This invention relates to apparatus for use in electric water heating vessels such as hot water jugs and kettles, and in particular to immersion heaters and control units for use therein.

Typical vessels of this type have a metal or plastics body within which the water is heated by means of an electric immersion heater. Such immersion heaters generally comprise a heating element located within the water receiving portion of the vessel which is carried by a head adapted to be secured in a water tight manner in relation to an opening in a generally vertical wall of the water receiving portion. The heating element is generally provided with so-called cold leads extending to the "dry" side of the head by means of which electrical connections are made to the immersion heater. Within the vessel, the element is bent into a tortuous shape in order to obtain a sufficient length and therefore an appropriate level of heat dissipation within the space available. In addition, about half way along its length, the exterior of the element is connected in good thermal contact with the head This is the so-called "hot return" part of the immersion heater and its function is to allow a thermally operated control to be connected to the "dry" side of the head in order to provide switch-on-dry protection. Thus, in the event of the kettle or jug boiling dry or being switched on with sufficient water therein to cover the element, heat from the element is conducted to the head from the hot return and causes a thermally operated switch arranged in series with the element to disconnect the electrical supply.

It is also necessary to provide a convenient means of connecting the kettle or jug to the electric supply.

This is generally achieved by providing a plug connector on the vessel body or on t e control arranged to mate with a socket connector on a mains lead or forming part of a separate base unit in a so-called "cordless" arrangement. The provision of such connectors allows the kettle or jug to be disconnected from the lead or base unit in order to fill it with water.

Although it is possible to construct an electric jug or kettle using discrete components to perform each of the above described functions, it is now general practice to use an integrated control unit which provides the plug connector and switch-on dry protection within a single unit. This type of unit is designed such that the necessary electrical and thermal connections to the immersion heater are made automatically as the control unit is attached to the heater head.

It is also known to provide control units with additional features, such as a back-up protection system. Such a system serves to disconnect the element from the electrical supply if overheating occurs and the switch-on-dry protection system fails. For example, GB- A-2204450 discloses a control having such a device in the form a plastics push rod extending from the unit and which in use abuts and is biased towards the heater head. The action of the heater head against the push rods causes the push rods to hold closed a pair of electrical contacts which are arranged in series with the heater element. However, the plastics material is chosen such that in the event of serious overheating occurring, the push rod will start to melt, and as it does so the contacts will be allowed to open. It will be appreciated that the operation of this back-up device permanently disables the faulty control unit which must then be replaced.

The most common use of electrical water heating kettles and jugs is to boil water in order to make tea,

coffee or other beverages. In the case of instant coffee, the water temperature is ideally somewhat below boiling. Further, in certain circumstances, such as when cooking, or when there is a fairly constant demand for beverages, it may be desirable to have boiling or near boiling water constantly available from the kettle or jug. To achieve this it has been proposed further to provide a kettle or jug with a "simmer control" in the form of an additional thermally operated switch having an actuating portion in thermal contact with the water and which is arranged to cycle, ie. repeatedly to disconnect the supply of power from the element at a certain water temperature and to reconnect it when the water has cooled to a slightly lower temperature. Thus, the water temperature is kept between the temperatures at which the switching occurs. The thermal actuator may typically be arranged to be in thermal contact with the water by being placed against the outer surface of the vessel water. According to a first aspect of the invention there is provided an electric immersion heater assembly for use in water heating vessels, the heater having a head connected in good thermal contact with an element via a hot return, the element being in series electrical connection with a cycling thermally operated switch, and the switch having a thermally responsive actuator arranged in good thermal contact with the head and being adjustable to cycle at different temperatures.

The invention extends to a water heating vessel incorporating an immersion heater and switch in accordance with the first aspect of the invention.

Thus, by appropriate adjustment of the thermally operated switch it is possible to employ such a heater in a water heating vessel in order to cause the water contained therein to simmer continuously, or to remain at some other predetermined temperature. By providing the thermally responsive actuator in good thermal

contact with the heater head, advantages are achieved as compared with locating an actuator against the vessel wall. Since water heating vessels often have walls formed of plastics materials, which are poor conductors of heat, there will be a delay between the water reaching a particular temperature and its being sensed by the actuator. In contrast, in the present invention, as the actuator is in good thermal contact with the metal heater head the actuator will be able to sense the water temperature more quickly and so the water may be kept at a more constant temperature.

