Patent Publication Number: US-2022239184-A1

Title: Electric motor

Description:
TECHNICAL FIELD 
     The present disclosure relates to an electric motor. 
     BACKGROUND ART 
     A typical motor includes a shaft, a rotor fixed to the shaft and rotating integrally with the shaft, and a stator facing the rotor with a spacing in the radial direction. The energization of the motor increases the temperatures of a stator core and a stator coil included in the stator, and the temperatures of a rotor core and a rotor conductor included in the rotor. As the temperature of the rotor increases, the temperature of the shaft provided with the rotor also increases. The temperature rise in the shaft leads to an increase in the temperatures of bearings to support the shaft such that the shaft is rotatable, and an increase in the temperature of a lubricant charged in the bearings. The increased temperatures of the bearings and the lubricant cause problematic phenomena, such as variations in the sizes of the spaces inside the bearings, and deterioration of the lubricant. 
     Some existing techniques have been trying to cool components, such as stator core, stator conductor, rotor core, and rotor conductor, by introducing ambient air from an air-sending device disposed outside the motor to an inside of the motor, and causing the ambient air introduced into the motor to flow via air passages extending through the stator core or the gap between the stator core and the rotor core, for example. The techniques also have been trying to cool bearings by causing ambient air to flow in the vicinity of the bearings in an electric motor including brackets that retain the bearings, one of which brackets has introduction holes and the other of which has discharge holes. The ambient air is introduced by the rotation of a fan fixed to the shaft via the introduction holes of the bracket into the motor. A typical motor of this type is disclosed in Patent Literature 1. In the motor disclosed in Patent Literature 1, a frame has an introduction hole on the side surface, and a bracket that faces a fan has an introduction hole, a first discharge hole, and a second discharge hole adjacent to the first discharge hole. The ambient air is fed from an air-sending device disposed outside the motor, enters the motor via the introduction hole of the side surface of the frame, and exits the motor via the first discharge hole of the bracket. The rotation of the fan fixed to the shaft causes the ambient air entering the motor via the introduction hole of the bracket to exit the motor via the second discharge hole. This configuration can cool bearings as well as the stator core, the stator conductor, the rotor core, and the rotor conductor. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Unexamined Japanese Patent Application Publication No. 2017-046377 
     SUMMARY OF INVENTION 
     Technical Problem 
     The ambient air entering the motor via the introduction hole of the bracket contains foreign materials, such as dust and water. In the motor disclosed in Patent Literature 1, the ambient air entering via the introduction hole of the bracket may flow in the opposite direction without exiting via the second discharge hole and may come into contact with the components, such as the stator conductor and the rotor conductor. The contact of the ambient air containing foreign materials with the components, such as the stator conductor and the rotor conductor, may cause a failure in the motor. This problem may also occur in an outer-rotor motor, although the motor disclosed in Patent Literature 1 is an inner-rotor motor. 
     An objective of the present disclosure, which has been accomplished in view of the above situations, is to provide an electric motor less susceptible to failures caused by foreign materials contained in the ambient air and capable of cooling the components inside the motor. 
     Solution to Problem 
     In order to achieve the above objective, an electric motor according to an aspect of the present disclosure includes a shaft, a rotor, a stator, bearings, a fan, a frame, and a guide. The shaft is supported to be rotatable about a rotational axis. The rotor is disposed outwardly of the shaft in the radial direction, and rotates integrally with the shaft. The stator faces the rotor with a spacing therebetween in the radial direction. The bearings support the shaft such that the shaft is rotatable. The fan rotates integrally with the shaft. The frame has a shape of a cylinder having closed ends, accommodates the rotor, the stator, and the fan, and retains the bearings. The guide is disposed outwardly of the fan in the radial direction. The frame has inlet holes and outlet holes. The inlet holes are disposed in the surface facing the fan in the direction of the rotational axis to allow ambient air to flow into an inside of the electric motor. The outlet holes are disposed outwardly of the inlet holes in the radial direction in the surface facing the fan in the direction of the rotational axis, to allow the ambient air entering through the inlet holes to flow out to an outside of the electric motor. The guide has a shape for suppressing foreign materials contained in the ambient air entering through the inlet holes from coming into contact with the stator and the rotor. 
