GB2292841A - Contact arrangement for a liquid heating vessel - Google Patents

Abstract

A contact arrangement for a liquid heating vessel 1 comprises means to open electrical contacts 21, 25 when the vessel is lifted from a supporting surface. The contact arrangement may be part of a thermal control device 4 and may include resilient means 50 and pin 60 to open said contacts 21, 25 when the vessel 1 is lifted. The control device 4 may include bimetal elements 38, 40 and a lever arm arrangement 30 and be formed in tray-like body which secures to, and forms part of, the bottom of said vessel 1. The control device 4 fastens to a printed circuit heating element 3 and may provide means to open the electrical contacts 21, 25 manually, using a knob 80; or when the water boils, using a steam sensitive bimetal 38; or when the heating element overheats, using a heat sensing bimetal 40. The tray may be arranged to include drainage points for condensed steam. Cord and cordless versions are disclosed. <IMAGE>

Description

Thermally Sensitive Controls This invention relates to thermally sensitive controls for use in water heating vessels, for example electric kettles and water heating jugs, and also extends to vessels incorporating such controls.

Electric water heating kettles and jugs generally comprise a metal or plastics body for receiving water which is to be boiled within which is located an electric immersion heater. The immersion heater typically comprises an elongate metal sheathed element which is welded onto a generally cylindrical head. The element is connected to the jug by passing the head through an opening in the side wall of the jug and clamping it against a thermally sensitive control. A resilient seal is usually provided around the head in order to prevent the leakage of water from the interior of the jug.

Other types of vessel include heating elements mounted to the underside of the floor of the water containing part of the vessel, for example the German Wasserkocher.

Known thermally sensitive controls incorporate switch means adapted to disable the heater in the event of its overheating as a result of, for example, the container having boiled dry or having been switched on with insufficient liquid inside it. In addition, the control may be provided with a mechanism which will switch off the heater in response to liquid within the vessel boiling. The latter mechanism traditionally incorporates an over-centre spring mechanism comprising an over-centre lever arranged to cooperate with a thermally sensitive actuating means, for example a bimetal, which is exposed to steam or vapour egressing from the vessel during boiling.The over-centre lever is coupled to a set of switch contacts and is movable via an unstable dead centre position by snap-action in response to operation of the actuating means from a first stable condition in which the contacts are closed to a second stable condition in which the contacts are open and the heater is thus disabled. A manually operable reset mechanism is also provided so that the user may return the lever to the first position to reenergise the heater. An example of such a control is described in GB-A-2181598. Many other arrangements are known.

The control may be wired directly to an electric cable, which is known a "fixed cord" arrangement or it may be arranged to be freely disconnectable from the cable. This may be achieved either by providing male terminal pins which project from the back of the control for cooperation with a female socket connector, or by providing terminal pins on the bottom of the jug which cooperate with a socket in a discrete base unit. This is known as a "cordless" arrangement. The latter of these arrangement is becoming increasingly popular because it allows the jug to be moved away from the electric outlet for the purposes of filling or pouring simply by lifting it from the base unit.

Although these known arrangements have been very successful, a modified design has been proposed which avoids the need to have a control mounted on the side of the jug. Thus, in GB-A-2222025 a cordless electrical water heating jug is described in which a modified heater element is mounted through an opening in the floor of the water containing part of the jug and clamped to a thermally sensitive control. The control used is a modified version of that described in GB-A2181598 and in order to accommodate it a relatively large compartment is provided under the floor of the jug. This compartment is closed by means of a cover.

Part of the cover incorporates a recess into which the terminal pins projecting from the back of the control protrude. This recess enables the pins to cooperate with a socket projecting from the base unit with which the jug is used.

One object of the invention is to provide an improved form of control suitable for use in an underfloor context and an improved vessel incorporating such a control.

According to a first aspect of the present invention there is provided a thermally sensitive control for an electric water heating vessel, the control preferably being arranged to be mounted to an immersion heater via an opening in the floor of the liquid containing part of the vessel, a body of the control having a bottom surface which forms part of the base of the vessel in use.

The invention also extends to a water heating vessel incorporating a thermally sensitive control located beneath the floor of the liquid containing part of the vessel, wherein a part of the control body forms part of the base of the vessel.

The control body preferably includes a substantially flat bottom surface which forms part of the external base of the vessel.

Where the vessel is of the so-called cordless type, it is particularly preferred that the control bottom surface includes a recess in which are located downwardly projecting terminals arranged for engagement with a socket connector of an associated base unit, the socket connector being received by the recess when the vessel is placed on the base unit.

