Induction coil for an electric cooking appliance and electric cooking appliance

Abstract

Induction coil (26) for an electric cooking appliance, in particular for a hob (11) with a hob plate (12) and with at least one induction coil (26) arranged below it, wherein the induction coil (26) comprises: - a winding body (27) in the form of a flat, spirally wound coil, which is wound from coil wire and which has a center point, an inner terminal (29) and an outer terminal (28), - at least four individual identical ferrite bodies (30) under the winding body (27), characterized by the fact that: - the ferrite bodies (30) each have two areas, wherein: - a first inner area is a stem area (31), - the stem area (31) runs essentially in a radial direction, - a second outer area is a head area (37), and - the head region (37) adjoins the stem region (31) and is wider in degrees at its greatest width than the stem region (31) at its greatest width and is more than 50% wider in absolute width than the stem region (31) at its greatest width, - the head area (37) extends at least partially beyond and overhangs the winding body (27) in a radial direction, - the stem area (31) widens in absolute width in a radial direction from radially inward to radially outward, - the stem area (31) narrows in a radial direction from radially inward to radially outward in degrees in a range between 40% and 80% of the radius (r) of the winding body (27) and / or in a range between 25% and 75% of the length of the ferrite body (30).

Description

[0001] The invention relates to an induction coil for an electric cooking appliance, wherein the induction coil comprises several ferrite elements. Furthermore, the invention relates to the use of certain ferrite elements in such an induction coil to inductively transfer power from the induction coil to an electrical load with a counter-induction coil or receiver coil, which is positioned at a certain distance from the induction coil. Finally, the invention relates to an electric cooktop with a cooking surface and several induction coils according to the invention.

[0002] From DE 10 2016 208 233 A1, an induction coil with several ferrite bodies is known, which are arranged below the induction coil to prevent the unwanted downward propagation of its magnetic field or to guide the magnetic field lines downwards. These ferrite bodies can either have the shape of long rectangles or of circular segments, in particular approximately sixths of a circle. These circular segment-shaped ferrite bodies are advantageously arranged in corner regions of approximately rectangular induction coils.

[0003] Alternative designs of ferrite bodies for induction coils are known from EP 1 991 030 A2. They essentially have shapes that start from elongated rectangles and are shaped differently at one end in the end region.

[0004] From JP 2010-15764 A, an induction coil for an induction cooktop is known, which has a coil body wound in a circular shape with a central point. Eight elongated and flat ferrite rods are arranged radially beneath the induction coil. The ferrite rods have a constant width or cross-section and are only tapered near the central point, where they are close together. This allows them to be positioned closer to the central point, or to extend closer to it, because they are narrower there.

[0005] From JP 2007-328917 A, another induction coil for an induction cooktop is known, featuring a round winding body with a central core. Here, too, elongated ferrite rods, extending essentially radially, are arranged beneath the induction coil. These rods can be multi-sectioned. Advantageously, they are narrower or tapered in their inner region near the center. This allows them to be positioned further towards the center, thus enabling the magnetic field of the induction coil to be guided as close as possible to the center. Task and solution

[0006] The invention is based on the objective of creating an induction coil mentioned above, a use of ferrite bodies in such an induction coil mentioned above, and an electric cooktop with several such induction coils, with which problems of the prior art can be solved and it is particularly possible to guide the magnetic fields generated by the induction coil well and efficiently, especially in the case of a use for inductive power transmission, which can be carried out according to the Ki standard.

[0007] This problem is solved by an induction coil with the features of claim 1, by the use of ferrite bodies in an induction coil with the features of claim 21, and by an electric cooktop with a cooktop plate and several induction coils below it with the features of claim 23. Advantageous and preferred embodiments of the invention are included in the dependent claims and are explained in more detail below. Some of the features are described only for the induction coil, only for the use, or only for the electric cooktop. However, they should be able to apply independently and separately to such an induction coil, such a use, and such an electric cooktop. The wording of the claims is made clear by express reference to the content of the description.

[0008] The induction coil according to the invention is intended to be installed and used in an electric cooktop, particularly under a cooktop element, advantageously in conjunction with other induction coils. The induction coil comprises a winding body in the form of a flat, spirally wound coil, as is customary. The winding body has a central point and is wound from coil wire or so-called coil strands, and has an inner and an outer connection. These connections advantageously extend from the winding body as a continuous coil wire. Furthermore, the induction coil has at least four individual and identical ferrite elements arranged beneath the winding body. The ferrite elements are advantageously arranged adjacent to one another in the circumferential direction of the induction coil. They can cover between 30% and 70% of the area of ​​the winding body.

[0009] According to the invention, the ferrite bodies each have two regions, a first region being arranged internally and forming a stem region. This stem region extends substantially in a radial direction. A second region is arranged radially externally and is a head region. This head region adjoins the stem region, advantageously in a transition region formed therein. The head region is wider at its greatest width (in degrees) than the stem region at its greatest circumferential width, or more than 50% wider at its greatest circumferential width. In other words, the head region can be more than 50% wider at its greatest width (in degrees) than the stem region where it has its smallest width (in degrees or arc angle).Advantageously, the head region is no more than 150% wider than the stem region at its greatest circumferential width. Thus, the ferrite body can be roughly approximated as T-shaped.

