US2838738A

US2838738A - Variable inductance device

Info

Publication number: US2838738A
Application number: US520332A
Authority: US
Inventors: John J Antalek; Robert W Saville
Original assignee: Radio Industries Inc
Current assignee: Radio Industries Inc
Priority date: 1955-07-06
Filing date: 1955-07-06
Publication date: 1958-06-10
Anticipated expiration: 1975-06-10

Description

`Fune 10, 1958 J. J. ANTALEK ET AL VARIABLE INDUCTANCE DEVICE Filed July e, 1955 N TAL 5A V/ m) VIE/@Toes JOHN am! 05527- .Y Y

Arrow/EY;

verneem tNDUCTANCE DEVICE Application July 6, 1955, Serial No. 520,332

8 Claims. (Cl. 336-136) The present invention relates to variable inductance devices, and more particularly to variable inductance devices of the type having one or more conductive coils mounted on a tubular form in the bore of which a threaded core member is adjus'tably positioned by rotation of the core relative to the form.

lviany different variable inductance devices of the above mentioned type are available commercially, some of which include a coil form having a pre-tapped or pre-formed threaded bore for the accommodation of the threaded core and others of which include a coil form in which threads are cut by the threaded core as it is rotated while initially being inserted into the form. Both of these prior art arrangements leave much to be desired when the fabrication thereof by automatic assembly apparatus is attempted. For example, in both instances it is necessary to rotate the core member as it is initially inserted into the coil form, thus requiring rather complex apparatus for accurately positioning the core with respect to the coil which is wound on the outside of the form. Furthermore, relatively small variations in the dimensions of the core and of the coil form result in wide variations in the torque required to adjust the position of the core in the form. Therefore, in order to maintain this torque within permissible limits when the inductance devices are manufactured on a quantity basis, the dimensions of the core and of the form must be held within close tolerances, thereby causing the manufacturing cost of such devices to be relatively high.

it is an object of the present invention to provide a new and improved variable inductance device.

Another object of the invention is to provide a new and improved variable inductance device of the above mentioned type wherein the core is assembled with the coil form merely by pressing it into the form.

Still another object of the present invention is to provide a new and improved variable inductance device which may be manufactured on a mass production basis and in which the torque required to reposition the core in each of the devices is approximately the same even though the dimensions of the various elements of the inductance devices are not held within close tolerances.

A further object of the invention is to provide a new and improved coil form which facilitates fabrication of variable induetance devices.

A still further object of the invention is to provide a new and improved variable inductance device which is reliable in operation, simple in design, and inexpensive to manufacture.

Briefly, the above objects are realized in accordance with the present invention by providing a tubular coil form, on the wall of the bore of which is provided a plurality of spaced, inwardly extending longitudinal ribs, the ribs being relatively thin and made of a deformable material having relatively good elasticity. When, therefore, a threaded core having a major diameter which is greater than. that of the cylinder defined by the inside edges of the ribs but less than the inside diameter of the States Patent O coil form proper is inserted therein, the ribs undergo deformation so as to permit the core to be placed at the desired position in the form, no relative rotation of the core and form being necessary during the assembly operation. As the ribs return to their normal positions because of the natural elasticity thereof they press against the threads on the core, and a thread, conforming to that of the core, is molded in the ribs so as to secure the core in a fixed position within the form while enabling adjustable movement thereof in the usual manner by rotation of the core relative to the form.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following detailed description taken in connection with the accompanying drawing in which:

Fig. l is a front elevation view of a variable induc tance device embodying the present invention;

Fig, 2 is a longitudinal sectional view of the device;

Fig. 3 is an enlarged section of Fig. 2 taken along the line 3 3 thereof;

Fig. 4 is a fragmentary sectional view of the upper portion of the device of Fig. l as the core member is being inserted into the form;

Fig. 5 is an enlarged fragmentary sectional view of a portion of the device as the core is being inserted into the coil form; and

Fig. 6 is an enlarged fragmentary view of a portion of the device as shown in Fig. 3.

Referring now to the drawing, and more particularly to Fig. l thereof, there is shown a variable inductance device 16 consisting of a tubular coil form 11 having an enlarged lower portion 12 on which is mounted a plurality of conductive terminal and mounting members 135. The coil form l1 is molded of an insulating material, and in the particular device shown, a pair of

helical coils

15 and 16, which may conveniently be formed of insulated copper wire, are wound on the coil form 11 and have the ends thereof conductively connected to different pairs of the terminal members 13. At their lower ends, the terminal and mounting members 13 are each provided with a reverse band to facilitate attachment of the device 10 to a chassis. it will be understood that although the inductance device shown in Fig. l to illustrate the invention is a transformer utilizing a pair of

coils

15 and 16, a greater or lesser number of coils may be provided on the form 11, if desired.

