GB2202376A - Electrical appliances - Google Patents

Abstract

An electrical appliance such as a cordless jug or kettle has a base 20 with an electrical mains connection and a working part 10 which can be separated from the base when in actual use. The working part includes a manually operated on/off switch 26-32 controlling an electrical load and suitable mating contacts 24, 25 are provided on the working part 10 and on the base 20 for connecting the power supply to the load via the switch when the working part is positioned on the base. To avoid the risk of the working part being removed from the base whilst current is flowing through the contacts, a weighted sensing member 40 is provided in the working part. When the working part is positioned on the base, the sensing member 40 is supported through contact with the base and remains stationary in an elevated position. As the working part 10 is lifted away from the base 20, the weighted sensing member 40 drops and, if the manual switch has been left in the "on" position - engages a switch member 26, 46 to move it to the "off" position before the electrical contacts become separated. <IMAGE>

Description

IMPROVEMENTS IN ELECTRICAL APPLIANCES This invention relates to electrical appliances and more particularly to such appliances having a base part adapted for connection with an external power supply and a working part which can be separated from the base when in actual use. There are a variety of electrical appliances of this nature which are commercially available.

So-called "cordless" jugs or kettles have been produced with a base part having a mains lead and electrical contacts which engage complementary contacts on the jug part. With the jug resting on the base and the manual"on/off"switch actuated, current is supplied through the contacts and the switch to the heating element to boil the water. The jug can then be lifted from the base to facilitate carrying and pouring. It will be understood that if the jug is positioned on the base with the switch in the "on" position - the jug contacts being thus electrically interconnected through the element - there is a real likelihood of arcing occurring across the jug and base contacts.

Any such arcing will considerably reduce the operating life of the contact arrangement. It is accordingly highly desirable to ensure that the jug contacts are open (that is to say not interconnected through the heating element) when they come into engagement with the base contacts.

It is an object of this invention to provide an improved electrical appliance comprising a working part and a base part for connection with an external power supply in which contacts in the working part are normally isolated from each other when coming into engagement with contacts in the base part.

Accordingly, the present invention consists in an electrical appliance comprising a working part incorporating a manual switch controlling an electrical load and a base part for connection with an external power supply, the working and base parts having respective mutually engaging electrical contact means serving in an operative position of the working part on the base to establish via the switch electrical connection between the power supply and the load; wherein there is provided a trip mechanism comprising a weighted sensing member mounted for generally vertical movement in the working part and adapted to engage in said operative position a surface of the base part, this engagement holding the sensing member in an elevated position; a switch control member so associated with the switch that movement in one sense of the control member brings the switch to the "off" position and abutment means provided on the sensing member and so positioned as the sensing member falls substantially under gravity from said elevated position upon separation of the working part from the base to move the switch control member in said one sense to bring the switch to the "off" position prior to separation of the respective working and base part contact means.

The invention will now be described by way of example with reference to the accompanying figure which is a part diagrammatic section through an electrical appliance according to this invention.

There is shown in the drawing the relevant portions of a cordless jug. The jug part is shown generally at 10 and can be seen to comprise a main housing 12 defining a water container 14; an electrical component support moulding 16 and a switch cover 18. The base part underlies the jug and the profile of the base part in the region of interest is shown in outline at 20.

The support moulding 16 defines in the lower region an inverted cup 22. Three electrical connector pins 24 are positioned in this part with only one pin being visible in the drawing. The connector pins 24 engage respective spring biased contacts 25 in the base. The connector pins 24 are electrically connected with the heating element through an "on/off" switch. The switch itself is not shown in the drawing but is operated through a switch plate 26 which is pivotally mounted at 28 on the support moulding 16. The switch incorporates an over-centre spring arrangement, urging the switch plate 26 to either the "on" position shown in full outline in the drawing or the "off" position shown in dotted outline. The switch plate carries upper and lower fingers 30 and 32 which are shown in outline in the drawing.The fingers are preferably moulded integrally with the switch plate, the moulding being arranged to define a web hinge 34 between each finger and the corresponding end of the switch plate. Both fingers project through apertures 36 in the switch cover 18, the ends of the fingers defining switch buttons 38. It will be recognised that manual pressure on the upper button will cause the switch plate to move to the "on" position whilst pressure on the lower button will effect movement of the switch to the "off" position.

There will now be described a mechanism for ensuring that, under normal operating conditions, the switch plate is moved to the "off" position prior to disengagement of the jug from the base and remains in the "off" position until the jug is repositioned on the base and engagement re-established between the jug and base contacts.

The mechanism comprises a push rod 40 which is mounted for generally vertical displacement between opposing bearing formations 42 and 44. in the main housing 12 and support moulding 16 respectively. At its lower end, the push rod 40 projects into the cup 22 so as to engage an upper surface of the base. With the jug correctly positioned on the base, this contact between the push rod and the base serves to hold the push rod in the elevated position shown in the drawing.