     Advantageous Effects of Invention 
     According to an aspect of the present disclosure, the ambient air entering the motor through the inlet holes disposed in the surface facing the fan in the direction of the rotational axis is discharged through the outlet holes disposed outwardly of the inlet holes in the radial direction, thereby cooling the components inside the motor. The motor includes the guide having a shape for suppressing foreign materials contained in the ambient air entering through the inlet holes from coming into contact with the stator and the rotor, and is therefore less susceptible to failures caused by foreign materials contained in the ambient air entering through the inlet holes. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of an electric motor according to Embodiment 1 of the present disclosure; 
         FIG. 2  is a side view of the motor according to Embodiment 1; 
         FIG. 3  is a side view of a fan according to Embodiment 1; 
         FIG. 4  is a partial cross-sectional view of the motor according to Embodiment 1; 
         FIG. 5  illustrates flows of ambient air in the motor according to Embodiment 1; 
         FIG. 6  is a cross-sectional view of an electric motor according to Embodiment 2 of the present disclosure; 
         FIG. 7  is a cross-sectional view of an electric motor according to Embodiment 3 of the present disclosure; 
         FIG. 8  is a cross-sectional view of an electric motor according to Embodiment 4 of the present disclosure; 
         FIG. 9  is a cross-sectional view of an electric motor according to Embodiment 5 of the present disclosure; 
         FIG. 10  is a side view of a fan according to Embodiment 5; 
         FIG. 11  is a cross-sectional view of an electric motor according to Embodiment 6 of the present disclosure; 
         FIG. 12  is a cross-sectional view of an electric motor according to Embodiment 7 of the present disclosure; 
         FIG. 13  is a cross-sectional view of an electric motor according to Embodiment 8 of the present disclosure; 
         FIG. 14  is a cross-sectional view of an electric motor according to Embodiment 9 of the present disclosure; and 
         FIG. 15  is a side view of the motor according to Embodiment 9. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An electric motor according to embodiments of the present disclosure is described in detail below with reference to the accompanying drawings. In the drawings, the components identical or corresponding to each other are provided with the same reference symbol. 
     Embodiment 1 
     An electric motor according to Embodiment 1 is described below focusing on an exemplary motor used to drive a railway vehicle.  FIG. 1  illustrates the motor according to Embodiment 1. An electric motor  1  illustrated in  FIG. 1  includes a frame  11 , a shaft  15  accommodated in the frame  11 , a rotor  16  to rotate integrally with the shaft  15 , and a stator  17  mounted on the frame  11 . In  FIG. 1 , the Z axis corresponds to the vertical direction, the Y axis is parallel to a rotational axis AX of the shaft  15 , and the X axis is orthogonal to the Y and Z axes. The rotational axis AX is represented by the dashed and single-dotted line in  FIG. 1 . Since the motor  1  is used to drive the railway vehicle, the frame  11  is fixed to the bogie of the railway vehicle, and one end of the shaft  15  is coupled to the axle of the railway vehicle via joints and gears. The frame  11  includes a stator frame  12  having a cylindrical shape and brackets  13  and  14  that close both ends of the stator frame  12  in the Y-axis direction. The rotor  16  is disposed outwardly of the shaft  15  in the radial direction. The rotor  16  includes a rotor core  18  engaging with the shaft  15 , and a rotor conductor  19  inserted in a groove on the outer periphery of the rotor core  18 . The stator  17  includes a stator core  20  mounted on the stator frame  12  of the frame  11 , and a stator conductor  21  inserted in a groove on the stator core  20 . The outer periphery of the rotor core  18  and the inner periphery of the stator core  20  face each other while being spaced from each other. The motor  1  further includes bearings  22  and  23  to support the shaft  15  such that the shaft  15  is rotatable. The bearing  22  is retained by the bracket  13 , while the bearing  23  is retained by the bracket  14 . The end of the shaft  15  adjacent to the bracket  13  is coupled to the axle of the railway vehicle via joints and gears, which are not illustrated, so that the rotation of the shaft  15  drives the railway vehicle. The end of the shaft  15  coupled to the axle is called the inboard end, while the other end is called the outboard end. 
