GB2128029A - Thermal switch units - Google Patents

Abstract

A thermally responsive switch unit for an electrically heated water boiling vessel has a snap-acting bimetallic actuator located to be heated by steam vented from the vessel interior when water is boiled in the vessel, and the actuator operates upon one end of a pivoted lever 51 in an overcentre spring mechanism with the other end of the lever arranged to determine the position of the moving contact 30 of a pair of switch contacts in the electrical supply line to the electrical heating element 1 of the vessel so that the heating element is automatically switched off when water boils in the vessel. A manually- operable, rocker type control 109 is assembled to the switch unit, either through the provision of a clip-on mounting or by means of a cover assembly of the switch unit, and provides for manual on-off operation of the switch contacts. <IMAGE>

Description

SPECIFICATION Improvements relating to electric immersion heaters This invention concerns improvements relating to thermally-controlled electric immersion heaters for liquid heating vessels such as kettles, jugs, urns, pans and the like having associated therewith electrical switch means sensitive to liquid boiling within the vessel.

More particularly this invention concerns an improvement in the kind of switch unit, for incorporation with such a liquid heating vessel, as is described in British Patent Specifications Nos. 1 470 365,1 470 366 and 1 470 367 for example the disclosures whereof are incorporated herein by way of reference. As may be seen for example from Figure 1 of GB 1 470 367 abovementioned, the switch unit has a lever 51 pivoted at one end (the upper end as Figure 1 is viewed) and carrying at its other end a reset button 61.The lever 51 is shown more clearly in Figure 3 of GB 1470367 and can be seen to include a portion 58 which cooperates with a resilient, electrically-conductive strip 30 which carries the movable contact 34 of a contact set 34,35 which is connected between with the heating element 1 and the line terminal pin 31 so as to control the supply of electrical power to the element.

The arrangement of the unit is such that in response to liquid boiling in the associated vessel and generating steam which is vented onto a bimetallic actuator, the actuator moves with a snap action which causes lever 51 to pivot outwardly so as to cause the portion 58 to move the strip 30 so as to break the contacts 34, 35 and terminate the supply of power to the element.

As will be appreciated, the button 61 not only enables the lever 51 to be moved to reset the contacts 34,35 so that the element 1 can be powered again once the bimetallic actuator has reset, but also enables the element to be manually switched off. It has been found that some users of electric kettles fitted with the switch unit in question habitually use the reset button 61 as an on-off switch for the kettle, leaving the mains lead to the kettle permanently connected and the mains outlet to the lead permanently switched on. In order better to accommodate such users, a requirement exists for a more positive on-off movement than that provided by the push button 61 of the unit of GB 1 470 367 and there are further aesthetic and practical reasons which emphasize this requirement.

The present invention according to one of its aspects resides in the concept of providing a carrier for a manually-operable rocker type control for the switch unit, the carrier being adapted to make a simple snap fit with the switch unit and the rocker type control being adapted to engage with the lever of the switch unit such that a rocking movement of the control effects a corresponding movement of the switch unit lever for opening and closing the switch contacts.

According to another of its aspects, the invention provides a rocker type control affixed to an outer cover of the switch unit and arranged to cooperate with a modified form of the lever thereof in such manner as to enable the condition of the lever to be positively determined by corresponding operation of the rocker control.

The invention will be better understood from consideration of the following description made with reference to the accompanying drawings wherein Figure 1 shows a view of an electric kettle fitted with a switch unit substantially as described in GB 1 470 367 aforesaid; Figures 2A to 2D show a snap-fit carrier adapted to be fitted onto the switch unit of Figure 1; Figure 3 shows the electric kettle of Figure 1 with the switch unit fitted with the carrier of Figures 2A to 2D; Figure 4 is similarto Figure 3 but with a rocker type control shown fitted into the carrier and cooperating with the lever of the switch unit; and Figures 5A to 5C are fragmentary views of another exemplary embodiment of the invention.

