EP0284916A2 - Thermostat with a housing - Google Patents

Abstract

The invention proposes a temperature monitor with a housing with a pot-shaped lower part and a cover part, a bimetallic disc being arranged in the lower part and at least one movable contact part being connectable to a stationary counter contact under the action of the bimetallic disc, so that an electrical connection between the lower part, movable contact part and counter-contact part can be produced before that between the contact part and the lower part there is a fixed electrical higher-resistance connection through a resistance element in order to ensure that the temperature monitor does not close automatically after opening as long as a main switch for the power supply has not been interrupted.

Description

The invention relates to a temperature monitor with a housing with a pot-shaped lower part and a cover part, wherein a bimetallic disc is arranged in the lower part and at least one movable contact part can be connected to a stationary counter contact under the action of the bimetallic disc, so that an electrical connection between the lower part, movable Contact part and counter contact part can be produced.

Generic miniature temperature monitors of this type are known in various configurations from the following published documents: 17 90 103, 21 21 802, 24 33 901, 24 42 090, 24 42 397, 25 05 966, 25 11 314, 26 44 411, 29 17 482 , 31 22 899. For details, reference is made to the publications there, the content of which is made the disclosure content of the present application. It is a very small compact switch with a housing and a pot-shaped lower part and an upper part that closes it, whereby a switching mechanism is arranged in the housing that has one or more contacts that are carried and switched centrally by a bimetallic disc. A temperature monitor to which the invention relates has dimensions in the range of a few millimeters, typically a diameter of 5 to 8 mm and a height of less than 5 mm. If there is only one contact pair consisting of a movable contact part and a stationary counter-contact part, the current flow can be carried out in the simplest form via the bimetal disc itself, but is preferably carried out via an additional spring snap disc to the pot-shaped housing. In the case of two movable contacts with a corresponding counter contact, these are carried by a common support member moved by the bimetallic disc and the current flows directly. The current can be tapped from the mating contacts, which are generally arranged on the fixed part, via a current transmission element at one or more external connection contacts. Temperature switches, namely temperature limiters, are known which only interrupt the electrical contact and can either be switched back by hand to re-establish the electrical connection or can be replaced. Temperature monitors are known which automatically return to themselves after a substantial change in temperature and restore the electrical connection. It can then happen that after the bimetallic disc has cooled down, it switches back again and restores the electrical connection without eliminating the fault that resulted directly from increased current flow or indirectly increased temperature development and thus the separation of the electrical connection by the bimetallic disc. Then there are so-called controller cycles.

It is already known in the case of open switches of another type to arrange high-resistance resistors parallel to the switch contact between the connection ends, through which a small current flows and generates heat when the switch is opened. by which the bimetal disc is kept at a higher temperature so that it keeps the switch open. The current flow is only interrupted by an external interruption of the power supply, such as by switching off a main switch, so that only then can the bimetal disc spring back again. The invention has for its object to design generic miniature temperature switch of the type mentioned as a self-holding temperature switch. The small dimensions of these switches and the arrangement in a closed small housing are to be maintained and more effective heat generation to keep the switch open is to be achieved.

According to the invention, this object is achieved with a temperature monitor with a housing with a pot-shaped lower part and a cover part, a bimetallic disc being arranged in the lower part and at least one movable contact part being able to be connected to a stationary counter contact under the action of the bimetallic disc, so that an electrical connection between Lower part, movable contact part and counter-contact part can be produced, solved in that there is a permanent higher-resistance electrical connection between the counter-contact part and the lower part through a resistance part.

To optimally achieve the object, the invention does not go the way of bridging the external connection contacts, which are connected to connecting wires, by a high-resistance, as is generally done in known open switches, in order to make them self-retaining. In the miniature switches according to the invention, this would lead to a substantial enlargement of the entire assembly, so that they would ultimately no longer be usable for the intended purposes. A disadvantage of such a design would also be that the heat transfer from the high resistance to the bimetallic disc would be extremely poor. In contrast, the invention rather proposes an integrated solution with an integrated design of the high-resistance resistor in existence which housing before.

A preferred embodiment provides. that the resistance part is a PTC element. The use of such PTC _- elements for bridging ansich is known. An extremely preferred embodiment provides that the electrical resistance of the resistance part is adjustable. As a result, a single high-resistance part can be used with a resistance part that has different bimetallic disks with different switching temperatures for different switches that have the same construction, which is set and adapted to the bimetallic disc used and its switching temperature. In a preferred embodiment it is provided that the resistance part is a metal or carbon resistance part guided in arcs, it being possible in particular to provide that the resistance part is punched out of a metal disk or the carbon resistance is applied as a layer, in particular printed on a support, and from a solidified one Glass melt is covered. For the setting, an extremely preferred embodiment provides that bridges which can be removed exist between individual sections of the resistance part.

