Patent Publication Number: US-2010117473-A1

Title: Robust permanent magnet rotor assembly

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to permanent magnet rotor assemblies for electric motors, and more specifically to a more robust rotor assembly that provides for release of gases from an enclosed portion thereof thus reducing pressure in the enclosed portion of the rotor assembly. 
     Permanent magnet rotors for electric motors typically comprise a rotor assembly having a rotor iron shaft with a plurality of magnets adhered to an outer surface thereof. The magnets may have an arcuate cross-sectional configuration with a longitudinal axis extending a portion of the outer surface of the rotor shaft and retained thereto with an adhesive. The rotor may be constructed with a single magnet. This magnet may also be cylindrical in cross-section, with or without a cylindrical aperture through the center. This cylindrical magnet may be an assembly of a plurality of pieces, retained together by an adhesive. The magnets are typically permanent magnets and may be rare-earth or ceramic magnets. The magnets may be adhered to the shaft with an adhesive. A non-magnetic cylindrical sleeve may then be positioned about the magnets and may be retained to outer surfaces thereof with an adhesive to inhibit longitudinal movement of the magnets about the shaft. A disk shaped end cap may then be placed within or on each end of the cylindrical sleeve. The end caps may have a central aperture about an outer circumference of the shaft adjacent the plurality of arcuate magnets and have an inner surface adhesively retained to longitudinal ends of the cylindrical magnets or the plurality of arcuate magnets. The end caps may also be adhesively or mechanically retained within the cylindrical sleeve. The end caps may aid in maintaining alignment of the magnets and balance of the rotor assembly. 
     These typical rotor assemblies have adhesives about portions of the shaft, magnets, sleeve, and end caps. During construction and use, the rotor assembly may be subject to heat. The heat may cause gases to evolve from the adhesive which may become trapped within portions of the rotor assembly. These gases may exert pressure forcing components of the assembly apart, weakening the rotor assembly. For example, end caps of the rotor may become displaced, which may cause misalignment and unbalance of the rotor assembly and may lead to catastrophic failure of the electric motor. 
     As can be seen, there is a need for a more robust rotor assembly for an electric motor. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a rotor assembly for an electric motor is provided having a rotor shaft, a plurality of magnets longitudinally extending a portion of an outer surface of the rotor shaft and being retained thereto with an adhesive, a cylindrical sleeve positioned about the plurality of magnets, and a disk shaped end cap adhesively or mechanically retained adjacent each end of the cylindrical sleeve. Each end cap has a central aperture about an outer circumference of the shaft adjacent the plurality of magnets and has a surface adhesively or mechanically retained adjacent longitudinal ends of the cylindrical sleeve. At least one hole, channel, or bevel is in at least one of the rotor shaft, cylindrical sleeve, non-magnetic wedge spacers, or end caps providing a gas flow through passage in flow communication with the enclosed portion and an environment outside of the enclosed portion thereof. 
     In another aspect of the present invention, end caps are provided for a rotor assembly having a disk with an inside face, an outside face, and a round central aperture suitable for closely receiving a portion of a rotor shaft. At least one vent hole extends from an outer edge of the inside face of the disk to the outside face of the disk and from an inner edge adjacent the central aperture of the inside face to the outside face. 
