US3768057A - Thermal switch with small switching temperature difference - Google Patents

Abstract

A thermal switch with a thermo-bimetal-snap disc having in its free state a large transfer temperature difference as a temperature sensor, the snap stroke of which is limited by at least one abutment for provision of small switching temperature differences, which comprises a spring-biased contact carrier, and a transmission member. The thermo-bimetal-snap disc is in operative connection with the contact carrier by means of the transmission member. An adjusting screw for adjusting of the contact distance is provided as well as an immovable contact. The contact carrier comprises a rigid pivotal one-armed lever, and the adjusting screw is adjustingly secured to the lever and is in engagement at its end-side with the transmission member.

Description

United States Patent n 1 Sekira et a1.

THERMAL SWITCH WITH SMALL SWITCHING TEMPERATURE DIFFERENCE Inventors: Peter Sekira; Helmut Bayer, both of Vienna, Austria Electrovac Fabrikation elektrotechnischer Spezialartikel Gesellschaft m.b.H., Wien, Austria Filed: June 21, 1971 Appl. No.: 155,175

Assignee:

Foreign Application Priority Data June 19, 1970 Austria 5535 July 31, 1970 Austria 7005 U.S. Cl 337/349, 337/354, 337/375 Int. Cl. H01h 37/52 Field of Search 200/166 BH; 337/343,

References Cited UNITED STATES PATENTS 3,005,076 10/1961 Mertler 337/343 2,897,321 7/1959 Patti 337/375 X 2,753,422 7/1956 Mertler 337/354 2,753,421 7/1956 Mertler 337/347 2,714,644 8/1955 Harrison 337/348 Primary Examiner-Bernard A. Gilheany Assistant Examiner-F. E. Bell I Attorney-Ernest G. Montague [57] ABSTRACT A thermal switch with a thermo-bimetal-snap disc having in its free state a large transfer temperature difference as a temperature sensor, the snap stroke of which is limited by at least one abutment for provision of small switching temperature differences, which comprises a spring-biased contact carrier, and a transmission member. The thermo-bimetal-snap disc is in operative connection with the contact carrier by means of the transmission member. An adjusting screw for adjusting of the contact distance is provided as well as an immovable contact. The contact carrier comprises a rigid pivotal one-armed lever, and the adjusting screw is adjustingly secured to the lever and is in engagement at its end-side with the transmission member.

9 Claims, 4 Drawing Figures PAIENIEDHBT 23 m5 3.768.057

v SHEET 10F 2 FIG. I,

THERMAL SWITCH WITH SMALL SWITCHING TEMPERATURE DIFFERENCE The present invention relates to a thermal switch with a thermo-bimetal-snap disk with a great changing temperature difference in the free state as a temperature feeler, the snap stroke of which is limited for obtaining of small switching temperature differences by at least one abutment, whereby the thermo-bimetal-snap disk, is in non-positive connection by means of a transmission member with a spring biased contact carrier carrying the movable contact of a contact system and is provided for the adjustment of the contact distance of the adjusting screw.

Thermo-bimetal disks with a snap effect combine two functions, namely, that of a temperature feeler and that of another quick break cut-out mechanism, and make possible thus price-favorable and space saving constructions of thermal switches. The switching temperature difference of the thermal switch, which is the difference between the switch-off and the switch-on temperature, is thereby of about the order of the changing temperature difference of the free thermo-bimetalsnap disk. From that, however, result difficulties during the production of thermal switches with a small switch temperature difference. In order to avoid an ignition between the open switch contacts, a certain minimum distance is required therebetween, which distance again requires a certain minimum snap stroke. Due to the monotenous combination between a snap stroke and the changing temperature difference of the snap disk thus also a minimum switch temperature difference is required, whereby a lower tolerance limit for the switching temperature difference is conventionally at 4 to 5 C. Now, however, as an upper tolerance limit for example in the climate techniques, aviation, space exploration and nautics, smaller switching temperature differences of about a maximum of 3 C or even a maximum 1 C are required. It is to be observed thereby, that in connection with thermal switches one deals today with mass articles, thus a small switching temperature difference must be obtained uniformly. Furthermore, the small switching temperature difference of the individual switch should remain at least substantially constant for the life, by example, 100,000 switching cycles. These requirements cause particular constructive measures.

In F. Kaspar, Thermo-bimetal Electrotechnique VEB Verlag Technik, Berlin 1960, it is suggested to use therefor a thermo-bimetal-snap-disk with large revolving temperature difference in its free state, about 40 C and thus, a large snap stroke and to limit a large part of the snap movement by at least one abutment.

