Abstract:
Provided is a bearing electrolytic corrosion countermeasure technology achieving excellent reliability without increasing the number of components. A rotating electrical machine of the invention includes: a stator; a shaft penetrating the stator; a rotor facing the stator via a gap in an axial direction; and a housing holding the stator, in which: the stator includes, in a circumferential direction, a plurality of stator units each of which includes a grounded first conductive member, a core, a bobbin, and a winding wound around the bobbin; the bobbin has a flange portion provided between the winding and the rotor; the first conductive member is provided between the flange portion and the rotor and is in contact with the core, and, in a case where projection is performed in the axial direction, the winding is provided such that a projected portion of a part of the winding wound around the bobbin is within a projected portion of the flange portion; and the first conductive member is provided such that the projected portion of the first conductive member is included in the projected portion of the flange portion.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a rotating electrical machine and particularly relates to an axial-type rotating electrical machine. 
       BACKGROUND ART 
       [0002]    In recent years, variable speed operation of a rotating electrical machine using an inverter power supply has been widely performed in view of energy saving. One of problems remarkably caused when an inverter is driven is electrolytic corrosion of a bearing. As a countermeasure against this, there is a method of preventing electrolytic corrosion of a bearing by blocking, with a conductive material, electrostatic coupling of an inverter common mode voltage from a winding to a rotor to reduce a common mode voltage (hereinafter, axis voltage) induced in the rotor, thereby reducing a voltage applied between an inner ring and an outer ring of the bearing supporting the rotor. 
         [0003]    In recent years, an axial-type rotating electrical machine has attracted attention. This rotating electrical machine has a structure in which a disk-shaped rotor and a stator are provided to face each other and is advantageous in thinning and flattening of the rotating electrical machine. This rotating electrical machine can be also structured as a double-rotor-type rotating electrical machine in which a stator is interposed between two rotors in an axial direction. In a general double-rotor-type rotating electrical machine, a plurality of independent cores each of which is wound by a winding are provided in a circumferential direction, and the general double-rotor-type rotating electrical machine includes a stator molded with resin and a rotor in which a yoke is connected to a plurality of permanent magnets provided in the circumferential direction. A torque of a motor is in proportion to a gap area that is a facing surface of the rotor and the stator. However, the double-rotor-type rotating electrical machine can increase the gap area per dimension and is therefore effective for increasing output and improving efficiency in the rotating electrical machine. The rotating electrical machine has a structure to which new magnetic materials having a low-loss property, such as amorphous, FINEMET, and nanocrystal, is effectively applicable. Those new magnetic materials are all rigid and fragile, and therefore processing thereof is difficult. In the double-rotor-type rotating electrical machine, by forming a stator core having an open slot, the core can be structured to have an extremely simple shape that is substantially a rectangular parallelepiped. Therefore, the magnetic materials can be processed to have a core shape with a simple process. 
         [0004]    Meanwhile, in a case of the double-rotor structure described above, a facing area between the winding and the rotor is large because the double-rotor structure is the open slot structure, and the core is not grounded in many cases because the double-rotor structure is covered with resin. In this case, electrostatic coupling between the winding and the rotor becomes stronger, and therefore the common mode voltage is easily induced in the bearing. 
       CITATION LIST 
     Patent Literatures 
       [0000]    
       
         PTL 1: JP-A-2004-297876 
         PTL 2: JP-A-2012-5307 
       
     
         [0007]    PTLs 1 and 2 disclose a structure for blocking a space between a stator winding and a rotor. By blocking the space between the winding and the rotor, it is possible to reduce an axis voltage to suppress electrolytic corrosion of a bearing. In PTL 1, an insulating sleeve obtained by covering, with an insulator, a whole surface of a nonmagnetic conductive plate processed to have a rectangular shape is inserted into an opening of a slot, and a core grounded on the nonmagnetic conductive plate is caused to be conductive. In PTL 2, an insulator is provided on a surface of a winding, and a conductor and an insulator are alternately provided thereon in a direction orthogonal to a flow of a magnetic flux. PTL 2 also discloses a method of using a bobbin wound by the winding as the insulator. 
