US2180421A - Control device - Google Patents

Description

NOV 21', 1939. M, LEONARD 2,180,421

Filed 20, 36

WITNESSES:

NTOR

Merl-ii] goflard Patented Nov. 21, 1939 UNITED STATES CONTROL DEVICE Merrill G. Leonard, Sharon, Pa., assignor to Westinghouse Electric & Manufacturing Company,

East Pittsburgh, Pa.,

sylvania a corporation of Penn- Application November 20, 1936, Serial No. 111,816

11 Claims.

My invention relates to control devices in general, and more particularly to current-responsive control devices for actuating mechanisms, overload relays, circuit breaker trip devices, meas- 5 uring or indicating instruments or the like.

Bimetallic elements comprising two metals having dissimilar coeflicients of expansion secured together so that when subjected to heat produced either by an ambient temperature or by the passage of an electric current therethrough the element is flexed or bent, having been used for controlling various types of devices, some of which have been mentioned above. In most applications of bimetallic elements of the currentresponsive type the desired objectives consist in general of Obtaining minimum length to reduce the space factor, suflicient thickness to secure necessary force for controlpurposes combined with maximum deflection, and also of obtaining relatively high temperature rise for overload currents of lower magnitude.

The very rapid temperature rise at short circuit current usually determines the minimum cross sectional area of bimetal which can be used. To obtain maximum temperature rise on overloads of lower magnitude it is desirable to construct the bimetallic element so that its surface area is a minimum for a given length in order to reduce the heat radiation losses. This would require the use of bimetal whose cross-section is substantially square. The use of a bimetallic element whose cross-section is substantially square is entirely impractical because of the limited length and large cross sectional area required in present designs. A bimetal of limited length having a square cross section of sufficient area to carry short circuit current would be too stiff to bend or flex any appreciable amount under overload conditions. It has accordingly been necessary heretofore to construct bimetallic elements for given current ratings relatively thin and 5 stiilness'ior usual application.

The modern types of circuit breakers are designed to control extremely heavy currents and consequently the bimetallic trip elements thereof must have a relatively large cross sectional area. The bimetallic trip elements must also be very short in order to reduce the space factor.

It is accordingly one object of my invention to provide an improved current-responsive bimetallic control device which has a minimum heat radiating surface per unit of greatest dimension to insure a more eflicient heating action by the current traversing the same and yet which is capable of flexing with a facility comparable to similar devices of like current rating and which is capable of exerting a comparable or greater force for a given deflection. I

It is a further object of my invention to provide an improved current-responsive bimetallic control device capable of producing a greater temperature rise and deflection than similar bimetallic devices of the same cross-sectional area and length for a given value of current.

A further object of my invention is to provide an improved current-responsive bimetallic device Whose cross-sectional area is substantially square to reduce the heat radiating surface of the device, and yet which is capable of flexing in response to the heating action of the current with the same facility as a similar device of the same length and rating whose cross-sectional dimensicns are more favorable to flexing.

A further object of my invention is to provide a more efficient and improved thermal trip device for a circuit breaker.

Briefly, my invention consists in constructing a current-responsive bimetallic control device which is capable of carrying out the foregoing objects by mounting a plurality of bimetallic elements or strips in'face-to-face engagement and securing them to a support in such a manner that they all flex in the same direction when heated by the current, the faces of the unsecured portions being adapted to slide one over the other when the elements are flexed, and the number and dimensions of the several elements being such that the cross-section of the composite device formed by the bimetallic elements is substantially square to reduce the heat radiating surface area and increase theheating action of the current.

The principal field for immediate application of the invention is in connection with electrical circuit controlling devices, such as switches, circuit breakers, thermal overload relays and the like, or in connection with measuring or indicating devices. It will readily appear, however, that my 55 invention is equally applicable to various other uses in which a bimetallic device having a maximum deflection and a minimum space factor would be desirable.

I shall hereinafter describe several modifications of my invention and the application of one such device to a circuit breaker to illustrate a specific use of the device without, however, in any way intending to restrict the application or scope of my invention, except as indicated by the appended claims and the prior art.

