US2199477A - Releasing device for electric switches - Google Patents

Description

May 7,1940. E. BES/,G f 2,199,477

RELEASING DEVICE FOR ELEGTIC SWITCHES Filed Jan. 24, 1958 2 sheets-sheet 1 Patented May 7, 1940 PATENT ori-ICE RELEASIG DEVICE FOR ELECTRIC SWITCHES Ernst Besag, Baden-Baden, Germany Application January 24, 1938, Serial No. 186,673

In Germany August 20, 1937 12 Claims.

The present invention relates to releasing devices for multipolar electric switches of the type in which a plurality of thermal or thermally-responsive releasing ,elements are employed for the purpose of releasing the switch on the occurrence of an inadmissible load. From a more limited point of View, the invention relates to releasing devices which are adapted to release automatic Aswitches on the occurrence of overloads, or loads of inadmissibly high current strength or amperage and duration, after the lapse of a predetermined time lag, on the occurrence of smaller loads when said loads are unsymmetrical. Such releasing devices are used, for example, in threephase-current net works for the protection of three-phase motors.

Releasing devices of the above-desribed character heretofore in use have not been entirely satisfactory. According to one of the well known devices, as an illustratiomtwo abutment members for the thermal releasing elements are held yieldingly, each by a separate spring, so as to be movable in opposite directions with respect to a stationary bearing member upon lwhich the thermal releasing elements are mounted. Under symmetrical loads, the releasingelements become simultaneously subjected to similar or equal thermal expansive deformations. On the occurrence of simultaneous equal deformations-of this character in all the thermal releasing elements, one of the abutment members becomes released, whereupon its spring actuates it over a distance dependentI upon the rate of movement of the releasing elements. The releasing elements themselves act, at the same time, to actuate the other abutment member over the same distance,'in opposition to the force exerted upon it by the other spring. As long as the load is symmetrical, therefore, the abutment members are actuated as a unit, without any relative movement between them. When the load is unsymmetrical, however, one of the abutment members is held `against movement by the thermal releasing element that is subjected to the smallest expansion and the other abutment member is moved according to the rate of expansion of the releasing element that is subjected to the greatest expansion. One of the abutment members is then moved with respect to the other to release the .switch that is controlled by the releasing device. Such releasying operation, it should be emphasized, takesl movement of one of the abutment members, so as to limit its movement, there will be a relative movement of the abutment members ,even in the vcase of equal deformations of the thermal releasing elements occurring under conditions of symmetrical loads; for the stop will prevent further movement of the said one abutment member, notwithstanding that the thermal releasing elements are subjected to additional deformation. The relative movement of the abutment members effected by such a stop is utilized to release the switch controlled by the releasing device on the occurrence of symmetrical loads of inadmissible current strengths and duration.

Due to the fact that the abutment members are actuated as a unit with respect to the stationary bearing member according to the rate of deformation of the thermal releasing elements, the design of a switch of this character involves difllculties. These difficulties are especially great if the releasing device is relied upon to control an operating-and-locking mechanism of the tripfree-from-the-handle type. A non-closable switch mechanism should be maintained stationary with respect tothe stationary bearing member of the two abutment members; but it is'not easy to control a stationary mechanism through the medium of the relative movement of two abutment members that are moved as a unit with .respect to said stationary-mechanism according to changes in the working conditions.

It is therefore an object of the present invention to provide a new and improved releasing device of the above-described character according to which this drawback is overcome.

A further object is to provide a new'and improved releasing device having additional advantages over prior-art releasing devices, as will hereinafter appear.

The invention will now be more fully described in connection with the accompanying drawings, in which Fig. 1 isa plan view illustrating-an embodiment of the invention with the parts occupying their initial positions, the bearing-member housing being shown in section;

Figs. 2 and 3 are similarv views of the releasing deviceillustrated in Fig. 1, with the parts occupying other operating positions;

Fig. 4 is a diagrammatic plan ofstill another embodiment of the invention, with the parts occupying initial positions corresponding to those of Fig. 1;

Figs. 5 and 6 are views of the releasing device illustrated in Fig. 4, with the parts occupying operating positions corresponding to those shown in Figs. 2 and 3, respectively;

Fig. 7 is a diagrammatic perspective of another releasing device embodying the present invention;

Fig. 8 is a similar diagrammatic perspective View of a further releasing device according to the present invention; and

Fig. 9 is a plan illustrating still another embodiment of the invention.

