GB2445780A

GB2445780A - Electrical induction heating liquid boiling appliance

Info

Publication number: GB2445780A
Application number: GB0701166A
Authority: GB
Inventors: Antonio Martin Gaeta
Original assignee: Otter Controls Ltd
Current assignee: Otter Controls Ltd
Priority date: 2007-01-22
Filing date: 2007-01-22
Publication date: 2008-07-23
Also published as: GB0701166D0

Abstract

In inductively heated kettle (1) having a floor 4 comprising inductively heated material is mountable on an inductive heating base (2). In one embodiment, steam passes from the kettle (1) to the base (2) via pipe 9 to switch off or reduce inductive heating. Alternatively the Curie effect is used to control the kettle (1) either by arranging a sensor in the base to detect changes in a Curie effect sensor embedded in the floor 4 or arranging for the floor to become paramagnetic above the Curie temperature whereby it is no longer heated.

Description

* 2445780 Electrical Heating Appliance

Field of the Invention

100011 The present invention relates to electrical heating appliances, particularly but not exclusively to liquid heating appliances.

S Background of the Invention

100021 Electric liquid heating appliances, such as electric kettles, saucepans and the like, commonly use a resistive heating element to heat up liquid in a reservoir. The heating element may be immersed in the reservoir, or may be attached to or formed on the underside of an element plate forming the bottom surface of the reservoir.

100031 Cordless electrical connectors, by which an electrical liquid heating appliance is removably connected to an electrical power base, are well known. 360 cordless electrical connectors, by which a liquid heating vessel may be located on its power base in any azimuthal orientation, are described in the applicant's patent publication WO 94/06185.

100041 Although cordless electrical connectors have been widely adopted for electric kettles and the like, it would be advantageous to provide an electric heating appliance where no electrical connection is required to the appliance proper. Such an appliance would have improved safety characteristics and its manufacture would be simplified.

100051 It is of course well known to heat up liquid in a kettle or saucepan on an electric * hotplate; no electrical connection to the appliance proper is required, but heat transfer to the liquid is relatively inefficient, because the hotplate must be heated up, and heat transfer to the kettle or saucepan requires good thermal contact with the hotplate. Also the hotplate provides an exposed hot surface, which is a safety hazard.

100061 Induction hobs are also known; these use an induction coil to induce heating in a ferromagnetic or femmagnetic container by magnetic hysteresis and eddy currents. Stand-alone induction hobs that can be plugged into an electrical outlet are also known. However, induction heating has not been adopted for kettles and other types of liquid heating or liquid boiling appliances.

[00071 One problem that has prevented the adoption of induction heating in electric kettles is the need to switch off or reduce power to the kettle as soon as the liquid has boiled.

Induction hobs can detect temperature indirectly by sensing heat conducted into the hob from a pan placed on the hob, or directly from a sensor within the pan. The former approach would not respond quickly to boiling in a kettle, while the latter approach is complex and expensive, not least because it requires wireless reception of the sensor output.

Statement of the Invention

j0008J According to one aspect of the present invention, there is provided an electric liquid boiling appliance comprising an induction heating base for generating an electromagnetic field for induction heating and a liquid reservoir mountable on or to the induction heating base so as to be inductively heated thereby so as to heat liquid within the reservoir, the liquid reservoir being arranged to conduct steam from the liquid reservoir to the induction heating base, and the induction heating base including a steam sensor for sensing steam conducted from the liquid reservoir and being arranged to cease or reduce inductive heating of the Liquid reservoir in response to the steam sensor.

100091 An advantage of this arrangement is that the appliance using induction heating is able to respond rapidly to boiling, without the need to include a temperature or steam sensor within the reservoir.

100101 Preferably the reservoir includes no electrical or moving parts. One advantage of this arrangement is that the reservoir is easy to clean, and may be cleaned in a dishwasher.

Another advantage is that the reservoir is simple and cheap to manufacture.

100111 According to another aspect of the present invention, there is provided an electrically heated liquid heating appliance comprising an induction heating base and a liquid reservoir detachably mountable to the induction heating base, the reservoir being inductively heatable by the base; the reservoir including a Curie effect temperature sensor and the base including a Curie effect detector to detect a change of state of the temperature sensor.

100121 Preferably the reservoir includes no electrical or moving parts. One advantage of this arrangement is that the reservoir is easy to clean, and may be cleaned in a dishwasher.

Another advantage is that the reservoir is simple and cheap to manufacture.

100131 According to another aspect of the present invention, there is provided an induction-heated kettle comprising an induction heating base and a liquid reservoir detachably mountable to the induction heating base, the reservoir being inductively heatable by the base.

Brief Description of the Drawings

(00141 Embodiments of the present invention will now be described with reference to the accompanying drawing identified below.

100151 Figures la and lb are cut-away perspective views of a kettle in a first embodiment, respectively detached from and attached to an inductive heating base.

(00161 Figures 2a and 2b are cut-away perspective views of a kettle in a second embodiment, respectively detached from and attached to an inductive heating base.

Detailed Description of the Embodiments

First embodiment 100171 As shown in Figures la and lb. an appliance according to the first embodiment comprises a kettle I detachably mountable on an inductive heating base 2. The kettle 1 comprises sidewalls 3 and a substantially planar floor 4 which together form a liquid reservoir 5 within the kettle I. The floor 4 comprises inductively heatable material, such as ferromagnetic or ferrimagnetic material, preferably iron or steel, such as stainless steel. The floor 4 may have a core of such inductively heatable material, with one or more surface layers or coatings resistant to corrosion while allowing thermal conduction from the core into the reservoir 5. The sidewalls 3 may be of plastics or other suitable material.