ln order to adjust the magnetic coupling between the

coils

15 and 16 as well as to change the inductance of each of these coils, a cylindrically shaped ferromagnetic core member 18 is provided which is arranged within the bore 11a of the tube 11 so as to intercept at least a portion of the magnetic field which surrounds the coils le' and 16 when current traverses these coils. As best shown in Fig. 2, the core member 18 is provided with a helical male thread 19 on the outer surface thereof and with a hexagonal, longitudinally directed aperture 20 for accommodating the hexagonal head of a wrench used to rotate the core 18 relative to the form 1l.

ln accordance with the present invention, a plurality of thin ribs 21 are provided on the internal wall 11a of the tubular coil form 11 and extend longitudinally from the top of the form 11 to the vicinity of the enlarged portion 12. r[The ribs 21 are formed integral with the form 11 and the roots are relatively thin as compared with the inwardly directed length thereof. Since the ribs 21 are made of a plastic material which is relatively deformable, and since the outside diameter of the threads 19 on the core 1S is greater than the diameter of the cylinder defined by the inside edges of the ribs 21, but less than the internal diameter of the tubular form 11, the ribs 2l are deformed, being bent over as shown in Fig. 5, so as to permit the core 18 to be accurately located axially within the bore 11a, as the core 18 is inserted into the bore 11a either from the bottom or top thereof and is pressed into that portion of the form 11 in which the ribs 21 are located. Once the relative longitudinal movement between the core 18 and the form 11 is terminated, the ribs 21, because of the elasticity thereof, immediately begin to return to their normal positions and as this occurs a thread is molded into the ribs by the threads on the core member 18. Although the ribs 21 are not sufficiently long to engage the core at the inner diameter of the threads 19, they do not return to their original positions wherein they extended inwardly along different radii of the form 11, but remain partially bent over transversely to their respective radii as best shown in Figs. 3 and 6. When the ribs 21 occupy these final somewhat deformed positions, however, there is suiiicient frictional engagement between the ribs and the core 18 to insure that under normal conditions the core 18 will not move around loosely within the form 11. It will be understood, therefore, that once the core is properly positioned within the form 11 with respect to the coils 1S and 16, it cannot move of its own volition when the device 10 is subjected to vibration or sudden shocks. Furthermore, normal variations in the diameter of the bore 11a or of the outside dimension of the threads 19, which obtain when normal shop tolerances are permitted in the manufacture of these components, are insufficient greatly to affect the torque required to rotate the core 1S within the form 11 for adjustment of the degree of coupling between the

coils

15 and 16 or the inductance of one or both of the coils` Another important advantage achieved by the described structure is that as soon as axial movement of the core 18 in the form 11 is terminated during assembly of the device 10, the ribs 21 begin returning toward their normal position so that further axial movement between the core 18 and the form 11 is prevented unless these parts are relatively rotated.

It has been found desirable to employ threads 19 on the core member 1S'which are relatively sharp at the outer portion thereof and which are spaced relatively far apart as best shown in Figs. 2 and 4 thereby to minimize the torque required to move the core 18 in the form 11 for adjustment of the inductance or the coupling between the coils, as the case may be, of the inductance device 1G.

Although many materials having the required characteristics of deformability and elasticity may be employed in the construction of the coil form 11, it has been found that nylon which will withstand the high temperatures encountered in the applications for which the inductance device of the present invention is most suitable and which has suicient strength and hardness to prevent the ribs 21 from peeling off as the crore 1S is inserted into the tubular form 11 is most satisfactory.

As best shown in Figs. 3 and 6, when the ribs 21 take their final set postion in engagement with the threads 19 they are in a somewhat bent-over position. Furthermore, even though the dimensions of the threads 19 may vary throughout a wide rangefrom one core to another, the area of those portions'of the ribs 21 which engage the threads 1% remain substantially constant due to the fact that the bend obtained in the'ribs 21 in their iinal set position is dependent upon the relative dimensions of the threads 19V and the inner diameter of the form 11. For example, as the outer diameter of the threads approaches the value of the inner diameter of the form 11, the permanentV bendV in the ribs 21 increases.Y It will be apparent, therefore, that the torque required to relatively rotate the core 13' and the form 11 also remains substantially constant irrespective of wide variations in the l. D. ofthe form`11 and the O. D. of the threads 19.

It has been found that when six internal ribs 21 spaced at 60 degree intervals areV provided inV a coil form 11 and the following dimensions are held within Vthe tolerances indicated, the torque required to rotate the cores 18 in the forms 11 varies within a range of from 2 inch-ounces to 6 inch-ounces. As will be appreciated by those skilled in the art, these tolerances are easily met and the range of torque is particularly limited, thus preventing, under normal'conditions, undesired spurious movement of the core 18 while permitting easy adjustment of the degree of coil coupling and inductance of the device 1t):

Form material 11. Nylon 10001. Diameter of the bore 11a a .2551.0015 inch. Width of the ribs 21 .004i-0005 inch. Radial length of the ribs 21 .0088i-00l inch.