A further advantage of the present invention is that controls with different operating characteristics may be provided. With the known arrangements, it is only possible for the actuators to sense the water temperature, whereas in accordance with the invention, the operation of the switch may also, if desired, be adapted to more closely follow the heater temperature. This latter characteristic is particularly beneficial if it is desired to keep water as near to boiling as possible. As water cannot be raised above 100 ^β C under normal atmospheric conditions without it turning to steam, it is not possible for any water- temperature operated actuator to be set to disable the power at a higher temperature than this. For practical purposes a slightly lower temperature than 100°C must be selected - otherwise a rolling boil may be established and the simmer control will not operate. Furthermore, a temperature differential is required to allow the actuator (commonly a snap-acting bimetal) to cycle. This differential may be 10 ^β C or as high as 20°C. It will therefore be appreciated that any system based upon the water temperature will lead to a maximum setting in which at some point in each cycle the water temperature will be 90°C or lower. The cycling is also relatively slow, particularly when the vessel is full, as a consequence of the heat capacity of the volume of water

being heated and cooled by 10°C or 20°C during each cycle.

These drawbacks can be avoided in accordance with certain embodiments of the invention in which the thermally responsive actuator is arranged to sense the heater temperature. This is because the switch will cycle more quickly across the temperature differential of the actuator as a consequence of the heater having a lesser thermal capacity than the water in the vessel and because the disabling temperature of the heater can be above 100°C such that the average water temperature during cycling can be maintained closer to 100°C if desired.

For example, the switch may be adjusted to cycle between 95°C and 105°C. Such temperature variations of the heater head would result in a lesser fluctuation in water temperature about an average somewhere between 95°C and 100°C. The water temperature lags behind heater temperature, and a more constant water temperature may be provided in the simmer mode. It will be appreciated that this system of operation is equally applicable for other desired water temperatures. However, for the sake of brevity, the term "simmer control" is used herein to define this mode of operation, regardless of the water temperatures concerned.

It is a consequence of this system of operation that when a vessel full of cold water is first heated up, the thermally operated switch will tend to cycle a few times before the water reaches its desired temperature. This is the result of the heater head reaching its operating temperature before the water reaches the desired temperature. In fact, this should not unduly delay the time which the water takes to reach the desired temperature, but if the water must be heated as quickly as possible, the switch may be temporarily disabled.

One way to do this is to provide a non-cycling

steam operated actuator in parallel with the thermally actuated switch controlled By the actuator. This will maintain the supply of current to the heater, regardless of the operation of the cycling switch until the water has boiled.

It is not, however, always most appropriate to arrange the actuator to sense the heater temperature in the manner just described. For example, in hard water areas, scale will build up on the heater and this will have the effect of insulating the heater from the water, although it will not affect the flow of heat to the thermal actuator. This will result in the control switching off the heater at a lower water temperature than desired. Although if the scale is not heavy this effect may be compensated for by adjusting the thermal actuator, such adjustment is, of course, limited and therefore with heavy scale it may become impossible to set the vessel to boil water.

This problem may be overcome by arranging the thermal actuator so that it is primarily responsive to water temperature. To achieve this, the actuator should be located in good thermal contact with a part of the head which is not significantly heated directly by the immersion heater. In the case of a standard immersion heater this means locating the actuator remote from the hot return, eg. towards the perifery of the head. One way of doing this is to provide a surface on the heater head against which the actuator may abut. However, a preferred arrangement takes advantage of the control mounting studs which are provided on standard immersion heater heads by arranging the actuator to sense the temperature of the head via one of these studs, preferably the upper one. Since the space around the studs is limited, it is preferred to provide a heat bridge to connect the stud to a remote actuator. This is conveniently a collar of a high conductivity metal (eg. copper) within which the stud is received.

The thermally operated cycling switch may be provided in addition to conventional switch on dry apparatus, in which case it may be disabled by being short circuited. However, it is particularly preferred for the operations of simmer control and switch-on-dry protection to be combined. This is achieved by allowing the cycling thermally operated switch to be adjustable to a "boil" setting in which it does not cause the current to be disconnected from the immersion heater in normal operation. Thus, typically the actuator has a maximum setting which causes it to disconnect the current when the heater head reaches about 135°C. Such a temperature should only be reached when the vessel boils dry or is switched on with insufficient water in the vessel to cover the element.

