GB2093275A

GB2093275A - Switch Assemblies for Electric Kettles

Info

Publication number: GB2093275A
Application number: GB8104685A
Authority: GB
Original assignee: DH Haden Ltd
Current assignee: DH Haden Ltd
Priority date: 1981-02-14
Filing date: 1981-02-14
Publication date: 1982-08-25
Also published as: GB2093275B

Abstract

In an automatic electric kettle, a switch assembly is provided in which a rocking lever 100 is interposed between a movable switch contact blade 64 and both a boil dry overload protective switch actuating mechanism 41, 42 and 43 and a steam responsive actuating mechanism 74, 106 and 88, so that the lever 100 responds to actuation by either of the mechanisms to open the switch. A latch 102 may be provided to hold the lever 100 after actuation of the boil dry actuating mechanism, which latch is releasable by means of the manually operated actuating lever 81 of the kettle. <IMAGE>

Description

SPECIFICATION Switch Assemblies for Electric Kettles This invention concerns switch assemblies for electric kettles and like vessels for heating liquids.

In our application No: 2036541 A there is described, with reference to Figures 4 to 9, a switch assembly which includes two contacts which can be separated to open an electrical circuit to a heating element assembly. One of these contacts is movable by an over-centre mechanism responsive to the production of steam, and the other of these contacts is movable by a protective actuating mechanism responsive to overheating of the element.

In order to prevent burning of the contacts and heating of the resilient conductors on which the contacts are mounted, it is necessary ta cause the contacts to open rapidly. This can be achieved in the switch assembly described in Specification No: 2036541A by careful design of the resilient conductors and said mechanisms and in particular of the geometrical and mechanical interrelationships thereof.

However, said geometrical and mechanical inter-relationships impose constraints upon the design and positioning of other parts of the switch assembly.

An object of the invention is to enable some of said constraints to be reduced.

According to the present invention there is provided a switch assembly for use with a heating element assembly, the switch assembly comprising a switch, a steam responsive actuating mechanism and a protective actuating mechanism, wherein said switch comprises a contact member movable to open and close the switch; and wherein a lever is interposed between at least one of said mechanisms and said contact member so that movements imparted to said lever by said actuating mechanism or mechanisms are relayed by the lever to the contact member.

The lever is preferably pivotally or hingedly mounted and interposed between both said actuating mechanisms and the contact member.

The switch is preferably provided with automatic catch means to retain the lever in an actuated position in which the lever holds the switch open, and with release means which is manually operable to release the catch means, and thereby to release the lever so as to allow the switch to close.

The steam responsive actuating mechanism is preferably arranged to serve as the release means and the arrangement is preferably such that this mechanism releases the catch means when the mechanism is moved to an off position, so that the mechanism then holds the lever in the actuated position until the mechanism is subsequently moved manually to an on position.

The invention will be described further, by way of example, with reference to the accompanying diagrammatic drawings, wherein: Figure 1 is a vertical section showing a lower portion of a switch assembly of the invention together with portions of a kettle and a heating element assembly; Figure 2 shows the general arrangement of electrically conductive components of the switch assembly; Figure 3 shows a section through the switch element assemblies on a line coresponding to the line Ill-Ill in Figure 2; and Figures 4 and 5 are sectional views, through portions of the switch assembly, on the line IV IV in Figure 2, showing catch means of the switch assembly in an operative condition (Figure 4) and in an inoperative condition (Figure 5).

The electric kettle body has a wall 10 and is provided with a handle, an immersion heater element assembly 12, an earth pin connector 13 and a switch assembly. The switch assembly comprises a protective dry overload responsive actuating mechanism 14, a switch 16, and a steam responsive actuating mechanism. A cover 1 5 is provided.

The element assembly 12 comprises an element 20 having a metal sheath 21; a metal head having a main panel 22; a peripheral rim 23 and an externally threaded cylindrical extension 24 perpendicular to the main panel; and an elongate post arrangement. As shown in Figure 1, the elongate post arrangement comprises a first post 25 which is secured perpendicularly to the main panel above a central axis 26 of the head, and a longer post 27 secured to the main panel so as to be parallel with and slightly above the post 25. The free end parts of the post are internally threaded to receive two fasteners 30 one of which ciamps the earth pin connector 13 directly to the post 27.The ends of the sheath 21 are secured to the main panel so as to leave cold tails of the element projecting into a socket defined by the extension 24 and the main panel, and an intermediate portion of the sheath is secured across one face of the main panel to provide a hot spot 29.

