EP0254740B1 - Safety disconnection device - Google Patents

Abstract

PCT No. PCT/EP87/00013 Sec. 371 Date Sep. 11, 1987 Sec. 102(e) Date Sep. 11, 1987 PCT Filed Jan. 14, 1987 PCT Pub. No. WO87/04560 PCT Pub. Date Jul. 30, 1987.A safety cutout device for electric loads, particularly for use in pressing irons and portable heating apparatus, has a temperature switch, such as a bimetallic switch, which is adapted to be connected in series with the electric load. An electrical component adapted to be connected in parallel with the load and having an open and a closed switching state, and being normally open, is connected in series with a resistor adapted to be connected in parallel with the load and arranged in heat transfer relationship with the temperature switch and for heating the temperature switch to its operating temperature to open the switch. A further resistor, which continuously bridges and heats the temperature switch to an extent sufficient to maintain the temperature switch in its actuated open position, is connected in parallel with the temperature switch and adapted to be connected in series with the load. The electrical component may be a position or acceleration responsive switch, level sensor, photocell, photodiode, mercury switch, etc. The temperature switch, resistors and electrical component are mounted on a ceramic plate.

Description

Technical field:

The invention relates to a safety switch-off device with the features specified in the preamble of claim 1.

State of the art:

Such a device is known from DE-A 35 06 784. It contains two components, namely a thermal switch, which is in series with the consumer, opens in the event of overheating and thus shuts off the consumer, and second, a position-sensitive switch, which is parallel to the consumer, is open in the normal position of the device and one Series resistor, which heats the thermal switch when the position-sensitive switch closes. As a result of the heating, the thermal switch exceeds its switching temperature after a while and opens, so that the consumer is also switched off due to the response of the position-dependent switch. Provided that the thermal switch is not in the circuit of the position-dependent switch, after its response, the thermal switch remains open due to its constant heating until the device is returned to its normal position, in which the position-dependent switch opens, which causes its series resistor Another disadvantage of the known device is that the thermal switch responds and opens relatively slowly after the position-dependent switch closes. The response speed can only be increased to a very limited extent by increasing the heating power of the resistor which heats it, because the heating which continues after the thermal switch is opened would otherwise overheat and damage it. However, if the thermal switch does not overheat from this series resistor, it is not ensures that the thermal switch remains open after it has responded, rather it will automatically switch on again after it has cooled, regardless of whether the fault that led to the overheating has been eliminated or not.

From EP-A-0 102 574 it is known that a thermal switch can be kept open when it is heated by a resistor bridging it.

Disclosure of the Invention:

The invention has for its object to develop a safety switch-off device of the type mentioned in such a way that the thermal switch that switches off the consumer opens quickly after the position or acceleration-dependent switch closes and is automatically kept open after every response, for whatever reason .

This object is achieved by a device with the features specified in claim 1. Advantageous developments of the invention are the subject of the dependent claims.

The resistance value of the additional resistor is selected in adaptation to the respective switching and monitoring task of the thermal switch and to the resistance value of the consumer so that when the thermal switch is closed, the vast majority of the current flowing through the consumer takes the path directly via the thermal switch and only one relatively small part of the current flows through the additional resistor, so that the ohmic heat generated in the resistor is not sufficient to heat the thermal switch to its switching temperature. However, if the thermal switch responds due to overheating, then only current flows through the additional resistor and through the series resistor of the switch which responds preferably in relation to position and / or acceleration, provided that the switch is closed. The resistance value of the further resistor bridging the thermoswitch must therefore be selected on the other hand so that when the thermoswitch is open, the ohmic heat generated as a result of the higher current passage through the additional resistor is sufficient to keep the thermoswitch open. The heating power required for this is typically on the order of a few watts. At a supply voltage of 220 volts, suitable resistance values for the additional resistance are of the order of 10 kΩ, for example between 5 kΩ and 25 kΩ. The series resistor belonging to the switch, which responds to changes in position or accelerations, must be able to heat the thermal switch in an appropriate time from its normal operating temperature to above its switching temperature, which requires a somewhat greater heating output than simply keeping it open. It is therefore advisable to choose the resistance value of this series resistor somewhat lower than the resistance value of the additional resistor, which continuously bridges and heats the thermal switch.