     In order to cool the rotor  16  and the stator  17 , the frame  11  has an inlet opening  24  to allow ambient air to flow into an inside of the motor  1 , and an outlet opening  25  to allow the ambient air entering through the inlet opening  24  to flow out to an outside of the motor  1 . In detail, the inlet opening  24  and the outlet opening  25  are disposed in a portion of the stator frame  12  of the frame  11  including the top end in the Z-axis direction. The inlet opening  24  is provided with a duct  30  therearound, so that the air fed from an air-sending device, which is not illustrated, disposed outside the motor  1  flows through the duct  30  into the motor  1  via the inlet opening  24 . The outlet opening  25  is provided with a cover  32  to suppress foreign materials, such as dust, rain, and snow, which fall in the vertical direction from entering the motor  1 . The stator core  20  has air passages  31  that extends through the stator core  20  from one to the other ends in the direction of the rotational axis AX, and thereby allows the ambient air entering via the inlet opening  24  to flow inside the motor  1 . 
     In order to cool the bearing  22 , the bracket  13  has inlet holes  27  to allow ambient air to flow into an inside of the motor  1 , and outlet holes  28  to allow the ambient air entering through the inlet holes  27  to flow out to an outside of the motor  1 . As illustrated in  FIG. 2 , which is a view of the motor  1  as seen toward the negative side in the Y-axis direction, the inlet holes  27  are disposed around the rotational axis AX while being spaced in the circumferential direction. The outlet holes  28  are also disposed around the rotational axis AX while being spaced in the circumferential direction. 
     The motor  1  further includes a fan  26  to rotate integrally with the shaft  15 , in order to introduce ambient air via the inlet holes  27 . The fan  26  includes a primary blade  261  mounted on the shaft  15  and having a circular profile in a section orthogonal to the rotational axis AX, and secondary blades  262  extending from the primary blade  261 . 
     The diameter of the primary blade  261  in a section orthogonal to the rotational axis AX increases as the section approaches the bracket  13 . As illustrated in  FIG. 3 , which is a view of the fan  26  mounted on the shaft  15  as seen toward the negative side in the Y-axis direction, the primary blade  261  is provided with a plurality of secondary blades  262  spaced from each other in the circumferential direction. The secondary blades  262  extend from the primary blade  261  in the direction toward the bracket  13 . 
     The inlet holes  27  are closer to the ground and to the wheels of the railway vehicle than the inlet opening  24 . The ambient air entering through the inlet holes  27  thus may contain foreign materials, such as dust and water, splashed during running of the railway vehicle, and tends to contain more foreign materials than those of the ambient air entering through the inlet opening  24 . In order to suppress the ambient air entering through the inlet holes  27  containing more foreign materials from coming into contact with the components, such as the rotor conductor  19  and the stator conductor  21 , and thereby causing a trouble in the motor  1 , the motor  1  further includes a guide  29  disposed outwardly of the fan  26  in the radial direction and having a shape for suppressing the ambient air entering through the inlet holes  27  from coming into contact with the stator  17  and the rotor  16 . The guide  29  is mounted on the bracket  13 , extends toward the edge of the fan  26  in the radial direction, and has a shape for suppressing the ambient air entering through the inlet holes  27  from flowing through the gap between the fan  26  and the guide  29 . 
     The guide  29  and the fan  26  are shaped to define a labyrinth channel therebetween so as to suppress the ambient air entering through the inlet holes  27  from flowing through the gap between the guide  29  and the fan  26  and coming into contact with the components, such as the rotor conductor  19  and the stator conductor  21 . In detail, as illustrated in  FIG. 4 , the edge of the guide  29  that faces the fan  26  has a first uneven portion  291  including annular recesses recessed in the direction of the rotational axis AX and extending around the central axis coinciding with the rotational axis AX, and annular protrusions protruding in the direction of the rotational axis AX and extending around the central axis coinciding with the rotational axis AX. The annular recesses and the annular protrusions of the first uneven portion  291  are alternately arranged in the radial direction. The edge of the fan  26  in the radial direction that faces the guide  29  has a second uneven portion  263  including annular recesses recessed in the direction of the rotational axis AX and extending around the central axis coinciding with the rotational axis AX, and annular protrusions protruding in the direction of the rotational axis AX and extending around the central axis coinciding with the rotational axis AX. The annular recesses and the annular protrusions of the second uneven portion  263  are alternately arranged in the radial direction. The first uneven portion  291  and the second uneven portion  263  face each other in the direction of the rotational axis AX and thereby define a labyrinth channel therebetween. The above-described structures of the guide  29  and the fan  26  allow the fan  26  to rotate integrally with the shaft  15  and define a labyrinth channel between the guide  29  and the fan  26 . For example, the recesses in the first uneven portion  291  and the protrusions in the second uneven portion  263  face each other with a spacing of less than  10  millimeters in the direction of the rotational axis AX, while the protrusions in the first uneven portion  291  and the recesses in the second uneven portion  263  face each other with a spacing of less than  10  millimeters in the direction of the rotational axis AX. 
