Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2003-02-03
2004-08-31
Lam, Thanh (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
Reexamination Certificate
active
06784588
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to amorphous metal magnetic components, and more particularly, to a high efficiency electric motor having a generally polyhedrally shaped, low core loss, bulk amorphous metal magnetic component.
2. Description of the Prior Art
An electric motor typically contains magnetic components made from a plurality of stacked laminations of non-oriented electrical steel. In variable reluctance motors and eddy current motors, the stators are made from stacked laminations. Both the stator and the rotor are made from stacked laminations in squirrel cage motors, reluctance synchronous motors and switched reluctance motors. Each lamination is typically formed by stamping, punching or cutting the mechanically soft, non-oriented electrical steel into the desired shape. The formed laminations are then stacked and bound to form rotors or stators which have the desired geometry, along with sufficient mechanical integrity to maintain their configuration during production and operation of the motor.
The stator and the rotor in a machine are separated by small gaps that are either: (i) radial, i.e., generally perpendicular the axis of rotation of the rotor, or (ii) axial, i.e., generally parallel to the rotation axis and separated by some distance. In an electromagnetic machine, lines of magnetic flux link the rotor and stator by traversing the gaps. Electromagnetic machines thus may be broadly classified as radial or axial flux designs, respectively. The corresponding terms radial and axial gap designs are also used in the motor art. Radial flux machines are by far most common. The aforesaid punching and stacking methods are widely used for constructing rotors and stators for radial flux motors.
Although amorphous metals offer superior magnetic performance when compared to non-oriented electrical steels, they have long been considered unsuitable for use in bulk magnetic components such as the rotors and stators of electric motors due to certain physical properties and the ensuing impediments to fabrication. For example, amorphous metals are thinner and harder than non-oriented steel, and consequently cause fabrication tools and dies to wear more rapidly. The resulting increase in the tooling and manufacturing costs makes fabricating bulk amorphous metal magnetic components using such conventional techniques, such as punching and stamping, commercially impractical. The thinness of amorphous metals also translates into an increased number of laminations in the assembled components, further increasing the total cost of an amorphous metal rotor or stator magnet assembly.
Amorphous metal is typically supplied in a thin continuous ribbon having a uniform ribbon width. However, amorphous metal is a very hard material, making it very difficult to cut or form easily. Once annealed to achieve peak magnetic properties, amorphous metal ribbon becomes very brittle. This makes it difficult and expensive to use conventional approaches to construct a bulk amorphous metal magnetic component. The brittleness of amorphous metal ribbon may also cause concern for the durability of the bulk magnetic component in an application such as an electric motor.
Magnetic stators are subject to extremely high magnetic forces, which vary rapidly at the frequencies needed for high rotational speed. These magnetic forces are capable of placing considerable stresses on the stator material, and may damage an amorphous metal magnetic stator. Rotors are further subjected to mechanical forces due both to normal rotation and to rotational acceleration when the machine is energized or de-energized and when the loading changes, perhaps abruptly.
A limited number of non-conventional approaches have been proposed for constructing amorphous metal components. For example, U.S. Pat. No. 4,197,146 to Frischmann discloses a stator fabricated from molded and compacted amorphous metal flake. Although this method permits formation of complex stator shapes, the is structure contains numerous air gaps between the discrete flake particles of amorphous metal. Such a structure greatly increases the reluctance of the magnetic circuit and thus the electric current required to operate the motor.
The approach taught by German Patents DE 28 05 435 and DE 28 05 438 divides the stator into wound pieces and pole pieces. A non-magnetic material is inserted into the joints between the wound pieces and pole pieces, increasing the effective gap, and thus increasing the reluctance of the magnetic circuit and the electric current required to operate the motor. The layers of material that comprise the pole pieces are oriented with their planes perpendicular to the planes of the layers in the wound back iron pieces. This configuration further increases the reluctance of the stator, because contiguous layers of the wound pieces and of the pole pieces meet only at points, not along full line segments, at the joints between their respective faces. In addition, this approach teaches that the laminations in the wound pieces are attached to one another by welding. The use of heat intensive processes, such as welding, to attach amorphous metal laminations will recrystallize the amorphous metal at and around the joint. Even small sections of recrystallized amorphous metal will normally increase the magnetic losses in the stator to an unacceptable level.
Another difficulty associated with the use of ferromagnetic amorphous metals arises from the phenomenon of magnetostriction. Certain magnetic properties of any magnetostrictive material change in response to imposed mechanical stress. For example, the magnetic permeability of a component containing amorphous materials typically is reduced and the core losses increased when the component is subjected to stress. The degradation of soft magnetic properties of the amorphous metal device due to the magnetostriction phenomenon may be caused by stresses resulting from any combination of sources, including: (i) magnetic and mechanical forces during the operation of the electric motor; (ii) mechanical stresses resulting from mechanical clamping or otherwise fixing the bulk amorphous metal magnetic components in place; or (iii) internal stresses caused by the thermal expansion and/or expansion due to magnetic saturation of the amorphous metal material. As an amorphous metal magnetic stator is stressed, the efficiency at which it directs or focuses magnetic flux is reduced, resulting in higher magnetic losses, reduced efficiency, increased heat production, and reduced power. The extent of this degradation may be considerable depending upon the particular amorphous metal material and the actual intensity of the stresses, as indicated by U.S. Pat. No. 5,731,649. The degradation of core loss is often expressed as a destruction factor, i.e., a ratio of the core loss actually exhibited by a finished device and the inherent core loss of the constituent material tested under stress-free, laboratory conditions.
Moreover, amorphous metals have far lower anisotropy energies than other conventional soft magnetic materials, including common electrical steels. As a result, stress levels that would not have a deleterious effect on the magnetic properties of these conventional metals have a severe impact on magnetic properties important for motor components, e.g. permeability and core loss. For example, the '649 patent further discloses that forming amorphous metal cores by rolling amorphous metal into a coil, with lamination using an epoxy, detrimentally restricts the thermal and magnetic saturation expansion of the coil of material, resulting in Is high internal stresses and magnetostriction that reduces the efficiency of a motor or generator incorporating such a core. In order to avoid stress-induced degradation of magnetic properties, the '649 patent discloses a magnetic component comprising a plurality of stacked or coiled sections of amorphous metal carefully mounted or contained in a dielectric enclosure without the use of adhesive bonding.
A number of applicatio
DeCristofaro Nicholas J.
Fish Gordon E.
Kroger Carl E.
Lindquist Scott M.
Buff Ernest D.
Ernest D. Buff & Associates LLC
Fish Gordon E.
Lam Thanh
Metglas Inc.
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