WO1998006309A1

WO1998006309A1 - Improvements relating to liquid heating appliances and controls therefor

Info

Publication number: WO1998006309A1
Application number: PCT/GB1997/002096
Authority: WO
Inventors: Robert Andrew O'neill
Original assignee: Otter Controls Limited
Priority date: 1996-08-08
Filing date: 1997-08-06
Publication date: 1998-02-19
Also published as: GB2316229A; AU3778697A; GB9616652D0; GB2316229B

Abstract

A cordless liquid heating appliance comprises a vessel part incorporating an electrical heating element (15) and a base part for powering the electrical heating element when the vessel part is operatively positioned relative to the base part and an inlet connector (2) on the vessel part is mated with an outlet connector (1) on the base part. The vessel part includes a thermally conductive heat transfer element (18) for transferring to the base part of the appliance heat from liquid contained in the vessel part, and the appliance base part includes temperature control means (21) for cyclically determining the supply of power to the electrical heating element in the vessel part via the base part so as to tend to maintain the contents of the vessel part at a desired temperature. The temperature control means (21) includes a thermally responsive element which is arranged to be responsive to heat transferred by said thermally conductive heat transfer element (18) from the vessel part and to be responsive additionally to heat generated locally with respect to said thermally responsive element when, in use of the appliance, the temperature control means is in condition to power the vessel part. The additional heat input to the temperature control means results in a more precise control of the temperature of the vessel contents.

Description

IMPROVEMENTS RELATING TO LIQUID HEATING APPLIANCES AND CONTROLS THEREFOR

Field of the Invention:

This invention concerns improvements relating to 5 liquid heating appliances and controls therefore and has particular application to so-called "cordless" appliances which comprise an appliance proper (or vessel) part for containing the liquid that is to be heated and a base part upon which the vessel part can 0 be removably seated and which serves for the supply of electrical energy to a heating element of the vessel part when the vessel part is seated upon the base part, there being co-operating parts of a connection system provided in the vessel part and in the base 5 part which come together when the former is seated upon the latter and provide for mains electrical power supplied to the base part to be supplied to the heating element in the vessel part. Cordless electrical appliances such as water boiling kettles 0 and hot water jugs are well known, and the invention is applicable to such well known appliances and additionally to other liquid heating appliances such as pots, pans, urns, laboratory equipment and the like. Background of the Invention:

Cordless electrical appliances are well known, as aforementioned, and electrical connection systems for use with such cordless appliances are likewise well known in the patent literature. For example, in our GB-A-2 241 390 there is described an exemplary form of cordless connection system which requires the vessel part to be seated upon the base part in a particular orientation to enable the co-operating parts of the connection system to come together, and in our O94/06185 there is described an alternative cordless connection system which enables the vessel part to be seated upon the base part throughout a full 360° of relative rotational orientation, or throughout substantially 360°, with the connector system parts still coming together. Connector systems according to the teachings of GB-A-2 241 390 are manufactured by us and marketed under the CS2 type designation, and connector systems according to the teachings of WO94/06185 are manufactured by us and marketed under the CS4 and CP7 type designations, the CS4 being the base connector part and corresponding substantially to Figures 7 and 8A of the drawings of WO94/06185 and the CP7 being the appliance connector part and corresponding substantially to the connector part shown in Figure 8B of the drawings of 094/ 06185. Thermally-responsive controls for use with cordless electrical liquid heating appliances, particularly water boiling appliances, are also well known. One kind of such control is a so-called element protector control which is adapted to sense overheating of the vessel element and to disconnect the power supply to the heating element, such overheating being caused for example as a result of the vessel heating element being powered without any liquid in the vessel (a so-called "dry boil" situation) . In Figure 8B of the drawings of WO94/06185, in the upper part of the Figure, there is shown an exemplary form of element protector control in accordance with the teachings of our GB-A-2 194 099 which provides two levels of element protection. A first or primary level of element protection is provided by means of a bimetallic blade arranged to be in close thermal contact with the heating element of the appliance and to open a set of switch contacts in the event of the heating element overheating, and a second or secondary level of element protection is provided by mounting the bimetallic blade in a collapsible carrier which bears against the heating element of the appliance under spring pressure and is arranged to collapse if the element overheats and the primary protection provided by the bimetal fails to operate, for whatever reason, the collapse of the carrier disrupting the supply of electricity through the control to the heating element of the appliance.

An alternative form of the abovementioned element protector control is manufactured and marketed by us as the XI control and corresponds substantially to the control described in GB-A-2 194 099 with reference to

Figures 3A, 3B and 3C of the drawings thereof. A modified form of this control is manufactured and marketed by us as the X2 control and corresponds substantially to the control described in

GB-A-2 287 829. Different ways of assembling an X2 control with a CS4/CP7 cordless connection system and with the heating element of a cordless electrical appliance are described in our British Patent

Applications Nos. 9524176.6 and 9607413.3. The disclosures of O94/06185, GB-A-2 194 099,

GB-A-2 287 829 and of our British Patent Applications

Nos. 9524176.6 and 9607413.3 are incorporated herein by reference.

