Magnetic Core Apparatus and Method of Constructing the Same

This invention relates to magnetic components and in particular to a particular magnetic core construction and a method for assembling magnetic cores from separate core components and to the magnetic apparatus resulting therefrom.

Magnetic cores for inductors and transformers are often constructed from two core components which are abutted together to form the desired unitary magnetic structure having a closed flux path. The two core components are normally secured together with a mechanical clamp that grips the two components together in the desired manner. In a conventional construction utilizing two "E" configured cores; the ends of the core protuberances are held in abutting relationship with each other by securing them together with a metallic frame and a spring-biased clip apparatus. An alternative method of securing the two core components together utilizes glue in the gap where the two components abut together. This second method may be supplementary to the first method described and both methods may be used in one construction. It has been found that magnetic cores made by the first method of construction are susceptible to vibration damage which may alter a critical air gap dimension and in addition it is a relatively costly construction method. Furthermore, the metallic frame and clip may provide spurious flux paths and degrade the core's magnetic performance. The use of glue has also been found to be unsatisfactory because it is dimensionally unstable during construction and stresses adjacent laminations and alters the air gap dimension.

A technique fo assembling a transformer core from two separate core components uses a thermo shrinkable elastomer band or tubing in place of the more conventional glues and metallic clips to secure the components into a unitary structure. In a particular embodiment of the invention a thermo shrinkable mylar plastic tubing is placed around a periphery of a core formed by abutting two separate "E" configured core components together so as to form a closed magnetic path. Application of heat shrinks and thermosets the tubing and secures the two separate core components into one unitary core structure.

An understanding of the invention may be readily attained by reference to the following specification and the accompanying drawing in which:

FIGS. 1 and 2 are plan and elevation views of a prior art transformer construction whose two core components are secured together by a bracket and a clamp;

FIGS. 3 and 4 are plan and elevation views of another prior art transformer construction whose two core components are secured together by two spring clamps.

FIGS. 5 and 6 are plan and elevation views of a transformer construction embodying the principles of the invention wherein the two core components are secured together by a thermosetting elastomer tubing; and

FIG. 7 is a perspective view of a technique by which the magnetic core apparatus is assembled.

A conventional transformer construction of the prior art is shown in plan and elevation views in FIGS. 1 and 2, respectively. A power transformer 10 is shown constructed with first and second "E" shaped individual core components 12 and 14, respectively. The first core 12 has a lower yoke portion 15 and three legs 16, 17, and 18; the second core 14 includes a yoke portion 19 and three legs 20, 21, and 22. The ends of legs 16, 17, and 18 are abutted against the ends of legs 20, 21, and 22 to form the closed flux paths of the transformer core. The abutting ends of each of the juxtaposed legs are normally opposing magnetic poles and the resulting magnetic attraction helps to secure the proper abutment of the two core components 12 and 14.

To maintain the proper abutment and secure a continuous solid core assembly, a bracket and an associated clamp are used to positively secure the two core sections 12 and 14 together. A three sided frame, 24, is fitted about one side of the yoke 15 of the assembled core and along the sides comprising the abutting legs 16-20 and 18-22, respectively. A U shaped spring clamp 25 is positioned along the yoke 19 to engage the free ends of the frame and secure it into place and thereby hold the two core components 12 and 14 together and in place to form the completed transformer core. The pins 27, shown in FIG. 2 are utilized for connection with corresponding receptacles of a circuit board. The windings 28 are wound on a bobbin, 26, whose end view is shown in FIG. 2.

Another conventional prior art transformer construction is shown in plan and elevation views in FIGS. 3 and 4, respectively. In the thinner surface mount transformer 30 shown, two "E" shaped cores 32 and 33, are held together by two U shaped spring clamps 34 and 35 each of which contact and supply force to the end yokes of the two core components in order to force the opposing legs of the two core components 32 and 33 together.

In some instances the gap between the abutting legs of the two core components of both the aforementioned contacts may be glue filled to provide adhesion and control the gap between the two.

The aforementioned construction methods in some instances may adversely affect the magnetic performance of the transformer core. The metallic frame and clips being in pressure contact with the core may adversely affect the flux path and the flux distribution of the flux conducted by the transformer core. The glue used in the airgap tends to be dimensionally unstable when subjected to thermal stress and may forcefully alter the airgap width and/or defect the laminations of the cores at the airgap.

A transformer core construction embodying the principles of the invention is shown in plan and elevation views in FIGS. 5 and 6, respectively. The transformer 110 shown is similar in form and function to the transformer in FIGS. 1 through 4, except the two core components 112 and 114 are secured together by an elastomer holder 140 in place of the aforedescribed metallic frame, spring clip, and glue.

The elastomer holder 140 is a continuous tubing that fits initially loosely around the perimeter of the transformer core formed by abutment of the two core components 112 and 114. The elastomer is made of a non-metallic thermo setting elastic material. The tubing 140 is initially stretched and of sufficient width to fully cover the width of the stacked laminations of the core and the top surface of the top lamination to edge 141, and is of sufficient diameter to readily surround the perimeter of the core formed by the abutting core components. A suitable elastomer material for example is stretched mylar plastic. The tubing in its stretched condition is placed around the perimeter of the two abutted core components 112 and 114 and heat from a hot airgun is applied uniformly and repeatedly about the surface of the elastomer to cause it to shrink about the core and as shown hold the two core components 112 and 114 into a secure abutting arrangement. This technique of securing the two core components 112 and 114 together does not require application of glue or provide spurious flux paths and it provides a strong uniform compressive force at the abutting surfaces of the two core component 112 and 114. It also advantageously provides a shield for the core from dirt and contaminating elements.

The technique of construction may be readily appreciated from the perspective view shown in FIG. 7 of two abutting core components 112 and 114 positioned to receive a stretched elastomer tubing 140 positioned to be placed around the periphery at the core. Hot airguns 150 are positioned to heat the tubing thereby causing it to thermally shrink and secure the two core components together. In order to heat the tubing uniformly, the core may be rotated or a plurality of airguns may be positioned around the core.