TEMPERATURE-DEPENDENT SWITCH AND METHOD OF MANUFACTURING A TEMPERATURE-DEPENDENT SWITCH

A temperature-dependent switch having a first electrode, a second electrode, a temperature-dependent switching mechanism, and a housing that accommodates the switching mechanism. The first electrode is connected to a stationary contact that is arranged inside the housing and the switching mechanism comprises a component that is movable relative to the housing, on which movable component a movable contact member is arranged. The switching mechanism is configured to switch, depending on its temperature, between a closed state of the switch and an open state of the switch. A first terminal member is attached to the first electrode by a first welded joint produced by ultrasonic welding and/or a second terminal member is attached to the second electrode by a second welded joint produced by ultrasonic welding and/or the stationary contact is attached to a part of the first electrode arranged inside the housing by a third welded joint produced by ultrasonic welding and/or the movable contact member is fastened to the movable component by a fourth welded joint produced by ultrasonic welding.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from German patent application DE 10 2019 110 448.3, filed on Apr. 23, 2019. The entire content of this priority application is incorporated herein by reference.

BACKGROUND

This disclosure relates to a temperature-dependent switch. Furthermore, the disclosure relates to a method of manufacturing a temperature-dependent switch.

An exemplary temperature-dependent switch is disclosed in DE 10 2014 116 888 A1. Such temperature-dependent switches are typically used to protect electrical devices, such as hair dryers, lye pump motors, irons etc., from overheating and/or excessive current.

To this end, the temperature-dependent switch is connected electrically in series with the device to be protected in its supply circuit, so that the operating current of the device to be protected flows through the temperature-dependent switch. Furthermore, the switch is mounted on the device to be protected in such a way that it assumes the temperature of the device to be protected.

The temperature-dependent switch disclosed in DE 10 2014 116 888 A1 comprises a temperature-dependent switching mechanism which is arranged in a housing of the switch and which, depending on its temperature, opens or closes an electrical connection between two electrodes of the switch.

The term “electrode” is to be interpreted in its most general way in this respect. It is an electrical contact point which serves to connect the switch to the electrical device to be protected, or which is in electrically conductive connection with such an external terminal of the switch. The electrodes may therefore also be referred to as terminal electrodes. The electrodes may be inserted from outside into the inside of the housing, they may be attached to the housing of the switch, or they may be formed by parts of the housing itself.

In the case of the switch disclosed in the aforementioned DE 10 2014 116 888 A1, the housing includes an electrically conductive upper part and a lower part which is electrically insulated from the upper part, wherein the upper part forms the first electrode and the lower part forms the second electrode.

To enable the above-mentioned switching function, the switching mechanism of the switch, which is arranged inside the housing, usually comprises a bi-metal member which, when reaching its switching temperature, abruptly deforms from its low-temperature position to its high-temperature position, thereby lifting off a movable contact member, which is arranged at a component that is movable relative to the housing, from a stationary contact.

The stationary contact is connected to one of the two electrodes, while the movable contact member interacts either via the bi-metal member or a spring member assigned to the bi-metal member, which spring member may be configured, for example, as a spring snap disc, for example.

Designs are also known in which the movable component is configured as a contact bridge, which is supported by the bi-metal member and directly establishes an electrical connection between the two electrodes.

An example of such a temperature-dependent switch is disclosed in DE 197 08 436 A1. In this case not only the first electrode but also the second electrode is located on the upper part of the housing. The upper part of the housing is then made of insulating material or PTC-material. A stationary contact is arranged at each of the two electrodes. In the closed state of the switch, the current flows from the first electrode via the stationary contact assigned to the first electrode, through the contact bridge, to the other stationary contact, and from there to the second electrode, so that the operating current does not flow through the bi-metal member and the spring member itself.

This design is chosen in particular in case very high currents occur which can no longer be easily conducted via the spring member and/or the bi-metal member.

In the two design variants mentioned above, the bi-metal member is preferably configured as a bi-metal disc, which in the low-temperature position is preferably arranged in a force-free manner in the switching mechanism. The spring member, which is preferably configured as a spring snap disc, is mechanically coupled to the bi-metal member. The spring member is clamped in the housing, connected to it with a material bond or inserted into the housing.

In principle, however, it is also possible to dispense with the spring member completely, which is particularly the case in cheaper versions of such temperature-dependent switches. In such a case, the function of the spring member is taken over by the bi-metal member.

To connect the known temperature-dependent switches with the device to be protected, the switch is typically provided with supply lines or terminal members which are attached to the two electrodes. Usually, flexible stranded wires or rigid terminal lugs are connected to the electrodes by means of a material bond. The stranded wires or terminal lugs are often soldered or welded to the switches known from the state of the art. The pre-assembled switches provided with stranded wires or terminal lugs are then provided with a cap or shrink cap to electrically insulate the switches from the outside.

However, soldering or welding the supply lines or terminal members has proven to be problematic in many respects. Especially the common welding methods have a number of disadvantages. They pollute the environment, require special designs for the switch, and are time-consuming and costly. Furthermore, they lead to a strong heating of the switch, which can cause the welding to trigger a switching operation, which is generally undesirable and causes problems especially with one-time switches, which only produce a single irreversible switching operation.