In the arrangement of the two resistors according to the invention, these bridge the thermoswitch lying in series and, at the same time, are series resistors of the switch which responds preferentially depending on the position and / or acceleration. In undisturbed conditions (the thermal switch is closed and the switch which responds to changes in position and / or accelerations is open) only a negligible current flows through the two resistors in series, which is not sufficient to open the thermal switch. If, however, the switch responding to changes in position and / or accelerations is closed, then a current flows through it, which branches through the two resistors, so that ohmic heat is generated in both resistors, which heats and finally opens the thermal switch. After opening the thermoswitch, the current path is then interrupted via one of the two resistors, so that only the ohmic heat generated in one of the resistors is used in the desired manner to keep it open. This type of arrangement of the resistors thus allows the thermal switch to be kept open with a lower heating power and a rapid response of the thermal switch as a result of higher heating power of the resistors after the switch responding to changes in position and / or accelerations has been closed. If overheating occurs without the switch responding to changes in position and / or accelerations responding, the response speed of the thermal switch depends on the type of fault and the same resistance is responsible for keeping the thermal switch open in this case as when closing the change in position and / or Accelerating switch. This resistance is therefore expediently chosen so that it is as low as possible, but to keep the thermoswitch open provides sufficient heating capacity in all circumstances. The other resistor can then be selected or - in the case of a potentiometer - set so that the desired response speed of the thermal switch is obtained by closing the switch which responds to changes in position and / or accelerations.

In order to achieve a favorable heat transfer from the resistors to the thermal switch, it is advisable to arrange them next to the thermal switch. It is particularly advantageous to supplement a bimetal switch with thick-film resistors in such a way that the contact spring and the two switching contacts of the bimetal switch are on one side of an electrically insulating carrier and the resistors on the other side of the carrier, with either the resistors and the bimetal element lie on the same side of the carrier or an opening is provided in the carrier through which heat transfer from the resistors on one side of the carrier to the bimetallic element on the other side of the carrier is as unimpeded as possible.

Another advantageous possibility is to choose a ceramic plate (wafer) as the carrier of the thermal switch, which carries the contact spring and the switching contacts on one side and the resistance layers on the opposite side.

The use of thick-film resistors has the further advantage that the switch, which responds to the position and / or acceleration, can be attached directly to the carrier (s) of the thick-film resistors, which results in an easy-to-use, compact unit. The position and / or acceleration-responsive switch is best accommodated in a cuboid, preferably cube-shaped housing, which has means for mounting on several, preferably on three mutually perpendicular sides, so that one and the same switch in different orientations depending on the respective application can be assembled.

In addition, suitable as position and / or acceleration-dependent switches are those which have two isolated electrodes in one housing and a freely movable, electrically conductive ball between them, which contact the two electrodes only in a predetermined position or when there is no acceleration makes. Switches with a suitable shape for the electrodes are described, for example, in DE-OS 31 11 099, in DE-OS 22 61 974, in DE-OS 28 24 210 and in DE-GM 85 10 110.

Another possibility for forming a positionally responsive switch is to provide two mutually insulated electrodes in one housing, one of which is bell-shaped and the other of which is arranged in the manner of a freely oscillating clapper, the latter The switch closes when the clapper touches the bell-shaped electrode.

In an advantageous further development of the invention, the position and / or acceleration-responsive switch can be replaced by another electrical or electronic switchable component which is conductive in one switching state and blocks in another switching state, e.g. a photodiode, a transistor, an arbitrarily actuable microswitch, a level sensor or the like. A photodiode as a switch can be actuated by a light source, a transistor can be actuated by a sensor with an electrical output signal, a microswitch can be actuated by hand or by a machine part , a level sensor can become conductive when immersed in an electrolyte etc.. You can monitor a wide variety of parameters and, if a limit value is exceeded, switch off the associated consumer using a thermal switch, which also offers protection against overheating.

