GB2366183A

GB2366183A - An electric kettle with a pressure sensitive cut-off switch

Info

Publication number: GB2366183A
Application number: GB0020699A
Authority: GB
Inventors: Neil Martin Gould; Vei Lee Wuu
Original assignee: KETTLETECH Ltd
Current assignee: KETTLETECH Ltd
Priority date: 2000-08-22
Filing date: 2000-08-22
Publication date: 2002-03-06
Anticipated expiration: 2020-08-22
Also published as: CN1339282A; GB2366183B; GB0020699D0

Abstract

An electric kettle 2 comprises a water carrying body 4, an electrical heating element 6 disposed in the body, a pressure sensitive switch 12 (which is responsive to an increased pressure), in communication with the interior of the body and electrically connected to the heating element 6. The water carrying body 4 is preferably made up of two chambers, a main water carrying chamber and a secondary chamber 56 which is closed at its upper end. The pressure sensitive switch 12 is preferably in communication with the secondary chamber 56 via tube 58 and comprises a movably mounted piston means 24 which is displaced under the pressure of the steam generated in the secondary chamber 56. As the piston means 24 is displaced the circuit is broken and the heating element 6 and therefore the kettle 2 is switched off.

Description

<Desc/Clms Page number 1> MZCTRIC PMTTLE The present invention relates to an improved electric kettle for boiling water.

Electric kettles of tho type used for boiling water in the home (also referred to as "jugs" or "'electric jugs" in some countries) are generally provided with a switch mechaniom which is activdted by the user to turn on the kettle, and which automatically turns off the kettle when the water inside is boiling. Conventionally, the switch inQludeb a bimetallic memberp usually a disc or a strip. Steam from the boiling water condenses on the bimetallic member which bends under the influence of the heat, opening an adjacent electrical contact which is in series with the heating element, and thereby automatically switching off the kettle.

It has also been proposed to utilise a temperature sensitive electronic device employing a thermistor or thermocouple mounted in the kettle so that steam from the boiling water passes over the sensing area of the device. The thermocouple or thermistor is connected to an appropriate electronic circuit which operates as a switch

on receipt of a signal indicative of boiling.

Such switches suffer several drawbacks, the most significant for the user being the fact that it takes some time for the bimetallic-type switch to cool sufficiently so that it can be re-set. in order to facilitate the cooling of the switch the switch is open to the environment, and this allows steam to escape near the user's hand and condensed steam to drip out of the switch, and water from outside the kettle to enter into the switch, neither of which are deuirable in view of the live elecbric connectione in the switch.

The switch structure also requires a relatively large communicating duct to lead the steam onto the switch, which restricts the aesthetic design of the kettle.

The present inventors have proposed to provide a switch which operates on a quite different physical principle. According to the invention, there is provided an electric kettle for boiling water comprising a water carrying body, an electrical heating element disposed in the body, and a pressure- sensitive switch means in communication with the interior of the bodyt electrically connected to the heating element, and responsive to increased pressure

within the body.

By utilising the change in volume of water as it boils which in the confines of the kettle produces an increase in pressure, a switch can be provided which can immediately be reset.

In one embodiment the water-carrying body is provided with a main water receiving chamber and a secondary chamber in communication with the main chamber and closed at its upp#ar 4and, said owitch means being in communication with the secondary chamber. This arrangement means that even in the caae of a pQQzly f itting lid or even no lid, a pressure increase is generated, allowing the switch to operate. A conduit may be provided extending f rom the switch to an upper region of said secondary chamber to provide said communication.

The pressure-sensitive switch may comprise a movably mounted piston displaceable under the influence of increased pressure operatively connected to a trip switch which is adapted to break an electrical contact in series with the heating element in response to piston displacement. The trip switch includes a bi-stable rocker member biased by resilient means into one of two possible positions, including an OFF position in which the

electrical contacts are urged apart by a part of the rocker, and an ON position in which the electrical contacts touch. The piston is operatively connected to the rocker in order to move it in the OFF position in response to an increased pressure. The connection between piston and rocker is provided by a plunger member biased by resilient means to act against the rocker and movable between a retracted position and an extended position, and a gripping lever one and of which engages the plungrer member assisting to hold it in the retracted position and the other end of which engages the piaton, whereby the lovor releases the plunger in reapon5e to displacement of the piBtQn on increazed pres5ure. A user-actuable button is connected to said rocker to allow a user to re-set the rocker to the ON positJQn.

