Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-03-01
2003-09-09
Lam, Thanh (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S254100, C310S06700R, C310S044000, C029S596000
Reexamination Certificate
active
06617740
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
Investigators in the electric motor arts have been called upon to significantly expand motor technology from its somewhat static status of many decades. Improved motor performance particularly has been called for in such technical venues as computer design and secondary motorized systems carried by vehicles, for example, in the automotive and aircraft fields. With progress in these fields, classically designed electric motors, for example, utilizing brush-based commutation, have been found to be unacceptable or, at best, marginal performers.
From the time of its early formation, the computer industry has employed brushless d.c. motors for its magnetic memory systems. The electric motors initially utilized for these drives were relatively expensive and incorporated a variety of refinements particularly necessitated with the introduction of rotating disc memory. For example, detent torque phenomena has been the subject of correction. The phenomena occurs as a consequence of the nature of motors configured with steel core stator poles and associated field windings performing in conjunction with permanent magnets. With such component combinations, without correction, during an excitation state of the motor windings which create motor drive, this detent torque will be additively and subtractively superimposed upon the operational characteristics of the motor output to distort the energized torque curve, increase ripple torque, reduce the minimum torque available for starting and, possibly develop instantaneous speed variations. Such instantaneous speed variations generally have not been correctable by electronics. Particularly over the recent past, the computer industry has called for very low profile motors capable of performing in conjunction with very small disc systems and at substantially elevated speeds.
Petersen, in U.S. Pat. No. 4,745,345, entitled “D.C. Motor with Axially Disposed Working Flux Gap”, issued May 17, 1988, describes a PM d.c. motor of a brushless variety employing a rotor-stator pole architecture wherein the working flux gap is disposed “axially” wherein the transfer of flux is parallel with the axis of rotation of the motor. This “axial” architecture further employs the use of field windings which are simply structured, being supported from stator pole core members, which, in turn, are mounted upon a magnetically permeable base. The windings positioned over the stator pole core members advantageously may be developed upon simple bobbins insertable over the upstanding pole core members. Such axial type motors have exhibited excellent dynamic performance and efficiency and, ideally, may be designed to assume very small and desirably variable configurations.
Petersen in U.S. Pat. No. 4,949,000, entitled “D.C. Motor”, issued Aug. 14, 1990 describes a d.c. motor for computer applications with an axial magnetic architecture wherein the axial forces which are induced by the permanent magnet based rotor are substantially eliminated through the employment of axially polarized rotor magnets in a shear form of flux transfer relationship with the steel core components of the stator poles. The dynamic tangentially directed vector force output (torque) of the resultant motor is highly regular or smooth lending such motor designs to numerous high level technological applications such as computer disc drives which require both design flexibility, volumetric efficiency, low audible noise, and a very smooth torque output.
Petersen et al, in U.S. Pat. No. 4,837,474 entitled “D.C. Motor”, issued Jun. 6, 1989, describes a brushless PM d.c. motor in which the permanent magnets thereof are provided as arcuate segments which rotate about a circular locus of core component defining pole assemblies. The paired permanent magnets are magnetized in a radial polar sense and interact without back iron in radial fashion with three core components of each pole assembly which include a centrally disposed core component extending within a channel between the magnet pairs and to adjacently inwardly and outwardly disposed core components also interacting with the permanent magnet radially disposed surface. With the arrangement, localized rotor balancing is achieved and, additionally, discrete or localized magnetic circuits are developed with respect to the association of each permanent magnet pair with the pole assembly.
Petersen in U.S. Pat. No. 5,659,217, issued Feb. 10, 1995 and entitled “Permanent Magnet D.C. Motor Having Radially-Disposed Working Flux-Gap” describes a PM d.c. brushless motor having outstanding performance characteristics which is producible at practical cost levels commensurate with the incorporation of the motors into products intended for the consumer marketplace. These motors exhibit a highly desirable heat dissipation characteristic and provide improved torque output in consequence of a relatively high ratio of the radius from the motor axis to its working gap with respect to the corresponding radius to the motors' outer periphery. The torque performance is achieved with the design even though lower cost or, lower energy product permanent magnets may be employed with the motors. See also: Petersen, U.S. Pat. No. 5,874,796, issued Feb. 23, 1999.
Over the years of development of what may be referred to as the Petersen motor technology, greatly improved motor design flexibility has been realized. Designers of a broad variety of motor driven products including household implements and appliances, tools, pumps, fans and the like as well as more complex systems such as disc drives now are afforded a greatly expanded configuration flexibility utilizing the new brushless motor systems. No longer are such designers limited to the essentially “off-the-shelf” motor variety as listed in the catalogues of motor manufacturers. Now, motor designs may become components of and compliment the product itself in an expanded system design approach.
During the recent past, considerable interest has been manifested by motor designers in the utilization of processed ferromagnetic particles in conjunction with pressed powder technology as a substitute for the conventional laminar steel core components of motors. With this technology, the fine particles which are pressed together essentially are mutually electrically insulated. So structured, when utilized as a motor core component, the product will exhibit very low eddy current loss which will represent a highly desirable feature, particularly as higher motor speeds and resultant core switching speeds are called for. As a further advantage, for example, in the control of cost, the pressed powder assemblies may be net shaped wherein many intermediate manufacturing steps and quality considerations are avoided. Also, tooling costs associated with this pressed powder fabrication are substantially low as compared with the corresponding tooling required with typical laminated steel fabrication. The desirable molding approach provides a resultant magnetic particle structure that is 3-dimensional magnetically and avoids the difficulties encountered in the somewhat two-dimensional magnetic structure world of laminations. See generally U.S. Pat. No. 5,874,796 (supra).
The high promise of such pressed power components, however, currently is compromised by the unfortunate characteristic of the material in exhibiting relatively low permeability as contrasted at least with conventional laminar core systems. Thus the low permeability has called for 1½ to 2 times as many ampere turn deriving windings. In order to simultaneously achieve acceptable field winding resistance values, the thickness of the winding wire must be increased such that the wire gauge now calls for bulksome structures which, in turn, limit design flexibility. Indeed, designers confronting the permeability values available with processed ferromagnetic particle technology will, as a first inclination, return to laminar structures. This is particularly true where control over the size of
Lam Thanh
Mueller and Smith LPA
Petersen Technology Corporation
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