Corresponding parts'are designated in all iigures by the same numerals.

. lating material that is longitudinally slidable in (not shown).

Three thermal or thermally-responsive releasing elements 2a, 2b, 2c, that may be constituted of equally shaped bimetallic strips, are fastened, or otherwise secured, as by means of rivets I3, to vertical extensions or ribs 3a, 3b, 3c of a cross bar or fixing member 3. Though the bimetallic strips are illustrated as riveted to the crossbar 3, this is for convenience only. As will be understood, they may be secured to the bar 3 in anyother desired manner, and they may even abut' loosely against, or otherwise connect with, the ribs vor other parts of the member 3. To save circumlocution of language, al1 such constructions will be referred to, in the specification and claims, by the term fixing member.

Though the thermally-responsive or thermal releasingelements are illustrated as bimetallic strips, other equivalent thermal releasing elements that change their shape upon being heated may be employed Vwithout departing from the spirit of the present invention. The fixing member 3 is constituted of an insulating strip that is mounted to slide longitudinally, to the right and to' the left, as viewed in Figs. l to 6, in a guiding groove Ia of a housing or casing I for the fixing member 3 and the thermally- responsive elements 2a, 2b, 2c carried thereby, and that constitutes a bearing member. The housing is supplied with a cover or equivalent closing means A manually operable adjusting member, such as an adjustable abutment screw 9, limits the left hand movement of the xing member 3. 'I'he abutment screw '9 may be adjusted along the scale 9a, the head of the screw 3 serving as a pointer or indicator for cooperating with the scale 8a to indicate the position of the screw 3. Abutments 6a 6b, 6c, one correspondingt eachof the releasing elements 2a, 2b, 2c, are carried by an abutment member 6 that, like the xing member 3, is constituted of a strip of insua guiding groove Ib within the bearing housing I. The abutment member 6 is normally maintained yieldingly in a normal or initial position, at the left, by a blade spring 3a that engages adepending hook I9, shown at the left of the abutment member 6 as overlapping the spring 8a.

The bimetallic releasing elements 2a, 2b, 2c are respectively heated by means of three heating windings or coils 4a, 4b,. lc that are fixed on the bearing member I. Instead of heating the bimetallic strips 2a, 2b, 2c indirectly, by means of additional heatingwindings, in thisy manner, they may be heated directly, by inserting them in thecircuit f the heating current; or a combination of direct and indirect heating may be adopted. Upon being heated by the coils la, 4b, 4c, the bimetallic strips 2a, 2b, 2c bend, as illustrated in Fig. 2.

The housing I carries two binding posts 1 .and 3, constituting connecting terminals of a control circuit, such as the energizing circuit of the actuating electromagnet of a remote-control switch of the electromagnetic-relay type. This switch may interrupt the load circuit to be controlled by the releasing device. The spring 3a is secured to the binding post 8, and normally presses against, so as to make contact with, the binding post 1. Upon the movement of the spring 3a towards the right, asillustrated in Fig. 3, the circuit between the binding posts 1 and 3 becomes interrupted. This effects the release of. the switch controlled by the releasing device, as, for example, the said remote-control switch.

The desired releasing current strengths may be adjusted by rotatable adjustment of the screw 9, as read oi from the scale 9a.

If the circuit of the actuating electromagnet of a remote-control switch of the electromagnetic-relay type is to be controlled by the auxiliary switch mechanism 1, 8, 8a, as above suggested, a switch mechanism should be used for the auxiliary switch that, upon its becoming opened in response to movement of the thermal releasing elements 4a, 4b, 4c, will remain in open position until it is closed by means of a handle or other manually actuating device. Otherwise, the main switch, which it is desired to control by the releasing device, might become closed, upon the cooling down of. the releasing elements 2a, 2b, 2c, before removal of the defective conditions that gave rise to the releasing operation and the subsequent opening of the main switch. It is not necessary, however, to illustrate auxiliary switches of this type, because they are well known.

Instead of acting .upon an auxiliary switch mechanism of this character, that remains in open position after `its release, until it becomes closed manually, the abutment member 6 might be employed to operate a switch lock, or an actuating-and-locking mechanism of a non-closable switch, that is a switch of the-tripfreefromthe handle type.