The novel features that I consider characteristic of my invention are set forth in particular in the appended claims. The invention itself, however, both as to structure and operation, together with additional objects and advantages thereof, will best be understood from the following detailed description of several embodiments thereof when read in connection with 'the accompanying drawing, in which:

Figure 1 is a vertical sectional view of a circuit breaker embodying my improved current-responsive bimetallic control device;

Fig. 2 is a front elevational view of the bimetallic control device shown in connection with Fig. 1;

Fig. 3 is a front elevational view of a modified form of my improved current-responsive bimetallic control device;

Fig. 4 is a side elevational view of the bimetallic control device illustrated in Fig. 3;

Fig. 5 is a side elevational view of a further modified form of my improved current-responsive bimetallic control device; and

Fig. 6 is a front elevational view of the bimetallic control device illustrated in Fig. 5.

The structure of the circuit breaker illustrated in Fig. 1, with the exception of the bimetallic control or trip device, is substantially the same as that disclosed in Patent No. 1,802,758, issued April 28, 1931, to H. D. Dorfman and assigned to the assignee of this invention, and hence, only a brief description of the structure of the circuit breaker will be given in this application. For details of construction reference may be had to the above referred to patent.

Referring to Fig. 1, the circuit breaker illustrated comprises a base 1, and a cover 9 of molded insulating material, end terminals H, a stationary contact |3, a movable contact l5, circuit breaker operating mechanism indicated generally at H, a current-responsive control or trip device indicated generally at I9, and an arc extinguishing means 2|.

The circuit for the breaker extends from the left-hand end terminal through the currentresponsive trip device l9, through aflexible shunt connection 23 to the movable contact l5, stationmy contact I 3, and through a conducting strip 25 to the right-hand end terminal The movable contact I5 is secured to a resilient arm 21 which is, in turn, secured by means of rivets to a channel-shaped movable contact carrying frame 29, which is pivotally supported by means of a pivot pin to a U-shaped main supporting frame 3|.

The operating mechanism for the circuit breaker comprises a bifurcated operating mem ber 33 having an operating handle 35 secured thereto, a cradle member 31, a pair of toggle links 39 and 4| and a pair of over-center springs 43. The legs of the bifurcated operating member 33, the cradle 31 and the channel-shaped movable contact supporting frame 29 are pivotally mounted by means of the pins, as shown,

to the U-shaped main'supporting frame 3|. The toggle links 39 and 4| are pivotally connected to the cradle member 31 and to the channelshaped movable contact supporting frame 29, re-

spectively. A knee pivot pin pivotally connectsv the toggle links 39 and 4| together as illustrated. The over-center springs 43 are connected at their lower ends to the knee pivot pin of the toggle links, and at their upper ends to the top of the bifurcated operating member 33. The cradle member 31 has a rearwardly extending portion 45 provided with a latch 41. The latch 41 is insulated from the cradle member 31 by means of a plurality of mica plates 49. operating member. 33 is provided with a hookshaped extension -5| adapted to engage a portion of the cradle member to reset the same after the breaker has been. tripped.

In Fig. 1 the circuit breaker is shown in the tripped position with the movable contact in the open circuit position. Before the circuit breaker can be closed the cradle member 31 must be reset to its latched-in position. To reset the circuit breaker, the operating handle 35 is moved toward the left, as viewed in Fig. 1, to the open circuit position. During movement of the operating member to its open circuit position, the hook extension 5| engages and moves the cradle in a counter-clockwise direction to position the latch 41 under the last piece 53 secured to the bimetallic trip device IS. The circuit breaker is now in the reset position. To close the contacts the op- -to move to their extended positions to effect movement of the movable contact to its closed circuit position with a snap action, the cradle member being held in its latched-in position against the biasing action of the over-center springs.

To open the contacts of the circuit breaker, the operating handle is moved to its full open position at the opposite end of the opening in the cover 9. Substantially the reverse action takes place, that is,. the over-center springs change their line of action and cause collapse of the toggle links 39 and 4|, which causes movement of the movable contact to its open circuit position with a-snap action.

When the circuit breaker is in the closed circuit position, if an overload of predetermined magnitude occurs in the circuit controlled by the breaker, the increased current in traversing the bimetallic trip device I9 causes heat to be produced therein and if the current persists for a predetermined length of time the heating action causes the bimetallic trip element to flex in a direction away from the operating mechanism I1 to release the latch 41 from its engagement by the latch piece 53 carried by the bimetallic trip element. The release of the latch 41 allows the over-center springs to rotate the cradle 31 in a clockwise direction. After the cradle has been rotated a short distance, the line of action of the over-center springs changes to cause collapse of the toggle links which, in turn, effects movement of the movable contact to its open circuit position with a snap action.