     The energization of the motor  1  having the above configuration increases the temperatures of the stator core  20 , the stator conductor  21 , the rotor core  18 , and the rotor conductor  19 . According to the temperature rises, the temperatures of the shaft  15  and the bearings  22  and  23  also increase. As represented by the solid-line arrows in  FIG. 5 , the air fed from the air-sending device disposed outside the motor  1  is introduced via the inlet opening  24 , flows through the air passages  31  or the gap between the rotor  16  and the stator  17 , and is discharged via the outlet opening  25 . The air fed from the air-sending device flows inside the motor  1  and can thereby cool the components inside the motor  1 . 
     When the rotor core  18  and the shaft  15  rotate integrally in response to energization of the motor  1 , the fan  26  rotates integrally with the shaft  15 , thereby introducing the air outside the motor  1  via the inlet holes  27 . As represented by the dashed-line arrows in  FIG. 5 , the ambient air entering through the inlet holes  27  flows in the vicinity of the bearing  22 , flows outward in the radial direction, and is discharged via the outlet holes  28 . The ambient air entering through the inlet holes  27  flows in the vicinity of the bearing  22  and can thereby cool the bearing  22 . 
     As described above, the frame  11  of the motor  1  according to Embodiment 1 has the inlet holes  27  and the outlet holes  28  as well as the inlet opening  24  and the outlet opening  25 . The ambient air fed from the air-sending device and entering the motor  1  via the inlet opening  24  flows through the air passages  31  or the gap between the rotor  16  and the stator  17 , and exits the motor  1  via the outlet opening  25 . The ambient air entering the motor  1  through the inlet holes  27  flows in the vicinity of the bearing  22 , flows outward in the radial direction along the fan  26  and the guide  29 , and exits the motor  1  through the outlet holes  28 . These flows of ambient air can cool the components inside the motor  1 . In addition, the guide  29  can suppress foreign materials contained in the ambient air entering the motor  1  through the inlet holes  27  from coming into contact with the components, such as the rotor conductor  19  and the stator conductor  21 . The motor  1  is therefore less susceptible to failures caused by foreign materials coming into contact with the components, such as the rotor conductor  19  and the stator conductor  21 . The motor  1  does not require an external component, such as filter or cover, for blocking foreign materials over the inlet holes  27 , and therefore has a sufficiently small size. 
     Embodiment 2 
     The fan  26  may have any shape that facilitates introduction of ambient air via the inlet holes  27 . The following description is directed to an example as Embodiment 2 in which both surfaces of the primary blade  261  of the fan  26  are provided with secondary blades. The fan  26  of an electric motor  2  according to Embodiment 2 illustrated in  FIG. 6  further includes secondary blades  264  extending from the primary blade  261  in the direction away from the bracket  13 , in addition to the configuration of the fan  26  of the motor  1  according to Embodiment 1. 
     The ambient air fed from the air-sending device, entering the motor  2  through the inlet opening  24 , and flowing through the air passages  31  or the gap between the rotor  16  and the stator  17 , is delivered outward in the radial direction due to the rotation of the fan  26  including the secondary blades  264 . The ambient air can therefore exit the motor  2  smoothly through the outlet opening  25 . 
     As described above, the fan  26  of the motor  2  according to Embodiment  2  has the secondary blades  264  in addition to the secondary blades  262 , and can thus facilitate discharge of ambient air through the outlet opening  25 . The ambient air in the motor  2  can therefore flow smoothly, leading to the higher cooling efficiency inside the motor  2  than that inside the motor  1 . 
