GB2146231A - Improvements in or relating to electric liquid heating apparatus - Google Patents

Abstract

An electric kettle has a body (1) with an enlarged water vapour exit (45) leading via an aperture (44) to a chamber (34) containing a bimetal strip (35) that operates via a push rod (37) an over-centre snap action switching mechanism including a pivotally mounted dolly (13) which de-energises the heating element of the kettle when water therein boils. The rod (37) has an extension (40) that closes the aperture (44) when the water boils. The size area of aperture (44) is such that the formation of a water film across it, during use, is precluded. The cross-sectional area of the vapour exit (45) is not less than that of the aperture (44). <IMAGE>

Description

SPECIFICATION Improvements in or relating to electric liquid heating apparatus This invention relates to electric heating liquid heating apparatus and has particular although not exclusive reference to electric kettles especially electric kettles for domestic use.

Some forms of domestic electric kettle are fitted with thermally responsive devices which, when water in the kettle boils become heated by emitted water vapour, actuate a switching device which "turns off" the kettle.

It is sometimes found however that the thermally responsive device fails to actuate the switch with the result that the kettle may boil "dry" and this may damage the kettle.

It is an object of the present invention to provide electric liquid heating apparatus that doen not suffer from the disadvantage just described.

According to the present invention, electric liquid heating apparatus is provided in which a thermally responsive device so located as to be exposed to vapour given off by the liquid during heating is operatively connected to a switching device for de-energising the apparatus when the liquid boils and in which the vapour obtains access to the thermally responsive device via an aperture whose size and shape are such as to preclude the formation of a liquid film across the aperture, and in which means are provided for closing the aperture when the thermally responsive device responds to boiling of the liquid.

The thermally responsive device may be located in a chamber to the interior of which the vapour has access via the aperture. The chamber may be positioned adjacent a vapour exit in the body of the apparatus, the aperture being in substantial alignment with the vapour exit. The means may comprise a link operatively interconnecting the thermally responsive device and the switching device via a manually-operable member operation of which actuates the switching device to energise the apparatus and also open the aperture.

The link may pass through the aperture and include an end portion of a shape and size effective to close the aperture when the thermally responsive device responds to boiling of the liquid.

In one embodiment of the invention, the response of the thermally-responsive device to boiling may move the link to position the end portion in the aperture to close the latter.

The link may be so shaped that its position remains unchanged on return of the thermally responsive device to its initial condition.

Preferably, the switching device is located in a switch housing secured to the apparatus.

Advantageously, the chamber is also located in the switch housing, the closure means also being located in the housing.

The aperture may be rectangular and of an area of about 25 mm2, the vapour exit also being rectangular and of an area of about 120 mm2.

By way of example only, an electric kettle embodying the invention will now be described in greater detail with reference to the accompanying drawings of which: Figure 1 is a section of a part of the kettle, Figure 2 is a view in the direction of arrow A of Fig. 1 of a mounting forming part of the kettle shown in Fig. 1 and Figures 3 and 4 are sections on an enlarged scale of a part of the kettle with certain components in different positions.

The kettle has a body 1 part only of which is shown in Fig. 1 and to which is attached a handle (not shown) by means of which a user can carry the kettle. Inside the kettle and adjacent the base 2 thereof is an electric immersion heater 3 part only of which is shown in Fig. 1.

The heater 3 is of convoluted shape with two end portions that are secured in a metal mounting plate 4 of dished form. A single fixing is used to secure the mounting plate 4 to the body 1 and this comprises a threaded metal stud 5 fixed to plate 4 and which passes through an aperture in the body and is secured to the latter by a nut 6 screwed over the stud.

A resilient seal 7 positioned in the mounting plate 4 is compressed as the nut 6 is tightened and provides a water-tight seal.

The ends of the heater 3 also pass through separate holes in the body 1 thereby preventing rotation of the heater relatively to the body, the resilient seal 7 also acting to prevent leakage of water through the separate holes.

Detachably secured to the body 1 at a position aligned with the projecting ends of the heater 3 is a one-piece switch housing 8 of a plastics material. The rear apertured face of the housing is contoured to mate closely with the body 1 and it has spaced side walls 9, 10 between which extend a bridge 11 whose lower surface (as seen in Fig. 1) is contoured to provide a knife edge pivot 1 2 for a switch dolly 1 3 having an inwardly-extending limb 14 with a V-shaped recess 1 5 on its undersurface and in which locates the pivot 12 as can be seen in Fig. 1.The dolly 13 is maintained with the pivot 1 2 located in the recess 1 5 by a bowed snap-action leaf spring 1 6 that is stressed between the lower surface of limb 14 and a second bridge 1 7 between the side walls 9, 10 of the housing 8. One end of the spring 1 6 locates in a shallow groove in the lower surface of limb 14 while the other end locates in a shallow groove in the upper surface of the bridge 1 7.

