EP0828273B1 - Switch with a safety element - Google Patents

Abstract

The electrical switch has a pair of conductors Ä14,15Ü ,one of which has a contact Ä21Ü on a bimetallic strip Ä25Ü and normally this engages a fixed contact Ä26Ü. When the current is such that a temperature threshold is exceeded the bimetallic strip responds and the contacts open. An additional safety feature is included in the form of a temperature sensitive spring Ä27Ü that expands and when a critical temperature value is reached opens the contacts.

Description

The present invention relates to a switch with a a switching temperature switching mechanism to open and Close one that can be connected to the switch's external connections Circuit, with a spring snap washer, approximately in the middle carries a movable contact and is circumferentially attached to one Supported part of the housing, via which they with an external connection is electrically connected, the movable contact depending of the temperature of a bimetal part in the system with a fixed, electrically with another external connection connected contact, and with a security element that its shape changes to a high temperature shape when its temperature reached a transition temperature that is above the response temperature lies.

Such a switch is known from DE-A-25 11 214.

In principle there are two different construction variants to be distinguished from switches called temperature monitors. In the first design, the moving contact is made by one cantilever spring element held while at the second, here in the foreground, the movable one Contact arranged approximately in the middle of a spring snap washer is, which is freely inserted in a housing and with her Edge supported on a housing part of the switch.

If a switch with spring element with its external connections is switched on in a circuit, so flows when closed Switch the current through the one external connection through the fixed and movable contact and the spring element to the other external connection. The spring element can either be made of Bimetal or be made of spring steel.

If the spring element is made of bimetal, the result is a structurally very simple design, which, however, the The disadvantage is that the switching properties of the bimetal through the self-heating of electricity. This prevents if a separate bimetal part is provided, that works against the force of the spring element.

Such switches can be used both as openers and Closer should be designed, with the bimetal part above its response temperature then either the moving contact pushes away from the fixed contact or in contact with this brings.

It is also known to switch such switches in series and / or Assign parallel resistors to further switching properties to achieve. A resistor connected in parallel gives you a self-holding function if the switch opens the bimetal part is created by that in the resistor Ohmic heat at a temperature above its response temperature and thus kept open.

A series resistor gives a switch provided with it additionally a current sensitivity by the switch flowing current namely heats the series resistance, whereby the ohmic heat generated in this increases the Temperature of the bimetal part above the response temperature and thus leads to the opening of the switch when the flowing Current has exceeded a certain limit.

Such switches are e.g. with a consumer to be protected connected in series to prevent this from overheating and / or to protect overcurrent. You will find in particular on Protection of electric motors, transformers, electrical Household appliances etc. use.

It is known that the switching behavior of the bimetal part changed over time, shifts as a result of aging the switching temperature up to 30 ° C, causing safety problems can lead. To avoid this disadvantage, it is already known with such a switch separate fuse in series, the above the response temperature of the switch, but below the permissible maximum temperature opens. Such fuses are used particularly in the transformer sector, where the use of temperature monitors without latching only in connection with a fuse connected in series he follows.

If due to the aging of the bimetallic part or another Defective switch at the desired response temperature does not switch, the temperature of the increases monitoring device with which the switch is in thermal communication stands until the melting temperature of the fuse is reached. The fuse then opens that the circuit is irreversibly interrupted by which the electrical consumers to be protected is fed.

The additional use of such a fuse however, has a number of disadvantages. On the one hand two separate components must be mounted on the device to be protected become, which not only increases the time required for assembly but also additional assembly space on the device requires. This is particularly disadvantageous because the known fuses are very voluminous, so that corresponding Space should be provided on the device to be protected got to.

A temperature monitor is known from DE-A-25 11 214 already mentioned at the beginning known in which two rear derailleurs with different high response temperatures in series are switched. The rear derailleur with the lower response temperature serves as a temperature controller, while the Switchgear with the higher response temperature than overtemperature circuit breaker serves. The two constructed in the same way Rear derailleurs have bimetallic snap disks on spring snap disks act, each one arranged centrally wear movable contact. The spring snap disc preferably has serving as a high temperature circuit breaker Rear derailleur only in a stable position, which they in the off position occupies. This prevents after a safety shutdown and subsequent cooling this spring snap washer back to its original position passes over and closes the contact again.

