TEMPERATURE-CONTROLLING SWITCH

Description

[0001] The present invention relates to a temperature-dependent switch according to claim 1, comprising a first and a second stationary contact and a temperature-dependent switching mechanism with a movable contact element. In its first switching position, the switching mechanism presses the contact element against the first contact, thereby establishing an electrically conductive connection between the two contacts via the contact element. In its second switching position, the switching mechanism holds the contact element at a distance from the first contact, thereby interrupting the electrically conductive connection between the two contacts.The temperature-dependent switching mechanism features a temperature-dependent snap-action element that, upon exceeding a switching temperature, snaps from its low-temperature geometric configuration to its high-temperature geometric configuration. Upon subsequent falling below a reset temperature, it snaps back from its high-temperature geometric configuration to its low-temperature geometric configuration. This snap-action from the low-temperature to the high-temperature geometric configuration moves the switching mechanism from its first switching position to its second switching position, thus opening the switch.The switch according to the invention further includes a locking mechanism that prevents the open switch from being closed again by holding the switching mechanism in its second switching position once activated. The locking mechanism has a locking element that is at least partially made of a shape-memory alloy and has an opening through which the movable contact member projects. The locking element is configured to change its shape, upon exceeding a locking element switching temperature, from a first shape in which the locking element does not activate the locking mechanism to a second shape in which the locking element activates the locking mechanism by exerting a force, directly or indirectly, on the contact member that holds the switching mechanism in its second switching position. The first contact is arranged on a first side of the temperature-dependent snap element.

[0002] A generic switch, which forms the basis for the preamble of claim 1, is already known from EP 0 828 273 A1. Further exemplary switches are known from JPH 09213182 A and from DE 10 2018 100 890 B3.

[0003] Such temperature-dependent switches are used in a known manner to protect electrical devices from overheating. For this purpose, the switch is electrically connected in series with the device to be protected and its supply voltage, and mechanically positioned on the device in such a way that it is in thermal contact with it.

[0004] A temperature-dependent switching mechanism ensures that the two stationary contacts of the switch are electrically connected below the switching mechanism's response temperature. Thus, the circuit is closed below the response temperature, and the load current of the protected device can flow through the switch.

[0005] If the temperature rises above a permissible value, the switching mechanism lifts the movable contact element from the mating contact, thereby opening the switch and interrupting the load current of the protected device. The now de-energized device can then cool down again. During this process, the thermally coupled switch also cools down, at which point it would normally close automatically.

[0006] In the switch known from DE 10 2018 100 890 B3, a locking mechanism prevents this reset in the cooling position, thus preventing the protected device from automatically switching back on after being switched off. The locking mechanism mechanically locks the switching mechanism, preventing it from closing again once opened, even in the event of strong vibrations or temperature fluctuations.

[0007] This is a safety feature that applies, for example, to electric motors used as drive units. Its purpose is to prevent damage to the device or even injury to the person using it.

[0008] Due to their switching behavior, such switches, which do not close again after being opened once, are also called one-time switches.

[0009] It is understood that "opening" the switch refers to interrupting the electrically conductive connection between the two contacts of the switch, and not to opening the switch housing in a mechanical sense.

[0010] Another switch of this type is known from DE 10 2013 101 392 A1. This switch has a temperature-dependent switching mechanism with a temperature-dependent bimetallic snap disc and a bistable spring disc which carries a movable contact or a current transfer element. When the bimetallic snap disc is heated to a temperature above its response temperature, it lifts the contact or the current transfer element away from the mating contact(s) against the force of the spring disc and thereby pushes the spring disc into its second stable configuration, in which the switching mechanism is in its high-temperature position.

[0011] When the switch and thus the bimetallic snap disc cool down again, it springs back to its low-temperature position. Due to its design, however, its edge cannot rest against a counter bearing, so the spring disc remains in the stable second configuration, in which the switch is open.

[0012] The switch therefore remains in its open position after being opened once, even after cooling down. However, tests at the applicant's company have shown that the switch known from DE 10 2013 101 392 A1 closes again under strong mechanical shocks, meaning that from a safety perspective it may not be optimally suited for use in some applications.

[0013] It is also known to equip such temperature-dependent switches with a so-called self-holding resistor, which is connected in parallel to the two opposing contacts, so that it carries part of the load current when the switch opens. This self-holding resistor then generates ohmic heat sufficient to keep the snap disc above its opening temperature.

[0014] This so-called self-holding function is only active as long as the electrical device is switched on. As soon as the device is disconnected from the power supply, no current flows through the temperature-dependent switch, and the self-holding function ceases. After the electrical device is switched back on, the switch would therefore be in the closed position again, allowing the device to heat up again, which could lead to consequential damage.

[0015] This problem is avoided in the switches known from DE 10 2007 042 188 B3 and DE 10 2013 101 392 A1, in which the self-holding function is not realized electrically, but by a bistable spring element that has two stable geometric configurations independent of temperature, as described in the above-cited documents.

[0016] In contrast, the snap disk is a bistable snap disk that adopts either a high-temperature configuration or a low-temperature configuration depending on the temperature.

[0017] In the aforementioned DE 10 2007 042 188 B3, the spring disc is a circular spring-loaded snap disc to which the contact element is attached centrally. The contact element is, for example, a movable contact part that is pressed by the spring-loaded snap disc against the first stationary contact, which is located inside a cover of the housing of the known switch. The edge of the spring-loaded snap disc presses against an inner base of a lower part of the housing, which acts as a second contact. In this way, the self-conducting spring-loaded snap disc establishes an electrically conductive connection between the two mating contacts.

[0018] In its low-temperature position, the bimetallic snap disc rests loosely against the contact element. As the temperature of the bimetallic snap disc rises, it switches to its high-temperature position, in which its inner edge presses against the upper part of the housing and its center presses against the spring-loaded snap disc, causing it to switch from its first to its second stable configuration. This lifts the movable contact element from the stationary contact and opens the switch.

[0019] When the switch temperature cools down again, the bimetallic snap disc returns to its low-temperature position. In doing so, its edge contacts the edge of the spring-loaded snap disc, and its center contacts the top of the housing. However, the actuating force of the bimetallic snap disc is insufficient to return the spring-loaded snap disc to its initial configuration.

[0020] Only when the switch cools down significantly does the bimetallic snap disc bend further, so that it can finally push the edge of the spring snap disc down onto the inner base of the lower part so far that the spring snap disc springs back into its first configuration and closes the switch again.

