kitchen appliance

Abstract

Kitchen appliance (100), comprising: - an inductor (1) comprising ferrite elements (5) and a winding (2) and by means of which an alternating magnetic field can be generated for heating a cooking vessel (200) in a first operating mode of the kitchen appliance (100) and by means of which an alternating magnetic field can be generated for transmitting energy towards an electrical consumer (300) by means of inductive coupling in a second operating mode of the kitchen appliance (100), - a cooking plate (19) with a support surface (12) on which the cooking vessel (200) to be heated or the electrical consumer (300) is to be placed as intended, and - an electrically conductive, in particular metallic, carrier (3) on which the inductor (1) is arranged, - wherein a distance (4) between a side of the winding (2) facing the electrically conductive carrier (3) and a side of the electrically conductive carrier (3) facing the winding (2) is at least 6 mm, - wherein a distance (13) between a side of the winding (2) facing the mounting surface (12) and the mounting surface (12) is a maximum of 9 mm, in particular a maximum of 7.5 mm, - wherein the distance (4) between the side of the winding (2) facing the electrically conductive carrier (3) and the side of the electrically conductive carrier (3) facing the winding (2) is greater than a height (7) of the ferrite elements (5), and - wherein a distance (8) between a side of the ferrite elements (5) facing the electrically conductive carrier (3) and a side of the electrically conductive carrier (3) facing the ferrite elements (5) is at least 2 mm.

