Induction heating device and induction hob with such an induction heating device

Abstract

Induction heating device (11), in particular for an induction hob (33), comprising: - an induction heating coil (12a, b), - a support (14) for the induction heating coil and - at least one ferrite (20a, b, 20'a, b, 120a), wherein the at least one ferrite is arranged on the support on one side, in particular on a flat side, of the induction heating coil, - a spring means (29, 129) on the induction heating device for spring-loaded pressing of the induction heating device against a cover above it, characterized in that - the spring means (29, 129) are held directly on a ferrite (20a, b, 120a), - a recess (22, 122) is provided on the ferrite for holding the spring means on the ferrite.

Description

The invention relates to an induction heating device, as can be used in particular for an induction hob, and to an induction hob provided with such an induction heating device.Induction heating devices, such as those used in an induction hob or generally for inductive heating, can have a flat induction heating coil. This is arranged close to a cover on which an object to be heated, for example a cooking vessel, is located. In order to direct and bundle the magnetic flux, in particular in order to keep the region below the induction heating device free from magnetic fields, ferrites are usually arranged below the induction heating coil. These may also be flat and flat and may be elongated or strip-like.EP 3 035 772 A1 discloses such an arrangement of an induction heating coil in an induction hob, wherein induction heating coil and ferrites are arranged on a carrier. Thus, the assembly of the induction hob can be improved. The carrier is then pressed against the underside of a hob plate as a cover.U.S. Pat. No. 4,029,926 A1 discloses an induction cooker with an induction heating coil. A ferritic support for windings of an induction heating coil has projections protruding on its underside, over which coil springs are guided. A resilient mounting relative to a base plate is thus achieved in order to press the induction heating coil resiliently against the underside of a hob plate as a cover.US 2008 / 0017633 A1 discloses an induction cooker in which an induction heating coil rests on a holder. This holder has pot-like holding sections on the underside, in which coil springs engage from below in order to press the holder from below resiliently against the underside of a hob plate as a cover.DE 10 2010 028 549 A1 discloses an induction hob with a multiplicity of induction heating coils. The individual induction heating coils are pressed via spring means from below onto the underside of a hob plate as a cover, wherein the induction heating coils are pressed upward by means of leaf springs which are bent several times on the one hand or coil springs on the other hand.KR 10 2007 0 000779 A discloses an induction cooker in which an induction heating coil embedded in a support is pressed from below with multiply bent leaf springs resiliently upwards on the underside of a hob plate as a cover.EP 2 096 897 A1 discloses an induction hob with a plurality of induction heating devices under a hob plate. In this case, the induction heating devices in the form of induction heating coils have a flat carrier on which they are placed. On the underside of the carrier, a plurality of ferrites are arranged in a manner customary per se. These serve in a known manner to direct or influence the magnetic field of the induction heating coil.OBJECT AND SOLUTIONThe object of the invention is to create an induction heating device mentioned at the beginning and an induction hob provided with it, with which problems of the prior art can be avoided and it is possible in particular to enable mounting or mounting of the induction heating device, preferably in an induction hob, in a simple and practical manner at low costs.This object is achieved by an induction heating device having the features of claim 1 and by an induction hob having the features of claim 16. Some of the features are described here only for the induction heating device or only for the induction hob. However, they should be able to apply independently both for the induction heating device and for the induction hob. The wording of the claims is made the content of the description by explicit reference.The induction heating device includes an induction heating coil and a support for the induction heating coil. Furthermore, it comprises at least one ferrite, advantageously a plurality of ferrites, such as, for example, 4 to 12 ferrites. The at least one ferrite is arranged on the carrier on one side of the induction heating coil. It is advantageously arranged on a flat side of the induction heating coil, particularly advantageously if it is of flat design. A distance of the ferrite from the induction heating coil can be at most 10 mm, advantageously at most 6 mm. For mounting reasons, a thin region of the carrier can be provided between the induction heating coil and ferrite. Furthermore, the induction heating device has a spring means in order to press the induction heating device against a cover arranged above it in a spring-loaded manner. This means that without direct permanent fastening of the induction heating device to the cover or to an underside of the cover, permanent and secure contact is nevertheless ensured. Furthermore, component and assembly tolerances can be compensated for by the resilient or spring-loaded pressing.According to the invention, the spring means are held or fastened directly on the ferrite or engage directly on the ferrite, wherein a recess is provided for this purpose on the ferrite. This results in a