GB2472477A

GB2472477A - Thermal control with sub-boil selection mechanism

Info

Publication number: GB2472477A
Application number: GB201000821A
Authority: GB
Inventors: Richard William Lindley; Robert Henry Hadfield
Original assignee: Otter Controls Ltd
Current assignee: Otter Controls Ltd
Priority date: 2009-05-07
Filing date: 2010-01-19
Publication date: 2011-02-09
Also published as: GB0907881D0; WO2010128334A2; GB201000821D0; EP2429355A2; CN102458194A; WO2010128334A3; GB2470053A

Abstract

A thermal control for a liquid heating appliance includes a subassembly that provides selection of a sub-boil mode. A bistable trip lever is selectively coupled to a sub-boil actuator by the subassembly and cooperating cam pins and slots. The subassembly further applies a bias to the trip lever when coupled which reduces the force required by the sub-boil actuator. This allows the sub-boil actuator to be constructed from a bimetal with a lower differential. Also disclosed are a lift-off switch-off mechanism, a selector for variation of the sub-boil temperature, a multistable mode selector, a pivot arrangement to reduce the travel of the control lever, and a thick film heating element.

Description

Thermal Controls

Field of the Invention

[0001] Aspects of the present invention relate to thermal controls in general and in particular, but not exclusively, to thermal controls for corded or cordless liquid heating vessels such as kettles, jugs and other appliances that heat liquid, particularly for food preparation. Other aspects of the invention relate to thick film heaters, particularly but not exclusively for liquid heating vessels.

Background of the Invention

[0002] GB-A-2397438 discloses a thermal control which switches off a liquid heating appliance when that liquid has reached boiling point.

[0003] GB-A-2438244 discloses a thermal control that provides the user with two temperature options -a boiling setting, where the liquid is heated to boiling point, and a sub-boiling setting, where the liquid is heated only to a predetermined temperature below boiling. This function is known in the art as bitemp' (i.e. bi-temperature). With one switch actuator, the user can choose either temperature setting and then manually switch off ahead of the temperature being reached if required.

[0004] GB-A-2439657 discloses a thermal control that automatically reverts to the off state when removed from or replaced onto a cordless base part; this function is known in the art as Lift Off Switch Off' or LOSO.

[0005] The proprietors of the above patents have successfully marketed components (the A12, A14 and A15 series respectively) based on each patent, but it would be advantageous to incorporate the functions of each component within one modular thermal control.

[0006] It would be even more advantageous if the modular thermal control minimised the number of parts.

[0007] JP-A-600 18124 discloses a water heating appliance wherein the water-sensing bimetal control is in close cooperation with the element substrate separate from the aluminium diffuser plate of the heating element, so that the bimetal actuator is more influenced by the water temperature in the appliance and less influenced by the heating means. JP-A60018124 also discloses a water-sensing bimetal control in close association with a sump in the element substrate.

[0008] GB-A-2347271 discloses a method of achieving a forced reset of the bimetal in which the reset mechanism incorporates a spring bias such that the mechanism can be manually pushed further than the state of equilibrium.

[0009] GB-A-2353927 discloses a method of providing the user with the means to vary the temperature at which a bimetal switch actuates.

[0010] GB-A-23 17991 discloses a thick film heating element in which an annulus of heat sink compound is printed under a carrier that retains the periphery of a bimetallic disc. A patch of low resistivity material may be printed over the heating tracks in an area within the annulus, so as to short-circuit the heating tracks and thereby reduce the power density in this area.

[0011] GB-A-2372421 discloses a variable temperature control in which either a variable sub-boil temperature or a boil setting can be chosen, but choosing the boil setting cancels the previous variable temperature selection; hence, the user must re-select the desired sub-boil temperature subsequent to any boil setting being selected.

Statement of the Invention

[0012] According to one aspect of the present invention, there is provided a thermal control wherein the user has the choice of temperature settings and, whichever temperature option is chosen, then the thermal control can be manually switched to the off position or alternatively will revert to the off state when removed from or replaced upon a base part.

The thermal control may be provided in a liquid heating appliance having two or more temperature settings.

[0013] According to another aspect of the invention, there is provided a thermal control for a liquid heating appliance which interacts with a subassembly to provide two or more temperature settings characterised in that the user has the option of manually reverting from the off state to a plurality of on positions and whichever temperature option is chosen the user can manually revert to the off state, or the control automatically reverts to the off position when the chosen temperature is reached. The user may manually revert to the off state prior to the selected temperature being achieved.

[0014] Embodiments of the invention provide a thermal control for a liquid heating appliance, including a tristable subassembly that can be added to the thermal control to enable selection of boil and sub-boil modes. The subassembly relies on the bias of a trip lever spring in the thermal control to achieve a stable off position, without requiring any additional spring in the subassembly. The subassembly includes a mode selection lever that is moveable by a user actuator, such that the subassembly can be manually moved from the boil or sub-boil modes to an off position. The user actuator may have a pivot point displaced beyond the pivot point of the mode selection lever, to reduce the travel of the end of the user actuator. A lift-off switch-off mechanism may be provided by means of a bifurcated spring.

[0015] According to another aspect of the invention there is provided a mechanism within an appliance control assembly that provides the means to supplement the force generated by a bimetal so that a bistable assembly can be activated to switch off an appliance.

Advantageously, this allows a bimetal with a lower natural differential to be selected, which can therefore be manually reset closer to the break temperature of the bimetal.

