EP0557744B1 - Thermostatic switch - Google Patents

Abstract

In order to create a thermostatic switch which consists of a small number of individual parts, can be produced simply in production engineering terms and as completely automatically as possible and is overall of simple design, the invention proposes a thermostatic switch which has two connecting parts which are mounted on a carrier part, one of which carries a fixed contact and the other of which is connected in a high-impedance manner to a moving contact which can be switched by a bimetallic element, the carrier part being a ceramic part and the connecting parts in each case engaging virtually completely around the carrier part in a force-fitting manner. <IMAGE>

Description

The present invention relates to a self-holding thermal switch with two non-positively attached connecting parts to a support part, one of which has a fixed contact, while the other is connected to a movable contact switchable by a bimetal element, the fixed contact, the movable contact and the bimetal element forming a switching mechanism , The support part is a ceramic part, and a heating resistor is electrically connected in parallel to the switching mechanism.

Such a self-holding thermal switch is known from DE-A-35 39 425.

The invention is based on so-called open thermal switches, which are installed, for example, in electrical heating devices, such as electrical radiators, hair dryers or the like, and are said to lead to a shutdown in the event of excess temperature. In the case of such switches, it is also desirable that, if the device malfunctions, clocking, ie switching the device on and off again, is prevented. Such clocking can occur if, as a result of a malfunction of the device, an overtemperature arises, which usually affects the temperature switch and its active switching element is a bimetallic element, opens so that no further current flow takes place and cooling can take place, through which the switch closes again, whereupon an overtemperature occurs again due to the malfunction of the device and the switch opens again. For this purpose, provision is made to arrange a resistor in parallel with the switch. Thick film resistors or PTC thermistors are known here, which are fixed to the switch, for example by clamping, by shrink sleeves or the like.

For example, DE-A-32 31 136 shows a bimetal switch with an insulating support part, in which connection elements are fixed, for example by the plastic support material being injection molded around the connection elements. Tongues are bent from the connecting elements, which carry the fixed and the movable contact. A thick-film resistor in the form of a flat, conductively coated ceramic plate is arranged below the supporting part and has rigid connecting lugs which are soldered to the actual connecting lugs of the switch.

In addition to the aforementioned elements, the switch naturally also has a spring element carrying the movable contact button and a bimetallic disc which effects the switching process.

Overall, the switch is complex. It is complex to manufacture. Assembly processes must be carried out by hand. In addition, it is disadvantageous that the switch consists of a variety of different materials, namely in addition to the metal sheet of the terminal lugs of the actual switch made of plastic, ceramic, a conductive thick layer. Disadvantageous is also that the bimetallic element is fixed both at its ends and in the center, which reduces its switching action and it can also be exposed to permanent forces which can change the switching point.

DE-A-35 39 425 shows a generic thermal switch. In this case, a thin insulating ceramic plate is arranged between tines bent out of connecting lugs and soldered to them. The ceramic plate is in turn metallized, a spring element of the movable contact is fixed to a connecting lug, while the other connecting lug is provided with the fixed contact button. A plunger or bolt is fixed in the middle of the spring element, for example by means of a rivet which projects through a bimetallic disc which rests on the ceramic part. The ceramic part is also metallized, so that the metallization forms the high-resistance parallel resistor for keeping the switch open after opening by the bimetal element. In practice, this switch only caused problems. It could not be realized in practice. It is again complex, since the insulating ceramic plate must also be provided with a conductive coating. The breakthrough through which the plunger centering the bimetal disc protrudes weakens the already thin ceramic plate, so that it can easily break. The switching path of the bimetallic disc is again limited by the central definition. The spring action and thus the switching action of the spring carrying the movable contact is also impaired by the rivet located on it.

Another self-holding thermal switch with a corresponding switching mechanism is known from US-A 4,703,928. In this thermal switch, the two connection parts are connected to one another by two bolts which run parallel to one another and are electrically connected in parallel with the switching mechanism. One or both of the two bolts are said to be made of PTC thermistor material, and on the other hand, it is expressly mentioned in this US patent that one of the two bolts can be made of an insulating material in order to ensure that the thermal switch is held mechanically.

