US2958840A

US2958840A - Variable resistor

Info

Publication number: US2958840A
Application number: US837269A
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 VARIABLE RESISTOR Filed Aug. 31, 1959 2 Sheets-Sheet 1 INSULATING COATING;

Nov. 1, 1960 w. A. BARDEN VARIABLE RESISTOR 2 Sheets-Sheet 2 Filed Aug. 31, 1959 jmdwfw 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. 837,269

14 Claims. (Cl. 338-174) This invention relates to variable resistorsof the type employed in radio and television receivers and has as its purpose and object to increase the load carrying capacity of such resistors without increasing the size thereof or adding to its cost. I

More specifically, it is an object of this invention to provide a variable resistor in which the base or substrate which carries the resistance path is of metal instead of the customary insulating material, so that heat generated when the resistor is under electrical load will be uniformly and rapidly conducted to all parts of the base and thence dissipated.

' this invention pertains, the base of the stator element is With the above and other objects in viev 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 varie able resistor embodying this invention;

Figure 2 is an end view of the resistor with its cover removed and with parts thereof broken away to better illustrate structural details;

Figure 3 is a fragmentary sectional view taken through Figure 2 on the plane of the line 3-3; and

Figure 4 is an exploded perspective view of those parts of the stator element of the variable resistor, with which the invention is primarily concerned, the parts of the stator element not shown being the resistance element, the collector ring or contact, and the terminals for both.

Referring now particularly to the accompanying drawings, in which like numerals designate like parts, the numeral 3 designates generally the stator element of the variable resistor which, together with a rotor element 4 and a cover 5 constitutes the entire unit.

The rotor element 4 is conventional and comprises the customary bridging contactor 6 with its spring fingers 7 and 8 respectively bearing upon the resistance element 9 and the collector ring or center contact 10 of the stator element to traverse the same as the resistor is adjusted. The bridging contactor 6 is carried by a drive arm 11 which, together with a stop plate 12, is fixed to the shaft 13 of the rotor. The stop plate 12 has the usual limit stop 14 which travels in an orbit to collide with a stationary stop 15' on the cover and thereby defines the limits .of rotation of the rotor element.

The shaft 13 of the rotor element is journalled in a thimble or bushing 16 which serves to tie the rest of the stator elements together, and also provides means for mounting the resistor upon a panel, not shown.

Ordinarily, in variable resistors of the type to which made of insulating material. Here it is a circular, generally flat metal disc 17. The marginal or peripheral portion 18 of this disc is fiat and has the means which provides the resistance path, i.e. the resistance element 9 or its equivalent, mounted thereon, but insulated therefrom by a thin coat 19 of insulation, such as varnish. It is significant and important that the resistance path is separated from the metal base 17 only by this thin coat or layer of insulation, and it is this feature which is primarily responsible for the improved heat dissipation achieved by this invention.

A segment of the fiat peripheral portion 18 of the disc 17 is cut away to form an interruption 20 which is occupied by the outer sector shaped part 21 of a terminal board 22. The inner part 23 of the terminal board is circular and is received within a central depression 24 in the base 17. This depression has a flat bottom 25 and a sloping sidewall 26, and is of such depth that with the underside of the terminal board resting on the bottom 25, the top face of the terminal board is flush with the insulation coated surface of the peripheral portion 18. Aligned holes 28 and 29 at the center of the base 17 and the circular inner part 23 of the terminal board receive one end portion 30 of the thinrble or bushing 16.

The segment-shaped interruption 20 has opposite side edges 31 which are parallel to one another and lie in planes equidistant from the axis of the hole 28. These edges 31 have a locating function for a purpose to be described, and the fact that they are parallel to one another is significant.

The edges 31 connect with diagonal edge portions 32 which extend across the sloping wall 26 and, as shown in Figure 2, are substantially radial to the axis of the hole 28. The inner ends of the diagonal edge portions 32 terminate at the junction of the fiat bottom wall 25 and the sloping wall 26 of the central depression 24, and between these points the interruption 20 is bounded by a continuation of the circumference of the circular bottom 25 of the depression. Here a flange 33 projects down from the bottom wall 25 for a purpose to be described.

The outer ends of the diagonal edge portions 32 extend across flanges 34 bent down from the ends of the arcuate peripheral portion 18. Since the junctions of the flanges 34 with the peripheral portion 18 are gently rounded, the insulating coating 19 may extend unbrokenly thereover.

