GB2329523A

GB2329523A - Thermally sensitive controls

Info

Publication number: GB2329523A
Application number: GB9719795A
Authority: GB
Inventors: John Crawshaw Taylor
Original assignee: Strix Ltd
Current assignee: Strix Ltd
Priority date: 1997-09-17
Filing date: 1997-09-17
Publication date: 1999-03-24
Anticipated expiration: 2017-09-17
Also published as: GB2329523B; GB9719795D0; DE29816711U1

Abstract

A thermally sensitive control intended to be mounted under the base of a water heating vessel such as a kettle or hot water jug includes a manually resettable spring loaded lever arm 14 which is tripped in response to the operation of either of two thermally sensitive actuators 4, 20 to open a set of contacts to disconnect the power supply to the heater. The first actuator may be an overheat protection 4 or boiling sensitive 16 bimetal actuator. The second actuator maybe bimetal actuator 20 in good thermal contact with the base of the vessel. A manually operable selector 34 selectively couples the movement of the second actuator 20 to the spring loaded lever arm 14 to trip the lever arm. The selector 34 allows the lever arm 14 to be tripped by the second actuator 20 at a temperature below boiling.

Description

1 - Thermally Sensitive Controls 2329523 The present invention relates to

liquid heating vessels and to thermally sensitive controls, in particular to thermally sensitive controls intended to be mounted under the base of a water heating vessel such as a kettle or hot water jug.

Such controls are disclosed for example in W095/34187, and typically comprise a thermally sensitive actuator, for example a bimetallic actuator arranged, in use, in good thermal contact with the base of the vessel and operable in the event of the vessel heater overheating to disconnect the power supply to the vessel heater. The vessel or the control may also comprise a steam sensitive actuator which operates in the event of liquid in the vessel boiling again to disconnect the power supply to the vessel heater. In the control disclosed in W095/34187 above, a steam sensitive actuator and overheat protection actuator both operate to trip a trip lever which must be reset manually after operation to once again supply power to the vessel heater.

In certain circumstances it is desirable to be able to heat water to temperatures below boiling point, and the present invention seeks to provide a thermally sensitive control which can operate to disconnect the power supply to the vessel heater at a water temperature below boiling.

From a first aspect, the invention provides a thermally sensitive control in or for a liquid heating vessel having an electrical heater provided on the base of the vessel said control comprising a first thermally sensitive actuator, a manually resettable spring loaded lever arm which is tripped in response to operation of said first thermally sensitive actuator to open a set of 2 contacts in the control to disconnect the power supply to the heater, a creep-action actuator, for example a creep action bimetallic actuator, arranged so as in use to make good thermal contact with the base of the vessel, and manually operable selector means selectively for coupling the movement of said creep action actuator to said spring loaded lever arm to trip the lever arm.

Thus in accordance with the invention, a thermally sensitive control can act to disconnect the power supply to the heater for example in the event that the heater overheats, and/or liquid in the vessel boils and also when liquid in the vessel reaches a predetermined temperature below boiling point. It will be understood that the creep-action bimetallic actuator will deflect continually as the vessel base heats and cools, and the selector means acts selectively to couple that movement to the lever arm for tripping the lever arm at a temperature below that at which the other actuator would do so. It will be appreciated that the hotter liquid in the vessel becomes, the hotter the base becomes, and the more the creep action actuator will deflect. The degree of deflection of the creep action actuator necessary to trip the lever arm and thus disconnect power to the heater of the vessel at a given liquid temperature in the vessel can be established empirically.

As stated above, the first actuator may be an overheat protection actuator, for example a bimetallic actuator, arranged in good thermal contact with the base of the vessel. Alternatively, the first actuator could be a boiling sensitive actuator, for example a steam sensitive actuator. Preferably, both an overheat protection actuator and a boiling sensitive actuator are provided which both act to trip the lever arm.

The selector means may be such as to allow tripping of the lever arm at a single liquid temperature in the vessel or at one of a number of temperatures, whereby in use a range of liquid temperatures in the vessel may be 3 - obtained. In the latter arrangement, the selector means may be such as to permit a continuous or stepwise variation in the operating temperature.

Accordingly, the selector means may comprise a continuously variable or a multi-level cam surface for engagement with the actuator, such that depending on the cam setting, a greater or lesser degree of movement of the creep actuator will be required to bring the creep actuator into engagement with the cam surface, thereby to trip the lever arm. The cam may be a rotary cam, but for simplicity, it is preferably a sliding cam.

