GB2552531A

GB2552531A - Temperature sensor in induction cooker

Info

Publication number: GB2552531A
Application number: GB1613059.3A
Authority: GB
Inventors: Hauser Glyn; James Michael; Meddick James
Original assignee: Morphy Richards Ltd; Morphy Richards NI Ltd
Current assignee: Morphy Richards Ltd; Morphy Richards NI Ltd
Priority date: 2016-07-28
Filing date: 2016-07-28
Publication date: 2018-01-31
Anticipated expiration: 2036-07-28
Also published as: GB201613059D0; GB2552531B

Abstract

An induction cooking apparatus comprises a base unit 100 having an induction heating coil; a cover plate 301 above said induction heating coil; and a temperature sensor 304, said temperature sensor being located in an aperture in said cover plate such that an outer surface of said temperature sensor is accessible from a position on top of said cover plate. The temperature sensor contacts the underside of a cooking vessel at a position which is not directly heated by induction, and which does not directly overlie the induction heating coil.

Description

(54) Title of the Invention: Temperature sensor in induction cooker Abstract Title: Temperature sensor in induction cooker (57) An induction cooking apparatus comprises a base unit 100 having an induction heating coil; a cover plate 301 above said induction heating coil; and a temperature sensor 304, said temperature sensor being located in an aperture in said cover plate such that an outer surface of said temperature sensor is accessible from a position on top of said cover plate. The temperature sensor contacts the underside of a cooking vessel at a position which is not directly heated by induction, and which does not directly overlie the induction heating coil.

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Intellectual

Property

Office

Application No. GB1613059.3

RTM

Date :9 January 2017

The following terms are registered trade marks and should be read as such wherever they occur in this document:

BLUETOOTH

Intellectual Property Office is an operating name of the Patent Office www.gov.uk/ipo

-1Temperature Sensor in Induction Cooker

Field of the Invention [0001] The present invention relates to an induction cooking apparatus, and to a method of sensing of temperature.

Background of the Invention [0002] Induction hobs are well-known for domestic cooking. A known induction hob works by having an electromagnetic coil which generates an electromagnetic field which extends above a cooking surface, for example a glass or ceramic hob, to interact with a ferrous element of a cooking vessel such as a saucepan, frying pan or the like placed on the hob. The electromagnetic radiation induces eddy currents within the ferrous material, which leads to heating of the material and therefore heating of the pan or other cooking vessel.

[0003] Induction hobs are highly controllable and are more energy efficient than conventional electric hobs which rely on an electric heating element and thermal conduction from the electric heating element to a cooking vessel.

[0004] A known induction hob has an electric coil to produce an electromagnetic field, a set of control electronics, a glass or ceramic hob, through which the electromagnetic waves pass to interact with an inductive material on the underside of a cooking vessel, and in some cases a cooling fan to blow air over the coil and control electronics for cooling. Heat generated in the inductive layer of the cooking vessel passes through thermal conduction to the base of the cooking vessel, and heats the contents of the cooking vessel.

[0005] In a known induction hob, a temperature sensor is provided which is placed in contact with the underside of the glass cover plate of the hob, in the heating area where the cooking vessel is placed over the electromagnetic coil. The temperature sensor measures the temperature of the underside of the glass, as being representative of the temperature of the base of the cooking vessel.

-2[0006] In a known induction hob, the temperature sensor is provided as a safety measure to make sure that the pan does not overheat.

[0007] There is an additional negative temperature coefficient (NTC) temperature sensor which is provided as a safety measure. In a typical known induction hob, cooking temperatures are set similarly to a conventional electric cooking hob, using heat controls which can be either manual rotatable rheostat type controls or touch sensitive electronic controls located on the upper surface of the hob adjacent heating areas.

[0008] Measurement of temperature in the known induction hob is made from underneath a glass plate, and underneath an induction heated ferritic part of the cooking vessel.

[0009] In order to produce an induction cooking hob which provides a level of automation of cooking procedures, it is desirable to measure the temperature inside a cooking vessel, and to provide a temperature signal which can be used to generate a temperature display to the user, and/or which can be used as an input to an automated or semi - automated cooking system which follows a predetermined recipe.

[0010] Known induction hobs do not generally have temperature sensors which are intended to measure the cooking temperature of food items within a cooking vessel.

[0011] One object of the embodiments described herein is to provide an accurate temperature measurement of cooking temperatures inside an induction heated cooking vessel which is heated on an induction powered hob.

-3[0012] Another object of the embodiments described herein is to provide an induction heated cooking vessel which is adapted for improved temperature measurement of the contents of the cooking vessel.

Summary of the Invention [0013] According to a first aspect there of the present invention, there is provided an induction cooking apparatus comprising:

a base unit having an induction heating coil;

a cover plate above said induction heating coil; and a temperature sensor, said temperature sensor being located in an aperture in said cover plate, wherein an outer surface of said temperature sensor is accessible from a position on said cover plate.

[0014] Preferably, said temperature sensor is movable relative to said cover plate.

[0015] Preferably, said temperature sensor is resiliently biased relative to said cover plate.

[0016] Said temperature sensor may protrude above a level of an upper surface of said cover plate, or may be flush with the upper surface.

