via the contact plates 82 of the heating elements 4. Here, the contact plates 82 clip into the holding element 81. There will also be relief enables the heating elements 4 against pressure and tension, since a large part of the forces are absorbed by the holding element 81.

According to a further exemplary embodiment, electrically well conductive current bands 91 are provided at the ends of the heating elements 4 which are connected to one another in order to reduce the current density in these regions, which serve only insignificantly for heating the fin packs 3. As shown in FIG. 22 a, the production can take place by means of continuous current bands 91, which are then cut through. The current strips 91, in the present case formed by flexible copper strips, can be attached by means of riveting, soldering, gluing, pressing or in some other way, the attachment or insertion taking place before or after the heating elements 4 are bent can. An overheating fuse 42 for protection against overheating can be integrated directly in one or both current strips 91. A detailed representation can be seen in FIG. 23c.

22b shows a current band 91 which only partially protrudes between two adjacent heating elements 4, but which represents the only electrical contact between them (application of the current band 91 after the shaping). In Fig. 22c, the current band 91 extends all the way into the resulting consequence of the forming groove inside (especially in the _case. Of attachment of the strip conductor 91 before forming). The individual adjacent heating elements 4 can have overlapping end regions (FIG. 22d), end regions arranged in abutment (FIG. 22e) or end regions spaced apart from one another (FIG. 22f). 22g shows a mechanical fixation by reshaping the current band 91, material from the current band 91 being pressed through openings in the heating elements 4. 22h shows a soldered or welded connection of current band 91 and heating elements 4. The design of the heating elements 4 corresponds to that shown in FIG. 18, that is to say to a short circuit prevent, the end regions 71 of the composite (aluminum / insulation film) consisting of the heat conductor and insulation layer 5 or 7 are turned over, the insulation layer 7 coming to the outside, as a result of which the heat conductor layer 5, which is on ground, lies in these end regions 71 is covered. The current band 91 (copper band) thus only contacts the heat-conducting element 8 (referred to as a steel heating element in FIGS. 22g and 22h).

To prevent excessive temperatures on the heating grid, overheating fuses 42 designed as fuses are provided, in the present case one for each heating register.

23a shows the attachment of a heating register to one of the two contact plates, which is made of spring steel, the attachment already being carried out when the heating register is connected under prestress and with the aid of low-melting solder.

23b shows a corresponding configuration of the overheating fuse 42, but in this case directly between two heating registers. 23c shows the use of a current band 91 with a targeted reduction in cross-section, which serves as overheating protection 42. At the narrow point, the temperature is greatly increased with a corresponding current flow, so that if the temperature increases too much, this point melts and interrupts the circuit.

LIST OF REFERENCE NUMBERS

I heat exchanger 2 flat tube

3 rib package

4 heating element

5 heating conductor layer, power supply layer

6 Adhesive layer 7 Insulation layer, polymer PTC layer 8 Thermal and protective layer

II connecting bridge

12 auxiliary connecting bridge

13 heating grid 21 gap

31 contact flag

32 contact conductor 32a ground rail

33 Contact tab 34 Connection

41 flags

42 Overheating protection 51 solder joint

61 sealing 71 end area

81 holding element

82 contact plates 91 current band

Claims

Patent claims

1. Heat exchanger, in particular for a heating or air conditioning system of a motor vehicle with a plurality of flat tubes (2) arranged parallel to one another and through which a heat transfer medium flows, wherein at least some of the flat tubes (2) are electrically operated after the heat exchanger (1) has been soldered on Heating element (4) is assigned as additional heating, which is fixed directly or indirectly to the heat exchanger (1), characterized in that the heating element (4) is formed at least in regions from at least three different layers which are firmly connected to one another over a large area.

That the heating element (4) is at least provided depending ^r a heat-conducting layer (5), an insulating layer (7) and a heat conducting protective layer (8) 2. A heat exchanger according to claim 1, characterized.

3. Heat exchanger according to claim 1 or 2, characterized in that the heating element (4) has a heating conductor layer (5) which is formed by a metal, in particular a stainless steel layer.

4. Heat exchanger according to one of the preceding claims, characterized in that the heating element (4) has a heating conductor layer (5) which has a thickness of 0.1 to 0.25 mm.

5. Heat exchanger according to one of the preceding claims, characterized in that the heating element (4) has a heating conductor layer (5) which is elastically deformable.

6. Heat exchanger according to one of the preceding claims, characterized in that the heating element (4) has an insulation layer (7) which is formed by a polymer, in particular a polyester, a PEN or polyimide layer.

7. Heat exchanger according to one of the preceding claims, characterized in that the heating element (4) has an insulation layer (7) which is formed from an insulating film or a lacquer.

