Coil former

Abstract: In order to protect a coil wound with fine wire against the stresses of encapsulation as well as handling, the coil former has one end flange (4) carrying two terminals (3, 6), a peripheral groove (13) ending adjacent one terminal (6) and beginning adjacent the tangentially exiting wire (14, 17) from the coil. At the beginning of the groove is a notch (12) and a projection (12A) for winding the exiting wire around in a loop (18), whereby the wire substantially reverses direction. The flange also has a depression (9) allowing access by the second wire end to a second groove extending radially inwards from a peripheral point between the two terminals (3, 6).

Description: The present invention relates to a coil former, on which fine wire so thin as to be easily fractured, is to be wound and attached at both of its ends to electrical terminals carried by the former. An object of the invention is to provide a former able to protect wire, e.g. of only 0.06 mm or less, that might be coiled thereon and electrically terminated. The invention also relates to the completed encapsulated coil on the former. In these days of miniaturisation, less amperage is consumed, but occupation of space and weight must be minimised, so that very thin wire not only can be used, but must be used for compactness and lightness; such wire can be hard to handle. Although modern machinery can be sufficiently delicate to wind such very thin wire, the two ends must generally exit from the main bulk of the coiled wire towards terminals, e.g. faston-type terminals, that nearly always have to be relatively close together for convenience in electrical access. The exiting geometry generally does not easily allow easy securing of both wires in safe routes, that do not interfere with each other, towards the close together terminals. The exiting parts of the wire are fragile single strands, and tend to be exposed to mechanical or human handling stresses. Furthermore, attempts to protect the coil itself, against both handling and the environment, by coating, can only be helpful if the coating material flows into every crack or gap, which in practice requires injection moulding or pressure feeding synthetic encapsulant material in hot (e.g. 250 degrees C) molten form. Unfortunately, the coating process itself can be prejudicial to the thin wire, because the exposed parts of the wire tend to have very vulnerable free unsupported lengths en route to the terminals, or tend to lie with some freedom of movement on an external surface of the coil former. Also, unfortunately, the encapsulation process can form moving waves of hot molten encapsulant which suddenly catch the wire in pulses of pressure, and either move it and break it, or rub it vigorously back and fore on the coil former surface with similar destructive results. Sometimes, more than one coil is wound on one former, which complicates the termination problem further. It has been proposed, e.g. in GB-A-1 422 988, and GB-A-1 110 192 and GB-A-1 574 977, to put entering and exiting wires in annular grooves at the edge of a flange, which in the last carries two terminals. However, none of these references is particularly concerned with space saving, because the grooves are relatively deep, presumably to enable better protection, as one might anticipate since the periphery of a flange is relatively exposed. Indeed, GB-A-1 110 192, the state of the art, puts terminal wires carrying insulated sleeves in the groove, these being flying leads with no terminals. The present invention aims to economise in space by avoiding requirement for a substantial peripheral groove depth, without loss in protection. Moreover, it is desirable often to have two terminals close together on a flange, yet it is desirable to avoid both wires being in peripheral grooves, because thin wire in a peripheral groove is still somewhat exposed, even after encapsulation. It is also desirable, in the interests of uniformity of wire tension and directness of wire paths, to have both wires entering, or leaving, the main body of the coil tangentially. GB-A-1 422 988 and GB-A-1 574 977 above, also DE-A-3 030 301 propose deliberately leaving slack portions in the exiting and entering coil wire, but this approach was not believed helpful by the present inventor; indeed, such calculatedly slack portions are contra-indicated by the inventive teaching. As aforesaid, the encapsulation process can set up oscillatory rubbing of lengths of wire with freedom of movement. An object is to provide a former on which even delicately thin wires can be wound, with protection of exiting lengths from rupture against the stresses produced by subsequent pressure moulding or by handling, particularly when two or more terminals therefore are grouped closely together. The insulating former tends to be bobbin shaped, i.e. cylindrical with a radially projecting flange at each end. The two or more terminals are typically