EP0557744A1 - 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 invention relates to a thermal switch with two attached to a support member connecting parts, one of which has a fixed contact, while the other high impedance with a switchable by a bimetallic movable contact, wherein the support member is a ceramic part, is connected.

The invention is based on so-called open thermal switches, which are installed for example in electric heaters, such as electric radiators, hair dryers or the like and should lead to a shutdown at excess temperature. In such switches, it is further desired that, as far as the device has a malfunction, a clock, ie, each turn on and off the device is prevented. Such a clocking may occur if, due to a malfunction of the device, an excess temperature is generated, the temperature switch whose active switching element usually a bimetallic element is open, so that no further current flow takes place and a cooling can take place, through which the switch closes again, whereupon due to the malfunction of the device in turn an excess temperature occurs and opens the switch again. For this purpose, it is provided to arrange a resistor parallel to the switch. Here, thick-film resistors or PTC thermistors are known which are fixed to the switch, for example by clamping, by shrink sleeves or the like.

Thus, DE-A-32 31 136 shows a bimetallic switch with an insulating support member in which connection elements are fixed, for example by the plastic carrier material is injected around the connection elements. From the connection elements tongues are bent, which carry the fixed and the movable contact. Below the support member, a thick film resistor in the form of a flat conductive coated ceramic plate is arranged, which has rigid terminal lugs, which are soldered to the actual terminal lugs of the switch.

Of course, in addition to the aforementioned elements, the switch also has a spring element carrying the movable contact button and a bimetallic disc which effects the switching operation.

Overall, the switch is elaborate. He is consuming in the production. It must be done by hand assembly operations. Moreover, it is unfavorable that the switch of a variety of different materials, namely next to the metal sheet of the terminal lugs of the actual switch made of plastic, ceramic, a conductive thick film consists. adversely is also that the bimetallic element is fixed both at its ends and in the middle, whereby its switching action is reduced and it may also be exposed to permanent forces that can change the switching point.

DE-A-35 39 425 shows a generic thermal switch. In this case, a thin insulating ceramic plate is disposed between and soldered out of terminal lugs tines. The ceramic plate is in turn metallized, on a terminal lug a spring element of the movable contact is fixed, while the other terminal lug is provided with the fixed contact button. In the middle of the spring element, a plunger or bolt is fixed, for example, by a rivet of a bimetallic disc protrudes, 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 bimetallic element. This switch has only led to problems in practice. He could not be realized in practice. He too is again elaborate, since the insulating ceramic plate must be additionally provided with a conductive coating. Also weakens the breakthrough, through which the bimetallic disc centering plunger protrudes, the already thin ceramic plate, so that it can easily break. The switching path of the bimetal disc is again limited by the central definition. Also, the spring action and thus the switching action of the movable contact bearing spring is affected by the rivet located on it.

The invention is therefore based on the object, while avoiding the disadvantages of the known switch to create an open self-holding switch, which consists of a few individual parts, itself is simple and manufacturing technology in a simple and largely automatable manner can be produced.

According to the invention, the stated object is achieved in a generic switch in that the connecting parts embrace the support member almost completely non-positively. As a result, a simple automatic production of a simple switch is made possible. It achieves a reliable hold, without perforations or holes for fixing rivets or the like in the ceramic support member are required. Such breakthroughs are only consuming and hardly produced with the desired accuracy. They would continue to weaken the support. In a preferred embodiment it is provided that the support member is a PTC thermistor.

The support member itself is designed as a PTC thermistor and carries as such the connection elements. The support member preferably has the shape of a block or cuboid, which in particular is not too thin, but has a thickness which is not substantially less than half the width of the cuboid, preferably over half the dimension of the width of the cuboid. The PTC thermistor itself assumes the supporting function without the risk of breakage or damage. In concrete embodiment may be provided to determine the terminal lugs on the support PTC thermistor that tabs of the connecting parts almost completely embrace the support member. To further secure a preferred embodiment provides that the terminal lugs are soldered to the PTC thermistor.

