US2389750A - Variable resistance device - Google Patents

Description

Nov. 27, 1945. B. s. TURNER ET AL VARIABLE RESISTANCE DEVICE Filed March 3, 1944 3 Sheets-Sheet 1 16M Basil E. Turner flEt'I z'n E. Erismsn Nov. 27, 1945. B. s. TURNER ET AL VARIABLE RESISTANCE DEVICE Filed March 3, 1944 3 Sheets-Sheet 2 Basil 5. TUZ'QTE'T i75 m/z'n E. Hm'sman Juseph 5. Yea zcl'z- Nov. 27, 1945. B. s. TURNER ET AL 2,389,750

VARIABLE RESISTANCE DEVICE Filed March 3, 1944 3 SheetsSheet 3 jig; 2/ 22 .5552! 5 firmer .ZTEFI/in El. Erz'aman JEEP 3Z1 E 1 552 ,g B

Patented Nov. 27, 1945 UNITED STATES PATENT OFFICE VARIABLE RESISTANCE DEVICE Application March 3, 1944, Serial No. 524,900

17 Claims.

This invention relates to variable resistance devices such as rheostats and potentiometers used in radio control apparatus and refers particularly to the so-called wire-wound type of variable resistance device.

As is well known, in variable resistance devices of this type, the resistance element comprises a coil of resistance wire wound upon a strip of insulating material. With the resistance wire wound thereon the strip is bent to circular form and is mounted in the housing of the unit concentrically to its operating shaft.

In the early forms of this type of variable resistance device, the contactor, which consisted merely of an arm extending from the radial control shaft, rode n the edge of the resistance element. In later constructions, as in Patent No. 2,019,997, issued to Newton C. Schellenger, November 5, 1935, the movable contactor incorporated a shoe which traversed the cylindrical inner-surface of the resistance element, moving transversely across its adjacent turns. To provide increased assurance that proper contact between the resistance element and the contactor would be had at all times, the contactor shoe engaged the resistance element at two axially spaced, but circumferentially aligned points. Hence, if dirt or the like interfered with one of the contacts, the other would suilice to provide a good electrical connection.

To insure smooth operation, both mechanically and electrically; the contactor construction of the past, as illustrated in the aforesaid Schellenger patent, was designed so that regardless of the direction of rotation the contactor wa pulled across the surface of the resistance element rather than pushed. Obviously, where the point of contact between the contactor and the resistance element trails the application of turning force to the contactor a smoother operation results than where the point 01' contact is directly radially in line with the application of thrust or leads the same.

However, in the devices heretofore in use which achieved this result the contactor consisted of a multipart assembly of complex design, which not only increasedthe cost of manufacture but also constituted a fruitful source of difllculty.

It is, therefore, an object or this invention to provide an improved and simplified contactor construction wherein the advantage oi! smooth operation in either direction of rotation is obtained without the objectionable necessity for a. multipart assembly.

More specifically, it is an object of this invention to provide a contactor for variable resistance devices of the character described, which is a one-piece stamping, and wherein spring contact arms approach the points of contact with the resistance element from opposite directions 50 that in either direction of rotation one of the contact arms is pulled across the surface oi the resistance element.

In this respect, it is a further object of this invention to provide a contactor wherein the spring arms or brushes are relatively long and approach their points of contact with the resistance element at a low angle to, thus, further insure smooth operation.

In resistance devices of this character, the.

contactor is preferably connected in the circuit by means oi a collector ring. The collector ring has a flat contact surface normal to the axis of the control shaft so that the spring arms or brushes of the contactor which ride thereon exert their spring thrust in an axial direction.

With a view toward achieving optimum simplicity in the design and construction of the contactor, this invention has, as another of its objects, the provision of a one-piece stamping, which not only has spring arms sprung radially outwardly to engage and press against the cylindrical surface of the resistance element, but also spring arms which are sprun axially out of the plane of the contactor stamping to engage and press against the collector ring.

In variable resistance devices of the wire wound type, it has always been a problem to effect good electrical contact between the ends of the resistance element and its terminals, and the present invention, therefore, has as another of its objects, to provide an improved manner 0 effecting this connection.

