GB2359978A

GB2359978A - Controlling electric liquid-heating appliance

Info

Publication number: GB2359978A
Application number: GB0005081A
Authority: GB
Inventors: Robert Andrew O'neill; Robin Keith Moore
Original assignee: Otter Controls Ltd
Current assignee: Otter Controls Ltd
Priority date: 2000-03-02
Filing date: 2000-03-02
Publication date: 2001-09-12
Anticipated expiration: 2020-03-02
Also published as: AU2001233972A1; WO2001064084A1; GB2359978B; GB0005081D0

Abstract

A control automating the operation of an electrically heated cafetiere or the like has two spaced-apart automatically-resetting bimetals 2, 3 which thermally contact the underside of a thick film heating element of the appliance, one in a region which has no heating tracks and the other in a region which is traversed by heating tracks. The "one" bimetal 2 has a cut-off temperature at about 90{C to 100{C and a small differential of about 10{C and the "other" bimetal 3 has a cut-off temperature at about 180{C to 200{C and a large differential of about 60{C to 80{C. The thick film heating element has main and auxiliary heating tracks. In normal operation, the "one" low temperature bimetal 2 switches the appliance into a "keep warm" mode by appropriately connecting the auxiliary track when water in the appliance has been heated by the main track to 90{C to 100{C. In abnormal operation for example if the appliance is switched on empty, the heating element temperature ramps up too quickly for the low temperature bimetal to operate, but is caught by the high temperature bimetal 3. As the appliance slowly cools, the low temperature bimetal 2 eventually responds and switches the appliance into its "keep warm" mode.

Description

2359978 1 IMPROVEMENTS RELATING TO LIQUID HEATING VESSELS AND CONTROLS

THEREFOR

Field of the Invention:

This invention concerns improvements relating to liquid heating vessels and controls therefor and more particularly concerns electrically powered water heating vessels such as percolators and cafetieres for example wherein there is a requirement to heat water relatively quickly to a first operating temperature of the appliance and thereafter to keep the hot water warm. Such vessels might for example comprise a main heating element and an auxiliary heating element which can either be energized instead of the main heating element or can be connected in series with the main heating element to reduce the overall power output after the main heating element brings the vessel contents quickly up to temperature.

Background of the Invention:

Controls for kettles and hot water jugs are well known which are designed to protect the heating element of the appliance against overheating on account of the appliance being switched on empty or being allowed to boil dry. Such dry boil controls have conventionally comprised primary and secondary thermally-responsive actuators arranged to be held in close thermal contact with the appliance heating element, the primary actuator being 2 designed to switch off the power supply to the appliance heating element in response to its temperature rising above a predetermined level and the secondary actuator providing a back-up facility which is operable in the event of failure of the primary to switch off the heating element. The thermally-responsive actuators of such controls have commonly been bimetallic actuators. particularly though not exclusively snap-acting bimetallic-actuators, though fusible component type actuators have also been employed, particularly for the secondary actuator.

Examples of such controls are the X4 series of controls which we manufacture and sell and which are substantially as described in WO-A-99/54903 and the U series of controls which are manufactured and sold by Strix Ltd. and which are substantially as described inWO-A-95/34187. Both of these series of controls include an integrated control cum. 3600 appliance inlet connector adapted for use with a cordless electric kettle or hot water jug, particularly a kettle or hot water jug incorporating a thick film heating element, and the two thermally responsive actuators of these controls are snap-acting bimetals which are set to nominally the same operating temperature, it being appreciated that two bimetals can act as primary and secondary or back-up protectors without having to be set to different operating temperatures.

We have previously proposed to modify an element protector (dry boil) control by provision of change-over switch contacts such that, in 3 response to operation of the control to switch off a main heating element, an auxiliary heating element is brought into operation. Such an arrangement is useful in a percolator device for example, the dry boil control operating when all of the water has been expelled from a reservoir of the appliance and the auxiliary heater then serving to keep the percolated beverage hot. See for example our British Patent Application No. 9923658.0 in this connection.

