Patent Publication Number: US-2023155435-A1

Title: Rotor for Electronically Commutated DC Motor

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
     This patent application is a continuation of application Ser. No. 17/145,724, filed Jan. 11, 2021, which claims priority from U.S. provisional patent application No. 62/961,446, filed Jan. 15, 2020, which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to electronically commutated DC motors (EC motors), and more particularly to an EC motor air cooling system, an optimized permanent magnet rotor, and a unitary over molded housing. 
     BACKGROUND OF THE INVENTION 
     In one embodiment, an internal rotor EC motor comprises a stator with a series of circumferentially spaced electromagnets and a rotor position inside the stator and mounted for rotation on a shaft. The rotor has circumferentially spaced permanent magnets. An electronic controller controls the electrical energy delivered to the coils of the electromagnets of the stator. By controlling the electrical energy delivered to the coils of the stator, a rotating magnetic field is created that in turn attracts the permanent magnets of the rotor to cause the rotor to spin on its shaft. 
     In another embodiment, an external rotor EC motor comprises a stator with circumferentially spaced electromagnets. Such an EC motor has a rotor with permanent magnets positioned on the outside of the stator. Whether an internal rotor or an external rotor, the operating principles of the EC motor are generally the same in that rotating magnetic field is created by the stator that attracts the permanent magnets of the rotor to cause rotation of the rotor. 
     During operation, heat is generated both by the electronic controller and in the stator coils. Consequently, an EC motor requires a system for dissipating the heat from the control circuitry and the stator coils. 
     The configuration of permanent magnets and steel laminates that make up the rotor can have an effect on the performance of an EC motor. Such performance can be improved by constructing a rotor with a combination of permanent magnets sized and spaced around the rotor. 
     During operation, the switching of the electric current in the stator coils can result in unwanted vibration and noise. Further, for certain applications for EC motors, the cost and weight of the motor components, including the motor housing, are important to purchasers. 
     SUMMARY OF THE INVENTION 
     In order to overcome the problem of heat dissipation in an EC motor of the present invention, the EC motor includes an impeller fan attached to a rotating shaft of the rotor. The impeller fan draws ambient air into the housing of the EC motor. The ambient air is drawn toward the impeller fan through circumferentially spaced air inlets and then through radially oriented air passages that are adjacent to the electronic controller. As ambient air passes through the radially oriented air passages, the ambient air absorbs heat from the electronic controller. Once the ambient air has been drawn through the radially oriented air passages and into the impeller fan, the air is forced by the impeller fan along axially oriented stator cooling channels between the coils of the stator. After absorbing heat from the stator coils, the air is exhausted axially or radially through air outlets in the housing. The impeller fan has planar fins oriented parallel to the rotor shaft so that the cooling air flows in one direction regardless of the direction of rotation of the rotor and attached impeller fan. 
     For the internal rotor embodiment, the stator comprises a structural circular core back with inwardly extending teeth of laminated steel. Energizing coils are wound around the individual teeth and insulated from the teeth. The teeth have concave inner ends that define a circular opening into which the circular internal rotor is positioned. The dimensions of the teeth and the rotor provide an air gap between the concave inner ends of the teeth and the outer circumference of the rotor. 
     The internal rotor EC motor includes an over molded housing that comprises a cylindrical outer shell and an inwardly extending stator coil section. The stator coil sections encapsulate the coils and the teeth (except for the concave inner ends). The housing is created by over molding the stator with plastic. The plastic is Rynite polyethylene terephthalate (available from DuPont) or any other plastic material having similar molding and heat transfer characteristics. Encapsulating the stator coils and teeth reduces noise and vibration. Further, replacing a metal cylindrical outer shell with a plastic shell contributes to weight reduction and lower cost of materials and manufacturing. 
     In order to optimize performance of the internal rotor EC motor of the present invention, the rotor has permanent magnets and silicon steel laminates positioned around a central hub. The silicon steel laminates are positioned around the outer circumference of the rotor and are spaced circumferentially around the rotor with gaps between the adjacent silicon steel laminates. Rectangular shaped permanent magnets are interposed in the gaps between the silicone steel laminates. Wedge-shaped magnets are aligned radially with the silicon steel laminates and between the steel laminates and the central hub of the rotor. The performance of the rotor is optimized by adjusting the sizes, shapes, and locations of the silicon steel laminates, the rectangular magnets, and the wedge-shaped magnets. 
