EP3739606B1 - Temperature-dependent switch - Google Patents

Description

The present invention relates to a temperature-dependent switch with a housing which has a cover part with an upper side and a lower part with a raised, circumferential wall, the upper section of which is bent over onto the upper side of the cover part and thereby holds the cover part to the lower part, wherein two contact surfaces are provided on the outside of the housing and a switching mechanism is arranged in the housing which is designed to switch, depending on its temperature, between a closed state in which the switching mechanism establishes an electrically conductive connection between the two contact surfaces, and an open state in which the switching mechanism opens the electrically conductive connection between the two contact surfaces, wherein a sealing ring is arranged on the upper side of the cover part and is in sealing contact with the bent over, upper section of the wall.

A temperature-dependent switch according to the preamble of claim 1 is known from FR 2 114 918 A5 Further examples of temperature-dependent switches are known from DE 196 23 570 A1 and the DE 10 2011 104 984 A1 known.

Such temperature-dependent switches are used in a conventional manner to monitor the temperature of a device. For this purpose, the switch is brought into thermal contact with the device to be protected, for example, via one of its outer surfaces, so that the temperature of the device to be protected influences the temperature of the switching mechanism.

The switch is electrically connected in series into the supply circuit of the device to be protected via connecting cables that are firmly attached to its outer contact surfaces (e.g. by soldering or welding), so that below the response temperature of the switch, the supply current of the device to be protected flows through the switch.

The one from the DE 196 23 570 A1 The known switch has a deep-drawn base with an inner circumferential shoulder on which a cover rests. The cover is held firmly on this shoulder by a raised and flanged edge of the base.

In the switch known from this publication, the cover and base are made of electrically conductive material. Therefore, an insulating foil is provided between them, which runs parallel to the cover and is laterally extended upwards so that its edge extends to the top of the cover. The flanged edge, i.e., the bent upper section of the wall of the base, presses against the cover in this switch with the insulating foil in between. The insulating foil thus serves to electrically insulate the two electrically conductive housing parts of the switch.

The one from the DE 196 23 570 A1 Known switches also include a temperature-dependent switching mechanism, which has a spring-loaded snap-action disc carrying a movable contact part, as well as a bimetallic disc placed over the movable contact part. The spring-loaded snap-action disc presses the movable contact part against a stationary counter-contact located inside the cover part.

The edge of the spring-loaded snap-action disc rests against the lower part of the housing, so that the electrical current flows from the lower part through the spring-loaded snap-action disc and the movable contact part into the stationary counter-contact and from there into the cover part.

The first external connection is a contact surface located centrally on the cover. The second external connection is a contact surface located on the flanged edge of the base. However, it is also possible to position the second external connection not on the edge, but rather on the side of the current-carrying housing or on the underside of the base.

From the DE 198 27 113 C2 It is also known to attach a so-called contact bridge to the spring-loaded snap-action disc, which is pressed by the spring-loaded snap-action disc against two stationary counter-contacts provided on the cover part. In this case, both contacts of the switch, to which the external connections are attached, are arranged on the cover part. The two contacts are electrically insulated from one another. In this design variant of the switch, the cover part is therefore preferably made of an insulating material or a PTC thermistor. Such PTC thermistors are also referred to as PTC resistors. They are made, for example, from semiconducting, polycrystalline ceramics such as barium titanate (BaTiO ₃ ).

In the case of the DE 198 27 113 C2 In this known switch, the current flows from one stationary contact through the contact bridge to the other stationary contact, which is also located on the cover, so that the spring-loaded snap-action disc itself is not subject to operating current. The contact bridge is therefore often referred to as a current transfer element.

This design is chosen especially when very high currents have to be switched, which can no longer be easily conducted via the spring washer itself.

In the two design variants mentioned above, a bimetallic disc is provided for the temperature-dependent switching function, which lies force-free in the switching mechanism below its transition temperature, whereby it is geometrically arranged between the movable contact part or the contact bridge and the spring snap disc.

