Heating device for an inductive cooking device

[0001] The basis of the invention is a heating device for an induction cooker according to the preamble of claim 1.

[0002] From US 6,633,023 B2, an induction cooker with several inductors is known, which is provided for heating a single heating element, for example one large pot, and is arranged accordingly. Depending on the size of the pot, one or several inductors can be connected via a connecting means to a generator which, when heating the heating element, will induce these inducers to vibrations (i.e. excite electromagnetic field vibrations). From EP 0 926 926 A1, an induction cooker is known which has several oscillating circuits, each with a single inductor and with at least one capacitor.

[0003] The object of the present invention is to provide such a device with which it is possible to efficiently heat various cooking containers.

[0004] According to the invention, this task is solved by the features of claim 1, while preferred embodiments and further developments of the invention are given in the dependent claims.

[0005] The basis of the invention is a heating device for an induction cooker with a first vibrating circuit, which comprises at least a first inductor for transmitting heating energy to a heated heating element and a first system for exciting the first vibrating circuit and supplying heating energy to the inductor.

[0006] It is proposed that the heating device includes at least one second inductor for the transmission of heating energy to the heated heating element, which will be part of the first vibrating circuit, and a switching means through which the heating energy can only be selectively supplied to one of the inducers or simultaneously to both inductors in a parallel system. By supplying heating energy of choice to only one of the inductors or simultaneously to both inductors, it is possible to heat both small and large or longitudinal cooking containers on one single heating zone. Thanks to the parallel connection of both inductors, inductors with different impedances can be used. Inductors need not necessarily have the same or at least similar impedances as it is advantageous for serial connection, but for example a large main inductor and a much smaller auxiliary or auxiliary inducer can be used. Thanks to the free choice of inductors, a large number of differently shaped induction cookers with a uniform concept can be designed.

[0007] One or two inductors can be connected via the connection means, preferably directly, to the system for excitation of the first vibrating circuit. An induction cooker can be particularly simple if the heating energy is supplied by connecting voltage drawn from the mains. An additional oscillating circuit can be dispensed with. The system for excitation of the first oscillating circuit preferably comprises a half-bridge system. In a particularly inexpensive embodiment of the invention, the second inductor only works together with the first inductor.

[0008] Both inductors are preferably used to heat a single heating element, for example a single pot. They are located in the immediate vicinity of each other. Large and oblong cooking appliances can be heated particularly efficiently if the inductors are placed in a continuous heating zone to heat one single heating element.

[0009] The threat of uneven heating of the cooking utensil by both inductors can be counteracted if the heating powers of both inductors are in a constant, predetermined proportion to each other. For example, one inductor, which, compared to the other inductor, is assigned a smaller part of the heating zone (subzone), can generally work with less power than the other.

[0010] Particularly convenient operation of the induction cooker can be achieved when both inductors can be connected individually to the first system via a switching (switching) means. The operator can treat both inductors in the same way, and a small pot can be adjusted for heating, e.g. to choose from one or the other inductor.

[0011] In a further embodiment of the invention, the heating device comprises a rectifier, to which is attached both the first vibrating circuit and the second vibrating circuit with the second arrangement for excitation of the second vibrating circuit and with the subsequent inductor. As a result, one single cooking zone for heating one single cooking utensil can be heated efficiently by three or more inductors, with only one generator and rectifier being used, and the high power required can be supplied by two vibrating circuits.

[0012] Unpleasant noises when heating the cooking utensil can be avoided by using a control unit that is prepared to control the systems in such a way that the first system excites the first vibrating circuit always at the same frequency with which the second system excites the second circuit vibrating. The simultaneous activation of the vibrating circuits can be performed independently of the operation of the induction cooker.

[0013] In addition, it is proposed that the heating device comprise a further system for excitation of another oscillating circuit with a subsequent inductor and a subsequent connecting means, the latter arrangement being able to be connected by this subsequent connecting means to a choice with the first or the subsequent oscillating circuit. Both excitation systems can send a lot of power to the first oscillating circuit, without requiring a particularly heavy load on the electrical components (components) of one of the systems. This next system can support the first system with its power.