Description

US 2021 / 0 159 730 A1 discloses a system and a device for wirelessly transmitting electrical power.DE 100 06 863 A1 discloses an induction cooking device.US 2016 / 0 135 255 A1 discloses an induction heating device.The object of the invention is to provide a kitchen appliance which can be operated as efficiently as possible in different operating modes.The kitchen appliance has an inductor or an induction coil. The inductor comprises a spiral, planar winding of an electrical conductor. In a first operating mode of the kitchen appliance, an alternating magnetic field for heating a cooking vessel can be generated by means of the inductor. The first operating mode corresponds here to the operating mode of a conventional induction hob. In a second operating mode of the kitchen appliance, an alternating magnetic field for transmitting energy in the direction of an electrical consumer can be generated by means of the inductor by means of inductive coupling. The second operating mode can be, for example, a so-called Ki mode of a wireless power transfer according to the Ki cordless Kithen standard, wherein the electrical load then forms a so-called Ki receiver.The kitchen appliance can be a so-called Ki-dual-function induction hob which, in addition to the direct inductive heating of cooking vessels in the first operating mode, can also be used for the power supply of electrical consumers or wireless kitchen appliances in the second operating mode. The kitchen appliance can have a plurality of hobs, at least one of which has a Ki-dual function.The kitchen appliance further has a hob plate, for example made of glass ceramic, with a placement surface on which the cooking vessel to be heated or the electrical consumer are to be placed as intended.The kitchen appliance further comprises an electrically conductive, in particular metallic, carrier on which the inductor is arranged. The carrier can consist, for example, of an aluminum alloy. The carrier may form a shielding plate in the direction of electronics for driving the inductor.A distance between an underside of the planar winding and a side of the electrically conductive carrier facing the winding is at least 6 mm, in particular at least 7 mm.A distance between a side of the winding facing the placement surface and the placement surface is at most 9 mm, in particular at most 7.5 mm. This spacing contains the hob plate or glass ceramic, which is usually 4 mm thick. The distance can be, for example, 7 mm.The kitchen appliance or the inductor has ferrite elements which are arranged in particular such that they completely cover the winding horizontally in their entirety.In one embodiment, the ferrite elements are arranged in such a way that they project at a minimum of 5 mm, in particular at a minimum of 10 mm, beyond a radially outer circumference or an outer radius of the winding.In one embodiment, the inductor comprises at least 10 ferrite elements distributed equidistantly over a circumference or a surface of the winding.A distance between the underside of the planar winding and the side of the electrically conductive carrier facing the winding is greater than a height of the ferrite elements.A distance between an underside of the ferrite elements and the side of the electrically conductive carrier facing the winding is a minimum of 2 mm.In one embodiment, ferrite elements having at least two different lengths are provided. A distance at the radially inner end of a shorter ferrite element from its adjacent ferrite element can be a maximum of 10 mm, in particular a maximum of 6 mm, in order to obtain, for example, as full-surface as possible an occupancy with very small distances from adjacent ferrites, in order to keep the coupling to the electrically conductive carrier low at Ki field strengths. The ferrite elements can be rectangular rod ferrites with parallel extending edges with at least 2 different rod lengths.In one embodiment, the winding is formed from a stranded wire, wherein the individual stranded wire has a diameter of at most 0.25 mm, in particular of at most 0.2 mm. The diameter can be, for example, 0.15 mm.In one embodiment, a specific electrical conductivity of the strand is substantially less than that of copper. In particular, the specific electrical conductivity of the stranded wire corresponds approximately to the specific electrical conductivity of aluminum or CCA (copper-clad aluminum).The inductor may be optimized for the second mode of operation.In the second operating mode, the kitchen appliance can set a working frequency which is lower than a resonant frequency of the electrical load.In the case of Ki dual-function induction hobs, at least one cooking point of an induction hob is extended for a Ki power transmission to an electrical consumer or a wireless kitchen appliance. A transmitter inductance is chosen at Kisuch that common inductor dimensions are compatible with Ki. For the resonant frequency or reactive power adaptation of the inductor as a Ki transmitter, the resonant resonant resonant circuit capacitance may have to be adapted, i.e. for the Ki operation, capacitors are switched off or connected in as a deviation from the induction operation for heating cooking vessels.In induction hobs, the inductors are usually constructed above a metallic carrier or shielding plate, for example from an aluminum alloy. The metallic carrier can be used on the one hand for holding or pressing the inductors against the hob plate, but in particular it has a shielding effect for the alternating magnetic field in the direction of electronics under the metallic carrier and thus allows a low installation height and flexible positioning of the inductor or inductors.However, it is disadvantageous that the metallic carrier is magnetically coupled to the inductor and an eddy current is thus induced in the metallic carrier, for which reason an electrically low-ohmic material is preferably selected for the metallic carrier and cross sections of ferrites under the inductor are dimensioned so large that saturation of the ferrite material begins only at currents in the vicinity of the maximum current and at high inductor temperatures.If a conventional inductor design is used for the second operating mode or the Ki operation, the power transmission to the electrical consumer or the kitchen appliance functions, but it is to be established that at particularly relevant operating points of the Ki transmitter with high power, in particular in the range of the maximum power of, for example, 2.2 kW, the losses in the second operating mode or in the Ki operation are substantially greater than in the first operating mode when induced with a comparable or even significantly greater booster power of 3.65 kW.In Ki operation, saturation occurs earlier compared to the induction heating operation in the inductor, i.e. the magnetic flux in the ferrites below the winding exceeds the saturation limit of the ferrites even with a smaller inductor current, so that the magnetic field above saturation couples very much more strongly to the metallic carrier.According to the invention, the inductor for a Ki dual function differs in relevant features from an inductor design of an induction hob in order to be able to achieve the required performance of the Ki specification and to reduce the additional losses in the Ki operation of an installed hob.In an induction heating device, the current in the cooking vessel counteracts its cause, the current lags behind its cause by almost -180°, i.e. the respective magnetic fields of the two currents are opposite and can be compensated vectorially. Accordingly, at high working frequencies, Ki behaves substantially greater than the resonant frequency of the electrical load or receiver.To understand the coil losses, a distinction must be made between proximity effect, which is caused by an external magnetic field, for example by adjacent turns