embedded in one flange, or are otherwise supported on or near one flange. Boths ends of wound wire(s) will exit adjacent this flange, hereinafter referred to as "the flange". Also both wire ends will need to exit tangentially, to control tension. According to this invention, which is defined in claim 1, the flange (4) has an external circumferential grove (13) extending generally in a plane of the flange intermediate its end surfaces (7,8), said groove (13) at its one end terminating adjacent a point (16) of an anchoring terminal (6) where said terminal is just extending free from its own support at, or embedded in, the flange, and said groove (13) at its other end terminating in a notch (12) over which notch a wire end (17) after exiting the coil substantially tangentially can be bent (18) in tension, substantially to reverse its direction and then to follow in a wire length portion (14) along the bottom of said groove over a very short exposed length (15) to an attachment at said extending point (16) of the terminal. The bracketed numbers serve for identication of specifically illustrated counterparts. Thus the exciting wire is wound over the notch, along the groove and is wrapped around and/or soldered to the terminal with virtually no exposed length except in the groove bottom where it has negligible freedom of movement. A second exiting wire length (2) can be catered for by the following feature of the former, the flange has a second groove (9) where the flange supports two terminals, so that the second exiting wire length (2) can exit tangentially of the coil (1) and along the bottom of the second groove over a short exposed length (11) to a point (10) of the second terminal (3) just extending from and near support by the flange (4). Thus, the whole coil can be effectively encapsulated, and the wires can be taut, and especially one is very well protected by an internal groove. There is, in practical cases, no room for two separated grooves between the terminals, such that both wire lengths could exit the coil tangentially. However, the external circumferential groove and notch allow both wire lengths to leave the coil tangentially, the second one (2) being especially well protected from external influences. GB-A-1 110 192 although having some similar structure, actually proposes a direction reversal in a sleeved wire, but one wire is already held down with slack by means of insulating tape, and the other wire (before sleeving) is led into a channel resembling a flanged groove without a directional reversal. The channel is so large that it accommodates not only the insulated sleeving, but also a solder joint for joining said other wire to sleeved wire. This disclosure is relatively unconcerned with the miniaturisation of today. Further features of the invention will appear from the following description of an embodiment thereof, given in conjunction with the drawings, in which:- Fig 1 shows in plan view just one length of wire, which is the start length of an inventive coil, which in Fig 1 is as yet unwound, on the inventive former: Fig 2 shows a front view of the coil of the invention wound on the inventive former; and Fig 3 and 4 show in side and plan views respectively, the wire at the other exiting length of the completed coil wound on the former. Referring to Fig 1, a coil 1 wound on a cylindrical former has, tangential thereto, an exiting length 2 which is soldered to a faston 3 embedded in a flange 4 of the former 5. A second faston terminal 6 is also embedded in flange 4 close to the first faston 3. The wire length 2 is wound along the bottom of a groove intermediate the outer surface 7 and the inner surface 8 of flange 4. The groove may be inclined to the general plane of the flange in order to progress the wire from the lower level (as viewed) of the tangential coil exit to the higher level of the faston 3. This part of the wire, which is not a primary concern of the invention, can be seen also in Fig 2 which is a plan view towards inner surface 8 of the flange, showing a slot shaped depression 9 providing access to the groove, whose course is visible by the representation of wire 2 in Figs 1 and 2. The wire length leaves the groove close to a point 10 of attachment by solder to faston 3, which point 10 is also close to where the faston is securely embedded in the flange. There is thus only a very short free wire length 11. The second faston 6 is closeby, similarly embedded in the flange. This arrangement is very satisfactory for one length of wire, but does not have room for similar exit of the second end length of wire, which also must exit in tension and tangentially from the coil 1. Accordingly, room is provided by the invention, facilitated by a novel notch 12 and projection 12A provided in the inner surface 8 of the flange through only to a circumferential groove 13 at an intermediate level in the flange, which will now be described in conjunction with Figs 3 