US2958839A

US2958839A - Variable resistor

Info

Publication number: US2958839A
Application number: US837131A
Authority: US
Inventors: Wayne A Barden
Original assignee: CTS Corp
Current assignee: CTS Corp
Priority date: 1959-08-31
Filing date: 1959-08-31
Publication date: 1960-11-01
Anticipated expiration: 1977-11-01

Description

Nov. 1, 1960 w. A. BARDEN 2,958,839

VARIABLE RESISTOR Filed Aug. 51, 1959 2 Sheets-Sheet 1 Nov. 1, 1960 w. A. BARDEN 2,953,339

VARIABLE RESISTOR Filed Aug. 31, 1959 2 Sheets-Sheet 2 mynEA.Bard=-m United States Patent VARIABLE RESISTOR Wayne A. Barden, Elkhart, Ind., assignor to CTS Corporation, Elkhart, Ind., a corporation of Indiana Filed Aug. 31, 1959, Ser. No. 837,131

8 Claims. (Cl. 3'38174) This invention relates to variable resistors of the type employed in radio and television receivers, and bears a close relationship to the invention forming the subject matter of the copending application Serial No. 837,269, filed Aug. 31, 1959.

The purpose and object of the invention is to improve the load carrying capacity of a variable resistor without increasing its size or cost of production, and, more specifically, to achieve this objective in a miniaturized variable resistor.

The small size of the so-called miniaturized variable resistors-they are housed in covers no larger in diameter than a dimein the past has placed a serious limitation upon their load carrying capacity. To a large extent the variable resistor of the present invention overcomes this handicap of small size through a novel construction and arrangement of its parts, characterized by the fact that its resistance path is bonded directly to a metal base or substrate by a thin layer or coat of insulation. Optimum heat transfer from the resistance path to the metal substrate or base is thus obtained, and, through it, an improved and better dissipation of the heat generated in tile resistance path when the resistor is under electrical To implement the purpose of this invention and provide for the mounting of the necessary terminals at the ends of the resistance path and for the collector ring or center contact of the variable resistor, this invention utilizes a novel stator assembly which consists essentially of a stamped sheet metal base and a punched out terminal board of insulating material, secured together in an interfitting manner which assures correct orientation of all parts of the stator assembly.

Another feature of the present invention concerns the Way in which the terminals for the ends of the resistance path are connected thereto; and, in this connection, it is a further object of the invention to provide an improved terminal construction in which only a predetermined contact pressure can be applied on the surface of the resistance path, or, more specifically, its low resistance hopoff area.

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 hereindisclosed 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 according to the best mode so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a longitudinal sectional view through a variable resistor embodying this invention;

Figure 2 is an end view of the variable resistor, with its cover removed and parts thereof broken away; 7

Figure 3 is a fragmentary perspective view with-parts Patented Nov. 1, 1960 broken away and in section, illustrating the specific terminal arrangement by which the ends of the resistance path are connected to their respective terminals;

Figure 4 is a detail sectional view through Figure 2 on the plane of the line 4-4;

Figure 5 is an exploded perspective view of those elements of the variable resistor with which this invention is primarily concerned, and which collectively constitute the essential parts of the stator assembly of the resistor; and

Figure 6 is a perspective view of one of the terminals for the ends of the resistance path.

Referring now particularly to the accompanying drawings in which like reference characters denote like parts, the numeral 5 designates generally the stator assembly of the variable resistor which, together with a rotor assembly 6 and a cover 7, comprises the entire structure.

The rotor assembly 6 is of conventional construction, and comprises the customary bridging contactor 8 carried by an insulated drive arm 9, which together with a stop plate 10 is fixed to a shaft 11. The shaft 11 is journaled in a thimble or bushing 12 which forms part of the stator assembly. It is restrained against inward axial displacement by a C-washer 13, or its equivalent, mounted on the shaft and bearing against the outer end of the bushing. In this manner, the rotor assembly is supported against the end thrust imposed thereon by the tension in the

spring contact fingers

14 and 15 of its bridging contactor -8, as a result of their engagement with the resistance path 16 and collector contact 17 of the variable resistor.

The main elements of the stator assembly 5 are a base 18 and a terminal board 19. These parts are of novel construction and design and together carry the resistance path 16, the collector ring 17, and their

respective terminals

20 and 20.