To this end, it is more specifically an object of this invention to provide a terminal which has a portion thereof engaged with the endmost turns of the resistance element and which is held in place by a rivet passing through the side wall of the housing, the terminal portion, and the resistance element strip, with the head of the rivet overlying the adjacent endmost turns of the wire so as to firmly clamp the wire between the head of the rivet and the terminal, 7 Thus, through the provision of a relatively heavy soft silver plating on the terminal portions the wires of the resistance element embed themselves in the surface of the terminal portion to obtain low stable contact resistance.

2 1 ascents Another object of'this invention concerns the manner of securing the resistance element in position, and while means have been employed in the past, as illustrated in the aforesaid Schellonger patent, to expand the resistance strip outwardly into contact with the side wall of the housing, this invention contemplates an improved and simplified manner of effecting this desirable result.

The sealing of variable resistance devices of this character against the ingress of dirt and dust has always been a problem. To ailord increased assurance against this objectionable possibility, the present invention has, as another of its objects, the provision of an improved manner of introducing the terminals into the interior of the housing by which the terminals completely fill the openings through which they pass, without interfering with the ease of their insertion for assembly purposes.

With the above and other objects in view, which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described, and more particularly defined by the appended claims, it

being understood that such changes in the precise embodiment of the herein disclosed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate one complete example of the physical embodiment of the invention, constructed in accordance with the best mode so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a perspective view of a variable resistance device embodying this invention and illustrating the same withpart of its cover broken away;

Figure 2 is a perspective view of the housing per se illustrating particularly the notches providing the openings through which the terminals enter the interior of the housing;

Figure 3 is a longitudinal sectional view through the resistance device and illustrating the same on an enlarged scale; I

Figure 4 is a plan view looking into the housin with the cover removed;

Figure 5 is a perspective view 0! the housing and the control shaft with the contactor mounted thereon disassembled, part of the housing being broken away and in section;

Figure 6 is a perspective view of the housing and the combined collector and terminal shown separated;

Figure '7 is a fragmentary detail sectional view, taken through Figure 9 onthe plane of the line 1-4, illustrating the manner in which electrical connection is established'between the ends of the resistance element and its terminals;

Figure 8 is a side view of the variable resistance device of this invention illustrating its combination with a switch; and

Figure 9 is a fragmentary detail sectional view taken through Figure 4 on the plane of the line 9-9.

Referring now particularly to the accompanying drawings, in which like numerals indicate like parts, the numeral 5 designates a cup-shaped housing molded from suitable insulating material and having a fiat bottom wall 6 which constitutes the front of the unit when mounted in position, and a cylindrical side wall 1.

Diametricallyopposite portions of the side wall have external bosses 8 and 9, the latter having a thickness substantially equal to the wall thickness of a cover is which fits over the open front of the housing. The other boss 8 is considerably thicker to provide added strength for the attachment of the terminals of the unit. Both of the bosses are set in from the open face of the housing to enable the cover to telescope over the side wall of the housing.

Gpposite extensions ii on the side wall of the cover fit snugly between the bosses .8 and 9 and extend for the full width of the side wall to have tangs l2 bent over the edges of a metal back plate it to hold the cover and the back plate in place. The back plate i3 extends across the bottom wall 6 of the housing and is apertured to receive an externally threaded bushing H embedded in and extending out from the bottom wall 6.

The threaded bushing It provides means for mounting the unit on' a supporting panel in the customary manner.

J ournaled in the bushing is a rotatable control shaft 55. The inner end of this shaft has a contactor, indicated generally by the numeral I6, mounted thereon, which cooperates with a resistance element i1 lining the inner surface of the side wall. a

The resistance element 11 is of the wire-wound type and comprises a strip N5 of suitable flexible insulating material upon which is wound a coil it of relatively fine resistance wire. The-resistance element is held in place against the inner surface of the side wall by having the ends of its strip l8 wedged against the sides of a v-shaped boss 20 on the inner surface of the side wall and centrally disposed with relation to the external boss 8, the ends of the insulating strip being cut off at an angle corresponding to the taper of the V-shaped boss.

Thus, by forcing the resistance element down into the housing with the ends of its strip l8 engagi g the sides of the tapered boss 20, the resistance element is expanded outwardly into firm contact with the housing side wall. It is held against displacement from this position by rivets 2| which also serve to secure terminals 22 for the ends of the resistance element in position.