and 4. Referring to Fig 3, the circumferential groove 13 can be seen occupied by a wire length portion 14 which extends outwardly to become a short free portion 15 before attachment at a point 16 on faston 6. Point 16 lies only close to where Terminal 6 is embedded in the flange 4. The flange extends in thickness each side of the groove, but the aforementioned notch 12 (not visible in Fig 3, only visible in Figs 2 and 4) and projection 12A only extend from the groove 13 down to surface 8. The wire length 17 tangentially leaving the coil 1, is bent in tension is bent around the notch 12 to form a direction reversing portion 18, which is protected against handling and securely retained in position against the pressure encapsulation process by the projecting portion 12A of the flange 4; the bent wire portion 18 then continues outwards successively as said wire length portion 14 in the circumferential groove 13, the short exposed portion 15, and finally attachment at 16. Encapsulation can now take place in relative safety as regards wire fracturing by the hot molten (e.g. 250 degrees C) flowing encapsulant. Just by way of example, typical miniature dimensions of a preferred embodiment are as follows. The groove 13 is 0.3 mm wide, the wire-reversing notch 0.5 mm wide, the protecting and retaining projection 12A is 0.8mm in width (taken on the outside of the wire), and the other groove protecting the other wire end 2 is 0.5 mm wide for the most part, tapering to 0.3 mm wide just adjacent faston terminal 3. The tapering assists resistance to movement, while the wider part makes the winding process not quite so critical. If the redirecting means 12, 12A for wire portion 18 did not exist, the only way for wire 2 to exit tangentially would be to have two external peripheral grooves in the manner of GB-A-1 574 977 above mentioned. Then there would be no wire section 2 protected in an internal groove, and the wire sections in the external grooves would not be isolated for stresses from the main body of wire in the coil by the redirecting means 12, 12A. These means enable the wire length 14 to be tensioned in isolation, and the short, redirecting length 18 is protected particularly by the projection from handling or encapsulation stresses.

Claims: A coil and coil former of bobbin shape, comprising a cylindrical part on which is wound wire (1) of the coil; an end flange (4); an external circumferential groove (13) located in said end flange at an axial location thereof intermediate the outer (7) and inner (8) faces of the flange, and a notch (12) connecting the groove (13) in the flange with the coil space beyond the inner face (8) of the flange (4), characterized in that the groove (13) extends from the notch (12) to a point adjacent one terminal (6) of terminals (3,6) terminating the coil and carried by the flange (4), said groove contains a terminal end portion (14) of the main wire portion wound on the cylindrical portion of the former, wherein there is an intermediate substantially tangential wire portion (17) which exits the coil and is bent in substantially direction-reversing manner and in tension over the notch (12), and wherein a short exposed length (15) of the coil wire extends from said adjacent point to a point of attachment (16) at said terminal (6). A coil and coil former according to Claim 1 comprising a projection (12A) adjacent the notch. A coil and coil former according to Claim 1 or 2 in which the notch (12) and any projection (12A) extend through the thickness of the flange only from the inner surface (8) of said flange (4) as far as the groove (13) thereof. A coil and coil former according to Claim 1, 2 or 3 comprising a further groove extending from a peripheral point of the flange intermediate the two terminals (3,6) radially inward and to a point of communication with the inner surface (8) of the flange, and a slot-shaped depression (9) extending from the outer surface (7) of the flange into its thickness to depth of said further groove for access to the length of said further groove, which latter exits peripherally adjacent the other terminal (3). A coil and coil former according to Claim 4 wherein the further groove extends tangentially to a point generally at a cylindrical portion; and the notch (12) is located adjacent a point on the cylindrical portion, whereat retained wire would exit in one direction tangentially towards the notch, and would substantially reverse direction to follow the path of the first said groove. A coil and coil former according to Claim 4 or 5, characterized in that said coil former has said groove, which is located between the terminals (3,6), for protecting the other wire end (2) of the coil en route to a short exposed wire portion (11) and to an attachment at a point (10) of the other terminal (3).

Inventors: BUFFET ERIC, BUFFET, ERIC
Applicants: EATON SA MONACO, EATON S.A.M.
Application year: 1989
Main classification: H01F5
IPC codes: H01F5