EP1519630B1 - Heater for cooking apparatus or the like - Google Patents

Abstract

Cooking apparatus heating device having:at least one electric heating plate (10, 12, 14), electric conductors (16) for supplying the plates, coupled to at least one of the plates, a dielectric layer in contact on one side with conductors (16), while the other side makes direct contact with the plates. Independent claims are included for: (1) a cooking apparatus with at least one heating plate; (2) a process for preparation of the cooking apparatus by mixing a sol/gel solution with up to 90 wt.% of a solution of electrically conductive powder to give a stable dispersion, where the powder is selected from:ceramics, metals, or semiconductors, coating of the dispersion onto a substrate, and stoving of the substrate.

Description

The invention relates to a heating device for a cooking appliance or the like according to the preamble of claim 1. Furthermore, the invention relates to a cooking appliance according to the preamble of claim 16.

Many household cookers include a hob or hot plate with a heater that generates heat radiation. The heating device is covered for example with a ceramic plate, in particular glass ceramic plate, which has a very low coefficient of thermal expansion.

The heat transfer from the heating device, which is arranged below the glass ceramic plate, to a cooking vessel, for example a pan or a cooking pot, which is on the glass ceramic plate, via two different heat transport processes. About a quarter of the energy is transferred by direct heat radiation from the heater through the glass ceramic plate on the cooking vessel. The remaining energy is transferred by thermal radiation from the heater to the underside of the glass ceramic plate, followed by a heat conduction from the bottom of the glass ceramic plate to the top and finally the heat is transferred from the top of the glass ceramic plate to the cooking vessel. At full power, a heating element of the heater can reach a temperature of about 1100 ° C, which requires a complex insulation below and to the side of the Heating device required to avoid unnecessary energy loss. The high temperature of the heating element is required to ensure the passage of heat radiation through the glass ceramic plate, which is possible only for a relatively narrow frequency range. In addition, the working temperature of the glass ceramic plate must be less than 550 ° C, which requires a temperature limiting device, which shuts off the heater at too high temperatures. At the working temperature, the glass-ceramic plate is not electrically insulating, so that an electrically insulating material and / or an air gap must be arranged between the heating device and the glass-ceramic plate. As a result, the heater has a thickness of about 3 to 4 cm. In contrast, the glass ceramic plate is usually about 4 mm thick.

Such heaters for glass ceramic cooktops have the disadvantage that the heat generated by the heater can not be used optimally. Another disadvantage is that relatively much space is required for the heater.

In the EP 1 107 648 A2 For example, a heating apparatus for a cooking appliance having a plurality of sheets for generating heat from electric power is described. The heater comprises electrical tracks for powering the patches coupled to the patches in a predetermined pattern. In addition, the heating device has a dielectric layer, on one side of which the conductor tracks and the surface pieces are attached and whose other side is provided for direct contact with a heating plate.

However, this device has the disadvantage that a uniform temperature distribution over the heater is not guaranteed. An annular surface is covered by elongated curved surface pieces whose longitudinal sides are coupled to the electrical conductor tracks. This results in an inhomogeneous temperature distribution within the curved surface pieces and also on the heating device.

From the US 5,932,128 An electric heating plate is known, which has rectangular heating layers, on the longitudinal sides of which the supply voltage is applied. The heating layers are made of graphite. The heating layers can also be arranged on both sides of the heating plate.

In the US 2002/0145134 A1 a heating device with a conductor track is described. In this device, the conversion of electrical current into heat takes place in the conductor track. Also, this device has the disadvantage that a uniform temperature distribution over the heater is not guaranteed. In the vicinity of the track high temperatures occur, while in the interstices, the temperatures are significantly lower. From the US 2002/0145134 A1 Also, a method for producing the heating device with the conductor track is known. In this case, a sol-gel solution is mixed with up to 90 wt .-% of the solution of an electrically conductive powder to form a stable dispersion, wherein the dispersion is applied to a substrate and then the substrate is fired.

