EP0285927B1 - Thermostat - Google Patents

Abstract

The invention proposes a thermostat having a support supporting at least two connections, a moving contact (supported by an elastic connecting member operated by a bimetallic strip) being electrically connected to one connection and a stationary mating contact being electrically connected to the other connection, and it being possible to connect a low-resistance connection of the contact to the mating contact, under the influence of a small bimetallic plate, in which a block-shaped retaining part (19) rests with a resting surface (21) on at least one side of the support, in that a switching member (24), supporting the contacts or a contact (16), rests on the surface opposite the resting surface, at a distance from the support (2) and in that rivet structures (9, 27), for solid riveting of at least one contact (14, 16) or the switching member (24), are constructed on the retaining part (19). <IMAGE>

Description

The invention relates to a temperature switch according to the preamble of claim 1.

Such so-called open switches are known in a variety of designs. For example, the elastic connecting element carrying the movable contact can itself consist of bimaterial or, as is even more the case with more recent designs, a separate bimetallic plate can be present which acts on the connecting element for switching the movable switching contact. Furthermore, the switch can be designed as a so-called non-clocking switch, in which a high-resistance, heat-generating resistor is provided in parallel to the switchable electrical connection from one connection via a contact, the mating contact to the other connection, for example in the form of a thick-film resistor, a PTC element or the like , which is subsequently applied to the carrier or in any other way to an existing switch as an additional Part is provided or attached. The known carriers have complicated shapes, on the one hand to carry the circuit diagram in a suitable manner, and on the other hand to provide recesses or other configurations for the additional high-resistance. If the carrier is a ceramic part, it must first be shaped as such by pressing and then sintered. This leads to the fact that these individually shaped and sintered complicated carrier parts are quite imprecise and require large tolerances, so that either reworking or adjustments are required. For example, ceramic carrier parts of this type are reworked with diamond disks, which in turn are expensive. Alternatively, the carrier parts can consist of suitable thermosets. Then they can be manufactured true to size, but they have the disadvantage of insufficient thermal resistance. In addition, these thermosets exhibit poor expansion behavior, which acts on fastenings and rivets in such a way that damage can occur here. Switches with thermoset support parts can therefore only be used at low temperatures. In both of the aforementioned cases, connections and contacts, in particular the connecting part for the movable contact, are riveted directly to the support part with rivets. If the rivet forms the stationary counter-contact to a movable contact, the rivet loosens due to the different temperature expansion behavior of the carrier and the rivet, this in turn can lead to higher contact resistances from the contact surface of the contact rivet to the connecting tab riveted through them, which in turn leads to an additional stronger warming results.

A bimetal switch for switching electrical loads is known from US-A-2 298 928. A bimetal plate acts on a flexible switching element. At the movable end of the switching element, a contact is arranged, which is electrically connected to a connection. The switching element is riveted to a carrier with a spacer bolt. A mating contact with an electrical connection is also arranged stationary on the carrier. The contact of the switching element is raised against the spring force of the switching element by the bimetal plate depending on the temperature from the counter contact. The bimetallic plate is arranged on the carrier with two separate attachments. One of the two fastenings can be adjusted in height to enable calibration of the thermostat.

This known training is technically and structurally complex. Furthermore, an individual calibration is required for each thermostat.

GB-A-531 794 discloses a thermostat with a bimetallic section which makes the electrical connection. The bimetallic section is riveted to a carrier with a spacer bolt and has at its free end a contact head which meets an adjustable counter contact arranged on the carrier. Each contact is electrically connected to a connector. A bearing bush is inserted in the carrier to adjust the mating contact. A screw carrying the mating contact engages in an internal thread of the bearing bush, so that the thermostat can be calibrated by rotating it. A separate switching element is not provided.

The invention has for its object to provide a switch of the generic type which avoids the aforementioned problems and in particular enables simple construction and manufacture. It should be possible to attach the switching mechanism precisely, in particular with regard to matching the movable contact and counter-contact, the connecting member carrying the movable contact and, if appropriate, an additional active switching member without post-processing and readjustments for high-temperature-resistant switches.

According to the invention, the stated object is achieved in a switch of the type mentioned at the outset by the characterizing features of claim 1.