The bifurcated For the trip device of the circuit breaker it has heretofore been the practice to use a single bimetallic strip or U-shaped member carrying a latch piece. The length of this single bimetallic strip or U-shaped member must be necessarily limited in order to provide a compact circuit breaker structure. Consequently, the strip has in the past, been constructed of a broad thin bimetal in order to allow the same to flex a sufllcient distance to release the cradle member of the breaker. The objectionable feature of this type of trip device has been that the heat radiating surface area of the broad thin blmetals is so large that it takes a considerable amount of overload current flowing for a considerable length of time to produce enough heat to cause suificient deflection of the element to release the cradle and trip the breaker. To reduce the heat radiating surface area it would be necessary to use a narrow thick bimetal so that the crosssection would approach a square. This usually cannot be done in the present designs with the limited bimetal length because the deflection of such a thick bimetal would be too small to trip the breaker. 1

Myimproved current-responsive bimetallic control device provides a device having a minimum surface areaior its length and rating, and yet which is capable of'flexing or bending with the same facility as the prior art devicm of the same current rating and length.

Referring to Figs. 1 and 2, one form of my improved current-responsive bimetallic control or trip device comprises a pair of angle-shaped terminals 55, a plurality of bimetallic strips or the operating mechanism 11 when heated by the.

overload current. The latch piece 53 is U shaped and has-one of its legs secured to one of the bimetallic strips 51 by means of a rivet 6!.

The legs of the U shaped latch piece hold the ends of the strips 51 in engagement and the bight portion of the latch piece is spaced from the ends of the strips in order to permit relative movement 'therebetween so that the strips are free to slide one over the other in flexing. This form of latch piece provides a means whereby both strips contribute to the tripping force for overcoming the friction of the latch so that the total tripping force exerted is the sum of the forces exerted by each strip alone, and also allows the strips to slide one over the other so that the composite member formed by the strips is capable of flexing the same amount and with the same facility as could a single one ofthe strips alone.

Various other types'oi latch means could be usedin connection with the composite bimetallic element. It is only necessary that the latch piece be moved with a force which is the sum of the forces exerted by each bimetallic strip alone and mounted so as to permit free sliding of the strips relative to one another. For example, ii the bimetal strips are of the'straight type, as shown in Figs. 3 and 4, they could be secured for movement together by a sleeve or split ring 68 (see Figs. 3 and 4) which ties the strips together and yet permits them to slide one over the other in flexing, and the latch piece could beformed integral with or secured to the sleeve or Instead of the latch piece being secured to the ring or sleeve 66, it could be secured to one of the strips 63. Another tripping arrangement of the composite bimetallic member formed by the bimetallic elements would not require the attachment of any latch piece to the member. An intermediate latch member may be provided which normally holds the latch 41 on the actuating member 31 in latched in position and the composite bimetallic member could be arranged to flex so that the free end would push the intermediate latch member to a releasing position to release the latch 41 and actuating member 31. This form of arrangement would be particularly adapted to multipole circuit breakers and in such case the intermediate latch member would constitute the trip bar which extends across all of the poles of the breaker.

The strips 51 are connected in parallel with each other and in series with the contact means of the breaker by means of the terminals 55. When the strips 51 are heated by the overload current, they each flex in a direction away from the operating mechanism I! and cause the latch piece 53 to release'the latch 41 and thus trip the circuit breaker.

In flexing, the faces of the unsecured portions of the bimetallic elements slide one over the other so that each strip is capable of flexing the same amount in response to the heat developed as though the other strip were not present. It will be noted that the number and dimensions of the bimetallic strips are such that the cross-section of the composite member formed by'the several strips approaches that of a square, so that the heat'radiating surface per unit length of the composite member formed by the strips is reduced to a minimum. With this construction, the heat radiation losses are materially reduced and consequently, the heating action for a given value of current is materially increased, and by reason of the particular manner of mounting the strips whereby the faces of the major portions slide one over the other, a maximum deflection or flexing of the composite member takes place for a given value of current. In' other words, for a current-responsive bimetallic trip device of given length and cross-sectional area (fixed usually by the short circuit current capacity), I have provided an improved structure which produces a greater temperature rise, together with a greater deflection than similar devices of the same crosssectional area and length.

