Induction coil for electric cooking appliance and electric cooking appliance
The T-shaped ferrite bodies in the induction coil design address magnetic field routing inefficiencies, reducing leakage and resistance, and improving inductive power transfer efficiency.
Patent Information
- Application Number
- JP2025065061
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-04-11
- Filing Date
- 2025-04-10
- Publication Date
- 2025-10-24
AI Technical Summary
Existing induction coils face challenges in efficiently routing magnetic fields for inductive power transmission, leading to magnetic field leakage, increased magnetic resistance, and resonant frequency issues, which affect the efficiency and effectiveness of power transfer.
The induction coil design incorporates T-shaped ferrite bodies with a wider head region and tapered stem region, arranged to minimize magnetic coupling with the support plate and optimize magnetic flux routing, ensuring efficient power transmission without saturation.
The design reduces magnetic field leakage, minimizes magnetic resistance, and prevents resonant frequency issues, enhancing the efficiency and effectiveness of inductive power transfer to electrical consumers.
Smart Images
Figure 2025161790000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to an induction coil having a plurality of ferrite bodies for an electric cooking appliance. Furthermore, the present invention relates to the use of certain ferrite bodies in such an induction coil for the transmission of inductive power to an electric consumer having an opposite induction or receiving coil located at a predetermined distance from the induction coil. Finally, the present invention also relates to a cooktop plate and an electric cooktop having a plurality of induction coils according to the present invention.
[0002] DE 10 2016 208 233 A1 discloses an induction coil having a plurality of ferrite bodies arranged below the induction coil to prevent unwanted downward propagation of the magnetic field or to route magnetic field lines downward. The ferrite bodies can have the shape of a rectangle or a portion of a circle, in particular, up to, for example, a sixth of a circle. The ferrite bodies in the shape of a portion of a circle are advantageously arranged in the corner regions of the induction coil, which is configured approximately rectangularly.
[0003] An alternative configuration of ferrite bodies for induction coils is known from EP 1991030 A2, in which the ferrite bodies have a substantially rectangular shape but are configured with a different shape at one end of the end region. Summary of the Invention
[0004] The object of the present invention is to provide an induction coil as described above, a use of a ferrite body in such an induction coil as described above, and an electric cooktop having a plurality of such induction coils, which overcomes the problems of the prior art and allows for efficient and good routing of the magnetic field generated by the induction coil, in particular in the case of such use for inductive power transmission, which may be carried out in accordance with the so-called Ki standard.
[0005] This object is achieved by an induction coil having the features of claim 1, the use of a ferrite body in an induction coil having the features of claim 22, and an electric cooktop having a cookplate 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. Although some of the features are described herein only for an induction coil, only for a use, or only for an electric cooktop, they are nevertheless intended to apply, singly and independently of one another, not only to such induction coils and such a use, but also to such an electric cooktop. The text of the claims is incorporated into the content of this description by explicit reference.
[0006] The induction coil according to the present invention is intended to be installed and used on an electric cooktop, in particular under the cooktop plate of the cooktop, preferably together with an additional induction coil. The induction coil here has a winding body in the form of a flat, spirally wound coil, as is conventionally known. The winding body is wound from coil wire or so-called stranded coil wire and has internal and external connectors, which advantageously extend from the winding body as forward-routed coil wire. Furthermore, the induction coil has at least four individual, uniform or identically shaped ferrite bodies, which are arranged below the winding body. The ferrite bodies here are advantageously arranged adjacent to one another in the circumferential direction of the induction coil. They can cover 30% to 70% of the area of the winding body.
[0007] According to the invention, each ferrite body has two regions. The first region is located inside and constitutes a stem region. This stem region extends substantially radially. The second region is located radially outside the stem region and is or forms a head region. This head region adjoins the stem region, advantageously at a transition region formed at this location. Angularly, the maximum width of the head region, viewed in the circumferential direction, is greater than the maximum width of the stem region, or, viewed in the circumferential direction, is greater than the maximum width of the stem region by 50% or more. In other words, the head region can be wider, or wider, in terms of angle or arc angle, than the stem region at its minimum width, by 50% or more. However, advantageously, the head region is in each case wider, viewed in the circumferential direction, by no more than 150% than the maximum width of the stem region. The ferrite body can therefore be considered to closely approximate a T-shape.
