Liquid Heating Vessels This invention relates to liquid heating vessels and to sub-assemblies therefor. It relates particularly, although not necessarily exclusively, to vessels and subassemblies which may be produced at a lower cost compared to conventional products without sacrificing safety performance. Liquid heating vessels used to boil water are commonly known as jugs or kettles. A polypropylene moulded type jug or kettle is commonly built as follows. An outer vessel wall with a lid forms the sides and top of the vessel. A heater plate having a heating element mounted to its underside forms some or all of the base of the vessel. The heater plate is attached to a thermally sensitive control unit such as one of the Applicant's widely used U18 series of control units. The control unit provides electrical and thermal functionality, such as switching off power to the element when water in the vessel boils or when the element begins to overheat. Additionally such control units permit a 360 degree cordless electrical connection with a power base, enabling the jug to be conveniently lifted and replaced onto the base in any angular orientation.

A significant proportion of the cost of producing such appliances is represented by the metal heater plate and heating element. The heater plate typically consists of two layers. The top layer is made of stainless steel, with a typical thickness of 0.4 or 0.5mm and is in contact with the water. The lower layer is made of aluminium and acts as a heat diffuser. The thickness of this layer is typically 1.5 to 1.8 mm.

The heating element is made from a tube between 10mm and 12.5mm diameter, and filled with MgO insulating powder, and a centrally disposed heating coil. The circular section is then compacted to a trapezoid shape. This increases the density of the MgO powder from 2.2g/cm3 to 3 g/cm3. The length of the heater tube is typically 285mm The larger flat of the heater trapezoid is brazed to the heat diffuser. The tube is generally formed into a circular arc, and the control unit with its heat sensors is mounted within the arc. Although the material cost of such heaters could theoretically be reduced by reducing the thickness of the heater plate and diffuser plate, in conventional designs this would give rise to certain problems. For example the reduced mass of the heater would mean that if it were switched on dry (i.e. with no water in the vessel) its rate of temperature rise would be increased for a given element power and this would therefore require any overheat detection sensor to respond more quickly to avoid serious overheating.

Reduced thickness of the heater and diffuser plates would also cause them to be more flexible and to have increased manufacturing tolerances. One impact of this is that contact between an overheat sensor and the diffuser plate would be made less reliable, exacerbating the problem outlined above by increasing the time for the sensor to respond to overheating. It would also run the risk of insufficient electrical contact between a control unit attached to the heater and a cordless electrical base and also of there being an unacceptable gap opening up between a base moulding attached to the control unit (and so to the heater) and a main body, particularly in a metal kettle.

When viewed from a first aspect the present invention provides a liquid heating vessel comprising:

a liquid receiving chamber;

a metal heater plate closing an opening in the base of the chamber;

a heating element in good thermal contact with the heater plate;

a control unit attached to the heater plate and arranged to sense an overheating of the heating element; and

a support member attached to said control unit and bearing on a peripheral region of said heater plate so as to apply a tension through the control unit which acts on the heater plate in a direction away from the interior of the liquid receiving chamber.

Thus it will be seen by those skilled in the art that in accordance with the invention the control unit and support member assembly act to place a tensile load on the heater plate. This will tend to give it a slight deformation and act to stiffen it. This allows a reduction in thickness of the material of the heater plate whilst maintaining good positional control and hence good performance under all thermal conditions. More specifically it means that the amount of deflection experienced in use by the heater is reduced compared to an unloaded heater plate and this permits better thermal contact between the control unit and the heater plate. It also means that the effect of increased manufacturing tolerance can be mitigated since the dimensions of the loaded heater plate are closer to the actual manufactured dimensions of the plate compared with the effective dimension of a plate deformed in an unpredictable manner due to thinner material distorting more easily.

The heater plate could comprise a single metal layer to which the heating element is mounted directly. In a set of embodiments however the heater plate comprises a heat diffuser bonded to a metal substrate so that the heat diffuser is sandwiched between the element and the substrate. Conveniently in such embodiments the control unit is mounted to the heat diffuser so that the heat diffuser acts to convey heat from the element to the control unit. This assists in the control unit being able to respond to the element overheating as quickly as possible.

