EP0789376A2 - Switch with a temperature-dependent switching device - Google Patents

Abstract

The switch comprises a control mechanism (13) and a casing (12) accommodating the control mechanism, which includes an electrically conducting lower part (14), as well as an electrically conducting cover part (15). The cover part is electrically isolated from the lower part. The control mechanism produces an electric connection between the cover part and the lower part in dependence on its temperature, and connects the circuit on one hand with the cover part and on the other hand with the lower part. At least one resistance (31, 32, 33, 34) is arranged directly inside the casing, and is connected in a switching position of the control mechanism (13) in series with it between cover part and lower part.

Description

The present invention relates to a switch for opening and / or closing a circuit, with a temperature-dependent switching mechanism and a housing accommodating the switching mechanism, which has an electrically conductive lower part and a closing, electrically conductive cover part, which is electrically insulated from the lower part, wherein depending on its temperature, the switching mechanism establishes an electrical connection between the cover part and the lower part and the circuit can be connected on the one hand to the cover part and on the other hand to the lower part.

Such a switch is known from DE 29 17 482 C2.

In the known switch, a metal housing is provided, the lower part being insulated from the cover part by the interposition of an insulating film. The cover part is captively attached to the lower part by a flanged edge. A temperature-dependent bimetal switching mechanism is provided in the interior of the housing, which comprises a spring washer which carries a movable contact part. A bimetallic snap disc is placed over the contact part.

Below the response temperature of the bimetallic snap disk, the spring washer presses the movable contact part against a projection provided on the inside of the cover part and, on the other hand, is supported with its edge on the inside on the lower part. Since the spring washer is made of an electrically conductive material, an electrical connection is made between the cover part and the lower part.

If the temperature of the switch is now increased, the bimetallic snap disk snaps, is supported with its edge on the inside of the cover part and presses the movable contact part away from the cover part against the force of the spring washer. Since the insulating film covers a large part of the inside of the cover part, the edge of the bimetallic disc which is now supported on the cover part is insulated from the cover part, so that after the contact part has been lifted off the projection, the electrically conductive connection between the cover part and the lower part is interrupted .

Such switches are connected in series with an electrical consumer in a circuit, for a good thermal connection between the electrical switch and the consumer to be protected is taken care of. Due to the above-described functional principle of the bimetallic switching mechanism, the consumer is supplied with electricity as long as its temperature is so low that the response temperature of the bimetallic snap disk is not reached. If the temperature of the consumer rises above a permissible value due to a malfunction, the circuit is interrupted and the consumer is switched off to protect against excess temperatures.

The known switch with its encapsulated metal housing is very robust and insensitive to mechanical influences, so that it satisfactorily fulfills the demands placed on it.

However, this switch has the disadvantage that it automatically switches on again when the consumer cools down, so that the consumer is repeatedly switched on and off if the fault is not eliminated after the first switch-off. Such clocking switching behavior is often undesirable.

In order to remedy this disadvantage, a further switch is known from EP 0 284 916 A2 which comprises a lower part which is closed by a cover part made of thermistor material and in which the switching mechanism is arranged. The bimetallic switching mechanism comprises, in a known manner, a bimetallic snap disk and a spring washer on which a movable contact part is held. Below the response temperature of the bimetallic snap disk, the movable contact part is pressed by the spring washer against a fixed contact part provided on the cover part, which extends like a rivet through the cover part and merges into a head on the outside. The lower part is made of electrically conductive material, so that Switchgear creates a conductive connection between the lower part and the head of the fixed contact part at low temperatures. The cover part is in conductive connection with both the fixed contact part and with the lower part, so that it is electrically connected in parallel to the switching mechanism.

If the switching mechanism now opens due to an excessively high temperature, the current flows from the fixed contact part through the PTC thermistor resistor forming the cover part to the lower part, as a result of which the PTC resistor heats up and the switching mechanism keeps open, even if the excess temperature triggering the switching is no longer present is. In this way, the PTC resistor acts in the sense of a self-holding function.

In a further exemplary embodiment from this document, the cover part comprises a ceramic support part, on which a carbon resistor is arranged, which provides the self-holding function as a heating resistor.

If the cover part is made of PTC thermistor material, it does not have the required pressure stability, which is often required in the rough everyday use of the known switches. Such switches are in fact used to monitor the temperature of motors, heating coils, etc., and they are often exposed to strong mechanical loads as a result of the vibrations associated with the operation of the consumers to be protected. Strong pressures can also be exerted on the cover of the temperature monitor.

If the parallel resistor is a carbon resistor, the cover itself can be made of a mechanically more stable material, but it is the same as for the cover part through-connection of the thermistor material through the cover to the outside is required, which is not required in the switch discussed above.

