Induction cooker with IR sensor

Abstract

Induction cooking appliance (1; 61; 81; 91), comprising at least one IR sensor (32) arranged beneath a cooking surface (15) with an IR sensor element (43) for detecting infrared light (IR) from a piece of cookware (12) placed on the cooking surface (15), wherein at least one IR reflector (49, 54; 82; 92) arranged beneath a cooking surface (15) is optically connected upstream of the IR sensor element (43), wherein at least one IR reflector (49, 54;92) is designed to focus the infrared light (IR) emitted by the cooking utensil (12) onto the IR sensor element (43) or onto an area in the vicinity thereof, wherein at least one IR reflector (49, 54) represents a part of the IR sensor (32), wherein at least one IR reflector (49, 54) has an electrically conductive sleeve (47) laterally surrounding at least the IR sensor element (43), characterized in that at least one IR reflector (49, 54) is plugged onto a housing (42) surrounding the IR sensor element (43), wherein the connection between the at least one IR reflector (49, 54) and the housing (42) is a clamping or pressing connection and / or an adhesive connection.;

Description

[0001] The invention relates to an induction cooking appliance, comprising at least one infrared light (IR) sensor arranged below a cooking plate with an IR sensor element for detecting infrared light from a cooking utensil placed on the cooking plate.

[0002] For hobs with cooking zones that are operated with a resistance heating element, it is known, for example from DE 10 2004 015255 A1, to sense the temperature of a side wall of a cooking pot by means of an IR sensor that protrudes from the top of the hob and is permanently assigned to one of the cooking zones.

[0003] For example, from DE 10 2006 026 907 A1 an induction hob is known with a sensor device having a first sensor which is designed to record measured values ​​for determining a temperature of a defined preparation zone (cooking zone) on which a preparation container (cookware) for receiving a preparation item can be placed, and having an IR sensor which is designed to detect heat radiation from the preparation zone and a base of the cookware, and an evaluation unit which is electrically connected to the sensor and the IR sensor and with which the temperature of the base can be determined depending on information transmitted by the sensors, wherein the two sensors are arranged such that their local detection areas overlap at least in some areas, in particular substantially completely.For this purpose, the sensors are arranged in a central recessed area of ​​each inductor, with each preparation zone being assigned a corresponding inductor.

[0004] An IR sensor for an induction cooktop is an IR sensor element with a lens in front of it. The lens focuses the IR radiation emanating from the bottom of the cookware onto the IR sensor element. The IR sensor is mounted on the front of a circuit board and faces vertically forward or upward. The back of the circuit board rests on the main circuit board of the induction cooktop.

[0005] EP 2 410 815 A1 discloses an induction cooking appliance with a duct that forms a cooling air path for directing the cooling air generated by the air blower to a control circuit and an infrared sensor. The infrared sensor and the control circuit are arranged at positions below the upper wall of the duct.

[0006] From JP 2009 - 252 633 A an induction cooking appliance with an infrared sensor is known, which is arranged in a cooling channel for introducing cooling air to cool the heating coil.

[0007] DE 10 2007 013 839 A1 discloses a hob sensor device for detecting a characteristic of a cooking utensil using radiation, comprising at least one sensor associated with at least a first spectral range of the radiation. An optical unit is connected upstream of the sensor.

[0008] US 2009 / 0 001 072 A1 discloses an induction cooking appliance with an infrared sensor arranged beneath the heating coil that detects the infrared light emitted by the pot. A light-conducting element is provided that guides the infrared light from the pot to the infrared sensor. The light-conducting element comprises a part made of non-metallic material, in which the upper opening is formed higher than a lower side of the heating coil.

[0009] From JP 2004 - 95 316 A an induction cooking appliance is known with a heating coil and an infrared sensor for detecting the infrared radiation emitted from a pot bottom, wherein a field of view for transmitting the infrared rays is located within the inner diameter of the heating coil.

[0010] It is the object of the present invention to at least partially overcome the disadvantages of the prior art and in particular to provide an induction cooking appliance which enables a particularly inexpensive and / or accurate temperature measurement of cookware by IR radiation measurement.

[0011] This object is achieved according to the features of the independent claims. Preferred embodiments can be found in particular in the dependent claims.

[0012] This object is achieved by an induction cooking appliance, comprising at least one IR sensor arranged below a cooking plate with an IR sensor element for detecting infrared light from a cookware placed on the cooking plate, wherein at least one IR reflector arranged below a cooking plate is optically connected upstream of the IR sensor element (ie, is arranged upstream of the IR sensor element in a beam path of the IR radiation from the cookware to the IR sensor element).