[0008] Furthermore, the head region at least partially extends radially beyond the winding body, or extends radially beyond it. This can be 5% to 30% of the radius of the winding body. The stem region does not extend with a constant absolute width, but rather widens radially from the radially inner side to the radially outer side. This is advantageously true for its absolute width, but not for its width in angle or arc angle. In these cases, it may vary, or its width may even decrease. Such width direction extends substantially circumferentially around the winding body or approximately perpendicular to the radial direction of the ferrite body or the stem region. The stem region narrows radially in angle from the radially inner side to the radially outer side over a range of 40% to 80% of the radius of the winding body and / or preferably over a range of 25% to 75% of the length of the ferrite body in the radial direction.
[0009] In other words, the lateral sides of the stem regions of two directly adjacent ferrite bodies can satisfy the condition that the sum of all distances between the ferrite bodies on any desired circle around the center point of the winding is at least 40%, preferably 50% to 70% of the circumference of this circle. The radius of the desired circle can be 40% to 90% of the radius of the winding. This can therefore be applied over a range of annular lengths from 70% to 90% of the radius of the winding. Advantageously, the sum of all distances can be 50% to 70% of the circumference of the circle.
[0010] This particular geometrical embodiment ensures that a reasonably large distance is provided between adjacent ferrite bodies in the central outer region, which ensures that magnetic coupling into the electrically low-resistance support plate below the induction coil in an electric cooktop, particularly for use in the aforementioned power transmission, remains small. In this way, on the one hand, losses in the support plate are limited, and on the other hand, the inductance of the aforementioned receiving coil is not significantly increased by significant openings or free areas between the ferrite bodies. This leads to a separation of the resonant frequencies for inductive power transmission. The occurrence of resonant frequencies is highly unfavorable and therefore desirable to prevent.
[0011] Furthermore, the enlarged head region outside 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 inner radial direction to the outer radial direction, and for that reason, the absolute width of the ferrite body advantageously increases in this direction. In the case of high-power inductive power transmission, particularly large magnetic fluxes are generated, and the specific shape of the ferrite body is intended to avoid saturation. For example, induction coils having ferrite bodies that are also or primarily used for inductive power transmission may advantageously have a differently configured ferrite body or a ferrite body configured in accordance with the present invention. The specific shape and the protrusion of the ferrite body beyond the winding also ensure that no magnetic field components are coupled into the regions located under the induction coil, radially inner and radially outer, particularly into the metal support plate.
[0012] In one advantageous embodiment of the present invention, the ferrite bodies of an induction coil are identically configured (i.e., have identically shaped head regions) at least in their head regions. This also advantageously applies to the stem regions, particularly their radially inner ends. All ferrite bodies of this induction coil can have the same configuration for one induction coil or for all identically sized induction coils of a corresponding cooktop, at least if they are also intended for inductive power transmission. The use of identically shaped regions or identical ferrite bodies simplifies installation and makes it more cost-effective. It is particularly advantageous for the ferrite bodies to have a one-piece configuration in their specific shape, i.e., not be assembled from different parts. This prevents magnetic field leakage at the joints between individual parts and magnetic field loss in the windings and support plate. Furthermore, it can simplify the mechanical fixation of the ferrite bodies during installation.
[0013] In one embodiment of the present invention, the lateral or outer sides of the stem regions can be radially straight over at least 50% of their length, preferably 65% to 90% of their length. This facilitates ensuring that they are specifically wider from the radially inner to the radially outer side, as described above. Instead of being straight, they can be slightly curved.
[0014] The angular distance between the two lateral sides of the stem region of the ferrite body can preferably decrease continuously from the radially inner side to the radially outer side. The decrease is continuous. In particular, the distance can decrease over a range between 20% or 30% and 80% of the maximum radius of the winding body.
[0015] In one embodiment of the invention, the angle of the arc between the two lateral sides of the stem region of the ferrite body can increase in angle from the radially outer side to the radially inner side, preferably continuously or monotonically or strictly monotonically. Thus, the width of the stem region can decrease in the millimeter range from the radially outer side to the radially inner side in a circular or circumferential direction, but the stem region of the ferrite body can advantageously occupy a large proportion in angle, preferably 50% or more.
[0016] In a further development of the invention, the radially inner end regions of the stem regions can be sharply tapered over a substantial portion of their length, preferably 60% to 90% of their length, compared to the lateral sides of the stem regions. These radially inner end regions can be 10% to 30% of the length of the ferrite body. This sharp tapering ensures that the stem regions can extend relatively far toward the center point of the induction coil without touching each other. The width between the two lateral sides of the end regions can increase or remain the same from the radially inner to the radially outer direction.