[0010] Furthermore, the head section extends at least partially beyond the winding body in the radial direction. This extension can be between 5% and 30% of the winding body's radius. The stem section does not have a continuous absolute width, but rather widens radially from the inner to the outer edge. This is advantageous for its absolute width, but not for its width in degrees or as an arc angle, where it can vary or even decrease. This width progression essentially runs along a circumferential direction of the winding body or approximately perpendicular to the radial extent of the ferrite body or the stem section.The stem area narrows in a radial direction from radially inward to radially outward in degrees in a range between 40% and 80% of the radius of the winding body and / or in a range between 25% and 75% of the length of the ferrite body, preferably viewed in the radial direction.

[0011] In other words, the lateral sides of the stem region of two directly adjacent ferrite bodies can be configured such that the sum of all distances between ferrite bodies along any circle around the center of the winding body is at least 40%, preferably between 50% and 70%, of the total circumference of that circle. The radius of this circle can be between 40% and 90% of the radius of the winding body. Thus, this can apply to an annular region with a radius between 70% and 90% of the radius of the winding body. Advantageously, the sum of all distances can be between 50% and 70% of the total circumference of said circle.

[0012] This specific geometric design ensures relatively large gaps between adjacent ferrite bodies in the central outer area. This spacing, particularly important for the aforementioned power transmission application, keeps magnetic coupling to a low-impedance mounting plate beneath the induction coils in an electric cooktop. This limits losses in the mounting plate and prevents the inductance of the receiver coil from being excessively increased by the large gaps or open areas between the ferrite bodies. Such an increase would disrupt the resonant frequencies for inductive power transmission, which would be highly detrimental.

[0013] Furthermore, the widened head areas on the outside of the induction coil and the relatively close radial inner ends of the ferrite bodies ensure that the inner winding circumference is almost completely magnetically short-circuited with the outer winding circumference. The magnetic flux increases radially from the inside to the outside, which is why the absolute width of the ferrite bodies is advantageously increased in this direction. In the case of inductive power transmission of high power, particularly large magnetic fluxes occur, and the specific shape of the ferrite bodies is intended to prevent saturation. Thus, it can be advantageously provided that an induction coil with its ferrite bodies, which is also or primarily used for inductive power transmission, has a different design or features differently designed ferrite bodies according to the invention.Due to their special shape and the overhang of the ferrite bodies above the winding body, no magnetic field components are coupled into an area located below the induction coil, especially into a metallic support plate, either radially inside or radially outside.

[0014] In an advantageous embodiment of the invention, the ferrite bodies of an induction coil can be identical, at least with respect to their head region. This also advantageously applies to the aforementioned stem region, particularly at its radially inner end. Overall, it can be provided that all ferrite bodies of this induction coil are identical for an induction coil or even for all induction coils of the same size in a corresponding cooktop, at least if they are also intended for inductive power transmission. The use of identical regions or even identical ferrite bodies simplifies assembly and reduces costs. It is particularly advantageous if the ferrite bodies are formed in one piece with their specific shape, i.e., not assembled from different parts.This prevents magnetic fields from escaping at the joints between individual parts, which can cause losses in the winding body and the mounting plate. Furthermore, it can simplify the mechanical fastening of the ferrite cores during assembly.

[0015] In an embodiment of the invention, the lateral sides or outer surfaces of the stem area can be straight for at least 50% of their length in the radial direction, preferably for 65% to 90%. This makes it easy to achieve that, as previously defined, they widen from the radial inside to the radial outside. Alternatively, instead of a straight direction, they can be slightly curved.

[0016] The angular distance in degrees between the two lateral sides of the stem region of a ferrite body can decrease from radially inward to radially outward, preferably continuously. This is a continuous decrease. In particular, the distance can decrease in a range between 20% or 30% and 80% of the maximum radius of the winding body.

[0017] In an embodiment of the invention, the arc angle, measured in degrees, between the two lateral sides of the stem region of a ferrite body can increase from the radial outside to the radial inside, preferably increasing continuously, monotonically, or even strictly monotonically. Thus, the width of the stem region, measured in millimeters, can decrease from the radial outside to the radial inside. However, with respect to a circle or in the circumferential direction, the stem regions of the ferrite bodies can occupy an increasingly larger proportion, advantageously exceeding 50% in degrees.

[0018] In a further development of the invention, the radially inner end regions of the stem regions can be tapered even more sharply than the lateral sides of the stem regions over their substantial length, preferably between 60% and 90% of the length. These radially inner end regions can comprise between 10% and 30% of the length of the ferrite bodies. This further tapering allows the stem regions to be positioned relatively close to the center of the induction coil without touching each other. Their angular width between the two lateral sides of the end regions can increase from radially inner to radially outer or remain constant.