Such an undesirably strong heat development at the switch components occurs especially with the hot welding or fusion welding processes that are usually used. Experiments by the applicant in which terminal lugs were soldered or welded to the cover part of the switch have shown, for example, that the heat development directly on the cover part causes the stationary contact located inside the housing to detach from the electrode or the cover part. Similarly, the heat development can also cause the stationary contact and the movable contact member to undesirably weld together or at least change their geometry in such a way that the pre-assembled switches no longer switch or at least no longer switch reliably. Furthermore, the heat penetrating into the interior of the housing during the welding process can cause the snap discs to be damaged, so that their required switching characteristics are inadmissibly altered. In thin-walled housings, perforation burning is often also a problem. In the worst case, all this can lead to a total failure of the switch.

The described heat development occurring inside the switch is particularly distinctive if the cover part and/or the lower part of the housing is made of metal and the supply lines or terminal members are welded or soldered directly to it. In this case a particularly strong heat development occurs inside the housing due to the very good heat conduction properties of the metal. This is all the more critical because the supply lines or terminal members are typically attached to the housing after the switching mechanism has already been mounted in the housing and this has been closed, i.e. after the switch itself is already provided as a finished or at least semi-finished component. It is then only possible to check to a limited extent, or at least only with great effort, whether the heat generated inside the switch has lead to any of the above-mentioned damage.

For the attachment of cable lugs, which are often used for the connection of the switch, welding methods are out of the question anyway, as multi-conductor stranded wires must not be welded. However, soldering these cable lugs also causes the above-mentioned strong heat development inside the switch, so that this is not an entirely satisfactory solution either.

On the other hand, a switch, such as the one disclosed in DE 20 2014 010 782 U1, for example, does not cause the above-mentioned problems associated with welding or soldering the supply lines or terminal members. In this case, the housing is made of plastic and the electrodes are led to the outside in the form of metal sheets or metal strips. Due to the low heat conduction properties of the housing and the fact that the welded or soldered connection is then made relatively far away from the inside of the housing and thus far away from the switching mechanism, neither the housing itself heats up nor are the components inside the housing exposed to a greater heat development.

Regardless of the design of the switch, welding or soldering of contact points to components inside the switch has also proven to be problematic. This is particularly true if these components are in indirect or even direct contact with the highly sensitive switching mechanism of the switch or if they form part of this switching mechanism. For example, the attachment of the movable contact member to the movable component of the switching mechanism by welding is particularly critical. As already mentioned above, the movable component of the switching mechanism typically comprises a spring snap disc and/or a bi-metal snap disc. Conventional spring snap discs and bi-metal snap discs have a very small thickness of, for example, 2 mm, 1 mm or less, so that optimal welded joints may only be achieved with great difficulty. If at all possible, this can also easily lead to damages of the spring snap disc and/or the bi-metal snap disc.

In addition to the above-mentioned environmental risks and cost risks, the joining processes typically used in the switch manufacture can result in an undesirably high reject rate.

SUMMARY

It is an objective to provide a temperature-dependent switch and a method for manufacturing the same, which reduce or even completely avoid the disadvantages mentioned above. In particular, it is an objective to reduce the production-related rejects and yet guarantee a cost-effective production of the switch.

According to a first aspect, a temperature-dependent switch is provided, which comprises:a temperature-dependent switching mechanism; anda housing that accommodates the switching mechanism and comprises an upper part and a lower part that is electrically insulated from the upper part;

wherein at least a part of the upper part is made of electrically conductive material and forms a first electrode, wherein at least a part of the lower part is made of electrically conductive material and forms a second electrode,

wherein the first electrode is connected to a stationary contact that is arranged inside the housing, and wherein the switching mechanism comprises a component that is movable relative to the housing, on which movable component a movable contact member is arranged,

wherein the switching mechanism is configured to switch, depending on its temperature, between a closed state of the switch, in which the movable contact member interacts with the stationary contact and establishes an electrically conductive connection between the first electrode and the second electrode, and an open state of the switch, in which the movable contact member is kept at a distance from the stationary contact and the electrically conductive connection be-tween the first electrode and the second electrode is disconnected, and

wherein (i) a first terminal member is attached to the first electrode by a first welded joint produced by ultrasonic welding and/or (ii) a second terminal member is attached to the second electrode by a second welded joint produced by ultrasonic welding.

The inventor has recognized that the manufacture of the two mentioned welded joints by means of ultrasonic welding eliminates the above-mentioned disadvantages to a large extent or even completely. This is all the more surprising as the inventor had originally assumed a complete renunciation of welded joints at the positions mentioned above.

However, it has turned out that welding the supply lines or terminal members directly to the housing by means of ultrasonic welding is not only possible, but also offers various unforeseen advantages.

Due to the comparatively low heat development that is generated during ultrasonic welding, temperature-related damages inside the switch, especially to the sensitive switching mechanism, can be effectively prevented. This also applies when the housing of the switch is largely made of metal. Despite the very good heat conduction properties of the metal, the comparatively low heat development that occurs during ultrasonic welding does not cause the stationary contact, which is typically located on the upper part of the housing, to become undesirably detached. There is also no risk that the stationary contact and the movable contact member are welded together during the ultrasonic welding process. The risk of the snap discs being damaged by the ultrasonic welding process is also reduced to a minimum.

Welded joints produced by ultrasonic welding therefore prove to be particularly advantageous for switches where the entire upper and lower parts are made of electrically conductive material.

Welded joints produced by ultrasonic welding have also proven to be advantageous for one-time switches, as there is no risk of triggering an undesired switching operation due to the comparatively low heat development.

In addition, cold soldering joints (i.e. soldering joints where there is no material connection between the soldering and joining partners) can be avoided through the use of ultrasonic welding.