The terminals 22 are stamped to form and legs 23 and 24, respectively. The inner legs 23 overlie the inner surface of the housing side wall in position to contact the endmost turns of the resistance wire, and the outer legs extend radially outwardly from the boss 8.

The manner in which the terminals enter. the housing is important as it combines facility in assembly with security against the ingress of dirt and dust. To this end the external surface of the bottom wall .6 has radial notches 25 extending in from the outer edge of the boss 8 for a distance substantially equal to the wall thickness of the adiacent portions or the boss 8, and the inner surface of the side wall is recessed as at 26 in line with the notches 25. The depth of the notches 25 exceeds the thickness of the adjacent portions of the bottom wall 6 by an amount substantially equal to the thickness of the terminals. Entrance openings are thus formed in the bottom comers of the notches 25 of a size to snugly receive the cross-section of theterminals so that the terminals have a close fit therein.

The depth of the recesses 28 is slightly less aaaarso than the thickness of the inner legs 23 o! the terminals so that the surfaces oi the terminals presented to the resistance element lie above the inner surface of the housing side wall. This insures intimate contact between the endmost turns of the resistance element and the terminals, first, by virtue oi the wedging action of the tapered boss 20 expanding the resistance element and, second, by virtue of the clamping eilect oi the rivets 2 I. These rivets pass through the housins side wall and the boss 8, through the inner legs 23 oi the terminals, and through apertures in the resistance element strip to have the heads of the rivets overlie the adjacent endmost turns of the coil, as best shown in Figure 7.

The turns of the resistance element are thus firmly clamped against the terminals, and by virtue of a relatively heavy soft silver plating on the terminals, the turns of the wire are embedded in the terminals to insure low stable contact resistance.

In order to preclude the possibility of inter ferenge with the wcdging action effected by the tapered or V-shaped boss 20, the openings in the resistance strip through which the rivets pass are elongated shown in Figures 7 and 9.

A third notch the external surface of the bottom wall 6 between the notches 25 provides for the admission into the interior of the hous-= ing of a combined terminal and collector ring 28. The notch 21" extends radially to a point in line with the inner surface of the tapered projection it as clearly shown in Figure 8, and the inner face of the bottom wall in line with the notch is recessed as The depth of the notch 21 overlaps the bottom of the recess it by an amount equal to the thickness of the combination terminal and collector ring so as to provide an entrance slot joining the notch 23) and the recess 29 of a width equal to the thickness of the terminal. The notch 2'! is Just slightly wider than the terminal and the entrance slot being formed in the bottom corner of the notch 217 is of corresponding width.

Hence, the outer terminal portion 3301' the combined terminal and collector ring completely fills the entrance slot.

The recess 29 has lateral extensions 3! to accommodate correspondingly located and shaped lateral projections 32 on the combination terminal and collector ring. The reception of these projections 32 in the recess extensions 3! holds the combination terminal and collector ring against radial shifting.

The recess 29 extends radially inwardly to the wall of a circular central boss 33 rising up from the bottom wall 8 oi the housing and encircling the control shalt. The collector ring portion 34 of the combined collector ring and terminal overlies this boss, being -connected to the outer terminal portion 30 by an intermediate offset or step portion 35.

Preferably a washer 33 of material having high dielectric value is interposed between the collector ring and the top 01' the central boss. Notches 31 at diametrically opposite points and in the outer edge of the washer have the offset portion 35 and a down turned ear 38 received therein to hold the washer assembled with the collector ring.

The collector ring presents a flat contact surface encircling the control shaft and lying in a. plane normal to the axis 1' the shaft and substantially bisecting the axial width of the resistance element.

The co'ntactor assembly, as best illustrated in Figure 5, comprises a driving arm or disc 39 of insulating material secured to the inner end of the control shaft by being clamped between the shouldered erillfot the shaft and a metal stop plate 40 non-rotatably and rigidly secured to the end of the shaft.

An inturned stop lug 4i received in a notch 42 in the edge of the driving arm or disc 39 holds the latter against turning with relation to the shaft and cooperates with a stop lug 43 molded as an integral, part of the housing and rising up from the bottom wall 3 and out from the side of the central boss 33 substantially diametrically opposite the tapered projection 20.

The contactor per se comprises a one-piece stamping 44 having a substantially U-shaped fiat body portion 45 which overlies the inner face of the driving disc 39 and is secured thereto by three tangs 48 wrapped around the bottom edges 01 the notches in the disc 39.