Referring first to Figure 1, many of the reference numerals therein denote parts which are correspondingly designated in the description of the switch unit in GB 1 470 367 to which reference may be made for a fuller description. An electric kettle has an element H fitted in an aperture in the kettle wall K and the switch unit C is mounted on a head plate 2 of the element proper 1 with the kettle wall clamped between the head plate 2 and an annular rim 19 formed on the switch unit. When the kettle boils, steam generated within the kettle vents onto the bimetallic actuator aforementioned which is mounted in hood portion 50 of the switch moulding.

The said actuator controls the movement of lever 51 which is pivotally mounted at its upper end between moulded bosses 66 and at its lower end cooperates with the switch comprised of contacts set 34,35 with movable contact 34 mounted on an electrically conductive spring strip 30 which is mounted at one end on the line pin 31 and has its other end located between projections 100, 101 formed on the moulded plastics lever 51. Moulded bosses 69 support a bar 68 (not shown) between them and a spring 52 is received in V-grooves formed in the bar 68 and in portion 67 moulded with the lever 51.As will be appreciated, an anti-clockwise movement of lever 51, caused either by steam tripping of the bimetallic actuator in hood portion 50 or by manual lifting of the end of lever 51 remote from its pivot point, will cause spring strip 30 to be lifted by projection 100 so as to open the switch contacts 34,35, and an opposite movement will cause projection 101 to restore the spring strip 30 and reclose the contacts.

Figures 2A to 2D show a carrier member, moulded of the same plastics material as that from which the switch unit moulding is formed, which is adapted to be snap fitted to the switch unit of Figure 1 in piggyback fashion. Figure 2A shows a side elevation view of the carrier, Fig. 2B shows a plan view, Figure 2C shows an end elevation from the right hand side of Figure 1 and Figure 2D is a section on line A ...A in Fig. 2B. The carrier 102 has spaced apart pairs of limbs 103, 104whichareadaptedforengagement with the moulded bosses 66, 69 of the switch unit, the limbs 103 each having a generally hemispherical projection 105 adapted to fit the bore in bosses 66 and the limbs 104 each having a wedge shaped projection 106 adapted to fit the channel provided through bosses 69 for receiving the bar 68 (not shown) which locates one end of spring 52. It will be understood that when the carrier 102 is mounted on the switch unit, the limbs 103 and 104 straddle the switch unit with bosses 66 between the limbs 103 and bosses 69 between the limbs 104.A channel 107 is moulded into the carrier on both sides of an upstanding portion 108, the channels 107 serving as a locating means for stub shafts formed on a rocker type control lever (to be described hereinafter) and the upstanding portion 108 serving as a mounting for a miniature neon bulb.

Figure 3 shows the carrier 102 mounted in piggyback fashion on the switch unit C, and Figure 4 shows a rocker control lever 109 mounted on the carrier 102, the control lever 109 being shown as transparent for clarity of illustration. Referring to Figure 4, the rocker control lever 109 has a limb 110 extending from it and the free end of this limb 109 extends between projection 101 and a further projection 111 formed on the lever 51. In this way, a connection is provided between the lever 51 and the rocker control lever 109 which permits a degree of relative movement between the two parts. The rocker control lever 109 could be arranged to be retained on the carrier 102 by arranging the stub shafts 112 to be a snap-fit into the channels 107.

Figure 4 also shows a neon lamp 113 retained in the carrier 102, the neon nestling in an accommodating recess formed in the carrier with the glass pip commonly provided on the top of the bulb engaged under a bridge portion 116 of the carrier and the leads 115 of the lamp spaced either side of a projecting part 114 of the carrier. The neon can be connected in various different ways as desired, for example to be lit so long as the kettle is powered from the mains, or only so long as the element is powered, or only after the switch unit has tripped in response to the kettle boiling, and the limbs 104 of the carrier 102 could be extended so as to guide and shield the connections of the neon lamp to the respective line pins or components of the switch proper comprised of contact set 34,35.