- switch. It is not, however, possible practically to manufacture thermal releasing elements of this character that shall have characteristics sumciently alike for this purpose. Especially 'in the case of bimetallic strips, inadmissibly great dierences occur in the individual releasing elements as they emerge from the manufacturing process. These differences ought to be compensated for by individually bending the bimetallic strips or individually adjusting their carrying means or supports.

Calibrating and adjusting are rendered particularly facile with the embodiment of the invention illustrated in Fig. 1 by provision for easily removing from the bearing-member housing I, the three releasing elements 2a, 2b,.2c and the fixing member 3 upon which they are mounted, and for replacing them readily after adjustment. Among other advantages of this construction, therefore, it is possible to test the conformity to one another of the three releasing ele- A ments, in a simple manner, kby means of appropriate mechanical gauges; and, by means of the said gauges, to adjust the releasing elements into such conformity. After such testing and adjusting of the highly sensitive thermal releasing elements by means of the said mechanical gauges, there will be no danger of their subsequently becoming involuntarily or accidentally bent.

There may be safely placed or replaced in their 16 common housing I, where they may be simultaneously calibrated and adjusted without need of removing, for such purpose, the said cover (not shown) of. the housing I. This is important, because the thermal conditions that prevail when the calibration is effected while the housing is open are not the same as those occurring when the housing is closed. The calibration is preferably carried out with the limiting-current strength. To this end, the heating windings 4a,

4b, 4c are heated long enough under the conditions of such limiting-current strength to establish stationary temperature conditions within the housing I. It is advisable to provide within the housing l partitions (not shown) in order thermally to insulate from one another the thermal releasing elements 2a, 2b, 2c and their corresponding heating coils 4a, 4b, 4c, thus preventing any undesirable reciprocal thermal influencing or losses of heat.

Upon the occurrence of equal thermal deformation of the three bimetallic strips 2a, 2b, 2c, their upper ends, that cooperate with; the abutments 6a, 6b, 6c, become subjected to equal thermal deformations with respect to one another. The same applies as to the deformation of thereleasing.eler nents at the ribs 3a, 3b, 3c to which they are fixed. At their said upper ends, the thermal releasing elements are subjected to thermal deformation that is not the same as that to which they are subjected at the places where they are fixed.

The fixing member 3 is spaced from an adjustable stop shown as constituted of the screw 9. The stop screw 9 permits movement towards the' left of the fixing member 3 with respect to the abutment member 6, but serves to limit further such movement upon the fixing member 3 becoming moved into engagement with the stop 9. I'he abutment member 6 is normally maintained yieldingly by the blade spring 8a in its normal, or initial position, and the releasing elements 2a, 2b, 2c engage the abutments 6a, 6b, 6c. Upon heating of the thermal releasing elements 2a, 2b, 2c, by means of the heating windings 4a, 4b, 4c, the said elements bend, as.il1ustrated in Fig. 2, thereby effecting movement of -the fixing member 3, upon which they are mounted, towards the left. This movement is effected without, at first, moving the abutment member 6, and is continued until the fixing member 3 is moved into engagement with the adjustable stop 9. Additional deformation of. the thermal releasing elements 2a, 2b, 2c then results in movement of the abutment member 6 in opposition to the force exerted by the blade spring 8a. This spring 8a is therefore moved to the right, interrupting the control circuit between spring 8a and the binding post 1, and effecting release of the main switch controlled. thereby. y

In addition to the elements described above, abutments a, 5b, 5c may be provided. The abutments 5a, 5b, 5c vare stationary with respect to the bearing member or housing I. These abutments are `illustrated as constituted of lateral projections of one of the sidewalls of the housing I. Therefore, the thermal releasing elements 2a, 2b, 2c are each provided with two abutments, one on each side of each releasing element. One of these two abutments 5a, 5b, or 5c, at the left of each thermal releasing element, is stationary with respect to the bearing member I, and the other abutment 6a, 6b or 6c, respectively, carried by the abutment member 6 at the right of the corresponding thermal element, is movable with respect to the bearing member I. Under the actionof thee. spring 8a, the upper ends of the 4bimetallic strips 2a, 2b,- 2c are clamped or clasped to move the fixing member 3- in response to the occurrence of an unequal deformation caused by an unsymmetrical load. On the occurrence of such a deformation, the thermal releasing element or elements that are less deformed abut against one or more of the stationary abutments 5a, 5b and 5c, but the more deformed thermal releasing element orelements will move the abutment member 6 against the action of the leaf spring 8a. The device will then operate, therefore,`as a differential releasing device. In response to an equal deformation of the thermal releasing elements 2a, 2b, 2c, on the other hand, the releasing, device of Figsjl to 3 will operate as described above, and if the differential releasing action is not needed, the abutments 5a, 5b,

5c may be -dispensed with.