     Embodiment 3 
     The following description is directed to another exemplary shape of the fan  26  as Embodiment 3 in which only one of the surfaces of the primary blade  261  of the fan  26  that faces the stator  17  is provided with secondary blades. The fan  26  of an electric motor  3  according to Embodiment 3 illustrated in  FIG. 7  includes the primary blade  261  as in Embodiments 1 and 2, and the secondary blades  264  as in Embodiment 2. The surface of the primary blade  261  that faces the bracket  13  is not provided with a secondary blade. The rotation of the primary blade  261  causes ambient air to enter the motor  3  through the inlet holes  27 , flow along the fan  26  and the guide  29 , and exit the motor  3  through the outlet holes  28 . Because of no secondary blade on the surface of the primary blade  261  that faces the bracket  13 , the motor  3  can reduce wind noise to leak from the motor  3  through the inlet holes  27  and the outlet holes  28 . 
     As described above, the primary blade  261  of the fan  26  of the motor  3  according to Embodiment 3 is provided with the secondary blades  264  extending in the direction away from the bracket  13 . Since the fan  26  includes no secondary blade on the surface of the primary blade  261  that faces the bracket  13 , the motor  3  can reduce wind noise to leak from the motor  3  through the inlet holes  27  and the outlet holes  28 . 
     This configuration can make the motor  3  quieter. 
     Embodiment 4 
     The following description is directed to another exemplary shape of the fan  26  as Embodiment 4 in which no secondary blade is provided on the primary blade  261  of the fan  26 . The fan  26  of an electric motor  4  according to Embodiment 4 illustrated in  FIG. 8  includes the primary blade  261  as in Embodiments 1 to 3, but no secondary blade is provided on the primary blade  261 . Because of no secondary blade on both main surfaces of the primary blade  261 , the motor  4  can reduce not only wind noise to leak from the motor  4  through the inlet holes  27  and the outlet holes  28  but also wind noise to leak from the motor  4  through the outlet opening  25 . 
     As described above, since the fan  26  of the motor  4  according to Embodiment  4  includes no secondary blade on both main surfaces of the primary blade  261 , the motor  4  can reduce not only wind noise to leak from the motor  4  through the inlet holes  27  and the outlet holes  28  but also wind noise to leak from the motor  4  through the outlet opening  25 . This configuration can make the motor  4  quieter. 
     Embodiment 5 
     The motor may exclude the guide when another component performs the functions of the guide. The following description is directed to an example as Embodiment 5 in which the fan performs the functions of the guide. An electric motor  5  according to Embodiment 5 illustrated in  FIG. 9  excludes the guide, and includes a fan  33  integrated with a guide, instead of the fan  26  of the motor  1  according to Embodiment 1. The fan  33  includes a primary blade  331  mounted on the shaft  15  and having a circular profile in a section orthogonal to the rotational axis AX, and secondary blades  332  extending from the primary blade  331 . 
     The primary blade  331  has a shape for suppressing the ambient air entering through the inlet holes  27  from coming into contact with the stator  17  and the rotor  16 . Specifically, the diameter of the primary blade  331  in a section orthogonal to the rotational axis AX increases as the section approaches the bracket  13 . The primary blade  331  has a curved portion  331   a  swelling outward in the radial direction, and an edge portion  331   b  continuous to the curved portion  331   a  and extending along the bracket  13 . The curved portion  331   a  guides the ambient air entering through the inlet holes  27  to the outlet holes  28 . The edge portion  331   b  is located adjacent to the bracket  13 . 
     Specifically, the edge portion  331   b  is located adjacent to the bracket  13  such that the configuration can suppress the ambient air entering through the inlet holes  27  from flowing through the gap between the edge portion  33  lb and the bracket  13  and coming into contact with the components, such as the rotor conductor  19  and the stator conductor  21 . The spacing between the edge portion  331   b  and the bracket  13  is preferably less than 5 millimeters. As illustrated in  FIG. 10 , which is a view of the fan  33  as seen toward the negative side in the Y-axis direction, the primary blade  331  is provided with a plurality of secondary blades  332  spaced from each other in the circumferential direction. The secondary blades  332  extend from the primary blade  331  in the direction toward the bracket  13 . 
     The fan  33  expands outward in the radial direction, and the edge of the fan  33  in the radial direction is located adjacent to the bracket  13 . For example, the edge of the fan  33  in the radial direction and the bracket  13  face each other with a spacing of less than 10 millimeters in the direction of the rotational axis AX. 
