Induction coil for an electric cooking appliance and electric cooking appliance

Abstract

An induction coil for a hob has a winding body in the form of a flat, spirally wound coil and at least four individual, identical ferrite bodies underneath. The ferrite bodies each have two regions, a first inner region being a stem region which runs in the radial direction, and a second outer region being a head region which adjoins the stem region and is wider at its greatest width in angular degrees than the stem region at its greatest width. In absolute width, it is more than 50% wider than the stem region at its greatest width and projects beyond the winding body in the radial direction. The stem region widens in the radial direction from radially inward to radially outward in absolute width, while it narrows in angular degrees from radially inward to radially outward in a range between 40% and 80% of the radius of the winding body.in a range between 25% and 75% of the length of the ferrite body.

Description

Area of ​​application and state of the art

[0001] The invention relates to an induction coil for an electric cooking appliance, wherein the induction coil comprises a plurality of ferrite bodies. Furthermore, the invention relates to the use of certain ferrite bodies in such an induction coil to inductively transmit power from the induction coil to an electrical load having a counter-induction coil or receiver coil positioned at a certain distance from the induction coil. Finally, the invention also relates to an electric cooktop having a cooktop plate and a plurality of induction coils according to the invention.

[0002] DE 10 2016 208 233 A1 discloses an induction coil with several ferrite bodies arranged below the induction coil to prevent the undesired downward propagation of its magnetic field or to guide the magnetic field lines downward. These ferrite bodies can be shaped either as long rectangles or as circular segments, in particular, as sixths of a circle. These circular segment-shaped ferrite bodies are advantageously arranged in the 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 originate from elongated rectangles and are shaped differently at one end in the end region. Task and solution

[0004] The invention is based on the object of creating an induction coil as mentioned above, an initially mentioned use of ferrite bodies in such an induction coil as well as an electric hob with several such induction coils, with which problems of the prior art can be solved and in particular it is possible to guide the magnetic fields generated by the induction coil well and efficiently, in particular in the case of an aforementioned use for inductive power transmission, which can be carried out according to the Ki standard.

[0005] This object is achieved by an induction coil having the features of claim 1, by the use of ferrite bodies in an induction coil having the features of claim 15, and by an electric hob with a hob plate and a plurality of induction coils below it having the features of claim 16. Advantageous and preferred embodiments of the invention are contained in the subclaims 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 hob. However, they are intended to be able to apply independently and independently of one another to such an induction coil, such a use, and such an electric hob. The wording of the claims is incorporated into the content of the description by express reference.

[0006] The induction coil according to the invention is intended to be installed and used in an electric hob, in particular beneath a hob plate of the hob, advantageously together with other induction coils. The induction coil has a winding body in the form of a flat, spirally wound coil, as is conventional. The winding body is wound from coil wire or so-called coil strand and has an inner connection and an outer connection. These advantageously extend from the winding body as a continued coil wire. Furthermore, the induction coil has at least four individual, identical or identically formed ferrite bodies arranged beneath the winding body. The ferrite bodies 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.

[0007] According to the invention, the ferrite bodies each have two regions, a first region being arranged on the inside and being a stem region. This stem region runs essentially in the radial direction. A second region is arranged radially on the outside and is a head region or forms a head region. This head region adjoins the stem region, advantageously in a transition region formed here. The head region is wider at its greatest width in angular degrees than the stem region at its greatest width viewed in the circumferential direction or more than 50% wider in the circumferential direction than the stem region at its greatest width viewed in the circumferential direction. In other words, the head region can be more than 50% wider or at its greatest width in angular degrees wider than the stem region where it has the smallest width in angular degrees or as an 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 considered to be T-shaped.

[0008] Furthermore, the head region at least partially projects beyond the winding body in the radial direction or protrudes beyond it in the radial direction. This can be between 5% and 30% of the radius of the winding body. The stem region does not run with a continuous absolute width, but widens in the radial direction from radially inward to radially outward. This advantageously applies to its absolute width, but not to its width in degrees or as an arc angle; here it can vary or its width can even decrease. Such a width direction runs essentially along a circumferential direction of the winding body or approximately at right angles to the radial extent of the ferrite body or the stem region.The stem region narrows in the radial direction from radially inside to radially outside in angular 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.

