Induction coil for electric cooking utensil and electric cooking utensil

Abstract

The invention discloses an induction coil for an electric cooking utensil and the electric cooking utensil. An induction coil for a cooking range has a winding body in the form of a flat, helically wound coil and at least four identical, separate ferrite bodies underneath the winding body. The ferrite bodies each have two regions, with a first inner region being a radially extending stem region and a second outer region being a head region which adjoins the stem region and which is angularly wider at its maximum width than at its maximum width. In terms of the absolute width, the width of the rod portion is larger than 50% of the maximum width of the rod portion, and the radial direction of the rod portion protrudes beyond the winding body. The shank region widens radially in terms of absolute width from the radially inner side to the radially outer side, where the shank region narrows radially in terms of angle from the radially inner side to the radially outer side over a range of between 40% and 80% of the radius of the winding body or over a range of between 25% and 75% of the length of the ferrite body.

Description

Technical Field

[0001] The present invention relates to an induction coil for an electric cooking appliance, wherein the induction coil comprises a plurality of ferrite bodies. Furthermore, the present invention relates to the use of specific ferrite bodies in such an induction coil for transmitting induced power from the induction coil to an electrical consumer having a counter-induction coil or receiving coil positioned at a given distance from the induction coil. Finally, the present invention relates to an electric cooktop (or "induction hob") having a cooktop and a plurality of induction coils according to the present invention. Background Art

[0002] DE 102016208233 A1 discloses an induction coil having a plurality of ferrite bodies arranged below the induction coil to prevent an undesired downward transmission of its magnetic field or a downward routing of magnetic field lines. The ferrite bodies can be in the form of either an elongated rectangle or a segment of a circle, in particular, for example, up to one-sixth of a circle. The ferrite bodies in the form of a circle segment are advantageously arranged in the corner regions of the substantially rectangular induction coil.

[0003] An alternative configuration of ferrite bodies for induction coils is known from EP 1 991 030 A2. These have a shape that is essentially based on an elongated rectangle, which can be configured differently at one end in the end region. Summary of the Invention

[0004] The object of the present invention is to provide an induction coil as mentioned above, the use as mentioned above of a ferrite body in such an induction coil and an electric cooktop having a plurality of such induction coils, with which the problems of the prior art can be solved and which in particular allow the magnetic field generated by the induction coil to be efficiently and effectively conducted, in particular in the case of the use as mentioned above 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 a ferrite body in an induction coil having the features of claim 22, and by an electric cooktop having a cooktop and a plurality of induction coils thereunder having the features of claim 24. Advantageous and preferred embodiments of the invention are contained in the dependent claims and are explained in more detail below. Some of the features are described herein with respect to the induction coil only, the use only, or the electric cooktop only; however, they are intended to be applicable on their own and are independent of each other, not only with respect to the induction coil and the use, but also with respect to the electric cooktop. The wording of the claims is expressly incorporated into the description by reference.

[0006] The induction coil according to the present invention is intended for installation and use in electric cooktops, particularly beneath the cooktop, advantageously in conjunction with another induction coil. The induction coil, as is conventional in principle, comprises a winding body in the form of a flat, spirally wound coil. The winding body is wound from coil wire or so-called stranded coil wire and has internal and external connections. These connections advantageously extend from the winding body as the coil wire progresses. Furthermore, the induction coil comprises at least four independent, identical or identically configured ferrite bodies arranged beneath the winding body. These ferrite bodies are advantageously arranged adjacent to one another in the circumferential direction of the induction coil. They may cover between 30% and 70% of the area of ​​the winding body.

[0007] According to the present invention, each ferrite body has two regions. The first region is arranged on the inner side and constitutes the shank region. The shank region extends substantially in the radial direction. The second region is arranged radially to the outer side and is or forms the head region. The head region adjoins the shank region, advantageously in a transition region formed at that point. Angularly, when viewed in the circumferential direction, the head region is wider than the shank region at its maximum width, or, when viewed in the circumferential direction, is wider than the shank region at its maximum width by more than 50%. In other words, the head region is angularly wider at its maximum width by more than 50% or more than the shank region at the point where the shank region has its minimum width, angularly or as a circular arc. Advantageously, however, in each case, when viewed in the circumferential direction, the head region is no more than 150% wider than the shank region at its maximum width. The ferrite body can thus be considered to be very close to a T-shaped configuration.

[0008] Furthermore, the head region at least partially protrudes radially beyond the winding body or projects radially beyond it. This can amount to between 5% and 30% of the radius of the winding body. The shank region does not extend with a continuous absolute width, but rather widens radially from the radial inside to the radial outside. This advantageously applies to its absolute width, but not to its angular width or width measured as a circular arc angle; in these cases, it can vary or even decrease in width. This width direction extends essentially in the circumferential direction of the winding body, or approximately at right angles to the radial extension of the ferrite body or the shank region. The shank region narrows radially angularly from the radial inside to the radial outside over a range between 40% and 80% of the radius of the winding body and / or over a range between 25% and 75% of the length of the ferrite body (preferably when viewed radially).

