Inductor devices – Core – Laminated type
Reexamination Certificate
2002-11-01
2004-05-18
Mai, Anh (Department: 2832)
Inductor devices
Core
Laminated type
C336S178000, C029S602100
Reexamination Certificate
active
06737951
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an inductive device, and more particularly, to a high efficiency, low core loss inductive device having a core assembled from a plurality of bulk amorphous metal magnetic components.
2. Description of the Prior Art
Inductive devices are essential components of a wide variety of modern electrical and electronic equipment, most commonly including transformers and inductors. Most of these devices employ a core comprising a soft ferromagnetic material and one or more electrical windings that encircle the core. Inductors generally employ a single winding with two terminals, and serve as filters and energy storage devices. Transformers generally have two or more windings. They transform voltages from one level to at least one other desired level, and electrically isolate different portions of an overall electric circuit. Inductive devices are available in widely varying sizes with correspondingly varying power capacities. Different types of inductive devices are optimized for operation at frequencies over a very wide range, from DC to GHz. Virtually every known type of soft magnetic material finds application in the construction of inductive devices. Selection of a particular soft magnetic material depends on the combination of properties needed, the availability of the material in a form that lends itself to efficient manufacture, and the volume and cost required to serve a given market. In general, a desirable soft ferromagnetic core material has high saturation induction B
sat
to minimize core size, and low coercivity H
c
, high magnetic permeability &mgr;, and low core loss to maximize efficiency.
Components such as motors and small to moderate size inductors and transformers for electrical and electronic devices often are constructed using laminations punched from various grades of magnetic steel supplied in sheets having thickness as low as 100 &mgr;m. The laminations arc generally stacked and secured and subsequently wound with the requisite one or more electrical windings that typically comprise high conductivity copper or aluminum wire. These laminations are commonly employed in cores with a variety of known shapes.
Many of the shapes used for inductors and transformers are assembled from constituent components which have the general form of certain block letters, such as “C,” “U,” “E,” and “I,”, by which the components are often identified. The assembled shape may further be denoted by the letters reflecting the constituent components; for example, an “E-I” shape would be made by assembling an “E” component with an “I” component. Other widely used assembled shapes include “E-E,” “C-I,” and “C-C.” Constituent components for prior art cores of these shapes have been constructed both of laminated sheets of conventional crystalline ferromagnetic metal and of machined bulk soft ferrite blocks.
Although many amorphous metals offer superior magnetic performance when compared to other common soft ferromagnetic materials, certain of their physical properties make conventional fabrication techniques difficult or impossible. Amorphous metal is typically supplied as a thin, continuous ribbon having a uniform ribbon width. However, amorphous metals are thinner and harder than virtually all conventional metallic soft magnetic alloys, so conventional stamping or punching of laminations causes excessive wear on fabrication tools and dies, leading to rapid failure. The resulting increase in the tooling and manufacturing costs makes fabricating bulk amorphous metal magnetic components using such conventional techniques commercially impractical. The thinness of amorphous metals also translates into an increased number of laminations needed to form a component with a given cross-section and thickness, further increasing the total cost of an amorphous metal magnetic component. Machining techniques used for shaping ferrite blocks are also not generally suited for processing amorphous metals.
The properties of amorphous metal are often optimized by an annealing treatment. However, the annealing generally renders the amorphous metal very brittle, further complicating conventional manufacturing processes. As a result of the aforementioned difficulties, techniques that are widely and readily used to form shaped laminations of silicon steel and other similar metallic sheet-form FeNi- and FeCo-based crystalline materials, have not been found suitable for manufacturing amorphous metal devices and components. Amorphous metals thus have not been accepted in the marketplace for many devices; this is so, notwithstanding the great potential for improvements in size, weight, and energy efficiency that in principle would be realized from the use of a high induction, low loss material.
For electronic applications such as saturable reactors and some chokes, amorphous metal has been employed in the form of spirally wound, round toroidal cores. Devices in this form are available commercially with diameters typically ranging from a few millimeters to a few centimeters and are commonly used in switch-mode power supplies providing up to several hundred volt-amperes (VA). This core configuration affords a completely closed magnetic circuit, with negligible demagnetizing factor. However, in order to achieve a desired energy storage capability, many inductors include a magnetic circuit with a discrete air gap. The presence of the gap results in a non-negligible demagnetizing factor and an associated shape anisotropy that are manifested in a sheared magnetization (B-H) loop. The shape anisotropy may be much higher than the possible induced magnetic anisotropy, increasing the energy storage capacity proportionately. Toroidal cores with discrete air gaps and conventional material have been proposed for such energy storage applications. However, the gapped toroidal geometry affords only minimal design flexibility. It is generally difficult or impossible for a device user to adjust the gap so as to select a desired degree of shearing and energy storage. In addition, the equipment needed to apply windings to a toroidal core is more complicated, expensive, and difficult to operate than comparable winding equipment for laminated cores. Oftentimes a core of toroidal geometry cannot be used in a high current application, because the heavy gage wire dictated by the rated current cannot be bent to the extent needed in the winding of a toroid. In addition, toroidal designs have only a single magnetic circuit. As a result, they are not well suited and are difficult to adapt for polyphase transformers and inductors, including especially common three-phase devices. Other configurations more amenable to easy manufacture and application are thus sought.
Moreover, the stresses inherent in a strip-wound toroidal core give rise to certain problems. The winding inherently places the outside surface of the strip in tension and the inside in compression. Additional stress is contributed by the linear tension needed to insure smooth winding. As a consequence of magnetostriction, a wound toroid typically exhibits magnetic properties that are inferior to those of the same strip measured in a flat strip configuration. Annealing in general is able to relieve only a portion of the stress, so only a part of the degradation is eliminated. In addition, gapping a wound toroid frequently causes additional problems. Any residual hoop stress in the wound structure is at least partially removed on gapping. In practice the net hoop stress is not predictable and may be either compressive or tensile. Therefore the actual gap tends to close or open in the respective cases by an unpredictable amount as required to establish a new stress equilibrium. Therefore, the final gap is generally different from the intended gap, absent corrective measures. Since the magnetic reluctance of the core is determined largely by the gap, the magnetic properties of finished cores are often difficult to reproduce on a consistent basis in the course of high-volume production.
Amorphous metals have a
Decristofaro Nicholas J.
Fish Gordon E.
Hasegawwa Ryusuke
Tatikola Seshu V.
Buff Ernest D.
Ernest D. Buff and Associates, LLC
Fish Gordon E.
Mai Anh
Metglas Inc.
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