GB2378818A

GB2378818A - Cordless water boiling vessel

Info

Publication number: GB2378818A
Application number: GB0227124A
Authority: GB
Inventors: Robert Henry Hadfield
Original assignee: Otter Controls Ltd
Current assignee: Otter Controls Ltd
Priority date: 1999-02-11
Filing date: 1999-02-11
Publication date: 2003-02-19
Anticipated expiration: 2019-02-11
Also published as: GB9903106D0; GB2346738B; AU2451900A; GB2346738A; GB2378818B; WO2000047095A1; GB0227124D0

Abstract

A cordless electrically heated water boiling appliance, in which power is supplied from a base to a vessel through co-operating connectors when the vessel is seated on the base, has a relay 5 in the base which is arranged to be responsive to the flow of current through a heating element 3 in the vessel so that power cannot be supplied to the base connector if the vessel is not seated on the base. On/Off controls 9,10 associated with the relay 5 are provided on the base, and the vessel has a thermal sensor 4 associated with the heating element 3.

Description

1 2378818

Improvements Relating to Control of Electric Heating Elements Field of the Invention:

This invention concerns improvements relating to the control of 5 electric heating elements, particularly though not exclusively electric heatin, elements of water boiling vessels such as kettles, jugs, pots, pans, laboratory equipment etc. Background ofthe Invention:

Electnc kettles and hot water jugs have conventionally been provided 10 with an element protector control, for protecting the heatin, element against overheating for example as a result of the vessel haven been switched on empty, and a separate steam sensor control for automatically switching off or reducing the supply of electricity to the heating element when water boils in the vessel and steam impinges upon the control. An example of an element 15 protector control is the X-senes control, available Tom us, which is substantially as described in GB-A-2 194 099 with reference particularly to Figures 3A, 3B and 3C thereof and provides two levels of overtemperature protection, and an exemplary steam control is the J-series control, also available Tom us, which is substantially as described in GB-A-2 212 664 with 20 reference particularly to Figures 3A to 3M thereof. Both of these controls, and other functionally solar controls, employ thermally-sensitive devices in the form of bimetallic actuators.

Proposals have been made to achieve the Unctions of heating element overtemperature protection and steam sensing by means of a single sensor. A single sensor electronic control is described in GI3-A-2 228 634, and in GB-A-1 143 834 there is described a proposal to incorporate an enclosure 5 within the water chamber of a water boiling vessel, the enclosure being arran,ed to fill with water when the chamber is filled and to be heated by the vessel heating element so that, when the water boils, the water in the enclosure is driven therefrom by steam, thereby simulating a dry boil situation within the enclosure which can be sensed by a bimetallic or other thermal 10 sensor.

Despite its apparent simplicity and promised advantages, the arrangement of GB-A-1 143 834 was, so as we are aware, never put into production. When we attempted to follow the teachings of GB-A-1 143 834 we found that we could not obtain a satisfactory single sensor control 15 arrangement with a heating element as described in GB-A-1 143 834. We were, however, able to devise solutions to the problem of making the enclosure idea of GB-A-1 143 834 work and these are described in WO-A-9318631, WO-A-9318632 andWO-A-9511 15. The first two of these mvolve the utilisation of heating elements of the conventional sheathed type 20 in which a resistance heating wire is paciced into a metal sheath with mineral insulating material between the wire and the sheath, and the latter makes use of socalled thick film heating elements which comprise an electrically

msulatin;, substrate, cornr.nonly of stainless steel with an insulating layer of glass for example, upon a surface of which a resistance-heating track or layer is provided. Thick film heating elements are becoming increasingly popular on account of their clean appearance and potentially high watts density which S gives reduced heating times.

