EP0778597A2 - Switch with a switching mechanism actuated at an excessive temperature - Google Patents

Abstract

The switch has a movable contact part (18). This cooperates at least with a first counter contact (19) forming, with this, a first switch contact (20). This contact is opened or closed in dependence in the temperature of the switch mechanism (16). The switch has at least a first heat resistor (35). This resistor is provided on the movable contact part (18). The switch may also have a second heat resistor which may also be formed on the movable contact part (18). This cooperates with a second counter contact forming a second switch contact. The second switch contact has a switch state opposite that of the first contact. The switch mechanism may be formed as an alternating switch. In a first switch state, in which the first switch contact is closed, the first heat resistor is connected in series between switch terminals. In a second switch state, in which the second switch contact is closed, the second resistor is connected in series between a different pair of terminals.

Description

The present invention relates to a switch with an overtemperature switching mechanism, on which a movable contact part is arranged, which interacts at least with a first counter contact and forms a first switching contact with it, which is opened or closed depending on the temperature of the switching mechanism, and with at least a first heating resistor.

Such a switch is known from DE-OS 37 10 672.

The known switch is a temperature monitor for an electrical consumer and comprises a bimetallic switching mechanism which opens at excess temperature and to which the heating resistor is connected in parallel.

The task of the known temperature monitor is to interrupt the flow of current through the electrical consumer if this consumer is too high a temperature. For this purpose, the known temperature monitor is connected in series with the consumer, so that the temperature monitor is flowed through by the current flowing through the consumer, the bimetal switchgear and thus the switch contact being closed at temperatures below the response temperature.

If the temperature of the consumer now exceeds a predetermined limit value, the bimetallic switching mechanism that is in thermal contact with the consumer suddenly opens its contacts by a bimetallic snap disk snapping around inside the bimetallic switching mechanism. The current now flows through the heating resistor connected in parallel with the switching mechanism, which has such a large resistance that the current is now much lower than the original operating current, so that the consumer is virtually switched off. Due to the heat in the heating resistor, the bimetallic snap disk is further heated so that it remains held in its position with the contacts open, so that an automatic restart is prevented when the consumer cools, which leads to a so-called contact flutter with periodic restart - and switching off could result.

In order to keep the size of the known temperature monitor small, the parallel heating resistor is in the Housing of the bimetal rear derailleur integrated. The housing comprises a pot-shaped lower part and an associated cover part, which can either consist of insulating material or of an electrically conductive resistance material.

The bimetallic snap disk and a spring washer are arranged in the housing part and carry the movable contact part, to which a fixed mating contact is assigned, which is carried by the cover part. The spring washer presses the movable contact part against the fixed counter contact and at the same time serves to forward the current flowing through the contacts to the base part, to which a first external connection is fastened. The second external connection of the known temperature monitor is arranged on the cover part and is in electrically conductive contact with the fixed mating contact of the bimetallic switching mechanism through the cover part. The spring bimetallic snap disk acts on the spring washer, which snaps suddenly when a certain response temperature is exceeded and thereby lifts the movable contact part from the fixed mating contact, so that the current flow through the bimetal switching mechanism is interrupted. The current now flows through the heating resistor connected in parallel and thus causes the self-retention already explained. The heating resistor can either consist of the resistance material of the cover part or can be printed on the cover part if it is made of insulating material.

In the known temperature monitor it is disadvantageous that in the embodiment where the cover part is made of electrically conductive resistance material, an insulating sleeve between the cover part and the base part is required in order to ensure a defined current path. Another disadvantage is that the housing in this embodiment none is able to absorb high pressures. If, on the other hand, the heating resistor is formed by a printed resistance path, it is disadvantageous that this resistance path must be formed spirally and / or in arcs in order to achieve the desired current profile. The disadvantages relate to the high manufacturing costs in both cases.