Projecting toward each other from the opposite ends of the Ushaped body portion are two spring contact arms or brushes 41 the extremities of which have rounded contact shoes 48 to press against and ride on the flat contact surface of the collector ring The thrust of these spring contact arms is axial and is opposed by a split ring 49 set into an annular groove in the shaft and bearing against the outer end of the bushing l4.

Attention is directed to the fact that the contact shoes 48 are so disposed with relation to each other that they ride on the collector ring at radially spaced points, thus increasing the assurance of good electrical contact between the contactor and the collector ring.

At points substantially diametrically opposite the anchorage for the spring arms 41 the body portion 44 has laterally bent lugs 5U. One of these lugs projects to one side of the contactor body portion and the other lug projects to the opposite side thereof. Extending from the in-- ner edges of the lugs 50 are spring arms 5|, the extremities of which are rounded to form contact shoes 52 which engage and press against the cylindrical contact surface of the resistance element.

In view of the fact that the lugs 50 project to opposite sides of the body portion one of the spring arms 5! lies to one side of the plane of the flat contact surface of the collector ring and the other is at the opposite side thereof. The contact shoes 52 are thus axially spaced, but they lie on the intersection of a common plane radial to the shaft axis with a plane parallel thereto'and are thus circumferentially aligned to both simultaneously contact the same turn of the resistance wire in any position of adjustment.

The intervening area f the resistance element between the tracks traversed by the contact shoes 52 is preferably coated with an adhesive to help hold the turns of the wire against displacement as the contact shoes ride thereover.

The points of anchorage of the spring arms 5i are spaced apart a substantial distance, hence the spring arms are relatively long and as their points of anchorage, the lugs 50, are quite close to the cylindrical contact surface of the resistance element, the spring contact arms approach their pointsof contact with the resistance element at relatively low angles. This is clearly illustrated in Figure 4. In view of this low angle, the relatively long length of the spring arms. and the fact that one arm is always pulled across the contact surface of the resistance element regardless of the direction of rotation, smooth operation both mechanically and electrically is assured.

If desired, the cover Ill may have an electric switch 53 of the toggle type mounted thereon as shown in Figure 8. In this event, the actuator 54 of the switch protrudes through the cover in position to have a switch actuating lug 55 projecting out from the stop plate 40 collide therewith.

From the foregoing description taken in connection with the accompanying drawings, it will be readily apparent to those skilled in the art, that this invention provides-a variable resistance device of the wire-wound type having numerous advantages over those heretofore in use, and that it particularly assures smooth operation both mechanically and electrically because of the novel arrangement of the contactor, and that it secures this desirable result with an exceedingly simple construction involving merely a single one-piece stamping as compared to the multipart assembly heretofore employed for the same purpose.

What we claim as our invention is:

1. In a variable resistor of the character described: a rotatable control shaft; a resistance element encircling the control shaft and having a cylindrical contact surface parallel with the axis of the shaft; and a contactor mounted on said shaft and having a substantially fiat body portion by which the contactor is mounted and a pair of spring arms extended from the body portion and pressing against the contact surface of the resistance element at axially spaced points lying in a plane radial to the shaft axis, said spring arms being located at opposite sides of the plane of the substantially flat body portion and being anchored thereto at points angularly spaced with relation to the shaft axis and at opposite sides of said radial plane so that the spring arms approach their points of contact with the resistance element from opposite directions transverse to the shaft axis whereby one of the spring arms is always pulled across the contact surface of the resistance element regardless of the direction of rotation of the control shaft.

2. In a variable resistance device: a rotatable control shaft; a stationary collector ring encircling the shaft and having a'contact surface substantially normal to the axis of the shaft; a resistance element encircling the shaft and having a cylindrical contact surface parallel with the shaft axis; an insulated contactor driver fixed to the control shaft and lying in a plane normal to the shaft and between the side edges of the cylindrical contact surface; and a contactor mounted on said driver and comprising an integral one-piece stamping having a flat body portion fixed to the contactor driver, and a pair of spring arms approaching each other from opposite sides of the body portion with their extremities formed as contact shoesto ride on and press radially against the cylindrical contact surface of the resistance element, said spring arms being disposed at opposite sides of the plane of the flat body portion so that their contact shoes engage axially spaced portions of the resistance element, and another pair of spring arms projecting toward each other from opposite sides of the body portion with their extremities formed as contact shoes to ride on and press axially against the fiat contact surface of the collector ring.

