GB2592869A

GB2592869A - Thermal control

Info

Publication number: GB2592869A
Application number: GB1915933.4A
Authority: GB
Inventors: William Lindley Richard; Sherratt Mark; Gabbitus Daniel
Original assignee: Otter Controls Ltd
Current assignee: Otter Controls Ltd
Priority date: 2019-11-01
Filing date: 2019-11-01
Publication date: 2021-09-15
Anticipated expiration: 2039-11-01
Also published as: GB2592869B; GB201915933D0; CN211743049U

Abstract

A thermal control 1 suitable for a cordless electrical appliance, such as a kettle, comprises a thermal actuator 4, a switch, a sliding member 6 and a latch 7. The cordless electrical appliance comprises a heater and a first cordless electrical connector 13 for connection to a second cordless electrical connector 20 suitable for electrical supply to the heater. The thermal actuator is arranged to change reversibly from a first state to a second state in response to an overheat condition of the heater. The switch is suitable for electrically connecting the heater to the first cordless connector. The switch is biased to be closed. The sliding member is arranged to be actuated by the thermal actuator in the second state so as to open the switch. The latch latches the sliding member so as to hold the switch open when the first electrical connector is connected to the second electrical connector, and to release the sliding member so as to allow the switch to close when the first and second cordless connecters are separated.

Description

Thermal Control

Field of the Invention

[0001] The present invention relates to a thermal control, for example a thermal cutout to prevent overheating in a liquid heating appliance.

Background of the Invention

[0002] Electrical appliances for heating and boiling water, such as kettles, require a thermal cut-out to prevent overheating in the event of the appliance being energised when there is little or no water present. Without a thermal cut-out the temperature reached in the appliance may be excessive, causing failure of the heating element, damage to the other components in the appliance or even causing flammable materials in the appliance to ignite.

[0003] A typical appliance is described in patent publication GB-A-2438244 which shows a cordless kettle comprising a planar heating element forming the bottom of the chamber in which the water is heated. The patent also shows the applicant's (Otter Controls Ltd.'s) Al type of thermal cut-out designed to protect the type of appliance described. The Al control includes a plug type connector for the appliance proper designed to fit the applicant's CS] socket connector fitted to a power base. The control uses two snap-action thermostatic bimetals, in contact with the heating element, designed to operate at a temperature above the normal operating temperature of the heating element and below a temperature where the appliance might be damaged. The control has two bimetals operating separate sets of electrical contacts to provide redundancy in case one bimetal or set of contacts fails. These are referred to as the dry boil cut-outs.

[0004] The thermal control in GB-A-2438244 has a manual reset feature. Without this feature the cut-out would re-energise the heating element when it cools to a predetermined reset temperature. This is referred to as a self-resetting cut-out. Whilst it is possible to provide an appliance with such a self-resetting cut-out, this type of cutout causes the appliance to cycle, heating up and cooling down repeatedly until the user intervenes or some component such as the heating element fails. Therefore it is desirable to include a manual reset feature in the cut-out assembly.

[0005] The applicant's AS thermal control (details of which were available on 30 October 2019 at http://www.ottercontrols.co.uk/a8-series.html) includes a third bimetal. This is set at approximately 80°C and receives steam from the kettle when it boils. The steam operates the third bimetal which acts upon a lever to open the two sets of contacts of the dry boil cut-outs. This is referred to as the steam control. The lever also acts as a switch for the user to turn the kettle on or off. The lever is part of a bistable or over-centre mechanism which biases the lever into either the on or off position. Because of the over centre mechanism the lever is referred to as a trip lever. When either of the dry boil bimetals operates, the lever is urged into the off position.

When the appliance cools down, the dry boil bimetals reset but the contacts remain in the off position. The power can only be re-connected by the user moving the lever to the on position. The effect of this is that the dry boil cut-out is manually reset.

[0006] The AS control is suited to kettles constructed with an operating lever towards the bottom of the appliance. When the kettle design calls for an operating switch at the top of the handle, the AS control is not convenient because the operating lever is some distance from the preferred position of the switch. In this case the applicant's ZS control (details of which were available on 30 October 2019 at http://www.ottercontrols.co.uk/z5-series.html) can be used to disconnect the heating element when the kettle boils. The 75 control comprises a steam switch having a single bimetal for a steam control and an operating lever for the user to turn the kettle on or off.

