PATENT DOCUMENT

Publication Number: US-10498280-B1
Application Number: US-201715682838-A
Country: US
Kind Code: B1

Title: Electric motor with shielded phase windings

Abstract:
An electric motor includes a configuration that directs at least a portion of an electric field generated by phase windings into a stator.

Claims:
What is claimed is: 
     
       1. An electric motor, comprising:
 a rotor that extends along a rotation axis and has an outer periphery; 
 a stator having an inner periphery that is separated from the outer periphery of the rotor by a radial air gap; 
 slots formed in the stator, each slot having a slot width, and each slot being oriented along a line; 
 phase windings connected to the stator and disposed at least partially in the slots, wherein the phase windings are energized and de-energized to induce torque on the rotor by interaction of magnetic fields generated by the phase windings with the rotor to cause rotation of the rotor around the rotation axis; and 
 openings that extend from each slot to the inner periphery of the stator, 
 wherein each opening is defined by opposed surfaces that are spaced apart by an opening width, 
 wherein the opposed surfaces of each opening are parallel to one another, 
 wherein the opposed surfaces of each opening are oriented at an opening angle between 15 degrees and 75 degrees relative to the line, and 
 wherein the opening width of each opening is between five percent and twenty-five percent of the slot width. 
 
     
     
       2. The electric motor of  claim 1 , wherein the opening width and the opening angle of the opening are configured such that any straight-line path between the phase windings and the rotor is obstructed by a portion of the stator. 
     
     
       3. The electric motor of  claim 1 , wherein the rotor is spaced from the stator by a radial air gap that is larger than the opening width. 
     
     
       4. The electric motor of  claim 1 , wherein the opening width is constant. 
     
     
       5. The electric motor of  claim 1 , wherein the stator includes internal radial walls that extend across each slot adjacent to the opening such that a portion of the stator is positioned between each slot and the rotor. 
     
     
       6. The electric motor of  claim 1 , wherein the phase windings are wire-wound type phase windings. 
     
     
       7. The electric motor of  claim 1 , wherein the phase windings are bar-wound type phase windings.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/379,289, entitled “Electric Motor with Shielded Phase Windings,” which was filed on Aug. 25, 2016 and is incorporated herein by reference in its entirety; this application also claims the benefit of U.S. Provisional Application No. 62/417,530, entitled “Electric Motor with Shielded Phase Windings,” which was filed on Nov. 4, 2016 and is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The application relates generally to electric motors. 
     BACKGROUND 
     Some electric motors are driven by multiphase pulse width modulation (PWM) voltages. Driving an electric motor with a PWM voltage creates a large amount of electrical noise, especially when compared with driving an electric motor with a continuous sinusoidal driving voltage. As a result of the electrical noise and parasitic capacitances, voltages build up on the rotor. When the voltage on the rotor becomes large, it may discharge from the rotor to the frame of the electric motor across the bearings. This may damage the bearings and/or the bearing races that retain and guide the bearings relative to the rotor and the frame of the electric motor. The damage to the rotor and bearing races that results from voltage discharge across the bearings may reduce the lifespan of the bearings and cause failure of the electric motor. 
     SUMMARY 
     One aspect of the disclosed embodiments is an electric motor that includes a rotor, a stator having an inner periphery, a slot formed in the stator, the slot having a slot width and the slot being oriented along a line, phase windings connected to the stator and disposed at least partially in the slot, and an opening that extends from the slot to the inner periphery of the stator. The opening is defined by opposed surfaces that are spaced apart by an opening width and the opening width is between five and twenty-five percent of the slot width. 
     Another aspect of the disclosed embodiments is an electric motor that includes a rotor, a stator, a slot formed in the stator, and phase windings that are connected to the stator and disposed at least partially in the slot. The electric motor also includes a shield that directs at least a portion of an electric field generated by the phase windings into the stator. The shield has a plurality of shield elements that are bonded together in an axially stacked configuration. 