When the control of this aspect of the invention is used in combination with a suitable vessel body, it simplifies the construction of the vessel because there is no need to provide a cover and associated fixing means to conceal the working parts of the control. This construction also has the advantage that the height needed to receive the control is reduced in that no separate cover is located beneath the control.

It is preferred for the control to have a body in the form of a tray within which the active components are received. By "tray" it is meant that the body has a bottom surface, more particularly but not exclusively, a generally planar bottom surface, with upstanding portions around some or all of its edges. The upstanding portions provide mechanical strength and may they also assist in locating the control within the base of the vessel. The tray is preferably formed of plastics.

It is believed that this tray-like construction of control provides significant advantages in itself and therefore viewed from a further aspect the invention provides a thermally sensitive control for an electric water heating vessel, the control having a body in the form of a tray within which the active components are received. As well as being a convenient way to provide a control according to the first aspect of the invention, this arrangement is particularly well suited to automated production, since the components may be inserted into the tray from one side only, thereby considerably facilitating construction.

As will be described further below, the preferred control comprises a steam operated bimetal, and in order for this to function, some steam must be allowed to reach the bimetal where it may condense. It is desirable to avoid the condensation reaching the active components of the control. Therefore, the tray preferably has a region for collecting condensation which may conveniently be formed by providing a barrier between the region of the tray where the steam operated bimetal is located and the remainder of the tray.

Openings in the bottom of the tray may be provided through which water may drain from the collecting region.

Controls according to the invention may be clamped to the traditional type of immersion heater discussed above, but these heaters are not ideally suited to being mounted through the base of a vessel. If such a heater is used, in order to allow the heater to be covered by the minimum amount of water, it is necessary for it to be bent into a more tortuous shape than when mounted in the traditional way. The advantages of the present invention are therefore more fully realised when the control is used in combination with a printed circuit heater, such as that described in our co-pending International patent application No. PCT/GB94/00300.

Elements of this type may comprise a substrate of stainless steel, for example in the form of a disc, coated on one side with a layer of insulating ceramic material. An electrically conductive track is then formed on the insulator which is subsequently covered with a further layer of insulating material. Because these heaters are most conveniently planar, in contrast to the traditional type, they are better suited to being mounted via an opening in the centre of the base of the jug. When mounted in this way, they are visually neat, and, as they are thin, may be mounted close to the base of the jug, such that only a small quantity of water is required to cover them.

It is possible to provide projecting studs on such heater elements which may pass through holes on the control and be secured by means of nuts or clips in a manner similar to that employed with traditional heaters. However, this is inconvenient because the studs will interfere with the apparatus used to deposit the conductive track. It is therefore preferred to provide holes in the heater element through which fixing elements such as screws or bolts may pass. The control of the invention is therefore preferably adapted to be clamped to the heater by means of fixing elements received in bores provided in an upper part of the control.This also further simplifies the assembly of a completed jug since after the control has been positioned under the opening in the jug body, the heater element may be lowered into position and connected to the control by means of, for example, two or three screws or bolts inserted from above into threaded bores.

The assembly of a complete jug may be further simplified if one of the threaded bores is formed in an electrically conductive member which is arranged to abut the lower face of the printed circuit heater element when the heater element is connected to the control.

This is because in this way the heater element is sandwiched between two metal surfaces (the head of the screw and the upper part of the electrically conductive member) and therefore a reliable earth connection may be formed. The electrically conductive member may be wired to a suitable earth, but in the case of a cordless arrangement it is particularly preferred for it to be formed integrally with an earth pin which is arranged to engage with a base unit.

The provision of an earth in this way is considered in itself to be a new departure and therefore from a further aspect the invention provides a thermally sensitive control for an electric water heating vessel, the control being arranged to be mounted to a printed circuit heater element via an opening in the vessel and having an electrically conductive member arranged to be clamped to a face of the printed circuit heater, in order to provide an earth connection thereto.

Preferably, the electrically conductive member is a metal bushing to which the control is attached, for example by means of a screw or bolt.

Printed circuit heaters may be provided with projecting terminals corresponding to the cold leads on an immersion heater for connection to the control in the traditional way. However, as in the case of projecting studs, this is inconvenient and it has been found to be preferable to provide terminals by removing an area of the outer insulating material over the ends of the tracks, leaving terminals which are virtually flush with the surface of the heater.

The control is therefore preferably provided with contacts arranged to form a connection with terminals on the surface of a printed circuit heater element.

Ideally, they comprise resiliently biased first contacts on the upper part of the control arranged for direct abutment against the heater terminals when the heater element is mounted to the control.

It will therefore be seen that in the preferred forms of the invention discussed above, the necessary mechanical and electrical connections (including an earth) to a plate heater may be formed simply by clamping the plate heater to the control.