The heat diffuser and element are typically provided in the central region of the heater plate which is likely to make the centre of the plate stiffer than the peripheral region thereof. It follows therefore that any deformation of the heater plate is likely to be most pronounced in such embodiments in a zone between the peripheral edge of the heat diffuser and the peripheral part of the heater plate on which the support member bears.

The heater plate could be broadly planar but in a set of embodiments it comprises a dished central region surrounded by an upstanding wall portion. Such a

configuration is well known in the art for providing a degree of stiffness to heater plates and is illustrated for example in WO 96/18331. Preferably the support member bears on a peripheral flange outward of the upstanding wall. The support member recited herein could take the form of an internal frame or web having an appropriate shape to attach to the control unit and to bear on the heater plate. The contact between the support member and the heater plate could be over a continuous ring or could be by means of a plurality of discrete protrusions. In a set of embodiments however the support member comprises a base cover - i.e. a cover which encloses the lower part of the vessel to conceal the heater, control unit etc.

In accordance with the invention the support member is arranged to bear on a peripheral region of the heater plate. It could actually be attached to the heater plate (as would be conventional where the support member comprises a base cover) as well as to the control unit. However in a set of embodiments the support member is attached only to the control unit and bears onto the heater plate to apply a force thereto without being attached to it.

Such an arrangement is novel and inventive in its own right and thus when viewed from a second aspect the invention provides a liquid heating vessel comprising: a liquid receiving chamber;

a metal heater plate closing an opening in the base of the chamber;

a heating element in good thermal contact with the heater plate;

a control unit arranged to sense an overheating of the heating element; and a support member attached to said control unit and bearing on a peripheral region of said heater plate without being attached thereto. As stated previously, the support member may comprise a base cover for the vessel. The control unit may be attached to the heater plate in such a way that the support member applies a tension to the heater plate acting in a direction away from the interior of the liquid receiving chamber. In accordance with either of the foregoing aspects of the invention, in some embodiments having the control unit attached only to the support member may be beneficial in facilitating alignment between the control unit and the heater plate as the control unit is mounted to the heater plate. The support member may be attached to the control unit by any suitable mechanism. Conveniently a snap-fit mechanism is used.

The control unit may be of any appropriate type. In a set of embodiments it comprises a substantially vertical mounting member on which one or more thermally sensitive actuators is mounted. The Applicant has appreciated an advantage of this arrangement in accordance with the features disclosed herein is that any small degree of tilting of the control relative to the heater plate can be accommodated because as a mounting force is applied to the control, the control is able to tilt relative to the heater plate about an axis parallel with the mounting member. The Applicant has also appreciated that this can be achieved with the advantageous use of only two mounting points between the control unit and the heater plate which gives a cost-saving. The control unit may, for example, be as described in WO 2012/164318 with particular reference to Figs. 14 to 25c thereof. In a set of embodiments the heater plate forms an integral part of the liquid receiving chamber. For example the vessel may comprise a stainless steel outer wall with which the heater plate substrate is integrally attached, e.g. by welding. The support member and control unit may then be fitted to the heater plate (e.g. to the heat diffuser if provided) to form a complete vessel.

In another set of embodiments the heater plate is a discrete component which may be fitted to a separate main vessel wall which may be of metal or plastics - e.g. polypropylene. As will be appreciated by those skilled in the art in accordance with such embodiments the heater plate, element, control unit and support member may comprise a self-contained sub-assembly which can simply be fitted into the open end of a main vessel wall to form a low-cost liquid heating vessel which

nonetheless has good reliable, performance. The attachment between such a subassembly and the main vessel wall could be achieved by any suitable mechanism but in a set of embodiments the support member comprises features - e.g. snap-fit features - allowing it to be connected to a downwardly depending skirt from the main vessel wall.

The provision of a heater-control sub-assembly as outlined above is advantageous in its own right as it allows appliance manufactures to produce a wide variety of different appliance designs at a very low cost without having to take into account the complex engineering factors involved in ensuring a reliable thermal

performance. It also reduces the amount of time necessary to design and produce a new appliance design. Thus when viewed from a third aspect the invention provides a sub-assembly for liquid heating vessel comprising:

a metal heater plate; a heating element in good thermal contact with the heater plate;

a control unit attached to the heater plate and arranged to sense an overheating of the heating element; and

a support member attached to said control unit and bearing on a peripheral region of said heater plate so as to apply a tension through the control unit which acts on the heater plate.

