EP2958125B1 - Temperature-dependent switch with a spacer ring - Google Patents

Description

The present invention relates to a temperature-dependent switch, which has a temperature-dependent switching mechanism and a housing receiving the switching mechanism, which comprises an upper part and a lower part, wherein on an inner side of the upper part, a first contact surface and inside a second contact surface are provided in the lower part, the rear derailleur temperature-dependent establishes an electrically conductive connection between the first and the second contact surface, the derailleur comprises a current transfer member, a bimetallic snap disk and a movable contact surface connected to the current transfer member, which cooperates with the first contact surface, and the bimetallic snap disk, the movable contact surface in dependence lifts from its temperature from the first contact surface.

Such a switch is from the DE 10 2011 119 637 A1 known.

The known switch has a pot-like lower part, which is closed by a lower part cross-top part. In the interior of the switch, a temperature-dependent switching mechanism is arranged, which carries a movable contact part, on which a movable contact surface is provided, which cooperates with a stationary counter-contact, which is arranged on an inner side of the upper part and forms a first contact surface. The first contact surface may also be formed directly on an inner side of the upper part.

The derailleur comprises as a current transmitting member a spring snap-action disc, which carries the movable contact part and presses against the stationary counter contact. In this case, the spring snap disc is supported with its edge on the inner bottom of the lower part, which forms the second contact surface. In this position, the two contact surfaces are thus electrically conductively connected to one another via the movable contact part and the spring snap-action disc.

The known switch is contacted from the outside via the electrically conductive cover part, which is electrically conductively connected to the stationary mating contact, and the likewise electrically conductive lower part, at the inner bottom of which the spring snap-action disk is supported.

Above the spring snap-action disc, a bimetallic snap-action disc is arranged, which rests loosely in the rear derailleur in its low-temperature position. When the temperature of the bimetallic snap-action disc rises to a value above its response temperature, it presses with its center the movable contact part, and thus the movable contact surface away from the stationary mating contact, for which it bears with its edge against an insulating film between the lower part and the upper part is provided. The spring snap-action disc jumps from its one to its other stable geometric configuration.

While in the exemplary embodiment described so far, the spring snap-action disc operates against the one bimetal snap-action disc, it is in the case of the DE 10 2011 119 637 A1 known switch also provided, only a bimetallic snap disk to use, so that the current flows directly through the bimetallic snap disk, which also causes the contact pressure between the movable contact part and the stationary mating contact when the switch is closed.

Snap discs of the type used here are slightly curved discs with slightly raised towards the edge center. The domes are generally rounded, circular, oval or similarly rounded, but may also be configured star-shaped or cross-shaped.

Bimetal domes have a high temperature position in which they are convex in one view while appearing concave in the same view when in their low temperature position.

By contrast, spring snap disks have two mechanically stable geometric positions or configurations which, depending on the view, appear as convex or concave.

Snaps snap from their one configuration to the other by moving their center, as it were, through the edge, which tends to make a radial evasive movement. When the edge is firmly clamped, snapping over is done by internal deformation while overcoming internal forces. These internal deformations and the resulting internal forces lead to mechanical stress and aging of the snap discs, which limits the life of the switches equipped with it.

In order to avoid or at least greatly reduce the occurrence of internal deformations and internal forces, it is therefore often avoided to mechanically clamp the snap-action disks at their edges.

The movable contact part bearing snap disc is in the from the DE 10 2011 119 637 A1 known switch, for example, a circular disc having an inner contact region, on which the movable contact part is welded on. In order to avoid internal tension in the snap disk, the inner contact area is separated by a semicircular gap of the snap disk, which extends over an angle of more than 180 °.

At the outer edge of the snap disc, a connecting web is formed, which serves together with the rest of the edge as a second contact area. This connecting bridge is used for better handling of the rear derailleur during its installation and when inserting into the lower part. The tie bar is then welded flat to the inner bottom of the base to provide a permanent electrical and mechanical connection between the snap disc and the second contact surface inside the base. The second contact region is thus permanently connected in the region of the connecting web and, in the region of the edge, with the switch closed, with the second contact surface.

This construction offers the advantage that the material and manufacturing costs for the known temperature-dependent switch are lower than other switches, because as a lower part no rotary member is required, and because can be dispensed with the silvering both the snap disc and the lower part. On the other hand, the assembly cost is higher than for switches in which the temperature-dependent switching mechanism is merely inserted, as is apparent from the DE 43 45 350 C2 is known.