[0017] In another further development of the invention, the lateral sides of the tapered end regions of adjacent ferrite bodies can be spaced apart from each other by at least 5% of the circumference of this region, or by at least 5 mm, preferably 8 mm to 12 mm. In this way, the above-mentioned internal connector can be routed between two adjacent ferrite bodies at the same height as them. Although this internal connector has to be routed between two adjacent ferrite bodies only in a single location, this spacing condition can be advantageous for achieving identical ferrite bodies and their regular arrangement under the winding.
[0018] In one embodiment of the invention, the tapered end regions of the stem region do not taper to a point, but can be cut perpendicular to the radial length of the stem region or perpendicular to the radial direction. They can be cut straight, or they can be cut curved, in particular inwardly curved.
[0019] A free region free of ferrite bodies or ferrite material and free of coil turns can be provided radially inward of the tapered end region of the ferrite body. Such a free region can have a diameter of 2% to 12% of the maximum radius of the winding. Such a free region is provided, particularly when the winding is in the form of a wide torus and also has a free inner region. Similarly, it is not necessary to provide ferrite material in the form of one or more ferrite bodies in the central inner region of the winding, and therefore, said region is free.
[0020] The radially innermost turn of the winding is disposed over a tapered end region such that the end region projects radially inward beyond the innermost coil turn, allowing the magnetic field of the induction coil to be routed both radially inward and radially outward as desired.
[0021] In a further configuration of the present invention, with respect to the end region, 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 can be 0.7 to 1.5, preferably 0.9 to 1.2, in terms of absolute width. The distance can be smallest, particularly at the inner end, when the ferrite bodies are at their narrowest point. Internal connectors may not need to be routed therethrough, so the distance between them can be smallest, particularly at this location. Alternatively or additionally, 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 can be 1.5 to 5, preferably 2.5 to 3.5, in terms of angle.
[0022] In one alternative embodiment of the invention, the distance between adjacent ferrite bodies in the head region can be exactly the same, in absolute terms, as the minimum distance in the end region.
[0023] The angular distance between two adjacent ferrite bodies in the head region can be an angle of 2° to 8°. The minimum distance between two adjacent ferrite bodies in the end region can be an angle of 10° to 20°.
[0024] In a further configuration of the invention, the percentage occupied by the distance between adjacent ferrite bodies in the circumferential direction, or as an arc angle relative to the angle of the entire circumference at any point in the radial range, can be 40% or more, with no smaller distance being provided anywhere between adjacent ferrite bodies. Advantageously, this percentage is 50% or more over more than half of the radial range. That is, advantageously, no more than 50% of the circle extends over a significant area of the ferrite body. This is particularly true in the above-mentioned radius range of 40% to 90% of the radius of the winding body.
[0025] In one further development of the invention, a transition region can be provided between the head region and the stem region. This can have a rounded configuration, thus improving the mechanical stability of the ferrite body and simplifying its manufacture. The radius of the rounded transition region can be 5% to 20% of the radius of the winding body. The distance in terms of absolute width between two adjacent ferrite bodies is preferably greatest in this transition region, and in particular the transition region is at or covers 70% to 105% of the radius of the winding body.
[0026] Furthermore, in the transition region mentioned above, the distance between adjacent ferrite bodies can be greatest, preferably 70% to 90% of the radius of the winding body, which ensures that the head regions can extend relatively quickly for a long distance on each side or can be very wide radially just outside the transition region, thus exhibiting their greatest width slightly radially outward from the outside of the winding body and that they substantially abut each other at their ends.
[0027] A significant proportion of the area of the head region can be located radially outside the winding body and therefore protrude radially beyond it. This proportion can be at least 50%, preferably 65% to 95%. In particular, the head region can be significantly wider radially outside the outermost turn of the winding body. The transition region here advantageously lies just below this outermost turn.
[0028] Overall, the ferrite bodies may cover 40% to 70% of the area of the winding, with this proportion being particularly advantageously between 45% and 60%, and thus for example approximately half.
[0029] The stem region is significantly longer radially than the head region, but the head region can have a radial extent that is 10% to 35% of the radial length of the stem region. Its width can be several times greater than its radial extent, thus achieving the T-shape described 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 stem region before the transition to the head region or before the aforementioned transition region. The aforementioned T-shape of the ferrite body can also be achieved thereby.
[0031] In a further embodiment of the present invention, the distance between two adjacent ferrite bodies can be an angle of 2° to 8° in the head region. The minimum distance between two adjacent ferrite bodies in the end region can be an angle of 10° to 20°. The angular distance in the end region of the stem region can be greater than in the head region. The reason for this can be primarily as described above: the need to route the internal connector between two adjacent ferrite bodies in the end region. This allows the structural height of the induction coil to remain small because the internal connector does not need to be routed under the ferrite bodies, and therefore their thickness is not added together.