[0019] In a further development of the invention, the aforementioned lateral faces of the tapered end regions of adjacent ferrite bodies can have a distance of at least 5 mm or 5% of the circumference of a circle in this region from each other, advantageously even 8 mm to 12 mm. Thus, a aforementioned internal connection can be routed between two adjacent ferrite bodies and at their level. Even if this internal connection only needs to be routed between two adjacent ferrite bodies at a single point, the aforementioned spacing requirement can be advantageous for realizing identical ferrite bodies and their regular arrangement under the winding body.

[0020] In one embodiment of the invention, the tapered end regions of the stem sections may not be pointed, but rather cut off at right angles to the radial direction or the radial longitudinal course of the stem sections. They may be cut straight, or alternatively, they may be cut in a curved shape, in particular curved inwards.

[0021] Radially within the tapered end regions of the ferrite cores, a free zone can advantageously be provided in which no ferrite cores or ferrite material, nor any coil windings, are present. Such a free zone can have a diameter between 2% and 12% of the maximum radius of the winding core. This free zone is particularly useful when the winding core is designed as a wide circular ring and also has a free inner region. In this central inner region, no ferrite material in the form of one or more ferrite cores is required, thus enabling the aforementioned free zone.

[0022] It can be arranged that the radially innermost winding of the winding body is positioned over the tapered end regions, so that it extends radially inwards beyond this innermost coil winding. In this way, the magnetic field of the induction coil can be guided both radially inwards and radially outwards as desired.

[0023] In a further embodiment of the invention with respect to the aforementioned end regions, the ratio between the smallest distance between adjacent ferrite bodies at the end regions and the smallest distance between adjacent ferrite bodies at the head regions can be between 0.7 and 1.5 in absolute width, preferably between 0.9 and 1.2. It can be provided that the distance is smallest where the ferrite bodies are narrowest, particularly at the inner ends. Here, the aforementioned internal connection may not even need to pass through, which is why they can have the smallest distance to each other precisely at these points. Alternatively or additionally, the ratio between the smallest distance between adjacent ferrite bodies at the end regions and the smallest distance between adjacent ferrite bodies at the head regions can be between 1.5 and 5 degrees in angular degrees, preferably between 2.5 and 3.5 degrees.

[0024] In an alternative embodiment of the invention, the distance between adjacent ferrite bodies at the head region, measured in absolute numbers, can be just as small as the smallest distance at the end regions.

[0025] The angular distance between two adjacent ferrite bodies at the head regions can range from 2° to 8°. The minimum angular distance between two adjacent ferrite bodies at the end regions can range from 10° to 20°.

[0026] In a further embodiment of the invention, the proportion of the distance between adjacent ferrite bodies along the circumferential direction, or as an arc angle in degrees, can exceed 40% of the total circumference at any point along the radial extent, so that, so to speak, no greater distance is provided between adjacent ferrite bodies at any point. Advantageously, it can even be provided that this proportion exceeds 50% over more than half of the radial extent, meaning that in a significant area, more than 50% of a circle does not pass over a ferrite body. This applies in particular to the radius range mentioned above, between 40% and 90% of the radius of the winding body.

[0027] In a further development of the invention, a transition area can be provided between the head region and the stem region. This transition area can be rounded, which improves mechanical stability and facilitates the manufacture of the ferrite bodies. The radius of the rounded transition area can be between 5% and 20% of the radius of the winding body. Preferably, the absolute width gap between two adjacent ferrite bodies is greatest in this transition area, with the transition area in particular being between 70% and 105% of the radius of the winding body.

[0028] Furthermore, in the aforementioned transition area, the distance between adjacent ferrite bodies can be greatest, advantageously ranging from 70% to 90% of the winding body's radius. This allows the head section to extend relatively quickly and significantly outwards radially from the transition area, becoming very wide. As a result, the head sections can reach their greatest width slightly radially outside the winding body, with their ends almost touching each other.

[0029] A significant portion of the head area can be arranged radially outside the winding body and thus project beyond it in a radial direction. This can be at least 50%, preferably between 65% and 95%. In particular, the head area can increase considerably in width radially beyond the outermost winding of the winding body. The transition area is advantageously located directly beneath this outermost winding.

[0030] Overall, the ferrite bodies can be designed to cover between 40% and 70% of the winding body's surface. A coverage of between 45% and 60%, for example approximately half, can be particularly advantageous.

[0031] Even if the stem area is considerably longer than the head area in the radial direction, it can still have a radial extent of between 10% and 35% of the radial length of the stem area. Its width can be several times greater than its radial extent, thus achieving the aforementioned T-shaped form.

[0032] For example, the absolute width of the head region along the circumference can be 30% to 100% greater than the absolute width of the stem region before the transition to the head region or before the aforementioned transition region. This can also result in the aforementioned T-shaped form of the ferrite body.

