US2118190A - Variable condenser - Google Patents

Description

May 24, 1938. F. w. GODSEY, JR., ET AL VARIABLE CONDENSER 2 Sheets- Filed Sept. 5, 1935 INVENTORS fizANK W GODSEYJ/Z. & ROBERT C. SPRAGUE ATTORNEYS May 24, 1938. F. w. GODSEY, JR, ET AL 2,118,190

VARIABLE CONDENSER 2 Sheets-Sheet 2 Filed Sept. 3, 1935 I I I v m ma m N E R E O EGW T H T .lwwm A G bm 6 T KR E Wm F Y B Patented May 24, 1938 UNITED STATES PATENT OFFICE VARIABLE CONDENSER Application September 3, 1935, Serial No. 39,020

2 Claims.

The present invention relates to variable condensers of the type as used for trimmer or padding condensers, antenna condensers, etc.

Condensers of this type have to meet various manufacturing and operating requirements. For instance, they must be small and compact, inexpensive, easily adjustable, and be so designed as to readily lend themselves to economical manufacture in mass'production. In addition, they must be mechanically stable and return to the same capacitive setting after being subjected to a heat cycle. Furthermore, the adjustments must be simple and continuously variable throughout the rated capacity range of the condensers, and any obstacle interfering with a continuous adjustment, suchas binding of the elements or of the adjusting means, undue friction, and the like, is to be avoided.

Such condensers usually consist of at least one fixed and at least one flexible and adjustable metal condenser plate, between which metal plates is disposed a plate or layer of dielectric material, for example of mica. To obtain a continuous variation of the capacity by manual adjustment, the flexible plate is made of resilient material having a high degree of elasticity, and its capacitive relationship to the fixed plateis varied by flexing it toward or away from the flxed plate by means of adjusting screws, nuts or the like.

The main difliculty heretofore encountered with this type of condensers, was due to a sidewise displacement of the flexible plate relative to the fixed plate, and/or a binding of the condenser plates and dielectric plates, due to inadequacy of the mounting and adjusting means, and especially due to a lack or inadequacy of the guiding means.

Such a relative displacement of the condenser plates or their binding was not only brought about in prior art condensers when the adjustment oi the condenser was changed, but also took place with a set adjustment, due to the successive expansions and contractions of the condenser plates, as a result of the heat cycle which the condensers undergo in use; this because the condensers are used as a rule in devices, for example in radio receiving sets, in which a considerable heat development takes place during operation, so that even if the heat development in the condenser per se is negligible, it heats up because of the heat developed in the radio set. Such heating up causes an expansion of the condenser plates, and when the radio set is placed out of operation and the condenser cools down, a corresponding contraction of the plates takes place.

To overcome some of these difliculties constructions have been suggested in which the end portions of the flexible condenser plates were riveted to the base. This expedient besides considerably increasing the size of the condenseras much of the total area of the plates merely serves for their anchoring without adding to the effective capacity of the condenser-permits the plates to expand only in one and not in two directions, as a result of which strains are set up during the heating and cooling cycle, which cause the buckling of the plates and may also result in other mechanical defects.

To permit the plates to have relatively free expansion and contraction in both directions, constructions were suggested which limited the freedom of the condenser plates merely by guides placed sidewise to the plates. Such guides as a rule are expensive and necessitate the use of excessive material.

It is the object of our invention to eliminate the above referred to dililculties, and to provide a condenser, which for a given capacity value, is more compact and requires less material than the prior art condensers.

Another object of the invention is to provide for guiding means of thecondenser plates, which provide merely the three guiding points theoretically required for the properlocation of one body with respect to another.

Another object of the invention is to combine two condensers into a. single unit with novel adjusting means permitting individual adjustment of either condenser from the same side of the unit.

A further object of our invention is to eliminate objectionable capacitive coupling in a multiple condenser structure.

Further objects and advantages of our invention will appear as the specification progresses.

In the drawings forming part of this specification,

Figure 1 is a plan view of one embodiment of our invention;

Fig. 2 is a cross-sectional elevation along lines 2-2 of Figure 1;

Fig. 3 is a cross-sectional elevation of a twin or dual condenser made in accordance with our invention;

Figs. 4 and 5 are plan views of a condenser in connection with the condensers shown in Figs. l-3;

plate and of an insulator plate respectively, used Fig. ii is a side elevation at the dual condenser of Fi 3;

Fig. 'i is a fractional bottom view of the corn denser of Figs. 3 and 6.