The optional and preferred features of the first and second aspects of the invention apply equally to the third aspect of the invention.

In a set of embodiments the sub-assembly comprises a cordless electrical connector permitting an electrical connection to be made to a corresponding cordless base regardless of their relative angular orientation. In a set of embodiments the sub-assembly comprises the cordless base having the corresponding cordless connector part thereon.

The Applicant has further appreciated that the provision of a sub-assembly as described above makes feasible further manufacturing improvements. In particular it has recognised that the sub-assembly can be produced as a single generic item for assembly elsewhere into a wide variety of different vessels, which subsequent assembly can be achieved without the level of precision engineering required to produce the sub-assembly itself. This makes it economically feasible to carry out further refined manufacture of the sub-assembly in a manner which could not easily be replicated at large numbers of appliance manufacturing facilities with lower capabilities which assemble the final vessels.

One example of this is in ensuring that there is a good electrical connection between the cordless connector parts whilst also ensuring that the vessel rests on the cordless base in a stable manner. The Applicant has appreciated that both of these are quite sensitive to the tolerances of the various components. For example for optimum technical performance it has been found that the contact between a cordless connector integrated into a control unit and a base cordless connector part should be maintained within a tolerance of 0 to +0.3mm, an effective tolerance of +/- 0.15 mm. If the separation between the underside of the vessel (defined by the sub-assembly) and the cordless base is insufficient, there will be good electrical connection since the cordless connector parts will form one the point of mutual contact, but there will be a tendency for the vessel to rock on the base as there is effectively only a single point of mutual contact in the centre. On the other hand if the separation is too great the vessel will be stable as it will be in contact with the cordless base around the periphery, but there may be insufficient contact pressure between the cordless connector parts to ensure a reliable electrical connection (the connector part on the vessel is lifted away from that on the base,

In a set of embodiments the sub-assembly comprises a cover moulding, which may be the support member or a separate member, which is arranged to bear on a or the cordless base, said cover moulding having at least one feature on the underside thereof which bears on said cordless base and which is reduced in vertical extent after the cover moulding has been moulded. In accordance with such

arrangements the aforementioned feature can therefore be adjusted to ensure exactly the right separation between the vessel and the base, For example it could be deliberately moulded to be longer than is required and cut, machined, melted etc. to the correct height once the sub-assembly has been fitted together. The feature could take any convenient form such as a peg, mound, foot etc. and more than one such feature can be provided.

In a set of embodiments the metal heater plate is provided with an aperture in which is received a tubular seal member, the support member being arranged to limit the depth to which the tubular seal member can be inserted into the aperture. This allows a simple rigid tubular member to be inserted into the tubular seal member and sealed against the heater plate in order to provide a steam tube - that is a tube providing in the finished vessel a gaseous communication between the upper part of the vessel and a steam switch provided as part of the control unit beneath the heater plate. One advantage of such an arrangement is that it obviates the difficulty of transporting the sub-assemblies if they were to be provided with a pre-fixed steam tube since these tend to project at right angles and extend for a considerable length relative to the dimensions of the heater sub-assembly. An advantage of the tubular seal member is that these are inexpensive to produce as compared to the cost of a moulding tool for moulding a dedicated seal part having a more complex form. ln accordance with all of the foregoing aspects of the invention the pre-loading provided by the arrangements recited may allow the parts thereof to be reduced in thickness as compared to conventional designs, thereby saving on material costs. In a set of embodiments for example the metal heater plate, or the heater plate substrate where a heat diffuser is provided, which in either case is preferably of stainless steel, has a thickness of between 0.2 and 0.3 mm. This compares with a typical value for a conventional heater of 0.4 mm.

In a set of embodiments the heat diffuser, which is preferably of aluminium, has a thickness of between 1.2 mm and 0.7 mm - e.g. between 1.1 mm and 0.8 mm. This compares with a typical value for a conventional heater of 1.4 mm.

The heating element may have a nominal power of at least 1.2 kW, e.g. at least 2 kW.

