US2411352A - Cutout - Google Patents

Description

NOV. 19, 1946. c ARMSTRONG 2,411,352

CUTOUT Filed May 23, .1944

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ATTORN EY Patented Nov. is, 1946 UNITED STATES PATENT OFFICE CUTOUT George C. Armstrong, Forest Hills, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 23, 1944, Serial No. 536,952

13 Claims. 1

My invention is related to that of my copencling application for Thermostatic overload relays, Serial No. 517,307, filed January '7, 1944, and concerns electric current or temperature-responsive protective devices such as electric cutouts for overload protection of electric motors and other electric apparatus.

It is an object of the invention to provide an overload or temperature-responsive contactor which, as to size and simplicity of design, is comparable with the known cutouts using a fusible element as a current-interrupting means, but which is not subject to the considerable ageing of such fusible devices and permits reclosing the electric circuit upon the occurrence of overloads.

Another object of my invention is to devise a thermally operated contactor of small size in which an extremely great holding or looking force is exerted on the movable contact means during normal operating conditions of the contactor so that it is not afiected by vibrations and shock forces.

A further object of my invention subsidiary to those aforementioned is to provide a contactor, especially an overload responsive cutout, whose overall dimensions are small enough to permit placing the control mechanism and the appertaining contact means within an enclosure having the shape and size of ordinary fuse plugs so as to be applicable in sockets of the type customary for receiving such plugs.

These and other objects of my invention, as well as the means proposed thereby for achieving them, will be understood from the following description of the embodiment illustrated in the drawing, in which:

Figure 1 represents a cross sectional perspective view of the cover portion appertaining to a plug-shaped thermal cutout according to the invention,

Fig. 2 represents a sectional perspective view of the main portion of the same contactor,

Fig. 3 is a lateral view of the device showing the exterior of the main portion assembled with the abovementioned cover portion, while Fig. 4 is a part sectional view of some of the elements shown in Fig. 1.

According to the drawing, a plug-shaped supporting body i of insulating material, such as glass or ceramic substance, is provided with an exterior metallic threaded sleeve 2 and a bottom contact 3. The threaded sleeve 2 and the contact 3 are dimensioned and arranged so as to fit the screw sockets customary for fuse plugs and the like devices.

A substantially cylindrical part, denoted as a whole by 4, is arranged centrally within the cupshaped hollow of the support I and is firmly secured thereto so as to remain stationary when the cutout is in operation. The part 4 consists of glass, ceramic or other refractory material and has an axial hollow extending over its entire length, In the illustrated embodiment, the contact 3 is designed as a rivet sleeve for attaching the part 4 to the insulating body l. The lower portion 5 of part 4 has a larger diameter than the upper portion 6.

A cylindrical sleeve member I, preferably of metal, surrounds the insulating part 4 and engages its lower portion 5 with a sliding fit so as to be rotatable about part 4. The member I has at least two notches in its upper edge. One of these notches, denoted by 8, has a relatively large peripheral length and serves for engaging a resetting member to be described hereinafter. A second notch is engaged by a movable contact 9 with a sufficiently close fit to prevent rotations of the contact relative to member I. The contact 9 has an annular portion journalled on the top face of the stationary part 4. A stationary contact It], which in the illustrated embodiment is formed by leaf springs, is mounted on an interior peripheral ledge ll of the insulating body i by means of a screw I2 which forms also a conduotive connection between the stationary contact l0 and the above-mentioned threaded sleeve 2.

A helical spring I3 has one end in engagement with a corresponding eye formed by the body I,

, while its other end enters into a bore of sleeve member 1. The spring 13 biases the sleeve member for rotation in the contact opening direction. When the movable contact 9 is in engagement with contact Iii and under normal operating conditions, however, such rotation is prevented by a heat-responsive clutching spring is which is frictionally seated on the upper portion 6 of the stationary part The lower end of this spring l4 (not visible in the illustration) is not attached to any of the stationary and rotatable elements of the mechanism, while its upper end i5 engages a notch of the sleeve member "I. The winding direction of spring i l is so chosen that the biasing force of spring l3 tends to coil up the spring l4 and hence to tighten the close fit of its turns on the peripheral surface of the stationary part 4. Consequently, as long as the clutching spring l4 remains cold, it maintains the movable contact 9 in engagement with the stationary contact to once these contacts have been closed. According to a preferred feature of my invention and as illustrated in the drawing, the clutching spring it consists of a helical bimetal winding which, when sufiiciently heated, expands its turns radially and hence loses its grip on the stationary part 4, thereby releasing the member 1 with contact 9 for rotation.