Embodiments of the invention are shown in the accompanying schematic drawings.

Brief description of the drawings

• 1 shows a longitudinal section through a combination of a bimetal switch with a switch which responds in a position and / or acceleration-dependent manner,
• 2 shows in longitudinal section another embodiment of a switch which responds in a position and / or acceleration-dependent manner,
• 3 shows a top view of the insert of the switch according to FIG. 2 carrying the electrodes,
• 4 shows a further embodiment of a switch which responds in a positional and / or acceleration-dependent manner on average,
• 5 shows an exemplary embodiment of a safety switch-off device according to the invention.

Detailed description of the drawings with ways of carrying out the invention:

Fig. 1 shows a bimetallic switch 1, in which two electrical connection lugs 2 and 3 with soldering eyes 4 and 5 are embedded in an electrically insulating, flat carrier 1a. Tongues 7 and 8 are punched out of the connecting lugs 2 and 3, raised in steps and also embedded in sections in the carrier 1a. The tongues 7 and 8 are in height and parallel to the top 9 of the carrier 1a, the connecting lugs 2 and 3 are in height and parallel to the bottom 6 of the carrier 1a.

On one tongue 8, a contact spring 10 is attached at one end, which carries at its movable end a switch contact 11, which cooperates with a stationary switch contact 12, which is attached to the other tongue 7. A bimetallic snap disk 16 is held loosely between hooks 15 at the front and rear on contact spring 10 and tabs 17 on the side of the contact spring. Alternatively, the bimetallic snap disk could also be arranged on the underside of the contact spring 10, that is to say between the contact spring 10 and the carrier 1 a.

A ceramic plate 18 is arranged on the underside of the carrier 1a and serves as a carrier for one or two thick-film resistors. On the ceramic plate 18, two rigid connecting lugs 20, 21 are attached, which protrude in opposite directions from the plate 18 and are soldered to the connecting lugs 2 and 3 of the bimetal switch.

The carrier 1 a has an opening 19 running from bottom to top through which the ohmic heat generated in the thick-film resistor or resistors can reach the bimetallic snap disk 16.

Furthermore, a switch 22 which responds to changes in position and / or accelerations is provided, which has a housing 23 with a continuous cylindrical bore. Two insert parts 24 and 25 are inserted into the bore, the mutually facing surfaces of which are weakly concave and are covered with two electrodes 26 and 27, respectively, which delimit a cavity in which a ball 28 is arranged to move freely.

The housing 23 and the two insert parts 24 and 25 are made of plastic. There is a plastic ring 29 between the two insert parts 24 and 25, which keeps the two insert parts and thus also the two electrodes 26 and 27 at a distance. Of the two electrodes, which can be formed, for example, by electroless metal deposition on the two insert parts 24 and 25, leads 30 and 31 each lead through the gap between the two insert parts 24 and 25 on one side and the housing 23 on the other side in opposite directions outside. With one of these connecting lugs 31, the switch 22 is soldered to a current path on the ceramic plate 18.
The ball 28 is made of metal at least on its surface. In the position shown, the switch 22 is open. With strong accelerations in a plane perpendicular to the plane of the drawing or when the switch 22 is tilted by 90 °, the ball 28 moves into a position in which it makes contact with both electrodes 26 and 27 by bridging the narrow ring 29 and thereby closes the switch .

A circuit example of the device shown in FIG. 1 is shown in FIG. 5.

FIG. 5 shows a consumer R fed from an AC voltage source, with which the bimetal switch 1 is in series.

