GB2101407A

GB2101407A - Automatic electric kettle

Info

Publication number: GB2101407A
Application number: GB08213922A
Authority: GB
Inventors: Harden Dunn
Original assignee: Bulpitt and Sons Ltd
Current assignee: Bulpitt and Sons Ltd
Priority date: 1981-05-14
Filing date: 1982-05-13
Publication date: 1983-01-12

Abstract

In an automatic electric kettle a thermally sensitive element 8 is exposed to steam expelled from the interior of the kettle through a vent 22 and steam tube 24 while switch contacts 20, 21, preferably of a trident blade snap-action switch-type, are closed. A shutter 50 movable by the switch 7 has an aperture (53, Fig. 3 not shown) which is aligned with the steam tube 24 while the switch contacts 20, 21 are closed and thereby permits steam to impinge on the thermally sensitive element 8. When the switch contacts 20, 21 open the aperture (53) in the shutter 50 is moved out of line with the steam tube 24 and further impingement of steam on the thermally sensitive element 8 is inhibited, allowing the element to cool. <IMAGE>

Description

SPECIFICATION Electric kettles This invention relates to electric kettles of the automatic kind in which hot water vapour expelled from the 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.

Steam continues to be given off after the electric heating element has been disconnected by the switch actuated by the thermally sensitive element. Hot vapour continues to pass through the steam vent and to heat the thermally sensitive element, causing a delay before the switch can be reset for re-boiling the water.

The problem is greater with spout-filling kettles and with kettles in which vapour outlets other than the steam vent are purposely restricted to ensure an adequate flow of steam through the steam vent so that the thermally sensitive element responds quickly to boiling conditions.

Such arrangements are particularly necessary with robust thermally sensitive elements having an appreciable thermal capacity.

It is an object of the present invention to reduce the delay before the switch can be reset.

The present invention consists in an electric kettle of the automatic kind in which water vapour expelled from the 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 wherein is provided inhibiting means, operated on actuation of the switch by the thermally sensitive element, for inhibiting hot vapour, which emanates from the steam vent, from impinging on the thermally sensitive element.

The inhibiting means could inhibit hot vapour from the steam vent from impinging on the thermally sensitive element-by-directing the jet of hot vapour away from the thermally sensitive element or by shielding the element from the jet, but is preferably in the form of a valve or flap arranged to close the steam vent on actuation of the switch.

The valve or flap may be directly coupled to some suitable portion of the mechanism actuated by the thermally sensitive element, such as a member actually carrying a movable contact of the switch, for example, in a switch of the known trident-blade, snap-action type, or to an element, having suitable movement, of actuating or resetting mechanism of the switch for example an element of an over-centre spring-toggle linkage.

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 ofa 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. 801 8984. 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 1 7 to a first current carrying pin of the inlet socket 9. The switch 7 is of a known trident-blade, snap-action type having outer prongs 19 which are bowed by the fitting of the switch to the carrier plate and urge a movable contact 20 towards extremes of its permitted movement. In an extreme position as shown in the drawing the movable contact 20 is urged against a fixed contact 21 on the end of a conductor strip 1 6 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 a 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 port at the outlet of the steam tube 24 onto the thermally sensitive element 8. The steam tube is attached tothe 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 shape memory effect ("SME") metal alloy, for example a copper-zinc-aluminium alloy, of which, after heat treatment of the alloy, the modulus of elasticity changes, increasing the stiffness markedly, with increase of temperature over a critical range.

When heated by the steam the characteristics of the alloy cause the coiled element to extend longitudinally of the axis about which it is coiled, and returns the element to its original 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, a middle 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 middle prong 36 with the free end of a bar 47 secured to the carrier plate 1 2.

The housing 1 1 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 an 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 1 9. When the switch contacts are open the prongs 1 9 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 middle 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 1 8 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 middle prong 36 and open the switch contacts 20, 21.

