US2511174A - Coil bobbin - Google Patents

Description

G. L. OSBORNE I COIL BOBBIN Filed April 20, 1948 June 13, 1950 INVENTOR. ird/0 L. [7560mm Patented June 13, 1950 UNITED STATES PATENT OFFICE 6 Claims.

This invention relates to a. coil bobbin, spool or the like.

It is an object of the present invention to provide a new bobbin construction having improved electrical insulation characteristics.

A further object of the present invention is to provide a compact, simple and inexpensive bobbin construction such as for transformer coils and which provides improved insulation between the coil turns and the iron core element.

More specifically, it is an object of the present invention to provide a new and improved flange structure for coil bobbins for transformers and the like electrical devices and which may be readily manufactured and assembled with a minimum of effort and without requiring expensive tools.

In accordance with an illustrated embodiment, the coil bobbin of the invention comprises :a core having end flanges mounted thereon and secured thereto by means of tab portions integral with the flanges and which are imbedded between superimposed turns of the core element, the end flanges being of rectangular shape and of flexible insulating material providing outer flap portions adapted to be folded over the peripheral outer surface of the coil and providing long creepage paths between the outer turns of the coil and the adjacent iron core structure.

For a consideration of what is believed novel and inventive, attention is directed to the following description taken in conjunction with the accompanying drawing while the features of novelty will be pointed out with greater particularity in the appended claims.

In the drawings, Fig. 1 is a view in perspective illustrating a transformer incorporating a coil unit wound on a bobbin constructed in accordance with one form of the present invention, a portion of the insulation covering being removed to illustrate certain details; Fig. 2 is a view in perspective illustrating a partially completed bobbin constructed in accordance with one form of the present invention; Fig. 3 is a longitudinal sectional view taken through a partially completed coil unit; Fig. 4 is a plan view illustrating one of the flange elements incorporated in the bobbin; Fig. 5 is an exploded view illustrating one manner in which the bobbin elements may be assembled; Fig, 6 is a view in perspective illustrating a transformer including a bobbin unit constructed in accordance with a second modification of the invention, a portion of the insulation covering for the bobbin unit being broken away so as more clearly to illustrate certain details of construction; Fig. 7 is a side elevation of a bobbin incorporated in the transformer shown in Fig. 6, a portion of the bobbin being removed for more clearly illustrating certain details of construction; and Fig. 8 is a plan view illustrating a flange unit incorporated in the bobbin shown in Fig. 7.

Referring now to the drawings, in Fig. 1 is shown a transformer comprising a laminated core unit It] having a coil unit Ii arranged upon the central leg 12 thereof. The coil unit it is wound upon a bobbin constructed in accordance with one form of the present invention and which is so designed as to be capable of inexpensive manufacture and at the same time provide high insulation strength between the coil turns and the iron core l0.

Referring now particularly to Figs. 2, 3, and 4, the coil bobbin consists of a rectangular core 14 having generally rectangular flanges I 5 mounted on each of the opposite ends thereof. While in the drawings, the corners are shown as being square, these may be rounded if desired. Preferably, though not necessarily, the core 14 consists of a plurality of turns of flexible insulating material, such as paper, suitably cemented together. The end flanges 15 are also made of a relatively flexible insulating material, such as paper, one of which is illustrated more clearly in the plan view of Fig. 4.

The flanges I5 are each provided with a central rectangular opening indicated by the dotted fold lines 16 corresponding to the outer dimensions of the core element 14. Tabs 11 are formed by slitting through the material along the crossed lines indicated at 18 and'the tab portions are bent outwardly along the fold lines It to a position at right angles with respect to the plane of the remainder of the flange 15. Each of the triangular tab portions 11 is, of course, integral with the flange 15 throughout the full extent of the edge portions thereof defining the opening therethrough. Particular attention is directed to the fact that the edges of the opening through the flange l5 extend at a 45 degree angle with respect to the outermost edges of the flange and which is important for reasons which will be described more fully hereinafter. While in the drawings, the tabs 11 are shown as being triangular in shape, it is understood that the tips may be cut off in the manufacture of short bobbins.

As illustrated in Fig. 2, the flanges 15 are assembled upon the opposite ends of the core element 14 with the triangular tab portions 11 of the flanges extending toward each other and positioned upon the outer surfaces of the core element. The flanges l5 may be secured in position upon the core element in any suitable manner, such as by a number of additional turns of insulating material wr'apped about the core 14 and over the upper surfaces of the triangular tab portions 11. These additional turns are indicated in Fig. 3 at 20.