The present iffliention relates to yet a further modification, particularly though not exclusively of an X4 control as aforementioned, which is useful in an electrically operated cafetiere.

Summ@ly of the Invention:

A cafetiere, as commonly used for making coffee, comprises a vessel provided with a filter which can be manually depressed through the vessel body so as to filter out coffee grounds from a hot water infusion and leave behind coffee ready for drinking. Conventional cafetieres do not have their own heating element and are intended to be used with water boiled in a kettle or hot water jug. The present invention proposes to provide a cafetiere with its own heating element, preferably a thick film heating element having main and keep warm heating facilities, and to provide a control associated with the heating element and having first and second bimetallic actuators, the first actuator being responsive at or around a normal use temperature for beverage prepared in the cafetiere and being operative to reduce the heating power of 4 the heating element to a keep warm level and the second actuator being responsive at a much higher temperature such as would be encountered if the cafetiere were to be switched on empty or were to be allowed to boil dry.

As aforementioned, the heating element of such a cafetiere can advantageously have main, high power and auxiliary, low power sections and the arrangement of the first (low temperature) actuator can be such as either to connect the low powelr section in circuit in place of the high power section or to connect the two sections in series, the result in either case being a reduction in the heating power output of the heating element. Such a dual power level heating element can advantageously and very conveniently be constructed using thick film technology. Thick film heating elements are currently very popular and becoming increasingly so in water boiling kettles and hot water jugs and their construction is well known in the water heating appliance art.

In the X4 control that is employed as a kettle or hot water jug control and has two bimetallic actuators, the two actuators are each generally rectangular, dished bimetallic blades having an X-shaped cut-out which increases the movement that is available from the blade for operating a push-rod to open a set of switch contacts when the blade snaps from its cold to its hot, oppositely dished configuration. This kind of bimetallic actuator is optimised for operation at high temperatures of the order of, say, 2000C and above such as would only ever be experienced in a water heating appliance if the appliance were to be switched on empty or allowed to boil dry.

Furthermore, this kind of bimetallic actuator exhibits a wide temperature differential, that is to say a wide difference between the temperature at which it will snap to its hot condition and the much lower temperature at which it will reset to its cold condition.

For element protection applications, where the function of the bimetallic actuator is to switch off the heating element at a sensed high temperature and then hold it off even as the heating element cools to ensure that the element is not again switched on when the vessel is empty, a high operating temperature and wide differential are advantageous attributes. For the purposes of the present invention, such a bimetallic actuator might be employed as the second, high temperature actuator, but it is not well suited for us as the first, low temperature actuator. For the first, low temperature actuator it is preferred to employ a simple dished bimetal having no cut- outs and exhibiting a fairly low operating temperature of the order of the temperature of the beverage that is to be prepared, say around 900C, and a low differential. A simple disc bimetal or its rectangular or otherwise shaped equivalent is appropriate for the first bimetal.

An X4 control modified for use with a cafetiere in accordance with the present invention might therefore comprise a first, low temperature bimetallic actuator comprising a simple dished bimetallic blade formed to fit the mounting in the X4 control that conventionally mounts an X cut-out type bimetallic blade. This low temperature bimetal might be operable from its 6 cold to its hot condition at a temperature of, say, WC and might be such as to reset automatically to its cold condition when its temperature cools to, say, 800C. The control might also comprise a second, high temperature bimetallic actuator of the X cut-out type arranged to operate from its low temperature condition to its high temperature condition at, say, 1 SOOC or thereabouts and to reset automatically to its low temperature condition at some temperature above 100T. Such d modified control might advantageously be adapted for use with a thick film heating element having high power and low power sections having a common connecting point by provision of an additional contact on the control for contacting the thick film heating element, such additional contact being associated with the switch means associated with the low temperature bimetal to enable the low power section of the heating element to be switched into and out of circuit. This additional contact connects within the control to the fixed contact of the set of contacts that is operated by the low temperature bimetal and provides access to one of the supply terminals of the X4 control. Externally of the control, this additional contact connects to the remote end of the low power section of the heating element. Depending on whether the two heating tracks are designed to be run in parallel, with the low power keep warm track section always energised, or 20 in series, with the low power keep warm track only energised during keep warm operation, the moving contact of the respective set of switch contacts is 7 connected either to the main element section remote connection (parallel) or directly to the common connecting point of the two heater tracks (series).