Whilst it would be possible to switch the supply of electrical current to the heater element by moving the first contacts on the control against and away from the terminals on the heater element, this could lead to arcing which in time could damage the heater element terminals, thereby shortening the life of the jug. It is therefore preferred for the first contacts to be arranged for permanent abutment against the heater element and for a second contact to be associated with at least one the first contacts, the second contact cooperating with a third contact to form a switch operable to control the flow of electric current to the first contact, and therefore to the heater element.

Viewed from a further aspect the invention provides a thermally sensitive control for an electric water heating vessel, the control being arranged to be mounted to a printed circuit heater element via an opening in the vessel, wherein first contacts are provided for abutment against exposed terminals of the heater element and a second contact associated with at least one of the first contacts, the second contact being arranged to co operate with a third contact to form a switch operable to control the flow of current to the first contact.

This arrangement can provide single pole operation.

However, by providing second and third contacts associated with each of the first contacts a double pole switch may be obtained.

The surf aces of the contacts forming the switch may conveniently be silvered in order to prevent excessive damage by arcing.

Preferably, the first and second contacts are mounted on opposite surfaces of metal leaf member which provides the resilient force for urging the first contact against the terminal of the heater. The first and second contacts may be arranged one on top of the other (with the leaf member in between) or may be spaced from one another somewhat along the leaf member.

In this embodiment, the third contacts are movable and are resiliently biased towards the second contacts, for example by mounting them on the ends of resilient conductive leaf springs. A particularly convenient method of construction is for the leaf springs to be formed integrally with the live and neutral terminals of the control. In the case of control designed for use with a cordless jug, these terminals may take the form of pins, or other suitable male terminals projecting downwardly for cooperation with a socket in a base unit.

Otherwise, they may be arranged for direct connection to an electric cable in order to provide a fixed cord jug.

If it is desired for the control to be capable of switching off a water heating vessel when water within that vessel boils, it may be provided with a generally horizontally disposed snap-acting lever arm which is operable to hold the switch contact open. The lever arm may most conveniently be actuated by means of a first snap-acting bimetal cooperating therewith. The bimetal is preferably laterally displaced along the control from the contacts so that it may be aligned with the end of a steam channel in a complete jug. Although the bimetal could be mounted on an upper part of the control body, it is preferably mounted on the lever arm itself with a reaction surface against which it may be act being provided on the tray of the control.This arrangement serves to improve the thermal isolation of the bimetal from the body of the vessel so that it is operated by the temperature of steam, rather than by heat conducted via the bottom of the vessel (which is in close proximity to the heating element). It also avoids the problem which would occur if the bimetal were to be located on the floor of the control where condensed water may accumulate, namely that such water could provide a heat sink sufficient to prevent the bimetal from reaching its operating temperature.

Thus, this arrangement provides significant advantages in its own right, and therefore viewed from a further aspect, the invention provides a thermally sensitive control for an electric water heating vessel, the control being arranged to be mounted beneath the floor of the water containing part of the vessel, the control comprising a bimetal actuated in response to liquid with the vessel boiling, and which in use serves to move a snap acting lever arm in order to switch off the heater of the vessel when water within it boils, wherein the bimetal is mounted on the lever arm.

The invention extends to a vessel incorporating such a control located beneath the floor of its water containing part.

Preferably the bimetal is actuated by steam impinging thereon.

Thus, in a vessel constructed with such a control, when water within the vessel reaches boiling point, steam will pass from the body of the vessel down a steam channel adjacent to the end of which the steam-sensitive bimetal of the control is located. This will cause the bimetal to move from its ambient configuration into its actuated configuration and in doing so it will trip the lever arm. This will in turn open a set of switch contacts and thereby disconnect the heater element.

If the vessel is turned on without any water inside it, no steam will be produced and so the steam-operated control will not work. It is therefore standard practice to provide a mechanism to prevent overheating in that event. This is preferably achieved by means of a second snap-acting bimetal mounted on the upper part of the control arranged to be in good thermal contact with the bottom of a heater element to which the control is mounted, the second bimetal being actuable to disconnect the heater element from the supply of current in the event of the heater overheating.

Although a further set of contacts may be provided for the second bimetal to operate on, a more efficient use of components is achieved in the preferred embodiment if the second bimetal is also actuable to separate the second and third contacts discussed above.

This is preferably achieved by providing a yoke which is movable by the second bimetal, that movement serving to separate the second and third contacts. The use of a yoke allows a comparatively small snap-acting bimetal to actuate a pair of comparatively widely spaced contacts in a double pole switch. In addition, the yoke may be provided with sufficient freedom of movement such that if one pair of contacts becomes welded closed, the other pair can still be operated by the yoke.