The switch known from EP 0 284 916 A2 thus has the advantage over the switch mentioned at the outset that it is provided with a self-holding function, but brings with it other disadvantages which lie in the complex construction and the lower mechanical strength.

Finally, DE 43 36 564 A1 discloses another self-holding switch with a PCT resistor connected in parallel, a further heating resistor being connected in series with the switching mechanism, which ensures that the known switch is sensitive to overcurrent.

This switch comprises a ceramic carrier plate provided with conductive and insulating coatings, on which an encapsulated bimetallic switching mechanism is arranged, next to which the PTC thermistor module sits, which is electrically connected in parallel with the switching mechanism. A thick-film resistor is also arranged on the ceramic carrier plate, which leads under the switching mechanism and is connected in series with it.

The known switch is also connected in series with a consumer to be protected, so that the operating current of this consumer flows through it. At the same time, this switch is in a known manner in thermal connection with the consumer to be monitored. If the operating current of the consumer increases in an impermissible manner as a result of a defect, the series-connected thick-film resistor heats the switching mechanism to such an extent that it opens so that the PTC resistor connected in parallel takes over the current.

Because of the high resistance of the PTC resistor, the operating current of the consumer now drops to a harmless level, which, however, is sufficient to maintain a temperature via the ohmic power loss in the PTC resistor, which keeps the switch mechanism open.

Of course, this switch is also opened when the temperature of the consumer to be protected is too high, the PTC resistor also ensuring that the switchgear that is now open remains locked.

This switch has the disadvantage that it has a relatively bulky and large construction, which is due in particular to the ceramic carrier plate.

The increasing safety requirements and new safety regulations require that the switch mentioned at the outset, which is often also referred to as a temperature monitor, be equipped with a self-holding function and / or with an overcurrent sensitivity. However, the known switches described above, which have such functions, are unsatisfactory from a mechanical as well as a constructional point of view, the high production costs being a disadvantage in particular.

Against this background, it is an object of the present invention to further develop the switch mentioned at the outset in such a way that it can optionally be equipped with a self-holding function and / or overcurrent sensitivity in a structurally simple manner, the new switch should be able to be manufactured further inexpensively.

According to the invention, this object is achieved in the switch discussed at the outset in that at least one resistor is arranged directly on the inside of the housing and is connected in series with the switching mechanism between the cover part and the lower part in a switching position of the switching mechanism.

The object underlying the invention is completely achieved in this way. The inventor of the present application has recognized that it is surprisingly possible to apply a resistor directly to the inside of the electrically conductive cover part or to the electrically conductive lower part and to set the required resistance value for the self-holding function and / or the overcurrent sensitivity.

If this resistor is arranged in such a way that it is connected in series with the switch mechanism when it is below the response temperature, the resistor ensures that the new switch is sensitive to current. The resistance should have a value between approx. 50 mΩ and 30 Ω. This can e.g. by bismuth ruthenate, which can be applied to the lid part or the bottom part by screen printing.

However, if the resistor is connected in series with the switching mechanism when it is above the response temperature, i.e. has opened the circuit, it ensures a self-holding function. In this case, the resistance value should be approx. 10 to 100 kΩ, which is achieved, for example, with barium titanate, which can be glued on with conductive adhesive or "sputtered on" by cathode sputtering.

The entire mechanical advantages that the generic switch provides can thus be retained, while in order to achieve the self-holding function and / or the overcurrent sensitivity, a correspondingly dimensioned resistance layer only has to be applied to the inside of the cover part or lower part. This means that only a further manufacturing step is required to give the known switch the desired additional safety function. Compared to the known switches discussed further at the beginning, the design is thus simplified considerably, which also entails very low additional manufacturing costs. In series production, in which the generic switch is manufactured, only the cover part and / or the lower part then have to be replaced in order to implement the additional safety functions. Since not one or both of these safety functions are required in all applications, the generic switch, a switch with overcurrent sensitivity or a switch with self-holding function can be manufactured in the series production mentioned, depending on requirements, so that a kind of modular principle arises, which of course makes the whole Reduce manufacturing costs significantly.

In one embodiment, it is preferred if a further resistor is arranged directly on the inside of the housing, which is connected in series with the switching mechanism in another switching position between the cover part and the lower part.

It is advantageous here that a resistor is now connected in series with the switching mechanism between the cover part and the lower part in both switching positions of the switching mechanism, so that in one switching position for a self-holding function and in the other Switch position for an overcurrent sensitivity of the new switch is ensured.