The inner end portion 21 of the thimble or bushing 12 passes through aligned holes 22 and 23 respectively in the base 18 and the terminal board 19, and is rolled over, as at 24, to clamp these parts tightly together and against hexagonal flange 25 on the thimble or bushing. In this manner, the thimble or bushing, the base and the terminal board are secured together into one unitary assembly.

The base 18 is a sheet metal stamping having a circular flat center portion 26 and an arcuate flat peripheral portion or rim 27 connected to the center portion in planar offset relation by a curved intervening wall 28. The wall 28, as best seen in Figure 5, joins the inner edge of the peripheral portion or rim 27 with the periphery of the center portion 26, but extends around only one half of the circumference of the latter. Hence, the intervening wall 28 may be loosely considered to be semi-cylindrical and, as shown, it lies diametrically opposite the ends of the arcuate peripheral portion or rim 27. More specifically, the wall 28 is bisected by a median plane containing the axis of the hole 22 and equispaced from the ends of the arcuate rim 27.

The ends 29 of the semi-cylindrical intervening wall 28 provide locating shoulders for a purpose to be described.

At the ends of the arcuate peripheral portion or rim 27, there are outwardly radiating fingers 30. These fingers are integral extensions of the peripheral portion or rim 27 and lie in the plane thereof. The entire front or top face of the base 18, i.e. the face from which the central portion 26 is depressed or set back, is covered with a thin coat of insulation 31 such as varnish, the insulating coating extending over the semi-cylindrical intervening wall 28 and over the entire adjacent face of the center portion 26. It is important that this coat of insulation be tightly bonded to the surface of the base,

The resistance path 16 is applied directly on and in fact is bonded to the insulation 31. In a sense, therefore, the resistance path is bonded to the metal base by the insulation. The resistance path 16 may be produced in any suitable manner. Thus, for instance, it might consist of a meta lized film deposited upon the insulated surface of the base by the screening process, and then fired or otherwise bonded to the insulation. The specific manner in which the resistance path is formed-and, for that matter, its composition-forms no part of this invention, it being important only that the resistance path be separated from the metal base solely by the thin coat of insulation therebetween, and that the end portions of the resistance path extend out over the fingers 30 in the form of low resistance hop-off areas 1 6'.

The terminal board 1 9 is-stamped from a sheet of stiff insulation, such as fibre glass and has a generally oblongshaped outer part 33 and a small inner part 34. The inner part has the hole 23 therein and is shaped to have 'interfitting engagement with the base. Accordingly, the edge 34' of the inner part which lies farthest from the outer part, defines a 180 are having a radius just slightly smaller than that of wall 28 so that this edge may be contiguous to the wall 28 when diametrically opposite shoulders 35 on the inner part abut the locating shoulders 29. The engagement of the

shoulders

35 and 29 holds the terminal board against rotation with respect to the base.

The thickness of the terminal board is substantially equal to the planar offset or difference in elevation between the center portion 26 of the base and its peripheral portion or rim 27, so that when the terminal board and base are assembled one face of the board lies flat against the center portion 26, while its other side or face lies fiat against the underside of the peripheral portion or rim 27 and the fingers 30 extending therefrom.

As best seen in Figure 5, the outer part 33 of the terminal board has oppositely projecting wings, each of which has a pair of slit-like holes 36. These holes are so placed that they lie at opposite sides of the fingers '30 but in spaced relation thereto, with the long sides of the holes parallel to the side edges of the fingers.

U-shaped terminals 37 embrace the fingers 30 and are properly positioned with respect thereto by having their legs 38 received in the holes 36. Since the edges of the fingers 30 may not be covered with insulation, it is important that the legs of the terminals be spaced therefrom. To this end, the distance between the legs and, of course, also between the holes 36, is greater than the width of the fingers; and the locating

shoulders

29 and 35 are so placed that their engagement centers the fingers between their respective holes 36.

Securement of the terminals is effected by clinching or bending the ends of their legs over the edges of the holes 36 and onto the adjacent side or face of the terminal board, and when so secured the bight portion 39 of the terminals is in electrical connection with the low resistance hop-oil areas 16' at the ends of the resistance path.