In Fig. 1, the three bimetallic strips 2b, 2b, 2c are shown unheated and, therefore, unbent. When a symmetrical load is present in the three phases, the three bimetallic strips 2a, 2b, 2c become bent to the same extent, whereupon they will actuate the fixing member 3 towards the left, as shown in Fig. 2. The condition of Fig. 3 obtains under an unsymmetrical load. The bimetallic strip 2a is shown unbent; and being unbent, it abuts against the stationary abutment 5a, thereby preventing the fixing member 3 from being actuated towards the left. The bent bi.- metallic strips 2b and 2c therefore actuate the abutment member 6 toward the right, effecting opening of the auxiliary switch 1, 8, 8a. The magnet system of a main switch of the relay type will thus become deenergized and the load, such as a three-phase-current motor will become disconnected from the mains.

According to the modifications of Figs. 4 to 6, the bimetallic-strip thermal releasing elements 2a, 2b, 2c are intermediately mounted on the fixing member 3. A spring 8a, shown helical, acts upon `the abutment member 6 to hold it normally yieldingly in a position at the right. It is, however, slidably movable towards the left, in opposition to the action of the spring 8a.. This movable abutment member 6 is provided with three abutments 6a, 6b, 6c for engaging the lower ends of the bimetallic strips 2a, 2b, 2c on their left-hand sides. The stationary abutments 5a, 5b, 5c are disposed at the upper ends of the bimetallic strips 2a, 2b, 2c on their right hand sides.

In Fig. 4, the said strips are illustrated in their unheated and, therefore, in their undeformed or unbent condition. In Fig. 5, the bimetallic strips are shown all bent to 'the same extent due to a symmetrical load of all three phases. They have, therefore, actuated their fixing member 3 towards the right. The stop screw 9 is positioned so as to limit the movement toward the right of the fixing member 3 upon the occurrence of a symmetrical load of inadmissible current strength andduration. After the xing inember 3 has been thus moved into engagement with the screw 9, any additional bending of the bimetallic strips 2a, 2b, 2c will cause the abutment member 6 to be shifted towards the left, in opposition to the action of the spring 8a. A catch 75 the shaft or abutment member 6.

I2 that is normally held by a spring I8v in engagement with the abutment `member 8, as illustrated in Figs. 4 and 5, becomes therefore released, so as to rotate anti-clockwise, under the action of the spring IB, into the position illustrated in Fig. 6, thereby releasing the beforementioned main switch that is controlled by the releasing device. If it be assumed, as in Fig. 6, that, vrdue to an unsymmetrical load, only the bimetallic strips 2b and 2c, but not the bimetallic strip 2a, has become bent, the fixing member 3 will remain in the initial position, and the abutment member 6 will become actuated, in opposition to the action of the spring 8a towards the left. In this case, too, thelatchv I2 will become released to actuate the switch controlled by the releasing device, thereby to disconnect the unsymmetrical load from the supply line.

Though the abutment member 6 and the iixing member 3 have been described above as 1ongitudinally slidable on'the bearing member I, they may be rendered rotatable or otherwise movable. One such embodiment is illustrated in Fig. 7. The ilxing member 3 that carries the bimetallic strips 2a, 2b, 2c is shown` journaled, so as to rotate like a shaft, in bearings I8 of a bearing member (not shown). 'I'he free ends of the bimetallic strips 2a, 2b, 2c rest on the stationary abutments 5a, 5b, 5c. Abutment fingers 6a, 6b, 6c engage the sides of the bimetallic strips 2a, 2b, 2c opposite the stationary abutments`i5a, 5b, 5c. The fingers 6a, 6b, 8c are mounted on a rotatable abutment member or shaft 8 that is journaled inbearings II of a bearing member (not shown). A catch I2, pulled downward by a spring 8a, is fixed to the right-hand end of The abutment ' fingers 6a, 8b, 6c, therefore, normally maintain the bimetallic strips 2a, 2b, 2c yieldingly in engagement with the stationary abutmentsia, 5b,

