Abstract:
According to various aspects, exemplary embodiments of an electric motor are provided herein. In one embodiment of this disclosure, an electric motor includes a rotor, at least one end of the rotor includes at least one blade and at least one array of micro-features, wherein heat generated by the rotor is dissipated by the at least one blade and the at least one array of micro-features. 
     In another embodiment, a method of manufacturing an electric motor having a rotor, the method comprising machining a piece of conductive material to create micro-features on at least one end of the conductive material; and inserting the conductive material into the rotor.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims priority from U.S. Provisional Patent Application No. 62/318,845, which was filed on Apr. 6, 2016, which application is hereby incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    Electric motors typically include two parts, a rotor and a stator. The stator is a stationary component, while the rotor rotates based on the relationship between the magnetic fields of the rotor and stator. The magnetic fields of the stator and rotor can be created in different ways including installing conductive windings around the teeth of a stator or rotor, using permanent magnets on rotors or stators, or employing rotor bars which are made of a conductor such as aluminum or copper. 
         [0003]    During operation, the rotor and stator generate heat, which if not dissipated, can lead to motor failure. In induction machines where rotor bars are employed, some designs include end rings on each end of the rotor. The end rings can include molded tabs, which are referred to as wafters. As the rotor rotates, heat will generate in the rotor bars. Because the wafters are molded on the end rings, the wafters will rotate along with the rotor and will work to cool the rotor bars and the end windings of the stator. 
         [0004]    In this setup, there are disadvantages. First, where the rotor includes rotor bars of aluminum or copper, heat generated in the rotor can move to the ends of the rotor because these materials are good thermal conductors. But for rotors constructed out of materials that are not good thermal conductors, such as permanent magnets, this design is not effective because it cannot effectively draw out the heat generated by the magnetics. Moreover, the wafters described herein, are not optimal; cooling of electric motors, including induction machines, can be enhanced. And this is desirable because enhanced cooling will allow the motor to receive more current and produce a higher power output. 
       SUMMARY 
       [0005]    According to various aspects, exemplary embodiments of an electric motor are provided herein. In one embodiment of this disclosure, an electric motor includes a rotor, at least one end of the rotor includes at least one blade and at least one array of micro-features, wherein heat generated by the rotor is dissipated by the at least one blade and the at least one array of micro-features. 
         [0006]    In another embodiment, a method of manufacturing an electric motor having a rotor, the method comprising machining a piece of conductive material to create micro-features on at least one end of the conductive material; and inserting the conductive material into the rotor. 
         [0007]    According to another embodiment, a method of manufacturing an electric motor having a rotor, the method comprising pouring and casting a piece of conductive material into the rotor, with the casting forming the conductive material into a conductive material having at least one end, wherein the at least one end includes micro-features. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of an electric motor. 
           [0009]      FIG. 2  is a side view of an electric motor. 
           [0010]      FIG. 3  is an axial view of components of an electric motor. 
           [0011]      FIG. 4  is a perspective view of components of an electric motor. 
           [0012]      FIG. 5  is an axial view of an end cap of an electric motor. 
           [0013]      FIG. 6  is a side view of an end cap of an electric motor. 
           [0014]      FIG. 7  is a perspective view of an end cap of an electric motor. 
           [0015]      FIG. 8  is a perspective view of an electric motor. 
           [0016]      FIG. 9  is an axial view of components of an electric motor. 
           [0017]      FIG. 10  is an axial view of components of an electric motor. 
           [0018]      FIG. 11  is a side view of components of an electric motor. 
           [0019]      FIG. 12  is a perspective view of components of an electric motor. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  is a perspective view of an electric motor  100 . The electric motor  100  includes a stator  102 , a rotor  104 , end caps  106  and  107 , a shaft  108  to which the rotor  104  delivers torque during operation, and a casing  109 . The left end of the rotor includes a plurality of blades  110  in between which are a plurality of arrays of micro-features  112 . Each of the arrays includes projections that are arranged in a trapezoidal fashion, but can be in other configurations such as rectangular, circular, or triangular. The configurations could also be staggered or aligned. The projections of the micro-features  112  have a circular cross-section, but the cross-section of the micro-features  112  could be other shapes such as rectangular, circular, ovular, rhomboidal, or the shape of a hydrofoil or an airfoil. The right side of the rotor  104  also includes a plurality of blades  118  and a plurality of arrays of micro-features, which cannot be observed in this perspective view but will be shown in subsequent figures. Each array of micro-features  112  on the left side of the rotor  104  corresponds with an array of micro-features on the right side of the rotor. Specifically, each corresponding pair of micro-feature arrays are two ends of an insert made of conductive material, referred to herein as a spreader and described in more detail below. In the embodiment of  FIG. 1 , there are six spreaders inserted into the rotor  104 , and as a result, there are six corresponding pairs of micro-feature arrays. Additionally, the blades  110  and  118  can be integral with the spreaders, or alternatively the blades  110  and  118  can be integral with the rotor  104 . The blades  110  and  118  could also be discrete components attached to either the rotor  104  or the spreaders. 