From EP-A1-0 041 823 is based on a different design principle based temperature monitor known, its rear derailleur comprises a spring element clamped on one side, at the free end of a movable contact is arranged. On the spring element two bimetal snap disks act via a transmission bolt with identical dimensions. The two Snap disks are freely movable in a housing and can snap independently. The one The snap pin closer to the transmission pin has a higher one Response temperature than the other snap disc so that it serves as a high temperature security element. Through integration this additional snap disc with a higher response temperature there is no need for a fuse.

A temperature monitor is known from EP-A2-0 451 678, which is constructed according to a different construction principle. A The bimetallic disc carries two movable contacts there at the same time when a response temperature of fixed Counter contacts lifted off and after cooling again at the same time be lowered on it. In one embodiment is the bimetal washer between two coil springs clamped, one of which is made from a shape memory alloy consists. If a temperature is higher than the response temperature Transition temperature exceeded, then the Coil spring made of the shape memory alloy irreversible together so that the other coil spring is the bimetal washer stands out from the counter contacts.

Against this background, it is an object of the present invention to further develop the switch mentioned at the beginning, that the above-mentioned in a structurally particularly simple manner Safety and assembly problems are eliminated.

According to the invention, this object is achieved with the above-mentioned Switch released in that the safety element on the spring snap disc acts, causing the movable contact in Dependence on the temperature of the safety element in the system with the fixed contact, and that the security element is made of a shape memory alloy, so that it is in its high-temperature shape even in moving contact a security situation holds when the temperature of the security element drops below the transition temperature again.

The object underlying the invention is based on this Way completely solved.

The advantage here is that such shape memory alloys, which are also called memory metal, a different switching and aging behavior than bimetal parts exhibit. However, the shape memory alloys show a slower switching behavior than bimetal parts. In advantageous Ways in this embodiment Bimetal part for quick switching and the safety element Made of shape memory alloy for a safe and irreversible Switching off when a maximum temperature is exceeded, namely the transition temperature of the security element used.

Such shape memory alloys have been around for several years known, they are characterized in that they are exceeded the high temperature form of the transformation temperature accept again, regardless of what form they are in the cold Condition previously brought. Further information for such shape memory alloys there are e.g. in the theme volume "Alloys with shape memory", contact and Studium, volume 259, Expertverlag, Ehningen, 1988, or Spektrum der Wissenschaft, 1980, Issue 1, pages 48-57, Donald Schetky: "Alloys that remember shapes".

In addition, the so-called one-way effect is used, the occurs when a shape memory alloy in martensitic Condition in the area below a critical degree of deformation is permanently deformed. When heated to the transition temperature, those in the range between -150 C and +150 C the original shape is restored, which is then retained even after cooling.

The advantage here is that the security element itself for this ensures that the movable contact part is permanently in its safety position remains. In other words, if the security element once to a temperature above its transition temperature has been heated, it irreversibly takes its High temperature mold in which there is the movable contact part permanently either in contact with the fixed contact part or holds out of contact with the fixed contact part, depending after whether the switch is a normally open or normally closed. The The advantage of this application is particularly in the constructive simple construction the new switch by using a shape memory alloy with one-way effect as Has security element.

The spring snap washer is usually free in a lower part of the housing inserted, which either consists of metal or but carries an insert on its bottom on which the Spring snap washer supported on the edge and to the outside is connected to the external connection. This lower housing part is closed with a cover part, which is either from electrically conductive material or of insulating material is made. If both the cover part and the lower part of the housing are electrically conductive, they are through an insulating film electrically isolated from each other. If only one of the two housing parts is electrically conductive the contacting is usually electrical on this one conductive housing part and the other through the wall of the other Part of the housing. It is also possible to use both housing parts made of electrically insulating or electrically conductive To manufacture material.

The spring snap washer is usually made of spring steel. With a temperature monitor designed as a break contact presses this spring snap disc below the response temperature the moving contact against the fixed contact, the current flowing through the switch via the spring washer to be led. Over the contact is a bimetallic snap disc put that above the response temperature against the force of the spring snap washer the moving contact pushes away from the fixed contact, which is why it turns around supported on a housing part.