[0017] Preferably, said temperature sensor comprises:

a semiconductor temperature sensing device; and

-4a housing, containing said semiconductor temperature sensing device.

[0018] Preferably said induction cooking apparatus further comprises a vessel proximity sensor, for sensing a vessel placed on said base unit.

[0019] Preferably, said housing comprises aluminium.

[0020] Preferably, said housing is movable relative to said cover plate.

[0021] Preferably, said housing is resiliently biased relative to said cover plate.

[0022] Preferably, said housing is mounted on a compression spring.

[0023] Preferably there is provided a heat resistant and fluid resistant membrane housing said temperature sensor. The membrane may comprise a flexible heat resistant collar located between said temperature sensor and said cover plate.

[0024] According to a second aspect, there is provided a method of measuring temperature of a cooking vessel on an induction cooking device, said induction cooking device comprising:

a base unit having an induction heating coil;

a cover plate above said induction heating coil; and a temperature sensor, said temperature sensor being located in an aperture in said cover plate

-5wherein an outer surface of said temperature sensor is accessible from a position above said cover plate;

said method comprising placing a cooking vessel on said induction cooking device, such that a region of an underside of said cooking vessel contacts said temperature sensor; and reading a temperature signal from said temperature sensor.

[0025] Preferably a first region of the underside of the cooking vessel where the temperature is to be measured is located directly over said temperature sensor and said first region is placed over an area of said cover plate which does not directly overlie an induction coil.

[0026] Preferably, said first region of said cooking vessel at which temperature is measured comprises a second region of an underside of said cooking vessel which has a reduced thickness relative to a first region surrounding said second region.

[0027] According to a third aspect, there is provided a method of measuring temperature in an induction cooking device, said method comprising:

providing a temperature sensor in a cover plate of said induction cooking device, said sensor being provided in a region of said cover plate which does not overlie an induction coil;

directly contacting said temperature sensor with an underside of a cooking vessel at a location of said cooking vessel which does not overlie an induction coil of said induction cooking device.

-6[0028] Preferably the method comprises directly contacting said temperature sensor with a region of an underside of said cooking vessel, which has a reduced thickness compared with a surrounding region of said underside of said cooking vessel.

[0029] According to fourth aspect there is provided a method of measuring temperature in an induction cooking device, said method comprising:

providing a temperature sensor in a movable housing in a region of said induction cooking device upon which a cooking vessel may be placed;

resiliently biasing said housing in an upward direction such that said temperature sensor contacts a part of the cooking vessel, which is heated primarily by conduction of heat.

[0030] Preferably said temperature sensor is resiliently biased so as to protrude beyond a level of a surrounding upper surface of said cooking plate, such that a cooking vessel placed on said cooking plate depresses the temperature sensor, thereby keeping the temperature sensor in continuous contact with the underside of the cooking vessel during operation of the induction cooking device.

[0031] In one specific method, the temperature sensor is urged into touching contact with a non-inductive part of said cooking vessel. The temperature sensor may contact a part of said cooking vessel which is nonferritic.

[0032] According to a fifth aspect there is provided a method of measuring temperature in an inductively heated cooking vessel, said method comprising:

providing an induction heating coil;

-7providing a temperature sensor arranged to make direct contact with an underside of said cooking vessel;

wherein the temperature sensor makes contact with the underside of the cooking vessel in an area which does not directly overlie said induction heating coil.

[0033] Preferably, contact is made between said temperature sensor and an underside of said cooking vessel at a region on said cooking vessel which has a reduced thickness of inductive material relative to a region of said cooking vessel surrounding said reduced thickness region.

[0034] In one specific method, contact is made between said temperature sensor and an underside of said cooking vessel at a region of said underside of said cooking vessel which contains no inductive material.

[0035] Preferably, the temperature sensor is resiliently biased so as to be urged against the underside of the cooking vessel in order to make firm and continuous contact between the temperature sensor and the underside of the cooking vessel.

[0036] According to a sixth aspect there is provided an induction heated cooking the vessel comprising:

a body portion which is intended to be in contact with a food item or a liquid to be heated;

said body portion having an underside comprising a first region of a first thickness, and a second region of a second thickness, said second region having a reduced thickness relative to the thickness of said first region.

[0037] Preferably said reduced thickness region may comprise an indent or cavity in a bottom plate or underside of the cooking vessel.

-8[0038] Preferably an outer surface on the underside of the second region is substantially flat so that a flat upper surface of a temperature sensor can make good thermal contact with the region on the underside of the cooking vessel, assisting in making an accurate temperature measurement.

[0039] In one embodiment, the first region which is relatively thicker compared to the second region, comprises one or a plurality of areas of inductive material embedded in a non-inductive material. The inductive material is preferably steel, and the non-inductive material is preferably aluminium.

[0040] In another embodiment, the first region which is relatively thicker compared to the second region comprises comprises an upper layer of noninductive material, and a lower layer of inductive material. The lower layer of inductive material provides inductive heating, and the upper layer of non-inductive material provides efficient conductive heat transfer from the inductive material to the contents of the cooking vessel. The upper layer of non-inductive material and said lower layer of inductive material may each have an aperture surrounding the second relatively thinner region, so that temperature can be measured at an area of the cooking vessel which is not directly over an induction coil, and which is not directly heated by induction.