[0009] In other words, the lateral sides of the shaft regions of two directly adjacent ferrite bodies can satisfy the following condition: the sum of all distances between the ferrite bodies on any desired circle around the center point of the winding body amounts to at least 40% of the total circumference of this circle, preferably between 50% and 70%. The radius of the desired circle can be between 40% and 90% of the radius of the winding body. Thus, this can apply to a circular ring ranging between 70% and 90% of the radius of the winding body. Advantageously, the sum of all distances can amount to between 50% and 70% of the total circumference of the circle.

[0010] This specific geometrical embodiment ensures that reasonably large distances are provided between adjacent ferrite bodies in the middle and outer regions. These distances ensure that (particularly for the use described above for power transmission) the magnetic coupling into the low-resistance support plate below the induction coil in the electric cooktop remains low. In this way, on the one hand, the losses in the support plate remain limited, and on the other hand, the inductance of the aforementioned receiving coil is not excessively increased by the openings or free areas of significant size between the ferrite bodies. This would lead to a detuning of the resonant frequency for inductive power transmission, which would be very disadvantageous for it.

[0011] Furthermore, the widened head region on the outside of the induction coil and the relatively closely adjacent radially inner end of the ferrite body ensure that the inner winding circumference is magnetically short-circuited with the outer winding circumference over substantially the entire circumference. The magnetic flux increases from the radial inside to the radial outside, so the absolute width of the ferrite body advantageously increases in this direction. In the case of high-power inductive power transmission, particularly high magnetic fluxes arise, and the specific shape of the ferrite body is intended to avoid saturation. For example, it can be advantageous to provide that the induction coil with its ferrite body (which is also used for inductive power transmission or primarily for inductive power transmission) is configured differently or has a differently configured ferrite body and a ferrite body configured according to the present invention. Its specific shape and the extension of the ferrite body beyond the winding body also ensure that no magnetic field components are coupled radially inwardly or radially outwardly into the area below the induction coil, in particular into the metal support plate.

[0012] In an advantageous embodiment of the present invention, the ferrite bodies of an induction coil or of the induction coil are configured identically at least in their head region, i.e., have a uniform head region. This also advantageously applies to the shaft region, particularly at its radially inner end. For an induction coil, or even for all induction coils of the same size for a corresponding cooktop, it can be provided that all ferrite bodies of the induction coil are configured identically, at least if they are also designed for inductive power transmission. The use of uniform regions, or even identical ferrite bodies, simplifies assembly or makes it more cost-effective. The ferrite bodies are particularly advantageous when they are configured as a single piece in their specific shape, i.e., not assembled from separate parts. This prevents magnetic fields from leaking at the joints between the individual parts and thus causing losses in the winding body and the support plate. Furthermore, it simplifies the mechanical fastening of the ferrite bodies during assembly.

[0013] In one embodiment of the invention, the lateral or outer sides of the shaft region can be extended in a straight line in the radial direction over at least 50% of their length, preferably over 65% to 90% of their length. This makes it easier to ensure that, as defined above, they widen in absolute terms from the radial inside to the radial outside. Instead of extending straight, they can also be slightly curved.

[0014] The angular distance between the two lateral sides of the shank region of the ferrite body can decrease (preferably continuously) from the radially inner side to the radially outer side. The decrease can thus be continuous. In particular, the distance can decrease over a range of between 20% or 30% and 80% of the maximum radius of the winding body.

[0015] In one embodiment of the invention, the arc angle between the two lateral sides of the shank region of the ferrite body can increase in angular terms from the radially outer side to the radially inner side, wherein it can preferably even increase continuously or monotonically or even strictly monotonically. Thus, although the width in the shank region can decrease by millimeters from the radially outer side to the radially inner side, the shank region of the ferrite body can occupy an increasingly larger proportion (or "ratio") relative to the circle or in the circumferential direction, which advantageously amounts to more than 50% in angular terms.

[0016] In another development of the invention, provision can be made for the radially inner end regions of the shaft region to taper even more sharply than the lateral sides of the shaft region over a substantial portion of its length (preferably between 60% and 90% of its length). These radially inner end regions can extend between 10% and 30% of the length of the ferrite body. This still greater taper ensures that the shaft regions can extend relatively far toward the center point of the induction coil without contacting each other. The width between the two lateral sides of the end regions can increase angularly from radially inward to radially outward or remain constant.