     In yet another aspect of the present invention, a rotor assembly is provided having a shaft with a plurality of longitudinally extending magnets adhesively retained to an outer surface thereof. Wedge shaped non-magnetic spacers are between each of the magnets. A rotor sleeve closely receives the magnets and spacers. An end cap having a central aperture closely receives a rotor shaft and is adhesively held within or to each end of the rotor sleeve forming an enclosure about the magnets. At least one gas vent for venting gases evolved from heating adhesives to an environment outside of the enclosure is provided. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a rotor assembly for an electric motor according to the present invention; 
         FIG. 2  is a cross-sectional view of the rotor assembly of  FIG. 1 ; 
         FIG. 3  is an exploded view of the rotor assembly of  FIG. 1 ; 
         FIG. 4A  is front view of an aspect of an end cap of the present invention having groves;  FIG. 4B  is a cross-sectional view of an end cap of the present invention shown in  FIGS. 1-3 ; 
         FIG. 5  is an axial cross-sectional view of a rotor assembly of an aspect of the present invention; 
         FIG. 6A  is a cross-sectional view of a stub shaft having venting holes; 
         FIG. 6B  is a side view of a stub shaft having venting grooves; 
         FIG. 7A  is a perspective view of a two pole magnet having a central venting hole; 
         FIG. 7B  is a perspective view of a two pole magnet having a solid core 
         FIG. 8A  is a cross-sectional view of a rotor assembly having a central venting hole; and 
         FIG. 8B  is a cross-sectional view of a rotor assembly having a solid central core. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     Various inventive features are described below that can each be used independently of one another or in combination with other features. However, any single inventive feature may not address any of the problems discussed above or may only address one of the problems discussed above. Further, one or more of the problems discussed above may not be fully addressed by any of the features described below. 
     The configuration of the rotor assembly for an electric motor of aspects of the present invention provides at least one means for venting gases from an enclosed portion thereof. The rotor assembly may be formed by adhering longitudinal extending magnets with or without a non-magnetic spacer therebetween, axially about a circumferential portion of the rotor with an adhesive. Alternatively, a two pole magnet may be used to make up the rotor where the rotor comprises a plurality of magnets adhesively bonded together. An outer sleeve may then be placed about an outer surface of the rotor and is optionally held to an outer surface thereof with an adhesive. End caps or stub shafts may be adhesively or mechanically retained to or within the ends of the outer sleeve and optionally adhesively held to longitudinal ends of the magnent(s) or magnets and spacers. The end caps may have a central aperture for closely receiving a rotor. The outer sleeve and end caps or stub shafts form an enclosed portion of the rotor assembly. During production or use, the rotor assembly may become heated and gases may be generated from the volatilization of a portion of the adhesives securing the component parts together. In the prior art, these evolved gases may become trapped within the enclosed portion of the rotor assembly. These trapped gases may exert pressure forcing components of the assembly apart, weakening the rotor assembly. For example, end caps or stub shafts of the rotor may become displaced, which may cause misalignment and unbalance of the rotor assembly and may lead to catastrophic failure of the electric motor. Aspects of the rotor assembly of the present invention provide at least one means for venting these trapped gases from the enclosed portion reducing the pressure within thus providing a more robust rotor assembly. 
     Referring to  FIG. 1 , there is shown rotor assembly  100  having cylindrical sleeve  114  (shown in  FIG. 2 ) removed. This aspect of the present invention has rotor shaft  110  with a plurality of magnets  118  longitudinally extending a portion of an outer surface of rotor shaft  110  in an axial direction and being retained thereto with an adhesive. Magnets  118  may be bar shaped as shown in the figures or may have an arcuate cross-sectional configuration, or may have other configurations as are known in the art. Magnets  118  may be permanent magnets and may be rare-earth, ceramic, or have other composition as is known in the art. Non-magnetic wedge spacers  126  may be positioned between each magnet  118  and may be adhered to rotor shaft  110  and/or magnets  118  with an adhesive. End caps  112  are shown positioned about rotor shaft  110  adjacent ends of magnets  118  and wedge spacers  126 . End caps  112  may have an inner surface  127  (shown in  FIG. 3 ) adhesively retained to the ends of magnets  118  and wedge spacers  126 . Alternatively, end caps  112  may be mechanically secured into position with a close fiting cylindrical sleeve  114 . 
