Heating device and electrical appliance with such a heating device

Abstract

A heating device comprises a support, an electrically insulating base insulation layer, and at least one heating conductor circuit on this base insulation layer. The heating conductor circuit includes at least one heating conductor and electrical connections thereon. An electrically insulating secondary insulation layer is arranged on the support below the base insulation layer and between the base insulation layer and the support. An electrically conductive conductive layer is distributed over the substrate such that the base insulation layer is directly adjacent to the conductive layer. A protective earth (PE) connection is provided on the support or on the secondary insulation layer and is connected to ground. A fusible link is provided between the conductive layer and the support or the PE connection, respectively, as the sole electrical connection between the conductive layer and the support or the ground connection.

Description

Application area and state of the art

[0001] The invention relates to a heating device with a support and at least one heating conductor circuit thereon, the circuit comprising at least one heating conductor. The invention further relates to an electrical appliance with such a heating device, in particular a water-bearing household appliance such as a washing machine or a dishwasher.

[0002] Heating devices, such as those used in washing machines, which incorporate so-called thick-film heating elements, are known from WO 2021 / 170 331 A1 or DE 10 2007 058 833 A1. A base insulating layer can be applied to a substrate, particularly if it is made of metal, and a heating circuit with multiple heating conductors is applied to or over this substrate. A potential problem during operation is that overheating of the thick-film heating element can damage the base insulating layer. If the substrate is then made of metal, a short circuit to the thick-film heating element or one of its electrical connections can occur, posing a corresponding risk to the operator. Task and solution

[0003] The invention is based on the objective of creating a heating device and an electrical appliance equipped with it, as mentioned above, with which problems of the prior art can be solved and in particular it is possible to increase the safety of the heating device or the electrical appliance during operation and to eliminate electrical hazards.

[0004] This problem is solved by a heating device with the features of claim 1 and by an electrical device with the features of claim 16. Advantageous and preferred embodiments of the invention are the subject of further claims and are explained in more detail below. Some of the features are described only for the heating device or only for the electrical device. However, they should be able to apply independently and autonomously to both such a heating device and such an electrical device. The wording of the claims is incorporated into the description by express reference.

[0005] The heating device comprises a support and an electrically insulating base layer on this support. Advantageously, this base insulating layer is applied directly to the support. The support can be made of metal, for example, but this is not mandatory. This will be explained in more detail below. At least one heating conductor circuit is arranged on or above the base insulating layer, and this circuit has electrical connections. Advantageously, these electrical connections are designed as plug-in terminals, for example, with plug-in tabs or sockets attached directly to the heating device. The at least one heating conductor circuit comprises at least one heating conductor, and advantageously several, with a wide variety of configurations possible, as are essentially known from the prior art. This will be explained in more detail below.

[0006] According to the invention, an electrically insulating additional insulating layer is provided below the base insulating layer, which primarily serves to electrically insulate the heating conductor circuit(s) directly from the substrate. This additional insulating layer is located between the base insulating layer and the substrate, and is advantageously applied directly to a top surface of the substrate, possibly after prior surface treatment. Thus, there is a two-layer electrical insulation structure between the substrate and the at least one heating conductor circuit. Advantageously, the layer structure of the additional insulating layer on the substrate and the base insulating layer above it is the same for all heating conductor circuits. Furthermore, an electrically conductive conductive layer is present on the additional insulating layer, arranged in a distributed pattern, preferably as a closed surface, or alternatively as a grid or mesh.The base insulating layer runs on top of this conductive layer, so that the conductive layer lies between the additional insulating layer and the base insulating layer. Essentially, there is at least a three-layer structure on the substrate: the additional insulating layer, the conductive layer, and the base insulating layer above it. The conductive layer is designed such that a current flowing through the heating circuit from a damaged base insulating layer (due to a fault) flows into the conductive layer. The conductive layer is accessible from the outside or has external access such that a ground connection is provided to it, preferably directly to it. Preferably, the connection to ground or to PE is not provided directly to it, but rather it is electrically connected to it. The ground connection is connected to ground or PE. Such a connection to ground or PE...A protective earth (PE) connection is typically present in electrical appliances connected to a household electrical system. This is highly advisable and also mandatory. The function of such a standard PE connection is well understood by electricians. The conductivity of the conductive layer should be such that, during normal operation, or when the current flowing through the heating element circuit passes through it, the layer does not experience any significant heating. To achieve this, its electrical resistance can be between 5 and 100 times lower than that of the heating element, preferably less than 0.1 ohms per millimeter. 2 / m be.