form-fit mounting of the spring means on the ferrite in at least one direction, advantageously transversely to the spring direction or transversely to a direction along the surface of the ferrite. Thus, the spring means cannot move laterally on the ferrite in an undesired manner, in particular not out of an provided advantageous position.In the prior art, the spring means are arranged on the carrier itself or press against the carrier itself, for example its material, which is advantageously plastic. However, for this purpose, a somewhat larger area is usually required on the carrier in order to be able to easily attach spring means which are advantageously designed in the form of a helical spring and therefore have a large diameter. Furthermore, a type of force introduction of this region of the carrier, on which the spring means abut, into the surrounding carrier is then also required in order to achieve a uniform and stable spring-loaded pressing with a few, for example four, spring means per induction heating coil. Because the spring means bear against the ferrite, a distribution of the applied spring force over a larger area, namely that of the ferrite, is automatically achieved in the same way on account of the rigid and stable configuration of such ferrites. Since this should in any case be mounted stably in the carrier, the spring forces acting on the ferrite can also be coupled well into the carrier. Further, by changing the ferrites as separate parts, the invention can be realized alone. The effort required to change an injection molding tool for the carrier can thus be saved, apart from the fact that under certain circumstances not enough space at all on the carrier is free for the arrangement and pressing of the spring means. Advantageously, for this purpose, the side of the ferrites on which the spring means are held is largely free.A recess in the ferrite can be produced subsequently, for example by drilling or advantageously milling or grinding. A recess may be produced during the production of the ferrite, since these are usually pressed before sintering. Thus, only the press mold or a press ram needs to be changed in a simple manner.A ferrite can be substantially flat with a thickness of at most 10 mm, advantageously approximately 3 mm to 8 mm. It can particularly advantageously have an approximated geometric basic shape such as an approximated triangle or an approximated square, in particular a square in the form of a trapezoid or rectangle. It is also possible to provide at least two or three types of ferrites per induction heating coil, wherein a spring means does not have to abut each ferrite.In one embodiment of the invention, the recess and for holding the spring means are provided on an underside of the ferrite, which faces away from the induction heating coil. A spring-loaded pressing against the underside of the ferrite and thus against the underside of the carrier can thus be achieved, which in turn presses the induction heating coil lying on its upper side upwards against an underside of the said cover.The recess may be spaced apart from an outer edge of the ferrite by at least the minimum thickness of the ferrite. In this way, it is essentially ensured that the stability of the ferrite and above all of the edge region holding the spring means is sufficiently good. It should be avoided that an excessively thin edge region of the ferrite towards the recess can break off during the production of the ferrite, during the assembly or during use. Advantageously, this distance is at least twice the minimum thickness of the ferrite.In an alternative embodiment of the invention, a recess can be provided in the ferrite for holding the spring means, which recess pulls as far as an edge of the ferrite, so that the recess is open towards this edge side of the ferrite. Towards the other edges, towards which the recess is then not open, the aforementioned spacing condition can apply in order to form the edge of the recess in a precisely sufficiently stable manner. The advantage of a recess for a spring means which is open to the side can be that, as will be explained in more detail below, an undercut can optionally be provided in the recess, which undercut is formed, for example, in the manner of a dovetail guide. A spring means can be inserted into the undercut from the edge. In the direction transverse to a base of the recess or transverse to the ferrite and away from the latter, the spring means is then secured by the undercut.In a further embodiment of the invention, a recess bottom can run parallel to the opposite flat side of a flat ferrite. Thus, a ferrite can be easily produced and a spring means according to the invention can also be arranged therein in a simple and advantageous manner. Advantageously, an entire ferrite for a spring means is plane-parallel and flat.In one embodiment of the invention, a bore can be provided in the ferrite, which bore is advantageously a blind bore. Such a bore can be provided particularly advantageously in a recess in the ferrite for mounting, but alternatively also on or next to an aforementioned projection. This bore serves to retain a protruding portion of the spring means therein to secure the spring means against displacement, rotation or generally removal from the spring means. Expensive fastenings such as adhesive bonding or the like can thus be dispensed with. Furthermore, such a bore can also be produced simultaneously during the production of the ferrite, in particular similar to a recess per se, for example during a pressing of the ferrite from corresponding starting material.An aforementioned bore can extend into the ferrite either substantially at right angles to the main