[0009] In other words, the lateral sides of the stem region of two directly adjacent ferrite bodies can meet the condition 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 entire circumference of this circle. The radius of this arbitrary circle can be between 40% and 90% of the radius of the winding body. Thus, this can apply in a circular ring region between 70% and 90% of the radius of the winding body. The sum of all distances can advantageously be between 50% and 70% of the entire circumference of said circle.

[0010] This specific geometric design ensures that reasonably large distances are provided between adjacent ferrite bodies in the central outer region. These distances, especially for the aforementioned power transmission application, ensure that magnetic coupling into a low-impedance support plate beneath the induction coils in an electric cooktop remains low. This way, on the one hand, losses in the support plate can be limited, and on the other hand, the inductance of the aforementioned receiver coil is not increased excessively by the significantly large recesses or free spaces between the ferrite bodies. This would lead to a detuning of the resonant frequencies for inductive power transmission, which would be very detrimental to this.

[0011] Furthermore, the widened head areas on the outside of the induction coil and the relatively close radially inner ends of the ferrite bodies ensure that the inner winding circumference is magnetically short-circuited with the outer winding circumference almost across its entire circumference. The magnetic flux increases radially from the inside to the radially outside, which is why the absolute width of the ferrite bodies advantageously increases in this direction. In the case of inductive power transmission of high power levels, particularly large magnetic fluxes occur, and the specific shape of the ferrite bodies is intended to prevent saturation. Thus, it can advantageously be provided that an induction coil with its ferrite bodies, which is also or primarily used for inductive power transmission, is designed differently or has differently designed ferrite bodies designed according to the invention.Due to their special shape and the projection of the ferrite bodies over the winding body, no magnetic field components are coupled into an area located below the induction coil, in particular into a metallic support plate, even radially inside and radially outside.

[0012] In an advantageous embodiment of the invention, the ferrite bodies of one or more induction coils can be designed identically, at least with their head regions, i.e., they can have identical head regions. This also advantageously applies to the aforementioned stem region, in particular at its radially inner end. Overall, it can be provided that all ferrite bodies of this induction coil are designed identically for an induction coil or even for all induction coils of the same size in a corresponding hob, at least if they are also intended for inductive power transmission. The use of similar regions or even identical ferrite bodies simplifies assembly and makes it more cost-effective. It is particularly advantageous for the ferrite bodies to be designed in one piece with their specific shape, i.e., they are 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 support plate. Furthermore, it can simplify mechanical fastening of the ferrite bodies during assembly.

[0013] In an embodiment of the invention, it can be provided that the lateral sides or outer sides of the stem region run straight in the radial direction for at least 50% of their length, preferably over a length of 65% to 90%. This makes it easy to achieve a widening, as defined above, from radially inward to radially outward in absolute terms. Alternatively to the straight direction, they can run in a slightly curved shape.

[0014] The distance in angular degrees between the two lateral sides of the stem area of ​​a ferrite core can decrease from radially inward to radially outward, preferably continuously. It is therefore 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 core.

[0015] In an embodiment of the invention, the arc angle in degrees between the two lateral sides of the stem region of a ferrite body can increase from radially outside to radially inside, whereby it can preferably even increase continuously or monotonically or even strictly monotonically. Thus, the width in the stem region, viewed in millimeters, can decrease from radially outside to radially 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, which advantageously amounts to more than 50% in degrees.

[0016] In a further development of the invention, it can be provided that the radially inner end regions of the stem regions taper even more sharply than the lateral sides of the stem regions over their essential length, preferably between 60% and 90% of the length. These radially inner end regions can be between 10% and 30% of the length of the ferrite bodies. This even greater taper can ensure that the stem regions are drawn relatively far toward the center of the induction coil without touching each other. Their width between the two lateral sides of the end regions in angular degrees can increase from radially inside to radially outside or remain the same.

[0017] In a further development of the invention, the aforementioned lateral sides of the tapered end regions of adjacent ferrite bodies can be spaced apart by at least 5 mm or 5% of the circumference of a circle in this region, advantageously even 8 mm to 12 mm. Thus, an aforementioned internal connection can be passed between two adjacent ferrite bodies and at their height. Even if this internal connection only needs to be passed at a single point between two adjacent ferrite bodies, the aforementioned spacing requirement can be advantageous for the realization of identical ferrite bodies and their regular arrangement under the winding body.