[0032] One embodiment of the ferrite bodies is advantageously mirror symmetric so that they can be mounted accurately even when positioned, for example, with the underside facing upwards, and this mirror symmetry is advantageously about an axis that extends exactly radially of the induction coil and windings.
[0033] The arrangement of the ferrite bodies is preferably axially symmetrical, and in particular also point-symmetrical. It is particularly preferred that it be axially symmetrical with respect to two symmetry axes extending at right angles to each other, which can extend between or through two ferrite bodies. Particularly advantageously, one symmetry axis extends exactly in the center through two opposing ferrite bodies, and the other symmetry axis is the same for two adjacent ferrite bodies or extends exactly halfway between them. 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.
[0034] In a further development of the invention, the head region can be formed by two head end portions or can have two head end portions. These are preferably arranged transversely or perpendicularly to the longitudinal direction of the stem region. They can be arranged to taper towards 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 protruding head end portions. In this way, an approximately or almost continuous ring of ferrite material can be produced, which extends around the winding body for the reasons mentioned above due to the special mode of operation for high-power wireless energy transmission.
[0035] Advantageously, the outer edge of the winding or its outermost turn extends exactly over the transition region between the stem region and the head region. This ensures that the region radially inside the ferrite body covered by the winding, i.e., the stem region, does not significantly protrude radially outside the winding. The head region provided here on the outside of the winding can be significantly wider outside the winding. The outermost turn of the winding can extend exactly between the stem region and the head region, and thus can extend as if centered between these two regions on the transition region.
[0036] The or each ferrite body preferably has a constant thickness, preferably the same as each other in each case. The thickness can be advantageously between 3 mm and 7 mm, particularly advantageously around 5 mm. This is sufficiently easy to route the magnetic field lines as described above. At the same time, the structural height of the finished induction coil is not consequently excessive.
[0037] As a further geometrical detail, the radial length of the ferrite body can be between 5 cm and 15 cm, advantageously 75% or more of which is taken up by the length of the stem region.
[0038] The ferrite bodies preferably have a one-piece construction, which makes them easy to install and allows them to better direct the magnetic flux. They can be made from pressed ferrite material, which can be ground to a defined shape. The contour of the ferrite body is preferably relatively complex, although within this contour the ferrite body need not have holes, openings, or recesses.
[0039] The aforementioned internal connector of the winding body can be routed from the innermost coil turn using coil wire or stranded coil wire and extend between the two radially inner ends of adjacent ferrite bodies or between the aforementioned end regions. It extends in the same plane as the ferrite bodies, rather than underneath them, thereby reducing the structural height. Here, the internal connector can extend radially outward from the innermost turn between the two ferrite bodies and emerge from underneath the winding body at the same location as, for example, the external connector. They can thus form a common connector strand, so to speak, thereby simplifying the installation and connection of the induction coil into the cooktop.
[0040] As explained above, the above-mentioned shaped, especially T-shaped, ferrite bodies are not only generally used for cooktops or induction cooktops in structural units with induction coils, but also primarily for inductive power transmission to electrical consumers, such as kitchen appliances, e.g., mixers, toasters, etc., with receiving coils. This results in the inductive power transmission known from the prior art, which provides the electrical consumers with current or electrical energy for their operation. Such inductive power transmission can advantageously be carried out in accordance with the Ki standard (see, e.g., US Pat. No. 1,169,924 B). The receiving coil, as described above, should have a similar size to the induction coil, but may also have a different size.
[0041] For such inductive power transmission, the shape of the ferrite body defined in the present invention is significant. It encompasses a substantially continuous ring of ferrite material in the outer region of the winding, substantially formed by the wide head region. In the intermediate region of the winding, less ferrite material is provided, or adjacent ferrite bodies are significantly spaced apart, since otherwise the magnetic resistance would be too high. In the radially inner region of the winding, the ferrite material is again provided in a similar circle with small interruptions, but this can be achieved without widening the width of the ferrite body, since, with a correspondingly small radius in this region, the ferrite bodies are anyway relatively close together or exhibit a relatively small distance from each other.
[0042] The electric cooktop according to the present invention comprises a cooktop plate and a plurality of induction coils, where a large number of such induction coils may be advantageous. The cooktop plate is advantageously made of a common material, such as vitreous ceramic, having a thickness of a few millimeters, preferably 3 to 5 mm, and in particular 4 mm. The distance between the top of the winding and the top of the cooktop plate should not be too large, on the one hand, for induction cooking, and on the other hand, for the aforementioned inductive power transmission to electrical consumers with receiving coils placed on the cooktop plate. Thus, the distance between the top of the winding and the top of the cooktop plate may be 5 to 13 mm, particularly advantageously around 8 mm.