While it is important that good electrical connection be established between the hop-cit areas and the terminals, this must not be obtained at the expense of possible fracture of the insulation which separates the hopoff areas from the underlying metal. To guard against this possibility, the terminals are so designed that only a predetermined contact pressure can be applied upon the hop-off areas regardless how much pressure is employed in clinching the terminals to the terminal board. Thus, the legs 38 of each terminal have downwardly facing shoulders 40 lying in a common plane so spaced from the underside of a pimple-like contact 41 projecting down from the bight portion 39, that when the contact engages the hop-ofl? area, the shoulders 40 are still slightly spaced from the adjacent surface of the terminal board.

When the terminals are clinched in place the bight portion 39 thereof is bowed or flexed, as best seen in Figure 4, and, as a result, the contacts 41 will be pressed tightly against the hop-ofi? areas but with a definitely limited pressure.

The terminals, of course, also have the usual solder lugs 42 which project from their bight portions 39.

In addition to the holes 36 the terminal board has a centrally located hole 44 and a notch 45 in line therewith. The hole 44 and notch 45 provide locating means for the collector ring or center contact 17 which is of conventional form. Hence, it has an annular contact portion 46 and a terminal strip 47 radiating therefrom, the latter being bent to have portions thereof in the hole 44 and in the notch 45. In this manner, the center contact or collector ring 17 is held in place with its annular contact portion 46 concentric to and substantially circumscribed by the resistance path. A washer 50 of insulating material, which seats upon the rolled-over end 24 of the bushing 12 supports the collector ring against the thrust of the spring fingers 15. The washer is held centered with the collector ring by a plurality of fingers 51 which project from the ring and engage the edge of the washer.

The cup-shaped housing 7 is secured in position by having its edge seated upon the peripheral portion of the base, in which position it is held by tangs 55 projecting from the edge of the cover and clinched over the edge of the base, the tangs being accommodated by notches 56 in the periphery of the base; and as is customary,-the cover 7' has a rotation limiting stop 57 with which an arm 58 on the stop plate 10 abuts.

From the foregoing description taken in connection with the accompanying drawings, it will be apparent to those skilled in the art that this invention provides an exceptionally compact construction for variable resistors and, at the same time, achieves better dissipation of the heat generated in the resistor under electrical load, so that the .load carrying capacity of the resistor is materially increased.

What is claimed as my invention is:

1. A variable resistor having cooperating stator and rotor assemblies, the former comprising a generally flat base, and means providing an arcuate resistance path and a collector contact concentric with the resistance path at one side of the base, and'the latter comprising a bridging contactor having contact fingers bearing on the resistance path and on the collector contact and a shaft to rotate the bridging contactor, the resistor being characterized: by the fact that the base is of metal and has an arcuate peripheral portion with a flat surface; outwardly radiating metal fingers at the ends of the arcuate peripheral portion, said fingers being integral With the peripheral portion and having flat surfaces flush with that of the arcuate peripheral portion; a thin coat of insulation bonded to said flat surfaces, means providing the resistance path bonded directly to the insulation on the arcuate peripheral portion; and means providing low resistance hop-offs for the ends of the resistance path joined thereto and bonded directly to the insulation on said fingers, so that the resistance path and its hop-offs are separate from the metal base only by the thin coat of insulation, whereby heat generated when the resistor is under electrical load will be quickly conducted into the metal base and thence dissipated.

2. A variable resistor having cooperating stator and rotor assemblies, the former comprising a generally fiat base, and means providing an arcuate resistance path and a collector contact concentric with the resistance path at one side of the base, and the latter comprising a bridging contactor having contact fingers bearing on the resistance path and on the collector contact and a shaft to rotate the bridging contactor, the resistor being characterized: by the fact that the base is a sheet metal stamping having a circular center portion and a flat arcuate peripheral portion connected at its inner edge to the periphery of the center portion by a curved portion which is substantially diametrically opposite the ends of the fiat arcuate peripheral portion and extends for no more than half the circumference of the center portion, whereby the ends of said curved portion define locating shoulders facing the ends of the arcuate peripheral portion; a terminal board of stiff insulating material having an inner part seated upon the center portion of the stamped metal base, and an outer part underlying the end portions of its arcuate peripheral portion; locating shoulders on opposite side edges of the terminal board engaging said locating shoulders on the base to hold the terminal board and base correctly oriented with one another; rivet means passing through the inner part of the terminal board and the center portion of the base to secure the terminal board and base together; means on the top face of the peripheral portion of the base but insulated therefrom, providing the arcuate resistance path with low resistance hop-off areas at its ends; and terminals clinched to the terminal board and having portions thereof in intimate engagement with said low resistance hop-off areas.