In normal operation of such a modified X4 control in a cafetiere provided with a thick film heating element as described, with the cafetiere filled with cold water and switched on, the water will be heated at full power until the low temperature bimetal operates at around WC, whereupon the power output of the heating element will be reduced to keep the water hot. An indicator lamp might conveniently be arranged to be lit when the low temperature bimetal operates to indicate to a user that the cafetiere is ready for the addition of ground coffee. After a short wait, the user then depresses the filter and the coffee is ready for consumption. Given that the modified X4 control retains its 3600C cordless inlet connector, if this is indeed the case, the lifting of the cafetiere from its base to pour the prepared coffee will disconnect the heating element completely from its power supply. If the coffee cools during this time to the point where the low temperature bimetal resets, then the heating element will again be powered at full power once the cafetiere is reset on its base and the coffee will be reheated until the low temperature bimetal again operates, which again reduces the power of the heating element.

In abnormal operation, for example when the cafetiere is switched on empty, the second, high temperature bimetal, which has a rapid response to a high temperature situation, will cause the heating element to be switched off 8 before any damage to the heating element or to the cafetiere can occur. The low temperature bimetal has a slower response to rising temperature and, advantageously, will be juxtaposed with a region of the heating element which has no heater track so as to be responsive to the water temperature rather than the track temperature, whereas the high temperature bimetal will advantageously sense the track temperature by being juxtaposed with a region of the heating elembnt that is traversed by one or more heater tracks.

However, because the low temperature bimetal is set to a relatively low temperature, it will operate after operation of the high temperature bimetal as the high temperature gradually spreads to the region of the low temperature bimetal. With both bimetals thus operated, the heating element will cool and the high temperature bimetal will reset first, typically at some temperature above IOTC. As a result, the heating element will operate in its low power mode, since the low temperature bimetal has not reset, and this will maintain the heating element above the remake temperature of the low temperature bimetal without causing any damage either to the heating element or, more generally, to the cafetiere as a whole. The result is an electrically- maintained, non-self-resetting, safety cut-out which obviates the need for any other manual reset components for the high temperature bimetal, thus providing cost advantages. Of course, filling of the cafetiere with cold water or removing it from its base, thus disconnecting the power supply from the heating element, and allowing it to cool, will reset the low temperature bimetal.

9 The present invention thus provides a manually resettable dry boil protection system, without the need to provide additional mechanical components to form a latching mechanism and making use of no more controls and heating element features than are conventionally provided.

The above and further features of the present invention are set forth in the appended claims and will be well understood from consideration of the following descriptiongiven with reference to the accompanying drawings.

Description of the Drawings:

Figures 1 A to I G show an exemplary embodiment of control cum 360' power inlet connector according to the present invention, this embodiment being a modification of our currently made and sold X4a control, Figure 1A being a plan view of the underside of the embodiment (namely the side of the control which faces a heating element in use), Figure IB being a plan view of the opposite (upper) side of the control, Figures IC, 1D and IE being side elevation views from the directions C, D and E shown in Figure IA, and Figure IF and 1G being isometric views of the under and upper sides respectively of the control; Figures 2A and 2B show how the control of Figures IA to I G might be used with a heating element having main and keep warm element sections, Figure 2A showing a circuit diagram wherein the two heating element sections are electrically in parallel and Figure 2B showing a circuit diagram where they are in series; Figure 3 shows the track layout of a thick film heating element for use with a control according to Figures IA to IG in an electrically heated cafetiere; and Figure 4 shows the track layout of a thick film heating element for use with a control according to Figures IA to 1G in an electrically heated coffee percolator.

