GB2097593A - Safety device, having an automatic trigger mechanism, for use in electrical appliances - Google Patents

Abstract

A safety device, e.g. in an electrical appliance for heating a liquid medium, is installed in the handle 2 of the appliance and constitutes an electrical switch 7 which comprises a bracing wire 6, a resilient electrical insulator member 10, a resilient electrical conductor member 9 and a gable-shaped spring 8. The bracing wire 6 is guided and releasably anchored in a tube 15 in a heating tube 3 of the appliance. The wire 6 extends into a meltable mass 12 in the bottom of tube 15 and an electrical heating coil 13. The free arm 17 of the spring 8 is coupled, in the closed position of the switch, to the free end of the insulator 10 adjacent the mounting of wire 6, which position is obtained by depressing a push button 11. When the appliance reaches a predetermined critical temperature, the melting mass 12 releases the bracing wire 6 which causes the switch 7 to open. On opening, the insulator member 10 is released by the spring 8 and the bracing wire is therefore allowed to return down the tube 15 and be re-anchored on cooling of the mass 12 thereby enabling re- closing by depression of a button 11. <IMAGE>

Description

SPECIFICATION Safety device, having an automatic trigger mechanism, for use in electrical apparatus This invention relates to a safety device, having an automatic trigger mechanism, for use in electrical installations and appliances, for example electrical heating appliances for heating liquid media, in particular immersion heaters for heating water. A safety device of this kind may also be used for switching purposes in the case of excess current loading of electrical apparatus, for example fuses.

Electrical installations, preferably heating appliances for heating water, may be provided with a safety device in order to prevent to a large degree, in the case of accidental operating irregularities, in particular "drying out" of the above-mentioned appliances, the burning out of the heating elements (heater coil) disposed in these appliances. Using these safety devices it is therefore possible to substantially avoid the risk of fire and destruction of the appliances.

In contrast to other types of electrical heating appliances, the installation of a safety device in an immersion heater leads to certain difficulties in that a switch must be provided in the electric power connection portion or handle portion which is located at unheated tube ends, whilst a trigger element (sensor) must be located as close as possible to the concentration point of the heat (signal location). This may be clearly seen from the fact that during operation in the atmosphere the immersion heater handle zone remains comparatively cool, whilst the zone in which the heating element is disposed in the immersion heater has already reached approximately 1173 K.

It is necessary, therefore, for the sensor element and the switch of a so-called safety device to be in operational connection with one another.

Furthermore, it is necessary for the entire safety device to be arranged in a leak-tight manner in the heating appliance and the switch located in the power connection or handle portion of the heating appliance must be actuated externally.

These requirements necessitate considerable expenditure with respect to technology and materials.

Safety devices known at present operate on different principles, such as, for example, those known from the German Patent Specifications 1 074 778, 1 099 661 (Principle of liquid or gas expansion); German Offenlegungsschrifts 2 104618,2238341 (Temperature regulation or Curie mechanisms); German Auslegeschrift 1 241 619 (Bimetallic combina- tions), German Offenlegungsschrift 2 540 034 (Temperature safety device) and East German Patent Specification 29 170 (Solder release principle).

The German Patent Specifications 1 074 778 (21 h 13/17) and 1 099 661 (21 h 13/10) disclose switching devices which operate in accordance with a fluid or gas expansion principle. This relates to a closed container system which comprises a so-called pressure housing disposed in the immersion heater handle and a capillary or temperature sensor tube disposed externally of the heating tube.

The pressure housing is formed as a spring membrane which returns under certain pressure conditions in a reversible manner to a new stable rest position. The closed container system is filled with a thermally expanding material. If a predetermined temperature is exceeded at the sensor tube end the medium disposed in the container system expands. Consequently an increasing inner pressure causes the membrane to spring into a convex rest position. Further current supply to the heating appliance is therefore prevented. The heating process may only be continued when the membrane is brought into a concave rest position by means of a switch knob.