Whilst simply moving the contacts apart in this way should prevent serious damage as a result of overheating, it will not permanently turn off the current to the heater since as soon as the heater has cooled down, the second bimetal will move back to its ambient position and allow current to flow to the heater. It will therefore result in the current to the heater element cycling and the heater remaining hot, but not dangerously overheated.

However, a more satisfactory result may be achieved if the yoke is arranged such that further movement of it, beyond the point at which the contacts first open, serves to actuate the snap-acting lever arm as if the kettle had boiled. The lever arm will thereby further open the contacts and hold them in the open position until reset by a user.

It should be noted that the initial movement of the yoke preferably opens the contacts prior to the lever being tripped. This means that the heater will still be disabled (and will cycle) in the event that a user should manually hold the lever in the "on" condition during overheating.

Of course it would always be possible to provide two further actuators, rather than just a single second actuator as overheat protection means. In such an arrangement, individual actuators may contact different parts of the heater and act to open the contacts in the respective poles of the supply to the heater, without the need for a yoke. The actuators may each trip the snap-acting lever arm so as to disable the heater.

A further useful feature which may be conveniently provided in a control of the present invention is means to prevent the vessel in which it is incorporated from being picked up and moved with the element is still switched on. In the case of a corded apparatus, it is clearly dangerous for a person to carry a vessel of boiling water which is still being heated. In the case of a cordless apparatus, whilst the act of lifting the jug from its base will obviously disconnect the supply of current, this may lead to arcing between the female connector of the base unit and the male terminals of the control which could damage the terminals.Thus, the preferred embodiment of control further comprises means responsive to the movement of the control from a surface on which it is placed, which means is arranged to separate the switch contacts when such movement occurs. A convenient way of achieving this is to provide a resilient member which may act upon the yoke in order to open the switch contacts, together with a movable member such as a pin passing through the base of the control, the arrangement being such that engagement of the pin with a surface on which the control is placed will restrain the resilient member from engaging the yoke.

Thus, as long as the control is left upon a surface, the resilient member has no effect on the operation of the control and the control may be turned on as previously described. However, if the jug is raised from that surface, the resilient member is released and will cause the yoke to open the switch contacts. Preferably, the resilient member will move the yoke far enough to trip the lever arm in order to fully open the switch contacts.

This arrangement is believed to be a new departure in its own right, and therefore viewed from a still further aspect the invention provides a thermally sensitive control for an electric water heating vessel, the control having switch contacts for controlling the supply of electric current to the vessel, wherein resilient means are provided to hold the contacts open, the resilient means being disabled when the vessel is placed on a support surface.

Stated more generally, the invention provides a thermally sensitive control for an electric water heating vessel, the control having switch contacts for controlling the supply of electric current to the vessel, wherein resilient means are provided which are arranged such that, when the vessel is lifted from a support surface there for said means act to open the switch contacts.

In the preferred embodiment discussed above a movable member may conveniently pass through the base of the control, the arrangement being such that abutment of the movable member against a support surface disables the resilient means.

The resilient means may comprise be a spring such as a leaf spring and may act to trip a spring loaded mechanism, such as an over-centre lever arm, so as to open the contacts when the vessel is lifted from a support surface. The resilient means'may be disabled by being deflected by a movable actuating member which in use will extend from the bottom of the control so as to be engageable with a support surface. The actuating member may be formed integrally with the spring. For example, the spring may be generally T-shaped, with one of the top arms of the T being fixedly supported in the control, and the vertical arm of the T acting as the actuating member, and the other arm of the T acting on the lever arm. Such an arrangement will allow a pivotal actuating movement of the top arms of the T.

The trip arm may also be the arm which is acted on by the boiling sensitive bimetal and by the overheat bimetal and by the overheat protection bimetal or bimetals, that arm also being coupled to manually operable knob or the like to allow a user of the vessel to switch the vessel on or off.

Accordingly, double pole protection may be provided with a single trip lever which is trippable by four different mechanisms - manually by a user, in response to liquid in the vessel boiling, in response to the vessel being lifted from a support surface and upon one or more portions of a heater overheating.

The invention also extends in broad terms to a water heating vessel incorporating an electrical control with switch means for disabling an electrical heater of the vessel, the vessel or control including a resiliently biased member engageable with a support surface when the vessel is placed thereon, such engagement enabling the heater to be energised but the heater being disabled whenever the vessel is lifted up from the support surface.