[0014] The heating device preferably comprises a means that is intended to measure one property of the vibrating circuit, in turn with the connection means open and closed, and to recognize whether the heating element is positioned above only one or both inductors. It can be automatically recognized, for example by means of the control unit, whether the heating element is to be sufficiently heated by one inductor or more evenly by both inductors, and the switching means can be switched on automatically according to the more effective variant. The operator can be saved the decision whether to use one or two inductors for heating the heating element.

[0015] The heating device preferably comprises a control unit which is intended to activate the switching means at a time when no voltage is applied to the oscillating circuit excitation system. This makes it possible to achieve safe switching of the switching means without particularly stressing the electric components of the induction cooker. The control unit is preferably prepared to interrupt the voltage before switching on the switching means or to set it to the set value.

[0016] Further advantages result from the following description of the drawings. The drawing shows embodiments of the invention. The drawing, description and claims contain numerous features in combination with each other. The skilled person will consider these features preferably individually and will be able to combine them into further advantageous combinations.

[0017] The figures show:

fig. 1 schematic cross-sectional view of the pot and induction hob part, fig. 2 connection diagram of the vibration circuit With two inductors and the connecting means between the two inductors, fig. 3 five different cooking zones for an induction hob with several sub-zones (partial zones) heating devices, each of which is assigned to one inductor, Fig. 4 block diagram of a heating unit as in Fig. 2, Fig. 5 block diagram of another heating unit with three inductors and two systems, each to excite one vibrating circuit, Fig. 6 connection diagram of another heating device with two inductors and one connecting means, with which one of both inducers or both inductors can be selected at the same time, fig. 7 heating powers of different vibrating circuits or inductors, each marked on its excitation frequency and fig. 8 connection diagram of another heating device with three inductors and a second system that can be used to strengthen the first circuit to excite the vibrating circuit.

[0018] Figure 1 shows a cross section through a pot 2 with the bottom of the pot, which is provided as a heating element 4 for the liquid or food contained in the pot 2. The pot 2 stands on the support plate 6 of the induction cooker cooking field 6, under which the support plate is located there is a heating device 8 for induction heating of the heating element 4. The heating device 8 comprises several winding blocks 10, each comprising an inner coil and an outer coil. At the same time, the internal coils form the first inductor 12 and the external coils form the second inductor 14. The magnetic field created by both inductors 12, 14 is directed by the directional structure towards the heating element 4 and, when flowing through the heating element 4, produces eddy currents that heat the heating element. 4. The control unit 18 controls the production of the magnetic field.

[0019] Figure 2 shows a connection diagram of a heating device 8, which is designed for an alternating voltage of the electrical network 20. The heating device 8 includes both inductors 12, 14, capacitive element 22 with two capacitors, made as a half-bridge circuit, system 24 with two transistors power 28 for connecting the switching voltage to one or both of the inducers 12, 14 and comprising two diodes. By means of the system 24, in addition to the first inductor 12, a second inductor 14 can be connected. System 24, capacitive element 22 and one or both of the inductors 12, 14 form an oscillating circuit 32, which can be excited by the system 24, the system 24 supplies heating energy to heat the heating element 4 to one or both of the inducers 12, 14.

[0020] The elements of the heating device 8 shown in figures 1 and 2 will be used below to explain some examples, the same or similar elements being given the same references, respectively. [0021] The first inductor 12 is located under the first heating subzone 34 (a partial area of ​​the heating zone) of the support plate 6, which zone is shown in the connection figure supplying the rectifier 26, connecting 30

3. The second inductor 14 is located under the second heating subzone 36 (partial heating zone area). The two heating subzones 34, 36 are located directly next to each other and together form a heating zone 38 for heating the oval or elongated heating element 4 of a cooking utensil, e.g. a saucepan or roasting pan. In the position of the connecting means 30 shown in Figure 2, only the first inductor 12 is connected to the system 24 to excite the oscillating circuit 32.