Electric heating elements for liquid heating appliances are commonly either of the metal sheathed, insulated, resistance heating wire type which is designed to be immersed in the liquid that is to be heated, or of the planar type which is designed to form a wall (commonly a base wall) of the liquid vessel. Planar heating elements are known which comprise a metal plate having a metal sheathed, insulated, resistance heating wire type of heating element clamped or otherwise clenched to one side thereof. Alternative planar heating elements have been proposed which comprise a resistance heating track, pattern or layer formed or deposited onto an insulating, thermally conductive substrate. One such element comprises a stainless steel plate having on its undersurface, that is to say its surface which in use will not come into contact with the liquid that is to be heated, an electrically insulating layer of glass for example, and having a resistance heating track or pattern formed on the glass and covered with a further electrically insulating glass layer. Planar heating elements are sometimes preferred to the immersion type of metal sheathed, insulated, resistance heating wire element on account of the readiness with which a vessel equipped with a planar heating element can be cleaned.

Whilst it has been known to provide corded electrical liquid heating appliances with adjustable thermostats enabling the temperature of liquid heated in the appliance to be held at or around a certain level, the thermostat cycling so as to switch the appliance heating element alternatively on and off and thereby maintain the temperature of the heated liquid, no such provision has been made in cordless electrical appliances, so far as we are presently aware. A corded electrical liquid heating appliance, of course, is one in which the appliance proper itself has an electrical supply directly from the mains and no base part is required to achieve this function. The adjustable thermostat of such a corded electrical appliance can for example comprise a creep-acting bimetallic blade (as opposed to one which is snap-acting, for example by virtue of having a dished configuration) which acts upon an adjustable switch, or alternatively the bimetal operation itself can be adjustable. An exemplary arrangement of the first-mentioned type is described in W095/ 19129 and an exemplary arrangement of the second-mentioned type is described in our GB-A-774911. Other adjustable thermostat arrangements are of course known.

Objects and Summary of the Invention: Given that thermostatically-controlled cordless liquid heating appliances have not previously been known, so far as we are aware, it is a principal object of the present invention to provide such an appliance and, furthermore, to provide such an appliance wherein the thermostat and its adjustment facility are housed in the base part of the cordless appliance.

According to the present invention, the above object is enabled to be met by the provision of a cordless liquid heating appliance wherein a thermally conductive heat transfer member is provided on the vessel part of the appliance for transferring to the base part of the appliance heat from liquid heated by the appliance in use and contained within the appliance vessel part and, in the appliance base part there is provided temperature control means for cyclically determining the supply of power to the vessel part via the base part, said control means including a thermally responsive element arranged to be responsive to heat transferred by said thermally conductive heat transfer member from the vessel part and additionally to heat generated locally with respect to said thermally responsive element when the control means is in condition to power the vessel part.

The use of a heat transfer member to conduct the heat of the liquid in the vessel part of the appliance to the temperature control means in the base part would cause the temperature control means to have only relatively slow response characteristics were it not for the additional locally generated heat, and this would result in the cyclical operation of the temperature control means corresponding to a relatively large temperature variation of the liquid in the vessel part. However, by the addition of locally generated heat the liquid temperature variation can be significantly reduced. Where the thermally responsive element of the temperature control means is a bimetallic element for example, the locally generated heat can be generated by including the bimetallic element itself in the electric current path to the heating element of the appliance and/or a heating element connected in such electric current path may be provided thermally coupled with the bimetallic element. Other thermally responsive elements are known, for example utilizing shape memory effect materials, and similar arrangements are possible with these.

In an exemplary embodiment of the invention which will be described hereinafter, the aforementioned CS4/CP7 cordless connection system is utilized and the heat transfer member is constituted by a copper or copper alloy pin having a head portion in close thermal contact with the contents of the vessel part of the appliance and a shank or body portion received within the folded metal control earth terminal of the CP7 vessel input connector. This pin, together with the CP7 earth terminal and the co-operating earth contact parts of the CS4 base outlet connector, constitutes the heat transfer member of the embodiment and provides for the transfer of heat from hot liquid contained in the vessel part of the appliance to the base part of the appliance and, more particularly, to a temperature control means affixed to the underside of the CS4 base outlet connector. This arrangement is particularly convenient since it does not require any substantially redesign of the CS4 and CP7 components. The temperature control means may be adjustable, to provide for a range of different heat settings, or may be a fixed control means, for example for use in a coffee making appliance for maintaining the prepared coffee at an ideal temperature. Furthermore, the temperature control means may be arranged so that it can be switched into and out of circuit, so that an appliance can be used either for bringing a liquid to the boil or to bring it up to a certain simmering temperature.