A block-shaped design of the holding part ensures a more precise alignment with respect to the carrier and optimal heat conduction due to the large contact surfaces. This ensures good reproducibility of the switching temperature. Furthermore, the graduated rivet formation provided on the holding part enables the bimetal plate to be held optimally. This results in the advantage that by adjusting the height of the wider section, the pretensioning of the bimetal plate can be optimally determined, and thus the switching temperatures can also be optimally determined. The distance between the wider section and the edge of the holding part must also be taken into account. In addition, the small number of parts allows optimal miniaturization of the switch and cost-effective production.

It follows from the overall configuration of the invention that the block-shaped holding part connects corresponding contact with the associated connecting element, it follows that the holding part itself is electrically conductive. It is therefore preferably made of a suitable metal and is designed as a rotating part on which the fastening pins for fastening the connecting part, contact or such a load-bearing connecting part are formed by means of rivets. According to the invention, a separate holding part for the corresponding elements of the switch is therefore provided in addition to the carrier, but with the rivet attachments and devices for fixing said elements are formed integrally with rivets. With the holding part according to the invention, the accuracy requirements are therefore taken over by the carrier, while the holding part used according to the invention is a dimensionally stable, high-temperature-resistant part.

The object according to the invention designed in this way now advantageously offers the possibility of designing the carrier in a completely cuboid and thus simple outer contour. The carrier can be formed from a carrier plate or a plurality of stacked carrier plates of cuboid shape. In any case, with such a cuboid configuration of the carrier, the aluminum oxide ceramic can be produced in the following manner: A large-area plate made of aluminum oxide ceramic is pre-pressed, from which the cuboid carrier parts are then punched out and sintered. This method is praiseworthy, it does not have to be pressed the individual parts in their complicated shape, as is the case with the prior art, but simple flat plates are produced, which can be made much more dimensionally. Although these cuboid or plate-shaped parts also have a shrinkage, they can be taken into account with sufficient accuracy. In particular, there are no curvatures as in the case of complicated shapes with elevations and depressions which are used in the prior art. Carrier parts made of aluminum oxide ceramic are hard and have good thermal conductivity.

To form the switch as a self-holding, a resistance track can be printed on the ceramic carrier, preferably on the side facing away from the switching mechanism. In the case of a carrier composed of two or more carrier plates, the resistance can preferably be arranged between them and thus protected.

PTC elements are oxide-ceramic resistance elements that are usually designed as cuboid plates. The solution according to the invention therefore creates the possibility of producing the carrier immediately from PTC material or, if there are several layers, of producing one of the layers from PTC material. It is thereby avoided that if the two connections can be bridged by a high-resistance resistor in addition to the actual switching mechanism, separate additional complicated devices with clamping devices or the like must be provided here. It has been found that when PTC material is used as the carrier, a plate thickness of 2 mm is sufficient to form a sufficiently stable carrier. In the configuration of the switch according to the invention, it is also possible to proceed in such a way that aluminum oxide ceramic is coated with PTC material and is sintered together and suitable metallizations are provided.

The bimetallic plate lies directly on the surface of the holding part and is penetrated by a wider section of a rivet attachment, the height of the wider section of the rivet attachment being penetrated, the height of the wider section of the rivet attachment corresponding at least to the thickness of the bimetallic washer while the connecting member is on the wider shoulder of the rivet attachment rests and surrounds a thinner section thereof. This ensures that the bimetallic sheet can be fixed and riveted directly with a separate elastic connecting link, without it being pinched at its attachment point, thereby adversely affecting its switching behavior (for example DE-GM 86 25 990). To avoid this latter disadvantage, it has already been proposed that small tabs are provided on the connecting members carrying the contact, under which the bimetallic plates have been arranged (for example EP-OS 58 372). These designs had the disadvantage that the complicated hooks, which are easily damaged, had to be provided in addition. In a further development it is provided that the connections at least partially encompass the carrier and optionally the holding part laterally by means of tabs. In this way, a relative definition of the individual parts is achieved before rivets are finally attached, thereby facilitating this.

In such switches, a high current flow - and thus low resistance - through the movable contact, which is designed in particular as a switching element in the form of a spring, is sought, which requires large cross sections and a high spring strength, which the high-temperature bimetal position (when opening ) counteracts, but this counterforce may not be sufficient, particularly with extensive miniaturization. In a preferred embodiment it is therefore provided that by means of a weaker counter-spring which counteracts the spring action of the switching element, the additional spring thus supports in particular the bimetallic action. The counterspring itself contributes in an extremely advantageous manner to increasing the cross-sectional area available for the leakage flux and thus to reducing the resistance without increasing the force to be returned by the bimetallic element, rather it reduces it.