5c. As long as the shaft or abutment member G is not rotated by the bimetallic strips 2a, 2b;

2c, a latch I2a is held in its initial position by the catch I2. An additional bimetallic strip 2d, not heated by means of a heating current, is mounted upon the right-hand side of the xing-member shaft 3 to compensate for the influence of the ambient or room temperature onh the bimetallic releasing- strips elements 2a, 2b, 2c. The adjustable stop screw 9 is arranged in the path of movement of the bimetallic compensation strip 2d and its position may be read ofi on the scale 8a.

On the occurrence of an unsymmetrical load of the three phases, the bimetallic strips, which are subjected to the greater expansion rotate the abutment-member shaft 6 anti-clockwise. Upon a predetermined and very small angle of rotation, the latch I2a, released by the catch '|2, is actuated by its spring I8, causing operation of the said switch to disconnect the load from the mairfs. When a symmetrical load is present, the fixing-member shaft 3 is rotated by the bimetallic strips 2a, 2b, 2c in the direction of the arrow p, whereupon they become bent into the dotted-line positions. When thel symmetrical load is of inadmissible current strength and duration, the compensation strip 2d abuts against the screw 9, thereby preventing further rotation of the member 3 in the direction of the arrow p. Any additional bending of the bimetallic strips 2a, 2b. 2c thereupon effects a rotation of the abutmentmember shaft 6 anti-clockwise, whereupon the catch I2 releases the latch I2a, thus causing the said switch to be released or tripped.

According to Fig. 8, curved bimetallic strips 2a, 2b, 2c are heated by means of the heating coils 4a, 4b, 4c, arranged on the inner sides of the strips. The right-hand ends of the bimetallic strips' 2a, 2b, 2c are pivotally mounted on projections 3a, 3b, 3c of a fixing-member shaft 3 that vis rotatably mounted in bearings III of a bearing member (not shown). The shaft 3 carries the bimetallic compensation strip 2d cooperating with the adjustable stop-screw 8, the position of which may be read off fromthe scale 8a. The

left-hand ends of the ` bimetallic strips 2a, 2b, 2c areA clamped between the stationary ' abutments 5a, 5b, 5c and the movable abutments 8a, 8b, 8c, the latter being constituted of fingerlike projections on the abutment-member shaft 8, rotatably mounted in bearings II. The abutment 8c is bell-crank shaped to form a catch I2 holdingin position the latch I2a. The spring 8a connects catch I2 with the latch I2a.

The mode of operation of the releasing device shown in Fig. 8 is the same as that shown in Fig. 7.

According to the modification/of Fig. 9, a hublike `fixing member 3, carrying the bimetallic strips 2a, 2b, 2c, is rotatably mounted on an axle I5, secured to the bottom of the cylindrical bearing member I. Ihe bimetallic strips 2a,l 2b, 2c are clamped between pairs of abutments 5a and 8a, 5b and 8b, and 5c and 8c. The abutments 8a, 5b, 5c are stationary and form part of the bearing member. The abutments 8a, 6b, 8c are constituted of radial projections of an abutment member 8 that is rotatable about the axle I5 independently of the iixing member I. The abutment member 6 is acted upon by a spring I1 that tends to rotate the abutment member clockwise, in order to maintain the releasing elements 2a, 2b and 2c clamped between the respective pairs of xed and movable abutments.

OnI the occurrence of a symmetrical load, all three bimetallic strips 2a, 2b, 2c become heated so as to become bent to the same extent, thereby rotating the fixing member 3 clockwise, until its projection 3d abuts against the stop screw 8, carried by a stop member 8c. Upon further heating and bending of the bimetallic strips 2a, 2b, 2c, the abutment member B is rotated anti-clockwise, in the direction of the arrow PI, until its projection 6d abuts agains a contact member 8, thus separating the contact member 8 from engagement with a contact member 1. 'Ihis effects opening of the circuit, normally closed by the contact members 'I and 8, of the switch controlled by the releasing device, to effect disconnection of the overload from the supply line. On the occurrence of an unsymmetrical load, the bimetallic strip or strips' that are bent more causes the abutment member 6 to rotate anti-clockwise, in

-opposition to the action of the said spring I1 acting upon same. The projection 6d abuts against the leaf spring l8, thus interrupting the circuit normally closed by the cooperating contact members 'l and 8.