     For the external rotor EC motor, the stator has a central hub from which the steel laminate teeth extend radially outward. The outer end of each of the teeth has a convex outer surface. The outer surfaces of the teeth form a circle. The rotor comprises a cylindrical shell with a series of spaced apart permanent magnets attached to the internal surface of the cylindrical shell. The permanent magnets are dimensioned with an inwardly facing concave surface that matches the convex outer surface of the teeth. The cylindrical shell and magnets are dimensioned so that an air gap exists between the convex outer surfaces of the teeth and the internal concave surfaces of the permanent magnets. The rotor has a disc shaped end cover with fan blades attached to the internal surface of the end cover. The cylindrical shell also has a series of circumferentially spaced openings that serve as air outlets for the air pressure created by the fan blades. 
     The fan of the external rotor EC motor draws air into the EC motor. The air enters the EC motor on one side of the stator, passes by heatsinks attached to the electronic circuitry, passes axially through stator air channels, and exits through the air outlets in the cylindrical shell of the rotor. Because the fan blades of the impeller fan are planar and not curved, the cooling air is unidirectional regardless of the direction of rotation of the rotor and the fan. 
     The stator is over molded with plastic in order to dampen vibrations. Likewise, the housing surrounding the stator and the electronic controller is over molded. 
     Further objects, features and advantages will become apparent upon consideration of the following detailed description of the invention when taken in conjunction with the drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of an internal rotor EC motor in accordance with the present invention. 
         FIG.  2    is a side elevation view of the internal rotor EC motor in accordance with the present invention. 
         FIG.  3    is a left end elevation view of the internal rotor EC motor in accordance with the present invention. 
         FIG.  4    is a section view of the internal rotor EC motor as seen along line  4 - 4  of  FIG.  3    in accordance with the present invention. 
         FIG.  5    is a section view of the internal rotor EC motor as seen along line  5 - 5  of  FIG.  3    in accordance with the present invention. 
         FIG.  6    is a perspective view of the internal rotor EC motor with the electronic controller removed to show internal detail in accordance with the present invention. 
         FIG.  7    is a right end elevation view of the internal rotor EC motor with the electronic controller and impeller fan removed to show internal detail in accordance with the present invention. 
         FIG.  8    is a perspective view of the stator, the rotor, and the impeller fan of the internal rotor EC motor in accordance with the present invention. 
         FIG.  9    is a perspective view of the stator and the rotor of the internal rotor EC motor in accordance with the present invention. 
         FIG.  10    is a perspective view of the stator and the rotor of the internal rotor EC motor in accordance with the present invention. 
         FIG.  11    is a right end elevation view of the stator and the rotor of the internal rotor EC motor in accordance with the present invention. 
         FIG.  12    is a perspective view of a first embodiment of the rotor (ferrite rotor) of the internal rotor EC motor in accordance with the present invention. 
         FIG.  13    is an elevation view of the first embodiment of the rotor (ferrite rotor) of the internal rotor EC motor in accordance with the present invention. 
         FIGS.  14 A and  14 B  are schematic views of the first embodiment of the rotor (ferrite rotor) of the internal rotor EC motor in accordance with the present invention. 
         FIGS.  15 A and  15 B  are schematic views of the first embodiment of the rotor (ferrite rotor) of the internal rotor EC motor in accordance with the present invention. 
         FIG.  16    is an elevation view of a second embodiment of the rotor (neo-ferrite rotor) of the internal rotor EC motor in accordance with the present invention. 
         FIGS.  17 A and  17 B  are schematic views of the second embodiment of the rotor (neo-ferrite rotor) of the internal rotor EC motor in accordance with the present invention. \ 
         FIG.  18    is a schematic view of the second embodiment of the rotor (neo-ferrite rotor) of the internal rotor EC motor in accordance with the present invention. 
         FIGS.  19 A- 19 D  are schematic views of the second embodiment of the rotor (neo-ferrite rotor) of the internal rotor EC motor in accordance with the present invention. 
         FIG.  20    is a schematic view of the second embodiment of the rotor (neo-ferrite rotor) of the internal rotor EC motor in accordance with the present invention. 
         FIG.  21    is a perspective view of an external rotor EC motor in accordance with the present invention. 
         FIG.  22    is a perspective view of the external rotor EC motor in accordance with the present invention. 
         FIG.  23    is a perspective view of the external rotor EC motor with the external rotor removed in accordance with the present invention. 
         FIG.  24    is a perspective view of the external rotor EC motor with the external rotor removed in accordance with the present invention. 
         FIG.  25    is a perspective view of the external rotor EC motor with the external rotor and the stator cowl removed in accordance with the present invention. 
         FIG.  26    is a front elevation view of the external rotor EC motor with the external rotor, the stator cowl, and the stator removed in accordance with the present invention. 
         FIG.  27    is a right side elevation view of the external rotor EC motor with the external rotor, the stator cowl, and the stator removed in accordance with the present invention. 
         FIG.  28    is a side elevation view of the external rotor EC motor in accordance with the present invention. 
         FIG.  29    is a perspective view of the rotor of the external rotor EC motor in accordance with the present invention. 
