Patent Publication Number: US-2006006754-A1

Title: D.C. brushless motor

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention pertains to rotors for electric motors. It specifically pertains to permanent magnet rotors formed by dynamic magnetic compaction for brushless dc motors.  
      2. Description of Related Art  
      Generally, a brushless dc motor has a rotor comprised of a shaft, a magnetic return path and a permanent magnet. A brushless dc motor also has a stator comprised of electrical windings (usually insulated copper windings) that are wound on or embedded into a core material such that once the windings are energized, a magnetic field is formed that interacts with the magnetic field of the permanent magnet of the rotor in a manner such that torque and subsequent rotation is produced in the rotor. In some instances, the permanent magnet of the rotor may be a ring of magnetic material that encompasses a core material with the core material surrounding the shaft of the rotor. Permanent magnet rotors of this type are generally formed by producing a cylindrical core ring and a cylindrical, hollow permanent magnet ring wherein the inside diameter of the magnetic ring is just slightly larger than the outer diameter of the core material. The magnetic ring is placed over the core and affixed, and the core is placed over and affixed to a shaft.  
      Various electrical components such as rotors and stators have been formed using dynamic magnetic compaction (DMC). Dynamic magnetic compaction generally involves metallic powders that are placed into a conductive container. The conductive container is then placed within an electrical coil or otherwise exposed to a magnetic field that is created by an electrical current passing through a conductor. A large current is pulsed through the electrical coil thus creating a very strong magnetic field. This magnetic field will collapse the conductive container and compact the metallic powders into a solid object. U.S. Pat. Nos. 5,405,574; 5,611,139; 5,611,230; 5,689,797; 6,273,963 and 6,432,554 (all assigned to LAP Research, Inc.), each fully incorporated herein and made a part hereof, disclose methods of dynamic magnetic compaction and are related to the formation of electrical components. DMC allows the formation of components of various shapes. DMC also reduces production time as electrical windings may be incorporated into a component during the formation process. Furthermore, DMC produced components may have magnetic flux densities greater than that of components produced by other means because of the ability of the DMC process to compact the material to nearly full density.  
      For example, U.S. Pat. No. 5,405,574, “Method for Compaction of Powder-Like Materials,” was issued to Chelluri et al. on Apr. 11, 1995 from an application filed on Feb. 10, 1992 and is assigned to IAP Research, Inc. This patent is generally directed toward the DMC process and describes methods of producing a wire-like electrically conductive body comprising dense highly compacted particulate material, methods of producing an electrically conductive member, and methods of producing highly dense body superconductive materials.  
      U.S. Pat. No. 5,611,139, “Structure and Method for Compaction of Powder-Like Material,” issued to Chelluri et al. on Mar. 18, 1997 from an application filed on Apr. 6, 1995 as a continuation-in-part of an application filed Feb. 10, 1992 that issued as U.S. Pat. No. 5,405,574. This patent is assigned to IAP Research, Inc. It is directed toward structures and devices that utilize dynamic magnetic compaction of powdered material to form high-density bodies of varying shapes and sizes such as rods, tapes, tubes, plates, wheels, etc.  
      U.S. Pat. No. 5,611,230, “Structure and Method for Compaction of Powder-Like Material,” issued to Chelluri et al. on Mar. 18, 1997 from an application filed on Jan. 3, 1995 as a division of an application filed Feb. 10, 1992 that issued as U.S. Pat. No. 5,405,574. This patent is assigned to LAP Research, Inc. This patent is generally directed toward the DMC process and again describes a system for producing a body of dense highly compacted particulate material.  
      U.S. Pat. No. 5,689,797, “Structure and Method for Compaction of Powder-Like Materials,” issued on Nov. 18, 1997 to Chelluri et al. from an application filed Apr. 6, 1995 as a continuation-in-part of an application filed Feb. 10, 1992 that issued as U.S. Pat. No. 5,405,574. This patent is assigned to IAP Research, Inc. This patent is also generally directed toward DMC and producing bodies, including annular bodies, from powdered materials through DMC.  
      U.S. Pat. No. 6,273,963, “Structure and Method for Compaction of Powder-Like Materials,” issued on Aug. 14, 2001 to Barber from an application filed on Jul. 29, 1996 as a continuation-in-part of an application filed on Jan. 3, 1995, now U.S. Pat. No. 5,611,230. A divisional application claiming priority upon this patent has also been filed and was published on Dec. 13, 2001 as U.S. Patent Application Publication No. 2001/0051104. Both the patent and the published application are assigned to IAP Research, Inc. The patent and the published application disclose “over-pressuring” a powdered material through DMC to densify the material to over 90 percent of its maximum density.  