Due to the permanent galvanic connection of the snap disc with the second contact surface is at the out of the DE 10 2011 119 637 A1 known switch ensured that the contact resistance between the snap disc and lower part is very low. This eliminates one possible source of error that can occur during the final continuity test of a fully assembled temperature-dependent switch. It is quite possible that due to manufacturing tolerances of the contact resistance between the lower part of the housing and the snap-action disc is so large that the finished temperature-dependent switch must be discarded as broke.

Normally, however, temperature-dependent switches of the type mentioned above are provided with snap discs, loose with their edge, so freely movable resting on the inner bottom of the base or an inner circumferential shoulder in the lower part, so that the entire edge forms an outer contact area. Such switches are, for example, from the above-mentioned DE 43 45 350 A1 known. When jumping from one to the other geometric configuration, the snap disc stretches until its edge stands out when jumping from the bottom of the base or the peripheral edge.

Because the spring-snap disc is at the out of the DE 43 45 350 A1 supported switch on a circumferential shoulder, it can move when snapping with its center through the shoulder and its resting on the shoulder edge "through" on the lower ground to move, so snap through the edge, while at the same time mechanically radially outstretched, which allows snapping without overcoming external mechanical counter forces.

These mechanical degrees of freedom when snapping between the two geometric configurations are desired because they have a positive effect on the life of the derailleur and the long-term stability of the switching temperature.

In order to meet the heights and / or the desired function of the individual components of such a switch, it is known to arrange a spacer ring between the upper part and the lower part, which creates the corresponding receiving space in the interior of the switch depending on the height of the temperature-dependent switching mechanism , The spacer ring can according to DE 195 27 253 B4 be formed as an insulator or as a heating resistor, which is electrically connected to both the upper part and with the lower part. This heating resistor is then used for latching, as will be described below.

Although from the DE 10 2011 119 637 A1 known switch brings many advantages in terms of cost and installation, it has some disadvantages on what the life of the rear derailleur and the long-term stability of the switching temperature, because the snap disc is mechanically connected via the connecting web at one point of its circumference with the inner bottom of the lower part. This design allows neither a radial stretching nor an unobstructed snapping through the center of the snap-action disc, which is consequently subjected to external mechanical forces when it is being folded over.

The known temperature-dependent switches are used to protect an electrical device from excessive temperature. For this purpose, the supply current for the device to be protected is passed through the temperature-dependent switch, wherein the switch is thermally coupled to the device to be protected. At a predetermined by the critical temperature of the bimetallic snap disc response the respective switching mechanism then opens the circuit by the movable contact surface is lifted from the stationary counter contact.

The movable contact surface may be formed on a contact part moved by the snap-action disk or directly on the snap-action disk.

Thus, the switch does not close again after cooling the device, it is for example from the above DE 195 27 253 B4 known, parallel to the temperature-dependent switching mechanism to provide a self-holding resistor, preferably a PTC resistor which is electrically short-circuited by the latter when the temperature-dependent switching mechanism is closed. When the rear derailleur now opens, the self-holding resistor takes over a portion of the current flowing so far and heats up enough to generate enough heat to keep the bimetal snap-action disc at a temperature above the response temperature. This process is called latching, it prevents a temperature-dependent switch closes uncontrollably again when the device to be protected cools down again.

While self-heating of the snap-action disk by the flowing current is often undesirable in such temperature-dependent switches are Also switch known, in which a series resistor is additionally provided, which heats up in a defined manner by the flowing operating current of the device to be protected. If the current flow is too high, this series resistance heats up to such an extent that the transition temperature of the bimetallic snap disk is reached. In addition to monitoring the temperature of the device to be protected, the flowing current can be monitored in this way, the switch then has a defined current dependence.

Such switches have proven sufficiently in everyday use. If the switches do not open at the zero crossing of an AC supply voltage or DC voltage applied, form arcing when lifting the movable contact part of the stationary counter contact and / or lifting the edge of the power snap disc of the second contact surface and it comes to flying sparks.

The arcs that form and sparks that result lead to contact erosion and, consequently, to a long-term change in the geometry of the buttons of the movable contact part and stationary counter contact, which over time also leads to an increase in the contact resistance.

In addition to the contact erosion on the stationary counter contact and the movable contact part contact erosion also occurs at the contact points, where contact resistances form, ie between the edge of the snap discs, which carry the movable contact part, and the second contact surface inside the housing base. In the course of the switching cycles, this leads to damage to the edge of the snap discs also to an increase in volume resistance, but should be as low as possible to keep an undefined and changing over the course of the switching cycles influence of the current self-heating on the switching behavior as low as possible.