The drawback of such switching device is that it is relatively complex to manufacture with respect to filling a predetermined volume in the container system with a predetermined amount of expanding fluid.

Furthermore, such switching device for electrical installations and appliances is not suitable in cases in which the signal location and switch (receiver) must be locally disposed separate from one another as a result of particular conditions.

Moreover, the arrangement of the temperature sensor tube outside of the heating tube is not advantageous as lime residues and deformations of the immersion heater which may not always be avoided may lead to substantial deterioration in operation.

The East German Patent Specification DD-PS 29 170 (HO5b, 1/02) discloses a device for protecting immersion heaters from "boiling dry" in accordance with a solder release principle. In this a pre-stressed leaf spring with a pin or wire disposed rigidly with this spring is provided in the immersion heater handle, this pin being surrounded by a small tube and having its other end rigidly enclosed in the tube by means of tin solder.

The pin and the leaf spring together maintain closed a contact element also disposed in the imersion heater handle under the action of a compression spring. If the immersion heater "boils dry" the liquid tin solder releases the pin. Consequently the leaf spring is lifted from the contact element and the circuit is broken.

Such device is disadvantageous in that it is constituted by a complicated, costly re-switching process which is liable to problems.

Switching on must either be concluded within the phase of the cooling tin solder or undertaken by means of an external heat source or using the heater coil already installed.

The invention aims at providing a safety device, having an automatic trigger mchanism, for use in electrical installations and appliances, which is low in terms of the use of materials and technically simple, which device enables with a relatively high degree of safety in operation a remote control of a corresponding signal both for comparatively large and small appliances.

It is an object of the invention to provide a safety device which releases a bracing wire located in the signal production zone in the case of an accidental operating defect, and which may be immediately returned to its original starting position, in that in this respect a circuit breakage previously caused by the bracing wire cannot be automatically countered, but in which a condition in which the safety device may be switched on is enabled.

Accordingly, the present invention consists in a safety device, having an automatic trigger mechan ism,for use in electrical installations and appliances, for example electrical heating appliances for the heating of liquid media, said device being arranged in a power connection portion or handle portion of the installation or appliance and comprising a bracing wire and a mechanical switch, the bracing wire being guided within a tube up to the zone of signal production for triggering the device, in which tube the bracing wire is anchored, characterised in that the mechanical switch comprises a resilient electrical insulator member, a resilient electrical conductor member and a gable-shaped spring which are connected together in the power connection or handle portion of the installation or appliance, in that one of the two arms of the gable-shaped bent spring is coupled to the electrical insulator member in the zone thereof in which the bracing wire is located, and in that the resilient conductor member is arranged between the insulator member and the gable-shaped bent spring.

The arm of the gable-shaped spring which is coupled to the insulator member/bracing wire zone preferably has its end shaped as an S.

Conveniently, the conductor member is shorter than the insulator member and the gable-shaped spring.

Advantageously, a support is disposed in the power connection portion or handle portion of the appliance under the resilient insulator member and preferably in the zone in which the bracing wire is disposed. Preferably, the support simultaneously constitutes the electric current connection member between the resilient conductor member and the tube in which the bracing wire is guided, in a known manner, from the switch to the signal production area.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example an embodiment thereof, and in which Figure 1 is a sectional view of a heating appliance having the safety device of the invention, and Figures 2 to 5 show diagrams of the positional change of the safety device of Figure 1.

In accordance with Figure 1, the safety device of the invention is shown diagrammatically in an electrical heating appliance for heating liquid media, preferably in an immersion heater 1 for heating water.

The immersion heater 1 shown in Figure 1 com prises a handle 2 and a heating tube 3. The handle 2 comprises two parts 4,5. In the handle parts 4,5 and the heating tube 3 there is disposed the safety device of the invention, the automatic trigger mechanism of which operates in accordance with the solder release principle and comprises a mechanical-tension proof bracing wire 6, a melting substance or a meltable mass 12 and a switch 7.