[0041] In one embodiment, the apertures in the lower inductive material layer and an intermediate said non-inductive material layer are closed off by a part of said body portion.

[0042] In one embodiment, the body portion comprises steel; said layer of inductive material comprises a ferrous material; and there is a layer of aluminium located between said body portion and said inductive material.

-9[0043] In another embodiment, the cooking vessel comprises a body of non-inductive material into which are embedded one or a plurality of regions of inductive material; and there being a region of said body of reduced thickness, surrounded by a region of increased thickness, there being no said inductive material in said region of reduced thickness.

[0044] The induction heated cooking the vessel may comprise a pan; a griddle; a steamer; an egg poacher, or a like vessel. In the general case, the induction heated cooking vessel may comprise any cooking vessel type which can be inductively heated and fitted on top of an induction hob base unit [0045] On the underside of the cooking vessel there is provided a layer of inductive material which heats up when exposed to an electromagnetic field. The inductive material is bonded to the underside of a body of the cooking vessel, so that heat generated in the inductive material is transferred by conduction to the floor and/or sides of the cooking vessel.

[0046] In one embodiment, the layer of Inductive material has at least one aperture, being an area where the inductive material is absent, the aperture being surrounded by the layer of inductive material. Preferably the aperture area is located substantially centrally to the base of the cooking vessel.

[0047] On the base unit, there is provided a protruding housing region which protrudes above the surrounding substantially flat upper surface area of the induction hob onto which the inductive plate of the cooking vessel sits.

[0048] The raised housing contains a negative temperature coefficient thermistor (NTC). The negative temperature coefficient thermistor may be located within the aluminium housing with heat conductive paste being provided between the thermistor and the inside of the housing, to ensure efficient heat transfer, and

-10accurate temperature measurement. An objective is to physically locate the negative temperature coefficient thermistor device itself as close as possible to the inside surface of the cooking vessel, whilst the thermistor remains part of the induction hob base unit, by arranging the housing to contact the underside of the cooking vessel, as closely as possible to the interior of the cooking vessel, and with thermal conduction between the material of the cooking vessel and the thermistor being as efficient as possible, with the minimum amount of temperature gradient between the thermistor and the material of the cooking vessel immediately adjacent the food to be cooked.

[0049] In use, the housing engages a recessed region in the underside of the cooking vessel, in which there is either no inductive material, or a relatively thinner region of inductive material such as steel. The housing engages the reduced thickness region, so that the upper part of the housing is in direct contact with the material of the floor of the cooking vessel, rather than in direct contact with the main layer of inductive material. This means that the temperature sensor is measuring the temperature of the cooking vessel at a position in the base of the cooking vessel which is heated substantially only by conduction of heat from the induction layer to the base material, and which is not heated by induction. The temperature sensor is not measuring the temperature of the induction layer itself at a place where it is directly heated by induction.

[0050] This temperature measurement is a more accurate reflection of the temperature of the base or floor of the cooking vessel than is produced by measuring the temperature of the induction material layer only, at a position underneath the cooking vessel where the layer is directly overlying an inductive coil.

[0051] In the embodiments herein, the thermistor housing is preferably aluminium. The aluminium shell of the thermistor housing projects through the upper surface plate of the base unit upon which a cooking vessel is placed, so

-11that when a cooking vessel is present, the temperature sensing housing is in direct contact with the underside of the cooking vessel.

[0052] In an improvement to the system, the aluminium housing of the temperature sensor is placed in direct contact with the non- inductive floor material of the cooking vessel in a region where there is no inductive material, for example in an aperture in the inductive layer of the cooking vessel. This enables the temperature sensor to be in direct contact with the part of the cooking vessel, the other side of which is in contact with the contents of the cooking vessel, and gives a more reliable measurement of cooking vessel temperature.

[0053] The aluminium housing is preferably spring mounted, so that in the absence of any pressure the housing protrudes slightly above the surrounding upper surface of the base unit, ensuring that when the cooking vessel is placed on the base unit, there is a good contact between the underside of the cooking vessel and the temperature sensor. The full weight of the cooking vessel depresses the resiliently biased temperature sensor housing, so that the surrounding inductive layer rests upon the upper surface of the hob, and the temperature sensor remains urged against an in contact with the underside of the cooking vessel.

[0054] In embodiments presented herein, the NTC temperature sensor is used to measure cooking temperatures, rather than being used as a safety cut out temperature sensor. The required accuracy of temperature measurement is greater than for a prior art temperature sensor used solely to detect overheating of the cooking vessel the safety reasons.

[0055] In the presently disclosed embodiments, temperature information from the temperature sensor may be used in automated menus and cooking methods, and may be used as a data import to generate a temperature display on the base unit.

-12[0056] Preferably measurement of temperature is taken from a non-ferritic part of the cooking vessel.

[0057] Other aspects are as set out in the claims herein.