       SUMMARY OF INVENTION 
     Technical Problems 
       [0008]    PTL 1 needs to add the insulating sleeve to a preexisting structure in order to block the space between the winding and the rotor, and thus, when comparing the number of components before and after the countermeasure, the number of components is increased. Meanwhile, a method of directly providing the conductor on a surface of the bobbin in PTL 2 does not increase the number of components. However, because the conductor is exposed to the surface, there is a fear that dielectric breakdown occurs between the conductor and the winding, which results in damage of the rotating electrical machine unless an insulation distance is securely provided. In a case where either disclosed technology is applied to a double-rotor-type axial-type rotating electrical machine, a ground structure of the conductor is problematic. 
         [0009]    Thus, the invention provides a bearing electrolytic corrosion countermeasure technology achieving excellent reliability without increasing the number of components and provides a technology also applicable to a double-rotor-type axial-type rotating electrical machine whose core is insulated. 
       Solution to Problems 
       [0010]    In order to solve the problems, a rotating electrical machine of the invention includes: a stator; a shaft penetrating the stator; a rotor facing the stator via a gap in an axial direction; and a housing holding the stator, in which: the stator includes, in a circumferential direction, a plurality of stator units each of which includes a grounded first conductive member, a core, a bobbin, and a winding wound around the bobbin; the bobbin has a flange portion provided between the winding and the rotor; the first conductive member is provided between the flange portion and the rotor and is in contact with the core, and, in a case where projection is performed in the axial direction, the winding is provided such that a projected portion of a part of the winding wound around the bobbin is within a projected portion of the flange portion; and the first conductive member is provided such that the projected portion of the first conductive member is included in the projected portion of the flange portion. 
       Advantageous Effects of Invention 
       [0011]    In a rotating electrical machine of the invention, electrostatic coupling between a winding and a rotor is blocked by a grounded conductor, and therefore it is possible to reduce an axis voltage to suppress electrolytic corrosion of a bearing. Further, a distance between the conductor and the winding can be secured, and therefore it is possible to secure reliability in terms of dielectric breakdown. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  is a perspective view of an axial-type rotating electrical machine according to this embodiment. 
           [0013]      FIG. 2  is a cross-sectional view taken along an arrow A of  FIG. 1 . 
           [0014]      FIG. 3  is a perspective view of a stator unit  115  forming a stator  100 . 
           [0015]      FIG. 4  is an enlarged view of a part surrounded by an alternate long and short dash line C of  FIG. 1 . 
           [0016]      FIG. 5  is a cross-sectional view of an axial-type rotating electrical machine, illustrating another embodiment of a first conductive member. 
           [0017]      FIG. 6  is a perspective view of a stator unit  115  forming a stator  100 . 
           [0018]      FIG. 7  is an enlarged view of a part surrounded by an alternate long and short dash line C of  FIG. 5 . 
           [0019]      FIG. 8  is a cross-sectional view of an axial-type rotating electrical machine, illustrating another embodiment of a first conductive member. 
           [0020]      FIG. 9  is a cross-sectional view of an axial-type rotating electrical machine, illustrating another embodiment of a core. 
           [0021]      FIG. 10  is a cross-sectional view illustrating an axial-type rotating electrical machine  1  according to another embodiment to which a second conductive member is added. 
           [0022]      FIG. 11  is a perspective view of a stator unit  115  forming a stator  100  and a periphery thereof. 
           [0023]      FIG. 12  is a perspective view of a stator unit, illustrating another example of a first conductive member which is applicable to this embodiment illustrated above. 
           [0024]      FIG. 13  is a perspective view of a stator unit, illustrating another example of a first conductive member which is applicable to this embodiment illustrated above. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]    Hereinafter, an example of the invention will be described with reference to drawings. 
         [0026]      FIG. 1  is a perspective view of an axial-type rotating electrical machine according to this embodiment.  FIG. 2  is a cross-sectional view taken along an arrow A of  FIG. 1 . FIG.  3  is a perspective view of a stator unit  115  forming a stator  100 .  FIG. 4  is an enlarged view of a part surrounded by an alternate long and short dash line C of  FIG. 1 . 
         [0027]    A rotating electrical machine  1  includes the stator  100  and two rotors  200   a  and  200   b  between which the stator  100  is interposed in an axial direction. In the stator  100 , the plurality of stator units  115 , each of which includes a core made of a soft magnetic material, a bobbin  120  surrounding a core  110 , and a winding  130  wound around the bobbin  120 , are provided in a circumferential direction. Further, the stator  100  is integrally molded with a housing  300  made of resin  150 . That is, the housing  300  holds the stator  100 . 