Fig. 8 is a partial vertical sectional view showing a variation in the adjusting means of the condenser of Figs. 3 and d; I

Fig. 9 is a plan view of another form of coin denser, in accordance with our invention;

Fig. 10 is a vertical section taken on the lines lfl-IO of Fig. 9;

Fig. ii is a plan view of still another i'orm of condenser, in accordance with our invention.

Fig. 12 is a vertical section on the lines Eli-l2 of Fig. ll.

Referring to Figs. 1 and 2, a molded base it of insulating material such as artificial resin or the like, having rounded corners ii, is provided on its top with an open-ended shallow recess, between the side walls l8 of which is placed a condenser assembly A, later more fully described, and has on. its twosides upwardly-projecting integral mounting lugs iii-412 having holes l3--li'i to receive suitable attachment bolts.

A central hole M of the base it is adapted to receive a. slotted-end screw [15, which screw pro- ,iects upwardly above thetop face i6 of the base it and passes through the condenser assembly A. The screw l5 with a nut l1 forms the adlusting means for the condenser. inwardly from the lugs l2-l2 extend rounded guide'ribs 202il, which are preferably integrally molded with the base it. The ribs 20-20 serve to locate the condenser assembly A and to guide the flexible plate condenser assembly A and contact with parts 1 thereof alon g a semicircle of small radius.

The condenser assembly A consists of two metallic condenser plates 25 and 25' (see Fig. 4) of identical shape except that plate 25 is flat, whereas plate 25' is concave downward. The plate 25' is of highly resilient spring material, for example phosphor bronze, whereas plate 25 may be of the same material, but may also be of non-resilient-material.

The plates 25 and 25' are provided with central clearance holes 26 and 26' respectivelywhich are sufllciently large to permit noncontacting passage oi screw l5-and also with extending integral and inclined connection lugs ill and 21 respectively. The plates 25 and 25' furthermore are provided with two rounded end notches 29 and 30, and 29' and 30' respectively.

The notches 30 and 30' are of a size to fittingly surround the ribs 2020, whereas notches 29 and 29 are larger so as not to engage the ribs 20-20 when the plates 25 and 25' are mounted on the base.

When assembling the condenser the plates 25 and 25 are placed with identical faces turned toward each other, i. e., with lugs 21 and 21' on opposite sides and with notches 29 and 30' and notches 29' and 30 respectively on the same side of the assembly. I

A thin plate 35 (see Fig. 5) of dielectric matelie], for instancemica, and having a slightly greater length and width than metal plates 25 and 25', is interposed between plates 25 and 26'. The dielectric plate 35 is provided with two identical notches 31-31 adapted to snugly engage ariareo plate 3.5 register with the hole I and the ribs 20-20 respectively.

It will be noted from Fig. 1 that in the assembled condenser one of the metal plates, for example the flat plate 25, engages with its notch Blithe corresponding left-hand rib 20, whereby its left-hand edge 98 ialls at a distance L from the left-hand wall I8 of base in; whereas the right-hand edge 99 contacts with the right side wall l8. Thus, when plate 25 is expanded by heat, it can freely expand in both length and width directions, whereas at the same time it is securely guided at the three theoretically required points; two such points being provided by its right side edge 99 hearing against side wall i8, and the third point being aiforded by the semicircle contact between notch 30 and the lefthand rib 20. To be able to freely expand in all directions there must be a slight clearance between the end rib 20 and notch 30.

The insulating plate 35 is placed on top of plate 25 and extends substantially irom one side wall E8 to the other side wall 58, and also extends beyond both ends of plates 25 and 25'.

The vaulted and adjustable plate 25 lies with its left-hand edge 98 close to the left-hand wall l8, whereas its right-hand edge 98' is spaced from the right side walllii, and its notch 30 engages the right-hand rib 2m in a manner similar to that of plate 25.

It will be also noted that the inclined extension lugs 21 and 21' extend at the'same end, but at opposite sides of the assembly.

On top of the flexible plate 25' there is provided a concave spring washer 40, by which a uniformpressure can be exerted on the assembly A under action of nut l1.