The provision of the thermally responsive actuator in the region of the heater head has a still further advantage which relates to the convenience of producing water heating vessels. That is, it makes it possible to produce an integrated control unit which provides a simmer control.

Thus, according to a second aspect of the invention there is provided an integrated control unit for use in a water heating vessel, the control unit having an insulating body arranged to be attached to a mounting location which is in thermal contact with part of an electric heater of the vessel, means for providing electrical connection to the cold leads of such a heater upon attachment, terminal pins for connection to a supply of electric current, and a thermally operated cycling switch arranged to control the flow of current between the pins and the heater, the switch having a thermally responsive actuator arranged to be in good thermal contact with said mounting location upon attachment of the control thereto and being adjustable to cycle at different temperatures.

Where the heater is an immersion heater as

discussed above, the mounting location is preferably the heater head. Alternative arrangements include "underfloor" systems in which the heater is secured in good thermal contact to the underside of a metal vessel base. In such a system, the mounting location may, for example, be a metal member located in good thermal contact with the heating element, other arrangements are possible.

Thus, the connection and switch-on-dry protection facilities of known integrated controls, together with an additional simmer facility are provided within a single unit which may be connected directly to e.g. an immersion heater in a single operation. This is highly advantageous when producing water heating vessels because the vessels are mass produced in great numbers, and any reduction in production steps leads to significant cost savings. Moreover, the integrated control, in combination with an immersion heater provides the advantages set out in respect of the first aspect of the invention.

The control unit may also be arranged to provide one or more of the preferred features discussed above in respect of the first aspect of the invention. Thus, although the switch-on-dry facility may be separate from the simmer control, and the simmer control may be disabled by short circuiting it, it is possible to use the same switch to provide both functions. Thus, with such a unit incorporated within a vessel, when it is desired to boil water the thermally operated switch should be adjusted so that it disconnects the current from the immersion heater at a head temperature which will only occur in the event of the vessel boiling dry or being switched on when dry.

The integrated control according to the second aspect of the invention may also provide other functions found in known controls. Thus, a back-up protection system may be provided, for example using a meltable

push rod holding a set of contacts closed against a bias spring, the push rod being arranged to be in thermal contact with the heater head. Alternatively, or additionally, the control may be provided or used in conjunction with a steam operated switch which serves to switch off the vessel when water is boiled. Such switches are well known in the art.

The cycling thermally operated switch may be electronic, possibly comprising a thermistor, but it is preferred to have an actuator in the form of a bimetal arranged to operate a set of contacts preferably operated via a snap-acting over-centre mechanism. An adjusting mechanism is provided such that the amount of movement of the bimetal required to trip the mechanism can be varied. Many such mechanisms are known in adjustable cycling switches used in thermostats etc. The presently preferred arrangement is to provide an over-centre switch mechanism having a movable pivot point. In this arrangement movement of the pivot point serves to vary the distance which the bimetal must move in order to cause the over-centre mechanism to change condition. Thus, for example, the over-centre mechanism may have a switch arm having a contact mounted at a first end for co-operation with a fixed contact, the second end of the switch arm being mounted on a support member and being displaceable therewith by the bimetal, there being provided at an intermediate portion of the switch arm a tongue which is held in compression and which is movable relative to the body of the switch arm. The distal end of the tongue is located against a first pivot point on a tensile portion of a support member, the tensile portion being movable relative to the remainder of the support member. The arrangement is such that displacement of the second end of the switch arm by a given amount causes the contacts to open or close. By moving the tensile portion relative to the support member, the pivot point is moved. By moving the

pivot point towards the bimetal, the distance which the bimetal must move in order to cause the over-centre mechanism to operate is reduced and therefore the temperature required to operate the switch is also reduced. Likewise, moving the pivot point further from the bimetal increases the temperature at which the switch operates.