In conventional heater designs the heating element is arranged in an arcuate (i.e. part-circular) shape around the edge of a circular diffuser plate. In accordance with some embodiments of the invention however the ends of the heating element project inwardly from a central arcuate portion. This gives an advantage that the ends of the element may be located closer to a thermally sensitive overheat actuator - e.g. if a control unit similar to that described in WO 2012/164318 is provided whereby one thermal actuator is located close to the element at the centre of its length and the other actuator is located in the vicinity of the ends of the element. Such an arrangement may serve partially to offset the effect of the cold tails - that is the substantially non-heating conductors which extend into the element tube at its end to facilitate electrical connection with the resistive heating wire proper. The result may be that the actuators are able to respond more quickly to the element overheating. The ends of the element may extend in converging directions - e.g. along a direction tangential to the arcuate portion. Alternatively the ends may extend towards each other before becoming parallel or less rapidly converging - i.e. to give the element a bulbous shape. Allowing thermal actuators to respond more quickly to overheating may allow the element to be reduced in length and/or diameter compared to conventional designs, thereby saving more on material costs. For example in a set of embodiments the heating element comprises an outer tube having a length of between 230 mm and 260 mm. e.g. between 240 mm and 250 mm. This compares with a typical value for a conventional heater of 285 mm. Additionally or alternatively the diameter of the heating tube is between 9 and 11 mm, e.g. 10 mm. This compares with a typical value for a conventional heater of 12 mm. A particular embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 is an overall view of a cordless liquid heating vessel in accordance with the invention;

Fig. 2 is an exploded view of the components making up the main part of the vessel;

Figs. 3 and 4 are underside views of the heating element and control unit attached to the heater plate;

Fig. 5 is a sectional view of the base cover and heater plate before assembly, with the control unit removed for clarity; Fig. 6 is a sectional view of the base cover and heater plate after assembly, with the control unit removed for clarity;

Figs. 7a and 7b are sectional views illustrating, in an exaggerated fashion, deformation of the heater plate;

Fig. 8 is a sectional view showing the assembled components of the heater subassembly;

Figs. 9 and 10 are respective views from above and below of a heater sub- assembly for fitting into a main vessel wall; Fig. 1 1 is a sectional view showing attachment of the sub-assembly of Figs. 9 and 10 to the vessel wall; Fig. 12 is a sectional view showing an intermediate stage of an alternative method of assembly;

Fig. 13 is a view from beneath of a sub-assembly according to another

embodiment;

Figs. 14a and 14b are side views of the sub-assembly of Fig. 13 placed on a cordless base respectively before and after trimming of the moulded feet;

Fig. 15 is a perspective view of the cassette showing an arrangement for fitting a steam tube; and

Fig. 16 is a close up exploded view of the steam tube sealing arrangement.

Fig. 1 shows a liquid heating vessel in accordance with the invention. The vessel comprises a main vessel part 2 and a cordless base 4 which permits a cordless connection with a mains electrical supply by means of an electrical plug 6. The main vessel part 2 comprises a liquid receiving chamber therein defined largely by an outer wall 8, a spout 10 for pouring heated liquid out of the vessel, a handle 12 at the rear for lifting and pouring the vessel and a lid 14 which may be opened for filling the vessel with fresh water.

Fig. 2 shows an exploded view of the main vessel 2 showing particularly the components which form the lower part of the main vessel. These components will be described in greater detail with reference to the later drawings. Starting at the bottom, there may be seen a moulded base cover 16 which is broadly circular in shape with a peripheral upstanding rim 18 on which are defined a number of snap- fit features 20 the purpose of which will be described later. In the centre of the base cover 16 is an aperture 22 which also defines inwardly projecting clip features. Again, these will be described later. The next component up is the control unit 24 which acts to transfer electrical power to the heating element by means of a cordless electrical connector and a number of switch contacts. The control unit also comprises thermally sensitive bimetallic actuators to detect overheating of the element and to disconnect power in such an event and also to detect steam upon boiling. Further operation of the control unit is given in WO 2012/164318.

Above the control unit 24 is the sheathed heating element 26 which is brazed to an aluminium heat diffuser plate 28. Also attached to the diffuser plate 28 are a pair of mounting bosses 30 to which the control unit 24 can be screwed.