In our British Patent Application No. 9816645.7 there is described a solution to the problem which can arise, particularly with Me proposal of WO-A-9511515, that the operation of the control may be voltage sensitive This is a particularly European problem, since supply voltages in Europe can 10 vary from one country to another within a range of from 210 volts to 250 volts. According to the solution described in GB 9816645.7 abovementiorled, the resistance heating track of a thick film heating element has a portion designated to register with an enclosure Or, described in WO-A-9SIl lS and formed of a material having a negative temperature coefficient of resistance, 15 the remainder ofthe heating element track being formed of a material having a positive temperature coefficient of resistance. As is explained in GB 9816645.7, this arrangement can compensate for differences supply voltage insofar as the operation of the enclosure and its attendant bimetallic sensor is concerned.

20 The single bi netal control principle as described in the foregoing thus enables a single bimetallic sensor, responsive to the temperature of a particular part of the heating element underlying an enclosure, particularly a

thick film heating element, to fimction both to protect the heating element against overheating and also to switch off the electricity supply to the heating element when water boils in the vessel. The vessel still has to have an on/off switch and this can be arranged by use of a manually resettable control to which the appliance (vessel) manufacturer can affix his styled rocker knob.

However, this er orces design limitations as regards the location of the rocker knob (on/off switch) and requires an element temperature control having the facility to be switched both on and off.

Obiects and Snmrnarv ofthe Invention: 10 It is the prmcip l object of the present invention to overcome or at least substantially reduce the abovementioned problem.

Accorded to the present invention a single sensor control in accordance win the teachings of any of our above-n entioned proposals fiercer includes a relay cormected in series with the heating element and the 15 control, the relay operation being arranged to be dependent upon Me flow of electric current to the heating element, for evocable by provision of a current transformer in the circuit, and the relay fire more being manually operable.

A water boiling vessel in accordance with the teachings of the present invenhon includin,, a single bimetallic control and an electromagnetic relay 20 switch would thus operate as follows: (1) Start - the relay switch is de-energised, its contacts are open, and no current flows through the heat=, element.

(2) The contacts of the relay are manually closed (by an 'COn'' switch or push button. Current flows, via the current transformer, to the heating element. The output of the transformer serves to ener se the relay coil, holding the contacts closed, so the "On" switch may be S released.

(3) When the water boils, the single bimetal control switches off the element. No current flows, so the output of the current transformer drops to zero and the relay is de-ener sed' opening its contacts.

(4) The water ceases boiling and the single bin etal control resets 10 automatically. No current flows because the relay contacts are open.

(5) The cycle may be repeated by closing the relay contacts again The boil cycle may be interrupted at any time by manually breaking the circuit, for example by manually opening the relay contacts or by operaiin, a separate CON' switch.

15 (6) the event of switching on dry or boiling dry, the normal finctions of the element protector control serve to protect the element by switch it off. In this case the relay circuit will de-energise and refill require the user to switch on to reset.

The relay and switches may be situated on the vessel, but preferably 20 We vessel is cordless and the relay and switches are situated within the cordless base. This gives a very simple appliance, in which the vessel proper has only We element and its protector, and as with the above single bimetal

control arrangements, no steam duct or separate steam control is required. In addition, however, no rocker or manual control of any type is required on the vessel proper, giving complete freedom of design. This is particularly appropriate for metal vessels, where the provision of plastics mouldings and 5 rocker knobs spoils an otherwise clean design. By situating the controls withm the cordless base a furler advantage arises in that as soon as the vessel is lifted Mom the base, the circuit is broken and the relay is de-energised.

Thus the corrector part in the base is not connected to the supply and additional safety is achieved. addition, even if the vessel is replaced on the 10 base, it will have to be manually switched on. The control system additionally means that the vessel cannot be left switched on but unplugged (or plu,Oed into a switched o ff socket outlet) so that accidental dry switch on is less likely.

Of course, any type of cordless correction system could be utilized, such as for example the 360 cordless connection system made and sold by us as the 15 CS4/CP7 system which is substantially as described in WO-A-9406185. We believe that such a construction is inventive in itself, in that it provides a cordless appliance connector which cannot be switched on without the appliance proper being in place.