For the purposes of the present invention, a bimetallic part is understood to be a multi-layer, active, sheet-metal component consisting of two, three, or four inseparably connected components with different thermal expansion coefficients. The individual layers of metals or metal alloys are bonded or positively connected and are achieved, for example, by rolling.

Such bimetallic parts exhibit a first stable geometric conformation in their low-temperature position and a second stable geometric conformation in their high-temperature position, between which they switch depending on the temperature in a hysteresis manner. When the temperature changes above their response temperature or below their recovery temperature, the bimetallic parts snap into the respective other conformation. The bimetallic parts are therefore often referred to as snap disks, and they can have an elongated, oval, or circular shape when viewed from above.

If the temperature of the bimetallic disc increases as a result of a temperature increase in the device to be protected above the transition temperature, the bimetallic disc changes its configuration and works against the spring snap disc in such a way that it lifts the movable contact part from the stationary contact or the contact bridge/current transfer element from the two stationary counter contacts, so that the switch opens and the device to be protected is switched off and cannot heat up any further.

In the above-mentioned designs of the temperature-dependent switch, the bimetallic disc is mechanically supported without force below its transition temperature, whereby the bimetallic disc is also not used to conduct the current.

This has the advantage that the bimetal disc has a long service life and that the switching point, i.e. the transition temperature of the bimetal disc, does not change even after many switching cycles.

If lower demands are placed on mechanical reliability or the stability of the transition temperature, the bimetallic snap-action disc can also take over the function of the spring snap-action disc and possibly even the current transmission element, so that the switching mechanism only comprises one bimetallic disc, which then carries the movable contact part or has two contact surfaces instead of the current transmission element, so that the bimetallic disc not only ensures the closing pressure of the switch, but also carries the current when the switch is closed.

It is also known to equip such switches with a parallel resistor connected in parallel with the external terminals. This parallel resistor absorbs part of the operating current when the switch is open and keeps the switch at a temperature above the transition temperature, so that the switch does not automatically close again after cooling down. Such switches are called latching switches.

It is also known to equip such switches with a series resistor through which the operating current flows. This generates ohmic heat in the series resistor, which is proportional to the square of the current flowing. If the current exceeds a permissible level, the heat generated by the series resistor causes the switching mechanism to open.

In this way, a device to be protected is disconnected from its supply circuit as soon as an excessive current flow occurs, which has not yet led to excessive heating of the device.

All these different design variants can be realized with the switch according to the invention.

Instead of a usually round bimetallic disc, a bimetallic spring clamped on one side can also be used, which carries a movable contact part or a contact bridge or a current transmission element.

However, temperature-dependent switches can also be used that do not have a contact plate as the current transfer element, but rather a spring element that carries the two mating contacts or on which both mating contacts are formed. The spring element can be a bimetallic part, in particular a bimetallic snap disc, which not only provides the temperature-dependent switching function but also simultaneously ensures the contact pressure and conducts the current when the switch is closed.

From the DE 195 17 310 A1 is a to the one from the above-mentioned DE 196 23 570 A1 A similarly constructed temperature-dependent switch is known, in which the cover part is made of a PTC thermistor material and can rest on an inner circumferential shoulder of the lower part without the interposition of an insulating film, onto which it is pressed by the flanged edge of the lower part.

In this way, the PTC thermistor cover is electrically connected in parallel to the two external terminals, thus giving the switch a self-holding function. This is also the case with the above-mentioned DE 198 27 113 C2 This is the case with the well-known temperature-dependent switch with contact bridge.

In the case of known switches, the external contact surfaces and the electrically conductive parts of the housing must still be electrically insulated after the connecting cables have been attached.