Certain embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a sectional view of part of a cordless electric water heating jug employing a control according to the invention; Figure 2 is a plan view of the control with the outline of the water heating jug in which it is employed indicated in phantom; Figure 3 is a partially cut-away plan view of the control; Figure 4 is a sectional view along the line A-A of Figure 3; Figure 5 is a partially sectional view generally corresponding to Figure 1 in which the heater of the jug is energised; Figure 6 is a view corresponding to Figure 5 in which the heater is isolated; Figure 7 is a sectional view along the line B-B of Figure 1 illustrating the contacts in a closed configuration;; Figure 8 is a view corresponding to Figure 7 in which the contacts are in their open position; Figure 9 is a perspective view illustrating a yoke and a spring which form part of the control; and Figure 10 is a sectional view corresponding to Figure 1, illustrating a modified control used in a fixed cord jug.

As may be seen in Figures 1 and 2 an electric water heating jug 1 has a moulded plastics body 2 within which are located a printed circuit heating element 3 and a control 4. The illustrated jug is of the so-called cordless type and is designed to co-operate with a base unit (not shown). The upper part of the jug is not illustrated, but it may be of any conventional shape.

The control is located within a recess 5 in the bottom of the jug and it has a generally flat bottom surface 5' which forms part of the outer surface of the base of the jug. In the centre of the bottom surface there is a recess in which the earth pin 11, live pin 15 and neutral pin 16 are located (see Figure 4). These pins are received within a corresponding socket in the base unit which would in turn be connected to a source of electrical power. The water heating jug may be removed from the base unit in order to fill it with water at a remote location.

The upper part of the control is received within a circular opening 7 at the bottom of the water receiving part of the jug. Mounted directly over the opening is the heater element 3, and this is connected to the control 4 by means of metal screws 8 and 9 passing through holes in the heater element. The bottom of the jug is therefore clamped between the heater element the control. A ring shaped seal 10 is provided around the circumference of opening 7 to prevent leakage of water from the jug. The seal is also provided with inwardly projecting portions 10' which surround the parts of the heater element in which the screws 8 and 9 are received in order to prevent leakage of water via the screw holes in the heater element.

Whilst screw 9 serves only to connect the heater element 3 to the control 4, screw 8 also serves to earth the heater element. It is received within a threaded brass bushing 12 in the control which is formed integrally with earth pin 11. As the screw is tightened it compresses the seal 10 until the heater element 3 abuts the bushing. In this way, the heater element is directly clamped between two metal surfaces, and so a reliable earth connection is formed.

The jug is further provided with a steam channel 13 which communicates via a hole through the wall of an upper part of the jug with the water receiving portion thereof. The purpose of this channel is to allow steam to reach steam bimetal 14 in the control in order to switch off the jug when it boils as will be described below.

Turning now to the construction of the control itself, the live pin 15 and the neutral pin 16 are in the form of hollow tubes of copper and extending from the upper parts thereof are leaf springs 20 which lie at right angles to the axis of the pins. As will be seen most clearly in Figure 3, the leaf springs 20 extend longitudinally towards the left (as shown in that Figure) of the control. At the distal end of each leaf spring 20 is provided a movable electrical contact 21.

Mounted above each contact 21 is a double contact arrangement 22 (one of which has been omitted from Figure 3 for reasons of clarity). Each of these arrangements has a metal support leaf 23 which is fitted into an opening 24 at the edge of the body of the control. As may be seen in Figure 8, beneath each metal support leaf 23 carries a lower contact 25 which in combination with the contact 21 on the underlying leaf spring forms a pair of switch contacts. Above each contact 21 is an upper contact 26 which is biased by the metal support leaf 23 against the heater element 3 as the heater element 3 is secured to the control 4. The upper contacts are aligned with terminals at each end of a conductive track of the heating element 3, and in this way, electrical connection is made to the heater element 3.

It will be seen that if the leaf springs 20 are allowed to bias the contacts 21 against the lower contacts 25, the heater element may be energised via the live and neutral pins 15 and 16.

The plastic body of control 4 is in the general form of a tray 4'. Within this is provided a horizontally arranged over centre lever arm 30 which cooperates with the leaf springs 20 to move the contacts 21 against on away from lower contacts 25 in order to connect or disconnect the heater element from the electrical supply. As may be seen from Figures 2 and 3, the lever arm extends almost the full length of the control 4, its central part passing around each side of the recess in which the pins 11, 15 and 16 are located.

Projecting laterally from each side of it are forwardly facing knife edge pivots 31 which are received within Vshaped recesses 32 located each side of the tray. (The engagement of the knife edge pivots in the recesses may be seen most clearly in Figures 5 and 6). In addition, at the bottom of the lever arm there is a lug 33' having a further V-shaped recess 33 in which is received one end of a C-spring 34 (see Figure 1). The other end of the C spring 34 is mounted within a further V-shaped recess in a pip 39 provided on the base of the tray 4.