In addition, ultrasonic welding can be used to achieve clean and sustainable joints between the components mentioned above. In contrast to the typically used fusion welding processes, the surface finishing of the surfaces is not adversely affected by ultrasonic welding. This also leads to comparatively lower contact resistances at the mentioned joints.

A further advantage is that no filler materials are required for ultrasonic welding. This allows more compact welding seams to be produced. In addition, the environment is significantly less polluted, as the use of environmentally harmful materials, which are typically included in the filler materials, may be completely avoided.

In ultrasonic welding, the welding of the components to be joined is achieved by means of a high-frequency mechanical oscillation. The generated oscillation leads to heating between the components to be joined due to molecular friction and interfacial friction. If the components to be joined are metals, the mechanical oscillation generated by ultrasound causes the joining partners to indent and interlock at the joint.

In ultrasonic welding tools, a generator generates electronic oscillations which are converted into mechanical oscillations by an ultrasonic converter. These are fed to the components to be joined via a so-called sonotrode. Within fractions of a second, the ultrasonic oscillations generated in this way generate frictional heat on the joining surfaces of the components to be joined, which causes the material to melt and to join the components together.

The parameters to be set during ultrasonic welding, such as amplitude and frequency, can be adapted to the conditions. The parameters to be set and their respective values are known to the skilled person and can be taken from the relevant standards.

In a refinement, the first terminal member and/or the second terminal member comprises a terminal lug or stranded wire. These are preferably attached directly to the housing by ultrasonic welding.

For example, when terminal lugs are used, a first terminal lug may be attached by ultrasonic welding to a first shoulder provided at the upper part and a second terminal lug may be attached by ultrasonic welding to a second shoulder provided at the lower part. Due to the small thickness of such terminal lugs as well as due to their attachment to the aforementioned shoulders of the housing, the overall height of the switch is comparatively low.

In a further refinement, the shoulders are each configured as an annular shoulder and the respective first end of the terminal lugs is ring-shaped.

This further facilitates the manufacture, as no positioning work is required between the terminal lug and the housing part. Instead, the housing part is inserted with its underside into the annular end in such a way that it rests on the shoulder, i.e. automatically centers itself.

In a further refinement, the first terminal lug or stranded wire is attached at its first end to the first electrode by means of the first welded joint, and its second end that is remote from the first end serves as the first connection. Similarly, the second terminal lug or stranded wire may by at its first end to the second electrode by the second welded joint, and its second end that is remote from the first end may serve as the second terminal.

According to a second aspect, there is provided a temperature-dependent switch comprising:a first electrode;a second electrode;a temperature-dependent switching mechanism; anda housing accommodating the switching mechanism;

wherein the first electrode is connected to a stationary contact that is arranged inside the housing, and wherein the switching mechanism comprises a component that is movable relative to the housing, on which movable component a movable contact member is arranged,

wherein the switching mechanism is configured to switch, depending on its temperature, between a closed state of the switch, in which the movable contact member interacts with the stationary contact and establishes an electrically conductive connection between the first electrode and the second electrode, and an open state of the switch, in which the movable contact member is kept at a distance from the stationary contact and the electrically conductive connection between the first electrode and the second electrode is disconnected, and

wherein (i) the stationary contact is attached to a part of the first electrode by a third welded joint produced by ultrasonic welding, said part of the first electrode being arranged inside the housing and/or (ii) the movable contact member is attached to the movable component by a fourth welded joint produced by ultrasonic welding.

The inventor has recognized that the disadvantages mentioned at the beginning can also be largely or even completely eliminated by producing these two welded joints by means of ultrasonic welding.

Welding of the stationary contact with the part of the first electrode arranged in the inside and/or welding of the movable contact member with the movable component of the switching mechanism by means of ultrasonic welding also leads to the aforementioned advantages of ultrasonic welding at these positions of the switch.

In a refinement, the temperature-dependent switching mechanism of the switch includes a bi-metal member.

A bi-metal member may be a multilayer, active, sheet metal shaped component comprising two, three or four inseparably connected components with different coefficients of thermal expansion. The connection of the individual layers of metals or metal alloys is by means of a material bond or positive locking and is achieved, for example, by rolling.

Such bi-metal members have a first stable geometrical conformation in their low-temperature position and a second stable geometrical conformation in their high-temperature position, between which they switch in a temperature-dependent manner in the manner of a hysteresis. If the temperature changes beyond their response temperature or below their reset temperature, the bi-metal members snap over into the other conformation, respectively. The bi-metal members are therefore often referred to as snap discs, wherein they can have an elongated, oval or circular shape when viewed from above.

If the temperature of the bi-metal member rises above the transition temperature as a result of an increase in the temperature of the device to be protected, the bi-metal member changes its configuration so that the movable contact member is kept at a distance from the stationary contact, thereby opening the switch and switching off the device to be protected and preventing further heating.

Below its transition temperature, i.e. in its low-temperature position, the bi-metal member is preferably mounted in the housing of the switch in a mechanically force-free manner. The bi-metal member is preferably not to used for conducting the current.

It is advantageous that such bi-metal members have a long mechanical service life and that the switching point, i.e. the transition temperature of the bi-metal member, does not change even after many switching cycles.

According to another refinement, the bi-metal member is the movable component on which the movable contact member is arranged.