In the DE 195 10 989 A1 is a component combination for electric heating plates described. The resistance elements are formed as rectangular area pieces which extend in a star shape. Due to the dimensions and arrangement of the patches is a uniform temperature distribution not possible above the heater. The electrical tracks are coupled to a location on the face of the patches.

From the US 4,034,206 An arrangement of electric heating elements is known. The heating elements are formed as rectangular patches and sized and arranged to cover a circular area. The end faces of the patches are coupled with electrical conductors. The patches are electrically connected in series.

Based on the prior art according to EP 1 107 648 A1 It is therefore an object of the invention to provide a heating device for a cooking appliance, which allows a uniform temperature distribution.

With regard to the heater, this object is achieved by the subject matter of claim 1.

• die Heizvorrichtung ein rechteckiges zentrales Flächenstück und zwei rechteckige laterale Flächenstücke aufweist, die zueinander parallel und symmetrisch angeordnet sind,
• das zentrale Flächenstück und die zwei lateralen Flächenstücke so bemessen und angeordnet sind, dass sie eine Kreisfläche möglichst vollständig abdecken,
• das zentrale Flächenstück etwa doppelt so breit wie die lateralen Flächenstücke ausgebildet ist,
• die elektrischen Leiterbahnen mit den Stirnseiten der Flächenstücke gekoppelt sind, und
• die lateralen Flächenstücke miteinander parallel und mit dem zentralen Flächenstück in Reihe geschaltet sind.

According to the invention, it is provided

• the heating device has a rectangular central surface piece and two rectangular lateral surface pieces which are arranged parallel to one another and symmetrically to one another,
• the central area piece and the two lateral area pieces are dimensioned and arranged such that they cover a circular area as completely as possible,
• the central surface piece is approximately twice as wide as the lateral surface pieces,
• the electrical interconnects are coupled to the end faces of the patches, and
• the lateral patches are connected in parallel with each other and in series with the central patches.

Under the surface piece is a three-dimensional body to understand the spatial extent along a first direction is small compared to the spatial dimensions along the other two directions that are orthogonal to the first direction. The direct contact between the heat source and the heating plate prevents heat radiation loss. The hot plate is, for example, a hotplate, which may in particular be made of glass ceramic or cast iron. Likewise, the heating plate may be formed as a wall of a cooking chamber, for example a baking oven. Thereby, the maximum temperature of the heater compared to the prior art can be reduced to about 450 ° C. This leads to an increase in the efficiency. Tests have shown that efficiencies of up to 80% can be achieved in accordance with the IEC 350 (1970) standard. In any case, an efficiency of 70% can be achieved. The heating device according to the invention also has the advantage that the heating plate together with the heating device can be designed to be particularly flat, since the air gap between the heating plate and the heating device and a thick insulation are not required. Due to this design, the hob or the oven can be heated very quickly and the desired temperatures are quickly adjustable.

As regards the geometric configuration of the heating device, it is provided that the heating device has a plurality of rectangular area pieces, which are interconnected according to a predetermined scheme. For rectangular area pieces, the electrical resistance and thus the heating power can be calculated exactly in advance, so that a desired temperature distribution can be set.

Furthermore, it is provided that the heating device has a central rectangular area piece and at least two lateral rectangular area pieces which are arranged parallel to one another and symmetrically. This can be influenced by the dimensions of the patches their ohmic resistance and thus their heat output, so that the temperature distribution in a simple manner adjustable.

In addition, it is provided that the central rectangular area piece and the at least two lateral rectangular area pieces are dimensioned and arranged such that they cover a circular area as completely as possible. Since the circular area is usually the preferred form of a cooking plate, can be adjusted in this way the highest possible efficiency.

Circuit technology is provided that the lateral surface pieces are connected in parallel with each other and in series with the central surface piece. As a result, a symmetrical temperature distribution is ensured and there is also the possibility of influencing the radial temperature distribution on the circular area by the choice of the widths of the patches.