The C spring is held in compression and serves to push the knife edge pivots 31 into the V-shaped recesses 32, thereby holding the lever arm within the tray 4'.

The combination of the C spring and lever arm provides an over-centre mechanism in which the lever arm has two stable positions. As shown in Figure 5, if the right end (as shown) of the lever arm 30 is pressed fully towards the tray 4' a first stable position is achieved. If the lever arm is then pivoted towards the position shown in Figure 6, it passes through an unstable dead centre position before reaching the second stable position shown in that figure. The position shown in Figure 5, in which the contacts 21 and 25 are closed is considerably nearer the dead centre position than that shown in Figure 6 in which they are open. The former is therefore less stable. In a complete jug, a control knob 80 (Fig. 5) would be provided on the end of the lever arm which would project through an opening 81 in the wall of the jug to enable a user to move the lever arm.

The left end of the lever arm 30 is provided with abutment surfaces 35 which cooperate with respective leaf springs 20. When the lever arm is in the position illustrated in Figure 5, the abutment surfaces are clear of the leaf springs, but as the lever arm moves towards the position shown in Figure 6, the abutment surfaces 35 move downward into contact with respective leaf springs 20 and as they do so serve to move the contacts 21 away from lower contacts 25, thereby disconnecting the heater element 3 from the live pin 15 and neutral pin 16. The contacts are separated by at least 3mm and therefore the control knob may, according to industry standards, be marked with the word "off" corresponding to this configuration.

As may be seen in Figure 2, a snap acting bimetal 36 is mounted to the lever arm 30 over an opening. The bimetal is of a type described in UK Patent No. 1542252 Its outer margin is held in place on the lever arm by means of pips 37, but its central tongue 38 is free to move downwardly through the opening in the lever arm.

This will occur when the bimetal reaches its nominal actuating temperature (around 800C) as a result of steam passing down steam channel 13 from the body of the jug 1. If the lever arm is initially in the position illustrated in Figure 5, as the tongue 38 moves downwards it will abut pip 39 on the base of the tray and the reaction to this force will pivot the lever arm past its dead centre position and into the position shown in Figure 6.

In use, in order to switch on the jug, the user will move the lever arm 30 into the position shown in Figure 5 by means of knob 80. This will also cause the contacts 21,25 to close, and thereby energise the heater element 3. When water within the jug boils, steam will be forced down steam channel 13 to the control 4 where it will heat steam bimetal 14 to its actuating temperature. As discussed above, this will cause the lever arm to snap into the position shown in Figure 6, and will therefore disconnect the heater element 3.

The control also provides dry switch on protection in order to prevent serious overheating if the jug is switched on without any water in it. This is achieved by means of a second snap-acting bimetal 40, having a nominal actuating temperature of about 1400C, whose tongue is screwed to the upper part of the control 4 so that its marginal portion is in thermal contact with the bottom of the heater element 3. A yoke 41, shown in detail in Figure 9, is mounted beneath the movable free edge 40' of the marginal portion of the bimetal which is adjacent to the free end of the torque. The yoke has a downwardly projecting pin 42 which is slidably received within a vertical hole in the control, allowing the yoke to move up and down. The yoke 41 is provided with ears 43 at its lateral edges and each of these rests upon one of the leaf springs 20.On the base of the yoke, slightly inboard of the ears are further abutment surfaces 45 which are aligned above extreme end portions 46 of the lever arm 30. The central portion of the top of the yoke 41 has a pip 44 on which the free edge 40' of the second snap-acting bimetal 40 may act.

If the heater element reaches an excessively high temperature then it will cause the free edge part 40' of the second snap-acting bimetal to move downwardly. As it does so it will depress the yoke 41, whose ears 43 will in turn depress the leaf springs 20. Initially, the leaf springs will be moved downward so that the contacts 21 and 25 separate by about imam. However, further downwards motion of the yoke will cause the abutment surfaces 45 to depress the end portions 46 of the lever arm 30 located under surfaces 45 (Figure 2).

This movement will be sufficient to move the lever arm past its over-centre position, causing it to attain the configuration of Figure 6. Thus, overheating will cause the contacts to become fully separated as if the control had operated in the normal way in response to boiling.

Because the initial movement of the yoke opens the contacts without moving the lever arm 30, this lost motion provides an additional safety feature because even if a user were to hold the lever arm in the "on" position he would not be able to hold the contacts closed against the operation of the second snap-acting bimetal 40.