Brief Description of the Drawings [0058] For a better understanding of the invention and to show how the same may be carried into effect, there will now be described by way of example only, specific embodiments, methods and processes according to the present invention with reference to the accompanying drawings in which:

Figure 1 illustrates schematically a cooking system comprising an induction heater base unit and a plurality of induction heated cooking vessels;

Figure 2 illustrates schematically an induction cooker base unit and an induction heated cooking vessel;

Figure 3 illustrates schematically the induction cooker base unit in perspective view from the front and above;

Figure 4 illustrates schematically one example of an induction heated cooking vessel of the cooking system;

Figure 5 illustrates schematically in cutaway view the induction heated cooking vessel of figure 5 herein, placed upon the induction cooker base unit;

Figure 6 herein illustrates schematically in cutaway view a temperature sensor comprising the induction heater base unit;

Figure 7 herein illustrates schematically an underside of the induction heated cooking vessel as shown in figure 2, turned upside down to show an inductive material;

-13Figure 8 herein illustrates schematically in cutaway view the temperature sensor positioned in an aperture in a cover plate, having the bottom of a cooking vessel positioned on the cover plate of the hob, with the temperature sensor in touching contact with the base of the cooking vessel during a cooking operation;

Figure 9 herein illustrates schematically a circuit diagram of electronic control components for the induction hob base unit as shown in figure 1 herein;

Figure 10 illustrates schematically a second base for an induction heated cooking vessel, the second base comprising a non-inductive material embedded with regions of inductive material, and having a temperature sensing region on the underside of the base; and

Figure 11 herein illustrates schematically a third type of base for an induction heated cooking vessel, the third type of base comprising a layer of inductive material comprising a vessel body, second layer of inductive material and a layer of non-duct inductive material there between, and showing a temperature sensing region on the underside of the base.

Detailed Description of the Embodiments [0059] There will now be described by way of example a specific mode contemplated by the inventors. In the following description numerous specific details are set forth in order to provide a thorough understanding. It will be apparent however, to one skilled in the art, that the present invention may be practiced without limitation to these specific details. In other instances, well known methods and structures have not been described in detail so as not to unnecessarily obscure the description.

[0060] Referring to Figure 1 herein, there is illustrated schematically in perspective view, an induction cooking set comprising an induction hob 100,

-14together with a set of induction powered cooking appliances or vessels 101 106, and a cooking apparatus controller unit 107.

[0061] The induction hob unit 100 comprises one or a plurality of induction coils, positioned underneath an upper surface onto which the cooking appliances 101 - 106 can be placed. Numerous types of cooking appliances may be placed for use on the induction hob unit 100 and by way of example only the cooking vessels 101 - 106 include:

- a slow cooker 101;

- a rice steamer 102;

- a steamer 103;

- a grill 104;

- a soup cauldron 105; and

- an oven 106.

[0062] The cooking apparatus controller unit 107 can plug directly into the induction hob unit 100, for example by means of a USB connector or other similar or equivalent convenient electronic connector, or can communicate with the hob wirelessly using a known wireless protocol, for example Bluetooth or equivalent. The cooking apparatus controller unit 107 may alternatively be integrated with the induction hob unit 100. The induction hob unit 100 can be controlled remotely from an application (app) on a mobile phone or hand held device, to set or program cooking parameters of the hob as hereinafter described. The induction hob unit 100 can also be controlled by directly entering commands into the cooking apparatus controller unit 107 using an interface provided on the controller, for setting cooking times and selecting pre-stored cooking programs or menus.

[0063] Referring to figure 2 herein, there is illustrated schematically in perspective view from the front and above the induction hob base unit 100 having seated thereon a tray or pan shaped cooking vessel 200. The shape of the lower

-15part of the cooking vessel 200 matches the shape of an upper surface of the base unit 100, so that the tray 200 locates securely on top of the induction base unit 100.

[0064] Referring to figure 3 herein, there is illustrated schematically in perspective view from the front and above the induction cooker base unit of figures 1 and 2.The induction base unit 100 comprises an outer casing 300; an upper surface 301 upon which a cooking vessel may be placed, the upper surface 301 having an outer peripheral rim 302 which assists in locating the underside of the cooking vessel on top of the induction base unit 100; a central raised platform 303 which, in use, locates in a correspondingly opposite shaped recess in the underside of the cooking vessel, the central raised platform 303 housing thereunder a metallic coil which when energized using alternating current produces an alternating electromagnetic field which extends in the vicinity immediately above the central raised platform area 303 to interact with an inductive material on a lower part of a cooking vessel placed upon the induction heating hob; a central region 304 containing a temperature sensor which, in use, contacts the underside of a cooking vessel for measuring a temperature of the underside of the cooking vessel; the controller unit 107, in this case shown integrated with the casing 300, but in the general case which can be either integral with the base unit, or a separate unit attachable to and detachable from the outer casing 300; and within the casing 300, a power supply unit for supplying AC mains power from an external AC mains power supply. Controller unit 107 comprises a set of control electronics for controlling the unit; a set of display control electronics for controlling a liquid crystal display on the control unit 107. The base unit 100 comprises a set of drive electronics for driving the metallic induction coil.