Overall, it is preferred if the switching mechanism comprises a movable contact part which is supported by an electrically conductive spring washer which can be moved by a bimetallic snap disc and which, in a first switching position of the switching mechanism, rests on the inside against a contact area of the cover part, the spring washer engaging with it Edge supported on a contact area of the lower part.

The advantage here is that the known switching mechanism can also be used with the new switch, so that no additional design measures are required to manufacture the new switch. This also significantly reduces costs.

It is further preferred if, in a second switching position of the switching mechanism, the contact part rests on the inside against a further contact area of the lower part and the edge of the spring washer is in contact with a further contact area on the cover part.

The advantage here is that a changeover switch is provided, so to speak, but which can use the known switching mechanism. In the generic switch, it is only necessary to attach the insulating film so that the inside of the cover part is no longer insulated from the inside of the housing, i.e. from the edge of the bimetallic snap disk and / or the spring washer. The known switching mechanism thus connects the cover part and the lower part on the one hand in that the movable contact part on the cover part and the edge of the spring washer on the lower part abuts, while in the other switching position, the movable contact part on the lower part and the edge of the spring washer, possibly with the interposition of the edge of the bimetallic snap disc on the inside of the cover part. In this way, a very simple changeover switch is created, in which the individual resistors can now be arranged on the inside of the cover part and lower part as required.

The resistance can e.g. be designed as a disc and then be arranged in the contact areas of the movable contact part on the cover part or on the bottom part. On the other hand, it is possible to design the resistor as a ring and thus to arrange it at the contact areas for the edge of the spring washer on the inside of the cover part or of the base part. Other geometries are also conceivable with regard to the setting of the resistance value, e.g. Meandering or spiral shapes.

Depending on the desired function of these resistors, the resistance values must be set as described above by the geometric dimensions of the resistor and the specific resistance of the resistance material according to the known relationship.

Further advantages result from the description and the attached drawing.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combinations but also in other combinations or on their own without departing from the scope of the present invention.

An embodiment of the invention is shown in the drawing and explained in more detail in the following description.

The single figure shows a basic illustration of the new switch in longitudinal section.

In the single figure, 10 denotes a switch which comprises a housing 12 in which a temperature-dependent switching mechanism 13 is arranged. The housing 12 comprises a lower part 14 made of electrically conductive material and also a likewise electrically conductive cover part 15, which is electrically insulated from the lower part 14 by an insulating ring 16. The mechanical cohesion between lower part 14, cover part 15 and insulating ring 16 can e.g. be produced by a flanged edge (not shown for reasons of clarity), by gluing, by jamming or other suitable measures. However, this mechanical fastening does not play an important role for the present invention. For further information in this regard, reference is made to the publications mentioned at the beginning.

The switch 10 is connected via its underside 17 and a locking recess 18 on the cover part 15 to a circuit in which it is connected in series with a consumer to be protected.

The bimetallic switching mechanism 13 comprises a spring washer 21 which carries a movable contact part 22. A bimetallic snap disk 23 is placed over the movable contact part 22. In the switch position shown in Figure 1, the bimetallic snap disk is below its response temperature.

In this switching position, the spring washer 21 is supported with its edge 24 on a contact area 25 on the inside of the lower part 14 and presses the movable contact part 22 against a contact area 26 which is provided on the inside on a projection 27 of the cover part 15. This projection 27 corresponds to the locking recess 18 on the outside of the cover part 15.

In the switching state shown, a current flows from the cover part 15 via the movable contact part 22 and the spring washer 21 to the lower part 14.

If the temperature of the switch and thus the bimetallic snap disk 23 rises above its response temperature, the bimetal snap disk 23 changes from the convex shape shown to a concave shape, is supported on the inside against a further contact area 28 of the cover part 15 and is pressed then the movable contact part 22 against the force of the spring washer 21 away from the contact area 15.

The switching mechanism 13 then finally reaches its second switching state, in which the movable contact part 22 is supported on the lower part 14 on a further contact area 29, while the edge 24 of the spring washer 21 now optionally with the bimetallic snap disk 23 interposed on the contact area 28 is present. In this way, an electrically conductive connection between the cover part 15 and the lower part 14 is again established. The switch 10 thus works as a changeover switch.

In order to give the switch 10 an overcurrent sensitivity and / or self-holding function, resistors can optionally be attached to the contact areas 25, 26, 28, 29. In Figure 1 there is a resistance ring 31 at the contact area 25, a resistance disk 32 on the contact area 26, a further resistance ring 33 on the contact area 28 and a further resistance disk 34 on the contact area 29. In this way, in the rest position of the switching mechanism 13 shown in FIG. 1, the resistance disk 32 and the resistance ring 31 are connected in series with the switching mechanism 13 between the cover part 15 and the lower part 14, thus causing the new switch to be sensitive to overcurrent.

