GB2178900A - Switching device for an electric water boiler - Google Patents

Abstract

A switching device for an electric heating element 2 of an water boiler 1 has a steam chamber 18 with a bimetallic element 21. The heating element 2 is switched off by the bimetallic element 21 when the water boils and by a safety device when the heating element 2 overheats. The safety device comprises an hydraulic temperature sensor 4 operating a switching diaphragm 6. The switching diaphragm 6 and the bimetallic element 21 both act on a common actuating member 28 which actuates a movable switch contact to switch off the heating element 2. A manual actuator 30 is fastened directly to the actuating member 28. <IMAGE>

Description

SPECIFICATION Switching device for an electric water boiler The invention relates to switching devices for the electric heating element of water boilers of the known form having a steam chamber, in which is arranged a bimetallic element which, when steam is generated, opens a switch contact which is also operable by a manual actuator and also incorporating a safety switch which, when the heating element is overheated, switches it off.

Such a switching device can be used either on electric kettles or on stationary water boilers.

A switching device of the form mentioned is described in German Patent Specification 2,205,353.

When steam from the boiling water escapes from the kettle into the steam chamber, the bimetallic element switches off the electric heating element.

A manual actuator is provided for switching it on again. However, in German Patent Specification 2,205,353, the heating element can only be switched on by means of the manual actuator, but cannot be switched off.

In the switching device according to German Patent Specification 2,205,353, the safety switch has an additional switch contact, and the electrical connections entail a correspondingly high outlay.

German Utility Model 6,607,924 describes a water boiler in which there are two switch contacts switched by means of a single bimetallic element which is under the influences of two heat bridges.

Here again, two contacts have to be connected electrically. An auxiliary heating element is necessary, in addition, for heating the heat bridge which is intended to ensure that the appliance is switched off when steam is generated. This also entails a high outlay.

According to the present invention there is provided a switching device for an electric heating element of a water boiler, comprising a bimetallic element disposed in a steam chamber and arranged, when steam is generated in the chamber, to open a switch controlling the supply of current to the element, a manual actuator for opening and closing of the switch and an hydraulic temperature sensor responsive to overheating of the heating element to actuate a switching diaphragm, the bimetallic element and the said diaphragm both operating upon a movable contact member of the said switch.

The term "hydraulic temperature sensor" is used herein to indicate a sensor in which hydraulic or gaseous pressure is generated in response to increases in temperature.

With this arrangement, construction of the switching device is simplified, since only one switch is required for control by the bimetallic element, and the temperature sensor. Also, the user is able to switch the heater element off manually.

Preferably, the switching diaphragm is coupled to the switch contact member by a switch actuating member to which the manual actuator is also coupled. This enables the user to see from the position of the manual actuator whether the heating element is on or off.

Some embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows, in section, a kettle and switching device; Figure 2 shows an enlarged part view of the switching device according to Figure 1; Figure 3 shows a further exemplary embodiment of the switching device, and Figure 4 shows.a third exemplary embodiment of the switching device.

Arranged in the bottom of a kettle 1 is an electric heating element 2. There rests against the latter a protective sheath or tube 3, housing an hydraulic temperature sensor 4, connected by a capillary tube 5 to a space 7 closed off by a switching dia phragm 6. The temperature sensor 4, the capillary tube 5 and the space 7 are filled with a liquid which expands and/or evaporates in response to a temperature increase.

The heating element 2 and the protective tube 3 are led through a wall 9 of the water vessel 1' of the kettle 1 by means of a flange plate 8. A moulded cover 10 attached to the wall 9 forms a space 11 for receiving the switching device. A han dle 12 is also formed on the moulded cover 10.

Under the handle 12 there is a socket 13, which may be formed as an integral part of the handle 12.

The kettle 1 has a lid 14 which, in the region of the spout 15 of the water vessel 1', has a wall piece 16 which largely shuts off the spout 15, so that steam arising during boiling does not escape freely.

Formed opposite the spout 15 in the top of the kettle 1 is a channel 17 opening into a steam chamber 18 which communicates with atmosphere through an outflow hole 19.

Fastened in the space 11 is a carrier 20, on which the steam chamber 18 is formed. The steam cham ber 18 is closed off on one side by a bimetallic ele ment 21 formed by a'thermostatic bimetallic snap disc, also called Spencer disc. The switching dia phragm 6 is arranged next to the Spencer disc 21.