[0065] Referring to figure 4 herein, there is illustrated schematically in perspective view an induction heated cooking vessel 400 comprising the cooking system of figure 1 herein. The vessel comprises a vessel body 401 having a perimeter sidewall extending around a vessel base 402; first and second handles

-16403, 404 at opposite ends of the vessel; and a ceramic or glass lid 405 for closing off an upper opening of the vessel.

[0066] The vessel base 402 comprises a vessel floor, the vessel floor having an inductive material, for example a ferritic material. When vessel 400 is placed upon the induction hob 100, and the electromagnetic coil in the induction hob is energized, the inductive material of the vessel base heats up and heat is transmitted by conduction to the vessel floor and to a lesser extent, to the sides 401 of the vessel, thereby heating the contents of the vessel.

[0067] The vessel base 402 has a region of reduced thickness in which the base material, suitably steel, is thinner than in the surrounding region. This region is designed to fit over a corresponding region of the base unit which houses the temperature sensor, so that when the vessel is placed on the induction hob base unit the reduced thickness region under the vessel sits over the temperature sensor, allowing the temperature sensor to contact the underside of the vessel at its reduced thickness region.

[0068] Referring to figure 5 herein, there is illustrated schematically in cutaway view from the side, the cooking vessel 400 of figure 4 as placed on top of the induction hob base unit 100 of figures 1 to 3. On the underside of the vessel floor 402, there is a layer of inductive material which heats up when exposed to electromagnetic radiation. The inductive layer has a recess or aperture 500 being a region in which the inductive material is thinner than the surrounding regions of inductive material, or in which the inductive material is absent altogether.

[0069] The base unit comprises a platform area 502 having a central aperture 503 in which there is provided a temperature sensor 504 which projects through the aperture, beyond the upper surface of the raised platform 502 to contact an underside of the vessel floor 402 in the thinner region 500 of the base of the vessel where the inductive material is absent, or of reduced thickness

-17relative to the inductive material surrounding that region. The temperature sensor 504 is resiliently biased, for example by means of being mounted on a compression spring, so that the sensor is always in contact with the reduced thickness region 500 of the vessel floor 402. In this manner, the temperature sensor measures the temperature of the vessel floor through contact with the vessel floor, at a position which is not directly heated by an immediately adjacent induction coil. Rather, the reduce thickness region 500 of the vessel floor 402 is heated by conduction through the surrounding material of the floor 402, and is not directly heated by induction. The temperature as measured in this region more accurately represents the temperature of the inner surface of the vessel floor 402 and vessel wall 400, than the temperature of the adjacent regions of the inductive layer 505, surrounding the thinned floor region 500.

[0070] Referring to figure 6 herein, there is illustrated schematically in cut away view the temperature sensor 504 of the base unit 100. The temperature sensor comprises a negative temperature coefficient (NTC) thermistor 600 mounted within an aluminium housing 601. The aluminium housing 601 is surrounded by or substantially surrounded by a flexible silicone collar 602 which is movable in a vertical direction, but at the same time allows for a fluid tight seal between the lower parts 603 of the collar 602 and adjacent layer 502 of the induction platform of the induction hob base unit. The silicone collar 602 fits into an aperture in the cover plate 502. The silicone collar comprises a heat proof membrane which can withstand the cooking temperatures underneath the cooking vessel, and allows for a generally up/down movement of the temperature sensor, with a small degree of lateral movement or lateral play, and at the same time makes a fluid tight seal between the aluminium housing 601 of the temperature sensor, and between the outer portions of the silicone seal and the cover plate 502. The cover plate 502 of the base unit may be for example a glass or ceramic plate.

[0071] The aluminium housing 601 is movable in a vertical direction and is resiliently biased upwardly by means of a compression spring 605 or other like

-18resilient biasing means which performs the same function, such that normally the housing 601 is urged upwardly. This means that when a cooking vessel, such as induction heated cooking vessel 400 of figure 4, is placed on top of the platform layer 502, the cooking vessel will depress the upwardly resiliently biased sensor housing 601, with the compression spring 605 or other like resilient biasing means urging the aluminium housing 601 into direct contact with the lower part of the cooking vessel.

[0072] The aluminium housing 601 in use is pressed directly against the lower surface of the vessel floor 402 at a location which is not directly heated by an induction coil immediately underneath it. In the best mode embodiment, the upper part of the aluminium housing of the temperature sensor protrudes above the level of the upper surface of the surrounding cover plate 502, to a sufficient extent that the aluminium housing makes touching contact with a reduced thickness region of a cooking vessel placed upon the induction hob, the reduced thickness area having a reduced thickness of (or absence of) inductive material compared to the surrounding parts of the base of the cooking vessel, such that the part of the cooking vessel which the temperature sensor contacts is substantially not directly heated by heat generated from induction in the reduced thickness area, but rather the temperature of that region is determined by conduction of heat from surrounding areas of the base plate of the cooking vessel which have been directly inductively heated.

[0073] The protruding negative temperature coefficient thermistor or temperature sensor fits closely within the recess 500 in the cooking vessel base 402 when the cooking vessel is placed on the base unit. This means that the temperature sensor measures the temperature of the vessel, such as a pan, at a place where the pan material is heated only by convection from the surrounding inductive material and material of the pan itself, rather than at a position where the base of the pan is directly inductively heated. This therefore gives a more accurate measure of the actual pan temperature, compared to if the temperature sensor were abutted directly up to the inductively heated material 505.