[0017] In another development of the invention, the lateral sides of the tapered end regions of adjacent ferrite bodies can be spaced apart from one another in this region by at least 5 mm, or 5% of the circumference of a circle, and advantageously even by 8 to 12 mm. In this way, the aforementioned internal joint can pass between two adjacent ferrite bodies or be as high as them. Although such an internal joint has to pass between two adjacent ferrite bodies at exactly a single point, these spacing conditions can be advantageous for achieving a regular arrangement of identical ferrite bodies and their arrangement below the winding body.

[0018] In one embodiment of the invention, it can be provided that the tapered end regions of the shank region do not taper to a point, but are cut off at right angles to the radial direction or radial length of the shank region. They can be cut off in a straight line, or they can be cut off in a curve, in particular curving inwards.

[0019] A free region (in which no ferrite bodies or ferrite material are provided and no coil turns are provided) can advantageously be provided radially in the tapered end region of the ferrite body. This free region can have a diameter between 2% and 12% of the maximum radius of the winding body. This free region is primarily provided when the winding body is in the form of a wide annular ring and also has a free inner region. It is also unnecessary to provide any ferrite material in the form of one or more ferrite bodies in the central inner region of the winding body, thereby allowing this region to be free.

[0020] Provision can be made to arrange the radially innermost turns of the winding body on the tapered end region so that they protrude radially inwardly beyond the innermost turns. This allows the magnetic field of the induction coil to run both radially inwardly and radially outwardly as desired.

[0021] In another embodiment of the invention, with respect to the end regions described above, the ratio of the minimum distance between adjacent ferrite bodies in the end region to the minimum distance between adjacent ferrite bodies in the head region in terms of absolute width is between 0.7 and 1.5, preferably between 0.9 and 1.2. Provision can be made for the distance to be at its minimum at the point where the ferrite body is narrowest, in particular at the inner end. The inner joint may not even necessarily pass through here, so that the distance between them can be at its minimum, in particular at this point. Alternatively or in addition, the ratio of the minimum distance between adjacent ferrite bodies in the end region to the minimum distance between adjacent ferrite bodies in the head region in terms of angle is 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 just as small in absolute numbers as the minimum distance at the end.

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

[0024] In another embodiment of the invention, the portion of the distance between adjacent ferrite bodies in the circumferential direction or as a circular arc angle at any point in the radial extension, relative to the angle of the total circumference, can reach more than 40%, so to speak, without providing a greater distance between adjacent ferrite bodies at any point. It can even be advantageous to provide that this portion reaches more than 50% over more than half of the radial extension (i.e., the ferrite bodies do not extend over a significant area of ​​more than 50% of the circle). This is particularly true for the radius range between 40% and 90% of the radius of the winding body mentioned above.

[0025] In another development of the invention, a transition region can be provided between the head region and the shaft region. This region can be configured with rounded corners, thereby simplifying the mechanical stability and manufacturing of the ferrite body. The radius of the rounded transition region can be between 5% and 20% of the radius of the winding body. The distance between two adjacent ferrite bodies in terms of absolute width can preferably be at its maximum in this transition region, with the transition region in particular being located at or covering between 70% and 105% of the radius of the winding body.

[0026] Furthermore, in the transition region described above, provision can be made for the distance between adjacent ferrite bodies to be at its maximum there, advantageously amounting to between 70% and 90% of the radius of the winding body. This allows the head region to be extended relatively quickly far to each side or to become very wide immediately radially outside the transition region, thereby ensuring that the head region exhibits its maximum width slightly radially outside the winding body and that they substantially abut one another at their ends.

[0027] A significant portion of the area of ​​the head region can be arranged radially outside the winding body and thus protrude radially beyond it. This portion can be at least 50%, and preferably between 65% and 95%. In particular, the head region can widen significantly radially outside the outermost turns of the winding body. Advantageously, the transition region is located precisely below this outermost turn.

[0028] In general, it can be provided that the ferrite body covers between 40% and 70% of the area of ​​the winding body. This portion can particularly advantageously be between 45% and 60%, for example thus approximately half.

[0029] Although the shank region is significantly longer radially than the head region, the latter region may have a radial extension of between 10% and 35% of the radial length of the shank region. Its width may be several times greater than its radial length, thereby achieving the T-shaped shape mentioned above.

[0030] For example, the absolute width of the head region in the circumferential direction can be 30% to 100% greater than the absolute width of the shank region before the transition to the head region or before the transition region stated above.The T-shaped shape of the ferrite body can also be achieved thereby.

[0031] In another embodiment of the present invention, the distance between two adjacent ferrite bodies in their head region can be between 2 and 8 degrees. The minimum distance between two adjacent ferrite bodies in the end region can be between 10 and 20 degrees. The angular distance in the end region of the shaft region can therefore be greater than in the head region. The reason for this can be primarily as explained above, namely, the need to pass the internal joint between two adjacent ferrite bodies in the end region. This makes it possible to keep the overall height of the induction coil small, since the internal joint does not have to run under the ferrite bodies, which would otherwise increase their thickness.