     Another aspect of the disclosed embodiments is an electric motor that includes a rotor, a stator having an inner periphery, a slot formed in the stator, phase windings connected to the stator and disposed at least partially in the slot, an insulating element disposed in the slot between the phase windings and the rotor. The insulating element extends axially along an axial length of the slot. A shield layer is disposed on the insulating element to direct at least a portion of an electric field generated by the phase windings into the stator, and the shield layer is in contact with the stator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram showing parasitic capacitances acting on an electric motor. 
         FIG. 2  is a side cross-section view of an electric motor according to a first example. 
         FIG. 3  is an axial cross-section view of an electric motor according to a second example. 
         FIG. 4  is an illustration showing a stator slot of the electric motor of  FIG. 3 . 
         FIG. 5  is an illustration showing a first alternative stator slot that can be used with the electric motor of  FIG. 3 . 
         FIG. 6  is an illustration showing a second alternative stator slot that can be used with the electric motor of  FIG. 3 . 
         FIG. 7  is an illustration showing a third alternative stator slot that can be used with the electric motor of  FIG. 3 . 
         FIG. 8  is a side cross-section view of an electric motor according to a third example. 
         FIG. 9  is a perspective view illustration that shows a shield assembly of the electric motor of  FIG. 8 . 
         FIG. 10  is an illustration showing a portion of the rotor and the stator of the electric motor of  FIG. 8 . 
         FIG. 11  is a side cross-section view of an electric motor according to a fourth example. 
         FIG. 12  is a perspective view illustration that shows a shield structure of the electric motor of  FIG. 11 . 
         FIG. 13  is an illustration showing a portion of the rotor and the stator of the electric motor of  FIG. 11 . 
         FIG. 14  is a side cross-section view of an electric motor according to a fifth example. 
         FIG. 15  is an illustration showing an axial cross-section a shielded insulator of the electric motor of  FIG. 14 . 
         FIG. 16  is an illustration showing a portion of the rotor and the stator of the electric motor of  FIG. 14 . 
         FIG. 17  is an illustration showing application of a shield coating to a portion of the stator of the electric motor of  FIG. 14  according to an alternative implementation. 
         FIG. 18  is an exploded view of a stator assembly that includes a stator and a plurality of winding units. 
         FIG. 19  is an illustration showing a portion of the stator assembly of  FIG. 16  and a portion of a rotor. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure herein is directed to shields for electric motors that reduce parasitic capacitance between phase windings and a rotor of an electric motor by directing at least part of an electric field generated by the phase windings into the stator. The shields are positioned between the phase windings and the rotor and are formed from materials that are able to conduct the electric field. The shields may be in contact with the stator or formed as part of the stator. 
       FIG. 1  is a circuit diagram showing parasitic capacitances acting on an electric motor  100 . The electric motor  100  includes a rotor  102 , phase windings  104 , a stator  106 , a frame  108 , and bearings  110 . Common mode noise is coupled from the phase windings  104  to the bearings by parasitic capacitances between different metal parts of the electric motor  100 . In particular, during operation of the electric motor  100 , a parasitic capacitance C_wr is present from the phase windings  104  to the rotor  102 , a parasitic capacitance C_wf is present from the phase windings  104  to the stator  106  and the frame  108 , a parasitic capacitance C_rf is present from the rotor  102  to the frame  108 , and a parasitic capacitance C_b is present across the bearings  110 . As can be appreciated with reference to  FIG. 1 , the voltage across the bearings  110  may be reduced by decreasing the parasitic capacitance C_wr. The voltage across the bearings  110  may also be reduced by increasing the parasitic capacitance C_wf, or increasing the parasitic capacitance C_rf if the common mode noise source from the phase windings  104  to the stator  106  and the frame  108  is more like a current source rather than voltage source. Since many motor drives are equivalent to a voltage source, the source of the common mode noise has a relatively stiff voltage supply, and reducing the bearing voltage is most readily accomplished by reducing the parasitic capacitance C_wr. 