      U.S. Pat. No. 6,156,264, “Electromagnetic Compacting of Powder Metal for Ignition Core Application,” issued to Johnston et al. on Dec. 5, 2000 from an application filed on Oct. 6, 1999. It is assigned to Delphi Technologies, Inc. and is fully incorporated herein and made a part hereof. The patent generally discloses a process for producing a cylindrical electromagnetic core by exposing powdered metals to an electromagnetic field. Among the parts fabricated according to this patent are AC cylindrical electromagnetic parts, such as AC cylindrical electromagnetic ignition coil cores.  
      U.S. Pat. No. 6,432,554, “Apparatus and Method for Making an Electrical Component,” issued to Barber et al. on Aug. 13, 2002 from an application filed on Feb. 15, 2000 as a continuation-in-part of an application filed on Jul. 29, 1996, now issued as U.S. Pat. No. 6,273,963. A continuation application has also been filed that was published on Aug. 12, 2002 as U.S. Patent Application Publication No. 2002/0192103. The patent and published application are assigned to LAP Research, Inc. This patent and published application disclose systems and methods wherein powdered materials are placed in a conductive container along with an electrically insulated coil and subjected to DMC to produce a component part, such as a transformer, choke, rotor or stator for an electric motor and the like, with an embedded electrically insulated coil.  
      U.S. Pat. No. 6,232,681, “Electromagnetic Device with Embedded Windings and Method for its Manufacture,” issued on May 15, 2001 to Johnston et al. from an application filed on Mar. 23, 2000. A divisional application claiming priority upon this patent has also been filed and was published on Jan. 17, 2002 as U.S. Patent Application Publication No. 2002/0005675. The patent and published application are assigned to Delco Remy International, Inc. The patent is incorporated herein and made a part hereof. The patent and published application disclose a stator core with embedded stator windings manufactured using DMC with radial compaction techniques. The patent and published application also describes a method of fabricating an electromagnetic device, such as a stator, with embedded windings.  
      U.S. Pat. No. 6,362,544, “Electromagnetic Device with Embedded Windings and Method for Manufacture,” issued to Johnston et al. on Mar. 26, 2002 from an application filed on Apr. 30, 2001 as a continuation of an application filed on Mar. 23, 2002, now issued as U.S. Pat. No. 6,232,681. It is assigned to Delco Remy International, Inc. and is fully incorporated herein and made a part hereof. It describes a cylindrical electromagnetic device with embedded insulated windings comprised of radially compacted powdered magnetic materials.  
      Other prior art references related to DMC include United States Patent Application Publication No. 2002/0036367, “Method for Producing &amp; Manufacturing Density Enhanced, DMC, Bonded Permanent Magnets,” filed by Walmer et al. on Feb. 13, 2001 as a non-provisional application of a provisional application filed on Feb. 22, 2000. In addition, United States Patent Application Publication No. 2002/0043301, “Density Enhanced DMC, Bonded Permanent Magnets,” filed by Walmer et al. on Feb. 13, 2001 as a non-provisional application of a provisional application filed on Feb. 22, 2000. Both applications were published on Apr. 18, 2002. Each application discloses a DMC method for producing stable, denser, bonded permanent magnets where the binder is inorganic or organic with up to about a 40 percent increase in magnetic saturation performance over magnets formed by traditional methods.  
      United States Patent Application Publication No. 2002/0117907, “Electromagnetic Pressing of Powder Iron for Stator Core Applications,” filed Feb. 27, 2001 by Gay et al. It was published on Aug. 29, 2002. It discloses a stator core for an electric motor made of compacted powder material with each particle electrically insulated from one another. For example, the published application describes a stator core to have a density of 98 percent of its theoretical density. The published application also describes methods of manufacturing such a stator core.  
      As shown above, many electromagnetic devices formed by DMC and methods of forming such devices through DMC are disclosed in the prior art. Specifically, most of the prior art discloses the use of DMC to form electromagnetic parts containing embedded insulated windings such as stators, rotors (not dc brushless motor rotors), inductors and transformers. The prior art referenced above disclose stators or rotors with embedded electrically insulated windings or shapes formed of magnetic material through the DMC process; however, what is needed is a rotor for a brushless dc motor formed by dynamic magnetic compaction techniques.  