When assembling the known thermal switch, the two connecting parts must be adjusted by moving the bolt so that the switching mechanism switches reliably.

The invention is therefore based on the object, while avoiding the disadvantages of the known switches, of creating an open, self-holding switch which consists of a few individual parts, is itself of simple design and can be produced in a simple and largely automated manner in terms of production technology.

In the case of the thermal switch mentioned at the outset, this object is achieved in that the support part is a block-shaped or cuboid-shaped PTC thermistor, which the connection parts each grip almost completely in a non-positive manner.

Because the connecting parts each grip the support part almost completely non-positively, a simple automatic manufacture of a simply designed switch is made possible. A reliable hold is achieved without the need for openings or bores for fixing rivets or the like in the ceramic supporting part. Such breakthroughs are only complex and can hardly be produced with the desired accuracy. You would continue to weaken the support member.

The support part is itself designed as a PTC thermistor and as such carries the connection elements. The supporting part has the shape of a block or cuboid, which in particular is not too thin, but has a thickness that is not substantially less than half the width of the cuboid, preferably above half the dimension of the width of the cuboid. The PTC thermistor itself takes over the supporting function without the risk of breakage or damage. In a specific embodiment, it is provided for fixing the connection lugs on the support part PTC thermistor that lugs of the connection parts encompass the support part almost completely. For further security, a preferred embodiment provides that the connecting straps are soldered to the PTC thermistor.

A preferred development is characterized in that tabs formed by at least one connecting part are provided by U-shaped punched lines.

Alternatively, it can be provided that one leg of a connecting part is bent by 180 ° under another leg of the connecting part and holds a movable contact made of bimetal between the two parts, or that on one connecting element one leg is 180 ° below another Leg is bent and both a movable contact and a switching bimetallic element are fixed between the two legs. In the former embodiment, the active element, the bimetal element, thus carries the movable contact button itself, while in the latter embodiment, a bimetal element acts on a spring carrying the movable contact button. In both cases, a preferred development for fixing the corresponding parts provides for jamming of movable contact and, if necessary, bimetallic element against the leg bent by 180 ° by means of a bent tab, wherein additional soldering can optionally be provided.

While in principle the bimetallic disc, as is known per se in the prior art, can also be mounted in the center, either by pressing against the spring with the center and with its edge being supported on a rigid abutment, or vice versa, see the aforementioned configurations before that the bimetallic element is only fixed on one side at the edge and causes the switching effect with the diagonally opposite edge. This also avoids openings in the ceramic part to accommodate central centering or fastening elements for the bimetallic disc.

A further preferred embodiment provides that the bent tab is punched out of the leg under which the leg was bent by a U-punching.

Figur 1

einen erfindungsgegemäßen Thermoschalter in Seitenansicht;

Figur 2

den Schalter der Figur 1 in Draufsicht, wobei teilweise mehrere Ebenen dargestellt sind;

Figur 3

den Schalter der Figuren 1 und 2 in Stirnansicht;

Figur 4

das den beweglichen Kontakt tragende Anschlußteil; und

Figur 5

das Anschlußteil für den Festkontakt.

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

Figure 1

a thermal switch according to the invention in side view;

Figure 2

the switch of Figure 1 in plan view, partially several levels are shown;

Figure 3

the switch of Figures 1 and 2 in front view;

Figure 4

the connector carrying the movable contact; and

Figure 5

the connector for the fixed contact.

In the exemplary embodiment shown, the thermal switch 1 according to the invention has, as a supporting part 2, a PTC thermistor in the form of a cuboid based on barium titanate or solid solutions of barium titanite and strontium titanate with further additives.

At a distance from each other, two connecting parts 3, 4 are fixed on the PTC thermistor 2. The connecting parts 3, 4 are shown wound up in detail in FIGS. 4 and 5.