[0033] In a further embodiment of the invention, the distance between two adjacent ferrite bodies at their head regions can be between 2° and 8° in degrees. A minimum distance between two adjacent ferrite bodies at their end regions can be between 10° and 20° in degrees. Thus, the distance in degrees at the end regions of the stem regions can be greater than at the head regions. This can be justified primarily by the previously explained objective of routing the internal connection between two adjacent ferrite bodies at the end regions. This allows the overall height of the induction coil to be reduced, since the internal connection does not have to be routed below a ferrite body, which would otherwise cause their thicknesses to add up.

[0034] One advantageous design of the ferrite bodies is mirror-symmetrical, so that, for example, they can be correctly mounted with the underside facing upwards. This mirror symmetry is advantageously related to an axis that runs in the exact radial direction of the induction coil and the winding body.

[0035] An arrangement of the ferrite bodies is preferably axially symmetric, and in particular also point-symmetric. It is especially preferred that it is axially symmetric about two mutually perpendicular axes of symmetry, wherein these axes of symmetry can run between or through two ferrite bodies. Particularly advantageously, one axis of symmetry passes exactly midway through two opposing ferrite bodies, and the other either also passes through or runs exactly between two adjacent ferrite bodies. Additionally or alternatively, the arrangement of the ferrite bodies on an induction coil can be point-symmetric, preferably about a center point of the induction coil and the winding body.

[0036] In a further development of the invention, the head region can be formed by two head end sections, or it can have such head end sections. These are preferably formed transversely or at right angles to the longitudinal direction of the stem region. They can be tapered towards their free ends, and in particular, they can be rounded at the free ends. It is particularly advantageous that these projecting head end sections have the smallest possible distance between adjacent ferrite bodies, both in absolute width and in angular degree. In this way, a largely or almost completely closed circumferential ring of ferrite material can be created, which runs around the winding body for the reasons mentioned above, due to the specific operating principle of high-power wireless energy transmission.

[0037] It is advantageous that the outer edge of the winding body, or its outermost winding, runs precisely over the transition area between the stem and head regions. This ensures that the radially inner part of the ferrite body, namely the stem region covered by the winding body, does not protrude significantly outwards. The head region, located outside the winding body, can be considerably wider. It is also possible for the outermost winding of the winding body to run precisely between the stem and head regions, essentially midway between them, over the transition area.

[0038] Preferably, the ferrite bodies, or each ferrite body individually, have a constant and uniform thickness. Advantageously, this can be between 3 mm and 7 mm, with approximately 5 mm being particularly advantageous. This is sufficient to guide the magnetic field lines as described above. At the same time, this keeps the overall height of the finished induction coil from becoming too high.

[0039] As a further geometric specification, it can be stipulated that the radial length of the ferrite bodies is 5 cm to 15 cm. Advantageously, more than 75% of this length should be the stem sections.

[0040] The ferrite bodies are preferably manufactured as a single piece, which simplifies their assembly and allows them to better direct the magnetic flux. They can consist of pressed ferrite material, which can then be ground to achieve a defined shape. Preferably, the outer contour of the ferrite bodies is relatively complex, but within this outer contour, the ferrite body must not have any holes, openings, or recesses.

[0041] The aforementioned internal connection of the winding body can extend from the innermost coil winding with coil wire or stranded wire and run between two radially inner ends or previously described end regions of adjacent ferrite bodies. It can therefore run in the same plane as the ferrite bodies and not below them, thus reducing the overall height. Here, the internal connection can then run radially outwards from the innermost winding between two ferrite bodies and, for example, emerge below the winding body at the same point where the external connection originates. In this way, they can form a common connection strand, which simplifies the installation and connection of the induction coil in the cooktop.

[0042] As previously explained, ferrite bodies with a previously described shape, particularly the T-shaped form, are not only generally used in a cooktop or induction cooktop in a unit with an induction coil, but primarily for inductive power transfer to a certain electrical appliance, such as a kitchen appliance like a mixer, toaster, or the like, which has a receiver coil. This results in inductive power transfer known from the prior art, which provides current or electrical energy to the electrical appliance for its operation. Such inductive power transfer can advantageously be carried out according to the Ki standard; see, for example, DE 10 2021 201 220 A1. The receiver coil should be of a similar size to the induction coil, but can also have a different size.

[0043] The inventive shape of the ferrite bodies is particularly important for such inductive power transmission, as it features a nearly closed ring of ferrite material in the outer area of ​​the winding body, formed essentially by the widened head regions described above. In the central area of ​​the winding body, less ferrite material is provided, or adjacent ferrite bodies are spaced significantly apart, since otherwise the magnetic resistance would become too high. In the radially inner area of ​​the winding body, ferrite material is also provided in a circular pattern with minor interruptions; however, this can be achieved without widening the ferrite bodies, as they are already relatively close together or have a relatively small distance between them due to the correspondingly small radii of this area.

[0044] An electric cooktop according to the invention comprises a cooktop surface and several induction coils; advantageously, there can also be several such induction coils. The cooktop surface can advantageously be made of a conventional material such as glass-ceramic with a thickness of a few millimeters, preferably 3 mm to 5 mm, and particularly 4 mm. The distance between the top of the winding body and the top of the cooktop surface should not be too large, both for inductive cooking and for the aforementioned inductive power transfer to an electrical appliance with a receiver coil placed on the cooktop surface. Thus, the distance between the top of the winding body and the top of the cooktop surface can be between 5 mm and 13 mm, and particularly advantageously about 8 mm.