Another temperature monitor is known from DE-OS 41 42 716. This temperature monitor comprises a bimetallic switching mechanism which opens in the event of overtemperature or overcurrent, to which a first heating resistor is connected in parallel and with which a second heating resistor is connected in series. The heating resistor connected in series ensures current monitoring. If the current through the consumer and thus through the bimetal switching mechanism reaches a predetermined limit value, the heating resistor connected in series heats up to such an extent that the bimetal switching mechanism finally reaches and opens its response temperature. In this case, the self-retention takes place in the same way as already described above.

The heating resistor connected in series is arranged as an etched or stamped part or as a film printed with a resistor in the immediate vicinity as well as thermal and electrical contact with the spring washer of the bimetallic switching mechanism so that it comes to rest in the bottom part of the housing.

In addition to the complex assembly of the known temperature monitor, it is also disadvantageous that the etched or stamped parts used here as heating resistors require an additional insulating component between themselves and the housing base, with an additional, externally mounted further high-impedance resistor usually being added in series for reasons of resistance setting the series resistor mentioned is required, which increases the overall manufacturing costs.

Proceeding from this, it is an object of the present invention to develop the switch mentioned at the outset in such a way that as few components as possible are required, so that the new switch can be produced quickly and inexpensively.

According to the invention, this object is achieved in that the first heating resistor is provided on the movable contact part.

The object underlying the invention is completely achieved in this way. With the new switch, it is no longer necessary to provide the heating resistor as a separate component and, if necessary, to mount it in the housing with the interposition of an insulating part. A first advantage of the new switch is that the number of components is significantly reduced, in addition to the contact part required anyway, no further components are required to implement the heating resistor and possibly an insulating layer. A second advantage of the new switch, however, results from the simplified assembly, since now only the contact part to be installed anyway has to be inserted into the switch, as a result of which the heating resistor is also installed, so that additional assembly steps during production are eliminated.

This heating resistor can now be used depending on the circuit for a self-holding function, overtemperature protection or just for preheating to set the switching point, for which purpose it must be connected in series with the switchgear between the switch's external connections, either when the switchgear is open or closed this will be explained in more detail below using the specific examples.

It is preferred if a second heating resistor is provided, which is also formed on the movable contact part, which cooperates with a second mating contact and forms a second switching contact with it, which has a switching state opposite to the first switching contact.

The advantage here is that the second heating resistor is also implemented on the contact part, so that switches with overtemperature and overcurrent protection can be constructed much more simply since considerably fewer components are required. As a result, the costs are reduced not only because of the reduced stockkeeping and the smaller number of components, but also because of the simplified assembly.

It is preferred if the switching mechanism is designed as a two-way switch, in a first switching state in which the first switching contact is closed, the first heating resistor is connected in series between external connections of the switch, and in a second switching state in which the second switching contact is closed, the second heating resistor is connected in series between the external connections.

This design of a switching mechanism as a changeover switch is already known from the unpublished German patent application 195 27 254. There, however, the heating resistors are not arranged on the contact part, but are provided as separate components. In contrast, in the new design of the new switch, particularly few components are provided in order to implement both overtemperature and overcurrent protection. In addition to the switching mechanism and the contact part, only two counter contacts must be provided, which are usually suitably arranged on the housing of the switch.

In one embodiment, it is preferred if the movable contact part is made of resistance material in at least one resistance area.

The advantage here is that the resistance value of the heating resistors can be determined by the geometry and the material. For example, constantan or other suitable alloys, PTC thermistor material or other suitable ceramics, doped semiconductor materials, graphite etc. can be used as the resistance material. The choice of material and geometry means that the new switches can be easily adapted to the required response values with regard to latching or overcurrent protection or preheating. Switchgear with different response parameters can thus be constructed in the manner of a modular system, with different contact parts being used depending on the requirements.

In a further exemplary embodiment, it is preferred if the movable contact part is coated at least in regions with resistance material.

It is advantageous here that resistors can also be arranged on already existing contact parts without the contact parts having to be redesigned. These resistors can be provided, for example, in thick-film or thin-film technology, as a carbon resistor or, for example, by sputtering on as a PTC resistor. On the other hand, it is also possible to produce new contact parts which are formed with a plate on their side facing the countercontact in order to be able to provide a correspondingly large area for the formation of the resistance.