extent, advantageously in an aforementioned recess base. Alternatively, it can also be provided in a recess edge, so that at this location the edge of a recess, which is round for example, has a small bulge of a length of a few millimeters.In one embodiment of the invention, the spring means can be designed as a wire spring. A metal wire spring is suitable here. Advantageously, it is designed as a helical spring and can have a diameter which is between 10% and 50% of the maximum extent of the ferrite. Such a helical spring can have a substantially round outer shape, and with a diameter mentioned it is ensured that a recess for receiving the helical spring has a sufficient distance from the edges or edge sides of the ferrite. Such metal wire coil springs have permanent spring properties with a high spring force, and in addition they are very temperature-resistant.Particularly preferably, a helical spring can have a decreasing diameter, so that it also has a certain helical shape in plan view. In this case, it can be provided that an end with the greater width or the greater diameter abuts the ferrite or is held thereon by means of the recess and / or depression.The advantage of this certain helical spring shape is that the spring can be compressed almost completely and then only has a height which corresponds to the diameter of the wire. With an imperceptible reduction in the spring force, a spring means with a smaller space requirement can thus be created.In an alternative embodiment of the invention, the spring means can be designed as a leaf spring. They can have at least one bend or at least one bend, i.e. either as a type of U spring with a small spacing between the two limbs in the compressed state, or as a so-called Z spring. Such spring means can also have a relatively small space requirement or relatively small height when compressed, but at the same time also have a sufficient spring length in order to bridge larger distances or to act resiliently on larger distances. They are advantageously made of metal.In yet another embodiment of the invention, it is also conceivable for the spring means to be designed as block-shaped spring bodies. For this purpose, they can preferably consist of a voluminous elastic plastic material, for example in foamed form. Heat-resistant rubber or silicone rubber is suitable in particular as material. A temperature resistance of the spring means should be at least 100° C., advantageously at least 120° C., because of the use in an induction heating device or an induction hob and because of the direct contact with the readily thermally conductive ferrites.An aforementioned undercut configuration at a recess can be engaged behind by a section of the spring means in order to thus fasten the spring means to the ferrite in a form-fitting manner. Thus, an captive attachment of the spring means to the ferrite can be provided which, at least during assembly of the induction heating device, secures the spring means to the ferrite against movement vertically away from the surface of the ferrite. In the insertion direction or along the undercut recess, the spring means can in principle still be moved. By means of a corresponding clamping or the like, if, for example, the diameter of a lowermost winding of a helical spring as spring means is somewhat greater than the width of the recess above the recess base, a moving out of the spring means can be prevented.An undercut recess is advantageously open as far as a side edge or outer edge of the ferrite and also has the undercut over its entire length. In order to prevent the aforementioned automatic and undesired moving out or falling out of the spring means from the undercut recess, provision can be made to arrange a projection on the recess base and / or on a recess wall. This projection can be flattened or beveled counter to an insertion direction, so that the spring means slide over the projection so to speak when being inserted into the recess. On the other side or opposite to a pushing-out direction, the projection can be designed to be approximately rectangular, so that an automatic moving out over the projection is avoided.Whereas, above all, in the case of a configuration of the spring means as a helical spring with a slight helical portion, the height of the compressed spring means can be approximately the diameter of a winding of the helical spring, a height of the unloaded spring means can generally be twice to twenty times greater than the maximum thickness of the ferrite. Thus, a greater distance of the spring means between counter bearing and ferrite can also be bridged.An induction hob according to the invention can have a housing for accommodating at least one, preferably a plurality of, aforementioned induction heating devices. This housing is arranged under a hob plate as a cover mentioned at the beginning, in particular is fastened thereto. For example, a housing as a flat housing shell with a housing base can be fastened or screwed or suspended on rails which are glued to the underside of a hob plate. The induction heating device is pressed from below against the hob plate, serving for this purpose are the spring means which are supported against the housing base as a counter bearing.An induction heating coil can be pressed against the underside of the hob plate either directly or advantageously by means of a thermal barrier coating placed on it. This heat insulation layer serves to achieve a certain heat insulation with respect to a hot hob plate which is heated by a heated pot placed above it.The spring means in turn should advantageously not bear or rest directly against the housing base, but rather can press indirectly against the housing base. Intermediate