     BRIEF SUMMARY OF THE INVENTION  
      Therefore, the permanent magnet rotor of the present invention may be used in a brushless dc motor and is formed by DMC, but does not include embedded windings for use in a brushless dc motor. Furthermore, an efficient manufacturing process is disclosed for producing the DMC rotor by forming the core of the rotor by either compacting the powdered core material directly onto the non-insulated shaft of the rotor and then compacting the powdered permanent magnet material onto the core material, or simultaneously compacting the powdered core and permanent magnet material onto the non-insulated shaft rather than separately manufacturing the components and then assembling them onto a shaft. The powdered material that forms the rotor is compacted in such a way as to engage or be affixed to the embedded member (shaft), as contrasted to conventional techniques such as those described in U.S. Pat. Nos. 6,432,554 and 6,273,963, that require special procedures to be taken in order to protect the embedded windings from the compacted metallic material during the compaction process. U.S. Pat. No. 6,432,554 discloses a rotor formed through DMC; however it fails to disclose a rotor formed through the compaction of a powdered permanent magnet material to form a permanent magnet simultaneously with a soft iron powdered core material to form a core, together forming a rotor. Therefore, one aspect of the present invention is a rotor for a dc brushless motor formed through DMC techniques. Another aspect of the present invention is methods of forming such rotor by either simultaneously compacting the permanent magnet material and the powdered core onto a non-insulated shaft, or compacting the core material onto the shaft and then compacting the permanent magnet material onto the core material.  
      The permanent magnet of the present invention is a ring magnet that substantially overlays the core material in a radially outward direction from the core material. The core is attached to the rotor&#39;s shaft along a portion of the axial length of the shaft and extends radially outward from the shaft. By utilizing DMC to simultaneously compact onto a shaft more than one type of metallic powder material to form the permanent ring magnet and the core for the rotor or forming the rotor by compacting the core material onto the shaft and then compacting the permanent magnet material onto the core material or by using DMC to compact the permanent magnet material onto a core that is about the shaft, the fabrication process is facilitated. Furthermore, the shaft of the rotor is a non-insulated member as contrasted to the insulated embedded windings of conventional designs, merely simplifying the fabrication process.  
      Embodiments of the present invention utilize materials such as isotropic neodymium powder, anisotropic neodymium and exchange spring nano-powder neodymium, as well as others, in forming the permanent magnet. The core is generally formed of soft iron powders. Rotors formed through magnetic compaction techniques generally have a higher flux density than rotors formed through traditional manufacturing techniques.  
      Various embodiments of this invention include methods and systems for: Simultaneous compaction of permanent magnet and core powdered materials onto a non-insulated member (shaft) to form a rotor for an electric motor; forming a rotor for an electric motor by first compacting a powdered core material onto a non-insulated member and then compacting a powdered permanent magnet material onto the core; and forming a rotor by compacting permanent magnet material onto a non-insulated member.  