It is understood that the above and those below Features still to be explained not only in the specified Combination, but also in other combinations or can be used alone without the scope of the to leave the present invention.

Fig. 1

ein erstes Ausführungsbeispiel des Schalters, der nicht Gegenstand der Erfindung ist, wobei sich das Schaltwerk unterhalb der Ansprechtemperatur befindet;

Fig. 2

den Schalter aus Fig. 1, wobei das Schaltwerk eine Temperatur oberhalb der Ansprechtemperatur eingenommen hat;

Fig. 3

einen Schalter wie in den Fig. 1 und 2, wobei das Schaltwerk jetzt eine Temperatur oberhalb der Umwandlungstemperatur eingenommen hat; und

Fig. 4

ein Ausführungsbeispiel des neuen Schalters, wobei das Schaltwerk eine Temperatur unterhalb der Ansprechtemperatur aufweist.

The invention is illustrated in the drawing and is explained in more detail in the following description. Show it:

Fig. 1

a first embodiment of the switch, which is not the subject of the invention, wherein the switching mechanism is below the response temperature;

Fig. 2

the switch of Figure 1, wherein the switching mechanism has reached a temperature above the response temperature.

Fig. 3

a switch as in Figures 1 and 2, wherein the switching mechanism has now reached a temperature above the transition temperature; and

Fig. 4

an embodiment of the new switch, wherein the switching mechanism has a temperature below the response temperature.

In Fig. 1, 10 generally designates a switch that there is shown schematically in longitudinal section. The Switch 10 comprises a housing 11 made of insulating material in which a temperature-dependent switching mechanism 12 is arranged.

The switch 10 has two external connections 14, 15, via which in series with an electrical consumer to be protected and its supply voltage is switched. Internally the switch 10, two contact rails 17, 18 are arranged, which are electrically connected to the external connections 15 and 14, respectively are.

The switching mechanism 12 comprises a movable contact 21 which is connected to a free end 22 one at its other end 23 on the Contact rail 17 attached spring element 24 is arranged. In the exemplary embodiment shown, the spring element 24 a bimetallic part 25 in the position shown in FIG. 1 presses the movable contact 21 against a fixed contact 26, which is attached to the upper contact rail 18.

In the position shown in Fig. 1, the switch 10 is closed, between the two external connections 14 and 15 via the contact rail 18, the fixed contact 26, the movable Contact 21, the spring element 24 and the contact rail 17 a low-resistance electrically conductive connection.

If now the temperature of the spring element 24 over the Response temperature is increased, then moves the spring element 24 due to the deformation of the bimetallic material movable contact 21 away from the fixed contact 26 so that the switch assumes the position outlined in FIG. 2, in which has no electrically conductive connection between the external connections 14 and 15 through switch 10 exist more. The temperature of the spring element 24 decreases the switch closes again 10 again.

The switch 10 also includes a security element 24 in the form a compression spring 28 made of a shape memory alloy. The Compression spring 28 is on the top of an insulating piece 29 Contact rail 18 attached.

In the temperature ranges corresponding to the switch positions 10 from FIGS. 1 and 2, the compression spring 28 the helical shape shown there. If the However, the temperature of the compression spring is above the response temperature lying transformation temperature increases, so converts their shape into the high temperature shape shown in Fig. 3 31, in which it the spring element 24 in the indicated at 32 Security situation presses.

The compression spring 28 is made of a shape memory alloy Made one-way effect, which means that the compression spring 28th maintains its high temperature shape 31 even when the Temperature back to well below the transition temperature decreases. This means that the compression spring 28 the Switch 10 keeps open permanently (even if the temperature drops again). Of course, this requires that the Force that the compression spring 28 in its high temperature form 31st exerts on the spring element 24 is greater than the closing force, with which the spring element 24, the movable contact 21 on the to press fixed contact 26.

The necessary setting of the spring constant of Spring element 24 and compression spring 28 can be selected by the Adjust alloys and normal deformation.

4 is a second embodiment of a switch 40 shown, the lower housing part 41 and one of these closing cover part 42 includes. In the lower part of the housing 41 is a temperature-dependent switching mechanism indicated at 43 43 arranged.