     The fan  33  rotates integrally with the shaft  15  in response to energization of the motor  5  having the above configuration, thereby introducing the air outside the motor  5  into the motor  5  via the inlet holes  27 . The ambient air entering through the inlet holes  27  flows in the vicinity of the bearing  22 , flows outward in the radial direction along the fan  33 , and exits the motor  5  through the outlet holes  28 . The ambient air entering through the inlet holes  27  flows in the vicinity of the bearing  22  and can thereby cool the bearing  22 . 
     As described above, the components inside the motor  5  according to Embodiment 5 are cooled by flows of the ambient air entering the motor  5  through the inlet opening  24  or the inlet holes  27 . Since the edge of the fan  33  in the radial direction is located adjacent to the bracket  13 , the configuration can suppress foreign materials contained in the ambient air entering the motor  5  through the inlet holes  27  from coming into contact with the components, such as the rotor conductor  19  and the stator conductor  21 . The motor  5  is therefore less susceptible to failures caused by foreign materials coming into contact with the components, such as the rotor conductor  19  and the stator conductor  21 . The motor  5  does not require an external component, such as filter or cover, for blocking foreign materials over the inlet holes  27 , and therefore has a sufficiently small size. 
     Embodiment 6 
     The fan  33  may have any shape that facilitates introduction of ambient air through the inlet holes  27  and suppress foreign materials contained in the ambient air from coming into contact with the components, such as the rotor conductor  19  and the stator conductor  21 . The following description is directed to an example as Embodiment 6 in which both surfaces of the primary blade  331  of the fan  33  are provided with secondary blades. The fan  33  of an electric motor  6  according to Embodiment 6 illustrated in  FIG. 11  further includes secondary blades  333  extending from the primary blade  331  in the direction away from the bracket  13 , in addition to the configuration of the fan  33  of the motor  5  according to Embodiment 5. 
     The ambient air fed from the air-sending device, entering the motor  6  through the inlet opening  24 , and flowing through the air passages  31  or the gap between the rotor  16  and the stator  17 , is delivered outward in the radial direction due to the rotation of the fan  33  including the secondary blades  333 . The ambient air can therefore exit the motor  6  smoothly through the outlet opening  25 . 
     As described above, the fan  33  of the motor  6  according to Embodiment 6 includes the secondary blades  333  in addition to the secondary blades  332 , and can thus facilitate discharge of ambient air through the outlet opening  25 . The ambient air in the motor  6  can therefore flow smoothly, leading to the higher cooling efficiency inside the motor  6  than that inside the motor  5 . 
     Embodiment 7 
     The following description is directed to another exemplary shape of the fan  33  as Embodiment 7 in which only one of the surfaces of the primary blade  331  of the fan  33  that faces the stator  17  is provided with secondary blades. The fan  33  of an electric motor  7  according to Embodiment 7 illustrated in  FIG. 12  includes the primary blade  331  as in Embodiments 5 and 6, and the secondary blades  333  as in Embodiment 6. The surface of the primary blade  331  that faces the bracket  13  is not provided with a secondary blade. The rotation of the primary blade  331  causes ambient air to enter the motor  7  through the inlet holes  27 , flow along the fan  33 , and exit the motor  7  through the outlet holes  28 . Because of no secondary blade on the surface of the primary blade  331  that faces the bracket  13 , the motor  7  can reduce wind noise to leak from the motor  7  via the inlet holes  27  and the outlet holes  28 . 
     As described above, the primary blade  331  of the fan  33  of the motor  7  according to Embodiment 7 is provided with the secondary blades  333  extending in the direction away from the bracket  13 . Since the fan  33  includes no secondary blade on the surface of the primary blade  331  that faces the bracket  13 , the motor  7  can reduce wind noise to leak from the motor  7  via the inlet holes  27  and the outlet holes  28 . This configuration can make the motor  7  quieter. 
     Embodiment 8 
     The following description is directed to another exemplary shape of the fan  33  as Embodiment  8  in which no secondary blade is provided on the primary blade  331  of the fan  33 . The fan  33  of an electric motor  8  according to Embodiment 8 illustrated in  FIG. 13  includes the primary blade  331  as in Embodiments 5 to 7, but no secondary blade is provided on the primary blade  331 . Because of no secondary blade on both main surfaces of the primary blade  331 , the motor  8  can reduce not only wind noise to leak from the motor  8  via the inlet holes  27  and the outlet holes  28  but also wind noise to leak from the motor  8  via the outlet opening  25 . 