[0013] The use of an IR reflector to direct the IR light onto the IR sensor element has the advantage over a plastic lens, among other things, that, unlike a lens used as a transmitted-light element, there is no or much less attenuation of the IR radiation at the IR reflector. Regarding a lens, this attenuation could be counteracted with a lens made of silicon or germanium, although germanium is expensive and silicon has the disadvantage of a temperature dependence of its emission and reflection. Furthermore, with silicon, the refractive index can be dependent on temperature. A further problem with such lenses lies in the coating (surface coating) that is usually present on the silicon. Coatings are applied to optimize the reflection behavior and / or to define a wavelength range in which the lens has particularly high transmission.This allows a filter function to be achieved. However, these coatings generally only tolerate low temperatures. Since temperatures of up to over 150 °C can occur in the area of ​​an inductor, transmission disturbances and / or destruction of the coating can be expected with a silicon lens. The optical properties of IR reflectors, on the other hand, generally do not depend on the temperature of their reflective surface, especially the reflective layer. The lower attenuation and lower temperature dependence of at least one IR reflector improves measurement accuracy and is also cost-effective to implement.

[0014] The induction cooking appliance can have at least one inductor, in particular a plurality of inductors, arranged beneath the cooktop. A cooking zone can be assigned to each of several inductors, or a cookware item can be freely positioned on the cooktop, particularly if the at least one inductor is configured as a (comparatively smaller) array of inductors.

[0015] A shielding plate may be arranged underneath the inductor to shield the (electro)magnetic field generated by the inductor. Device electronics may be arranged underneath the shielding plate. The device electronics may, in particular, comprise electronic switches, e.g., semiconductor power switches, for switching an excitation current flowing through the respective inductor or inductor group on and off. The semiconductor power switches may, for example, be designed as IGBTs, bipolar transistors, field-effect transistors, etc. A part of the IR sensor, in particular also a part of an IR sensor module, is also mounted underneath the shielding plate.

[0016] The IR sensor element can be, for example, an IR diode element, e.g., a diode chip. However, the type of IR sensor element is fundamentally unlimited and can also be, for example, a thermopile, etc.

[0017] In a further development, at least the IR sensor (and possibly also at least one electronic component such as a resistor, a coil, a capacitor, an integrated circuit, etc.) is arranged on a circuit board, thus forming an IR sensor module. In the following, IR sensor module and IR sensor can be used interchangeably, unless the context contradicts this.

[0018] According to the invention, at least one IR reflector is designed to focus the infrared light emitted by the cookware onto the IR sensor element or onto an area in the vicinity thereof. This makes it possible to achieve a high IR radiance at the location of the IR sensor element and consequently increased measurement accuracy. In a further development, the infrared light is or is focused onto the IR sensor element, which enables a particularly high radiance even with small and inexpensive IR sensor elements. In a further development, the infrared light is or is focused nearby (i.e. in particular at a short distance in front of or behind the IR sensor element), which is particularly easy to implement, especially if the IR sensor element is not visible from the outside. The light spot at the location of the IR sensor element is larger than with precise focusing, but is still sufficiently increased.In particular, it can be or will be focused on a window or filter of a housing surrounding the IR sensor element.

[0019] According to the invention, at least one IR reflector forms part of the IR sensor. This allows for a particularly simple construction and assembly of the IR measurement setup (with the at least one IR reflector and the IR sensor). Furthermore, a particularly robust IR measurement setup with minimal adjustment is possible.

[0020] In yet another embodiment, at least one IR reflector is designed as an optical concentrator, in particular an IR reflector positioned directly or immediately upstream of the IR sensor element. A concentrator is not an imaging optic, but rather focuses incoming radiation with particularly high efficiency onto a locally defined area. This takes advantage of the fact that temperature measurement generally does not require an image of the measurement spot, but rather only the integral radiance, IR power, or similar.

[0021] In a further development, the concentrator is a CEC (Compound Elliptic Concentrator) or a CHC (Compound Hyperbolic Concentrator). The CEC and CHC concentrators can be used, in particular, to concentrate light from a planar IR radiator within a short distance, especially onto a surface. Such a concentrator can have a particularly low installation height.

[0022] However, to generate a particularly high radiance on a particularly small, in particular approximately point-like, surface of the IR sensor element, the use of a CPC (Compound Parabolic Concentrator) concentrator is preferred, in particular a rotationally symmetric CPC concentrator, which is also referred to as a "Winston Cone." Thus, a preferred embodiment is for at least one IR reflector to be designed as a Winston Cone.

[0023] However, in principle, a different concentrator (such as a non-rotationally symmetric CPC concentrator) can also be used instead of a Winston cone. In addition, simple focusing IR reflectors, particularly paraboloidal, ellipsoidal, or even freely shaped ones, can also be used, especially rotationally symmetric cup reflectors.

[0024] According to the invention, at least one IR reflector is plugged onto a housing surrounding the IR sensor element. This enables precise positioning and simple assembly. The housing is preferably a TO housing. The IR reflector has, in particular, a tube or nozzle that can be plugged onto the TO housing and, in particular, contacts a lateral surface of the TO housing. According to the invention, the connection between the at least one IR reflector and the housing is a clamp or press connection and / or an adhesive connection.