The switching diaphragm 6 and the Spencer disc 21 are jointly clamped at their outer edges. An intermediate spacer piece 22 is arranged between the Spencer disc 21 and the switching diaphragm 6. On the side of the Spencer disc 21 facing away from the intermediate piece 22, there is a switch tappet 23 which is guided in a bore 24 of the car rier 20 and which is sealed off by means of a sealing ring 25.

Above the bore 24, an arm 26 is arranged on the carrier 20 and has a recess 27, in \ e n,! end of a switch ptl:: '= ;eo means of a knife edge fulcrr- 99. The swit-'- fa- ret 23 abuts against the lever 28.

The lever 28 extends downwardly in the space 11 and has fast with its bottom end a manual actuator 30, which is located in a slot 31 in the han dle 12. It is visible to the user and can be actuated manually to displace t ever C.

The lever 28 is prestressed towards the carrier 20 by means of a spring 32.

Arranged on the lever 28 between the switch tappet 23 and the manual actuator 30 is a movable contact bridge 33 which co-operates with a pair of fixed contacts or studs. One switch stud is connected electrically to one terminal of the electric heating element 2, and the other to one pin of the socket 13. The other terminal of the heating element 2 is connected to the other pin of the socket 13.

The carrier 20, together with the parts fastened to it, can be mounted in the space 11 in a simple way. During assembly, the temperature sensor 4, connected to the carrier 20, is inserted into the protective tube 3.

The switch tappet 23, the contact bridge 33 and the manual actuator 30 are arranged relative to the lever 29 in suc a way that a switching stroke of the Spencer disc 21 of approximately 0.4 mm is sufficient to lift the contact bridge 33 sufficiently, for example 1.6 mm, and to shift the hand-switching part 30 far enough in the indentation 31, for example 5 mm. This ensures, on the one hand, that the switch contact is at a sufficient distance when opened to avoid arcing and, on the other hand, that there is a clearly visible shift.of the manual actuator 30. A stroke of the manual actuator 30 which is greater than the stroke of the Spencer disc 21 also makes it easier to actuate. The switching stroke of the switching diaphragm 6 is greater than that of the Spencer disc 21. It amounts, for example, to 1.1 mm.However, since the distance between the switching diaphragm 6 and the Spencer disc 21 is greater than the difference between the two switching strokes, the intermediate spacing piece 22 is provided, to compensate for the difference, so that when the switching diaphragm 6 responds, the switch tappet 23 is moved via the Spencer disc 21 just as far as it is when the Spencer disc 21 responds.

The mode of operation of the switching device described is as follows: To switch on the heating element 2, the manual actuator 30 is moved into the position shown in Figure 1. The lever 28 thereby assumes the position shown in Figures 1 and 2.

When the water in the water vessel 1' boils, steam escapes into the steam chamber 18. The Spencer disc 21 is heated there and then snaps over, causing the switch tappet 23 to pivot the lever 28 so that the switch contacts are opened and consequently the heating element 2 is switched off.

At the same time, the manual actuator 30 snaps over to the right in the slot 31. This position is clearly discernable to the user. The snap action is improved by the spring 32.

If the electric heating element 2 is switched on when the water vessel 1' is empty, the temperature sensor 4 heats up much more rapidly and to a greater extent than when it is in water. The switching diaphragm 6 then changes over and, acting through the intermediate piece 22 and the Spencer disc 21, presses on the switch tappet 23, which thereby pivots the lever 28 so that the switch contacts open and the heating element 2 is switched off. At the same time, the manual actuator 30 is also moved to the right in Figure 1. It is possible to switch on again, after cooling, by actuating the manual actuator 30.

The actuator 30 can be pulled to the right in Figure 1 at any time, thus switching off the electric heating element 2.

In the exemplary embodiment according to Figure 3, parts corresponding to the embodiment of Figure 2 bear the same reference symbols. In the embodiment of Figure 3, the switching diaphragm 6 is arranged at a distance below the Spencer disc 21. It acts directly on the lever 28 through its own switch tappet 34. The distance between the switch tappet 34 and the knife edge 29 is greater than the distance between the switch tappet 23 and the knife edge 29. Since the switching force of the Spencer disc 21 is higher than that of the switching diaphragm 6, the distances can be calculated so that the moments acting on the lever 28 are of approximately the same magnitude.

In the embodiment according to Figure 3, the manual actuatcr includes a press-button 30. This serves only to switch on the heating element 2. To switch off the heating element 2 there is provided a further press-button 35 on which is guided a rocker 37 pivotable about a pivot pin 36 and resting against the lever 28. When pressure is exerted on the press-button 35, the rocker 37 pivots the lever 28 so that the contact bridge 33 of the switch contact lifts off. The press-button 35 is reset when the press-button 30 is actuated to switch on the heating element 2. Here again, the particular switching condition can be seen easily by the user.