In an alternative airangement the pressure switch includes a pressure-sensitive diaphragm of flexible material operatively connected to a trip switch which is adapted to break an electrical contact in series with the heating element in response to displacement of the diaphragm.

Embodiments of the invention are described, by way of example only, with reference to the following drawings in which:

Figure 1 is a rear perspective view of a kettle in accordance with an embodiment of the invention showing the location of a cut-off switch; Figure 2 is a part cutaway view of the kettle of Figure 1; Figure 3 is an enlarged sectional view along the line A-A in Figure 2 in the region of the switch; Figure 4 is an enlarged sectional view of the switch; and Figure 5 is an exterior view of the switch.

Turning to the Figures, Figures I and 2 show a kettle (or ""jug") in accordance with an embodiment of the invention, generally deeignated 2, with the lid removed and with the handle al5o removed in order to better show the position of a cut-off switch and associated components. The kettle 2 compri*e5 a water-receiving body 4 having an electrical resistance heating element 6 arranged in the bottom of the body as is conventional. An exposed or "immersed" element is shown, but equally a hidden heating element structure whereby the heating means is placed on the lower side of a metal plate forming the base of the body could be utilised. The heating element 6 makes electrical connection with the external electrical contact pins 8 and 10 through switch 12. The external electrical contact pins also include an earth contact 14. The contacts 8, 10 and 14 are shown extending rearwardly from the kettle base for connection to a socket which is connected through a length

of cable to a plug for plugging into domestic mains a.c. supply; however,, a structure could be,utilized where the contact pins are received in a separate base part on which the kettle removably sits, with the base being connected to the mains supply, ie a so-called cordless, kettle.

As can be better seen in Figures 3, 4 and 5 the switch includes a switch housing 16 having a generally cylindrical wall 18, a top plate 20 and a separate base plate 22. The housing 16 encloses a piston 24 which is mount-ad to slidingly move within a cylindrical skirt 26 depending from the top plate 20. The upper surface or crown of the piston faces an opening 28. which communicates with the interior of the kettle, as discussed further below. The piston 24 co-operates with a trigger catch 30 which Is pivotably mounted in the housing having one end :32 which engages beneath the piston, and an opposite end 34 formed with a finger which engages a plunger 36. The plunger 36 is mounted to slide axially, being biased upwardly by a compression spring 38. The f inger of the end 34 of the catch 30 engages a ledge 40 on the plunger. Located on the top plate 20 is a bi-stable trip levex 42 having opposite parallel arms 43, 45 and which is mounted for rocking by means of knife edges 39 which extend from the arms 43 into corresponding V-slots in supports 47. As

best seen in Figure 3 a curved. strip spring 46 is provided between supports 48 and the arm 45 urging the lever 42 into one of two positions, either, as shown with the arm 45 adjacent the top plate 20 and arm 43 spaced therefrom (which constitutes an "ON" position), or a position where the arm 45 is raised rom the top plate 20 sitting adjacent stops 50 (the ""OFF" position). The arm 45 is arranged to lie between opposed arms of electrically conductive springy material of a contact sot 52 which has electrical contacts 54 urged together by the resilience of the arms - in the ON position as shownr the top of the plunger lies adjacent to the arm 45 liem adjacent the top plate 20 abutting the top of the plunger 36 which is in a retracted positionp and the contacts 54 being in physical contact. In the OVF position the arm 45 engages the upper 5trip 52 forcing the contacts 54 apart. The contacts 54 form part of the electrical circuit with pins 8, 10 and the heating element 6t so that when the electrical contact is broken no power is provided to the heating element 6. An appropriate button is provided which fits over the switch operably engaging the lever 42 at oppositely extending pins 44 so that the user can manually depress the lever 42 into the ON pQsition.

The kettle 2 is provided with an internal duct or chamber 56 open at its bottom extending down into the body 4 of

the kettle, having a steam catcher in the form of a narrow tube or conduit 58 extending from the top of the duct 56.