[0018] In one embodiment of the invention, it can be provided that the tapered end regions of the stem regions do not taper to a point, but are cut at right angles to the radial direction or the radial longitudinal extension of the stem regions. They can be cut straight, or alternatively, they can be curved, in particular curved inward.

[0019] A free zone can advantageously be provided radially within the tapered end regions of the ferrite bodies, in which no ferrite bodies or no ferrite material, and also no coil windings, are provided. Such a free zone can have a diameter between 2% and 12% of the maximum radius of the winding body. Such a free zone is provided primarily when the winding body is designed as a wide circular ring and also has a free inner zone. In this case, no ferrite material in the form of one or more ferrite bodies needs to be provided in its central inner zone, thus enabling the aforementioned free zone.

[0020] It can be provided that the radially innermost winding of the winding body is arranged above the tapered end regions, so that they extend radially inward beyond this innermost coil winding. This allows the magnetic field of the induction coil to be directed both radially inward and radially outward as desired.

[0021] In a further embodiment of the invention with regard 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 in absolute width can be between 0.7 and 1.5, preferably between 0.9 and 1.2. It can be provided that the distance is smallest where the ferrite bodies are narrowest, in particular at the inner ends. In some circumstances, the aforementioned internal connection does not even have to be passed through here, which is why they can have the smallest distance from one another precisely here. 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 in angular degrees can be between 1.5 and 5, preferably between 2.5 and 3.5.

[0022] In an alternative embodiment of the invention, the distance between adjacent ferrite bodies at the head region can be as small as the smallest distance at the end regions, measured in absolute numbers.

[0023] The distance in angular degrees between two adjacent ferrite bodies at the head regions can be between 2° and 8°. The minimum distance between two adjacent ferrite bodies at the end regions can be between 10° and 20°.

[0024] 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, of the total circumference can be more than 40% at any point of the radial extension, so that, so to speak, no point is an even greater distance between adjacent ferrite bodies provided. Advantageously, this proportion can even be more than 50% for more than half of the radial extension, i.e., in a significant area, more than 50% of a circle does not extend 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.

[0025] In a further development of the invention, a transition region can be provided between the head region and the stem region. It can be rounded, which facilitates mechanical stability and the production of the ferrite bodies. The radius of the rounded transition region can be between 5% and 20% of the radius of the winding body. Preferably, the absolute width distance between two adjacent ferrite bodies can be greatest in this transition region, with the transition region in particular lying between or covering 70% and 105% of the radius of the winding body.

[0026] Furthermore, the distance between adjacent ferrite bodies can be provided in the aforementioned transition region, so it can advantageously be between 70% and 90% of the radius of the winding body. This makes it possible for the head region to be pulled very far to the side or become very wide relatively quickly, radially adjoining the transition region. This allows the head regions to have their greatest width slightly radially outside the winding body, with their ends almost touching one another.

[0027] A significant portion of the surface of the head region can be located radially outside the winding body and thus protrude radially beyond it. This can be at least 50%, preferably between 65% and 95%. In particular, the head region can increase significantly in width radially outside the outermost winding of the winding body. The transition region is advantageously located directly beneath this outermost winding.

[0028] Overall, the ferrite bodies can be designed to cover between 40% and 70% of the winding body's surface. Particularly advantageously, this can be between 45% and 60%, for example, approximately half.

[0029] Even if the stem section is considerably longer than the head section in the radial direction, it can still have a radial extension of between 10% and 35% of the stem section's radial length. Its width can be several times greater than its radial extension, thus achieving the T-shaped shape mentioned above.

[0030] For example, the absolute width of the head region along the circumferential direction can be 30% to 100% larger than the absolute width of the stem region before the transition to the head region or before the aforementioned transition region. This can also achieve the aforementioned T-shaped shape of the ferrite body.

[0031] 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 angular degrees. A minimum distance between two adjacent ferrite bodies at the end regions can be between 10° and 20° in angular degrees. Thus, the distance in angular degrees can be greater at the end regions of the stem regions than at the head regions. This can be justified primarily by the previously explained goal 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 beneath a ferrite body, which would otherwise add up their thicknesses.