[0021] The switch known from DE 10 2007 042 188 B3 therefore remains open after being opened once until it has cooled down to a temperature below room temperature, for which, for example, a freezing spray can be used.

[0022] Although this switch meets the relevant safety requirements in many applications, it has been found that, in rare cases, the tensioning of the bimetallic snap disc between the upper part of the housing and the edge of the spring-loaded snap disc can lead to an unintentional rebound of the spring-loaded snap disc.

[0023] From DE 10 2013 101 392 A1 it is further known to use a current transmission element, for example in the form of a contact plate, as a movable contact element, which is supported by the spring-loaded snap disc. Both stationary contacts are now arranged on the inside of the housing cover, whereby an electrically conductive connection between these two contacts is established by contacting the contact plate with them.

[0024] In this switch, the spring-loaded snap disc is fixed with its edge to the lower part of the housing, while the bimetallic snap disc is provided between the spring-loaded snap disc and the inner bottom of the lower part.

[0025] Below the activation temperature of the bimetallic snap disc, the spring-loaded snap disc presses the contact plate against the two stationary contacts. When the bimetallic snap disc switches to its high-temperature position, its edge presses against the spring-loaded snap disc, and its center pulls the spring-loaded snap disc away from the upper part, thus disengaging the contact plate from the two mating contacts. To enable this geometrically, the contact plate, spring-loaded snap disc, and bimetallic snap disc are captively connected by a centrally located rivet.

[0026] When the temperature of the bimetallic snap disc drops again, it does spring back to its low-temperature position, but the spring disc remains in its current configuration because the bimetallic snap disc lacks a counter bearing for its edge, so it cannot press the current transfer element back against the two stationary contacts.

[0027] This switch therefore has a self-holding function due to its design. However, in rare cases, strong mechanical shocks can cause the spring-loaded snap disc to retract unintentionally.

[0028] From DE 25 44 201 A1, a temperature-dependent switch with a current transmission element designed as a contact bridge is further disclosed, in which the contact bridge is pressed against two stationary mating contacts by a closing spring. The contact bridge is in contact with a temperature-dependent switching mechanism via an actuating bolt. This mechanism consists of a bimetallic snap disc and a spring disc, both of which are clamped at their edges.

[0029] As with the switch known from DE 10 2007 042 188 B3, in this switch the spring disc and the bimetallic snap disc are both bistable, the bimetallic snap disc in a temperature-dependent manner and the spring disc in a temperature-independent manner.

[0030] If the temperature of the bimetallic snap disc increases, it pushes the spring disc into its second configuration, in which the spring disc pushes the actuating bolt against the contact bridge and lifts the bridge against the force of the closing spring from the stationary counter-contacts.

[0031] Even when the bimetallic snap disc cools down, the spring disc remains in this second configuration and keeps the familiar switch open against the force of the closing spring.

[0032] From the outside, pressure can now be applied to the contact bridge by pressing a button, so that the spring disc is pushed back into its first stable configuration via the actuating bolt.

[0033] Besides its very complex construction, this switch has the disadvantage that, in the open position, the spring washer lifts the contact bridge against the force of the closing spring from the mating contacts. Therefore, in its second configuration, the spring washer must reliably overcome the force of the closing spring. However, because the closing spring ensures the contact bridge is securely seated against the mating contacts in the closed position, a spring washer with very high stability is required in this second configuration.

[0034] Another switch with three switching positions is known from DE 86 25 999 U1. In this known switch, a spring tongue is provided that is clamped on one side and carries a movable contact part at its free end, which interacts with a fixed counter-contact.

[0035] A calotte is formed on this spring tongue, which is pressed into its second configuration by a bimetallic plate also attached to the spring tongue, in which it distances the movable contact part from the stationary counter-contact.

[0036] In this switch, the dome must hold the movable contact part at a distance from the fixed counter-contact against the closing force of the spring tongue clamped on one side, so that the dome in its second configuration must exert a high actuating force.

[0037] The well-known switch thus exhibits the disadvantages already discussed above, namely that high actuating forces have to be overcome, which leads to high manufacturing costs and an unsafe state in the cooling position.

[0038] The switch described in DE 10 2018 100 890 B3 mentioned at the beginning has the most mechanically stable locking mechanism compared to the other switches mentioned. Due to the mechanical locking of the switching mechanism, which is achieved by the locking mechanism, accidental re-activation after the switch has been opened is virtually impossible.

[0039] However, it has been shown that the locking mechanism known from DE 10 2018 100 890 B3 is relatively complex to manufacture, so that the manufacturing costs of the switch are comparatively high.

[0040] Against this background, the present invention is based on the objective of further developing the aforementioned switch in such a way that it has an alternative locking mechanism that is simple and therefore inexpensive to manufacture and yet ensures a safe interruption of the circuit even in the cooling position of the switch and in the event of strong vibrations.

[0041] According to the invention, this problem is solved in a switch of the type mentioned above according to claim 1 by arranging the locking element on a second side of the temperature-dependent snap part opposite the first side.

[0042] The locking mechanism according to the invention is therefore a temperature-dependent locking mechanism that is activated when a predefined temperature, referred to here as the locking element switching temperature, is reached or exceeded. As long as the locking element switching temperature is not reached or exceeded, the locking mechanism is not activated.

[0043] The locking mechanism utilizes the temperature-dependent deformation effect (memory effect) of a shape-memory alloy. It features a locking element that is at least partially made of such a shape-memory alloy. This locking element has an opening through which part of the switching mechanism protrudes.

[0044] In particular, the movable contact element of the switching mechanism protrudes through this opening and can move through it during the switching action of the switch without colliding with the locking element. The shape of the opening can be various, e.g., round or square.

[0045] The temperature-dependent deformation effect of the shape-memory alloy of the locking element is preferably utilized according to the invention as follows: As long as the locking element's switching temperature is not exceeded, the locking element remains in its first form. In this first form, the locking element exerts no force on the switching mechanism. Preferably, the locking element does not even touch the switching mechanism while it is in its first form. The switching function of the switching mechanism, which is effected in particular by the temperature-dependent snap element, is thus not impaired as long as the locking mechanism is not activated. This is only activated when the locking element assumes its second form, which occurs due to the shape-memory alloy when the locking element's switching temperature is exceeded. In its second form, the locking element exerts a force on a part of the switching mechanism.This force holds the switchgear in its second switching position and prevents it from switching back to its first, closed switching position.