As will be evident from the above description, in assembling the cores 18 in the tubular coil forms 11 all that is required is to position the cores opposite the bores of the coil forms and then push the cores, without rotation, into the coil forms. These assembly steps may be rapidly and easily performed through the use of automatic assembly apparatus of relatively simple construction.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein which are within the true spirit and scope of the invention as defined in the appended claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A variable inductance device comprising a tubular coil form made of insulating material, a plurality of thin, circumferentially deflectable ribs provided at spaced intervals on the internal wall of said form and extending longitudinally a substantial distance therealong, a core member having an outwardly threaded portion disposed within said tubular coil form, the outside diameter of said threads being less than the internal diameter of said form and greater than the diameter of a cylinder defined by the inner ends of said ribs, and at least one coil supported by said form.

2. A variable inductance device, comprising, a tubular coil form at least partially constructed ofV an insulating material, a coil mounted on said form, a plurality of circumferentially deiiectable longitudinal ribs extending inwardly from spaced positions on the inner wall of coil form, and a ferromagnetic core member disposed within said coil form and having a threaded portion which is threadedly engaged by the ends of said ribs, whereby said core member is adjustably positioned with respect to said coil.

3. A variable induetance assembly comprising a tubular coil form, a coil of conductive material provided on the outer wall of said form, a core of magnetic material having a threaded portion on the outer wall thereof, the outerdiameter of said threaded portion being less than the internal diameter of said coil form, said core being disposed within said coil form in close proximity to said coil, and a plurality of flexible and circumferentially deflectable ribs protruding from the inner wall of said form '13 and extending along said tubular coii form longitudinally thereof, the inwardly extending dimension of each of said ribs being such that said ribs extend at least partially into the threads of said core.

4. A coil form for a variable inductance assembly,

n comprising, a molded tubular member formed of a exible material and adapted to have a coil wound on the `outer surface thereof, said tubular member having a plurality of integral, longitudinal ribs which extend inwardly along respective radii from the inner wall of said i tubular member, the root thickness of said ribs being substantially less than the radial length thereof and said radial' length being very small as compared with the inner diameter of said form, and a ferromagnetic core disposed within said form, said core being externally threaded for cooperation with said ribs to hold said core in a fixed position within said form, the inwardly extending dimension of each of said ribs being such that said ribs extend at least partially into the threads on said core.

5. A coil form for a variable inductance assembly,

comprising, a molded tubular member formed of a nylon and adapted to have at least one conductive coil wound on the outer surface thereof, said tubular member having a plurality of integral and longitudinally extending rectangularly shaped ribs on the inner wall thereof, said ribs protruding inwardly of said tube along spaced radii thereof, the root thickness of said ribs being substantially less than the radial length thereof and said radial length being appreciably less than the inner diameter of said form, and a ferromagnetic core disposed within said form, said core being externally threaded for cooperation with said ribs to hold said core in a ixed position within said form, the inwardly extending dimension of each of said ribs being such that said ribs extend at least partially into the threads of said core. 6. A variable inductance device of the type including a threaded core member, comprising, a tubular supporting element constructed of a plastic insulating material, said element having a plurality of thin circumferentially spaced and integrally formed ribs on the internal surface thereof which extend along said tubular supporting element longitudinally thereof, each of said ribs being deflectable about an axis passing longitudinally along the length of the rib so that said threaded core member may be inserted into said element by means of an axial force applied to said core member, the outer ends of said ribs extending into interlocking engagement with said threaded core member.

7. A coil form for use in a variable inductance device of the type described in which a threaded core is movably mounted in the form, comprising, an insulating structure formed of nylon and having a bore therein for the reception of said core, and a plurality of spaced yieldable ribs extending longitudinally along said bore and projecting radially therein for interlocking engagement with the threads on said core, said ribs having a width no greater than thirty-six one-hundredths of the radial length thereof and said ribs defining an opening having a diameter less than the external diameter of said core.

8. An assembly for use with a variable inductance device comprising a core supporting member at least partially formed of insulating material and defining an axially extending opening; a plurality of peripherally spaced and circumferentially deectable elements on said supporting member extending at least partially along the axial length thereof and projecting into said opening; and a core member having a threaded portion, said core member being inserted into said opening to circumferentially deflect said elements to permit translatory axial passage of said core member through the opening in said supporting member to a desired position, said deected elements moving into interlocking engagement with said threaded portion when said core member is disposed in said desired position to permit subsequent axial movement of said core member by rotation of said core member.

References Cited in the le of this patent UNITED STATES PATENTS 2,462,822 Wood Feb. 22, 1949 2,581,165 Bonanno Jan. 1, 1952 2,631,192 Wallin Mar. 10, 1953