It is preferably provided that the at least one surface piece is made essentially of graphite. It is a low-cost and easily processable material that has suitable specific electrical resistance values.

For example, it can be provided that the at least one surface piece has a sheet resistance between 5 and 200 ohms per cross-sectional area. With such resistance values can be achieved at usual electrical voltages, the desired temperature values and heat outputs.

In the preferred embodiment it is provided that the conductor tracks are made of metal. Metals have a relatively low electrical resistance, so that the heat losses are kept low and no heating takes place in those places where this is not desirable.

In particular, it can be provided that the interconnects are made of aluminum, gold, silver and / or similar metals. These metals are particularly resistant to corrosion.

Furthermore, it is provided that the interconnects have a sheet resistance of less than 200 milliohms per cross-sectional area. These resistance values can be used to prevent unnecessary energy losses and unwanted heating.

In the preferred embodiment it is provided that the dielectric layer is made of ceramic powder and a sol-gel solution. This can be a suitable mixture put together to obtain the desired electrical and mechanical properties of the dielectric layer.

In particular, it can be provided that the ceramic powder comprises one or more metal oxides, metal nitrides, metal carbides and / or the like. For example, aluminum oxide or silicon oxide as well as aluminum nitride or silicon nitride are suitable for this purpose.

Furthermore, it can be provided that the sol-gel solution comprises one or more silicon compounds. Thus, the dielectric layer is inexpensive and easy to produce. Corresponding methods for applying the dielectric layer are in the international applications WO 96/29447 and WO 02/72495 described.

Furthermore, it is provided that the dielectric layer is applied to a substrate. This makes it possible to produce particularly thin dielectric layers with the desired properties. Experiments, in particular the high-voltage test according to the standard IEC 335-2-6, have shown that with cooktops a layer thickness of, for example, 500 μm is sufficient to meet the requirements.

It is preferably provided that the dielectric layer is applied to the heating plate. This can be provided with little material-technical effort a hob with heater. In this case, the dielectric layer can be applied directly to the underside of the cooking plate and on the dielectric layer are the heat-generating surface pieces and the electrical conductor tracks. In this way, a particularly compact glass-ceramic hob with integrated heating device can be provided. Similarly, this technology can provide a heater for an oven. In this case, one or more walls of the oven are designed as a hot plate or equipped with a hot plate. This can provide an oven that has a large in relation to its external dimensions interior.

According to a further aspect, it can be provided that the heating device has a plurality of similar area pieces, which are arranged in such a way around a circular ring surface as completely as possible. This makes it possible to obtain a substantially uniform temperature distribution within the annular surface. The annular surface is a preferred geometric section for a hob.

For this purpose, it can be preferably provided that the similar surface pieces are electrically connected in series and / or parallel to each other, wherein the row always has the same number of surface pieces. This also contributes to a uniform temperature distribution.

Furthermore, it can be provided that the annular surface is arranged concentrically with the circular surface. This makes it possible to provide a cooking surface consisting of a circular surface and a circular ring surface, in which the temperature distribution can be set as desired.

In addition, there is the possibility that the heating device has a plurality of concentric annular surfaces, each having similar surface pieces. This makes it possible to provide a hob, which can be actuated area-wise and in which any desired temperature distribution can be set.

According to the invention, a cooking appliance is furthermore provided which has at least one heating plate and at least one heating device described above. Due to the inventive design of the heater, the cooking appliance can be made very compact. As a result, the space requirement compared to the prior art is substantially reduced. If the cooking appliance is a cooking plate, then it can be made particularly flat with the heating device according to the invention. Is it in the cooking appliance to an oven in which one or more side walls have the heating device according to the invention, so the oven can form thin-walled. This has the advantage that the interior of the oven is relatively large in relation to its outer dimensions. In addition, the oven has a relatively high efficiency due to the heating device according to the invention.

