US1913686A - Rheostat - Google Patents

Description

June 13, 1933. i N. c. SCHELLENGER v 1,913,686v

RHEOSTAT Filed Jan. 31, 1930 g Fig] F 3/ .33 0 37 4 g 32 g 36 5/ k 46 //7) ll'i v J [72 v-en for Newton Cfic/ZcZlerzyer M an};

Patented June 13, 1933 UNITED STATES PATENT. OFFICE NEWTON G. SCHELLENGER, OF'ELKHART, INDIANA, ASSIGNOR 'I'O CHICAGO TELEPHONE SUPPLY 00;, OF ELKHAR'I', INDIANA,

A CORPORATION OF I INDIANA Application filed January 31, 1930. Serial 1%. 424,775.

This invention relates to electrical rheostats and has for its principal object the production of a new and improved rheostat that can be cheaply manufactured without sacrificing quality of workmanship and materials and this is a continuation in part of my application granted September 15, 1931, No. 1,823,472.

r Electrical rheostats such as are used in radio sets, and other similar apparatus frequently' comprise a metallic shell containing a centrally located threadedbushing which serves as a bearing for the shaftof the rheostat and also as. a mounting means for attaching the rheostat to a suitable panel or other supporting framework. Rheostats of this type are of very sturc construction and when securel mounted can give satisfactory service over a long period of time without attention.

In my present invention I have provided a new and improved rheostat of this type, the improvement not only making the manufacture of the rheostat a less costly operation but also making the finished product a more sturdv andtreliablerheostat than has been available heretofore. Rheostats built in accordance with the teachings of my n1- vention are comnact in size and of simple design so that they may be mounted in a small and somewhat inaccessible place and successfully operated since they require a minimum of attention.

Now to acquaint those skilled in the art with the teachings of my invention, reference is madeto the accompanyin drawing in which a preferred embodiment of it is shown by way of example and in which:

Figure 1 is a vertical section taken through a completely assembled and mounted rheostat;

Figure 2 is an end view-of the-rheostat shown in Figure 1;

Figure 3 is a detail view of one of the terminals of the rheostat;

Figure 4 is a plan view of the end of the resistant element and the terminalattached to it;

Figure 5 IS a cross-sectional view of Fig.'

vsulating strip 21.

are 4, taken along the line 5-5 looking in the direction of the arrow;

Figure 6 is a fra mentary view ofthe planar portion of the shell, showing the serrated hole therein; and

Figure. 7 is a fragmentary view taken along. the line 7-7 of Fi ure 2 showing the details of the terminal portion of the shell.

The rheostat comprises a cup-like metallic shell 1, which is preferably made of sheet brass or other non-magnetic material and formed in the shape of a cup by a punchpress operation. The circular central portion 2, of the shell forms a mounting plate and the flange 3, is formed integral with this central portion 2, and disposed around its periphery at right angles to its plane. Centrally located in the planar portion 2, is a serrated hole 4, through which the bushing 5, is projected with the shoulder 6, disinto the serrations in the perforation 4,

thereby securing the bushing against rotation with respect to the shell.

The bushing 5, is also provided with a threaded portion 8, adapted to receive a mounting nut 9 which mounts the rheostat on a suitable panel 10. Prefer-ably a washer 11, is interposed between thenut, 9 and the panel although this may be omitted if desired.

The resistance. element of the rheostat comprises wire 20 space wound upon an' in- The insulating strip is of generally rectangular cross-section with its edges chamfered as at 22, to slightly round them so that the wire can be against the strip without necessitating its being bent at a sharp angle. The wire is laid in grooves 23, which are cut in the end of the strip between the chamfered corners 22. The grooves partly encircling the wire hold it rigidly in place space it so that adjacent convolutions of the winding do not touch each other. Preferably the chamfers are cut at an angle of on the strip and closely laid approximately to the side of the strip, although an arcuate chamfer may be substituted. The strip 21 is preferably made of a moisture proofed insulating material such as treated fiber or a phenol condensation product.