Particularly at high switched currents of, for example, 20 to 50 amperes, the material heats up strongly in the area of the contact resistances, see above that due to the low-resistance structure of the switch, the essential heat source is often not the heat of the component to be protected but the contact resistance. As a result, the contact erosion at the anyway heated contacts and contact surfaces increases sharply.

These problems even increase with the number of switching cycles, so that the switching behavior of the known switches deteriorates over time. Against this background, the life, ie the number of permissible switching cycles of the known switches is limited, the lifetime also depends on the Abschaltleistung, ie the current of the switched currents.

The DE 977 187 A suggests, therefore, in a temperature-dependent switching mechanism, which has only a bimetallic snap disk to relieve them from the current flow, that the movable contact part is connected via a sun-wheeled metal spider to the housing of the switch. In this way, the current no longer flows only through the bimetallic snap disk but mainly through the metal spider.

A similar approach chooses the AT 256 225 A in which on the remote from the stationary mating contact surface of the bimetallic snap disk, a copper lead is provided, which connects the movable contact part with the housing.

The copper lead and the metal spider do not contribute to the mechanical function of the switch, on the contrary they must be moved by the bimetallic snap disk when opening and closing the switch, so they represent an additional mechanical load for them. This leads to fatigue and concomitantly not only to an undesirable shift in the switching temperature but also to a deteriorated opening and closing behavior, which greatly limits the life.

While these switches, the bimetallic snap disk must indeed provide the closing pressure of the rear derailleur, but this mechanical stress can be taken into account in certain types of switches.

Based on that suggests the DE 21 21 802 A prior to arrange a spring snap-action disc parallel to the bimetal snap-action disc, which produces the closing pressure of the switching mechanism and supports both the opening and closing the Umschnappbewegung the bimetallic snap disk. In addition, it also carries the electrical power. In this way, the bimetallic snap disk is both mechanically and electrically relieved, so that their life is significantly extended.

There is this switch already at the beginning of which from the DE 43 45 350 A1 Known switch described problem with the inevitably forming arcs and sparks, the more limit the life of the known switch, the higher the switched current.

In the from the DE 10 2011 119 637 A1 Although known switch the contact erosion at the edge of the snap-action disc is reduced by the permanent electrical connection of the snap-action disc with the second contact surface, but still flows with the switch closed, so if the edge of the snap-action disc on the second contact surface, power not only via the connecting web but also over the edge of the snap disk in the second contact surface, so that the edge is damaged by contact erosion when opening the switch, which does not deteriorate the volume resistance but probably the mechanical switching behavior and thus the life.

In order to be able to carry higher currents over temperature-dependent switches, which nevertheless have a long life, therefore, a current transfer member in the form of a contact bridge or a contact plate is often used, which is moved by a bimetal or spring snap-action disc and carries two contact parts, with two co-operate with stationary counter contacts.

In this way, the operating current of the device to be protected flows from the first mating contact via the first contact part into the contact plate, through it to the second contact part and from this into the second mating contact. The snap-action disc is therefore de-energized and the above-described problems with the contact erosion at the edges of the snap discs are avoided. However, these switches, such as those from the DE 26 44 411 A1 or the DE 198 27 113 A1 are known, a larger height than the generic switch on and are structurally complex.

Against this background, the present invention seeks to provide a structurally simple way a temperature-dependent switch of the type mentioned above, which is easy to assemble and even at high currents connected has sufficient for normal applications life.

According to the invention, this object is achieved in that a resistance ring is disposed between the upper part and the lower part, which is electrically in series with the current transfer member between the first and the second contact surface when the switch is closed.

In this way, the switching current also flows through the resistance ring, where it generates ohmic heat. The resistance value of the resistance ring can then be designed in relation to the contact resistance so that it generates most of the heat in the switch. The contacts and contact surfaces on the contact resistors therefore no longer heat up as much as is the case with comparably constructed switches without the resistance ring.

By choosing the resistance value of the resistance ring can now be realized in a structurally simple manner a current-dependent switching, so a defined current dependence.

The new switch is also easier to assemble than the one from the DE 10 2011 119 637 A1 Known switch and avoids the local disadvantages.

A major advantage, however, is that it comes in the new switch despite simple design and easy installation to a much lower contact erosion at the edges of the snap discs than in the from DE 43 45 350 A1 known switch.

The life of the known switch is thereby significantly extended, which was not expected and was surprising.