[0007] Finally, the heating device also features a fusible link, which is provided between the conductive layer and the substrate or between the conductive layer and the ground connection, and serves as the sole electrical connection between the conductive layer and the ground connection. Advantageously, this fusible link is not replaceable but permanently installed or permanently connected to the heating device, particularly advantageous as an integral, inseparable component of the heating device.

[0008] This design of the heating device allows for a temporary current flow from the heating conductor to the conductive layer through the base insulation layer if the base insulation layer is damaged or fails to provide complete electrical insulation for the heating conductors. This can occur if the heating device runs dry or the generated heat cannot be dissipated, leading to temperatures of 500°C to 700°C. This current then flows through the base insulation layer from the conductive layer, via the electrical connection, to the substrate or to the ground / PE connection, and may be the only electrical connection of this type.The current flows through the fuse, which is designed to be destroyed by the current flowing through it—the primary function of a fuse. For this purpose, it can be designed to be destroyed by a current exceeding 100 mA, allowing it to conduct a high current for a very short time. The fuse can be a fast-acting fuse, as commonly known, meaning it will trip or be destroyed within less than 100 ms or even less than 5 ms at the specified current. When the fuse blows, the heating element is usually already damaged.

[0009] The invention ensures safety in the event of excessively high temperatures due to the operation of the heating conductor or heating circuit, which could burn out and damage or destroy the base insulation layer, causing it to lose its electrically insulating properties at least at one point. If current then flows from the heating circuit or from one of the heating conductors through it, it flows through the damaged base insulation layer into the electrically conductive layer below, thus allowing it to dissipate and preventing it from flowing through the additional insulation layer to the substrate and potentially damaging it as well. From there, the current flows through the fuse to the PE connection. The resulting current flow destroys the fuse beyond a certain point, depending on its design.By applying the additional insulating layer directly to the substrate or between the substrate and the base insulating layer, the substrate remains electrically insulated, thus eliminating any risk to the operator. Therefore, the destruction or breakdown of the uppermost electrical insulation, namely the base insulating layer, triggers or destroys the fuse, which can briefly divert current to the PE terminal before it is itself destroyed. This can be detected by an evaluation unit of the heating device or by a control unit or power supply for the heating device, for example, because no current flows through the damaged heating circuit, no temperature increase is registered by separate temperature sensors, or the destruction of the fuse has been registered.

[0010] In a further development of the invention, it is possible that each of the aforementioned layers, i.e., base insulating layer, additional insulating layer, and conductive layer, consists of several sequentially applied layers. However, they each function as a single layer.

[0011] In an advantageous embodiment of the invention, the carrier is electrically conductive, for example, it consists of metal or a so-called thick-film steel. The PE connection is then arranged on the carrier, in particular directly on it, preferably welded to it. The fusible link can extend or run from the conductive layer directly onto the carrier, being connected to both the carrier and the PE connection, advantageously as a plug-in connection.

[0012] In a further embodiment of the invention, an electrically conductive contact field can be applied to the carrier in addition to the aforementioned additional insulating layer, for example, soldered or welded on, and electrically connected to the carrier. The fuse can then extend directly from the conductive layer onto this contact field and be electrically connected to it. For this purpose, the carrier is advantageously designed to be electrically conductive and has the ground connection, or the ground connection is arranged or attached to it. It can be advantageously provided that the contact field is as high as the conductive layer, or that one upper surface of the contact field is approximately as high as one upper surface of the conductive layer. The fuse can then run, so to speak, parallel to the carrier from the conductive layer to the contact field. In this way, it can be securely applied and attached, for example, in a manufacturing process by soldering, in particular by SMD soldering.The contact area can be soldered. It can have a lateral distance to the additional insulating layer and, advantageously, also to the conductive layer, to prevent a short circuit that might persist after the fuse is blown. The contact area can also overlap, at least partially, the additional insulating layer.

[0013] In an alternative embodiment of the invention, an additional contact field can be applied to the additional insulating layer itself, which in turn is electrically connected to the ground connection or the PE connection. The fuse is then electrically connected to this additional contact field. Thus, while in the first case described above the electrical contact exists with the carrier and a ground connection or PE connection provided thereon, in the second case described here, an electrical connection via the fuse is only provided to the ground connection. Therefore, a further ground connection or PE connection is required, since the carrier, especially if the heating device is intended for heating water, should have its own ground connection.

[0014] In an embodiment of the invention, the fuse can be metallic or designed as a metal part, advantageously as an exposed or free-running metal part. Preferably, the fuse is designed as an SMD component so that it can be attached to the heating device by SMD soldering and electrically connected. This enables automated attachment and connection.