[0025] According to the invention, the IR reflector has an electrically conductive sleeve that laterally surrounds at least the IR sensor element. This sleeve can laterally shield at least the IR sensor element from interference fields. Furthermore, the IR sensor can then also be introduced into a space flooded by the alternating (electro)magnetic field generated by the coil(s), since the sleeve can protect at least the IR sensor element from destruction by these alternating fields. Thus, the IR sensor can be brought particularly close to the cooktop plate and at least partially guided through a shielding plate. It is particularly preferred that the sleeve also laterally surrounds a (typically thin) reflective layer of the IR reflector. This can prevent damage or even destruction to the layer by eddy currents induced therein, in particular by the coil(s). The sleeve may also surround electronic components and / or conductor tracks.

[0026] Another design feature is that the IR sensor, or rather its field of view, is directed directly at the cooktop plate. This enables a particularly simple and loss-free measurement setup.

[0027] In addition, one design allows the IR sensor to partially protrude through a shielding plate. This allows for particularly close positioning to the coil(s) and thus to the cooktop plate, thus increasing measurement accuracy.

[0028] Another embodiment provides for at least one IR reflector to be positioned upstream of the IR sensor at a distance from the sensor. This allows for more freedom in positioning the IR sensor, particularly in areas of lower temperature and / or in areas with larger installation space. It also allows for a simple horizontal positioning of the IR sensor, which reduces the overall height. The horizontal positioning of the IR sensor can be achieved, in particular, by arranging or attaching it to a side edge of an associated circuit board (with which the IR sensor can form an IR sensor module).

[0029] In yet another embodiment, the at least one spaced-apart IR reflector has an ellipsoidal basic shape. This allows at least a portion of the incident IR radiation to be focused onto a narrowly defined focal point, preferably onto the IR sensor element or onto a region in its vicinity.

[0030] Another embodiment includes at least one optical filter connected upstream of the IR sensor. This allows, in particular, interference effects on the operation of the IR sensor element caused by radiation (IR radiation, visible light, etc.) outside a desired spectral measurement range to be suppressed.

[0031] Another design is that at least one non-focusing deflecting mirror is installed upstream of the IR sensor. This allows for even more flexible beam guidance and even greater freedom of positioning of the IR sensor.

[0032] Another embodiment is for the IR sensor to be positioned off-center relative to an associated inductor. This has the advantage that stamps, color markings, etc., sometimes found in the center of the base of a cookware item are not detected and thus cannot distort a temperature measurement. For this embodiment, the inductor may, in particular, have a continuous off-center recess through which the IR radiation can pass.

[0033] A further development is that the IR sensor is thermally connected to a heat sink. In contrast to a design in which the IR sensor is arranged essentially directly (i.e. not via a dedicated heat sink) on the electronics board of the induction cooker, heat can now be dissipated particularly effectively by the IR sensor. As a result, the IR sensor does not heat up significantly or only minimally. In addition, temporal and / or spatial temperature gradients at the IR sensor can be avoided or at least greatly suppressed. This in turn enables temporally stable IR measurement and correspondingly high measurement accuracy. In addition, the IR sensor can now be brought closer to the cooktop plate, which heats up during operation, which increases the analyzable IR light intensity and thus also the measurement accuracy.

[0034] The fact that the IR sensor is thermally connected to a heat sink can, in particular, mean that heat from the IR sensor can be significantly dissipated via the heat sink, or that heat from the IR sensor can be transferred to the heat sink to a considerable extent. The heat sink is therefore intended, in particular, as a dedicated heat sink for the IR sensor.

[0035] One embodiment includes connecting at least the IR sensor module to the heat sink via the circuit board. This allows for additional cooling of an electronic circuit formed by the at least one electronic component. This improves reliability. Furthermore, mounting the circuit board is easier this way than on a flat surface.

[0036] Another embodiment provides that the heat sink serves as a heat sink for at least one other electronic component of the induction cooking appliance, in particular a power switch. This allows the number of heat sinks to be limited, simplifying assembly and reducing costs.

[0037] In a further embodiment, the IR sensor is arranged on the upper side of the heat sink facing the cooktop plate. This provides the advantage that the IR sensor can be easily positioned close to the cooktop plate for effective cooling, enabling high measurement accuracy. Furthermore, simply by positioning the IR sensor or the IR sensor module in this way, it can be at least partially shielded from interference emitted by the cooking appliance electronics on the electronic circuit board.

[0038] In yet another embodiment, the heat sink has multiple cooling fins, in particular arranged parallel to one another, and the IR sensor is arranged on at least one cooling fin. This enables particularly simple installation, in particular by supporting the heat sink. The cooling fins can generally be arranged on each side, in particular on the top side or on the top and bottom side of the heat sink. The cooling fins are, in particular, continuous cooling fins, which enables effective heat dissipation and simple forced ventilation. The cooling fins can, in particular, be straight.