In a further development it can be provided that the counter spring is connected at one end to the connecting member and engages with its opposite end on the carrier. This configuration further improves and supports the switching process against the spring force of the connecting element carrying the movable contact, in that the bimetallic element can be supported on the carrier at a location remote from the clamping point of the connecting element and thus better use of force can be made. This is particularly the case if such a bimetallic element is provided in addition to the bimetallic snap disc clamped with the connecting member. With this configuration, too, the cross section of the connecting and transmission link can be increased with only one bimetallic snap disc compared to the configuration mentioned above.

Fig. 1

eine Seitenansicht der bevorzugten Auführungsform des Schalters;

Fig. 2

eine Aufsicht auf den Schalter der Figur 1;

Fig. 3

eine Stirnansicht entsprechend der Pfeile III-III;

Fig. 4

eine Stirnansicht entsprechend der Pfeile III und IV in den Figuren 1 und 2.

Fig. 5

eine vergrößerte Darstellung des Festlegungsbereichs von Übertragungsglied für den beweglichen Kontakt und Bimetallelement;

Fig. 6

eine andere bevorzugte Ausgestaltung in Seitenansicht, in Schließstellung;

Fig. 7

die Ausgestaltung der Fig.6 in Öffnungsstellung;

Fig. 8

eine Aufsicht auf die Ausgestaltung der Figuren 6 und 7;

Fig. 9

eine weitere bevorzugte Ausgestaltung der Erfindung und

Fig. 10

eine Aufsicht auf die Ausgestaltung der Fig.9 entsprechend der Aufsicht der Fig.8.

Further advantages and features of the invention result from the claims and from the following description, in which an embodiment of the switch according to the invention is explained in detail with reference to the drawing. It shows:

Fig. 1

a side view of the preferred embodiment of the switch;

Fig. 2

a top view of the switch of Figure 1;

Fig. 3

an end view corresponding to the arrows III-III;

Fig. 4

an end view corresponding to the arrows III and IV in Figures 1 and 2.

Fig. 5

an enlarged view of the definition of the transmission member for the movable contact and bimetallic element;

Fig. 6

another preferred embodiment in side view, in the closed position;

Fig. 7

the configuration of Figure 6 in the open position;

Fig. 8

a supervision of the configuration of Figures 6 and 7;

Fig. 9

a further preferred embodiment of the invention and

Fig. 10

a supervision of the configuration of Figure 9 corresponding to the supervision of Figure 8.

The illustrated embodiment of the switch 1 according to the invention has a flat cuboid carrier 3 made of insulating material or high-resistance material. The carrier 2 preferably consists of hard aluminum oxide ceramic, which has good thermal conductivity. If the switch is to be designed as a non-clocking but self-adhesive switch, the carrier 2 can, for example, be printed with a resistive force or be made of a suitable PTC material.

In the exemplary embodiment shown, the carrier consists of two carrier plates 2a and 2b, one (2b) of which has a lateral fastening projection 2c with fastening openings 3. Instead, the carrier 2 could also be formed in one piece in the form of a one-piece cuboid. In addition, the attachment lug 2c on the carrier 2 can also be omitted if care is taken in a suitable manner for fixing the switch 1, for example by means of suitable fastening breakthroughs on the connections 4, 6 of the switch corresponding to the opening 3 (not shown here).

At both ends 7, 8, the connections 4, 6 are fixed by rivets 9, 11 which protrude through the carrier 2 or are formed integrally therewith. The connection 6 monitors the rivet 11 and carries on its connection end 12 the end 13 facing away from a stationary counter contact 14 for a movable contact 16 of the switch 1. The connection 6 furthermore has lateral straps 17 which at least partially encompass the carrier 2 and through which a certain fixation is effected before the riveting by means of the rivet 11, so that the riveting process is facilitated. The terminal 6 is flat from the mating contact to its terminal end 12, but could also be crimped instead, similar to how the other terminal 4 in the illustrated embodiment is crimped up by means of a crimping. In any case, it is desirable that the two connections 4, 6 lie in one plane. The connection 4 is fixed via the rivet pin 9 protruding through the support 2 in principle in the same way to the support 2 as the connection 6. The rivet pin 9 is formed in one piece on a block-shaped holding part 19 which rests on the side 2 of the support which also the stationary counter contact 14 is arranged. In the present case, this is the upper side of the carrier 2, the side of the carrier 2 opposite the riveted area of the connection 4. The block-shaped holding part 19 lies with its lower contact surface 21 on the carrier 2 and carries on its surface 22 opposite the contact surface 21 Bimetallic plate 23 and over this an elastic, the movable contact 16 supporting link 24 in the form of a flat spring. Bimetal plate 23 and connecting member 24 are riveted to the pot-shaped holding part 19 by a rivet head 26.