The contact erosion on the edge of domes leads, according to a preliminary and non-binding statement of the present inventors, to limiting the maximum switching power and the achievable switching cycle number more than by the contact erosion on the stationary mating contact and the movable contact part. Alone through the resistance ring results in an improvement of the contact erosion at the edge of the current-carrying snap discs, which increases unexpectedly the life of a temperature-dependent switch.

The object underlying the invention is completely solved in this way.

It is preferred if the resistance ring comprises an upper annular surface and a lower annular surface, the current transmission member has an edge which rests on the upper annular surface, and the lower annular surface rests directly or indirectly on the second contact surface.

This measure is structurally advantageous because during assembly of the new switch, only the resistance ring must be inserted into the lower part, where it rests either directly on the second contact surface, or with interposition, for example, a spring-snap disc, as described below becomes. The current transfer member is then placed on the resistance ring, and this is then possibly pressed by an applied spacer ring with its edge on the upper annular surface.

In this way arise between the edge of the current transfer member and the upper annular surface and between the lower annular surface and the second contact surface only very low contact resistance, which reduces the risk of contact erosion. Furthermore, the edge of the current transfer member does not lift off the upper ring surface when the switch is opened, which also reduces contact wear.

Against this background, it is preferred if between the edge of the current transfer member and the upper part, a spacer ring is arranged, and the edge of the current transfer member between the spacer ring and the resistance ring is fixed.

Further, it is preferred if the current transmission member is designed as a spring snap-action disc.

Here it is advantageous that the bimetallic snap disk is mechanically relieved, and that a conventional temperature-dependent switching mechanism of movable contact part, spring snap disk and bimetallic snap disk can be used.

On the other hand, it is preferable if the derailleur comprises, in addition to the current transmitting member, a spring snap-action disc which carries the movable contact part.

The derailleur thus includes in addition to the usual way existing components movable contact part, spring snap-action disc and bimetallic snap disk nor a power transmission member, so that not only the bimetallic snap disk mechanically relieved in the usual way by the spring snap disk is, according to the invention, the spring snap-action disc is at least largely relieved by the series connection of the current transfer member and the resistance ring of the power supply. The spring snap-action disc can also be completely relieved of the current conduction if, for example, it is electrically insulated with its edge opposite the second contact surface and / or with its center opposite the movable contact part.

In this case, it is preferred if the spring snap-action disc is arranged between the current-transmitting member and the bimetal snap-action disc, more preferably the spring snap-action disc has an edge which is held between the resistance ring and the second contact surface.

In the context of the present application, a "held" edge is understood to be both pinching and definition of the edge, which allows the spring snap-action disc to expand when it snaps, thus moving outwards with its edge, as described above has already been explained.

In this way, the spring snap-action disc can be electrically connected in parallel to the series connection of the current transfer member and the resistance ring.

In this context, it is preferred if the spring snap-action disc has a greater electrical resistance than the series connection of the current transfer member and the resistance ring, preferably made of stainless steel, wherein the current transfer member is further preferably made of a material having a lower electrical resistivity than the spring snap-action disc, and more preferably having a conductivity-improving coating, for example a silver coating.

Here it is first of all an advantage that an inexpensive material without additional coating, for example with silver, can be used for the spring snap-action disc.

In this way, the spring divider on the one hand and the series circuit of the current transfer member and resistor ring on the other hand formed flow divider is also designed so that the majority of the operating current of the device to be protected flows through the series circuit of the current transfer member and the resistance ring.

The heat generated in the resistance ring is thus transmitted directly into the housing of the switch and thus to the bimetallic snap-action, which reduces the trip time of the switch, the contacts and contact surfaces remain colder, and the life is increased.

Applicant's experiments have shown that the new switch survives more than 3,000 switching cycles with a switching current of 25 A without impairing the function. Such a long life at such a high switching current had not previously been expected for a generic switch, even in a construction with a movable contact, spring snap and bimetallic snap-action and power transmission, but still without a resistance ring.

The resistance of the spring snap disk made of stainless steel is, for example, 150 mΩ, the resistance of the power transmission member designed as a current transfer member few mΩ. The resistance of the resistance ring between the two ring surfaces should be 10 to 15 mΩΠ.

The current transmission member is preferably formed as a disc and preferably has curved, radially outwardly extending slots.

These slots reduce the spring action of the current transfer disc, so that it does not counteract when switching the spring force of the bimetallic snap disk and the spring snap-action disc.

In this context, it is preferred if the resistance ring made of a material, preferably made of a metal or a metal alloy is, and at 20 ° C has a specific electrical resistance which is greater than that of copper.