[0016] According to another aspect of the present invention, there is provided a mechanism within an appliance control assembly that provides the means to force reset a bimetal so that the appliance can be reenergised and means to maintain a desired gap between the bimetal and the part with which the bimetal interacts whilst the appliance is energised. The means to maintain the desired gap may comprise a biasing means, which holds the appliance control assembly in a stable position. The biasing means may additionally supplement the force generated by the bimetal so that a bistable assembly can be activated to switch off an appliance.

[0017] According to another aspect of the invention there is provided a means to modify the heat below a bimetal in an appliance control so that the user has the ability to choose the temperature at which a sub boil control activates.

[0018] According to another aspect of the invention, there is provided a variable temperature thermal control for a liquid heating appliance, the control being actuable to reduce or switch off heating in response to the liquid being heated up to a user-selected temperature threshold, wherein the control is selectively operable in a boil mode in which the control is actuable in response to the liquid being heated up to boiling, and in a sub-boil mode in which the control is actuable in response to the liquid being heated up to a user selected sub-boil temperature, the control comprising a boil/sub-boil selector for user selection between the boil and sub-boil modes, and further comprising a variable temperature selector for user selection of the sub-boil temperature, the boil/sub-boil selector by actuable by the user independently of the variable temperature selector. Advantageously, this allows the user to maintain a preferred sub-boil temperature without the need to reselect this sub-boil temperature subsequent to the boil mode being selected.

[0019] According to another aspect of the invention, there is provided a thick film heating element comprising a thick film heating track printed on an electrically insulated substrate having an area arranged to interface with a snap-acting bimetallic thermal sensor such that a periphery of the sensor is proximate a portion of the heating track, wherein said track portion is of lower resistivity than an adjacent portion of the heating track, such that heating of the periphery of the sensor by the heating track is reduced.

[0020] According to another aspect of the invention there is provided means to identifiy to the user that the sub boil mode is within a temperature band that is close to the temperature at which the sub boil mechanism operated, so that there is no need to reenergise the appliance and/or so that if the appliance does not reenergise when the actuator is pressed then the user knows that the water is at the desired temperature. This means may comprise an arrangement whereby the user is prevented from reenergising the appliance when the temperature of the liquid is within the temperature band. The arrangement may comprise a configuration of a control actuator.

[0021] Embodiments of the invention provide the ability to develop a suite of controls whereby additional parts required are designed to optimise more than one function, with the result that economies of scale are achieved and fewer parts, such as resilient metal parts, are required.

[0022] Preferred embodiments of the invention allow either a preset or user-set sub-boil temperature option that the user can reset quickly so that the sub boil mode can operate within a narrow temperature band.

Brief Description of the Drawings

[0023] There now follows, by way of example only, a detailed description of preferred embodiments of the present invention, with reference to the figures identified below.

Figure 1 is a perspective view of a thermal control based on the Otter A12 series, with a modified trip lever suitable for use in embodiments of the invention.

Figure 2 is an exploded view of a bitemp subassembly in an embodiment of the invention, that can be attached to the thermal control of Figure 1.

Figure 3 is a perspective view of the complete bitemp sub assembly shown in Figure 2, together with a user actuator.

Figure 4 shows a complete assembly of a bitemp thermal control, combining the thermal control of Figure 1 with the bitemp sub assembly and user actuator of Figures 2 and 3.

Figure 4a shows a detail of a sub-boil bimetal mounting arrangement in the control of Figure 4.

Figures 5a, 5b and Sc show the three stable states of the bitemp sub assembly, respectively: off, boil on and sub-boil on.

Figures 6a and 6b show close up views within the subassembly of the relative positions of a trip beam and a flexible arm in the boil and sub boil modes.

Figure 7 is a schematic diagram showing the interrelationship between the user actuator, the mode selection lever, the trip beam and the sub-boil bimetal.

Figure 8a shows an exploded view of an alternative user actuator.

Figure 8b shows an assembled view of the alternative user actuator.

Figure 8c shows the alternative user actuator assembled on the bitemp thermal control.

Figures 9a and 9b show the positions of the alternative actuator in the boil and sub boil modes.

Figure 10 is an exploded view of a thermal control in a further embodiment, incorporating a bifurcated resilient spring to enable a Lift Off Switch Off function.

Figures 11 a to 11 c show the relative positions of the bifurcated spring and a trip lever when the appliance is placed on and removed from a corresponding base part.

Figure 1 2a is a schematic diagram showing an alternative interrelationship between the mode selection lever, adjustment cam spindle and the trip beam.

Figure 12b is an exploded view of a bitemp subassembly including the mode selection lever, adjustment cam spindle and trip beam of Figure 1 2a.

Figure 1 3a shows an exploded view of an alternative user actuator interfacing with a control including the bitemp subassembly of Figure 12.

Figure 1 3b shows the alternative user actuator assembled onto the bitemp thermal control.

Figures 14a and 14b show the positions of the alternative actuator in the boil and sub boil modes.

Figure 15 is a schematic diagram showing the interrelationship between the user actuator, the mode selection lever, the trip beam, the dual function spring and the sub-boil bimetal in a second embodiment.

Figure 16a is an exploded view of the mode selection lever, the trip beam and the dual function spring in the second embodiment.

Figure 1 6b is an assembled view of the mode selection lever, the trip beam and the dual function spring.

Figure 17 is a plan view of a thick film printed element suitable for use with a variable temperature bitemp control.

Figure 18a is an exploded view of variable temperature and bitemp subassemblies.

Figure 1 8b is an underside isometric view of a control mechanism of a variable temperature bitemp control interfacing with specific track segments. For clarity the thermal control and other track parts have not been illustrated.

Detailed Description of the Embodiments

[0024] In the following description, functionally similar parts carry the same reference numerals between different embodiments. Reference is made to the above-mentioned patent publications GB-A-2397438, GB-A-2438244 and GB-A-2439657, which describe the functions of the various control types; the following description will focus on improvements to these control types.