[0015] In a further development of the invention, the fuse can be designed as a so-called fast-acting or quick-delay fuse. It can be designed for a reaction time of less than 50 ms, advantageously less than 5 ms, so that it blows after a maximum of 50 ms or 5 ms when a specific current or a higher current flows through it. Generally, this blowing of the fuse can be detected by a control unit that controls the heating device or provides its power supply. For example, a test circuit can be formed via an electrical connection to the conductive layer on one side and to the ground connection on the other, through which a test current flows, thus also passing through the fuse.If this layer is damaged, the test circuit is interrupted, which can be interpreted as a sign of damage and thus a failure of the base insulation layer and consequently of the entire heating device. As a rule, this heating device is then permanently inoperable and destroyed, which is due to the rupture or destruction of the base insulation layer anyway; it must then be replaced.

[0016] The aforementioned current at which the fuse is destroyed or blows, particularly within the specified time, can be a maximum of 0.5 A. A lower current is advantageous, for example, a maximum of 0.1 A. Thus, even relatively minor damage to the base insulating layer and relatively small current flows through it and across the conductive layer to the fuse are sufficient to trip or destroy it. Nevertheless, the fuse can also conduct significantly higher currents for very short periods.

[0017] The fuse should ideally be designed so that, if it blows or is destroyed, it does not damage the additional insulating layer, ensuring that the latter can continue to electrically insulate the heating conductors from the substrate. Thus, the conductive layer, together with the fuse, serves to protect and maintain this electrical insulation of the substrate under all circumstances. This increases the safety of the heating device and the electrical appliance it is used with during operation.

[0018] In a further development of the invention, the conductive layer and the base insulating layer can have such a planar extent that the heating conductors of the at least one heating conductor circuit, in particular of a single heating conductor circuit, run within or above them. Furthermore, the base insulating layer should extend within the planar extent of the conductive layer, so that in the event of any breach of the base insulating layer, a portion of the conductive layer is exposed. In a further development of the invention, the conductive layer can be arranged to run parallel to the at least one heating conductor or all heating conductors of a heating conductor circuit. In the case of multiple heating conductor circuits, each can have its own conductive layer. These conductive layers can then advantageously be separated from one another. Alternatively, a continuous, electrically conductive, or common conductive layer can be provided.However, even with such a corresponding course, the conductive layer should run in a direction corresponding to the heating conductors, but should exceed them in width.

[0019] In a possible embodiment of the invention, the conductive layer can be planar, possibly covering at least 70% to 90% of the substrate or the additional insulating layer. It can form a closed surface. Alternatively, the conductive layer can also be designed as a network or grid, wherein the total area of ​​the network or grid conductors is less than the total uncovered area of ​​the additional insulating layer. Alternatively, the conductive layer can also be meandering and run in tracks, preferably also for the heating conductors above it, so that the shape of the conductive layer can advantageously be adapted to the shape of the heating conductors. These tracks can have a maximum width of 3 mm, with the heating conductors having a maximum width of 2.5 mm or a maximum of 2 mm. Preferably, the width of the tracks of a meandering conductive layer should be equal to or exceed the maximum width of the heating conductors by 5% to 50%.In this case, the conductive layer can run between all the heating conductors and the support or the additional insulating layer.

[0020] In a further development of the invention, the heating device can have several separately operable heating conductor circuits, each of which has at least one heating conductor, advantageously several heating conductors. Then, a separate and correspondingly extensive conductive layer can be provided for each of these heating conductor circuits, with each of these heating conductor circuits running on and within the boundaries of this conductive layer.

[0021] It can be designed that the fuse and the entire heating device are configured such that a common base insulation layer is provided for all conductive layers beneath all heating circuits. Each heating circuit and its associated conductive layer can have its own separate fuse, which has an electrically conductive connection to a ground terminal. This allows the identification of which of the multiple fuses blows due to a damaged base insulation layer beneath a specific heating conductor. This heating circuit can then be switched off by the control system as described above. Operation can then continue with the other heating circuits, possibly as an emergency measure, which is still preferable to no operation at all. It would be possible to provide three or four separate heating circuits, which may be of similar size.exhibit similar heating performance.

[0022] In a further development of the invention, at least one temperature sensor can be arranged on the heating device. A favorable arrangement for this is on or above the base insulation layer in the area of ​​a heating conductor circuit or one of its heating conductors, preferably at a distance of less than 3 cm. This temperature sensor can then also detect a significant instance of overheating at the heating device, in addition to the possibility that the base insulation layer may be penetrated or locally damaged shortly thereafter, using the previously described methods for detecting this.