As insulation and pressure protection, the known switches are therefore often used in enclosures or protective caps, which serve as mechanical and/or electrical protection and often also protect the enclosure from the ingress of contamination. Examples of this can be found in the DE 91 02 941 U1 , dem DE 92 14 543 U1 , the DE 37 33 693 A1 and the DE 197 54 158 A1 .

Furthermore, the DE 41 43 671 A1 known to overmold the external connections with a one-component thermoset. DE 10 2009 039 948 It is known to cast terminal lugs with an epoxy resin.

However, the use of enclosures or terminal caps is often considered to be too complex in terms of construction and unsatisfactory in terms of thermal connection to the protective device.

Therefore, after the connecting wires have been soldered on, these switches are often coated with a varnish or protective coating. Some switches are also provided with resin caps, which, however, significantly increase the overall height of the switch. Furthermore, it is often impossible to ensure that the resin will flow completely. There is also a risk that the resin will penetrate open gaps and then enter the interior of the switch.

In switches where the cover is pressed onto the base with an insulating film in between, a problem with the switch's lack of tightness is often due to the insulating film rippling or wrinkling when bent over onto the top of the cover. This results in a kind of wrinkle in the insulating film, which means that the wall of the base cannot be bent far enough over onto the top of the cover. Furthermore, this waviness of the insulating film on the top and on the circumferential end face of the cover creates leakage paths for liquids, allowing them to seep into the interior of the switch when the switch is impregnated with protective coating.

Even compared to other electrical insulation materials, the flanged edge of the base does not seal the top surface sufficiently to ensure that no liquid can penetrate the switch during resinification. This is particularly problematic because such leakage paths are barely visible from the outside and therefore difficult to detect through visual inspection alone.

Even when soldering connecting cables to the top or the contact surface provided there, it cannot be completely ruled out that solder or corresponding liquids will get into the interior of the switch.

In the above-mentioned DE 196 23 570 A1 An attempt is made to reduce this problem by means of a circumferential bead which runs radially outwards on the underside of the cover part and presses on the insulating film arranged between the lower part and the cover part.

In the DE 10 2015 114 248 A1 It is also proposed to provide a circumferential cutting burr on the shoulder of the lower part, which cuts into the insulating foil. Although this solution has proven to be quite advantageous with regard to the mechanical sealing of the switch, it nevertheless has disadvantages. Particularly when the housing components are stored and processed in bulk, these cutting burrs can be damaged or ground off, which in turn insufficiently ensures tightness. Furthermore, such damage to the cutting burrs is hardly visible to the naked eye, so that potential problem areas are usually not even noticed during a visual inspection.

The previously mentioned problem of flowering or rosette formation of the insulation foil when bending the upper section of the cover part is solved according to the DE 10 2013 102 089 A1 This problem was solved by making a V-shaped cut in the edge of the insulating foil from the outside, which significantly reduces waviness. This also led to improved sealing of the switch.

Nevertheless, there is still a need to improve the mechanical tightness of such a temperature-dependent switch, since all of the above-mentioned solutions have led to at least minor disadvantages in practice.

It is therefore an object of the present invention to improve the mechanical sealing of the switch in a structurally simple and inexpensive manner.

This object is achieved according to the invention starting from the switch of the type mentioned at the outset in that the upper section of the wall with its free circumferential front edge penetrates at least partially into the sealing ring.

During manufacture, a sealing ring is arranged on the upper side of the lid part, preferably before the upper section of the raised, circumferential wall of the lower part is bent or flanged, which sealing ring is in sealing contact with this upper wall section after the bending or flanged thereof.

It has been shown that a sealing ring arranged at the mentioned location improves the mechanical sealing of the switch interior many times over.

Since, unlike many previously known solutions, no insulating foil is used to mechanically seal the interior of the switch, but rather the aforementioned additional sealing ring, the center of the cover can remain free for the connecting cables to be attached. This means that the semi-finished switch is already completely sealed before the connection technology is attached to the switch. This has the immense advantage that, for example, when soldering the connecting cables to the contact surface(s) provided in the center of the cover, no solder or soldering flux can penetrate the interior of the switch. A final manual sealing of the switch is no longer necessary.