Further modifications will occur to persons skilled in the art, and all such are considered to fall within the spirit and scope of the invention, as defined in the appended claims.

What isclaimed is:

l. A releasing device for electric switches having, in combination, a bearing member, an abutment member carried by and movable with respect to the bearing member, a fixing member carried by the bearing member and movable with respect to the bearing member and the abutment 15 ing provided with abutments arrangedto cooperate with other corresponding portions of the thermal releasing elements, the thermal releasing elements being so disposed as to become deformed diiferentlybetween the first-named and the second-named portions, means for heating the thermal releasing elements individually, thereby to efi'ect actuation of the abutment member in response-to the'deformations of the thermal ref leasing elem-ents, and means for releasing a Aswitch in response to the actuation of the abutment member.

2. A releasing device for electric switches having, in combination, a housing, an abutment member and a fixing member movably disposed in the housing and movable with respect to each other, a plurality of substantially identical bimetallic strips disposedin the housing and connected with the fixing member at corresponding portions of the bimetallic strips, the abutment member being provided with abutments arranged to cooperate with other corresponding portions of the bimetallic strips, the bimetallic strips being so disposed as to bend between the first-named and the second-named portions, thereby to effect f actuation of the abutment member in response to the deformations of the bimetallic strips, and means for releasing a switch in response to the actuation of the abutment member.

3. A releasing device for electric switches having, in combination, a bearing member, an abutment member carried by and movable with respect to the bearing member, means for normally maintaining the abutment member yieldingly in a normal position, a fixing member carried b'y the bearing member and movable with respect to the bearing member and the abutment member, a stop for limiting the movement of the xing member in one direction relative to the abutment member, a plurality of 'substantially identical thermal releasing 'elements connected with the fixing member at corresponding portions of the thermal releasing elements, the thermal releasing elements being adapted to be subjected to deformation under heat, the abutment member being provided with. abutments arranged to cooperate with other corresponding portions of the thermal releasing elements, the thermal re leasing elements being so disposed as to become A deformed differently between the first-named and the second-named portions, means for heating the thermal releasing elements individually, thereby to effect actuation of the abutment member away from the normal position in response to the deformations of the thermal releasing elements in opposition to the action of the yielding -maintaining means-'and means for releasing a switch in response tothe actuation of the abutment member. I

4. A'releasing device for electric switches having, in combination. a bearing member, an abutment member carried by and movablewith respect to the bearing member, a xing member carried by the bearing member and movable with respect to the bearing member and the abutment member, a plurality of substantially identical thermal releasing elements connected with the fixing member at corresponding portions of, the thermal releasing elements, the .thermal releas-l tionary cooperating abutments, one corresponding to each abutment-member abutment, means for normally clamping each thermal releasing element yieldingly between one of the stationary abutments and the corresponding abutmentmember abutment, the thermal releasing elements being so disposed as to become deformed differently between the first-named and the second-named portions, means for heating the thermal releasing elements individually, thereby to effect actuation of the abutment member in response to the deformations of the thermal releasing elements. and means for releasing a switch in response to the actuation of the abutment member.

5. A releasing device for electric switches having, in combination, a bearing member, an abutment member carried by and movable with respect to the bearing member, means movably maintaining the abutment member yieldingly in a normal position, a fixing member carried by the bearing member and movable with respect to the bearing member and the abutment member, a stop for limiting the movement of the fixing member in one direction relative to the abutment member, a plurality of substantially identical thermal releasing elements connected withA the fixing member atl corresponding portions of the thermal releasing elements, the thermal releasing elements being adapted to be subjected to deformation under heat, the abutment member being provided with abutments arranged to cooperate with other corresponding portions of the thermal releasing elements, a plurality of stationary cooperating abutments, one corresponding to each abutment-member abutment, means for normally clamping each thermal releasing element yieldingly between one of the stationary abuments and the corresponding abutmentmember abutment, the thermal releasing vele-- ments being so disposed as to become deformed differently between the first-named and the second-named portions, means for heating the thermal releasing elements individually, thereby to effect actuation of the abutment member vaway from the normal position in response to the deformations of the thermal releasing elements in vopposition to the action of the yielding maintaining means and the yielding clamping means, and means for releasing a switch in response to the actuation of the abutment member.