[0039] In a further embodiment, at least one electrical supply line to the IR sensor is laid in a gap between two cooling fins, in particular between cooling fins on which the IR sensor is arranged. The cooling fins effectively shield the at least one electrical supply line, e.g., the measuring line, from interference fields, which further improves measurement accuracy in a particularly simple and cost-effective manner. Supply lines can be laid in the same gap between two cooling fins or in different gaps.

[0040] Another embodiment provides for the IR sensor to be arranged in a receptacle formed by a recess in at least one cooling fin, and for air to be forced through at least the cooling fins supporting the IR sensor, or their gap. As a result, at least the part of the IR sensor or IR sensor module recessed into the cooling fins is exposed to the (cooling) air and thus additionally cooled. Furthermore, the air striking the IR sensor or IR sensor module is deflected along the part protruding from the cooling fins, thereby cooling this part as well. For an IR sensor, etc., arranged on the top side of the heat sink, this also creates an upward airflow that cools the components arranged on or in front of the IR sensor, etc. Consequently, the IR sensor or IR sensor module can be positioned even closer to the cooktop while maintaining high measurement accuracy.Furthermore, at least the part of the IR sensor or IR sensor module that is recessed into the cooling fins is even better shielded against electromagnetic fields by the cooling fins (made of metal) that surround it laterally. The part of the IR sensor or IR sensor module that is recessed into the cooling fins can, in particular, comprise the at least one electronic component and / or the IR sensor element.

[0041] Another embodiment provides for at least some of the forced-air cooling fins to be covered by a cover plate, e.g., cooling fins arranged on top. This allows for a sufficiently strong airflow over the entire length of these cooling fins, thus achieving a particularly uniform and powerful cooling effect. The cover plate is, in particular, electrically conductive, particularly metallic (e.g., made of aluminum), so that the area of ​​the heat sink covered by it is also shielded from interference fields from above.

[0042] Another design is that the IR sensor is essentially freestanding (i.e., not sealed at the sides). This prevents any obstruction to airflow along the IR sensor.

[0043] Another embodiment provides for the IR sensor, in particular an IR reflector of the sensor, to be guided through at least one cover with a gap. This allows the IR sensor to be positioned particularly close to the hotplate cover. The cover can comprise at least one cover for thermal insulation (e.g., made of mica or insulating cardboard). Additionally or alternatively, the cover can comprise at least one shield against an electromagnetic field (e.g., a shielding plate and / or a heat sink cover).

[0044] The induction cooker is primarily a household appliance.

[0045] The invention is described in more detail schematically in the following figures using exemplary embodiments. For clarity, identical or equivalent elements may be provided with identical reference numerals. Fig. 1 shows a sectional side view of a section of an induction cooking appliance according to a first embodiment with a cookware placed thereon; Fig. 2 shows a sectional side view of an IR sensor of the induction cooking appliance according to the first embodiment; Fig. 3 shows an induction cooking appliance according to a second embodiment comprising a heat sink equipped with the IR sensor; Fig. 4 shows the heat sink equipped with the IR sensor in top view; Fig. 5 shows a sectional side view of a section of an induction cooking appliance according to a third embodiment with a cooking utensil placed thereon; and Fig. 6 shows a sectional side view of optical components of an induction cooking appliance according to a fourth embodiment with a cookware placed thereon.

[0046] Fig. 1 shows a section of an induction cooking appliance 11 according to the invention with a cookware 12 placed thereon, wherein the induction cooking appliance 11 and the cookware 12 are shown spaced apart from one another merely for the sake of clarity.

[0047] The induction cooking appliance 11 has a housing base 13 of a housing 14, which is covered on top by a cooking plate 15. The cooking plate 15 can be made of glass, including tempered glass, or glass ceramic, for example. Directly below the cooking plate 15 is a thin plate 16 made of mica, for example, for thermal shielding of components located beneath the plate 16.

[0048] Attached to the underside of plate 16 is an annular inductor 17, which has a support housing 18, e.g. made of plastic, which has a field guide 19, e.g. made of ferrite, and a coil 20 for generating an alternating (electro)magnetic field at an associated cooking zone. The alternating field has a frequency of approximately 25 to 30 kHz or higher. Higher values ​​can occur, especially with harmonics. The alternating magnetic field can generate an induction current in a base 21 of the cookware 12 placed on the respective cooking zone, which heats the base 21 for preparing food located in the cookware 12.

[0049] A metallic shielding plate 22, e.g., made of aluminum, is located beneath the inductor 17. The shielding plate 22 at least partially shields an electronics board 23, which contains the device's electronics, from the alternating electric field. The electronics board 23 rests with its unpopulated rear side on the housing base 13.