[0046] Once the locking element's switching temperature is reached, the switch remains in its second, open position. The locking mechanism prevents the switch from closing again.

[0047] Shape memory alloys make it very easy and reliable to ensure such temperature-dependent shape changes of components. The locking element according to the invention is therefore relatively inexpensive to manufacture. Since the design of the switch and the switching mechanism contained therein does not otherwise need to be changed, but only the locking element needs to be added to the switch, the implementation of the entire locking mechanism according to the invention is very simple and cost-effective from a manufacturing perspective. The overall cost of the switch is therefore hardly increased by the locking mechanism according to the invention.

[0048] Depending on the design of the switching mechanism, the locking element can either directly contact the temperature-dependent snap element and exert the force directly on it, or it can contact another component of the switching mechanism, so that it only exerts the force indirectly on the temperature-dependent snap element. Both cases have the advantage that a direct force application to both the temperature-dependent snap element and the temperature-independent spring element is easily possible, since both components are typically designed with a relatively large surface area and thus offer large areas for the force to act upon.

[0049] Viewed from the temperature-dependent snap element, the locking element, according to the invention, is not located on the side of the first contact (first side), but rather on the opposite second side of the temperature-dependent snap element. Upon reaching the locking element's switching temperature, it exerts the force that holds the switching mechanism in its second switching position, preferably directly on the movable contact element. This has the advantage that the force exerted by the locking element is applied directly to the part that is to be kept at a distance from the first contact when the locking mechanism is activated. Furthermore, since the movable contact element is usually a solid component, there is hardly any risk of damage to the switching mechanism from the locking mechanism.

[0050] It should be noted here that the terms "open switch" and "closed switch" do not refer to the position of the housing, but rather to the electrically conductive connection. These terms have nothing to do with whether the switch housing is open or closed. Instead, they refer to whether the electrically conductive connection between the two stationary contacts of the switch is open or closed.

[0051] Regarding the terminology used here, it should be further noted that, according to the definition of the invention, the deformation of the shape-memory alloy of the locking element occurs when the locking element's switching temperature is "exceeded." In principle, the deformation occurs as soon as the locking element's switching temperature is reached. However, the word "exceeded" is used here to clarify that the deformation of the locking element occurs after a heating process, i.e., when the locking element's switching temperature is reached from a lower temperature, and not during a cooling process when the locking element's switching temperature is reached from a higher temperature.

[0052] The locking element can, for example, be configured to change its shape from the first shape to the second shape when the locking element switching temperature is reached during a heating process, but to retain its second shape when the locking element switching temperature is subsequently reached again during a cooling process.

[0053] The shape change that the locking element undergoes when the locking element switching temperature is exceeded can be varied. For example, the locking element can change its shape from a flat or straight cross-section to a convex or concave cross-section. It is also conceivable that the locking element bends, folds over, or expands in a different way when the locking element switching temperature is reached.

[0054] Preferably, the shape-memory alloy of the locking element is configured to move the locking element towards the switching mechanism when the locking element's switching temperature is reached, to make contact with it, and to exert a compressive force that holds the switching mechanism in its second switching position. This force exerted by the locking element on the switching mechanism is preferably higher than the force exerted by the temperature-dependent snap element, by which the temperature-dependent snap element, in its low-temperature configuration, attempts to close the switch, i.e., to move the switching mechanism into its first switching position.

[0055] If the switch is open after reaching the switching temperature and the locking mechanism is activated after reaching the locking element switching temperature, the locking mechanism prevents the switch from closing again, even if its temperature falls below the reset temperature and the temperature-dependent snap element attempts to snap back into its low-temperature geometric configuration.

[0056] According to a preferred embodiment, the locking element is essentially designed in the shape of a plate or disc.

[0057] This has the advantage that the locking element, and therefore the entire locking mechanism, hardly increases the switch's overall height. The switch dimensions and the design of the switching mechanism require little to no modification compared to regular switches without a locking mechanism.

[0058] In this context, "plate-shaped" and "disc-shaped" mean that the length and width of the locking element are significantly greater than its thickness. While "plate-shaped" encompasses almost any shape for the locking element when viewed from above, "disc-shaped" preferably refers to a circular, oval, or elliptical shape for the locking element.

[0059] According to a further embodiment, the opening in the locking element is designed as a through-hole.

[0060] This has the advantage that such a hole can be produced relatively easily and inexpensively. The locking element can thus be manufactured, for example, as a type of perforated plate, i.e., a plate with a through-hole. Such a locking element can be very easily mounted in the switch housing and placed over the movable contact element of the switching mechanism. Preferably, the opening or through-hole is located centrally in the locking element.

[0061] Both the locking element and the rest of the switch's structure can, for example, be designed to be rotationally symmetrical.

[0062] In a further embodiment, it is provided that the locking element has at least one slot that penetrates the locking element and adjoins the opening.

[0063] Such a slot has the advantage of increasing the deformation effect. In other words, the locking element, with the aid of the shape memory alloy, can achieve a greater deformation with the same force. Furthermore, the at least one slot in the locking element prevents internal stresses that could otherwise arise due to the deformation of the locking element caused by the shape memory alloy.

[0064] It is preferred that the at least one slot runs in a straight line and extends radially outwards from the opening.

[0065] This has the advantage that the locking element can curve more strongly. Parts of the locking element can open or fold out along the slot without creating significant shear forces in the area of ​​the opening.

[0066] Particularly preferably, the locking element has two, three, four or more slots, each adjacent to the opening, running in a straight line and extending radially outwards from the opening.

[0067] According to this design, the slots are essentially arranged in a star shape radiating from the hole into the locking element. Each of these slots preferably penetrates the entire thickness of the locking element. This has the advantage that the slots create individual, separate areas within the locking element, which can bend separately when the locking element's switching temperature is reached, in order to exert the force required for locking on the switching mechanism independently of one another.

[0068] The locking element can be a type of slotted spring disc or slotted disc spring, which in its first form is flat, i.e. purely disc-shaped, and in its second form is convexly or concavely curved.

[0069] In a further embodiment, the switch is provided for in a housing, and the locking element is attached to the housing with its edge.