In particular, the bimetallic disk 23 is not tightly clamped and clamped between the block 19 and the connecting member 24, but only sufficiently defined, as can be seen from FIG. 5. A bimetallic plate 23 and Ver connecting member 24 protruding pin extension 27 of the holding part 19 is formed with sections of larger and smaller diameters. The bimetallic plate 23 has an opening which corresponds to the section with the larger diameter of the pin 27 and surrounds it. This section with a larger diameter just as high or slightly higher than the thickness of the bimetallic plate 23, so that, as said, this is not jammed between the surface 22 of the holding part 19 and the connecting member 24, but can freely perform its switching function without being too loose is or rattles.

The connection 4 also has the carrier 2 and here also the holding part 19 laterally encompassing tabs 28 for better fixing of the parts before final fixing by rivets. The movable contact 16 itself is welded to the connecting member 24, since riveting is problematic here.

The connections 4, 6 also have tapered portions 31, which serve as predetermined bending points, in order to avoid disadvantageous force transmission to the rivet points of the switch 1 and thus damage the same in the event of tensions or the like. The switch itself works in the usual way. It is shown in its low-temperature position, in which contact 16 and counter-contact 14 are pressed against one another under the action of the elastic connecting member and are in contact with one another, so that there is a low-resistance electrical connection between terminals 4 and 6. The bimetal plate 23 is bent in its low temperature position with its free end 29 downward from the connecting member 24 and in particular also largely relieved due to the clamping described. If the temperature rises above the changeover temperature of the bimetallic plate 23, it folds upward, so that its convex side is directed downward toward the carrier 2. The bimetallic plate 23 is supported on the surface 22 of the holding part 19 and lifts the connecting member with its free end 29 24 and thus the movable contacts 16 from the stationary counter contact 14, so that the low-resistance connection between the connections 4 and 6 is interrupted. In the event that the carrier 2 consists of PTC material, or has such (for example in the form of one of the two carrier parts 2a, 2b), there is still a high-resistance electrical connection between the connections 4, 6, which leads to the fact that at very low current flow, the PTC part heats up and thus generates heat which acts on the bimetallic plate 23 by radiation and conduction via the relatively massive holding part 19, so that it is held in its high-temperature position and the switch remains open until the power supply is external is interrupted.

In the embodiments of FIGS. 6 to 10, the same features and elements are denoted by the same reference symbols as in the embodiments described above. In this respect, reference is also made to the above explanations, so that they are not repeated.

In the embodiment of FIGS. 6 to 8, in addition to the bimetallic snap disk 23, a further bimetallic element 31 is provided, which with its end 32 is also clamped like the bimetallic element 23 and the connecting member 24 carrying the movable contact 16, and in any case preferably between the holding part 19 and the rivet head 26 The free end 33 of the bimetal element 31, on the other hand, is bent into a U-shape, so that the free leg 34 of the U-shaped fold 36 extends essentially parallel to the clamped leg 37, but directly above the upper side of the carrier 2. Between the two legs 34, 37 protrudes the free end of the bimetal element 23. The bimetal element 31 could also be provided instead of the bimetal element 23 and not only in addition.

When the temperature rises, the free end 34 of the bimetallic element 31 bends, which is bent under due to the U-shaped fold a strong internal tension is present, comes to rest on the upper side of the carrier 2 and then presses itself away from the latter when the temperature rises further, and in this way lifts the connecting part 24 of the movable contact 16 from the stationary counter contact 14 or supports it by lifting off the bimetal element 23.

With this configuration, the transmission element 24 with the cross section required for sufficient current transmission (through which the required low resistance is achieved), but the relatively large spring force associated therewith, can nevertheless be lifted safely and reliably with its movable contact 16 from the stationary counter contact 14. The cross section can in particular be designed such that the disk 23 could not lift the contact 16 from the counter contact 14 alone, but this is now made possible by the preferred embodiment explained.

