The present invention relates to the field of inductive devices, and more particularly to wire core inductive devices such as transformers, chokes, coils, ballasts, and the like.
It is common and universal for low frequency application transformers and other inductive devices to be made up of a magnetic core comprising a plurality of sheets of steel, the sheets being die cut and stacked to create the desired thickness of a core. For many years the thickness (thus number of necessary pieces) of the stampings has been determined by a strict set of constraints-magnitude of eddy currents versus number of necessary pieces. For that reason, individual sheets of selected thickness are oxide-coated, varnished or otherwise electrically insulated from one another in order to reduce/minimize eddy currents in the magnetic core.
The magnetic core of a transformer or the like generally passes through the center of the electric winding, and closes on itself to provide a closed magnetic circuit. Since the magnetic core then supports the electric windings, it is natural that the core has also been used as the support for the transformer. That is to say, one attaches the magnetic core to a container or baseboard in order to support the transformer.
Transformers and other inductive devices inherently generate heat, and the heat must be dissipated or the power characteristics of the device will change. If the transformer or other device becomes too hot, the electric windings can become short circuited and burn out. In small devices, one usually relies on air cooling, sometimes with metal fins/heat sinks or the like to assist in dissipating the heat. In large devices, the windings and magnetic core may be cooled by forced air or immersed in an oil or other fluid. One then may use fins on the container, radiator pipes, or both, so convection currents move the heated fluid through the cooling fins or pipes. If further cooling is needed, one generally resorts to pumps to force fluid movement and/or fans to move more air across the cooling means.
When a stack of metal sheets is used as the magnetic core for an inductive device, it is usual to provide a shape, such as an E with the electric windings on the center leg of the E. After the windings are in place, an additional stack of sheets usually in an I configuration is applied to connect the ends of the E, thereby completing the magnetic circuit. Using such a technique, it will be understood that the windings are necessarily wound separately, and subsequently placed on the magnetic core. The windings must therefore be large enough to slip onto the magnetic core. Such construction contributes to the inherent noisiness of an inductive device, because the electric windings must be somewhat loose on the core. As a result, when an alternating voltage is applied to the electric windings, the sheets making up the core tend to vibrate with the alternating magnetic field or in sympathy in a subharmonic. Any resulting gaps and spaces between the electrical components and the magnetic components also reduce coupling and efficiency of action.
Transformers and other inductive devices also inherently generate electromagnetic fields. Such fields external to the device lessen efficiency, as well as pose interferences to the immediately surrounding environment. Although the strength of these electromagnetic fields decreases with distance from the transformer, shielding of either the electromagnetic field source or the affected components is often required. As components in today""s electronics are made more sensitive and their packaging more dense, susceptibility to electromagnetic interaction increases dramatically. To assure optimum performance of these components, stray electromagnetic fields must be minimized often at a substantial cost. As noted above, one manner in which these fields may be minimized is to provide shielding around the source in order to contain the electromagnetic fields and to prevent interference from external sources.
Accordingly, it is a primary object of the present invention to provide a method and apparatus for overcoming the limitations of the prior art, and to provide an improved inductive device having a magnetic core formed from a plurality of wires.
Another object of the present invention is to provide an inductive device by extending wires forming the magnetic core around the electric windings and the magnetic core to substantially contain electromagnetic fields emanating from the device.
It is another object of the present invention to provide a method of making an inductive device utilizing a plurality of wires to form the magnetic core and to provide shielding.
Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, there is provided an improved inductive device, the magnetic core comprising a plurality of wires bundled to form the core. The electric windings are either wound directly onto the magnetic core, or are wound separately and slipped over the core.
In accordance with an important aspect of the present invention, the ends of the wires forming the magnetic core are spread and formed over the electric windings, the two ends of the wires meeting to form a complete magnetic circuit. A band or other connector means holds the ends of the wires together. Advantageously, the wires formed in this manner envelop the electric windings and magnetic core to provide a shield substantially containing the electromagnetic fields emanating from the device and reducing the intrusion of electromagnetic fields from external sources. Additional shielding may be provided by binding at least a portion of the wires forming the shield with a transversely wound wire.
The inductive device may include a mounting post bound within the plurality of wires forming the magnetic core and extending therefrom for supportably mounting the device. The mounting post may extend from either side or both sides of the magnetic core as desired. Also, the make-up of the magnetic core may be otherwise varied considerably. Wire of various diameters may be used to achieve greater density of the core; a few large wires may be spaced around the core to provide rigidity; and, one or more tubes may be incorporated into the core, the tubes carrying a fluid for cooling the inductive device. The cooling tubes are preferably constructed of non-magnetic and non-electrical-conducting material.
In carrying out the inventive method, the step of forming the magnetic core includes forming a magnetic core from a plurality of wires, placing at least one electric winding along the length of the formed core, and forming the wires of the magnetic core over the at least one electric winding to envelop the winding and form a complete magnetic circuit.
Still other objects of the present invention will become apparent to those skilled in this art from the following description wherein there is shown and described the preferred embodiments of this invention, simply by way of illustration of some of the modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.