US2378648A - Electric switch - Google Patents

Description

June 19, O. MASENG ELECTRIC SWITCH Filed oct. 29, 1945 v v INVENTOR. lav Mderzeg.

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/ZTraK/VE Z Patented June 19, 1945.

ELECTRIC SWITCH Olav Maseng, Detroit, Mich., asslgnor to Squarel D Company, Detroit, Mich., a corporation of Michigan Application october 29, 1943, serial No. 508,138

(ci. zoo-113) 8 Claims.

This invention relates to electric switches automatically operable in response to current overload and more particularly to a current responsive bimetallic element utilized to effect automatic opening oi' such switches. l

In the operation of automatically opening electric switches, relays, and circuit breakers, the

ment as it is heated results in a motion effecting l the automatic tripping operation.

The object of this invention is to provide a bimetallic element which shall have af greater working force and/or a greater movement in response to a given temperature and/or current.

Another object of the invention is to provide a bimetallic element which shall be so supported ast to lessen its tendency to take. a permanent se Other objects and features of this invention will be readily apparent to those skilled in the art from the specification .and appended drawing illustrating certain preferred embodiments in which:

Figure 1 is a,4 sectional view of an automatic electric circuit breaker utilizingr the bimetallic trip element according to the present invention.

Figure 2 is a perspective detail view of the bimetallic element and its supporting connector.

The drawing shows the circuit breaker mecha.- nism described and claimed in the copending application of John G. Jackson and Reinhold Muel-` arm 'l carries a movable contact 9 cooperating with stationary contact 5, and about the stationary contact and the path movement of the movable contact 9 is disposed an arc suppressor structure indicated generally at Il. The contact arm I is provided with a slot I2 in which isdisposed a slidable pin I3 on which is pivoted one end of a link I4, whose other end is connected at the pivot I5 to a link I6, the link I6 being pivotally supported upon the pivot 8. Also pivotally mounted on the pin I3 is a spring guide II which, in conjunction with the opposite spring guide I8; carries an operating spring I9 which supplies a tensile force upon the pin I8. 'I'he spring guide I8 ispivoted at 2| to a trip lever 22 mounted on a ilxed pivot 23. The operating handle has an interior arm 24 carrying a pin 25 which isdisposed within an opening 28 in a wall of the link I8. A light spring 21 bearing against the pin biases the handle in a clockwise direction.

The trip lever 22 is latched at 26 to a latch 29 The mechanism, which will be only 'broamy rotatively mounted adjacent:y a mid point at 3l and normally maintained thereby in the position shown in Figure 1. At its upper end, the latch 29 is provided with a spring 32 biasing it in a counterclockwise direction to latched position and is provided with a pin 33 adaptedto be engaged by the blmetallic element 34 to rotate the latch into -unlatched position. A flexible lead 35 interconnects a point on the bimetal 34 and the switch arm 1. mounted at its lower end on a connector 36 which extends to the exterior of the breaker and is mounted upon the end ledge at the left end thereof. A magnetic tripping device is supplied to supplement the action of the bimetallic element 34 and this embodies a stationary magnetic Apiece 3l and a U-shaped armature 38 carried on an arm 39 pivoted at 4| and carrying an adjustable screw 42 which engages latch 29 and is adapted to effect movement thereof on heavy overloads and short circuits when the armature` is attracted to the plate 31.

The-action of the circuit breaker mechanism will now be broadly described. The parts are shown in contacts engaged position. To manually move the parts to off position, the handle is moved t0 a counterclockwise direction which effects rotation of the link I6 in a clockwise direction to move the .pivot I5 downwardly. When pivot I9 passes the centerline between the pivot 8 and the pin I3, the linkage formed by the links I 6 and I4 will lapse downwardly, and the switch arm `I will be moved in a counterclockwise direction to move the contact 9 upwardly and disengage it The bimetallic element 34 is rigidly.

from the stationary contact l. The manual operation to move the contacts to engaged position is the reverseof this action.