Extending from the rear end of limb 14 on one side thereof is an extension 1 8 while from the other side projects a second extension 1 9 with a downwardly directed arm 20. Extensions 1 8 and 1 9 co-operate with stop surfaces 21, 22 respectively which depend from bridge 11 to limit movement of the dolly 1 3 in a clockwise direction as seen in Fig. 1.

Arm 20 is an operating arm for one limb of a resilient, electrically-conductive, member 23 of inverted, generally U-shape form having one limb 24 that carries an electrical contact 25 and a second limb that extends downwardly behind bridge 1 7 (when viewed as in Fig. 2) and is secured to the rear face of the bridge 1 7. A projection 26 extending sideways from wall 9 forms a pivot (or limb 24). Contact 25 co-operates with a fixed contact (not shown) secured to the one end of the heater 3.

Also secured to the rear face of bridge 1 7 is a second resilient, electrically-conductive member of inverted, generally U-shape form one limb 27 of which is visible in Fig. 2 through an aperture in the base of the housing 8. Limb 27 is in electrical contact with the other end of the heater 3.

The inner limbs (not shown) of the two electrically-conductive members are electrically connected to terminal pins 28, 29 that project outwardly from the front surface of the bridge 1 7 as viewed in Fig. 2. An "earth" pin 29A is located between pins 28, 29 as shown.

Also secured to the rear face of bridge 1 7 is a bimetal strip 30 that extends upwardly behind the dolly 1 3 and terminates adjacent an inner face 31 of an upward extension 32 of the dolly. The lower end of the strip 30 is in good thermal contact with the outer end of stud 5 to which it is secured by a screw 33.

As will be described below, the bimetal strip 30 acts as a safety cut out operated to protect the heater 3 against overheating.

At its upper end, the rear face of the housing 8 has a chamber 34 in which is housed a second bimetal strip 35 that extends downwardly from a fixing point 36 to a push rod 37 freely movable in a passageway 38 in an upper bridge 39 between the side walls 9, 10.

Those parts just described are shown on a larger scale in Figs. 3 and 4. The push rod 37 is rounded at one end and is of cruciform transverse cross section over that part of its length that is movable within the passageway 38. The push rod is cranked as at 37a and has an outer limb 40 inclined to lie parallel to the surface of the body 1 at this location. The limb 40 is of rectangular shape as will be made clearer below. As can be seen from Figs. 3 and 4, the lower end of the bimetal strip 35 locates in the cranked portion 37a of the push rod 37.

The chamber 34 is bounded at its rear by the bridge 39, at its sides by the side walls 9, 10 and across its front by a cover 41 with a part 42 that extends downwardly and forwardly from the upper part of the housing 8 to the body 1, and a second part 43 that inclines downwardly in a direction parallel with the body 1, the lower end of the second part 43 being located between a sealiny gasket (not shown) and the inner face of the housing 8. Portion 43 has a rectangular aperture 44 aligned substantially with a rectangular vapour exit 45 in the body 1. Portion 43 also has an aperture 42a whose function will be described below.

The size of the aperture 44 will be described in more detail later. Vapour exit 45 is of a size not less than that of aperture 44 and preferably is somewhat larger.

Limb 40 is sized to approximate to the size of aperture 44.

A snap-on cover (not shown) fitted between the walls 9, 10 closes the housing 8 and has an elongated aperture through which projects the right-hand (as seen in Fig. 1) surface of dolly 13.

In use, having filled the kettle with water, a user presses dolly 1 3 inwardly to the position shown in Fig. 3 and in which arm 20 pivots limb 24 about pivot 26 so bringing contact 25 into electrical connection with an adjacent contact on one end of the heater 3 to completing the energising circuit for the latter. As it pivots, dolly 1 3 slides the rod 37 into the Fig. 3 position. The snap action spring 1 6 has an over-centre action and this holds the dolly 13 in the Fig. 3 position.

In due course, the water in the kettle boils and water vapour escapes through the vapour exit 45 in the body 1 and enters the chamber 34 via the aperture 44 in the portion 43 of the cover 41. The vapour heats the bimetal strip 35 causing the latter to distort and the lower end to move into contact with push rod 37 and to move the later to an extent sufficient to pivot the dolly 1 3 against the action of spring 1 6 to a position of the dolly shown in Fig. 4. During that movement of the dolly, spring 1 6 is stressed and moved through its over-centre position and thus holds the dolly in the Fig. 4 position. Arm 20 of the dolly 1 3 pivots limb 24 about pivot 26 and contact 25 is moved away from the co-operating fixed heater contact and the heater energising circuit is broken. That this has happened is clearly visible to the user by virtues of the position of the dolly.