[0032] An embodiment of the ferrite body is advantageously mirror-symmetrical so that when mated, they can, for example, also fit correctly with their bottom sides facing upwards. This mirror symmetry can advantageously be formed about an axis extending precisely in the radial direction of the induction coil and the winding body.

[0033] An arrangement of the ferrite bodies is preferably axially symmetrical, in particular also point-symmetrical. It is particularly preferably axially symmetrical with respect to two axes of symmetry extending at right angles to one another, wherein these axes of symmetry can extend between or through the two ferrite bodies. Particularly advantageously, one axis of symmetry runs exactly centrally through two opposing ferrite bodies, and the other axis either runs identically or exactly halfway between two adjacent ferrite bodies. Additionally or alternatively, the arrangement of the ferrite bodies on the induction coil can be point-symmetrical, preferably with respect to the center point of the induction coil and the winding body.

[0034] In another development of the invention, provision can be made for the head region to be formed by or to have two head end sections. These head end sections are preferably arranged transversely or at right angles to the longitudinal direction of the shaft region. They can be configured to taper toward their free ends; in particular, they can be rounded at their free ends. Particularly advantageously, the smallest distance between adjacent ferrite bodies, both in terms of absolute width and angle, is at these projecting head end sections. In this way, a largely or almost continuous circumferential loop of ferrite material can be produced, which, for the reasons stated above, runs around the winding body due to the specific mode of operation for high-power wireless energy transmission.

[0035] Advantageously, provision can be made for the outer edge of the winding body or its outermost turns to run precisely in the transition region between the shank region and the head region. This ensures that, in particular, the radially inwardly located region of the ferrite body covered by the winding body (i.e., the shank region) does not protrude significantly radially outside the winding body. The head region provided on the outside of the winding body can be significantly wider than the outside of the winding body. Provision can be made for the outermost turns of the winding body to run precisely between the shank region and the head region, thus extending, so to speak, centrally between the two in the transition region.

[0036] The or each ferrite body preferably has a substantially constant thickness that is identical in each case. This can advantageously be between 3 mm and 7 mm, particularly preferably approximately 5 mm. This makes it sufficiently easy for the magnetic field lines to travel as described above. At the same time, the overall height of the finished induction coil is therefore not excessive.

[0037] As a further geometrical detail, a length of the ferrite body in the radial direction of up to 5 cm to 15 cm can be provided. Advantageously, more than 75% of this length is taken up by the length of the shaft region.

[0038] The ferrite bodies are preferably constructed in a single piece, making them easier to assemble and enabling better magnetic flux guidance. They can be made from a pressed ferrite material that can then be ground into a defined shape. Although the outer contour of the ferrite body is preferably relatively complex, it is not necessary for the ferrite body to have any holes, openings, or recesses within this outer contour.

[0039] The aforementioned internal joints of the winding bodies can be formed with coil wire or stranded coil wire, extending from the innermost coil turns, and running between the two radially inner ends or end regions of the adjacent ferrite bodies described above. They can thus extend in the same plane as the ferrite bodies and not underneath them, thereby reducing the overall height. Here, the internal joints can then extend radially outward from the innermost turns between the two ferrite bodies and meet, for example, below the winding bodies at the same point where the external joints also meet. They can thus form a common joint strand, so to speak, simplifying the assembly and connection of the induction coil in the stove.

[0040] As explained above, ferrite bodies of the shapes described above, particularly the T-shaped shape, are not only commonly used in induction cooktops or induction cooktops in a structural unit with an induction coil, but are also primarily used for inductive power transmission to electrical consumers, such as kitchen appliances like blenders, toasters, or the like, which have a receiving coil. This results in inductive power transmission, as is known from the prior art, which supplies current or electrical energy to the electrical consumer for its operation. This inductive power transmission can advantageously be performed according to the Ki standard, see, for example, US Pat. No. 11,699,924 B. As mentioned above, the receiving coil should be of similar size to the induction coil, but may also be of different sizes.

[0041] It is precisely for this inductive power transmission that the shape of the ferrite body according to the invention is significant. This shape comprises a substantially continuous ring of ferrite material in the outer region of the winding body, which is essentially formed by the widened head region described above. In the middle region of the winding body, less ferrite material is provided, or adjacent ferrite bodies are at a significant distance from each other, because otherwise the magnetic resistance would become too high here. In the radially inner region of the winding body, the ferrite material is again provided in a circle (also with small interruptions), but this can be achieved without widening the ferrite body, because, given the correspondingly small radius in this region, they are all located relatively close together or at a relatively small distance from each other.