[0043] A flat support plate is preferably provided below the cooktop, on which the induction coils according to the invention, particularly preferably all induction coils of the cooktop, are arranged. The flat support plate can be made of metal, in particular aluminum. It should have a low electrical resistivity, for example, be made of an aluminum alloy or exhibit an electrical conductivity of more than 20 MS / m.
[0044] These and further features appear in the description and drawings, as well as in the claims, and individual features may be realized singly or in multiples in subcombinations in one embodiment of the present invention and in other areas, and may themselves constitute advantageous embodiments desirable for protection, for which protection is hereby sought. The subdivision of the application into individual sections and subheadings does not restrict in general validity the text made thereunder. [Brief explanation of the drawings]
[0045] Further advantages and aspects of the present invention can be found in the following description of exemplary embodiments thereof, with reference to the drawings, and in the claims.
[0046] [Figure 1] FIG. 1 is a schematic cross-sectional view of a cooktop according to the present invention having three conventional induction heating coils and an induction coil according to the present invention. [Figure 2] FIG. 2 is a plan view of the cooktop of FIG. 1 with an induction coil in accordance with the present invention at the front right side. [Figure 3] FIG. 3 is a plan view of an induction heating coil according to the present invention having a round winding and six T-shaped ferrite bodies. [Figure 4] FIG. 4 is a perspective view of the induction coil of FIG. 3 on a support plate of a cooktop. [Figure 5] FIG. 5 is a plan view of one of the ferrite bodies of FIG. [Figure 6] FIG. 6 is a front perspective view of the ferrite body of FIG. [Figure 7] FIG. 7 shows an enlarged portion of the induction coil of FIG. 3, including a percentage scale for the radius of the wire and windings corresponding to different angles. DETAILED DESCRIPTION OF THE INVENTION
[0047] 1 is a cross-sectional side view of a cooktop 11 according to the present invention, of generally known construction. The cooktop 11 has a typical cooktop plate 12 with an upper portion 13 and a lower portion 14. A housing 16 is arranged on the lower portion 14, in which the various functional units of the cooktop 11 are arranged. A support plate 18, preferably made of aluminum with a high thermal conductivity of 20 MS / m or more, extends parallel to the cooktop plate 12 within the housing 16. In front of it, an actuation means 20 is arranged in its own housing. The actuation means 20 has, in particular, a rotary knob 22 that can be arranged on the upper portion 13 in order to actuate the cooktop 11.
[0048] Three induction coils 24a-24c are placed on the support plate 18 and opposite the lower part 14. Instead of the four typical induction heating coils, an induction coil 26 according to the invention is arranged, particularly at the front right in FIG. 2. The induction heating coils 24a-24c serve only for the induction heating of the cooking vessels placed thereon. On the one hand, the induction coil 26 according to the invention can, of course, be used for the induction heating of cooking vessels. However, on the other hand, it can also be used to operate consumers placed on the cooktop plate 12 in accordance with the above-mentioned Ki standard. However, the cooktop 11 can also have more or only induction coils according to the invention.
[0049] The consumer here is a mixer 40, which has a mixer vessel 41 containing a stirrer (not shown here). The mixer vessel 41 is seated in a mixer base 42, so that the mixer 40 is placed on the upper part 13 of the cooktop plate 12. A receiving coil 43 is provided in the mixer base 42, advantageously as below the mixer base 42 as possible, or as close as possible to the cooktop plate 12 and thus to the induction coil 26 arranged below it. This induction coil 26 may be slightly smaller than the induction coil 26 according to the invention, but the size can vary greatly. As a result of the inductive energy transmission from the induction coil 26 to the receiving coil 43, the mixer 40 is wirelessly supplied with electrical energy for its operation.
[0050] 3 is a plan view of an induction coil 26 according to the invention. It comprises a general winding 27, which is wound helically and flat in a single layer from so-called coil wire, which comprises a plurality of individual stranded wires, which are advantageously twisted together. On the outside, an external connector 28 extends uninterruptedly from the winding 27, advantageously extending several centimeters in the plane of the winding 27, in particular all the way to an electrical terminal in the housing 16. Similarly, on the inside, an internal connector 29 extends uninterruptedly from the innermost turn of the winding 27 and is routed radially outward and then together with the external connector 28.