As the push rod 37 is moved to the right as viewed in Figs. 3 and 4, the limb 40 moves from the position shown in Fig. 3 to that shown in Fig. 4 and in which the aperture 44 in the portion 43 of the cover 41 is substantially closed thereby preventing further water vapour entering the chamber 34. This allows the bimetal strip 35 to cool rapidly and resume its Fig. 3 position. Rapid cooling is also assisted by the passage of water vapour from the chamber 34 to atmosphere via opening 42a. The kettle is therefore quickly ready for re-use if desired and the user is able to reset the dolly 1 3 and rod 37 to their Fig. 3 positions. It will be appreciated that as the bimetal strip 35 cools and returns to is initial condition as shown in Fig. 3, the position of the push rod 37 remains unchanged i.e. the rod remains in its Fig. 4 position.The lower end of the bimetal strip moves across the cranked portion 37a of the push rod 37 without contacting and moving the latter.

The aperture 44 must be of a size which permits a flow of water vapour into the chamber 34 that is sufficiently rapid to ensure a quick response of the bimetal 35 and thus a quick "turn off" once the water in the kettle boils. The size must also be such that the likelihood of blockage by the formation of a film of water across the aperture is eliminated.

However, it is found that increasing the size of the aperture 44 to eliminate the likelihood of water film formation so increases the rate of flow of steam into the chamber 34 that the bimetal 35 remains hot for an unacceptably long time period and this prevents the resetting of the dolly 1 3 by a user until the bimetal has cooled.

That problem is overcome in the embodiment described above by closing the aperture 44 once the bimetal has responded thereby stopping the entry of water vapour into the chamber 34 and facilitating the rapid return of the bimetal to the Fig. 3 position.

A typical size for aperture 44 is 25 mm2 the thickness of the part 43 which is of metal being 0.4 mm.

Vapour exit 45 in the body of the kettle is larger than aperture 44 so as to accommodate the limb 40 and provide sufficient space around it to allow free flow of water vapour to the chamber 34. Film formation over vapour exit 45 does not take place because the vapour exit 45 is of a size sufficient to prevent it.

The cross-sectional area of aperture 45 is, in the case of the 25 mm2 size aperture 44, 1 20 mm2 although it could of course be larger as has been explained above.

Another advantage of the construction described above is that the limb 40 can be located accurately with respect to the hole 43.

Both components are parts of the one-piece switch housing 8 and their relative positions are accurately determined.

In the event that due to some malfunction or misuse, bimetal 35 fails to switch off the kettle, bimetal 30 will become hot as the temperature of the heater 3 rises as water in the kettle is boiled off and eventually the dolly 1 3 will be pivoted by the bimetal 30 to its "off" position as described above and in this way damage to the kettle and the element due to overheating is avoided.

It will be understood that the invention may be embodied in liquid heating apparatus other than kettles, for example tea makers, milk warmers, coffee percolators and immersion heaters.

Claims (11)

1. Electric liquid heating apparatus in which a thermally responsive device so located as to be exposed to vapour given off by the liquid during heating is operatively connected to a switching device for de-energising the apparatus when the liquid boils and in which the vapour obtains access to the thermally responsive device via an aperture whose size and shape are such as to preclude the formation of a liquid film across the aperture, and in which means are provided for closing the aperture when the thermally responsive device responds to boiling of the liquid.

2. Apparatus as claimed in claim 1 in which the thermally responsive device is located in a chamber to the interior of which the vapour has access via the aperture.

3. Apparatus as claimed in claim 2 in which the chamber is positioned adjacent a vapour exit in the body of the apparatus, the aperture being in substantial alignment with the vapour exit.

4. Apparatus as claimed in claim 3 in which the means comprises a link operatively interconnecting the thermally responsive device and the switching device via a manually operable member operation of which actuates the switching device to energise the apparatus and also open the aperture.

5. Apparatus as claimed in claim 4 in which the link passes through the aperture and includes an end portion of a shape and size effective to close the aperture when the thermally responsive device responds to the boiling of the liquid.

6. Apparatus as claimed in claim 5 in which the response of the thermally-responsive device to boiling moves the link to position the end portion in the aperture to close the latter.

7. Apparatus as claimed in claim 6 in which the link is so shaped that its position is unchanged on return of the thermally-responsive device to its initial condition.

8. Apparatus as claimed in claim 2, 3, 4, 5, 6 or 7 in which the switching device is located in a switch housing secured to the apparatus.

9. Apparatus as claimed in claim 8 in which the chamber is located in the switch housing, the closure means also being located in the housing.

10. Apparatus as claimed in any one of claims 2-9 in which the aperture is rectangular and of an area of about 25 mm2, the vapour exit also being rectangular and of an area of about 120 mm2.

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