US2555103A - Electric controlling apparatus - Google Patents

Description

May 29, 1951 R. A. ANDREWS ELECTRIC commune APPARATUS 2 Sheets-Sheet 1 Filed March 5, 1947 KSJ y 1951 R. A. ANDREWS 2,555,103

ELECTRIC CONTROLING APPARATUS Filed March 5, 1947 2 SheetsSheet 2 INVENTOR. lia -vs /9. fl/mms'ms Patented May 29, 1951 ELECTRIC CONTROLLING APPARATUS Rufus A. Andrews, Mamaroneck, N. Y., assignor to Ward Leonard Electric Company, a corporation of New York Application March 5, 1947, Serial No. 732,421

6 Claims.

This invention relates to improvements in variable voltage devices and particularly in variable voltage transformers wherein the voltage is variable in small steps from the maximum voltage to zero voltage. This invention is an improvement over the disclosures in the pending application of Frank G. Logan, Serial No. 593,344, filed May 12, 1945, now Patent Number 2,515,782.

One object of the present invention is to provide a unitary structure which will dissipate the heat readily from the winding, from the contact segments and from resistors connected between the winding and the segments. Another object is to provide and locate resistors connected between the segments and the winding so that not only will the heat be freely dissipated therefrom but will form part of the unitary transformer structure and permit the use of low resistance brushes. Other objects and advantages will be understood from the following description and accompanying drawings showing a preferred emshowing the brush holder assembly; Fig. 4 is an end view of Fig.3; and Fig. 5 is a section on the line 55 of Fig. 1 showing the contact assembly of the contacts engaging the fixed collector ring.

Referring to Fig. 2 a circular iron core 6 is of laminated form with the laminations extending in an axial direction and built up by winding a ribbon of iron or steel on itself from the inner diameter of the core to the outer diameter. The core is covered with a winding of insulating tape. The winding 7 on the core, which may be of glass insulated copper wire of square section, or other form, covers the core except a small section at the top. The inside and outside dimensions of the core are preferably selected so that the portions of the turns on the inside of the core are bank wound while those portions on the outside of the core are adjacent to each other and form a single layer.

The fixed contact segments 8 are in the form of radial outwardly extending long wedge-shaped strips, preferably of hard brass. As shown in Fig. 2, they have an elongated main contact portion with an outer end portion 8a extending forwardly and a portion 8b at right-angles thereto extending outwardly. At the inner end of the segment, a portion 80 extends forwardly. The tapered form of the faces of the segments and their radially extending edges insure that all of the brushes may make contact with each segment substantially simultaneously as the brushes are advanced to a higher voltage contact segment. The contact segments are electrically connected to every other turn of the winding in the form shown although they may be connected to successive turns in some cases or to every third turn, etc.

Each segment is electrically connected to its respective turn of the winding through a resistor 9, as shown in Fig. 2. This is preferably a narrow thin strip of resistive metal, such as a copper nickel alloy, and is corrugated as shown for obtaining a sufficiently high resistance. The outer flat end of the resistor is silver soldered to the front face of the outer end of the segment. The inner end of each resistor is silver soldered to its respective turn of the winding after removal of insulation from those portions of the winding Where the connections are made. The connection of the resistors to the Winding is facilitated by causing portions of the winding to project from the main portion. Thus as shown in Fig. 2, a portion of the turn "la projects outwardly and a portion of the next turn lb to which a segment is to be connected projects forwardly at a front corner of the winding. These projecting portions of the winding may be formed by use of removable pins over which the projecting portions are wound during the process of winding.

The transformer unit is carried and supported by a circular dished base plate [0 covering the front of the apparatus and having a rim which projects rear wardly. This plate may be of sheet steel or sheet brass and is shaped to conform to the required support and protection of the parts. At the center of the plate is fixed a metal cup-shaped piece II with its open end at the rear. Adhesive insulating material l2, such as cement, fills the space between the base plate and the winding up to the rim of the cup or retainer ll, embedding about half of the Winding, fully embedding the resistors 9, and likewise embedding the segments 8 up to near their faces and filling the spaces between the segments. When the embedding material is matured, it firmly supports the segments in fixed position, the forwardly extending legs 8a, 8b and 8c of the segments being covered. It likewise holds the resistors 9 in fixed position and similarly supports the winding. The embedding insulation also serves to effectively and efiiciently conduct the heat from the winding, the contact segments and the resistors mainly to the metal base plate where it is dissipated to the air over its exposed front face and rim. The open cup, or retainer II, also aids in dissipation of the heat to its open central space.