         [0028]    The rotor  200   a  includes a yoke  220   a  made of soft magnetic material and a plurality of permanent magnets  210   a  provided in the circumferential direction and connected to the yoke  220   a.  The rotor  200   b  includes a yoke  220   b  made of soft magnetic material and the plurality of permanent magnets  210   a  provided in the circumferential direction and connected to the yoke  220   b.  The rotor  200   a  and the rotor  200   b  are connected via a bearing  500  to a shaft  400  rotatably fixed to the housing  300 . 
         [0029]    The bobbin  120  has a tubular portion  122  forming a housing space for housing the core  110 , a flange portion  121   a  connected to one end surface in the axial direction of the tubular portion  122  and protruded between the rotor  200   a  and the winding  130 , and a flange portion  121   b  connected to the other end surface in the axial direction of the tubular portion  122  and protruded between the rotor  200   b  and the winding  130 . 
         [0030]    A first conductive member  140   a  is provided on a surface of the flange portion  121   a,  the surface facing the rotor  200   a,  and is in contact with the core  110 . A first conductive member  140   b  is provided on a surface of the flange portion  121   b,  the surface facing the rotor  200   b,  and is in contact with the core  110 . The first conductive member  140   a  and the first conductive member  140   b  are grounded. 
         [0031]    As illustrated in  FIG. 2 , in a case where projection is performed from an arrow B in parallel with the axial direction, the winding  130  is provided such that a projected portion  131  of a part of the winding wound around the bobbin  120  is within a projected portion  128  of the flange portion  121   a  or the flange portion  121   b.  The first conductive member  140   a  or the first conductive member  140   b  is provided such that a projected portion  148  of the first conductive member  140   a  or the first conductive member  140   b  is included in the projected portion  128  of the flange portion  121   a  or the flange portion  121   b.  With this structure, as illustrated in  FIG. 4 , a shortest one-line distance  124  between the first conductive member  140   a  and the winding  130  is smaller than a shortest creepage distance (sum of a distance  123   a  and a distance  123   b ) between the first conductive member  140   a  and the winding  130 . 
         [0032]    Operation of the axial-type rotating electrical machine of this embodiment will be described. Herein, a motor operation example will be described. An alternating current is caused to flow through the winding  130  with the use of an inverter and an AC power supply (not illustrated). With this, an alternating magnetic field is generated on a surface of the stator  100 . This alternating magnetic field and a static magnetic field of the rotor  200   a  and the rotor  200   b  caused by the permanent magnet  210   a  and permanent magnet  210   b  are attracted and repelled, and thus the rotor  200   a  and the rotor  200   b  are rotated to generate a torque. 
         [0033]    An effect of the axial-type rotating electrical machine of this embodiment will be described. The space between the winding  130  and the rotor  200   a  or the rotor  200   b  is blocked by the grounded first conductive member  140   a.  This suppresses generation of a potential difference between the winding  130  and the rotor  200   a  or the rotor  200   b.  Therefore, a potential difference between inner and outer rings of the bearing  500  is also reduced. As a result, it is possible to suppress generation of an axis current caused by breakage of an oil film in the bearing  500  and suppress generation of electrolytic corrosion in the bearing  500  caused by the generation of the axis current. 
         [0034]    The first conductive member  140   a  provided on the surface of the flange portion  121   a  and the winding  130  are provided to have a thickness of the flange portion  121   a  (distance  123   a  illustrated in  FIG. 4 ) and a creepage distance (distance  123   b  illustrated in  FIG. 4 ) which is a distance between a tip of the flange portion  121   a  and the winding  130 . This makes it possible to secure an electrical insulation property between the first conductive member  140   a  and the winding  130  to suppress dielectric breakdown between the first conductive member  140   a  and the winding  130 . 
         [0035]    Note that, although an example of providing the two rotors  200   a  and  200   b  at both ends of the stator  100  has been described in this embodiment, another axial-type rotating electrical machine in which a single rotor facing a single stator including a back yoke is provided may be also employed. Further, still another axial-type rotating electrical machine in which a single rotor is interposed between two stators  100  including a back yoke may be also employed. 