       FIG. 2  shows cylindrical sleeve  114  optionally positioned about magnets  118  and non-magnetic wedge spacers  126 . Disk shaped end caps  112  may be adhered to an inner surface  115 , to each end  117  of cylindrical sleeve  114 , or mechanically retained within cylindrical sleeve  114 . Advantageously, end caps with central aperture  124  (shown in  FIG. 3 ) closely receive an outer circumferential surface of rotor shaft  110  adjacent longitudinal ends  119  (shown in  FIG. 3 ) of magnets  118  and longitudinal ends  121  (shown in  FIG. 3 ) of wedge spacers  126 . End caps  112  may have an outer circumferential edge  123  (shown in  FIG. 3 ) or inner surface  127  (shown in  FIG. 3 ), or both, adhesively retained proximate ends  117  (shown in  FIG. 3 ) of cylindrical sleeve  114 , forming an enclosed portion  125  of rotor assembly  100 . Optionally, end caps  112  may be adhered to longitudinal ends  119  of magnets  118  and/or longitudinal ends  121  of spacers  126  with an adhesive material. Alternatively or additionally, end caps  112  may have an outer edge  123  adhesively adhered to inner surface  115  of cylindrical sleeve  114  or have inner surface  127  adhered to ends  117  of cylindrical sleeve  114 . End caps  112  may be mechanically secured within cylindrical sleeve  114  without adhesives forming an enclosed portion  125  of rotor assembly  100 . 
     In  FIG. 3  there is shown an exploded view of rotor assembly  100 . Cylindrical sleeve  114  is shown removed from an outer portion of magnets  118  and wedge spacers  126 . Magnets  118  and non-magnetic wedge spacers  126  are shown removed from each other and rotor shaft  110 . End caps  112  are shown positioned about rotor shaft  110  adjacent ends of magnets  118  and wedge spacers  126 . End caps  112  are shown removed from rotor shaft  110 . 
     Cylindrical sleeve  114  may have ends  117  and inner surface  115 . Rotor shaft  110  may have central hollow portion  116 . Magnets  118  may have ends  119  and non-magnetic wedge spacers  126  may have ends  121 . Disk shaped end caps  112  are shown removed from rotor shaft  110 . End caps  112  may have central aperture  124 , outer circumferential edge  123 , and inner surface  127 . End caps  112  may have at least one gas vent hole  120  which may be in flow communication with the enclosed portion  125  of rotor assembly  100  and the outside of enclosed portion  125 . Gas vents  120  may provide rotor assembly  100  with a means for releasing gases generated from the heating of adhesives within enclosed portion  125 . 
     In the aspect of the present invention shown in  FIGS. 1-3 , each end cap  112  may have at least one vent hole  120  extending from an inside face  127  adjacent the plurality of magnets  118  to an outside face  129  thereof. Additionally, this aspect of the invention may incorporate a solid rotor  110  as opposed to the rotor  110  having central hollow portion  116  as shown. 
       FIG. 4A  shows a side cross-sectional view of an end cap  112  for rotor assembly  100  for an electric motor. End cap  112  may be disk shaped and may have an inside face  127 , an outside face  129 , and a round central aperture  124  suitable for closely receiving a portion of rotor shaft  110 . Advantageously, end cap  112  may closely receive rotor shaft  110  such that a seal is formed therebetween forcing gases generated from the heating of adhesives within enclosed portion  125  through vent holes  120  and  121 . A plurality of vent holes  120  may extend from an outer edge  141  of inside face  127  to outside face  129 . A plurality of vent holes  121  may extend from an inner edge  143  adjacent central aperture  124  of inside face  127  to outside face  129 . Advantageously, each vent hole  120  extending from the outer edge  141  of inside face  127  of disk or end cap  112  and each vent hole  121  extending from the inner edge  143  of inside face  127  may be radially aligned about disk  112 . More advantageously, each vent hole  120  and  121  in disk  112  may be radially aligned thereabout so that disk  112  is substantially balanced about central aperture  124 . This aspect of the present invention may help to provide for a balanced rotor assembly  100  which may reduce a wobbling tendency and be advantageous for use in high speed electric motors. Optionally, vent holes  120  and  121  may be angled from the inside edges  141  and  143  from which they extend on front face  127  toward a radius  145  between outer edge  141  and inner edge  143  on outside face  129 . 