In a preferred embodiment, the invention proposes that the hitherto exclusively insulating cover part, which establishes a mechanical connection between the stationary mating contact or the current transmission element connected to it from the stationary mating contact to an outer connection contact part and the lower housing part, is designed as a high-resistance element or with a is provided so that a high-resistance connection between the stationary counter contact and the metallic housing lower part is made.

The switch according to the invention can be used in particular in places that are difficult to access, where there is also little space and / or contamination is to be feared. It can be used in particular within windings of electric motors, but also under pressure in front of lamps and in heaters. A particular advantage results from the combination of encapsulated miniature version and self-holding in that the switch can replace switches that can be reset by hand, solely because of the reset device, which still required a relatively large amount of space, which can be reduced by the switch according to the invention with the same level of safety.

• Fig. 2 eine andere Ausführungsform des erfindungsgegemäßen Temperaturwächters im Schnitt;
• Fig. 3 einen Schnitt entsprechend 111-111 in der Figur 2 im wesentlichen durch das Widerstandselement.
• Fig. 4 eine weitere Ausführungsform des erfindungsgemäßen Temperaturwächters in einem Schnitt entsprechend dem Schnitt der Fig.1 und
• Fig. 5 eine Aufsicht auf das Deckteil der Ausgestaltung nach Fig.4 entsprechend der Pfeile V - V;
• Fig. 6 einen Schnitt entsprechend dem der Fig. 4 durch eine Ausführungsform ähnlich der der Fig.4 mit einer zusätzlichen Isolierscheibe und
• Fig. 7 eine Seitenansicht eines erfindungsgemäßen Schalters mit vergossenem Deckteil.

Further advantages and features of the invention emerge from the claims and from the following description, in which two exemplary embodiments of the temperature monitor according to the invention are explained in detail with reference to the drawing. 1 shows a first embodiment of the temperature monitor according to the invention in section:

• Fig. 2 shows another embodiment of the temperature monitor according to the invention in section;
• Fig. 3 is a section corresponding to 111-111 in Figure 2 substantially through the resistance element.
• Fig. 4 shows a further embodiment of the temperature monitor according to the invention in a section corresponding to the section of Fig.1 and
• 5 shows a top view of the cover part of the embodiment according to FIG. 4 in accordance with the arrows V - V;
• 6 shows a section corresponding to that of FIG. 4 through an embodiment similar to that of FIG. 4 with an additional insulating washer and
• Fig. 7 is a side view of a switch according to the invention with potted cover part.

The temperature monitors according to the invention from FIGS. 1 and 2 are essentially circular, as can be seen from FIG. 3 for the temperature monitor according to FIG. 2.

The temperature monitors have a housing 1 with a cup-shaped lower part 2 and a cover part 3 closing this. The cover part 3 sits in a manner known per se either directly or indirectly on a circumferential shoulder 4 of the lower part and is pressed against it by a crimping 6 or flanging of the lower part 2 provided on the opposite side of the cover part 3. In known temperature monitors, the cover part is made of insulating material, such as a ceramic or plastic part, or, insofar as it is conductive, it is used in an electrically insulated manner from the pot-shaped lower part. In the latter case, the electrically conductive part of the cover part serves as a counter-contact part (for example DE-OS 29 17 482). In the former case, the cover part 3 is penetrated by one or more current transmission members 7, which on the inside carry a stationary counter-contact part 8 to a movable contact part 9, on the outside a connection contact element 11 and electrically connect them to one another.

In the illustrated embodiment, a bimetallic disk 12 and a spring snap disk 13 are seated in the lower housing part 2, which surround and carry the movable contact part 9 in central openings. In the position shown, the bimetallic snap disk 12 is relieved and the contact part 9 is pressed against the stationary counter contact 8 by the spring snap disk 13. When a predetermined temperature limit is exceeded, the bimetallic disc 12 flips over, coming to a shoulder 14 with its outer edge System and presses the contact 9 against the action of the spring snap disk 13 from the mating contact 8, so that the current flow, which in the illustrated closed position from the terminal contact 11 via the connecting part 7, the mating contact 8, the movable contact 9, the spring snap disk 13 to the housing 2 , to which the additional external connection can be connected, is routed, is interrupted.