Thermal Control [0025] Figure 1 is a schematic perspective view of a thermal control 1 in a first embodiment. This control is similar to the A12 series from Otter Controls Ltd, which acts as both a dry boil protector and a thermal control 1 for a liquid heating appliance. The thermal control 1 interfaces with the appliance actuator and switches off the appliance automatically when the liquid has reached boiling point. The full function of this control is described in GB-A-2397438. The thermal control 1 includes a trip lever 2 which has bistable on and off positions for respectively closing and opening electrical connections to a heating element.

An over-centre trip lever spring 3 biases the trip lever 2 into either of its stable positions.

The trip lever 2 is moved manually to its on position, and is moved to its off position either manually or automatically by means of a boil sensing bimetal 5 or optionally by a dry boil sensing bimetal 6. The thermal control 1 includes a chassis 4 incorporating mounting points for attaching a sub boil bimetal 40, where the sub boil bimetal 40 is required to be integrated with the control assembly. Variants of the thermal control are suitable for use with mechanical, sheathed, diecast or thick film printed underfloor elements.

[0026] The thermal control 1 of Figure 1 is operable as a thermal control in its own right, but also enables the addition of a subassembly 20 as described below. The control includes attachment features 14 enabling the positioning and engagement of a sub assembly. The attachment features include push-fit or click-fit arrangements for engagement with the sub assembly.

[0027] In this embodiment, the trip lever 2 includes a sub-boil cam pin 10 and a boil cam pin 12, which interact with the subassembly 20 as described below.

Bitemp Subassembly [0028] Figures 2 to 6 show a tn-stable bitemp subassembly 20, for use with the thermal control 1 of Figure 1. The subassembly 20 relies on the resilience of the trip lever spring 3 to achieve its tn-stable states, and therefore does not require its own spring or other resilient means. In this way, the number of parts, particularly resilient metal parts, is reduced. The exploded view of the bitemp subassembly 20 in Figure 2 shows that there are only five component parts, identified below.

i) A mode selection lever 21 which includes an M' shaped slot 22 within which the cam pins 10 and 12 are located so as to interface with the trip lever 2 and enable off, sub boil and boil positions to be chosen. The mode selection lever 21 includes a flexible arm 23 to interface with the trip beam 26 in sub boil mode, and slots 24 for the positioning of the user actuator.

ii) A pivot pin 25 about which the mode selection lever 21 pivots.

iii) A trip beam 26 which acts as a push rod between the sub boil bimetal 40 and the mode selection lever 21.

iv) An adjustment cam spindle 27 for adjusting the gap between the trip beam 26 and the sub boil bimetal 40 of the thermal control 1.

v) A pivot moulding 28 that combines with the mode selection lever 21 to house the trip beam 26, adjustment cam spindle 27 and the pivot pin 25. The pivot moulding 28 ensures that the pivot point of the subassembly 20 is geometrically correct.

[0029] Figure 3 shows the five components assembled together, and the interface between the subassembly 20 and the appliance actuator 30. The actuator 30 may be push or click fitted onto the subassembly 20.

[0030] Figure 4 shows the complete thermal control assembly, including the subassembly and the actuator 30. In this figure, the sub boil bimetal 40 is attached to the chassis 4 of the thermal control 1, by means of a sub boil bimetal mount 42 as shown in Figure 4a. In other embodiments the sub boil bimetal 40 may be attached to the element plate 8, for example as described in W0-A-2007/045812.

[0031] The tn-stable bitemp subassembly 20 acts as an interface between the user and the onloff function of the thermal control 1; the trip beam 26 interacts with the sub boil bimetal and the mode selection lever 21 when the sub boil mode is selected in the subassembly 20.

[0032] Figures 5a, Sb and 5c show how the mode selection lever 21 engages with the trip lever boil and sub boil cam pins 10 and 12. Advantageously the M' shaped slot 22 in the S mode selection lever 21 interfaces with the boil and sub boil cam pins 10 and 12 in such a way that, whichever mode is chosen, the trip lever 2 is moved into the correct position -either on or off In the off position shown in Figure 5a, the cam pins 10 and 12 rest in the upper points of the M-shaped slot 22. When the boil mode is selected as shown in Figure 5b, the sub boil cam pin 10 does not contact the sides of the slot 22, while the boil cam pin 12 is engaged in the bottom right hand end of slot 22. When the sub boil mode is selected as shown in Figure Sc, the boil cam pin 12 does not contact the sides of the slot 22, while the sub-boil cam pin is engaged in the bottom left hand end of the slot 22. Thus, in each position, the mode selection lever 21 is engaged with the trip lever 2.

[0033] The sub boil bimetal 40 will be activated when the sub boil temperature is reached; however, the movement from the sub boil bimetal 40 will only be transferred to the mode selection lever 21 when the trip beam 26 is closely associated with (i.e. close to or in contact with) the flexible arm 23. The interface between the flexible arm 23 and the trip beam 26 is shown in detail in Figures 6a and 6b. In the boil mode shown in Figure 6a, the flexible arm 23 is positioned away from the trip beam 26, so that the mode selection lever 21 cannot be actuated by the sub boil bimetal 40. In the sub-boil mode shown in Figure 6b, the flexible arm 23 is positioned close to or in contact with the trip beam 26, which therefore transfers the movement of the sub boil bimetal 40 to the flexible arm 23, so as to move the trip lever 2 into the off position. The position of the flexible arm 23 can be fine-tuned by the adjustment cam spindle 27, which is shown in the minimum' position in Figures 6a and 6b.