     In the electric motors described herein, structures are configured or incorporated to at least partially shield the rotor  102  from the electric field generated by the phase windings  104 . As one example, shielding the rotor  102  may include interposing electrically conductive pathways between the phase windings  104  and the rotor  102 , to cause the electric field from the phase windings  104  to flow into the stator  106  instead of into the rotor  102 . 
       FIG. 2  is a side cross-section view of an electric motor  200  according to a first example. The electric motor  200  has a rotor  202 , phase windings  204  that are connected to a stator  206 , a frame  208 , bearings  210 , a shaft  212 , and a shield  214 . The stator  206  may be a laminated structure that is formed from a plurality of plates that are stacked axially and joined together. The stator  206  extends from an inner periphery  218  to an outer periphery  232 . A plurality of slots  216  are formed in the stator  206 . The phase windings  204  are partially disposed in the slots  216  and include end turn portions  205  that extend out of the slots  216 . The shaft  212  is connected to the rotor  202  and is supported with respect to the frame  208  by the bearings  210 . The phase windings  204  are energized and de-energized to induce torque on the rotor  202  in a conventional manner by interaction of magnetic fields generated by the phase windings  204  with magnets disposed in the rotor  202 . 
     The shield  214  is positioned at the interior periphery of the stator  206  adjacent to a radial air gap between the stator  206  and the rotor  202 . The shield  214  is formed from a material that is able to conduct the electric field, such as metal. The shield  214  functions to direct at least some of the electric field that is generated by the phase windings  204  back into the stator  206  so that it does not cross the radial air gap and enter the rotor. By reducing the amount of the electric field that is incident on the rotor  202 , the parasitic capacitance C_wr is reduced. In some embodiments, the shield  214  may be an integral portion of the stator  206 , formed by a geometric arrangement that guides the electric field. In some embodiments, the shield  214  may be formed separately from the stator  206  and are connected to the inner periphery of the stator  206 . 
       FIG. 3  is an axial cross-section view of an electric motor  300  according to a second example. The electric motor  300  has a rotor  302 , phase windings  304  that are connected to a stator  306 , a frame  308 , bearings  310 , a shaft  312 , and slots  316  that are formed in the stator  306  between portions of the stator  306  (e.g. stator teeth). The stator  306  may be a laminated structure that is formed from a plurality of plates that are stacked axially and joined together. The shaft  312  is connected to the rotor  302  and is supported with respect to the frame  308  by the bearings  310 . The shaft  312  extends along an axis that defines a center of rotation for the rotor  302 . 
       FIG. 4  is an illustration showing a portion of the rotor  302  and the stator  306  including one of the slots  316  of the stator  306  electric motor  300  of  FIG. 3 . The phase windings  304  are disposed at least partially in the slots  316  that are formed in the stator  306 . In the illustrated example, the phase windings  304  are bar-wound type phase windings, but other configurations may be used. The slots  316  are closed ended slots that lack openings to an inner periphery  318  of the stator  306 . Thus, a portion of the stator  306  is positioned between an internal radial wall  320  of the slot  316  and the inner periphery  318  of the stator  306  in the radial direction. This portion of the stator  306  serves as a shield and directs at least some of the electric field that is generated by the phase windings  304  back into the stator  306  so that it does not enter the rotor  302 . 
     A radial air gap  322  is present between the inner periphery  318  of the stator  306  and an outer periphery  324  of the rotor  302 . In some embodiments, a radial width of the radial air gap  322  is larger than a radial distance between the inner periphery  318  of the stator  306  and the internal radial wall  320 . The internal radial wall  320  may be the closest portion of each of the slots  316  to the inner periphery  318  of the stator  306 . 
     By reducing the electric field that is incident on the rotor  302 , the parasitic capacitance C_wr is reduced. Thus, by connecting the stator teeth, inward facing radial slot openings are avoided, and the rotor  302  is naturally shielded from the winding by changing the configuration of the stator  306 , which may be done without adding additional parts to the electric motor  300 . Eddy current is also well controlled in embodiments where the stator  306  is formed from a stack of laminated metal plates. In some embodiments, the electric motor  300  may be a bar-wound type motor in which the phase windings  304  do not need to be inserted through radially open ends of the slots  316 . 