8. Heat exchanger according to one of the preceding claims, characterized in that the heating element (4) has an insulation layer (7) which has a thickness of 10 μm to 100 μm, in particular 15 μm to 50 μm.

9. Heat exchanger according to one of the preceding claims, characterized in that the heating element (4) has a heat conducting and protective layer (8) which is formed by an aluminum layer.

10. Heat exchanger according to one of the preceding claims, characterized in that the heating element (4) has a heat conducting and protective layer (8) which has a thickness of 20 μm to 200 μm, in particular 50 μm to 100 μm.

11. Heat exchanger according to one of the preceding claims, characterized in that the heating element (4) has an adhesive layer (6) and / or at least one of the layers (5, 7 and / or 8) at least has a self-adhesive coating (6) or a heat seal coating.

12. Heat exchanger according to one of the preceding claims, characterized in that the heating element (4) is designed as a heating grid or a plurality of heating elements (4) are connected to form a heating grid (13).

13. Heat exchanger according to one of the preceding claims, characterized in that the heating element (4) on the air outflow side is attached to the front with respect to the corresponding flat tube and running parallel to it.

14. Heat exchanger according to one of the preceding claims, characterized in that the heating element (4) is accommodated at least in regions between the above rib packets (3).

15. Heat exchanger according to claim 14, characterized in that the heating element (4) or essential areas of the heating element (4) is at least partially inserted between the above rib packets (3).

16. Heat exchanger according to one of the preceding claims, characterized in that at least the heating conductor layer (5) is formed in a meandering manner, individual heating elements (4) running parallel to one another on each side with at least one adjacent heating element (4) via connecting webs (11 ) are connected.

17. Heat exchanger according to claim 16, characterized in that overheating protection is provided on at least one connecting web (11).

18. Heat exchanger according to claim 17, characterized in that the overheating protection is designed as a solder joint.

19. Heat exchanger according to one of the preceding claims, characterized in that the heating element (4) is arranged between the • rib packets (3) in such a way that the heat conducting and protective layer (8), directly or under arrangement, is adjacent to the rib packs (3) the insulation layer (7) is then arranged from one or more intermediate layers and the heat conductor layer (5) is arranged directly or with one or more intermediate layers arranged.

20. Heat exchanger according to one of the preceding claims, characterized in that at least one overheating fuse (42) is provided.

21. Heat exchanger according to claim 20, characterized in that the overheating protection (42) is formed by one or more soldered connections, in particular two adjacent heating elements and / or by a cross-sectional constriction.

22. Heat exchanger according to one of the preceding claims, characterized in that a plurality of heating elements (4) by means of flags (41) are connected to adjacent heating elements (4).

23. Heat exchanger according to one of the preceding claims, characterized in that a plurality of heating elements (4) are arranged in a grid-like manner.

24. Heat exchanger according to one of the preceding claims, characterized in that the heating conductor layer (5) is formed by a heating plate, in particular stainless steel heating plate.

25. Heat exchanger according to claim 25, characterized in that the heating conductor layer (5) has an elongated rectangular shape with at least two tabs (41) at the ends, which extend laterally in the direction of the adjacent heating element (4).

26. Heat exchanger according to one of the preceding claims, characterized in that on the heating conductor layer (5) of a heating element (4) a combined insulation layer (7) and heat conducting and protective layer (8) is attached, which has an elongated rectangular shape.

27. Heat exchanger according to one of the preceding claims, characterized in that at least one power supply layer (5), one polymer PTC layer (7) and one heat conducting and protective layer (8) is provided.

28. Heat exchanger according to one of the preceding claims, characterized in that the electrical resistance is adjustable by means of recesses.

29. Heat exchanger according to one of the preceding claims, characterized in that on the heat-conducting element (8) a composite consisting at least of the heat conductor layer (5) and Insulation layer (7) is sealed on, at least one end region (71) of the composite being turned over such that the insulation layer (7) lies on the outside in the end region (71).

30. Heat exchanger according to one of the preceding claims, characterized in that a current band (91) is provided.

31. Heating element for use with a heat exchanger (1) as an additional electrical heater, characterized by a structure according to one of claims 1 to 30.

32. A method for producing a heating element according to claim 31, characterized in that a deburring process follows after the stamping, laminating or forming process.

33. The method according to claim 32, characterized in that the deburring is carried out by means of a pulsed voltage.

34. The method according to claim 33, characterized in that the voltage increases from pulse to pulse.

35. The method according to any one of claims 32 to 34, characterized in that the cutting edges are sealed after deburring.

36. A method for producing a heating element according to claim 31, characterized in that at least one edge region is sealed.