Next is the heater plate substrate 32 which is formed from a thin sheet of stainless steel. It may, for example, have a thickness of approximately 0.3mm. The heater plate 32 has a projecting disc-shaped feature at its centre which provides clearance beneath in use for moving parts of the control unit 24. Above the heater plate substrate 32 is a seal 34 which provides a seal between the heater plate 32 and the main vessel wall 8.

Figs. 3 and 4 show a partial assembly of the components shown in Fig. 2. Thus referring to both of these figures there may be seen a sheathed heating element 26 brazed to the heat diffuser 28 which is in turn brazed to the central part of the heater plate substrate 32. The substrate 32 and heat diffuser 28 together form the heater plate. It may be seen that the heating element 26 has a converging U- shape such that the mid portion of its length is arcuate and the ends extend in mutually converging tangential directions. The control unit 24 is attached to the heater plate by a pair of screws (not shown) which are used to screw it against the bosses 30 attached to the heat diffuser 28.

As is described in more detail in WO 2012/164318, the control unit 24 comprises two thermally sensitive bimetallic actuators 34, 36 on an upper face thereof which are therefore held against the underside of the heat diffuser 28 when the control unit 24 is screwed on to it. As maybe seen particularly from Fig. 3, one of the bimetallic actuators 34 is in the close vicinity of the middle, arcuate part of the element 26 whilst the other bimetallic actuator 36 is in the vicinity of the two end arms of the element 26. The convergence of the aforementioned element arms ensures that the net amount of heat received by the actuator 36 is increased compare to a standard, fully arcuate element and allows the actuator 36 to respond to an element overheat situation within a similar order of time to the actuator 34 which is placed close to the middle part of the element. Referring to Fig. 4, it may be seen that the heater plate substrate 32 has a central, inwardly dished portion 32a, a peripheral region 32b which is substantially planar and a downwardly depending skirt portion 32c.

A further feature to be noted is the 360° cordless connector 38 which is an integral part of the control unit 24. In particular it should be noted that there are elongate arcuate recesses 40 spaced around the circumference of the connector part 38, the purpose of which will be explained later.

Fig. 5 shows a cross-sectional view of the heater plate 28, 32 and the element 26. This Figure also shows the base cover moulding 16 including the upstanding side wall 18 and the clip features 20 referred to hereinabove. The central aperture 22 of the base cover may also be seen along with its inwardly projecting clip features 42. These features are arranged so that they engage and cooperate with the slots 40 in the 360° connector portion 38 of the control unit.

Fig. 5 shows the base cover 16 in its pre-assembly state. By contrast, Fig. 6 shows a similar diagram with the base cover 16 clipped to the control unit 24 by means of the cooperating clips 42 and slot 40. It should be noted however that the control unit 24 is omitted from Fig. 6 for clarity. What may be seen, however, by comparing Fig. 6 with Fig. 5 is that the base cover 16 is somewhat deformed as a result of its being pressed up to clip on to the control unit 24. It can be seen that the upstanding wall 18 of the base cover bears on the peripheral downwardly depending wall 32c of the heater plate. Although the upstanding wall 18 is shown as continuous it may equally comprise a plurality of discrete protrusions. There is a reaction force provided by the inherent resilience of the base cover 16 which tends to pull the control unit 24 downwardly. Since the control unit 24 is screwed to the heater plate 28, 32 this gives rise to a tension in the heater plate substrate 32 which tends to cause it to deform slightly in a downward direction, that is in a direction away from the interior of the vessel in use. This can be seen more dramatically by comparing Figs. 7a and 7b which are respective cross-sections of the heater plate substrate 32 in the deformed and undeformed conditions.

As will be appreciated by those skilled in the art, the deformation of the heater plate substrate 32 tends to give it a greater stiffness and therefore less movement in the face of thermal loads. It also tends to give it a more predictable shape i.e. reducing the positional tolerance of the base of the heater plate 28, 32 which ensures that good thermal contact between the heat diffuser 28 and the bimetallic actuators 36, 38 of the control unit is achieved.