In automatic operation, the latch 18 is moved in a clockwise direction under the action either of the bimetal 34 cr the magnetic armature ls, or by a combination of both their movements until it unlatches the trip lever 22. This trip lever then rotates in a clockwise direction, under the action of both the operating spring i9 and a trip spring 43 which biases it in a direction for clockwise movement, Such movement both moves the contact arm l directly and nally effects collapse of the linkage l4-I8 as the spring I! passes through their center of operation. To reset the breaker after automatic operation, the handle 3 is moved to the on position to again move the tnp lever 22 to its latched position after which the contacts may be engaged by moving the handle to the position shown in Figure l. The breaker mechanism and its operation have been only generally shown and described because it is disclosed and claimed in the application previously named.

The bimetallic element 34 shown in Figures 1 and 2 is of strip form and comprises an elongated arm 44 connected at one end at 45 to the connector 36. A thin sheet 40 oi' mica or other insulating material insulates the arm 44 from the connector 3B except adjacent the point 4l where they are electrically and mechanically connected. rihe arm 44 is return bent to form a smaller arm 46, the structure being then of U shape with one leg elongated. vThe flexible lead 35 is connected to the short arm 44 so that the curved portion is heated by the current passing through the bimetallic element. -The connector is extended to form the abutment arm 41 and the end of the arm 4B is provided with an insulating button 48 adapted to engage the arm 41 as an abutment. As the bimetallic element $4 is heated by the passage of an overloadcurrent therethrough, the arm 44 bends to flex in a clockwise direction in the normal manner of a straight bimetai. However, the curved portion at which the strip is return bent is also heated and this tends to straighten out, forcing the arm 48 against the abutment 41. As this abutment is a rugged stationary piece the resultant force thereon works by reaction to effect a further movement of the bimetallic element; or, if this movement is restricted, it results in a greater i'orcebeing exerted by the bimetallic element on the member against which it presses. With the bimetal constructed as shown, the result is either to produce a greater movement of the latching surface of the latch29 due to the passage of any given current or the attainment of any given temperature than would be the case with a straight bimetallic strip; or, for the same movement, a greater force will be exerted by the bimetallic element at the said given current or given temperature. This is particularly desirable in the automatic operation of the switch or other device to be controlled by the bimetallic element where the resistive force to the movement of thebimetal may be considerable or where a relatively large movement for a relatively heavy and inexible element is desired. For example, in the construction of an automatic circuit breaker for relatively heavy currents, it may be necessary to use a bimetal of considerable cross-section so as to avoid burning thereof on short circuit. Such a bimetal is usually relatively inactive and does not have a high degree of movement on small overload currents. With the bimetal of this invention, the movement of the bimetal on such small overload currents is greatly increased and, hence, a greater movement of the latch 2l is produced and a larger overlap at latch 28 may be provided so that the operation of the circuit breakerV is more reliable. Similarly, with the bimetal having the same movement as in a normal bimetal, considerably greater force may be exerted upon the working part due tothe combination of the force produced by the flexing of the long arm 44 and the reaction force from the pressing of the point 4l on the arm 41 caused by the straightening of the curved portion of the bimetal.

Another feature of the invention lies in the function of the bimetallic element in resisting the taking of a permanent set which might destroy its calibration. In the carrying of heavy short circuit currents, the current traversed blmetal can be heated to relatively high temperatures at which its resistance to permanent set is relatively low. When the bimetallic element is in the form of a straight strip attached at one end and applying force at the other end, it acts as a cantilever beamand at temperatures experienced on heavy short circuit it is possible that a permanent set will be taken which will destroy the proper calibration of the breaker. According to the present invention, the return bent arm of the bimetal engages its abutment to change the character of the beam formed by the bimetallic element and by this additional support adjacent the force-applying end substantially overcomes the tendency of the bimetal to take its permanent set. Thus, the calibration upon the occurrence of short circuit current becomes more reliable.