[0051] Six identical ferrite bodies 30 are arranged below the windings 27 and are indicated by dotted lines in this area. These ferrite bodies 30 are evenly distributed and protrude slightly below the windings on the inside and outside. Figure 4 shows the induction coil 26 in a perspective view, resting on the support plate 18 with the ferrite bodies 30 facing downwards.
[0052] The specific shape of the ferrite bodies 30 will be explained in more detail with reference to Figures 5 and 6 and the detailed reference numbers given therein. Basically, they have an elongated stem region 31, which has a left side 32a and a right side 32b. At its lower end, which is in the central free area of the winding 27, according to Figure 3, the stem region 31 merges into a tapered end region 34. At the very bottom end, this end region 34 is cut at a right angle to the longitudinal direction of the stem region 31, which may also have a more or less rounded configuration, and the corners may likewise be rounded.
[0053] The stem region 31 extends radially outward relative to the induction coil 26 or its windings 27 according to FIG. 3, in particular by approximately 35%. Advantageously, it has straight lateral sides 32a and 32b and thus extends uniformly. The extended stem region 31 is adjacent to the head region 37 via a transition region 36. In the transition region 36, the ferrite body 30 widens, starting from the lateral sides 32a and 32b, with a wide radius. The ferrite body 30 then merges into the head region 37, where it widens significantly. There, it forms a head end portion 38a facing outward to the left and a head end portion 38b facing outward to the right. The outwardly facing outer edge of the head region 37 is wide and rounded and extends approximately parallel to the outer edge of the windings 27 (see FIG. 3), so that the entire outer edge of the ferrite body 30 lies on a single circle.
[0054] The lateral sides 32a and 32b here have a generally linear configuration from the tapered end region 34 to just before or substantially to the transition region 36. The transition to the tapered end region 34 is provided at an angle, but can also be rounded. The lateral sides of the tapered end region 34 can also be slightly curved or arched. The inward-facing end faces can be provided with slight radii instead of the illustrated corners.
[0055] Therefore, the specific shape of the six ferrite bodies 30 according to FIG. 3 provides advantages for manufacturing and installation, and is therefore more cost-effective, even for the same embodiment. Furthermore, the shape of the ferrite bodies 30 helps ensure that as much ferrite material as possible is provided in the innermost and outermost turn regions or radially inner and outer ends of the winding 27 in the circumferential direction, or that the material is present as much as possible in a substantially continuous circle. Radially inward, the ferrite bodies 30 must have a specific distance between each other, which in practice can be the above-mentioned 8 mm. In this way, the internal connectors 29 can be routed in the plane of the winding 27 without having to increase the structural height of the induction coil 26. On the other hand, if the ferrite bodies 30 contact the internal connectors 29 under the free internal region or the innermost turn of the winding 27, or extend so close to each other that the internal connectors 29 must be routed under the ferrite bodies 30, the structural height of the induction coil 26 would need to be increased. At the same time, however, it is clear from FIG. 3 that the relatively small distance between the tapered end regions 34 of the ferrite body 30 provides a large amount of ferrite material in this region. This means that the entire magnetic flux can be routed through the ferrite material, and ultimately there is no magnetic field component below it that can couple with the support plate 18. It is necessary for the ferrite body 30 to have sufficient volume in these end regions 34, particularly in situations where a relatively large magnetic flux can be generated in the induction coil 26 and the receiving coil 43 without saturation, such as in the case of an insufficient phase angle between the currents. Therefore, in this region, the width of the ferrite body 30 also increases with angle, or at any rate does not decrease significantly, as shown here. This is also clear from FIG. 7.
[0056] Correspondingly, the ferrite body 30 is also configured in the region of the outermost turns of the winding 27, or indeed radially outward thereof, such that its protruding head end portions 38a and 38b are almost tangential compared to the majority of the circumference, so that even in this region it is possible to route the entire magnetic flux in the ferrite body 30, or simply in the head region 37, i.e., in the ferrite material.
