US2889524A

US2889524A - Miniature inductive assembly

Info

Publication number: US2889524A
Application number: US566835A
Authority: US
Inventors: Doris R Schmitz
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1956-02-21
Filing date: 1956-02-21
Publication date: 1959-06-02
Anticipated expiration: 1976-06-02

Description

.. June 2, 1959 D. R. SCHMITIZ 2,

MINIATURE INDUCTIVE ASSEMBLY Filed Feb. 21, 1956 //v VE/V TOR D. R. SCHM/TZ fw mm A T TORNEV United States Patent Patented June 2, 1959 2,889,524 MINIATURE INDUCTIVEASSEMBLY llor'is R. Schmitz, Morristown, N.J., assignor to Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporation of New.York

Application February 21, 1956, Serial No. 566,835

Claims. (Cl. 336-192) This invention relates to inductive devices and more Particularly to miniaturized inductance devices, such as communication transformers.

In the design of communication transformers, for example, for use in carrier telephone systems, the comparatively recent development of high permeability magnetic core materials, such as the polycrystalline ceramic-like ferrites disclosed in the Patents 2,452,529, 2,452,530, and 2,452,531, to I. L. Snoek, allows marked reduction in the size of the magnetic core. In order to obtain the advantages of decreased size afforded by the use of ferrites, it is desirable to employ windings of fine wire. In low voltage applications, wire as fine as 46-gauge (0.0016 inch diameter) is desirable.

In attempting to attain a high degree of miniaturization in the past, it has been found that a limiting factor in the reliability of the devices has been the likelihood of'breakage of the fine wire, particularly of the leads in the region of attachment to their terminals. Another factor of importance in the design of miniaturized inductive devices is, that with decreased size, when employing conventional designs, a high degree of skill and manual dexterity of the assembler is required. Primary causes of winding failures have been found to be improper manipulation during the assembly, in particular, the steps of securing the winding to the terminal, and because of stress applied to the windings due to relative movement of the winding assembly with respect to the terminals.

It is desirable for moisture and mechanical protection to encapsulate or pot devices of this type in catalyzed, thermosetting or thermoplastic sealing compounds. The failure of a winding or lead due to any cause results in a totally defective nonrepairable component owing to the extreme difliculty in removing the sealing compound. Therefore, the reliability of leads is of prime practical importance in the design of miniature inductive devices.

Accordingly, it is a general object of this invention toattain miniaturized inductive devices having a high degree of reliability.

More specific objects of this invention are to provide a miniature inductor or transformer of simple design and low cost in which the terminals constitute a pro tective enclosure for the winding assembly; to prevent relative movement of the winding assembly with respect to the terminals; and to enable the securing of all the fragile winding leads simultaneously to their respective terminals with a minimum of strain thereon and requiring a minimum of skill and mechanical dexterity of the assembling operator.

These objects are accomplished in accordance with one specific embodiment of this invention comprising an insulating terminal plate or button having a plurality of wire segments extending therethrough and arranged in a spaced or circular array to form a cage-like structure on at least one side of the terminal plate. A winding bobbin having notched flanges corresponding to the terminals is nested coaxially within the cage-like structure. One U-shaped magnetic core part is positioned between the terminal plate and one flange of the bobbin and extends into the cage-like structure. Overlying the outer flange of the bobbin is a second U-sha'ped magnetic core part the ends of which are cemented to the ends of the first core part. Wound upon the bobbin between the flanges are a plurality of turns of insulated wire comprising the winding or windings of the inductive device. The lead ends of the windings pass through openings in the outer bobbin flange, are fanned outward, and are secured to certain of the terminal wires. I

As discussed above, it is necessary in miniature devices of this type to insure against relative motion of the winding, winding spool, terminals, and magnetic core. Particularly, it is important to prevent motion between the winding or windings and the terminals to which their ends are secured, which motion can introduce strains into the winding ends or rupture the electrical connection between the winding and the terminal. In accordance with one aspect of this invention, a tensioned insulating band encircles the terminals between the bobbin flanges mechanically biasing them by distorting them slightly against the bobbin flanges and thereby maintaining the bobbin immobile with respect to the terminals. Motion between other parts of the device is prevented by seating the base of the magnetic core in a depression in the insulating terminal plate through which the terminals extend and by proportioning the parts so that the lower notched flange of the winding spool rests on the upper surface of the base of the core.