The adjustment of the condenser depends on the position of nut I1, and by exerting a greater or smaller pressure on plate 25 this plate is flexed to a greater or lesser amount and thereby accordingly changes its capacitive relation to the and downwardly-extending mounting lugs i' I2. The condenser assemblies B and placed within the recesses formed on the and lower portion of the base 50, in the a manner as has been described in connection with condenser assembly A of Figs. 1 and 2.

For the individual adjustment of the two con densers there are provided adjusting means whl sh comprise a metallic bushing 5| having at the lower end two preferably knurled annular flanges molded into the middle portion 01' the base 50.

The bushing 5| extends upwardly beyond the base 50 and is provided with internal and external threads.

- Against the bottom face of the condenser assembly B lies a washer 56 (see Fig. 7) of insulating material having a substantially elliptical contour} a flat bearing face, and a conical face.

The washer 56 is provided with a central counterbored hole I00 and with two notches 63-43 provided at the two ends of its long axis. Into the counterbore, of hole I00 fits the head 51 of a ydepressions I0.

bolt 55, which is provided at its upper end with a slot 65 and engages the internal threads of bushing 5|. The notches 58-58 engage the lower ribs 2020, and thereby fixedly hold the washer 58 against rotation. A nut 54 engages the external threads of bushing 5| and presses against the spring washer 40.

The adjustment of the'upper condenser assembly B is eii'ected in a manner similar to that explained in connection with Fig. 1 by turning the nut 54. Adjustment of the capacity of the lower condenser assembly B takes place by moving the bolt 55' along the internal threads of bushing 5I using slot 65.

It will be thus noted that the capacities of the two condenser assemblies B and B, can be adjusted independently, and that both adjustments can be eflected from the same side of the unit, which is especially desirable when the condenser is mounted on a panel or in an inaccessible place.

A variation of the adjusting means shown in Figs. 1, 3, and 6 is shown in Fig. 8, wherein a metallic insert 60 is rigidly molded in the insulating base of the condenser, and is provided with an externally-threaded extension 6|. The extension 8| is provided with a smooth inner bore adapted to snugly receive a bolt 82 recessed into the washer 58 to prevent turning, and extending upwardly through same and beyond the top of the extension 5| to receive an adjusting nut 63.

In the constructionshown in Fig. 8 adjustment of the lower condenser B is effected by turning the nut 83 against the upper end of extension iI, whereby condenser B is to a greater or lesser extent compressed. Condenser B is adjusted by turning nut 54adapted to fit the external threads of extension IiI-whereby pressure is transmitted through the concave washer 40 to the condenser assembly B.

Referring to Figs. 9 and 10, a molded base I20 of a suitable vitreous insulating material and having parallel faces 68 and 88 and rounded corners 88 is provided with three mounting holes 81 located on one central axis'thereof. On either side of the central axis are disposed identical condenser assemblies C-C later to be more fully described.

The face 68 is provided with two identical depressions I0'I0 having octagonal cross sections arranged with their longer'axes parallel to the axis of the holes 5'I-6I. The depressions connect along their respective outer side with openings II II and' with indentations I2I2 along their inner sides; openings 'IIII and indentations I2--'I2 extending in the same direction as the depressions III--I0which also connect at both ends with molded channels 13-13 extending through the base I20.

The base I20 is also provided with two similar internally-threaded metallic inserts I4 (only one oi. which is shown), having hexagonal heads I5 recessed in corresponding indentations I6 in the face 58 and having their upper ends crimped, as indicated at 11 upon cushioning washers I8 centrally located in recesses I9 in the bottom of the The washers I8 may be omitted ii the base I20 is made of bakelite or similar type of molded plastics, but are used when the base is of vitreous material, for example, porcelain or the like.

The condenser assemblies CC (only one of which is shown in section in Fig. 10) comprise a lower metal plate 80 and an upper metal plate rower in width than the depressions 10 into which it fits. One end of the plate 80 is provided with an extension or terminal lug 8I, which passes slopingly downwards through the channel I8, whereas the other end of the plate 80 falls short of the opposite end of depressions 10.

The short oblique edges of plate 80 (see Fig. 9) are so proportioned as to guide the plate in the depressions "I0 by the matching oblique sides 83 thereof. A central clearance hole 84 within plate 80 permits the passage of an adjusting screw 85 therethrough.

Plates 90, which are similar in size and shape to the plate 80, are provided with lugs 8| passing slopingly down through the right-hand channels I3. The plates 90, which are of heavy and resilient material, for instance phosphorus bronze, are concave downwards and are also provided with central clearance holes 92 for the passage therethrough of the adjusting screw 85.