[0045] A flat support plate is preferably provided below the cooktop, on which one of the aforementioned induction coils according to the invention is placed; all induction coils of this cooktop are particularly advantageously placed on this support plate. The flat support plate can be made of metal, in particular aluminum. It should have low electrical resistance and can, for example, be made of an aluminum alloy or have an electrical conductivity greater than 20 MS / m.

[0046] 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

[0047] Further advantages and aspects of the invention will become apparent from the claims and from the description of exemplary embodiments of the invention, which are explained below with reference to the figures. These figures show: Fig. 1 a sectional view through a cooktop according to the invention with three conventional induction heating coils and one induction coil according to the invention, Fig. 2 a top view of the hob from Fig. 1 with the induction coil according to the invention at the front right, Fig. 3 a top view of an induction heating coil according to the invention with a round winding body and six T-shaped ferrite bodies, Fig. 4 an oblique view of the induction coil made of Fig. 3 on a support plate of the hob, Fig. 5 a top view of one of the ferrite bodies made of Fig. 3, Fig. 6. A slant view from the front of the ferrite body. Fig. 5 and Fig. 7 an enlarged section of the induction coil Fig. 3 with lines drawn corresponding to different degrees of angle and a percent scale based on the radius of the winding body. Detailed description of the exemplary implementations

[0048] In the Fig. Figure 1 shows a cooktop 11 according to the invention in a side sectional view, which is largely constructed as is known. The cooktop 11 has a conventional cooktop surface 12 with a top surface 13 and a bottom surface 14. A housing 16 is arranged on the bottom surface 14, in which the various functional units of the cooktop 11 are arranged. A support plate 18 made of aluminum, advantageously with a high conductivity of 20 MS / m or even higher, runs parallel to the cooktop surface 12 within the housing 16. In front of this, a control device 20 is arranged in a separate housing, which includes, among other things, a rotary knob 22 that can be placed on the top surface 13 for operating the cooktop 11.

[0049] Three induction coils 24a to 24c are placed on the support plate 18 and rest against the underside 14. In place of a conventional fourth induction heating coil, an induction coil 26 according to the invention is arranged, specifically at the front right as shown. Fig. 2. The induction heating coils 24a to 24c serve only for the inductive heating of a placed cooking vessel. The induction coil 26 according to the invention can, of course, also be used for the inductive heating of a cooking vessel. Furthermore, it can also be used to operate a device placed on the cooktop 12 above it, in accordance with the aforementioned Ki standard. The cooktop 11 could, however, also have more or even only such induction coils according to the invention.

[0050] The consumer here is a mixer 40, which has a mixer container 41. Advantageously, this container houses a stirring mechanism or the like, which is not shown here. The mixer container 41 sits on a mixer base 42, with which the mixer 40 is placed on the top 13 of the cooktop 12. A receiver coil 43 is provided in the mixer base 42, and advantageously as low as possible or as close as possible to the cooktop 12 and thus also to the induction coil 26 arranged below it. This receiver coil 43 can be somewhat smaller than the induction coil 26 according to the invention, but the sizes can also differ more significantly. Through the inductive energy transfer from the induction coil 26 to the receiver coil 43, the mixer 40 is wirelessly supplied with electrical energy for its operation.

[0051] The Fig. Figure 3 shows a top view of the induction coil 26 according to the invention. It has a conventional winding body 27, which is wound flat and spirally in a single layer from so-called coil wire, wherein the coil wire has several individual strands that are advantageously twisted together. An external connection 28 extends continuously from the outside of the winding body 27 and advantageously runs a few centimeters further in the plane of the winding body 27, in particular continuously to electrical connection terminals in the housing 16. Similarly, an internal connection 29 extends continuously from the innermost winding of the winding body 27, which is led radially outwards and then runs together with the external connection 28.

[0052] Below the winding body 27 are six identical ferrite bodies 30, which are shown as dashed lines in this area. Their arrangement is evenly distributed, with the ferrite bodies 30 projecting slightly below the winding body on the inside and outside. In the Fig. Figure 4 shows the induction coil 26 in oblique view, where it is placed on the support plate 18 with the ferrite bodies 30 facing downwards.

[0053] In connection with the Fig. 5 and Fig. Section 6 and the detailed description provided therein explain the specific shape of the ferrite bodies 30 in more detail. Basically, they have an elongated stem region 31, which has a left lateral side 32a and a right lateral side 32b. At the lower end, which according to Fig. Since point 3 lies in a central free area of ​​the winding body 27, the stem region 31 transitions into the tapered end region 34. At its very lower end, this end region 34 is cut off at a right angle to the longitudinal direction of the stem region 31, although this could also be more or less rounded, and the corners could also be rounded.