An example of such thermal switch is described in British Pat. No. 626,114. There the thermo-bimetal disk has a bore, which is passed by the neck of an adjustment screw. The projecting neck is deformed with the maintenance of a certain play to a rivet head which forms an abutment. The second abutment is given by the shoulder at the neck set-off. For setting the contact distance, the adjustment screw is screwed through a base body consisting of insulating material of the thermal switch and after the adjustment secured by means of a counter nut. The small switch temperature difference is obtained by the narrow distance between the abutments.

Furthermore by the US. Pat. No. 3,005,076 it has been known to limit the snap movement of the thermo bi-metal-disk by a single abutment only, which is formed by the head of an adjustment screw, which is screwed into the metallic housing. The snap disk has a bore, through which projects the adjustment screw, and a longitudinal bore, through which a pin enters in order to secure the snap disk against rotation. The snap movement of the thermo bi-metal-disk is transmitted by means of a ball-shaped transmission member onto the contact system. The small switching temperature difference is obtained by the low tensioning of the snap disk by means of the head of the adjustment screw.

The known embodiments of thermal switches with a small switch temperature difference have drawbacks, which are to be seen as cumbersome structure, complicated mounting, bores in the snap disk and thereby reduced life term, as well as non-suitability for 220 volts.

It is one object of the present invention to provide a thermal switch with a small switch temperature difference, which avoids the drawbacks of the known structure.

Contrary to the known thermal switching with a small switch temperature difference and to those conventional thermal switches in which a blade spring is used as a carrier of the movable contact, the blade springs, being however, bendably soft and therefore, able to serve as an abutment and which in series have a larger switching temperature difference than about 4 5 C, there is provided in accordance with the present invention a contact carrier comprising a non-bendable pivotally mounted, and in particular one-armed lever, on which the adjustment screw is adjustably secured at the end side in engagement with the transmission member.

In addition to the small switch temperature difference, the structure, according to the present invention, bring a simple structure of the thermal switch, a simple adjustment also in the finished mounted state, the possiblity, to comply with the safety provisions also for 220 volts, as well as the possiblity, to avoid bores in the thermo bi-metal-disk.

Since the contact carrier is formed as a comparatively rigid lever swingably mounted on the insulating housing, during the switching off process for obtaining of a non-positive connection between the contact car rier and the snap disk over the transmission member a spring effective in the direction from the contact carrier to the thermo bi-metal is necessary. The latter can constitute for example, a shaped pressure spring between the insulating housing and the contact carrier. It is advantageous, however, for obtaining a pivotal and resilient connection that the contact carrier is secured by means of a blade spring on the insulating housing.

Since in case of a very strong suppression of the snap stroke, a small bending of the blade spring results in the immediate vicinity of the securing point, in accordance with a further development of the present invention, in view of particularly small switching temperature differences, it is suitable to provide a second rigid abutment, in particular in the form of an edge or the like disposed cross-wise to the longitudinal direction of the lever, in the insulating housing and in the vicinity of the bearing point of the swingably mounted lever.

By this arrangement it is brought about, that directly after the abutment of the movable contact on the immovable contact a practically rigid abutment for the limitation of the snap stroke of the thermo-bimetal disk is obtained.

Advantageously the lever comprises a blade spring with a stiffening sheet secured thereto, whereby only the blade spring secured on the insulating housing and the stiffening plate extend beyond the abutment in the direction towards the securing point of the blade spring.

Suitably the stiffening plate is bent away from the abutment and from the blade spring at its end opposite from the movable contact;

By this measure, on the one hand, in the contact open-position the blade spring due to its pretension can follow the thermo-bimetal snap-disk, whereby the adjustment screw and the transmission member are always in engagement, and, on the other hand, in the contact closed-position the previous bending in the immediate vicinity of the securing point is avoided, since the blade spring can support itself on the stiffening plate.

A further advantage results in relation to the selection of material. The contact carrier passes current and therefore, for its dimensioning the narrowest, is decisive and for selection of working material its electric conductivity is decisive; and the blade spring e.g., is produced of well conducting spring materials, or, copper beryllium.

In accordance with the present invention the stiffening plate contributes also in the vicinity of the securing point the current feeding which permits to make the blade spring of the spring steel.