An electric heater consisting of a Winding i8 is arranged in the hollow of the stationary part 4. One end of the heater i6 is attached to the bottom contact 3 whil the other end is in electric connection with movable contact 9. Hence when the cutout is in circuit closing condition, a current path is formed from bottom contact 3 through heater it, movable contact 9 and stationary contact is to the threaded sleeve 2. As long as the electric current remains below the rated value of the cutout, the diameter of the bimetal winding i4 is so small as to retain contact 9 in the circuit-closing position in opposition to the bias of spring 23. When the current increases above the rated value and this overload persists for a sufiicient length of time, the bimetal winding is heated and gradually expanded until it releases its frictional grip on the stationary part t and permits the spring l3 to move the sleeve 7 and the contact 9 into the circuit interrupting position. Upon sufficient cooling of the winding M, the sleeve 7 can be turned back into the contact-closing position. Although in the meantime, the turns of the bimetal winding l4 may have contracted to their original small diameter, the closing'motion of sleeve 1 and contact 9 is in the unwinding direction of the winding l4, so that this motion causes mechanically a widening of the turns so that the friction between elements and M is insufficient to block this return motion. After the contact 9 has been returned to the closing position, the spring [3 tends to move it in the coiling-up direction of the winding i l so that the frictional grip becomes again effective and holds the sleeve 5 and contact 9 in the closing position.

Substantially the same operation is obtained if th heater I6 is omitted, i. e; replaced by an or-- dinary conductor, so that the bimetal strip I l serves also as the heating element of the device. While this is satisfactory for some current ratings, it does not readily afiord the possibility of exchanging the heater for difierent ratings.

The supporting structure I of the cutout is provided with a cover 5'? of sheet metal whose peripheral portion l3 is turned at aright angle and has a peripheral depression is which engages a peripheral groove of body I thereby securing the cover I? in proper position. A resetting knob 2! is rotatably mounted on the cover I1 and has a centering projection 22 which enters into the opening of sleeve 8 and has a flange 23 which lies closely above the upper end of sleeve 8 when the cover IT is properly attached to the body of the plug. Projection 22 and flange 23 thus secure and guide the cylinder '1 in its proper position. A lateral projection 24 of knob 2|, when the cover is attached to body I, engages the notch 8 of the sleeve member I. Hence, when upon an operation of the cutout, the knob 2i is turned in the contact-closing or resetting direction, the projection 24 abuts against the vertical end of notch 8 and entrains the sleeve 1 and contact 9 for motion in the same direction. Due to the larg peripheral length of notch 3, the projection 23 is free to move in the opposite direction without entraining the sleeve 7 once the contacts are closed. As a result, the contacts cannot be forcibly opened by manual actuation after the cutout has been reset. It will be understood that when manufacturing and assembling the device, the depression is i produced only after all other parts are properly assembled.

The holding force of a clutch spring as represented by the bimetal winding M in the abovedescribed embodiment is extremely great as compared with other releasabl latching devices of known type. This is due to the fact that the frictional grip of the clutch spring i efiective around the entire periphery of the stationary part it and extends over a plurality of turns. This great holding force has the advantage that the cutout cannot open the circuit accidently when subjected to vibration or shock. Such disturbances are also rather ineffective on the clutch grip because the clutch means according to the invention have low inertia, and are symmetrical and relatively balanced in static and dynamic respects as compared with unilaterally operating pawl or latch means. The use of a helical clutch spring, especially of the bimetal type, has the further advantage that it is not as subject to ageing as ar fusible elements. Thus while, for instance, solder joints are apt to change their overload characteristic upon repeated beatings and operations, a device according to my invention has considerably less tendency to develop such changes in characteristic.

Referring to the illustrated embodiment, the use of glass or other transparent material for part t has the advantage that the bimetal strip is heated not only by thermal conduction but, to an i: appreciable extent, also by heat radiation. As a result, the bimetal strip is heated more rapidly at high overloads and hence respond more quickly to especially detrimental current conditions.

It will be obvious to those skilled in the art that devices according to my invention can be modified in various respects, especially as to the design and arrangement of its individual parts, Without departing from the objects, features and advantages of the invention. Therefore, I wish thi specification to be understood as illustrative rather than in a limiting sense.

I claim as my invention:

1. A contactor comprising, in combination, a stationary structure having a cylindrical part, a member rotatable about said part and biased for rotation in one direction, contact means control1ed by said member, a radially expansible thermo-responsive spring winding connected with said, member and frictionally seated on said part so as to prevent said rotation when cold, and heating means for thermally expanding said winding in order to release aid member.

2. A contactor comprising, in combination, a stationary structure having a cylindrical part, a member rotatable about said part and biased for rotation in one direction, contact means controlled by said member, a radially expansible bimetal winding having one end engaged by said member and being seated on said part so as to prevent when cold said rotation of said part, and electric current-responsive heating means for thermally expanding said winding in order to release said member;

3. A contactor comprising, in combination, a stationary structure having a hollow cylindrical part, a member rotatable about said part and biased for rotation in one direction, contact means controlled by said member, a radially expansible thermo-responsive spring Winding connected with said member and frictionally seated 5 on said part so as to prevent said rotation when cold, and electric heating means disposed within said hollow part for thermally expanding said winding in order to release said member.

