US2736781A - Variable resistor - Google Patents

Description

Feb. 28, 1956 A M, DAILY ETAL 2,736,781

VARIABLE RESISTOR Filed June 8, 1955 3 Sheets-Sheet 1 Feb. 28, 1956 A. M. DAILY ETAL VARIABLE RESISTOR 3 Sheets-Sheet 2 Filed June 8, 1955 zw K Fb., 2B, 1958 A. M. DAILY ETAL VARIABLE RESISTOR 3 Sheets-Sheet 3 Filed June 8, 1953 United States Patent Oliice 2,736,78 1 Patented Feb. 2s, 195e VARIABLE RESISTOR Arthur M. Daily and Mervin B. Arisman, Elkhart, Ind., assignors to Chicago Telephone Suppiy Corporation, Elkhart, Ind., a corporation of Indiana Application June 8, 1953, Serial No. 360,047

10 Claims. (Cl. 201--48) This invention relates to variable resistors used in radio and television sets, and particularly to the Wire wound type wherein the resistance element comprises a coil of resistance wire wound toroidally about a strip of insulating material curled into a hoop and lining the side wall of the housing of the unit concentrically with its operating shaft.

For many years wire wound variable resistors have been made with metal or molde-d insulation housings. Patent No. 1,913,686 is an example of the metal shell construction and Patent No. 2,389,750 is representative of the molded shell type of unit. Each housing type has advantages not possessed by the other.

One of the chief advantages of the metal shell type housing for wire wound resistors is that it provides a large heat conducting surface which in turn allows a relatively large amount of power to be dissipated, but,

of course, the resistance element must be electrically insulated from the metal housing. Heretofore this necessary insulation was provided in the manner illustrated in the aforesaid Shellenger Patent No. 1,913,686 wherein an` insulating washer overlies the at end wall of the housing and an insulating strip covers the inside surface of its cylindrical side wall. This manner of insulating the resistance element from the housing meant extra parts in production and consequently longer assembly time.

The molded base or housing construction of the Turner et al. Patent No. 2,389,750 obviates the need for such extra parts, but a control with a molded housing has poor power dissipation characteristics and hence cannot be rated very high. A further objection to the molded base type construction concerns the manner in which the terminals for the resistance element are mounted. Invariably in such units the terminals are riveted to a wall of the molded base with the Contact portion of terminal in engagement with the resistance element. This limits the rivet pressure that can be used and often results in a poor connection between the terminal and the resistance element for `when greater rivet pressure is ernployed the molded base cracks and breaks.

ln recognition of these shortcomings of the wire wound type of variable resistor heretofore available, the present invention has as its purpose to provide a variable resistance device or" the wire wound type which possesses only the advantages of both the metal shell and the molde-d base type of unit. It achieves this objective through the use of a novel manner of insulating the resistance element from a metal shell type housing, and a novel resistance element and terminal combination made up as a subassembly and installed as a unit in the metal shell.

With the above and other objects in View, which will the Cil

appear as the description proceeds, this invention resides in the novel-construction, combination and arrangement of parts substantially as hereinafter described and more particularly dened by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate two complete examples of the physical embodiments of the invention constructed according to the best modes so far devised for the practical application of the principles thereof, and in which:

Figure l is a longitudinal sectional View through a variable resistance device embodying this invention;

Figure 2 is a front View thereof;

Figure 3 is a rear View of the unit but with the back removed;

Figure 4 is a longitudinal sectional view through the device upon the plane of the line 4*4 in Figure l;

Figure 5 is a perspective View showing the resistance element and terminal subassembly and the housing, separated but in their proper relative positionsof assembly;

Figure 6 is an exploded perspective view of the terminal board and the adjacent portion of the resistance element; and

Figure 7 is a view similar to Figure 6 illustrating a slightly modified manner of connecting the elements of the resistance element and terminal subassembly.

Referring now particularly to the accompanying drawings in which like numerals indicate like parts throughout the several views, the numeral 4 designates the shell or housing of the variable resistance device of this invention. As already indicated this housing is a cupshaped metal stamping having a substantially at end wall 5 which forms the front wall of the housing and a cylindrical side wall 6. A flanged cylindrical cap 7 secured over the open rear end of the cup-shaped stamping provides a back wall for the housing, and if desired a switch 8 is mounted on this back wall to be actuated during part of the rotary adjustment of the control shaft 9 ofthe unit.

The control shaft 9 is journalled in a mounting bushing 10 fixed to the front wall 5 of the housing. To secure the bushing 10 against rotation it has a hexagonal ange ll'received between opposite llat sides 12 of an indentation in the wall 5 and to hold the bushing upon the wall 5 the inner end of the bushing passes through a hole in the bottom of the indentation and is rolled over the edge of the hole as at 13.