[0050] In the area of ​​a central hole 24 of the annular inductor 17, both the plate 16 and the shielding plate 22 have concentric holes 25 and 26, respectively. A contact temperature sensor in the form of an NTC sensor 27 is passed through the hole 25 in the plate 16 and attached to the underside of the cooktop plate 15 to sense its temperature. Electrical leads 28 of the NTC sensor 27 are led out through the hole 24 of the inductor 17 and the hole 26 of the shielding plate 22.

[0051] Also in the area of ​​the inductor 17 (and thus off-center) there is a vertically continuous recess 29, and in the plate 16 and in the shielding plate 22 there is a recess 30 and 31 concentric thereto, respectively. Below the recess 29 of the inductor 17 there is an infrared (IR) sensor 32, which is inserted into the recess 31 of the shielding plate 22 and whose field of view is directed through the recesses 29 and 30 onto the hob plate 15. The hob plate 15 is permeable to at least part of the IR measurement spectrum of the IR sensor 32, so that the IR sensor 32 can sense IR radiation IR emanating from a measurement spot M on the base 21 and a temperature of the base 21 can be derived therefrom.

[0052] This temperature can be used in particular to regulate the temperature of the cookware 12 or the temperature of a content of the cookware 12, e.g. for frying, grilling, deep-frying or the like. The temperature may also be used to detect dangerous situations (e.g. overheating of a cookware 12 filled with oil or fat), e.g. to avoid a fire hazard and, for example, to switch off the power supply if the content of the cookware overheats.

[0053] A preferably permeable range of the IR measurement spectrum of the IR sensor 32 lies between one and five micrometers, in particular between one and three micrometers. Using the temperature of the cooktop plate 15 sensed by the NTC sensor 27, any measurement distortion of the IR measurement of the base 21 due to the temperature of the cooktop plate 15 can be corrected.

[0054] The off-center arrangement of the IR sensor 31 has the advantage that stamps, color markings, etc., sometimes located at the center of the base 21 are not detected and consequently cannot falsify a temperature measurement.

[0055] The electronics board 23 is spaced apart from the shielding plate 22, forming a space between them that serves as an air duct 33. A fan 34 can be provided on the side of the air duct 33, for example, generating a flow of air K in the air duct 3. The air flow can both directly cool the electronics board 23 and dissipate waste heat from the floor or the inductor 17 via the shielding plate 22.

[0056] The induction cooking appliance 11 has in particular several cooking zones, each with an associated inductor 17, IR sensor 32 and NTC sensor 27, etc.

[0057] Fig. Figure 2 shows a sectional side view of the IR sensor 32 in greater detail. The IR sensor 32 has an IR diode 41, which has an IR sensor element 43 housed in a metallic housing 42. A window 44, possibly designed as a filter, is located on the top side of the housing 42, through which IR radiation can fall onto the IR sensor element 43. On the rear side, the IR diode 41 has electrical connections 45. The housing 42 is designed as a TO (“Transistor Single Outline”) package.

[0058] An IR reflector 46 is mounted on the housing 42. The IR reflector 46 has an outer can or sleeve 47 that laterally surrounds the IR diode 41. The sleeve 47 is tubular and made of a material with good electrical conductivity, such as copper or aluminum. The sleeve 47 can be manufactured, for example, by deep-drawing or turning.

[0059] Attached to its front edge 48 is a shell-shaped inner support 49 made of plastic, which is surrounded by the sleeve 47 and has a front light exit opening E and a rear opening ("neck hole") 51. The front, further opening 50 is located in the region of a front open end of the sleeve 47, which serves as a light transmission opening E. The neck hole 51 is closed, in particular covered, by the IR diode 41. In particular, a tubular nozzle 52 may be connected to the rear of the neck hole 51 and can be plugged onto the housing 42, which simplifies assembly. The light transmission opening E can be open or closed by an IR-transparent cover 50.

[0060] The carrier 49 has an IR-reflecting, particularly mirror-like, reflection layer 54 on its inner side 53 and may be at least partially IR-mirrored on its outer side 55. The reflection layer 54 is preferably a (thin) aluminum layer, which is easy and inexpensive to apply and also enables high reflection levels (often 96% or more).

[0061] The use of an IR reflector 46 or a reflective layer 54 as opposed to a plastic lens as a beam-concentrating or focusing element upstream of the IR diode 41 has, among other advantages, that, unlike a lens used as a transmitted-light element, no or much less attenuation of the IR radiation occurs at the IR reflector 46. Regarding a lens, the attenuation could be counteracted with a lens made of silicon or germanium, although germanium is expensive and silicon has the disadvantage of a temperature dependence of its emission and reflection. Furthermore, with silicon, a dependence of the refractive index on temperature can occur. A further problem lies in the coating (surface coating) typically present on the silicon.Coatings are applied to optimize reflection behavior and / or define a wavelength range in which the lens exhibits particularly high transmission. This allows a filter function to be achieved. However, these coatings generally only tolerate low temperatures. Since temperatures of up to over 150°C can occur in the area of ​​the inductor 17, disturbances in transmission and / or destruction of the coating can be expected with a silicon lens. The optical properties of IR reflectors 46, on the other hand, generally do not depend on the temperature of the reflective layer 54.