Overall, it is preferred if the switching mechanism comprises an electrically conductive spring element which carries the movable contact part and is mechanically and electrically connected to it via a contact area, the heating resistor between the contact area and a contact surface with which the contact part comes into contact with the counter contact.

This measure has the advantage known per se that the contact part is moved on the one hand via the spring element and on the other hand electrically contacted, so that the structure is also significantly simplified as a result. The spring element can either be a bimetallic snap disk or a spring washer working against the bimetal snap disk. In the case of a change-over switch, for example, the bimetallic snap disk in one switching position and the spring washer in the other can provide the electrical connection of the movable contact part to the external connections.

It is further preferred if the contact part is made almost entirely of resistance material and the resistance value of the heating resistor is determined by the geometry of the contact part between the contact area and the contact surface and the specific resistance of the resistance material.

This measure is also advantageous in terms of production technology, since the entire movable contact part can be produced from a single material, so that production can be carried out very easily and inexpensively. It is then only necessary to pay attention to the geometry of the movable contact part in the area between the contact surface and the contact area in order to be able to set the correct resistance value of the heating resistor for the respectively valid specific resistance.

On the other hand, it is preferred if the resistance layer forms the contact area and / or the contact area.

The advantage here is that a series connection between the contact part, the heating resistor, the mating contact and the electrically conductive spring element is achieved in a simple manner. Depending on the geometric conditions, the resistance layer be applied to the support area or on the contact surface, so that existing contact parts can be provided with a heating resistor in a simple manner.

It is preferred if the spring element is a spring washer, which works against a bimetallic snap disk, and the switch comprises a housing with an electrically conductive lower part, in which the switching mechanism is arranged, and a cover part closing the lower part, on which the first Counter contact is arranged, wherein the spring element presses the contact part against the first counter contact and is supported on the inside on the lower part.

The advantage here is that a simple mechanical structure is achieved, as is known per se from the prior art. Such switches are also known as encapsulated switches, in which the switching mechanism is protected against external influences, contact being made via the lower part and the cover part, which is either itself electrically conductive or consists of an insulating material and a plated-through hole to the first mating contact having.

It is further preferred if the second mating contact is arranged on the bottom of the lower part.

The advantage here is that a bimetal switching mechanism known per se from the design can be used which, in its switching position assumed at excess temperature, now presses the movable contact part downward onto the second mating contact provided there.

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.

Fig. 1

eine geschnittene Seitenansicht eines ersten Ausführungsbeispieles des neuen Schalters; und

Fig. 2

in einer Darstellung wie Fig. 1 ein zweites Ausführungsbeispiel des neuen Schalters.

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

Fig. 1

a sectional side view of a first embodiment of the new switch; and

Fig. 2

in a representation like Fig. 1, a second embodiment of the new switch.

In Fig. 1, 10 denotes a switch which comprises a housing 11 with a lower part 12 and a cover part 13. The lower part 12 has a flanged edge 14 through which the cover part 13 is pressed onto a shoulder 15 of the lower part 12, so that an encapsulated housing 11 is formed overall.

Arranged in the interior of the lower part 12 is a bimetallic switching mechanism 16 which comprises a spring element in the form of a spring washer 17 which carries a movable contact part 18. A mating contact 19 is assigned to the movable contact part 18 and is arranged on the inside of the cover part 13. The movable contact part 18 and the counter contact 19 form a switch contact 20.

The spring washer 17 is supported with its edge 21 on the bottom 22 of the lower part 12 in order to press the contact part 18 against the mating contact 19.

A bimetallic snap disk 23 is placed over the contact part 18 and, in the state shown in FIG. 1, is below its response temperature.

On the inside of the cover part 13, a heating resistor 24 is provided, which is in electrical connection via a contact ring 25 with the shoulder 15 of the lower part 12 made of electrically conductive material. Via an inner contact ring 26, the heating resistor 24 is electrically connected to the counter contact 19, which is connected through a rivet 28 to a first connection 28 provided on the outside of the cover part 13 made of insulating material. A second connection 29 of the switch 10 is formed by the lower part 12 itself.