The invention is not restricted to utilization of bunetallic temperature 20 sensitive controls and any kind of thennally responsive switch could be employed. Additionally, sensors could be utilized compusi PTC (positive temperature coefficient of resistance) materials as disclosed for example in

our British Patent Application No. 9807385.1 which describes and claims a thick film heating element having associated therewith a PIC material for determimng the current supply to the coil of an electromagnetic relay switch.

It is thus not necessary to break the circuit to cause operation. The 5 current sensing component may also use a reduction in the load current below a set value to de-energise the relay When applied to a PTC protected element, the reduction of current caused as the PTC resistance rises can be used. This has an advantage in that it is not necessary to maintain the PTC at a high temperature (using energy) to hold the element off, which means that 10 the whole element will be cold and hence safer. in one implementation on a thick fimn printed element, the PTC resistor would be located under the enclosure to sense both boil and dry boil. The rise in resistance, giving rise to a fall in element current, would de- energise the relay. this application a PTC having a knee characteristic (giving a rapid rise in resistance above a set 15 temperature) would be preferred. Since PTC thick fiLn printing materials are not readily available, the PTC sensor could be a discrete surface mount component A nonnal linear characteristic could also be made to work and would lead to an element with no additional control components assembled to it, which would be a cheap solution. Nl C and PTC tracks provided on the 20 heating element to give a sort of thermal runaway may be used, where the power of the element as a whole is transferred from the TIC to the PTC

portions as the PTC resistance rises on sensing a rise in temperature, leading to an overall drop in current.

The teachings of the present invention could also be applied to a conversationally constructed vessel with a steam tube and a steam switch, 5 allowing a retrofit to an existing design. In this case the steam switch need only be a simple self-resetting thermal cut-out, with no manual actuator. A sealed contactstat could be used. The lack of a manual rocker and linkage would have safety and constructional advantages, and would simply the design of switches of a smiably sealed design to resist condensation.

10 - A furler advantage arises because the invention can be implemented using standard, readily available, components. No additional contacts we needed on the cordless system, as were required by the electronic kettle (GB 7 228 634) so the standard CS4/CP7 or CS2 described in GB-A-2 241 90 may be used. The element protector control can be of any 15 auto-reset type, such as our X2 or X3 controls. The latching relay is readily available, and together with the current transformer, costs around 1. This will replace around 60p of components, together with the necessary cover mouldin,s normally found on a conventional kettle. It has the constructional advantages claimed for the single biinetal control, includin;, lack of steam 20 sealing and spillage problems.

The teachings of the present invention are applicable to vessels incorporating any kind of electric heating element, though in the case of die

cast elements or elements of the mechanical Blitzkocher construction, modification of the heating element to pronde a location which is normally cooled by the presence of water, and which has a heater between it and the control actuator may be necessary. Ibis can be achieved by providing a sump 5 in the water-side surface of a die cast element, situated very close to the inner side of part of the sheathed heating element which is enclosed in the casting, and providing an apertured cover over the sump. A similar modification of a Blitzkocher type heating element could be effected.

The above and further features of the present invention are set forth 10 with particularity in the appended claims and, together with the advantages thereof, will be well understood from consideration of the following description given with reference to the accompanying drawings.

Descnption of the Drawings: Figure I is a schematic circuit diagram of a heating element control 15 circuit embodying the teachin;,s of the present invention; and Figures A, 2B and 2C show, respectively, a perspective view of Be underside of an exemplary die cast heating element, a view similar to Figure 2A but with a bimetallic control shown affixed to the heating element, and a perspective view of the upper (water) side of the heated element of Figures 90 2A and 2B showing a sump-deftnn g pocket donned in the surface Hereof.

Detailed Descnption of the Embodiments:

Referring to Fioaure 1, the circuit shown is for a cordless electric water heating appliance, such as a kettle or hot water jug, cornpusing a vessel part and a base part and wherein a heating element in the vessel part is arranged to be powered via the base through the intermediacy of co-operating connectors 5 provided on the two parts which operatively engage when the vessel part is set down on the base part In Fiche 1, the co-cperating cormectors are shown at 1 and 2, the vessel part is to the nght hand side of Me connectors 1 and 2, and the base part is to the left hand side of the connectors 1 and 2.