         [0036]    Note that the first conductive member  140   a  and the first conductive member  140   b  are desirably made of a nonmagnetic material. This makes it possible to suppress flux leakage to the first conductive member  140   a  and the first conductive member  140   b  to improve output and efficiency of the rotating electrical machine. The first conductive member  140   a  and the first conductive member  140   b  are provided on the bobbin  120  by a post-process such as plating, deposition, or adhesion. Alternatively, the first conductive member  140   a  and the first conductive member  140   b  may be integrally formed with the bobbin  120 . The first conductive member  140   a  and the first conductive member  140   b  may be embedded in the flange portions, instead of being provided on the surfaces of the flange portion  121   a  and the flange portion  121   b  of the bobbin  120 . 
         [0037]      FIG. 5  is a cross-sectional view of the axial-type rotating electrical machine, illustrating another embodiment of the first conductive member. Description of a structure, operation, and an effect that are the same as those of  FIG. 1  to  FIG. 4  are omitted.  FIG. 6  is a perspective view of the stator unit  115  forming the stator  100 .  FIG. 7  is an enlarged view of a part surrounded by an alternate long and short dash line C of  FIG. 5 . 
         [0038]    In this embodiment, a first conductive member  141   a  is provided such that a projected portion  132  of the first conductive member  141   a  is within the projected portion  148  of the flange portion  121   a.  A first conductive member  141   b  is provided such that the projected portion  132  of the first conductive member  141   b  is within the projected portion  148  of the flange portion  121   b.    
         [0039]    That is, as illustrated in  FIG. 7 , a tip of the flange portion  121   a  and the first conductive member  141   a  have a distance  123   c.  This makes it possible to wind the winding  130  to the vicinity of the tip of the flange portion  121   a  and the flange portion  121   b  to effectively use a stator space. 
         [0040]      FIG. 8  is a cross-sectional view of the axial-type rotating electrical machine, illustrating another embodiment of the first conductive member. 
         [0041]    Description of a structure, operation, and an effect that are the same as those of  FIG. 1  to  FIG. 4  are omitted. 
         [0042]    A first conductive member  142  is also formed in a space between the tubular portion  122  and the core  110 . The first conductive member  142  is in contact with a core surface  111  of the core  110 , the core surface  111  facing the tubular portion  122 . With this, the first conductive member  142  is firmly fixed between the tubular portion  122  and the core  110 . This makes it possible to improve connection reliability with the core  110 . 
         [0043]      FIG. 9  is a cross-sectional view of the axial-type rotating electrical machine, illustrating another embodiment of the core. Description of a structure, operation, and an effect that are the same as those of  FIG. 1  to  FIG. 4  are omitted. 
         [0044]    The core  110  has a core-side flange portion  112   a  provided between the first conductive member  140   a  and a rotor (not illustrated) provided in the axial direction. The core-side flange portion  112   a  is in contact with a surface  145   a  of the first conductive member  140   a,  the surface  145   a  being an opposite surface of a surface that is in contact with the flange portion  121   a.  The core  110  also has a core-side flange portion  112   b  provided between the first conductive member  140   b  and a rotor (not illustrated) provided in the axial direction. The core-side flange portion  112   b  is in contact with a surface  145   b  of the first conductive member  140   b,  the surface  145   b  being an opposite surface of a surface that is in contact with the flange portion  121   b.  Note that, although the core  110  is grounded in this embodiment, the first conductive member  140   a  may be grounded. With this, the first conductive member  140   a  or the first conductive member  140   b  is firmly fixed between the flange portion  121   a  or the flange portion  121   b  and the core-side flange portion  112   a  or the core-side flange portion  112   b  the core  110 . This makes it possible to improve the connection reliability with the core  110 . 
         [0045]      FIG. 10  is a cross-sectional view illustrating the axial-type rotating electrical machine  1  according to another embodiment to which a second conductive member is added.  FIG. 11  is a perspective view of the stator unit  115  forming the stator  100  and a periphery thereof. 
         [0046]    A second conductive member  160   a  is provided between the first conductive member  140   a  and a rotor (not illustrated) provided in the axial direction. A second conductive member  160   b  is provided between the first conductive member  140   b  and a rotor (not illustrated) provided in the axial direction. The second conductive member  160   a  has a first contact surface  161   a  that is in contact with a surface  146   a  of the first conductive member  140   a,  the surface  146   a  being an opposite surface of a surface that is in contact with the flange portion  121   a  and a second contact surface  162   a  that is in contact with an inner wall of the housing  300 . The housing  300  is grounded. The second conductive member  160   b  has a similar structure. 