Figs. 3 and 4 illustrate a modified form of my improved current-responsive bimetallic control device. In this form, instead of a plurality of U-shaped bimetallic strips, a plurality of straight strips are provided. This form of my invention comprises an angle-shaped terminal 62, a pair of straight bimetallic strips 63 and a second terminal indicated generally at 55. The bimetallic strips 63 are secured to the lower terminal 62 by means of a pair of rivets 61. As in the modification illustrated in Figs. 1 and 2, the number. and dimensions of the strips are such that the crosssection of the composite members formed thereby is substantially square so as to reduce'heat radiation losses, and the faces of the unsecured portic-ns are adapted to slide one over the other when the strips are heated by the passage of current therethrough. The terminal 65 provides a means for connecting a conductor to the upper end of each strip 63, and also allows the ends of the strips to move or slide relative to one another.

The terminal comprises a flexible strap 68 of "I5 conducting material, such as copper. One end of the strap is connected to one of the bimetal strips by means of a rivet H and the other end of the strap is connected to the second bimetallic strip by means of a rivet I3. A flexible conductor wire 15 is adapted to be secured to the body portion of the flexible strap 69 by any suitable means, such as soldering, for example.

The operation and advantages of this form of current-responsive control device are similar to that described in connection with the form illustrated in Figs. 1 and 2. If this form of my invention is'to be used in connection with a circuit breaker, latch means similar to the forms described in connection with the trip device shown in Figs. 1 and 2 may be provided; and the composite device formed by the two.strips is con-v nected in circuit with the contact means of the breaker by means of the terminals 62 and 65.

Figs. 5 and-6 illustrate a slightly modified form of a current-responsive bimetallic control device similar to the form shown in Figs. 3 and 4. In this form of the invention, a plurality of bimetallic strips 11, four in the instance shown, have their lower ends secured to a terminal means 19 by means of rivets 8 I. The faces of the unsecured portions (which constitute the major portions of the strips) are adapted to slide one over the other when the strips are flexed by the heating action of the current traversing them.

The outer strips 11 are slightly shorter than the inner pair of strips, in order to cooperate with a terminal 83. The terminal 83 consists of a strap 85 of flexible conducting material, such as copper. One end of the strap is connected to one of the outer bimetal strips 11 by means of a rivet 81, while the other end of the strap 85 is secured to the opposite outer bimetallic strip H by means of a rivet89. A terminal 9| is connected to the projecting ends of the inner bimetallic strips H. The terminal BI is similar to the terminal 69 illustrated in Figs. 3 and 4, and comprises a strap 93 of flexible conducting material, the ends of which are secured to the bimetal strips 11 by means of rivets 95.

The compound terminal formed by the terminals 83 and 9| provides a means for connecting a flexible conductor 91 to each of the individual bimetallic strips 11 and allows the ends of the individual strips to move relative to one another, so that the faces of the strips can slide one over the other when the strips are flexed by the passage of current. This form of current-responsive bimetallic control device may be used in connection with a circuit breaker as a trip device in the same manner as the form illustrated and described in connection with Figs. 1 and 2. An additional advantage of this form of my invention is to secure a bimetallic control device having a larger cross-sectional area for higher current ratings.

It will be noted that in all the forms of my invention the surface area of the composite bimetallic control device is reduced to a minimum for a given length and cross section, and hence the heating action of the current in traversing the device is materially increased. It will also be noted that in all cases, the major portions of the strips of the composite member are free to slide one over the other whereby the composite member formed by the individual strips may be deflected the same'amount as a single or individual strip, due to the sliding action of the strips with respect to one another. The invention also allows for a wider range of. adjustment of the control While in accordance with the patent statutes I have given the foregoing details of several embodiments of my invention, it is to be understood that many of these are merely illustrative and that variations in their precise form will be desirable in some applications. I desire, therefore, that the language of the accompanying claims be accorded the 'broadest reasonable construction and that my invention be limited only by what is explicitly stated in the claims and by the prior art. v

I claim as my invention:

1. In a circuit controlling device, contact means, a current responsive composite control member connected in a circuit and operable in response to predetermined current conditions in said circuit to control said contacts, said member consisting of a plurality of bimetal elements disposed in face-to-face engagement and secured to a common support so that they all flex in the same direction when heated by the current, and means connecting the free ends of said elements for simultaneous deflecting movement together, said connecting means permitting relative sliding movement between said elements so that the faces of the unsecured portions of the elements slide one over the other when the elements are flexed.

2. A current responsive control device comprising a plurality of bimetal elements disposed in face-to-face engagement and secured to a common support so'that they all flex in the same direction when heated by predetermined values of current, means connecting the free ends of said elements for deflecting movement together, said connecting means permitting relative sliding movement between said elements, and means for electrically connecting said device in a circuit.