The connecting part 4 carries a fixed contact 6, while the connecting part 3 in the exemplary embodiment shown holds a movable contact 7 which can be switched by a bimetallic element 8 likewise fixed on the connecting part 3. While the bimetallic element could in principle also be fixed, for example, with its center point to an arm 11 projecting over a spring element 9 of the movable contact 7 (similar to the fixing in DE-A-35 39 425), in the exemplary embodiment shown it is on one side (at 12 ), while it projects freely from there over its entire length. The arm 11 provided with reinforcing beads 10 thus protects the sensitive switching mechanism 7, 8, 9, in particular when the switch is installed in a device to be protected by it, against contact which could lead to a change in the switching characteristic.

The switch works in a manner known per se of a self-holding switch. If the ambient temperature, be it external, be it so high due to excessive power supply and heating of the conductive parts that the switching temperature of the bimetallic element 8 is exceeded, this switches from the contact 6 and 7 shown in FIG. 1 permitting low temperature position in its high temperature position, in which it lifts the movable contact 7 from the fixed contact 6. If the low-resistance connection via the contacts 6, 7 is interrupted in this way, there is a greater current flow from the connecting straps 13, 14 via the PTC thermistor 2, which is heated thereby and through its heat keeps the bimetallic element 8 in its temperature position and thus the contacts 6, 7 in the open position.

The connecting part 4 is T-shaped. A middle leg 21 forms the connecting lug 22 of the connecting element 4 and a support surface 23 for the PTC thermistor 2. A T-web 24 of the T-shaped connecting element 4 is bent at 90 ° at lines 26, 26a, 27, 27a, whereby side walls 28, 28a and cover parts 29, 29a for the PTC thermistor 2 are formed. The PTC thermistor 2 can be held by these parts or walls 23, 28, 28a, 29, 29a which are bent 90 ° along the lines 26, 26a, 27, 27a. Preferably, however, the connecting element 4 is soldered to the PTC thermistor in the sections 23, 28, 28a, 29, 29a comprising the PTC thermistor 2. At the ends of the T-web 24 and the sections 29, 29a, tabs 31, 31a are formed which extend parallel to the central T-leg 21 and which, after the connecting element 4 has been bent, come to lie parallel to one another in the manner described. On them a contact button 32 is fixed (welded) as a fixed contact 6.

The further connection element 3 also consists, like the connection element 4, of a flat material with a metal sheet. In the coiled, ie not bent state, which is shown in FIG. 4, it has the basic shape of a cross 41. A first leg 42 of the cross 41 forms the arm 11 projecting above the switching elements (spring element 9 with movable contact, bimetal element 8). The leg or arm 43 opposite this is 180 ° (FIG. 1) under the central part 44 of the cross 41 and the leg 42 bent and forms a lower holding part for the switching elements - spring element 9 and bimetallic element 8. These are held clampingly between it and a tab 47 punched out of the leg 42 by a U-shaped punching 46. For additional securing, soldering can be provided. The flap 47 is for this purpose after bending the leg 42 against it downwards (bent towards the PTC thermistor 2), so as to fix the bimetallic element 8 and the spring element 9 between it and the leg 42.

Further legs 51, 51a extend from the middle part 44 of the cross perpendicular to the legs 42, 43 in opposite directions. At bending lines 52, 52a, these are bent downwards by 90 °. They also have further bending lines 53, 53a at a greater distance than the distance of the bending line 27 and 26 or 26a and 27a - corresponding to the thickness of the PTC thermistor 2 - at which the legs 51, 51a in the same direction contribute to the bends 52, 52a are bent. In this way, the bent legs 51, 51a enclose a rectangular contour. The free ends of U-shaped punchings 54, 54a are located at a distance from the bending lines 53, 53a, by means of which tabs 57, 57a which are connected to the legs 51, 51a and which are also formed around the bending lines 56, 56a are formed in the case of bending lines 56, 56a. 56a are bent in the same direction and even at 58, 58a - at a distance from the bending lines 56, 56a, which corresponds to just half the width of the PTC thermistor 2 - are again bent in opposite directions, so that the free ends 59, 59a of the tabs 57, 57a are parallel abut each other. The free ends 59, 59a can optionally be welded together. As a result of this shaping, as can be seen from FIG. 1, the PTC thermistor 2 is gripped and held by the connecting part 3 at a distance from the connecting part 4, with additional securing soldering between the connection part 1 and the PTC thermistor 2 can also be provided. On the free leg 51a extends parallel to the tab 43, a connecting tab 61, on which the further contact to the switch according to the invention can be made.