The vesse! pert has a heating element 3 and an element protector 10 control 4. The heating element can for example be a thick film heating element provided with an enclosure as described in WO-A-9511515. The element protector control 4 can be an X-senes control as descnbed GB-A-2 194 099 for example, the X-series controls providing dual protection for We heating element as is well Imowrt. The connector set 1, 2 can for 15 example be of the 360 kind described in WO-A-9406185 which enables the vessel part to be seated upon the base. part irrespective of the relative rotational orientation of the two parts.

The base part has an electromagnetic relay comprising contacts set 6 and operating coil 7, a current transformer 8 coupled to the relay coil 7 and 20 avenged so that the relay coil 7 is energised so low as current is flowing in the heating element 3 of the vessel.

!

An "on" switch 9 is connected across the relay contacts 6 and an "off' switch 10 is connected in series with the relay contacts 6.

The contacts of the element protector control 4 are nounaIly closed, but will open when water is boiled ir1 the vessel, by virtue of the provision of 5 the enclosure aforementioned, and also if the heating element 3 is powered without the vessel having been filled. The relay coil 7 is energized via current transformer 8 when the heating element 3 is powered. Otherwise, because the "oh" switch 10 has been operated or the element protector control 4 has operated to oper1 its contacts or the vessel part has been lifted omits base part, 10 no current flows in the heating element 3 and the relay coil 7 is de-enerOised.

When relay coil is de-energised the relay contacts 6 are open The "on" switch 9 enables the open relay contacts 6 to be bypassed so as, to cause the heating element 3 to be powered, so long as the vessel is seated on its base and the element protector 4 has not operated, and operation of the "on" switch 1: 9 will, subject to these conditions, cause the relay coil 7 to be energised thereby closing relay contacts 6. The "off" switch I0, which can be fate grated with the "on" switch 9 in an appropriate toggle switch, enables the circuit through the base and to the vessel to be broken. Otherwise, the operation and advantages of the circuit will be clear from the explanations provided 20 herebefore.

Whilst the teachings of the present invention are, in principle, applicable to vessels incotporahn heating elements of all the commonly used

kinds, some modification of die cast elements or elements of Me mechanical Blitzkocher type construction:, compnsin a sheathed heating element clamped or clenched lo the underside of a metal plate, may be necessary. This is because there is no location on such elements which is normally cooled by the presence of water, and which has a heater between it and the control actuator. To overcome this we propose to provide a sump in the water-side surface of the die cast element, situated very close to the inner side of part of the sheathed heating element which is enclosed in the casting. On a test sample this was done by machining a pocket in the upper surface of the 10 heating element. The particular element that we used has a platform built (cast? up on its lower surface close to the heatin;, element proper and an X2 control is mounted on this platform. Heat from the heating element proper is conducted to the platform sideways and lost to the water upwards, which gives a suitable running temperature for normal use and gives a rapid 15 temperature rise when no water is present. The pocket abovementioned was machined from the upper surface of the heating element, effectively hollowing out the platform Dom above. A cover, formed of moulded plastics material for example, was secured over We pocket, and one or more suitably sized holes left to allow water to enter and steam to leave. The size of the hole(s) is 20 determined by trial and error and depends on the heatm;, element configuration and power density. Since the pocket is sunk below the top surface of the heating element, the cover may be made flush, giving a neat

appearance. A simalar construction may be applied to heating elements of mechanical Blitzkocher type. Where such elements are used with metal bodied vessels, a hole might be cut in the vessel bottom and a sump welded ir place underneath. The sump may be provided with a thermal link to the 5 heating element, for example a copper loop pressed onto the outside of Me element sheath or breed to it, and the thermal control may be placed in thermal contact with the sump to create an equivalent construction to the die cast element described above. It is conceivable that a sump could be designed which has a restricted operung such that a separate cover is not required.