and counter-field of the cooking vessel or electrical consumer, and skin effect, which is caused by the internal magnetic field of the current flow in the conductor itself and increases with increasing frequency.For operating frequencies below the resonant frequency of the electrical load, the phase difference is small in terms of amount, i.e. the magnetic fields of the inductor and of the electrical load reinforce one another. The larger (external) magnetic field increases the proximity losses of the two inductors or coils and the coupling to the electrically conductive carrier, which again increases significantly when the ferrites saturate and leads to appreciable losses in the electrically conductive carrier despite low-resistance material. In particular, the additional, uncompensated magnetic field of a coil of the electrical load significantly increases the losses in the electrically conductive carrier.The following features of the inductor according to the invention reduce the above-mentioned effects:a small diameter, reduced conductivity winding strand, for example of aluminum.A sufficient number and mass of ferrites, at least 50% more than for a conventional inductor of an induction heating device despite only 60% Ki power in comparison with the induction heating device, realized by a higher number of ferrites, enlargement of the cross section by broader ferrites with the same overall height or higher cross sections by stacking ferrites. The ferrite elements protrude significantly beyond the outer edge of the winding by a minimum of 5 mm, in particular a minimum of 10 mm or even significantly more than 10 mm.Higher distance of the winding from the support plate or electrically conductive carrier. For the use of conventional inductor ferrites, the inductor including the ferrites can preferably also be raised to a distance of at least 1 mm, preferably at least 2.5 mm, between ferrite and electrically conductive carrier.The invention will be described in detail below with reference to the drawings. The following shows: FIG. 1 is a highly schematic block diagram of a kitchen appliance according to the invention, FIG. 2 shows a view from below of an inductor of the kitchen appliance according to the invention, FIG. 3 shows a lateral cross section of the inductor and an electrically conductive carrier of the kitchen appliance according to the invention, and FIG. 4 shows a transmission function of a Ki transmitter of the electrical kitchen appliance with 2 maxima.FIG. 1 shows a highly schematic block diagram of a kitchen appliance 100 according to the invention with an inductor 1, FIG. 2 shows a view from below of the inductor 1 and FIG. 3 shows a lateral cross section of the inductor 100 including an electrically conductive carrier.Referring to FIG. 2, the inductor 1 has a spiral winding 2 which can be coupled to power electronics of the kitchen appliance 100 via connecting lines 14. By means of the inductor, an alternating magnetic field is generated for heating a cooking vessel 200 in a first operating mode of the kitchen appliance 100 and in a second, alternative operating mode of the kitchen appliance 100, an alternating magnetic field is generated for transmitting energy in the direction of an electrical consumer 300 by means of inductive coupling. In this respect, reference is also made to the relevant technical literature.The kitchen appliance 100 can have a plurality of cooking zones, wherein at least one of the cooking zones is assigned to the inductor 1.The kitchen appliance 100 further comprises a support or shielding plate 3 made of aluminum, on which the inductor 1 is arranged.The kitchen appliance 100 further comprises a hob plate 19 with a placement surface 12, on which the cooking vessel 200 to be heated or the electrical consumer 300 is to be placed as intended. Below the hob plate 19 there is an NFC antenna 20 for communication with the electrical load 300. In addition to the communication, the NFC antenna 20 also serves to supply the batteryless electrical load 300 before the power transmission via the inductor 1, for which reason a distance of 2.5 mm is preferably maintained between the NFC antenna 20 and the inductor 1 in order to limit the shielding effect by the winding 2.A distance 4 between a side of the winding 2 facing the electrically conductive carrier 3 and a side of the electrically conductive carrier 3 facing the winding 2 is a minimum of 6 mm, for example 7 mm.A distance 13 between a side of the winding 2 facing the placement surface 12 and the placement surface 12 is a maximum of 9 mm, in particular a maximum of 7.5 mm.The kitchen appliance 100 or the inductor 1 has 12 ferrite elements 5 distributed equidistantly over a circumference of the winding 2 and having two different lengths, wherein a distance 11 at the inner end of a shorter ferrite element 5 from its adjacent longer ferrite element 5 is at most 10 mm, in particular 6 mm. The longer ferrite elements 5 completely cover the winding 2 or have a length which is greater than a radius of the winding 2.The ferrite elements 5 are arranged in such a way that they project at a minimum of 5 mm beyond an outer circumference 6 or an outer radius of the winding 2.A distance 4 between a side of the winding 2 facing the electrically conductive carrier 3 and a side of the electrically conductive carrier 3 facing the winding 2 is greater than a height 7 of the ferrite elements 5.A distance 8 between a side of the ferrite elements 5 facing the electrically conductive carrier 3 and a side of the electrically conductive carrier 3 facing the ferrite elements 5 is a minimum of 2 mm. The distance 8 can be adjusted, for example, by means of suitable spacers which are arranged on the underside of the ferrite elements 5 and which are supported on the electrically conductive carrier 3.The winding 2 is wound from a stranded wire 9 which has a diameter 10 of at most 0.25 mm, in particular at most 0.2 mm. A specific electrical conductivity of the stranded wire 9 is substantially smaller than that of copper, in particular it corresponds to the specific electrical conductivity of aluminum or CCA.The inductor 1 is optimized with respect to the second operating mode.The kitchen appliance 100 sets a working frequency in the second operating mode which is lower than a resonant frequency of the electrical load 300.FIG. 4 shows a transfer function P(f) of a Ki transmitter of the 2-peak kitchen appliance 100, wherein #1 represents the transmitted electrical line P as a function of the frequency f, #2 represents a phase difference Ph between a current through the inductor 1 and a current through a receiver coil in the electrical load or Ki receiver 300 as a function of the frequency f, and #3 represents a current I through the inductor 1 as a function of the frequency f.The Ki receiver 300 has a resonance frequency of 30 kHz. The phase difference between the current through the inductor 1 and the current through the receiver coil in the electrical load or Ki receiver 300 is comparable to an induction heating device for high operating frequencies and is approximately -180°. For low frequencies, in particular lower than the resonant frequency of the Ki receiver 300, the phase difference, however, becomes very small in terms of amount, i.e. a vectorial addition of the two magnetic field-forming currents leads to a vector which is significantly larger in terms of amount than in the case of opposite phase of the two currents.The two arrows show operating frequencies 25 and 43 kHz with the same power, the current at the lower-frequency operating point being somewhat greater because of the poorer efficiency. A distinct difference is the phase difference, which at 43 kHz is -155°, while the phase difference at 25 kHz is very much smaller with -65° in terms of amount, i.e. a resulting magnetic field of the two currents is substantially greater at 25 kHz than at 43 kHz.