3. The variable resistor of claim 2, further characterized by: a finger projecting out from each end of the arcuate peripheral portion of the base and forming an extension thereof, the low resistance hop-off areas at the ends of the resistance path being on but insulated from said fingers; the terminal board having a pair of slit-like holes adjacent to each of said fingers with the distance between adjacent holes greater than the width of the fingers, the interengagement of said locating shoulders on the base and terminal board holding the fingers centered between their respective slit-like holes; said terminals being U-shaped stampings embracing the fingers with their legs passing through the slit-like holes and hence spaced from the edges of the fingers, the legs being bent over the edges of the slit-like holes and being the means by which the terminals are clinched to the terminal board, the portions of the terminals which have intimate contact with the low resistance hop-off areas being inward protrusions on the bights of the U-shaped terminals; and means for limiting the contact pressure that can be applied on the hop-off areas of the resistance path by said protrusions as a result of the legs of the terminals being clinched to the terminal board, said last named means comprising shoulders on the legs of the terminals bearing upon the terminal board.

4. In a variable resistor: a base in the form of a sheet metal stamping having a flat peripheral portion with a finger projecting therefrom; a thin coat of insulation bonded to one face of said peripheral portion of the base and continuing uninterruptedly over said finger; means forming a resistance path bonded to the insulation on the peripheral portion and on said finger; a terminal board of stiff insulating material underlying said projection and having slit-like holes therethrough adjacent to but spaced from the opposite side edges of the finger; a U-shaped terminal embracing the finger with its legs passing through the slit-like holes, said legs being spaced apart a distance corresponding to the spacing between the slit-like holes and hence greater than the width of the embraced portion of the finger; localized contact means on the bight of the U-shaped terminal seated upon the adjacent portion of the resistance path; the legs of the terminal being clinched over the underside of the terminal board and clamping said localized contact means to the resistance path; and shoulders on the legs of the terminal abuting the top side of the terminal board to limit the contact pressure between said localized contact means and the resistance path.

5. A variable resistor having cooperating stator and rotor assemblies, the former comprising a substantially flat base, and means providing an arcuate resistance path and a collector contact concentric with the resistance path at one side of the base, and the latter comprising a bridging contactor having contact fingers bearing on the resistance path and on the collector contact and a shaft to rotate the bridging contactor, the resistor being characterized: by the fact that the base is a sheet metal stamping having a flat arcuate rim and a flat outwardly radiating finger at each end thereof; a thin coat of insulation bonded to one face of said arcuate rim and the fingers at the ends thereof; means providing a resistance path bonded to said coat of insulation and having low resistance hop-off areas overlying the fingers; a terminal board of stifl insulating material underlying the end portions of the arcuate rim and the fingers at the ends thereof; and terminals for the ends of the resistance path embracing said fingers and clinched to the terminal board to secure the base and terminal board together, said terminals having no part thereof in contact with the metal of the base but having good electrical contact with the low resistance hop'off areas of the resistance path.

6. The variable resistor of claim 5, further characterized by the fact that the base has a flat circular center portion inside its arcuate rim and joined thereto by a curved intervening wall which extends around substantially only half the circumference of the circular center portion and lies diametrically opposite the ends of the arcuate rim, said rim and center portion lying in parallel planes which are normal to the axis of the resistor and are spaced apart substantially the thickness of the terminal board; and the terminal board having one face thereof flatwise engaged with the fingers and the adjacent end portions of the rim and its other face fiat- Wise engaged with the center portion.

7. The variable resistor of claim 6, wherein the part of the terminal board which overlies and engages the center portion of the base has a semicircular edge portion contiguous to said curved intervening wall; and shoulders at the ends of its semicircular edge portion engaging the ends of said curved intervening wall.

8. The variable resistor of claim 6, wherein the circular center portion of the base and the part of the terminal board overlying it have aligned holes coaxial with the center of the base; and a bushing secured in said aligned holes and providing a bearing for the rotor shaft.

References Cited in the file of this patent UNITED STATES PATENTS 2,179,566 Stoekle Nov. 14, 1939 2,717,944 Daily et al Sept. 13, 1955 2,736,783 Daily Feb. 28, 1956