Detailed Description of the Embodiments:

Referring first to Figures IA to IG the control cum. 360' connector inlet shown therein is a modification of our X4a control which is commercially available and is substantially as described in WO-A-99/54903 with reference to Figures 2A to 2D thereof with the addition of a third spring terminal for contacting a respective terminal pad of a thick film heating element. Given that the Figures IA to 1G embodiment is but a modification of our X4a control and that the construction and operation of the X4a control is known, inter alia from WO-A-99/54903 the disclosure whereof is incorporated herein by way of reference, the description of the Figures IA to

1 G control that follows will be correspondingly (and thankfully) abbreviated.

The X4a control comprises a moulded plastics material body 1 which is formed so as to define on its upper side (Figure IA) locations for the 11 assembly of first and second bimetallic switches 2 and 3 and on its lower side (Figure IB) a site for assembly of the electrical connector parts of a CP7 360' cordless connector inlet 4 for co-operating with a CS4 base outlet connector, the CS4 and CP7 connectors being available from us and being substantially as described in GB-A-2 285 716 with reference to Figures 7 to 11 thereof. Each of the bimetallic switches 2 and 3 in the X4a control comprises a bimetallic actuator which is carried in a spring metal carrier and co-operates with a push rod to determine the status of a respective set of switch contacts. As described in WO-A- 99/54903 the spring carriers co-operate with the push rods to define respective overcentre mechanisms which require normal intervention after operation to reset the associated switches, but this feature is not required in the practice of the present invention and the carrier springs are modified so that the push rods simply follow the bimetal movements.

In the X4a control, both of these bimetallic actuators are of a dished, snap-acting kind having an X-shaped central cut-out. In the embodiment of the present invention, as shown in Figures IA and IF, only one of the bimetallic actuators is of this kind, namely the bimetallic actuator 5 of the switch assembly 3, and the other bimetallic actuator 6 is a simple dished, snap-acting bimetal shaped similarly to the bimetallic actuator 5 so as to fit into and be carried by the spring carrier of the first switch 2 but having no X-shaped cut-out.

12 Whereas the X cut-out bimetal 5 is selected to have a high operating temperature of the order of 1 SOT or 200T, namely the temperature at which it snaps from its cold condition to its hot condition so as to open its associated switch contacts, and a large differential so that it cannot reset automatically until its temperature falls to somewhere of the order of 11 OT to 120T, the plain, dished bimetal 6 is selected to have a much lower operating temperature of about 90T and a relatively small differential so that it will reset automatically at about 80T.

The X4 control as described in WO-A-99/54903 with reference to Figures 2A to 21) thereof has two spring contacts foi making electrical contact with respective terminal pads of a thick film heating element and these are designated 11 and 12 in Figures IA to IG of the accompanying drawings.

The X4a control has a third spring contact for making electrical contact with a third terminal pad of a thick film heating element and, like the X4a control, the control of Figures 1 A to 1 G has this third spring contact, designated 13 in the accompanying drawings. The spring contact 13 provides access to the fixed contact of the set of switch contacts actuated by bimetal 6 and to one of the supply terminals of the connector part of the control. This contact 13 is provided to connect to the remote end of a low power heating track of a thick film heating element. Depending on whether the two heating tracks are intended to be run in parallel (with the keep warm track always energised) or in series (with the keep warm track only on during keep warm), the moving 13 contact of this set is connected to the main element remote connection (parallel) or directly to the common connecting point of the two heater tracks (series) as is shown in Figures 2A and 2B respectively.

