WO1987004559A1

WO1987004559A1 - Method of manufacturing toroidal coils

Info

Publication number: WO1987004559A1
Application number: PCT/US1987/000103
Authority: WO
Inventors: Theodore Wroblewski
Original assignee: American Light Corporation
Priority date: 1986-01-15
Filing date: 1987-01-15
Publication date: 1987-07-30

Abstract

Wire (10) is wound around a mandrel (14) until a desired number of turns have been wound. The mandrel (14) is then removed, and the resultant coil (16) is slipped over the end of a C-shaped core (18) having a relatively large gap (20). The core (18) is then bent to reduce the size of the gap (20). Preferably, the core is made in layers (24, 26, and 28) to facilitate bending of the core.

Description

METHDD OF MAMFACTURI G TOROIDAL COILS

Background of the Invention

The present invention is directed to the manufacture of coils such as those in inductors and transformers. It relates particularly to the manufacture of toroidal coils having ferromagnetic cores.

Complicated methods and apparatus have been proposed in the past for winding coils around C-shaped cores. The complexity arises principally from the fact that the wire is typically drawn from a spool, and it is difficult to avoid having to pass the spool through the "doughnut hole" of the core. Therefore, relatively elaborate mechanisms must be provided to pass the spool through the hole, and the spool used must be small enough to fit through the hole. A spool that small sometimes does not hold enough wire to wind the entire coil, so the spool must be replaced and the wire spliced during the operation.

The object of the present invention is to simplify the manufacture of toroidal coils having ferromagnetic cores.

Summary of the Invention

The foregoing and related objects are achieved in a method that includes winding the coil wire around a mandrel and then removing the mandrel to leave a coil that can be bent into a generally toroidal shape. A C- shaped ferromagnetic core is provided with a gap large enough to permit the wire at the end of the coil to fit into the gap so that the end of the core can be inserted into the end of the coil. The coil is then slipped over the core in a manner similar to that in which a sock is slipped over a foot. The core is preferably deformable so that it can be bent to reduce the size of the core gap after the coil has been slipped over it.

By employing this method, it is possible to manufacture a toroidal core without having to pass a spool through a core aperture.

Brief Description of the Drawings

These and further features and advantages of the present invention are described in connection with the accompanying drawings, in which:

FIG. 1 is a diagrammatic illustration of coil wire being wound around a mandrel;

FIG. 2 is a plan view of the coil and the core showing the core being slipped into the coil; FIG. 3 is a plan view of the core after it has been bent to reduce the size of its gap;

FIG. 4 is a detailed plan view of the ends of the core before it has been bent; and

FIG. 5 is a detailed plan view of the ends of the core after it has been bent.

Detailed Description of the Preferred Embodiment

FIG. 1 shows coil wire being unwound from a spool 12 that is large enough to contain all of the wire needed to wind a coil of the desired size. It is wound onto a rotating mandrel 14 to which a strip 16 of adhesive tape is removably attached. The adhesive side of the tape faces outward so that it adheres to the forming coil. When enough windings have been wound onto the mandrel 14, the mandrel is removed from the interior of the resulting coil, and the tape holds the wire in a wound form.

For some types of wire, the tape may be unnecessary. For other types, it may be preferable to make the tape 16 long enough to extend around the outside of the coil so that it sticks to both the inside and the outside. Additionally, more than one strip of tape may be used if desired.

With the mandrel 14 removed, the wire 10 forms a coil 16, as FIG. 2 shows, that is ready to be placed on a C-shaped ferromagnetic core 18. The core 18, for reasons that will become clear presently, should be deformable. The gap 20 in the core is relatively large so that the wire at the end of the coil 16 can fit into the gap 20 and the end of the core 18 can be fit into the open end of the coil 16. The coil 16 is then slipped onto the core 18 in a manner similar to that in which a sock is slipped onto a foot, and a toroidal core like that shown in FIG. 3 results. It may be advantageous to provide a strap 22 around the outside of the core 18 before the coil is slipped on, as FIG. 2 shows, so that the ends of the strap can be pulled together and twisted to bend the core and thereby reduce the gap. The twisted strap can also serve to hold the core in its reduced-gap shape if the core is made of resilient material.

Although the last step in the process has been described as "bending" the core into the desire shape, the final shape of the core can be its rest shape, and the shape shown in FIG. 2 can be the result of applying force to the core to keep it spread while the coil is being slipped onto it. The "bending" would then be the relaxation of the core.

To facilitate the bending of the core, it can be provided as a group of thin concentric arcuate layers that are separate so that they can slide longitudinally with respect to each other. FIGS. 4 and 5 show the ends of such a core in detail as they look before and after bending to reduce the size of the gap 20. The core is shown for the sake of simplicity as being formed of only three layers 24, 26, and 28. FIGS. 4 and 5 show that the ends of the layers are staggered with respect to each other before bending but are lined up after bending. This reflects the fact that the relative lengths of the layers have not been changed by the bending. If the layers were secured together so as to prevent relative longitudinal motion, the ends would be lined up both before and after bending, so the relative lengths of the layers would change. It would thus be necessary to apply significantly more compressive and tensile stress to the inner and outer layers 28 and 24 in order to bend the core 18. Of course, this would make bending the core more difficult. Providing the core 18 in layers may therefore be beneficial in certain manufacturing situations.

This method has been used to produce a toroidal inductor having 2600 turns of-^** No. 31 magnet wire and a core consisting of six layers of 0.025-inch-thick electrical-grade steel 0.75 inches wide. The layers were concentrically arranged so that the diameter of the outer layer was 1.813 inches.

It is apparent that the method of the present invention significantly reduces the complexity that formerly attended the manufacture of toroidal coils with ferromagnetic cores. This method thus constitutes a significant advance in the art.

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

Claims

1. A method of manufacturing a toroidal coil with a ferromagnetic core comprising the steps of: A. winding a length of wire around a mandrel to make a coil of wire with first and second open ends through which the mandrel extends; B. removing the mandrel from the coil to leave a central void extending between the open ends so that the coil can be flexed to form the coil in the shape of a C; C. providing a C-shaped ferromagnetic core with a gap between its ends; D. inserting one end of the C-shaped ferromagnetic core into one open end of the coil and slipping the coil over the core so that the coil is wrapped around the C-shaped core.

2. A method as defined in claim 2 further including the step of bending the core, after the coil has been slipped onto it, to reduce size of the gap.

3. A method as defined in claim 3 wherein: A. the method further includes the step of providing a strap extending longitu inally along the periphery of the core; B. the step of slipping the coil over the core includes simultaneously slipping it over the strap so that the ends of the strap extend out of the open ends of the coil; and C. the step of bending the core includes drawing on the ends of the strap to bend the core and reduce the core gap.

4. A method as defined in claim 2 wherein the step of providing the core comprises providing a plurality of separate concentric arcuate core layers that can move longitudinally with respect to each other to facilitate core bending.