The bracing wire 6 is anchored in the zone of the meltable mass 12 and a heater coil 13 - constituting the trigger signal production zone. The mechanicaltension proof bracing wire 6 forms a mechanical connection element between the signal production zone 12,13 and the switch 7.

The heater coil 13 is disposed in the heating tube 3 which may be a nickel-plated copper tube.

The switch 7 comprises three spring elements 8,9, 10 and an insulated push button 11. The push button 11 is arranged in the handle part 4.

The three spring elements 8,9, 10 are arranged in the immersion heater handle 2 between the push button 11 and a support 19, at a common connection means 18 which may preferably be a screw connection. The support 19 may both counteract any deformation of the bracing wire 6 and act as part of a current supply.

The spring 8 lying close to the push button 11 is bent in the shape of a gable. Moreover, this gableshaped spring 8 has its end opposite the connection point 18 in the shape of an S. This S-shaped construction 14 on one of the two arms 17 of the spring 8 acts as a coupling with the spring 10 which is constructed as a leaf spring and consists of an electrically insulating material (hereafter referred to as insulator 10). The bracing wire 6 is disposed in the zone in which the gable-shaped spring 8 is coupled to the insulator 10.

The spring 9, which may also advantageously be constructed as a leaf spring, is located between the gable-shaped spring 8 and the insulator 10.

In the clamped and unclamped condition of the safety device of the invention, i.e. when the bracing wire 6 is disposed, in accordance with Figures 2 and 5 respectively, in the signal production zone 12, 13, the insulator 10 and the bracing wire 6 form an angle of 90". The spring force of the insulator 10 must be large enough in the case of boiling dry of the immersion heater 1 to immediately urge the bracing wire 6 to return to its original starting position, i.e. to the signal production zone 12, 13, in accordance with a switching off process. In this stage the meltable substance 12 must still be liquid.

The leaf spring 9 disposed between the gableshaped spring 8 and the insulator 10 should be considered as the active portion of the safety device of the invention. This spring 9 should be so prestressed that the insulator 10 is released from the gable-shaped spring 8 as shown in Figure 4.

The spring 9 may be constructed shorter than the other spring elements 8, 10.

Furthermore, the spring 9 may be constructed as the current supplying element of the safety device of the invention, for example by mounting one of the switching contacts 20 of the appliance on the spring 9.

The gable-shaped spring 8 may be pre-stressed at a predetermined angle at the connection 18.

Moreover, the gable-shaped spring 8 may also be constructed as a current supplying element.

The heater coil 13 is connected to a tube 15 disposed within the heating tube 3, which tube 15 is sealed at the contact point 16 in the direction of the heater coil 13. This tube 15may also act as a conductor between the support 19 and the signal production zone 12, 13. In the above-mentioned zone the meltable mass or melting substance 12 is provided within the tube 15, the bracing wire 6 having its end opposite the insulator 10 anchored therein and forming a material connection.

The tube 15 advantageously consists of aluminium, the bracing wire 6 of a magnesium-aluminium alloy and the meltable mass 12 of a eutectic substance.

The operation of the safety device of the invention is as follows: In the switched condition of the safety device corresponding switching contacts are closed by means of the spring formed as a conductor. The bracing wire is still locked in the area of signal production. The spring disposed between the insulator and the gable-shaped arcuate spring is then gripped by a push-button disposed on the handle of the appliance. This clamped spring, as the active part of the switching functions of the protection device, exerts by means of the gable-shaped spring engaged in the area of the bracing wire disposed rigidly on the insulator a tractive force on the bracing wire.

The gable-shaped spring is unclamped at its highest point (first point) and clamped at the level of anchorage.

In the case of an accidental operating defect, the bracing wire is released from the area of signal production. The active or current supplying spring is unclamped and in this respect pulls the insulator coupled with the gable-shaped spring in the direction of the push button.