This refinement is particularly suitable if low demands are made on the mechanical reliability or the stability of the transition temperature. The bi-metal member may then also take over the function of the spring member or of the spring snap disc and possibly even of the current transfer element, so that the switching mechanism includes only one bi-metal member, which then carries the movable contact member. The bi-metal member then not only provides the closing pressure of the switch, but also carries the current in the closed state of the switch. In the closed state of the switch, the bi-metal member is thus electrically connected in series between the first and the second electrode, which form the external terminals of the switch, or at which the external terminals of the switch are arranged.

The welded joint produced by means of ultrasonic welding (here called fourth welded joint) is in this refinement thus provided between the bi-metal member, which forms the movable component of the switching mechanism, and the movable contact member. Due to the usually very thin-walled bi-metal members, this type of welded joint between the bi-metal member and the movable contact member is particularly advantageous, since the risk of damage and/or the risk of the bi-metal member snapping over unintentionally is considerably reduced due to the comparatively low heat development during the ultrasonic welding process. This has a beneficial effect on the functioning of the bi-metal member and also extends its service life.

In a further refinement, the temperature-dependent switching mechanism includes a bi-metal member and a spring member that interacts with the bi-metal member.

The bi-metal member is preferably a temperature-dependent bimetal snap disc. The spring member is preferably a bistable spring snap disc.

The spring snap disc operates against the bimetal snap disc and generates the closing pressure of the switch. If the switch cools down again after a switching operation which has brought the switch to its open state, the spring snap disc operating against the bi-metal snap disc ensures that the bi-metal snap disc is reset to bring the switch back to its closed state.

If the switching mechanism includes such a spring member in addition to the bi-metal member, it is preferred that the spring member is the movable component on which the movable contact member is arranged.

The movable contact member is, in this refinement, thus attached to the spring member by the fourth welded joint produced by ultrasonic welding. Depending on the design of the switch, the spring member can, in the closed state of the switch, then be electrically connected in series between the first and the second terminal electrode. In the closed state of the switch, the spring member then carries the current flowing through the switch.

According to a further refinement, the bi-metal member is held captive with clearance on the movable contact member, wherein the movable contact member is attached to the spring member, which is achieved by the fourth welded joint produced by ultrasonic welding.

Since the spring member, the bi-metal member and the movable contact member then form a single unit, the switching mechanism can be stored temporarily as a separate semi-finished part before it is mounted in the housing of the switch. A separate test of the switching mechanism is thus also possible, as the bi-metal member is held captive but has a clearance so that it can deform in an unhindered manner between its low-temperature position and its high-temperature position.

The use of ultrasonic welding to connect the spring member to the movable contact member is particularly advantageous for a switch according to the aforementioned refinement. Since the movable contact member is attached to the spring member by means of ultrasonic welding and the bi-metal member is held captive but with clearance on the movable contact member, the bi-metal member is hardly subjected to any thermal stress during the ultrasonic welding process. It is particularly preferred that the welding process between the spring member and the movable contact member occurs before the bi-metal member is attached to the movable contact member. In this case, the bi-metal member is not stressed at all by the welding process.

Preferably, the housing comprises an upper part and a lower part that is electrically insulated from the upper part, wherein the upper part forms the first electrode and the lower part forms the second electrode, and wherein the stationary contact is arranged on an inner side of the upper part facing the interior of the housing.

In this refinement, the upper part and the lower part of the housing are preferably made of an electrically conductive material, for example metal. As contact terminals for the external connections of the switch, an outer side of the upper part facing away from the inside of the housing can be used on the one hand and an outer side of the lower part facing away from the inside of the housing can be used on the other hand. Hence, the upper part and the lower part themselves form the terminal electrodes.

The lower part of the housing can, for example, be pot-shaped and accommodate the temperature-dependent switching mechanism. After insertion of the temperature-dependent switching mechanism, the lower part of the housing is closed, for example by the upper part of the housing, which can be configured as a kind of cover, with an insulating foil inserted between. For this purpose, a surrounding edge of the lower part of the housing can be flanged to secure the cover part.

Before the housing is closed, the stationary contact is attached by means of ultrasonic welding (presently referred to as the third welded joint) to the inner side of the upper part, which inner side faces the inside of the housing.

In an alternative refinement, the housing comprises an upper part made of insulating material or PTC-material and a lower part, wherein the first and the second electrode are arranged at the upper part.

The lower part can also be made of insulating material or PTC material in this refinement. However, it can also be made of metal, which is preferred, as this improves the thermal coupling of the switch to the device to be protected. In this case, however, the raised metallic edge of the lower part often has to be electrically insulated from the outside.

The movable component of the switching mechanism is in the last-mentioned configuration preferably a contact element coupled to a bi-metal member, on which contact element a second movable contact member is arranged in addition to the (first) movable contact member, wherein a second stationary contact is attached to a part of the second electrode arranged inside the housing by a fifth welded joint produced by means of ultrasonic welding.

In this case, there are thus two stationary contacts, each of which is attached to one of the two electrodes arranged at the upper part of the switch by a welded joint produced by ultrasonic welding. The movable component of the switching mechanism is assigned to the two stationary contacts, wherein the movable component is in this refinement preferably designed as a current transfer element in the form of a movable contact bridge which is mechanically connected to the bi-metal member. Corresponding to the two stationary contacts, two contact surfaces are provided on this contact bridge, wherein the two contact surfaces are herein designated as first and second movable contact member, respectively.