In the preferred embodiment, the selector means comprises a slide member which is slidably movable into and out of a position of engagement with the creep actuator. In a single temperature embodiment, the slide member is simply movable selectively between two positions in which the slide member will or will not engage with the actuator as the latter deflects. However in a multi-temperature embodiment, it is movable between three or more positions. The slide member may be provided with one or more engagement surfaces as described above, or the actuator may be provided with such engagement surfaces to allow the lever arm to be tripped at a number of temperatures.

The engagement surface of the actuator may be provided by a portion of the actuator itself, but it may be formed by an adjustable member such as a set screw to allow for easy calibration of the device. Calibration of the device otherwise may be obtained by deforming the actuator by the requisite amount.

For ease of manufacture, the selector means is preferably mounted on the lever arm. This allows for a simple sliding mounting to be achieved with respect to the creep actuator. Such an arrangement is believed to be novel and inventive in its own right, so from a further aspect the invention provides a thermally sensitive control in or for a liquid heating vessel 4 having an electrical heater provided on the base of the vessel said control comprising a first thermally sensitive actuator, a manually resettable spring loaded lever arm which is tripped in response to operation of said first thermally sensitive actuator to open a set of contacts in the control to disconnect the power supply to the heater, a second thermally sensitive actuator, arranged so as in use to make good thermal contact with the base of the vessel, and manually operable selector means selectively for coupling the movement of said actuator to said spring loaded lever arm to trip the lever arm, said selector means being mounted on said lever arm.

In this aspect of the invention, the second actuator could for example be a snap acting bimetallic actuator, and need not be a creep action actuator. Preferably, the selector means is slidably mounted, but other forms of selector as described above may also be contemplated.

It will be appreciated that the control of the invention may be embodied as an integrated control unit for mounting to a vessel or a number of individual components assembled separately.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings:

Figure 1 is a plan view of an integrated control unit embodying the invention; Figure 2 is a side view of the control in a first operative condition, and Figure 3 is a side view of the control in a second operative condition.

The control unit 2 shown in Figure 1 is a modification of that shown in Figures 15 and 16 of W095/34187, to which reference may be made for a full description of the basic components of the control unit. The relevant disclosure of W095/34187 is hereby incorporated by reference.

Briefly, however, the control unit 2 comprises a pair of snap acting bimetallic actuators 4 mounted on a metallic carrier plate 6 provided on a moulding 8 which mounts or incorporates various electrical components. The control unit is mounted to the base 10 of a liquid heating vessel, as shown schematically in Figure 2. The base 10 is provided with a heater, for example a thick film heater, or a conventional sheathed heating element, as shown for example in W096/18831. The base may be an integral part of the vessel or a separate component mounted in an opening in the bottom of the vessel body.

In operation, should the vessel overheat, for example in the event that it is switched on without any liquid in it, one or other of the actuators 4 acts via a is push rods 11 to open a set of contacts 12 in the moulding. This also acts to trip a spring-loaded lever arm 14, which opens the contacts 12 fully, and also opens a corresponding set of contacts in the other pole of the supply. The lever arm 14 is also tripped by a steam sensitive bimetallic actuator 16 mounted at one end of the control unit 2 when liquid in the vessel boils. Further details of this control and its mode of operation can be found in W095/34187.

A modification of this control unit in accordance with this invention allows the control to disconnect the electrical supply to the vessel heater in the event that liquid in the vessel reaches a predetermined temperature or temperatures below boiling. To this end, the control unit 2 further comprises a creep-action bimetallic actuator 20 which is mounted to plate 6 by a thermally conductive rivet 22 e.g. of copper. The creep-action bimetallic actuator 20 is stepped at its free end 24, for clearance purposes, and two set screws 26,28 are mounted on the free end 24. As will be seen, the screws 26, 28 project from the creep-action bimetallic actuator 20 by different amounts, for reasons which will be discussed further below.

- 6 is Also, the control is provided with manually operable selector means in the form of a generally L shaped slide member 34 which is slidably received in a bore 32 formed in an integrally moulded lateral extension 30 of the trip lever arm 14. One end of the slide member 34 is provided with a knob 36 which extends externally of the base 38 of the vessel for manipulation by a user. The knob 36 may match a knob 40 attached to the other side of the lever arm 14 and which is provided for switching the vessel on and off. The other end of the slide member 34 has a cross limb 42 with a projecting abutment 46. The bore 32 and slide member 34 are provided with detents such as notches 48 for selectively retaining the slide member 34 in one or more desired positions.

operation of the control unit will now be described. In the condition shown in Figure 2, the contacts 12 are closed and the slide member arranged at its left most (in the sense of Figure 2) position. In this condition, as water in the vessel is heated, the creep bimetal 20 will heat and will deform causing it s free end 24 to move away from the vessel base. This movement is unobstructed by the slide member 34 and will continue until such time as the liquid in the vessel boils, which causes the control to operate via the steam sensitive actuator 16 to open the contacts 12. The vessel base will then cool, and the creep bimetal 20 return to its original position. This condition is shown in Figure 3. Should a user then wish again to boil liquid in the vessel, the knob 36 can be pushed down to re-close the contacts 12 once more.