3. A current-responsive control device comprising a terminal, a pair of bimetallic strips disposed in face-to-face engagement, means for securing said strips together at one end and to said 1 terminal, the faces of the unsecured portions of said strips'adapted to slide one over the other in response to the passage of predetermined values of current through said strips, and means for connecting the free ends of said strips to a conductor, said connecting means permitting sliding of said strips relative to each other.

4. A current-responsive control device comprising a terminal, a pair of bimetallic strips disposed in fa ceto-face engagement and being secured together at one end to said terminal, the faces of the unsecured portions of said strip being slidable one over the other when said strips are heated by the passage of predetermined values of current therethrough, means including a flexible strap of conducting material for connecting the free ends of said strips to a conductor, said strap having one end secured to one strip and its other end secured to the other strip to permit relative movement of the free ends of said strips.

5. A current-responsive composite control device comprising a terminal, a plurality of strips of bimetallic material disposed in'face-to-face engagement and having their ends secured together to said terminal, the faces of the unseopening of said contact means, a trip device norcured portions of said strip adapted to slide one over the other when said strips are flexed by the passage of predetermined values of current therethrough, the number and dimensions of said strips being such that the cross-section of the assembled strips approaches that of a square so that the heat radiating surface area of the device per unit length is minimized and means permitting relative movement of the free ends of said strips for connecting said free ends to a conductor. a

6. In a trip device for a circuit breaker, a composite current-responsive member comprising a plurality of bimetallic elements, means securing said elements on a common support in faceto-iace engagement in such a manner that said elements flex in the same direction and the faces of the unsecured portions slide one over the other when said elements are heatedby the passage of predetermined values of current therethrough, the number and dimension of said elements being such that the radiating surface area of said composite member is reduced to a minimum whereby a maximum temperature rise and deflection of said member is produced by the passage of said predetermined values of current therethrough, and terminal means connecting said elements in parallel for connecting said compositemember in a control circuit.

7. A current-responsive composite circuit controlling device comprising a plurality of bimetallic elements, means for securing said elements to a common support in face-to-face engagement so as to permit unrestrained flexing of the elements in the same direction in response to the heat produced by the flow of current therethrough, the number and dimensions of said elements being such that the radiating surface area of said device is reduced to a minimum to produce a maximum temperature rise and deflection of said elements and member for a given value of current traversing the same, and terminal means for connecting said device in the circuit to be controlled.

8. A current responsive composite control device comprising a plurality of bimetallic elements, means for securing said elements to a support in face-to-face engagement so that the major portions of said elements flex in the same direction and the engaging faces of said elements slide one over the other during flexing, means permitting free relative sliding movement of the engaging faces for connecting said elements for movement together so that the force exerted by said composite device in flexing is substantially the sum of forces exerted by the individual bimetallic elements, and terminal means for connecting said elements in parallel to an external circuit. 4

9. In a circuit breaker having contact means and a spring biased member releasable to cause mally restraining said spring biased member, said trip device having a composite current responsive member operable in response to predetermined overload conditions to cause said trip device to release said spring biased member, said composite member comprising a plurality of bimetal elements, means securing said elements to a common support in face to face engagement so as to permit unrestrained flexing of the elements in the same direction in response to the heat produced by the flow of current therethrough, the number and dimensions of said elements being such that the heat radiating surface area of the composite member is a minimum to produce a maximum temperature rise and deflection of said elements and member for a given value of current traversing the same, and terminal means for connecting said member in circuit with said contact means.

10. In a circuit controlling device, contact means, a current responsive composite control member operable in response to predetermined current conditions to control said contacts, said composite member comprising a plurality of U shaped bimetal elements, means for securing said elements to a support in face to face engagement so as to permit unrestrained flexing of said elements in the same direction in response to the heat produced by the flow of current there! through, the number and dimensions of said elements being such that the heat radiating surface area of said member is reduced to a minimum to produce a maximum temperature rise and deflection of said elements and member for a given value of current traversing the same, and terminal means for connecting said member in an electrical circuit.

11. In a circuit controlling device, contact means, a current responsive composite control member operable in response to predetermined current conditions to control said contacts, said composite member comprising a plurality of bimetal elements, means for securing said elements member for a given value of current traversing the same, and means electrically connecting said composite member in circuit with said contact means to be traversed by the current flowing through said contact means.

MERRILL G. LEONARD.

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