In the other switching position (not shown) of the switching mechanism 13, the resistance disk 34 and the resistance ring 33 are now in series with the switching mechanism 13 between the cover part 15 and the lower part 14, thus ensuring a self-holding function.

Of course, it is not necessary to design all four resistors 31, 32, 33, 34 in the new switch. For example, are sufficient to provide only the resistors 32 and 33 on the cover part 15 or only the resistors 31 and 34 on the lower part 14.

In this way, a kind of modular principle is possible in which, depending on the desired safety function, e.g. the lower part 14 remains unchanged, while the cover part 15 is equipped with one or both of the resistors 32 and 33. On the other hand, it is of course also possible to design the cover part 15 without resistance and, depending on the desired safety function, to provide the lower part 14 with one or both of the resistors 31 and 34.

Of course, when selecting the values of the resistors 31, 32, 33, 34, the safety function to be provided by this must be taken into account.

The resistance disc 32 "responsible for overcurrent sensitivity" on the cover part 15 is e.g. Made from bismuth ruthenate, has a diameter of 1.5 mm and a layer thickness of 0.05 mm, which results in a resistance value of approx. 4 Ω, which is suitable for overcurrent sensitivity. On the other hand, the resistance ring 31, which is also made of bismuth ruthenate, has an outer diameter of 9 and an inner diameter of 8 mm, so that it has a total resistance of 0.5 Ω at a thickness of 0.05 mm, which also has a Provides overcurrent sensitivity.

The resistance disc 29 responsible for self-retention is e.g. made of barium titanate and is a round disc with a thickness of 1 mm, which is glued on with conductive adhesive. Alternatively, e.g. conductive plastic can also be used.

The resistance value of the resistance disk 29 is set in accordance with the known geometric relationships so that it is 10 to 100 kΩ in the warm state. A corresponding resistance value can also be achieved by suitable dimensioning of the resistance ring 28. It is also possible to sputter the barium titanate or a comparable PTC semiconductor by sputtering.

It should be noted that instead of bismuth ruthenate as the resistance material, e.g. Ru oxide or Ag-Pd-Ag oxide can also be used.

Claims (10)

Switch for opening and / or closing a circuit, with a temperature-dependent switching mechanism (13) and a housing (12) accommodating the switching mechanism, which has an electrically conductive lower part (14) and an electrically conductive cover part (15) that closes the opposite the lower part (14) is electrically insulated, the switching mechanism (13) depending on its temperature making an electrical connection between the cover part (15) and the lower part (14) and the circuit on the one hand with the cover part (15) and on the other hand with the Lower part (14) can be connected,
characterized in that at least one resistor (31, 32, 33, 34) is arranged directly on the inside of the housing (12), which in a switching position of the switching mechanism (13) is in series therewith between the cover part (15) and the lower part (14) is switched. Switch according to Claim 1, characterized in that a further resistor (31, 32, 33, 34) is arranged directly on the inside of the housing (12), which in another switching position of the switching mechanism (13) is in series with the latter between the cover part (15 ) and lower part (14) is switched. Switch according to Claim 1 or 2, characterized in that the switching mechanism (13) comprises a movable contact part (22) which is carried by an electrically conductive spring washer (21) which can be moved by a bimetallic snap disc (23) and in a first switching position of Switch mechanism (13) rests on the inside on a contact area (26) of the cover part (15), the spring washer (21) being supported with its edge (24) on a contact area (25) of the lower part (14). Switch according to Claim 3, characterized in that the resistor (32, 31) is arranged on the contact area (26, 25) on the cover part (15) or on the lower part (14). Switch according to claim 3, characterized in that the movable contact part (22) in a second switching position of the switching mechanism (13) rests on the inside against a further contact area (29) of the lower part (14) and the spring washer (21) with its edge (24) is in contact with a further contact area (28) on the cover part (15). Switch according to Claim 5, characterized in that the resistor (33, 34) is arranged on the further contact area (28, 29) on the cover part (15) or on the lower part (14). Switch according to claims 2, 3 and 5, characterized in that both resistors (32, 33; 31, 34) are arranged on the cover part (15) or on the lower part (14). Switch according to claims 3 and 5, characterized in that the resistor (32, 34) is designed as a disc and on the contact area (26) on the cover part (15) and / or the further contact area (29) on the lower part (14) is glued on. Switch according to claims 3 and 5, characterized in that the resistor (31, 33) is designed as a ring and on the contact area (25) on the lower part (14) and / or the further contact area (28) on the cover part (15) is preferably applied by screen printing. Switch according to one of the resistors (1 to 7), characterized in that the resistor (31, 32, 33, 34) is applied by sputtering.

Images