In contrast, the second inductor 14 does not vibrate simultaneously when the oscillating circuit 30 0 is excited by the system 24. The heat in the heating element 4 is therefore only generated by the magnetic field generated by the first inductor 12. This position of the connecting means 30 is suitable for heating a small pot 2 with a small heating element

4, which stands on the first heating subzone 34. If a larger, elongated pot 2 can be used, the connection means 30 can be closed and a second inductor 14 can be connected to the system 24. Now both inductors 12, 14 vibrate, thus the field is fed into the full heating zone 38 magnetic element intended for heating the heating element 4. The second inductor 14 may have less power in this example than the first inductor, because the second heating subzone 36 is slightly smaller in surface area than the first heating zone 34. The heating powers of inductors 12, 14 are always in a fixed, predetermined proportion to each other.

[0023] For heating large, circular pots, a heating zone 40 with two subzones 42, 44, arranged concentrically to each other, as shown in figure 3, is particularly suitable. The smaller first heating subzone 42 is in this case surrounded by a larger ring shape, the second heating subzone 44. To heat the small pot 2, the connecting means 30 is open, therefore the first inductor 12 is connected to the system 24. To heat the larger pot 2, the connecting means 30 closes, and the second inductor 14, which in this example is made more powerful than the first inductor 12, is also connected to the system 24 to excite the vibrating circuit 32.

[0024] Figure 4 shows a block diagram of the heating device 8 of figure 2. The heating device 8 comprises a rectifier 26, system 24, both inductors 12, 14 and connection means 30.

[0025] The block diagram in figure 5 shows an alternative heating device 46 in which two systems 50, 52 are connected to its rectifier 48 to excite the respective vibrating circuits 54, 56. The first oscillating circuit 54 includes two inducers 58, 60, with whose inductor 60 can be connected to the first system 50 via a connecting means 62. The second oscillating circuit 56 comprises only one single inductor 64. Both systems 50, 52 can be controlled each separately by the control unit 18, therefore one, two or three inductors 58, 60, 64 can be activated by means of the switching means 62. Such a heating device 46 is particularly suitable for the heating zone 66 shown in figure 3 with three heating subzones 68, 70, 72 for a small, medium and very large pot 2. To heat a large pot 2 or large heating element 4 on heating zone 66 when using both systems 50, 52, the control unit 18 always drives both systems 50, 52 so that all induced inducers 58, 60, 64 are excited to vibrations with the same frequency to avoid interference in the pan 2.

[0026] Figure 6 shows a heating device 74, which is particularly suitable for heating zones 76, 78, as shown in Figure 3. For excitation of the oscillating circuit 32, two inductors 80, 82 can be individually or jointly connected to the system 24, each at with one connecting means 84, 86. Inductors 80, 82, for example, have the same power ranges and are therefore particularly suitable for placing under the same heating subzones 88, 90 or 92, 94 heating zones 76 or 78, each of which is intended for heating a very small or small pot 2 or for joint heating of medium (medium-sized) or large elongated pot 2. To heat a very small or small round pot 2, inductors 80, 82 can be connected to each separately in system 24. To heat a medium-sized or large, elongated pot 2, both connecting means 84, 86 are closed and connects both inductors 80, 82 with the system 24, and thus they are stimulated to transmit energy to the heating element 4.

[0027] The diagram in figure 7 shows the power P of inductors 12, 14 or 80, 82 applied depending on the switching frequency f_s of system 24. The power P is plotted as related to the maximum power P_maxinductor 12 or 80 or 82 connected individually, and the switching frequency f_s is normalized to the resonance frequency f_r oscillating circuit 32 with only one connected inductor 12 or 80 or 82. The curve 96 indicates the power of inductor 12 or 80 or 82 connected individually to system 24. To control the power P of inductor 12 or 80 or 82, the control unit 18 sets the corresponding switching frequency fs in the range between e.g. 1.0 f_r and 1.8 f_r. In this example, the power may vary between P_maxand 0.2 P._max · If two systems 50, 52 are available, as in the heating device 46 of figure 5, then the total power of both inducers 58, 64 together - with the inductor disconnected 60 can reach the value of 2 Pmax, as shown in curve 98. If, on the other hand, as shown in figures 2 and 4, only one system 24 with two inductors 12, 14, both of which are connected to and excited by system 24, only the maximum total power of both inductors 12, 14 is available, amounting to approximately 1 , 4 Mon,_ax, as shown in curve 100. The power of each individual inductor 12, 14 is represented by curve 102.