[0070] Since the opening is preferably located centrally in the locking element, such an edge-side attachment of the locking element has the advantage that the shape change caused by the shape memory alloy is hardly affected. Furthermore, the locking element can be fixed to the housing at its edge in a very stable manner.

[0071] The locking element is preferably attached to the housing along its entire circumferential edge. The attachment can be force-fit, form-fit, and / or material-fit. Particularly preferably, the locking element is clamped in the housing with its circumferential edge. Such an attachment is the most cost-effective to implement from a manufacturing perspective.

[0072] It is further preferred that the edge of the locking element is made of an electrically insulating material or is coated with an electrically insulating material.

[0073] For example, a central portion of the locking element can be made of a shape memory alloy bonded to an electrically insulating material around its outer circumference. Alternatively, the entire locking element can be made of the shape memory alloy and coated along its perimeter with an electrically insulating material, such as plastic. Furthermore, an adhesive film can be applied to the edge or circumference of the shape memory alloy to electrically insulate the edge of the locking element. The coating or adhesive film can be applied to one or both sides (top and bottom) of the locking element.

[0074] The electrical insulation of the locking element's edge has the advantage that it allows for electrical isolation between two housing parts of the switch. Since the locking element's edge is preferably attached to the housing and current flows through parts of the housing, this type of insulation also has the advantage that the locking element itself does not carry current. This, in turn, has a positive effect on the function and service life of the shape memory alloy.

[0075] According to a further embodiment, the housing has a lower part closed by an upper part, wherein the locking element rests on a circumferential shoulder arranged in the lower part and is clamped between the lower part and the upper part.

[0076] This arrangement of the locking element has the advantage that during manufacturing it only needs to be placed on the shoulder in the lower part and is automatically clamped and thus fixed between the upper and lower parts when the switch housing is closed. Typically, the lower part has a raised edge that, when the switch housing is closed, is at least partially bent or crimped onto the upper part to hold the upper part to the lower part.

[0077] Furthermore, it is preferred that the first stationary contact or each of the two stationary contacts is arranged on an inner side of the upper part.

[0078] This design feature is known in itself. It ensures that when the upper part of the switch is mounted to the lower part, the geometrically correct alignment between the first contact, or between the first and second contacts, is simultaneously established with respect to the movable contact element.

[0079] According to a further embodiment, the shape memory alloy of the locking element is a shape memory alloy with a one-way memory effect.

[0080] By using a shape memory alloy with a one-way memory effect, the locking element, and thus also the locking mechanism, can be designed to be irreversible. In this case, the switch according to the invention is a so-called one-time switch. The shape memory alloy allows the locking element to change shape only once. After it has changed its shape from the first shape to the second shape when the locking element's switching temperature is exceeded, subsequent cooling does not cause a further shape change in such a one-way shape memory alloy.

[0081] Alternatively, the shape memory alloy can be a shape memory alloy with a two-way memory effect, wherein the locking element is configured to change its shape from the second shape to the first shape when a locking element reset temperature is undershot, and wherein the locking element reset temperature is lower than the locking element switching temperature.

[0082] The switch in question is a locking switch with a reversible locking mechanism, meaning it can be released again. Shape memory alloys with a two-way effect can, so to speak, "remember" two shapes: one at high temperature and one at low temperature. With such a two-way shape memory alloy, the locking element can change its shape from the first to the second shape when the locking element's switching temperature is reached, and then, upon subsequent cooling, return to its first shape once the locking element's reset temperature is reached.

[0083] According to a further embodiment, it is provided that the locking element switching temperature is equal to or higher than the switching temperature of the temperature-dependent snap-action part.

[0084] If both switching temperatures are set to the same level, the locking mechanism is activated at the same time the switch opens. However, if the locking element's switching temperature is set higher than the switching temperature of the temperature-dependent snap-action element, the locking mechanism is only activated after the switch opens. Although the circuit is interrupted when the switch opens, the switch typically heats up slightly in practice due to residual heat remaining in the protected device before the cooling process begins. The temperature thus exceeds the set temperature slightly after the switch opens, which is why this is referred to as the "overshoot temperature range." It is therefore possible to set the locking element's switching temperature within this overshoot temperature range.

[0085] According to a further embodiment, the locking element reset temperature is lower than the reset temperature of the temperature-dependent snap-action part.

[0086] This has the advantage that, during normal cooling of the switch after opening, the locking mechanism remains activated even when the temperature-dependent snap-action mechanism reaches or falls below the reset temperature. Deactivation of the locking mechanism (provided it is reversible) can then be achieved, for example, by applying a suitable cold treatment. For instance, the switch can be manually treated with a freeze spray, which deactivates the locking mechanism and allows the switch to close again.

[0087] According to a further embodiment, the switching mechanism comprises a temperature-independent spring element connected to the movable contact element, wherein the temperature-dependent snap element acts on the temperature-independent spring element when the switching temperature is exceeded, thereby lifting the movable contact element from the first contact. It is particularly preferred that the spring element is a bistable spring element with two temperature-independent, stable geometric configurations.

[0088] If the spring element is designed as a bistable spring disc, it is preferred that in its first stable configuration the spring disc presses the movable contact element against the first contact, and in its second stable configuration keeps the movable contact element spaced apart from the first contact. This has the advantage that, in the closed state of the switch (in the first switching position of the switching mechanism), the spring disc provides the closing force and thus the contact pressure between the movable contact element and the first contact. This mechanically relieves the temperature-dependent snap element, which positively influences its service life and the long-term stability of its response temperature (switching temperature).

[0089] If the spring part is designed as a bistable spring disc with two temperature-independent stable geometric configurations, this has the additional advantage that the bistable spring disc holds the switch in its open state after opening.

[0090] The temperature-dependent snap element is preferably designed as a bi- or tri-metal snap disc.

[0091] According to a further embodiment, it is preferred that the movable contact element comprises a movable contact part that interacts with the first contact, and that the spring part interacts with the second contact, wherein it is further preferred that the spring part is electrically connected to the second contact at least in its first geometric configuration via its edge.

[0092] This design is known in principle from DE 10 2018 100 890 B3, DE 10 2007 042 188 B3 or DE 10 2013 101 392 A1. It results in the temperature-dependent snap-action element not carrying a current in any position of the switch, but rather the load current of the electrical device to be protected flows through the spring element.

[0093] In an alternative embodiment, the movable contact element comprises a current transmission element that interacts with both stationary contacts.