The drive shaft l3 extends axially through the base plate and cup II and is provided with a pulley l4 coupled to the shaft by a removable cross pin l4a for actuation of the contact arm, or a removable handle may be fixed to the front end of the shaft for that purpose. A metal strip I5 is shown fixed within end slots of the pulley by the end nut [41), the strip extending horizontally in the position shown and has a pair of forwardly projecting ends l5a to form a coupling with other similar apparatus when several of them are banked for simultaneous operation. A plate 7 I6 is fixed to the inner end of the pulley over projecting end portions and in the position shown extends upwardly to engage a stop I 1a which projects forwardly from a plate I! fixed to the base plate. The shaft is journaled in a pair of oilless type bushings l8, one at the front portion of the shaft and one at the rear portion. A hearing sleeve or hearing hub l9 encloses the bushings and has an outwardly extending bead |9a which seats against the central portion of the cup H. The front end Nb of the bearing sleeve is turned outwardly to engage the central part of the stop plate IT. The sleeve is thus held in fixed position. A thrust bearing washer 2!! is interposed between the plates l6 and i1. On the inner portion of the bearing sleeve is mounted the collector ring hub 2| of moulded insulation material. It is held in fixed position by a pin 22, the rear end of which projects within an opening in the hub and the front end of which is riveted over the face of the plate H. A metal spacing sleeve 23 extends between the hub and the central portion of the cup II and bears on the bead 19a. A reduced portion of the hub extends rearwardly and on this is mounted the collector ring plate 24, preferably of brass. It is secured to the enlarged portion of the hub by angularly spaced screws 24a.

On the top of the rim. of the base plate is mounted a terminal block 25 of moulded insulating material. Near its two ends are mounted upwardly extending terminal bolts 26, the heads of the bolts being moulded Within the terminal block. A hole is formed in the block at the inner side of each terminal bolt. One free end Tc of the winding 1 passes from the winding through the embedding insulation l2, then out near the hole in the terminal block, then through the hole to its terminal bolt. The other free end 10 of the winding similarly extends to the other terminal bolt. A terminal washer 21 of moulded insulating material is positioned on the inside of the rim of the base plate and has an upwardly extending portion which passes through the rim and within an opening in the lower central portion of the terminal block, as well shown in Fig. 2. A through terminal bolt 28 passes through the terminal block and washer 21 and serves to clamp the block in fixed position on the rim. This bolt serves as one terminal to which the load is connected,

I the other terminal of the load being connected to one of the bolts 26. A terminal lead 29 in the form of a fiat copper strip is secured at its upper end to the terminal bolt 28 and then passes downwardly over the core 6 to the collector ring 24 and is silver soldered to the upper part of the ring on its front side.

The contact arm 30 is preferably of brass for magnetic reasons and for good conductivity and 3 lb by which it is fastened by screws to the under side of the contact arm. At the lower portion of the open side of the holder is secured by welding a sheet metal brush guide plate 34. Six

\ brushes 32 are shown positioned in the holder within this guide plate so as to be freely movable therein, or any other appropriate number of brushes may be used. The guide plate is provided with six vertically extending slots opposite the brushes respectively, these slots being open at the top. Flexible pig-tail leads 35 are connected to the brushes respectively at one end, then pass through the slots of the guide plate, then under the contact arm and over the extended edge of the terminal plate 33, then down through six holes in this plate to its under side where the ends are silver soldered to the plate. During the wear of the brushes, their pig-tail leads pass respectively within the slots in the guide plate. The side of the brush holder is provided with holes 310 for the circulation of cooling air. Each brush is individually pressed against the contact segments by its coiled spring 36 which seats at one end on the top of its brush around a projection on the brush and at its other end against the inner side of the terminal plate. Eyelets 31 are fixed in the terminal plate at their outer ends and project inwardly within the ends of the springs 36 opposite each brush respectively, and serve to position and guide the springs and also to prevent the brushes from moving up so far as to be dislodged from the holder. The brush holder and terminal plate are fixed at their ends to the contact arm by screws 38, giving good electrical surface contact therewith. The side extension 3lb of the brush holder is secured to the contact arm by the screw 38a.

The electrical connection from the contact arm to the collector ring 24 is made by two contact assemblies on opposite sides of the center line of the contact arm, as shown in Fig. 1, each contact assembly being spaced a considerable distance from the center line. The detail of each of these contact assemblies is shown in Fig. 5. The con tact shoe 39 of each assembly is provided with a copper strip 40 moulded within the outer end of the shoe or brush and extends around the side edge of the contact arm and over its face and is fastened thereto by screws 40a, as shown in Fig. l. A hollow cylindrical spring holder 4| of brass is provided with a rounded reduced end 4 la which projects into a central hole in the shoe. A coiled spring 42 within the holder seats at one end against the inner portion of the holder and at its other end passes through a hole in the contact arm and seats against a strap of metal 43 serving as a stop. This strap is secured to the face of the contact arm by the screws 43a. The spring holder is freely movable and guided in its movement against the collector ring by a cylindrical guide 44, preferably made of steel tubing and fixed at one end to the contact arm.

The contact arm is actuated by a drive arm 45 of sheet steel. It is fixed to the end of the drive shaft by brazing or staking. At opposite ends bf the drive arm are carried bushings IE or moulded insulation, the inner portions of which pass into openings in the contact arm. On the inner face of the contact arm are mica washers 41 covered by steel washers 4B. Rivets 49 pass through the bushings 46 and the washers and have their inner ends spun over the washers 48 for fastening theparts together. One end of the drive arm is bent outwardly at 45a and a metal clip 451) with an outwardly extending end is welded to thedrive armfor the purpose of coupling the device to another similar device for simultaneous operation when desired.