Also arranged to act upon the yoke 41 is a spring 50 shown in detail in Figure 9. One end 51 of the spring 50 is provided with laterally projecting fingers 53 which secure it within a recess formed centrally in the control body portion. Its distal end is provided with two arms 54 which are received within slots 55 in the yoke 41. The spring 50 serves to bias the yoke 41 downwards against leaf springs 20 in such a way to hold the contacts 21,25 open. In fact, the spring urges the yoke downwardly with sufficient force to move the lever arm 30 past its dead-centre position and so if not restrained it will prevent the contacts from closing.

However, beneath the central part of spring 50 is a pin 60 which is slidably received within a hole passing through the bottom of the tray. The upper part of the pin is provided with a circumferential flange 61 which serves to retain it within the control. As may be seen in Figure 8, the pin is long enough to project slightly from the base of the control. If the jug is placed upon a flat surface, however, then the pin will be pushed upwards by the reaction of that surface to the position shown in Figure 7. This pushes spring 50 upwards, thereby preventing its arm 54 from depressing yoke 41.

Thus, provided that the jug is placed on a surface, the control will operate as previously described.

However, if the jug is switched on and is then lifted from its base unit, or, in the case of a jug having a fixed cord (as described below) lifted from the flat surface on which it is used, the pin will drop to the position shown in Figure 8 which will allow the yoke to open the contacts and move the lever arm into the off position. In the case of a cordless vessel this ensures that no arcing will occur between the pins when it is lifted from the base unit, and, in the case of a corded jug, the dangerous practice of moving an energised jug is prevented.

A further feature of the control is the provision of an upstanding wall 61 (Figure 1) which extends laterally across most of the width of the tray. This is to retain condensation from the steam channel 13 in order to keep it away from the electrical contacts at the opposite end of the control. At each side of the wall 61, there are openings through which the side portions 30' of the lever arm extend. In order to avoid water from passing through these openings, drainage holes are provided adjacent to them through the base of the control through which any water may flow. As a further safety measure, it will be noted that all the electrical contacts within the control are spaced away from the bottom of the tray, and so even if water passes the wall 61, it will be retained well below the electrical contacts.

As discussed above, the bottom of the control 4 forms the base of the complete water heating jug and therefore no separate cover is necessary. The assembly of a jug using this control is thereby simplified. The electrical connections to the heater element are made upon mounting the heater element to the control, as is the mechanical connection of both of these to the jug.

This further simplifies assembly. As a third level control or backup protection system can be built into the heater element itself, by means of a narrow portion of track which will fail in the event of serious overheating, no such protection is necessary in the control in the illustrated embodiment.

The control has also been designed to enable it to be constructed in a particularly economical manner.

This is because its body is formed in the shape of a tray into which all its components may be placed from above, thereby greatly simplifying mechanisation of assembly. The complete control may be assembled as follows. After providing the tray, the pin 60 is dropped into its hole in the base of the tray. Next, the boss carrying the earth pin 11 and also the live and neutral pins 15,16 are inserted into their openings. It will be appreciated that this also provides the leaf springs and the contacts mounted thereon. Next, the metal support leafs 23 carrying contacts 25,26 are inserted into their mounting holes.

The next stage is for the C-spring to be positioned on the bottom of the tray with one end in the V-shaped recess in pip 39. Two longitudinal ribs are provided to support the C-spring above the floor of the tray such that its other end may engage with the V-shaped recess in the lug 33' on the lever arm. The lever arm carrying the steam bimetal is then dropped downwardly into the tray and the C-spring engaged with its V-shaped recess.

The lever arm is then moved rightwardly, compressing the C-spring, until the knife edge contacts 31 on the edges of the lever arm are able to engage within the V-shaped recesses at the sides of the tray. The lever arm is then released.

Next, the yoke is dropped into position so that the pin 42 locates within its hole and its ears 43 rest upon the leaf springs 20. The spring 50 is then mounted in place with its arms 54 located within the slots 55 in the yoke. Finally, the second snap-acting bimetal 40 is screwed to the top of the control.

The control described may also be employed in a corded jug with only minor modifications. Figure 10 illustrates part of such a jug 100 having a control 101.

This control is similar to control 4, except as described below.

As no pins are required to project from the bottom of the control, there is no recess provided for cooperation with the base unit. Instead, a modified bushing 102 is provided in through-hole 103. The upper end of this abuts the heater element in the same way as bushing 12, but its opposite end is provided with a threaded hole for receiving a screw 104. This secures a conductive strip 105 to the bushing. The strip 105 passes through a small opening in the wall of the control into a chamber where its distal end 106 provides a terminal for connection to an earth cable (not shown).

As no live or neutral pins are required, the leaf springs 20 instead have rearwardly projecting portions 107 which form terminals for direct connection to an electric cable.