However, such a resistance ring would possibly have too low volume resistance between the two annular surfaces, which is why it is preferred if the upper annular surface is provided in a first portion and the lower annular surface in a second portion with an electrically conductive coating having a lower specific electrical Resistance than the material of the resistance ring, more preferably, the resistance ring between the first and the second portion has an ohmic resistance which is between 2 and 50 mΩ, preferably between 5 and 30 mΩ, and further preferably the first and / or the second Section covered less than 50%, preferably less than 35% of the respective annular surface.

In this technically simple way, resistance values between the two sections in the desired range can be realized. The current does not flow along the thickness or thickness of the resistance ring, but especially along the diameter. The proportion of the area of the coated sections on the respective annular surface determines the resistance value for a given material.

Against this background, the present invention also relates to a resistance ring for a temperature-dependent switch having an upper annular surface and a lower annular surface is made of a material, preferably of a metal or a metal alloy, and at 20 ° C has a specific electrical resistance, is larger than that of copper, wherein the upper annular surface is provided in a first portion and the lower annular surface in a second portion with an electrically conductive coating having a lower electrical resistivity than the material of the resistance ring, preferably the first and / or the second section cover less than 50%, preferably less than 35% of the respective annular surface, more preferably the resistance ring consists of an iron or copper alloy, preferably brass, bronze, constantan or stainless steel.

It is preferred if the coating is a silver-containing coating, more preferably, the resistance ring between the first and the second section has an ohmic resistance, which is between 2 and 50 mΩ preferably between 5 and 30 milliohms.

The resistance ring has Favor an outer diameter between 8 and 20 mm, an inner diameter between 5 and 10 mm and between the annular surfaces has a thickness between 0.1 and 0.5 mm.

Finally, the invention relates to the use of the new resistance ring for producing a temperature-dependent switch, preferably the new switch.

The new switch can also be equipped in a conventional manner with a parallel resistor for latching.

Further advantages will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Fig. 1

eine schematische, geschnittene Seitenansicht eines temperaturabhängigen Schalters in geschlossenem Zustand;

Fig. 2

eine Explosionsdarstellung des Schalters aus Fig. 1; und

Fig. 3

den Widerstandsring aus Fig. 2 in einer schematischen Draufsicht und im Schnitt längs der Linie A-A.

Embodiments of the invention are illustrated in the accompanying drawings and are explained in more detail in the following description. Show it:

Fig. 1

a schematic, sectional side view of a temperature-dependent switch in the closed state;

Fig. 2

an exploded view of the switch Fig. 1 ; and

Fig. 3

the resistance ring Fig. 2 in a schematic plan view and in section along the line AA.

In Fig. 1 is a schematic side view and not to scale a circular in plan view of temperature-dependent switch 10 is shown, which has a temperature-dependent switching mechanism 11 which is arranged in a housing 12.

The housing 12 comprises an upper part 14 which closes a pot-like lower part 15.

The upper part 14 carries a stationary counter contact 16, whose outer side serves as the first outer terminal 17 for the switch 10. The lower part 15 has a bottom 18 whose outer side serves as a second outer connection 19 for the switch 10.

On an inner side 21 of the upper part 14, a first contact surface 22 is provided for the rear derailleur 11, which is formed on the stationary counter contact 16.

In the lower part 15, a circumferential shoulder 23 is arranged, which serves as a second contact surface 24 for the rear derailleur 11.

On the circumferential shoulder 23 is a to be described later resistance ring 25 on which a spacer ring 26 is arranged. On the spacer ring 26 is an insulating film 27, on which in turn the upper part 14 rests.

The insulating film 27 is pulled up between the upper part and a raised edge 28 of the lower part 14, where it is pressed by the flanged edge 28 to the upper part 14.

On the upper part 14, a further insulating film 29 is arranged.

In this way, the switch 10 is hermetically sealed, the insulating films 27 and 29 ensure that between the raised edge 28 and the top 14 neither dust nor moisture or other foreign substances can penetrate into the interior of the switch 10.

The electrically conductive upper part 14 and the electrically conductive lower part 15 are electrically insulated from one another by the insulating film 27, wherein an electrically conductive connection between the first contact surface 22 and the second contact surface 24 is produced by the temperature-dependent switching mechanism 10.

The switching mechanism 11 comprises for this purpose a movable contact part 31, on which a movable contact surface 32 is provided, which faces the first contact surface 22. In the closed state of the switch 10, as in Fig. 1 is shown, first contact surface 22 and movable contact surface 32 abut each other.