The switching mechanism 43 includes one freely in the lower housing part 41 inserted spring snap disk 45, which is approximately centric carries movable contact 46, over which a bimetallic snap disc 47 is turned over. The spring snap disk 45 supports with its edge 49 on the inside of the lower housing part 41 and presses the movable contact 46 against one inside the fixed part 51 provided for the cover part 42. The fixed contact Contact 51 extends through the rivet 52 Cover part 42 and goes outside into a first outer connection 43 over. This forms in the switch 40 from FIG. 4 Lower housing part 41 has a second external connection 54 since it is made of electrically conductive material is made while the Cover part 42 consists of electrically insulating material.

The switching mechanism 43 also has a security element 55 in Form a disk 56 made of a shape memory alloy. The disc 56 is with its center hole 57 over the movable Contact 46 is turned over and is supported with its edge 58 on one Shoulder 59 of the lower housing part 41. Sitting on the edge 58 the cover part 42 with a circular ring projection 61. The cover part 42 is through a flange 62 of the lower housing part 41 held captive on this. So that the edge 58 the disc 56 still has a certain mobility compared to the Receives shoulder 59 is a circumferential on the ring projection 61 Collar 63 is provided, which is directly on the shoulder 59 rests. The game between ring projection 61 and edge 58 of Disc 56 is not shown in FIG. 4 for reasons of clarity to see.

The position of the switch 40 in Fig. 4 corresponds to the position of the switch 10 in FIG. 1, the bimetallic snap disk 57 is below their response temperature. Increases the temperature of the bimetallic snap disk 47 to above the Response temperature, this presses with its edge 64 from below against the disc 56 and presses against the force of the spring snap disc 45 the movable contact 46 from the fixed Contact 51 gone. The position that the switch 40 then occupies corresponds to that shown in FIG. 2 for the switch 10.

When the temperature of the bimetallic snap disk 47 again drops, the switch 40 goes back to that shown in FIG. 4 Position back.

Due to aging processes it can now happen that the Response temperature of the bimetallic snap disk 47 by up to 30 ° C increases so that it is above a transition temperature the disc 56 lies. Now reaches the temperature of the bimetallic snap disc 47 and the disk 56 the transition temperature, the bimetallic snap disk 47 may not yet speak on, however, the disc 56 goes into its high temperature form above, in which it has a concave shape and the movable Contact 46 against the force of spring snap washer 45 as well Bimetallic snap disk 47 pushes away from the fixed contact 51. This high temperature form of disk 56 is irreversible remains even if the temperature is clear again drops so that the switch 40 remains open when once to a temperature above the transition temperature the disk 56 was heated.

Claims (5)

1. A switch having a switching mechanism (43) switching at a response temperature to interrupt and close, respectively, a circuit connectable to external terminals (53, 54) of said switch (40), comprising a spring snap disk (45) which carries approximately centeredly a movable contact (46) and is braced peripherally against a housing part (41) by means of which it is electrically connected to one external terminal (54), whereby the movable contact depending on the temperature of a bimetallic part (47) rests on a fixed contact (51) that is electrically connected with another external terminal (53), and comprising a safety element (55) that changes its shape into a high-temperature shape if its temperature reaches a transformation temperature which is above the response temperature,
   characterized in that the safety element (55) acts on the spring snap disk (45), whereby the movable contact (46) depending on the temperature of the safety element (55) rests on the fixed contact (51), and that the safety element (55) is produced from a shape-memory alloy, such that it, in its high-temperature shape, holds the movable contact (46) in a safety position even if the temperature of the safety element (55) again drops below the transformation temperature.
2. The switch of claim 1, characterized in that the spring snap disk (45) is associated with a bimetallic snap disk (47) that is slipped over the movable contact (46) and that, above the response temperature, is braced peripherally against a housing part (41).
3. The switch of claim 2, characterized in that the safety element (55) is a disk (56) which is slipped over the movable contact (46) and is braced, at least in its high-temperature shape, against a housing part (61).
4. The switch of claim 3, characterized in that the disk (56) is retained peripherally on a housing part (61, 59).
5. The switch of claim 4, characterized in that the disk (56) is held peripherally on a shoulder (59) between a lower housing part (41) and a cover part (42).

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