       FIG. 5  is an illustration showing a slot  516  that can be used with the electric motor  300  of  FIG. 3 , which is as previously described except as stated herein. 
     The slot  516  is open-ended at the inner periphery  318  of the stator  306 , with an opening  526  extending from the interior of the slot  516  to the radial air gap  322 . The opening  526  has a width that is less than the full width of the slot  516 . As an example, the width of the opening  526  may be selected so that it is sufficient to allow winding of phase windings  504  with respect to the stator  306 . In the illustrated example, the phase windings  504  are of the wire-wound type, but other configurations may be utilized. The width of the opening  526  may be, for example, between five percent and twenty-five percent of the width of the slot  516 . In some embodiments, the width of the opening  526  is smaller than the radial width of the radial air gap  322 . An internal radial wall  520  may extend radially across the end of the slot  516  adjacent to the opening, such that a portion of the stator  306  is positioned between the slot  516  and the radial air gap  322  adjacent to the opening. 
       FIG. 6  is an illustration showing a slot  616  that can be used with the electric motor  300  of  FIG. 3 , which is as previously described except as stated herein. 
     The slot  616  is open-ended at the inner periphery  318  of the stator  306 , with an opening  626  extending from the interior of the slot  616  to the radial air gap  322 . The opening  626  has a width that is less than the full width of the slot  516 . As an example, the width of the opening  526  may be selected so that it is sufficient to allow winding of phase windings  604  with respect to the stator  306 . In the illustrated example, the phase windings  604  are of the wire-wound type, but other configurations may be utilized. The width of the opening  626  may be, for example, between five percent and twenty-five percent of the width of the slot  516 . In some embodiments, the width of the opening  626  is smaller than the radial width of the radial air gap  322 . An internal radial wall  620  may extend radially across the end of the slot  516  adjacent to the opening, such that a portion of the stator  306  is positioned between the slot  516  and the radial air gap  322  adjacent to the opening  526 . 
     The opening  626  is oriented at an angle relative to the slot  616 . As an example, the slot  616  may be oriented along a line  627  that extends in the radial direction of the electric motor  300  (i.e., radially outward from center of the shaft  312  and/or the rotor  302 ). The opening is defined by opposed surfaces  628 . In some embodiments, opposed surfaces  628  may be spaced at a constant distance, and may be parallel to one another. The opposed surfaces  628  may extend at an angle relative to the line  627 , such as at an angle between 15 degrees and 75 degrees. In some implementations, the width and angle of the opening are configured such that any straight-line path between the phase windings  604  and the rotor  602  is obstructed by a portion of the stator, while maintaining an unobstructed non-straight-line path through the opening  626 . 
       FIG. 7  is an illustration showing a slot  716  that can be used with the electric motor  300  of  FIG. 3 , which is as previously described except as stated herein. 
     The slot  716  is close-ended at the inner periphery  318  of the stator  306 , and has an open end  730  at an outer periphery  732  of the stator  306 . Phase windings  704  are disposed in the slot  716 . In the illustrated example, the phase windings  704  are of the wire-wound type, but other configurations may be utilized. To retain the phase windings  704  in the slot  716 , a retaining structure  734  is positioned radially outward from the stator  306  and may be in engagement with the outer periphery  732  of the stator  306 . In some embodiments, the retaining structure is a sleeve, and may be a laminated sleeve formed of stacked plates. In some embodiments, the retaining structure  734  is the frame  308  of the electric motor  300 . 