[0034] The security of the tn-stable mechanism is a key requirement for the user. The movement of the actuator 30 must be consistent, particularly when manually turning to the centre off position. In particular, the actuator should move positively into, and be held stably in the off position, rather than being loose in that position.

[0035] It would normally be expected that the tn-stability of the bitemp sub assembly would require a resilient member within the subassembly 20; however in this embodiment the resilience is achieved by the engagement of the subassembly 20 with the trip lever 2 of the main thermal control 1. The force required for the central off position of the subassembly 20 is achieved by the force of the trip lever spring 3, acting on the trip lever 2. When the main trip lever 2 is in the off state, the force from the trip lever spring 3 biases the trip lever 2 upwards and this bias is employed to maintain the position of the cam pins 10, 12 within the M shaped slot 22 of the mode selection lever 21.

[0036] When the boil mode is chosen, the mode selection lever 21 acts on the boil cam pin 12 of the trip lever 2, thereby switching the trip lever 2 to the on position and energising the appliance. When boiling point is reached, the trip lever 2 is sprung back into the off position, which in turn returns the mode selection lever 21 back to the centre off position.

[0037] In sub boil mode the mode selection lever 21 acts on the sub boil cam pin 10 of the trip lever 2, thereby switching the trip lever 2 to the on position to energise the appliance. In this mode the sub boil bimetal is able to act on the trip beam 26 and mode selection lever 21 so that, as the sub boil bimetal 40 reaches its set temperature, it acts upon the trip beam 26 thereby returning the mode selection lever 21 to the centre off position which in turn returns the trip lever 2 to the off position.

[0038] In either of the boil or sub boil modes the user may manually de-energise the appliance by returning the actuator 30 to the centre off position, thereby moving the trip lever 2 to the off position.

[0039] Figure 7 further explains the relationship between the mode selection lever 21, the adjustment cam 27, the trip beam 26 and the sub boil bimetal 40 when the mode selection lever 21 is in the sub boil position. For clarity, the trip lever 2 is not illustrated and the flexible arm 23 is shown extending in the plane of the diagram.

[0040] The sub boil bimetal 40 is shown with solid lines in its cold' position. When the sub boil bimetal 40 has reached its set temperature, it trips to the hot' position (indicated by dotted lines), causing the trip beam 26 to rotate anticlockwise about pivot P1 which in turn causes the mode selection lever 21 to rotate clockwise about pivot P2, into the central off position (indicated by line 90).

[0041] The user will require the appliance to switch off in sub boil mode within a predetermined temperature range. It would be advantageous for the user to be able to re-energise the appliance in sub boil mode without having to wait for the bimetal to reach its natural reset temperature, because the natural reset temperature may be below the temperature desired by the user. For example typically a 1.7 litre plastic jug kettle cools down at a rate of around 10 C a minute when full and around 2°C per minute when filled to around 0.5 litres. Given that the user would expect a temperature band of around 5°C then it would be desirable to be able to reset the appliance within say 5 minutes when full and within say 3 minutes when at 0.5 litres.

[0042] The type of heating element and relationship between the heating means and the position of the bimetal on the element substrate will also influence the reset time. For example, by mounting the bimetal away from the influence of the heating means as disclosed in JP-A-60018 124, then both the break and remake temperature of the bimetal is likely to be less influenced by the heating means. In preferred configurations the break temperature is influenced by both the heating means and the water temperature and the remake temperature is more influenced by the water temperature. In that case the setting of the bimetal blade is likely to be elevated so that nuisance tripping does not occur in the heating mode, which in turn enables the reset temperature to be closer to the temperature at which the bimetal actuates.

[0043] The shape of the bimetal can be configured so that the bimetal interfaces with different parts of the element substrate in the heating and cooling modes. For example if the edges of a concave circular bimetal are in contact with the element pate in the heating mode then when the bimetal actuates and becomes convex then edges will move away from the sub strate and the centre move toward it.

[0044] The degree of movement of the trip beam 26 is critical in ensuring that the sub boil bimetal 40 operates at the required temperature, and is dependent upon the gap G 1 between the trip beam 26 and the bimetal 40 in the cold position. If the gap Gi is too large, then the trip beam 26 will not move sufficiently to activate the tn-stable mechanism. If the gap G 1 is too small, the trip temperature of the bimetal 40 can be affected by the bias exerted by the bistable trip lever spring 3 through the trip beam 26. In addition, the ability to force the sub boil bimetal 40 to reset is dependent upon the gap Gi. If the gap Gi is too large in the cold state, then forced reset of the bimetal 40 in the hot state may not be possible.

[0045] Advantageously, the present embodiment incorporates means to adjust the gap G 1, comprising the adjustment cam spindle 27, arranged to interface with the flexible arm 23.

The adjustment cam spindle 27 can be rotated anti clockwise to deflect the flexible arm 23 towards the trip lever 2, and thereby cause the trip beam 26 to rotate clockwise so reducing the gap Gi. Figure 7 shows this rotation in a mid position. In this way the gap between the sub boil bimetal 40 and the trip beam 26 can be set to an optimum value to achieve one or more of the following: 1) Compensation for mechanism tolerances.

2) Control of the effective range of the sub boil bimetal trip temperature 3) Optimisation of the forced reset of the sub boil bimetal 40.

[0046] Upon completion of the calibration the adjustment cam spindle 27 is locked, thus fixing the flexure of the flexible arm 23. The locking may be achieved by a hot staking method.

Alternative Actuator [0047] Figures 8a to 8c show an alternative user actuator 30, which reduces the actuator travel when the boil or sub boil mode is chosen. A pivot attachment 32 is connected to the mode selection lever 21 of the bitemp subassembly 20. The actuator 30 pivots about a point P3 on the pivot moulding 28 and the ends of the pivot attachment 32 are located slidably within a slot 34 in the actuator 30.