[0094] The advantage here is that the switch can carry considerably higher currents than the switch known from DE 10 2007 042 188 B3. The current transfer element arranged on the contact element ensures an electrical short circuit between the two contacts when the switch is closed, so that not only the temperature-dependent snap-action element but also the temperature-independent spring element are no longer traversed by the load current, as is already known in principle from DE 10 2013 101 392 A1.

[0095] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0096] Exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the following description. They show: Fig. 1 a schematic sectional view of a switch useful for understanding the invention, in its low-temperature position; Fig. 2 a schematic sectional view of the Fig. 1 The switch shown is in its high-temperature position; Fig. 3 is a schematic sectional view of the switch shown in Fig. 3. Fig. 1 Fig. 4 shows a schematic sectional view of a first embodiment of the switch according to the invention in its low-temperature position; Fig. 5 shows a schematic sectional view of the switch shown in Fig. 4 in its high-temperature position with the locking mechanism activated; ... Fig. 4 first embodiment of the switch according to the invention shown in its high-temperature position; Fig. 6 a schematic sectional view of the Fig. 4 Fig. 7 shows a first embodiment of the switch according to the invention in its high-temperature position with the locking mechanism activated; Fig. 7 shows a schematic sectional view of a second embodiment of the switch according to the invention in its low-temperature position; and Fig. 8 shows a schematic top view of a locking element according to an embodiment of the present invention.

[0097] In Fig. 1 A schematic cutaway side view shows a switch 10 which is rotationally symmetrical in the top view and preferably has a circular shape.

[0098] The switch 10 has a housing 12 in which a temperature-dependent switching mechanism 14 is arranged. The housing 12 comprises a cup-shaped lower part 16 and an upper part 18, which is held to the lower part 16 by a bent or crimped upper edge 20.

[0099] In the Fig. 1 In the example shown, both the lower part 16 and the upper part 18 are made of an electrically conductive material, preferably metal. The upper part 18 rests on a shoulder 22 formed in the lower part, with an insulating film 24 interposed. The shoulder 22 is designed as a circumferential shoulder and has a substantially annular bearing surface on which the upper part 18 rests, with the insulating film 24 interposed.

[0100] The insulating film 24 provides electrical insulation of the upper part 18 from the lower part 16. The insulating film 24 also provides a mechanical seal, preventing liquids or contaminants from entering the interior of the housing.

[0101] Since the lower part 16 and the upper part 18 in this example are each made of electrically conductive material, thermal contact can be established with an electrical device to be protected via their outer surfaces. The outer surfaces also serve as the external electrical connection for the switch 10.

[0102] On the outside of the top part 18, as in Fig. 1 shown, another insulation layer 26 must be attached.

[0103] The switching mechanism 14 has a temperature-independent spring element 28 and a temperature-dependent snap element 30. The spring element 28 is preferably designed as a bistable spring disc. It therefore has two temperature-independent stable geometric configurations. Fig. 1 The first configuration of this device is shown. The temperature-dependent snap element 30 is preferably designed as a bimetallic snap disc. This disc has two temperature-dependent configurations: a high-temperature geometric configuration and a low-temperature geometric configuration. In the Fig. 1 In the first switching position of the switching mechanism 14 shown, the temperature-dependent bimetallic snap disc 30 is in its geometric low-temperature configuration.

[0104] The temperature-independent spring disc 28 rests with its rim 32 on a further circumferential shoulder 34 formed in the lower part 16. In its low-temperature configuration, the temperature-dependent bimetallic snap disc 30 can be suspended freely within the housing 12 such that its rim 36 does not touch the housing 12. This has the advantage, among others, that the closing pressure in the closed state of the switch 10 is generated solely by the spring disc 28. Likewise, in the closed state of the switch 10, the current then flows only through the spring disc 28 and not through the bimetallic snap disc 30.

[0105] However, in its low-temperature configuration, the rim 36 of the bimetallic snap disc 30 can alternatively also rest on the inner base surface 38 of the lower part 16. The inner base surface 38 can be used, as shown in Fig. 1 As indicated by the dashed line 39, the side of the switch 10 would be raised. In such a case, the closing pressure of the switch 10 in its closed state would be generated not only by the spring washer 28, but also by the bimetallic snap disc 30.

[0106] The temperature-independent spring washer 28 is fixed at its center 40 to a movable contact element 42 of the switching mechanism 14. The temperature-dependent bimetallic snap washer 30 is also fixed at its center 44 to this contact element 42.

[0107] The movable contact element 42 has a contact part 46 and a ring 45, which is pressed onto the contact part 46. The ring 45 has a circumferential shoulder 47 on which the bimetallic snap disc 30 rests with its center 44. The spring washer 28 is clamped between the ring 45 and the upper, widened section of the contact part 46. In this way, the temperature-dependent switching mechanism 14 is a captive unit consisting of the contact element 42, the spring washer 28, and the bimetallic snap disc 30. Therefore, when assembling the switch 10, the switching mechanism 14 can be inserted directly into the lower part 16 as a single unit.

[0108] The contact part 46 of the movable contact element 42 interacts with a fixed mating contact 48, which is located on the inside of the upper part 18. This mating contact 48 is also referred to here as the first stationary contact. The outside of the lower part 16 serves as the second stationary contact 50.

[0109] In the Fig. 1 In the position shown, switch 10 is in its low-temperature position, in which the spring disc 28 is in its first configuration and the bimetallic snap disc 30 is in its low-temperature configuration. The spring disc 28 presses the movable contact element 42 against the first stationary contact 48.

[0110] In the closed low-temperature position of switch 10 according to Fig. 1 Thus, an electrically conductive connection is established between the first stationary contact 48 and the second stationary contact 50 via the movable contact element 42 and the spring washer 28.

[0111] If the temperature of the device to be protected increases, and thus the temperature of the switch 10 and the temperature-dependent bimetallic snap disc 30 located therein, the latter snaps open from the Fig. 1 The low-temperature configuration shown transforms into its concave high-temperature configuration, which is in Fig. 2 As shown. During this snapping action, the bimetallic snap disc 30 rests with its edge 36 against a part of the switch 10, in this case against the edge 32 of the spring disc 28. With its center 44, the snap disc 30 pulls the movable contact element 42 downwards and lifts the movable contact element 46 from the first stationary contact 48. Simultaneously, it bends the temperature-independent spring disc 28 downwards at its center 40, so that the spring disc 28 is released from its position in Fig. 1 shown, first stable geometric configuration in their in Fig. 2 The second geometrically stable configuration shown snaps over. Fig. 2 This indicates the high-temperature position of switch 10, in which it is open. The circuit is therefore interrupted.

