US3106691A - Variable-inductance coil having core threaded in coil form - Google Patents

Description

061. s, 1963 HISAO MAEDA 3,106,691

VARIABLE-INDUCTANCE COIL HAVING CORE THREADED IN COIL FORM Filed May 24, 1960 FigAVQAb INVEIV ORX Mzw United States Patent Office dflhfi l Patented Get. 3, 1963 3,105,691 VARIABLEHNDUCTANCE CUlllL HAVKNG CQRE THREADED EN (191i, FURM Hisao lvi'aeda, l3 Shiba-ltoen, Minatodtu, Tokyo-to, Eapan Fiicd May 24, 1960, Ser. No. 31,376 (Claims priority, application Japan May 25, 1959 3 Claims. (Ci. 336-4136) This invention relates in general to variable inductors and in particular to a new and improved assembly of a hollow bobbin and a ferrite core for variable-inductance coils.

It is an object of this invention to provide a bobbin for variable-inductance coils wherein the disadvantages inherent in conventional bobbins of this type, as will be described hereinafter, have been eliminated.

It is another object of the invention to provide a bobbin for variable-inductance coils, employing movable ferromagnetic core slugs, which has a simple, yet strong, construction adaptable to and reproducible in mass production with a high degree of uniformity.

The manner in which the foregoing as Well as other objects and advantages may be best achieved will be understood more fully from a consideration of the following description of one representative embodiment of the invention, taken in conjunction with the accompanying drawing in which:

FIG. 1 is an elevational view, in longitudinal section, of a bobbin embodying the invention;

FIG. 2 is a cross-sectional view of the bobbin of FIG. 1 having a wedge member attached to it;

FIG. 3 is an elevational view of one example of a ferrite core to be fitted into the bobbin of FIGS. 1 and 2;

FIG. 4 is a plan view of the core of FIG. 3; and

FIGS. 5a and 5b are a perspective and a cross-sectional view of the Wedge member of FIG. 2, the latter being taken along the line VBVB of FIG. 5a.

In FIG. 1, the hollow bobbin cylinder or coil form 1 of the embodiment is made of a hard insulation material such as a hard synthetic resin and has one or more slots 2 cut in the longitudinal direction. Said slots 2 are adapted to receive the shank portion of one or more wedge-shaped bodies 3 which are made of a substance such as styrene, vinyl chloride, or other relatively soft insulating material, and which are provided with integrally formed flanges 4 of curved configuration and relatively reduced thickness for intimately contacting the outer surface of the bobbin cylinder 1. The member 3, or each of several such members, has a shank 3 adapted partly to protrude into the interior of the bobbin cylinder it upon insertion and to be held firmly thereto by the coil C wound about the bobbin cylinder 1.

In assembling the bobbin of the invention with an inductance-adjusting ferrite core Fe shown in FIGS. 3 and 4, the said core Fe is screwed directly into the bobbin interior, the outer screw threads of the core Fe thus cutting into and tapping the pliable, wedge-shaped member or members 3, whereby an extremely firm fitting is obtained between the mating parts.

The bobbin of this invention enables inductance adjustments to be made by causing the ferrite core Fe to move within the bobbin interior through the action of conventional threads on the outer surface of the said core. This bobbin has the further advantage of tight fit even if a certain dimensional difference exists between the inner diameter of the bobbin cylinder 1 and the outer diameter of the core Fe because the wedge-shaped member or members 3 have pliability. Moreover, it is possible to obtain a higher Q value than in the conventional core wherein a metal screw is used because the inner diameter of the bobbin cylinder 1 can be made closer to the outer diameter of the core Fe.

Furthermore, the bobbin of the invention has the advantage of being easily fabricated, there being no neces sity of carrying out the difiicult process of cutting precise screw threads on the inner surface of the bobbin cylinder made of hard insulation material, and there being only the necessity of cutting a slot, or slots, 2 in the bobbin cylinder 1 in the longitudinal direction. It is a special feature of the invention that, since the flange 4 of the member 3, on the outer surface of the bobbin cylinder 1, is held fast by the coil C wound about the said bobbin cylinder, the member 3 is fastened securely to the said bobbin cylinder, and the core Fe yielda-bly but positively engaged thereby is held securely in its selected axial pos tion relative to the coil whereby stability of operation 1s insured.

Although this invention has been described with respect to a particular embodiment thereof, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention, as defined by the appended claims.

What I claim is:

1. A variable-inductance coil comprising a tubular coil form of relatively hard electrically insulating material provided with at least one longitudinal slot, a body of relatively soft electrically insulating material engaging said slot and projecting therethrough into the interior of said form, said body having a flange thereon positively engaging said form and being held against inward radial displacement by said flange, said flange extending generally parallel to the axis of said form while overlying the periphery thereof, wire-coil means wound around the periphery of said form and said flange, thereby securing said body in said slot, and a core threaded into the interior of said form in engagement with said body.

2. A variable-inductance coil comprising a tubular coil form of relatively hard electrically insulating material provided with at least one longitudinal slot, a generally T-shaped body of relatively soft electrically insulating material having a shank portion engaging said slot and projecting into the interior of said form therethrough, said body further having a flange portion engaging the periphery of said form and held against inward radial displacement therein, wire-coil means wound around the periphery of said form and said body, thereby securing said body in said slot, and a core threaded into the interior of said form in engagement with said body.

3. A variable-inductance coil comprising a tubular coil form of relatively hard electrically insulating material provided with at least one longitudinal slot, a generally T-shaped body of relatively soft electrically insulating material having a shank portion engaging said slot and projecting into the interior of said form therethrough, said body further having a flange portion engaging the periphery of said form and held against inward radial displacement therein, wire-coil means wound around the periphery of said form and said body, thereby securing said body in said slot, and a core threaded into the interior of said form in engagement with said body, said flange portion bearing externally upon said form and having a thickness substantially less than that of said form.

References Cited in the file of this patent UNITED STATES PATENTS 2,838,738 Antalek June 10, 1958 FOREIGN PATENTS 193,453 Switzerland Mar. 1, 1938

Claims (1)

1. A VARIABLE-INDUCTANCE COIL COMPRISING A TUBULAR COIL FORM OF RELATIVELY HARD ELECTRICALLY INSULATING MATERIAL PROVIDED WITH AT LEAST ONE LONGITUDINAL SLOT, A BODY OF RELATIVELY SOFT ELECTRICALLY INSULATING MATEIRAL ENGAGING SAID SLOT AND PROJECTING THERETHROUGH INTO THE INTERIOR OF SAID FORM, SAID BODY HAVING A FLANGE THEREON POSITIVELY ENGAGING SAID FORM AND BEING HELD AGAINST INWARD RADIAL DISPLACEMENT BY SAID FLANGE, SAID FLANGE EXTENDING GENERALLY PARALLEL TO THE AXIS OF SAID FORM WHILE OVERLYING THE PERIPHERY THEREOF, WIRE-COIL MEANS WOUND AROUND THE PERIPHERY OF SAID FORM AND SAID FLANGE, THEREBY SECURING SAID BODY IN SAID SLOT, AND A CORE THREADED INTO THE INTERIOR OF SAID FORM IN ENGAGEMENT WITH SAID BODY.

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