The terminal board 22 is stamped from insulating material, such as Bakelite or fibreglass and, by virtue of its particular shape and thickness, its entire top surface is flush with the insulation coated fiat surface of the peripheral portion 18. Accordingly, the resistance element which lies upon the insulated fiat surface of the peripheral portion and the collector contact which lies upon the center portion of the terminal board are substantially coplanar.

At the junction of its circular inner part and sectorshaped outer part, the terminal board has parallel side edges 36 equispaced from a plane of symmetry passing perpendicularly through the terminal board and containing the axis of its hole 29. These side edges 36 engage the locating edges 31 on the base to hold the terminal board against rotation with respect to the base. Since the side edges 36 are spaced apart just slightly less than the distance between the locating edges 31 of the base, they have snug engagement therewith, and because of the parallel disposition of the

edges

31 and 36, the terminal board is secure against turning about its connection with the base, despite any possible radial misalignment between these parts.

At the opposite side of the base is a ground plate 40. This ground plate, like the base, is stamped from sheet down-turned flange 33 at the bottom of the segment-like interruption or cutout in the base received in a correspondingly placed notch 44 in the bottom of the cutout 43.

Thimble locating protrusions 45 project from the outer face of the ground plate to receive opposite corners of a hexagonal flange 46 on the thimble or bushing, and hold the latter against turning, and thus generally assist in the assembly of the unit, in which condition the flange 33 engages the adjacent flat face of the hexagonal flange.

Theground plate also has a pair of diametrically opposite lugs 47 projecting therefrom to engage in apertures in 'a panel (not shown) upon which the unit may be mounted to hold the same against turning, it being understood that a clamping nut (not shown) is threaded onto the thimble or bushing to secure the unit to the panel.

The central depressed portion 41 of the ground plate has a hole 48 at its center, which, like the holes 28 and 29 in the base and terminal board, receives the adjacent end portion 30 of the thimble or bushing. The ground plate, base and terminal board are held in their assembled relationship by being clamped between the hexagonal flange 46 against which the ground plate bears, and the rolled over edge 50 of the thimble portion 30.

heat generated in the resistance element when the unit is under electrical load, will be quickly conducted to and uniformly distributed in the metal base and ground plate and, thence, dissipated. Hot spots which are due to high resistance radiants are thus eliminated and, in addition, the resistor can easily handle loads that would seriously overload a comparable sized variable resistor having the conventional base of insulating material.

Other features of the disclosed and described construction contribute to the fulfillment of this main objective of the invention. Thus, the provision of the downturned flanges 34 at the ends of the arcuate peripheral portion 18, enable the insulating varnish or coat to extend over the flanges and. thereby assure against the presence of uninsulated edge portions of the base directly contiguous to the resistance element. While the locating edges 31 of the base may not be coated with varnish, they are covered by the adjacent locating edges 36 of the terminal board.

Another feature of the described and illustrated structure which contributes toward the overall improvement gained by this invention, is the parallel disposition of the engaging locating

edges

31 and 36; As can no doubt be appreciated in production the assembly of the parts may result in some slight radial displacement between the terminal board and the base; and since the ends of the resistance element are secured to the terminal board,

' relative rotation between the terminal board and base The arcuate length of the resistance element 9 is greater than that of the arcuate peripheral portion 18 of the base which it overlies. Hence, the end portions of the resistance element extend into the segment-like interruption 20 and overlie the adjacent portion of the terminal board, to which they are clamped by terminals 51. The terminals 51 are secured to the terminal board by rivets 52 which pass through flat attaching portions 53 of the terminals, through radially projecting low resistance terminal portions 54 on the ends of the resistance element, and through the terminal board. The fiat attaching portions 53 of the terminals are thus tightly clamped against the low resistance terminal portions 54; and to secure the terminals against rotation about their attaching rivets, the terminals have tangs 55 which are received in notches 56 in the side edges of the terminal board, and tongues 57 which are received in other notches 58 and are bent down and back to provide the terminals with solder lugs 59.

The collector ring or contact 10, as already noted, overlies and is supported upon the circular inner part 23 of the terminal board, where it is held by the reception of part of it's terminal 60 in a slot 61 in the terminal board, and another part 62 thereof in a notch 63, the part 62 being extended to provide the solder lug 64 for the collector contact. Of course, the center Contact or collector ring is also held in place by the contact pressure of the fingers 8 of the bridging contactor riding thereon, it being understood that the rotor element of the control is secured against rearward axial displacement in any conventional manner, as by a C-washer 66 snapped onto the shaft 13 and bearing against the front end of the thimble or bushing 16.