The assembly 12 is secured in a predetermined position in the body by an internally threaded clamping ring 31 which is secured onto the extension 24 so as to clamp the rim 23 and a seal 32 to the wall 10.

The dry overload responsive actuating mechanism > 14 comprises a moulded member 40 of a heat resistant thermal insulating material; a bimetal 41 of stressed snap-acting dished form located on one side of the member 40 by a cylindrical flanged metal retainer 42, and a push rod 43 which extends perpendicularly from the bimetal through a cylindrical guideway through the member 40 to project from the other side of the member-40. The member 40 is apertured to provide passages through which the posts 25 and 27 and cold tails 28 extend, and to receive projections or pegs 60.Said one side of the member 40 provides an abutment face which confronts and abuts the main panel 22, and is shaped to allow the bimetal to snap from a convex dished form to a concave dished form, upon being heated to a predetermined temperature by the hot spot 29, to thrust the push rod 43 away from the hot spot.

The switch 1 6 comprises a set of switch contacts 65, which are arranged on a mounting 61 , together with electrical connectors as shown in Figure 2. The connectors comprise a live electrical supply connector pin 62, and a similar neutral pin 63. The pin 62 extends through the mounting and is rivetted over to secure one end of a first spring connector 64 to an inside face of the mounting. Said one end is further held by a projection 66 of the mounting. The neutral pin 63 similarly extends through the mounting and is rivetted over to secure a neutral connector 67 to the mounting which neutral connector has an extension which is clamped to one of the cold tails 28 by a cylindrical collar.A second spring connector 69 is secured to the inside face by two projections 70, and similarly has an extension which is secured to the other cold tail by a further collar. The set of switch contacts 65 comprises a first contact mounted on a free end of the connector 64 and a second contact mounted on a free portion of the second spring connector 69.

The Inside face of the mounting and the other side of the moulded member 40 are shaped to interengage and define therebetween a switch contact chamber 75, and the projections 60 are provided with terminal heads, after assembly, to secure together the mounting and the member 40. The peripheral surfaces of the member 40 and an adjacent portion of the mounting 61 are shaped so as to be a close sliding fit in the socket, and the outside face of the mounting is provided with a recess 77 and an abutment 76 which enables the mounting and member 40 to be clamped to the head by the second of the two fasteners 30, independently of the earth pin connector 13 which is partially accommodated in said recess.

The steam responsive actuating mechanism comprises a lever 81, and a steam actuable bimetal not shown The mounting has an upper portion 83 which extends upwards from adjacent the ring 31 so as to confront the wall 10 of the kettle body to define a steam space therebetween. The bimetal is mounted, at its upper end on a top part of the upper portion so as to depend within the steam space alongside that side of the upper portion which confronts the wall.

10. The lever 81 is pivotally mounted on a pivot 80 on the mounting so as to have an upper portion which lies alongside the other side of the upper portion of the mounting, and is engaged by a spring which is located by the top part of the mounting, and is arranged so that the lever 81 is movable between a first stable position in which an abutment of the lever abuts the upper portion of the mounting and a second stable position of the mounting. The lever has a lower portion 88 which in the first position is spaced apart from a second push rod 74 and the outside face of the mounting, and in the second position abuts the push rod and is proximal to or abuts the outside face of the mounting. A knob, not shown, projects through the cover 1 5 and is provided on the lever to allow the lever to be moved manually.

The wall 10 has an upper steam vent which allows steam to pass from the kettle into the steam space so as to heat the bimetal, whereby to cause the bimetal to bend outwards away from the wall 10 to contact an abutment on the upper portion of the lever, which abutment extends through an aperture in the upper portion of the mounting into the steam space, so that the movement of the bimetal is transmitted to the lever to cause the lever to move to the second position via an unstable intermediate position.