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
      Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:  
       FIG. 1A  is an exploded view of an exemplary dc brushless electric motor with a DMC rotor and a wound laminated stator in an embodiment of the invention;  
       FIG. 1B  is an exploded view of an exemplary dc brushless electric motor with a DMC rotor and a DMC produced stator in an embodiment of the invention;  
       FIG. 2A  is an exemplary cross-sectional illustration of a permanent magnet rotor with a magnetic core formed by DMC in an embodiment of the invention;  
       FIG. 2B  is an exemplary cross-sectional illustration of a permanent magnet rotor without a magnetic core formed by DMC in an embodiment of the invention;  
       FIG. 3A  is an exemplary cross-sectional view of an apparatus for forming the permanent magnet rotor of the present invention by DMC by compacting a powdered permanent magnet material substantially about a magnetic core that was previously formed by compacting a powdered core material substantially about a non-insulated shaft of relatively incompressible material in an embodiment of the invention;  
       FIG. 3B  is an exemplary cross-sectional view of an apparatus for forming the permanent magnet rotor of the present invention by DMC by compacting a powdered permanent magnet material substantially about a magnetic core that was previously formed by compacting a powdered core material substantially about a non-insulated shaft of relatively incompressible material to form various layers of the core in an embodiment of the invention;  
       FIG. 4A  is an exemplary cross-sectional view of an apparatus for forming the permanent magnet rotor of the present invention by DMC by simultaneously compacting a powdered permanent magnet material and a powdered core material substantially about a non-insulated shaft of relatively incompressible material to form a magnetic core and a permanent magnet in an embodiment of the invention;  
       FIG. 4B  is an exemplary cross-sectional view of an apparatus for forming the permanent magnet rotor of the present invention by DMC by compacting a powdered permanent magnet material substantially about a non-insulated shaft of relatively incompressible material to form a permanent magnet in an embodiment of the invention;  
       FIG. 4C  is an exemplary cross-sectional view of an apparatus for forming the permanent magnet rotor of the present invention by DMC by compacting various layers of a powdered permanent magnet material and a powdered core material substantially about a non-insulated shaft of relatively incompressible material to form various layers of the core and the permanent magnet where such layers may be compacted simultaneously or sequentially, beginning with the layer nearest the shaft, in an embodiment of the invention;  
       FIG. 5  is an exemplary flowchart for the process of producing the permanent magnet rotor of the invention by DMC techniques in an embodiment of the invention;  
       FIG. 6A  is an exemplary plot of the back EMF produced by a permanent magnet rotor of an embodiment of the invention, the magnetic core and the permanent magnet of this rotor produced by DMC techniques;  
       FIG. 6B  is an exemplary plot of the back EMF produced by a permanent magnet rotor, the magnetic core is formed of machined bar stock and the permanent magnet of this rotor is produced by compression molding techniques, the performance of this rotor is to be compared with the performance of the rotor illustrated in  FIG. 6A ;  
       FIG. 6C  is an exemplary plot of the back EMF produced by a permanent magnet rotor, the magnetic core and the permanent magnet of this rotor produced by compression molding techniques, the performance of this rotor is to be compared with the performance of the rotor illustrated in  FIG. 6A ;  
       FIG. 7A  is an exemplary plot of the back EMF produced by a permanent magnet rotor of an embodiment of the invention, the magnetic core and the permanent magnet of this rotor produced by DMC techniques and the permanent magnet formed of exchange spring nano-powder neodymium; and  
       FIG. 7B  is an exemplary plot of the back EMF produced by a permanent magnet rotor, the magnetic core is formed of machined bar stock and the permanent magnet of this rotor is produced by compression molding, the performance of this rotor is to be compared with the performance of the rotor illustrated in  FIG. 7A .  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.  
      A brushless dc motor  100 ,  112  such as that shown in  FIGS. 1A and 1B  is comprised of a stator member  102 ,  104  and a rotor member  106  that are joined by a bearing  108  and end plate  110  system.  FIG. 1A  is an exploded view of an exemplary dc brushless electric motor  100  with a DMC rotor member  106  and a traditional wound laminated stator  102  in an embodiment of the invention.  FIG. 1B  is an exploded view of an exemplary dc brushless electric motor  112  with a DMC rotor member  106  and a DMC produced stator member  104  in another embodiment of the invention.  
       FIGS. 2A and 2B  are exemplary cross-sectional illustrations of a permanent magnet rotor formed by DMC in an embodiment of the invention. As shown in more detail in  FIG. 2A , a typical embodiment of the rotor member  106  is comprised of a shaft  202 , magnetic core  204  and permanent magnet  206 , although the magnetic core  204  is not required to practice this invention, as is illustrated in the rotor  106  of  FIG. 2B . The permanent magnet  206  and the core  204  (if utilized), generally combine to form a cylindrical shape, having an outer diameter  208 , an inner diameter  210  and an axial length  212 . The shaft  202  is generally comprised of a solid material, also in a cylindrical shape, having an outer diameter  214  and an axial length  216 . The axial length  216  of the shaft  202  is generally greater than that of the cylindrical permanent magnet  206  and core  204  assembly so that bearings  108  and end plates  110  may be affixed to the shaft  202  for mounting the rotor  106  within the stator member  102 ,  104  and so that the shaft  202  may be externally connected to some device in order to perform work.  