[0023] It is considered preferred to provide a covering on an exposed upper surface of the heating conductor circuit or its individual heating conductors, particularly for electrical insulation, protection against damage, and protection against contamination. This covering layer should cover all heating conductors of a heating conductor circuit and, advantageously, all heating conductor circuits of the heating device. Preferably, this is achieved with a single, common covering layer. The covering layer can be glass-like, similar to the base insulating layer and / or the additional insulating layer, or may contain glass for its excellent electrical insulation properties and temperature resistance.

[0024] These and other features are evident not only from the claims but also from the description and the drawings, whereby the individual features, either alone or in combination, may be implemented in one embodiment of the invention and in other fields, and may represent advantageous and individually protectable embodiments for which protection is claimed here. The division of the application into individual sections and subheadings does not limit the general validity of the statements made therein. Brief description of the drawings

[0025] Exemplary embodiments of the invention are shown schematically in the drawings and are explained in more detail below. The drawings show: Fig. 1 a rear view of a steam cooker as an electrical appliance according to the invention with a steam generator at the rear, which has a heating device according to the invention, Fig. 2 a simplified schematic sectional view through a heating device according to the invention and Fig. 3 a top view of a specific embodiment of a heating device according to the invention. Detailed description of the exemplary implementations

[0026] In the Fig. Figure 1 shows a steam cooker 11 as an electrical appliance according to the invention; it is even a water-bearing household appliance as mentioned above. The steam cooker 11 has a housing 12, on the rear of which a steam generator 13 is arranged in a known manner. This steam generator 13 has a heating device 15 according to the invention. With this device, water can be evaporated in a steam generation chamber or the like in a known manner, and this steam is then introduced into the interior of the steam cooker 11 for the preparation of food. The heating power for such a steam generator 13 or a steam cooker 11 should be relatively high so that a sufficient quantity of steam can be generated as quickly as possible. At the same time, a high level of safety must be maintained, since the housing 12 of the steam cooker 11 can easily be touched by an operator, and the steam generator 13 is arranged on its rear.

[0027] From the schematic sectional view of the Fig. Figure 2 shows that a flat metal support 17 is provided. It can advantageously be flat or planar, but this is not mandatory. On the upper surface 18 of the support, a PE connection 20 corresponding to a ground connection mentioned earlier is provided on the far left. It is advantageously designed as a contact, for example as a protruding plug contact. As the Fig. As shown in Figure 3, it can either be applied directly to the top surface of the carrier 18, for example by soldering or welding. Alternatively, it can also be attached to a contact field provided thereon. This PE connection also serves, in a known manner, to ensure the safety of the operation of the heating device 15.

[0028] A substantial area of ​​the surface of the carrier 17, or the carrier's upper surface 18, is covered by an additional insulating layer 22. This layer can be glassy or glass-containing, as is known. It can be applied to the carrier's upper surface 18 by screen printing with a suitable paste and then baked on. It can be a single layer or, alternatively, a multi-layer layer.

[0029] A conductive layer 24, of a slightly smaller size, can be applied to the additional insulating layer 22. It can be applied either as a closed surface, or alternatively in a mesh or grid form, as is known from the prior art. The conductive layer 24 is electrically conductive or consists of electrically conductive material, and can therefore contain graphite and / or metal.

[0030] A so-called base insulating layer 26 is applied to the conductive layer 24, with a slightly smaller area or contour. It can consist of a similar or identical material to the additional insulating layer 22. It can also be applied in the same way, possibly as a single layer or in multiple layers.

[0031] On top of the base insulating layer, three heating conductors 28 are schematically applied; this applies only to this embodiment, there could be more or fewer. Thick-film heating conductors are advantageously used, which are applied by a screen-printing process and then baked on. Reference is made to the prior art mentioned at the outset.

[0032] The heating conductors 28 are covered from above by a cover layer 35, so that they are completely sealed and protected against both external mechanical damage and contact with atmospheric oxygen. Furthermore, they can also be electrically insulated if a suitable cover layer is used. The heating conductors 28 are electrically connected in a manner not shown.

