US2417188A - Variable inductance - Google Patents

Description

'March 11, 194:7. R, Q CLARK VARIABLE INDUCTANCE Filed July 15, 1944 Pateiied Mar. 11, 1941 VARIABLE INDUCTANCE Robert George Clark, London, England, assigner to The Hartford National Bank and Trust Company, Hartford, Conn., trustee Application Jiuy 13, 1944, serial No. 544,791 In Great Britain September 23, 1942 This invention relates to variable inductances ofthe kindcomprising two coils usually connected in series and movable in relation to each other to effect the variation. The invention is concerned more particularly with variable inductances of this kind in which the coils are constructed and mounted so as to slide one within the other, e. g. are wound on cylindrical formers of different diametersand are arranged coaxially.

The object of the present invention isto provide an improved variable inductance comprising axially aligned and relatively movable sections, wherein the range of variation in inductance which can be achieved is similar to that normally achieved by the use of a fixed inductance and variablcondenser; the relation between lowest and highest frequency is usually roughly 1:3 and if tuning is to be effected by a variable inductance the corresponding ratio between the inductance values is 1:9 which is far greater than can be attained with a two part coil having its parts arranged co-axially with one part sliding within the other. adapted for ganglng and afford a simple arrangement for tuning in wireless receiving apparatus.

According t the invention, with this object in view, the inductance consists of two co-axially mounted parts connected in series and in such manner as to provide vpositive mutual inductance between them and adapted to slide onewithin the other, and at least one of the two parts is rigidly connected with a co-axial auxiliary winding which when the two parts are one Within the other in their position of maximum coupling is substantially without effect but when the two parts are moved apart the auxiliary winding rigidly connected with one of the parts assumes a position of maximum coupling in relation' to the other part and reduces the total inductance.

In order that the invention may be more readily understood, it will now be described with reference to the accompanying drawing in which two embodiments of the invention are shown and in which:

Fig. l is a schematic diagram illustrating a coaxal coil arrangement for obtaining maximum coupling between two coils;

Fig. 2 is a schematic diagram illustrating a similar coaxial coil arrangement with minimum coupling between the two coils;

Fig. 3 is anl exploded longitudinal sectional view of a coaxial coil arrangement for varying the coupling between the two coils;

Such variable lnductances are well- 8 Claims. (Cl. 171-4-119) Fig. 4 is a longitudinal sectional view of a coaxial coil according to the invention for varying the ycoupling between the two coils;

Fig. 5 is a schematic illustration of a second embodiment of the invention in which the coils are arranged for minimum coupling;

Fig. 6 is a schematic illustration of a second embodiment of the invention in which the coils are arranged for maximum coupling;

Fig. 7 is a sectional view of the second embodiment of the invention for varying the coupling between a pair of coaxial coils;

Fig. 8 is a schematic circuit arrangement showing the parallel connection ofthe coils illustrated in Fig. 5; and

Fig. 9 is a schematic circuit arrangement showing the series connection of the coils illustrated in Fig. 5.

The principle on which the embodiment of Figs. 3 and 4 is based, will first be explained with reference to Figs. 1 and 2. Here, L1 and L2 are the two parts of the inductance which are mounted coaxially and are connected in series in such manner as to produce positive mutual inductance between them. Associated with the part L1' is a short circuited winding S1 and associated with I the part L2 is a short circuited winding Sz, the 1 i disposition of the components being such that when L1 and L2 are one within the other in they." position of maximum coupling (Fig. l) the short j circuited windings S1 and Sz are on opposite sides of the coupled parts L1 and L2 and are substan- 1 On relative displacement tially Without effect. into the position of minimum coupling (Fig. 2) each of the parts L1 ,and L2 is closely coupled with the short circuited winding (S2 and S1) associated with the other, whereby coupling between L1 and L2 is substantially eliminated. The position of maximum coupling (Fig. l) between L1 and Le affords the maximum inductance value whereas the minimum inductance value is obtained when the positions are such that the short circuit windings have the maximum coupling with the inductances. Intermediate settings between Figs. l and 2 give corresponding intermediate inductance values. The short circuit wind-L ings Siv and S2 are most conveniently constituted by metal cylinders or collars, preferably of copper.

In the embodiment shown in Figs. 3 and 4 the part L1 of the variable inductance is wound on a former F1 to one end of which .is secured a plate P serving to mount the variable inductance. Also secured to the plate Pand extending into the former F1 is a copper cylinder S1. The cylinder S1 and the plate P are provided with a central aperture to receive the rod R on which the other part of the inductance is secured. The copper cylinder S1 constitutes the short circuited winding associated with L1 and the gap between S1 and the former F1 on which L1 is wound is so dimensioned as to enable the former F2, on which the other part L2 of the inductance is wound, to pass into the gap. The former F2 is secured to a copper cylinder S2 which is co-axial with and rigidly secured to the rod R. This cylinder S2 constitutes the short-circuited winding associated with La. The axial length of S1 should be not less than the axial length of Le, and similarly for Se and L1. Fig. 3 shows the two parts L1 and L: widely separated in order that the details of construction should be clearly seen. Fig. 4 shows an actual working position in which the total value of the inductance is a. maximum. For smaller values, the rod R is moved to the right together with the copper cylinder S2, the former F2 ,and the part Le of the inductance. With this construction an induction ratio of at least :1 and a Q of approximately 50 can readily be attained. By disposing both S1 and S1 so as to be within the coils L2 and L1 with which they co-operate as shown in Figs. 3 and 4 it is found possible to achieve more favourable Q values than by arranging one inside and the other outside as in the explanatory diagrams of Figs. l and 2.

In the embodiment of Figs. 3 and 4, and in general for constructions based on' the principle of Figs. land 2, itis preferred that the parts L1 and L2 of the inductance should be of the same axial length and also have the same inductance value.