[0048] Figures 9a and 9b show the travel required at the user end of the actuator 30 for the boil and sub boil modes respectively. The degree of travel is less than that of the user actuator 30 in the embodiment of Figures 2 to 7, since the pivot point P3 is further away from the user end of the actuator than the pivot pin of the mode selection lever 21, so that the angle of travel of the actuator is less than that of the mode selection lever 21.

Lift Off Switch Off [0049] The embodiment shown in Figures 10 and ha to lic is a development of the previous embodiments to include a Lift Off Switch Off function. The control 1 includes a bifurcated resilient spring which interfaces with a lift off switch off cam in a similar manner to that described in GB 2439657, to prevent the trip lever 2 reaching its on position when the appliance is removed from a corresponding base part. However, the integration of the bitemp subassembly 20 with the trip lever 2 spring in the above embodiments brings new problems that cannot be solved by the resilient spring design put forward in GB2439657.

[0050] The present embodiment incorporates a resilient spring 46 which is bifurcated to enable a degree of lateral play in the spring. The bifurcated spring 46 abuts against a pair of shoulders 48 on the trip lever 2. The gap between the shoulders 48 and the bifurcations of the spring 46 avoids interference with the trip beam 26.

[0051] Figure 11 a shows the position of the bifurcated spring 46 when the appliance is on its base and the trip lever 2 is in the off position. Figure ha shows the position of the bifurcated spring 46 when the appliance is on its base and the trip lever 2 is in the on position: the upwardly turned ends of the bifurcated spring 46 project past the shoulders 48 and do not prevent the trip lever 2 from moving into the on position. When the appliance is removed from the base part, the ends of the resilient spring 46 are moved towards the shoulders 48 by the LOSO cam 9, thus applying an upward force to the trip lever 2 and preventing it from reaching the on position. The bifurcated shape of the resilient spring 46 balances the upward force of the trip lever 2 when the appliance is removed from base, ensuring that the tn-stable mechanism is not subjected to uneven forces on either side of the trip lever 2. In turn this prevents twisting of the resilient spring 46 at the point where the resilient spring interacts with the LOSO cam 9.

Alternative Bitemp Subassembly [0052] Figure 12a shows a schematic view of a bitemp subassembly 20 which incorporates an alternative means to adjust the gap G 1. This alternative means comprises an adjustment cam spindle 27, arranged to interface directly with the trip beam 26. The adjustment cam spindle 27 can be rotated anti clockwise to cause the trip beam 26 to rotate clockwise so reducing the gap Gi. Figure 12a shows this rotation in a mid position.

[0053] The trip beam 26 includes a flat portion at the interface with the adjustment cam spindle 27. The gap between the sub boil bimetal 40 and the trip beam 26 can be set to an optimum value to achieve one or more of the following: 1) Compensation for mechanism tolerances.

[0054] Upon completion of the calibration the adjustment cam spindle 27 is locked. The locking may be achieved by a hot staking method with the embodiment as illustrated in Figure 1 2b incorporating hot stake serrations 70 positioned at the end of the cam spindle housing 29 to facilitate the hot staking process.

[0055] Figures 13a, 13b and 13c show an alternative user actuator 30 which further reduces the actuator travel when the boil or sub boil mode is chosen. The apertures 33 at one end of the switch link 35 are connected to the mode selection lever 21 of the bitemp subassembly at the pivots P4. The other end of the switch link 35 includes a pivot PS which interfaces with the hooked attachment 36 of the appliance actuator 30. The actuator 30 is positioned through the appliance cover 80 with the actuator apertures 33 interfacing with the pivot points P6. This arrangement significantly reduces the travel of the actuator, with the double pivot action of the actuator 30 and switch link 35 ensuring that the switch mechanism acts in a similar manner to the bitemp control: this is up for sub boil mode and down for boil mode.

[0056] It is envisaged that an alternative pivoted switch mechanism could be employed that reverses the direction of the switch mechanism so that it is up for the boil mode and down for sub boil mode.

[0057] It is also envisaged that the any one of the user actuator mechanism embodiments could be used with any one of the bitemp subassemblies. Advantageously, different user actuator mechanisms and bitemp subassemblies may be interchangeable.

Optimisation of break and remake temperatures [0058] It has previously been stated that it is important for the user to be able to reset the sub boil bimetal within an acceptable time and/or temperature range and it has been shown how the gap Gi can be controlled by the use of the adjustable cam spindle 27 to ensure that the bimetal operates at the correct temperature. In addition there are other areas that can be addressed in order to improve the reset times.

[0059] First there is the natural differential of the bimetal the blade (i.e. the difference between the break and remake temperature); the narrower the differential the quicker the bimetal will naturally reset.

[0060] Second, there is the ability to force reset the blade; however, ideally, this should be achieved without compromising the gap G 1.

[0061] It is known that there is a relationship between the natural differential of a bimetal blade and the force generated when the bimetal is activated. Generally the lower the differential, the lower the force and in some cases the differential of the bimetal has to be increased in order that there is sufficient force to activate the over centre control mechanism of a thermal control. Therefore it would be desirable if the force required to overcome the bias of the over centre mechanism on which the bimetal is acting is minimised.

[0062] In a second embodiment of the present invention a spring acts as a bias to reduce the force required so that lower differential bimetals can be incorporated into the control assembly. The spring may also act as a return spring such that the bitemp mechanism, such as the trip beam 26 and/or the user actuator 30, returns to a state of equilibrium after a forced reset of the bimetal. Hence, the same spring may have a dual function, although alternatively separate springs or other biasing means may be used for each function.