[0007] WO-A-2019/162689 discloses a thermal control with a manual reset mechanism having a single pivoting latch arm that extends across the control to latch both pairs of contacts. Although this reduces the number of components, the use of a single latch for both sets of contacts may compromise the redundancy provided by having two pairs of latchable contacts. For example, if the latch arm were to jam when the contacts are in the closed condition it could prevent both sets of contacts from opening.

[0008] The direct engagement of the latch arm with the contact springs increases the risk of jamming. The latch arm may become jammed for example, if in the closed position the latches are in contact with the moving contact springs and those springs overheat due to high electrical resistance between the fixed and moving contacts. The hot moving contact springs could locally melt the plastic of the latch arm causing the two components to become stuck together.

[0009] Another problem with the manual reset mechanism of WO-A-2019/162689 is that if a first pair of contacts is latched open and the corresponding first bimetal then resets before the second bimetal trips, the tripping of the second bimetal will reset the latch of the first pair of contacts. This problem may be avoided by setting the trip temperatures of the first and second bimetals to be close together, but this nevertheless compromises the independence and therefore redundancy of the latching of the first and second pairs of contacts.

[0010] The problems identified above are not restricted to the specific controls described above, but may occur in other thermal controls.

Statements of the Invention

[owl] Aspects of the invention are defined by the accompanying claims.

[0012] In order to produce a manual reset thermal cut-out, a mechanism may be provided to hold the contacts in an open position until the user performs an action to reset the cut-out. This action may be to lift and return the appliance proper from its power base.

[0013] In an embodiment, the mechanism includes, for the or each bimetal actuator and associated moving contact spring, a sliding intermediate member or push rod that carries the motion of the bimetal actuator to the moving contact spring. The push rod may be provided with an engagement portion, such as a step. A resilient member such as a spring is arranged to engage with the engagement portion of the intermediate member as it slides, so retaining the intermediate member in position to prevent the contacts from closing when the bimetal actuator cools and resets.

[0014] A cam is provided which bears against the socket connector when the appliance is placed on its powerbase. When the appliance is removed from the power base, the cam releases the spring from the step on the push rod, allowing the moving contact to move into the closed position. There may be a separate spring and cam for each pair of contacts, but preferably a single spring component and cam are provided for both pairs of contacts, while allowing both pairs of contacts to be latched independently.

[0015] Embodiments of the invention may provide a thermal cut-out suitable for a kettle with a manual control that is separate from the thermal cut-out, such as a switch at the top of the handle of a kettle.

[0016] Various embodiments and aspects of the invention are described without limitation below, with reference to the figures.

Brief Description of the Drawings

[0017] 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 shows a side view of a thermal control integrated with a cordless plug connector in a first embodiment of the invention, separated from a cordless socket connector.

Figure 2 shows a plan view from above of the thermal control of Figure 1, with one bimetal removed.

Figure 3 shows a side view of the thermal control with switch contacts closed, with the cordless plug connector connected to the cordless socket connector.

Figure 4 shows a plan view from above of the thermal control of Figure 3, with one bimetal removed.

Figure 5 shows a side view of the thermal control with the bimetal tripped and switch contacts open, with the cordless plug connector connected to the cordless socket connector.

Figure 6 shows a plan view from above of the thermal control of Figure 5, with one bimetal removed.

Figure 7 shows a perspective view of a thermal control in a second embodiment with the bimetals removed, with the cordless plug connector connected to the cordless socket connector and with the latch mechanism engaged.

Figure 8 shows a close-up view of part of Figure 7.

Figure 9 shows the same view as Figure 8, with the cordless plug connector separated from the cordless socket connector.

Figures 10 shows a perspective view of the latch and reset mechanism of the control of the first embodiment, without the mounting portion of the control.

Figure 11 shows a side view of the latch and reset mechanism of the control of the second embodiment, without the mounting portion of the control.

Figure 12 shows a perspective view of the control of the second embodiment from below.

Detailed Description of the Embodiments

[0018] Embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings. In this description 'above', 'downwards', 'lower' and similar terms are defined with reference to a vertical direction of the appliance in a normal upright orientation in use. 'Inward', 'outward' and similar terms are defined relative to a notional centre or midpoint of the control.

[0019] A typical appliance to which embodiments of the invention may be applied is a cordless kettle comprising an appliance proper (in this case, the kettle body) having a cordless plug connector for connection to a corresponding cordless socket connector on a power base to which the appliance proper may be connected. The appliance proper may have a planar heating element forming the bottom of a chamber or reservoir in which the water is heated.