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

Alternatively, it may be provided that a leg of a connecting part is bent by 180 ° under another leg of the connecting part and holds a movable contact between the two parts, which is formed of bimetal or that at a connecting element, a leg 180 ° under another Leg is bent and between both legs, both a movable contact and a switching bimetallic element are fixed. In the former embodiment, therefore, carries the active element, the bimetallic element, the movable contact button itself, while in the second-mentioned embodiment, a bimetallic element acts on a spring carrying the movable contact button. In both cases, a preferred development for fixing the corresponding parts against the 180 ° bent leg takes place jamming of movable contact and optionally bimetallic element by a bent tab before, where appropriate, in addition, a soldering can be provided.

While in principle, the bimetallic disc, as is known per se in the prior art, may be mounted centrally by either pressing with the center against the spring and is supported with its edge on a rigid abutment or vice versa, see the aforementioned embodiments before that the bimetallic element is fixed only on one side of the edge and causes the switching action with the diagonally opposite edge. This also avoids breakthroughs in the ceramic part for receiving central centering or fastening elements for the bimetal disc.

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

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 will become apparent from the claims and from the following description in which an embodiment of the invention with reference to the drawings is explained in detail. Showing:

FIG. 1

a thermal switch according to the invention in side view;

FIG. 2

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

FIG. 3

the switch of Figures 1 and 2 in front view;

FIG. 4

the movable contact-carrying terminal part; and

FIG. 5

the connection part for the fixed contact.

The thermal switch 1 according to the invention has in the illustrated embodiment as a supporting part 2 a PTC thermistor in the form of a cuboid on the basis of barium titanate or solid solutions of barium titanite and strontium titanate with other additives.

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

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

The switch works in a conventional manner a self-holding switch. If the ambient temperature, be it externally or too high due to excessive current supply and heating of the conductive parts so that the switching temperature of the bimetallic element 8 is exceeded, it switches from its illustrated in Figure 1, a contact of the contacts 6 and 7th permitting low temperature position in its high temperature position, in which it lifts the movable contact 7 from the fixed contact 6. If so the low-resistance connection is interrupted via the contacts 6, 7, so there is a stronger current flow from the terminal lugs 13, 14 via the PTC thermistor 2, which is thereby heated and by its heat holds the bimetallic element 8 in its temperature position and thus via this 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 bearing surface 23 for the PTC thermistor 2. A T-bar 24 of the T-shaped connecting element 4 is at lines 26, 26a, 27, 27a each bent at 90 °, whereby side walls 28, 28a and cover parts 29, 29a are formed for the PTC thermistor 2. The PTC thermistor 2 can be frictionally held by these by 90 ° along the lines 26, 26a, 27, 27a bent parts or walls 23, 28, 28a, 29, 29a. Preferably, however, the connection element 4 is soldered to the PTC thermistor in sections 23, 28, 28a, 29, 29a comprising the PTC thermistor 2. At the ends of the T-bar 24 and the portions 29, 29 a are parallel to the central T-leg 21 extending tabs 31, 31 a formed, which come to lie in the manner described parallel to each other after bending of the connecting element 4. On them a contact button 32 is attached as a fixed contact 6 (welded).

The further connection element 3 is also made, like the connection element 4, of a flat material, with metal sheet. In the wound-up, 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 over the switching elements (spring element 9 with movable contact, bimetallic element 8). The arm or arm 43 opposite this is at 180 ° (FIG. 1) below the middle part 44 of the cross 41 and the legs 42 bent and forms a lower holding part for the switching elements - spring element 9 and bimetallic element 8. These are clamped between it and a punched out of the leg 42 by a U-shaped punch 46 tab 47. For additional security soldering can be provided. The tab 47 is for this purpose after bending the leg 42 against this downward (in the direction of the PTC thermistor 2 out), so as to define between it and the leg 42, the bimetallic element 8 and the spring element 9.