3. In a variable resistance device: a substantially cup-shaped housing having a boss projecting from the inner face of the bottom wall thereof; an operating shaft rotatably mounted in the bottom wall of the cup-shaped housing andpro truding through said boss; a stationary collector ring supported on said boss and encircling the operating shaft, said collector r g; having a flat contact surface normal to the shaft axis and encircling the shaft; a resistance'element along the cylindrical wall of the cup-shaped housing having longitudinally spaced cylindrical contact surfaces disposed beneath and above th'e plane of said stationary collector ring; and a one-piece contactor mounted on the control shaft and having apair of spring arms projecting toward each other from opposite sides with their extremities formed as contact shoes to ride on and press radially against the cylindrical contact surfaces of the resistance element, one of said spring arms being disposed above and the other beneath the plane of the stationary collector ring so that their contact shoes engage axially spaced portions of the resistance element,

and said contactor having another pair of spring arms projecting toward each other from opposite sides with their extremities formed as contact shoes to ride on and press axially against the flat contact surface of the collector ring.

4. In a variable resistance device of the character described: the combination of a rotatable operating shaft; a stationary collector ring hav-' collector ring and resistance element, the contact arms which engage the collector ring extending toward each other from opposite sides of the contactor and having their extremities formed as contact shoes spaced different distances out from the axis of the shaft so as to engage and press axially against the fiat surface of the collector ring along radially spaced arcs, and the contact arms which engage the resistance element being disposed, one beneath and the other above the plane of the flat contact surface of the collector ring, with each arm in line with one of the axially spaced cylindrical contact surfaces, and approaching each other from opposite sides of the contactor with their extremities formed as contact shoes lying in a common plane radial to the control shaft to simultaneously engage and press radially against axially spaced portions of the same turn of the wire wound resistance element.

5. As an article 'of manufacture, a contactor for variable resistors, comprising: an integral stamping having a substantially U-shaped flat body portion to overlie and be secured to a flat carrying member; a pair of spring arms extending inwardly from the opposite sides of the U- shaped flat body portion and sprung out of the plane of the fiat body portion to have theiradjacent ends resiliently engageable with a contact surface parallel to the fiat body portion; and another pair of spring arms extending toward each other from the opposite sides of the U- assa'no shaped body portion, each of said last named spring arms hang a lateral extension on the inneredgeotalugintegralwiththebodyportion and bent substantially at right angles from the outer-.edge thereof, one of said lugs being bent up while the other is bent down so that the spring arms occupy positions at opposite sides of the plane defined by the flat body portion, the extremities of said last named spring arms being formed with contact shoes lying in a plane perpendicular to the plane of the body portion to be engageable with a cylindrical contact surface at longitudinally spaced but circumierentially aligned points.

6. In a resistance device of the characted described: a substantially cup-shaped insulated housing; a wire wound resistance element mounted on a ribbon of insulating material and disposed along the inside of the cylindrical side wall of the cup-shaped housing; terminals for the ends of the resistance element having portions inside the housing in position to contact the endmost turns of the resistance element; and rivets passing through the side wall of the housing, said portions of the terminals and the ribbon upon which the resistance element is wound, the rivets passing through the ribbon directly adjacent to the endmost turns of the resistance element so that the clamping action of the rivets holds the endmost turns of the resistance element firmly against said terminal portions.

7. In a variable resistance device of the character described: a molded substantially ,cupshaped housing having a cylindrical side wall with slots therethrough for the reception of terminals; a resistance element comprising a band of insulating material with resistance wire wound thereon, said resistance element lining the inner surface of the cylindrical side wall of the housing with the ends thereof adjacent to said slots; terminals in said slots having contact portions overlying the inner surface of the side wall and contacting the adjacent endmost turns of the wire wound resistance element, the surfaces of said contact portions of the terminals engaged by the end turns of the resistance element beinii the sole support for the resistance element end portions so that outward radial pressure on the resistance element firmly presses the wire turns against said contact portions; and rivets passing through the side wall of the housing, through the contact portions of the terminals and the band of the resistance element for securing said par-ts assembled with the endmost turns of the resistance element clamped against the contact portions of the terminals.