[0112] If the device to be protected, and thus the switch 10 including the temperature-dependent bimetallic snap disc 30, cools down again, the bimetallic snap disc 30 would actually snap back into its low-temperature configuration upon reaching its reset temperature, as shown in Fig. 1 as shown. Then the bimetallic snap disc 30 would actually return the spring disc 28 to its first position, in Fig. 1 The configuration shown is moved back, thus closing the switch again. However, this switching back process can be prevented in the switch 10 according to the invention by a closing interlock 52.

[0113] The locking mechanism 52 has a locking element 54, which is essentially plate- or disc-shaped. This locking element 54 is located in the Fig. 1-3 In the example shown, the locking element 54 is clamped between the lower part 16 and the upper part 18. More precisely, the locking element 54 is clamped between the circumferential shoulder 22 and the insulating foil 24. In addition to this clamping arrangement, the locking element 54 can also be materially bonded to the lower part 16 (e.g., glued, welded, or soldered).

[0114] An embodiment of the locking element 54 is shown in Fig. 8 shown in a schematic top view. The locking element 54 is made at least largely of a shape memory alloy. This shape memory alloy is designed to change the shape of the locking element 54 from a first shape to a second shape when a predefined temperature, referred to here as the locking element switching temperature, is exceeded. Fig. 8 The first form of the locking element 54 is shown. This also corresponds to the one in Fig. 1 and 2The schematic section shows the shape of the locking element 54, in which the locking mechanism 52 is not yet activated.

[0115] The locking element 54, in its first form, essentially has the shape of a circular disk. It has an opening 56, which in the embodiment shown here is designed as a centrally arranged hole. The movable contact element 42 of the switching mechanism 14 projects through the opening 56 (see Fig. 1-3 The opening 56 is therefore preferably dimensioned such that the contact element 42 does not collide with the switching mechanism 14, either in its first switching position or during its switching movement. It is understood that the opening 56 need not necessarily be designed as a round hole, but can also have another shape, e.g., oval, elliptical, or rectangular.

[0116] The rim 58 of the locking element 54, with which it is attached to the housing 12, is preferably made of or coated with an electrically insulating material. This further improves the electrical insulation between the lower part 16 and the upper part 18. It also increases the stability of the clamping of the locking element 54 in the housing 12.

[0117] For example, the base body of the locking element 54 can be made entirely of the shape memory alloy, which is provided with an adhesive film or plastic coating 60 at the edge 58. This adhesive film or plastic coating 60 is preferably applied to both sides of the base body made of shape memory alloy.

[0118] The in Fig. 8 The locking element 54 shown further comprises four slots 62, which extend radially outwards from the opening 56 in a star-shaped pattern. The slots 62 extend through the entire thickness of the locking element 54. They are therefore not merely superficially incorporated into the locking element 54, but rather penetrate it. Starting from the central opening 56, they extend radially outwards, but terminate before the outer edge 58 of the locking element 54.

[0119] The slots 62 allow the locking element 54 to unfold when the shape-memory alloy brings the locking element 54 into its second shape upon reaching the locking element switching temperature. The four sectors of the locking element 54, separated from each other by the slots 62, then unfold as shown in Fig. 3 shown, downwards. The individual sectors of the locking element 54 curve or arch downwards.

[0120] In Fig. 3 The curvature of the locking element 54 in its second form is such that it is convex on its upper surface and concave on its lower surface. Depending on the specific configuration of the shape-memory alloy, the curvature of the locking element 54 in its second form can also be reversed, so that its upper surface is concave and its lower surface is convex (similar to the two disks 28, 30 in Fig. 3 ).

[0121] Such a temperature-induced deformation can, in principle, also be achieved with a locking element made of shape memory alloy without slots 62 or with fewer slots 62. However, the slots 62 help to reduce internal stresses caused by the deformation of the locking element 54. Furthermore, this allows the deformation of the locking element 54 to be increased.

[0122] At the in Fig. 1-3 In the example shown, the following interaction occurs between the switching mechanism 14 and the locking device 52 or the associated locking element 54: As long as the switching temperature of the bimetallic snap disc 30 is not exceeded, the switch remains in its closed position. Fig. 1 The closed position shown. Upon reaching the switching temperature, the bimetallic snap disc 30 snaps into its closed position, as already mentioned. Fig. 2 The high-temperature configuration shown is converted and lifts the movable contact element 42 from the first stationary contact 48, thereby opening the switch 10 and interrupting the current flowing through the switch 10 up to that point. The locking element switching temperature, i.e., the temperature at which the shape-memory alloy brings the locking element 54 into its second shape, is preferably selected to be somewhat higher than the switching temperature of the bimetallic snap disc 30. For example, the shape-memory alloy of the locking element 54 can be designed such that the locking element switching temperature is 5–40 K above the switching temperature of the bimetallic snap disc 30. Upon reaching the switching temperature, the locking element 54 therefore initially remains in its first shape, as shown in Fig. 2 The locking mechanism 52 is shown in the Fig. 2 The situation shown is therefore not yet activated.

[0123] If the temperature of switch 10 and thus also the temperature of the locking element 54 increases further, the shape memory alloy, upon reaching the locking element switching temperature, causes the aforementioned change in shape of the locking element 54, so that it returns to its original position. Fig. 3 the second form shown. In this second form or configuration, the locking element 54 expresses, as in Fig. 3 The locking element 54 exerts a force on the switching mechanism 14, acting directly on the spring disc 28 and indirectly on the movable contact element 42. This force holds the switching mechanism 14 in its second switching position. The locking mechanism 52 is activated.

[0124] Even if switch 10 is now moved from the position in Fig. 3 As the situation shown cools down again, the switching mechanism 14 can no longer be returned to its first switching position as long as the locking interlock 52 is activated. Although if the switch 10 cools below the reset temperature, the bimetallic snap disc 30 would return to its position. Fig. 1 The low-temperature configuration shown would snap back. However, the switching mechanism 14 would still remain in its second switching position, since the edge 36 of the bimetallic snap disc 30 snaps into thin air, so to speak, without being able to rest against the housing 12.