[0020] The planar heating element may comprise a substrate having an upper surface that forms part of the inner surface of the chamber. The substrate may be of stainless steel. The substrate may have a sheathed heating element or thick film heating element on its underside, and optionally a thermal diffuser plate, made for example of aluminium.

[0021] Within the appliance proper there may be provided a thermal control comprising a thermal cut-out according to an embodiment of the present invention, to prevent overheating of the heating element, for example in a dry boil condition. There may also be provided a boiling, steam or temperature sensor to switch off or reduce the heating when the water reaches a predetermined temperature, and a user-controlled switch for controlling the heating. The thermal cut-out, sensor and/or user-controlled switch may be integrated together, but the thermal cut-out embodiments below are particularly advantageous when separate from the sensor and/or user-controlled switch.

[0022] Figures 1 to 6 and 10 show a thermal control or cut-out 1 in a first embodiment, while Figures 7 to 9 and 11 show a thermal control or cut-out 1 in a second embodiment. The same reference numerals are used for similar parts between the embodiments.

[0023] Both embodiments comprise a mounting plate 2 for mounting the control 1 onto the lower surface of a planar heating element (not shown). The control 1 also comprises one or more mounting portions, such as a plastic moulding 3 into which the functional components of the control 1 are mounted. For clarity, one or more mounting or housing portions may be omitted from the drawings.

[0024] The control 1 has a pair of snap action bimetal actuators 4 which are arranged to contact the underside of the heating element, such as the aluminium diffuser plate, when the control 1 is mounted on the heating element. The snap action bimetal actuators 4 are of a known type that is designed to snap from a first state to a second state (i.e. to 'trip', 'operate' or 'set') above a first (operational or overheat) temperature, and to return ('reset') from the second state to the first state below a second (reset) temperature lower than the first temperature. The bimetal actuators 4 may have a dished shape that changes from a concave shape in the first state to a convex shape in the second state, or vice versa. The bimetal actuators 4 are mounted in the control 1 so as to be in thermal contact with the heating element in the first position, but out of thermal contact with the heating element in the second position. [0025] The cut-out 1 is proximate to or is integrated with a cordless plug connector 13, for mounting in an appliance proper, arranged to mate or connect with a corresponding cordless socket connector 20, mounted for example on a cordless base (not shown), to supply electrical power to the heating element. The cordless socket connector 20 may be of conventional type, such as the CS8 connector available from Otter Controls Ltd. [0026] The cut-out 1 includes electrical tab terminals 14, 15 to which the heating element is connected.

[0027] Two pairs of electrical contacts are provided, each pair being associated with a corresponding one of the bimetal actuators 4. Each pair of contacts acts an electrical switch for selectively connecting and disconnecting the cordless connector 13 to the terminals 14, 15. The pairs of contacts are connected in series so that opening either pair of contacts will disconnect the terminals 14, 15 from the cordless connector 13. Each pair of contacts comprises a fixed contact 10 and a moveable contact 11 mounted on a contact spring 9 that biases the moveable contact 11 into contact with the fixed contact 10.

[0028] A pair of push rods 6 are slidably mounted, each push rod 6 having an upper end positioned below a moveable part of the respective bimetal actuator 4 and a lower end positioned above the corresponding contact spring 9, so that when the bimetal actuator 4 trips, it acts upon the push rod 6 to push the contact spring downwards, thus separating the corresponding moveable contact 11 from the fixed contact 10 and opening the switch. When the bimetal actuator 4 resets, the push rod 6 is no longer pushed downwards and the bias of the contact spring 9 is able to move the moveable contact 11 into contact with the fixed contact 10, subject to a latching mechanism as described below.

[0029] The latching mechanism comprises a latch member 7 that is able to engage an engagement portion of the push rod 6 when the push rod 6 moves into a downward position, thus latching the push rod 6 in the downward position and holding the corresponding moveable contact 11 in an open position. Preferably, a latching mechanism is provided for both of the push rods 6. The same latch member 7 may engage both of the push rods 6, or there may be a separate latch member 7 for each of the push rods.

[0030] The latch member 7 is preferably resiliently biased against the side of the push rod 6 so that the latch member 7 makes sliding contact with the side of the push rod 6 and can move into engagement with the engagement portion when the push rod 6 is pushed by the bimetal actuator 4 into the downward position.