The switch plate,26 is formed with an integral lever 46 having forks 46a and 46b passing either side of the push rod.

A washer 48 freely mounted on the push rod rests through gravity on the lever forks. A relatively short distance above the position of the washer shown in the drawing, a circlip 50 is mounted on the push rod. A weak compression spring 52 encircles the push rod and is trapped between the circlip and the annular end surface 54 of the bearing formation 42. The compression spring is weak in the sense that the vertically downward force it applies to the push rod is insufficient as a moment on the switch lever to move the switch plate to the "off" position against the action of the over-centre spring.

A further circlip 56 is secured to the push rod a sufficient distance beneath the switch assembly to avoid fouling.

There rests upon this circlip a substantial weight 58 of annular configuration.

The manner of operation of the described mechanism can now be understood.

In the position shown in the drawing, the switch plate can be moved through finger 30 to the "on" position enabling the supply of current to the heating element. The switch can be moved to the "off" position through finger 32 when desired or, alternatively, a bi-metallic or other thermally responsive device may be provided to move the switch automatically to the "off" position when the contained water reaches boiling point.

The push rod 40 plays no part in these normal switch movements.

If, however, it is attempted to remove the jug from the base with the switch plate in the "on" position, release of the push rod from engagement with the base will permit the push rod to fall relatively to the jug housing under the combined action of the weight 58 and the spring 52. This downward movement of the push rod will after a short travel bring the circlip 50 into engagement with the washer 48 and will thereafter act on lever 46 to urge the switch plate to the "off" position.

The amount of linear movement of the washer 48 necessary to force the switch arrangement over-centre is indicated in the drawing at A and it will be seen that the degree of movement of the push rod as the jug leaves the base is more than sufficient to ensure that the spring arrangement passes over-centre.

The amount of force necessary to move the switch between the "on" and "off" positions cannot be reduced indefinitely since the switch would become unstable and there would be a risk of the appliance being turned on or off inadvertently through vibration or other disturbance. The trip mechanism must be capable of overcoming the over-centre or other switch biassing arrangement and is therefore required to produce a force of or above a calculated minimum. Generally speaking the most convenient means of providing a biassing force in a mechanism of this nature is a spring. The arrangement of the present invention in which a weight is employed gives - however - an important advantage over a spring powered system.It will be recognised that a spring biassing arrangement demands a reaction from its support and in this context the reaction would typically be an upward force exerted on the jug part. Such an upward force would be likely to interfere with proper placements of the jug upon the base particularly when summed with the upward force exerted by the spring base contacts By utilising a weight, the present invention enables the use of.a much smaller spring or no spring at all and so neatly avoids the difficulty.

It should be recognised that the weight contemplated in this invention is considerably in excess of the weight of the sensing member itself. In the described example, the sensing member formed of steel might be expected to weigh around 3grams, whereas the additional weight that is added in accordance with the invention amounts to 27 grams. In this example, space considerations limit the size or weight that can be employed and a spring is used to give the required total operating force.

If in other arrangements it became desirable to avoid completely the use of a spring and subject to space considerations, a weight of, say, 77 grams might be employed.

The specific weights are quoted by way of example only to illustrate magnitudes in comparison with the normal weight of components and spring forces in the mechanism.

Claims (6)

1. An electrical appliance comprising a working part incorporating a manual switch controlling an electrical load and a base part for connection with an external power supply, the working and base parts having respective mutually engaging electrical contact means serving in an operative position of the working part on the base to establish via the switch electrical connection between the power supply and the load; wherein there is provided a trip mechanism comprising a weighted sensing member mounted for generally vertical movement in the working part and adapted to engage in said operative position a surface of the base part, this engagement holding the sensing member in an elevated position; a switch control member so associated with the switch that movement in one sense of the control member brings the switch to the "off" position and abutment means provided on the sensing member and so positioned as the sensing member falls substantially under gravity from said elevated position upon separation of the working part from the base to move the switch control member in said one sense to bring the switch to the "off" position prior to separation of the respective working and base part contact means.

2. An appliance according to Claim 1, wherein there are further provided finger operated means for actuating said switch member without movement of said sensing member.

3. An appliance according to Claim 1 or Claim 2, wherein said weighted sensing member comprises a generally vertically disposed rod projecting from the working part for engagement with said base part surface.

4. An appliance according to Claim 3, wherein the sensing member further comprises a weight having a mass substantially in excess of that of the rod.

5. An appliance according to any one of the preceding claims, wherein said electrical load comprises a water heating element.

6. An appliance substantially as hereinbefore described with reference to and as shown in the accompanying drawing.