The cover 5 has the conventional stamped sheet metal construction, cup-shaped as shown, with tangs extending from its edge to be received between segments 70 projecting from the edge of the base 17, and then clinched over the front of the 'ground'plate.

From the foregoing description taken in connection with the accompanying drawings, it will be apparent to those skilled in the art that the variable resistor of this invention possesses several important and significant advantages. First and foremost is the fact that, since the base is of metal, and is spaced from the resistance ele- "ment only by the'thin coat of insulation on the. base, all

must be prevented. By having the

edges

31 and 36, or at least one of these edges, i.e. either the edges 31 or the edges 36 parallel to one another, as shown and described, it follows that the desired security against relative rotation is achieved, despite any possible radial misalignment between the terminal board and base.

What is claimed as my invention is:

1. A variable resistor having cooperating stator and rotor elements, 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 means to rotate the bridging contactor, the resistor being characterized: by the fact that the base is a generally circular metal disc having a peripheral portion with a fiat surface at the side of the base at which the resistance path and collector contact are located, the disc having a notch in its periphery forming an interruption in its peripheral portion; a terminal board of insulating material filling said interruption and having a flat surface which is flush with said flat surface of therperipheral portion; a thin coat of insulation on said flat surface of the peripheral portion; the means providing the resistance path overlying said flat surface of the peripheral portion and being spaced therefrom solely by said coat of insulation, and the end portions of the resistance path extending onto the adjacent flat surface of the terminal board; and terminals for the ends of the resistance path fixed to the terminal board.

2. The variable resistor of claim 1, further characterized by the fact that the terminal board has an inner portion overlying the central portion of the metal disc; and rivet means passing through the center of the metal disc and said inner portion of the terminal board securing said parts together.

3. The variable'resistor of claim 2, further character- 'ized by the fact that the central portion of the metal disc inside :its flat surfaced peripheral portion is depressed beneath the plane of its fiat surface; by the fact that the inner portion of the terminal board is nested within said depressed central portion of the disc; and by the fact that the peripheral portion of the disc has spaced apart locating edges between which the adjacent portion bf the terminal board is snugly received to Secure the terminal board and the disc against relative rotation.

' 4. The variable resistor of claim 3 further characterized by the fact that the locating edges on the said peripheral portion of the disc are parallel to and equispaced from a plane containing the axis of the rivet means, so that despite radial misalignment between the disc and the terminal board occasioned by production tolerances, said parts are held against relative rotation.

5. A variable resistor having cooperating stator and rotor elements, 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 means to rotate the bridging contactor, the resistor being characterized: by the fact that the base is a generally circular metal disc having a flat peripheral portion upon which the resistance path is located and a central portion depressed beneath the plane of the surface of the peripheral portion at which the resistance path is located, the peripheral portion being cut away for part of its circumferential extent to provide an interruption therein; a terminal board of insulating material having an inner part seated in the depressed central portion of the disc and an outer part received in and filling said interruption, said terminal board having a thickness substantially equal to the extent the central portion is depressed beneath the plane of said surface of the flat peripheral portion so that one face of the terminal board is substantially flush with said surface of the flat peripheral portion; a thin layer of insulation between said surface of the peripheral portion of the disc and the means providing the resistance path directly contiguous to both so that the means providing the resistance path is separated from the metal disc only by said insulation, and the end portions of the resistance path extending onto the adjacent surface of the terminal board; and terminals for the ends of the resistance path and for the collector contact carried by the terminal board.

6. A variable resistor having exceptional heat dissipating ability and comprising: a base in the form of a substantially circular metal disc having a peripheral flat faced portion which is interrupted by a notch extending generally radially into the disc; a thin coat of insulation covering the flat face of said peripheral portion of the metal disc; a flat arcuate resistance element overlying the flat face of said peripheral portion and directly contacting the coat of insulation thereon so that the only separation between the resistance element and the metal disc is said coat of insulation, the end portions of the resistance element extending into said notch; means providing a collector contact concentrically disposed inside the arcuate resistance element; a terminal for the collector contact projecting substantially radially therefrom into said notch and between the ends of the resistance element; terminals for the ends of the resistance element electrically connected to the end portions thereof; and a rotatable bridging contaotor having contact fingers bearing upon the resistance element and the collector contact.