       FIG. 8  is a side cross-section view of an electric motor  800  according to a third example. The electric motor  800  has a rotor  802 , phase windings  804  that are connected to a stator  806 , a frame  808 , bearings  810 , a shaft  812 , and a shield assembly. In the illustrated example, the phase windings  804  are of the wire-wound type, but other configurations may be utilized. The stator  806  may be a laminated structure that is formed from a plurality of plates that are stacked axially and joined together. The stator  806  extends from an inner periphery  818  to an outer periphery  832 . A plurality of slots  816  are formed in the stator  806 . The phase windings  804  are partially disposed in the slots  816  and include end turn portions  805  that extend out of the slots  816 . The shaft  812  is connected to the rotor  802  and is supported with respect to the frame  808  by the bearings  810 . To guide electric field from the phase windings  804  back into the stator  806 , the electric motor  800  includes a shield assembly  814  in the form of a thin-walled cylindrical structure that is positioned between the rotor  802  and the stator  806 , such as by attachment to an inner periphery of the stator  806 . Thus, the stator  806  is adjacent to and in contact with an exterior surface of the shield assembly  814 , and the rotor  802  is adjacent to an interior surface of the shield assembly  814  and is spaced from the interior surface of the shield assembly  814  by a radial air gap. 
       FIG. 9  is a perspective view illustration that shows the shield assembly  814 . The shield assembly includes a plurality of shield elements such as shield rings  815  that are connected together. Each shield ring  815  has an axial height that is a fraction of the axial height of the stator  806 . As an example, each shield ring  815  may have an axial height between 0.5 percent and five percent of the axial height of the stator  806 . Each shield ring  815  may be a one piece structure with a continuous outer periphery and a continuous inner periphery. As an example, the shield rings  815  may be formed by stamping. The shield rings  815  are stacked in an axially adjacent configuration with respect to each other to define a substantially cylindrical structure that is positioned at the interior periphery of the stator  806  adjacent to a radial air gap between the stator  806  and the rotor  802 . Thus, the shield assembly  814  may be a laminated structure formed from a plurality of the shield rings  815  that are bonded together. By forming the shield assembly  814  from a plurality of the shield rings  815 , eddy currents in the axial direction are reduced. During fabrication of the electric motor  800 , the shield rings  815  may be installed after the phase windings  804  are installed, which allows installation of the phase windings  804  with respect to the stator by winding. 
     The shield rings  815  are formed from a material that is able to conduct an electric field, such as metal. The shield rings  815  function to direct at least some of the electric field that is generated by the phase windings  804  back into the stator  806  so that it does not cross the radial air gap and enter the rotor. By reducing the electric field that is incident on the rotor  802 , the parasitic capacitance C_wr is reduced. The shield rings  815  are formed separately from the stator  806  and are connected to the inner periphery of the stator  806  in order to guide the portion of the electric field that is incident upon the shield rings  815  back into the stator  806 . 
       FIG. 10  is an illustration showing a portion of the rotor  802  and the stator  806  of the electric motor  800  of  FIG. 8 . The phase windings  804  are disposed at least partially in the slots  816  that are formed in the stator  806 . The slots  816  are open ended slots that extend radially outward from openings at the inner periphery  818  of the stator  806 . The shield assembly  814  is positioned radially inward from the stator  806  and may be in contact with the inner periphery  818  of the stator  806 . 
     A radial air gap  822  is present between the shield rings  815  and an outer periphery  824  of the rotor  802 . The shield rings  815  are positioned between the open ends of slots  816  and the rotor  802 . Thus, the shield rings  815  are also positioned between the phase windings  804  and the rotor  802 . Because the electric field generated by the phase windings  804  passes through the shield rings  815  before reaching the rotor  802 , at least some of the electric field that is generated by the phase windings  804  is directed back into the stator  806  by the shield rings  815  so that it does not enter the rotor  802 . By reducing the amount of the electric field that is incident on the rotor  802 , the parasitic capacitance C_wr is reduced. 