If the switch is provided with an impregnating varnish or protective varnish for electrical insulation after the connecting cables have been attached, the sealing ring provided according to the invention also guarantees an extremely good mechanical seal which prevents the penetration of such varnishes or resins into the interior of the switch.

The inventive solution also has immense advantages from a production-technical perspective. The individual components of the housing do not need to be provided with punched burrs or a bead to ensure mechanical sealing. The sealing ring simply has to be placed on the top of the cover part. preferably before the upper section of the wall is beaded. This can be done fully automatically.

The increased tightness achieved with the sealing ring and the associated greater flexibility during production far outweigh the costs of the additional sealing ring.

The sealing ring is typically a very cost-effective component that can be easily stored and handled in automated production.

According to the invention, the upper section of the wall penetrates at least partially into the sealing ring with its free circumferential front edge.

Although the sealing ring is partially destroyed by the penetration of the wall, the mechanical seal is further improved by the penetration of the wall at the sealing point, as an additional mechanical/physical barrier is created.

It should be expressly mentioned at this point that, in addition to the sealing ring according to the invention, an insulating film can also be used in the switch according to the invention. This is particularly preferred when both the cover part and the lower part of the housing are made of an electrically conductive material and the two housing parts must be electrically insulated. In such a case, however, the insulating film primarily performs the function of electrically insulating the two housing parts, since the mechanical seal, as already mentioned above, is achieved according to the invention via the sealing ring, which is in sealing contact with the bent, upper section of the wall.

If an insulating film is used for the electrical insulation of the two housing parts, it is preferred that the sealing point at which the sealing ring is arranged is free of the insulating film.

According to one embodiment of the present invention, the sealing ring is integrally connected to the upper side of the lid part and/or the bent upper section of the wall. Preferably, the sealing ring is integrally connected to both the upper side of the lid part and the bent upper section of the raised wall of the lower part.

This material-to-material connection further improves the sealing effect achieved by the sealing ring. From a manufacturing perspective, such a material-to-material connection can be produced very easily and cost-effectively.

Preferably, the sealing ring is glued, hot-stamped or welded to the upper side of the cover part and/or the bent upper section of the wall by means of a welded joint produced by means of ultrasonic welding.

Welding the sealing ring using ultrasonic welding has proven particularly advantageous. Ultrasonic welding allows a clean and permanent connection of the sealing ring to the top of the lid and/or the bent edge of the upper section of the wall of the base. This significantly improves the sealing effect at these connection points.

A further advantage is that, unlike gluing the aforementioned components, the ultrasonic welding process can be performed even after the sealing ring has been mounted on the top of the cover part and the upper section of the wall of the base part has been bent or flanged. This simplifies production handling considerably.

Due to the comparatively low heat development generated during ultrasonic welding, temperature-related damage inside the switch, especially to the sensitive switching mechanism, can be effectively prevented. This applies even if the switch housing is made largely of metal. Despite the excellent thermal conductivity of metal, the comparatively low The heat generated during ultrasonic welding does not cause the stationary contact, typically located on the housing cover, to become undesirably detached. There is also no risk of the stationary contact and the moving contact part of the switch mechanism becoming welded together during the ultrasonic welding process. The risk of damage to the snap domes during the ultrasonic welding process is also reduced to a minimum.

A further advantage is that ultrasonic welding requires no filler metals. This allows for compact weld seams. Furthermore, the environmental impact is significantly reduced, as the use of environmentally harmful materials can be completely avoided.

In ultrasonic welding, the components to be joined are welded using high-frequency mechanical vibration. The resulting vibration leads to heating between the components due to molecular and interfacial friction. Accordingly, ultrasonic welding is also suitable for joining a metal component to a plastic component, as is the case here with the switch housing and the sealing ring.