[0062] The inner side 53 of the carrier 49 and thus also the reflective layer 54 here specifically have the shape of a so-called "Winston cone." The Winston cone has a shape similar to a paraboloid of revolution and can, in particular, reflect incident, divergent radiation into a point in the region of the neck hole 51. A Winston cone can also be regarded as a rotationally symmetric CPC ("Compound Parabolic Concentrator") concentrator. Compared to, for example, a simple paraboloid or ellipsoid, the Winston cone has the particular advantage of high efficiency and high radiance at the point in the region of the neck hole 51. The Winston cone can, for example, be shaped such that this point lies on the window 44 or, preferably, is located on the IR sensor element 43. This achieves particularly high measurement sensitivity. The inner side 53 of the carrier 49 here has an opening angle between approximately 10° and approximately 20°.

[0063] A portion of the IR reflector 46 protrudes through the hole 31 in the shielding plate 22 and is consequently exposed to the strong (electro)magnetic alternating field of the coil 20 located above it with its high field strength. The alternating field can also, in principle, penetrate through the hole 31. To prevent interference from this alternating field, the sleeve 47 is made of a highly electrically conductive (solid) material and can therefore serve as a shield against the alternating field. This prevents, in particular, the induction of interference voltages in existing conductor loops, which would otherwise interfere with measurement signals and thus reduce measurement accuracy. This also prevents the generation of significant eddy currents in the reflective layer 54, which could otherwise damage or even destroy the reflective layer 54 (e.g., due to heating, electromigration, or a combination of both effects).

[0064] The IR sensor 32 is arranged vertically on a circuit board 56, which together, if necessary with electronic components 71 located on the circuit board 56 (see Fig. 4) form an IR sensor module 32, 56. If necessary, an optical filter and / or a diaphragm can be arranged in front of the IR sensor 32 (not shown).

[0065] Fig. 3 shows an induction cooking appliance 61 according to a second embodiment, which has a heat sink 62 equipped with the IR sensor 32. Fig. 4 shows the heat sink 62 equipped with the IR sensor 32 in plan view.

[0066] The induction cooking appliance 61 differs from the induction cooking appliance 11 in that the IR sensor 32 or the IR sensor module 32, 56 is mounted on the heat sink 62. This enables particularly precise sensing of the IR radiation and, consequently, temperature measurement at the base 21 of the cookware 12. The heat sink 62 is made of aluminum, for example.

[0067] Although the heat sink can in principle also be applied to a heat sink intended solely for cooling the IR sensor 32 or the IR sensor module 32, 56, the heat sink 62 here is a combined heat sink 62, which can also be used to cool at least one electronic component of the electronics board 23. In the present case, the combined heat sink 62 serves to cool electronic switches 63, which, for example, switch the coils 20 of the cooking zones on and off. The electronic switches 63 are designed here as power semiconductors, in particular IGBTs but also bipolar transistors or field-effect transistors, etc., and are applied flatly to a lateral, flat surface 64 of the heat sink 62 for cooling.

[0068] To enhance the cooling effect, the heat sink 62 has continuous cooling fins 65 on its upper side facing the hob plate 15 and on its underside serving as a support, which are forced to flow with air K along their longitudinal extent by means of the fan 34 (ie in particular that the air K can flow in a gap between two cooling fins 65).

[0069] On the top side of the heat sink 62, a receptacle 66 has been formed, e.g., milled, into the cooling fins 65, into which the IR sensor module 32, 56 is arranged or partially recessed. The IR sensor module 32, 56 thus rests with its circuit board 56 on several cooling fins 65, which have a recess in the area of ​​the receptacle 66. Alternatively, the cooling fins 65 can be completely removed locally in the area of ​​the receptacle 66, and the circuit board 56 can rest flat on the heat sink.

[0070] This arrangement provides the advantage that the IR sensor module 32, 56 heats up only minimally or not significantly during operation. Furthermore, the IR sensor module 32, 56 is thermally stable, meaning that it heats up only slowly and evenly when heated during operation of the induction cooking appliance 61, and thus, in particular, no significant temperature gradients occur at the IR sensor module 32, 56.

[0071] Furthermore, the electronic components 71, the IR sensor element 43, and connecting cables 69 of the IR sensor module 32, 56 can be reliably shielded from all typically occurring electrical and / or magnetic fields. Shielding the electronic components or IR sensor electronics improves their sensitivity. Shielding is optimized by the airflow over the heat sink 62. This is especially true if this airflow is formed from aluminum. For this purpose, the connecting cables 69 are laid in particular in the recesses or gaps between the cooling fins 65, particularly to prevent interference from the connecting cables (EMC problems). Furthermore, such an arrangement is inexpensive to implement and easy to install.