With these and other objects in view, which will become apparent in the following detailed description, the present invention, which is shown by example only, will be clearly understood in connection with the accompanying drawings, in which:

FIG. 1 is a thermal switch, designed in accordance with the present invention, in which a contact carrier is provided by means of a blade spring on an insulating housing;

FIG. 2 is a top plan view of another contact carrier suitable for the switch in accordance with FIG. 1;

FIG. 3 is a section along the lines III-III of FIG. 4; and

FIG. 4 is a section along the lines IVIV of FIG. 3, constituting a further embodiment of a thermal switch designed in accordance with the present invention.

Referring now to the drawings, and in particular to FIGS. 1 and 2, the thermal switch shown in the drawings has a housing cup 1 in which is provided a thermobimetal-snap disk 2 with relatively large changing temperature differences, for instance of about 25 C in its free state. The snap disk 2 is mounted above the cylindrical transmission member 3 of insulating material and an adjustment screw 5 with the contact carrier 4 in non-positive connection. The contact carrier 4 comprises a stiffening blade 6, of which a threaded eye 7 is formed for receiving the adjustment screw 5, and of the blade spring 8, the bore 9 of which is passed through the threaded eye 7 and which is rigidly rivetted by means of a movable contact 10 with the stiffening blade 6.

The plate spring 8 is secured overlappingly beyond the contact carrier 4 on the insulating housing 11 with I the rivet 12, whereby simultaneously also the one connection 13 is secured. The rigid switch contact 14 is formed as a rivet contact and serves simultaneously the securing of a second connection 15. The rigid contact 14 and the movable contact 10 are arranged in the insulating housing 11 on which the housing cup 1 by flanging (flange edge 16) is secured opposite of each other. Simultaneously with the insulating housing 11 is also the intermediate disk 17 of insulating material with the housing cup 1 secured. The intermediate disk 17 serves the guidance of the transmission 3, yet it is not by all means required.

During the mounting, first the contact carrier 4 is produced as mounting unit by riveting the blade spring 8 with the stiffening blade 6 by means of the movable contact 10, and the adjustment screw 5 is screwed into the eye 7. Then on the insulating housing 11 the connection 15 is rivetted with the rigid contact 14, whereupon the connection 13 with the contact carrier 4 is secured with the rivet 12, whereby it is to be observed, that the contacts 14 come into coinciding position relative to each other. Finally, the snap disk 2 and the intermediate disk 17, the transmission member 3, as well as the insulating housing 11 with the parts secured thereto are put into the housing cup 1 and the projecting edge 16 is flanged over. These 5 individual parts and mount ing units, respectively, can thereby be formed of circular symmetrically, so that they can be rotated into any selected angle, which simplifies very much an automatic mounting.

In the insulation housing 11 a bore 18 is provided substantially in the extension of the transmission member 3, which can be closed up after adjustment with a stopper 19. The stopper 19 comprises preferably, a heat resistant synthetic material and is pressed in the bore 18. By this arrangement a thermal switch is closed up dust proof. Suitably on the upper side of the stopper 19 the writing of a switch temperature normally desired by the users of the thermal switch is provided, so that one requires four switches of different switching temperatures only other snap disks 2 and stoppers 19, while all remaining parts remain equal.

The thermal switch is shown in the contact open position. For the sake of clarification the curvature of the snap disk 2, the angle between the contact carrier 4 and the horizontal and the contact distance 10 -14 is shown withexaggeration. If in case of a temperature change the snap disk 2 reaches its changing temperature, it rapidly snaps the shown curved position into the opposite curved position-The start of this switching process takes place practically without retardation, since the snap disk 2 at first provides as opposite force only the low pretensioningforce of the blade spring 8. The pre tension is achieved by the blade spring '8 beingbent over about a predetermined angle at a point 20.

As soon as the two switching contacts 10 and 14 come into engagement and the contact carrier 4 supports itself with the movable contact 10 on the rigid contact 14, the bearing point 20 is effective as a pivot and the contact carrier 4 operates as a one armed rigid lever, which does not bent by itself anymore, and limits the snap movement of the thermo-bi-metal-disk 2. The snap 2 thus, cannot snap from the shown curve position in the opposite curvature, rather only from the originally stronger curved into a lesser curved position to which reduced snap stroke corresponds a strongly reduced, snap switching temperature difference of about 3C. relatively to the revolving temperature difference of the free disk. If the temperature changes in the opposite direction, the snap disk tube snaps again into the shown position upon reaching the return snap temperature based on the abutment by the contact carrier 4 and such return snap temperature, whereby the contacts and 14 are separated by the pretension of blade spring 8 from each other.

The adjustment of the contact distance 110-14 takes place by rotation of the adjustment screw 5.