The pivot point may most conveniently be moved by providing an adjustment member arranged to move the tensile member on which the pivot is formed. This may be provided in the form a threaded rod received within a threaded bore formed in the body of the control unit so that by turning the rod, the pivot point may move towards or away from the bimetal. However, a camming arrangement may be preferred in certain circumstances since this may provide a greater linear movement for a given rotation of the rod.

Preferably the control member is arranged so that it may be easily adjusted by users of vessels in which the control is located either to change the desired water temperature or to override the simmer function in order to allow water to boil or to heat up quickly before the unit is reset to a simmering temperature. In addition, in hard water areas, as a result of the element becoming covered in scale, it will become less effective over time and therefore a higher element temperature will be required for a given water temperature. Consequently, it will be necessary to make corresponding adjustments to the temperature at which the thermally operated cycling switch operates.

It is possible to make a control according to this aspect of the invention having a generally cylindrical form with a diameter similar to that of the heater head. Such an arrangement is compact, but it does have the disadvantage that, due to space limitations, only a comparatively short bimetal can be used to form the thermal actuator. For a given type of bimetal material,

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the greater its length, the greater will be the movement of its free end for a given temperature rise. Therefore, if a longer bimetal can be used, the temperature variation required to cause it to cycle will be reduced and therefore a steadier water temperature may be obtained.

In order to achieve this objective, certain embodiments of the invention comprise an elongate bimetal extending beyond the outer circumference of the heater head. This is most easily achieved when a heat bridge is provided (as discussed above) . This is because it is necessary to provide a seal between the heater head and the vessel adjacent the control, and the heater bridge (eg. a collar) is suitable for spacing the bimetal from the seal.

In order to ensure maximum heat transmission along the length of the actuator it is particularly preferred to use a trimetal, which is a bimetal with an extra layer of high thermal conductivity material such as copper.

Certain embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which:-

Fig. 1 is an exploded schematic perspective view of an immersion heater head and integrated control unit according to a first embodiment of the invention with certain portions removed for clarity;

Fig. 2 is a plan view of the immersion heater head and control with the main moulding of the control unit removed;

Figs. 3 and 4 are further perspective views of the head and control unit;

Fig. 5 is an elevation, on an enlarged scale, of the system of Fig. 2 and viewed in the direction of the arrow shown in that figure,-

Fig. 6 is a schematic side elevation of the control unit and immersion heater;

Fig. 7 is a graph illustrating the operation of the control unit and immersion heater;

Fig. 8 is a perspective view of the rear of a control according to a second embodiment of the invention;

Fig. 9 is a perspective view of the front of the control of Fig. 8;

Fig. 10 is a plan view of the control of Fig. 8 with its cover removed to show the internal components; Fig. 11 is an exploded perspective view of the control of Fig. 8; and

Fig. 12 is an exploded sectional view of part of the control of Fig. 8.

Turning first to Fig. l there is illustrated an immersion heater of which only the head 1 and certain associated parts are shown, together with certain parts of the control unit. Projecting from the heater head 1 are the cold leads 2 and 3 of the heater element and fixing studs 4,5 and 6. The head is brazed to the element (not shown) in the usual manner.

The control unit has a main moulding 7 formed of thermoplastics material. It has apertures 8, 9 and 10 for receiving studs 4, 5 and 6 respectively and three further apertures 11, 12 and 13 for receiving pins 14, 15 and 16 which form the neutral, earth and line connections of a standard plug connector' (see Figs. 3 and 4) . A further aperture 17 is provided through which passes adjustment spindle 18 whose function will be discussed in detail below. The main moulding 7 co- operates with base portion 18 (shown in Figs. 2 to 5) to close the control unit. The control unit is attached to the heater head by means of screws or bolts which pass through apertures 8, 9 and 10 and are received in threaded bores in studs 4, 5 and 6. The internal components of the apparatus will now be described. From Fig. 4 it may be seen that pin 16 abuts a contact on conducting strip 20 which forms a

connection between it and cold lead 2. The strip is flexible and is biased away'from pin 16 by means of a spring 21. The strip is held against the terminal by means of a push rod 22 formed of low melting point plastics material. The rod 22 passes through a hole in base portion 18 and abuts a convex portion 23 of the heater head. On the opposite side of this portion of the head is mounted the hot return. The purpose of this arrangement is to provide a back-up protection system to disable the control unit in the event that it becomes seriously overheated. Should this occur, the push rod 22 will be seriously distorted or melted by the heat which will allow spring 21 to move strip 20 away from terminal 16, thereby disconnecting the line supply from the element.

