Device for converting inductively transmitted electric power, and method for the production of such a device

A consumer unit (7) for converting inductively transmitted electric power. The device comprises at least one secondary coil (5) for accepting power from a alternating electromagnetic field. The secondary coil (5) is electrically connected to at least one consumer in which the electric power is converted. The consumer unit (7) is designed as a replaceable module for an induction furnace (25).

This application is a National Stage completion of PCT/EP2008/000458 filed on Jan. 22, 2008, which claims priority from German patent application serial no. 10 2007 004 275.4 filed Jan. 23, 2007.

FIELD OF THE INVENTION

The invention relates to a device for converting inductively transmitted electrical energy in an accommodating unit and a consumer unit, to a consumer unit for converting inductively transmitted electrical energy and to a method for the production of a consumer unit according to the invention.

BACKGROUND OF THE INVENTION

Such consumer units may be in particular cooking vessels for use in induction ovens. The mode of operation of an induction oven is based on the fact that such cooking vessels exhibit metal layers, in which heat is produced by means of eddy current generation by induction owing to the nonreactive resistance of the metal layers. Such a metal layer may be, for example, a metallic pot base, an aluminum shell or else a metal layer which has been glazed into a porcelain shell. Said metal layers make it possible to rapidly heat food by means of a high level of power transmission. However, there is often the difficulty of achieving a desired heat distribution, such as homogeneous heating, for example, over a relatively large area of the cooking vessel. This problem in particular arises from the fact that it is difficult primarily with the flat coil arrangements often used for producing the required electromagnetic alternating field to achieve a defined, in particular homogeneous heat distribution.

The abovementioned problem has a disadvantageous effect in particular when comparatively dry products need to be heated or when the geometry of the cooking vessel does not exhibit rotational symmetry, or only exhibits a small amount of rotational symmetry. When designing the described systems for inductively heating food, there is therefore often a conflict of aims which consists in on the one hand designing said conducting layer in such a way that defined heating, such as heating which is as homogeneous as possible, for example, of the area of interest results, but on the other hand achieving an efficiency which is as high as possible of the electromagnetic coupling of the cooking vessel to the alternating field achieving the desired currents. Similar conflicts of aims also result when realizing other withdrawable elements in induction ovens, where it is likewise necessary to find a compromise between good coupling to an external electromagnetic alternating field and efficient utilization of the electrical energy transmitted.

SUMMARY OF THE INVENTION

It is therefore the object of the present invention to specify a device and a method which makes it possible to design cooking vessels or other withdrawable elements for induction ovens with coupling to an external electromagnetic alternating field which is as efficient as possible in such a way that, at the same time, utilization which is as efficient as possible of the electrical energy transmitted is ensured.

This object is achieved by the devices having the features mentioned in claims1and13and by the method having the features mentioned in claim11. The dependent claims relate to advantageous developments and variant embodiments of the invention.

The device according to the invention for converting inductively transmitted electrical energy exhibits an accommodating unit for accommodating at least one replaceable consumer unit.

The consumer unit according to the invention for converting inductively transmitted electrical energy exhibits at least one secondary coil for drawing energy from an electromagnetic alternating field. In this case, the secondary coil is electrically connected to at least one consumer, in which the electrical energy is converted. Said consumer unit is in the form of a replaceable module for an induction oven.

In accordance with the teaching of the invention, the consumer unit therefore exhibits at least two regions, which need to meet different demands. The first region is the region in which the secondary coil is arranged. The main demand placed on this region and therefore on the secondary coil consists in ensuring that electrical energy is drawn from said electromagnetic alternating field in a manner which is as efficient as possible. However, owing to the configuration of the consumer unit according to the invention, there are also further options for the design of the secondary coil. The secondary coil can be optimized to the extent that it draws the electromagnetic energy particularly efficiently from the electromagnetic alternating field; this is primarily possible by virtue of the fact that it is not necessary for any further consumers to be arranged in the region of the secondary coil which would give reason for compromises in the design of the region. In one variant of the invention, the secondary coil is formed as part of a printed circuit board, in particular as ring-shaped or spiral-shaped conductor tracks.