The precise nature of the temperature control means is not the essence of the present invention. Rather the invention resides in the use of a heat transfer member to conduct heat from hot liquid in the vessel part of the appliance to the temperature control means in the base, and the use of additional heating in the temperature control means to compensate for the slow response and correspondingly imprecise temperature control that would result. As mentioned hereinbefore, the additional heating can be achieved by arranging a bimetallic switch-actuating element of the temperature control means so that it carries at least part of the electric current flowing through the heating element of the vessel part of the appliance, the electrical resistance of the bimetallic element providing the requisite heating. Alternatively or additionally, a separate heating device can be provided for pumping heat into the thermally responsive element of the temperature control means. For example, in the case where the thermally responsive element is a bimetallic element, the separate heating device could be a resistance wire round around an insulator on the bimetal or could be a small thick film heater suitably positioned relative to the bimetal. The above and further features of the present invention are recited in the appended claims and will be described in the following, by way of example, with reference to the accompanying drawings.

Description of the Drawings: Figure 1 is a sectional view of the CS4 base outlet connector and CP7 vessel input connector as currently manufactured and marketed by us; and

Figure 2 shows the CS4 and CP7 components of Figure 1 in operative relationship with the underside of a heating element, and with a heat transfer member coupling the heating element to the earth pin of the CP7 and thence to a temperature control means coupled to the CS4, this arrangement embodying the present invention.

Detailed Description of the Embodiment:

Referring first to Figure l, the cordless connection system shown therein substantially corresponds to the connection system described in WO94/06185 with reference to Figures 7 to 9 thereof. A base unit output connector 1 corresponds to the CS4 connector which we currently manufacture and sell, and a vessel input connector 2 corresponds to our CP7 connector. Both connectors 1 and 2 are rotationally symmetrical so that a vessel part equipped with the CP7 input connector 2 can be seated on a base part equipped with the CΞ4 outlet connector 1 in any relative rotational orientation of the vessel and base parts and the connectors 1 and 2 will still mate correctly with each other. The CS4 base output connector 1 comprises a generally cylindrical plastics body moulding 3 within which there is housed a central plastics moulding 4 which has a hollow centre housing spring metal earth terminals 5. Neutral and live terminals 6 and 7 are defined by cylindrical metal components secured respectively on the inside of the body moulding 3 and on the outside of the central moulding 4. A shutter

8 is biassed by spring means (not shown) into the annular space between the upper ends of body moulding 3 and central moulding 4 and has to be depressed against its spring bias to obtain access to the neutral and live terminals 6 and 7.

The CP7 vessel inlet connector 2 comprises a generally cylindrical plastics moulding 9 which is open at its lower end (as viewed in Figure 1) , closed at its upper end and has a re-entrant generally cylindrical central portion 10. The plastics moulding

9 supports neutral and live spring metal terminals 11 and 12 respectively which are adapted to engage the neutral and live terminals 6 and 7 of the base outlet connector 1 when the two connector parts are mated with each other, and an earth terminal 13 formed of folded sheet metal is centrally mounted coaxially with respect to the moulding 9 and is adapted to engage the earth terminal 5 of the base outlet connector 1. The free (lower) end of the re-entrant central portion 10 is adapted to depress the shutter 8 as the two connector parts l and 2 are brought together, and the tabs 14 provide for the mounting of the CP7 connector. Referring now to Figure 2 , this shows the CP7 and CS4 connector parts of Figure 1 in fully engaged condition with the shutter 8 fully depressed, and with live terminals 7 and 12 in contact, and neutral terminals 6 and 11 likewise in contact. There is also shown in Figure 2, the underside of a planar heating element 15 comprising a metal plate 16 having affixed thereto a metal sheathed, insulated, resistance wire type heating element proper 17. The metal plate 16 may for example constitute the bottom of a vessel for heating liquid. Affixed centrally of the plate 16 is a heat transfer element 18 comprising a copper or copper alloy pin having a heat portion 19 secured to the plate 16 and a depending shank portion 20 which, as shown, is engaged with the folded metal earth terminal 13 of the CP7 vessel inlet connector 2. Although not shown in Figure 2, the CP7 vessel inlet connector 2 is connected to the vessel part of the cordless appliance with the neutral and live terminals 11 and 12 connected to the element proper 17. By virtue of this arrangement, the heat from liquid contained in the vessel is transferred through the heat transfer element 18 to the earth pin 13 of the CP7 vessel inlet connector 2 and thence to the earth terminal parts 5 of the CS4 base unit outlet connector 1.