In the closed state of the switch, the current flows according to this refinement from the first electrode, via the first stationary contact and the first movable contact member contacting the first stationary contact, through the contact element acting as a contact bridge, via the second movable contact member and the second stationary contact, to the second electrode. Neither the bi-metal member nor the spring member of the switching mechanism carries current according to this refinement.

In a further refinement, at least a part of the housing is made of insulating material or PTC-material, wherein (i) a first portion of the first electrode extends into the interior of the housing and a second portion of the first electrode extends outward from the interior of the housing and/or (ii) a first portion of the second electrode extends into the interior of the housing and a second portion of the second electrode extends outward from the interior of the housing.

The housing may be constructed in one or more parts according to this refinement. It may be completely or only partially made of insulating material or PTC-material. Each of the two electrodes are preferably inserted from outside as contact plates or connection plates into the interior of the housing through one opening, respectively. The electrodes may abut the inner wall of the housing or they may be at least partially freely suspended in it. For example, this may correspond to arrangements of the switching mechanism as disclosed in DE 196 09 310 A1 or EP 2 511 930 A1.

According to a third aspect, a method of manufacturing a temperature-dependent switch is presented, comprising:a) providing a switching mechanism and a housing having an upper part and a lower part, wherein at least a part of the upper part is made of electrically conductive material and forms a first electrode and at least a part of the lower part is made of electrically conductive material and forms a second electrode,b) mounting the switching mechanism in the housing such that the first electrode is connected to a stationary contact that is arranged inside the housing and the switching mechanism comprises a component that is movable relative to the housing, on which movable component a movable contact member is arranged, and such that the switching mechanism switches, depending on its temperature, between a closed state of the switch, in which the movable contact member interacts with the stationary contact and establishes an electrically conductive connection between the first and the second electrode, and an open state of the switch, in which the movable contact member is kept at a distance from the stationary contact and an electrically conductive connection between the first and the second electrode is open,c) closing the housing by attaching the upper part to the lower part, wherein the upper part is electrically insulated from the lower part;d1) attaching of a first terminal member to the first electrode by a first welded joint produced by ultrasonic welding, and/ord2) attaching a second terminal member to the second electrode by a second welded joint produced by ultrasonic welding.

It should be noted that the above-mentioned features and the features contained in the claims defined in relation to the switch may also be applied mutatis mutandis in the method.

In a refinement, it is preferred that step d1) and/or step d2) is carried out after step c).

The first and/or second terminal member is therefore preferably welded to the housing after the switching mechanism has already been inserted into the housing and the housing has been closed. Hence, already before welding the terminals, the switch is available as a finished component. By using ultrasonic welding for the subsequent attachment of the switch terminals, undesirable damages inside the switch can be effectively avoided, as mentioned above.

According to fourth aspect, a method of manufacturing a temperature-dependent switch is presented, comprising:a) providing a first electrode, a second electrode, a temperature dependent switching mechanism and a housing,b) mounting the switching mechanism in the housing, such that the first electrode is connected to a stationary contact that is arranged inside the housing and the switching mechanism comprises a component that is movable relative to the housing, on which movable component a movable contact member is arranged, and such that the switching mechanism switches, depending on its temperature, between a closed state of the switch, in which the movable contact member interacts with the stationary contact and establishes an electrically conductive connection between the first and the second electrode, and an open state of the switch, in which the movable contact member is kept at a distance from the stationary contact and the electrically conductive connection between the first and the second electrode is open, andc1) attaching the stationary contact to a part of the first electrode by a third welded joint produced by ultrasonic welding, said part of the first electrode being arranged inside the housing, and/orc2) attaching the movable contact member to the movable component by a fourth welded joint produced by ultrasonic welding.

According to a refinement of the method, the stationary contact is attached to the part of the first electrode arranged inside the housing by the third welded joint produced by ultrasonic welding and/or the movable contact member is attached to the movable component by the fourth welded joint produced by ultrasonic welding, before the switching mechanism is mounted in the housing in step ii).

The ultrasonic welded joints produced on the switching mechanism therefore have no effect on the remaining components of the switch, for example on its external contacts, which can be arranged subsequently on the finished assembled housing.

According to a further refinement, a bi-metal member and a spring member interacting with the bi-metal member are provided as parts of the switching mechanism in step a), wherein the spring member forms the movable component on which the movable contact member is arranged, and wherein the movable contact member is attached to the spring member by the fourth welded joint produced by ultrasonic welding, and thereafter the bi-metal member is captively attached with clearance to the movable contact member before the switching mechanism is mounted in the housing in step b).

This results in the above-mentioned advantage that the ultrasonic welded joint between the spring member and the movable contact member has no influence on the bi-metal member, as this is fitted to the switching mechanism thereafter. The switching mechanism can also be pre-assembled as a semi-finished component, which is then mounted in the housing as a whole.

Further features and advantages emerge from the attached drawings and their subsequent description.

It is to be understood that the features mentioned above and the features yet to be explained below are usable not only in the combination provided in each case but also in other combinations or standing alone without departing from the spirit and scope of the present disclosure.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1shows a first embodiment of the temperature-dependent switch in a schematic cross-sectional view. The switch is denoted in its entirety with the reference numeral10.

The switch10comprises a housing12and a temperature-dependent switching mechanism14accommodated therein. The housing12includes an upper part16made of electrically conductive material and a lower part18made of electrically conductive material.

Between the upper part16and the lower part18there is an insulating foil20, which electrically isolates the upper part16from the lower part18.