In series with the consumer R is the bimetal switch 1, which is bridged by the two series resistors R₃ and R₄. The component 22 having two switching states, which is in particular a switch which responds in a positional and / or acceleration-dependent manner, is parallel to the consumer R, in such a way that the one terminal of the switch 22 is connected to the connecting line 34 of the two resistors R₃ and R₄ is connected.

$$\text{R₄ = 15 k Ω .}$$

Based on a mains voltage of 220 V and a resistance of the consumer of R = 50 Ω, suitable resistance values for the two resistors R₃ and R₄ $$\text{R₃ = 50 kΩ}$$

$$\text{R₄ = 15 kΩ.}$$

In the normal operating state, when the bimetallic switch 1 is closed and the other switch 22 is open, only a negligible current flows through the resistors R₃ and R₄. If the switch 22 closes, for example as a result of a change in position, then the line voltage drops in full over each of the two resistors R₃ and R₄, in this case they are series resistors of the switch 22 which are connected in parallel with one another , 5 W generates ohmic heat, with which the bimetal switch 1 is heated until it exceeds its switching temperature and opens. Thereafter, the full mains voltage drops only across the resistor R₃ and the bimetallic switch 1 is practically only heated by the resistor R₃ with the reduced power of approximately 3.25 W, which is sufficient to keep the bimetallic switch 1 open. The resistor R₄ and the consumer R are practically currentless.

If the switch 22 does not speak, but only the bimetal switch 21 as a result of overheating, then in the circuit example according to FIG. 5 the entire current flows through the two resistors R₃ and R₄ lying one behind the other; the resistors R₃ and R₄ heat the bimetallic switch 1 with a total power of approximately 1.6 W and keep it open. Developed at the same time the consumer R due to the high-impedance series resistor R₃ + R₄ only a negligible performance.

1, the switch 22 can be replaced by a modified switch as shown in FIG. 2 or 4. The switch 40 shown in FIGS. 2 and 3 is particularly suitable for use in irons. The switch 40 has a housing 41 with a cylindrical recess 42 which is closed by an insert part 43.

The insert part 43 has a weakly concave, inner surface which is covered with two electrodes 44 and 45, the shape of which can be seen in the top view in FIG. 3. The housing 41 and the insert 43 are made of plastic. The electrodes 44 and 45 can be formed on the insert part 43 by electroless metal deposition.

The two electrodes 44 and 45 have the shape of a strip and both electrodes start from the lowest point of the concave surface of the insert part 43 and extend in opposite directions to the edge of the concave surface of the insert part 43. From there, two connecting lugs 46 and 47 lead through the gap between the housing 41 and the insert part 43 to the outside. In the middle of the insert part 43, where the two electrodes 44 and 45 meet, a circular-edged depression 48 is provided in the concave surface, which simultaneously delimits the two electrodes 44 and 45.

In the cavity 42 there is a freely movable ball 49, the radius of which is greater than the radius of the depression 48 and which consists of metal at least on its surface.

In the position shown in FIG. 2, the ball 49 lies in the lowest point of the insert part 43 and makes contact with both electrodes 44 and 45: the switch is closed. In the event of changes in position or accelerations in a plane perpendicular to the plane of the drawing, the ball 49 is deflected from its position shown in FIG. 2: the switch is open.

The switch shown in Fig. 2 is installed in the iron so that it occupies the position shown in Fig. 2 when the iron is on its soleplate. If the iron is at rest, the ball assumes the position shown in FIG. 2 and closes the switch, so that when the circuit example shown in FIG. 5 is used, the iron is switched off, so that the items to be ironed or the ironing pad are not accidentally scorched. When ironing, however, the iron is moved back and forth, which has the consequence that the ball on the concave surface of the insert 43 rolls back and forth and, if necessary, randomly and briefly connects the two electrodes 44 and 45 to one another. The short-term current flow that occurs through the resistors R₃ and R led does not last long enough to heat the bimetal switch 1 to above its switching temperature, so that normal ironing movements ensure that the soleplate is heated. The same applies if the iron is put up during ironing breaks, as is customary.

Fig. 2 shows two threaded holes 50 in the housing, which are used for mounting the switch 40.