       FIG. 11  is a side cross-section view of an electric motor  1100  according to a fourth example. The electric motor  1100  has a rotor  1102 , phase windings  1104  that are connected to a stator  1106 , a frame  1108 , bearings  1110 , a shaft  1112 , and a plurality of shield structures  1114  that are each associated with one of a plurality of slots  1116  of the stator  1106 . In the illustrated example, the phase windings  1104  are of the wire-wound type, but other configurations may be utilized. The stator  1106  may be a laminated structure that is formed from a plurality of plates that are stacked axially and joined together. The stator  1106  extends from an inner periphery  1118  to an outer periphery  1132 . The phase windings  1104  are partially disposed in the slots  1116  and include end turn portions  1105  that extend out of the slots  1116 . The shaft  1112  is connected to the rotor  1102  and is supported with respect to the frame  1108  by the bearings  1110 . 
       FIG. 12  is a perspective view illustration that shows one of the shield structures  1114 . The shield structure  1114  includes a plurality of shield elements such as shield plates  1115  that are connected together. Each shield plate  1115  has an axial height that is a fraction of the axial height of the stator  1106 . As an example, each shield plate  1115  may have an axial height between 0.5 percent and five percent of the axial height of the stator  1106 . The shield plates  1115  are stacked in an axially adjacent configuration with respect to each other to define elongate structures that are each positioned within one of the plurality of slots  1116  of the stator  1106 , radially outward from the inner periphery  1118  of the stator  1106 . In addition, the shield plates  1115  may be bonded together to form a laminated structure. Thus, each shield structure  1114  may be in the form of an axial stack of a plurality of the shield plates  1115  that is present in each of the slots  1116  of the stator  1106 . By forming the shield assembly from a plurality of the shield plates  1115  that are segmented axially, eddy currents in the axial direction are reduced. During fabrication of the electric motor  1100 , the shield plates  1115  may be installed after the phase windings  1104  are installed, which allows installation of the phase windings  1104 . 
     The shield plates  1115  are formed from a material that is able to conduct the electric field, such as metal. The shield plates  1115  function to direct at least some of the electric field that is generated by the phase windings  1104  back into the stator  1106  so that it does not cross the radial air gap and enter the rotor. By reducing the amount of the electric field that is incident on the rotor  1102 , the parasitic capacitance C_wr is reduced. The shield plates  1115  are formed separately from the stator  1106  and are connected to the stator  1106  inside the slots  1116  in order to guide the portion of the electric field that is incident upon the shield plates  1115  back into the stator  1106 . 
       FIG. 13  is an illustration showing a portion of the rotor  1102  and the stator  1106  of the electric motor  1100  of  FIG. 11 . The phase windings  1104  are disposed at least partially in the slots  1116  that are formed in the stator  1106 . The slots  1116  are open ended slots that extend radially outward from openings at the inner periphery  1118  of the stator  1106 . The shield plates  1115  are positioned radially inward from the inner periphery  1118  of the stator  1106  and extend across the slots  1116  such that they are in contact with opposed internal surfaces of the slots  1116 . 
     The shield plates  1115  are positioned between the phase windings  1104  and the open ends of slots  1116 . A radial air gap  1122  is present between inner periphery  1118  of the stator  1106  and the outer periphery  1124  of the rotor  1102 . Thus, the shield plates  1115  are also positioned between the phase windings  1104  and the rotor  1102 . Because the electric field generated by the phase windings  1104  passes through the shield plates  1115  before reaching the rotor  1102 , at least some of the electric field that is generated by the phase windings  1104  is directed back into the stator  1106  by the shield plates  1115  so that it does not enter the rotor  1102 . By reducing the amount of the electric field that is incident on the rotor  1102 , the parasitic capacitance C_wr is reduced. 