As shown in Figure 1 the clamping ring 31 is provided with an extension 34 which extends into an annular recess 50 in the mounting, and a sealing ring 51 is compressed between the mounting and the extension 34 so as to seal the joint therebetween and close the recess 50 whereby to prevent steam, condensate water and flood water, which flow down the steam space, from entering the socket in the head and the switch contact chamber 75. The second push rod 74 is a close sliding fit in a way in the mounting so as to effectively seal the way against ingress of any steam or water which may, upon rare occasions, pass round the upper portion of the mounting to the side remote from the wall 10, but if necessary the push rod or way may have a small amount of silicone grease applied thereto to serve as further seal in said way.

An outwardly open plug socket 52 is provided in an extension 53 of the cover to receive an electrical supply connector (not shown), for connecting to the live, neutral and earth pins, 62, 63 and 13 which extend into said plug socket52.

In the present invention the switch assembly includes a switch lever 100 which is disposed in the switch chamber so as to be movable by the push rods 43 and 74.

In this example, the switch lever 100 (as shown in Figure 3) has first and second limbs which extend in opposite directions from a central portion. The central portion has trunnions 101 which pivotally support the lever 100 on the mounting. The first limb is interposed between the push rod 43 and the first connector 64 so that when the bimetal 41 responds to overheating the push rod 43 causes the lever 100 to turn in a clockwise direction (Figure 3) to move the connector 64 in a direction away from the hot spot so as to move the first contact off the second contact to interrupt a circuit from the live pin 62 to the element 20. The second push rod 74 abuts, or is arranged to abut, the second limb so that movement of the lever 81 from the first to the second stable position, in response to actuation of the steam responsive bimetal, also causes the lever 100 to be turned in the clockwise direction to open said circuit.

In the example shown in Figure 3 the rate of movement of the connector 64 is equal to the rate of movement of whichever of the thrust rods is causing the movement, because the distances from the axis of the trunnions of the points at which the thrust rods and the connector 64 contact the lever are equal.

In practise the total displacement and rate of movement of the push rod 74 are usually greater than those of the push rod 43. The provision of the lever 100 enables this disparity to be offset, if desired, by arranging the dry overload mechanism so that the distance between the point of contact of the push rod 43 and said trunnion axis is reduced. Alternatively, the trunnions could be repositioned to move their axis to the right in Figure 3. Thus, the designer of the apparatus is afforded considerable freedom to vary the arrangement to suit particular conditions. This freedom is not restricted to varying said ratios. For example, the push rods can be inclined to the lever or replaced by other means for transmitting movement to the lever, to facilitate the design and construction of the apparatus whilst maintaining a rapid opening movement of the first contact.

Referring to Figures 3, 4 and 5 the switch is provided with, catch means to retain the lever in a displaced condition so as to hold the circuit open after actuation of the mechanism 14, whereby to prevent the switch assembly cycling between the on and off conditions when operated with insufficient water in the kettle to prevent overheating of the element. The catch means comprises a catch or blocking member 102 which is constituted by a flexible tongue integral with the mounting 61; the member 102 and mounting are moulded so that member 102 is bent or inclined towards the central line 103 of the push rod 74, as shown in Figure 4. In the on condition of the switch, the member 102 overlaps and rests on a side 104 of the second limb of the lever 100, as shown in Figure 5.If the dry overload actuating mechanism 14 is caused to act by overheating of the bimetal 41, the push rod 43 moves the lever 100 clear of the free end of the member 102 so that the member 102 returns to the as moulded condition and causes the free end to move to confront a rear face 105 of the second limb of the lever 100, as shown in Figure 4. The catch means is then in an operative condition in which it holds the lever 100 in a position in which the lever holds the switch open when the bimetal 41 cools and reverts to the condition shown in Figure 3.