An appreciation of the size of miniature inductors in accordance with this invention can be gained from the fact that the overall volume of one specific illustrative embodiment comprising a carrier frequency transformer is less than one-half cubic inch exclusive of external terminals. The attainment of such a degree of miniaturization by utilizing ferrite core material and exceedingly fine wire windings imposes severe requirements on the connections between the windings and the terminals and on the making of such connections. Specifically, not onlymust relative motion between the parts that would tend to rupture the very fine wire connections be pre vented, but also, in accordance with another aspect of this invention, the structure must be such as to lend itself readily to fabrication without the introduction of strains or deleterious forces during the fabrication by relatively unskilled personnel.

One feature of this invention relates to the arrangement of terminals forming a protective cage for the winding assembly of the device.

Another feature involves the winding bobbin having discontinuities corresponding to the terminals whereby the bobbin and winding are positioned coaxially within the terminal cage.

Another feature relates to the terminals extending beyond the bobbin flange to afford a point for simultaneous attachment by dip soldering of all of the winding leads at a remote point on the terminal.

Another feature involves the employment of a tensioned band mechanically to bias the terminals in and about the winding bobbin to prevent movement of the bobbin parallel to the terminals.

Still another feature resides in the arrangement of the winding bobbin whereby it serves to clamp the magnetic core securely in position against the terminal plate.

These and other features of this invention may be understood by reference to the following detailed de scription and to the accompanying drawing, in which:

Fig. 1 is an exterior view of a completed assembly in accordance with this invention;

Fig. 2 is an elevational view of the device of Fig. l with the enclosure shown in section for clarity; and

Fig. 3 is an exploded and enlarged representation of the device of Fig. 1.

Referring now to Figs. 1 and 2, a transformer assembly may be seen comprising generally a terminal plate 11 of insulation such as molded phenolic material in the form of a circular disk having a peripheral step 12 in one face. Passing through the terminal plate at right angles to its major faces are a plurality of wires 13 constituting the terminals of the transformer. Enclosing the assembly is a tubular housing 14 having a rolledover lip 15 at one end corresponding to the peripheral step 12 in the terminal plate 11. Enclosing the open end of the tubular member is an insulating disk 17.

The terminal wires 13 are arranged in a circular array. Positioned within the cage-like structure formed by the terminal wires 13 on one side of the terminal plate is a coil bobbin about which a plurality of turns 21 of insulated wire are wound. The winding terminations or leads 22 pass through openings or slots 41, seen in Fig. 3, in a flange 23 of the bobbin 20 and are wound about certain terminal wires 13 near the adjacent end of the wires 13.

Between the terminal plate 11 and the bobbin 20 is a U-shaped magnetic core part 25 of, for example, manganese zinc ferrite. The bottom surface of the core part 25 rests in a groove 28 in the terminal plate 11 and the

legs

26 and 27 of the core part are upturned, the leg 26 being substantially on the common axis of the coil bobbin 20 and the terminal wires 13. The leg 27 extends upward outside of the cage of terminal wires 13. The core part leg 26 is positioned to extend through a lower flange 24 and into a central opening 30 in the coil bobbin 20, best seen in Fig. 3. A core part 29 similarly of U configuration is positioned over the outer flange 23 of coil bobbin 20, with

legs

31 and 32 of core part 29 in juxtaposition with those of the core part 25. The

core parts

25 and 29 are cemented together and thereby define a closed rectangular magnetic core structure having one side passing through the central opening 30 in the coil bobbin 20 and an adjacent side clamped by the coil bobbin 20 against the terminal plate 11.

Encompassing the terminals in the region intermediate the outer flange 23 and an inner flange 24 of the bobbin 20 is a tensioned insulating band 35, for example, a plurality of turns of insulating pressure sensitive tape. The band is tightly wound around the terminal wires 13 and in so doing mechanically biases them into corresponding notches 36 in the bobbin flanges as is best seen in Fig. 2. The terminal wire sections between the

flanges

23 and 24 are bowed inward slightly by the band 35 thereby preventing movement of the coil bobbin 20 along the terminal wires 13. In Fig. 2, the bowing of the terminal wires 13 is exaggerated for the purposes of illustration. Several notches 36 in the

bobbin flanges

23 and 24 prevent movement of the winding assembly perpendicular to the axis of the terminal array while the band 35 of insulating tape and bowed portion of the terminals effectively prevent movement of the bobbin 20 in a direction generally parallel to the terminal wires 13 and away from the terminal plate 11. The core part 25, clamped between flange 24 of bobbin 2i) and terminal plate 11, prevents movement of the bobbin 20 toward the terminal plate 11. In this arrangement, the winding, although a separate assembly from the magnetic core and terminals, is positively fixed with respect to those elements in the transformer. The leads of the winding need traverse only the short distance from the bobbin 20 to the terminal wire ends within the protective cage thereby minimizing the likelihood of breakage.