For the method for producing a heating device for a cooking appliance or the like, it is provided according to the invention that the substrate is formed by a heating plate. In the method according to the invention, the electrically conductive layer is applied directly to the heating plate. In particular, the substrate can be formed by a hob. Since the hob is heated directly, relatively low temperatures are sufficient to provide the required cooking performance. At low temperatures, the glass ceramic hob acts as an electrical insulator. This has the advantage that an additional electrically insulating layer can be made thin or is not required at all.

Further features, advantages and particular embodiments of the invention are the subject of the dependent claims.

FIG. 1

eine schematische Ansicht einer bevorzugten Ausführungsform der erfindungsgemäßen Heizvorrichtung.

A preferred embodiment of the invention is explained below in the figure description with reference to the accompanying drawings. It shows:

FIG. 1

a schematic view of a preferred embodiment of the heating device according to the invention.

In FIG. 1 a schematic view of a heating device according to the invention is shown. The heating device comprises a plurality of rectangular patches 10, 12, 14 and electrical traces 16, which are arranged substantially in a plane. Both the surface pieces 10, 12, 14 and the electrical interconnects 16 are applied to a dielectric layer, not shown, which in turn is applied to the underside of a hotplate of a glass ceramic cooktop. The patches 10, 12, 14 are made of graphite and have a relatively high electrical resistance. The electrical sheet resistance is preferably between 5 and 200 Ω per unit area. About the electrical traces 16, the patches 10, 12, 14 connected to an electrical power source P, N, where P represent the phase terminals and N represent the neutral terminals. The electrical conductor tracks 16 are made of metal, preferably of aluminum, gold, silver or the like. The electrical sheet resistance of the conductor tracks 16 is preferably less than 200 mΩ per unit area. Since the electrical resistance of the sheets 10, 12, 14 is relatively large compared to that of the printed conductors 16, almost all the electrical energy from the sheets 10, 12, 14 is converted into thermal energy. Since the patches 10, 12, 14 are particularly flat and lie directly against the dielectric layer of a heating plate, the efficiency is particularly high. Experiments have shown that up to about 80% of the electrical energy is converted into heat energy that can be used on the glass ceramic hob. The maximum temperature of the surface pieces 10, 12, 14 is about 450 ° C. This temperature is sufficient because the surface pieces 10, 12, 14 are very close to the glass ceramic hotplate. Conventional heaters require a temperature of about 1100 ° C.

In the Fig. 1 shown heater is provided for a hob, which has an inner zone 18 and an outer zone 20 includes. The inner zone 18 is in the form of a circular area, while the outer zone 20 is in the form of a circular ring area, so that the two zones 18 and 20 together form an enlarged circular cooking surface. The inner zone 18 comprises three area pieces, namely a central area piece 10 and two lateral area pieces 12. The central area piece 10 is approximately twice as wide as the lateral area pieces 12. The central surface piece 10 and the two lateral surface pieces 12 are arranged parallel to one another. With regard to their dimensions, the surface pieces 10 and 12 are designed so that they cover the circular inner zone 18 as completely as possible. The two lateral surface pieces 12 are connected in parallel with each other. Furthermore, the two lateral surface pieces 12 are connected in series with the central surface piece 10. The electrical conductors 16 are always coupled to the end faces of the surface pieces 10 and 12. The interconnection and dimensions of the patches 10 and 12 cause the heating power and the temperature within the inner zone 18 to be substantially evenly distributed.

In the outer zone 20, which is formed as a circular ring surface, there are nine rectangular outer surface pieces 14 which are arranged approximately uniformly. Adjacent area pieces 14 are electrically coupled via their end faces. By means of the electrical conductor tracks 16, the nine outer surface pieces 14 are connected to one another in such a way that in each case three surface pieces 14 are interconnected in series and these three groups are in turn connected in parallel to one another. By choosing the dimensions of the surface pieces 14 and their interconnection, the desired heating power and the temperature distribution can be fixed. The surface pieces 14 are arranged within the outer zone 20 so that they are as possible allow uniform distribution of the heating power and the temperature within the zone 20.