In ultrasonic welding tools, a generator generates electronic vibrations, which are converted into mechanical vibrations by an ultrasonic converter. These vibrations are transmitted to the components to be joined via a so-called sonotrode. Within fractions of a second, the resulting ultrasonic vibrations generate frictional heat at the joining surfaces of the components to be joined, melting the material and bonding the components together.

The parameters to be adjusted during ultrasonic welding, such as amplitude and frequency, can be adjusted to suit the specific circumstances. The parameters to be adjusted and their respective values are known to the expert and can be found in the relevant standards.

According to a further preferred embodiment of the present invention, the sealing ring is designed as a circular plastic ring.

The cross-section of the sealing ring can be chosen arbitrarily, for example, circular (O-ring), triangular (delta ring), rectangular, square (quad ring), or oval. More complex cross-sectional shapes are also conceivable. The sealing ring can also be a standard flat gasket.

All common sealing materials, such as fluoroplastics, polyaryletherketones, polyamides, polyacetals or polyethylenes, can be considered as materials for the sealing ring.

According to a further embodiment, it is provided that the upper section of the wall is bent by at least 90°, preferably by at least 120°, when viewed in a cross-section.

The upper section of the wall can also be bent or curved by approximately 180°, forming a circumferential bead that is, for example, U-shaped in cross-section. However, according to the invention, it is preferred if the upper section of the circumferential wall is bent inward by at least 120°, because then the end face of the bent wall section comes into contact with the top side of the cover part or with the insulating film arranged thereon from above, so that the cover part is held sufficiently well to the bottom part of the housing.

As already mentioned at the beginning, it can be provided in one embodiment that the lower part and the cover part are each made of electrically conductive material and that an insulating film is arranged between the cover part and the lower part.

In this case, it is preferred that a first of the two contact surfaces is arranged on the cover part and a second of the two contact surfaces is arranged on the lower part, and that the switching mechanism carries a movable contact part which cooperates with a stationary counter-contact which is arranged on an inner side of the cover part and interacts with the first of the two contact surfaces. This corresponds, for example, to a basic switch structure as shown in DE 10 2013 102 089 A1 is known.

According to a further embodiment of the switch according to the invention, it is provided that the lower part is made of electrically conductive material and the cover part is made of insulating material or PTC material.

In this case, the two contact surfaces can be arranged on the cover part, and the switching mechanism can carry a current transmission element that interacts with two stationary counter-contacts arranged on an inner side of the cover part and each interacting with one of the two contact surfaces. Such a basic switch structure corresponds, for example, to the structure shown in DE 198 27 113 C2 is known.

Regardless of the type of construction of the switch housing and the switching mechanism, it is preferred in the switch according to the invention that the switching mechanism has a bimetallic part which carries a movable contact part and thus conducts the current through the switch.

The bimetal part can be a round, preferably circular bimetal snap-action disc, although it is also possible to use an elongated bimetal spring clamped on one side as the bimetal part.

However, it is preferred if the switching mechanism also has a spring-loaded snap-action disc, which then supports the movable contact part and conducts the current through the closed switch, providing the contact pressure when closed. This relieves the bimetallic part of both the current conduction and the mechanical stress when closed, which increases the service life of the switch and ensures that the switching temperature remains stable over the long term.

The present invention is particularly suitable for round temperature-dependent switches, which are therefore round, circular or oval when viewed from a top view of the lower part, although other housing shapes can also be used according to the invention.

Further features and advantages are apparent from the description and the attached drawings.

" Fig. 1

eine schematische Schnittansicht eines Ausführungsbeispiels des erfindungsgemäßen temperaturabhängigen Schalters.

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

" Fig. 1

a schematic sectional view of an embodiment of the temperature-dependent switch according to the invention.