- acter described:

8. In a variable resistor of the character described: a cup-shaped housing of insulating m terial having a radial notch in the exterior of the bottom wall extending in from the outer edge of the housing for a distance equal to the thickness of the adjacent portion of the side wall, said notclrbeing' slightly deeper than the thickness of the adiacent portion of the bottom wall so that an opening into the interior of the housing is formed at the bottom corner of the notch; a.

the close fltofthe termlnalportion in the opening acting in conjunction with the pressure of the contactor on the collector ring portion holds the combination collector ring and terminal in position. 7 i

9. In a variable resistance device of the chara substantially cup-shap housing having bottom and side walls; a resistance element in said housing; terminals for the ends of the resistance element, the terminais being substantially angular so as to have an inner leg to overlie the inner face of the side wall and an outer leg to extend radially on the outside .of the housing; said housing having notches in the exterior of its bottom wall extending radially in from the edge of the housing a distance. equal to the thickness of the adjacent portions of the side wall and having a width equal to that of the outer legs of the terminals and a uepth exceeding the thickness of the ad- Jacent portions of the bottom wall an amount equal to tne thickness of the terminals so as to provide entrance openings into the interior of the housing at the bottom corners of the notches and substantially corresponding in size to the cross-section of the outer legs of the terminals, said terminals having their outer legs disposed in said notches with their inner legs overlying the mner surfaces of the side walls; and common means for effecting electrical connections between the ends of the resistance element and said inner legs of the terminals and for securing said terminals in position in the housing.

10. In a variable resistance device of the character described: a substantially cup-shaped housing having a notch in the inner surface 0: its bottom wall extending in from the side wall and having a notch in the outer surface of the bottom wall extending radially inwardly from the periphery of the housing in line with and toward the notch in the inner face of the bottom wall, said external notch being deep enough to slightly overlap the bottom of the notch in the inner surface so as to provide an entrance opening into the housing; and a one-piece combination collector ring and terminal therefor comprising a stamping formed with a flat terminal portion of a width to snugly lit the external notch and of a thickness substantially equal to the amount said external notch overlaps the bottom of the inner notch so as to completely fill the entrance opening and having a. ring on its opposite end offset from the terminal portion to position the ring above the bottom wall oi the housing.

11. In a variable resistance device of the character described: the combination of a cupshaped housing molded of insulating material and having aligned notches in the-exterior and interior surfaces of its bottom wall; the notch in the exterior surface opening radially to the periphery of the housing and the notch in the interior surface extending radially for a substantial distance in from the side wall of t housing; said notches being of such relative depths that the bottoms thereof lie in parallel planes spaced apart a slight distance to provide an entrance slot joining the notches; and a onepiece combination terminal and collector stamped from sheet metal and having one end,

thereof formed as a flat terminal portion occupying said notches and completely the entrance slot, and having its opposite end portion formed as a. ring connected to the terminal portion by an intermediate oilset portion which housing molded 12. In a variable resistance device of the char-.

acter described: the combination of a cup-shaped of insulating material and having aligned notches in the exterior and interior surfaces of its bottom wall; the notch in the exterior surface opening radially to the periphery of the housing and the notch in the interior surface extending radially for a substantial distance in from the side wall of the housing; said notches being of such relative depths that the bottoms thereof lie in parallel planes spaced apart a slight distance to provide an entrance slot joining the notches; a one-piece combination terminal and collector ring staniped from sheet metal and having one end thereof formed as a flat terminal portion occupying said notches and completely filling the entrance slot, and having its opposite end portion formed as a ring connected to the terminal portion by an intermediate oflset portion which spaces the ring above the bottom of the cup-shaped housing, the notch in the interior surface having lateral enlargements; and lateral projections on the terminal portion disposed in said enlargements .to lock the combined terminal and collector ring against radial movement in the housing.

13. In a variable resistance device of the character described: a substantilaly cup-shaped housing having an inner cylindrical side wall; a v-shaped projection integral with said side wall, the base of which is adjacent to the bottom wall and the apex of which. is adjacent to the open face of the housing; and a resistance element lining the inner side wall of the housin and comprising a strip of insulating material with resistance wire wound thereon, the ends of said strip being cut on at angles correspond ing to the angle formed by the sides of the V- shaped projection, and said ends of the strip engaging the sides of the projection, whereby, in assembling said resistance element with the housing, the resistance element is properly located in the housing and expanded outwardly into firm engagement with the side wall of the housing.