         [0021]    The end caps  106  and  107  includes a plurality of arrays of micro-features  114  and  116  respectively. Each array of micro-features  114  and  116  is arranged in a rectangular fashion but can be in other configurations such as circular, triangular, or trapezoidal. Like the micro-features  112 , the micro-features  114  and  116  have a circular cross-section, but the cross-section of the micro-features  114  and  116  could be other shapes such as rectangular, circular, ovular, or rhomboidal. 
         [0022]    During operation of the motor  100 , the rotor  104  rotates and because the blades  110  and  118  and the micro-features  112  (and the corresponding micro-features on the right side of the rotor) are on the rotor, they also will rotate. Overtime, the rotor and stator will generate heat. The heat generated by the rotor will be conducted to the ends of the rotor  104  via the spreader. When the heat reaches the ends of the rotor, the blades  110  and  118  and the micro-features  112  (and the corresponding micro-features on the right side of the rotor  104 ) will cool the rotor and stator by dissipating the heat generated in the rotor. 
         [0023]    More specifically, the rotation of the blades  110  and  118  causes an axisymmetric circulation of air that goes from the rotor  104 , to the stator  102 , to the end caps  106  and  107 , and back to the rotor  104 . In this circulation, the heat from the rotor gets dissipated by flowing from the rotor along the described axisymmetric circulation. When the heat reaches the end caps  106  and  107 , the micro-features  114  and  116  of the end caps will cause the heat to dissipate to the ambient air outside the motor  100 . 
         [0024]    The micro-features described enhance the cooling of the motor  100 . As described, heat generated by the rotor  104  will be thermally conducted to the ends of the rotor  104  via the spreaders. The blades  110  and  118  generate the axisymmetrical circulation of air, which will flow in between the gaps of, and around individual micro-features. The surface of the micro-features increases the area of the ends of the rotor (where generated heat is conducted to via the spreaders) and the flow of the circulating air increases its velocity as it flows in between and around individual micro-features. The increase in area and velocity enhances the heat dissipation from the rotor  104 . 
         [0025]    Similarly, when the heat dissipated from the rotor flows along the axisymmetric airflow and reaches the micro-features  114  and  116  on the end caps  106  and  107 , the micro-features  114  and  116  will enhance the cooling of the motor  100  by dissipating the heat out to the ambient air outside the motor  100  due to the surface area of the micro-features and the increased velocity of the air flow in between and around the micro-features. 
         [0026]    The arrangement of micro-features and blades described are useful in rotors that comprise permanent magnets. In permanent magnet machines, magnets can generate heat through eddy currents. These eddy currents generate heat on the magnets that can degrade their function. One problem is that magnets are not good thermal conductors, so the generated heat tends to stay with the magnet. When used in permanent magnet machines, the spreader acts as a thermal capacitance that conducts the heat from the magnets and moves it to the ends of the rotor, where it is dissipated as described. 
         [0027]      FIG. 2  is a side view of motor  100  so that internal parts of the motor  100  can be observed.  FIG. 2  illustrates the stator  102 , a rotor  104 , end caps  106  and  107 , a shaft  108 , and a casing  109 . On the left side of the rotor are blades  110  and micro-features  112 , and on the right side of the rotor are blades  118  and micro-features  120 . On the end caps  106  and  107  are micro-features  114  and  116  respectively.  FIG. 2  shows arrows  122  and  124  which illustrate the generally axisymmetric circulation created by the blades  110  and  118 . 
         [0028]      FIG. 3  is an axial view of components of the electric motor  100 . This figure shows the stator  102  inside of which is the rotor  104 . One of the ends of the rotor  104  includes blades  110  and micro-features  112 .  FIG. 3  also shows end cap  107  having micro-features  116 .  FIG. 4  is a perspective view of components of the electric motor  100 . This figure shows the stator  102 , rotor  104 , and the shaft  108 . On the rotor  104  are the blades  110  and micro-features  112 . 