4. A contactor comprising, in combination, a stationary structure having a hollow cylindrical part, a member rotatable about said part and biased for rotation in one direction, contact means controlled by said member, a radially expansible bimetal winding having one end engaged by said member and being seated on said part so as to prevent when cold said rotation of said part, and electric current-responsive heating means disposed within said hollow part for thermally expanding said winding in order to release said member.

5. A contactor comprising, in combination, a stationary structure having a cylindrical part, a member rotatable about said part and biased for rotation in one direction, contact means controlled by said member, a radially expansible thermo-responsive spring winding connected with said member and frictionally seated on said part so as to prevent said rotation when cold, heating means for thermally expanding said winding in order to release said member for rotation in said direction, and manually operable resetting means for rotating said member in the opposite direction.

6. A contactor comprising, in combination, a

stationary structure having a cylindrical part, a member rotatable about said part and biased for rotation in one direction, contact means controlled by said member, a radially expansible bimetal winding having one end engaged by said member and being seated on said part so as to prevent when cold said rotation of said part, electric current-responsive heating means for thermally expanding said winding in order to release said member for rotation in said direction, and manually operable resetting means for rotating said member in the opposite direction.

'7. A thermal cutout for electric circuits, comprising a support, a stationary cylindrical part disposed on said support, a substantially cylindrical member surrounding and rotatable about said part and biased for rotation in one direction, contact means controlled by said member, a radially expansible therrno-responsive spring winding having one end engaged by said member and being seated on said support for frictionally preventing said rotation when cold, heating means for thermally expanding said Winding in order to release said member for rotation in said direction, and manually operable resetting means for rotating said member in the opposite direction.

8. A thermal cutout for electric circuits, comprising a support, a hollow cylindrical part rigidly disposed on said support, a substantially eylindrical member surrounding and rotatable about said part and biased for rotation in one direction, contact means controlled by said member, a radially expansible bimetal winding having one end engaged by said member and being seated on said part so as to prevent when cold said rotation of said part, electric current-responsive heating means disposed within said hollow part for thermally expanding said winding in order to release said member for rotation in said direction, and manually operable resetting means for rotating said member in the opposite direction.

9. A thermal cutout for electric circuits, comprising a plug-shaped hollow support, a cylindrical part stationary relative to said support and disposed centrally in its interior, a rotatable mem ber surrounding said part within said support, a stationary contact mounted on said support, a movable contact controlled by said member for engaging and disengaging respectively said stationary contact, a spring disposed between said member and said support for rotating said member toward disengagement of said contacts, a radially expansible thermo-responsive spring Winding connected with said member and frictionally seated on said part so as to prevent said rotation when cold, and electric heating means disposed within said support for thermally expanding said winding in order to release said member.

10. A thermal cutout for electric circuits, comprising a plug-shaped hollow support, a cylindrical part stationary relative to said support and disposed centrally in its interior, a rotatable member surrounding said part within said support, a spring disposed between said member and said support for biasing said member in one direction of rotation, contact means having a stationary contact on said support and a movable contact controlled by said member, a radially expansible bimetal winding having one end engaged by said member and being seated on said part so as to prevent when cold said rotation of said part, and electric current-responsive heating means disposed within said support for thermally expanding said winding in order to release said member.

11. A thermal cutout for electric circuits, comprising a plug-shaped hollow support, a cylindrical part stationary relative to said support and disposed centrally in its interior, a rotatable member surrounding said part within said support, a stationary contact mounted on said support, a movable contact controlled by said member for engaging and disengaging respectively said stationary contact, a spring disposed between said member and said support for rotating said member toward disengagement of said contacts, a radially expansible thermo-responsive spring winding connected with said member and frictionally seated on said part so as to prevent said rotation when cold, electric heating means disposed within said support for thermally expanding said winding in order to release said member, a cover disposed on said support, and resetting means arranged on said cover and engaging said member for rotating it in the engaging direction of said contacts.

12. A thermal cutout for electric circuits, comprising a plug-shaped hollow support, a cylindrical part stationary relative to said support and disposed centrally in its interior, a rotatable member surrounding said part within said support, a spring disposed between said member and said support for biasing said member in one direction of rotation, contact means having a stationary contact on said support and a movable contact controlled by said member, a radially expansible bimetal winding having one end engaged by said member and being seated on said part so as to prevent when cold said rotation of said part, electric current-responsive heating means disposed within said support for thermally expanding said winding in order to release said member, a cover disposed on said support, and resetting means arranged on said cover and engaging said member for rotating it in the engaging direction of said contacts.

13. A thermal cutout for electric circuits, comprising a plug-shaped hollow support, a hollow cylindrical part stationary relative to said suppart so as to prevent when cold said rotation of said part, electric current-responsive heating means disposed Within said part for thermally expanding said winding in order to release said member for rotation in said direction, a cover disposed on saidrsupport, and resetting means arranged on said cover and engaging said member for rotating it in the opposite direction.

GEORGE C. ARMSTRONG.

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