In this embodiment, the upper part16and the lower part18form the two electrodes22,24of the switch10. The two electrodes22,24serve as contact points at which external terminals can be arranged to connect the switch10to a device to be protected. However, depending on the application, the two electrodes22,24of the switch10can also be connected directly to the device to be protected.

For better differentiation, the electrode22formed by the upper part16is referred to below as “first electrode” and the electrode24formed by the lower part18is referred to as “second electrode”.

A stationary contact28is attached to an inner side26of the upper part16facing the inside of the housing12, which comprises a contact surface30facing the lower part18.

The stationary contact28is preferably attached to the inner side26of the upper part16by a welded joint produced by ultrasonic welding, wherein the inner side26forms the first electrode22. The stationary contact28is thus electrically connected to the upper part16, so that an upper side32of the upper part16facing away from the inside of the housing is available as the first external terminal of the switch.

The lower part18, which functions as a second electrode24, comprises a second contact surface36on its inside34. Since the lower part18is also electrically conductive, its outer or lower side38serves as the second external terminal of switch10.

Contact to the first electrode22is made via a first terminal member31, which is attached to the upper part16by a welded joint produced by ultrasonic welding. The first terminal member31is configured as a terminal lug51in the embodiment shown inFIG. 1, wherein the terminal lug51is of annular shape at one end35. With this annular end35, the terminal lug51is supported on an outer, circumferential shoulder37of the upper part16, which is set back in relation to the upper side32. The extent of the recess of the shoulder37and the thickness of the terminal lug51are such that the terminal lug51does not project upwards beyond the upper part16in the region of its annular first end35. In this way a low overall height is made possible.

In a similar way, in the embodiment shown inFIG. 1, contact to the second electrode24is made by a second terminal member33, which is also configured as a terminal lug53, which is attached to the lower part18by a welded joint produced by means of ultrasonic welding. The terminal lug53is of annular shape at its first end39. With this annular end39, the terminal lug53is supported on an outer circumferential shoulder43of the lower part18, which is set back in relation to the underside38. The extent of the recess of the shoulder43and the thickness of the terminal lug53are also selected so that the terminal lug53does not project downwards beyond the lower part18in the region of its annular first end39. In addition to the resulting low overall height of the switch10, this has the advantage that the lower part18can, if desired, be supported directly on the device to be monitored, which ensures good heat transfer.

Furthermore,FIG. 1shows that the two terminal lugs51,53are angled in such a way that their two second ends47,49, which are remote from the first ends35,39, are set back from the shoulders37,43of housing12. These second ends47,49of the terminal lugs51,53serve as terminals of the switch10. For example, a stranded wire not visible inFIG. 1may be attached to each of the two second ends47,49of the terminal lugs51,53.

Depending on its temperature, the switching mechanism14located in the housing12establishes an electrically conductive connection between the upper part16and the lower part18and disconnects this electrically conductive connection abruptly when a response temperature or transition temperature is exceeded.

The switching mechanism14comprises a movable contact member40which is attached to a component42which is movable relative to the housing12. In this embodiment, the movable component42of the switching mechanism14is a spring member44which is integrally connected to a lateral connecting bar which is attached at a point marked48to the second contact surface36provided on the lower part18.

The spring member44is configured as a slightly domed spring snap disc, which centrally supports the movable contact member40. The movable contact member40is attached to the spring snap disc44by a welded joint produced by ultrasonic welding. The lateral connection between the spring snap disc44and the contact surface36arranged on the lower part18is preferably also produced by ultrasonic welding.

A bi-metal member52with a central opening50sits on the movable contact member40with clearance but captive. In the state shown inFIG. 1, the bi-metal member52is in its low-temperature position in which it rests in a force-free manner on the spring snap disc44. The bi-metal member52is designed as a bi-metal snap disc.

The movable contact member40has a dome-shaped tip54, which, is, in the closed state of the switch10shown inFIG. 1, in contact with the stationary contact28or its contact surface30. Below the dome-shaped tip54, a flange56is provided on the movable contact member40, to the lower end of which a cylindrical extension58is attached. As can be seen fromFIG. 1, the flange56of the movable contact member40has a larger diameter than the central opening50provided in the bi-metal snap disc52. The cylindrical projection58, which extends through the central opening50of the bi-metal snap disc52, has a smaller diameter than the central opening50. This ensures that the bi-metal snap disc52is held captive but with clearance on the movable contact member40.

When manufacturing the switching mechanism14, the movable contact member40is first welded onto the spring snap disc44with the underside of the cylindrical extension58. This welded joint is made by means of ultrasonic welding. Since ultrasonic welding generates considerably less heat between the two components to be joined than the fusion welding methods conventionally used, the spring snap disc44is hardly stressed. This is particularly advantageous because the spring snap disc44is usually a very thin-walled component with a thickness of only a few millimeters or even less. In addition, ultrasonic welding does not require any filler materials that are harmful to the environment. Nevertheless, the welded joint produced by ultrasonic welding creates a mechanically extremely stable and electrically highly conductive connection between the movable contact member40and the spring snap disc44.

After producing the welded joint between the movable contact member40and the spring snap disc44, the bi-metal snap disc52is placed from above with its central opening over the movable contact member40. During this process, the flange56still has a smaller diameter than the central opening50, as it is not yet spread or expanded laterally as shown inFIG. 1. The flange56of the movable contact member40is only expanded or widened after the bi-metal snap disc52has been inserted or turned over, which can be done by pressing, for example. The bi-metal snap disc52is then held captive, but with clearance, on the movable contact member40, which in turn is connected to the spring snap disc44.