Referring to Figures 2A and 2B, wherein the same references designate the same or similar parts, a thick film heating element has a main heater track 20 delivering 1000 Watts of power, for example, and a keep warm track 21 delivering just 50 Watts for example. The low temperature bimetallic actuator of the control described with reference to Figures IA to I G determines the operating condition of a set of switch contacts 22 and the high temperature bimetallic actuator of the control determines the operating condition of a set of switch contacts 23. A neon indicator lamp 24 is connected across the low temperature bimetallic switch contacts 22. The spring contact 11 of the control of Figures 1 A to 1 G will, in operation with the heating element configurations shown in Figures 2A and 2B, be connected to the heating element terminal pad designated 11 in Figures 2A and 2B, and likewise the spring contacts 12 and 13 will be connected to the terminal pads designated 12 and 13. Figure 3 shows an exemplary track layout for a thick film heating element for a cafetiere wherein the main heating element track 20 is shown in dark and the keep warm heating element track 21 is shown in light, the two track sections 20 and 21 being in a parallel configuration as shown in Figure 2A and the termination pads for connection with the spring terminals 11, 12 and 13 being indicated. Figure 4 shows an alternative track 14 layout for a coffee percolator where the two track sections are in series as in Figure 2B.

In operation of the thus described control with a heating element in a cafetiere, for example, in normal usage cold water is placed in the vessel of the cafetiere and the appliance is switched on. The water is heated until its temperature reaches around 90T, which is sensed by the low temperature bimetal 6 which operfites and opens its associated contacts. This either places the low power element 21 in series with the main heating element 20 or disconnects the high power element 20, thus reducing the power output of the whole to that required to keep the water close to 900C. A neon 24 connected across the contacts 22 lights as a result of the voltage drop across the low power element 21 and this advises the user that it is time to add the coffee.

After a short wait, the user then depresses the filter and the coffee is ready to drink. After pouring, during which time the heating element is completely disconnected from its power supply (having been lifted from the CS4 connector in the base), if the liquid has cooled the low temperature bimetal 6 resets automatically and closes its contacts, allowing the main element 20 to reheat the brew. When the bimetal 6 senses that it has returned to WC it operates to open its contacts, thereby reducing the heating element power once more and keeping the brewed beverage warm.

On the other hand, if the heating element is energised with no water in the cafetiere then the bimetal 5 will switch off in the normal way to protect it.

The bimetal 6 will not sense the temperature rise fast enough since it is located away from the heater track in the region designated 30 in Figure 3 so that it can sense the water temperature. In fact it may be located on a specially provided clear area of the metal substrate of the thick film heating element which is not covered by dielectric, in order to give a more accurate measure of the water temperature. However, because it is set at a low temperature, it will operate on overshoot of the high temperature bimetal 5, which operates at around 1800C. As the whole heating element cools, the high temperature bimetal 5 will reset first, typically above 1 OTC. This energises the low power element 21, since the low temperature bimetal 6 is not yet reset. The output of the low power element 21 is sufficient to keep the heating element above the remake temperature of the low temperature bimetal 6, around 800C, and is sufficiently low powered not to cause any damage. Thus an electrically maintained, non-self-resetting cut-out is provided, which removes the need for any other manual reset components for the high temperature bimetal 5, thus reducing cost.

The control can be reset by either filling the vessel with cold water, or removing it from its base, thus disconnecting the power supply. Either action will reset the low temperature bimetal 6, allowing the brew cycle to be repeated. The invention thus provides a manually resettable dry boil protection system, without the need to provide additional mechanical components to form a latching mechanism.

16 Having thus described the invention by reference to specific embodiments, it is to be understood that the embodiments described are exemplary only and that modifications and variations thereto can be made without departure from the spirit and scope of the invention. For example, the low temperature bimetal does not have to be just a plain, dished bimetal, rather it could be any kind of bimetal, even a bimetal with an X-shaped cut-out, having the re4uired characteristics. The high temperature bimetal is similarly susceptible to modification and variation.