[0032] The ferrite bodies are advantageously designed with mirror symmetry, allowing them to be correctly mounted, for example, with the bottom facing up. This mirror symmetry is advantageously related to an axis that runs exactly radially in the direction of the induction coil and the winding body.

[0033] The arrangement of the ferrite bodies is preferably axially symmetrical, in particular also point-symmetrical. It is particularly preferably axially symmetrical to two mutually perpendicular axes of symmetry, whereby these axes of symmetry can run between two ferrite bodies or through two ferrite bodies. Particularly advantageously, one axis of symmetry runs exactly centrally through two opposing ferrite bodies, and the other either also runs or runs exactly between two adjacent ferrite bodies. Additionally or alternatively, the arrangement of the ferrite bodies on an induction coil can be point-symmetrical, preferably to a center point of the induction coil and the winding body.

[0034] In a further development of the invention, it can be provided that the head region is formed by two head end sections or that it has such head end sections. They are preferably formed transversely or at right angles to the longitudinal direction of the stem region. They can be tapered towards their free ends, in particular they can be rounded at the free ends. Particularly advantageously, the smallest distance between adjacent ferrite bodies in absolute width and in degrees of angle exists at these protruding head end sections. In this way, a largely or almost closed circumferential ring made of ferrite material can be created, which runs around the winding body for the reasons stated above due to the specific mode of operation in wireless energy transmission with high power.

[0035] It is advantageous that the outer edge of the winding body or its outermost winding runs exactly over the transition area between the stem area and the head area. This ensures that the radially inner area of ​​the ferrite body, namely the stem area, which is covered by the winding body, does not protrude significantly radially outwards. The head area provided here outside the winding body can be considerably wider outside the winding body. It can be provided that the outermost winding of the winding body runs exactly between the stem area and the head area, i.e., centrally between the two, so to speak, above the transition area.

[0036] Preferably, the ferrite bodies, or each ferrite body, have a constant and identical thickness. This can advantageously be between 3 mm and 7 mm, particularly advantageously approximately 5 mm. This is sufficient to guide the magnetic field lines as described above. At the same time, the overall height of the finished induction coil is not excessively high.

[0037] As a further geometric specification, the ferrite bodies can be 5 cm to 15 cm in the radial direction. Advantageously, more than 75% of this length is the length of the stem regions.

[0038] The ferrite bodies are preferably formed as a single piece, which simplifies assembly and allows them to better direct the magnetic flux. They can be made of pressed ferrite material, which can then be ground to a defined shape. While the outer contour of the ferrite body is preferably relatively complex, a ferrite body cannot have any holes, openings, or recesses within this outer contour.

[0039] The aforementioned internal connection of the winding body can be extended from the innermost coil winding with coil wire or coil strand and run between two radially inner ends or the previously described end areas of adjacent ferrite bodies. It can therefore run in the same plane as the ferrite bodies and not beneath them, thereby reducing the overall height. In this case, the internal connection can then run radially outward between two ferrite bodies from the innermost winding and emerge, for example, below the winding body where the external connection also branches off. Thus, they can form a common connection strand, which simplifies the installation and connection of the induction coil in the cooktop.

[0040] As previously explained, ferrite bodies with a previously described shape, in particular the T-shaped shape, are not only generally used in a hob or in an induction hob in a unit with an induction coil, but primarily for inductive power transmission to a named electrical consumer, for example, a kitchen appliance such as a mixer, toaster, or the like, which has a receiver coil. This results in an inductive power transmission known from the prior art, which provides current or electrical energy in the electrical consumer for its operation. Such inductive power transmission can advantageously be carried out according to the Ki standard, see, for example, DE 10 2021 201 220 A1. A named receiver coil should be similar in size to the induction coil, but can also have a different size.

[0041] The inventive shape of the ferrite bodies is particularly important for such inductive power transmission, in which an almost closed ring of ferrite material is present in the outer region of the winding body, which is essentially formed by the widened head regions described above. In the central region of the winding body, less ferrite material is provided, or neighboring ferrite bodies are spaced significantly apart, since otherwise the magnetic resistance would become too great. In the radially inner region of the winding body, ferrite material is also provided in a circular pattern with slight interruptions; however, this can be achieved without widening the ferrite bodies, since with correspondingly small radii in this region they are relatively close to one another or have a relatively short distance between them.