[0054] The stem area 31 widens in a radially outward direction, with respect to the induction coil 26 or its winding body 27 according to Fig. 3, specifically by about 35%. Advantageously, it has straight lateral sides 32a and 32b, thus widening uniformly. A head section 37 adjoins the widened stem section 31 via a transition section 36. In the transition section 36, the ferrite body 30 widens from the lateral sides 32a and 32b with a further curvature. The ferrite body 30 then transitions into the head section 37, where it is significantly widened. There, it forms the outwardly pointing head end sections 38a on the left and 38b on the right. The outwardly pointing outer edge of the head section 37 is widely rounded and runs approximately parallel to the outer edge of the winding body 27, see Fig. 3, so that all outer edges of the ferrite bodies 30 lie on a circle.

[0055] The lateral sides 32a and 32b are largely straight between the tapered end region 34 and almost to the transition region 36. The transition to the tapered end region 34 has a corner, but could also be rounded. Likewise, the lateral sides of the tapered end region 34 could be slightly curved or arched. Instead of the corners shown, a slight curve could also be provided on the inwardly facing end side.

[0056] The specific shape of the six ferrite bodies 30 according to Fig. 3. This stems from the fact that, on the one hand, an identical design offers advantages for its manufacture and assembly and is therefore more cost-effective. Furthermore, the shape of the ferrite bodies 30 serves to ensure that as much ferrite material as possible is provided radially far inwards and radially far outwards, i.e., in the area of ​​the innermost and outermost windings of the winding body 27, viewed in the circumferential direction, or that this material is present in a nearly continuous circle. Radially inwards, the ferrite bodies 30 must have a certain distance from each other, which in practice can be the aforementioned 8 mm. This allows the inner connection 29 to pass through in the plane of the winding body 27 without having to increase the overall height of the induction coil 26. This would otherwise be the case if the ferrite bodies 30 were located in the inner free space or...would touch under the innermost winding of the winding body 27 or would run so close together that the inner connection 29 would have to pass under the ferrite bodies 30. At the same time, one can see in the . Fig. 3. However, it is also evident that the relatively small distance between the tapered end regions 34 of the ferrite bodies 30 means that a significant amount of ferrite material is provided in this area. This allows the entire magnetic flux to be guided within the ferrite material, preventing any magnetic field components from coupling with the underlying support plate 18. Especially when a relatively large magnetic flux can occur with a poor phase angle between the currents in the induction coil 26 and the receiver coil 43 without saturation, the ferrite bodies 30 in these end regions 34 should have sufficient volume. Therefore, the width of the ferrite bodies 30, measured in degrees, increases in this area, or, as shown here, does not decrease significantly. This can also be seen from the Fig. 7 can be seen.

[0057] Similarly, the ferrite bodies 30 are also designed to be so wide in the area of ​​the outermost winding of the winding body 27, and even radially outside of it, that they almost touch with the projecting head end sections 38a and 38b, given their large circumference. Thus, in this area as well, the entire magnetic flux can be guided in the ferrite bodies 30, specifically in the head sections 37, i.e., again within the ferrite material.

[0058] In the substantial area of ​​the winding body's surface, particularly in an outer region, the ferrite bodies 30 with their stem regions 31 are relatively narrow, or even become narrower from the radial inside to the radial outside towards the head regions 37. This is illustrated by the representation in degrees according to Fig. 7 in the range between 60% or 70% and 90%. This creates large, approximately triangular free areas between adjacent ferrite bodies 30, in which no ferrite material is arranged under the winding body 27. This reduces an overall excessive magnetic coupling to the receiver coil 43 as well as the effect of the ferrite bodies 30 on the self-inductance of the receiver coil 43, which is also known as the cross effect of the induction coil 26 on the receiver coil 43. The coupling here is relatively high due to the relatively small distance, in practice between 8 mm and 13 mm, between the induction coil 26 and the receiver coil 43. Fig. 1. In such inductive power transfer, high powers are transferred with strong coupling at operating frequencies significantly below the resonant frequency of the receiver coil 43, with relatively small phase angles between the currents in the induction coil 26 on the one hand and in the receiver coil 43 on the other. An increased inductance of the receiver coil 43 reduces its resonant frequency. In combination with the aforementioned strong coupling, the operating frequency for the inductive power transfer can fall below the permissible minimum operating frequency of 20 kHz if a nominal power of, for example, 2200 W is to be achieved in the load. Furthermore, the phase angle of the current through the receiver coil relative to the current through the induction coil 26 would otherwise deteriorate. This would result in an even larger current through the induction coil 26 being required to induce the same power in the receiver coil 43.the mixer 40 or the consumer requires, which would increase losses. This can be reduced by the larger free areas between two adjacent ferrite bodies 30.

[0059] In comparison to a simple T-shape of the ferrite bodies 30, which would essentially consist of two joined elongated rectangles, the shape according to the invention exhibits good coupling due to the relatively strong circumferential connection of the ferrite material of the ferrite bodies 30 at their innermost and outermost edges. Furthermore, the ferrite material at the inner circumference of the innermost winding of the winding body 27 can be magnetically connected with low resistance to the outer circumference or outermost winding of the winding body 27. Due to the large free areas between adjacent ferrite bodies 30, the aforementioned cross-effect on the receiver coil 43 can be reduced. The magnetic flux density reaches its maximum at the transition from the stem region 31 to the head region 37, i.e., in the region of the transition area 36.