This process is additionally supported by the gable-shaped spring, until the latter has its uppermost point within the connection or handle portion of the appliance. In this phase the circuit in the appliance is broken.

The gable-shaped spring which is now adjacent is opened out by the active spring which is no longer supplying current.

This opening out causes an uncoupling of the insulator from the gable-shaped arcuate spring. The spring-shaped insulator may therefore have its bracing wire unclamped in the direction of the signal production area.

This uncoupling and unclamping stage of the spring elements takes place within a time interval in which the signal production area is still in the condition which arose as a result of the appearance of the accidental operating defect.

The bracing wire is disposed, after the termination of the above-mentioned stage, in the signal production area again and is held by a reversibility of the condition of the signal production area.

The protection is therefore ready to be switched on.

After removing the accidental operating defect the gable-shaped arcuate spring is moved in the direction of the location of the insulator, by actuation of the push button, until it is again coupled in the zone of the insulator in which the bracing wire is disposed. Both the gable-shaped spring and the spring disposed between the latter and the insulator and the bracing wire are therefore clamped again. The circuit only closes again after the above has taken place.

The safety device of the invention may also be arranged in other electrical appliances or installations, which are not described here in detail and where similar accidental operating defects occur.

The advantages of the safety device of the invention are as follows: As can be seen from Figures 1 to 5, the safety device of the invention is comparatively simple from a technological point of view, is robust and uses small amounts of material. Furthermore, with respecs to the simplicity of this device, it may be used both for comparatively large and small appliances and is characterised by a high degree of reliability in operation. These features of the safety device ensure, in contrast to known safety switches and devices, a reliable switching off and an immediate switching on of the device in question as a result of a simple manual actuation of the push button.

Adjustment of the safety device may be to a large extent disregarded as a result of its advantageous arrangement and the construction of its components.

The bracing wire 6 may on one hand fulfil a purely mechanical function and, on the other hand, may carry out an electrical function of the kind in which it acts as an electrical protection, in particular in the case of earth connection of a heating body in a particular device.

The construction of the invention is also preferably suitable for electrical installations of the kind in which locally separated arrangements of the zones of the signal location from the switch (current separation device) are required for particular conditions, such as for conditions of heat, moisture, vibrations, electrical insulation etc. which make ample remote transmission of signals to the switch 7 necessary.

Claims (6)

1. A safety device, having an automatic trigger mechanism, for use in electrical installations and appliances, for example electrical heating appliances for the heating of liquid media, said device being arranged in a power connection portion or handle portion of the installation or appliance and comprising a bracing wire and a mechanical switch, the bracing wire being guided within a tube up to the zone of signal production for triggering the device, in which tube the bracing wire is anchored, characterised in that the mechanical switch comprises a resilient electrical insulator member, a resilient electrical conductor member and a gable-shaped spring which are connected together in the power connection or handle portion of the installation or appliance, in that one of the two arms of the gable-shaped bent spring is coupled to the electrical insulator member in the zone thereof in which the bracing wire is located, and in that the resilient conductor member is arranged between the insulator member and the gable-shaped bent spring.

2. A safety device as claimed in claim 1, wherein the arm of the gable-shaped spring which is coupled to the insulator member/bracing wire zone has its end shaped as an S.

3. A safety device as claimed in claim 1 or 2, wherein the resilient electrical conductor member is shorter than the insulator member and the gableshaped spring.

4. A safety device as claimed in any of claims 1 to 3, wherein a support is disposed in the power connection or handle portion of the appliance below the resilient insulator member and in the zone in which the bracing wire is located.

5. A safety device as claimed in claim 4, wherein the support also constitutes an electrical current connection element between the resilient conductor member and the tube guiding the bracing wire.

6. A safety device, substantially as herein described with reference to and as shown in the accompanying drawings.