The immersion heater and control unit assembly are both earthed by means of pin 15 which is connected via a conducting strip (not shown) to one of the studs 4, 5 or 6. Neutral pin 14 is connected to cold lead 3 of the immersion heater via a thermally actuated switch assembly 30. This assembly is actuated by a creep bimetal 34 which is attached at one end 34' to the heater head at or adjacent to the convex portion 23. The precise position of attachment may be varied; attaching it directly to convex portion 23 will lead to the assembly 30 being controlled almost entirely by the heat of the element via the hot return, whereas moving it further away will allow the temperature of water touching the other side of the heater head to have some influence on the operation.

The bimetal 34 is arranged such that its free end moves gradually away from the head 1 as it heats up. Connected to the free end of the bimetal is a push rod 33 formed of an insulating material such as plastics.

It is riveted at one end to the bimetal and at the other end to a microswitch arm 32 and microswitch carrier 31,

the joined ends of which are free to move with the push rod 33 and bimetal 34.

The opposite end of the microswitch carrier 31 is provided with an aperture which provides an interference fit around neutral pin 14, thereby supporting it and providing an electrical connection. The microswitch carrier 31 is formed of metal which is sufficiently flexible to allow the opposite end to be moved by the push rod as previously described. In the centre of the microswitch carrier 31 there is provided a tongue 35 which is only connected to the remainder of the carrier at a small area near the neutral pin. Thus, the tongue 35 is free to flex independently of the remaining portion of the carrier. Arranged towards the free end of the tongue is a hole 36 one edge 36' of which forms a knife edge pivot for the microswitch arm 32.

Abutting only a central portion of the tongue 35 is one end of calibration screw 37 which is threadedly and axially received within adjustment spindle 18. The arrangement is such that relative rotation of the adjustment spindle 18 and calibration screw 37 serves to vary their combined length. The adjustment spindle is provided with a helical portion 38 which is received within a corresponding portion of the main moulding so that the rotation of the adjustment spindle relative to the main moulding causes the spindle and calibration screw to move back and forth together. As the calibration screw 37 abuts the tongue portion of microswitch carrier 31 this causes the tongue to move in a corresponding manner, thereby moving the pivot formed by the edge 36' of hole 36 towards or away from the bimetal 34.

As discussed previously, push rod 33 is connected to microswitch arm 32 as well as microswitch carrier 31. The arrangement is such that the microswitch arm and the microswitch carrier lie generally parallel to each other. The microswitch arm is also formed of a flexible

metal and is shorter than the microswitch carrier so as not to foul neutral pin 14. ^* It is provided at its free end with an electrical contact 39 which cooperates with a further, fixed, contact 40 which is in electrical connection with cold lead 3 via conducting strip. The microswitch arm 32 is free to move towards or away from microswitch carrier 31 in order to make or break electrical connection between contacts 39 and 40.

Microswitch arm 32 itself has a tongue 41 in its central region which is connected to the remaining portion of the microswitch arm by a small region adjacent contact 39. The free end of the tongue is adapted to locate against edge 36' of hole 36 and pivot thereagainst. The arrangement is such that tongue 41 is in compression and tongue 35 is in tension. In combination the microswitch arm 32 and microswitch carrier 31 form an over-centre mechanism. Thus, when the free end of the bimetal 34 moves away from the head l it causes push rod 33 to move the joined ends of the microswitch arm and microswitch carrier to which it is attached in the same direction. When they reach a certain point relative to the position of the pivot formed by edge 36' of hole 36, the over-centre mechanism operates by snap action to move contact 39 away from contact 40.

As discussed above, the position of the pivot point is varied by the use of adjustment spindle 18. In this way, the distance which bimetal 34 must move in order to actuate the mechanism may be varied. The distance moved by the end of the bimetal is, of course, dependent upon its temperature and therefore turning adjustment spindle 18 has the effect of varying temperature at which the contacts are disconnected from each other. Movement of the end of bimetal 34 back towards the head 1 which will occur as the bimetal cools down will, in turn, cause the contacts 39 and 40 to close thereby reconnecting neutral pin 14 to the cold lead.3.

