GB2078011A - Electric kettles - Google Patents

Abstract

In an automatic electric kettle a snap-action switch 7 opened by a thermally- sensitive element 8 and closed by a switch operating member 40 can be manually opened by a plunger 27 of insulating material which projects from the inside of the handle 2. The thermally sensitive element 8 is a bimetal or as shown is of helically coiled form which extends longitudinally when heated and is mounted on a larger diameter cap 32 of the plunger 27. One end of the element 8 abuts a flange 32 on the cap 31 and the other a slidable ring 35 which bears on the handle 2. When the kettle boils steam passing through a vent 22 heats the element 8 which expands and opens the switch 7 through a rod 28 forming part of the plunger 27. When the switch 7 opens, a shutter 50 moves to close the steam vent 22. When the switch has been closed by the operating member 40, it can be opened manually by pressing on the projecting end of the cap 31 of the plunger 27. <IMAGE>

Description

SPECIFICATION Electric kettles This invention relates to electric kettles of the automatic kind in which water vapour expelled from a steam vent when the water boils impinges on a thermally sensitive element to actuate an associated switch and thereby affect the power supply to the electric heating element of the kettle.

In one type of electric kettle of this general kind, the thermally sensitive element is enclosed in a housing outside the body of the kettle. The housing also encloses the electrical inlet socket of the kettle and the connections to the electric heating element, .and extends upwards from the region of the inlet socket to above the level of the top side wall of the kettle. A manual operating member is mounted in the upper region of the housing for closing the switch to connect the power supply to the heating element. It is in the upper region of the housing also that the thermally sensitive element is mounted. The steam vent is provided in the top of the kettle body and water vapour from it is directed onto the thermally sensitive element to open the switch and disconnect the power supply to the heating element.

Such kettles are hereinafter referred to as "of the type described".

It is an object of the invention to provide a simple means of opening the switch manually, if desired, before the water boils.

The present invention consists in an automatic kettle of the type described wherein a plunger is mounted in and adapted to project from the housing, which plunger is connected to the switch in such a way that, when the switch has been closed by means of the manual operating member the plunger is accessible to be moved by hand to open the switch.

Preferably the plunger is movable by the switch when the switch is closed by means of the manual operating member to a position in which it projects from the housing and is accessible to be moved by hand to open the switch.

The plunger may be connected to the switch through the thermally sensitive element or through a member acted upon by the thermally sensitive element to open the switch. It is preferred, however, that the plunger is connected directly to the switch and that it is also connected to the thermally sensitive element and is movable by the thermally sensitive element to open the switch when steam impinges upon the thermally sensitive element.

From this aspect the present invention comprises an automatic kettle of the type described wherein a plunger is mounted in and adapted to project from the housing, which plunger is connected to the thermally sensitive element and to the switch, is movable by the thermally sensitive element to open the switch when steam impinges upon the thermally sensitive element, and is movable by the switch when the switch is closed by means of the manual operating member to a position in which it projects from the housing and is accessible to be moved by hand to open the switch.

The plunger may project from the opposite side of the housing to the manual operating member, that is from the side which normally is towards a central vertical axis of the kettle, the plunger being disposed above the body of the kettle. Where the upper region of the housing is disposed adjacent a supporting limb of a handle of the kettle and the said side of the housing is against the supporting limb, the plunger extends through and projects from the supporting limb so as to be accessible by hand to open the switch.

The thermally sensitive element may be of a helically coiled form which extends longitudinally when heated by the steam. Such an element may conveniently be mounted co-axially on the plunger and be engaged at one end with a fixed abutment in the housing and at the other end with a bearing part of the plunger, the arrangement being such that when the element extends longitudinally and bears on the bearing part it moves the plunger towards the switch to open the switch. The co-axial arrangement of the thermally sensitive element and plunger provides a composite assembly which is readily accommodated in, and occupies a minimum of space in, the housing.

Alternatively the thermally sensitive element may be of a blade form which deflects when heated to move the plunger.

