GB2470053A

GB2470053A - Thermal control for liquid heating appliance.

Info

Publication number: GB2470053A
Application number: GB0907881A
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: 2009-05-07
Publication date: 2010-11-10
Also published as: GB2472477A; EP2429355A2; WO2010128334A2; WO2010128334A3; GB0907881D0; GB201000821D0; CN102458194A

Abstract

A thermal control for a liquid heating appliance includes a tristable subassembly 20 that can be added to the thermal control 1 to provide selection of boil and sub-boil modes. The subassembly relies on the bias of a trip lever spring 3 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 21 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 30 may have a pivot point P3 displaced beyond the pivot point 25 of the mode selection lever 21, to reduce the travel of the end of the user actuator. A lift-off switchoff mechanism may be provided by means of a bifurcated spring (Figs 10,11).

Description

S

Thermal Controls

Field of the Invention

100011 The present invention relates to thermal controls in general and in particular, but not exclusively, to thermal controls for liquid heating vessels such as kettles, jugs and other appliances that heat liquid, particularly for food preparation.

Background of the Invention

100021 GB-A-2397438 discloses a thermal control which switches off a liquid heating appliance when that liquid has reached boiling point.

[0003] GB-A-243 8244 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.

10006] It would be even niore advantageous if the modular thermal control minimised the number of parts.

Statement of the Invention

[0007] 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 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.

10008] 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.

10009] 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.

[00101 Embodiments of the invention provide the ability to develop a suite of controls whereby addition 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.

Brief Description of the Drawings

100111 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, Sb 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.

Figure 9 shows 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 1 la to lic 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.

Detailed Description of the Embodiments

[0012] 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 100131 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 I 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 I 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.

100141 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.

100151 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 [00161 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 it 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 25 ensures that the pivot point of the subassembly 20 is geometrically correct.

[00171 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.

10018] 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, for example as described in W0-A-2007/045812.

[0019] 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.

[00201 Figures 5a, Sb and Sc show how the mode selection lever 21 engages with the trip lever boil and sub boil cam pins 10, 12. Advantageously the M' shaped slot 22 in the mode selection lever 21 interfaces with the boil and sub boil cam pins 10, 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 5c, 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.

[0021] 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.

100221 The security of the ti-i-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 maintained stably in the off position, rather than being loose in that position.

[0023] 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.

(0024] 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 reverts the mode selection lever 21 back to the centre off position.

[00251 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.

100261 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.

10027] Figure 7 further explains the relationship between the mode selection lever 21, the adjustment cam, 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.

[0028] 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.

10029] 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.

100301 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 dependant upon the gap Gi 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 Cl is too small, the trip temperature of the bimetal 40 can be affected. In addition, the ability to force the sub boil birnetal 40 to reset is dependant 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.

[00311 Advantageously, the present embodiment incorporates means to adjust the gap GI, comprising the adjustment cam spindle 27, arranged to interface with the flexible ann 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.

100321 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 [0033] 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.

100341 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 tTavel of the actuator is less than that of the mode selection lever 21.

Lift Off Switch Off 10035] The embodiment shown in Figures 10 and 1 la to 1 Ic 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.

10036] 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.

[0037] Figure 1 la 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 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 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 fri-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 Embodiments [0038] 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.

100391 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.

[0040] 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 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 at least 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 maintained in at least one of the states thereof by the bias of the trip lever.
2. The control of claim 1, wherein the heating mode selector is maintained in the off state thereof by the biasing of the trip lever to the off state thereof.
3. The control of claim 1 or claim 2, wherein the heating mode selector does not comprise additional biasing means.
4. The control of any preceding claim, 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 thereof.
5. The control of any preceding claim, 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 thereof.
6. The control of any preceding claim, wherein the actuation of the heating mode selector to the off state thereof causes the trip lever to be moved to the off state thereof.
7. A thermal control for a liquid heating appliance, comprising a bistable trip lever and a multistable heating mode selector manually actuable from an off state to at least a boil state and a sub boil state, wherein the heating mode selector is coupled to the trip lever such that the boil state and the sub boil state are selectable by manual actuation in opposite directions from said off state thereof, the coupling comprising first and second discrete cams arranged such that in the boil state the first cam couples to the trip lever, and in the sub boil state the second cam couples to the trip lever.
8. The control of claim 7, wherein the first cam comprises a first pin moveable within a first slot portion, such that in the boil state the first pin engages with the first slot portion, and the second cam comprises a second pin moveable within a second slot portion, such that in the sub boil state the second pin engages with the second slot portion.
9. The control of claim 8, wherein at feast one of the first and second pins engages with the corresponding slot portion when the heating mode selector is in the off state.
10. The control of claim 9, wherein the first and second slot portions are portions of a unitary slot.
11. The control of claim 10, wherein the unitary slot is M-shaped.
12. The control of any preceding claim, 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.
13. The control of claim 12, wherein the heating mode selector is actuable to the off state thereof before the trip lever is actuated by the sub boil sensor.
14. The control of claim 12 or 13, 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.
15. The control of any one of claims 12 to 14, wherein the temperature at which the trip lever is actuated by the sub boil sensor is adjustable by means of the coupling of the trip lever to the sub boil sensor.
16. The control of any one of claims 12 to 15, wherein the heating mode selector includes a pivoting member arranged to couple the trip lever to the sub boil sensor.
17. The control of any one of claims 12 to 16, wherein the coupling of the trip lever to the sub boil sensor is arranged to reset the sub boil sensor.
18. The control of claim 17, wherein the heating mode selector is arranged to manually reset the sub boil sensor so as to allow the trip lever to be moved to the on position thereof before the sub boil sensor has reset automatically.
19. The control of any preceding claim, including means arranged to prevent movement of the trip lever into the on position thereof when the appliance is separated from a base.
20. 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.
21. The control of claim 20, wherein the means for switching off the appliance comprises a trip lever and a moveable member arranged to prevent movement of the trip lever whenIthe 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.
22. The control of any preceding claim, wherein the heating mode selector comprises a modular assembly attachable to the remainder of the thermal control.
23. 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.
24. The thermal control of claim 23, wherein the resilient spring is bifurcated, so as to contact the trip lever at either side of the bifurcation.
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 substantially as herein described with reference to and/or as shown in * 20 the accompanying drawings. *
29. A bitemp subassembly substantially as herein described with reference to and/or as shown in the accompanying drawings.
30. A user actuator substantially as herein described with reference to the accompanying drawings.
31. A liquid heating appliance substantially as herein described with reference to and/or as shown in the accompanying drawings.