     As described above, since the fan  33  of the motor  8  according to Embodiment 8 includes no secondary blade on both main surfaces of the primary blade  331 , the motor  8  can reduce not only wind noise to leak from the motor  8  via the inlet holes  27  and the outlet holes  28  but also wind noise to leak from the motor  8  via the outlet opening  25 . This configuration can make the motor  8  quieter. 
     Embodiment 9 
     The bracket  13  may have any shape that is located in the vicinity of the fan  33  and suppress foreign materials contained in the ambient air from coming into contact with the components, such as the rotor conductor  19  and the stator conductor  21 . The following description is directed to an example as Embodiment 9 in which the edge of the fan  33  is located inside a groove provided on the bracket  13 . The bracket  13  of an electric motor  9  according to Embodiment 9 illustrated in  FIG. 14  is provided with a groove  131 . As illustrated in  FIG. 15 , which is a view of the motor  9  as seen toward the negative side in the Y-axis direction, the groove  131  has an annular shape around the central axis coinciding with the rotational axis AX. The inlet holes  27  are disposed around the rotational axis AX while being spaced in the circumferential direction. The outlet holes  28  are also disposed around the rotational axis AX while being spaced in the circumferential direction. As illustrated in  FIG. 14 , the edge of the fan  33  is located inside the groove  131 . 
     The fan  33  rotates integrally with the shaft  15  in response to energization of the motor  9  having the above configuration, thereby introducing the air outside the motor  9  via the inlet holes  27 . The ambient air entering through the inlet holes  27  flows in the vicinity of the bearing  22 , flows outward in the radial direction along the fan  33 , and exits the motor  9  through the outlet holes  28 . The ambient air entering through the inlet holes  27  flows in the vicinity of the bearing  22  and can thereby cool the bearing  22 . 
     As described above, since the edge of the fan  33  of the motor  9  according to Embodiment  9  is located inside the groove  131 , the configuration can suppress foreign materials contained in the ambient air entering the motor  9  through the inlet holes  27  from coming into contact with the components, such as the rotor conductor  19  and the stator conductor  21 . The motor  9  is therefore less susceptible to failures caused by foreign materials coming into contact with the components, such as the rotor conductor  19  and the stator conductor  21 . 
     The above-described embodiments are not intended to limit the scope of the present disclosure. The above-mentioned position of the inlet opening  24  is a mere example, and the inlet opening  24  may also be provided in the bracket  14 . The air-sending device disposed outside the motors  1  to  9  may be a fan to rotate in accordance with the rotation of the shaft  15 . Although the motors  1  to  9  in the above-described embodiments are of an inner-rotor type in which the rotor  16  is disposed on the inner side of the stator  17  in the radial direction, the motors according to the embodiments of the present disclosure may also be of an outer-rotor type in which a rotor is disposed outwardly of a stator in the radial direction. 
     The guide  29  may have any shape that suppresses the ambient air entering through the inlet holes  27  from coming into contact with the stator  17  and the rotor  16 . For example, the guide  29  may have a curved surface swelling outward in the radial direction. 
     The primary blade  331  may have any shape that suppresses the ambient air entering through the inlet holes  27  from coming into contact with the stator  17  and the rotor  16 . 
     The foregoing describes some example embodiments for explanatory purposes. Although the foregoing discussion has presented specific embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention is defined only by the included claims, along with the full range of equivalents to which such claims are entitled. 
     REFERENCE SIGNS LIST 
       1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8 ,  9  Electric motor 
       11  Frame 
       12  Stator frame 
       13 ,  14  Bracket 
       15  Shaft 
       16  Rotor 
       17  Stator 
       18  Rotor core 
       19  Rotor conductor 
       20  Stator core 
       21  Stator conductor 
       22 ,  23  Bearing 
       24  Inlet opening 
       25  Outlet opening 
       26 ,  33  Fan 
       27  Inlet hole 
       28  Outlet hole 
       29  Guide 
       31  Duct 
       32  Air passage 
       32  Cover 
       131  Groove 
       261 ,  331  Primary blade 
       262 ,  264 ,  332 ,  333  Secondary blade 
       263  Second uneven portion 
       291  First uneven portion 
       331   a  Curved portion 
       331   b  Edge portion 
     AX Rotational axis