The switch assembly incorporates release means to release the catch means from its operative condition. In this embodiment the release means is constituted by the steam responsive actuating mechanism, which is arranged so that the lever 81 can be moved manually from the first to the second stable position to cause an end part 106 of the push rod 74 to move towards the rear face 105 and thrust the free end away from said central line 103, so that the free end is moved clear of said rear face 1 05. In the second position, the steam responsive actuating mechanism serves to hold the switch open and holds the member 102 clear of the lever 100, and thus this second position constitutes both a switch off position and a catch reset position.The switch can thereafter be switched on by moving the steam responsive actuating mechanism manually to its first position, and during this movement the lever 100 is urged by the connector 64 to turn in said anti-clockwise direction to cause the push rod 74 to follow the lower portion 88, and the face 105 of the lever 100 moves past the free end of the member 102, until the lever 100 and catch means reach the position shown in Figures 3 and 5 in which the catch is inoperative. During the initial part of said movement the end part 106 holds the member 102 clear of said side 104 to prevent the catch means re-engaging the lever 100.

A spring, such as the spring 107 shown in broken lines in Figure 3, may be provided in the chamber 75 to bias the lever 100 in the anticlockwise direction.

The invention is not confined to the details of the foregoing example, and many variations and modifications are possible within the scope of the invention. For example, instead of the end part 106 being enlarged to serve as a head on the push rod 74, the other end part may be enlarged to provide a head 109 which is thrust towards the portion 88 by a bias spring 110 as shown in broken lines in Figure 3. The spring 110 is located in a recess in the mounting, and serves to provide insufficient bias to overcome friction produced by the catch means when the latter is being released, which bias is insufficient to render the steam responsive actuating mechanism unstable in the second position.

The lever 100 may have a single arm, if both the means for transmitting movement thereto are arranged to move in the same direction to move the lever to open the switch.

The release means may be separate from the actuating mechanism so as to be independently actuable, or the catch means may be incorporated into or actuable by the steam responsive actuating mechanism either when the latter is moved to the switch off position, e.g. as described, or to the switch on position.

An arrangement wherein the steam responsive actuating mechanism has to be moved to release the catch means is preferred, because such an arrangement obviates the provision of separate manual release means and gives a clear indication to the user that overheating has occurred, as the kettle has to be switched off and then on again before the kettle will operate, which indication is lacking in other automatic switches in which the manually actuable member is moved to the offposition automatically when either of the actuating mechanisms switches the switch off.

Furthermore, an arrangement wherein the steam responsive actuating mechanism releases the catch means when moved to the off-position gives the further advantage of preventing a user attempting to over-ride the dry overload mechanism (to boil rapidly a quantity of water which is insufficient for safe operation of the kettle) by holding the steam responsive mechanism in the on-position.

Claims (Filed 8 Feb 82) 1. A switch assembly for use with a heating element assembly, the switch assembly comprising a switch, a steam responsive actuating mechanism and a protective actuating mechanism, wherein said switch comprises a contact member movable to open and close the switch; and wherein a lever is interposed between at least one of said mechanisms and said contact member so that movements imparted to said lever by said actuating mechanism or mechanisms are relayed by the lever to the contact member.

2. A switch assembly as claimed in Claim 1, wherein the lever is pivotally or hingedly mounted and interposed between both said actuating mechanisms arid the contact member.

3. A switch assembly as claimed in Claim 1 or 2, wherein the switch is provided with automatic catch means to retain the lever in an actuated position in which the lever holds the switch open, and with release means which is manually operable to release the catch means, and thereby to release the lever so as to allow the switch to close.

4. A switch assembly as claimed in Claim 1,2 or 3, wherein the steam responsive actuating mechanism is arranged to serve as the release means and the arrangement is preferably such that this mechanism releases the catch means when the mechanism is moved to an off position, so that the mechanism then holds the lever in the actuated position until the mechanism is subsequently moved manually to an on position.

5. A switch assembly substantially as hereinbefore described with reference to the accompanying drawing.

6. An electric vessel for heating liquids incorporating a switch assembly as claimed in any preceding claim.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. kettle) by holding the steam responsive mechanism in the on-position. Claims (Filed 8 Feb 82)

1. A switch assembly for use with a heating element assembly, the switch assembly comprising a switch, a steam responsive actuating mechanism and a protective actuating mechanism, wherein said switch comprises a contact member movable to open and close the switch; and wherein a lever is interposed between at least one of said mechanisms and said contact member so that movements imparted to said lever by said actuating mechanism or mechanisms are relayed by the lever to the contact member.