As the plunger is operable by hand and is exposed to steam it is essential for it to be electrically and thermally insulated. For this purpose the plunger preferably comprises a rod which is made from a suitable moulding material such as heat resistant plastics, glass or ceramic material, and which engages with the switch at one end, and is formed as, or provided with a cap at the other end of the rod which serves as a button or knob for moving the plunger by hand.

The plunger may be permanently connected to the switch or it may be releasably connected to it. The latter connection may be made simply by abutting engagement of an end of the plunger with a part of the switch.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a vertical section through part of a kettle according to the invention and Figure 2 is a fragmentary view of part of Figure 1 as seen in the direction of arrow II.

Figure 3 is a fragmentary sectional view on line Ill-Ill of Figure 1.

The kettle illustrated in the drawing is a modified form of the kettle described and illustrated in the specification of our Patent Application No. 8018984.

The kettle comprises a body 1, a loop handle 2 mounted on the top of the body over a filling opening fitted with a lid 3. An immersion heater (not shown) near the base 5 of the kettle body extends through an aperture in the side wall 6 of the kettle body to be electrically connected through a switch 7 associated with a thermally sensitive element 8 to an inlet socket 9, only a part of which is shown.

The switch 7 and thermally sensitive element 8 are mounted on the upper part of an elongate insulating carrier plate 12 which is mounted on the kettle by the same means which secures the immersion heater 4 to the kettle body, as described in the Specification of Application No. 8004470.

One side of the switch 7 is connected by a conductor strip.17 to a first current carrying pin of the inlet socket 9. The switch 7 is of a known trident-biade, snap-action type having outer prongs 19 which are bowed by the fitting of the switch to the carrier plate and urge a moving contact 20 towards extremes of its permitted movement. In an extreme position as shown in the drawing the moving contact 20 is urged against a fixed contact 21 on the end of a conductor strip 16 connected to one cold lead of the immersion heater. The other cold lead is connected to a second current carrying pin of the inlet socket 9.

A steam vent 22 through the wall of the kettle body close to the fixing of rear limb 23 of the loop handle 2 to the body opens into the bottom end of a plastics steam tube 24 vertically located in a channel recess 25 in the outer face of the handle limb 23, that is the face directed outwards away from a central vertical axis of the kettle. Steam expelled through the vent 22 when the kettle boils is directed by the steam tube 24 onto the thermally sensitive element 8. The steam tube is attached to the rear limb 23 of the handle 2 and is automatically positioned over the vent 22 as the handle 2 is mounted on the kettle body during assembly of the kettle.

The thermally sensitive element 8 is helically coiled like a spring and is made of a metal alloy which when heated by the steam will cause the coiled element to extend longitudinally of the axis about which it is coiled, and which returns the element to its original close-coiled condition after heating. The element is co-axially mounted on a substantially horizontally disposed plunger 27 supported by the carrier plate 12. The plunger 27 comprises a plastics rod 28 which is slidable in a hole through aligned bosses 29 and 30 on opposite faces of the carrier plate, and a plastics cap 31 fixed to one end of the rod 28 or formed integrally with it.

The cap is cylindrical with an annular external flange 32 near one end, being the end nearest to the carrier plate. At its free end 33 remote from the flange 32 the cap extends into an aperture 34 in the handle limb 23 and projects from the inner face of the limb above the top of the kettle body. It is on the cap 31 that the coiled thermally sensitive element 8 is mounted, one end of the element being arranged to engage a ring 35 slidable on the cap 31 and abutting against a surface of the handle limb within the recess 25 around the aperture 34 and the other end engaging with the flange 32 of the cap.When the switch is in its open position the end of the rod 28 remote from the cap is just out of contact with, or in only light abutting contact with, the centre prong 36 of the trident blade, and the free end of the cap projects only a short distance from the inner face of the handle limb. When the thermally sensitive element 8 is heated by the steam and extends it bears on the flange 32 of the cap and urges the plunger in the direction towards the switch 7 so that the free end of the rod 28 is urged against the centre prong 36 of the trident blade. When the pressure of the rod is sufficient the trident blade deflects to its other extreme position, opening the switch contacts 20, 21.The limit of movement of the plunger towards the switch is determined by abutment of a spigot 37 projecting beyond the flange 32 against an end face of the boss 29 on the carrier plate 12 towards which the cap moves as the plunger is urged towards the switch. Outward movement of the trident blade is limited by the engagement of the centre prong 36 with the free end of a bar 47 secured to the carrier plate 12.