In Fig. 1 is shown schematically, not to scale and in lateral section, an embodiment of the temperature-dependent switch 10 according to the invention, which has a housing 12 which has an electrically conductive, pot-like lower part 14 and an electrically conductive, plate-like cover part 16.

In the lower part 14, which is circular in plan view, an inner circumferential shoulder 18 is provided, on which the cover part 16 rests with an insulating film 20 interposed, which closes the lower part 14.

The cover part 16 has a circumferential end face 22 that separates an upper side 24 from an inner side 26. The insulating film 20 extends along the inner side 26 and along the end face 22, and its upper edge extends to the upper side 24.

The lower part 14 has a cylindrical, raised wall 28, the upper section 30 of which is bent or flanged onto the upper side 24 of the cover part 16. In this way, the cover part 16 is held to the lower part 14 with the insulating film 20 interposed.

The insulating film 20 provides electrical insulation between the cover part 16 and the base part 14. The insulating film 20 also provides a mechanical seal that prevents liquids or contaminants from entering the housing interior from the outside. For additional mechanical sealing, however, the invention also provides a sealing ring 32 that is in sealing contact with the bent upper section 30 of the wall 28. This sealing ring 32 is arranged on the upper side 24 of the cover part 16.

The upper section 30 of the wall 28 penetrates at least partially into the sealing ring 32. The upper section 30 of the wall 28 penetrates the sealing ring 32 with its free, end-face edge 56 along the entire outer circumference. Particularly preferably, the penetration depth is at least 10% of the diameter of the sealing ring 32.

In the illustrated embodiment, the upper section 30 of the wall 28 penetrates laterally from the outside into the sealing ring 32. However, it is also entirely possible for the upper section 30 of the wall 28 to penetrate from above into the sealing ring 32. For this purpose, the upper section 30 of the wall 28 would simply have to be flanged slightly further than in Fig. 1 shown, for example by a total of 180°.

By penetrating the peripheral edge 56 of the wall 28 into the sealing ring 32, the sealing effect of the sealing ring 32 can be further improved since a further mechanical barrier is created.

The sealing ring 32 is inserted into the Fig. 1 In the embodiment shown, the bent or flanged upper section 30 of the wall 28 continues to press against the upper side 24 of the cover part 16. In this way, the sealing ring 32 also seals the interface between the underside of the sealing ring 32 and the upper side 24 of the cover part 16.

It is preferred that the sealing ring 32 is integrally connected to the upper side 24 of the cover part 16 and/or the upper section 30 of the wall 28. As above As already mentioned, this can be done by gluing, hot stamping or welding the components using ultrasound.

Depending on the clamping force created by the bent or flanged upper section 30 of the wall 28, it may also be sufficient to simply place the sealing ring 32 onto the cover part 16 and clamp it between the upper section 30 and the top side 24.

The sealing ring 32 is a plastic O-ring. Generally, other circular plastic rings can be used in the same or similar manner, for example, with a triangular, rectangular, square, oval, or complex cross-section.

In the housing 12 of the switch 10 formed by the lower part 14 and the cover part 16, a temperature-dependent switching mechanism 34 is arranged, which comprises a spring snap-action disc 36 which centrally carries a movable contact part 38 on which a freely inserted bimetallic snap-action disc 40 is seated.

The spring snap-action disc 36 is supported on a base 42 on the inside of the lower part 14, while the movable contact part 38 is in contact with a stationary counter-contact 46, which is arranged on the inside 26 of the cover part 16, through a central opening 44 in the insulating film 20.

The external connection of the switch 10 is made of Fig. 1 two contact surfaces 48, 50. A first contact surface 48 is formed in a central region of the upper side 24 of the cover part 16. A second contact surface 50 is formed on the bent upper section 30 of the wall 28. However, a contact surface formed on the circumferential outer housing wall 52 or on the underside 54 of the lower part 14 can also serve as the second contact surface 50.

The underside 54 of the lower part 14 is preferably flat. This underside 54 allows the switch 10 to be thermally coupled to a device to be protected.