The coil may then be wound about the bobbin in accordance with customary practice, the low voltage turns being provided next adjacent the core element 14 of the bobbin and the high voltage turns wound thereabout. As illustrated, the coil winding 2| consists of a multiplicity of turns of suitably insulated conductor with no interlayer insulation. After a requisite number of turns have been provided upon the bobbin, a layer 22 of insulation may be wrapped about the coil and the corner portions of the flanges, indicated at 23, are then folded tightly thereagainst and further secured in place by one or more turns of insulating material 24 wrapped thereabout. The entire coil unit may then be treated in the usual manner such as by immersion in an insulating varnish or other'resinous insulating material and baked.

As illustrated more clearly in the view of Fig. 1, in which a portion of the outer wrapping 24 of insulation has been removed from the periphery of the winding unit, it will be observed that the ends of the winding coil are completely covered with a continuous layer of insulating material between the winding and the outer corners 26 of the iron core structure Hi. It will be observed that the outer corner portions 23 of the flange elements extend from each of the opposite sides of the iron core structure 58, at the outer corner edges of the winding by a considerable distance indicated at 27. In other words the maximum width of the folded corner portions 23 is considerably greater than the width of the iron core. A long leakage path is thus provided between the iron core H3 and the winding turns around the edges of the flange elements 15 of the bobbin and which, accordingly, provides a high value of insulation between the iron core and the winding,

1' am well aware of the fact that it has been long recognized in the art that it is necessary to provide adequate insulation between the corners of the winding unit and the adjacent corner portions of the iron core, indicated at 26, and which points are recognized as the points of great electrical weakness in a transformer structure. Ihave discovered that with the coil bobbin structure of the present invention, I have been able to provide adequate insulation strength between the winding and thecore structure and at the same time achieve a greatly improved space factor between the coil unit and the iron core structure so that the over-all dimensions of the transformer are reduced substantially as compared with other prior art devices of similar capacity. Thisreduction in overall size of the transformer unit is of vital importance in many applications where space is at a premium. Moreover, with the bobbin and insulation arrangement as disclosed, the overall manufacturing cost of the transformer unit is reduced very substantially as compared with usual costs for transformers of the type described.

Referring now to Fig. 5 a modification of the invention will be described and in which the core unit 14 is formed by wrapping a relatively few turns 30 about a mandril, following which the end flanges l5 as previously described may be assembled upon the opposite ends of the partially formed core element. It will be observed that the unwound portion 3| of the web of insulating material will extend through the corners between adjacent pairs of triangular tabs of the end flanges so as to permit assembly of the flange units [5 upon the open ends of the partially formed core element. The remaining turns of the web 3! may then be wound upon the core unit over the triangular tab portions 5'! as previously described securely anchoring the flanges 15 in place.

Referring again to the view of Fig. 1, it will be observed that the thickness of the winding coil 2| corresponds substantially to the distance between the corners of the openings in the end flanges and the adjacent outer edges of the flanges, which distance is indicated at 35 in Fig. 4. The reason for this is to facilitate the folding over of the outer corner portions 23 of the flanges without causing buckling of the flange portions at the corners 35 of the coil as indicated in Fig. 1. In the modification illustrated in Figs. 6, '7 and 8 the end flanges All of the bobbin are formed of a semi-elastic flexible insulating material. While various suitable materials are available upon the market, I prefer to use a resinous thermo-plastic insulating material. By using such a material the creepage paths around the end; flanges of the bobbin may be considerably increased. As illustrated in Fig. 8, the triangular tab portions 33- are formed by cross slitting along the lines 4|. The cross slits 4| are somewhat shorter than the diagonals of the ultimate opening to be formed therein and indicated by the fold lines 12. In Fig. 7 the flanges 3% are shown mounted upon a core element 44 with the triangular tab portions 43 extending at right angles with respect to the plane of the flange do and positioned against the opposite sides of the core element 44. The corner portions integral with each of the adjacent tabs 43 are formed by stretching the plastic material suiflciently to permit mounting of the flanges upon the core. The corner portions 45 thus formed increase very substantially the leakage path between the central leg of the iron core and the innermost turns of the winding coil.

As illustrated in Fig. 6 the flanges it are in this instance somewhat larger than the previously described flanges l5, as compared with the dimensions of the winding coil, and particularly as regards the distance between the corners of the inner opening and the outer edge indicated at 41 in Fig. 8. Due tothe plastic nature of the insulatingmaterial, the portions 48 of the flange between the corner portions 49 may be folded smoothly over the corners of the coil to permit the outer insulation wrapping layer 5i to lie smooth thereabout. By virtue of the fact that the portions 48 of end flanges extend over the corners of the winding coils as shown in Fig. 6 a substantial increase in creepage path distance is accomplished as compared with the modification of Fig. 1.