As will be appreciated from the foregoing, the piggyback mounted carrier member 102 enables the switch unit, which otherwise is an available commercial device, to be modified for use with a rocker type manual control lever rather than the conventional push button, without prohibiting its use with the conventional push button which can simply be connected to the end of lever 51. The versatility of the switch unit thus is enhanced in that the same unit can be used with push button and rocker type controls simply by provision of the snap-on carrier.

Figures 5A, 5B and 5C illustrate an alternative embodiment of the invention in which a switch unit substantially as described in the foregoing is formed with a modified trip lever 51' pivoted mounted near its upper end and cooperating at its lower end with spring strip 30' mounting moving contact 34' of switch contacts set 34',35' by virtue of projections 100', 101' engaging on opposite sides ofthe strip 30'.The lever 51' constitutes part of an overcentre spring mechanism, as in the case of the previously described embodiment, as is described more fully for example in GB 1 470 367 and has two stable states on either side of an intermediate unstable state the two stable states corresponding to the most clockwise position of the lever 51' and the most anti-clockwise position respectively corresponding to the contacts-closed and contacts-open conditions of the contracts set 34',35'.

The lever 51' has a portion 200 extending above its pivotal mounting 201 and a self-centering rocker action control 202 is pivotally mounted in a moulded outer cover 203, the self-centering of the control being achieved for example by means of a spring biassing of the control towards a central position. As shown in Figure 5B depression of the upper part of the control 202 causes depression of the upwardly extending portion 200 of lever 51' which causes the lever to pivot anti-clockwise so as to open the switch contacts 34', 35'. Correspondingly, depression of the lower part of the control 202 as represented in Figure 5C will cause the lever 51' to be pivoted clockwise so as to close the switch contacts 34',35'. The unit of Figures 5A to 5C thus not only provides the automatic functions of the unit described for example in GB 1 470 367 but also has a manual override facility.

The inventive concept herein disclosed is applicable also to the switch unit of British Patent Application 7901395 (2 040 572A).

Claims (10)

1. A thermally responsive switch unit for an electrically heated water boiling vessel, said unit comprising a bimetallic actuator arranged to be responsive to steam venting from the vessel when water boilstherewithin, and a pivotally mounted lever the pivotal condition whereof is determined by means of said bimetallic actuator and serves to determine the state of a pair of switch contacts, the unit further comprising a manually-operable rocker type control cooperating with the lever such that a respective rocking action of the control effects a corresponding movement of the switch unit lever for opening and closing the switch contacts.

2. A thermally responsive switch unit as claimed in claim 1 wherein said bimetallic actuator is arranged to be snap acting.

3. A thermally responsive switch unit as claimed in claim 1 or 2 wherein said lever forms part of an overcentre spring mechanism serving to bias the lever towards respective contacts-open or contacts-closed conditions in dependence upon the pivotal condition of the lever.

4. A thermally responsive switch unit as claimed in any of the preceding claims wherein said rocker type control is assembled in operative relationship with the lever by virtue of a carrier for said control being fitted to the switch unit.

5. A thermally responsive switch unit as claimed in claim 4 wherein the switch unit has a body portion whereto components of the switch unit are assembled and said carrier is adapted to make a snap fit engagement with said body portion.

6. Athermally responsive switch unit as claimed in claim 5 wherein said switch unit body portion and said carrier are both formed as plastics mouldings.

7. A thermally responsive switch unit as claimed in any of claims 1 to 3 wherein the control is assembled in operative relationship with the lever by virtue of being mounted in a cover housing for the switch unit.

8. A thermally responsive switch unit as claimed in any of the preceding claims wherein the rocker type control is arranged to be self-centering.

9. A thermally responsive switch unit substantially as herein described with reference to Figures 1 to 4, or Figures 5A to 5C of the accompanying drawings.

10. An electrically heated water boiling vessel fitted with a switch unit according to any of the preceding claims.