[0057] Over a substantial area of the winding, particularly in the outer region, the ferrite bodies 30 are relatively narrow in the stem region 31 or narrow radially from the inner to the outer radial direction toward the head region 37. This is shown by the angular representation in FIG. 7, ranging from 60% or 70% to 90%. This creates large, approximately triangular free areas between adjacent ferrite bodies 30 where no ferrite material is located underneath the winding 27. This reduces the overall excess magnetic coupling to the receiving coil 43 and the influence of the ferrite bodies 30 on the self-induction of the receiving coil 43 (also known as the cross effect between the induction coil 26 and the receiving coil 43). The coupling is relatively significant here due to the relatively small distance, actually 8 mm to 13 mm, between the induction coil 26 and the receiving coil 43, as shown in FIG. 1. In the case of such inductive power transfer, high power is transferred during primary coupling at operating frequencies significantly below the resonant frequency of the receiving coil 43, and a relatively small phase angle exists between the current in the induction coil 26 and the current in the receiving coil 43. The increased inductance of the receiving coil 43 reduces its resonant frequency. In combination with the above-mentioned strong coupling, the operating frequency for inductive power transfer may fall below the minimum permissible operating frequency of 20 kHz if, at the same time, a nominal power output of, for example, 2200 W is to be achieved at the consumer. Furthermore, the phase angle of the current through the receiving coil relative to the current through the induction coil 26 will also decrease. This requires an increase in the current through the induction coil 26 for the same power induction in the receiving coil 43 or mixer 40 or consumer, which would result in increased losses. This can be reduced by a relatively large free area between pairs of adjacent ferrite bodies 30.
[0058] Compared to a simple T-shaped ferrite body 30 consisting of two assembled elongated rectangles, the shape according to the present invention exhibits better bonding of the ferrite material of the ferrite bodies 30, which are relatively closely adjacent in the circumferential direction at the inner and outer ends. Furthermore, the ferrite material of the innermost turn or inner circumference of the winding body 27 can be connected with the outermost turn or outer circumference of the winding body 27 with low magnetic resistance. Due to the large free area between adjacent ferrite bodies 30, the cross effect on the receiving coil 43 described above can be made insignificant. The magnetic flux density here has its maximum value at the transition from the stem region 31 to the head region 37, i.e., in the transition region 36.
[0059] For an explanation of the exact shape of the ferrite body 30 in terms of angle, please refer to FIG. 7. The axis of symmetry of the axisymmetric ferrite body 30 lies at an angle of 0°. The smallest width in terms of angle is at or just before the transition region 37, i.e., at the 13° angle line. In contrast, it can be seen that the 15° angle line is intersected by the left side 32a, particularly approximately in its central region. This results in the stem region 31 in particular narrowing in terms of angle from the radially inner to the radially outer direction, while of course the stem region 31 widens in terms of absolute width measured in millimeters. The transition region 36 lies at the 15° angle line, or alternatively, this line also marks half of a twelfth of a circle. Slightly outside this line, the outer periphery of the winding 27 intersects the edge of the ferrite body 30.
[0060] The sides of the end region 34 extend substantially radially, here in particular at an angle of about 22°, so that the end region 34, like the stem region 31, narrows slightly from the radially inner side to the radially outer side.
[0061] The outermost edge of the head end portion 38a is at an angle of approximately 27.5°, its distance from a 30° angle line extending exactly midway between two adjacent ferrite bodies 30 being an angle of just 2.5°. In practice, the distance between adjacent head ends can be between 8 mm and 15 mm, i.e., the same as the distance between adjacent tapered end regions 34.
[0062] As explained above, the width of the stem region 31 or the distance between the two lateral sides 32a and 32b is reduced in the radial direction by less than 40% to about 80%, while radially inward, the sides of the ferrite body 30 extend to tapered end regions 34 such that the distance between the angularly tapered end regions 34 remains substantially unchanged.
[0063] FIG. 7 also shows that the radial extent of the head region 30 is relatively small, only about 15% of the maximum radius of the windings 27 .
Claims
1. 1. An induction coil for an electric cooking appliance, the induction coil comprising: - a winding in the form of a flat, spirally wound coil from a coil wire, having an internal and external connector; - at least four separate identical ferrite bodies beneath said windings and the ferrite body has two regions, namely a first inner region and a second outer region, the first inner region being a stem region, the stem region extending in a substantially radial direction, the second outer region being a head region, the head region being adjacent to the stem region and having a maximum width greater than a maximum width of the stem region in terms of angle and greater than a maximum width of the stem region in terms of absolute width by 50% or more; the head region at least partially projects radially beyond or projects beyond the winding; the stem region radially widens in absolute width from radially inner to radially outer; 1. An induction coil, wherein the stem region narrows radially in relation to an angle from the radially inner side to the radially outer side over a range of 40% to 80% of the radius of the winding body and / or over a range of 25% to 75% of the length of the ferrite body.
2. 2. The induction coil of claim 1, wherein the ferrite bodies have the same construction at least in the head region, or all of the ferrite bodies of the induction coil are constructed identically.
3. 2. The induction coil of claim 1, wherein the angular distance between the two lateral sides of the stem region of the ferrite body decreases from the radially inner side to the radially outer side over a range of 20% to 80% of the maximum radius of the winding body.