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limited thereto, as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

What is claimed is:

1, A heat-responsive bimetallic element comprising a bimetallic strip return bent about a transverse axis parallel to its fiat surfaces to form two generally parallel legs, means rigidly securing one leg of said bimetallic strip to a support to mount the same, a force-applying point on said element adjacent to the looped portion thereof, and a fixed abutment surface engageable by the second leg of said bimetallic element as the element ilexes upon heat application.

2. A heat-responsive bimetallic element comprising a bimetallic strip return bent about a transverse axis parallel to its ilat surfaces to form two generally parallel legs, means rigidly supporting one of said legs adjacent the end thereof, means forming an abutment surface against which the second leg may press when flexed. and a member to be moved by said bimetallic element and having its point of force reception located adjacent to the looped portion of said element.

3. A heat-responsive bimetallic element comprising a bimetallic strip of substantially U shape, with the fiat surface of the strip at right angles to the plane of the U, and with the high expansion side of the strip at the interior of the U, means securing one leg of said U to a support to mount the element, a force-applying point on said element adjacent to the bight of the U,

and a fixed abutment surface engageable by the prising a bimetallic strip of substantially U shape,

with the flat surface of the strip disposed at right angles to the plane of the U and with the high expansion side of the strip at the inside of the U, the legs of said U being of unequal length, means'supporting the longer leg ofthe U adiacent to the end'thereof, means forming an abutment surface against which the shorter leg of the U may press when flexed, and a force-applying point on said bimetallic element adjacent to the bight of the U.

5. An electric switch having a thermally responsive element for effecting automatic operation thereof, comprising stationary and movable contacts and means for effecting movement of said movable contacts including a movable member and a bimetallic element for effecting movement of said member, said element comprising a bimetallic strip return bent about a transverse axis parallel to its flat surfaces to form two g'enerally parallel legs, means rigidly supporting one of said legs adjacent to the end thereof, and means forming an abutment surface against which the second leg may press when flexed, said bimetal engaging said movable member adjacent to the free looped portion thereof.

6. In an electric switch, stationary and movable contacts, means for effecting automatic separation of said contacts including a movable member and a current responsive element 4for moving the same, said current responsive element comprising a bimetallic strip return bent about a transverse axis parallel to its flat surfaces to form two generally parallel legs, an electrical connector in the circuit of said switch, means mounting one of the legs of said bimetallic element upon said connector in conducting relation,

means providing an abutment surface against which the second leg of the bimetallic element may press when flexed, said bimetallic element engaging the movable member adjacent to its free looped portion, and a 'flexible lead interconnecting a point on said second leg with the movable contact so as to include the looped por- 3 non' of the bimetauic dement in the circuit through the switch.

1. In an electric switch, stationary and movable contacts, means for effecting automatic separation of said contacts including a movable member and a current responsive element for moving the same, said current responsive element comprising a bimetallic strip return bent about a transverse axis parallel to its flat surfaces to form-two generallyl parallel legs,an elec-v trical connector in the circuit of said switch, means mounting one of the legs of said bimetallic element upon said connector in conducting re- Ilation, an extension on said connector forming an abutment surface against which said second leg may press when flexed, means electrically insulating the point of engagement of said second leg with said abutment surface, said bimetallic element engaging the movable member adjacent to its free looped portion, and a flexible lead interconnecting a point on said second leg with the movable contact so as to include the looped portion of the bimetallic element in the circuit through the switch.

8. 9In an electric switch; stationary and movable contacts, means for effecting automatic separation of said contacts including a movable member and a current responsive element for moving the same,4 said current responsive element comprising a bimetallic strip of U shape with the flat surface of the strip disposed at right angles to the plane of the U, and with the high expansion side of the strip at the inside of the U, the legs'of said U being of dierent lengths, an electrical connectorI in the circuit of said switch, means mounting the longer leg of said U-shaped element upon said connector in conducting relation, a fixed abutment disposed adjacent the end of the shorter leg of the U-shaped element and against which it presses when flexed, said element engaging the movable member adjacent to the bight of the U, and a flexible lead interconnecting a point on said shorter leg with the movable contact so as to include the bight of the U-shaped'element in the electrical circuit through the switch.

OLAV MASENG.

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