100181 The inductive heating base 2 comprises an induction coil 6 mounted within a housing 7, which also includes an AC frequency converter (not shown) for converting AC mains power to a suitable frequency for induction heating. The induction coil 6 is mounted in an upper surface 8 arranged to abut the lower surface of the floor 4 of the kettle I so that the induction coil 6 is in close proximity to the floor 4 when the kettle I is mounted on the base, as in Figure lb. [0019j The kettle 1 has a lid 14 which traps steam at the top of the reservoir 5 when the liquid boils, and further includes a steam passage 9 that is open at the top of the reservoir 5 and passes down through the floor 4 into an aperture 10 at the bottom of the kettle 1. The aperture 10 connects to a corresponding aperture 11 in the housing 7 of the base 2, so that steam is able to pass from the top of the steam passage 9, through the floor 4, into the housing 7 when liquid in the reservoir 5 boils. The housing 7 includes a steam sensor 12 arranged to disconnect or reduce electrical power to the induction coil 6 in response to *1 steam entering the housing 7. In this way, the appliance is able to respond rapidly and reliably to boiling of the liquid, so that an induction-heated kettle becomes feasible.

[00201 The kettle I requires no electrical or moving parts and is therefore very simple to manufacture and to clean. In particular, the kettle I may be washable in a dishwasher because there is no need to protect electrical or moving parts from the hostile environment within a dishwasher.

[00211 In the first embodiment, the steam passage 9 has the form of a tube passing centrally through the reservoir 5; this allows for a convenient arrangement in the base 2, where the aperture 11 passes through the centre of the induction coil 6. Alternatively, the steam passage 9 may be formed against or within the sidewalls 3, and the apertures 10 and 11 would then be offset to one side of the kettle I and the base 2 respectively.

[00221 The apertures 10 and 11 may be formed centrally within conical mating parts IOa, ha, to facilitate location of the kettle I on the base 2 while allowing relative rotation therebetween. The sidewalls 3 include a lower portion 3a that fits around the periphery of the housing 7; this also assists in locating the kettle 1 on the base 2.

3] The base 2 also includes a power switch 13 for manually switching power to the induction coil 6.

Second Embodiment [0024J The second embodiment, as shown in Figures 2a and 2b, differs from the first embodiment in that steam is not sensed directly within the base 2: the steam passage 9 and apertures 10 and 11 are omitted and the floor 4 is continuous. Embedded within the floor 4 is a temperature sensor 15 that changes state in response to the floor 4 reaching a temperature characteristic of the liquid boiling within the reservoir 5. The temperature sensor 15 may be a Curie effect temperature sensor having a Curie temperature set at the temperature characteristic of liquid boiling in the reservoir 5. The base 2 includes a Curie effect sensor 16 which detects when the Curie temperature of the temperature sensor 15 has been reached.

[00251 Alternatively, the floor 4 may be constructed so as to have a Curie temperature characteristic of liquid boiling in the reservoir, so that the floor 4 acts as a temperature sensor and no separate temperature sensor 14 is required. In this alternative, the Curie effect sensor 16 may not be required, since the floor 4 becomes paramagnetic above the Curie temperature and is no longer inductively heated.

Alternative Embodiments The embodiments described above are illustrative of rather than limiting to the present invention. Alternative embodiments apparent on reading the above description may nevertheless fall within the scope of the invention. *1

Claims

Claims 1. An electrically heated liquid boiling appliance comprising:

a. an induction heating base; and b. a liquid reservoir detachably mountable to the induction heating base, the reservoir being inductively heatable by the base; c. the reservoir having a steam passage arranged to convey steam from the liquid reservoir to the base; and d. the base including means for sensing steam conveyed from the liquid reservoir and for reducing or removing the inductive heating of the liquid reservoir in response thereto.
2. The appliance of claim 1, wherein the means for sensing steam comprises a steam sensor located within the base, and the base includes an aperture for receiving steam from the steam passage.
3. The appliance of claim 2, wherein the base includes an inductive heating coil and the aperture passes through a central section of the coil.
4. The appliance of claim 3, wherein the steam passage passes substantially centrally through the reservoir.
5. The appliance of claim 2, wherein the reservoir and the base include mutually conforming portions arranged to locate the reservoir on the base so that steam is able to enter the aperture.
6. The appliance of any preceding claim, wherein the reservoir includes an inductively

heatable floor.
7. The appliance of claim 6, wherein the reservoir includes a downwardly depending peripheral wall extending below the floor, and arranged to fit around the periphery of the base.
8. An electrically heated liquid heating appliance comprising: a. an induction heating base; and b. a liquid reservoir detachably mountable to the induction heating base, the reservoir being inductively beatable by the base; c. the reservoir including a Curie effect temperature sensor; and d. the base including a Curie effect detector to detect a change of state of the temperature sensor.
9. The appliance of claim 8, wherein the reservoir includes an inductively heatable floor.
10. The appliance of claim 9, wherein the temperature sensor is contained within the inductively heatable floor.
11. The appliance of claim 9, wherein the inductively heatable floor comprises the Curie effect temperature sensor.
12. An electrically heated liquid heating appliance comprising: a. an induction heating base; and b. a liquid reservoir detachably mountable to the induction heating base, the reservoir being inductively heatable by the base and having a Curie temperature such that the temperature of the liquid is automatically maintained around an elevated temperature below boiling.
13. An induction-heated kettle comprising an induction heating base and a liquid reservoir detachably mountable to the induction heating base, the reservoir being inductively heatable by the base.
14. An appliance substantially as herein described with reference to Figures la and lb of the accompanying drawings.
15. An appliance substantially as herein described with reference to Figures 2a and 2b of the accompanying drawings.