Fig. 8 shows a cross-sectional view of the sub-assembly once it has been assembled. Similarly Figures 9 and 10 show views from above and below respectively of the sub-assembly comprising the heater plate 32, base cover 16, control unit 24 (not visible in these drawings) and the seal 34 (mentioned in relation to Fig. 2) which sits on the downwardly depending peripheral wall 32c of the heater plate. The sub-assembly shown in Figs. 9 and 10 is a completely self-contained arrangement and may be thought of as "cassette" in which the heater and control unit may be supplied as a finished package which may be simply clicked in to place in the bottom of a moulded main vessel 8. The result of which is shown in Fig 1 1. It may be seen from here that the clip features 20 of the base cover clip into corresponding slots 44 formed on the inner surface of the main vessel wall moulding 8 the result is an extremely low cost way to manufacture a liquid heating vessel such as a jug or kettle in which the "cassette" takes care of all of the thermal and electrical engineering requirements and all that an appliance manufacturer is required to do is to mould the body of the vessel with the appropriate slots 44 for receiving the "cassette".

An alternative way of assembling the "cassette" shown in Figs. 9 and 10 will now be explained with reference to Fig. 12. In this example, the control unit 24 is not initially screwed to the bosses 30 of the heat diffuser plate but rather it is first clipped into the base cover 16 by means of the mutually cooperating clip and slot features 40, 42. The base cover 16 and control unit 24 may then be offered up to the underside of the heater plate 28, 32 and the control unit screwed to the bosses 30 in order to tighten the attachment, deform the base cover 16 and heater plate 32 and thereby apply the pre-loading discussed hereinabove. Apertures 46 are provided in the base moulding 16 in order to allow access to the screws for attaching the control unit to the heat diffuser.

Fig. 13 shows a "cassette' according to another embodiment of the invention. In this embodiment the base cover moulding 50 is moulded with a pair of protruding feet 52 which are intended to bear on the upper surface of the cordless base 54 as shown in Fig. 14a. As may be observed in Fig. 14a, the feet 52 are initially moulded to protrude further than is required for the cassette (comprising the base cover moulding 50 etc. attached to the heater plate 32) to sit flat on the cordless base 54. Left unchanged this would risk there being too low a contact pressure between the cordless connector parts. However once the cassette is assembled, post-moulding trimming of the feet 52 is carried out to ensure that the separation between the base cover moulding 50 and the cordless base 54 is exactly right, taking into account the cumulative effect of the various tolerances involved. This is shown in Fig. 14b.

It should be appreciated that although this is apparently a simple manufacturing operation, it would be highly counter-intuitive in the context of the dispersed mass production of kettles to perform such individual and precision operations at each factory. However the fact that the cassettes can be produced as a generic item in a single facility for incorporation in many different kettles makes it feasible to set up such processes at the productions facility, thereby allowing high quality, reasonable cost manufacture of a wide variety of vessels. Turning now to Figs. 15 and 16, a further beneficial feature will be described which may be used in association with the other features described herein. Referring to both Figs. 15 and 16, it may be seen that the metal heater plate has an aperture 56 defined in the upper peripheral flange thereof. This might, for example, have a diameter of 9-10 mm. The aperture 56 receives a short section of synthetic rubber tubing 58 which acts as a tubular seal member. The tubular seal member in turn receives the end of a stainless steel tube 60 of diameter 6.5 - 8 mm which acts as a steam tube in the finished vessel. The cassette can thus be produced and shipped with just the tubular seal member 58 inserted into the aperture 56. The steam tube 60 is sealingly fitted during final assembly at the customer's factory by pushing it into the seal 58. This avoids the need to package and ship an awkwardly shaped part which would be produced if the steam tube 60 were to be permanently attached in production of the cassette. On the other hand it is not necessary for either production facility to produce or fit specially shaped seals. It may be seen from Fig. 16 that a ledge 62 is moulded into the base cover moulding to limit the depth to which the seal member 58 can be inserted into the aperture 56.

It will be appreciated by those skilled in the art that many modifications and variations to the embodiment described herein above may be made without departing from the scope of the invention. For example it is not essential to form a "cassette" including the heater plate; the heater plate could be integrally provided on the underside of a metal water vessel wall for example.