[0028] As can be seen from the curves 96, 98, 100, 102, not only the power P is shifted when the switching means 30 is switched on, but also the resonant frequency f_r oscillation circuit 32. Therefore, before switching on the switching means 30, the control unit 18 interrupts the voltage supplied to the inductors 12, 14 or 80, 82 to avoid a high load on the electrical components of the heating device 8, 46, 74. As can be seen from Figure 7, the closing of the connection means 30 leads to an increase in the total power of both inductors 12, 14 together compared to the power of a single inductor 12, but the individual powers of inducers 12, 14, which are represented by curve 102, decrease in relation to to the individual power of the inductor 12 alone connected to the system 24, [0029] Figure 8 shows another embodiment with which this relative power loss can be counteracted. A heating device 104 is shown in which those elements which are the same as in the heating element 8 are marked with substantially the same reference numerals. With regard to features and functions that have remained the same, reference may also be made to the embodiment in Figures 2 and 4. The heating device 104 has a further circuit 106 to excite another vibrating circuit / circuit 108 with a further inductor 110. In addition, the heating device 104 includes two further connecting means 112, 114, which - like the connecting means 30 are actuated by the control unit 18. Depending on the position of the connecting means 112, 114, the inductor 110 can be connected to the system 106, and the inductors 12, 14 with system 24, or inductor 110 with systems 24 and 106, or inductors 12, with systems 24 and 106. With closed connection means 30 both systems 24 and 106 can thereby induce inductors 12, 14 and thus - without a heavy load of electrical components 24, 106 - both inductors 12, 14 can work individually, each according to curve 96 shown in Figure 7, or together with the power P according to curve 98. It is particularly suitable for use with a heating zone 40 with correspondingly large heating subzones 42, 44 for heating a very large pot 2. However, it is also possible to position all three inductors 12, 14, 110 directly next to each other for use with heating zone 66, so that heating subzones 68, 70 work with particularly high power P, or that all three heating subzones 68, 70, 72 work with the power of P.

[0030] To recognize whether, for example, in the heating zone 40 a small pot 2 is set only on a heating subzone 42 or if the large pot is also set up in a subzone 44, a control unit 18 is provided for determining the size associated with the inductance of the vibrating circuit 32 . By measuring this value, both with the connection means 30 and the connection means 30 open, it can be concluded whether the cooking zone 40 has a large or small pot 2, and the connection means 30 can be switched accordingly to effectively heat the pot 2 or. its heating element 4.

References [0031] pot heating element support plate heating device winding blocks inductor inductor inductor control unit electric power supply element system rectifier power transistor connecting means vibrating circuit heating subzone (partial area heating subzone (partial area heating zone heating zone heating subzone (partial area heating subzone (partial area heating device rectifier system layout vibrating circuit vibrating circuit inductor inductor connection means inductor heating zone heating subzone (partial area heating subzone (partial area heating subzone (partial area heating device heating zone heating zone heating zone heating zone inductor) heating zone) heating zone) cooking zone) cooking zone) cooking zone) heating zone) inductor connection medium connection medium heating subzone heating subzone heating subzone heating subzone curve curve curve curve heating device system oscillating circuit inductor connection center connection center (area (area (partial area partial partial heating zone) cooking zone) cooking zone) cooking zone)

BSH Bosch und Siemens Hausgerate GmbH Representative:

83P3O192PLO0 EP 1 854 337 Bl