-19[0074] Referring to figure 7 herein, there is illustrated schematically in perspective view and underside of the pan type cooking vessel 200 as shown in figure 2 herein, with the vessel turned upside down to better show the features of the underside of the cooking vessel.

[0075] The cooking vessel comprises a base portion 700; an upright perimeter wall portion 701; first and second handles 702, one on either end of the vessel. The base portion comprises a protruding perimeter region 703 which is shaped to fit into the corresponding moat like region 301 of the base unit, the protruding perimeter region 703 surrounding a recessed region 704 in which is located, in this example, a flat annular layer of inductive material 705, the annular layer of inductive material having a central region 706 where the inductive material is absent, or is of reduced thickness compared to the surrounding region.

[0076] The protruding perimeter region 703 is shaped such that it engages in the recessed region 301 of the cover plate, and such that the recessed region 704 on the underside of the cooking vessel fits closely over the protruding platform region 303 of the induction base unit 100. In the best mode, the cooking vessel may comprise one or a plurality of shaped interlock regions which engage with one or a plurality of protruding interlock features 305, 306 on the raised platform portion 303 of the base unit.

[0077] The temperature sensor 304, being resiliently biased automatically presses upwardly into the central region 706 on the underside of the cooking vessel such that a relatively large surface area of the aluminium housing of the temperature sensor contacts with the underside of the cooking vessel. In the best mode, the contact area on the top of the temperature sensor may be in the region 78 mm²to 700 mm², corresponding to a circular contact area having radius between 5 mm and 15 mm

-20[0078] Referring to figure 8 herein, there is illustrated schematically in cutaway view a base portion 800 of a cooking vessel positioned on top of a temperature sensor as described herein before with reference to figure 6. The underside of the cooking vessel comprises a solid plate of inductive ferritic material having a circular recess region 801 in which the plate thickness is relatively thinner or reduced, compared to the regions 802 surrounding the recessed region 801. The surrounding regions 802 lay directly over an induction coil 803, whilst the recessed region 801, in use, with the cooking vessel on the cover plate 502 lies directly over the temperature sensor such that the aluminium housing 601 of the temperature sensor contacts and underside of the reduced thickness recess region 801. Since the recess region 801 does not lie directly over an induction coil, the material in the recessed region is not directly heated by induction from an electromagnetic coil 803. There may be a residual amount of open overlap of the electromagnetic field generated by the coils 803 and the material in the thinned region 801, but the induction heating effect in the thinned region is insignificantly small compared to the induction heating effect of the surrounding full thickness portions 802 of the bottom of the cooking vessel which lie directly over the electromagnetic coils 803, although there may be a small amount of direct induction heating due to overlap directly over the induction coils 803. In this way, the temperature of the thinned region 801 is close to the temperature of the inner surface 804 of the bottom of the vessel.

[0079] Direct contact between the aluminium housing 600 of the temperature sensor and the underside of the thinned region 801 means that the temperature sensor measures as closely as possible the temperature of the inner surface 804, that is the floor, of the cooking vessel. Compression spring 605 makes sure that the aluminium housing 601 of the temperature sensor is pressed against the underside of the recessed region 801 to ensure efficient contact between the temperature sensor and the underside of the cooking vessel for temperature measurement.

-21[0080] Referring to figure 9 herein, there is illustrated a schematic block diagram of an electric circuit 900 which, in a preferred embodiment, is comprised as part of the cooking hob base unit 100. Electric circuit comprises a controller unit 901, to which are coupled a clock 902, a user interface 903 which includes a visual display 904 and a set of user controls 905; a memory module 906 which can be used to store a set of recipes in electronic format; an appliance interface module 907 for reporting back to the controller unit with parameters such as temperature and coil operation/activation; an electromagnetic induction coil 908; a coil driver unit 909 for energising the electromagnetic coil; a temperature sensor 910 containing a negative temperature coefficient thermistor.

[0081] In use, the control unit may carry out a cooking sequence, being a sequence of electronic instructions to drive the electromagnetic coil 908 in response to pre-stored recipe data stored in the memory module 906 and/or cooking instructions entered via the user interface 903. The control unit 901 sends instructions to the appliance interface module 907 and the coil driver 909 to energise the electromagnetic coil 908 in a manner appropriate to the cooking profiles for various recipes. Temperature is monitored by the temperature sensor 910 which feeds back a signal representing temperature to the appliance interface module, which forwards a temperature signal to the control unit 901 which is in overall control of energising the coil 908 via the electromagnetic coil driver circuit 909.

[0082] The temperature sensor 910 measures a temperature which represents the temperature inside the cooking vessel, and therefore represents a cooking temperature of the contents of the cooking vessel. Having an accurate measurement of temperature of the cooking vessel enables the control unit 901 to follow a predetermined set of memory instructions representing a cooking operation, and to make variations of that cooking programme depending upon the real-time temperature measurements generated by the temperature sensor 910.