1, the cover part 3 now has a so-called PTC element 16 which surrounds and carries the current transmission element 7 and is in electrical connection with the latter and on the one hand with the crimping 6 with the lower housing part 2. In order to make the current flow path via the PTC element 16, and thus the electrical resistance caused by this, as large as possible here, an insulating sleeve is arranged between the PTC element 16 and the current transmission element 7, so that the PTC element 16 is only inside lower area is in electrical connection with the stationary counter contact 8. In the same way, between the circumferential wall of the PTC element 16 and the axially parallel housing wall of the lower housing part 2, insulating material 18 is arranged, which is also drawn in the area 19 under the PTC element 16. This leads to the contacting of the PTC; Elements 16 with the lower housing part 2 only in the area of the upper outer circumference, when the crimping 6 takes place.

When the temperature monitor is closed (position shown), the current flows in the manner indicated above via the contact 9 and the spring snap disk 13, whereas a current flow through the PTC element 16 is negligible, since its resistance to the aforementioned current path is relatively large is. If the switch now opens by lifting the contact 9 from the mating contact 8, a current determined by the resistance of the PTC element 16 flows through it and heats it. The heating maintains a temperature at which the bimetallic snap disk 12 keeps the contact 9 away from the mating contact 8, so that this current path remains interrupted. A snap back of the bimetallic disc 12 is only possible if the over the guard 1; applied voltage is interrupted so that no more current can flow through the PTC element 16. As a result of the cooling, the bimetallic disc can spring back into its relieved position, so that the connection between the contact and counter-contact is restored under the action of the spring snap disc 13. After the voltage has been applied again, current can then flow back into contact 9 via mating contact 8.

In the exemplary embodiment in FIG. 2, a resistance element 20 is arranged on a ceramic carrier 21 in such a way that it forms a high-resistance conductive resistance connection between the current transmission element 7 and the wall of the lower housing part 2. In order to achieve a desired high resistance of the resistance element 20, it does not connect the current transmission element 7 directly radially to the lower housing part 2, but has a curved or serpentine shape with part-ring-shaped interruption areas, as shown in FIG. 3. The resistance element 20 has contact rings 20 and contacts the current transmission element 7 at 26, then runs a bit radially and continues initially in a partially annular circle 27 to just before the extension 26, at 28, there again somewhat further radially outwards and then in a second annular part 29 to a region 31 lying radially outside the region 26 and there again radially up to the bearing on the wall of the lower part 2, where the outer contact ring 20 contacts the lower part 2 via its crimping 6. A further ceramic part 22 is arranged below the ceramic carrier 21, between which an intermediate layer 23 made of Teflon, Kapton or the like is used for sealing. is arranged, which is bent slightly upward and clamped between the wall of the lower part 2 and the insulating support 21 (Figure 2, right). The branches 27, 29 are provided with radial connecting pieces 32. If all of the radial connectors 32 are maintained, the current can flow through the first radial connector 32a and the resistance is low. However, starting with the radial connecting piece 32a, these connecting pieces can also be broken out, as a result of which the resistance of the resistance element 20 increases, and it can thus be gradually adjusted to a desired value. Here, too, heat is generated in the resistance element 20, which contributes to keeping the bimetal snap disk 12 in its high-temperature position and thus the switch in its open position.

In the illustrated embodiment, two ring-shaped metallic contacts 20 were first installed on the outer and inner circumference of the ring-shaped ceramic carrier. The resistance element 20 is a carbon resistor applied to the ceramic carrier 21, which was first applied to the surface of the ceramic carrier as a mass containing carbon and glass mass in the described contour. When heated, the glass mass melts and covers the carbon on its top iso as a covering layer streaking, fixing it in the applied contour. The connecting pieces 32a can be separated by means of sand or laser beams - specifically. since the resistance element 20 is arranged on the upper side of the ceramic carrier 21, even after the switch has been installed, so that resistance changes or corrections can subsequently be made, such as from a silver-palladium alloy.