[0042] The electric cooktop according to the present invention comprises a cooktop and a plurality of induction coils, wherein a plurality of such induction coils may advantageously be present. The cooktop can advantageously be formed from conventional materials, such as glass ceramic, having a thickness of a few millimeters, advantageously 3 to 5 mm, and in particular 4 mm. The distance between the top of the winding body and the top of the cooktop should not be excessive, either for induction cooking or for the aforementioned inductive power transmission to electrical consumers with receiving coils placed on the cooktop. The distance between the top of the winding body and the top of the cooktop can therefore be between 5 mm and 13 mm, and particularly advantageously up to approximately 8 mm.

[0043] A flat support plate is preferably provided beneath the cooktop, on which the aforementioned induction coils according to the invention (and particularly advantageously all of the induction coils of this cooktop) are placed. The flat support plate can be made of metal, particularly aluminum. It should have low electrical resistance and, for example, be composed of an aluminum alloy or exhibit an electrical conductivity greater than 20 MS / m.

[0044] These and further features are disclosed in the description and in the drawings, as well as in the claims, wherein the individual features can be implemented individually or in subcombinations in one embodiment of the invention or in other fields, and can constitute advantageous embodiments worthy of protection in themselves, for which protection is hereby sought. The subdivision of the present application into individual sections and subheadings does not limit the statements made thereunder in terms of their general validity. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Further advantages and aspects of the invention can be found in the claims and in the description of exemplary embodiments of the invention, which are explained below with reference to the accompanying drawings, in which:

[0046] Figure 1 is a cross-sectional view through a cooktop according to the invention having three conventional induction heating coils and one induction coil according to the invention,

[0047] Figure 2 yes Figure 1 A plan view of a stove with the induction coil according to the invention at the front right.

[0048] Figure 3 is a plan view of an induction heating coil according to the present invention having a circular winding body and six ferrite bodies in a T-shaped configuration,

[0049] Figure 4 It is on the support plate of the stove Figure 3 Tilt diagram of the induction coil,

[0050] Figure 5 yes Figure 3 A plan view of one of the ferrite bodies,

[0051] Figure 6 It is from Figure 5 An oblique view of the leading edge of the ferrite body, and

[0052] Figure 7 Graphic Figure 3 An enlarged portion of an induction coil including lines corresponding to different angles and a percentage scale with respect to the radius of the winding body. DETAILED DESCRIPTION

[0053] Figure 1 The figure shows a side cross-section of a stove 11 according to the present invention, which is largely of known construction. The stove 11 has a conventional cooktop 12 with a top 13 and a bottom 14. A housing 16 is arranged on the bottom 14, within which the various functional units of the stove 11 are housed. An aluminum support plate 18 (advantageously having the aforementioned high conductivity of 20 MS / m or even higher) extends parallel to the cooktop 12 within the housing 16. An operating element 20 is arranged in its own housing at the front. This operating element 20 comprises, in particular, a rotary knob 22 that can be positioned on the top 13 for operating the stove 11.

[0054] The three induction coils 24a to 24c are placed on the support plate 18 and against the bottom 14. Instead of the conventional fourth induction heating coil, the induction coil 26 according to the present invention is arranged, in particular according to Figure 2 Located at the front right, the induction heating coils 24a to 24c are used solely for inductively heating cooking vessels placed thereon. The induction coil 26 according to the present invention can also be used for inductively heating cooking vessels. However, it can also be used to operate electrical appliances placed thereon on the cooktop 12 (according to the aforementioned Ki standard). However, the cooktop 11 can also include more induction coils according to the present invention, or even only one such induction coil according to the present invention.

[0055] The electrical appliance is a blender 40, which has a mixing container 41. This mixing container contains a mixing device or the like (not shown here). The mixing container 41 sits on a mixing base 42, with which the blender 40 is positioned downwardly on the top 13 of the stovetop 12. A receiving coil 43 is advantageously provided in the mixing base 42, preferably as low as possible or as close as possible to the stovetop 12 (and therefore also as close as possible to the induction coil 26 arranged below it). This can be slightly smaller than the induction coil 26 according to the invention, but the dimensions can also be more different. As a result of the transmission of induction energy from the induction coil 26 to the receiving coil 43, the blender 40 is wirelessly supplied with electrical energy for its operation.

[0056] Figure 3is a plan view illustrating an induction coil 26 according to the present invention. It has an essentially conventional winding body 27, which is made of a so-called coil wire, flat, wound in a spiral, and in a single layer, wherein the coil wire comprises a plurality of individual strands of wire, advantageously twisted together. On the outside, an external terminal 28 extends uninterrupted from the winding body 27 and advantageously extends a few centimeters further in the plane of the winding body 27, in particular to an electrical terminal in the housing 16. Likewise, on the inside, an internal terminal 29 extends uninterrupted from the innermost turns of the winding body 27, runs radially outward, and then together with the external terminal 28.

