GB2061013A - Electric switches - Google Patents

Abstract

A switch assembly, for an electric kettle, includes a switch actuating lever 70 pivotally mounted on a body 73 for movement between an off position in which the lever causes a pair of contacts to be held open, and an on position in which the contacts are closed. A bimetal device, mounted on the body 73, is operative when subjected to a flow of steam, to cause the lever 70 to move from the on position to the off position. An over-centre spring 111 acts between the body 73 and lever 70 and is of a Z or reverse Z shape comprising two parallel limbs 120, 121 located in opposed grooves in the body 73 and lever 70; each one of the limbs 120, 121 is provided with a free end portion 124, 126 which is bent to project from the limb in a direction away from the other limb so as to lie alongside the body 73 or lever 70. <IMAGE>

Description

SPECIFICATION Switch assemblies for electric kettles This invention concerns switch assemblies, for electric kettles and like vessels of the kind having a vessel wall and an electric immersion heater device, controlled by the switch assembly, wherein the vessel wall has a lower aperture through which the heater device extends and an upper steam outlet, and wherein the switch assembly is responsive to steam issuing from the steam outlet and to overheating of the heater device so as to switch off the electric power supply to the heater device, a vessel of this kind being hereinafter referred to as a "vessel of the aforesaid kind" for the sake of brevity.

According to the present invention there is provided a switch assembly, for a vessel of the aforesaid kind, comprising a body, switch contacts mounted on the body and an actuating mechanism; wherein the actuating mechanism includes a lever pivotally mounted on the body for movement between an off position in which the lever causes a pair of the contacts to be held open, and an on position in which said pair of the contacts are closed, includes a bimetal device mounted on the body and operative, when subjected to a flow of steam, to cause the lever to move from the on position to the off position, and includes an over-centre spring acting between parts of said body and lever so that the lever is positionally stable only in said on and off positions; characterised in that: said spring is of a Z or reverse Z shape comprising two parallel limbs and a connecting part joining said limbs; each one of the limbs is provided with a free end portion which is bent to project from the limb in a direction away from the other limbs; and said free end portions are disposed opposite each other diagonally of the spring, so as to lie alongside said parts of said body and said lever.

The limbs are preferably located in grooves provided in said parts of said body and said lever. The limbs are preferably of circular cross section, and the grooves are preferably of V-shaped cross section.

The invention will be described further, by way of example, with reference to the accompanying drawings, wherein: Figure I shows, in vertical cross section, part of a kettle incorporating a switch assembly of the invention; Figure 2 shows a rear elevation of the switch assembly; and Figure 3 shows an inside face of a carrier moulding of the switch assembly.

The switch assembly generally comprises a body, a steam actuated switch having an actuating mechanism 70 and a thrust member 71, and a dry overload switch 72.

The body is an assembly of three moulding, a main moulding 73, a carrier moulding 74 and a spacer moulding 75, which assembly is secured to a head 21 of an immersion heater device 20 as hereinafter described.

The head 21 is provided with a metal support member 25, which extends rearwards towards the body, and a cylindrical extension 26 which is exter nallythreaded to receive a fastener ring 27 for clamping a wall 10 of the kettle between the seal 22 and the fastener ring in known manner to secure the device 20 to the kettle.

The support member 25 is of elongate form and is formed to serve as a socket for a fastener 76.

The spacer moulding is an insulating heat resistant plastics member and is shaped to fit closely within the extension 26 and around the support member 25. The spacer moulding is apertured to provide two ways through which cold tails 24 of the element device extend and a guideway through which extends a further thrust member 78 of the switch 72; and is shaped to provide a mounting for a bimetal 80 of dished circular snap acting form. The bimetal 80 is peripherally located on the mounting by a cylindrical flanged metal retainer 81 which is a push fit around a peripheral surface of the mounting.

The retainer 81 may have a lug (not shown) which can be bent over around a shoulder on the spacer moulding to retain the bimetal in position on the spacer moulding.

The carrier moulding 74 is shaped peripherally to fit closely in the extension 26; has an exterior or rear face from which live and neutral pins 82 and 83 project; and has an inside face (Figure 3) which is shaped to inter-engage with the spacer moulding 75 in a predetermined mutual orientation to define therewith an internal chamber to receive resilient conductors 84 and 85 and a fixed conductor 86.

Stepped openings are provided in the carrier moulding to receive the cold tails 24, part cylindrically curved portions 88 of the conductors 84 and 86 and fasteners 89, which fasteners close the openings and clamp the portions 88 to the cold tails 24. The carrier moulding is moulded to include short pegs 90 upon which the conductors 84 and 85 are located during assembly, the pegs 90 being heated under pressure thereafter to form heads thereon to retain the conductors in position. Further pegs 91 are provided which are engaged in sockets in the spacer moulding 75, which pegs are headed during assembly of the switch assembly to retain the spacer and carrier mouldings together.The live and neutral pins 82 and 83 have stepped hollow ended extensions 92 which extend through the carrier moulding and are rivetted or swaged so as to be secured to the conductors 85 and 86 whereby to secure the latter and the pins 82 and 83 in position. Separable movable contacts 93 are provided on the conductors 84 and 85 which contacts 93 are common to the dry overload and steam actuated switches. The further thrust member 78 acts on the conductor 85.