14. In a variable resistance device of the char acter described: a substantially cup-shaped housing having an inner cylindrical side wall; a V-shaped projection fixed on said side wall. the base of which is adjacent to the bottom wall and the apex of which is adjacent to the open face of the housing; a. resistance element lining the inner side wall of the housing and comprising a strip of insulating material with resistance wire wound thereon, the ends of said strip being out off at angles corresponding to the angle formed by the sides of the V-shaped projection, and said ends of the strip engaging the sides of the projection, whereby, in assembling, said resistance element with the housing, the resistance element is properly located in the housing and expanded outwardly into firm engagement with the side wall of the housing; and terminals for the ends of the resistance element having portions thereof exposed on the inside of the side wall at each side of said V-shaped projection so as to engage the adjacent endmost turns of the resistanceelement and whereby the wedging'oi the resistance element into position presses said endmost turns against the contact portions of the terminals.

15. In a variable resistance device acter described:

of the chara substantially cup-shaped housing having an inner cylindrical side wall: a

V-shaped projection on said side wall, the base of which is adjacent to the bottom wall and the apex of which is adjacent to the open face of the housing; a resistance element lining the inner side wall of the housing and comprising a strip of insulating material with resistance wire wound thereon, the ends of said strip being cut oil-at angles corresponding to the angle formed by the sidesof the V-shaped projection, and said ends of the strip engaging the sides of the projection, whereby, in assembly, said resistanceelement is expanded outwardly into firm engagement with the side wall of the housing; terminals for the ends of the resistance element having portions thereof exposed on the inside of the side wall at each side of said V-shaped projection so as to engage the adjacent endmost turns of the resistance element and whereby the wedging of the resistance element into position presses said endmost turns against the contact portions of the terminals; and rivets passing. through'the side wall of the housing, the contact portions of the terminals, and said insulating strip, of the resistance element to clamp said parts together, the holes in the insulating strip through which the rivets pass being elongated so that the insertion of the rivets does not interfere with the functioning of the wedging action, and the heads of the rivets overlying the adjacent endmost turns of the resistance element.

16, In a variable resistance device of the character described: a molded cup-shaped housing of insulating material having a central hole through the bottom wall thereof; a control shaft rotatable in said hole; a central boss rising up from the bottom of the housing and encircling the control shaft; a one-piece combined collector ring and terminal having a ring at one end thereof supported on said boss and a terminal portion protruding through an opening in the side wall of the housing; an insulated contactor carrier fixed on the control shaft inside the housing; a contactor mounted on said carrier and including brushes riding on said collector ring; a stop plate secured to the inner end of the control shaft over said insulated carrier; a stop on said plate directed downwardly toward the bottom of the housing; and a stop abutment molded as an integral part of the housing rising up from the bottom and radially out from said central boss in position to have said stop collide therewith.

17. In a variable resistor of the character described: a rotatable control shaft; a resistance element encircling the shaft and having a cylindrical contact surface concentric to the shaft axis; a stationary collector ring encircling the shaft and having a fiat contact surface normal to the shaft axis; an insulated contactor driver fixed to the control shaft and lying in a plane normal to the shaft adjacent to but spaced from the flat contact surface of the collector ring; and a one-piece contactor mounted on said insulated driver and comprising a substantially flat body portion overlying said driver and interposed between it and the flat contact surface of the collector ring, the plane of said body portion intersecting the cylindrical contact surface of the resistance element medially of the side edges thereof, a pair of spring arms extending inwardly from opposite sides of the fiat body portion and sprung out of the plane of the fiat body portion toward the collector ring so that the ends thereof resiliently engage said fiat contact surface of the collector ring, and another pair of spring arms extending toward each other from opposite sides of the body portion, said last named spring arms occupying positions at opposite sides of the plane defined by the flat body portion and the extremities of said last named spring arms being formed with contact shoes lying in a plane perpendicular to the plane of the body portion and radial to the shaft axis so as to engage the cylindrical contact surface of the resistance element at longitudinally spaced but ciroumferentially aligned points.

. BASIL S. TURNER.

MERVIN B. ARISMAN. JOSEPH G. VEATCH.

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