         FIG.  30    is a perspective view of the stator of the external rotor EC motor in accordance with the present invention. 
         FIG.  31    is a section view of the external rotor EC motor as seen along line  31 - 31  in  FIG.  22    in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning to  FIGS.  1 - 6   , an internal rotor, electronically commutated DC motor  10  (internal rotor EC motor) has a housing  20  that includes a cylindrical controller shell  14 , a cylindrical stator shell  16 , and a right end portion  12 . The cylindrical controller shell  14  is attached to the cylindrical stator shell  16  by means of circumferentially spaced screws  21 . An electronic controller  22  is mounted inside the cylindrical controller shell  14 . The internal rotor EC motor  10  has a left end  24  and a right end  26 . 
     The internal rotor EC motor  10  has an outer stator  30  and an internal ferrite rotor  62 . With reference to  FIGS.  8 - 11   , the stator  30  has a structural circular core back  32  with inwardly extending steel laminate teeth  34  that terminate in concave inner ends  35 . The teeth  34  are circumferentially spaced around the circular core back  32  and define an opening  28  for accommodating the rotor  62 . The teeth  34  are wound with electromagnetic coils  38  that are insulated from the teeth  34 . 
     The right end portion  12 , the cylindrical stator shell  16 , and the stator coil section  18  of the housing  20  are produced by plastic over molding of the stator  30 . The plastic over molding encapsulates all of the stator circular core back  32 , the stator coils  38 , and the teeth  34  except for the concave inner ends  35  of the teeth  34 . As a result of over molding of the circular core back  32 , the teeth  34 , and the stator coils  38 , axially oriented stator coil open passages  48  ( FIGS.  5  and  7   ) our created between the teeth  34 . The plastic used to over mold the stator and create the housing  20  is Rynite polyethylene terephthalate (available from DuPont) or any other plastic materials having similar molding and heat transfer characteristics. 
     The ferrite rotor  62  is mounted on a shaft  56 . The shaft in turn is mounted on bearings  58  for rotation of the rotor and shaft inside the opening  28  of the stator  30  ( FIGS.  7  and  9   ). An impeller fan  60  with impeller fan blades  61  is attached to the shaft  56  for rotation with the shaft  56  and the rotor  62 . 
     The electronic controller  22  controls the energization of the coils  38  of the stator  30  to produce a rotating magnetic field to interact with permanent magnets comprising part of the rotor  62  to produce rotation of the rotor  62 . As a result, the electronic controller  22  produces heat that must be dissipated from the EC motor  10 . In addition, energization of the electromagnetic stator coils  38  to produce the rotating magnetic field also produces heat that must be dissipated from the internal rotor EC motor  10 . 
     In order to deal with the heat produced by the electronic controller  22  and the stator coils  38 , the internal rotor EC motor  10  has an air management system that includes the impeller fan  60 , air inlets  44 , radially oriented air passages  46 , axially oriented stator cooling passages  48  in the stator  30 , and air outlets  50  in the right end portion  12  of the housing  20 . The radially oriented air passages  46  are routed adjacent to the cylindrical controller shell  14  and thereby adjacent to the electronic controller  22 . The proximity of the radially oriented air passages  46  to the electronic controller  22  assists in dissipating heat from the electronic controller  22 . Likewise, the axially oriented open cooling passages  48  pass directly through the stator  30  and adjacent to and between the stator coils  38 . In operation, ambient air is drawn into air inlets  44  and through the radially oriented air passages  46  by the impeller fan  60 . The air is then expelled from the impeller fan through the axially oriented cooling passages  48  and out of the air outlets  50 . As best shown in  FIG.  6   , the impeller fan blades  61  of the impeller fan  60  are planar. Consequently, the air flows from the air inlets  44  to the air outlets  50  regardless of the direction of rotation of the impeller fan  60 . While the air management system  42  of the present invention has been described with respect to the internal rotor EC motor  10 , the operative principles of the air management system  42  are equally applicable to other electric motors. 
     Turning to  FIGS.  12  and  13   , the ferrite rotor  62  has a hub  64  attached to the shaft  56 . The hub  64  supports  10  silicon steel laminates  66  evenly spaced around an outer circumference  63  of the rotor  62 . Rectangular shaped permanent ferrite magnets  70  are positioned within gaps between adjacent steel laminates  66  and are slightly recessed from the outer circumference  63  of the rotor  62 . Wedge-shaped permanent ferrite magnets  68  are positioned radially between the silicon steel laminates  66  and the hub  64  and are spaced circumferentially from each other. 
     Turning to  FIGS.  14 A and  14 B , the ferrite rotor  62  was optimized using Maxwell 2D FEA software. The width and length of the rectangular magnets  70  were varied to maximize torque output. The width of the rectangular magnets  70  was first set, and then the maximum length of the rectangular magnets was determined so that the rectangular magnets fit in the rotor without the magnets interfering with each other (see  FIGS.  14 A and  14 B ). The area of each configuration was calculated, and the maximum area was selected (see Table 1).) 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Area of 
                 Area of 
                 Total 
               