The movable contact part 31 is mushroom-shaped in cross-section, wherein on the trunk a stepped retaining ring 33 is placed, which carries a bimetallic snap disk 34, a spring snap-action disk 35 and a current transmission member 36.

The bimetallic snap disk 34 is supported with its edge 37 inside on the bottom 18 of the lower part 15.

The spring snap-action disc 35 rests with its edge 38 between the resistance ring 25 and a step 40 on the peripheral shoulder 23.

The current transmission member 36 is clamped with its edge 39 between the resistance ring 25 and the spacer ring 26.

In Fig. 2 the switch is shown in an exploded view, from which it can be seen that the bimetallic snap disk 34 and the spring snap-action disc 35 as well as the current transfer member 36 are formed as circular discs. Alternatively, these three components 34, 35 and 36 may also be oval or star-shaped or cross-shaped.

In the closed state of the switch 10 according to Fig. 1 the spring snap-action disc 37 presses the movable contact part 31 against the stationary counter-contact 16, so that the first contact surface 22 and the movable contact surface 32 are mechanically connected to one another in an electrically conductive manner.

Because the edge 38 of the spring snap-action disc 35 is supported on the shoulder 40, the spring snap-action disc 35 is electrically conductively connected to the second contact surface 24.

In the closed switch 10 according to Fig. 1 Thus, a first current path is formed between the stationary counter contact 16, the movable contact part 31, the spring snap-action disc 35 and the electrically conductive lower part 15.

Parallel to this current path, a current path formed by the current transfer element 36 and the resistance ring 25 is connected so that a current divider is formed.

The movable contact part 31 is electrically connected to the current transmitting member 36, which in turn rests with its edge 39 on the resistance ring 35, which in turn rests directly on the second contact surface 24.

In particular in Fig. 2 It can be seen that the current transmission member 36, the spring snap-action disc 35 and the bimetallic snap disk 34 each have a central bore 41, 42 and 43 which rest on the steps of the retaining ring 33.

While the current transmitting member 36 and the spring snap-action disc 35 via its openings 41 and 42 electrically conductive and mechanically fixed between the retaining ring 33 and the movable contact member 31 are clamped, the bimetallic snap disk 34 is loosely with its opening 43 on a lowermost step 44 of the retaining ring 33.

As it is in Fig. 2 can be seen, the current transmitting member 36 is further provided with curved, radially outwardly extending slots 45. These slots 45 cause that the current transmitting member 36 has no mechanical spring action, so that it does not or only imperceptibly influences the temperature-dependent switching function of the temperature-dependent switching mechanism 11.

The rear derailleur 11 could alternatively be designed so that the spring snap-action disc 35 is moved to the position of the current transfer member 36, that is clamped with its edge 38 between the spacer ring 26 and the resistance ring 25. The current transmitting member 36 would then be formed by the quasi snap spring 35 so that the rear derailleur 11, the bimetallic snap disk 34 and a current transmitting member 36 which now takes over the function of a spring snap-action disc 35 with.

In the rear derailleur 11 according to Fig. 1 However, the current transmitting member 36 is substantially the power management, because the resistance of the series circuit of the current transmitting member 36 and the resistance ring 25 is significantly lower than the resistance of the spring snap disk 35th

The spring snap-action disc 35 serves primarily to keep the switch closed, that is to say to exert the contact pressure with which the movable contact part 31 bears against the stationary counter-contact 16.

The bimetallic snap disk 34 is located in the in Fig. 1 shown closed position of the switch 10 loosely on the stage 44, so it is neither electrically nor mechanically in function.

As the temperature in the interior of the switch 10 increases, so does the temperature of the bimetallic snap-action disc 34, which then moves upwardly with its rim 37 and comes into abutment with the edge 38 of the spring snap-action disc 35. Upon further bending of the bimetallic snap disk 34, the latter then presses the movable contact part 31 downwards, thereby lifting off the movable contact surface 32 from the first contact surface 22, so that the switch 10 is opened.

In this opening movement arcs may arise between the movable contact part 31 and the stationary contact 16, wherein it may also come to flying sparks.

Further, in a switch which has neither a resistance ring 25 nor a current transmitting member 36, sparking also occurs at the edge 38 of the spring snap-action disc 35.

As already described above, the arcing and in particular the sparking lead to the contact surfaces 22 and 24 and the movable contact surface 32 and the edge 38 of the spring snap-action disc 35 leads to contact erosion, which in particular at higher currents, the life, ie the number of permissible switching cycles of such a switch 10, limited.