The thin octagonal-shaped pieces 86 of mica or other insulating material which separate the plates 80 and 90, have a greater width and length than do the plates 80 and 90 and extend longitudinally to the ends of the depressions IO-I0 and laterally into the openings II-II and indentations I2-12, whereby the plates 80 and 80 are effectually insulated from one another. The insulating pieces 86 are. each provided with a central hole 88, of smaller diameter than that of the holes 84 and 92, whereas oblique sides closely fit the matching oblique sides of the depressions and are fixed thereby.

A circular washer 85 of bakelite or other insulating material, and a thicker metallic washer 58 of similar size and shape are placed over the upper plate 88 in the order given; the latter washer bearing against the under side of the head of the adjusting screw 85 which extends through the holes of washers and 96 and into the threaded portion of the insert 14. Rotation of screw 85 changes the capacitive adjustment of the condenser by decreasingor increasing the flexure of the upper metallic plate 80.

Figures 11 and 12 illustrate a form of construction adapted to multiple condensers; only one unit being shown here. In the form shown in these figures the base H5, which is of metal, acts as a fixed plate for condenser D, and is provided with upturned edges II5, one of which is extended to form'a mounting and terminal lug III.

The condenser unit, later to be more fully described, is rectangular in shape and is guided on three sides by the upturned edges H8, while the fourth side is guided by two tabs I I8 pressed upwards from the bases II5, which tabs also serve to guide one side of an adjacent unit (not shown).

The upper plate I05 is rectangular in shape and has a narrow downwardly-bent terminal lug I05; the base H5 and one side H6 being cut away in Fig. 12'at .I III to more clearly show this.

As shown in Fig. 12, the upper plate I05 is completely compressed, but in its free condition this plate is concave downwards in the direction of its long axis. A thin rectangular-shaped separator I0I of mica or other insulating material (as seen in place in Fig. 12), separates the base H5 and the plate I05, and overlaps all edges of the plate I05.

An upper insulating plate III of the same size and shape as the separator I01, but of greater thickness, is placed over the plate I05 and transmits the pressure of the adjusting screw III to the flexed plate I05; plates I05, I01 and III being each provided with central clearance holes, periii 4 aria,

mltting the noncontacting passage of the screw H2 therethrough and onto cooperating threads in the lease lid.

The plate ill is oi such length that it substantially fills the space between the upturned edges iii, and is provided on its shorter sides with slots ll! adapted to receive upturned extensions tilt of the plate 105, which extensions terminate helow the top suriace of plate ill when assembled, and whereby the plate M5 is effectively guided.

We have iound that in past constructions in which two condenser assemblies were mounted on a common loose, a capacitive intercoupling occurred between the two condensers due to the metallic parts or the adjusting means.

This drawback is eliminated in our construction by making the bolt 55 (see Fig. 3) ct insulating material, or by so dimensioning the metallic partsof the adjusting means that the capacitive eilfect of the third condenser so formed remains below objectionable values. .As a rule it is sumclent it the capacity of this third condenser does not exceed 2% of the capacity oi the condensers oi assemblies B and B.

While we have described our invention on hand or specific examples and in specific applications, we do not wish to he limited thereto, but desire the appended claims to he construed as broadly as permisoihle in View at the prior I What we claim is:

l. in an adjustable condenser, a base of insulating material provided with a lateral recess open at the ends, each side wall of said recess being provided with an inwardly-projecting rib, a condenser plate provided on one side edge with a small notch and on its opposite edge with a larger notch, said plate being disposed in said recess with the larger notch clearing one of said ribs and with the corresponding edge in contact with the side wall, the opposite edge of the plate losing spacedly located from the opposite side wall with the small notch fittingly engaging the corresponding rib.

2. in an adjustable condenser, a base of insulating material provided with a recess having two opposite side walls each provided with an inwardly-projecting rib, a condenser plate provided on one side edge with a small notch and on its opposite edge with a larger notch, said plate being disposed in said recess with the larger notch clearing one of the said ribs and with the corresponding edge contacting the side wall, the opposite edge oi the plate being spaced from the opposite side wall with the small notch fittingly engaging the corresponding rib.

IFRANK W. GODSEY, Jn. RQBERT C. SPRAGUE.

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