As is customary the unit is mounted upon its supporting panel (not shown) by passing the bushing through a hole in the panel and clamping the panel between the flange 11 and a nut threaded on the bushing, the unit being held against turning by two diametrically opposite pierced and formed lugs 14 projecting forwardly from the front wall 5.

An ordinary C-Washer 15 secured in a groove of the control shaft restrains the shaft against inward axial displacement, outward displacement being prevented by the engagement or" spring contact ngers 16 forming part of a rotatable contacter 17 with an annular collector ring 18 which forms part of the resistance element-terminal sub-assembly to be hereinafer described,

The contactor 17 is similar to that employed in the aforesaid Turner et al. Patent No. 2,389,750 and in addition to .its spring fingers 16 has another pair of spring contact fingers i9 arranged to ride along the inside of the resistance element indicated generally by the nurneral 29. Tangs 21 on the contactor received in notches in opposite side edges of an insulated driver disc 22 and bent around the bottoms of these notches secure the contacter to the disc, and the disc in turn is mounted upon the inner end of the control shaft in the conventional manner which includes a metal stop plate 23. This stop plate has a forwardly directed arm 24 cooperable with a lug 25 pierced and formed from the front wall of the housing, to define the limits of rotation of the control shaft, and a rearwardly projecting lug 26 on the stop plate 23 coacts with the actuator of the switch 8 to open and close the switch in the customary manner during part of the rotation of the shaft.

The resistance element comprises a strip 27 of moisture-proof insulating material of such length that when curled into a hoop with its ends abutting, the outside diameter of the hoop is but slightly smaller than the inside diameter of the side wall 6. A coil of resistance wire 28 is wound toroidally about the strip 27 with the ends of the coil spaced a short distance from the extremities of the strip so as to leave the end portions 29 of the strip bare. At each end of the coil a group of the endmost turns is secured together by areas 30 of silver solder or other suitable metal of good conductivity at both sides of the strip. These areas provide low resistance terminal portions for the resistance element and facilitate the attachment thereto of the end terminals 3l.

The end terminals 31 have U-shaped attaching portions 32, the legs of which-in that form of the resistance element-terminal subassembly shown in Figure 6-are spaced apart a distance to receive therebetween not only the resistance element but also a terminal board 33. The terminal board is punched from a sheet of moistureproof insulating material and has a length to overlie both contact areas 30 and a width somewhat greater than that of the resistance element.

In that embodiment of the resistance element-terminal subassembly shown in Figure 6, one side edge 33 of the terminal board has notches 34 therein to accommodate the bights 36 of the attaching portions of the terminals 31. This allows the terminal board to project beyond the side edge of the resistance element embraced by the terminals a distance necessary to have the opposite edge 37 of the terminal board iiush with the adjacent side edge of the resistance element. The notches 34 also enable Vthe 'nights of the attaching portions to be spaced from the edge 33.

' Aligned rivet holes through the legs of the U-shaped attaching portions of the end terminals, the terminal board (in the case of the Figure 6 embodiment) and the resistance element at the Contact areas 3? receive fastening rivets 33 by which the end terminals and the terminal board are secured to the resistance element. With this arrangement the bottom leg of the U-shaped attaching portion of each end terminal directly engages the adjacent contact area 3% of the resistance element and is drawn rmly into contact therewith since substantial rivet pressure can be developed without incurring danger of breakage of any part of the assembly; and the solder lug portion 39 of each terminal projects perpendicularly from the terminal board.

A center terminal di) completes the resistance elementterminal subassembly. This center terminal has a U-shaped attaching portion 41 similar to the attaching portion 32 of the end terminals and embraces the contiguous bare end portions 29 of the winding strip and the medial portion of the terminal board. A notch 35 in the terminal board accommodates the bight of the U-shaped attaching portion 41 and a rivet 42 passes through aligned holes in the legs of the attaching portion Y 41, the terminal board and the contiguous end portions 29 of the winding strip to iirmly clamp these parts together and join the center terminal to the resistance element with `its solder lug portion 43 projecting perpendicularly from the terminal board.