The cable may be routed from the control via apertures in its sides, and if required, additional portions may be moulded to the edges of the control to hold the cable in the correct position.

It will be appreciated that the corded jug operates in exactly the same manner as the cordless version, and that apart from the changes to the components forming connections to the electrical supply outlined above, the constructional steps are also identical.

It will of course be appreciated that the invention in its various aspects is applicable not only to arrangements in which a plate heater is arranged within a vessel, electrical connection being made to the heater via an opening in the base of the vessel but also to arrangements wherein the heater forms a part of or all of the vessel base.

Claims (26)

Claims

1. A thermally sensitive control for an electric water heating vessel, the control having switch contacts for controlling the supply of electric current to the vessel, wherein resilient means are provided which are arranged such that, when the vessel is lifted from a support surface therefor said means act to open the switch contacts.

2. A thermally sensitive control as claimed in claim 1 wherein the resilient means comprises a spring member acted on by a movable actuating member extending in use from the bottom of the control.

3. A thermally sensitive control as claimed in claim 2 wherein the actuating member is integral with said spring member.

4. A thermally sensitive control as claimed in any preceding claim wherein said switch contacts are also opened by thermally sensitive actuators of the control.

5. A thermally sensitive control as claimed in claim 4 wherein said contacts are opened by actuators responsive to liquid in the vessel boiling or to the vessel heater overheating.

6. A thermally sensitive control as claimed in any preceding claim wherein said resilient means acts to trip a spring loaded mechanism for opening the contacts.

7. A thermally sensitive control as claimed in claim 6 wherein spring loaded mechanism comprises an over-centre spring-loaded lever arm mechanism.

8. A thermally sensitive control as claimed in claim 7 wherein the resilient means acts on the lever arm via a yoke which is also operated on by an actuator or actuators responsive to the vessel heater overheating.

9. A thermally sensitive control as claimed in claim 7 or 8 wherein the lever arm also mounts a boiling responsive actuator.

10. A thermally sensitive control for an electric water heating vessel, the control being arranged to be mounted beneath the floor of the water containing part of the vessel, the control comprising a bimetal actuated in response to liquid with the vessel boiling, and which in use serves to move a snap acting lever arm in order to switch off the heater of the vessel when water within it boils, wherein the bimetal is mounted on the lever arm.

11. A thermally sensitive control as claimed in claim 9 or 10 wherein the lever arm is also tripped in response to the vessel heater overheating.

12. A thermally sensitive control as claimed in claim 11 wherein a second bimetallic actuator is provided on an upper part of the control so as to be in good thermal contact with the bottom of a heater element to which the control is mounted, the said second bimetal being actuable to trip the lever arm in the event of the heater overheating.

13. A thermally sensitive control as claimed in any of claims 7 to 12 wherein the lever arm acts to open respective sets of contacts in both sides of the supply to the vessel heater.

14. A thermally sensitive control as claimed in any preceding claim comprising a body in the form of a tray in which control components are mounted.

15. A thermally sensitive control for an electric water heating vessel, the control having a body in the form of a tray within which the active components are received.

16. A thermally sensitive control as claimed in claim 14 or 15 wherein the tray has a region for collecting condensation.

17. A thermally sensitive control as claimed in any preceding claim wherein the body of the control is adapted to form a part of the base of the vessel when mounted thereto.

18. A thermally sensitive control as claimed in any preceding claim comprising means for making electrical contact with a planar heating element.

19. A thermally sensitive control as claimed in claim 18 wherein said means comprise contacts formed on a face of the control to engage a surface of said heater.

20. A thermally sensitive control as claimed in any preceding claim comprising electrical connection means for engagement with an external electrical supply.

21. A thermally sensitive control for an electric water heating vessel, the control having switch contacts for controlling the supply of electric current to the vessel, wherein resilient means are provided to hold the contacts open, the resilient means being disabled when the vessel is placed on a support surface.

22. A liquid heating vessel comprising a thermally sensitive control as claimed in any preceding claim.

23. A liquid heating vessel comprising a planar heater and a control as claimed in claim 19 mounted in face to face relationship therewith.

24. A water heating vessel incorporating an electrical control with switch means for disabling an electrical heater of the vessel, the vessel or control including a resiliently biased member engageable with a support surface when the vessel is placed thereon, such engagement enabling the heater to be energised but the heater being disabled whenever the vessel is lifted up from the support surface.

25. A liquid heating vessel comprising means for opening a set of electrical contacts within a control of the vessel when the vessel is lifted from a supporting surface.

26. A liquid heating vessel as claimed in claim 25 wherein said means extends from a bottom surface of said vessel.