[0063] Figure 15 shows a schematic illustration of the second embodiment in which the spring 60 is positioned above the trip beam 26. The spring 60 is deflected by the trip beam 26 when the actuator 30 is set to the On position 91 in sub boil mode. Deflecting the spring causes a biasing force Fl to act on the trip beam 26 tending to rotate the beam in an anti-clockwise direction thus enabling the use of a lower power (differential) bimetal blade 40.

The position of the spring 60 that would exert force F 1 is as illustrated in Figure 15 by the spring 60 with the solid line.

[0064] Calibration would take place after the control 1 has been assembled and the mode selection lever 21 is placed in the sub boil On mode position 91; at which time, prior to the calibration of the gap Gi (when there is no gap between the trip beam 26 and the sub boil bimetal 40) it is expected that the spring 60 will exert little or no force on the trip beam. The cam 27 will then be adjusted to achieve the optimum gap Gi which in turn will increase the value of F 1. Fl will then be measured and if necessary, when G 1 is set, the value of F 1 may be increased or decreased by modifying the height of the dimple 61 on the spring 60 that acts on the trip beam 26. The dimple 61 height may be adjusted individually within each control or preferably by modifying the tooling, on a statistical batch basis, during production. It is expected that there will be tolerance issues to be considered; however, as an example in its simplest terms, if the force required to activate the over centre mechanism of the control 1 is 500 grams and the active force of the bimetal is 300 grams then the spring will need to exert a minimum force (Fl) of 200 grams on the trip beam.

[0065] Once the gap Gl is set the bitemp control will be in a stable state (equilibrium) with the spring 60 holding the trip beam 26 against the adjustment cam spindle 27.

[0066] A forced reset may then be achieved in the appliance by moving the user actuator 30 to position 92 enabling the trip beam 26 to be rotated further than the state of equilibrium and thus applying additional force onto the bimetal blade 40. In doing so the spring 60 will be extended further (as illustrated by the spring with the dotted lines in Figure 15) and subsequently the biasing force generated by the spring 60 will be increased to F2.

[0067] Once the user has removed the pressure on the actuator the spring 60 will cause the control mechanism to return to the state of equilibrium at which stage the force Fl will take up any slack in the mechanism, and in doing so will create and hold a consistent On position 91 for the user actuator. It will be necessary to ensure that the spring 60 cannot apply a greater force than that required to activate the over centre mechanism. Given the above example then this maximum force F2 at the extreme of the trip beam 26 movement would need to less than 500 grams.

[0068] In the embodiment shown in Figures 1 6a and 1 6b the spring 60 is attached to a retention feature 65 on the pivot moulding 28 but in further embodiments it is envisaged that other spring types and attachment methods may be used.

[0069] It is also expected that other methods of calibrating the relationship between Gi and F 1 may be implemented.

[0070] Some embodiments may not require both the force reduction and forced reset functions in which case the spring 60 can be included so as to provide either one or other of the functions.

[0071] The appliance may include one or more indicator light(s) to show the user which function has been chosen as detailed in patent application PCT/GBO8/002404.

[0072] It will also be possible to add additional mechanisms to indicate that the water is at the required sub boil temperature. However it is expected that, with the rapid reset function described above, it will be understood by the user that if the appliance cannot be reset in the sub boil mode, then this indicates that the water is at the required temperature.

[0073] GB-A-2354927 puts forward a control system that relies on modifying the heat input below a sub boil bimetal so that the user can choose the temperature at which the water is controlled. This is achieved in one embodiment by positioning the controlling bimetal in proximity to a thick film printed heater and employing a potentiometer as part of the circuit to vary the power of the printed heating circuit in proximity to the bimetal.

[0074] The following embodiments will rely upon the teachings of GB-A-2354927 whilst seeking to make improvements to the user function; in particular when combined with the new bitemp assemblies embodiments previously disclosed. The following embodiments will focus on bitemp controls that interface with thick film printed elements but do not preclude other heating types, other potentiometers or any combination that achieves the same effect.

[0075] Figure 17 illustrates a thick film printed element suitable for use with a variable temperature bitemp control. The element 100 is manufactured in a standard manner and comprises a stainless steel element plate 8 overprinted with a suitable dielectric (not shown).

The dielectric includes gaps for the mounting points 107 for the bitemp control chassis 4. In this embodiment the chassis 4 would be connected to the plate 8 via a laser welding process but in other embodiments the chassis 4 may be fixed by alternative methods.

[0076] The dielectric may also include a gap 126 below the bimetal so that the bimetal can more readily sense the actual water temperature within the appliance and gap 125 in order that a blade mount can be assembled to the element plate 8.

[0077] The element 100 includes two power connection pads 107 which connect directly onto the control 1. There are two main heating tracks 115 and 116 with the potentiometer 101, selector contact pads 102, wiper track 103 and sub boil bimetal heater track 104 connected in parallel with the heating track 116. The element 100 includes specific areas for the bitemp bimetal 40 and 106 for the two overheat protection bimetals 6. In this embodiment the power of the track 104 below the sub boil bimetal 40 can be varied typically between 20 and 80 watts. In other embodiments the power of track 104 may be higher or lower depending on the specific requirements of the application.

[0078] In this embodiment the sub boil bimetal actuator 40 is circular and convex so that the perimeter of the bimetal is positioned in proximity to the sub boil birnetal tracks in the heating mode.

[0079] In this embodiment the tracks 115 and 116 below the overheat protection bimetals 6 include links 108 of lower resistivity material so that the edge parts of the bimetal 6 in contact with the tracks are not subjected to excessive heat and thus prevent early tripping of the bimetals 6. In other embodiments where the bimetals 6 are required to activate earlier then either the links 108 can be omitted or if necessary links of higher resistivity material may be employed.