The details of the transformer of Figs. 1 and 2 may be more clearly seen by reference to Fig. 3 which is an exploded view of the winding and core assembly. The tubular enclosure 14 is shown with the lip portion 15 at lead except for the molten solder.

the bottom in position to receive the terminal plate 11 with embedded terminal wires 13. The groove 28 in which the core part 25 rests is clearly shown extending into the circular array of terminal wires 13. The terminal wires 13 may be unequally spaced in the array for identification purposes and to fit a particular mounting for the device. Positioned to encompass the cage structure of terminal wires 13 is tensioned band 35, only a fragment of which is shown in Fig. 3. The core part 25, as well as the core part 29, includes

legs

26 and 32, respectively, which are arranged to extend into the substantially rectangular hole 30 in the winding bobbin 20.

Legs

27 and 31 fit along flattened edges 40 of the

flanges

23 and 24 of the bobbin 20. The winding leads 22 may be seen emerging from slots 41 in the flange 23 of the bobbin in a position convenient for attachment to the terminal ends. .Uppermost in Fig. 3 is the insulating disk 17 which serves to complete the assembly after filling the enclosure 14 with a sealing compound having good insulating qualities.

In assembly, the core part 25 is positioned in groove 28 and bobbin 20 having turns 21 thereon is slid into the cage formed by terminals 13 coming to rest on core part 25. Band 35 shown in Fig. 2 is placed about the terminals 13 between'flanges 23 and 24 and is drawn up tight forcing the terminal wires 13 into notches 36 of bobbin 20. The winding leads are drawn through the slots 41 in the winding flange 23, are separated, stripped of insulation, if necessary, and wound about the correct terminal. The entire assembly then is inverted and the ends of the terminal wires 13 adjacent the bobbin 20 are immersed in 'a molten solder bath to secure all of the winding leads to their terminals simultaneously. After this step, the

core part 29 is positioned over bobbin 20 and cemented to the core part 25. After a dip coating of insulation or after vacuum impregnation with wax, the transformer assembly is complete and in usable form. To prevent 'closed in the tubular housing 14 which is subsequently filled with a sealing compound and closed with disk 17; the sealing compound is also omitted from the drawing for clarity sake. In this form, the only exposed elements connected to the winding leads are the terminal ends which are the extreme opposite ends from the point of lead attachment. Therefore, movement of a terminal wire has virtually no chance of producing strain in its winding lead. Similarly, the leads during manufacture are subjected only to handling in being threaded through the bobbin slots and wound about the terminal wire. Soldering is accomplished with no physical contact to the These features, in addition to the arrangement for effectively securing the winding assembly as a whole from moving with respect to the terminal wires, practically eliminate the introduction of unwanted strain into the Winding leads resulting in increased reliability in the transformer. I

It is to be understood that the above described arrangements are merely illustrative of the application of the principles of this invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. An inductive assembly comprising an insulating terminal plate, a plurality of spaced terminals extending through said terminal plate and secured therein, the portions on one side of said terminal plate forming a cagelike structure and the portions on the opposite side of said terminal plate constituting the external connectors for the inductive assembly, an insulating winding bobbin including end flanges and a central opening extending through said bobbin positioned within said cage-like structure with the end flanges extending transverse to the terminals, a. winding on said bobbin, a magnetic core for said winding positioned at least partially within said cagelike structure and having a portion extending through said winding bobbin, the ends of said winding emerging from said bobbin and secured each to a respective terminal, and insulating means encompassing said terminals between the end flanges and mechanically biasing said terminals against said winding bobbin end flanges tending to bow said terminals in the region between the end flanges to secure said Winding bobbin from movement.