The housing 11 comprises the carrier plate 12, a cover 39 which fits over, and closely around the periphery of, the carrier plate, and the recessed part of the rear limb 23 of the loop handle 2 with which the upper part of the cover 39 co-operates. In the wall of the cover 39 opposite the switch 7 and remote from the handle limb 23 on elongate, manual switch-operating member 40 is pivotally mounted by its upper end in an aperture in the cover. The operating member 40 is a hollow plastics moulding having a flange 41 around its open side which prevents the member from passing right through the aperture in the cover. A helical compression spring 42, engaging the flange 41 at one end and a lug 43 in the cover 39 at the other end, urges the operating member outwards. Teeth 44 projecting from the underside of the flange 41 are opposite the bowed outer prongs 19.When the switch contacts are open the prongs 19 abut the teeth 44. Pushing in the operating member re-sets the switch 7 to the closed position.

When the switch is set in the closed position the centre prong 36 of the trident blade bears on the rod 28 and urges the plunger away from the switch inwards towards the central vertical axis of the kettle so that the cap projects further from the face of the handle limb. The limit to the inward movement of the plunger is determined by abutment of the ring 35 at the end of the coiled thermally sensitive element 18 against the surface of the handle limb 23.

In the inward projected position the cap is readily accessible to be pressed by hand, if desired, to deflect the centre prong 36 and open the switch contacts 20, 21.

A shutter 50, formed by a strip of plastics or other suitable material, is slidable in a slot 51 in the carrier plate 12. One end has a projecting tag 52 which is passed through a small hole in the centre prong 36 near the moving contact 20. The free end of the tag 52 is enlarged, for example under heat, so as to attach the shutter 50 to the centre prong 36 while- allowing considerable freedom of angular move ment between the shutter and the centre prong. The other end of the shutter 50 overlies and rests on the upper end of the steam tube 24. A hole 53 in the shutter is aligned with the bore of the steam tube 24 when the switch 7 is in the closed position. When the switch is open the hole 53 is moved to the right (as viewed in Figure 1) and out of line with the face of the steam tube 24 which is covered by an imperforate end part of the shutter.

In use of the kettle, when the water boils steam issues from the steam tube 24 and passes through the hole 53 to impinge on the thermally sensitive element 8 which extends, as previously described, and opens the switch contacts 20, 21. The shutter is simultaneously moved to close the steam tube 24 and prevent further steam from inpinging on the thermally sensitive element 8. To avoid its interfer ing with the actuation of the switch, the shutter rests only lightly on the top of the steam tube 24. While some steam may still escape from the steam tube 24 the shutter serves at least as a baffle to direct any steam which may escape away from the thermally sensitive element 8.As the sensitive element 8 is no longer being heated by steam it cools more rapidly and contracts to its normal length, and in contracting will have moved clear of the surface of the handle limb. The switch can then be re-set by the manual operating member 40. The provision of the shutter 50 enables the switch to be re-set more quickly after operation of the thermally sensitive element than if it were not provided. This is an advantage as users often require water which is actually boiling and the invention enables the water in the kettle to be re-boiled that much sooner after actuation of the switch by the thermally sensitive element.