       FIG. 14  is a side cross-section view of an electric motor  1400  according to a fifth example. The electric motor  1400  has a rotor  1402 , phase windings  1404  that are connected to a stator  1406 , a frame  1408 , bearings  1410 , a shaft  1412 , and a shield assembly. In the illustrated example, the phase windings  1404  are of the wire-wound type, but other configurations may be utilized. The stator  1406  may be a laminated structure that is formed from a plurality of plates that are stacked axially and joined together. The stator  1406  extends from an inner periphery  1418  to an outer periphery  1432 . A plurality of slots  1416  are formed in the stator  1406 . The phase windings  1404  are partially disposed in the slots  1416  and include end turn portions  1405  that extend out of the slots  1416 . The shaft  1412  is connected to the rotor  1402  and is supported with respect to the frame  1408  by the bearings  1410 . 
     The shield assembly includes a plurality of shielded insulators  1414 . Each shielded insulator  1414  may have an axial height that is between eighty and one hundred and twenty percent of the axial height of the stator  1406 , and in some embodiments, each of the shielded insulators  1414  may have an axial height that is equal to or substantially equal to the axial height of the stator  1406 . Each shielded insulator  1414  may be an elongate structure that is positioned within one of the plurality of slots  1416  of the stator  1406 , radially outward from the inner periphery  1418  of the stator  1406 . Each shield insulator  1414  extends axially along an axial length of a respective one of the slots  1416 . During fabrication of the electric motor  1400 , the shielded insulators  1414  may be installed after the phase windings  1404  are installed, which allows installation of the phase windings  1404  through the openings of the slots  1416 , such as by winding. 
       FIG. 15  is an illustration showing an axial cross-section view of one of the shielded insulators  1414 . Each of the shielded insulators  1414  has an insulating layer  1436  and a shield layer  1438 . The insulating layer  1436  is made of a material that has electrical insulation properties, such as paper, and which does not readily conduct the electric field. The shield layer  1438  is disposed on one side of the insulating layer  1436  and is formed from a material that is able to conduct the electric field, such as metal. In some embodiments, the shield layer  1438  is a coating that is applied to the insulating layer  1436 , such as by spraying. In some embodiments, the shield layer  1438  is laminated to the insulating layer  1436 . 
     The shielded insulators are installed in the slots  1416  of the stator  1406  such that the insulating layer  1436  faces toward the phase windings  1404  and the shield layer  1438  faces away from the phase windings  1404 . The shielded insulators  1414  each extend axially along the length of a respective one of the slots  1416  along a slot opening. The shield layer  1438  of each of the shielded insulators  1414  contacts the stator  1406 , for example, at opposed internal walls of each of the slots  1416 , such that the shielded insulators  1414  function to direct at least some of the electric field that is generated by the phase windings  1404  back into the stator  1406  so that it does not cross the radial air gap and enter the rotor. By reducing the electric field that is incident on the rotor  1402 , the parasitic capacitance C_wr is reduced. 
     The shielded insulators  1414  are formed separately from the stator  1406  and are connected to the stator  1406  such as by placing them inside the slots  1416  in order to guide the portion of the electric field that is incident upon the shielded insulators  1414  back into the stator  1406 . 
       FIG. 16  is an illustration showing a portion of the rotor  1402  and the stator  1406  of the electric motor  1400  of  FIG. 14 . The phase windings  1404  are disposed at least partially in the slots  1416  that are formed in the stator  1406 . The slots  1416  are open ended slots that extend radially outward from openings at the inner periphery  1418  of the stator  1406 . The shielded insulators  1414  are positioned radially inward from the inner periphery  1418  of the stator  1406  and extend across the slots  1416  such that they are in contact with opposed internal surfaces of the slots  1416 . 
     The shielded insulators  1414  are positioned between the phase windings  1404  and the open ends of slots  1416 . A radial air gap  1422  is present between inner periphery  1418  of the stator  1406  and the outer periphery  1424  of the rotor  1402 . Thus, the shielded insulators  1414  are also positioned between the phase windings  1404  and the rotor  1402 . Because the electric field generated by the phase windings  1404  passes through the shielded insulators  1414  before reaching the rotor  1402 , at least some of the electric field that is generated by the phase windings  1404  is directed back into the stator  1406  by the shielded insulators  1414  so that it does not enter the rotor  1402 . By reducing the amount of the electric field that is incident on the rotor  1402 , the parasitic capacitance C_wr is reduced. 