      The stator  102  of a brushless dc motor  100  is typically comprised of iron laminations, insulated copper conductors, leads and insulation components as shown in  FIG. 1A , though a stator  104  may also be produced by DMC as shown in  FIG. 1B . The iron laminations are usually insulated to reduce eddy-current losses. The thin, iron larminations are “stacked” to form a conventional stator in a shape having a hollow, cylindrical void through its center. The inner circumference of the hollow cylinder generally has “teeth” about which insulated electrical windings are wrapped in such a manner to form a magnetic field in the teeth that simulates rotation about the interior of the stator. The inner diameter of the stator is just slightly larger than the outside diameter of the rotor  106 , such that an air gap exists between the rotor  106  and the stator  102 ,  104 . The magnetic field of the stator interacts with the magnetic field of the rotor such that the rotor turns within the stator. Embodiments of the present invention include a rotor member  106  produced by DMC that may be used in a brushless dc motor, while other aspects of the present invention are directed to methods of producing such a rotor  106 . The embodiments of the invention provide improved performance and reduced fabrication costs over traditional techniques.  
      The process of dynamic magnetic compaction has been described by U.S. Pat. No. 6,273,963, and other patents previously incorporated herein. In the embodiments of this invention however, a rotor member  106 ,  218  is produced by DMC techniques. The rotor  106 ,  218  may be used in dc brushless motors  100 ,  112  with conventional stator members  102  or with stator members  104  that are also produced by DMC techniques.  
       FIG. 3A  is an exemplary illustration of an apparatus for the compaction of a powdered permanent magnet material  300  substantially about a previously compacted core  204  in an embodiment of the invention. As shown in  FIG. 3A , the rotor  106  may be produced by compacting powdered permanent magnet material  300  by DMC substantially about the radial exterior area of a cylindrical magnetic core  204  having an axial length. The core  204  of this embodiment has, in turn, previously been powdered core material compacted by DMC substantially about a cylindrical non-insulated member  202  with the cylindrical non-insulated member  202  having an axial length greater than the axial length of the core  204 , although in other embodiments the core  204  may be comprised of a solid material or layers of material (not shown). The cylindrical non-insulated member forms the shaft  202  of the rotor  106  and is comprised of a relatively incompressible material as compared to the powdered core and permanent magnet material. For example, the shaft  202  may be formed of a material such as stainless steel. The stainless steel that forms such a shaft will not be in the form of a powdered material but will be in the form of a solid such that it will not be further compressed, or will only be minutely compressed by the dynamic magnetic compaction process. The shaft  202  may have a relatively smooth outer area or portions of the outer area may be scored, knurled, ridged, keyed or otherwise striated to better enable friction adhesion between the compacted powdered material and the shaft  202 . As shown in  FIG. 3B , the powdered core material may be sequentially compacted onto the shaft  202  in one or more layers  302 ,  304 ,  306  to form the core  204 . Each layer may be of the same or different thickness and of the same or different materials.  
      In other embodiments and as shown in  FIG. 4A , the rotor  106  may be formed by simultaneously compacting by DMC one or more separate and distinct powdered materials  400 ,  300  substantially about the exterior radial area of the shaft  202  for a portion of its axial length. In one instance when forming a rotor  106  and as shown in  FIG. 4B , only a powdered permanent magnet material  300  may be compacted by DMC directly onto and substantially about a portion of the axial length of the shaft  202 . In other instances, referring back to  FIG. 4A , a powdered core material  400  and the powdered permanent magnet material  300  may be simultaneously compacted by DMC substantially about a portion of the axial length of the shaft  202 . In yet other instances as shown in  FIG. 4C , various layers of powdered materials  404 ,  406 ,  408 ,  410  are compacted using DMC substantially about a portion of the axial length of the shaft  202  to form a rotor  106 .  
      The simultaneous compacting of separate and distinct powders to form a core  204  and permanent magnet  206  substantially about a shaft  202  may result in fewer steps in the manufacturing of a rotor  106  for a dc brushless motor, thus increasing production efficiencies and possibly lowering production costs.  
      Powdered permanent magnet material  300  that may be used to form the permanent magnet  206  of the rotor  106  by DMC techniques include neodymium-iron-boron powders such as, for example, isotropic neodymium powder, anisotropic neodymium and exchange spring nano-powder neodymium powder, although other types of permanent magnet powders are under development or may be developed and may be used in other embodiments of the invention. These neodymium powdered permanent magnet materials are available from Magnequench, Inc. of Indianapolis, Ind., among other suppliers. The powdered core material  400  is generally a soft iron material such as, for example, soft magnetic composites (SMC) as are available from Höganäs AB and Quebec Metal Powders, Ltd. of Montreal, Quebec (QMP), and Atomet TM powders available from QMP, although other types of core material may be used.  