An electric lamp bulb 45 is disposed inside the hollow operating member 40 and is connected by leads 46 to each of the conductor strips 16,17. When the switch contacts are open there is a circuit from the supply through the resistance element of the immersion heater to the bulb 45 which is illuminated whenever the supply cable is connected to the inlet socket and is energised. When the switch contacts are closed the immersion heater circuit is completed and the bulb, being short-circuited, goes out.

In the above-described embodiment the plunger is connected directly to the switch. The plunger may, instead, be connected to the switch through the thermally sensitive element or through a member acted upon by the thermally sensitive element to open the switch. For example in the kettle described and illustrated in the specification of our Patent Application No. 8004470, the plunger could be arranged to operate on the rod 36 (Figure 2 of Patent Application 8004470) by which the bi-metal thermal ly sensitive element 8 operates on the switch 7. The rod 36 and element 8 may be modified, if necessary, the rod 36 being extended to project through a clearance hole in the element 8 for engagement by the plunger and a collar or shoulder being provided on the rod 36 to enable the element 8 to move the . rod and actuate the switch. When the plunger is 'operated by hand it can then move the rod 36 to .actuate the switch without stressing the bi-metal element 8.

Claims (13)

1. An automatic kettle of the type described wherein a plunger is mounted in and adapted to project from the housing, which plunger is con nected to the switch in such a way that, when the switch has been closed by means of the manual operating memberthe plunger is accessible to be moved by hand to open the switch.

2. An automatic kettle according to Claim 1 wherein the plunger is movable by the switch when the switch is closed by means of the manual operating member to a position in which it projects from the housing and is accessible to be moved by hand to open the switch.

3. An automatic kettle according to Claim 1 or Claim 2 wherein the plunger is connected directly to the switch.

4. An automatic kettle according to Claim 1 or Claim 2 wherein the plunger is connected to the switch through the thermally sensitive element or a member acted upon by the thermally sensitive element to open the switch.

5. An automatic kettle according to any one of preceding Claims 1 to 3 wherein the plunger is connected to the thermally sensitive element and to the switch and is movable by the thermally sensitive element to open the switch when steam impinges upon the thermally sensitive element.

6. An automatic kettle of the type described wherein a plunger is mounted in and adapted to project from the housing, which plunger is connected to the thermally sensitive element and to the switch, is movable by the thermally sensitive element to open the switch when steam impinges upon the thermally sensitive element, and is movable by the switch when the switch is closed by means of the manual operating member to a position in which it projects from the housing and is accessible to be moved by hand to open the switch.

7. An automatic kettle according to any preceding claim wherein the plunger projects from the opposite side of the housing to the manual operating member, that is from the side which normally is towards a central vertical axis of the kettle, the plunger being disposed above the body of the kettle.

8. An automatic kettle according to any preceding claim wherein, where the upper region of the housing is disposed adjacent a supporting limb of a handle of the kettle and the said side of the housing is against the supporting limb, the plunger extends through and projects from the supporting limb so as to be accessible by hand to open the switch.

9. An automatic kettle according to Claim 5 or Claim 6, or Claim 7 or Claim 8 as appendant to Claim 5 or Claim 6 wherein the thermally sensitive element is of a helically coiled form which extends longitu dinallywhen heated by the steam.

10. An automatic kettle according to Claim 9 wherein the helically coiled element is mounted co-axially on the plunger and engaged at one end with a fixed abutment in the housing and at the other end with a bearing part of the plunger, the arrangement being such that when the element extends longitudinally and bears on the bearing part it moves the plunger towards the switch to open the switch.

11. An automatic kettle according to Claim 10 wherein the plunger comprises a rod or rod-like portion which is made from a suitable electrically and thermally insulating material such as heat resistant plastics, glass or ceramic material and which engages with the switch at one end and is formed as, or provided with a cap at the other end of the rod which serves as a button or knob for moving the plunger by hand.

12. An automatic kettle according to any one of preceding Claims 1 to 8 wherein the thermally sensitive element is of a blade form which deflects when heated to move the plunger.

13. An automatic kettle substantially as described herein with reference to and as illustrated by the accompanying drawings.