The bottom leg of the U-shaped attaching portion of the center terminal has a connecting strip 44 projecting radially inwardly therefrom to locate the annular flat collecting ring portion 13 concentrically with the resistance element and in a plane lying between the planes defined by the opposite side edges of the resistance element. The flat collecting ring portion l has diametrically opposite supporting legs i5 projecting therefrom toward the edge of the resistance element which is adjacent to the front wall of the housing and these legs are of a length such that their extremities lie in the plane defined by this front edge of the resistance element to rest upon the inner face of the front wall 5 of the housing and thus support the collector ring against forward axial displacement. i It will be noted that with the construction illustrated in Figure 6, one of the end terminals 31 and one end of the terminal board 33 can be secured to the resistance element while the latter is in its liat state. In the Figure 7 embodiment of the resistance element-terminal subassembly both end terminals can be secured to the resistance element while the latter is in its flat state. The Figure 7 construction also has the advantage of bringing both legs of the U-shaped attaching portions 32 of the terminals into direct contact with the resistance element. This, of course, requires the end terminal receiving notches 34 in the terminal board to be deep enough to accommodate the whole of the terminal portions overlying the outer face of the resistance element.

Regardless of which of the two resistance elementterminal subassemblies is employed, the mounting thereof in the housing and its securement against displacement is the same. ln each instance the resistance element tits snugly into the cup-shaped housing or shell 4 with the terminal board being received in an appropriately enlarged pocket formed by a slight outward projection 47 of the side wall 6. The wall of the projection has an opening 4S cut therein to accommodate the solder lug portions of the terminals and for the same purpose the flange of the rear wall '7 is cut away as at 49 (see Figures l and 4).

The terminal board closes the opening 43 and part of the opening 49, and being of a width substantially equal to the depth of the housing has its opposite side edges in engagement with the front and rear walls of the housing to hold the resistance element subassembly against endwise displacement from a position at which the front edge of the resistance element is in close juxtaposition to the front wall 5 of the housing. Rotation of the subassembly from its proper position in the housing is prevented by the engagement of a locating lug 50 in a notch 51 in the terminal board and the contiguous end portions 29 of the winding strip'. The lug 50 is preferably an integral part of the housing 4 being pierced and formed at the junction of its front and side walls.

The assembly of the resistance element and its terminals with the housing is thus an extremely simple procedure requiring no riveting or other similar fastening thereof to the housing; it being understood that after the resistance element-terminal subassembly has been inserted into the housing shell, and the operating shaft and contactor have been assembled therewith, the back wall 7 is fastened in place by striking over ears 52 projecting from the rear edge of the side wall 6.

The resistance element is electrically insulated from the metal housing by a coating or lining 53 of insulating varnish or other suitable material such as a silicone resin covering the inside surface of the housing. Preferably this coating 53 is sprayed on and applied in a plurality of coats, an inner coat formulated for good adhesion to metal, an intermediate coat formulated to produce thickness and build up the dielectric strength of the lining, and a final coat formulated to provide a hard, vitreous finish to resist abrasion. By virtue of this novel manner of insulating the inner surfaces of the metal shell the wire wound resistance element is almost in direct contact with the metal shell so that good heat conduction exists from the resistance element to the metal shell, and accordingly the wattage capacity of the unit is high.

This manner of insulating the resistance element from the metal shell, of course, also eliminates the use of separate insulating washers and strips, and Vsince the insulation used is impervious to moisture and possesses high dielectric strength it affords exceptional protection against insulation breakdown between current carrying parts and the metal shell not only at all normal operating voltages but also at high peak voltages.

From the foregoing description taken with the accompanying drawings it will be readily apparent to those skilled in this art that this invention provides a variable resistor especially well adapted to mass production, and to use in modern radio and television circuits since its assurance against insulation failure coupled with good heat dissipation makes it fully dependable under the severest operating conditions.

What we claim as our invention is:

l. A resistance element and terminal assembly for variable resistors, comprising: a winding strip of insulating material curled into a hoop with the ends thereof in abutting relation; a coil of resistance wire wound toroidally about said strip with the ends of the coil spaced a short distance from the extremities of the strip so that the end portions of the strip are bare; a terminal for each end of the coil, said end terminals each having a U-shaped attaching portion embracing a group of turns at one end of the coil and the winding strip about which they are wound; a rivet passing through the legs of each of the U-shaped attaching portions and through the portion of the strip and the coil between said legs, clamping one of the legs to the adjacent wire turns; an insulated terminal board directly overlying the contiguous end portions of said strip and the adjacent end portions of the coil; a center terminal for the resistance element having a U-shaped attaching portion embracing the contiguous bare end portions of the strip and the medial portion of the terminal board; a rivet passing through the legs of the U-shaped attaching portion of the center terminal and the portions of the winding strip and the terminal board therebetween to thus clamp said parts together; and other connecting means between the terminal board and the winding strip positively holding the ends of the strip against separation so that the resistance element, its terminals subassembly which is complete in itself, and as such may be incorporated in a variable resistor.