In the embodiment of FIGS. 4 and 5, a one-piece cover part 3, which consists of oxide ceramic and forms the ceramic carrier for the resistance element 20, is inserted into the pot-shaped lower part 2 of the housing 1. The resistance element 20 consists of a silver layer which is printed on the cover part 3 and which can also be branded. In this embodiment, contact or connection regions 26 are designed to be circumferentially widened, so that good contact is made with contact rings 41, 42. The contact ring 41 serves to establish the electrical connection to the lower housing part 2, while the contact ring 42 establishes the electrical connection to the mating contact part 8 or current transmission element 7. These contacts can only be supported by the fact that a tin layer is also provided in the areas 41, 42, which was also initially printed and was then heated to above the flow limit of the tin. The tin thus flows into the gaps between the lower part 2 and the cover part 3 on the one hand and between the cover part 3 and the current transmission element 7 on the other hand, and in addition to the good electrical contacting creates a seal to the interior of the housing 1, which other sealing measures, such as sealing rings (see also figure 6) between the shoulder 14 of the lower part and the associated shoulder 43 of the cover part 3, which can also be provided, supports, in part making it unnecessary. In this embodiment too, the upper edge of the lower part is bent inwards in the form of a flange 6. By tinning the conductor track at least in the ring area 41, the flanging 6 can press into the relatively soft tin during the flanging and thus also contribute to the tightness and to the electrical contacting in a simple and convenient manner. Furthermore, a thermal seal can then practically be achieved by soldering to the lower part 2 in the area of the flange 6 and / or the current transmission element 7 (connection or contact groove). To make contact with a stranded wire, in this exemplary embodiment the current transmission element 7 is provided with a connecting lug 46 projecting perpendicularly from the housing surface via a base part 47 thereof, which in a preferred manner enables the connecting stranded wire 48 to be welded on at the given temperatures without overheating the switching mechanism of the temperature monitor is to be feared, since the heat source given during welding is arranged relatively far from the switching mechanism due to the configuration of the connecting strap 46. Only then is the connecting tab 46 bent over, so that it extends parallel to its foot part 47 engaging the current transmission element 7 in the opposite direction to the latter over the cover part 3 (FIG. 7). The second connection is made by soldering a further wire to the lower part 2 (not shown). The cover part 3 is cast with the entire connection area - formed by the parts 7, 46, 47, 48 - by means of a conventional casting compound, which is transparent in the exemplary embodiment shown, but can also be opaque. The actual resistance element 20 can also be covered by an insulator material, for example by applying a lacquer, a plastic or the like.

FIG. 1 shows a configuration similar to that of FIG. 4, so that reference can be made to the above statements with regard to the same parts. Only a sealing washer 51 made of thermostable polyimide (Kapton) is inserted between the lower part 2 and the cover part 3 and is clamped between the shoulder 14 and the switch 43, so that a mechanical seal is provided. In certain cases, this design eliminates the need for sealing by means of tin and, if necessary, soldering, although this can also be provided in principle.

The main advantage of the switch according to the invention is that, despite its design as a self-holding switch, it can have the same extremely small dimensions as conventional miniature bimetallic switches due to its design when a high level of tightness is achieved, that is to say the design of the "self-holding" function compared to conventional switches does not require any additional volume bean speaks. The switch according to the invention can use conventional lower parts, switching mechanisms and contact and connection parts, so that only a few new parts have to be used, possibly only a cover part according to the invention instead of a conventional one, the necessary high-impedance resistance bridging the switching mechanism being achieved in the manner according to the invention. The switch according to the invention can, where conventional switches have been used up to now, replace them easily and in particular without taking up additional space. The switches shown have diameters of 8, for example up to 9 mm and heights of 2 to 2.5 mm (without sealing compound and connecting strap: with these 3.5 to 4 mm), with a cover part thickness including resistance track 20 of up to 1 mm with sufficient insulation.

Claims (13)

1. Temperature monitor with a housing, with a pot-shaped lower part and a cover part, wherein a switch mechanism with at least one bimetal disc and a movable contact part is arranged in the lower part and under the action of the bimetal disc, the movable contact part can be connected to a stationary counter contact, so that an electrical connection can be established between the lower part, the movable contact part and the counter-contact part, characterized in that there is a permanent, higher-resistance electrical connection between the counter-contact part (7, 8) and the lower part (2) through a resistance part (16, 21). 2. Temperature monitor according to claim 1, characterized in that the resistance part is a PTC element (16). 3. Temperature monitor according to claim 1, characterized in that the electrical resistance of the resistance part (16, 21) is adjustable. 4. Temperature monitor according to claim 1 or 3, characterized in that the resistance part is a metal resistance part guided in spiral arcs. 5. Temperature monitor according to claim 4, characterized in that the resistance part (21) is punched out of a metal disc. 6. Temperature monitor according to claim 1 or 3, characterized in that the resistance part is a resistance part (21) made of carbon. 7. Temperature monitor according to claim 6, characterized in that the resistor is melted or potted by an insulator cover. 8. Temperature monitor according to one of claims 4 to 7, characterized in that there are bridges (32, 32a) between individual sections (27, 29) of the resistance part, which are removable. 9. Temperature monitor according to one of the preceding claims, characterized in that the resistance parts (16, 21) are arranged on supports made of insulator material (22, 23). 10. Temperature monitor according to claim 9, characterized in that the carrier is made of ceramic. 11. Temperature monitor according to claim 9 or 10, characterized in that the resistance part is printed on the carrier. 12. Temperature monitor according to one of the preceding claims, characterized in that the switching mechanism (12, 13) is sealed by a seal (19, 23, 51), such as a sealing washer. 13. Temperature monitor according to one of the preceding claims, characterized by a seal by soldering.

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