A shutter 50, formed by a strip of plastics or other suitable material, is freely slidable in a slot 51 in the carrier plate 12. The slot is closely complementary to the cross-section of that portion of the shutter which is slidable in the slot in order to prevent or restrict the passage of vapour or moisture through the slot in the carrier plate 12. The carrer plate constitutes a wall that protects the switch from exposure to vapour. One end of the shutter 50 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 middle prong 36 while allowing considerable freedom of angular movement between the shutter and the middle prong.The other end of the shutter 50 overlies and rests on or lies close to the upper end of the steam tube 24. An aperture 53 in the shutter is aligned with the bore of the steam tube 24 when the switch 7 is in the closed position exposing the port formed by the outlet of the steam tube. When the switch is open the aperture 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 aperture 53 to impinge on the thermally sensitive element 8. As the shutter is coupled to the trident blade of the switch 7 the shutter does not move to shut off the steam until the trident blade moves with a snap action to open the contacts 20, 21. Until this occurs steam is permitted to play on the thermally sensitive element. When the thermally sensitive element has been heated sufficiently it 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 impinging on the thermally sensitive element 8. To avoid its interfering with the actuation of the switch, the shutter is freely slidable in the slot 51 and 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 reboiled 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 1 6, 1 7.

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.

Instead of the shutter 50, inhibiting means may be provided on the plunger 27, for example in the form of a flap extending below the plunger and parallel to its axis so as to overlie the upper end of the steam tube 24. The flap may be provided with an aperture which, when the switch contacts are closed, coincides with the bore of the steam tube 24 to allow steam to pass through the aperture and impinge on the thermally sensitive element.

When the contacts 20, 21 have opened the aperture is out of line with the steam tube the outlet of which is closed by the free end portion of the flap beyond the aperture.

Claims

1. An electric kettle of the automatic kind in which water vapour expelled from the 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 wherein is provided inhibiting means, operated on actuation of the switch by the thermally sensitive element, for inhibiting hot vapour, which emanates from the steam vent, from impinging on the thermally sensitive element.

2. An automatic electric kettle according to claim 1 wherein the inhibiting means inhibits hot vapour from impinging on the thermally sensitive element by directing the hot vapour away from the thermally sensitive element or by shielding the element from the hot vapour.

3. An automatic electric kettle according to claim 1 wherein the inhibiting means is in the form of a valve or flap arranged on actuation of the switch, to close a port through which hot vapour emanating from the steam vent passes to impinge on the thermally sensitive element.

4. An automatic electric kettle according to any preceding claims wherein the inhibiting means is a member mounted for axial movement between a first position in which hot vapour emanating from the steam vent is permitted to impinge on the thermally sensitive element and a second position in which such impingement is inhibited.

5. An automatic electric kettle according to any preceding claim wherein the inhibiting means is directly coupled to a part of a switch-actuating mechanism operable by the thermally sensitive element.

6. An automatic electric kettle according to claim 5 wherein the part carries a movable contact of the switch.

7. An automatic electric kettle according to claim 6 wherein the switch is of the trident-blade, snap-action type and the inhibiting means is coupled to the trident-blade.

8. An automatic electric kettle according to any preceding claim as appendant to claim 3 wherein the axially movable member has an aperture through which in the first position the port is exposed and in the second position the aperture is out of alignment with the port, to the extent that the port is closed by the member.

9. An automatic electric kettle according to claim 8 wherein the axially movable member extends through, and is freely slidable in, an opening in a wall that protects the switch from exposure to vapour, the opening being closely complementary to the cross-section of that portion of the member which is slidable in the opening.

10. An automatic electric kettle according to claim 8 or claim 9 wherein the axially movable member is a shutter, the port is the outlet of a steam tube leading from the steam vent to the outlet and the shutter lies on or close to the steam tube over the port.

11. An automatic electric kettle according to claim 10 wherein the shutter is coupled to a part of a switch actuating mechanism operable by the thermally sensitive element by a joint which enables the part to cause axial movement of the shutter but allows articulation between the shutter and part.

12. An automatic electric kettle according to claim 11 wherein the joint is formed by a tag on the shutter which projects through a hole in the part and is made captive therein.

13. An automatic electric kettle according to any of preceding claims 1 to 8 wherein the inhibiting means is formed or carried by a linearly movable member through which the thermally sensitive element actuates the switch.

14. An automatic electric kettle according to claim 13 wherein the thermally sensitive element is a helical coil which expands axially when heated and the linearly movable member is a plunger on which the helical coil is mounted and which the coil surrounds.

1 5. An automatic electric kettle according to claim 13 or claim 14 wherein the linearly movable member extends through, and is freely slidable in, an opening in a wall that protects the switch from exposure to vapour, the opening being closely complementary to the cross-section of that portion of the member which is slidable in the opening.

1 6. An automatic electric kettle according to any preceding claim wherein the thermally sensitive element is made of a shape memory effect alloy.

1 7. An automatic electric kettle substantially as described herein with reference to, and as illustrated by, the accompanying drawings.