The switching mechanism14manufactured in this way can then be inserted into the housing12as an already assembled semi-finished component and, as already mentioned, attached in the housing12by welding the spring snap disc44to the lower part18. Since the welded joint between the movable contact member and the spring member44is produced by ultrasonic welding before the bi-metal snap disc52is placed over the contact member40, the bi-metal snap disc52is not affected in any way by the welding process mentioned above. The welding process between the spring snap disc44and the lower part18also has no influence on the bi-metal snap disc52, as the latter is held with clearance on the movable contact member40and therefore no direct heat transfer by heat conduction to the bi-metal snap disc52takes place. This has a positive effect on the functioning and service life of the bi-metal snap disc52.

Due to the permanent mechanical and galvanic connection between the spring snap disc44and the lower part18, there is a very low contact resistance between the lower part18, acting as second electrode24, and the spring snap disc44.

Since the movable contact member40is welded to the spring snap disc44in the above mentioned manner, the contact resistance between the spring snap disc44and the movable contact member40is also extremely low.

By selecting a suitable surface finish of the dome-shaped tip54of the contact member40and the first contact surface30of the stationary contact28, the contact resistance is also very low there.

The ultrasonic welded joint produced between the stationary contact28and the upper part16also results in a very low contact resistance between these two components.

The upper part16and the lower part18can therefore be designed as inexpensive deep-drawn parts, because the quality of the contact resistances is provided by the described welded joints.

In this way, the entire switch10has only a very low contact resistance between the first electrode22and the second electrode24, so that it is virtually a galvanic short circuit.

If, starting from the closed state of the switch10shown inFIG. 1, its temperature now increases above the transition temperature of the bi-metal snap disc52, the latter moves downwards inFIG. 1with its still free edge60inFIG. 1until this edge60comes into contact with the insulating foil20where it is located below an annular rim62of the upper part16.

In doing so, the bi-metal snap disc52presses with its central area64centrally on the spring snap disc44and pushes it downwards as shown inFIG. 1, lifting the movable contact member40from the stationary contact28, so that the switch10opens.

When the ambient temperature and thus the temperature of the bi-metal snap disc52cools down again below the transition temperature, the bi-metal snap disc52returns to its low-temperature position shown inFIG. 1, causing the opening pressure on the spring snap disc44to decrease. Due to the internal forces, the spring snap disc44then resets to its rest position shown inFIG. 1, in which it is clamped between the inside34of the lower part18and the stationary contact28, thus ensuring an attached contact pressure and a securely closed switch10.

FIG. 2shows a second embodiment of a temperature-dependent switch, which in its entirety is also denoted with the reference numeral10. Components which correspond to the components of the switch according to the first embodiment shown inFIG. 1are marked with the same reference number inFIG. 2. For the sake of simplicity, only the essential differences to the first embodiment shown inFIG. 1are described below.

The housing12of the switch10shown inFIG. 2includes an electrically conductive, pot-like lower part18, which is closed by an electrically conductive upper part16, which is configured here as a cover part. The upper part16is held on the lower part18by a flanged edge66with an interposed insulating foil20.

The upper part16and the lower part18also in this case form the two electrodes22,24of switch10, and accordingly the upper side32of the upper part16serves as the first connection surface, and the outer side38of the lower part18serves as the second connection surface. Supply lines can be attached to these two connection surfaces by means of stranded wires or terminal lugs in order to connect switch10to a device to be protected.

Similar to the first embodiment, the second terminal member33is configured as a terminal lug53, the annular first end39of which is attached to the shoulder43surrounding the lower part18by a welded joint produced by ultrasonic welding. The first terminal member31ais configured here, however, as a stranded wire55, which is attached with its stripped first end35ato the upper side32of the upper part16by a welded joint produced by means of ultrasonic welding. It goes without saying that in principle the second terminal member33may also be configured as a stranded wire, which is attached to the underside38of the lower part18by a welded joint produced by means of ultrasonic welding. In the same way it is also possible with the switch design shown inFIG. 2to use a terminal lug51as shown inFIG. 1for the first terminal member31a.

The stationary contact28is, similar to the first embodiment, preferably attached to the inner or lower side26of the upper part16by a welded joint produced by ultrasonic welding.

In contrast to the first embodiment shown inFIG. 1, the switch10shown inFIG. 2does not comprise a spring snap disc44. Instead, the bi-metal snap disc52functions as movable component42, to which the movable contact member40is attached. The bi-metal snap disc52takes over the function of the spring snap disc44in the example of switch10shown inFIG. 2.

The bi-metal snap disc52is clamped in the housing12in such a way that in its low-temperature position, as shown inFIG. 2, it rests on and contacts the inner side34of the lower part18. In principle, however, the bi-metal member52may also be designed as a bi-metal spring clamped on one side, which is connected at a contact member to the inside34of the lower part18by means of a material bond.

Additionally, it is to be understood that with the same construction of the housing12, the switching mechanism14may also have a spring snap disc44according to this embodiment, so that a similar construction of the switching mechanism14as shown inFIG. 1then results.

In the embodiment shown inFIG. 2, the movable contact member40also has a dome-shaped tip54, at the lower end of which there is in this case a widened socket70, the underside of which is attached to the bi-metal snap disc52. This attachment is realized by a welded joint produced by ultrasonic welding. In addition to the above-mentioned advantages of ultrasonic welding, another advantage is that a welded joint produced by ultrasonic welding at this point protects the very sensitive and typically thin-walled bi-metal snap disc52. A hot welding process used at this point to connect the movable contact member40with the bi-metal snap disc52could damage the bi-metal snap disc52to such an extent that its function is permanently impaired.