The dielectric layer is arranged between the surface pieces 10, 12, 14 and the electrical conductor tracks on the one hand and the underside of the glass ceramic hot plate on the other. The dielectric layer is made of a ceramic powder and a sol-gel solution. The ceramic powder includes, for example, alumina and / or silica. Alternatively, the ceramic powder and other oxides or nitrides such. B. aluminum nitride or silicon nitride. The technology and the methods for producing the dielectric layer are described, for example, in the international applications WO 02/72495 and WO 96/29447 described.

reference numeral

10

central surface piece

12

lateral patch

14

outer surface piece

16

electrical trace

18

inner zone

20

outer zone

P

phase connection

N

Neutral connection

Claims (16)

1. Heating device for a cooking appliance or the like which has the following:

   - a plurality of surface elements (10, 12, 14) for producing heat from electric current;

   - electric conductive strips (16) for current supply to the surface element (10, 12, 14) which are coupled to the surface elements (10, 12, 14) according to a predetermined scheme; and

   - a dielectric layer, to the one side of which the conductive strips (16) and the surface elements (10, 12, 14) are attached and the other side of which is intended for direct contact with a heating plate,

   characterised in that

   - the heating device has a rectangular central surface element (10) and two rectangular lateral surface elements (12) which are arranged parallel and symmetrical to one another,

   - the central surface element (10) and the two lateral surface elements (12) have dimensions and are arranged so that they cover a circular area (18) as completely as possible,

   - the central surface element (10) is designed to be about twice as wide as the lateral surface elements (12),

   - the electric conductive strips (16) are coupled to the end-face sides of the surface elements (10, 12, 14), and

   - the lateral surface elements (12) are connected in parallel with one another and in series with the central surface element (10).
2. Heating device according to claim 1, characterised in that the surface elements (10, 12, 14) are produced essentially from graphite.
3. Heating device according to claim 1 or 2, characterised in that the surface elements (10, 12, 14) have a surface resistance between 5 and 200 Ohm per cross-sectional area.
4. Heating device according to one of claims 1 to 3, characterised in that the conductive strips (16) are produced from metal.
5. Heating device according to claim 4, characterised in that the conductive strips (16) are produced from aluminium, gold, silver and/or similar metals.
6. Heating device according to one of claims 1 to 5, characterised in that the conductive strips (16) have a surface resistance of less than 200 milliohm per cross-sectional area.
7. Heating device according to one of claims 1 to 6, characterised in that the dielectric layer is produced from ceramic powder and a sol-gel solution.
8. Heating device according to claim 7, characterised in that the ceramic powder comprises one or more metal oxides, metal nitrides, metal carbides and/or the like.
9. Heating device according to claim 7 or 8, characterised in that the sol-gel solution comprises one or more silicon compounds.
10. Heating device according to one of claims 1 to 9, characterised in that the dielectric layer is applied to a substrate.
11. Heating device according to claim 10, characterised in that the dielectric layer is applied to the heating plate.
12. Heating device according to one of claims 1 to 11, characterised in that the heating device has a plurality of similar surface elements (14) which are arranged so as to cover a circular ring surface (20) as completely as possible.
13. Heating device according to claim 12, characterised in that the similar surface elements (14) are connected electrically in series and/or in parallel to one another, wherein each parallel row always has the same number of surface elements (14).
14. Heating device according to claim 12 or 13, characterised in that the circular ring surface (20) is arranged concentrically with the circular surface (18).
15. Heating device according to one of claims 12 to 14, characterised in that the heating device has a number of concentric circular ring surfaces (20) having in each case similar surface elements (14).
16. Cooking appliance having at least one heating plate and at least one heating device according to one of claims 1 to 15.

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