     In another aspect shown in  FIG. 4A , outside edge  141  of inside face  127  of disk  112  has beveled edge  122 . Additionally, the inside edge  143  of inside face  127  may have beveled edge  123 . In the aspect shown here, both edges are beveled, however it is to be understood that only one or neither edge may have a bevel and be within the scope of the invention. Beveled edges  122  and  123  may provide a void space about inside edges of disk  112  which may provide for gas flow from the surface of rotor shaft  110  to which magnets  118  are adhered and from an inner surface of sleeve  114  to an environment outside of enclosed portion  125  of rotor assembly  100  through vent holes  120  and  121 . 
       FIG. 4B  shows a front face view of an end cap  212  for rotor assembly  100  for an electric motor. End cap  212  may be disk shaped and may have an inside face  127 , an outside face  129 , and a round central aperture  124  suitable for closely receiving a portion of rotor shaft  110 . Advantageously, end cap  212  may closely receive rotor shaft  110  such that a seal is formed therebetween. A plurality of channels  220  may extend from an outer edge  141  of inside face  127  to outside face  129 . A plurality of channels  221  may extend an inner edge  143  adjacent central aperture  124  of inside face  127  to outside face  129 . Advantageously, channels  220  and  221  are axial aligned and form gas flow through channels from inner surface  127  to an environment outside of enclosed portion  125 . Advantageously, each channel  220  extending from the outer edge  141  of inside face  127  of disk or end cap  212  and each channel  221  extending from the inner edge  143  of inside face  127  may be radially aligned about disk  212 . More advantageously, each channel  220  and  221  in disk  112  may be radially aligned thereabout so that disk  212  is substantially balanced about central aperture  124 . In another aspect shown in  FIG. 4B , outside edge  141  of inside face  127  of disk  212  has beveled edge  122 . Additionally, the inside edge  143  of inside face  127  may have beveled edge  123 . In the aspect shown here, both edges are beveled, however it is to be understood that only one or neither edge may have a bevel and be within the scope of the invention. Beveled edges  122  and  123  may provide a void space about inside edges of disk  112  which may provide for gas flow from the surface of rotor shaft  110  to which magnets  118  are adhered and from an inner surface of sleeve  114  to an environment outside of enclosed portion  125  of rotor assembly  100  through channels  220  and  221 . 
       FIG. 5  shows a cross-section of rotor assembly  200  for an electric motor. Rotor assembly  200  may comprise shaft  110  with a plurality of longitudinally extending, axially aligned magnets  118  adhesively retained to an outer surface thereof. A wedge shaped non-magnetic spacer  126  may be positioned between each magnet  118 . Rotor sleeve  114  may closely receive magnets  118  and spacers  126 . Optionally, rotor sleeve  114  may be attached to an outer surface of magnets  118  and spacers  126  with an adhesive. An end cap  112  may be adhesively held to or within each end of rotor sleeve  114  and optionally to each end of magnets  118  and spacers  126 . Each end cap  112  may have a central aperture closely receiving shaft  110  forming an enclosure about magnets  118  and spacers  126 . 
     Several gas vents  128 ,  130 ,  135  and/or  137  may be provided with different aspects of the present invention. These gas vents may be incorporated into rotor assembly  200  individually or in conjunction with other gas vents such as gas vent holes  120  in end caps  112 .  FIG. 5  shows several gas vents or flow through passages  128 ,  130 ,  135 , and  137  of aspects of the present invention incorporated into rotor assembly  200 . It is to be understood that only one of such gas vents shown in the figures or as will become apparent to one skilled in the art upon reading this disclosure need be incorporated into a rotor assembly to be within the scope of the invention. 