[0060] To explain the exact shape of the ferrite bodies 30 when viewed in degrees, reference is made to the Fig. Reference is made to Figure 7. At 0° lies an axis of symmetry of the axially symmetric ferrite body 30. The smallest width in degrees is located at or just before the transition region 37, namely at the line at 13°. In comparison with the line at 15°, it can be seen that the left lateral side 32a intersects it, approximately in its midpoint. This results in the stem region 31 becoming narrower from radially inward to radially outward when viewed in degrees, although it naturally becomes wider in absolute width, i.e., measured in millimeters. The transition region 36 lies at the line at 15°, and this line also marks half of a twelfth segment of the circle. Slightly outside this line, the outer circumference of the winding body 27 intersects the edge of the ferrite body 30.

[0061] The sides of the end region 34 extend almost radially, at an angle of approximately 22°. Thus, the end region 34, similar to the stem region 31, narrows slightly from the radial inside to the radial outside.

[0062] The outermost ends of the head end sections 38a are at an angle of approximately 27.5°, so that their distance to the line with an angle of 30°, which runs exactly between two adjacent ferrite bodies 30, is only 2.5°. In practice, the distance between adjacent head end sections can be 8 mm to 15 mm, thus similar to that at the tapered end regions 34.

[0063] As explained at the beginning, the width of the stem region 31, or the distance between the two lateral sides 32a and 32b, decreases radially in the area between just under 40% and about 80%. Radially within this area, the sides of the ferrite body 30 in the tapered end regions 34 run such that their distance in degrees remains almost unchanged.

[0064] The Fig. Figure 7 also shows that the radial extent of the head areas 30 is relatively small and is only about 15% of the maximum radius of the winding body 27.

Claims

[1] Induction coil (26) for an electric cooking appliance, in particular for a hob (11) with a hob plate (12) and with at least one induction coil (26) arranged below it, wherein the induction coil (26) comprises: - a winding body (27) in the form of a flat, spirally wound coil, which is wound from coil wire and which has a center point, an inner terminal (29) and an outer terminal (28), - at least four individual identical ferrite bodies (30) under the winding body (27), characterized by , that: - the ferrite bodies (30) each have two areas, wherein: - a first inner area is a stem area (31), - the stem area (31) runs essentially in a radial direction, - a second outer area is a head area (37), and - the head region (37) adjoins the stem region (31) and is wider in degrees at its greatest width than the stem region (31) at its greatest width and is more than 50% wider in absolute width than the stem region (31) at its greatest width, - the head area (37) extends at least partially beyond and overhangs the winding body (27) in a radial direction, - the stem area (31) widens in absolute width in a radial direction from radially inward to radially outward, - the stem area (31) narrows in a radial direction from radially inward to radially outward in degrees in a range between 40% and 80% of the radius (r) of the winding body (27) and / or in a range between 25% and 75% of the length of the ferrite body (30). [2] Induction coil according to claim 1, characterized bythat the ferrite bodies (30) are designed in the same way as at least the head region (37), preferably also as the stem region (31), and in particular all ferrite bodies (30) of the induction coil (27) are designed identically. [3] Induction coil according to claim 1 or 2, characterized by , that the distance in degrees between the two lateral sides (32a, 32b) of the stem region (31) of a ferrite body (30) decreases from radial inside to radial outside, preferably continuously, in particular in a range between 20% and 80% of the maximum radius (r) of the winding body (27). [4] Induction coil according to any one of the preceding claims, characterized by, that radially inner end regions (34) of the stem regions (31) taper even more sharply than the lateral sides (32a, 32b) of the stem region (31) over its substantial length, preferably between 60% and 90% of the length, wherein in particular the width in degrees of angle between the two lateral sides of the end regions (34) increases or remains constant from radially inner to radially outer. [5] Induction coil according to claim 4, characterized by , that the lateral sides of the tapered end regions (34) of adjacent ferrite bodies (30) have a distance of at least 5 mm or 5% of the circumference of a circle in this region from each other, preferably 8 mm to 12 mm. [6] Induction coil according to claim 4 or 5, characterized by, that radially within these tapered end regions (34) a free area is provided which is free of ferrite bodies (30) and windings, wherein preferably the diameter of the free area is 2% to 20% of the maximum radius (r) of the winding body (27). [7] Induction coil according to any one of claims 4 to 6, characterized by , that the innermost winding of the winding body (27) is arranged over the tapered end regions (34), preferably over approximately half their length in a radial direction. [8] Induction coil according to any one of claims 4 to 7, characterized by, that the ratio between the smallest distance between adjacent ferrite bodies (30) at the end regions (34) to the smallest distance between adjacent ferrite bodies (30) at the head regions (37) in absolute width is between 0.7 and 1.5 and / or the ratio between the smallest distance between adjacent ferrite bodies (30) at the end regions (34) to the smallest distance between adjacent ferrite bodies (30) at the head regions (37) in angular degrees is between 1.5 and 5, preferably between 2.5 and 3.