The operation of the immersion heater and control unit will now be briefly described in the context of an electric water heating jug in which they may be mounted in a conventional manner. The adjustment spindle 18 will be arranged to be accessible to the user via an opening in the outer shell of the jug. The jug is connected to the electric mains supply using a conventional plug and lead.

In order to boil the kettle it is necessary to turn adjustment spindle 13 anti-clockwise as far as possible in order to move the pivot point formed by the edge 36' of hole 36 as far as possible away from the heater head l. With this setting the water will reach boiling point and continue to boil since contacts 39 and 40 will remain closed under normal boiling conditions. However, should the kettle boil dry, or be switched on when dry, the head 1 will start to overheat and at a certain temperature (for example 135"C) the movement of bimetal 34 will be sufficient to cause the over-centre mechanism to operate thereby disconnecting the heater. In the event that this means of protection fails, and the head continues to heat up, pin 22 will melt and spring 21 will move strip 20 away from terminal 16, thereby disconnecting the line supply from the element. Thus, in this mode, the water heating jug operates substantially in the conventional manner.

When it is desired to keep the water within the jug simmering, or at a lower constant temperature, adjustment spindle 18 is turned clockwise to an appropriate position. Assuming that it is desired to cause the water to simmer at between 80° and 90 ^β C (for example for use in coffee making) the adjustment spindle is set accordingly and the jug is switched on. The water will rise in temperature and eventually stabilise within the desired range. In fact, since the heater head tends to increase in temperature more quickly than the water within the jug, it is likely that the

microswitch will disconnect the element briefly one or more times before the desired temperature is reached. This will cause a very slight delay in the time taken for the water to heat up, and if this is likely to cause a problem, the user may simply turn the adjustment spindle to the maximum position and then return it to the lower, simmering position when the water is at the desired temperature.

Fig. 7 illustrates the temperatures of the water and the hot return when water is heated up in the simmer mode. It will be noted that the thermally operated switch assembly has been adjusted to break connection between contacts 39 and 40 when the hot return reaches 100 ^β C and to remake connection when temperature of the hot return reduces to 80 ^β C. It will also be noted that the first time the element reached 100 ^β C, the water temperature has not yet reached the desired temperature of 90°C. However, subsequently the water temperature oscillates between 80 and 90" as desired. Because the water has a much greater thermal capacity than the heater element, the water temperature varies by only 10 ^β C, whereas there is a 20 ^β C temperature differential between the break and remake temperatures of the control apparatus. Thus it will be seen that for a given temperature differential between the break and remake temperature of the switching apparatus, by using the temperature of the head close to the hot return, rather than the temperature of the water to control it, a considerably more consistent water temperature may be achieved.

With a switch differential of 10 ^β C, it is envisaged that the water temperature might oscillate between a 5 ^β C differential. For example, if the upper and lower hot return limits of Figure 7 were replaced by 95 ^β C and 105 ^β C, it is envisaged that a water temperature oscillating between 95°C and slightly below 100°C might be provided.

A second embodiment of the invention is illustrated in Figures 8 to 12. As may'be seen from these figures, the external configuration of this control is generally similar to that of the commercially available Strix R32 control which is widely used in electric water heating jugs and kettles. Thus, the control of this embodiment may be substituted for an R32 in known designs of jugs and kettles with comparatively little modification being required to the vessel. As may be seen in Figure 8, which illustrates the rear of the control 50, apertures 51, 52 and 53 are provided for receiving the mounting studs of a typical immersion heater. Neutral 54, earth 55 and line 56 pins project from the rear of the control in the standard configuration for connection to a normal socket assembly. In the upper part of the control there are provided two terminals 57 and 58 which permit connection to an external steam operated control, and a control knob 9 whose function will be described below. The opposite side of the control is illustrated in Figure 9. Here, it may be seen that the body of the control is formed from a main moulding 61 and a cover 63. The cover is stepped midway along its length so that the lower part 62 of the cover, which, in use, abuts the heater head is flush with the top of the main moulding 61, and the upper part 63 is recessed. The lower part of the cover has apertures 51', 52' and 53' which are aligned with those on the rear of the control for receiving the heater studs. In addition, apertures 88,89 are provided for reserving the cold tanks of the heater. Mounted on the face of the lower cover part is a disk shaped bimetal 64 which, in use, is held against a projecting portion of the heater head in order to provide good thermal contact therewith. The bimetal is arranged to open a set of contacts located within the control by removal of a small push rod (not shown) to disconnect the supply current from the heater in the