In the exemplary embodiment according to Figure 4, the parts corresponding to those of Figures 1 and 2 again bear the same reference symbols.

The switch actuating member is formed as a switch tappet 38, one end of which is fastened to the Spencer disc 21. The other end of the switch tappet 38 is guided in a sleeve 39 fastened to the switching diaphragm 6. The movable switch contact has a resilient contact tongue 40 which rests against a contact face 41. On the switch tappet 38 there is a collar 42 designed to actuate the contact tongue 40. The manual actuator 30, pivotable about a pivot pin 44, abuts a further collar 43 of the switch tappet 38. When the Spencer disc 21 or the switching diaphragm 6 snap over, or when the manual actuator 30 is pivoted clockwise as viewed in Figure 4, the collar 42 stresses the contact tongue 40 so that the switch contact opens and the heating element 2 is switched off. It can be switched on again by means of the manual actuator 30.

In another embodiment of the invention, not shown, the switching diaphragm 6 and th me- tallic element 21 are arranged in the same way as in Figure 2, and the movable switch contact is arranged so that it is stressed by the switching diaphragm 6 or the bimetallic element 21 directly, that is to say without transmission via the lever 28.

There is then also no need for the switch tappet 23.

In this design, the manual actuator 30 is ar ranged to act directly on the switching diaphragm 6 and the bimetallic element 21, the movable switch contact being actuated at the same time.

The manual actuator can be of mechanical or hydraulic design.

Claims (19)

1. A switching device for an electric heating element of a water boiler, comprising a bimetallic element disposed in a steam chamber and arranged, when steam is generated in the chamber, to open a switch controlling the supply of current to the element, a manual actuator for opening and closing of the switch and an hydraulic temperature sensor responsive to overheating of the heating element to actuate a switching diaphragm, the bimetallic element and the said diaphragm both operating upon a movable contact member of the said switch.

2. A switching device according to claim 1, wherein a switch actuating member couples the switching diaphragm to the said switch contact member, and the manual actuator engages the said switch actuating member.

3. A switching device according to claim 2, wherein the switch actuating member is formed by a pivotable lever, to one end of which the manual actuator is fastened.

4. A switching device according to claim 3, wherein the bimetallic element and the switching diaphragm act on the said lever through a common switch tappet, and the bimetallic element is arranged between the switching diaphragm and the switch tappet.

5. A switching device according to claim 4, wherein the bimetallic element and the switching diaphragm rest against one another at their outer edges.

6. A switching device according to claim 5, wherein an intermediate spacing piece is arranged between the switching diaphragm and the bimetallic element.

7. A switching device according to claim 3, wherein the bimetallic element and the switching diaphragm act on the switch actuating lever at different distances from its fulcrum.

8. A switching device according to claim 7, wherein the bimetallic element is located nearer the fulcrum of the said lever than is the switching diaphragm.

9. A switching device according to any one of claims 4 to 8, wherein the switch actuating lever acts on the said contact member at a point located between the switch tappet and the manual actuator.

10. A switching device according to claim 2, wherein the switch actuating member is formed by a switch tappet abutting respectively against the bimetallic element and the switching diaphragm, and operatively engageable with the movable contact member.

11. A switching device according to claim 10, wherein the manual actuator is pivotally mounted and engages the said switch tappet.

12. A switching device according to any one of the preceding claims, wherein the bimetallic element is formed by a Spencer disc, the outer edge of which is clamped at the steam chamber.

13. A switching device according to claim 12, wherein the Spencer disc closes the steam chamber on one side.

14. A switching device according to any one of the preceding claims, wherein the switch actuating member is prestressed by means of a spring.

15. A switching device according to any one of the preceding claims, including a carrier which can be fastened in a space between a water vessel and a handle of the boiler.

16. A switching device according to claim 15, wherein the steam chamber is formed on the carrier and is connected at its upper region to the water vessel.

17. A switching device according to claim 15 or 16, wherein the hydraulic temperature sensor is inserted into a protective tube resting against the heating element and is connected by a capillary tube to the switching diaphragm, which is arranged on the said carrier.

18. A switching device according to claim 15 or 16, wherein the switch actuating member takes the form of a lever pivotally mounted at its upper end on the carrier and the manual actuator is located on the handle at the lower end thereof.

19. A switching device according to any preceding claim, wherein the manual actuator comprises one press-button for opening the switch and another for closing it