[0080] Figure 1 8a and 1 8b illustrate the mechanism that enables the sub boil bimetal tracks 104 to be modified. Figure 1 8b is inverted through 180° to illustrate the manner in which the mechanism interfaces with the element 8 in the area of the potentiometer.

[0081] The wiper arm assembly 111 incorporates a bus bar 120 including wiper contacts 117 and 118 which act to movably connect the selector contact pads 102 with the wiper track 103, in doing so connecting the sub boil bimetal track 104 to different parts of the potentiometer track 101 so that the sub boil bimetal track 104 can be increased or decreased as required. In this embodiment only one wiper arm assembly is employed but in other embodiments additional wiper arm assemblies may be incorporated. The bus bar 120 can include at least one additional electrical connector 119 which can act for example as a variable power supply for an alternative function or provide power to some form of indication of the status of the appliance.

[0082] The user actuator (not shown) is attached to the drive actuator 114 which in turn is supported by a moulding 113. The support moulding 113 incorporates click fits (not shown) so that the moulding 113 can be fitted directly onto the bimetal shroud area 7 of a standard thermal control 1. For additional security one end of the support moulding 113 can butt up to the pivot point P3 of the pivot moulding 28.

[0083] The moulding 113 includes a member 110 which in conjunction with the pivot pin 121 acts to support the wiper arm 111 as the said arm 111 moves across the tracks 102 and 103.

[0084] The drive actuator 114 is connected to the wiper arm 111 by a ratchet link 112. The ratchet link is movably connected to the wiper arm via a slot 24 that interfaces with the retention feature 126. The drive selector 114 and ratchet link 112 each incorporate reciprocating gear teeth 122 that act move the ratchet link as the drive actuator is turned.

The detent spring 123 in the support moulding 113 and the series of detent recesses 124 in the ratchet link 112 act to index the wiper arm 111 so that the wiper arm contacts 117 and 118 connect with correct parts of the selector contact pads 102 and the wiper track 103 respectively.

[0085] It may be necessary to electrically isolate the sub boil bimetal blade 40 in which case the sub boil blade mount 42 may be insert moulded into an electrically isolated material such as plastic or ceramic before attaching the blade mount 42 to the element plate 8 or chassis 4. In other embodiments an insulating layer, for example, Kapton may be used to electrically isolate the sub boil bimetal blade.

[0086] It can be seen that the present embodiment can be incorporated into any of the previous embodiments by the use of the pivot moulding 28 and so can benefit from all the bimetal reset and remake functions previously described.

Alternative Embodiments [0087] The present invention is not limited to the above embodiments -for example the thermal control 1 could incorporate more than one sub boil bimetal 40 for different water temperatures. Alternatively the adjustment cam spindle 27 may be adjustable by the user, to allow user choice of water temperature within a preset temperature band.

[0088] All the embodiments described above have a single energisation mode of the appliance for the sub boil mode; however a keep warm mode could also be used, to keep the heated liquid at the desired temperature.

[0089] Additional potentiometers may be employed to power additional functions not associated with the bitemp such as keep warm, lighting, agitation, stirring or pumping.

[0090] Each of the embodiments is suitable for corded and cordless water heating appliances, for example a jug or kettle including the applicant's CS7 360° cordless connector, but are also particularly suitable for on-demand hot water appliances, where pre-set or user requested volumes of water are dispensed by pump or gravity at boil or sub-boil temperatures.

[0091] The embodiments described above are illustrative of rather than limiting to the present invention. Alternative embodiments apparent on reading the above description may nevertheless fall within the scope of the invention.