4. 2. The induction coil of claim 1, wherein the stem region has a radially inner end region that tapers sharply relative to the lateral sides of the stem region over a substantial proportion of the length of the stem region, and wherein the angular width between the two lateral sides of the radially inner end region increases or remains the same from the radially inner to the radially outer direction.
5. 5. An induction coil according to claim 4, wherein the lateral sides of the tapered end regions of adjacent ferrite bodies are spaced apart from one another by at least 5% of the circumference of said regions or by at least 5 mm.
6. 5. The induction coil of claim 4, wherein a free region free of the ferrite body or windings is provided radially inward of the tapered end region, the diameter of the free region being 2% to 20% of the maximum radius of the winding body.
7. 5. The induction coil of claim 4, wherein the innermost turn of said winding is disposed radially over said tapered end region for approximately half its length.
8. 5. The induction coil of claim 4, wherein a ratio of a minimum distance between adjacent ferrite bodies in the end region to a minimum distance between adjacent ferrite bodies in the head region is 0.7 to 1.5 in terms of absolute width, and / or a ratio of a minimum distance between adjacent ferrite bodies in the end region to a minimum distance between adjacent ferrite bodies in the head region is 1.5 to 5 in terms of angle.
9. 2. The induction coil of claim 1, wherein the distance between two adjacent ferrite bodies in the head region is an angle between 2° and 8°, and / or the minimum distance between two adjacent ferrite bodies in the end region is an angle between 10° and 20°.
10. 2. The induction coil of claim 1, wherein the head region adjoins the stem region at a transition region, the transition region having a rounded shape, and the distance in terms of absolute width between two adjacent ferrite bodies is greatest at the transition region.
11. 11. The induction coil of claim 10, wherein the transition region is at or covers 70% to 105% of the radius of the winding.
12. 10. The induction coil of claim 1, wherein 65% to 95% of the area of the head region is disposed radially outside of the windings and protrudes radially beyond the windings.
13. 2. The induction coil of claim 1, wherein the ferrite body covers 40% to 70% of the area of the winding body.
14. 2. The induction coil of claim 1, wherein the head region has a radial length that is between 10% and 35% of the radial length of the stem region.
15. 2. The induction coil of claim 1, wherein the absolute width of the head region in the circumferential direction is 30% to 100% greater than the absolute width of the portion of the stem region adjacent to the head region.
16. 10. The induction coil of claim 1, wherein the ferrite body has a mirror-symmetric shape.
17. 2. The induction coil of claim 1, wherein the ferrite bodies are arranged axially symmetrically about two axes of symmetry extending at right angles to each other.
18. 2. The induction coil of claim 1, wherein the head region has two tapered head end portions that protrude transversely to or perpendicular to the longitudinal direction of the stem region, and the smallest distance between two adjacent ferrite bodies in terms of both absolute width and angle is at these protruding head end portions.
19. 2. The induction coil of claim 1, wherein an outer edge of the winding or an outermost turn of the winding extends over a transition region between the head region and the stem region of the ferrite body.
20. 10. The induction coil of claim 1, wherein the ferrite body has a one-piece construction and is made from pressed ferrite material.
21. 2. The induction coil of claim 1, wherein the stem region has a radially inner end region, and the internal connector extends radially outward from an innermost turn between two radially inner ends or end regions of the ferrite body or the stem region.
22. 1. Use of a plurality of ferrite bodies in an induction coil for transmitting inductive power from the induction coil to an electric consumer having a receiving coil and arranged at a distance from the induction coil, comprising: the ferrite body has two regions, namely a first inner region and a second outer region, the first inner region being a stem region, the stem region extending in a substantially radial direction, the second outer region being a head region, the head region being adjacent to the stem region and having a maximum width greater than a maximum width of the stem region in terms of angle and greater than a maximum width of the stem region in terms of absolute width by 50% or more; the head region at least partially projects radially beyond or projects beyond the winding; the stem region radially widens in absolute width from radially inner to radially outer; The stem region narrows radially in relation to an angle from the radially inner side to the radially outer side over a range of 40% to 80% of the radius of the winding body and / or over a range of 25% to 75% of the length of the ferrite body.
23. 23. The use according to claim 22, wherein the inductive power transfer is performed in accordance with the Ki standard.
24. 10. An electric cooktop comprising a cooktop plate and a plurality of induction coils according to claim 1 disposed below the cooktop plate, wherein the distance between the top of the winding and the top of the cooktop plate is between 5 mm and 13 mm.
25. 25. The electric cooktop of claim 24, wherein a flat support plate is provided below the cooktop plate, on which all induction coils of the cooktop are located, and the ferrite body is located below the winding body and above the support plate.