         [0029]      FIG. 5  is an axial view of end cap  106  and  FIG. 6  is a side view of end cap  106 .  FIG. 5  shows the array of micro-features  114  and  FIG. 6  shows from the side, the projection of the micro-features  114 .  FIG. 7  shows the micro-features on the end cap  106  from a perspective view, showing micro-features  114 . 
         [0030]      FIG. 8  is a perspective view of an electric motor  200 . The electric motor  200  includes a stator  202 , a rotor  204 , end caps  206  and  207 , a shaft  208  to which the rotor  204  delivers torque during operation, and a casing  209 . The left end of the rotor includes a plurality of blades  210  in between which are a plurality of arrays of micro-features  212 . Each of the arrays include projections that are arranged in a trapezoidal fashion, but can be in other configurations such as rectangular, circular, or triangular. The projections of the micro-features  212  have a circular cross-section, but the cross-section of the micro-features  212  could be other shapes such as rectangular, circular, ovular, or rhomboidal. The right side of the rotor  204  also includes a plurality of blades  218  and a plurality of arrays of micro-features, which cannot be observed in this perspective view. The micro-features on the right side of the rotor  204  are symmetrical to those on the left side, as described in  FIG. 1 . Each array of micro-features  212  on the left side of the rotor  204  corresponds with an array of micro-features on the right side of the rotor. Specifically, each corresponding pair of micro-feature arrays are two ends of an insert made of conductive material, referred to herein as a spreader and described in more detail below. In the embodiment of  FIG. 8 , there are six spreaders inserted into the rotor  204 , and as a result, there are six corresponding pairs of micro-feature arrays. Additionally, the blades  210  and  218  can be integral with the spreaders, or alternatively the blades  210  and  218  can be integral with the rotor  204 . The blades  210  and  218  could also be discrete components attached to either the rotor  204  or the spreaders. 
         [0031]    The end caps  206  and  207  includes a plurality of arrays of micro-features  214  and  216  respectively. Each array of micro-features  214  and  216  is arranged in a rectangular fashion but can be in other configurations such as circular, triangular, or trapezoidal. Like the micro-features  212 , the micro-features  214  and  216  have a circular cross-section, but the cross-section of the micro-features  214  and  216  could be other shapes such as rectangular, circular, ovular, or rhomboidal. 
         [0032]    During operation, the heat generated in rotor  204  is conducted to the ends of the rotor via the spreaders wherein the heat is dissipated via the blades and micro-features on the rotor  204 , similar to that described in  FIG. 1 . In  FIG. 8 , however, the motor  200  also includes ducts  222  and  224 . During operation, the blades  210  and  218  rotate to create a circulation of air. In  FIG. 1 , the circulation created by the blades directed airflow axisymmetrically from the rotor to the stator and then to the end caps. In the embodiment in  FIG. 8 , the circulated air does not flow to the stator due to the ducts  222  and  224 . Instead, in  FIG. 8 , due to the ducts, the air circulates from the rotor  204  to the end caps  206  and  207 . With the ducts  222  and  224 , there is a close coupling convection between the rotor  204  and the end caps  206  and  207  such that the heat dissipated from the rotor  204  is directed to the micro-features  214  and  216  of the end caps  206  and  207 . 
         [0033]      FIG. 9  is an axial view of components of the electric motor  200 . This figure shows the stator  202  inside of which is the rotor  204 . One of the ends of the rotor  204  includes blades  210  and micro-features  212 .  FIG. 9  also shows the duct  224  and end cap  207  having micro-features  216 . 
         [0034]      FIG. 10  is another axial view of components of the electric motor  200 , which shows the end cap  207  having micro-features  216 , and also shows the duct  224 . The duct  224  includes ribs  226 . The ribs  226  provide structural support for the duct  224  and also direct airflow to the micro-features  216 . During operation, some of the air flow from the rotor (via the blades  210  and  218 ) will contact the ribs  226  at which point the ribs  226  will assist in direct the airflow to the micro-features  216 . The ribs  226 , therefore, increase the efficiency of the heat transfer from the rotor to the end caps and ultimately out of the motor  200 . While end cap  207  is shown in  FIG. 10 , it will be appreciated that ribs, like ribs  226 , can be included on duct  222  on end cap  206 . 
         [0035]      FIG. 11  is a side view of the end cap  207  showing the micro-features  216  and duct  224  and ribs  226 , and  FIG. 12  is a perspective view showing these features. The ribs  226  are triangular, but it will be appreciated that other geometries such as cubical or pyramidal can be applied without departing from the scope of this disclosure. 
         [0036]    The rotors described herein may be manufactured where the spreaders are machined to include the micro-features on each end; alternatively the micro-features and the