The feature of the contact carrier 4 to be bendable at the bearing point and otherwise rigid, can also be obtained by an embodiment which is varied in relation to FIG. 1. This other possibility is shown in FIG. 2 and in particular is a top plan view. The contact carrier 21 is formed as a blade spring, has a bore 22 for the movable contact 10, a recess 23 for the rivet 12 and by example by soldering or a sleeve 24 with threads for the adjustment screw 5, secured by example by soldering of or by rolling over. In order to make it bendable at the securing point 20 and for the rest rigid, on the one hand, a bore 25 the diameter of which responds to about the half width of the contact carrier 21, on the other hand, two stiffening beads 26 and 27 are arranged. The material strength of the contact carrier 21 is to be selected for the same thermal switch somewhat stronger than that of the blade spring 8 in accordance with FIG. 1. Also with the contact carrier 21, the pretension necessary for the sudden contact opening is obtained such, that it is bent over at the height of the center point of the bore 25 about a certain angle.

Only one of the two features, namely, the bore 25 or the stiffening'beads 26 and 27, do not suffice unless one is satisfied with a reduction of the switching temperature difference of the free snap disk.

Referring now again to the drawings and in particular to FIGS. 3 and 4, in which a second embodiment of the present invention is disclosed, those parts which coincide with the respective parts of FIGS. 1 and 2 have been provided with the same numerals.

Relative to the embodiment shown in FIGS. 1 and 2, yet, however, the insulating housing 11 of the thermal switch disclosed in FIGS. 3 and 4 there is in the direct vicinity of the bearing point 20, an edge 28, behind which the hollow space 29 widens into the insulating housing 11 and provides space for its movement during the switching process. On this edge 28, the blade spring 8 is bent downwardly to a certan angle, whereby the pretension is achieved, under the effect of which the contact carrier 4 is in non-positive connection in the contact open position of the contact carrier 4, with a snap disk 2 by means of the transmission member 3, and the adjustment screw 5. The stiffening blade 6 lies from the movable contact 10 up to the edge 28 on the blade spring 8 and is bent away from the blade spring 8. Since a securing of the blade spring 8 on the insulating housing 11 takes place by means of a rivet 12, the stiffening blade 6 is forked from the point 30 into extensions 31 and 32, in order to provide room for the rivet head 33 of the rivet 12. If one would eliminate the rivet head 33, and the blade spring 8 was welded to the shaft of the rivet 12 the fork of the stiffening blade 6 would be unnecessary and the stiffening blade 6 could be continued up to its end. The curvature of the stiffening blade 6 and the projections 31 and 33, respectively, have the purpose to make possible the movement of the contact carrier 4, during switching off over the horizontal position downward.

The thermal switch is shown in the contact open position. If in case of a temperature change the snap disk reaches the revolving temperature, it is then to snap through from the shown curved position into the oppositely curved position. The start of this switch process takes place practically without retardation, since only the low pretensioning force of the blade spring 8 operates against the snap disk 2. As soon as two switching contacts 10 and 14 come into engagement and the contact carrier can support itself with the movable contact 10 on the rigid contact 14 and by the blade 6 formed in accordance with the present invention also at the bearing point 20 a good support is provided, the contact carrier operates as abutment and limits the snap movement of the thermo bi-metal disk. The snap disk 2 can thus not snap from the shown curved position into a position with opposite curving, rather only from the originally stronger curved into a lesser curved position, which reduced snap stroke reduced switch temperature corresponds relative to the revolving temperature difference of the free disk. Compared with a previous structure by the improved bearing mounting of the contact carrier 4 a further reduction of the switch temperature difference, for example, to maximum 5C. results.

While we have disclosed several embodiments of the present invention it is to be understood, that these embodiments are given by example only and not in a limiting sense.

We claim:

1. A thermal switch with a thermo-bimetal-snap disc having in its free state a large transfer temperature difference as a temperature sensor, the snap stroke of which being limited by at least one abutment for provision of small switching temperature differences, comprising a housing in which is disposed,

a spring-biased contact carrier,

a transmission member,

a thermo-bimetal-snap disc being in operative connection with said contact carrier by means of said transmission member,

a movable contact of a contact system disposed on said contact carrier,

an immovable contact of the contact system secured to said housing and adjacent said movable contact and defining a contact distance relative thereto in an inoperative position of the switch,

an adjusting screw for adjusting of the contact distance,

the spring biasing of said contact carrier biasing said movable contact away from said immovable contact,

said contact carrier comprising a bending-stiff,

swingably mounted, one-armed lever operatively pivoted to said housing, and said adjusting screw being adjustingly secured to said one-armed lever and being in forced engagement at its end-side with said transmision member by means of the spring biasing of said contact carrier. 2. The thermal switch, as set forth in claim 1, which includes a blade spring connected to said housing, said contact carrier is secured to said housing by means of said blade spring, the latter constituting the spring biasing of said contact carrier and pro viding a pivotal and resilient connection. 3. The thermal switch, as set forth in claim 2, which includes a stiffening plate extending close to its securing point to said blade spring.