Referring now to the explanatory diagrams of Figs. 5 and 6, L1 and La have the same signicance as before. However the coil La has associated with it a supplementary coaxial coil In which is secured in fixed relation to the coil Ln and is electrically connected so as to produce negative mutual inductance effects with L1. The coils La and La are preferably spaced axially by a distance equal to the axial length of L, and the arrangement is such that by relative axial movement between L1 on the one hand and La and La on the other hand, L1 may be disposed formaximum coupling with La or with La or in any intermediate position. Fig. 5 shows the minimum total inductance position and Fig. 6 shows the setting for maximum total inductance.

Fig.- 'l shows a construction based on Figs. 5 and 6. \In Fig. '1, the part L1 of the inductance is wound on a formerF1, whereas the part Le and the supplementary coil Le are wound on a common former Fa which is of external diameter to fit within the former F1. By relative axial-move- 'ment of F1 and Fa the part L1 -of the inductance can be brought into any desired position in relation to La and le, between a minimum total inductance setting equivalent to Fig. 5 and a maximum total inductance setting equivalent to Fig. 6.

Advantageously the lcoils L1, Lz and 1c all have the same axial length as shown in Fig. 7.

The coils L2 and La may be connected either in series or in parallel, but in either case the combination of Le and L1. Fig. 8 shows the circuit arrangement when L2 and Le are in parallel, and Fig. 9 shows a oircuit arrangement whenL1, Ln and'Ls are all in series. With a circuit as in Fig. 8 it is preferred that Le and La should have the same inductance value. numerically equal to twice the value of L1. With a circuit as in Fig. 9 it is preferred that La is connected in series with 4 L1. La and Le should all have equal inductance values.

I claim:

1. A variable inductance comprising two coaxially mounted parts connected in series so' as to provide positive mutual inductance between them and adapted to slide one within the other, at least one of said parts being rigidly connected with a coaxial short-circuited winding arranged to be substantially without effect when the two parts are one within the other in their position of maximum coupling, but to assume when the two parts aremoved apart, a position of maximum coupling in relation to the other part whereby to reduce the total inductance.

2. A variable inductance comprising two coaxially mounted parts connected in series so as to provide positive mutual inductance betweeny them and adapted to slide one within the other, at least one of said parts being rigidly connected with a coaxialshort-circuited winding arranged to be substantially without effect when the two lparts are one within the other in their position of maximum coupling, but to assume when the two parts are moved apart, a position of maximum coupling in relation to the other part whereby to reduce the totall inductance, said short-circuited winding being provided in the form of a metal collar.

3. A variable inductance'comprising two coaxially mounted parts connected in series so as to provide positive mutual inductance between them and adapted to slide one within the other, each of said parts being rigidly connected with a coaxial short-circuited winding arranged to be substantially without effect when the two parts are one within the other in their position of maximum coupling, but to assume when the two parts are moved apart, a position of maximum coupling in relation to the other part whereby to reduce the total inductance.

4. A variable inductance comprising two coaxially mounted parts connected in series so as to provide positive mutual inductance between them and adapted to slide one within the other,

each' of said parts being rigidly connected with a coaxial short-circuited winding arranged to be substantially without effect when the two parts are one within the other in their position cf maximum. coupling, but to assume when the two parts are moved apart, a position of maximum coupling in relation to the other part whereby to reduce the total inductance, said short-circuited winding' being provided in the form of a metal collar.

5. A variable inductance comprising two coaxially mounted parts connected in series so as to provide positive mutual inductance between them and adapted to slide one within the other. each o! said parts being rigidly connected with a coaxial short-circuited winding arranged to be substantially without eiect when the two parts are one within the other in theirv position of maximum coupling, but to assume when the two parts are moved apart, a position of maximum coupling in relation to the other part whereby to reduce the total inductance, the short-circuited winding associated with the outer part being mounted within it at such spacing as to permit the passage of the inner part between the outer part and the short-circuited winding associated therewith.

6. A variable inductance comprising two coaxially mounted partsconnected in series so as to provide positive mutual inductance between tnem and adapted to slide one within the other, at least one of said parts being rigidly connected with a coaxial short-circuited winding arranged to be substantially without effect when the two parts are one within the other in their position of maximum coupling, but to assume when the two parts are moved apart, a position of maximum coupling in relation to the other part whereby to reduce the total induetance, the axial lengths of the two parts of the inductance and of the short-circuited winding being mutually equal.

7. A variable inductance comprising two coaxially mounted parts connected in series so as to provide positive mutual inductance between them and adapted to slide one within the other, each oi' said parts being rigidly connected with a coaxial short-circuited winding arranged to be substantially without eiect when the two parts are one within the other in their position of maximum coupling, but to assume when the two parts are moved apart, a position of maximum coupling in relation to the other part whereby to reduce the total inductance, the axial lengths of the two parts of the inductance and of the short-circuited windings associated therewith being mutually equal.

8. A variable inductance comprising two tubular parts slidably arranged one within the other for longitudinal displacement relative to one another, series-connected coils mounted on each oi said parts and adapted to provide positive mutual inductance between them, a cylinder constituting one short-circuited winding connected to and arranged within the outer part spaced from the interior wall thereof, and a second cylinder constituting another short-circuited winding connected to and mounted on the inner part, the tubular portion of said inner part being adapted to slide into the space between the outer part and said rst-named cylinder whereby each cylinder is positioned within the part of the inductance with which it cooperates.

ROBERT GEORGE CLARK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,441,532 Fortin Jan. 9, 1923 2,334,178 Dodge Nov. 16, 1943 FOREIGN PATENTS Number Country Date 388,571 British Mar. 2, 1933

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