         [0047]    Thus, the first conductive member  140   a  and the second conductive member  160   a  are in surface contact with each other, which results in easy conduction. A heat dissipation path of internal components of the axial-type rotating electrical machine is mainly provided in a direction from the inner wall to an outer wall of the housing  300 . In view of this, by using the second conductive member  160   a  of this embodiment, heat generated in the stator can be transmitted to the inner wall of the housing  300  via the second conductive member  160   a.  This makes it possible to improve a heat dissipation property of the axial-type rotating electrical machine. 
         [0048]    Because the core  110  is molded with the resin  150 , it is necessary to additionally provide means for grounding the plurality of cores  110  that are provided in the circumferential direction and are electrically independent. In view of this, the second conductive member  160   a  has a third contact surface  163   a  that is in contact with the core  110 . A third contact surface  163   b  has a similar structure. This makes it possible to simultaneously secure grounding of the first conductive member  140   a  and the core  110 , reduce the number of components, and simplify the structure. This can improve electrical connection reliability for grounding. 
         [0049]    Note that, although the second conductive member  160   a  is assumed to have a 360° continuous ring shape in  FIG. 10  and  FIG. 11 , a shape of the second conductive member  160   a  is arbitrary. The second conductive member  160   a  may be divided into a plurality of parts in the circumferential direction. The individual second conductive members  160   a  may be separated. The second conductive member  160   a  is desirably formed by a nonmagnetic conductor made of aluminum or the like. This makes it possible to reduce flux leakage to the second conductive member  160   a  to improve output and efficiency of the rotating electrical machine. Note that, in a case where the second conductive member  160   a  and the core  110  are caused to be conductive by different means, the second conductive member  160   a  may be provided on arbitrary one of end surfaces in the axial direction. In a case where the second conductive member  160   a  is formed by a high thermal conductor such as aluminum, a heat dissipation property of the stator can be also improved. In this case, by providing the second conductive members  160   a  at the both end surfaces of the stator, a heat dissipation effect can be doubled. 
         [0050]      FIG. 12  is a perspective view of a stator unit, illustrating another example of the first conductive member which is applicable to this embodiment illustrated above. 
         [0051]    The stator unit has a cut portion  143   a  so that a first conductive member  143  provided around a tip of a core is discontinuous in the circumferential direction. With this, a necessary minimum shield area is reduced, and thus a loop of an eddy current flowing through the first conductive member  143  around the core can be cut off and generation of a loss can be suppressed. This makes it possible to improve output and efficiency of the rotating electrical machine. 
         [0052]    Note that, although a single cut portion is provided in the circumferential direction in this embodiment, a plurality of slits may be provided so as not to largely reduce the shielding area and separate the first conductive member. Further, as illustrated in  FIG. 13 , a first conductive member  144  may be meshed. An arrangement pattern of the first conductive member  144  can be formed by a pattern at the time of printing or deposition. Alternatively, the first conductive member  144  can be discontinuously grounded by providing protrusions and recesses corresponding to a pattern on a conductor placement surface of the bobbin in advance. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  . . . rotating electrical machine,  100  . . . stator,  110  . . . core,  111  . . . core surface,  112   a  . . . core-side flange portion,  115  . . . stator unit,  120  . . . bobbin,  121   a  . . . flange portion,  121   b  . . . flange portion,  122  . . . tubular portion,  123   a  . . . distance,  123   b  . . . distance,  123   c  . . . distance,  124  . . . one-line distance,  128  . . . projected portion,  130  . . . winding,  131  . . . projected portion,  132  . . . projected portion,  140   a  . . . first conductive member,  140   b  . . . first conductive member,  141   a  . . . first conductive member,  141   b  . . . first conductive member,  142  . . . first conductive member,  143  . . . first conductive member,  144  . . . first conductive member,  143   a  . . . cut portion,  145   a  . . . surface,  145   b  . . . surface,  146   a  . . . surface,  146   b  . . . surface,  148  . . . projected portion,  150  . . . resin,  160   a  . . . second conductive member,  160   b  . . . second conductive member,  161   a  . . . first contact surface,  162   a  . . . second contact surface,  163   a  . . . third contact surface,  163   b  . . . third contact surface,  200   a  . . . rotor,  200   b  . . . rotor,  210   a  . . . permanent magnet,  210   b  . . . permanent magnet,  220   a  . . . yoke,  220   b  . . . yoke,  300  . . . housing,  400  . . . shaft,  500  . . . bearing