6. A releasing device for electric switches having, in combination, a housing, an abutment and axing member movably disposed in the housing and movable with respect to each other, a plurality of substantially identical bimetallic strips disposed in the housing and connected with the fixing member at corresponding portions of the bimetallic strips, means for normally maintaining the abutment member yieldingly in a normal position, a stop for limiting the movement of the fixing member in one direction, the abutment member being provided with abutments arranged 'to cooperate with, other corresponding portions of the bimetallic strips, a plurality of stationary cooperating abutments, one corresponding to each abutment-member abutment, means for normally clamping each bimetallic stop yieldingly between one of the stationary'abutments and the-corresponding abutment-member abutment, the bimetallic strips being so disposed as to bend between the ilrstnamed and the second-named portions, means for heating the bimetallic strips individually, thereby to effect actuation of the abutment member away from the normal position in response to the deformations of the bimetallic strips in opposition to the action of the yielding maintaining means and the yielding clamping means, and means for releasing a switch in response to the actuation of the abutment member.

7. A releasing device for electric switches having, in combination, a movable abutment member, a fixing member movable with respect 4to the abutment member, a plurality of substantically identical thermal releasing elements connected with the fixing member at corresponding portions of the thermal releasing elements, the thermal releasing elements being adapted to be subjected to deformation under heat, the abutment member being provided with abutments disposed normally to engage other corresponding portions of the thermal releasing elements at one side of each releasing element, a plurality of stationary abutments, one corresponding to each abutment-member abutment disposed normally to engage the said other portions ofthe thermal releasing elements at the other sides of the respective releasing elements, means normally `clamping each thermal releasing element yieldingly between one of the stationary abutments and the corresponding abutment-member abutment, the thermal releasing elements beingso disposed as to become deformed differently between the first-named and the second-named portions, means for heating said thermal releasing elements individually, thereby to effect actuation of the abutment member in response to the deformations of the thermal releasingelements in opposition to the action of the yielding clamping means, and means for releasing a switch in response to the actuation of the abutment member.

8. A releasing device for electric switches having, in combination, a movable abutment member, a fixing member movable with respect to the abutment member, a stop for limiting the movement of the fixing member in one direction relative to the abutment member, a plurality of substantially identical bimetallic strips connected with the-fixing member at corresponding portions of the bimetallic strips, the abutment member being provided with abutments disposed normally to engage other corresponding portions of the bimetallic strips at one side of each bimetallic strip, a plurality oi' stationary abutments, one corresponding to each abutmentmember abutment, disposed normally to engage the said other portions of the bimetallic strips at the other sides of the respective bimetallic strips, means normally maintaining the abutment member yieldingly in one extreme position of its movement to effect a yielding clamping of each bimetallic strip between one `of the stationary abutments and the corresponding abutment- 'member abutment, the bimetallic strips being so disposed as to bend between the first-named and the second-named portions, means for. heating the bimetallic strips individually, thereby to effect actuation of the abutment memberin response to the deformations of the bimetallic.

strips in opposition to the action of'the yielding maintaining means, and means for releasing a Switch in response to the actuation Of the abutment member.

9. A releasing device for electric switches having, in combination, a movable abutment member, a fixing member movable with respect to the abutment member, a stop for limiting the movement of the fixing member in one direction relative to the abutment member, a plurality of substantially identical thermal releasing elements connected with said fixing member at corresponding portions of the thermal releasing elements, the thermal releasing elements being adaptedgto ,be subjected to deformation under heat, the. abutment member being provided with abutments arranged normally to engage other corresponding portions of the thermal releasing elements at one side of each releasing element, means normally maintaining the abutment member yieldingly in one extreme position of its movement, the thermal releasing elements being so disposed as to become deformed dierently between the first-named and the second-named portions, means for heating said thermal releasing elements individually, thereby, in response to substantially equal deformations of the thermal releasing elements, to effect actuation first of the fixing member into engagement with the stop and then of the abutment member in opposition /to the action of the yielding maintaining means, and a plurality of stationary abutments, one corresponding to each abutment-member abutment, disposed normally to be engaged by the respective thermal releasing elements at the other side of the respective thermal releasing elements, one

or more of the thermal releasing elements being adapted, in response to substantially unequal deformations only of the thermal releasing elements, to effect actuation of the abutment member only, in opposition to the action of the yielding maintaining means while the remaining undeformed thermal releasing element or elements are, maintained in engagement with its corre- .sponding stationary abutment member or members, and means for releasing a switch in response to the said actuation of the abutment member.