17

Claims

CLAIMS:

1. An electrically powered liquid heating appliance having first and second temperature sensors responsive, respectively, to a relatively low normal operating temperature at the appliance heating element and to a relatively high abnormal temperature at the appliance heating element, operation of said first sensor in normal operation of the appliance causing a reduction in the power output of the appliance heating element to set the appliance into a "keep warm" mode, and operation of said second sensor in an abnormal overtemperature condition of the appliance causing disconnection of the appliance heating element and, as the heating element cools, reconnection but only in said "keep warTn" mode due to operation of said first sensor in sympathy with said second sensor, the "keep warm".mode of the heating element being sufficient to prevent said first sensor from resetting.

2. An appliance as claimed in claim 1 wherein said sensors comprise bimetallic elements.

3. An appliance as claimed in claim 2 wherein the relatively low temperature bimetallic element has a small temperature differential and the relatively high bimetallic element has a large temperature differential.

18

4. An appliance as claimed in claim 3 for heating water and wherein the low temperature bimetallic element has an operating temperature in the region of the boiling temperature of water (eg around WC) and a temperature differential of about 1 OT, and the high temperature bimetallic element has an operating temperature in the region of 200T (eg around 180T) and a temperature differential in the region of 800C to I OOOC.

5. An appliance as claimed in claim 3 or 4 wherein the low temperature bimetallic element is a dished bimetallic blade having no cut-out, and the high temperature bimetallic element is a dished bimetallic blade having a cut out.

6. An appliance as claimed in any of the preceding claims wherein the appliance heating element comprises a main, high power portion and an auxiliary, low power portion.

7. An appliance as claimed in claim 6 wherein the main and auxiliary portions of the appliance heating element are connected in parallel and the operation of said first sensor determines when said main heating element portion is powered with the auxiliary heating element portion.

8. An appliance as claimed in claim 6 wherein the main and auxiliary portions of the appliance heating element are connected in series and the 19 operation of said first sensor determines when said auxiliary heating element portion is powered.

9. An appliance as claimed in any of the preceding claims wherein the appliance heating element is a thick film heating element.

10. An appliance as claimed in claim 9 wherein said first sensor is associated with a region of the thick film heating element which has no heater tracks and said second sensor is associated with a region of the thick film heating element which has heater iracks.

11. An appliance as claimed in any of the preceding claims configured as a cafetiere.

12. An appliance substantially as herein described with reference to the accompanying drawings.

13. A control for use in an appliance as claimed in any of the preceding claims, the control including said first and second sensors.

14. A control as claimed in claim 13 which is formed integrally with a 3600 appliance power inlet connector part.

A control for an electrically powered water heating appliance, said control comprising a first bimetal which operates at a temperature in the region of the boiling temperature of water and a second bimetal which operates at a very much higher temperature, both of said bimetals being automatically resetting and said first bimetal having a small differential whereas said second 1:imetal has a large differential.

16. A control for automating the operation of an electrically heated cafetiere or the like and also protecting it from damage should its heating element overheat, the control having two spaced-apart birnetals which thermally contact the underside of a thick film heating element of the appliance, one in a region which has no heating tracks and the other in a region which is traversed by heating tracks, said "one" bimetal having a cut-off temperature at about WC to 1OTC and a small differential of about 1 OT and said "other" bimetal having a cut-off temperature at about 18 OT to 200T and a large differential of about WC to 800C, and said thick film heating element having main and auxiliary heating tracks, the arrangement being such that in normal operation, the "one" low temperature bimetal controls the action of the appliance and switches it into a "keep warm" mode by appropriately connecting the auxiliary track when water in the appliance has been heated by the main track to 90T to 100T whereafter the "one" 21 bimetal operates as a thermostat to keep the water warm, and in abnormal operation for example if the appliance is switched on empty, the heating element temperature ramps up too quickly for the low temperature bimetal to operate, but is caught by the high temperature bimetal, and as the appliance slowly cools, the low temperature bimetal eventually responds and switches the appliance into its "keep warm" mode which powers the heating element at such a low level as to cause no damage and the heat produced keeps the low temperature bimetal operated so that the appliance cannot revert to its high power mode.