[0031] In the first and second embodiments, the latch member comprises a wire spring 7 having opposite arms or ends 7a, 7b that are mounted at respective mounting points 8a, 8b (e.g. clips) so that, when the centre 7c of the spring 7 is pulled outwards in a generally horizontal direction, the arms 7a, 7b rotate into contact with the sides of the respective push rods 6, in a plane substantially perpendicular to the generally vertical sliding movement of the push rods 6.

[0032] The engagement portion may comprise a recess, step, indentation or projection on the side of the push rod 6. The profile of the engagement portion is preferably designed to prevent the latch member 7 from slipping out of the engagement portion: for example, the lower face of the engagement portion may be substantially horizontal. As shown in Figures 7 to 11, the push rod 6 may have a portion 6a that extends radially outwardly so as to create a step which the spring arm 7a, 7b may abut so as to latch the push rod 6. Advantageously, the push rod 6 is symmetrical about a central horizontal plane so that the push rod may be mounted either way up. [0033] A reset mechanism for the latching mechanism comprises a latch enabling member or cam 12 that projects into the interior of the cordless plug connector 13 such that the cordless socket connector 20 pushes against the cam 12 when the plug connector 13 and socket connector 20 are connected together. In that configuration, the cam 12 acts on the latch member 7 so as to cause the latch member 7 to be biased against the push rods 6, thus enabling latching of the push rods 6.

[0034] Figures 1 and 2 show the spring 7 in a rest position in which the outer ends of the arms are out of contact with the push rods 6. When the plug connector 13 is connected to the socket connector 20 as shown in Figures 3 to 6, the cam 12 pushes the spring centre 7c outwards so that the arms 7a, 7b rotate inwards into contact with the corresponding push rods 6, thus allowing engagement with the engagement portions of the push rods 6 when the bimetal actuator 4 operates as shown in Figures 5 and 6.

[0035] When the plug connector 13 is separated from the socket connector 20, as shown in Figures 1 and 2, the cam 12 no longer pushes the centre of the spring 7 and the spring 7 returns to a rest state in which its arms are no longer in contact with the push rods 6, thus releasing the latch mechanism [0036] The cam 12 may be slidably mounted in an approximately vertical direction such that the socket connector 20 pushes the cam 12 upwards. In that case, the cam 12 has a cam surface that abuts against the centre of the spring 7, so that upward motion of the cam 12 causes outward motion of the centre of the spring 7.

[0037] Alternatively, as shown in more detail in Figures 7 to 11, the cam 12 may be pivotally mounted about a pivot axle 12a such that the socket connector 20 causes the upper end of the cam 12 to pivot outwardly. For example, the pivot axle 12a may be towards a lower end of the cam 12 such that the socket connector 20 abuts a projecting part 12b of the cam 12 above the pivot axle 12a. The projecting part 12b projects into the interior of the cordless plug connector 13 so as to contact the outer surface of the cordless socket connector 20, as shown in Figures 10 to 12. In this case, the projecting part 12b acts as a cam surface. The upper part of the cam 12 may comprise a spring holder 12c that prevents the spring centre 7c from slipping downwards.

[0038] In either of the above cases, the resilience of the spring 7 may cause the cam 12 to return to a position in which the projecting part 12b projects into the plug connector 13 when separated from the socket connector 20. Advantageously, this avoids the need for separate resilient means for returning the cam 12 to that position.

[0039] In the first and second embodiments, the spring] is bent so that its centre 7c is positioned outwardly relative to its arms 7a, 7b, thus allowing the cam 12 to be positioned towards the outside of the plug connector 13. The shape and configuration of the spring 7 may depend on the preferred locations of the push rods 6 and cam 12. [0040] In the embodiments shown in the Figures, the spring 7 is biased against the outer sides of the push rods 6 and the cam 12 causes the spring arms 7a, 7b to move outwards, away from the push rods 6. Alternatively, the spring 7 may be biased against the inner sides of the push rods 6 and the cam 12 may cause the arms 7a, 7b to move inwards, away from the push rods 6. Advantageously the latching mechanism and reset mechanism may be adapted to different layouts.

[0041] In alternative embodiments, the latch member 7 need not be made completely of resilient material. For example, it is not essential that the centre 7c is resilient. However, the use of a single wire spring reduces costs and facilitates assembly.

[0042] Embodiments of the invention advantageously may be assembled automatically or semi-automatically, with the parts being automatically placed in sequence in the mounting portion(s).

[0043] If no latching and reset mechanism is required, the spring 7 and cam 12 may be omitted, without affecting the functionality of other parts. In particular, the engagement portions of the push rods 6 need not affect the functionality of the push rods 6. However, alternative push rods without the engagement portion may be used if no latching or reset mechanism is required.