Characterized in that the switch 10 now has a resistance ring 25, the resistance value in relation to the resistance of the current transfer member 36 and the contact resistance between the contact surfaces 22 and 32 and the edges 38 and / or 39 of spring snap-action disc 35 and / or power transmission member 36 large is, the majority of the heat in the switch 10 is now due to the flow of current through the resistance ring 25th

In this way, the contact surfaces on the contact resistes just described are not so much heated, which already leads to the fact that the contact erosion is significantly reduced.

Due to the resistance of the resistance ring, the switch can switch in this way with a defined current dependence, because the resulting heat in the resistance ring 25 is conducted directly into the interior of the switch 10 and thus to the bimetallic snap disk 34.

This protective function unfolds the resistance ring 25 already in a rear derailleur 11, which has a spring snap-action disc 35 as a current transmission member 36.

However, the protective effect is particularly efficient in the embodiment according to the Fig. 1 because there namely the resistance of the spring snap-action disc 35 in relation to the resistance of the resistance ring 25 can be made very large, so that the majority of the operating current of the device to be protected through the series circuit of the current transfer member 36 and the resistance ring 25 flows.

The spring snap-action disc is made, for example, of stainless steel and, contrary to the usual practice, has no silver coating, so that it has a resistance of 150 mΩ between its opening 42 and its edge 38.

By contrast, the current-transmitting member 36 is made of a copper alloy, for example, and also provided with a silver coating, so that it has a resistance of a few mΩ between its opening 41 and its edge 39.

The resistance ring 25 is designed in a manner to be described so that it has a resistance of 5 to 15 mΩ in the current flow.

Such a switch has survived in continuous operation in the premises of the applicant at an operating current of 25 amperes more than 3000 switching cycles, so shown a performance, as otherwise constructed only much more complicated Show switch with contact bridge, as for example from the above-mentioned DE 26 44 411 A1 are known.

In other words, the spring snap-action disc has a greater electrical resistance than the series connection of the current transfer member and the resistance ring.

Namely, the current transmitting member 36 is made of a material having a lower electrical resistivity than the spring snap-action disc, the current transmitting member further comprising a conductivity-improving coating of silver.

The resistance ring 25 is made of a material, in particular a metal or a metal alloy, which has a specific electrical resistance at 20 ° C, which is greater than that of copper. The resistance ring 25 is made for example of Konstantan.

In order now to design the resistance ring 25 so that it has a resistance of 5 to 15 milliohms between the edge 39 of the current transfer member 36 and the second contact surface 24, it is provided with a selective coating, as now with reference to FIG Fig. 3 is discussed.

In Fig. 3 Below, the resistance ring 25 is shown in plan view, in Fig. 3 cut out along the line AA Fig. 3 below.

The resistance ring 25 has an upper annular surface 46, on which rests the edge 39 of the current transmission member 36.

In parallel, the resistance ring 25 has a lower annular surface 47, with which it rests directly on the second contact surface 24.

The resistance ring 25 is configured annularly with an outer diameter indicated at 48 and an inner diameter indicated at 49. Between the two annular surfaces 46 and 47, the current transmitting member 26 has a thickness indicated at 51.

In the embodiment shown, the outer diameter 49 is approximately 10.5 mm, the inner diameter 49 is approximately 8.5 mm and the thickness 51 approximately 0.35 mm.

As a material spring band was used, which was coated selectively.

The upper annular surface 46 is provided in a portion 52 with a silver coating 53, while the lower annular surface 47 is provided in a portion 54 with a silver coating 55.

The two sections 52 and 54 are thus circumferentially offset from each other on different annular surfaces 46, 47 and are offset in the embodiment shown by 180 ° to each other, so are diametrically opposite each other. They each occupy about one third of the total area of the respective annular surface 46 and 47, respectively.

Through the silver coating 53 or 55 now flows the operating current of a device to be protected from the edge 39 of the current transfer member 36 in the section 52 and from there, so to speak, longitudinal or circular through the resistance ring 25 to the portion 54, where the current in the second contact surface 24 enters.

By the sizes of the sections 52 and 54, the resistance value between these two sections 52 and 54 can thus be changed, which is why even with a resistance ring 25 made of constantan with a thickness of only 0.35 mm volume resistivities between 2 and 50 mΩ can be realized.