-22[0083] In addition to the temperature sensor 910, there may be provided an additional temperature sensor for the purposes of safety cut out in case of malfunction of the electromagnetic coil 908 or other electrical fault, as is known in the prior art. This additional temperature sensor is not shown in figure 9.

Cooking Vessels [0084] The cooking vessels may be of two basic types being firstly an aluminium body having a bonded ferritic inductive layer, and secondly a steel body having a ferritic layer of material which can be heated through induction. The ferritic layer is preferably steel.

[0085] In the second type of cooking vessel disclosed herein, the vessel comprises a steel body, on the base of which is provided a steel inductive layer. Between the steel inductive layer and the underside of the steel body is provided a layer of aluminium, which serves the purpose of distributing heat generated in the inductive layer by conduction laterally across the base area of the cooking vessel, and upwardly towards the steel base of the cooking vessel to ensure more even heat distribution across the base of the cooking vessel.

[0086] Another possibility is the provision of a magnet detection cover which performs the function of housing the magnet aligning the pan on the base and some degree of heat insulation between the remainder of the hot pan and the base excluding the central portion which contains induction coil, and with the components made out of a high temperature plastic. By high temperature, it is meant a temperature of 270°C as an upper limit. This component is for use on the stainless steel or aluminium versions of the cooking vessel, and all on all versions which fit on the base unit.

[0087] In general, the cooking vessels each comprise a main body portion, for example in the shape of a pan, bowl, wok, griddle or the like, and a layer of inductive material underneath the main body portion. The main body portion may be steel, for example stainless steel, or aluminium.

-23[0088] The lower part of the cooking vessel comprises a body portion which is intended to be in contact with a food item or a liquid to be heated. The lower part of the body portion of the cooking the vessel comprises a region of reduced thickness relative to a region of said body portion which surrounds the reduced thickness region. The reduced thickness region can be made of an inductive material such as steel, or a non-inductive material such as aluminium. However this reduced thickness region is not intended to be a region which is directly heated by induction, since when the cooking vessel is placed upon the base unit the reduced thickness region does not directly sit upon an electromagnetic inductive coil, but rather the inductive coils surround the region of reduced thickness.

[0089] Referring to figure 10 herein, there is illustrated schematically a base portion of a second embodiment of a base plate 1000 of a cooking vessel as is configured in accordance with the present invention. The base portion comprises a plate of non-inductive material 1001, for example aluminium, having embedded therein a plurality of blocks of inductive material 1002, for example stainless steel. The blocks of inductive material may be formed within the plate of non-inductive material 1001. During heating, the non-inductive material is not directly heated by the electromagnetic field of the energising coil, but rather is heated through convection of heat from the individual blocks of inductive material 902 which are directly heated by the electromagnetic induction coil. There is provided a recessed region 1003 having an underside 1004 where the noninductive material is relatively thinner compared to the plate material surrounding the thinned region 1003. On the other side of the base plate 1000 of the cooking vessel the plate may be in direct contact with food items. In the relatively thinner region 1003, the temperature of the underside 1004 of the region more closely approximates the temperature on the upper surface 1005 of the base plate than the temperature underneath the other regions containing inductive material. Using the inductive hob having the novel temperature sensor described herein, the temperature of the underside of the cooking vessel can be measured, and

-24represents fairly accurately the temperature of the upper surface 1005 upon which food is cooked, of the cooking vessel.

[0090] Referring to figure 11 herein, there is illustrated schematically a preferred embodiment third base portion 1100 of a third cooking vessel. The base portion comprises a stainless steel plate 1101, and underneath the stainless steel plate 1101 a second stainless steel plate 1102. Between the first and second stainless steel plates 1101, 1102 there is provided a layer of noninductive material 1103, such as aluminium. The purpose of the non-inductive layer is to distribute heat more evenly through conduction of heat, across the area of the base from the second inductive layer 1102 to the first inductive layer 1101.

[0091] There is provided an aperture region 1103 in the second inductive layer 1102 where the second inductive layer and non-inductive layer are absent, and allowing direct access to the underside of the first stainless steel inductive layer 1101. In this region 1103, the temperature of the underside of the first inductive layer 1101 can be measured as hereinbefore described by a resiliently biased temperature sensor housing which is urged upwardly against the underside of the first inductive layer of the cooking vessel. When placed upon the cooking hob, the region of the base of the cooking vessel containing the recessed region 1103 lays directly over the depressable resiliently biased temperature sensor and the temperature sensor urges against the underside of the first layer 1001 to give an accurate temperature measurement of the first layer 1101.

[0092] The cooking vessel may be typically pressed, formed from a metal sheet such as sheet steel or aluminium, together with a ferrous-based inductive heating member welded, brazed or otherwise fixed to an underside of the cooking vessel to form part of the base.

[0093] In the best mode, the region of the upper surface of the heating area of the induction hob in which the temperature sensor is located is

-25substantially central, and surrounded by an induction coil underneath the cover plate. However, depending upon the architecture and layout of the heating area of the induction hob and the induction coil underneath the cover plate, the temperature sensor could be positioned offset towards the edge of the cooking area over which a given cooking vessel fits. In the best mode arrangement, the temperature sensor is located within the area upon which the cooking vessel sits on the hob at a position on the base of the cooking vessel which does not directly overlie an electromagnetic induction heating coil.