[0057] Six identical ferrite bodies 30 are arranged below the winding body 27, which are illustrated in this area by dashed lines. They are arranged evenly distributed, with the ferrite bodies 30 protruding a little from below the winding body on the inside and outside. Figure 4 The induction coil 26 is shown in an oblique view, wherein it has been placed onto the support plate 18 here, with the ferrite body 30 facing downwards.

[0058] The specific shape of the ferrite body 30 will be referred to Figure 5 and Figure 6 Explain in more detail and in Figure 5 and Figure 6 Detailed markings are provided in FIG. Basically, they have an elongated shaft region 31 with a left lateral side 32a and a right lateral side 32b. At the lower end (which is Figure 3 The shank region 31 merges into a tapered end region 34 (located in the central free region of the winding body 27). At the very bottom end, this end region 34 cuts off at a right angle to the longitudinal direction of the shank region 31, wherein this can also be a more or less rounded configuration; the corners can likewise be rounded.

[0059] The shaft area 31 is based on Figure 3 It widens in the radially outward direction relative to the induction coil 26 or its winding body 27, in particular by approximately 35%. Advantageously, it has straight lateral sides 32a and 32b and therefore widens uniformly. Via the transition region 36, the widened shaft region 31 adjoins the head region 37. In the transition region 36, the ferrite body 30 begins to widen from the lateral sides 32a and 32b and with large roundings. The ferrite body 30 then merges into the head region 37, where it widens considerably. There, it forms outwardly pointing head end parts (on the left) 38a and (on the right) 38b. The outwardly pointing outer edges of the head region 37 are heavily rounded and, in particular, extend roughly parallel to the outer edges of the winding body 27, see Figure 3 , so that all outer edges of the ferrite body 30 are located on a single circle.

[0060] Here, the lateral sides 32a and 32b are configured to be mostly straight from the tapered end region 34 immediately before (or substantially until) the transition region 36. The transition to the tapered end region 34 is provided with a corner, but can also be rounded. The lateral sides of the tapered end region 34 can also be slightly curved or arched. Instead of the illustrated corner, a slightly rounded corner can also be provided at the inwardly pointing end faces.

[0061] according to Figure 3 The specific shape of the six ferrite bodies 30 is therefore due to the fact that, on the one hand, the same embodiment offers advantages with regard to manufacturing and its fitting and is therefore more cost-effective. Furthermore, the shape of the ferrite bodies 30 is such as to ensure that as much ferrite material as possible is provided at the radially inner and outer ends or in the region of the innermost and outermost turns of the winding body 27, as seen in the circumferential direction, or that said material is present as much as possible in a substantially continuous circle. The ferrite bodies 30 facing radially inwards must have a determined distance between each other, which can in practice be up to the 8 mm mentioned above. In this way, the internal joint 29 can pass through in the plane of the winding body 27 without the structural height of the induction coil 26 having to be increased. This would also be the case otherwise, if the ferrite bodies 30 were to touch in the inner free area or under the innermost turns of the winding body 27 or extend so close to each other that the internal joint 29 would have to pass under the ferrite body 30. At the same time, however, from Figure 3 It can also be seen that, due to the relatively small distance between the tapered end regions 34 of the ferrite body 30, a large amount of ferrite material is provided, so to speak, in this region. This means that the entire magnetic flux is able to travel in the ferrite material, so that ultimately no magnetic field component is able to couple with the support plate 18 below it. The ferrite body 30 also needs to have sufficient volume in these end regions 34, in particular in the case where relatively large magnetic fluxes can occur in the induction coil 26 and in the receiving coil 43, provided that the phase angle between the currents is not ideal without saturation. Accordingly, in this region, the width of the ferrite body 30 also increases in terms of angle, or, as shown here, does not in any case decrease significantly. This also derives from the fact that Figure 7 Clearly seen in.

[0062] Correspondingly, the ferrite body 30 is also configured to be of such a width in the region of the outermost turns of the winding body 27 (or indeed radially outside thereof) that its protruding head end portions 38a and 38b are almost in contact over a large part of the circumference. Thus, in this region as well, it is possible for the entire magnetic flux to pass through the ferrite body 30 or simply through the head region 37 (i.e., again through the ferrite material).