The switch according to the invention consists of a few parts, namely from the PTC thermistor 2 forming a supporting part, the connecting parts 3, 4, the bimetallic element 8, the spring element 9 and the contact buttons 7, 32. The latter are firmly connected to the spring element 9 or the art-fitting part 4 how welded or soldered.

The switch according to the invention is also produced in a simple and inexpensive manner and can be carried out fully automatically.

The connecting parts 3, 4 are punched out of sheet metal with the contour shown in FIGS. 3, 4. At the same time, the eyelets 30, 60 on the connecting parts 22, 61 and the U-shaped punchings 46, 54, 54a are made. Then reinforcing beads 50 are stamped into the arm 11 or the leg 42 and the middle part 44 of the connecting part 3. At the connecting part 3, the bending of the leg 43 and the bending at the bending lines 53, 53a, 56, 56a, 57, 57a continue, as in the same way the bending at the bending lines 26, 26a, 27, 27a at the connecting part 4. On the connecting part 4, the contact button 43 is attached in a further step, while on the connecting part 3 the switching elements - bimetallic element 8 and spring element 9 are fixed with the contact button, by inserting them between the end of the leg 42 and the tab 47 and by bending the latter between this and the leg 42 are clamped, while still a additional securing can be done by soldering. Finally, the pre-bent connecting parts 3, 4 are pushed over the supporting part 2 (PTC thermistor), continue to be non-positively pressed with this and optionally additionally soldered.

Claims (10)

1. Self-locking thermal switch (1) including two connecting parts (3, 4) non-positively fixed to a supporting part (2), wherein one of the connecting parts comprises a fixed contact (6) whereas the other is connected to a movable contact (7, 9) switchable by a bimetallic element (8), the fixed contact (6), the movable contact (7, 9) and the bimetallic element (8) forming a switching device, the supporting part (2) being a ceramic part, and a heater resistor being connected in parallel to the switching device, characterized in that the supporting part (2) is a block-shaped or parallelepipedic PTC resistor almost completely encompassed by each connecting part (3, 4) in an exclusively non-positive manner.
2. Switch according to claim 1, characterized in that the supporting part (2) is a PTC resistor based on barium titanate and/or strontium titanate.
3. Switch according to any of the preceding claims, characterized in that lugs (51, 51a, 57, 57a; 23, 28, 28a, 29, 29a) of the connecting parts (3, 4) almost completely engage around the supporting part.
4. Switch according to any of the preceding claims, characterized in that the connecting parts (3, 4) are soldered to the supporting part (2).
5. Switch according to any of the preceding claims, characterized in that at least at one connecting part (3, 4) lugs (47, 57, 57a) formed by U-shaped punching lines are provided.
6. Switch according to any of the preceding claims, characterized in that a leg (43) of a connecting part (3) is bent by 180° below a further leg (42) of the connecting part (3) and holds between said two parts a movable contact (7, 9), which is formed from bimetal.
7. Switch according to any of claims 1 - 6, characterized in that on one connecting element (3) a leg (43) is bent by 180° below another leg (42, 43) and that a movable contact (9, 7) as well as a bimetallic element (8) switching the latter are fixed between both parts.
8. Switch according to claim 6 or 7, characterized by a bent lug (47) for the jamming fixing of the movable contact (7, 9) and optionally the bimetallic element (8) against the leg (43) bent around by 180°.
9. Switch according to claim 8, characterized in that the bent lug (47) is punched by a U-shaped punch-out (46) from the leg (42) below which the leg (43) was bent.
10. Switch according to any of the preceding claims, characterized in that an arm (11, 42) covering the contact area is provided with reenforcing beads (50).

Images