5. [9] Induction coil according to any one of the preceding claims, characterized by , that the distance between two adjacent ferrite bodies (30) at the head regions (37) is between 2° and 8° in degrees and / or the minimum distance between two adjacent ferrite bodies (30) at the end regions (34) is between 10° and 20° in degrees. [10] Induction coil according to any of the preceding claims, characterized by , that the head region (37) connects to the stem region (31) in a transition region (36) and the transition region (36) is rounded, wherein preferably the distance in absolute width between two adjacent ferrite bodies (30) is greatest in this transition region (36), wherein in particular the transition region (36) lies between 70% and 105% of the radius (r) of the winding body (27) or covers it. [11] Induction coil according to any of the preceding claims, characterized by , that at least 50%, preferably between 65% and 95%, of the area of ​​the head region (37) are arranged radially outside the winding body (27) and project beyond it in a radial direction. [12] Induction coil according to any of the preceding claims, characterized by , that the ferrite bodies (30) cover between 40% and 70% of the area of ​​the winding body (27), in particular between 45% and 60%. [13] Induction coil according to any of the preceding claims, characterized by , that the head region (37) has a radial extent between 10% and 35% of the radial extent of the stem region (31). [14] Induction coil according to any of the preceding claims, characterized by , that the absolute width of the head region (37) along the circumferential direction is 30% to 100% greater than the absolute width of the stem region (31) before the transition to the head region (37). [15] Induction coil according to any of the preceding claims, characterized by , that the ferrite bodies (30) are mirror-symmetrical, in particular with respect to an axis that runs in exactly radial direction. [16] Induction coil according to any of the preceding claims, characterized by , that the arrangement of the ferrite bodies (30) is axially symmetric, in particular also point-symmetric, preferably axially symmetric with respect to two perpendicular axes of symmetry. [17] Induction coil according to any of the preceding claims, characterized by , that the head region (37) has two head end sections (38a) projecting transversely or perpendicularly to the longitudinal direction of the stem region (31), which are tapered, in particular rounded at the free ends, wherein preferably the smallest distance in absolute width and in degrees between two adjacent ferrite bodies (30) is at these projecting head end sections (38a). [18] Induction coil according to any of the preceding claims, characterized by , that the outer edge of the winding body (27) or the outermost winding of the winding body (27) runs over the transition area (36) between stem area (31) and head area (37) of the ferrite body (30), wherein preferably the outermost winding runs exactly between stem area (31) and head area (37). [19] Induction coil according to any of the preceding claims, characterized by, that the ferrite bodies (30) are formed in one piece and preferably consist of pressed ferrite material. [20] Induction coil according to one of the preceding claims, characterized by , that the internal connection (29) runs between two radially inner ends or end regions (34) according to one of claims 4 to 9 of the ferrite body (30) or the stem region (31), in particular in the same plane as the ferrite bodies (30), preferably extending radially outwards from the innermost winding. [21] Use of ferrite bodies (30) in an induction coil (26) for inductive power transfer from the induction coil (26) to an electrical load (40) positioned at a distance from the induction coil (26), which has a receiver coil (43), wherein the induction coil (26) has a winding body (27) in the form of a flat, spirally wound coil having a center point and wound from coil wire, wherein the ferrite bodies (30) are constructed as follows: - the ferrite bodies (30) each have two regions, wherein: - a first inner area is a stem area (31), - the stem area (31) runs essentially in a radial direction, - a second outer area is a head area (37), and - the head region (37) adjoins the stem region (31) and is wider in degrees at its greatest width than the stem region (31) at its greatest width and is more than 50% wider in absolute width than the stem region (31) at its greatest width, - the head area (37) extends at least partially beyond and overhangs the winding body (27) in a radial direction, - the stem area (31) widens in absolute width in a radial direction from radially inward to radially outward, - the stem area (31) narrows in a radial direction from radially inward to radially outward in degrees in a range between 40% and 80% of the radius (r) of the winding body (27) and / or in a range between 25% and 75% of the length of the ferrite body (30). [22] Use according to claim 21, characterized by that the inductive power transfer is carried out according to the Ki standard. [23] Electric hob (11) with a hob plate (12) and several induction coils (26) according to one of claims 1 to 20 under the hob plate (12), wherein preferably a distance between the top of the winding body (27) and the top (13) of the hob plate (12) is between 5 mm and 13 mm. [24] Electric cooktop according to claim 23, characterized by , that a flat support plate (18) is provided below the hob plate (12), on which all induction coils (26) of the electric hob (11) are placed and preferably fastened, wherein the ferrite bodies (30) are arranged below the winding body (27) and above the support plate (18), wherein in particular the support plate (18) is electrically conductive with an electrical conductivity of at least 20 MS / m, preferably made of aluminium.

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