The consumer unit can have, as first consumer, an induction coil which is electrically connected to the secondary coil in particular by means of lines.

In addition, a temperature-regulated switch such as a thermostat, for example, can be arranged in the electrical connection between the secondary coil and the consumer.

A further advantage of the above-described solution according to the invention consists in the fact that the energy transmission from the induction oven into the consumer unit takes place in wireless fashion, i.e. without a DC link. This opens up the possibility in particular of using the control device, the coding system and the control panel of the induction oven such that the electrical internals in the consumer unit can be provided with a simple design, especially for applications in which the consumers are in the form of heating elements. This provides the possibility of transmitting high powers with the compact arrangements and in particular designing heating devices in such a way that they can be used as storage and transport containers specifically for applications in the catering sector in passenger aircraft.

Since the energy transmission takes place in a defined region, namely in particular in the region of the secondary coil, furthermore those regions of the overall arrangement, in particular the consumer unit, which are affected by strong electromagnetic alternating fields can be effectively limited. This means that legal requirements as regards electromagnetic compatibility which are of considerable importance in particular in the field of aviation can be adhered to more easily.

The consumers in the form of heating elements can in this case be realized as structured conducting regions in cooking vessels which are suitable for converting electrical current, owing to its nonreactive resistance, into heat and which are designed in such a way that the total flux beneath them results in a desired heat distribution. In this way, the above-described problem of undefined heating is effectively counteracted, and the formation of hot spots or else cold spots is avoided. Since, in accordance with the teaching of the invention, the consumers are used exclusively for converting the electrical energy drawn on the part of the secondary coil, there is an increased degree of freedom in terms of the design of the consumers, which in this case are formed as structured conducting regions, with the result that the design can be optimized in terms of the above-described desired heat distribution in certain regions of the cooking vessels. Such a desired heat distribution could, for example, consist in the fact that a higher temperature, in comparison with the peripheral regions of the base, is set in the region of the center of the base of a cooking vessel. As a result of this temperature distribution, the fact that, in cooking vessels, the greatest volume of food to be heated is generally located in the central region of the vessel is taken into account. The desired temperature distributions can be achieved, for example, by virtue of the fact that the dimensions, in particular the thickness or the width of the conducting regions are varied suitably.

Designing the cooking vessels to be formed from porcelain has proven to be particularly successful in this context; said conducting regions can be overglazed in a simple manner onto such vessels. In one variant of the invention, the conducting regions can also be applied by virtue of the fact that the cooking vessel is initially provided with a conducting layer, which is then partially removed by means of a sandblasting method. For the structuring of the conducting regions, it has in this case proven advantageous to remove the conducting layer using a mask, by means of which individual regions of the layer can be protected from the sandblasting.

It goes without saying that it is also conceivable, as an alternative to an embodiment made from porcelain, to produce the cooking vessels at least partially from cardboard, which results in a cost and weight advantage. Conducting regions for example in the form of a structured aluminum layer can also be applied to such cooking vessels.

There is a large number of possibilities for the selection of the consumer; in particular the consumer may be a coffee machine, a toaster, a waffle iron, a fryer, a sandwich maker, a baking oven, in particular a hot air oven, a water heater or water boiler, a grill plate, an egg cooker, an extractor hood or a microwave.

It is apparent from the outlined choice that the invention opens up the possibility of converting the energy transmitted inductively via the secondary coil into the consumer unit, whilst producing heat, into a large number of energy forms, in particular kinetic energy or electromagnetic field energy.