2. The resistance element and terminal assembly of claim 1 further characterized by the fact that said other means connecting the terminal board and the winding strip comprises notches in one edge of the terminal board having the bights of the U-shaped attaching portions of the end terminals received therein.

3. The resistance element and terminal assembly of claim 1 further characterized by the fact that the U-shaped attaching portions of the end terminals also embrace the adjacent portions of the terminal board.

4. The resistance element and terminal assembly of claim l further characterized by the fact that said terminal board is wider than the winding strip and has one edge thereof protruding beyond the adjacent edge of the strip, while the opposite edge of the terminal board is substantially flush with the edge of the strip adjacent thereto.

5. The resistance element and terminal assembly of claim 4 further characterized by the fact that said protruding edge portion of the terminal board has notches therein in which the bights of the U-shaped attaching portions of the terminals are received.

6. The resistance element and terminal assembly of claim 4 further characterized by the fact that one of said and terminal board constitute a 6 edges of the terminal board has a notch therein adapted to be engaged by a locating lug in the housing of the variable resistor into which the resistance element is assembled.

7. A resistance element and terminal assembly for variable resistors, comprising: a winding strip of insulating material curled into a hoop with its ends abutting one another; a coil of resistance wire wound toroidally about said strip with the ends of the coil spaced a short distance from the extremities of the strip so that the contiguous end portions of the winding strip are bare; an area of metal of good conductivity bonded to the endmost turns at each end of the coil to provide a low resistance contact area at each end of the coil; a terminal board of insulating material overlying the contiguous end portions of the winding strip and extending far enough to encompass the contact areas at the ends of the coil; a center terminal having a U-shaped attaching portion embracing the contiguous bare end portions of the winding strip and the medial portion of the terminal board overlying the same; a rivet passing through the legs of said U-shaped attaching portion and the terminal board and winding strip portions therebetween clamping said parts together; and terminals for the resistance coil, each having a U-shaped attaching portion embracing and riveted to the winding strip with one leg thereof in direct engagement with one of said contact areas at the ends of the coil; and the terminal board having notches in one edge thereof in which the bights of the U-shaped attaching portions of the terminals are received.

8. The resistance element and terminal assembly of claim 7 further characterized by the fact that the insulating terminal board is wider than the winding strip; and by the fact that the side edge of the terminal board in which the notches are located protmdes beyond the bights of the terminals and the adjacent side edge of the resistance element, while the opposite side edge of the terminal board is substantially flush with the adjacent side edge of the resistance element.

9. A variable resistor, comprising: a substantially cupshaped housing having an end wall and a cylindrical side wall; a wire wound resistance element comprising a coil of resistance wire wound upon a winding strip, said resistance element lining the inside surface of the side wall; terminals for the resistor, including a center terminal having a U-shaped attaching portion and an annular collector ring portion; means securing said attaching portion to the winding strip of the resistance element with the annular collecting ring portion concentric to the resistance element and in a plane spaced between and parallel to the planes defined by the side edges of the resistance element; and supporting legs integral with the annular collector ring portion projecting substantially perpendicularly therefrom toward and into engagement with the end wall of the housing to support the collector ring portion from said end wall of the housing.

10. A variable resistor comprising: a cup-shaped housing having a flat end wall and a cylindrical side wall, the inner surfaces of said walls being of insulating material; a resistance element of the wire-wound type comprising a winding strip of flexible insulating material having a length of resistance wire wound toroidally thereon with the endmost turns of the winding spaced from the ends of the strip; a terminal at each end of the resistance element having a U-shaped attaching portion embracing a group of the endmost turns of the winding and the strip about which they are wound, and secured in place by a rivet passing through both legs of the U-shaped attaching portion and the portion of the strip and the winding embraced thereby; each terminal having an end portion providing a solder lug projecting substantially perpen` dicularly from one of the legs of its attaching portion; said resistance element with its end terminals constituting a subassembly which is seated in the cup-shaped housing lining the cylindrical wall thereof, with the ends of the winding strip contiguous to one another and one edge of the element abutting against the end Wall of the housing and the solder lug portions projecting Iradially outthrough the side wall of the housing; the side wall of the housing being cut away to accommodate the solder lug portions of the terminals and to enable axial insertion ofthe resistance element subassembly into the housing; the side wall of the housing being higher than the Width of the resistance element; a metal cover for the open end of the housing; means securing said cover in position over the open end of the housing; and abutment means coacting between the References Cited in the file of this patent UNITED STATES PATENTS 1,987,118 Lodge Jan. y8, 1935 2,031,211 Dumke Feb. 18, 1936 2,155,309 Henton et al. Apr. 18, 1939 2,159,369 Draving et al May 23, 1939 2,460,795 Warrick Feb. 1, 1949

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