Near the ends of the strip 21, are circular perforations 24 and 25 through which the prongs 26 and 27 of the'term'inal 28 are projected. These prongs are formed as integral projections of the body of the terminal and are pushed through the openings 24 and 25 and between adjacent convolutions of the wire 20 on the strip, the projecting ends then being bent over and pressed down firmly against the wire 20 to securely hold the terminal on the strip and to also hold the wire end securely thereon. This clamping of the end of the wire 2O secures a good electrical contact between the wire and the terminal 28 as well as securely holding the wire on the strip 21.

An insulating washer 30 is disposed against the planar portion 2 of the shell and an insulating strip 31 is disposed against the inside surface of the flange 3 and against the washer 30. The washer 30 and the strip 31 may be a moisture proofed fiber or a phenol condensation productor any' other preferred insulating material. Theinsulating strip 31 is longer than the inside periphery of the flange 3 so that its ends are overlapped as shown at 32 Figure 2, and these overlapped ends are subsequently perforated to receive a rivet for holding the parts in the frame. The resistance element 29 is disposed inside the cup against the washer 30 and strip.

The resistance element 29 is placed in the shell 1 with the ends 36 of the strip 21 butting against each other so that the hoop strength of the strip holds it and the in: sulator 31 in the shell. Terminals 28 are located on the outside surface of the element adjacent the insulator 31.

After the element 29 has been placed in place in the shell 1, the flange 3 of that shell is shrunk by a punch-press-operation to reduce the perimeter of the shell and thereby cause it to exert a radial force on the element; 29 to securely bind the element against the inside surface of the flange by its own hoop strength, which resists the tendency of this radial force to reduce its circumference. This shrinking also creases the flange 3 as shown at 38 Figure 1, said crease tendin' to stiffen the flange to thereby enable it to securely hold the resistance element under compression and in place against it. v

The dies employed in the shell shrinking operation are provided with slots which permit leaving the portions 28 of the shell behind the terfninals 28, undisturbed so that two socket like outwardly extending projections are left in the finished shell. The terminals 28 and insulator 31 liein these projections, the walls of which prevent turning of the terminals and thereby enhance the mechanical strength of the rheostat: This shrinking of the shell binds the resistance element 29 so tightly in place that an element cannot warp even though the insulating strip on which its is wound absorbs a considerable amount of moisture. This arrangement and the use of a moisture proof material in the construction of the strip insures that the rheostat will remain in good operating condition over a long period of time without attention.

The central terminal 33 is fitted on the inside of the element 29, and insulated therefrom by an insulating washer 34 which may be made of any preferred moisture proof insulating material. The terminal 33 is long enough to span over the contacts 23 at the ends of the resistance element, and is held in place by a rivet or eyelet projecting through a hole 35 in the terminal 33 and through the abutting ends 36 of the insulating strip 21 on which the element 29 is wound. The rivet 37 also extends through overlapped ends 32 of the insulator 31 and through the flange 3 of the shell 1, to securely bind the resistance element, the insulating washer, and the terminal in place in the shell.

To establish a connection with the resistance element 29, I provide a contactor 40 which is riveted to the end .of the shaft 41 which projects through an opening in the bushing 5 and terminates in a larger diameter portion 42 on which is located a knob or other suitable handle 43 for adjusting the rheostat. The shoulder 44 formed between the large and small portions of the shaft 41 fits against the threaded end 8 of the bushing 5, and a spring washer 45 may be interposed between the shoulder and end of the bushing to keep the shaft tightly in place in the bushing.

The contactor 40 is provided with a serrated or hexagonal-shaped opening through which the end of the shaft 41 is projected and then riveted over as shown at 46, the riveting operation swedging the end of the shaft into the serrations in the contactor 40 to securely lock the contactor on the shaft against rotation with respect to it. The inside end of the bushing 5 is countersunk as at 47 to prevent the shaft from binding should the shaft be enlarged slightly at its extreme end portion during the riveting op eration.