4. The thermal switch, as set forth in claim 3, wherein said movable contact is formed as a rivet contact, and

said stiffening plate is secured to said blade spring by means of said movable contact.

5. The thermal switch, as set forth in claim 1, which includes a blade spring to constitute said contact carrier having stiffening heads which extend close to the securing point, and

said blade spring has a reduced cross section in the immediate vicinity of said securing point and has a bore disposed symmetrically relative to said spring axis, the diameter of said bore amounting to about half of the width of said blade spring.

6. The thermal switch, as set forth in claim 1, wherein a housing including an insulating housing having a cylindrical opening disposed substantially axially aligned with said transmission member, said cylindrical opening being adapted to insert a tool therein for adjusting of said adjusting screw.

7. The thermal switch, as set forth in claim 6, which includes a second rigid abutment provided on said housing in the vicinity of the connection point of said swingably mounted lever to said housing,

said second abutment is formed as an edge disposed crosswise to the longitudinal direction of said lever.

8. The thermal switch, as set forth in claim 7, wherein said lever comprises a blade spring with a stiffening plate secured thereto,

said blade spring only being secured to an insulating housing, and

said stiffening plate extends in the direction toward the securing point of said blade spring beyond said second abutment.

9. The thermal switch, as set forth in claim 8, wherein said stiffening plate is bent away in the direction towards its end opposite to the movable contact starting with said second abutment from said blade spring.

Claims (9)

1. A thermal switch with a thermo-bimetal-snap disc having in its free state a large transfer temperature difference as a temperature sensor, the snap stroke of which being limited by at least one abutment for provision of small switching temperature differences, comprising a housing in which is disposed, a spring-biased contact carrier, a transmission member, a thermo-bimetal-snap disc being in operative connection with said contact carrier by means of said transmission member, a movable contact of a contact system disposed on said contact carrier, an immovable contact of the contact system secured to said housing and adjacent said movable contact and defining a contact distance relative thereto in an inoperative position of the switch, an adjusting screw for adjusting of the contact distance, the spring biasing of said contact carrier biasing said movable contact away from said immovable contact, said contact carrier comprising a bending-stiff, swingably mounted, one-armed lever operatively pivoted to said housing, and said adjusting screw being adjustingly secured to said one-armed lever and being in forced engagement at its end-side with said transmision member by means of the spring biasing of said contact carrier.

2. The thermal switch, as set forth in claim 1, which includes a blade spring connected to said housing, said contact carrier is secured to said housing by means of said blade spring, the latter constituting the spring biasing of said contact carrier and providing a pivotal and resilient connection.

3. The thermal switch, as set forth in claim 2, which includes a stiffening plate extending close to its securing point to said blade spring.

4. The thermal switch, as set forth in claim 3, wherein said movable contact is formed as a rivet contact, and said stiffening plate is secured to said blade spring by means of said movable contact.

5. The thermal switch, as set forth in claim 1, which includes a blade spring to constitute said contact carrier having stiffening heads which extend close to the securing point, and said blade spring has a reduced cross section in the immediate vicinity of said securing point and has a bore disposed symmetrically relative to said spring axis, the diameter of said bore amounting to about half of the width of said blade spring.

6. The thermal switch, as set forth in claim 1, wherein a housing including an insulating housing having a cylindrical opening disposed substantially axially aligned with said transmission member, said cylindrical opening being adapted to insert a tool therein for adjusting of said adjusting screw.

7. The thermal switch, as set forth in claim 6, which includes a second rigid abutment provided on said housing in the vicinity of the connection point of said swingably mounted lever to said housing, said second abutment is formed as an edge disposed crosswise to the longitudinal direction of said lever.

8. The thermal switch, as set forth in claim 7, wherein said lever comprises a blade spring with a stiffening plate secured thereto, said blade spring only being secured to an insulating housing, and said stiffening plate extends in the direction toward the securing point of said blade spring beyond said second abutment.

9. The thermal switch, as set forth in claim 8, wherein said stiffening plate is bent away in the direction towards its end opposite to the movable contact starting with said second abutment from said blade spring.

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