Claims (18)

1. Temperature-dependent switch, which comprises a temperature-dependent switching mechanism (11) and a housing (12) which accommodates the switching mechanism (11) and comprises an upper part (14) and a lower part (15), wherein a first contact area (22) is provided on an inner side (21) of the upper part (14) and a second contact area (24) is provided internally in the lower part (15), the switching mechanism (11) producing, in temperature-dependent fashion, an electrically conductive connection between the first and second contact areas (22, 24), wherein the switching mechanism (11) comprises a current transfer element (36), a bimetallic snap-action disc (34) and a movable contact area (32), which is connected to the current transfer element (36), said movable contact area (32) interacting with the first contact area (22), and wherein the bimetallic snap-action disc (34) lifts off the movable contact area (32) from the first contact area (22) depending on the temperature of said bimetallic snap-action disc (34),
   characterized in that a resistance ring (25) is arranged between the upper part (14) and the lower part (15) and is electrically in series with the current transfer element (36) between the first and second contact areas (22, 24) when the switch (10) is closed.
2. Switch according to Claim 1, characterized in that the resistance ring (25) comprises an upper ring area (46) and a lower ring area (47), the current transfer element (36) has a rim (39), which rests on the upper ring area (46), and the lower ring area (47) rests indirectly or directly on the second contact area (24).
3. Switch according to Claim 2, characterized in that a spacer ring (26) is arranged between the rim (39) of the current transfer element (36) and the upper part (14), and in that the rim (39) of the current transfer element (36) is fixed between the spacer ring (26) and the resistance ring (25).
4. Switch according to anyone of Claims 1 to 3, characterized in that the current transfer element (36) is embodied as a spring snap-action disc.
5. Switch according to anyone of Claims 1 to 3, characterized in that the switching mechanism (11) comprises, in addition to the current transfer element (36), a spring snap-action disc (35), which bears the movable contact area (32).
6. Switch according to Claim 5, characterized in that the spring snap-action disc (35) is arranged between the current transfer element (36) and the bimetallic snap-action disc (34).
7. Switch according to Claim 6, characterized in that the spring snap-action disc (35) has a rim (38), which is held between the resistance ring (25) and the second contact area (24).
8. Switch according to anyone of Claims 5 to 7, characterized in that the spring snap-action disc (35) has a greater electrical resistance than the series circuit comprising the current transfer element (36) and the resistance ring (25), and is preferably manufactured from stainless steel.
9. Switch according to anyone of Claims 5 to 8, characterized in that the current transfer element (36) consists of a material that has a lower specific electrical resistance than the spring snap-action disc (35).
10. Switch according to anyone of Claims 5 to 9, characterized in that the current transfer element (36) has a coating which improves conductivity, in particular a silver coating.
11. Switch according to anyone of Claims 5 to 10, characterized in that the current transfer element (36) comprises bent slots (45) extending radially outwards.
12. Switch according to anyone of Claims 1 to 11, characterized in that the resistance ring (25) is manufactured from a material, preferably from a metal or a metal alloy, and has a specific electrical resistance at 20ºC which is greater than that of copper.
13. Switch according to anyone of Claims 2 to 12, characterized in that the upper ring area (46) in a first section (52) and the lower ring area (47) in a second section (54) are provided with an electrically conductive coating (53; 55), which has a lower specific electrical resistance than the material of the resistance ring (25).
14. Switch according to Claim 13, characterized in that the resistance ring (25) has an ohmic resistance of between 2 and 50 mΩ, preferably between 5 and 30 mΩ, between the first and second sections (52, 54).
15. Switch according to Claim 13 or 14, characterized in that the first and/or second sections (52, 54) cover less than 50%, preferably less than 35% of the respective ring area (46, 47).
16. Switch according to anyone of Claims 13 to 15, characterized in that the first section (52) is circumferentially offset with respect to the second section (54).
17. Switch according to anyone of claims 13 to 16, characterized in that the resistance ring has an outer diameter (48) of between 8 and 20 mm, an inner diameter (49) of between 5 and 10 mm and a thickness (51) between the ring areas (46, 47) of between 0.1 and 0.5 mm.
18. Resistance ring for a temperature-dependent switch (10) of anyone of claims 1 to 17, which resistance ring comprises an upper ring area (46) and a lower ring area (47), is manufactured from a material, preferably from a metal or a metal alloy, and has a specific electrical resistance at 20ºC that is greater than that of copper, wherein the upper ring area (46) in a first section (52) and the lower ring area (47) in a second section (53) are provided with an electrically conductive coating, which has a lower specific electrical resistance than the material of the resistance ring (25), and wherein the first section (52) and the second section (54) are circumferentially offset with respect to each other.

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