In the embodiment of FIG. 9, during the production of the connecting member 24, lug-like parts 41 are punched out in one piece with it, which have a web 42 extending laterally from the connecting member 24 and a web 42 which is connected to the connecting part 24 only via the web 42 and extends parallel to the latter Counter spring section 43 has. The web 42 is bent perpendicular to the plane of the connecting member 24. The counter-spring section is likewise perpendicular to the web 42 and thus initially bent parallel to the connecting member 24 below it. Furthermore, with its free end region 44 it is bent further away from the connecting member 24 with respect to the connecting region determined by the width of the web 42, the distance of the free end region 44 of the counter spring from the connecting member 24 being greater in the relieving state than the height of the holding part 19 after clamping of the connecting member 24. In the manner already described, this presses under its own spring action with the movable contact 16 carried by it against the stationary counter-contact 14 and at the same time prestresses the counter-spring parts 43, the spring force of which is such is set to be less than the spring force of the link 24.

The bimetallic element 23 is clamped in the same way as in the above embodiments and engages between the space given by the webs 42. When the temperature rises, the bimetallic member 23 jumps over, presses against the connecting member 24 and lifts the contact 16 from the mating contact 14. It is supported in the configuration of FIGS. 9 and 10 by the counter-spring parts 43 which, due to their prestressing, press against the spring action of the connecting member 24. The connection is then interrupted by the jointly acting force of the bimetallic element and counter spring parts 43 that have jumped over. In this configuration, too, the cross section of the connecting member 24 can be made larger and thus a higher current flow can be achieved than would be the case if only the force of the bimetallic disk 23 were available for lifting off.

Claims (15)

1. Thermostat (1) with a support (2) carrying at least two terminals, an elastic switching element (24), a separate bimetallic plate (23) operating the switching element and a holding part (19) holding the switching element at one end and in spaced manner with respect to the support (2), one terminal (4) being connected to a contact (16) located on the movable part of the switching element (24) and the other terminal (6) is connected to a stationary opposite contact (14) and the switching element (24) is riveted to the holding part (19) with the rivets (9,26,27) of the holding part (19), characterized in that the holding part (19) has a block-like construction, that the bimetallic plate (23) rests directly on the face (22) of the holding part (19) facing the same and is traversed by a first portion with a larger diameter of a rivet shoulder (27) of a rivet (26,27), the height of the first portion of the rivet shoulder (27) corresponding at least to the thickness of the bimetallic plate (23), whilst the switching element (24) rests on the wider part of the rivet shoulder (27) and surrounds a second, smaller diameter portion thereof.
2. Thermostat according to claim 1, characterized in that at least one weaker return spring (43) acting against the spring action of the switching element (24) is provided.
3. Switch according to claim 2, characterized in that one end of the return spring (43) is connected at (42) to the switching element (24) and engages with its opposite end (44) on the support (2).
4. Thermostat according to claim 2 or 3, characterized in that the free end of the bimetallic plate (23) projects into a free space between the switching element (24) and the return spring (43).
5. Thermostat according to one of the preceding claims, characterized by a further bimetallic element (31) engaging on the support (2) between the rivet (26,27) and its contact (16) of the movable switching element (24) and under the action of its bimetallic property raising the movable contact (16) from the opposite contact (14).
6. Thermostat according to claim 5, characterized in that the further bimetallic element (31) is fixed on one end (32) with the switching element (24) of the movable contact (16) and is bent round in U-shaped manner with its other, free end (34) and engages there with the bend-over (36) on the support (2).
7. Thermostat according to one of the preceding claims, characterized in that the terminals (4,6) laterally at least partly engage round the support (3) and optionally the holding part (19) by means of clips (17,28).
8. Thermostat according to one of the preceding claims, characterized in that the outer contour of the support (2) forms a completely flat parallelepiped.
9. Thermostat according to claim 8, characterized in that the support has at least one supporting part made from a light metal oxide, particularly an alumina-ceramic.
10. Thermostat according to one of the preceding claims, characterized in that the support (2) has at least one PTC material supporting part.
11. Thermostat according to one of the preceding claims, characterized in that the movable contact (16) is welded to the elastic switching element (24).
12. Thermostat according to one of the preceding claims, characterized in that the support (2) comprises at least two superimposed supporting parts (2a,2b).
13. Thermostat according to one of the preceding claims, characterized in that the terminals (4,6) have weaknesses, tapers or the like (30) as predetermined bending points.
14. Thermostat according to one of the preceding claims, characterized in that a terminal part (2c) is constructed integrally with at least one part (2b) of the support (2).
15. Thermostat according to one of the preceding claims, characterized in that the rivets (9,27) are constructed integrally with the holding part (19).

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