[0042] An electric hob according to the invention has a hob plate and several induction coils; advantageously, there can also be several such induction coils. The hob plate can advantageously be made of conventional material such as glass ceramic with a thickness of a few millimeters, advantageously 3 mm to 5 mm, in particular 4 mm. The distance between the top side of the winding body and the top side of the hob plate should not be too large, both for inductive cooking on the one hand and for the aforementioned inductive power transmission to an electrical consumer with a receiver coil placed on the hob plate on the other. Thus, the distance between the top side of the winding body and the top side of the hob plate can be between 5 mm and 13 mm, particularly advantageously approximately 8 mm.

[0043] Below the hob plate, a flat support plate is preferably provided, on which an aforementioned induction coil according to the invention is placed, particularly advantageously all induction coils of this hob. 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 of greater than 20 MS / m.

[0044] These and other features emerge not only from the claims but also from the description and the drawings. The individual features may be implemented individually or in combination in an 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 generality of the statements made therein. Brief description of the drawings

[0045] Further advantages and aspects of the invention emerge from the claims and from the description of exemplary embodiments of the invention, which are explained below with reference to the figures. In the figures: Fig. 1 a sectional view through a hob according to the invention with three conventional induction heating coils and one induction coil according to the invention, Fig. 2 a plan view of the hob from Fig. 1 with the induction coil according to the invention at the front right, Fig. 3 a plan 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 from Fig. 3 on a support plate of the hob, Fig. 5 a plan view of one of the ferrite bodies from Fig. 3 , Fig. 6 an oblique view from the front of the ferrite body made of Fig. 5 and Fig. 7 an enlarged section of the induction coil from Fig. 3 with drawn lines corresponding to different angle degrees as well as a percentage scale related to the radius of the winding body. Detailed description of the implementation examples

[0046] In the Fig. 11 shows a hob 11 according to the invention in a side sectional view, which is largely constructed as known. The hob 11 has a conventional hob plate 12 with a top side 13 and a bottom side 14. A housing 16 is arranged on the bottom side 14, in which the various functional units of the hob 11 are located. A support plate 18 made of aluminum, advantageously with the aforementioned high conductivity of 20 MS / m or even higher, runs parallel to the hob plate 12 and extends within the housing 16. In front of this, an operating device 20 is arranged in a separate housing, which, among other things, has a rotary knob 22 that can be placed on the top side 13 for operating the hob 11.

[0047] 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, namely at the front right according to the Fig. 2 The induction heating coils 24a to 24c serve only for the inductive heating of a cooking vessel placed on top. The induction coil 26 according to the invention can, of course, also be used for the inductive heating of a cooking vessel. On the other hand, however, it can also be used to operate a consumer placed above the cooktop plate 12 in accordance with the Ki standard mentioned above. However, the cooktop 11 could also have more or even only such induction coils according to the invention.

[0048] The consumer here is a mixer 40 having a mixer container 41. This advantageously contains a stirrer 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 upper side 13 of the cooktop plate 12. A receiver coil 43 is provided in the mixer base 42, advantageously as far down as possible or as close as possible to the cooktop plate 12 and thus also to the induction coil 26 arranged underneath. This receiver coil 43 can be somewhat smaller than the induction coil 26 according to the invention, but the sizes can also differ 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.

[0049] The Fig. 3shows a plan view of the induction coil 26 according to the invention. It has a conventional winding body 27, which is wound flat, spirally, and 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 seamlessly 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 up to electrical connection terminals in the housing 16. Similarly, an internal connection 29 extends seamlessly from the innermost winding of the winding body 27, which is guided radially outwards and then runs together with the external connection 28.

[0050] Below the winding body 27, six identical ferrite bodies 30 are arranged, which are shown in dashed lines in this area. Their arrangement is evenly distributed, with the ferrite bodies 30 protruding slightly below the winding body on the inside and outside. Fig. 4 the induction coil 26 can be seen in an oblique view, where it is placed on the support plate 18 with the ferrite bodies 30 facing downwards.