[0094] Embodiments described herein may find particular application in controlling the temperature of the contents of a cooking vessel which is inductively heated when seated on an induction cooking hob.

Claims

Claims

1. An induction cooking apparatus comprising:

an induction heating coil;

a cover plate above said induction heating coil; and a temperature sensor, said temperature sensor being located in an aperture in said cover plate, wherein an outer surface of said temperature sensor is accessible from a position above said cover plate.
2. The induction cooking apparatus as claimed in claim one, wherein said temperature sensor is movable relative to said cover plate.
3. The induction cooking apparatus as claimed in claim 1 or 2, wherein said temperature sensor is resiliently biased relative to said cover plate.
4. The induction cooking apparatus as claimed in any one of the preceding claims, wherein said temperature sensor protrudes above a level of an upper surface of said cover plate.
5. The induction cooking apparatus as claimed in any one of the preceding claims, wherein said temperature sensor comprises:

a semiconductor temperature sensing device; and a housing, containing said semiconductor temperature sensing device.

-276. The induction cooking apparatus as claimed in any one of the preceding claims, further comprising a vessel proximity sensor, for sensing a vessel placed on said base unit.
7. The induction cooking apparatus as claimed in claim 5 or claim 6, wherein said housing comprises aluminium.
8. The induction cooking apparatus as claimed in any of claims 5 to 7, wherein said housing is movable relative to said cover plate.
9. The induction cooking apparatus as claimed in any one of claims 5 to 8, wherein said housing is resiliently biased relative to said cover plate.
10. The induction cooking apparatus as claimed in any one of claims 5 to 9, in which said housing is mounted on a compression spring.
11. The induction cooking apparatus as claimed in any one of the preceding claims, comprising a heat resistant and fluid resistant membrane housing said temperature sensor.
12. The induction cooking apparatus as claimed in any one of the preceding claims, comprising a flexible heat resistant collar located between said temperature sensor and said cover plate.
13. A method of measuring temperature of a cooking vessel on an induction cooking device, said induction cooking device comprising:

an induction heating coil;

a cover plate above said induction heating coil; and a temperature sensor,

-28said temperature sensor being located in an aperture in said cover plate, wherein an outer surface of said temperature sensor is accessible from a position above said cover plate;

said method comprising placing a cooking vessel on said induction cooking device, such that a region of an underside of said cooking vessel contacts said temperature sensor; and reading a temperature signal from said temperature sensor.
14. The method as claimed in claim 13, wherein a first region of the underside of the cooking vessel where the temperature is to be measured is located directly over said temperature sensor; and said first region is placed over an area of said cover plate which does not directly overlie an induction coil.
15. The method as claimed in claim 13 or 14, wherein said first region of said cooking vessel at which temperature is measured comprises a second region of an underside of said cooking vessel which has a reduced thickness relative to a first region surrounding said second region.
16. A method of measuring temperature in an induction cooking device, said method comprising:

providing a temperature sensor in a cover plate of said induction cooking device, said sensor being provided in a region of said cover plate which does not overlie an induction coil;

-29directly contacting said temperature sensor with an underside of a cooking vessel at a location of said cooking vessel which does not overlie an induction coil of said induction cooking device.
17. The method as claimed in claim 16, comprising:

directly contacting said temperature sensor with a region of an underside of said cooking vessel, which has a reduced thickness compared with a surrounding region of said underside of said cooking vessel.
18. A method of measuring temperature in an induction cooking device, said method comprising:

providing a temperature sensor in a movable housing in a region of said induction cooking device upon which a cooking vessel may be placed;

resiliently biasing said housing in an upward direction such that said temperature sensor contacts a part of the cooking vessel, which is heated primarily by conduction of heat.
19. The method as claimed in claim 18, further comprising resiliently biasing said temperature sensor to protrude beyond a level of surrounding upper surface of said cooking plate, such that a cooking vessel placed on said cooking plate depresses said temperature sensor.
20. The method as claimed in claim 18 or 19, comprising urging said temperature sensor into contact with a non-inductive part of said cooking vessel.
21. The method as claimed in any one of claims 18 to 20, wherein said temperature sensor contacts a part of said cooking vessel which is non-ferritic.

-3022. A method of measuring temperature in an inductively heated cooking vessel, said method comprising:

providing an induction heating coil;

providing a temperature sensor arranged to make direct contact with an underside of said cooking vessel;

wherein the temperature sensor makes contact with the underside of the cooking vessel in an area which does not directly overlie said induction heating coil.
23. The method as claimed in claim 22, comprising making contact between said temperature sensor and an underside of said cooking vessel at a region on said cooking vessel which has a reduced thickness of inductive material relative to a region of said cooking vessel surrounding said reduced thickness region.
24. The method as claimed in claim 22 or 23, comprising making contact between said temperature sensor and an underside of said cooking vessel at a region of said underside of said cooking vessel which contains no inductive material.
25. The method as claimed in any one of claims 22 to 24, comprising resiliently biasing said temperature sensor to urge against said underside of said cooking vessel.

Intellectual

Property

Office

Application No: GB1613059.3 Examiner: Mr Tony Oldershaw