structural units of the induction hob can be provided, for example a flat plate or a flat component carrier. Further functional units of the induction hob can be arranged on the latter, in particular a controller for the induction heating coil. Furthermore, an electrical plug connection to a plug which is fastened to the carrier for the induction heating coil can be provided. This is known from the aforementioned EP 3 035 772 A1 with filing date of Dec. 16, 2015, to which express reference is made in this respect.These and further features are evident, apart from from the claims, also from the description and the drawings, wherein the individual features are each realized by themselves or in the form of sub-combinations in an embodiment of the invention and in other fields and can represent advantageous and separately protectable embodiments for which protection is claimed here. The subdivision of the application into individual sections and intermediate headings does not restrict the generality of the statements made under them.BRIEF DESCRIPTION OF THE DRAWINGSFurther advantages and aspects of the invention are evident from the claims and from the following description of preferred exemplary embodiments of the invention, which are explained below with reference to the figures. The following are shown: FIG. 1 is a perspective view from below of an induction heating device according to the invention with two induction heating coils on a carrier on which flat ferrites are arranged, some of which have recesses for springs, FIG. 2 is an enlarged plan view of a part of the support according to FIG. 1 without an induction heating coil with springs in the recesses in the ferrites, FIG. 3 is an oblique view of an enlarged ferrite from below in the form of a sector of a circle with a circular recess, FIG. 4 shows the ferrite from FIG. 3 with a helical spring introduced into the recess, FIG. 5 shows a modification of a ferrite similar to FIG. 3 with an elongate undercut slot as a recess, FIG. 6 shows the ferrite from FIG. 5 with a helical spring inserted into the undercut slot, FIG. 7 shows a view from behind of the ferrite from FIG. 6 with a viewing direction along the undercut recess, and FIG. 8 shows a schematic section through an induction hob according to the invention with an induction heating device according to FIG. 1.DETAILED DESCRIPTION OF THE EMBODIMENTSFIG. 1 shows an oblique view of an induction heating device 11 according to the invention. This has an induction coil 12 aand an induction coil 12 bwhich have an approximately rectangular shape, as can be seen substantially from the aforementioned EP 3 035 772 A1. The induction coils 12 could, however, naturally also have a circular and other shape. The induction heating device 11 has a carrier 14 made of plastic, which can be seen in a plan view in FIG. 2 and has grid-like arrangements with a plurality of individual fields and planar apertures through which the induction heating coils 12 aand 12 bcan be seen. Above all, the carrier 14 also has pockets 15 as such fields, into which ferrites 20a and 20b and 20a' and 20b' can then be introduced, as will be explained in more detail below. On the edge of the pockets 15 retaining lugs 16 can be formed which engage in the pockets 15. On the underside, covering induction heating coils 12a and 12b, a flat cover 17 is provided. This should have electrical insulation properties and thermal insulation properties. Finally, the carrier 14 also has a plug connection 18, from which connections to the induction coils 12 aand 12 bgo. However, this is also easy to implement in principle by the person skilled in the art and does not play any role for the invention.FIG. 2 also shows a plan view of the double mirror-symmetrical arrangement of the ferrites 20a and 20'a on the underside of the carrier 14 in corresponding pockets 15. This will be explained in more detail below. It can also be clearly seen how the ferrites 20a, 20'a are held in the pockets 15 by means of the holding lugs 16, namely both the ferrites 20a in the shape of a circular sector and the rectangular ferrites 20'a. However, no spring means are provided in these rectangular ferrites 20'a.FIGS. 3 and 4 show a ferrite 20 ain an enlarged oblique view. The circular sector shape can also be seen. Furthermore, along the longitudinal edges, two retaining depressions 21 are provided in each case as oblique depressions. These are overlapped by the correspondingly configured retaining lugs 16 on the carrier 14, so that a type of latching and form-fitting fastening of the ferrites 20 ato the carrier 14 and thus below the induction heating coils 12 aand 12 bis provided.In a central region, a circular recess 23 is provided on the underside of the ferrite 20 a. The diameter thereof can vary between 2 cm and 3.5 cm for an overall length of the ferrite 20 aof about 10 cm. It has a planar recess base 23, which, however, does not have to be so. Advantageously, such a ferrite 20 ais produced during production in the desired shape, particularly advantageously by pressing. In a shape corresponding to the basic shape of the ferrite 20a, which is already present and in which the retaining depressions 21 are also formed, then only an additional punch need be provided for producing the recess 22. A depth of the recess 22 may be about half the thickness of the ferrite 20 a. It may generally be between 10% and 80% or even 90% of the thickness of the ferrite.In FIG. 4 it can be seen how a spring 29 is inserted into the recess 22. The spring 29 is substantially designed as a helical spring, but is also slightly helical. The end of the spring 29 in the recess 22 has a larger diameter than the free upwardly projecting end. As