[0072] To maintain an effective air flow even away from the fan 34, the top of the heat sink 62, as in Fig. 3, by means of a cover plate 67 serving as an air guide and as further shielding against electrical and / or magnetic fields. The cover plate 67 can be attached, e.g., screwed or glued, to the shielding plate 22. The cover plate 67 can be made of aluminum, for example.

[0073] Between the cover plate 67 and the shielding plate 22, there may be (at least) one intermediate layer 68, which has a hole 70 for the passage of the IR sensor 32. The cover plate also has a hole here. The intermediate layer 68 serves as thermal shielding between the shielding plate 22 and the cover plate 67 and can be made of mica or insulating cardboard, for example. It is preferred that the intermediate layer 68 completely covers the cover plate 67, but at least in the area around the hole 70 for the passage of the IR sensor 32 or its sleeve 47.

[0074] The holes 70, 31 in the intermediate layer 68 or in the shielding plate 22 (as well as in the cover plate 67) do not adjoin the sleeve 47 tightly, but leave an associated annular gap. The sleeve 47 is thus free. Since the air K flowing through the heat sink 62 is prevented from flowing horizontally by the IR sensor module 32, 56, in particular the sleeve 47, it is deflected upwards at the sleeve 47 and flows upwards through the holes 70, 31, passing over the sleeve 47. As a result, the sleeve 47 or the IR reflector 46 is surrounded by relatively cool air K at a relatively constant temperature, thus controlling its temperature. In addition, the air K flowing around the sleeve 47 also cools or at least controls the temperature of its immediate surroundings, which further reduces interference with the radiation measurement. By cooling the environment, especially the inductor 17 and the shielding plate 22, the temperature stability of the IR sensor 32 is further improved.

[0075] The IR sensor module 32, 56 can in principle be mounted in any way, e.g. in or on the heat sink 62, on the shielding plate 22, etc.

[0076] Fig. 5 shows a sectional side view of a section of an induction cooking appliance 81 according to a third exemplary embodiment with a piece of cookware placed thereon. In contrast to the induction cooking appliance 11, the IR sensor 32 (of which only the bowl-shaped inner support 49 is shown here) is not oriented vertically in the direction of the cookware 12, but horizontally. In order to still be able to receive IR radiation IR from the base 21 of the cookware 12, an IR radiation-reflecting deflecting mirror 82 is arranged below the holes 29 to 31, which deflects IR radiation passing through the holes 29 to 31 at least partially into the IR sensor 32. In principle, the distance between the IR sensor 32 and the deflecting mirror 82 spaced therefrom can be as large as desired.

[0077] The induction cooking appliance 81 has the advantage that the IR sensor module 32, 56 is already reliably shielded from the field generated by the coil 20 by the shielding plate 22. For example, the sleeve 47 can be omitted in principle, or a sleeve made of plastic can be used, for example. Furthermore, the overall height required for the IR sensor module 32, 56 can be reduced. Furthermore, positioning can be selected more flexibly, e.g., even to the side next to the inductor 17. In particular, when positioned next to the inductor 17, the IR sensor module 32, 56 is not heated as much, and cooling the sensor module 32 is structurally simpler.

[0078] Fig.6 shows a sectional side view of optical components 92, 93, 41, 56 of an induction cooking appliance 91 according to a fourth exemplary embodiment with a cookware 12 mounted thereon. In contrast to the induction cooking appliance 81, the deflecting mirror 92 is now itself designed as a focusing element, so that an IR reflector 46 on the IR diode 41 itself can be dispensed with. The deflecting mirror 92, as a focusing IR reflector, is thus arranged at a distance from the IR diode 41, which serves as an IR sensor. This type of construction also allows, among other things, a simple arrangement of (at least) one spectral filter 93.

[0079] The deflecting mirror 92 is configured here as an ellipsoidal surface (in particular as a partial surface of a rotational ellipsoid), so that IR radiation IR emanating from the floor 21, which is directed from a virtual first focal point above the floor 21, is focused onto a second focal point F2 at the location of the IR sensor element 43. An advantage of the focusing, in particular ellipsoidal, deflecting mirror 92 lies in the fact that alignment problems between the otherwise independent (pure) deflecting mirror and reflector are eliminated.

[0080] To further reduce the height of the present IR sensor module 41, 56, the IR sensor 41 is not attached to a large side surface of the circuit board 56, but rather to the side of the circuit board 56. The entire IR sensor module 41, 56 then fits much more easily into the induction cooking appliance 91, especially if deflecting mirrors are used.

[0081] The examples shown are highly accurate and can be implemented comparatively inexpensively.

[0082] Of course, the present invention is not limited to the embodiments shown.

[0083] In particular, features of the various embodiments can also be combined, for example an arrangement of the IR sensor module on a heat sink with each of the embodiments shown.