Alternative Embodiments [0044] The embodiment described above is 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.

Alternative Statements of Invention

[0045] Alternative Statements of invention are defined by the numbered clauses below.

1. A manual reset thermal cut-out for a cordless electrical appliance comprising at least one sliding push rod to transfer the motion of at least one thermal bimetal actuator to at least one moving electrical contact and at least one spring member which moves to engage its associated sliding push rod when its associated thermal bimetal actuator operates to maintain the associated moving contact in the open position.

2. A manual reset thermal cut-out of clause 1 where there is a step or a groove in the at least one sliding push rod arranged to interact with the at least one spring member when the thermal bimetal actuator operates.

3. A manual reset thermal cut-out of clause 1 or 2 also comprising at least one cam to move the at least one spring member out of engagement with the at least one sliding push rod when the appliance is removed from its power base.

4. A manual reset thermal cut-out of clause 3 where a single spring member engages with more than one sliding push rod.

5. A manual reset thermal cut-out of clause 3 or 4 where a single cam is arranged to move the at least one spring member out of engagement with the at least one push rod when the appliance is removed from its powerbase.

6. An appliance comprising a manual reset thermal cut-out of any preceding clause.

References 1 Thermal control or cut-out 2 Fixing plate 3 Mounting portion or moulding 4 Bimetal actuator 6 Push rod 6a Engagement portion 7 Latch member or spring 7a, 7b Arms 7c Spring centre 8a, 8b Spring mounting points 9 Contact spring Fixed contact 11 Moveable contact 12 Latch enabling member or cam 12a Pivot axle 12b Projecting part 12c Spring holder 13 Cordless plug connector 14 Tab terminal Tab terminal Cordless socket connector

Claims

Claims 1. A thermal control for a cordless electrical appliance having a heater and a first cordless electrical connector for connection to a second cordless electrical connector for electrical supply to the heater, the thermal control comprising: a thermal actuator arranged to change reversibly from a first state to a second state thereof in response to an overheat condition of the heater; a switch for electrically connecting the heater to the first cordless connector, the switch being biased to be closed; a sliding member arranged to be actuated by the thermal actuator in the second state so as to open the switch; and a latch arranged to latch the sliding member so as to hold the switch open when the first electrical connector is connected to the second electrical connector, and to release the sliding member so as to allow the switch to close when the first and second cordless connectors are separated.
2. The thermal control of claim 1, wherein the latch comprises a latch member that is biased against the sliding member when the first electrical connector is connected to the second electrical connector.
3. The thermal control of claim 2, wherein the sliding member includes an engagement portion that engages with the latch member when the first electrical connector is connected to the second electrical connector and the sliding member is actuated by the thermal actuator.
4. The thermal control of claim 3, wherein the engagement portion comprises a recessed or projecting portion of the sliding member.
5. The thermal control of any one of claims 2 to 4, wherein the latch member comprises a spring.
6. The thermal control of any one of claims 2 to 5, including a latch enabling member actuable by the second cordless connector so as to cause the latch member to be biased against the sliding member.
7. The thermal control of claim 6, wherein the latch enabling member is slidably mounted and includes a cam surface that abuts the latch member so as to cause the latch member to be biased against the sliding member.
8. The thermal control of claim 6, wherein the latch enabling member is pivotally mounted and has a portion that abuts the latch member so as to cause the latch member to be biased against the sliding member.
9. The thermal control of any preceding claim, wherein the switch comprises a moveable contact mounted on a contact spring that biases the moveable contact into contact with a fixed contact, wherein the sliding member is arranged to act on the contact spring so as to open the switch.
10.The thermal control of any preceding claim, having first and second said thermal actuators, corresponding first and second said switches and corresponding first and second sliding members, and having at least one part of the latch in common between the first and second sliding members.
11.The thermal control of claim 10 when dependent on claim 2, wherein a single said latch member is biased against said first and second sliding members.
12. The thermal control of claim 11 when dependent on claim 5, wherein the spring has opposite arms that are biased respectively against said first and second sliding members when the first electrical connector is connected to the second electrical connector.
13.The thermal control of claim 11 when dependent on claim 6, wherein a single said latch enabling member is provided.
14.The thermal control of any preceding claim, having the first cordless connector integrated therein.
15. A cordless electrical appliance comprising the thermal control of any preceding claim.
16. The appliance of claim 15, further comprising a user-actuable switch for switching the electrical supply to the heater.