An earth pin 94 has a foot 95 which is clamped rigidly to the support member 25 by the fastener 76, so that the foot bears against the bottom of a further opening in an outside or rear face of the carrier moulding to urge the latter and the spacer moulding towards the head 21 so as to thrust the bimetal 80 against a hot spot 23.

The rear or outside face of the carrier moulding 74 engages in a recess provided in a lower part of the main moulding 73. A peripheral surface 97 of the carrier moulding extends between and forms a seal between said lower part and the extension 26, and terminates at a sealing flange 98 which sealingly engages the spacer moulding around said chamber.

The lower part provides an annular channel 99 around the recess, into which channel 99 the ring 27 projects so as to shroud the surface 97 and define a moisture draining path 100 therebetween, which path 100 leads to a bottom drain 101 let into the bottom of the channel 99.

The lower part is secured to the carrier moulding, by two fasteners 102 which are received in blind sockets, so as to close the openings and to cover the further opening in the carrier moulding. A plug socket 103 extends rearwards from the lower part to shroud the live, neutra! and earth pins which project through close fitting ways in the lower part.

The main moulding has an upper part 104 which extends upwards to a hood 105 which overlies a steam outlet 12 and carries a steam actuated bimetal 106 so that the latter extends downwards within a steam space 13 defined between the wall 10 and the upper part 104. The steam space 13 extends downwards to a liquid drain path 14 around the ring 27 between tghe body and the wall 10.

The actuating mechanism 70 includes a lever 107 having a knob 108 which projects through the cover (not shown), a lower portion which encircles the plug socket 103 and is pivotally carried thereon by two co-axial pivots 109, and a bottom part 110 which is disposed below the socket 103 for actuating the thrust member 71. The knob 108 extends to engage an over centre spring 111 which abuts the upper part 104, and extends from that side of the body which is remote from the steam space 13 into the steam space through an opening 112 in the part 104 for actuation by the bimetal 106. The thrust member 71 is disposed below the socket 103 and extends slidably into said chamber through close fitting ways in the lower part of the main moulding 73 and the carrier plate 74 for actuating the switch contacts 93 by abutting and moving the conductor 84.

As shown in Figures 1 and 2 the spring is of Z-shape or reversed Z-shape, and comprises two parallel limbs 120 and 121, of circular cross-section, and a connecting part 123 joining said limbs 120 and 121. The limb 120 has a free end portion 124 which is bent upwards away from the limb 121 so as to lie alongside the upper part 104, and a V-shaped open ended groove 125 is formed in the upper part 104 to receive the limb 120. The limb 121 similarly has a free end portion 126 which is diagonally opposite to the portion 124, and is bent downwards away from the limb 120 so asto lie alongside part 127 ofthe knob 108 of the lever 107. The part 127 has a groove 128 similarto the groove 125 to receive the limb 121.

A cover is secured to the main moulding by means of fasteners inserted into sockets 113 in the main moulding.

In use, if the hot spot reaches a predetermined temperature, the dry overload bimetal moves rapidly from a convex to a concave shape, thereby displacing the further thrust member so that-the latter abuts and moves the conductor 85 to separate the contacts 93 and break the electrical circuit from the live pin to the element.

When the vessel boils, steam from the opening 12 will cause the bimetal 106 to bend outwards displacing the lever 107 from the on position shown to an off position, thereby moving the thrust member 71 forwards to abut and move the conductor 84 to open the contacts 93. The lever is stable only in the on and off positions.

It will be readily appreciated that the contacts operate in a closed or substantially closed chamber so as to be protected from dirt, which chamber is separated from the hot spot by the spacer plate and the bimetal device.

The invention is not confined to the precise details of the foregoing examples. For example, otherforms of bimetal, e.g. rectangular or elongate, or snap or progressively acting, can be used, and the fasteners 89 may be in the form of spring clips.

Also the steam actuated switch and the dry overload switch may have respective pairs of contacts, one contact of each pair being fixed.

Claims (6)

1. A switch assembly, for a vessel of the aforesaid kind, comprising a body, switch contacts mounted on the body and an actuating mechanism; wherein the actuating mechanism includes a lever pivotally mounted on the body for movement between an off position in which the lever causes a pair of the contacts to be held open, and an on position in which said pair of the contacts are closed, includes a bimetal device mounted on the body and operative, when subjected to a flow of steam, to cause the lever to move from the on position to the off position, and includes an over-centre spring acting between parts of said body and lever so that the lever is positionally stable only in said on and off positions; characterised in that: said spring is of a Z or reverse Z shape comprising two parallel limbs and a connecting part joining said limbs; each one of the limbs is provided with a free end portion which is bent to project from the limb in a direction away from the other limbs; and said free end portions are disposed opposite each other diagonally of the spring, so as to lie alongside said parts of said body and said lever.

2. An assembly as claimed in claim 1, wherein said limbs are located in open ended grooves in said parts of said body and lever.

3. An assembly as claimed in Claim 2, wherein said limbs are of circular cross section.

4. An assembly as claimed in Claim 2 or 3, wherein said grooves are of V-shaped cross section.

5. An assembly as claimed in Claim 1,wherein the actuating mechanism is substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

6. An assembly as claimed in Claim 1, wherein the spring is substantially as herein before described with reference to and as shown in Figures 1 and 2 of the accompanying drawings.