l0. A releasing device for electric switches hav-- engage other corresponding portions of the thermal releasing elements at one side oi.' each releasing element, means for normally maintaining the second shaft yieldingly in one extreme position of its movement, the bimetallic releasing elements being disposed so as to bend between the first-named and the second-named portions, heating windings respectively disposedA on Ithe concave sides of the bimetallic releasing elements for heating the bimetallic releasing elements individually, thereby, in' response to substantially equal deformations of the bimetallic releasing elements, to effect rotatable actuation first of the first-named shaft into engagement with the stop and then of the second-named shaft in opposition to the action of the yielding maintaining means, and a plurality of stationary abutments, one corresponding to each of the firstnamed abutments, disposed normally to be engaged by the respective bimetallic releasing elements at the other side of the respective bimetallic releasing elements, one or more of the bimetallic releasing elements being adapted, in response to substantially unequal deformations only, of the bimetallic strips, to effect rotatable actuation of the second shaft only, in opposition to the action of the yielding maintaining means while the remaining undeformed bimetallic releasing element or elements are maintained in engagement with the corresponding stationary abutment member or members. and means for releasing a switch in responseto the rotation of the second shaft.

11. A releasing device for electric switches having, in combination, amovable abutment member, a fixing member movable with respect to the abutment member, a stop for limiting the movement of the fixing member in one direction relative to the abutment member,A a plurality of substantially identical thermal releasing elements connected with the fixing member at corresponding portions of the thermal releasing elements,

the thermal releasing elements being adapted to be subjected to deformation under heat, the abutment. member being provided with abutments arranged normally to engage other corresponding portions of the thermal releasing elements at one side of each releasing element, a plurality of further abutments, one corresponding to each abutment-member abutment, disposed normally to engage the said other portions of the thermal releasing elements at the other sides of the respective thermal releasing elements, means normally maintaining the abutment member yieldingly in one extreme position of its movement to effect a yielding clamping of each thermal releasing element between one ofthe further abutments and the corresponding abutment-member abutment, the thermal releasing elements being so disposed as to become deformed differently between the first-named and the second-named portions, means for heating the thermal releasing elements individually, thereby. in response to substantially equal deformations of ,the thermal releasing elements, to effect actuation first of the xing member into engagement with the stop and then-of the abutment member in opposition to the action of theyielding maintaining means, one or more of the thermal releasing elementsv being adapted, in're- 4sponse to substantially unequal deformations only, of the thermal releasing elements, to effect actuation of the abutment member only inopposition to the action of the yielding maintaining means, and a latch operable in response to the actuation of the abutment member to release a switch.

12. A releasing device for electric switches having, in combination, a rotatable shaft, a stop for limiting the rotative movement of the shaft inA one direction, a plurality of substantially identical bimetallic releasing elements connected with the shaft at corresponding portions of the bimetallic releasing elements, a second rotatable shaft provided with abutments arranged normally to engage other corresponding portions oi the thermal releasing elements at one side of each releasing element, means for normally maintaining the second shaft yleldlngly in one'extreme position of its movement, the bimetallic releasing elements being disposed so as to bend between the first-named and the second-named portions, means for heating the bimetallic releasing elements individually, thereby, in response to substantially equal deformations of the bimetallic releasing elements to effect rotatable actuation first of the first-named shaft into engagement with the stop and then of the second-named shaft in opposition to the action of the yielding maintaining means. and a plurality of stationary abutments, one corresponding to each of the firstnamed abutments, disposed normally to be engaged by the respective bimetallic releasing elements at the other side of the respective bimetallic releasing elements, one or moreof the bimetallic releasing elementsy being adapted, in response to substantially unequal deformations only, of the bimetallic strips, to effect rotatable actuation of the second shaft only, in oppositionA means responsive to the rotation of the second shaft to release a switch in response to the rotative movement of the second shaft.

ERNST BESAG.

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