       FIG. 17  is an illustration showing application of a shield coating  1738  to a portion of the stator  1406  of the electric motor  1400  of  FIG. 14  according to an alternative implementation. The previously described portions of the stator  1406  are the same except as noted herein. The shielded insulators  1414  are omitted and replaced with insulators  1736  that are similar to the insulating layer  1436  of the shielded insulators except that they lack the shield layer  1438 . The stator  1406  is assembled by first installing the phase windings  1404 , and then installing the insulators  1736  in each of the slots  1416  of the stator  1406 . After the insulators  1736  are installed in each of the slots  1416  of the stator  1406  in the manner described with respect to the shielded insulators  1414 , a shield coating  1738  is applied to the interior of the stator  1406 , by forming a layer of material on the interior of the stator  1406  including on the inner periphery  1418  and on the insulators  1736 . The shield coating  1738  may be, for example, a material that is able to conduct the electric field, such as metal that can be spray applied in melted state and subsequently harden on the inner periphery  1418  of the stator  1406  and on the insulators  1736 . The shield coating  1738  may be applied to the interior of the stator  1406  using a tool such as an applicator  1740 . As an example, the applicator  1740  may be operable to emit a spray  1742  of the material that becomes the shield coating  1738 . 
       FIG. 18  is an exploded view of a stator assembly  1807  that includes a stator  1806  and a plurality of winding units  1844  that are received in slots  1816  of the stator  1806 . The stator assembly  1807  can be incorporated in an electric motor, such as in the electric motor  200  in place of the stator  206  and the shield  214 . 
     The winding units  1844  each include a bracket  1846  and a phase winding  1804  that is disposed on the bracket  1846 . The brackets  1846  may be formed from a material that does not readily the electric field, such as plastic. A shield layer  1814  may be disposed on an interior surface of each of the brackets  1846 . 
       FIG. 19  is an illustration showing a portion of the stator assembly  1807  and a portion of a rotor  1802 . The phase windings  1804  are disposed at least partially in the slots  1816  that are formed in the stator  1806 . The slots  1816  are open ended slots that extend radially outward from openings at the inner periphery  1818  of the stator  1806 . The phase windings  1804  are further disposed in a channel  1848  that is formed on and extends peripherally around the bracket  1846 . The channel  1848  may be substantially u-shaped and defined by adjacent wall portions of the bracket  1846 . 
     The shield layer  1814  is disposed on a surface of the bracket  1846  and is positioned at the open end of the slot  1816  such that it extends between portions of the stator  1806  that are adjacent to the slot  1816  (e.g. stator teeth). The shield layer  1814  may be in contact with the stator  1806  on opposed sides of the slot. A radial air gap  1822  is present between inner periphery  1818  of the stator  1806  and the outer periphery  1824  of the rotor  1802 . Thus, the bracket  1846  serves as an insulating element that is positioned between the phase windings  1804  and the rotor  1802 , while the shield layer  1814  is disposed on the bracket  1846  and is therefore positioned between the phase windings  1804  and the rotor  1802 . Because the electric field generated by the phase windings  1804  passes through the shield layer  1814  before reaching the rotor  1802 , at least some of the electric field that is generated by the phase windings  1804  is directed back into the stator  1806  by the shield layer  1814  so that it does not enter the rotor  1802 . By reducing the amount of the electric field that is incident on the rotor  1802 , the parasitic capacitance C_wr is reduced.

Metadata:
Filing Date: 20170822
Publication Date: 20191203
Grant Date: 20191203
Priority Date: 20160825
Inventors: NIU, Li
THOMASSON, DILLON J.
ZHOU, Kan
NELSON, DAVID F.
GUAN, RUI
Assignee: APPLE INC
CPC Classifications: [{"code": "H02K2213/03", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02P29/50", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02P25/22", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02P25/26", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02P25/26", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02P25/22", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02K1/146", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 68696107