Due to the selected construction, the heating resistor 24 is connected in parallel to the bimetallic switching mechanism 16 and is electrically bridged by it in the switching state shown in FIG. 1. If the bimetallic snap disk 23 is now heated to a temperature above its response threshold, it snaps from the convex shape shown into a concave shape and presses the movable contact part 18 away from the mating contact 19 so that it lifts off from it. For this purpose, the bimetallic snap disk can be supported on the inside of the cover part 13. If the bimetallic snap disk 23 can come into contact with the heating resistor 24, suitable insulation measures are to be provided, which are not shown in FIG. 1 for reasons of clarity.

In this open state, the current now flows through the heating resistor 24, which heats up and thus acts in the sense of a self-holding function, since it keeps the bimetallic switching mechanism 16 open.

The movable contact part 18 is a substantially cylindrical part with a centrally arranged annular shoulder 31, through which the contact part 18 is clamped between the spring washer 17 and the bimetallic snap disk 23. The annular shoulder 31 comes to rest with a support area 32 on the spring washer 17, as a result of which it is connected not only mechanically but also electrically to the electrically conductive spring washer 17.

Facing the counter contact 19, the contact part 18 has a projection 33, on which a resistance layer 34 is provided, which forms a heating resistor 35 which, in the switching state shown in FIG. 1, is in contact with the counter contact 19 with its contact surface 36.

In the switching state shown in FIG. 1, the heating resistor 35 is flowed through by the current flowing through the switch 10, since it is connected in series with the bimetallic switching mechanism 16 between the external connections 28 and 29. The tuning of the resistance values of the heating resistors 24 and 35 is selected so that when the switch 10 is closed, the current essentially flows through the heating resistor 35. This heating resistor 35 can now either be used for preheating the bimetallic switching mechanism 16, so that the switching point can be set precisely. On the other hand, it is possible to set a current sensitivity through the heating resistor 35, so that when the current flows through the switching mechanism 10 too strongly, the response temperature of the bimetallic snap disk 23 is exceeded and the switch 10 opens the switching contact 20.

It should also be noted that the resistive layer 34 can be applied to the movable contact part 18 using thick-film or thin-film technology, as a carbon resistor, as a PTC element, for example by sputtering, or in any other suitable technique.

In a representation similar to FIG. 1, FIG. 2 shows a further switch 10 ', in which the cover part 13 consists entirely of insulating material and has no heating resistor.

The spring washer 17 carries a movable contact part 40, which cooperates not only with a first counter-contact 19 but also with a second counter-contact 41, which is arranged on the bottom 22 of the lower part 12. The contact part 40 has an upper projecting resistance area 42, which acts as a heating resistor 35 and is in contact with the mating contact 19 via the contact surface 36 when the switching state shown in FIG. 2 has been reached.

On its opposite side, the movable contact part 40 has a second projecting resistance region 43, which acts as a heating resistor 44 and takes over the role of the heating resistor 24 from FIG. 1. The resistance region 43 can be brought into contact with the second mating contact 41 via its contact surface 45, with which the movable contact part 40 forms a second switching contact 46.

In the construction shown in FIG. 2, the bimetallic switching mechanism 16 is designed as a changeover switch 47. For this purpose, the first mating contact 19 is connected to a contact layer 48 which is arranged on the inside of the cover part 13. If the temperature of the switch 10 'shown in FIG. 2 is increased above the response temperature, the bimetal snap disk 23 snaps again here and comes into contact with the contact layer 48. At the same time, the movable contact part 40 in FIG. 2 pressed down so that it comes into contact with the second mating contact 41 and closes the second switching contact 46 while the first switching contact 20 is opened.

Depending on the design of the change-over switch 47, the current flowing through the switch 10 'now flows from the external connection 28 via the contact layer 48 into the bimetallic snap disk 23 and from this either into the spring washer 17, which with its edge 21 is still in contact with this bimetal - Snap disk 23, or via the bimetal snap disk 23 and a support area 49 on the annular shoulder 31 in the contact part 40. From here, the current passes through the heating resistor 44 and the second counter-contact 41 to the external connection 29, so that the second Heating resistor 44 is connected in series with the bimetallic switching mechanism between the external connections 28, 29.