In the upper parts of subfigures1a-1c,FIG. 1shows various variants for the design of the consumers designed as conducting regions1, in a plan view of the base of a cooking vessel2. The conducting regions1in the example shown are produced by virtue of the fact that insulating regions3are removed from an overall conducting region. In the lower parts of subfigures1a-1c, the corresponding temperature distributions are illustrated as thermal images. In this case it can easily be seen fromFIG. 1athat a ring-shaped configuration of the insulating regions3in the peripheral region of the base of the cooking vessel2results in comparatively strong heating of the peripheral regions of the base of the cooking vessel2, while the central region remains relatively cool. The secondary coil is in this case formed by the connected conducting regions1. The design of the conducting regions1in this case in particular opens up the possibility of compensating for local inhomogeneities in the electromagnetic field produced by the primary coil or altering the heating in a defined manner.

Heating of the central region of the base of the cooking vessel2can be achieved by the measure shown in subfigure 1b: in this case, a further insulating region3′ is arranged in the central region. The influence of the alignment of the further insulating region3′ can be seen from subfigure 1c.

FIG. 2shows, in a sectional illustration, a further embodiment of the invention in which the consumer is in the form of a toaster. In this case, the secondary coil5and the heating elements12, which are connected to the secondary coil5via electrical conductors10, are arranged in the interior of the consumer unit7. The grating13, which is used for mounting the slices of toast14, is fitted in the region between the flat heating elements12. The overall consumer unit7can be introduced into and removed from an induction oven (not illustrated) by means of the handle16in the direction of the arrow15. Since the functionality of the toaster merely consists in providing electrical power loss in the form of heat in the heating elements12acting as nonreactive resistors owing to the current induced in the secondary coil5, when realizing the toaster according to the invention it is possible to dispense with providing complex passive and active electronic components in the interior of the consumer unit7. As a result, this leads to a very simple possibility of realizing the toaster according to the invention.FIG. 2shows the components outside of an induction oven (not illustrated); naturally these components are arranged in the interior of an induction oven during normal operation.

FIG. 3represents a variant of the invention in which an extractor with the fans8is realized by means of the consumer unit7. The figure illustrates the arrangement of the consumer unit7in relation to a withdrawable unit9arranged beneath the consumer unit7; in this case, the withdrawable unit9is configured, for example, in such a way that it can accommodate cooking vessels with food to be heated. In order to improve the clarity of the figure, the induction oven which accommodates the consumer unit7and the withdrawable unit9during operation is omitted; the arrow10indicates the direction in which the consumer unit7and also the withdrawable unit9can be removed from the induction oven (not illustrated) or in which the steam guided away by the extractor escapes. The secondary coil5, which is electrically connected to the fans8and draws electrical energy from an electromagnetic alternating field produced by a primary coil (not illustrated), is arranged in the rear region of the consumer unit7.

FIG. 4illustrates the arrangement shown inFIG. 3using an equivalent circuit diagram. The full mid-frequency voltage is present at the primary coil17in the form of an AC voltage where UMF rms=130-320 volts and at a frequency F of approximately 35-60 kHz. The AC voltage induced in the secondary coil5is converted in the rectifier18into a DC voltage and smoothed by means of the capacitor19. In this case, the capacitor19can have a capacitance of approximately 100 μF. The consumers which, in the case ofFIG. 3, are in the form of fans8are symbolized inFIG. 4as an equivalent resistance23, for example with a resistance value R of approximately 9 ohms. In conjunction with an output voltage of approximately 12 volts at the rectifier, a current of approximately 1.33 A results.

FIG. 5illustrates the geometrical relationships in the region of the rear wall of the induction oven (not illustrated inFIG. 5). In the cooking area rear wall20, the primary coil17is arranged in the housing21. The ferrite22, which extends, via a bay in the housing21and via a recess in the rear side24of the consumer unit (not illustrated) as far as into the inner region of the secondary coil5and in this way ensures a high degree of penetration of the region of the secondary coil5with magnetic flux, is located inside the primary coil17. The ferrite22can in this case exhibit dimensions of approximately 8×22×10 mm; the primary coil17can in particular be formed from eight wires, each having a wire diameter of approximately 0.1 mm with in each case250turns. This results in an expected value for Rcuof approximately 2.7 to 4 ohms and for the inductance L of approximately 2.3 mH. Six wires each having a diameter of 0.2 mm and a respective overall length of approximately 180 cm can be used for the secondary coil5. This results in approximately 20 turns given an average diameter of approximately 38 mm and thus an inductance of approximately 12 μH.