[0051] In connection with the Figs. 5 and 6 and the detailed designation provided therein, the special shape of the ferrite bodies 30 is explained 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. 3Located in a central free area of ​​the winding body 27, the stem region 31 merges into the tapered end region 34. At the very lower end, this end region 34 is cut off at a right angle to the longitudinal direction of the stem region 31, whereby this could also be more or less rounded, and the corners could also be rounded.

[0052] The stem area 31 widens in a radially outward direction, relative to the induction coil 26 or its winding body 27 according to Fig. 3, namely by approximately 35%. It advantageously has straight lateral sides 32a and 32b, thus widening evenly. A head region 37 adjoins the widened stem region 31 with a transition region 36. In the transition region 36, the ferrite body 30 widens from the lateral sides 32a and 32b with a wide curve. The ferrite body 30 then transitions into the head region 37, where it is greatly widened. There, it forms the outwardly facing head end sections 38a on the left and 38b on the right. The outwardly facing outer edge of the head region 37 is highly rounded and runs, in particular, 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.

[0053] The lateral sides 32a and 32b are largely straight here between the tapered end region 34 and just before the transition region 36, or almost to it. The transition to the tapered end region 34 is provided with a corner, but could also be rounded. Likewise, the lateral sides of the tapered end region 34 could be slightly curved or arched. A slight rounding could also be provided on the inward-facing end side instead of the corners shown.

[0054] The specific shape of the six ferrite bodies 30 according to Fig. 3is due to the fact that, on the one hand, an identical design offers advantages for their manufacture and assembly and is therefore more cost-effective. Furthermore, the shape of the ferrite bodies 30 ensures that as much ferrite material as possible is provided radially far in and radially far out, or in the area of ​​the innermost winding and the outermost winding of the winding body 27, viewed in the circumferential direction, or that this material is present as nearly as possible in a circle. Radially on the inside, the ferrite bodies 30 must have a certain distance from one another, which in practice can be the 8 mm mentioned at the beginning. In this way, the inner connection 29 can be led through in the plane of the winding body 27 without the structural height of the induction coil 26 having to be increased. This would otherwise be the case if the ferrite bodies 30 were in the inner free area orunder the innermost winding of the winding body 27 or would be so close to each other that the inner terminal 29 would have to be passed under the ferrite bodies 30. At the same time, one can see in the . Fig. 3but also that due to the relatively small distance between the tapered end regions 34 of the ferrite bodies 30, a lot of ferrite material is provided in this area. Thus, the entire magnetic flux can be guided in the ferrite material, so that ultimately no magnetic field components can couple with the support plate 18 below. Especially when a relatively large magnetic flux can occur without saturation due to a poor phase angle between the currents in the induction coil 26 and in the receiver coil 43, the ferrite bodies 30 should have sufficient volume in these end regions 34. Therefore, the width of the ferrite bodies 30 in angular degrees also increases in this area, or, as shown here, at least does not decrease significantly. This can also be seen from the Fig. 7 can be seen.

[0055] Similarly, the ferrite bodies 30 are also designed to be so wide in the area of ​​the outermost winding of the winding body 27, or even radially outside of it, that they almost touch the protruding head end sections 38a and 38b, compared to their large circumference. Thus, in this area as well, the entire magnetic flux can be conducted in the ferrite bodies 30, or rather, in the head regions 37, i.e., again in the ferrite material.

[0056] In the main area of ​​the surface of the winding body, especially in an outer area, the ferrite bodies 30 with their stem areas 31 are relatively narrow or even become narrower from radially inside to radially outside towards the head areas 37. This is illustrated by the representation in angular degrees according to Fig. 7in the range between 60% or 70% and 90%. This creates large, approximately triangular free surfaces between adjacent ferrite bodies 30, in which no ferrite material is arranged under the winding body 27. In this way, 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, can be reduced. The coupling here is relatively large due to the relatively small distance of in practice between 8 mm and 13 mm between the induction coil 26 and the receiver coil 43 according to. Fig. 1. With such an inductive power transmission, high powers are transmitted with high coupling at operating frequencies significantly below the resonant frequency of the receiver coil 43, with relatively small phase angles in terms of magnitude existing 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 transmission can fall below the permitted minimum operating frequency of 20 kHz if a rated power of, for example, 2200 W is to be achieved in the consumer. Furthermore, the phase angle of the current through the receiver coil to the current through the induction coil 26 would otherwise deteriorate. This would require an even larger current through the induction coil 26 to induce the same power in the receiver coil 43 orthe mixer 40 or the consumer, which would increase losses. This can be reduced by the larger free areas between two adjacent ferrite bodies 30.