[0063] In the substantial area of ​​the region of the winding body, in particular in the outer region, the ferrite body 30 is relatively narrow in its shank region 31 or becomes even narrower from the radial inside to the radial outside towards the head region 37. It is in the range between 60% or 70% and 90% according to Figure 7 This is illustrated in terms of angles. This results in large, nearly triangular free areas between adjacent ferrite bodies 30, in which no ferrite material is arranged below the winding body 27. This reduces the overall excess magnetic coupling into the receiving coil 43 and the influence of the ferrite bodies 30 on the self-inductance of the receiving coil 43, which is also referred to as the cross-effect between the induction coil 26 and the receiving coil 43. Due to the relatively small distance between the induction coil 26 and the receiving coil 43, which is actually between 8 mm and 13 mm, as shown in FIG. Figure 1 As shown in the figure, the coupling is relatively significant here. In this type of inductive power transmission, high power is transmitted, provided that the coupling is primarily at an operating frequency significantly lower than the resonant frequency of the receiving coil 43. A relatively small phase angle exists between the currents in the induction coil 26 on the one hand and the receiving coil 43 on the other. The increased inductance of the receiving coil 43 reduces its resonant frequency. Combined with the strong coupling described above, if a nominal power of, for example, 2200 W is to be delivered to the consumer, the operating frequency for inductive power transmission may drop below the minimum permitted operating frequency of 20 kHz. Furthermore, the phase angle of the current through the receiving coil relative to the current through the induction coil 26 would otherwise be degraded. For the same power to be inducted in the receiving coil 43, stirrer 40, or consumer, this would require an even greater current through the induction coil 26, resulting in increased losses. This can be mitigated by the relatively large free area between pairs of adjacent ferrite bodies 30.

[0064] Compared to a simple T-shape of the ferrite body 30 (which can be said to consist of two assembled elongated rectangles), the shape according to the present invention exhibits good coupling due to the relatively close circumferential proximity of the ferrite material of the ferrite body 30 at the inner and outer ends. In addition, the ferrite material at the inner circumference of the innermost turns of the winding body 27 can be connected with the outer circumference or outermost turns of the winding body 27 with low magnetic resistance. Due to the large free area between adjacent ferrite bodies 30, the cross-effects mentioned above on the receiving coil 43 can be kept insignificant. The magnetic flux density here reaches its maximum at the transition from the shaft region 31 to the head region 37 (i.e., in the transition region 36).

[0065] For an explanation of the exact shape of the ferrite body 30 in terms of angles refer to Figure 7The axis of symmetry of the axially symmetrical ferrite body 30 lies at 0 degrees. The minimum width, in terms of angle, is located at or just before the transition region 37, i.e., at the 13-degree line. By contrast, it can be seen that the 15-degree line intersects the left-hand side 32a, in particular roughly in its middle region. This results in the shaft region 31 becoming narrower in terms of angle from the radial inside to the radial outside, although it certainly becomes wider in terms of absolute width, i.e., measured in millimeters. The transition region 36 lies at the 15-degree line, or alternatively, this line also marks half of a segment that reaches one-twelfth of a circle. At a point outside this line, the outer circumference of the winding body 27 intersects the edge of the ferrite body 30.

[0066] The sides of the end region 34 extend in a substantially radial direction, here in particular at an angle of approximately 22. The end region 34 thus (like the shank region 31) narrows slightly from the radial inside to the radial outside.

[0067] The outermost end of the head end portion 38a is located at approximately 27.5 degrees, so that its distance from the 30-degree line, which extends exactly in the middle between two adjacent ferrite bodies 30, reaches exactly 2.5 degrees. In practice, the distance between adjacent head end portions can reach 8 mm to 15 mm, that is, it can be similar to the distance at the tapered end region 34.

[0068] As already explained above, the width of the shank region 31 or the distance between the two lateral sides 32a and 32b decreases radially in a range between just below 40% and approximately 80%. Radially inside thereof, the sides of the ferrite body 30 extend in a tapered end region 34 so that the distance between them remains substantially unchanged in terms of angle.

[0069] Figure 7 It is also illustrated that the radial extension of the head region 30 is relatively small and only amounts to approximately 15% of the maximum radius of the winding body 27 .

Claims

1. An induction coil for an electric cooking appliance, wherein the induction coil has: a winding body in the form of a flat, spirally wound coil, which is wound from a coil wire and has an inner connection and an outer connection, and - at least four separate identical ferrite bodies below said winding body, in: - the ferrite bodies each have two regions, wherein - the first inner region is the shaft region, - the shaft region extends substantially radially, - the second outer region is the head region, and - the head region is adjacent to the shaft region and is wider at its maximum width in terms of angle and wider in terms of absolute width than the shaft region at its maximum width by more than 50%, the head region at least partially protrudes radially beyond the winding body or projects beyond the winding body, - the shaft region widens radially in terms of absolute width from the radial inside to the radial outside, and The shank region narrows radially angularly from the radial inside to the radial outside over a range between 40% and 80% of the radius of the winding body and / or over a range between 25% and 75% of the length of the ferrite body. 2 . The induction coil according to claim 1 , wherein the ferrite bodies are of identical configuration at least in the head region, or all of the ferrite bodies of the induction coil are of identical configuration. 3 . The induction coil according to claim 1 , wherein the angular distance between two lateral sides of the shank region of the ferrite body decreases from the radial inside to the radial outside over a range from 20% to 80% of the maximum radius of the winding body.