event of overheating, for example as a result of a vessel being switched on- whilst dry. The provision of such a "dry switch on" (DSO) bimetal is well known in the art. Directly above the DSO bimetal is a thermal fuse in the form of a meltable pin 65. As the control is clamped against a heater head, this pin is pressed into the body of the control, against the force of a biasing spring, and thereby holds a set of contacts closed. In the ev^nt of serious overheating, the pin will melt and allow these contacts to open, and this disconnects the supply of current from the heater. It will be appreciated that this a one-shot protection arrangement, and therefore it is intended as a final backup in the unlikely event that the DSO bimetal fails.

The upper stud receiving opening of 51' in cover 62 is enlarged in order to accommodate one end of a creep bimetal 66 which is located around a copper collar 68. The collar 68 is aligned with aperture 51 in the main moulding such that when the control 8 is mounted to heater head, the collar surrounds the upper stud of the heater and is pressed against the heater head. Also within aperture 51 are provided two projections 69 which are formed integrally with the main moulding 61. They serve to locate and secure the bimetal 66 and the collar 68.

The internal arrangement of components is illustrated in Figures 10 and 11. It will be noted that the arrangement of components in the lower part of the control is similar to that found in the R32 and therefore only a brief summary is included herein.

Leading from the earth pin 55, a conductive strip 70 extends towards the stud receiving aperture 53. Its distal end is provided with a screw receiving hole 53"so that when the control is mounted to a heater head, the conductive strip 70 is clamped against the respective heater stud by a mounting screw, thereby providing a

secure earth connection.

A further conductive sέrip 71 which is in the form of a leaf spring is connected to live terminal 56. The distal end of this strip is provided with a silvered contact 72 which is biased upwardly by the strip against a further contact 73 located on the lower side of a rigid conductive strip 74. This strip is formed integrally with fixed contact carrier 75 which is part of the thermostat arrangement 90 which will be discussed below.

The strip 71 has a portion 71' on which the end of the push rod associated with the DSO bimetal may abut. Normally the biasing of this strip maintains contacts 72 and 73 closed, but in the event of over heating, the DSO bimetal will depress the push rod against portion 71' and thereby open the contacts 72,73.

Returning from the thermostat arrangement is a further conductive leaf spring 77 having a cold tail contact portion 78 which is aligned with cold tail aperture 88 so that in use the cold tail contact 78 is biased against the respective cold tail of a heater.

A further conductive strip 79 is connected neutral terminal 54 and has a silvered contact 80 towards its distal end. This is biased upwardly against a further contact 81 on conductive leaf spring 82. The central part of the leaf spring 82 is connected to main moulding 61 by means of pips 83 and its distal end forms the second cold tail contact 84 which is biased upwardly in alignment with cold tail aperture 89. Thus the strip 79 and leaf spring 82 form the connection between the neutral pin and the second cold tail of the heater.

Contacts 80 and 81 form part of the one shot protection system of the control. A projection from the spring (not shown) which biases meltable pin 65 extends underneath leaf spring 82 such that when the spring is extended, conductor 82 is lifted away from conductor 79. Thus, unless the spring is compressed by pressing

meltable pin 65 into its aperturewhich will occur when the control is mounted to a ^" heater head, contacts 80 and 81 will remain open. It will be appreciated that if the pin 65 melts, as a result of serious overheating, this spring will be released and contacts 80 and 81 will be allowed to open, thereby permanently disconnecting a supply of current from the heater.