:jowever, if it is desired to heat liquid to a temperature below boiling, the knob 36 may be pushed inwardly so that the slide member 34 slides in the direction of arrow A.

If the slide member 34 is moved in this direction by one notch the abutment 46 will move into a position under the set screw 26, and if moved in by two notches, it will move into position under set screw 28. As stated above, the set screws 26,28 project by predetermined amounts from the free end 24 of the creep acting bimetallic actuator 20. These distances are chosen to correspond to a desired water temperatures. Set screw 28 projects by a greater amount than set screw 26, so that the free end of the actuator 20 does not need to deflect as far to cause set screw 26 to move into engagement with abutment 46 and trip the lever arm 14 and so open the contacts 12 as it does to move set screw 26 into engagement with the abutment 46. Thus set screw 28 will cause the lever arm 14 to trip at a lower water temperature than set screw 26. Thus if a low water temperature, say 600C, is required the slide member 34 should be moved in the direction of arrow A by two notches so that the abutment 46 lies under setscrew 28, while if a higher temperature say 800C is required, it can be moved in by just one notch so that the abutment lies under set screw 26.

The degree of projection of the set screws 26,28 to achieve a desired water temperature can be determined empirically, and the control calibrated accordingly. the described embodiment, this can be done merely by turning the set screws 26, 28.

Thus in the embodiment described the control unit will operate in the event of liquid in the vessel boiling if the slide member 34 is in its left most position when the liquid reaches 800C when the slide member 34 is in its middle position and when liquid reaches 600C when the slide member is in its right most position.

It will be appreciated that various modifications may be made to the embodiment described above within the scope of the invention. For example the slide member 34 could be provided with a cam surface at its free end which would engage with a corresponding operating 8 surface on the creep-action bimetallic actuator 20. This could provide a continuous, or stepwise adjustment of the operating temperature. It would also be possible to mount the slide member independently of the trip arm, but this is not preferred. Also, the particular slide mechanism described could be replaced by a slidable or rotary cam mechanism.

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Claims

Claims is 1. A thermally sensitive control in or for a liquid heating

vessel having an electrical heater provided on the base of the vessel said control comprising a first thermally sensitive actuator, a manually resettable spring loaded lever arm which is tripped in response to operation of said first thermally sensitive actuator to open a set of contacts in the control to disconnect the power supply to the heater, a creep-action actuator, arranged so as in use to make good thermal contact with the base of the vessel, and manually operable selector means selectively for coupling the movement of said creep action actuator to said spring loaded lever arm to trip the lever arm.
2. A control as claimed in claim 1 wherein said first actuator is an overheat protection actuator.
3. A control as claimed in claim 1, wherein said first actuator is a boiling sensitive actuator.
4. A control as claimed in claim 1 comprising both an overheat protection actuator and a boiling sensitive actuator operable to trip the lever arm.
5. A control as claimed in any preceding claim wherein said selector means is arranged so to allow tripping of the lever arm by the creep action actuator at a plurality of temperatures.
6. A control as claimed in any of claims 1 to 5 wherein said selector means comprises a movable cam.
7. A control as claimed in any preceding claim wherein said selector means comprises a slide member.

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8. A control as claimed in any preceding claim wherein said selector means or slide member is mounted on said lever arm.
9. A control as claimed in any preceding claim wherein said creep action actuator is provided with adjustable calibration means.
10. A control as claimed in claim 11 or 12 wherein said calibration means comprise one or more members adjustably mounted to and projecting from the actuator.
11. A control as claimed in any preceding claim wherein said creep action actuator is a bimetallic actuator.
12. A thermally sensitive control in or for a liquid heating vessel having an electrical heater provided on the base of the vessel said control comprising a first thermally sensitive actuator, a manually resettable spring loaded lever arm which is tripped in response to operation of said first thermally sensitive actuator to open a set of contacts in the control to disconnect the power supply to the heater, a second thermally sensitive actuator, arranged so as in use to make good thermal contact with the base of the vessel, and manually operable selector means selectively for coupling the movement of said actuator to said spring loaded lever arm to trip the lever arm, said selector means being mounted on said lever arm.