Claims

Kitchen appliance (100), comprising: - an inductor (1) comprising ferrite elements (5) and a winding (2) and by means of which an alternating magnetic field can be generated for heating a cooking vessel (200) in a first operating mode of the kitchen appliance (100) and by means of which an alternating magnetic field can be generated by means of inductive coupling in a second operating mode of the kitchen appliance (100) for transmitting energy in the direction of an electrical consumer (300), - a hob plate (19) having a placement surface (12) on which the cooking vessel (200) to be heated or the electrical consumer (300) are to be placed as intended, and - an electrically conductive, in particular metallic, carrier (3) on which the inductor (1) is arranged, - wherein a distance (4) between a side of the winding (2) which faces the electrically conductive carrier (3) is arranged, and a side of the electrically conductive carrier (3) facing the winding (2) is a minimum of 6 mm, - wherein a distance (13) between a side of the winding (2) facing the placement surface (12) and the placement surface (12) is a maximum of 9 mm, in particular a maximum of 7.5 mm, - wherein the distance (4) between the side of the winding (2) facing the electrically conductive carrier (3) and the side of the electrically conductive carrier (3) facing the winding (2) is greater than a height (7) of the ferrite elements (5), and - wherein a distance (8) between a side of the ferrite elements (5) facing the electrically conductive carrier (3) and a side of the electrically conductive carrier (3) facing the ferrite elements (5) is a minimum of 2 mm.Kitchen appliance (100) according to claim 1, characterised in that - the ferrite elements (5) are arranged in such a way that they completely cover the winding (2).Kitchen appliance (100) according to claim 1 or 2, characterised in that - the ferrite elements (5) are arranged in such a way that they project at least 5 mm beyond an outer periphery (6) of the winding (2).Kitchen appliance (100) according to one of the preceding claims, characterised in that - the inductor (1) has at least 10 ferrite elements (5) which are distributed equidistantly over a circumference of the winding (2).Kitchen appliance (100) according to one of the preceding claims, characterised in that - ferrite elements (5), in particular rod-shaped ferrite elements (5), having at least two different lengths are provided, wherein in particular a distance (11) at the inner end of a shorter ferrite element (5) from its adjacent ferrite element (5) is at most 10 mm, in particular at most 6 mm.Kitchen appliance (100) according to one of the preceding claims, characterised in that - the winding (2) is formed from a stranded wire (9), wherein the stranded wire has a diameter (10) of at most 0.25 mm, in particular of at most 0.2 mm.Kitchen appliance (100) according to claim 6, characterised in that - a specific electrical conductivity of the stranded wire (9) is smaller than that of copper, in particular corresponds to the specific electrical conductivity of aluminium or copper clad aluminium.

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