The assembly of the thermostat arrangement 90 is best understood from Figures 11 and 12. As discussed previously, the -eree bimetal 66 is mounted on collar 68. Since, in use, the collar is held around the upper stud of a heater and pressed against the heater head, this collar provides good thermal conductivity between the heater and the bimetal. In order to provide good thermal conductivity along its length, the bimetal may comprise a third payer of a high conductivity metal such as copper, thereby forming a "trimetal". At the distal end of the bimetal 64, is located a push rod 92 which passes through an opening 93 in the upper part of cover 63. The other end of the push rod is received within an opening in a microswitch 94 located within the main moulding of the device. The opposite end of the microswitch 94 is attached to the main moulding 61 by means of a metal rivet 95 which passes through the cover and the main moulding. That end is also attached to an annular portion 91 of conductive strip 77 and thus the microswitch is directly connected to cold tail contact 78. A further portion of the conductive strip 77 extends beyond the rivet and into an opening 96 in the main moulding to form steam control terminal 58.

The rivet also passes through fixed contact carrier 75 and a ceramic spacer 97 which insulates the contact carrier 75 from the microswitch 94. As discussed previously, one end of the contact carrier 75 leads, via the DSO contacts 72,73 to the line terminal 56. Two portions of the fixed contact carrier extend beyond the rivet, one of hese 98 is received within opening 99 in

the main body and forms the second steam control terminal 57 and the other portion extends in the same direction as the microswitch and has on its lower face a silvered contact 100 which cooperates with a contact 101 on the microswitch. It will be appreciated from the foregoing that contacts 100 and 101 control the supply of current from line terminal 56 to cold tail contact 78.

The microswitch 94 is formed from a single conductive strip which is folded at its distal end to form two parallel parts: 102 which is held in place by the rivet, and 103 on which the movable contact 101 is mounted. Tongues 104,105 are formed in parts 102 and 103 respectively. Tongue 105, which is in compression, is engaged with tongue 104, thereby holding tongue 104 in tension. The arrangement is such that if a pivot point is provided behind tongue 104 and the upper part of the microswitch is moved in the direction of the pivot point, whilst the pivot point prevents movement of tongue 104, at a certain point the movable contact 101 will be forced to snap away from fixed contact 100.

The movement of the upper part of the microswitch is caused by bending of creep bimetal 66 acting via push rod 92. The pivot point is provided by the end of a grub screw 106 which is threadedly received within an insert 107 in the main moulding. The distal end of the grub screw is tightly threadedly received within the adjustment spindle 59' which forms part of control knob 59. By rotating the control knob, the grub screw is caused to move towards or away from the microswitch 102, thereby varying the distance which the creep bimetal 60 must move in order to cause the contacts 100,101 to open in the manner previously described.

In use, the control 80 will be incorperated into an electrical water heating kettle or jug in the known manner by clamping it against the head of an immersion heater. A seal will be provided around the opening

through which the heater is mounted in order to prevent leakage of water.

When the jug or kettle is in use, as the water temperature increases, so will the temperature of the heater head and this heat will be conducted to the creep bimetal 60 via the upper heater stud and the collar 68. As the bimetal increases in temperature, its upper end will bend towards the main moulding 61 and will, via the push rod 92, push the outer parts 102,103 of the microswitch relative to the central tongues 104,105 which are set in position by the grub screw 106. As the temperature increases, the bimetal will bend further until the microswitch moves over centre, causing contact 101 to snap away from contact 100 and thereby disconnect the supply of current to the heater. The user is able to vary the temperature at which this occurs by turning adjustment spindle 59' in order to move the position of the grub screw.

After the current is disconnected the water will start to cool down, which will cause the bimetal to straighten to the point where the contacts 100 and 101 snap closed again, and then the heater will be reenergised. The heater will continue to cycle on and off in this manner, thereby maintaining the water at the desired temperature.

The position of the grub screw 106 relative to the adjustment spindle 59' may be preset when the vessel is manufactured in order to give a desired range of available temperature settings. It is envisaged that the maximum setting would be one which would allow a rolling boil.

It is also possible to connect a steam operated control across terminals 57 and 58. Such a control would provide a non-cycling switch in parallel to the thermostat arrangement 90. In this way, the jug or kettle could be set first to boil water and then to simmer or maintain the water at a lower temperature.

This may be particularly useful in areas where the available water should be boiled before it is drunk.

In the event of overheating, the DSO bimetal will operate in the well known manner. In the event that this fails, the thermal fuse arrangement will permanently disable the control, again in a well known manner.