From the central part 44 of the cross extending perpendicular to the legs 42, 43 respectively in opposite directions further legs 51, 51 a. These are bent at bending lines 52, 52a by 90 ° downwards. They continue to point at a greater distance than he at the distance of the bending line 27 and 26 or 26a and 27a - corresponding to the strength of the PTC thermistor 2 -, more bending lines 53, 53a, where the legs 51, 51a in the same direction at the bends 52, 52 a are bent over. Thus, the bent legs 51, 51a include a rectangular contour. At a distance from the bending lines 53, 53a, there are the free ends of U-shaped cutouts 54, 54a, through which tabs 57, 57a connected to the legs 51, 51a at bend lines 56, 56a are formed, which also surround the bending lines 56, 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 in parallel abut each other. The free ends 59, 59a may optionally be welded together. As a result of this shaping, as can be seen from FIG. 1, the PTC thermistor 2 is enclosed and held by the connecting part 3 at a distance from the connecting part 4, with additional securing being provided also soldering between the connector 1 and the PTC thermistor 2 may be provided. On the free leg 51a extends parallel to the tab 43, a connecting lug 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 the thermistor forming a supporting part 2, the connecting parts 3, 4, the bimetallic element 8, the spring element 9 and the contact buttons 7, 32nd The latter are firmly connected to the spring element 9 and the Artschlußteil 4 as welded or soldered.

The manufacture of the switch according to the invention also takes place in a simple and inexpensive manner and can be carried out fully automatically.

The connecting parts 3, 4 are punched out of sheets with the apparent from Figures 3, 4 contour. Here, at the same time the eyelets 30, 60 made on the connecting parts 22, 61 and the U-shaped punched-46, 54, 54a. Subsequently, reinforcing beads 50 are embossed in the arm 11 and the leg 42 and the middle part 44 of the connecting part 3. At the connection part 3, the bend of the leg 43 and also the bend continues at the bending lines 53, 53 a, 56, 56 a, 57, 57 a, as in the same way the bends on the bending lines 26, 26 a, 27, 27 a take place at the connection part 4. On the connector 4, the contact button 43 is mounted in a further step, while the connecting part 3, the switching elements - bimetallic element 8 and spring element 9 are fixed with contact button by inserted between the end of the leg 42 and the tab 47 and by bending the latter between this and the leg 42 are clamped, wherein a further additional security can be done by soldering. Finally, the pre-bent terminal parts 3, 4 are pushed over the support member 2 (PTC thermistor), with this further pressed non-positively and optionally additionally soldered.

Claims (10)

Thermal switch with two attached to a support member connecting parts, one of which has a fixed contact, while the other high impedance with a switchable by a bimetallic movable contact, wherein the support member is a ceramic part is connected, characterized in that the support member (2) is a block - or cuboidal PTC thermistor, which surround the terminal parts almost completely exclusively non-positively. Switch according to Claim 1, characterized in that the supporting part is a thermistor based on barium titanate and / or strontium titanate. Switch according to one of the preceding claims, characterized in that tabs (51, 51a, 57, 57a; 23, 28, 28a, 29, 29a) of the connecting parts (3, 4) almost completely surround the supporting part. Switch according to one of the preceding claims, characterized in that the connection parts (3, 4) are soldered to the support part (2). Switch according to one of the preceding claims, characterized in that tabs (47, 57, 57a) formed by U-shaped punched-out lines are provided at least on one connecting part (3, 4). Switch according to one of the preceding claims, characterized in that one limb (43) of a connection part (3) is bent by 180 ° under another limb (42) of the connection part (3) and a movable contact (9, 7) between the two parts. which is made of bimetal. Switch according to one of claims 1 to 6, characterized in that on a connecting element (3) a leg (43) by 180 ° under another leg (42, 43) both a movable contact (9, 7) and a switching this Bimetallic element (8) are fixed. Switch according to claim 6 or 7, characterized by a fixed against the bent by 180 ° leg (43) fixing of movable contact (7, 9) and optionally bimetallic element (8) bent tab (47). Switch according to claim 8, characterized in that the bent tab (47) is punched out by a U-punching (46) from the leg (42) under which the leg (43) has been bent. Switch according to one of the preceding claims, characterized in that an arm (11, 42) covering the contact region is provided with reinforcing beads (50).

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