[0057] Compared to a simple T-shape of the ferrite bodies 30, which would consist, so to speak, of two elongated rectangles joined together, the shape according to the invention exhibits good coupling due to the ferrite material of the ferrite bodies 30 being relatively closely connected to one another in the circumferential direction at the very inside and very outside. Furthermore, the ferrite material on the inner circumference of the innermost winding of the winding body 27 can be magnetically connected to the outer circumference or the outermost winding of the winding body 27 with a low-impedance magnetic connection. Due to the large free surfaces between adjacent ferrite bodies 30, the aforementioned cross-effect on the receiver coil 43 can be reduced. The magnetic flux density here is at its maximum at the transition from the stem region 31 to the head region 37, i.e., in the region of the transition region 36.

[0058] To explain the exact shape of the ferrite bodies 30 when viewed in angular degrees, reference is made to the Fig. 7At 0° angular degree lies an axis of symmetry of the axially symmetrical ferrite body 30. The narrowest width in angular degrees is at or just before the transition area 37, namely at the line at 13° angular degree. In comparison with the line at 15° angular degree, it can be seen that the left lateral side 32a intersects it, approximately in its central region. This results in the stem area 31 becoming narrower in angular degrees from radially inside to radially outside, although it naturally becomes wider in absolute width, i.e., measured in millimeters. At the line at 15° angular degree lies the transition area 36, ​​or 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.

[0059] The sides of the end region 34 run almost radially, at an angle of approximately 22° here. Thus, similar to the stem region 31, the end region 34 becomes slightly narrower from the radial inside to the radial outside.

[0060] The outermost ends of the head end sections 38a are at approximately 27.5°, so that their distance from the 30° line, 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, similar to that at the tapered end regions 34.

[0061] As explained above, the width of the stem region 31, or the distance between the two lateral sides 32a and 32b, decreases radially in the range between just under 40% and approximately 80%. Radially within this width, the sides of the ferrite body 30 extend in the tapered end regions 34 in such a way that their distance in angular degrees remains almost unchanged.

[0062] The Fig. 7 also shows that the radial extension of the head regions 30 is relatively small and amounts to only about 15% of the maximum radius of the winding body 27.

Claims

1. Induction coil for an electric cooking appliance, in particular for a hob with a hob plate and with at least one induction coil arranged underneath, wherein the induction coil comprises: - a winding body in the form of a flat, spirally wound coil, which is wound from coil wire and which has an inner terminal and an outer terminal, - at least four individual identical ferrite bodies under the winding body, characterized in that: - the ferrite bodies each have two regions, wherein: - a first inner region is a stem region, - the stem region runs essentially in the radial direction, - a second outer region is a head region, and - the head region adjoins the stem region and is wider in angular degrees at its greatest width than the stem region at its greatest width and more than 50% wider in absolute width than the stem region at its greatest width, - the head region at least partially projects beyond or protrudes over the winding body in the radial direction, - the stem region widens in absolute width in the radial direction from radially inside to radially outside, - the stem region narrows in angular degrees in the radial direction from radially inside to radially outside 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.

2. Induction coil according to claim 1, characterized in that the ferrite bodies are designed to be at least identical to the head region, preferably also to the stem region, and in particular all ferrite bodies of the induction coil are designed to be identical.

3. Induction coil according to claim 1 or 2, characterized in that the distance in angular degrees between the two lateral sides of the stem region of a ferrite body decreases from radially inside to radially outside, in particular in a range between 20% and 80% of the maximum radius of the winding body.

4. Induction coil according to one of the preceding claims, characterized in thatradially inner end regions of the stem regions taper even more sharply than the lateral sides of the stem region over its essential length, wherein in particular the width in angular degrees between the two lateral sides of the end regions increases from radially inside to radially outside or remains the same, wherein preferably the lateral sides of the tapered end regions of adjacent ferrite bodies have a distance of at least 5 mm or 5% of the circumference of a circle in this region from one another, in particular 8 mm to 12 mm.