In this way, the temperature-dependent switching mechanism 34 in the Fig. 1 shown low-temperature position, an electrically conductive connection is established between the two outer contact surfaces 48, 50, the operating current flowing via the stationary counter-contact 46, the movable contact part 38, the spring snap-action disc 36 and the lower part 14.

Increases at switch 10 from Fig. 1 If the temperature of the bimetallic snap-action disc 40 rises above its response temperature via the thermal contact of the underside 54 to the device to be protected, it snaps from the Fig. 1 shown convex position into its concave position, in which it lifts the movable contact part 38 against the force of the spring snap-action disc 36 from the stationary contact 46 and thus opens the circuit.

Claims (12)

1. A temperature-dependent switch (10) having a housing (12), which comprises a cover part (16) having an upper side (24) and a lower part (14) having a raised peripheral wall (28), the upper section (30) of which is bent onto the upper side (24) of the cover part (16) and thereby holds the cover part (16) on the lower part (14), wherein two contact surfaces (48) are provided outside at the housing (12, 50) and a switching mechanism (34) is arranged in the housing (12), wherein the switching mechanism (34) is configured to switch, depending on its temperature, between a closed state, in which the switching mechanism (34) establishes an electrically conductive connection between the two contact surfaces, and an open state, in which the switching mechanism (34) opens the electrically conductive connection between the two contact surfaces (48, 50),

   wherein a sealing ring (32) is arranged on the upper side (24) of the cover part (16), wherein the sealing ring (32) is in sealing contact with the bent upper section (30) of the wall (28),

   characterized in that the upper section (30) of the wall (28) penetrates with its free, circumferential edge at least partially into the sealing ring (32).
2. The switch according to claim 1, characterized in that the sealing ring (32) is connected to the upper side (24) of the cover part (16) and/or to the bent upper section (30) of the wall (28) by means of a material bond.
3. The switch according to claim 2, characterized in that the sealing ring (32) is glued, hot stamped or welded by a welded joint produced by means of ultrasonic welding to the upper side (24) of the cover part (16) and/or to the bent upper section (30) of the wall (28).
4. The switch according to one of claims 1 to 3, characterized in that the sealing ring (32) is configured as an annular plastic ring.
5. The switch according to one of claims 1 to 4, characterized in that the upper section (30) of the wall (28) is bent by at least 90°, preferably by at least 120°, when viewed in a cross-section.
6. The switch according to one of claims 1 to 5, characterized in that the upper section (30) of the wall (28) is formed as a bead with a U-shaped cross-section.
7. The switch according to one of claims 1 to 6, characterized in that each of the lower part (14) and the cover part (16) is made of an electrically conductive material and an insulating foil (20) is arranged between the cover part (16) and the lower part (14).
8. The switch according to claim 7, characterized in that a first one of the two contact surfaces (48) is arranged on the cover part (16) and a second one of the two contact surfaces (50) is arranged on the lower part (14), and that the switching mechanism (34) carries a movable contact member (38) which interacts with a stationary counter contact (46) arranged on an inner side (26) of the cover part (16) and interacting with the first of the two contact surfaces (48).
9. The switch according to one of claims 1 to 6, characterized in that the lower part (14) is made of an electrically conductive material and the cover part (16) is made of an insulating material or PTC material.
10. The switch according to claim 9, characterized in that the two contact surfaces (48, 50) are arranged on the cover part (16) and the switching mechanism (34) supports a current transfer member (70) which interacts with two stationary counter contacts (46, 47) arranged on an inner side (26) of the cover part (16) and each interacting with one of the two contact surfaces (48, 50).
11. The switch according to one of claims 1 to 10, characterized in that the switching mechanism (34) comprises a bi-metal member (40).
12. The switch according to one of claims 1 to 11, characterized in that the switching mechanism (34) comprises a spring snap disc (36).

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