               
                 Width 
                 Length 
                 Rectangle 
                 wedge 
                 Area 
               
               
                 (mm) 
                 (mm) 
                 (mm 2 ) 
                 (mm 2 ) 
                 (mm 2 ) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 5 
                 23.08 
                 115.4 
                 60 
                 175.4 
               
               
                 6 
                 21.54 
                 129.24 
                 46.83 
                 176.07 
               
               
                 7 
                 20 
                 140 
                 35.17 
                 175.17 
               
               
                 8 
                 18.46 
                 147.68 
                 25.14 
                 172.82 
               
               
                 9 
                 16.92 
                 152.28 
                 16.74 
                 169.02 
               
               
                 10 
                 15.38 
                 153.8 
                 9.99 
                 163.79 
               
               
                 11 
                 13.84 
                 152.24 
                 4.9 
                 157.14 
               
               
                   
               
            
           
         
       
     
     The outer radius  65  of the wedge-shaped magnet  68  was then increased to maximize torque output. Any increase in magnet material in the rotor would thus decrease performance. The rotor  62  requires that some area above the wedge-shaped magnet  68  have saliency (ferro-magnetic). Increasing the radius of the wedge-shaped magnet  68  ( FIG.  15 B  and  FIG.  15 A ) decreases the amount of saliency thus reducing torque output. 
       FIG.  16    shows an alternative rotor embodiment, namely a neodymium-ferrite (neo-ferrite) rotor  74  for the internal rotor EC motor  10 . The neo-ferrite rotor  74  has a center hub  76  attached to the shaft  56  of the internal rotor EC motor  10 . The hub  76  supports  10  silicon steel laminates  78  evenly spaced around an outer circumference  75 . Rectangular shaped permanent neodymium magnets  82  are positioned within gaps between adjacent steel laminates  78 , are spaced circumferentially from each other, and are slightly recessed from the outer circumference  75 . Wedge-shaped permanent ferrite magnets  80  are positioned radially between the silicon steel laminates  78  and the hub  76  and are spaced circumferentially from each other. The wedge-shaped permanent ferrite magnets  80  have outer radius  84  that contacts the silicon steel laminates  78  and an inner radius  86  that conforms to the circumference of the hub  76 . Each wedge-shaped ferrite magnet  80  has a step  88  on each side between the outer radius  84  and the inner radius  86 . Adjacent steps  88  between two adjacent the wedge-shaped ferrite magnets  80  create a recess that accommodates the inner end  90  of each of the rectangular neodymium magnets  82 . 
     With reference to  FIGS.  17 A and  17 B , the neo-ferrite rotor  74  includes alternate permanent neodymium magnets  82  and silicon steel laminates  78 . The neo-ferrite rotor  74  in  FIGS.  17 A and  17 B  was optimized by modeling neo-ferrite rotor  74  and reducing the thickness of the rectangular neodymium magnets  82  until performance dropped below the target performance. 
     With reference to  FIG.  18   , an interior permanent magnet spoke type rotor  74  was then simulated using less magnet material for the rectangular neodymiun magnets  82  than for the rotor  74  shown in  FIGS.  17 A and  17 B . Air gaps  92  were added between the rectangular neodymium magnets  82  to reduce magnetic leakage thus increasing performance. 
     With reference to  FIGS.  19 A- 19 D , the spoke type rectangular neodymium magnets  82  were then reduced in length until the performance dropped below the target performance. The air gaps  92  between the neodymium magnets  82  were then filled with wedge-shaped ferrite magnets  80  which increased performance. 
     With reference to  FIG.  20   , the inner and outer radius of the ferrite magnets  80  were varied to maximize performance of the neo-ferrite rotor  74  resulting in an optimal combination of neodymium magnets  82  and ferrite magnets  82  minimize cost and maximize performance. The ferrite rotor  62  is lower cost than the neo-ferrite rotor  74  because neodymium is an order of magnitude more expensive per kg compared to ferrite. Neodymium also has higher magnetic flux than ferrite. For those reasons, the neo-ferrite rotor  74  is more efficient but is higher cost then the ferrite rotor  62 . 