Having described and illustrated what is considered to be certain preferred embodiments thereof it is desired that it be understood that the present details shown are merely representative and that the invention may be carried out by other means.

I claim:

1. A coil bobbin, of the class described compris- 76 ing a core of rectangular cross section, flanges mounted on the opposite ends of said core, each of said flanges being of flexible insulating material and of rectangular shape, a centrally disposed rectangular opening in each of said flanges, the edges of said openings extending at a 45 degree angle with respect to the outer edges of said flanges, triangular tabs extending at right angles from the inner faces of each of said flanges and integral with each of the opposite edge portions defining said openings throughout the full extent thereof, a plurality of turns of insulating material covering said tabs and securing said flanges to said core, the outer corners of said flanges being adapted to be folded over the outer peripheral surface of a coil wound about said core between said flanges.

2. A coil bobbin of the class described comprising a core of rectangular cross section, flanges mounted on the opposite ends of said core, each of said flanges being of flexible insulating material and of rectangular shape, a centrally disposed rectangular opening in each of said flanges, the edges of said openings extending at a 45 degree angle with respect to the outer edges of said flanges, triangular tabs extending at right angles from the inner faces of each of said flanges and integral with each of the edge portions defining said openings throughout the full extent thereof, a plurality of turns of insulating material covering said tabs and securing said flanges to said core, a coil wound about said core, the width of said flanges between the corners of said openings and the adjacent outer edges of said flanges being at least equal to the thickness of said coil, the outer corner portions of said flanges being folded over the outer peripheral surface of said coil and extending parallel with the axis of said core.

3. A coil bobbin of the class described comprising a core of rectangular cross section, flanges mounted on the opposite ends of said core, each of said flanges being of flexible insulating material and of rectangular shape, the central portion of each of said flanges defining four triangular tabs, said tabs extending at right angles from the inner faces of said flanges, the fold lines of said tabs extending at a 45 degree angle with respect to the outer edges of said flanges, a plurality of turns of insulating material covering said tabs and securing said flanges to said core, the outer corners of said flanges being adapted to be folded over the outer peripheral surface of a coil wound about said core between said flanges, the width of said folded corner portions being greater than the width of said core.

4. A coil bobbin of the class described comprising a core of rectangular cross section adapted to have a coil wound thereabout, rectangular flanges mounted on the opposite ends of said core, the outer edges of said flanges extending at a substantially 45 degree angle with respect to the ad- Jacent flat sides of said core, each of said flanges being of flexible insulating material and having opposite corner portions extending outwardly from said core substantially beyond the outer edges of the coil wound upon said core, the outer corners of said flanges being adapted to be folded over the outer peripheral surface of the coil wound about said core between said flanges, the width of the fold lines of said corner portions being substantially greater than the width of said core.

5. A coil bobbin of the class described comprising a core of rectangular cross section adapted to have a coil wound thereabout, flanges mounted on the opposite ends of said core, each of said flanges being of flexible insulating material and of rectang111ar shape, the outer edges of said flanges extending at a substantially 45 degree angle with respect to the adjacent flat sides of said core, the central portion of each of said flanges being slit so as to define a plurality of tabs, said tabs extending at right angles from the inner faces of said flanges and secured to the outer surface of said core, the width of said flanges from the tips of the outer corner portions to said core being greater than the width of the coil wound on said core, the outer portions of said flanges being adapted to be folded over the outer peripheral surface of a coil wound about said core between said flanges.

6. A coil bobbin of the class described comprising a tubular core of rectangular cross-section, flanges mounted on the opposite ends of said core, each of said flanges being of flexible insulating material and of generally rectangular shape, the outer edges of said flanges extending at a substantially 45 degree angle with respect to the adjacent flat sides of said core, a coil wound about said core between said flanges, the minimum width of said flanges between the corners thereof and said core being at least equal to the thickness of said coil, the width of said flanges from the tips of the outer comer portions thereof to said core being substantially greater than the thickness of said coil, said corner portions being adapted to be folded over the outer peripheral surface of said coil and extending parallel with the axis of said core.

GERALD L. OSBORNE.

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

UNITED STATES PATENTS Number Name Date 1,481,190 Durbin et a1 Jan. 15, 1924 1,859,248 Strait May 1'7, 1932 1,997,641 Isenberg Apr. 16, 1935 FOREIGN PATENTS Number Country Date 4,306 Great Britain Oct. 22, 1880

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