2. An inductive assembly comprising an insulating terminal plate, a plurality of spaced terminals extending through said terminal plate and secured therein, the portions on one side of said terminal plate forming a generally circular cage-like structure and the portions on the opposite side of said terminal plate constituting the external connectors for the inductor assembly, an insulating winding bobbin including a central opening positioned within said cage-like structure, said bobbin including a pair of spaced end flanges in contact with said terminals and being positioned thereby substantially coaxially within said cage-like structure, a winding on said bobbin, a magnetic core for said winding including a portion extending through the opening in said winding bobbin, the ends of said winding emerging from said bobbin and secured each to a respective terminal, and insulating means encompassing said terminals between the end fl-anges of said Winding bobbin and mechanically biasing said terminals against said winding bobbin tending to bow said terminals in the region between the end flanges to secure said winding bobbin from movement.

3. An inductive assembly comprising an insulating terminal plate, a plurality of spaced terminals extending through said terminal plate and secured therein, the portions on one side of said terminal plate forming a generally circular cage-like structure and the portions on the opposite side of said terminal plate constituting the external terminals for the inductive assembly, an insulating winding bobbin having a central opening therethrough positioned within said cage-like structure, said bobbin including a pair of spaced end flanges in contact with said terminals and being positioned thereby substantially coaxial'ly Within said cage-like structure, said flanges having peripheral notches therein coinciding with the terminals, a winding on said bobbin, a magnetic core for said winding including a portion extending through the opening in said Winding bobbin, the ends of said winding emerging from said bobbin and secured each to a respective terminal, and insulating means encompassing said terminals between the end flanges of said winding bobbin and me chanically biasing said terminals against said winding bobbin at the peripheral notches tending to bow said terminals in the region between the end flanges to secure said winding bobbin from movement.

4. The inductive assembly in accordance with claim 3 wherein said insulating means comprises a closed tensioned band.

5. The inductive assembly in accordance with claim 3 wherein said insulating means comprises a band of pressure sensitive tape.

6. An inductive assembly comprising an insulating terminal plate, a plurality of spaced terminals extending through said terminal plate and secured therein, the portions on one side of said terminal plate forming a cagelike structure and the portions on the opposite side of said terminal plate constituting the external connectors for the assembly, an insulating winding bobbin having a central opening therethrough positioned within said cage-like structure, said bobbin including end flanges having peripheral notches coinciding with the terminals, a winding on said bobbin, insulating means mechanically biasing said terminals into the peripheral notches of said bobbin end flanges and a magnetic core extending through said bobbin and said winding, said magnetic core including a portion extending between said terminal plate and one bobbin end flange and secured therebetween.

7. An inductive device comprising a terminal plate of insulation, a plurality of elongated terminals secured in spaced array through said plate with portions extending from opposite sides thereof, the terminal portions on one side of the plate defining a cage-like enclosure and those on the other side being the external connectors, an insulating winding form within the enclosure including extended portions in contact with said enclosure, a winding on the form, winding ends protruding from the form within the enclosure and secured to respective terminals only in a region of said terminals remote from said terminal plate, and a tensioned band of insulation encompassing the terminals in the region of said extended portions of said winding form to bias said terminals against the winding form tending to bow said terminals in the region between the extended portions of said winding form to inhibit relative movement between the form and the terminals.

8. An inductive device comprising a plurality of terminal conductors arranged in a cage-like array, an insulating winding spool including end flanges within said array, a winding on said spool having its ends connected to respective ones of said conductors, and means for preventing relative motion between said conductors and said winding spool, said means including a tensioned band of insulation encompassing said conductors mechanically to bias said conductors against the end flanges of said winding spool.

9. A miniature inductive device comprising an insulating terminal plate having a depression in one side thereof, a plurality of terminals extending through said plate and arranged in a cage-like array adjacent to said one side of said plate, an insulating winding spool within said array and having a central aperture and spaced flanges having peripheral notches therein, a winding on said spool having its ends connected to said terminals, a magnetic core having one arm extending through said aperture, said core having a portion positioned in said depression, and a tensioned band of insulation encompassing said terminals between the flanges of said winding spool and mechanically biasing said terminals within said notches in said flanges.

10. A miniature inductive device in accordance with claim 9 wherein one of said flanges rests on a portion of said core and secures said core in said depression.

References Cited in the file of this patent UNITED STATES PATENTS 2,392,701 Sanders Jan. 8, 1946 2,535,203 Guthman Dec. 26, 1950 2,771,663 Henry Nov. 27, 1956 2,774,051 McCarthy Dec. 11, 1956