[0033] On the right side of the carrier surface 18, a stepped contact field 37 is applied, overlapping the additional insulating layer 22. This overlap is provided so that one upper surface of the contact field 37 is approximately at the same height as one upper surface of the conductive layer 24. Thus, the contact field 37 could also simply be located next to the additional insulating layer 22, but with a corresponding height. This height of the contact field 37 has the advantage that a fuse according to the invention, as an SMD component, can then be placed with one end onto this contact field 37 and secured there, and electrically connected. The other left end rests on the conductive layer 24 or an extension thereof. Thus, the fuse 39 is the only electrical connection from the conductive layer 24 to the outside, via the contact field 37 and the electrically conductive carrier 17, which is made of metal, to the PE terminal 20.

[0034] From the presentation of Fig. It is easy to see from Figure 2 that if the heating conductors 28 are operated and thus carry current and generate excessive heat, the base insulation layer 26 can be damaged. Damage to the base insulation can occur due to local or partial limescale deposits on the water side or underside of the carrier 17, or due to overheating across the entire surface, for example, from running dry. The heat generated by the heating conductors 28 is then not sufficiently dissipated, and the problems mentioned at the beginning occur.

[0035] If this damage is so extensive that the base insulation layer 26 burns through, ruptures, or loses its insulating properties, a current can flow from the heating conductors 28 through the base insulation layer 26 or its damaged area to the conductive layer 24 and from there via the fuse 39 to the contact field 37, carrier 17, and PE connection 20. If this current is large enough to exceed the aforementioned 0.5 A or 0.1 A, the fuse 39 will blow, for example, after 5 ms, depending on its design. The fuse should be designed so that the heating conductor is interrupted, thus preventing further operation. The current being diverted via the conductive layer ensures that the additional insulation remains unaffected and the insulation required by standards is still present after the failure. Monitoring of the fuse is possible but not mandatory.

[0036] Thus, the electrical contact between conductive layer 24 and contact field 37, and ultimately the PE connection 20, is lost. This can be detected as a fault and evaluated accordingly, for example, because current flowed through the PE connection 20 for a very short time, or because an electrical connection between conductive layer 24 and PE connection 20 has been interrupted. Experts are familiar with sufficient methods for evaluating this; further explanation is unnecessary.

[0037] In the Fig. Figure 3 shows a top view of a detailed embodiment of a heating device 15 according to the invention. A flat metallic support 17 has the additional insulating layer 22 on its upper surface 18. A first PE connection 20 is provided on the support 17, or rather on its upper surface 18, and thus connects directly to the support 17. A second PE connection 20' is provided on the far left, which connects via a conductor track and a fuse 39 to a mesh-like conductive layer 24, which is shown with dashed lines. Such a mesh-like design is generally known.

[0038] On the carrier surface 18, the network-like conductive layer 24 is applied next to or on top of the specially formed additional insulating layer 22, but only in the right-hand area and not in the left-hand area. To the right of the fuse 39, a conductor-like trace can be seen extending from the conductive layer 24 to the fuse 39, which serves as its contact point.

[0039] On the conductive layer 24, a base insulating layer is applied, which excludes the second PE connection 20' and the fuse 39, i.e., does not cover them. On the base insulating layer 26, the elongated and straight heating conductors 28 are provided. They run in parallel paths with 180° bends or short-circuit bridges 31 at the ends. The heating conductors 28 form a single heating circuit or have only two heating conductor contacts 29a and 29b. However, two or more heating circuits could also be provided, which can be controlled or operated separately.

[0040] Not shown, but easily imagined in the Fig. 3 is a cover layer, which can, for example, extend approximately according to the extent of the conductive layer 24.

[0041] In the event of a fault or damage to the base insulation layer 26, current from one of the heating conductors 28 will flow through the base insulation layer 26 and the conductive layer 24. This current will flow through the fuse 39, causing it to melt or burn out. The electrical connection to the PE terminal 20' will then be severed or no longer exist. This can be detected as described above.

[0042] A connector recess 43 is shown with dotted lines, as known, for example, from EP 2 741 371 A1. This recess can hold plug-in terminals which, with laterally projecting feet, rest on the PE terminals 20 and 20' and the heating conductor contacts 29a and 29b, and are soldered or welded in place. This allows for quick and easy electrical contacting using a suitable plug.

[0043] Separate temperature measurement can be achieved by a temperature sensor 41, which advantageously rests on the base insulating layer 26, particularly advantageously as an SMD temperature sensor. It has two temperature sensor contact fields 42a and 42b, which can also be electrically contacted by means of the aforementioned connector.

[0044] The diagrams clearly show that if there are multiple separate heating circuits, each should have its own fuse. This ensures that even if only one heating circuit fails or is permanently shut off, heating operation can continue. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2021 / 170 331 A1

[0002] DE 10 2007 058 833 A1

[0002] EP 2 741 371 A1

[0042]

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