     A second embodiment of the electrically commutated DC motor is an external rotor EC motor  110 . In the external rotor EC motor  110  in accordance with the present invention is shown in  FIGS.  21 - 31   . The external rotor EC motor  110  has a housing that includes a cylindrical controller shell  112  and a cylindrical stator cowl  150 . A stationary stator  130  is attached to the cylindrical controller shell  112  and the cylindrical stator cowl  130  by means of connection tabs  114 , cowl spacers  154 , stator standoff posts  140  ( FIG.  30   ), and connector screws  156  threaded into the stator standoff posts  140 . An electronic controller  116  is mounted inside the cylindrical controller shell  112 . Heatsinks  120  are thermally attached to the electronic controller  116  to dissipate heat generated by the electronics within the electronic controller  116  ( FIGS.  21 ,  23 ,  25   ,  26 , and  27 ). Electrical connectors  118  are provided to connect power and control signals to the external rotor DC motor  110 . 
     With reference to  FIGS.  23 ,  24 ,  25 , and  30   , the stationary stator  130  has a hub  132  within which are fitted stator bearings  144 . Reinforcing ribs  142  radiate from the hub  132  and terminate at their distal ends with stator standoff posts  140  that, as previously described, serve to connect the stator  132  to the cylindrical controller shell  112  and the stator cowl  150 . In the particular embodiment shown in  FIG.  30   , the stator  130  has 12 individual stator silicon steel laminate teeth  134 . A gap or air channel  138  circumferentially separates the individual teeth  134 . Each tooth  134  is wound with a conductive electromagnetic coil (not shown) to produce a rotating electromagnetic force as commonly understood in the art. The stator  130  has a plastic over molded structure  136  that covers the teeth  134  and the electromagnetic coil except for the convex outer tooth surface  146 . The over molded structure  136  further leaves gaps or air channels  138  between the individual teeth  134 . The plastic for the over molded structure is Rynite as previously described. 
     The rotor  160  includes a hub  164  to which a rotor shaft  166  is fixed. The rotor shaft  166  is mounted for rotation in stator bearings  144  ( FIG.  31   ). An end cover  168  extends from the hub  164  and terminates with a cylindrical rotor shell  162 . The end cover  168  has reinforcing ribs  170  on its outside surface. The inside surface of the end cover  168  comprises an impeller fan  174  ( FIG.  29   ). The impeller fan  174  includes planar radially extending inner fan blades  176  and planar radially extending outer fan blades  178 . The cylindrical rotor shell  162  has a number of air outlets  172  spaced around its periphery. A series of spaced apart permanent magnets  182  are attached around the internal surface of the cylindrical rotor shell and axially offset from the air outlets  172 . 
     In operation, the rotating magnetic field created by the teeth  134  of the stator  130  interact with the permanent magnets  182  of the rotor  160  causing the rotor  160  to spin on the rotor shaft  166  within the bearings  144 . As the rotor  160  spins, the fan blades  176  and  178  pull ambient air into the cowl inlet openings  152 , past the heatsinks  120 , through the stator air channels  138  and into the impeller fan  174 . The fan blades  176  and  178  then expelled the air through air outlets  172  as shown by line  180  in  FIG.  31   . Consequently, the ambient air first dissipates heat from the heatsinks  120  to keep the electronics of the electronic controller  116  cool. Next, the ambient air passes through the stator air channels  138  to keep the stator  130  cool. Because the fan blades  176  and  178  are planar and not curved, the ambient air is pulled into the cowl inlet openings  152 , through the stator air channels  138 , and pushed out through the air outlets  172  regardless of the direction of rotation of the fan  174 . 
     While this invention has been described with reference to preferred embodiments thereof, it is to be understood that variations and modifications can be affected within the spirit and scope of the invention as described herein and as described in the appended claims.