       FIG. 6A  shows a cross-sectional view of a stub shaft  312  for a rotor assembly for an electric motor. Stub shaft  312  may have an inside face  327 , an outside face  329 , and a round central aperture  324 . A plurality of vent holes  320  may extend from an outer edge  341  of inside face  327  to outside face  329 . Advantageously, each vent hole  320  in stub shaft  312  may be radially aligned thereabout so that stub shaft  312  is substantially balanced about central aperture  324 . This aspect of the present invention may help to provide for a balanced rotor assembly. Optionally, outside edge  341  of inside face  327  of stub shaft  312  has beveled edge  322 . Additionally, the inside edge  343  of inside face  327  may have beveled edge  323 . In the aspect shown here, both edges are beveled, however it is to be understood that only one or neither edge may have a bevel and be within the scope of the invention. Beveled edges  322  and  323  may provide a void space about inside edges of stub shaft  312  which may provide for gas flow from the surface of a rotor shaft and/or from an inner surface of sleeve  114  to an environment outside of enclosed portion  125  of a rotor assembly. 
       FIG. 6B  is a side view of a stub shaft  412  having venting grooves  420 . Stub shaft  412  may be may have an inside face  427  and an outside face  429 . A plurality of channels  420  may extend from an outer edge  441  of inside face  427  to outside face  429 . Advantageously, channels  420  are axial aligned and form gas flow through channels from inner surface  427  to an environment outside of enclosed portion  125 . More advantageously, each channel  420  in stub shaft  412  may be radially aligned thereabout so that stub shaft  412  is substantially balanced about a central axis  424 . In another aspect, outside edge  441  of inside face  427  may have a beveled edge  422 . Beveled edge  422  may provide a void space about an inside edge of stub shaft  412  which may provide for gas flow from the surface of a rotor shaft to which magnets may be adhered and/or from an inner surface of sleeve  114  to an environment outside of enclosed portion  125  of a rotor assembly through channels  420 . 
       FIG. 7A  shows rotor shaft  710  comprised of a two pole magnet having a central venting hole  724 . Rotor shaft  710  is comprised of a plurality of magnets  718 ,  719 ,  720 , and  721 . Each magnet  718 ,  719 ,  720 , and  721  has a configuration suitable for forming a cylindrical rotor shaft  710  when pieced together as shown in  FIG. 7A . Each magnet  718 ,  719 ,  720 , and  721  may be adhesively secured to adjacent magnets to form a two pole magnet. Rotor shaft  710  may have central vent hole  724  extending the central longitudinal axis thereof. Magnets  718  may have holes therein such that when axially aligned to form a portion of cylindrical rotor shaft  710 , central vent hole  724  is formed therein. Central vent hole  724  may form a gas flow through passage in rotor shaft  710  suitable for venting gases generated by heating of adhesives securing magnets  718 ,  719 ,  720 , and  721  together to an environment outside of enclosed portion  125 . 
       FIG. 7B  shows rotor shaft  810  comprised of a two pole magnet having a solid core. Rotor shaft  810  is comprised of a plurality of magnets  818 ,  719 ,  720 , and  721 . Each magnet  818 ,  719 ,  720 , and  721  has a configuration suitable for forming a cylindrical rotor shaft  810  when pieced together as shown in  FIG. 7B . Each magnet  818 ,  719 ,  720 , and  721  may be adhesively secured to adjacent magnets to form a two pole magnet. Rotor shaft  810  may have a solid core. 
       FIG. 8A  shows a cross-sectional view of rotor assembly  800  having a stub shaft  312  on each end of rotor shaft  710 . Stub shaft  312  may have an inside face  327 , an outside face  329 , and a round central aperture  324 . A plurality of vent holes  320  may extend from an outer edge  341  of inside face  327  to outside face  329 . Optionally, outside edge  341  of inside face  327  of stub shaft  312  has beveled edge  322 . Additionally, the inside edge  343  of inside face  327  may have beveled edge  323 . Beveled edges  322  and  323  may provide void spaces  325  and  327  about inside edges of stub shaft  312  which may provide for gas flow from the surface of rotor shaft  710  and/or from an inner surface of sleeve  114  to an environment outside of enclosed portion  125  of a rotor assembly. Rotor shaft  710  is a two pole magnet having a central venting hole  724  axially aligned with central aperture  324  in stub shaft  312  providing rotor assembly  800  with an axially extending central vent hole. Rotor shaft  710  is comprised of a plurality of magnets  718 ,  719 ,  720 , and  721 . Each magnet  718 ,  719 ,  720 , and  721  may be adhesively secured to adjacent magnets to form a two pole magnet. Magnets  718  may have holes therein such that when axially aligned to form a portion of cylindrical rotor shaft  710 , central vent hole  724  is formed therein. Central vent hole  724  may form a gas flow through passage in rotor shaft  710  suitable for venting gases generated by heating of adhesives securing magnets  718 ,  719 ,  720 , and  721  together through central apertures  324  to an environment outside of enclosed portion  125 . 