A temperature control means, or temperature regulator, 21 is shown affixed to the underside of the base unit outlet connector 1 so as to be responsive to the temperature of the earth terminal parts 5 of the base unit outlet connector. The temperature regulator 21 acts in the manner of a thermostatic switch to determine the supply of electricity to and through the base unit and vessel connectors 1 and 2 to the heating element proper 17 and is arranged so that not only is it responsive to the temperature of the earth terminal parts 5 of the base unit outlet connector 1, but also it is responsive to heat generated locally at the temperature regulator 21 as a consequence of electrical current flow therethrough en route to the element proper 17. By virtue of this additional heat input to the temperature regulator 21, the range of temperature variation that otherwise would result in the liquid contents of the vessel on account of the relatively long thermal conduction path from the liquid to the temperature regulator 21 and the corresponding delayed responsiveness of the temperature regulator 21 to changes in the temperature of the liquid in the vessel, can be reduced. The temperature regulator 21 can comprise a bimetallic switch actuator and the bimetallic switch actuator can be in direct physical and thermal contact with the earth terminal parts 5 of the base unit outlet connector 1. In this case, the bimetallic element will be earthed and cannot be directly heated by the passage electric current, and a separate heating device may be provided, electrically insulated from the bimetallic actuator, for pumping heat into the bimetal when the heating element proper 17 is powered. Alternatively, the bimetallic actuator could be electrically insulated from the earth terminal parts 5 of the base unit outlet connector, by means of a thin plastics film or mica sheet for example, in which case the heating element current could be passed through the bimetal. The bimetallic switch actuator might be arranged to operate a set of snap-acting switch contacts by way of an electrically insulating push rod for example. Other arrangements for the temperature regulator 21 will occur to those possessed of relevant skills.

There has thus been described a cordless electrical liquid heating appliance which incorporates temperature control means, preferably though not essentially an adjustable temperature control means, in the base part of the appliance. Because the temperature sensor of the temperature control means is inevitably located remotely from the temperature source that it is required to sense, it would normally give very coarse control (as in the case of the arrangement described in W095/ 19129) , but by providing additional locally generated heat so as to increase the sensed rate of temperature rise at the temperature control means, it is possible to compensate for the lag in the heat transfer from the vessel and this decrease the temperature variation of the controlled temperature. This effect may be optimised by changing the properties of electrically generated and conducted heat.

Having thus described the present invention by reference to an exemplary embodiment, it is to be well appreciated that modifications and variations are possible without departure from the spirit and scope of the invention as set forth in the appended claims. For example, in the arrangement of Figure 2 the heating element 16 could be of the immersion heater type.

Claims

CLAIMS :

1. A cordless liquid heating appliance comprising a vessel part incorporating an electrical heating element and a base part for powering said electrical heating element when the vessel part is operatively positioned relative to the base part and an inlet connector on the vessel part is mated with an outlet connector on the base part, said vessel part including a thermally conductive heat transfer element for transferring to the base part of the appliance heat from liquid contained in the vessel part, and said appliance base part including temperature control means for cyclically determining the supply of power to the electrical heating element in the vessel part via the base part, said temperature control means including a thermally responsive element arranged to be responsive to heat transferred by said thermally conductive heat transfer element from the vessel part and additionally to heat generated locally with respect to said thermally responsive element when in use of the appliance the temperature control means is in condition to power the vessel part.

2. A cordless liquid heating appliance as claimed in claim 1 wherein said temperature control means is adjustable to enable the temperature at which liquid is maintained in the vessel part to be adjusted.

3. A cordless liquid heating appliance as claimed in claim 1 or 2 wherein said thermally responsive element comprises a bimetallic element.

4. A cordless liquid heating appliance as claimed in claim 3 wherein said bimetallic element is arranged to carry current for generating said local heat.

5. A cordless liquid heating appliance as claimed in any of claims 1 to 3 wherein a separate heating device is associated with said thermally responsive element for generating said local heat.

6. A cordless liquid heating appliance as claimed in any of the preceding claims wherein said heat transfer element is arranged to transfer heat from the vessel part to the base part by way of said inlet and outlet connector parts.

7. A cordless liquid heating appliance as claimed in claim 6 wherein said heat transfer element is arranged to transfer heat to an earth terminal of said vessel inlet connector and thence to an earth terminal of said base outlet connector.

8. A cordless liquid heating appliance as claimed in claim 7 wherein said vessel inlet connector and said base outlet connector are concentrically arranged so as to permit seating of the vessel part on the base part throughout 360° or substantially 360° of relative rotational orientation, and said earth terminals are located centrally of said concentric arrangement.

9. A cordless liquid heating appliance as claimed in claim 8 wherein the earth terminal of the vessel inlet connector comprises a male part for engagement with a female earth terminal of the base outlet connector, and said male part is hollow for receiving therein a pin component constituting said heat transfer element.

10. A cordless liquid heating appliance substantially as herein described with reference to the accompanying drawings.