The spring arms 48 of the cont-actor 40 terminate in a contact member49 which is formed on a radius so that it will slit e over the wire-t2O on the element 29 without cut ting into or displacing that wire on the element. These spring arms are spaced outwardly from the base portion of the contactor by means of an integral offset connecting portion, which serves as a spacing member between the arms and the portion of the contactor which is secured to the shaft. This forms a contaetor having its base portion and its spring arms lying in substantially parallel spacedplanes, with the base portion being disposed within the confines of the resistance element. tacting portion 49, of the cont-actor 40 is formed at an angle of approximately (35 degrees to the side of the element so that it engages the element 49 tangentially to the chanifer 22 011 the corner of the strip ll. By this arrangement,-the point of contact between the contacting arm and the wire is immediately adjacent to the cross grooves 23 in the strip, so that the side thrust placed on the wire by the movement of the, contactor 40 will not displace the wires on the strip. Moreover the co-ntactor 49 does not bear on the wire over the slots 23 so that there is no likelihood of the contactor riding on the extreme edge of the insulating strip 21 rather than on the wire if the wire is extremely small and quite completely embedded in the slots 23.

The bending of the contacting arm 49 permits establishing a good contact with the resistance element 29 without projecting the end of the arm 49 beyond the outside edge of the element 29. In fact the extreme end portion of the contactor 49 falls of the outside edge of the element 29 an:l therefore is spaced a considerable distance. away from the insulating strip 31 and the flange 30f the shell, both of which project beyond the free edge of the resistance element 29.

Preferably the fi nge 3 of the shell is cut away asat 50 so that when the terminals 2 and 33 are bent outward they fall in a plane adjacent the plane containing the edge of the flange 3 so that the open or back face of the rheostat is perfectly flat and all moving and current carrying parts are/within that space so that the rheostat-"may be mounted in close proximity to other equipment.

The contact 33 is provided with a pair of projecting bosses 51 which lie in the path of the contacting arm 49 and limit its rotation to an arc of slightly less than 36!) degrees. The. projections 51 are so positioned that the contactor 49 engages the end turns of the winding 29 that are short-circuited by the terminal clips 26 and 27 so that the rheostat never open-circuits and a smooth take-off is assured when the contactor 49 is moved away from the stops 51.

The rheostat so constructed is compact and can be cheaply manufactured without sacrificing workmanship or material. Since the edge of the flange 3 projects beyond the free end of the resistance element 29, the rheostat is well ableto withstand the more or less rough handling to which it is sub- The con 'ing the rough handling a little short.

jected on the assembly line of a manufacturing plant, without damaging the resistance element 29. This is particularly advam tageous if the wire 20 on the element is as small as two or three thousandths of an inch in diameter, as I have found that a majority of the open-circuited rheostats are opened because the wires are nicked or broken durto which the. rheostat is subjected when it is being assembled in the electrical device in which it is used.

\Vhile I have chosen to disclosemy invention by illustrating a preferred einbodiment of it, I have done so by way of example only as there are many modifications and adaptations which ran be made by one skilled in the art without departing from the scope and teachings of the. invention.

Having thus complied with the statutes and shown and described a preferred embodiment of my invention, what I consider new and desire to have protected by Letters Patent is pointed out in the appended claims.

\Vhat is claimed is:

1. In a rheostat, an insulating winding strip' having a generally rectangular crossseetion and having a pair of perforations near each of its ends, a resistance wire wound on said strip, apair of terminals, and a pair of prongs on each terminal projected between the turns of said wire and through said'perforations and clinched on the opposite side of the strip to bind the terminal on the stripand to establish an electrical contact between the terminal and wire. I

2. In a rheostat, a moisture proof insulating strip having a plurality of perforations near each of its ends, a resistance wire wound on said strip and over said perforations with its adjacent convolutions spaced apart, and terminals clinched on said strip and over said winding by prongs projecting through said perforations and around said wire.