[0125] Even if the interior floor area is raised laterally by 38, as shown in Fig. 1-3 As indicated by the dashed line 39, the bimetallic snap disc 30, in its low-temperature configuration, could indeed rest its edge against the housing 12. However, as long as the locking mechanism 52 is activated, the spring disc 28 would still be pressed downwards by the locking element 54, so that the movable contact element 42 would remain spaced from the first stationary contact 48 and the switch 10 would remain open.

[0126] In order to effectively prevent accidental closing of the switch 10 when the locking mechanism 52 is activated, even when the bimetallic snap disc 30 can rest against the housing 12 in its low-temperature configuration, the spring constant of the locking element 54 simply needs to be higher than the spring constant of the bimetallic snap disc 30.

[0127] Depending on the design of the locking element 54, deactivation of the locking mechanism 52 is either not possible at all or possible by means of cold treatment.

[0128] In the first case of an irreversible locking mechanism 52, the switch 10 is a one-time switch. For this purpose, a shape-memory alloy with a one-way memory effect is chosen for the locking element 54.

[0129] Alternatively, by using a shape memory alloy with a two-way memory effect, the locking mechanism 52 can also be designed to be reversible. In this case, the shape memory alloy of the locking element 54 is configured to change the shape of the locking element 54 from the one in the Fig. 3 the second form shown in the Fig. 1 and 2 to restore the first form shown. In this case, the locking element 54 can, so to speak, remember both forms.

[0130] The shape memory alloy of the locking element 54 is preferably designed such that the locking element reset temperature is lower than the reset temperature of the bimetallic snap disc 30. For example, the shape memory alloy of the locking element 54 can be designed such that the locking element reset temperature is lower than room temperature and is, for example, in a temperature range of 0–15 °C. By means of appropriate cold treatment, the locking mechanism 52 can thus be released again, so that the switch 10 can be released from the Fig. 3 schematically shown switch position back to the in Fig. 1 The schematically shown switch position would occur.

[0131] Fig. 4-6 show a first embodiment of the switch 10 according to the invention.

[0132] Fig. 4 shows, similar to before Fig. 1 , the switch 10 in its closed position, in which the switching mechanism 14 is in its first switching position, the bimetallic snap disc 30 is in its low-temperature configuration and the locking mechanism 52 is not activated. Fig. 5 shows, similar to before Fig. 2 , the switch 10 in its open position, in which the switching mechanism 14 is in its second switching position, the bimetallic snap disc 30 is in its high temperature configuration and the locking mechanism 52 is not activated. Fig. 6 shows, similar to before Fig. 3 , the switch 10 in its open position, in which the switching mechanism 14 is still in its second switching position, but the locking interlock 52 is activated.

[0133] The switching function and the interaction between switching mechanism 14 and locking mechanism 52 take place in the Fig. 4-6 The first embodiment shown is the same as described above with regard to the in Fig. 1-3 as mentioned in the example shown.

[0134] Unlike the one in Fig. 1-3 The example shown is the locking element 54 of the locking mechanism 52 in which in Fig. 4-6 In the first embodiment shown, the locking element 54 is arranged on the opposite side of the switching mechanism 14. While the locking element 54 is located in the first embodiment shown in the first embodiment, the locking element 54 is located on the opposite side of the switching mechanism 14. Fig. 1-3 In the example shown, the switch 10 is located on the upper side of the switching mechanism 14 facing the first contact 48, and the locking element 54 is located in the Fig. 4-6 The first embodiment of the switch 10 shown is arranged on the lower side of the switching mechanism 14, away from the first contact 48.

[0135] The locking element 54 is clamped between two spacer rings 64 and 66. The first spacer ring 64 is arranged on the inner base surface 38 of the lower part 16. The locking element 54 rests on this first spacer ring 64. The second spacer ring 66 is arranged on top of the locking element 54. The bimetallic snap disc 30 rests with its rim 36 on the upper side of the second spacer ring 66.

[0136] A further spacer ring 68 is arranged at the point where the locking element 54 is located according to the diagram in Fig. 1-3 The spacer ring 68, as shown in the example, is arranged between the lower part 16 and the upper part 18. This spacer ring 68 serves as a spacer between the lower part 16 and the upper part 18. Furthermore, the spring washer 28 can be supported from below by this spacer ring 68 when the switching mechanism 14 is in its second switching position (see figure). Fig. 5 and 6 ).

[0137] At the in Fig. 4-6 In the first embodiment of the switch 10 shown, the movable contact element 42 is further configured somewhat differently. At its lower end, it has a laterally projecting base 70, the diameter of which is slightly larger than the diameter of the opening 56 provided in the locking element 54. The movable contact element 42 projects through the opening 56 provided in the locking element 54, with the widened base 70 being located below the locking element 54.

[0138] The locking element 54 is designed in the same way as described above in relation to the one in Fig. 1-3 The example shown is mentioned (see Fig. 8 In its second form, which it assumes after reaching the locking element switching temperature, the locking element 54 now directly engages the movable contact member 42. The locking element 54 presses, as in Fig. 6 The image shows the widened base 70 from above, which keeps the movable contact element 42 at a distance from the first stationary contact 48. Thus, in this embodiment as well, the switch 10 cannot be closed again as long as the locking mechanism 52 is activated.

[0139] In this embodiment as well, the locking mechanism 52 can be designed to be reversible or irreversible, depending on whether a shape memory alloy with a one-way memory effect or a shape memory alloy with a two-way memory effect is used for the shape memory alloy of the locking element 54.

[0140] Fig. 7 Figure 1 shows a second embodiment of the switch 10' according to the invention. The locking mechanism 52 is designed in the same way as in Figure 1. Fig. 4-6 switch 10 shown.

[0141] Since the interaction between the switching mechanism 14' and the locking mechanism 52 in the Fig. 7 The fact that the switch 10' shown is implemented in the same way as previously mentioned will not be explicitly discussed again here. Likewise, for the sake of simplicity, the switch 10' according to the second embodiment is only shown in its closed position, in which the switching mechanism 14' is in its first switching position.

[0142] The structure of the in Fig. 7 The switch 10' shown is slightly different from the construction of switch 10 according to the one in Fig. 1-3 the example shown and the one in Fig. 4-6 first embodiment shown.

[0143] The lower part 16' is made of electrically conductive material. The flat upper part 18', on the other hand, is made of electrically insulating material. It is held to the lower part 16' by the bent rim 20'.