      In producing a rotor  106  using DMC techniques, the non-insulated shaft  202  is securely placed in a die  308  and one or more powdered materials  400 ,  300  are placed in one or more chambers  310  circumferentially surrounding a portion of the axial length of the shaft  202 . The outer walls  312  of the chambers  310  are electrically conductive and are either deformable such that they may crush radially inwardly toward the shaft  202 , or are moveable such that they are mechanically able to move radially inwardly. The conductive chamber walls  312  are then exposed to a magnetic field created by a current pulsed through a nearby conductor  314 . The magnetic field creates an inwardly radial pressure on the chamber walls  312  thereby compacting the one or more powdered materials  400 ,  300  contained therein substantially about the shaft  202  and forming a solid from the powdered materials  400 ,  300 . These procedures are more fully explained in the referenced patents previously incorporated herein.  
      The process of forming the permanent magnet rotor of an embodiment of the invention is more fully described in the flowchart of  FIG. 5 . The process begins with Step  500 . In Step  502 , the shaft is mounted in a die to hold it in place during the DMC process. In Step  504 , it is determined whether the rotor will have a magnetic core. If the rotor will have a magnetic core, then in Step  506  it is determined whether the rotor will be formed by simultaneous DMC or by layered DMC. If it is determined that the rotor will be formed by simultaneous DMC, then in Step  508  the powdered core material and the powdered permanent magnet material are placed into a mold that has conductive walls that are capable of moving radially inward when exposed to a magnetic field. In Step  510 , the powdered core material and the powdered permanent magnet material are simultaneously compacted by DMC substantially about the shaft. The process then ends at Step  540 .  
      If it is determined in Step  506  that the rotor will be formed by layered DMC, then in Step  512  the powdered core material is placed into a mold that has conductive walls that are capable of moving radially inward when exposed to a magnetic field. In Step  514 , the powdered core material is compacted by DMC substantially about the shaft. In Step  516 , it is determined whether the core will be comprised of additional layers of compacted powdered core material beyond the first layer. If so, then in Step  518  additional core material is placed in the mold substantially about the previously compacted powdered core material and in Step  520 , this additional powdered core material is compacted into another layer of core material. These steps are repeated as many times as desired, as indicated by Step  522 . If no additional core layers are desired at Step  522 , or referring back to Step  516 , if it is determined that no additional core layers are desired beyond the first layer of core material, then the process moves to Step  524 . In. Step  524 , powdered permanent magnet material is placed in the mold substantially about the core. This powdered permanent magnet material is then compacted by DMC to form a permanent magnet substantially about the core in Step  526 .  
      It is then determined in Step  528  whether additional layers of permanent magnet beyond the first layer are desired. If so, then in Step  530  additional powdered permanent magnet material is placed in the mold substantially about the previously compacted powdered permanent magnet material and the additional powdered material is compacted by DMC in Step  532  into another layer of permanent magnet substantially about the previous layer. If additional layers of permanent magnet are desired, then Step  530  and  532  are repeated, as indicated by Step  534 . If no additional layers of permanent magnet are desired, then from Step  534  the process moves to Step  540  and ends, or referring back to Step  528 , if no additional layers of permanent magnet beyond the first layer are desired, then the process moves from Step  528  to Step  540  and ends.  
      Referring back to Step  504  where it is determined whether the rotor will have a magnetic core, if the rotor will not have a magnetic core, then the process moves to step  536  where a powdered permanent magnet material is placed in a mold substantially about the shaft and is compacted by DMC in Step  538  substantially about the shaft. Referring again to Step  528 , it is then determined whether additional layers of permanent magnet beyond the first layer are desired. If so, then the process goes through the iterative cycle defined by Steps  530 ,  532 , and  534  for as many layers as desired and then the process ends at Step  540 . If, at Step  528 , it is determined that no additional layers of permanent magnet beyond the first layer are desired, then the process moves to Step  540  and ends.  
      Once the rotor  106  is formed, in some instances it may require additional machining to meet tolerance requirements and generally, it is sealed with a substance such as, for example, polyurethane, although these additional steps may not be required to practice the invention.  