a result, the spring 29 can generally have a more stable shape even when compressed. Furthermore, it can be compressed very flat, so that its height in the extreme case is only one diameter of a wire turn, since it lies one inside the other with its turns during compression.It is shown how it is possible to provide a kind of bore 26 or a cut-out on the side of the recess 22. A radially outwardly projecting section 30 of the spring 29 can project into the latter. Thus, a rotation of the spring 29 in the recess 22 can be avoided. A possible fixing can also be effected by introducing adhesive exactly into this bore 26.As an alternative to a bore 26 extending radially outwards to the recess 22, a bore could also extend into the recess base 23, wherein the protruding portion 30 of the spring 29 would then not be radially outwards, but would be planar essentially perpendicular to the surface of the ferrite 20 aor at right angles to the recess base 23.Here, the recess 22 is made so to speak at right angles in the ferrite. A circumferential wall of the recess 22 is at right angles to the recess base 23 and at right angles to the surrounding surface of the ferrite 20 a. The spring 29 can thus be easily inserted into the recess 22, but could also be easily pulled out again even if it is secured against rotation by means of the bore 26.In a modification of a ferrite 120a according to FIGS. 5 to 7, it is provided that an elongate recess 122 in the manner of a wide slot is provided from the outside. This recess has an undercut 124 with respect to the recess base 123, as is shown above all in the side view of FIG. 7. A correspondingly designed spring 129 can be inserted into such an elongate undercut recess 122 from the outside into the slot thus formed until the spring 129 lies at the end of the recess 122 or at the desired location. Due to the undercut 124, the spring 129 can actually hardly be pulled out of the recess 122 and is thus seated in a permanently stable manner. This spring 129, like the spring 29 from FIGS. 3 and 4, is also designed as a type of combined helical spring and helical spring. It is very advantageous if, in the case of this spring 129, a one-time, substantially circular circulation is provided at the wide lower end as a kind of ring, without a helical shape and without only a minimal helical shape. As a result, the spring 129 can be held very well in the undercut recess 122.Similar to the illustration in FIG. 4 or to the explanation in relation to FIG. 4, a bore can be provided on the recess 122, namely either perpendicularly into the recess base 123 or transversely or parallel thereto. A correspondingly bent protruding portion of the spring 129 could then engage therein and cause a fixing of the spring 129. Furthermore, it is thus prevented that the spring 129 can be easily pushed out again. Above all, a bore into the recess base 123 with a direction at right angles to the recess base 123 is considered suitable for this purpose.It is easily conceivable with reference to FIGS. 3 to 7 how other types of springs could also be provided instead of a helical spring with a slightly spiral shape, which is shown here substantially identically, in particular also completely different types. On the one hand, they could be springs in the shape of a U or so-called Z springs, which have a spring direction transversely away from the surface of the ferrite. Alternatively, they could be bulky spring bodies, for example in block form, which then however have a much poorer ratio between minimum height and maximum height. Furthermore, springs made of wire or metal wire in the form shown here can better withstand the higher temperatures which can arise permanently beneath it in the case of an induction hob.FIG. 8 shows an induction hob 33 according to the invention in a type of schematic sectional illustration. Below a hob plate 34 there is a housing 36, or it is fastened, for example glued or screwed to glued-on holding rails, to an underside 35 of the hob plate 34. The housing 36 has a housing base 37, on which a component carrier 39 with a large-area profile rests. On this component carrier 39, the induction heating device 11 is in turn placed or mounted. By means of the plug connection 18, an electrical contact is established between the induction heating device 11 and the component carrier 39, as is known from the aforementioned EP 3 035 772 A1. However, no significant holding and / or pressing force is transmitted via the plug connection 18. The essential support of the induction heating device 11 downwards against the component carrier 39 is effected by means of the springs 29 which are seated in the ferrites 20a or are fastened in recesses therein. Thus, the ferrites 20 ain turn press the carrier 14 upwards, in which they are arranged. As a result, the induction heating coil 12 a, which is resting on the support 14, is pressed upward and then rests with the intermediate cover 17 against the underside 35 of the hob plate 34. Due to the resilient or spring-loaded contact of the induction heating device 11 on the underside 35 of the hob plate 34, both a very small and a constant distance is maintained. This is advantageous and of importance for heating a cooking pot placed on the hob plate 34 above the induction heating coil 12 a.FIG. 8, which is not necessarily to scale, also shows why a small overall height of the spring means or of the helical springs 29 consisting of metal wire is important. Thus, a distance of the underside of the ferrites 20 ato the component carrier 39 can be very small, advantageously be a few millimeters, for example only 2 mm to 4 mm. Nevertheless, a sufficiently elastic or resilient and strong pressing can take place.