[0144] A spacer ring 68' is provided between the upper part 18' and the lower part 16', which maintains a distance between the upper part 18' and the lower part 16'. On its inner surface, the upper part 18' has a first stationary contact 48' and a second stationary contact 50'. The contacts 48' and 50' are designed as rivets that extend through the upper part 18' and terminate on the outside in the heads 72, 74, which serve as the external connection for the switch 10'.

[0145] The movable contact element 42' here comprises a current transmission element designed as a contact plate, the upper surface of which is electrically conductive coated, so that the current transmission element 76 during the Fig. 7 In the closed position of the switch 10 shown, the contact 48' and 50' is connected to the contacts, ensuring an electrically conductive connection between them. The current transfer element 76 is connected to the spring washer 28 and the bimetallic snap disc 30 via a rivet 78, which is also considered part of the contact element 42'. If the switching temperature is exceeded, the bimetallic snap disc 30 of the switching mechanism 14', similar to the previous function, ensures that the switching mechanism 14' is moved into its second switching position, in which the current transfer element 76 is held spaced apart from the two contacts 48' and 50', and the circuit is therefore interrupted.

[0146] A key difference of the in Fig. 7 The switch configuration shown can be seen in that, unlike the one in Fig. 1-3 the example shown and the one in Fig. 4-6 In the first embodiment of the switch 10 shown, no current flows through either the spring disc 28 or the bimetallic snap disc 30 when the switch 10 is closed. When the switch 10' is closed, current flows only from the first external terminal 72 via the first contact 48', the current transmission element 76, and the second contact 50' to the second external terminal 74.

[0147] The locking element 54 of the locking mechanism 52 engages the rivet 78 as soon as the locking mechanism 52 is activated, i.e., as soon as the temperature of the switch 10' and thus the temperature of the locking element 54 exceeds the locking element switching temperature. The rivet 78 is designed for this purpose, similar to the one described in Fig. 4-6 In the first embodiment shown, a widened base 70 is provided at its lower end. The locking element 54 engages this base 70 to press down the rivet 78 and thus the entire movable contact element 42' and to hold the switching mechanism 14' in its second switching position as soon as the locking mechanism 52 is activated.

[0148] In principle, the locking mechanism 52 can also be used with switch 10', as it is in Fig. 7 It is shown schematically, and should be executed in the manner shown in the [document / model]. Fig. 1-3 The example shown is implemented using switch 10.

[0149] A reversible design of the locking mechanism 52 is also available in the one in Fig. 7 The second embodiment of switch 10' shown is also possible.

Claims

1. A temperature-dependent switch (10), which comprises a first and a second stationary contact (48, 50) and a temperature-dependent switching mechanism (14) having a movable contact member (42), wherein the switching mechanism (14), in its first switching position, presses the contact member (42) against the first contact (48) and thereby produces an electrically conductive connection between the two contacts (48, 50) via the contact member (42) and, in its second switching position, keeps the contact member (42) spaced apart from the first contact (48) and thereby disconnects the electrically conductive connection between the two contacts (48, 50), wherein the temperature-dependent switching mechanism (14) comprises a temperature-dependent snap-action part (30), which switches from its geometric low-temperature configuration to its geometric high-temperature configuration when exceeding a switching temperature, and switches back from its geometric high-temperature configuration to its geometric low-temperature configuration when subsequently falling below a reset temperature, wherein switching the temperature-dependent snap-action part (30) from its geometric low-temperature configuration to its geometric high-temperature configuration moves the switching mechanism (14) from its first switching position to its second switching position and thereby opens the switch (10), and wherein a closing lock (52) is provided that, as soon as it is activated, prevents the switch (10) once having opened from closing again by keeping the switching mechanism (14) in its second switching position, wherein the closing lock (52) comprises a locking element (54) which is at least partly made of a shape-memory alloy and has an opening (56) through which the movable contact member (42) protrudes, and which is configured to change its shape upon exceeding a locking element switching temperature from a first shape, in which the locking element (54) does not activate the closing lock (52), into a second shape, in which the locking element (54) activates the closing lock (52) by exerting a force, which holds the switching mechanism (14) in its second switching position, directly or indirectly on the contact member (42), wherein the first contact (48) is arranged on a first side of the temperature-dependent snap-action part (30), characterized in that the locking element (54) is arranged on a second side of the temperature-dependent snap-action part (30) opposite the first side.

2. The switch according to claim 1, characterized in that the locking element (54) is substantially plate-shaped or disc-shaped.

3. The switch according to claim 1 or 2, characterized in that the opening (56) is configured as a through hole.

4. The switch according to one of claims 1 to 3, characterized in that the opening (56) is centrally arranged in the locking element (54).

5. The switch according to one of claims 1 to 4, characterized in that at least one slit (62) that adjoins the opening (56) is provided in the locking element (54).

6. The switch according to claim 5, characterized in that the at least one slit (62) is rectilinear and extends radially outward from the opening (56).

7. The switch according to one of claims 1 to 4, characterized in that at least three slits (62) are provided in the locking element (54), each of which adjoins the opening (56), is rectilinear and extends radially outward from the opening (56).

8. The switch according to one of claims 1 to 7, characterized in that the switch (10) comprises a housing (12), and in that the locking element (54) is attached to the housing (12) with its edge (58).

9. The switch according to claim 8, characterized in that the edge (58) of the locking element (54) is made of an electrically insulating material (60) or is coated with an electrically insulating material (60).

10. The switch according to claim 8 or 9, characterized in that the housing (12) comprises a lower part (16) that is closed by an upper part (18), and in that the locking element (54) rests on a circumferential shoulder (22) that is arranged in the lower part (16) and is arranged clamped between the lower part (16) and the upper part (18).

11. The switch according to one of claims 1 to 10, characterized in that the shape-memory alloy is a shape-memory alloy with a one-way memory effect.

12. The switch according to one of claims 1 to 10, characterized in that the shape-memory alloy is a shape-memory alloy with a two-way memory effect, and in that the locking element (54) is configured to change its shape from the second shape to the first shape when falling below a locking element reset temperature, wherein the locking element reset temperature is lower than the locking element switching temperature and / or lower than the reset temperature of the temperature-dependent snap-action part (30).

13. The switch according to one of claims 1 to 12, characterized in that the locking element switching temperature is equal to or higher than the switching temperature of the temperature-dependent snap-action part (30).