[0084] Furthermore, a simple paraboloidal or ellipsoidal shaped reflection layer or reflector can be used instead of a Winston cone. Another optical concentrator can also be used instead of a Winston cone, e.g. a different CPC concentrator (such as a non-rotationally symmetric CPC concentrator), a CEC (“Compound Elliptic Concentrator”) concentrator or a CHC (“Compound Hyperbolic Concentrator”) concentrator. The CEC concentrator and the CHC concentrator can be used in particular to concentrate light from a planar IR radiator within a short distance, but usually not onto a point, but rather onto a surface. This can be advantageous, for example, with an IR sensor element 43 that covers a considerable area and / or with vertical installation with a low installation height.

[0085] In principle, at least one optical element effective for IR light can be connected upstream of the IR sensor, e.g. at least one aperture, at least one filter, at least one beam-forming transmitted light element, at least one reflector, etc.

[0086] An imaging, particularly focusing, deflection mirror may also be used together with an IR reflector attached directly to the IR sensor. List of reference symbols 11 Induction cooker 12 cookware 13 Case back 14 housings 15 Hob 16 plates 17 Inductor 18 carrier housings 19 Field tour 20 coil 21 Bottom of the cookware 22 Shielding plate 23 Electronic board 24 central hole of the ring-shaped inductor 25 hole of the plate 26 Hole of the shielding plate 27 NTC sensor 28 Electrical cable of the NTC sensor 29 Inductor recess 30 Recess in the plate 31 Recess in the shielding plate 32 IR sensor 33 Air duct 34 fans 41 IR diode 42 IR diode housing 43 IR sensor element 44 IR diode window 45 electrical connection of the IR diode 46 IR reflector 47 sleeve 48 Edge of the sleeve 49 carriers 50 IR-permeable cover of the IR reflector 51 Neck hole 52 nozzles 53 Inside of the carrier 54 reflective layer 55 Outside of the carrier 56 circuit board 61 Induction cooker 62 heat sinks 63 electronic switch 64 flat surface of the heat sink 65 cooling fin 66 recording 67 Cover plate 68 Intermediate layer 69 connecting cable 70 Hole in the intermediate layer 71 electronic components 81 Induction cooker 82 deflecting mirrors 91 Induction cooker 92 deflecting mirrors 93 spectral filter E Light exit opening F2 focal point IR IR radiation K Air M measuring spot

Claims

[1] Induction cooking appliance (1; 61; 81; 91), comprising at least one IR sensor (32) arranged beneath a cooking surface (15) with an IR sensor element (43) for detecting infrared light (IR) from a cooking utensil (12) placed on the cooking surface (15), wherein at least one IR reflector (49, 54; 82; 92) arranged beneath a cooking surface (15) is optically connected upstream of the IR sensor element (43), wherein at least one IR reflector (49, 54; 92) is designed to focus the infrared light (IR) emitted by the cooking utensil (12) onto the IR sensor element (43) or onto an area in the vicinity thereof, wherein at least one IR reflector (49, 54) represents a part of the IR sensor (32), wherein at least one IR reflector (49, 54) has an electrically conductive sleeve (47) laterally surrounding at least the IR sensor element (43), characterized bythat at least one IR reflector (49, 54) is plugged onto a housing (42) surrounding the IR sensor element (43), wherein the connection between the at least one IR reflector (49, 54) and the housing (42) is a clamping or pressing connection and / or an adhesive connection. [2] Induction cooking appliance (1; 61; 81) according to claim 1, characterized by that at least one IR reflector (49, 54) is designed as an optical concentrator. [3] Induction cooking appliance (1; 61; 81) according to claim 2, characterized by that at least one IR reflector (49, 54) is designed as a Winston cone. [4] Induction cooking appliance (1; 61; 81) according to one of claims 2 to 3, characterized by that the IR sensor (32) is directed directly at the hob plate (15). [5] Induction cooking appliance (1; 61; 81) according to one of claims 2 to 4, characterized by that the IR sensor (32) partially protrudes through a shielding plate (22). [6] Induction cooking appliance (1; 61; 81) according to one of the preceding claims, characterized by that at least one IR reflector (92) is arranged at a distance upstream of the IR sensor (32). [7] Induction cooking appliance (1; 61; 81) according to claim 6, characterized by that the at least one spaced IR reflector (92) has an ellipsoidal basic shape. [8] Induction cooking appliance (1; 61; 81) according to one of the preceding claims, characterized by that at least one filter is optically connected upstream of the IR sensor (32). [9] Induction cooking appliance (1; 61; 81) according to one of the preceding claims, characterized by that at least one non-focusing deflecting mirror (82) is connected upstream of the IR sensor (32). [10] Induction cooking appliance (1; 61; 81) according to one of the preceding claims, characterized by that the IR sensor (32) is arranged off-center with respect to an inductor (17) associated with it.

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