4. The induction coil according to claim 1 , wherein the shaft region has a radially inner end region, wherein the radially inner end region tapers even more sharply than the lateral sides of the shaft region over a majority of the length of the shaft region, and wherein the width in terms of angle between the two lateral sides of the end region increases or remains the same from radially inside to radially outside.

5. The induction coil according to claim 4, wherein the lateral sides of the tapered end regions of adjacent ferrite bodies are spaced apart from each other in this region by at least 5 mm or 5% of the circumference of a circle.

6. The induction coil according to claim 4, wherein free areas are provided radially in the tapered end regions, said free areas being free of ferrite bodies and turns, wherein the diameter of said free areas amounts to 2% to 20% of the maximum radius of the winding body. 7 . The induction coil according to claim 4 , wherein the innermost turns of the winding body are arranged radially over approximately half of their length on the tapered end region.

8. The induction coil according to claim 4 , wherein a ratio of a minimum distance between adjacent ferrite bodies at the end region to a minimum distance between adjacent ferrite bodies at the head region is between 0.7 and 1.5 in terms of absolute width, and / or a ratio of a minimum distance between adjacent ferrite bodies at the end region to a minimum distance between adjacent ferrite bodies at the head region is between 1.5 and 5 in terms of angle.

9. The induction coil according to claim 1 , wherein the distance between two adjacent ferrite bodies at the head region reaches between 2 degrees and 8 degrees, and / or the minimum distance between two adjacent ferrite bodies at the end region reaches between 10 degrees and 20 degrees.

10. The induction coil according to claim 1, wherein the head region adjoins the shaft region in a transition region, and the transition region is of rounded configuration, wherein the distance between two adjacent ferrite bodies in terms of absolute width is at its maximum in the transition region.

11. The induction coil as claimed in claim 10, wherein the transition region is located at or covers between 70% and 105% of the radius of the winding body. 12 . The induction coil according to claim 1 , wherein between 65% and 95% of the area of ​​the head region is arranged radially outside the winding body and protrudes radially beyond the winding body.

13. The induction coil of claim 1, wherein the ferrite body covers between 40% and 70% of the area of ​​the winding body.

14. The induction coil of claim 1, wherein the head region has a radial extent between 10% and 35% of the radial extent of the shaft region. 15 . The induction coil according to claim 1 , wherein an absolute width of the head region in the circumferential direction is 30% to 100% greater than an absolute width of the shaft region before the transition to the head region.

16. The induction coil according to claim 1, wherein the ferrite body is configured in a mirror-symmetrical manner. 17 . The induction coil according to claim 1 , wherein the ferrite body is arranged axially symmetrically with respect to two symmetry axes extending at right angles to each other.

18. The induction coil according to claim 1 , wherein the head region has two head end regions of a tapered configuration, the head end regions protruding transversely to the longitudinal direction of the shaft region or at a right angle to the longitudinal direction of the shaft region, wherein the minimum distance between two adjacent ferrite bodies in terms of both absolute width and angle is at these protruding head end portions. 19 . The induction coil according to claim 1 , wherein an outer edge of the winding body or an outermost turn of the winding body extends over the transition region between the shaft region and the head region of the ferrite body.

20. The induction coil of claim 1, wherein the ferrite body is of a single-piece configuration and is made of a pressed ferrite material.

21. The induction coil of claim 1, wherein the shaft region has a radially inner end region, wherein the inner joint extends radially outward from the innermost turns between the two radially inner ends or end regions of the ferrite body or the shaft region.

22. Use of a ferrite body in an induction coil for transmitting induced power from the induction coil to an electrical consumer, the electrical consumer having a receiving coil and spaced apart from the induction coil, wherein the ferrite body has the following structure: - the ferrite bodies each have two regions, wherein - the first inner region is the shaft region, - the shaft region extends substantially radially, - the second outer region is the head region, and - the head region is adjacent to the shaft region and is wider at its maximum width in terms of angle and wider in terms of absolute width than the shaft region at its maximum width by more than 50%, the head region at least partially protrudes radially beyond the winding body or projects beyond the winding body, - the shaft region widens radially in terms of absolute width from the radial inside to the radial outside, and The shank region narrows radially angularly from the radial inside to the radial outside over a range between 40% and 80% of the radius of the winding body and / or over a range between 25% and 75% of the length of the ferrite body.

23. Use according to claim 22, wherein the inductive power transfer is performed according to the Ki standard.

24. An electric cooktop having a cooktop and a plurality of induction coils according to claim 1 below the cooktop, wherein the distance between the top of the winding body and the top of the cooktop is between 5 mm and 13 mm.

25. The electric cooktop according to claim 24, wherein a flat support plate is provided below the cooktop, the induction coil of the cooktop is placed on the support plate, wherein the ferrite body is arranged below the winding body and above the support plate.

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