Claims

Induction heating device (11), in particular for an induction hob (33), having: - an induction heating coil (12a, b), - a carrier (14) for the induction heating coil and - at least one ferrite (20a, b, 20'a, b, 120a), wherein the at least one ferrite is arranged on the carrier on one side, in particular on a flat side, of the induction heating coil, - a spring means (29, 129) on the induction heating device for spring-loaded pressing of the induction heating device against a cover above it, characterized in that - the spring means (29, 129) are held directly on a ferrite (20a, b, 120a), - a recess (22, 122) on the ferrite is provided for holding the spring means on the ferrite.Induction heating device according to claim 1, characterised in that the spring means (29, 129) are held directly on the ferrite (20a, b, 120a) with a positive fit, wherein the positive fit is formed in a direction transverse to the spring direction or along the surface of the ferrite on which the spring means abuts the ferrite.Induction heating device according to claim 1 or 2, characterised in that the ferrite (20a, b, 20'a, b, 120a) is substantially flat, in particular with a geometric basic shape such as an approximate triangle or an approximate quadrilateral, in particular a trapezoid or a rectangle.Induction heating device according to one of the preceding claims, characterized in that the recess (22, 122) for mounting is provided on an underside of the ferrite (20a, b, 120a) facing away from the induction heating coil (12).Induction heating device according to one of the preceding claims, characterized in that a recess (22) for holding the spring means (29) is at a distance of at least the minimum thickness of the ferrite (20a, b) from an edge of the ferrite.Induction heating device according to one of the preceding claims, characterized in that the recess (122) pulls up to an edge of the ferrite (120a), or the recess (122) is open towards an edge side of the ferrite.Induction heating device according to one of the preceding claims, characterized in that the recess (22, 122) has a recess base which is plane-parallel on both sides of the flat ferrite.Induction heating device according to one of the preceding claims, characterized in that a bore is provided in the ferrite (20a), preferably as a blind bore (26), in particular in the recess (22), for holding the spring means (29), wherein preferably a protruding section (30) of the spring means (29) is held in the bore for securing the spring means against displacement.Induction heating device according to one of the preceding claims, characterized in that the spring means (29, 129) are designed as a wire spring, in particular as a metal wire spring, preferably as a helical spring, wherein in particular a diameter of a helical spring is between 10% and 50% of the maximum extent of the ferrite (20a, b, 20'a, b, 120a, b).Induction heating device according to one of the preceding claims, characterized in that the spring means (29, 129) are designed as a helical spring with a decreasing diameter, wherein preferably a broader end of the helical spring bears against the ferrite (20a, b, 20'a, b, 120a, b).Induction heating device according to one of Claims 1 to 8, characterized in that the spring means are designed as a leaf spring, preferably having at least one bend or having at least one bend.Induction heating device according to one of Claims 1 to 8, characterized in that the spring means are designed as block-shaped spring bodies, preferably consisting of a voluminous elastic plastic material.Induction heating device according to one of the preceding claims, characterized in that the recess (122) has an undercut (124), which is engaged behind by a section of the spring means (129), for the positive fastening of the spring means to the ferrite (120a) as a captive fastening during mounting of the induction heating device (11) by holding the spring means against a movement perpendicularly away from the surface of the ferrite.Induction heating device according to claim 13, characterised in that an undercut recess (122) is provided, in particular drawn or opened as far as a side edge of the ferrite (120a), wherein the spring means (129) are arranged in the recess so as to at least partially engage behind the undercut (124), in particular are secured against lateral displacement by a projection arranged on a recess base.Induction heating device according to one of the preceding claims, characterized in that a height of the unloaded spring means (29, 129) is twice to twenty times greater than the maximum thickness of the ferrite (20a, b, 120a).Induction hob (33) with at least one induction heating device (11) according to one of the preceding claims, characterised in that below a hob plate (34) as a cover of the induction heating device (11) a housing base (37) is arranged which is fastened to the hob plate (34), wherein the induction heating device is pressed from below against the hob plate by the spring means (29) which are supported against the housing base (37).Induction hob according to claim 16, characterised in that the induction heating coil (12a), optionally with a thermal barrier coating (17), is pressed directly against an underside (35) of the hob plate (34), wherein the spring means (29) are pressed indirectly against the housing base (37), in particular via intermediate structural units (39) of the induction hob (33).

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