10 Figures 2A, 2B and 2C of the accompanying drawings show an exemplary die cast heating element modified as above described. Figure 2A shows the heating element as comprising a die cast metal body 20 having a sheathed, spiral heating element 21 incorporated into the underside thereof, the upper surface of the heatin, element, as shown in Figure 2C, being planar.

15 The body 20 of the heating element has integral mounting posts 22 and the heating element cold tails 23 and 24 cart be seen. Also shown are integral cast metal pads 25, 26 and 27 which serve for the mounting to the heating element of an X2 control 30 in the maker shown in Figure 2B. As shown in Figure 2C, the metal pad 96 is hollow thus defining a sump 35 as aforementioned 20 which can be provided with an apernlred cover to define a single sensor enclosure as previously explained herein

Having thus described the invention by reference to specific embodiments, it is to be well understood that the embodiments are exemplary only and that modifications and variations thereto are possible without departure hom the spirit and scope of the invention. For example, whereas 5 the arrangement of Figure 1 employed an electromechanical relay, the same fimction could be performed electronically, for example by means of a triac circuit.

Claims

1. A cordless electrical appliance wherein means are provided in the base part of the appliance for disconnecting the base connector from the electrical 5 supply if the appliance part is not operatively in place on the base part.

2. A cordless electrical appliance comprising an appliance proper and a base and wherein co-operating electrical connectors are provided on the two parts for powering the appliance proper through the base when the former is 10 operatively seated on the latter, and wherein means are provided in the appliance to ensure that the base connector cannot be powered if the appliance proper is not seated on the base.

3. An appliance as claimed in claim 2 wherein said means to ensure that 15 the base connector cannot be powered if the appliance proper is not seated on the base comprises means responsive to current flow through the electrical connectors.

4. An appliance as claimed in claim 3 wherein said current responsive 20 means comprises an electromagnetic relay comprising a set of switch contacts and a coil, the state of the switch contacts being determined by whether or not the relay coil is energised and the state of energisation of the relay coil being

determined by whether or not curtest is flowing through the electrical connectors.

5. An appliance as claimed in claim 4 wherein manuallyoperable onJoff 5 switch means are associated with said relay.

6. An appliance as claimed in claim 3 wherein said current sensitive means comprises an electronic circuit or device.

10

7. An appliance as claimed in any of claims 3 to 6 wherein the appliance proper includes a heating element and a thermal sensor responsive to the temperature of the heating element for disconnecting the same in the event of a sensed element overtemperature condition, and the base includes the current responsive means.

8. An appliance as claimed in claim 7 adapted for boiling water and wherein means responsive to boiling of water within the appliance proper are provided for disconnecting a heating element in the appliance proper from its power supply.

9. An appliance as claimed in claim 8 wherein said means responsive to boiling of water within the appliance comprises an enclosure associated with the heating element of the appliance proper so as to simulate a dry boil

condition upon boiling of water in the vessel and said thermal sensor is responsive to said dry boil condition.

10. An appliance as claimed in claim 9 wherein the heating element in the S appliance proper comprises a die cast mass incorporating a heating element proper and the enclosure is defined by a sump formed in the die cast mass.

An appliance as claimed in claim 9 wherein the heating element in the appliance proper comprises a metal plate having a sheathed heating element 10 affixed to the underside thereof and the enclosure is defined by a sump formed in the metal plate.

12. An appliance as claimed in claim 7 or 8 wherein the heating element in the appliance proper is a thick film heating element.

13. An appliance as claimed in any of claims 7 to 12 wherein the thermal sensor comprises a bimetallic element.

14. An appliance as claimed in claim 13 wherein said bimetallic element 20 is an automatically-resetting bimetallic element.

15. An appliance as claimed in any preceding claim and wherein operating controls for the appliance are provided exclusively on the base.