An end of the tube 58 fits over a collar 60 extending from the top plate 20p defining the opening 28 therein. It can be seen in Figure 3 that the crown of the piston 24 is provided with a peripheral ring or step 62 so that the entire piston surface is in fluid communication with the tube 58 even when in the upper closed Position.

The operation of the switch is as follows. The user having filled the kettle with water depresnem the bottom sQ that the lover is moved into the ON pomition in which the contacts 54 engage and power is supplied to the heating element. On boiling the volume increase which accompanie,5 the change of state causes a pressure increase which urges the piston 24 downwardly, causing the lever 30 to pivot and releasing the finger at 34 from the step of the plunger 36 which is displaced upwardly to extend beyond the surface of the plate 20. T#e upper end of the plunger 36 pushes the arm 45 of the lever upwardly and over-centre whereby it snaps into the OFF position through the action of the spring 46, the arm 45 urging the contacts 54 apart and breaking the electrical circuit.

As soon as the electrical supply is terminated and boiling finishes the increased pressure will also quickly

dissipate, so that if desired the kettle can be switched bark on again without having to wait for the switch to cool.

In a modified arrangement, instead of providing an internal duct 56 from which to "'catch" the bubbles of steam, the duct can be removed altogether, the tube 28 merely communicating with the interior of the open kettle body. In this case, it is essential that the kettle lid is securely fitted during use so that a pressure increase can arise within the kettle.

It is found that to generate appropriate force for operating the mechanical switch a piston of at least 10mm diameter is preferred. To fit conveniently within the confines of a typical kettle a maximum diameter is about 30mm.

Although the switch is shown located near the electrical pins it could be in other locations, with suitable ducting to connect the air space above the water which develops the pressure increase to the switch. For example, it could be located in the handle near its upper end with the tube 58 removed and instead a short passageway from the duct 56 or kettle interior provided.

In a further alternative for incorporation into a kettle with a hidden element the switch could'be located beneath the heating plate, with a pipe extending through an opening in the plate to a position near the top of the kettle providing the connection between switch and steam. In a further modification the piston can be replaced by a diaphragm of flexible material. A similar mechaiiical. switch arrangement can be utilised, with an end of the lever 30 engaging the diaphragm,

Claims

1 An electric kettle for boiling water comprising a water carrying bodyp an electrical heating element disposed in the body, and a pressdre-sensitive switch means in communication with the interior of the body, electrically connected to the heating element, and responsive to increased pressure within the body.

2. An electric kettle according to claim 1 wherein the water-carrying body is provided a main water =eceiving chamber and a secondary chamber in communication with the main chamber and closed at it5 upper end, zaid switch means being in communication with the secondary chamber.

3. An electric kettle according to claim 2 wherein a conduit is provided extending from the switch to an upper region of said secondary chamber to provide said communication.

4. An electric kettle according to any preceding claim wherein the pressure-sensiti-ve switch comprises a movably mounted piston displaceable under the influence of increased pressure operatively connected to a trip switch which is adapted to break an electrical contact in series with the heating element in response to piston displacement.

5. An electric kettle according to claim 4 wherein the trip switch includes a bi-5table rocker member biased by resilient means into one of two possible positions, including an OFF position in which the electrical contacts are urged apart by a part of the rocker, and an OIq position in which the electrical contacts touch.

6. An electric kettle according to claim 5 wherein the piston is operatively connected to the rocker in order to move it in the OFF position in response to an increased pressure.

7. An electrio kettle according to claim 6 wherein the connection between piston and rocker is provided by a plunger member biased by resilient means to act against the rocker and movable between a retracted position and an extended position, and a gripping lever one end of which engages the plunger member assisting to hold it in the retracted position and the other end of which engages #be piston, whereby the lever releases the plunger in response to displacement of the piston on increased pressure.

S. An electric kettle according to any one of claims 5 to 7 wherein a user-actuable button is connected to said rocker to allow a user to re-set the rocker to the ON position.

9. An electric kettle according to any one of claims I to 3 wherein the pressure switch includes a pressure- sensitive diaphragm of flexible material operatively connected to a trip switch which is adapted to break an electrical contact in series with the heating element in response to displacement of the diaphragm.

10. An electric kettle according to any preceding claim being an electric kettle.

11. An electric kettlg substantially as hereinbeforo described with reference to and as illustrated in the accompanying drawings.