On the end of the contact arm opposite the brush assembly end and on the inside of the arm is fixed by screws 50a a counter-weight 50 of sheet brass, lead or other material. Its weight is made such that the contact arm and parts associated therewith are mechanically balanced on opposite sides of the drive shaft. This balanced relationship results in the same force being exerted to move the parts, regardless of their adjusted position, and also eliminates any selfmovement of the arm due to unbalanced gravitational forces.

It is apparent from the foregoing description that the central shaft [3 serves to hold the contact arm and drive arm in their proper axial position with reference to the contact segments and collector ring. This permits simplicity and ease of assembling and mounting these parts and likewise permits convenient dissembling for inspection, cleaning and the renewal of the brushes by merely removing the end nut 14b and the cross pin Ida and the pulley M. The shaft I3 together with the drive arm, contact arm and brushes may then be withdrawn as a unit from the rear of the device.

The central space is open for ventilation and the free dissipation of heat. The embedding of a portion of the winding and of the resistors 9 and segments 8 and their connections in the insulating material l2 fully protects them and gives excellent heat conduction from them to the metal base plate I and to the metal cup II.

The provision of two contact shoes or brushes which engage the collector ring on opposite sides of and spaced equi-distant from the longitudinal center line of the contact arm together with the approximate center line position of the brushes which engage the contact segments, serves to avoid any sidewise tipping of the contact arm, or tendency to turn on its longitudinal axis when moved. This aids in obtaining smooth movement of the brushes and contact shoes on their engaged surfaces and maintains the lever in its plane of rotation.

It will be noted that the brushes engaging the contact segments are at a greater distance from the axis of the central shaft than the contact shoes which engage the collector ring. The combined pressure of the shoes against the collector ring is made greater than that of the brushes against the segments in approximately the inverse ratio of their distances from the axis of the shaft by the design of the springs engaging the brushes and shoes. This gives a condition that the combined pressure of the contact shoes engaging the collector ring times their distance from the central axis approximately equals the combined pressure of the brushes engaging the segments times their distance from the central axis. Thus the turning force to overcome the friction of the brushes and shoes in their movement is approximately equal on opposite sides of the contact arm which avoids any unbalanced turning strain on the contactarm and actuating shaft. It should also be 'noted'that the distance from the bearing surface of the collector ring to the contact arm is less than the distance from the surface of the segments to the contact arm. In view of the pressure of the collector ring contacts exceeding the pressure of the segment contacts, the tendency to tip the contact arm in overcoming the frictional contact of the engaging surfaces when the arm is rotated is thus greatly reduced. This approaches the ideal condition in this respect of having the moment of the frictional resistance of the collector ring contacts with reference to the distance of their contact faces from the contact arm equal to the moment of the frictional resistance of the segment brushes with reference to the distance of their contact faces from the contact arm.

Although a particular embodiment of this improvement has been described and shown, it will be understood that various modifications may be made without departing from the scope thereof.

I claim:

1. Electric controlling apparatus comprising a circular core, a winding thereon, a series of fixed contact segments extending outwardly and radially from the winding, a series of resistors electrically connected between said segments and turns of the winding respectively and positioned under said segments, common means for supporting said segments, resistors and winding in fixed relation to each other, and movable contact means for successively engaging said segments.

2. Electric controlling apparatus comprising a.

circular core, a winding thereon, a series of fixed contact segments extending outwardly and radially from the winding, a series of resistors electrically connected between said segments and turns of the winding respectively, insulating material for embedding said resistors and at least partially embedding said winding and segments in fixed relation to each other, and movable contact means for successively engaging said segments.

3. Electric controlling apparatus comprising a core, a winding thereon, a series of fixed contact segments extending outwardly from the winding, a series of resistors electrically connected between said segments and turns of the winding respectively, insulating material for embedding said resistors and at least partially embedding said winding and segments in fixed relation to each other, said resistors being positioned under said segments, and movable contact means for successively engaging said segments.

4. Electric controlling apparatus comprising a circular core, a winding thereon, a circular base plate with a retaining rim, a series of fixed con tact segments extending outwardly from the winding, a series of resistors electrically connected between said segments and turns of the winding respectively, insulating material on said base plate embedding said resistors and at least partially embedding said winding and. segments, and movable contact means for successively engaging said segments.

5. Electric controllin apparatus comprising a circular core, a winding thereon, a circular base plate with a retaining rim, a series of fixed contact segments extending outwardly from the winding, a series of resistors electrically connected between said segments and turns of the winding respectively, insulating material on said base plate embeddin said resistors and at least partially embedding said winding and segments, said resistors being positioned under said-segments, and movable contact means for successively engaging said segments.

6. Electric controlling apparatus comprising a circular core, a winding thereon, a circular base plate with a retaining rim, a series of fixed contact segments extending outwardly from the winding, a series of resistors electrically connected between said segments and turns of the winding respectively, insulating material on said base plate embedding said resistors and at least partially embedding said Winding and segments, a retainer extending within the winding at the central portion of the base plate for providing an open central space and for retaining said insulating material from the central space, and

movable contact means for successively engagln said segments. 7

RUFUS A. ANDREWS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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