With regard to the embodiment shown inFIG. 2, it should also be mentioned that the upper part16does not necessarily have to be made of electrically conductive material. It can also be made of insulating material or Positive Temperature Coefficient (PTC) ceramics. In such a case, the first connection surface of the switch10is formed by a metal layer arranged on the upper side32, which metal layer is plated through the upper part16to the stationary contact28. Therefore, in this case only a part of the upper part16would be made of electrically conductive material (metal layer). This metal layer then forms the first electrode22of switch10, so that a corresponding lead can be attached to it, for example by means of a stranded wire or a terminal lug. According to the terminology used herein, the first electrode22of switch10would then not be formed by the entire upper part16, but only by a part of it or would be located on it.

FIG. 3shows a third embodiment of the temperature-dependent switch10. Components which correspond to the components shown inFIGS. 1 and 2are for the sake of simplicity again denoted here with the same reference numerals as before.

An essential difference to the two embodiments shown above is that both terminal electrodes22,24of the switch10are arranged at the upper part16. Accordingly, the construction of the housing12as well as the construction of the switching mechanism14differs in some features, which will be explained in the following in detail.

The housing12comprises a plate-like lower part18, on the raised edge72of which an external circumferential groove74is provided. The upper part16, which is in this case essentially cup-shaped, is supported on the raised edge72by an inner shoulder76. An edge78projects over the shoulder76, on which an inner circumferential bead80is provided, which engages with the groove74, whereby the lower part18is locked with the upper part16. The edge78merges into a ring-shaped overlap82, by means of which the lower part18is held further on the upper part16.

This overlap82can be created by embossing or welding a projecting area of the edge78.

While the upper part16is made of insulating material, the lower part18can also be made of insulating material or of metal, wherein a lower part18made of metal provides a better thermal connection of the switch10to a device to be protected.

The two electrodes22,24, which are located next to each other, are cast into the upper part16, each of which carries a stationary contact28,29. In contrast to the two embodiments mentioned above, the switch, according to the embodiment shown inFIG. 3, therefore, comprises not only one stationary contact28but also a second stationary contact29. The two stationary contacts28,29are each attached to the first and second electrode22,24, respectively, by a welded joint produced by ultrasonic welding. This welded joint produced by ultrasonic welding provides similar advantages as described above with regard to the connection of the stationary contact28with the upper part16forming the first electrode22.

A movable contact member84in the form of a movable contact bridge is assigned to the two stationary contacts28,29. In this example, this movable contact member84functions as movable component42of the switching mechanism14, on which a first and a second contact member40,41are arranged. The two movable contact members40,41are preferably integrally connected to each other.

The movable contact member84, configured as a contact bridge, is mechanically coupled with the spring snap disc44and the bi-metal snap disc52via a rivet86. The bi-metal snap disc52is supported with its edge68in the closed state of the switch10shown inFIG. 3on the inside34of the lower part18. The edge45of the spring snap disc44is circumferentially guided in a circumferential groove88, which is formed between the shoulder76of the upper part16and the edge72of the lower part18.

Depending on the temperature, the switching mechanism14brings the contact member84coupled with the bi-metal snap disc52into contact with the two stationary contacts28,29or lifts the contact member84from the two stationary contacts28,29.

Additionally, the two openings90,92inFIG. 3should be mentioned, which are located on the upper sides of electrodes22,24facing away from the stationary contacts28,29. These openings90,92, which lead outwards, serve on the one hand for a thermal coupling of the switch10to a device to be protected and on the other hand may be provided for test purposes, namely to heat up the inside of the switch10as quickly as possible by means of heating stamps and/or to contact the two stationary contacts28,29from the outside by means of test pins in order to test the function of the switch10.

FIG. 4shows a fourth embodiment in a schematic cross-sectional view. The basic construction of the switch shown therein is similar to switch10shown inFIG. 1.

Here, too, the switching mechanism14comprises a bi-metal snap disc52and a spring snap disc44coupled to it. The spring snap disc44again forms the movable component42, to which the movable contact member40is attached.

The housing12consists of one or more parts and is at least partially made of insulating material or PTC-material. Although this is not explicitly shown inFIG. 4, the housing12may comprise one or more openings which improve the thermal connection of switch10to the device to be protected.

In contrast to the embodiments shown above, the two electrodes22,24are here designed as connection plates which are passed through a side wall94of housing12. A first part96of the first electrode22protrudes into the interior of the housing12and a second part97of the first electrode22is led through the side wall94from the interior of the housing12to the outside. Likewise, a first part98of the second electrode24projects into the interior of the housing12and a second part99of the second electrode24is led out of the interior of the housing12. Preferably, the first two parts96,98of the electrodes22,24rest against an inner side of the housing12or are clamped in the housing12. In principle, however, it would also be possible for these two parts96,98of the electrodes22,24to be arranged freely suspended inside the housing12and to be clamped on one side only at the point where they pass through the housing wall94.

The stationary contact28is attached to the first part96of the first electrode22by means of a welded joint produced by ultrasonic welding. The movable contact member40is attached to the spring snap disc44by means of a welded joint produced by ultrasonic welding. In the low temperature position of switch10shown in FIG.4, the bottom or outer edge of the spring snap disc44rests on the first part98of the second electrode24, so that an electrical connection is established.