3. In a rheostat, a moisture proof insulating strip having a plurality of perforations near each of its ends, a resistance wire wound on said strip and over said perforations with its adjacent convolutions spaced apart, a pair of terminals, and a plurality of prongs on each terminal which are projected through said perforations to bind the terminal on the strip and to establish electrical connection with the windin 4 4. In a rheostat, a moisture proof insulating strip having a plurality of perforations near each of its ends, a resistance wire wound on said strip and over said perfora- 5. An electrical rheostat comprisin a frame consisting of a metallic disc having a flange disposed normally around its outer circumference, an insulating Washer dis posed against said disc, an insulating meinber disposed against said flange with its ends overlapping, a resistance element disposed within said frame and against said washer and insulating member, and having its ends abutting against the overlapped portion of said insulating member, the upper edge of said element falling short of the upper edge of said flange and insulating member, said elements being held in compression by said flange to bind said elements thereagainst, and a contactor having an arm which engages the edge of said element but falls short of said insulating member.

6. An electrical rheostat comprising a cuplike shell, an insulating disc disposed inside the planar portion of said shell, an insulating strip disposed inside said shell, said strip being longer than theinside perimeter of the shell and having its ends overlapping, a resistance element disposed against said disc and strip with its ends abutting over the lapped portion of said strip, said shell being placed in tension against said element to cause the hoop strength of the element in compression to bind the element, the strip and the disc in the shell, a clamping plate fitted inside said element but insulated therefrom, and means extending through said plate, the abutted ends of said element, the lapped portion of said strip and said shell for holding said plate in said shell 7. An electrical rheostat comprising a frame consisting of a metallic disc having a flange disposed normally around its outer circumference, an insulating washer disposed against said disc, an insulating strip disposed around said flange against said washer and having its ends overlapping, a resistance element disposed within said frame against said washer and insulating member, terminals on said element disposed between it and said insulating member, said element being longer than the inside perimeteu of said member and being disposed under compression with its ends abutting to hold it, the terminals, the members and washer in said frame, and a third terminal for said rheostat disposed inside said element but insulated therefrom and connected to said frame.

8. An electrical rheostat comprising a.

member, terminals on said element disposed between it and said insulating member, said element being longerthan the inside perimeter of said member and being disposed under compression with its ends abutting to hold it, the terminals, the member and washer in said frame, a third terminal for said rheostat disposed inside said element but insulated therefrom and connected to said frame, a contactor pivotall Y connected at the'center of said disc and engaging said arm, and a pair of stops carried by said third terminal for limiting the movement of said contactor about its pivot.

9. A contactor for a rheostat comprising a shaft, a base attached at one of its ends to the end of said shaft and projecting to one side of it, an integ 'al offset spacing portion, a pair of integral arms projecting from the free end of said spacing portion outwardly of the end of said shaft, and a contact member in which said arms verge.

10. A rheostat comprising a metallic cup, a resistance element disposed within said cup and insulated from it, a shaft pivotally supported in the center of said cup, a contactor attached to said shaft, said contactor including a member engaging said element and a pair of arms of length greater than the radius of said cup and verging in said member, said arms spaced outwardly of and normal to said shaft.

11. A rheostat comprising a cylindrical metallic cup, a pair of bosses projecting radially from said cup, a resistance element disposed in and insulated from said cup, terminals on said element disposed in and insulated from said bosses, said element being compressed in said cup to hold itself and said terminals in place, and a third terminal disposed against the inside surface of said element but insulated therefrom and connected to said shell.

12. A contactor for a rheostat comprising a shaft, a contactor base attached to said shaft, a pair of arms spaced outwardly from and substantially parallel to said base, and a contact member into which said arms converge.

13. A contactor for a rheostat comprising a shaft, a contactor base attached to said shaft, a pair of arms spaced outwardly from and substantially parallel to said base, an offset spacing portion formed integral with said arms and extending between said base and said arms, and a contact member into which said arms converge.

14. A contactor for a rheostat comprising a shaft, a contactor base attached to said shaft, a pair of arms spaced outwardly from and substantially parallel to said base, an offset spacing portion formed integral with and connecting said base and said arms, and an arcuately curved contact member into which said arms converge, said contact memher being angled with respect to the plane of said arms. I

15. In a rheostat, a shell, a resistance element disposed in said shell and insulated

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