Claims

Claims 1. A thermal control for a liquid heating appliance, comprising a bistable trip lever having on' and off' positions, and a sub-boil selection mechanism arranged selectively to couple a sub-boil thermal actuator to the bistable trip lever so as to switch the trip lever to the off' position when the liquid is heated to a sub-boil temperature, wherein the sub-boil mechanism is arranged to apply a bias to the trip lever when coupled thereto, so as to reduce the force required by the sub-boil thermal actuator to switch the trip lever to the off position.
2. The thermal control of claim 1, wherein the sub-boil selection mechanism comprises a member contactable by the sub-boil thermal actuator when the liquid is heated to a sub-boil temperature, the member being biased away from the sub-boil thermal actuator.
3. The thermal control of claim 2, wherein the sub-boil thermal actuator is a snap-acting bimetallic actuator, and the member is operable to contact and thereby reset the sub-boil thermal actuator and is biased to a stable position out of contact with the thermal actuator.
4. A thermal control for a liquid heating appliance, comprising a bistable trip lever having on' and off positions, and a sub-boil selection mechanism arranged selectively to couple a sub-boil snap-acting thermal actuator to the bistable trip lever so as to switch the trip lever to the off' position when the liquid is heated to a sub-boil temperature, wherein the sub-boil selection mechanism comprises a member operable to contact and thereby reset the snap-acting thermal actuator, the member being biased to a stable position out of contact with the snap-acting thermal actuator.
5. The thermal control of any preceding claim, wherein the member is user-actuable to reset the thermal actuator when the liquid temperature is below the sub-boil temperature by only a small temperature difference.
6. The thermal control of claim 5, arranged to indicate to a user that the liquid has cooled by less than said small temperature difference.
7. The thermal control of claim 5 or 6, wherein the small temperature difference is 5°C or less.
8. The thermal control of any one of claims 4 to 7, wherein the member is biased so as to reduce the force required by the sub-boil thermal actuator to switch the trip lever to the off position.
9. The thermal control of claim 8, wherein the same biasing means is used to bias the member to said stable position and to reduce the force required by the sub-boil thermal actuator to switch the trip lever to the off position.
10. The thermal control of any preceding claim, wherein the member is pivotable.
11. The thermal control of claim 10, wherein the pivotable member is biased away from the thermal actuator.
12. The thermal control of any one of claims 4 to 11, wherein the member is separated by a gap from the thermal actuator when the sub-boil switch is switched on.
13. The thermal control of claim 12, wherein the gap is adjustable.
14. The thermal control of any preceding claim, operable at a user-selectable temperature threshold, the control having boil and sub-boil modes in which the temperature threshold is respectively at boiling and sub-boiling, the control having a mode selector for user selection of the boil or sub-boil mode, and a variable temperature selector, operable independently of the mode selector, for variation of the sub-boil temperature threshold by the user.
15. A variable temperature thermal control for a liquid heating appliance, the control being operable at a user-selectable temperature threshold, the control having boil and sub-boil modes in which the temperature threshold is respectively at boiling and sub-boiling, the control having a mode selector for user selection of the boil or sub-boil mode, and a variable temperature selector, operable independently of the mode selector, for variation of the sub-boil temperature threshold by the user.
16. The thermal control of claim 15, wherein the mode selector also enables user selection of an off state of the control, to reduce or switch off heating.
17. The thermal control of claims 15 or 16, wherein the variable temperature selector is arranged to vary the heating of a thermal sensor responsive to the temperature of the liquid.
18. The thermal control of claim 17, wherein the variable temperature selector is arranged to vary the heat output of a local heater for heating the thermal sensor.
19. A thermal control for a liquid heating appliance, comprising a bistable trip lever resiliently biased to either one of an off state and an on state, and a multistable heating mode selector manually actuable from an off state to either one of a boil state and a sub boil state, wherein the heating mode selector is coupled to the trip lever such that the heating mode selector is biased to at least one of the states thereof by the trip lever.
20. The control of claim 19, wherein the heating mode selector is biased to the off state thereof by the biasing of the trip lever to the off state thereof.
21. The control of claim 19 or claim 20, wherein the heating mode selector is arranged so that the boil state and the sub boil state are selectable by manual actuation in opposite directions from said off state.
22. The control of claim 21, wherein actuation of the heating mode selector to either of the boil state and the sub boil state causes the trip lever to be moved to the on state.
23. The control of any one of claims 19 to 22, wherein the heating mode selector, when actuated to the sub boil state, is arranged to couple the trip lever to a sub boil sensor such that the trip lever is actuable by the sub boil sensor.
24. The control of claim 23, wherein the sub boil sensor comprises a snap-acting bimetallic actuator, and the control includes means for adjusting a gap between the snap-acting bimetallic actuator and an actuable portion.
25. A thermal control for a liquid heating appliance, comprising a pivotable control lever having a pivot point and a pivotable user actuator having a pivot end and a user actuable end, wherein the pivot point is disposed between the pivot end and the user actuable end.
26. The thermal control of claim 25, wherein the control lever comprises a multistable control selector.
27. The thermal control of claim 25 or 26, wherein the control lever is coupled to a trip lever.
28. A thermal control for a liquid heating appliance, comprising a trip lever and a resilient spring arranged to prevent movement of the trip lever when the appliance is separated from a base, wherein the resilient spring is arranged to provide a balanced force to either side of the trip lever.
29. The thermal control of claim 28, wherein the resilient spring is bifurcated, so as to contact the trip lever at either side of the bifurcation.
30. A thermal control for a liquid heating appliance, comprising means for switching off the appliance when the appliance is separated from a base, and a heating mode selector manually actuable to select a boil state or a sub boil state of the appliance.
31. The control of claim 30, wherein the means for switching off the appliance comprises a trip lever and a moveable member arranged to prevent movement of the trip lever when the appliance is separated from a base, and the heating mode selector includes a portion selectively actuable by a sub boil sensor, wherein said portion passes through an aperture in the moveable member.
32. The control of any preceding claim, wherein the thermal sensing mechanism is mechanical.
33. The control of any preceding claim, wherein the actuating mechanism is mechanical.
34. The control of any preceding claim, wherein the user interface is mechanical.
35. A thick film heating element comprising a thick film heating track printed on an electrically insulated substrate having an area arranged to interface with a snap-acting bimetallic thermal sensor such that a periphery of the sensor is proximate a portion of the heating track, wherein said track portion is of lower resistivity than an adjacent portion of the heating track, such that heating of the periphery of the sensor by the heating track is reduced.
36. The element of claim 35, wherein said localised portion does not extend proximate a central portion of the thermal sensor.
37. The element of claim 35 or 36, wherein the track portion of lower resistivity comprises a link of lower resistivity material connecting discrete adjacent portions of the heating track.
38. The element of claim 35 or 36, wherein the track portion of lower resistivity comprises a portion of lower resistivity material overprinted or underprinted on the heating track.
39. The element of any one of claims 35 to 38, wherein the heating track comprises a plurality of track sections each having a track portion of lower resistivity proximate the periphery of the sensor, wherein said track portions of lower resistivity are electrically interconnected only by said heating track.
40. A thermal control substantially as herein described with reference to and/or as shown in the accompanying drawings.
41. A bitemp subassembly substantially as herein described with reference to and/or as and/or as shown in the accompanying drawings.
42. A thick film heating element substantially as herein described with reference to and/or as and/or as shown in the accompanying drawings.
43. A liquid heating appliance substantially as herein described with reference to and/or as shown in the accompanying drawings.