7. A variable resistor having cooperating stator and rotor elements, 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 contaotor having contact fingers bearing on the resistance path and on the collector contact and means to rotate the bridging contaotor, the resistor being characterized: by the fact that the base is a generally circular metal disc having a peripheral portion with a flat surface at the side of the disc at which the resistance path and collector contact are located, the disc having a notch in its periphery forming an interruption in its peripheral portion, which notch is partially defined by opposed spaced apart downturned flanges on the disc that extend transversely across the peripheral portion of the disc and merge gradually and gently with the flat surface of the peripheral portion; a thin coat of insulation on said flat surface of the peripheral portion extending around the junction with and over said down-turned flanges; and the means forming the resistance path being directly contiguous to said coat of insulation, so that the resistance path overlies said flat surface of the peripheral portion and is spaced therefrom only by the insulation, the end portions of the resistance path extending beyond said down-turned flanges and into the notch; and terminal means for the ends of the resistance path.

8. The variable resistor of claim 7, further characterized by: the fact that the central portion of the disc is depressed beneath the plane of said flat surface of the peripheral portion, and is connected with the peripheral portion by a sloping wall that circumscribes said central portion and has an arcuate length less than that of said flat surface of the peripheral portion, the ends of said arcuately extending sloping wall being connected with the down-turned flanges by locating edge portions of the notch; a terminal board having an inner part seated upon the central depressed portion of the disc and an outer part received in the notch, said outer part having a surface which is flush with said flat surface of the peripheral portion, and the end pontions of the resistance path being on said fiat surface of the terminal board; the terminals for the ends of the resistance path being fixed to the terminal board; rivet means passing through the center of the disc and the adjacent portion of the terminal board clamping said parts together; and the terminal board having opposite locating edges engaging said locating edges of the notch in the disc, to hold the terminal board and the disc against relative rotation about the rivet means, at least the locating edges on one of said two parts being parallel to one another and lying in planes which are equidistant from the axis of the rivet means.

9. The variable resistor of claim 8, further characterized by: a metal ground plate generally conforming in size and shape to said disc and contiguous to the side thereof opposite that at which the resistance path and collector contact are located; the disc, ground plate and the inner part of the terminal board having aligned holes therein through which the rivet means passes; the rivet means being a bushing having shoulders bearing against the ground plate and the inner part of the terminal board; and the means for rotating the rotor element being a shaft journalled in the bushing.

10. The variable resistor of claim 9, further characterized by flange means on the disc engaging in a notch in the ground plate to secure said parts against relative rotation.

11. The variable resistor of claim 10, further characterized by cooperating means on the ground plate and the bushing by which the entire unit may be secured to a supporting panel, and held against rotation thereon about the bushing.

12. A variable resistor having cooperating stator and rotor elements, the former comprising a substantially flat base, means providing an arcuate resistance path with low resistance hop-offs at the ends thereof 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 the collector contact and means to rotate the bridging contaotor, the resistor being characterized: by the fact that the base is a generally circular metal disc having a central depression and an arcuate peripheral portion, the top surface of which is substantially flat and at an elevation above the bottom of the depression, the central portion of the disc which forms the bottom of the depression being substantially circular, and a curved intervening wall joining the arcuate peripheral portion to the bottom of the depression, said curved wall extending around only part of the circumference of the bottom of the depression and terminating short of the ends of the arcuate peripheral portion; a terminal board of insulating material having an inner part seated in the depression and an outer part bridging the space between the ends of the arcuate peripheral portion; means securing the terminal board to the metal disc; a thin coat of insulationon said substantially flat top surface of the peripheral portion; the means providing the resistance path overlying said flat surface of the peripheral portion and being spaced therefrom solely by said coat of insulation, and the low resistance hop-ofis at the ends of the resistance path overlying the terminal board; and terminals for the low resistance hop-offs fixed to the terminal board in good electrical contact with the hop-offs.

13. The variable resistor :of claim 12, further characterized by the fact that the :ends of said curved intervening wall form locating shoulders; and by the provisionrof abutments on the terminal board engaging said locating shoulders to thereby establish a predetermined positional re lationship between the terminal board and the metal disc.

14. The variable resistor of claim 13, funther characterized by the fact that the inner portion of the terminal board and the bottom of the depression have aligned centrally located holes; and by the fact that the means for securing the terminal board to the disc comprises a hub portion passing through said holes; and shoulders on the hub portion clamping the adjacent central portions of the terminal board and disc together.

References Cited in the file of this patent UNITED STATES PATENTS