       FIG. 8B  shows rotor assembly  900  having a solid central core. Stub shafts  412  extend from each axial end of rotor shaft  810  and may have an inside face  427  adjacent rotor shaft  810  and an outside face  429 . A plurality of channels  420  may extend from an outer edge  441  of inside face  427  to outside face  429 . Advantageously, channels  420  are axial aligned and form gas flow through channels from inner surface  427  to an environment outside of enclosed portion  125 . Outside edge  441  of inside face  427  may have a beveled edge  422 . Beveled edge  422  may provide a void space  325  about an inside edge of stub shaft  412  which may provide for gas flow from the surface of a rotor shaft to which magnets may be adhered and/or from an inner surface of sleeve  114  to an environment outside of enclosed portion  125  of a rotor assembly through channels  420 . Rotor shaft  810  is comprised of a two pole magnet having a solid core. Rotor shaft  810  is comprised of a plurality of magnets  818 ,  719 ,  720 , and  721 . Each magnet  818 ,  719 ,  720 , and  721  may be adhesively secured to adjacent magnets to form a two pole magnet. Rotor shaft  810  may have a solid core. 
     Shaft  110  may have a hollow interior  116  and bevels  132  adjacent each longitudinal end of each of magnet  118  and a vent hole  130  extending from bevel  132  to the hollow interior  116  thereof. Vent hole  130  may provide for gas flow communication between the interface of magnets  118  and shaft  110  and the hollow interior  116  of shaft  110 . Advantageously, at least one gas vent  130  in said shaft  110  may be radially aligned with a non-magnetic wedge spacer  126  as shown in  FIG. 5 . Additionally, wedge spacers  126  may have beveled edges  133  providing gas flow through passages  137  about each wedge spacer  126 . Optionally, at least one of the non-magnetic wedge spacer  126  may have a vent passage  128  in flow communication with bevel  132  in shaft  110  and the outside of the enclosure about shaft  110  through an aligned hole  135  in rotor sleeve  114 . Advantageously, rotor assembly  200  may be substantially balanced about a central longitudinal axis thereof providing a substantially smooth rotation at high rotational speeds. In aspects of the present invention not having a gas vent  130 , shaft  110  may be solid. 
     As shown in  FIGS. 1-5 , gases that may evolve from the heating of adhesives in enclosed portion  125  of rotor assembly  100  may be vented by one or more gas flow through passages. In at least one of the rotor shaft  110 , cylindrical sleeve  114 , non-magnetic wedge spacers  126 , or end caps  112  there may be a gas flow through passage providing flow communication with enclosed portion  125  and an environment outside of enclosed portion  125  of rotor assembly  100 . The gas flow through passage in rotor shaft  110  may be vent hole  130 . The gas flow through passage in cylindrical sleeve  114  may be vent hole  135 . The gas flow through passage in non-magnetic wedge spacers  126  may be gas flow through passages  137  and/or vent passage  128 . The gas flow through passages in end caps  112  may be vent holes  120 . Only one or any combination of gas flow through passages  120 ,  128 ,  130 ,  135 , and  137  or other passages that will become apparent to one skilled in the art upon this disclosure may be incorporated to into a rotor assembly to provide release of gases from a rotor assembly. 
     It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.