Characterized in that the bimetallic switching mechanism 16 is designed as a changeover switch 47, there is always a heating resistor 35 or 43 in series between the external connections 28, 29 of the switch 10 '. The heating resistor 35 connected in the idle state of the switch 10 'between the external connections 28, 29 serves to realize an overcurrent sensitivity or for preheating, while the heating resistor 44 realizes the self-holding function.

Of course, it is also possible to implement the switch 10 'without current sensitivity, for which purpose the heating resistor 35 would have to be dispensed with.

It should also be mentioned that the projecting resistance areas 42, 43 made of any suitable resistance material, such as. B. constantan, a conventional resistance alloy, a doped semiconductor material, a PTC ceramic or similar ceramics or graphite. The geometry of the contact part 40 between the contact surfaces 32 and 49 and the contact surfaces 36 and 45 is decisive for setting the resistance value of the respective heating resistor. Of course, the movable contact part 40 can be made entirely of a resistance material, which makes the production of the contact part 40 itself very simple.

Of course, it is also possible to provide the contact part 40 with projections 42, 43 instead of the resistance regions 42, 43, which are provided with a resistance layer, so that the heating resistors are designed in the same way as the heating resistor 35 in FIG. 1.

Claims (11)

Switch with an overtemperature switching mechanism (16) on which a movable contact part (18, 40) is arranged, which interacts at least with a first counter contact (19, 41) and forms a first switching contact (20, 46) with the latter is opened or closed depending on the temperature of the switching mechanism (16), and with at least one first heating resistor (35, 44), characterized in that the first heating resistor (35, 44) is provided on the movable contact part (18, 40) . Switch according to claim 1, characterized by a second heating resistor (44, 35), which is also formed on the movable contact part (18, 40), which cooperates with a second counter-contact (41, 19) and with this a second switching contact (46, 20), which has a switching state opposite to the first switching contact (20, 46). Switch according to Claim 2, characterized in that the switching mechanism (16) is designed as a changeover switch (47), in a first switching state in which the first switching contact (20) is closed, the first heating resistor (35) in series between external connections (128 , 29) of the switch (10, 10 '), and in a second switching state in which the second switching contact (46) is closed, the second heating resistor (44) is connected in series between the external connections (28, 29). Switch according to one of claims 1 to 3, characterized in that the movable contact part (40) is made of resistance material at least in a resistance region (42, 43). Switch according to one of claims 1 to 3, characterized in that the movable contact part (18) is coated at least in regions with resistance material. Switch according to one of claims 1 to 5, characterized in that the switching mechanism (16) comprises an electrically conductive spring element (16, 23) which carries the movable contact part (18, 40) and with it via a support area (32, 49) is mechanically and electrically connected, the heating resistor (35, 44) being formed between the support area (32, 49) and a contact surface (36, 45) with which the contact part (18, 40) is in contact with the mating contact (19, 41) arrives. Switch according to claims 5 and 6, characterized in that the resistance layer forms the contact surface (36, 45) and / or the contact area (32, 49). Switch according to claims 6 and 4, characterized in that the contact part (40) is made almost entirely of resistance material and the resistance value of the heating resistor (35, 44) by the geometry of the contact part (40) between the contact area (42, 49) and the contact surface (36, 45) and the specific resistance of the resistance material is determined. Switch according to one of claims 6 to 8, characterized in that the spring element (17, 23) is a spring washer (17) which works against a bimetallic snap disk (23). Switch according to Claim 9, characterized in that it comprises a housing (11) with an electrically conductive lower part (12), in which the switching mechanism (16) is arranged, and a cover part (13) which closes the lower part (12) and on which the first mating contact (18) is arranged, the spring element (17) pressing the contact part (18, 40) against the first mating contact (18) and being supported on the inside on the lower part (12). Switch according to claims 10 and 2, characterized in that the second counter-contact (41) is arranged on the bottom (22) of the lower part (12).

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