The switch 52 shown in FIG. 4 has a housing 53 with a bell-shaped cavity 54, which carries an annular electrode 55 in the lower region, from which a solder tail 56 leads through the gap between the housing 53 and a plate 57 closing the cavity 54 to the outside . A metallic clapper 58 is suspended in the cavity 54 in a freely swinging manner. Another solder tab 59 leads from the clapper 58 out of the housing. In the normal position shown in FIG. 4, the clapper does not touch the electrode 55: the switch is open. If the switch 52 is tilted over one of its edges by 90 ° or 180 °, the clapper 58 makes contact with the electrode 55: the switch is closed.

Claims (11)

1. Safety cutout device for electric loads (R), particularly for use in pressing irons and portable heating apparatus, comprising
   a temperature switch (1) which is located in series with the load (R), particularly a bimetallic switch,
   an electric component (22), which is connected in parallel with the load (R), having two switching states, particularly a switch operating in dependence on position and/or acceleration,
   and a series resistor, which is connected in series with the component (22) having the two switching states and heats the temperature switch (1) and which is also connected in parallel with the load (R),
   characterized in that there is provided a series circuit of two resistors (R₃, R₄) heating the temperature switch (1), said series circuit bridging the temperature switch (1), and that at the same time a parallel arrangement of the two resistors (R₃,R₄) forms said series resistor of the component (22, 40, 52) having two switching states.

2. Safety cutout device as claimed in claim 1, characterized in that the resistors (R₃, R₄) are arranged next to the temperature switch (1).

3. Safety cutout device as claimed in any of the preceding claims, characterized in that the resistors (R₃, R₄) are thickfilm resistors.

4. Safety cutout device as claimed in claim 3, characterized in that the bimetallic switch (1) has its contact spring (10) and its two switching contacts (11, 12) on one side of an electrically insulating base (1a) and the resistors (R₃, R₄) on the other side of this base (1a), and that either the bimetallic element of the bimetallic switch and the resistors (R₃, R₄) are located on the same side of the base (1a) or the base (1a) exhibits an opening (19) through which a heat transfer from the resistors (R₃, R₄) located on the one side to the bimetallic element (16) located on the other side is possible.

5. Safety cutout device as claimed in claim 3, characterized in that the base of the temperature switch (1) is a ceramic plate which carries on that other side the resistance layers.

6. Safety cutout device as claimed in claim 3, characterized in that the component (22) exhibiting two switching states is attached directly to the base or bases (18) of the thickfilm resistors.

7. Safety cutout device as claimed in any of the preceding claims, characterized in that the component exhibiting two switching states is a switch (22, 40) which operates in dependence on position and/or acceleration and which consists of a case (23, 41) having two mutually insulating electrodes (26, 27; 44, 45) and an electrically conductive sphere (28, 49) which can be freely moved between them and which makes contact with the two electrodes (26, 27; 44, 45) only in a predetermined position or in the absence of acceleration, resp. .

8. Safety cutout device as claimed in claim 7, characterized in that the two electrodes (44, 45) are formed by two strips on the slightly concave surface of a switch part (43), which strips are separated from one another by a circularly limited indentation (48) in the surface at the lowest point of this surface.

9. Safety cutout device as claimed in any of claims 1 to 6, characterized in that the component exhibiting two switching states is a switch (52) which operates in dependence on position and which consists of a case (53) having two mutually insulated electrodes (55, 58) one of which is constructed in the form of a bell and the other one of which is arranged inside it in the manner of a swinging clapper.

10. Safety cutout device as claimed in claim 7, 8 or 9, characterized in that the case (23, 41, 53) of the switch (22, 40, 52) operating in dependence on position is block-shaped, preferably cube-shaped, and has mounting means (50) at several mutually perpendicular sides.

11. Safety cutout device as claimed in any of claims 1 to 6, characterized in that the component (22) exhibiting two switching states is an electric or electronic component which is conductive in one switching state and blocks in another switching state, in particular a transistor, an arbitrarily actuable microswitch, a mercury switch or a sensor such as, for example, a photocell or photodiode, a level sensor, or such like.

Images