      A permanent magnet rotor  106  for a dc brushless motor formed by DMC exhibits increased torque constant over a similar rotor formed by the molding of the same powder materials. Torque constant is directly proportional to a material&#39;s flux density.  FIGS. 6A, 6B  and  6 C provide exemplary illustration of the improved performance of a rotor produced by DMC techniques.  FIG. 6A  is an exemplary plot of the back EMF produced by a rotor of one embodiment of the present invention produced by DMC techniques.  FIGS. 6B and 6C  are exemplary plots of the back EMF produced by rotors formed of the same materials as the rotor in  FIG. 6A , but formed by compression molding techniques, rather than by DMC.  FIG. 6A  is therefore to be contrasted with  FIGS. 6B and 6C , which illustrate the back EMF produced by rotors formed by traditional methods. Each of the rotors tested were of similar design with an outer ring-type permanent magnet over a magnetic core and affixed to a stainless steel shaft, each utilizing isotropic neodymium powders for its permanent magnet. Each of the rotors tested in  FIGS. 6A, 6B , and  6 C are comprised of permanent magnets formed of isotropic neodymium powder, cores of solid 12L14 steel, and shafts of 416 stainless steel. The results of the tests illustrated in  FIGS. 6A, 6B  and  6 C are summarized in Table 1.  
                                               TABLE 1                                               Per-       Torque                               cent   Volts/   Constant           Rotor   Test               Rip-   Radian/   (oz-       FIG.   Type   rpm   V MAX     V MIN     V RMS     ple   Second   in/Amp)                                                                    6A   DMC   1200   4.406   3.352   4.126   13.6   .0328   4.649       6B   Non-   1200   4.104   3.126   3.858   13.6   .0307   4.347           DMC       6C   Non-   1200   4.088   3.189   3.868   12.4   .0308   4.358           DMC                  
 
      The average torque constant for the two exemplary non-DMC rotors ( FIGS. 6B and 6C ) is 4.3525 oz-in/Amp; therefore, the DMC rotor of  FIG. 5A  has ((4.649/4.3525)−1)×100=6.8% greater torque constant than the average torque constant of the two non-DMC rotors.  
      Furthermore, a rotor  106  produced by the DMC techniques and utilizing exchange spring nano-powder neodymium as the powder material for the permanent magnet (not shown) exhibits from 18 to 33.5 percent greater magnetic flux density than a rotor  106  produced by compression molding of an isotropic neodymium powder for its permanent magnet.  FIGS. 7A and 7B  provide exemplary illustration of the improved performance of a rotor produced by DMC techniques utilizing exchange spring nano-powder neodymium.  FIG. 7A  is an exemplary plot of the back EMF produced by a rotor of one embodiment of the present invention produced by DMC techniques utilizing the exchange spring powder for its permanent magnet.  FIG. 7B  is an exemplary plot of the back EMF produced by rotors where the permanent magnet is formed of isotropic neodymium powder using compression molding techniques, rather than by DMC. As can be seen by comparing  FIGS. 7A and 7B , the back EMF of the exchange spring DMC rotor ( FIG. 7A ) is 5.200 volts peak, whereas the back EMF of the non-DMC rotor is 3.896 volts peak. Peak voltage is directly proportional to flux density, which is directly proportional to torque constant. Therefore, the exchange spring DMC rotor ( FIG. 7A ) has ((5.200/3.896)−1)×100=33.47 percent increase in torque constant over the non-DMC rotor of  FIG. 7B . These rotors were tested under similar circumstances and at the same rpm (1200 rpm).  
      Although the described inventive concepts disclose a rotor formed by compacting powdered permanent magnet material and, in some instances, powdered core material substantially about a relatively incompressible shaft, the same concepts can apply to other electromechanical and non-electrical devices for attachment to a shaft. For instance, the above invention is equally applicable to shaft-mounted devices such as, for example, gears, cams, cogs, tool heads and bodies, blades, flywheels where such devices may be compacted directly to the shaft by DMC. For example, a flywheel may be formed substantially about a non-insulated shaft by placing the shaft in a die that holds it in place substantially through a flywheel mold. The flywheel mold having deformable conductive sides or at least conductive sides that may mechanically move inwardly (toward the non-insulated shaft) when exposed to the magnetic field of the DMC process. Placing a suitable powdered material within the mold and exposing the mold (and the powdered material therein) to a DMC process such that the sides of the mold are compressed radially inward toward the shaft thereby forming a solid of the powdered material with said solid substantially in the desired shape.  
      Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.