5. Induction coil according to claim 4, characterized in that radially within these tapered end regions, a free area is provided which is free of ferrite bodies and windings, wherein the diameter of the free area is preferably 2% to 20% of the maximum radius of the winding body.

6. Induction coil according to claim 4 or 5, characterized in thatthe innermost winding of the winding body is arranged over the tapered end regions, preferably approximately over half their length in the radial direction.

7. Induction coil according to claim 4 or 5, characterized in that the ratio between the smallest distance between adjacent ferrite bodies at the end regions to the smallest distance between adjacent ferrite bodies at the head regions in absolute width is between 0.7 and 1.5 and / or the ratio between the smallest distance between adjacent ferrite bodies at the end regions to the smallest distance between adjacent ferrite bodies at the head regions in angular degrees is between 1.5 and 5, preferably between 2.5 and 3.

5.

8. Induction coil according to one of the preceding claims, characterized in thata distance between two adjacent ferrite bodies at the head regions is between 2° and 8° in angular degrees and / or a minimum distance between two adjacent ferrite bodies at the end regions is between 10° and 20° in angular degrees.

9. Induction coil according to one of the preceding claims, characterized in that the head region adjoins the stem region in a transition region and the transition region is rounded, wherein preferably the distance in absolute width between two adjacent ferrite bodies is greatest in this transition region, wherein in particular the transition region lies or covers between 70% and 105% of the radius of the winding body.

10. Induction coil according to one of the preceding claims, characterized in thatat least 50%, preferably between 65% and 95%, of the area of ​​the head region is arranged radially outside the winding body and protrudes radially beyond it and / or that the head region has a radial extension of between 10% and 35% of the radial extension of the stem region.

11. Induction coil according to one of the preceding claims, characterized in that an absolute width of the head region along the circumferential direction is 30% to 100% more than the absolute width of the stem region before the transition into the head region.

12. Induction coil according to one of the preceding claims, characterized in thatthe head region has two head end sections projecting transversely or at right angles to the longitudinal direction of the stem region, which are tapered, in particular rounded at the free ends, wherein the smallest distance in absolute width and in angular degrees between two adjacent ferrite bodies is preferably at these projecting head end sections.

13. Induction coil according to one of the preceding claims, characterized in that the outer edge of the winding body or the outermost winding of the winding body runs over the transition area between the stem area and the head area of ​​the ferrite body, whereby preferably the outermost winding runs exactly between the stem area and the head area.

14. Induction coil according to one of the preceding claims, characterized in thatthe inner connection runs between two radially inner ends or end regions according to one of claims 4 to 8 of the ferrite body or the stem region, in particular in the same plane as the ferrite bodies, preferably running radially outwards from the innermost winding.

15. Use of ferrite bodies in an induction coil for inductive power transmission, in particular according to the Ki standard, from the induction coil to an electrical consumer which is positioned at a distance from the induction coil and has a receiver coil, wherein the ferrite bodies are constructed as follows: - the ferrite bodies each have two regions, wherein: - a first inner region is a stem region, - the stem region runs essentially in the radial direction, - a second outer region is a head region, and - the head region adjoins the stem region and is wider in angular degrees at its greatest width than the stem region at its greatest width and is more than 50% wider in absolute width than the stem region at its greatest width, - the head region at least partially projects beyond the winding body in the radial direction orprotrudes beyond it, - the stem area widens in absolute width in the radial direction from radially inside to radially outside, - the stem area narrows in angular degrees in the radial direction from radially inside to radially outside 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.

16. Electric hob with a hob plate and several induction coils according to one of claims 1 to 14 under the hob plate, wherein preferably a distance between the top of the winding body and the top of the hob plate is between 5 mm and 13 mm.

17. Electric hob according to claim 16, characterized in thatA flat support plate is provided beneath the hob plate, on which all induction coils of the electric hob are placed and preferably fastened, wherein the ferrite bodies are arranged beneath the winding body and above the support plate, wherein in particular the support plate is electrically conductive with an electrical conductivity of at least 20MS / m, preferably made of aluminum.

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