FIG. 6illustrates the arrangement of the consumer unit7in an induction oven25. The figure shows the consumer unit7arranged above a withdrawable unit9when the door of the induction oven25is open.

FIG. 7shows a further variant of the invention which demonstrates the flexibility of design which can be achieved by the invention.FIG. 7illustrates a consumer unit7, which is arranged in the induction oven25and comprises the oven drawer with the first consumer72and the second consumer73. The oven drawer71in this case exhibits the induction coil5, which is connected to the first consumers72, which are likewise in the form of induction coils, via the lines31. The second consumer73has been illustrated in simplified form and schematically as an aluminum shell for heating food. In this case, in the induction oven25, the primary coil17is arranged in the region of the rear wall of the induction oven25; an electrical AC voltage is applied to said primary coil via the feed lines30from an MF generator (not illustrated) of the induction oven25. The electromagnetic alternating field thus produced couples to the secondary coil5when the consumer unit7is in the inserted state, which secondary coil is arranged in the rearward part of the consumer unit7. The electrical AC voltage thus induced is transmitted via the lines31in the oven drawer71to the induction coils72. The electromagnetic alternating field produced by the induction coils72induces electrical currents in the aluminum shell73which, owing to the nonreactive resistance, produce heat, as a result of which food in the aluminum shells73can be heated. In other words, what is involved is a series arrangement of two consumers within the consumer unit7. Owing to the particular arrangement illustrated inFIG. 7, the two consumers72and73are supplied with energy in contactless fashion, inductively and therefore in DC-isolated fashion. As a result, it is possible to convert the design of a contactless or cableless oven drawer71or consumer unit7which improves the operability of the induction oven25according to the invention more decisively. The primary coil17, the secondary coil5and the first consumers72can in this case in particular be in the form of copper coils.

The arrangement according to the invention is explained once again with reference toFIG. 8in a form of an equivalent circuit diagram for illustrative purposes. In this case, the illustration inFIG. 8is restricted to the consumer unit7and the primary coil17(illustrated in the right-hand part of the figure) with the feed lines30. It can clearly be seen fromFIG. 8that the arrangement comprising the secondary coil5, the lines31and the first consumers72is an advantageous possibility of transferring, for example, an electromagnetic alternating field to a point in the consumer unit7at which it is required, depending on the respective demand. The basic principle of the invention is in this case converted in the present example in such a way that the consumer is split into two subconsumers, namely the induction coils72and the aluminum shell73.

FIG. 9likewise shows, in the form of an equivalent circuit diagram, a further variant of the invention which makes very simple temperature regulation possible. In the consumer unit7illustrated inFIG. 9, the consumer74, which may have any desired design, is connected to the secondary coil5of the consumer unit7via the feed lines31. In the way which has already been described, an electrical AC voltage is induced in the secondary coil5via the electromagnetic alternating field of the primary coil17. The defined feed lines31, via which the consumer74, which may be in the form of a heating element, for example, is supplied with voltage, make it possible to introduce the thermostat35into the feed lines31. At a certain predefinable desired temperature, which may be configured so as to be completely controllable, the electrical connection is then isolated from the thermostat35between the secondary coil5and the consumer74. As a result, in comparison with the conventional solution in which there is no physically defined power supply to the heating elements but in which the heating elements are in the form of metallic layers in which physically undefined currents are induced, the particular advantage is achieved that simple temperature regulation can be realized in the consumer unit7itself.